NIMP| Iuliana PASUK, Author at NIMP

Publications

1. Physico-chemical characterization and in vitro biological study of manganese doped β-tricalcium phosphate-based ceramics for bone regeneration applications

Authors: Arpak, MC; Daglilar, S; Kalkandelen, C; Balescu, LM; Sasmazel, HT; Pasuk, I; Stan, GE; Durukan, K; Gunduz, O

Published: SEP 2023, JOURNAL OF THE AUSTRALIAN CERAMIC SOCIETY, 59, DOI: 10.1007/s41779-023-00889-5

This work evaluates the effects of manganese (Mn) doping on the morpho-structural features, mechanical performance, and in vitro biological response of beta-tricalcium phosphate (beta-TCP) derived bioceramics for bone tissue engineering applications. Five different Mn doping levels (i.e., 0.01%, 0.05%, 0.1%, 0.5%, and 1 wt.%) were investigated, with the beta-TCP-based bioceramics being sintered at four temperatures (i.e., 1000, 1100, 1200, and 1300 degrees C). A densification improvement was induced when using Mn in excess of 0.05 wt.%; the densification remained stationary in the sintering temperature range of 1200 - 1300 degrees C. The structural analyses evidenced that all samples sintered at 1000 and 1100 degrees C were composed of beta-TCP as major phase and hydroxyapatite (HA) as a minor constituent (similar to 4-6 wt.%). At the higher temperatures (1200 and 1300 degrees C), the formation of alpha-TCP was signalled at the expense of both beta-TCP and HA. The Mn doping was evidenced by lattice parameters changes. The evolution of the phase weights is linked to a complex inter-play between the capacity of the compounds to incorporate Mn and the thermal decomposition kinetics. The Mn doping induced a reduction in the mechanical performance (in terms of compressive strength, Vickers hardness and elastic modulus) of the beta-TCP-based ceramics. The metabolic activity and viability of osteoblastic cells (MC3T3-E1) for the ceramics were studied in both powder and compacted pellet form. Ceramics with Mn doping levels lower than 0.1 wt.% yielded a more favorable microenvironment for the osteoblast cells with respect to the undoped beta-TCP. No cytotoxic effects were recorded up to 21 days. The Mn-doped beta-TCPs showed a significant increase (p < 0.01) in alkaline phosphatase activity with respect to pure beta-TCP.

2. Experimental Band Structure of Pb(Zr,Ti)O-3: Mechanism of Ferroelectric Stabilization

Authors: Popescu, DG; Husanu, MA; Constantinou, PC; Filip, LD; Trupina, L; Bucur, CI; Pasuk, I; Chirila, C; Hrib, LM; Stancu, V; Pintilie, L; Schmitt, T; Teodorescu, CM; Strocov, VN

Published: FEB 2023, ADVANCED SCIENCE, 10, DOI: 10.1002/advs.202205476

Pb(Zr,Ti)O-3 (PZT) is the most common ferroelectric (FE) material widely used in solid-state technology. Despite intense studies of PZT over decades, its intrinsic band structure, electron energy depending on 3D momentum k, is still unknown. Here, Pb(Zr0.2Ti0.8)O-3 using soft-X-ray angle-resolved photoelectron spectroscopy (ARPES) is explored. The enhanced photoelectron escape depth in this photon energy range allows sharp intrinsic definition of the out-of-plane momentum k and thereby of the full 3D band structure. Furthermore, the problem of sample charging due to the inherently insulating nature of PZT is solved by using thin-film PZT samples, where a thickness-induced self-doping results in their heavy doping. For the first time, the soft-X-ray ARPES experiments deliver the intrinsic 3D band structure of PZT as well as the FE-polarization dependent electrostatic potential profile across the PZT film deposited on SrTiO3 and LaxSrMn1-xO3 substrates. The negative charges near the surface, required to stabilize the FE state pointing away from the sample (P+), are identified as oxygen vacancies creating localized in-gap states below the Fermi energy. For the opposite polarization state (P-), the positive charges near the surface are identified as cation vacancies resulting from non-ideal stoichiometry of the PZT film as deduced from quantitative XPS measurements.

3. Experimental Band Structure of Pb(Zr,Ti)O-3: Mechanism of Ferroelectric Stabilization

Authors: Popescu, DG; Husanu, MA; Constantinou, PC; Filip, LD; Trupina, L; Bucur, CI; Pasuk, I; Chirila, C; Hrib, LM; Stancu, V; Pintilie, L; Schmitt, T; Teodorescu, CM; Strocov, VN

Published: JAN 2023, ADVANCED SCIENCE, DOI: 10.1002/advs.202205476

4. Influence of on-off pulsed current pattern on processes during spark plasma sintering of MgB2 superconductor

Authors: Aldica, G; Sandu, V; Popa, S; Pasuk, I; Enculescu, M; Ionescu, AM; Badica, P

Published: DEC 2023, OPEN CERAMICS, 16, 100441, DOI: 10.1016/j.oceram.2023.100441

High density samples (92-94.5 %) of MgB2 were prepared by Spark Plasma Sintering (SPS). The on-off pulsed current patterns of SPS processing were 8-4, 12-2, 24-2, 99-1. Patterns with more on pulses favor formation of a higher amount of the secondary MgB4 phase through the decomposition of MgB2. They also promote enhancement of larger MgO crystallites without a strong increase in the amount of this phase. Densification rate and pressure in the SPS chamber show a similar behavior, but their amplitude varies and the temperatures defining different stages present some shifts. As-revealed differences induced by pulsed patterns impact superconducting properties in a complex manner. An attempt to assess correlations between the pattern and different superconducting parameters is presented.

5. Physico-chemical characterization and in vitro biological study of manganese doped beta-tricalcium phosphate-based ceramics for bone regeneration applications

Authors: Arpak, MC; Daglilar, S; Kalkandelen, C; Balescu, LM; Sasmazel, HT; Pasuk, I; Stan, GE; Durukan, K; Gunduz, O

Published: 2023 MAY 12 2023, JOURNAL OF THE AUSTRALIAN CERAMIC SOCIETY, DOI: 10.1007/s41779-023-00889-5

6. Experimental Band Structure of Pb(Zr,Ti)O₃: Mechanism of Ferroelectric Stabilization

Authors: Popescu, DG; Husanu, MA; Constantinou, PC; Filip, LD; Trupina, L; Bucur, CI; Pasuk, I; Chirila, C; Hrib, LM; Stancu, V; Pintilie, L; Schmitt, T; Teodorescu, CM; Strocov, VN

Published: FEB 2023, ADVANCED SCIENCE, 10, DOI: 10.1002/advs.202205476

7. Columnar Liquid Crystals of Copper(I) Complexes with Ionic Conductivity and Solid State Emission

Authors: Circu, V; Ganea, CP; Secu, M; Manaila-Maximean, D; Marinescu, GC; Popescu, RG; Pasuk, I

Published: MAY 19 2023, MOLECULES, 28, 4196, DOI: 10.3390/molecules28104196

Two neutral copper(I) halide complexes ([Cu(BTU)(2)X], X = Cl, Br) were prepared by the reduction of the corresponding copper(II) halides (chloride or bromide) with a benzoylthiourea (BTU, N-(3,4-diheptyloxybenzoyl)-N '-(4-heptadecafluorooctylphenyl)thiourea) ligand in ethanol. The two copper(I) complexes show a very interesting combination of 2D supramolecular structures, liquid crystalline, emission, and 1D ionic conduction properties. Their chemical structure was ascribed based on ESI-MS, elemental analysis, IR, and NMR spectroscopies (H-1 and C-13), while the mesomorphic behavior was analyzed through a combination of differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and powder X-ray diffraction (XRD). These new copper(I) complexes have mesomorphic properties and exhibit a hexagonal columnar mesophase over a large temperature range, more than 100 K, as evidenced by DSC studies and POM observations. The thermogravimetric analysis (TG) indicated a very good thermal stability of these samples up to the isotropization temperatures and over the whole temperature range of the liquid crystalline phase existence. Both complexes displayed a solid-state emission with quantum yields up to 8% at ambient temperature. The electrical properties of the new metallomesogens were investigated by variable temperature dielectric spectroscopy over the entire temperature range of the liquid crystalline phase. It was found that the liquid crystal phases favoured anhydrous proton conduction provided by the hydrogen-bonding networks formed by the NH horizontal ellipsis X moieties (X = halide or oxygen) of the benzoylthiourea ligand in the copper(I) complexes. A proton conductivity of 2.97 x 10(-7) S.cm(-1) was achieved at 430 K for the chloro-complex and 1.37 x 10(-6) S.cm(-1) at 440K for the related bromo-complex.

8. Ferroelectricity modulates polaronic coupling at multiferroic interfaces

Authors: Husanu, MA; Popescu, DG; Bisti, F; Hrib, LM; Filip, LD; Pasuk, I; Negrea, R; Istrate, MC; Lev, L; Schmitt, T; Pintilie, L; Mishchenko, A; Teodorescu, CM; Strocov, VN

Published: AUG 15 2022, COMMUNICATIONS PHYSICS, 5, 209, DOI: 10.1038/s42005-022-00983-3

A deeper understanding of the coupling at the interface of multiferroics heterostructures is being achieved by the use of synchrotron radiation techniques. Here, the authors use k-resolved soft X-ray photoemission spectroscopy and first principles calculations to investigate the band structure of several multiferroic heterostructures, isolating the distinct signature of the interface. Physics of the multiferroic interfaces is currently understood mostly within a phenomenological framework based on screening of the polarization field and depolarizing charges. Additional effects still unexplored are the band dependence of the interfacial charge modulation and the associated changes of the electron-phonon interaction, coupling the charge and lattice degrees of freedom. Here, multiferroic heterostructures of the colossal-magnetoresistance manganite La1-xSrxMnO3 buried under ferroelectric BaTiO3 and PbZrxTi1-xO3 are investigated using soft-X-ray angle-resolved photoemission. The experimental band dispersions from the buried La1-xSrxMnO3 identify coexisting two-dimensional hole and three-dimensional electron charge carriers. The ferroelectric polarization modulates their charge density, affecting the coupling of the 2D holes and 3D electrons with the lattice which forms large Frohlich polarons inherently reducing mobility of the charge carriers. Our k-resolved results on the orbital occupancy, band filling and electron-lattice interaction in multiferroic oxide heterostructures modulated by the ferroelectric polarization disclose most fundamental physics of these systems needed for further progress of beyond-CMOS ferro-functional electronics.

9. Negative Capacitance and Switching Dynamics Control Via Non-Ferroelectric Elements

Authors: Boni, AG; Patru, R; Filip, LD; Chirila, C; Pasuk, I; Pintilie, I; Pintilie, L

Published: MAR 15 2022, ACS APPLIED ENERGY MATERIALS, 5, DOI: 10.1021/acsaem.1c03890

Complex ferroelectric structures with dielectric interlayers may become possible alternatives for neuromorphic computing and low-power field-effect transistors since they exhibit multiple polarization states and negative capacitance. However, the effects on the switching characteristics due to the electric properties of the nonferroelectric circuit element have not been clearly evaluated so far. A high-resistance or low-capacitance element is usually associated with an increased depolarization field and eventually with suppression of polarization but without further consideration of the electrostatic differences. Therefore, we show that switching behavior is dramatically changed if the non-FE element is a resistive component or a capacitive one. This is reflected by either an increased apparent coercive field or imprint, respectively. A negative capacitance regime was observed at different moments but strongly depends on the nature of the nonferroelectric element. The voltage on the ferroelectric component remains constant during switching, which is a fingerprint of the system passing through non-equilibrium states. Therefore, we propose an algorithm to recover the S-shape of polarization dependence on the ferroelectric internal voltage during the slowed transition between the two stable states of polarization.

10. MICROSTRUCTURE, MAGNETIC AND MAGNETOSTRICTIVE BEHAVIOUR IN RAPIDLY QUENCHED OFF-STOICHIOMETRIC Ni-Mn-Ga FERROMAGNETIC SHAPE MEMORY ALLOYS

Authors: Sofronie, M; Tolea, F; Enculescu, M; Pasuk, I; Popescu, B

Published: 2022, ROMANIAN REPORTS IN PHYSICS, 74, 503, DOI:

This work reports the effect of the rapid solidification technique and thermal treatment on the martensitic transformation (MT), magnetic and magnetostrictive properties on the off-stoichiometric Ni49Mn31Ga20 and Ni51Mn28Ga21 ferromagnetic shape memory ribbons. The samples were investigated by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, magnetic and magnetostrictive measurements. The temperature dependence of the X-ray phases analysis shows the presence of martensite structures, both tetragonal and monoclinic, at room temperature and allowed to study their evolution through MT. The thermal treatment induces changes in the microstructure with implications in MT and Curie temperatures evolution. The competition between the magnetization orientation and twin boundary motion within martensitic variants under magnetic field evidenced in the magnetic-strain curves was discussed and correlated with the magnetic data.

11. Controlling polarization direction in epitaxial Pb(Zr0.2Ti0.8)O-3 films through Nb (n-type) and Fe (p-type) doping

Authors: Chirila, CF; Stancu, V; Boni, GA; Pasuk, I; Trupina, L; Filip, LD; Radu, C; Pintilie, I; Pintilie, L

Published: JAN 14 2022, SCIENTIFIC REPORTS, 12, 755, DOI: 10.1038/s41598-022-04802-1

Fe (acceptor) and Nb (donor) doped epitaxial Pb(Zr0.2Ti0.8)O-3 (PZT) films were grown on single crystal SrTiO3 substrates and their electric properties were compared to those of un-doped PZT layers deposited in similar conditions. All the films were grown from targets produced from high purity precursor oxides and the doping was in the limit of 1% atomic in both cases. The remnant polarization, the coercive field and the potential barriers at electrode interfaces are different, with lowest values for Fe doping and highest values for Nb doping, with un-doped PZT in between. The dielectric constant is larger in the doped films, while the effective density of charge carriers is of the same order of magnitude. An interesting result was obtained from piezoelectric force microscopy (PFM) investigations. It was found that the as-grown Nb-doped PZT has polarization orientated upward, while the Fe-doped PZT has polarization oriented mostly downward. This difference is explained by the change in the conduction type, thus in the sign of the carriers involved in the compensation of the depolarization field during the growth. In the Nb-doped film the majority carriers are electrons, which tend to accumulate to the growing surface, leaving positively charged ions at the interface with the bottom SrRuO3 electrode, thus favouring an upward orientation of polarization. For Fe-doped film the dominant carriers are holes, thus the sign of charges is opposite at the growing surface and the bottom electrode interface, favouring downward orientation of polarization. These findings open the way to obtain p-n ferroelectric homojunctions and suggest that PFM can be used to identify the type of conduction in PZT upon the dominant direction of polarization in the as-grown films.

12. Effect of the supersaturation with nitrogen on the structure refinement and magnetic properties of mechanically alloyed and heated Fe14Cr ferritic alloys

Authors: Mihalache, V; Pasuk, I; Mercioniu, I

Published: SEP-OCT 2022, JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 20, DOI: 10.1016/j.jmrt.2022.07.190

Nano-nitride reinforcement of Fe-Cr alloys are under intense investigations, e.g., along with oxide-strengthened, nitride-strengthened reduced activation steels with superior high temperature mechanical properties are developed as materials for nuclear energy applications. Fe14Cr alloy powders were produced by mechanical milling for up to 170 h under a nitrogen atmosphere followed by heating under an Ar5%H-2 atmosphere to 600 degrees C-1120 degrees C. The samples were investigated by means of X-ray diffraction, DTA/TG and magnetic measurements. CrN, detected after milling for 58 h, reached 39 wt % (5.3 wt.% total N) at 170 h milling. The ferrite supersaturated with nitrogen shows a strong decrease in grain size and saturation magnetization, an increase in lattice constant, microstrain and coercivity, H-c. Upon heating, the metastable ultrafine alpha-ferrite and CrN in the as-milled samples undergo transformations and recrystallization into ferrite grains free of super-saturation, whose microstructure follows a continuous relaxation. The supersaturation with nitrogen was retained upon heating in the relatively stable ferrite crystalized at the milling stage. This microstructure undergoes a discontinuous relaxation in the 800 degrees C-1120 degrees C region: a pronounced decrease of grain size (down to similar to 25 nm), an increase of lattice constant, microstrain and H-c. These improvements were associated with features of discontinuous precipitation reaction of coherent nitride precipitates (involving a new alpha ''-phase with expanded lattice), in connection with the heating in the austenite phase field. Such microstructure refinement or (nitride) strengthening of Fe14Cr alloys can be achieved on powders milled for much less time as compared to previously reported (oxide dispersion) strengthening of Fe14Cr-W-Ti ferritic steels. (C) 2022 The Authors. Published by Elsevier B.V.

13. MgB2 with Addition of Cubic BN and Ge2C6H10O7 Obtained by Spark Plasma Sintering Technique

Authors: Ionescu, AM; Aldica, G; Popa, S; Enculescu, M; Sandu, V; Pasuk, I; Burdusel, M; Grigoroscuta, MA; Miu, L; Badica, P

Published: JUL 2022, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, DOI: 10.1007/s10948-022-06350-1

High density (94-98% of the theoretical density) MgB2 samples added with C6H10Ge2O7 and cubic BN with compositions (MgB2)(1-x)(Ge2C6H10O7)(0.0028)(cBN)(x) (x = 0.003, 0.005, 0.007, 0.01) and (MgB2)(1-y)(Ge2C6H10O7)(y)(cBN)(0.005) (y = 0.0014, 0.0028, 0.005, 0.0075) were obtained by spark plasma sintering technique. For optimum doped samples with x = 0.005-0.007 and y = 0.0028-0.005, a weak enhancement of zero-field critical current density J(c0), irreversibility field H-irr, and volume pinning force F-p,F-max was determined. This behavior is very different from similar samples added with a single additive for which H-irr has a large enhancement. Consequently, it suggests the presence of opposite structural and microstructural effects induced by the additives. These effects, on the one hand, are discussed to decrease the sensitivity of MgB2 superconducting properties in the co-added samples comparative to samples added with C6H10Ge2O7, and, on the other hand, they contribute to anomalies that were found when assessing the pinning force-related parameters by the universal scaling law.

14. Full Length Article Towards high degree of c-axis orientation in MgB2 bulks

Authors: Grigoroscuta, MA; Aldica, GV; Burdusel, M; Sandu, V; Kuncser, A; Pasuk, I; Ionescu, AM; Suzuki, TS; Vasylkiv, O; Badica, P

Published: AUG 2022, JOURNAL OF MAGNESIUM AND ALLOYS, 10, DOI: 10.1016/j.jma.2021.10.013

The paper presents fabrication and characterization of spark plasma sintered textured (001) MgB2 with a record degree of orientation of about 40% and 16% by high-energy ultra-sonication and slip casting in high magnetic field (12 T) and 0 T magnetic field, respectively. Structural characterization was performed by X-ray diffraction, and electron microscopy. The analysis revealed unexpected preferred orientation also in the MgO secondary phase due to the epitaxial growth of (111) MgO on (001) MgB2. The influence of oriented microstructure on the superconducting characteristics expressed by critical current density (Jc), irreversibility field ( H irr), and on the pinning properties were assessed. High anisotropy versus sample orientation in applied magnetic field, H , was observed for Jc, Hirr, pinning activation energy ( U *) extracted from relaxation measurements. The zero-field critical current, Jc0 and Fp,maxare weakly or not dependent on the direction of H , while the other indicated parameters are significantly influenced. Results enable control of superconducting parameters by further optimization of microstructure through MgB2 texturing as a novel and viable strategy for development of bulk MgB2 with enhanced properties when taking advantage of its anisotropy.(c) 2021 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ) Peer review under responsibility of Chongqing University

15. Sr and Mg Doped Bi-Phasic Calcium Phosphate Macroporous Bone Graft Substitutes Fabricated by Robocasting: A Structural and Cytocompatibility Assessment

Authors: Besleaga, C; Nan, B; Popa, AC; Balescu, LM; Nedelcu, L; Neto, AS; Pasuk, I; Leonat, L; Popescu-Pelin, G; Ferreira, JMF; Stan, GE

Published: SEP 2022, JOURNAL OF FUNCTIONAL BIOMATERIALS, 13, 123, DOI: 10.3390/jfb13030123

Bi-phasic calcium phosphates (BCPs) are considered prominent candidate materials for the fabrication of bone graft substitutes. Currently, supplemental cation-doping is suggested as a powerful path to boost biofunctionality, however, there is still a lack of knowledge on the structural role of such substituents in BCPs, which in turn, could influence the intensity and extent of the biological effects. In this work, pure and Mg- and Sr-doped BCP scaffolds were fabricated by robocasting from hydrothermally synthesized powders, and then preliminarily tested in vitro and thoroughly investigated physically and chemically. Collectively, the osteoblast cell culture assays indicated that all types of BCP scaffolds (pure, Sr- or Sr-Mg-doped) delivered in vitro performances similar to the biological control, with emphasis on the Sr-Mg-doped ones. An important result was that double Mg-Sr doping obtained the ceramic with the highest beta-tricalcium phosphate (beta-TCP)/hydroxyapatite mass concentration ratio of similar to 1.8. Remarkably, Mg and Sr were found to be predominantly incorporated in the beta-TCP lattice. These findings could be important for the future development of BCP-based bone graft substitutes since the higher dissolution rate of beta-TCP enables an easier release of the therapeutic ions. This may pave the road toward medical devices with more predictable in vivo performance.

16. Evidence of Counterion Size Effect on the Stability of Columnar Phase of Ionic Liquid Crystals Based on Pyridinium Salts Derived from N-3,4,5-Tri(alkyloxy)-benzyl-4-pyridones

Authors: Dumitru, I; Chiriac, FL; Ilis, M; Pasuk, I; Manaila-Maximean, D; Micutz, M; Staicu, T; Circu, V

Published: MAY 2022, CRYSTALS, 12, 715, DOI: 10.3390/cryst12050715

The synthesis and characterization of novel ionic liquid crystals based on pyridinium salts with Br- and PF6- counterions are described in this work. These pyridinium salts were derived from 4-hydroxypyridine, both by N- and O-alkylation. The 3,4,5-tri(alkyloxy)-benzyl mesogenic unit was attached to the nitrogen atom of the pyridinium ring. Alkyl chains with a different number of carbon atoms (6, 8, 10, 12 and 14) were employed in order to show the effect on the stability of mesophase. The POM (polarizing optical microscopy) and XRD (powder X-ray diffraction) studies indicated that bromide salts with shorter chains C-6, C-8 and C-10 do not show mesomorphic properties, while longer chain analogues with C-12 and C-14 exhibit two enantiotropic columnar phases. Surprisingly, the pyridinium salts with the larger size PF6- counterion do not exhibit liquid crystal properties.

17. Effect of disubstitution pattern of the terminal alkyl chains on the mesophase of liquid crystals based on lanthanide(III) complexes: A study of the thermal, emission and dielectric behavior

Authors: Ilinca, TA; Chiriac, LF; Ilis, M; Manaila-Maximean, D; Ganea, PC; Pasuk, I; Circu, V

Published: AUG 15 2022, JOURNAL OF MOLECULAR LIQUIDS, 360, 119425, DOI: 10.1016/j.molliq.2022.119425

In the present work, new luminescent lanthanide complexes with extended mesomorphic range were prepared by coordination to lanthanide ions (Eu3+, Sm3+ and Tb3+) of the new 4-pyridone based organic ligands (L) with 3,4-(7-n) and 3,5-di(alkyloxy)benzyl (8-n) mesogenic groups and variable length (n = 12 or 14 carbon atoms) onto the benzyl unit. The cumulative results of the elemental analyses as well as the H-1, C-13 NMR and IR spectroscopies support the structure of the organic derivatives and their lanthanide complexes [LnL(3)(NO3)(3)] (9-n/Ln and 10-n/Ln) described in this work. These complexes show characteristic lanthanide solid state emission, both at room and elevated temperatures corresponding to crystalline, glassy or liquid crystal states. The long range SmA phases displayed by all complexes were supported by a combination of characterization methods, including: differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and variable-temperature powder X-ray diffraction (XRD). This work shows that the number, substitution pattern and length of flexible alkoxy chains are important parameters to control the phase-transition characteristics of the lanthanide complexes. Complexes with 3,4-disubstituted pattern (9-n/Ln) show higher clearing temperatures (nearly 60 degrees C for Eu3+, 70 degrees C for Sm3+ and 85 degrees C for Tb3+ complexes) compared to their counterparts with 3,5-disubstituted pattern (10-n/Ln). Moreover, complexes 9-n/Ln crystallize when cooling their LC phase while complexes 10-n/Ln are stable in glassy state at room temperature as a consequence of the different close interdigitated molecular packing evidenced by XRD measurements. Dielectric spectroscopy was employed to detect the changes of order degree specific to each phases (crystalline, LC or isotropic). The variation of dielectric constant and the electrical conductivity versus temperature shows three transition intervals for selected complexes 10-14/Sm and 10-14/Tb, which delimit the main intervals: 45-60 degrees C, 90-110 degrees C; 140-160 degrees C corresponding to the Cr-1-Cr-2, Cr-2 - SmA and SmA-Iso transitions, and agree very well with the DSC results. The change of characteristic time, obtained by Havriliak-Negami fit function, with temperature also provides a very good correlation with the DSC and POM results. (C) 2022 Elsevier B.V. All rights reserved.

18. Sintered and 3D-Printed Bulks of MgB2-Based Materials with Antimicrobial Properties

Authors: Badica, P; Batalu, ND; Chifiriuc, MC; Burdusel, M; Grigoroscuta, MA; Aldica, GV; Pasuk, I; Kuncser, A; Popa, M; Agostino, A; Operti, L; Padhi, SK; Bonino, V; Truccato, M

Published: OCT 2021, MOLECULES, 26, DOI: 10.3390/molecules26196045

Pristine high-density bulk disks of MgB2 with added hexagonal BN (10 wt.%) were prepared using spark plasma sintering. The BN-added samples are machinable by chipping them into desired geometries. Complex shapes of different sizes can also be obtained by the 3D printing of polylactic acid filaments embedded with MgB2 powder particles (10 wt.%). Our present work aims to assess antimicrobial activity quantified as viable cells (CFU/mL) vs. time of sintered and 3D-printed materials. In vitro antimicrobial tests were performed against the bacterial strains Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus ATCC 25923, Enterococcus faecium DSM 13590, and Enterococcus faecalis ATCC 29212; and the yeast strain Candida parapsilosis ATCC 22019. The antimicrobial effects were found to depend on the tested samples and microbes, with E. faecium being the most resistant and E. coli the most susceptible.</p>

19. Accidental Impurities in Epitaxial Pb(Zr0.2Ti0.8)O-3 Thin Films Grown by Pulsed Laser Deposition and Their Impact on the Macroscopic Electric Properties

Authors: Boni, GA; Chirila, CF; Stancu, V; Amarande, L; Pasuk, I; Trupina, L; Istrate, CM; Radu, C; Tomulescu, A; Neatu, S; Pintilie, I; Pintilie, L

Published: MAY 2021, NANOMATERIALS, 11, DOI: 10.3390/nano11051177

Structural and electrical properties of epitaxial Pb(Zr0.2Ti0.8)O-3 films grown by pulsed laser deposition from targets with different purities are investigated in this study. One target was produced in-house by using high purity precursor oxides (at least 99.99%), and the other target was a commercial product (99.9% purity). It was found that the out-of-plane lattice constant is about 0.15% larger and the a domains amount is lower for the film grown from the commercial target. The polarization value is slightly lower, the dielectric constant is larger, and the height of the potential barrier at the electrode interfaces is larger for the film deposited from the pure target. The differences are attributed to the accidental impurities, with a larger amount in the commercial target as revealed by composition analysis using inductive coupling plasma-mass spectrometry. The heterovalent impurities can act as donors or acceptors, modifying the electronic characteristics. Thus, mastering impurities is a prerequisite for obtaining reliable and reproducible properties and advancing towards all ferroelectric devices.

20. MgB2 powders and bioevaluation of their interaction with planktonic microbes, biofilms, and tumor cells

Authors: Badica, P; Batalu, ND; Chifiriuc, MC; Burdusel, M; Grigoroscuta, MA; Aldica, G; Pasuk, I; Kuncser, A; Enculescu, M; Popa, M; Marutescu, LG; Gheorghe, I; Thamer, O; Bleotu, C; Pircalabioru, GG; Operti, L; Bonino, V; Agostino, A; Truccato, M

Published: MAY-JUN 2021, JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 12, 2184, DOI: 10.1016/j.jmrt.2021.04.003

Commercial nanopowders of MgB2 were characterized from the viewpoint of granulometric distribution, structure, microstructure, and pH behavior in water. The powders are very different: a higher amount of the MgB2 phase with a lower tendency for agglomeration determines a higher rate of pH-increase. A higher rate of pH-increase usually produces a stronger antimicrobial activity against Staphylococcus aureus, Enterococcus faecium, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, and Candida parapsilosis reference strains. The variation of the pH-increase rate suggests the possibility of temporo-spatial control of MgB2 bioactivity, although the contribution of other factors should not be neglected. Remarkably, the efficiency of the MgB2 powders is higher against biofilms than on microbes in the planktonic state. Further, our experiments confirm the antimicrobial efficiency of MgB2 in the in vitro tests against 29 methicillin resistant clinical S. aureus isolates and 33 vancomycin resistant E. faecium/faecalis strains, but in this case the biofilms are more resistant than planktonic cells. The MgB2 treatment of infected mice led to a significant decrease of E. coli colonization in liver, spleen and peritoneal liquid and it also caused changes in the intestinal microbiota. The activity of powders on HeLa and HT-29 tumor cell lines was assessed by inverted microscopy, flow cytometry, and evaluation of the cellular cycle. MgB2 inhibits tumor cell growth influencing DNA synthesis (S-phase). The obtained results indicate that the tested powders could provide promising solutions for the development of large-spectrum multifunctional antimicrobial and anti-biofilm agents, and/or for anti-cancer therapies. (C) 2021 The Authors. Published by Elsevier B.V.

21. Hard/soft effects of multivalence co-dopants in correlation with their location in PZT ceramics

Authors: Amarande, L; Cioangher, MC; Toma, V; Miclea, CF; Stefan, M; Pasuk, I; Iuga, AR; Negrila, C; Matei, E; Palici, AM; Joita, AC

Published: DEC 1 2021, CERAMICS INTERNATIONAL, 47, 33389, DOI: 10.1016/j.ceramint.2021.08.243

Piezoelectric hard/soft effects of multivalence co-dopants (Sb and Mn) in correlation with their location in the lattice, were investigated in PZT ceramics, prepared by conventional ceramic technology, with the following compositions: Pb0.98Sr0.02 ((Ti0.49Zr0.51)(1-0.015-x)Mn0.015Sbx)O-3 with x = 0, 0.005, 0.01, 0.02, 0.03, where antimony was initially assumed to substitute for Ti/Zr ions. The antimony valence state was found to be +3 in all samples by X-ray Photoelectron Spectroscopy investigations. The Electron Paramagnetic Resonance spectra evidenced a steep enhancement of the Mn2+ concentration upon increasing antimony doping level, explained by a charge compensation mechanism, between the Sb3+ ions substituting Pb2+ at the A-sites and the Mn2+ ions, localized at the B-sites. The incorporation of Sb3+ at the A-site of the PZT lattice is also supported by the variation of the lattice parameters, determined by X-ray Diffraction, with the increasing Sb concentration. The investigation of the dielectric, electromechanical and ferroelectric properties evidenced a hard piezoelectric behavior, mainly attributed to the presence of large sized Mn2+ ions, localized at B-sites. Our results prove that the piezoelectric hard/soft response is decisively influenced by the interplay between multiple valence states and locations of the co-dopants, on one hand, and the charge compensation mechanisms, on the other hand. This provides indirect information about the location of some co-dopants which can substitute for both cationic sites in the PZT based ceramics.

22. Effect of strain and stoichiometry on the ferroelectric and pyroelectric properties of the epitaxial Pb(Zr0.2Ti0.8)O-3 films deposited on Si wafers

Authors: Chirila, C; Boni, GA; Filip, LD; Husanu, M; Neatu, S; Istrate, CM; Le Rhun, G; Vilquin, B; Trupina, L; Pasuk, I; Botea, M; Pintilie, I; Pintilie, L

Published: APR 2021, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 266, DOI: 10.1016/j.mseb.2021.115042

Properties of epitaxial PbZr0.2Ti0.8O3 (PZT) films deposited on Si substrates were investigated for integration in the present CMOS technology. Polarization is downward oriented, in association with the presence of an internal electric field, and has a lower value compared to the PZT films deposited on single crystal perovskite SrTiO3 (STO) substrates (40 mu C/cm(2) versus 80 mu C/cm(2)), while the dielectric constant is larger (180 versus 120). Large value for the pyroelectric coefficient was also found, 1.22 x 10(-3)C/m(2)K, as for PZT grown on single crystal STO. The macroscopic ferroelectric and pyroelectric properties appear to be affected by the structural quality and stoichiometry of the PZT film. The changes in the electric properties are an effect of the strain gradients induced by the large difference between the thermal expansion coefficients of PZT and Si substrate, leading in turn to Pb oxidation and antisite defect formation compared to PZT films deposited on STO substrates.

23. Partially-oriented MgB2 superconducting bulks with addition of B4C and cubic BN obtained by slip casting under high magnetic field and spark plasma sintering

Authors: Grigoroscuta, MA; Aldica, G; Pasuk, I; Burdusel, M; Sandu, V; Kuncser, A; Suzuki, TS; Vasylkiv, O; Badica, P

Published: FEB 2021, MATERIALS RESEARCH BULLETIN, 134, DOI: 10.1016/j.materresbull.2020.111103

Partially-oriented MgB2 bulk discs (13 and 9 %) with the starting compositions of (MgB2)(0.99)(B4C)(0.01) and (MgB2)(0.99)(c-BN)om were fabricated by slip casting under an H-0 = 12 T magnetic field (perpendicular to the disc surface) and subsequent spark plasma sintering. The maximum critical current density and irreversibility field are for H//H-0 (H=applied field). These values are higher or similar to the randomly-oriented samples with the same composition. The maximum volume pinning force (F-p) is lower in the partially-oriented ones than in the randomly-oriented samples. The pinning-force-related parameters depend on the additive and orientation. Assessment of the major pinning mechanism within the scaling and percolation models considering these parameters shows significant limitations. A method to scale F-p is proposed; for the randomly and partially-oriented samples (that show an extra peak in F-p), the single and double Gaussian functions fit well. The results suggest an anisotropic influence of carbon substituting for boron in the MgB2.

24. Structural Details of BaTiO3 Nano-Powders Deduced from the Anisotropic XRD Peak Broadening

Authors: Pasuk, I; Neatu, F; Neatu, S; Florea, M; Istrate, CM; Pintilie, I; Pintilie, L

Published: MAY 2021, NANOMATERIALS, 11, DOI: 10.3390/nano11051121

In this study, nano-BaTiO3 (BTO) powders were obtained via the solvothermal method at different reaction times and were investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. The results were compared with those obtained for a larger crystallite size BTO powder (BTO-m). The sizes of the cuboid crystallites (as determined by XRD and TEM) ranged from about 18 to 24 nm, depending on the reaction time. The evolution with temperature of the structure parameters of nano-BTO was monitored by means of X-ray diffraction and Raman spectroscopy and no signs of phase transition were found up to 170 degrees C. Careful monitoring of the dependence of the XRD peak widths on the hkl indices showed that the effect of the cubic crystallite shape upon the XRD peak widths was buried by the effect of hidden tetragonal line splits and by anisotropic microstrain. The good correlation of the line widths with the tetragonal split amplitudes, observed especially for BTO-m above the transition temperature, indicates tetragonal deformations, as also revealed by Raman spectroscopy. The large anisotropic microstrain shown by the nano-powders, which had a maximum value in the directions, was considered evidence of the phenomenon of surface relaxation of cubic crystallites edged by {100} faces. The observed behavior of the nano-BTO structures with increasing temperature may suggest a correlation between the surface relaxation and tetragonal deformation in the nano-cubes. The experimental results for both nano-BTO and mezoscale-BTO are in agreement with the core-shell model.

25. The Physico-Chemical Properties and Exploratory Real-Time Cell Analysis of Hydroxyapatite Nanopowders Substituted with Ce, Mg, Sr, and Zn (0.5-5 at.%)

Authors: Chirica, IM; Enciu, AM; Tite, T; Dudau, M; Albulescu, L; Iconaru, SL; Predoi, D; Pasuk, I; Enculescu, M; Radu, C; Mihalcea, CG; Popa, AC; Rusu, N; Nita, S; Tanase, C; Stan, GE

Published: JUL 2021, MATERIALS, 14, DOI: 10.3390/ma14143808

Cation-substituted hydroxyapatite (HA), standalone or as a composite (blended with polymers or metals), is currently regarded as a noteworthy candidate material for bone repair/regeneration either in the form of powders, porous scaffolds or coatings for endo-osseous dental and orthopaedic implants. As a response to the numerous contradictions reported in literature, this work presents, in one study, the physico-chemical properties and the cytocompatibility response of single cation-doped (Ce, Mg, Sr or Zn) HA nanopowders in a wide concentration range (0.5-5 at.%). The modification of composition, morphology, and structure was multiparametrically monitored via energy dispersive X-ray, X-ray photoelectron, Fourier-transform infrared and micro-Raman spectroscopy methods, as well as by transmission electron microscopy and X-ray diffraction. From a compositional point of view, Ce and Sr were well-incorporated in HA, while slight and pronounced deviations were observed for Mg and Zn, respectively. The change of the lattice parameters, crystallite size, and substituting cation occupation factors either in the Ca(I) or Ca(II) sites were further determined. Sr produced the most important HA structural changes. The in vitro biological performance was evaluated by the (i) determination of leached therapeutic cations (by inductively coupled plasma mass spectrometry) and (ii) assessment of cell behaviour by both conventional assays (e.g., proliferation-3-(4,5-dimethyl thiazol-2-yl) 5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay; cytotoxicity-lactate dehydrogenase release assay) and, for the first time, real-time cell analysis (RTCA). Three cell lines were employed: fibroblast, osteoblast, and endothelial. When monophasic, the substituted HA supported the cells' viability and proliferation without signs of toxicity. The RTCA results indicate the excellent adherence of cells. The study strived to offer a perspective on the behaviour of Ce-, Mg-, Sr-, or Zn-substituted HAs and to deliver a well-encompassing viewpoint on their effects. This can be highly important for the future development of such bioceramics, paving the road toward the identification of candidates with highly promising therapeutic effects.

26. New superconductor/ferromagnet heterostructure formed by YBa2Cu3O7-x and CaRuO3

Authors: Ivan, I; Pasuk, I; Crisan, A; Sandu, V; Onea, M; Leca, A; Cosar, C; Burdusel, M

Published: NOV 2021, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 34, DOI: 10.1088/1361-6668/ac2622

Almost all proposed configurations and practical achievements based on superconductor/ferromagnet (S/F) heterostrucutres focus on s-wave superconductors. However, several attempts targeted also high temperature superconductors, most of them using manganite ferromagnets LaXMnO3 (X: Ca or Sr) and Y1Ba2Cu3O7-x (YBCO). Here we propose a new ferromagnetic material that can be used with YBCO for the fabrication of S/F hybrid structures. We show that a ferromagnetic order can be induced in a thin layer (similar to 130 nm thickness) of CaRuO3 grown by pulsed laser deposition on epitaxial YBCO film. Detailed magnetic and structural investigations show that the observations of the weak ferromagnetism are consistent with the magnetic order induced by in-plane tensile strain of about 1.7% and the easy-magnetization axis forms an angle of similar to 180o with the layer plane. The value of the Curie temperature T (Curie) estimated using the Curie-Weiss law was 340 K. An unusual temperature dependence of the magnetic moment around the superconducting transition was observed in both field-cooled and zero-field-cooled configurations which is attributed to the paramagnetic Meissner effect.

27. Influence of Thickness on the Magnetic and Magnetotransport Properties of Epitaxial La0.7Sr0.3MnO3 Films Deposited on STO (001)

Authors: Greculeasa, SG; Stanciu, AE; Leca, A; Kuncser, A; Hrib, L; Chirila, C; Pasuk, I; Kuncser, V

Published: DEC 2021, NANOMATERIALS, 11, DOI: 10.3390/nano11123389

Epitaxial La0.7Sr0.3MnO3 films with different thicknesses (9-90 nm) were deposited on SrTiO3 (0 0 1) substrates by pulsed laser deposition. The films have been investigated with respect to morpho-structural, magnetic, and magneto-transport properties, which have been proven to be thickness dependent. Magnetic contributions with different switching mechanisms were evidenced, depending on the perovskite film thickness. The Curie temperature increases with the film thickness. In addition, colossal magnetoresistance effects of up to 29% above room temperature were evidenced and discussed in respect to the magnetic behavior and film thickness.

28. Tetragonal-Cubic Phase Transition and Low-Field Dielectric Properties of CH3NH3PbI3 Crystals

Authors: Patru, RE; Khassaf, H; Pasuk, I; Botea, M; Trupina, L; Ganea, CP; Pintilie, L; Pintilie, I

Published: AUG 2021, MATERIALS, 14, DOI: 10.3390/ma14154215

The frequency and temperature dependence of dielectric properties of CH3NH3PbI3 (MAPI) crystals have been studied and analyzed in connection with temperature-dependent structural studies. The obtained results bring arguments for the existence of ferroelectricity and aim to complete the current knowledge on the thermally activated conduction mechanisms, in dark equilibrium and in the presence of a small external a.c. electric field. The study correlates the frequency-dispersive dielectric spectra with the conduction mechanisms and their relaxation processes, as well as with the different transport regimes indicated by the Nyquist plots. The different energy barriers revealed by the impedance spectroscopy highlight the dominant transport mechanisms in different frequency and temperature ranges, being associated with the bulk of the grains, their boundaries, and/or the electrodes' interfaces.

29. Antimicrobial and Cytocompatible Bovine Hydroxyapatite-Alumina-Zeolite Composite Coatings Synthesized by Pulsed Laser Deposition from Low-Cost Sustainable Natural Resources

Authors: Popescu-Pelin, G; Ristoscu, C; Duta, L; Stan, GE; Pasuk, I; Tite, T; Stan, MS; Bleotu, C; Popa, M; Chifiriuc, MC; Oktar, FN; Nicarel, A; Mihailescu, IN

Published: MAR 16 2020, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, 8, 4036, DOI: 10.1021/acssuschemeng.9b05031

Bovine hydroxyapatite (BHA) and BHA blended with clinoptilolite (CLIN) and alumina (Al2O3) coatings were synthesized using pulsed laser deposition (PLD) with a KrF* excimer laser source (lambda = 248 nm, tau(FWHM) <= 25 ns). Physical-chemical characteristics and the potential use of coatings for preventing bacteria adhesion and biofilm formation were investigated. Optimized PLD conditions were selected for coatings with rough morphologies, suitable for good cell adhesion and implant anchorage and good replication of the source target composition. The crystallinity of composite coatings was progressively decreasing with the augment of the Al2O3 and CLIN contents, which in turn can facilitate an efficacious release of active components. Al2O3- and CLIN-containing coatings exhibited high cytocompatibility and specific antibiofilm profiles, preventing the initiation and maturation of bacterial biofilms. Optimum biological activity profiles associated with the use of sustainable and/or inexpensive materials are, in our opinion, of key importance for the future development of performant implant coatings, which should he perfectly compatible with the surrounding tissue while preventing postsurgical endogenous or nosocomial infections.

30. Effect of the processing parameters on surface, physico-chemical and mechanical features of bioceramics synthesized from abundant carp fish bones

Authors: Maidaniuc, A; Miculescu, F; Ciocoiu, RC; Butte, TM; Pasuk, I; Stan, GE; Voicu, SI; Ciocan, LT

Published: JUN 1 2020, CERAMICS INTERNATIONAL, 46, 10171, DOI: 10.1016/j.ceramint.2020.01.007

Aim of this research was to evaluate the effect of an improved processing thermal method of calcium phosphates obtained from a natural source of high availability (i.e. cyprinids bones). Thereby, the sinterability of the naturally-derived ceramics has been explored. The samples were characterized before and after sintering in terms of surface features (morphology, roughness, wettability and surface energy), weight loss, shrinking, composition, structure, and mechanical properties. The results showed that the initial processing has a significant effect on the sintering outcomes: the morphology and mechanical features were clearly influenced by the processing temperature, while minor effects were observed on the surface and structure properties. Therefore, the study unveils suitable strategies for controlling the characteristics of cost-effective bioceramics and opens up new perspectives for the sustainable manufacturing of highly valuable biomedical products from abundant carp fish bones.

31. High magnetic shielding properties of an MgB2 cup obtained by machining a spark-plasma-sintered bulk cylinder

Authors: Gozzelino, L; Gerbaldo, R; Ghigo, G; Torsello, D; Bonino, V; Truccato, M; Grigoroscuta, MA; Burdusel, M; Aldica, GV; Sandu, V; Pasuk, I; Badica, P

Published: APR 2020, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 33, DOI: 10.1088/1361-6668/ab7846

Superconductors are key materials for shielding quasi-static magnetic fields. In this work, we investigated the shielding properties of an MgB2 cup-shaped shield with small aspect-ratio of height/outer radius. Shape and aspect-ratio were chosen in order to address practical requirements of both high shielding factors (SFs) and space-saving solutions. To obtain large critical current densities (J(c)), which are crucial for achieving high magnetic-mitigation performance, a high-purity starting MgB2 powder was selected. Then, processing of the starting MgB2 powder into high density bulks was performed by spark plasma sintering. The as-obtained material is fully machinable and was shaped into a cup-shield. Assessment of the material by scaling of the pinning force showed a non-trivial pinning behaviour. The MgB2 powder selection was decisive in enlarging the range of external fields where efficient shielding occurs. The shield's properties were measured in both axial- and transverse-field configurations using Hall probes. Despite a height/outer radius aspect ratio of 2.2, shielding factors higher than 10(4) at T = 20 K up to a threshold field of 1.8 T were measured in axial-field geometry at a distance of 1 mm from the closed extremity of the cup, while SFs > 10(2) occurred in the inner half of the cup. As expected, this threshold field decreased with increased temperature, but SFs still exceeding the above mentioned values were found up to 0.35 T at 35 K. The shield's shape limits the SF values achievable in transverse-field configuration. Nevertheless, the in-field J(c) of the sample supported SFs over 40 at T = 20 K up to a field of 0.8 T, 1 mm away from the cup closure.

32. Enhanced critical current density at high magnetic fields in MgB2 with Ga/In acetylacetonate processed by spark plasma sintering

Authors: Batalu, D; Aldica, G; Burdusel, M; Grigoroscuta, M; Pasuk, I; Kuncser, A; Ionescu, AM; Badica, P

Published: MAY-JUN 2020, JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 9, 3733, DOI: 10.1016/j.jmrt.2020.01.109

Dense samples (94-96%) with starting composition (MgB2)(0.99)(X-acac)(0.01) (X-acac denotes Ga or In acetylacetonate) were obtained by spark plasma sintering. The resulting material is a superconducting composite, where carbon substitutes for boron in the crystal structure of MgB2. Added samples show enhanced critical current density at high magnetic fields and this is reflected in high values of irreversibility field (H-irr) at temperatures below 25 K when compared to a pristine sample. More efficient is In-acac addition and it promotes a H-irr of similar to 12.4T (100 A/cm(2) criterion) at 5 K. Carbon substitution for boron in the crystal structure of MgB2 has a strong influence on the pinning force and its related parameters and promotes in the added samples a grain boundary pinning mechanism as the dominant one, whereas the pristine sample with a low amount of carbon shows a major mechanism of point pinning type. However, our analysis indicates on the synergetic effects of the carbon substituting for boron and of the microstructural details on pinning and critical current density. The result strongly emphasizes the significantly different behavior of the additive during processing of the MgB2 samples, although thermal analysis experiments on both additives show very similar decomposition patterns. (C) 2020 The Authors. Published by Elsevier B.V.

33. Reproducibility of small Ge2C6H10O7-added MgB2 bulks fabricated by ex situ Spark Plasma Sintering used in compound bulk magnets with a trapped magnetic field above 5T

Authors: Badica, P; Aldica, G; Grigoroscuta, MA; Burdusel, M; Pasuk, I; Batalu, D; Berger, K; Koblischka-Veneva, A; Koblischka, MR

Published: JUN 29 2020, SCIENTIFIC REPORTS, 10, DOI: 10.1038/s41598-020-67463-y

Bulk discs (20 mm diameter and 4.3 mm thickness) of MgB2 added with Ge2C6H10O7 were obtained by Spark Plasma Sintering. Six samples with composition Mg B 2 (Ge2C6H10O7)(0.0014) and one undoped sample were fabricated under similar conditions and were magnetically characterized in order to determine the scattering of properties and reproducibility. The main source of the scattering of the properties is the decomposition of the additive due to elimination of the organic part in gas form, which occurs stepwise with intensive vacuum drops at around similar to 560 and similar to 740 degrees C. A third drop, which is sometimes not well resolved being part of the second peak at 740 degrees C, occurs at similar to 820 degrees C. The critical temperature at the midpoint of the transition, T-C, shows only a relatively small variation between 37.4 and 38 K, and the irreversibility field at a low temperature of 5 K takes values between 8 and 10 T. The pinning force and pinning force related parameters do not correlate with the carbon substituting for boron in MgB2 and suggest a synergetic influence of the microstructural details and carbon. Overall, despite the superconducting properties scattering, the samples are of high quality. Stacked into a column of six samples, they can trap at the center and on the surface of the column a magnetic field of 6.78 and 5.19 Tat 12 K, 5.20 and 3.98 Tat 20 K and 2.39, and 1.96 Tat 30 K. These promising values, combined with facile fabrication of the samples with relatively high quality and reproducibility, show the feasibility of their use in building complex and large compound arrangements for bulk magnets and other applications.

34. Polarized emission and dielectric studies of novel lanthanidomesogens based on 4-pyridone ligands

Authors: Ilinca, T; Manaila-Maximean, D; Ganea, PC; Pasuk, I; Circu, V

Published: 2020, ADVANCED TOPICS IN OPTOELECTRONICS, MICROELECTRONICS AND NANOTECHNOLOGIES X, 11718, DOI: 10.1117/12.2572109

Novel lanthanidomesogens based on lanthanide nitrates carrying three 4-pyridone ligands having two alkoxy chains at the periphery were synthesized and their structure was assigned based on IR spectroscopy and elemental analysis. Their thermal stability was evaluated by TG analysis confirming that the decomposition starts at very high temperatures around 300 degrees C. The liquid crystalline properties were investigated by using a combination of techniques: polarized optical microscopy (POM) and differential scanning calorimetry (DSC) and, for selected compounds, by variable-temperature powder X-ray diffraction. The new liquid crystal display a hexagonal columnar phase (Col(h)) between 63 degrees C and 242 degrees C, depending on the length of the alkyl chain Dielectric spectroscopy on a wide frequency range was used to evaluate the dipolar relaxation processes. The emission properties of a mixture of E7 doped with a selected europium complex filled in a planar cell were investigated on changing the applied voltage, ranging from 0V up to 15V.

35. Polarization-dependent magnetism of the Ni/BaTiO3 interface

Authors: Bocirnea, AE; Popescu, DG; Chirila, C; Costescu, RM; Kuncser, V; Stancu, V; Trupina, L; Pasuk, I; Vlaicu, AM; Husanu, MA

Published: MAR 4 2020, PHYSICAL REVIEW MATERIALS, 4, DOI: 10.1103/PhysRevMaterials.4.034402

We explore the cross coupling between the ferroelectric and ferromagnetic phases in Ni/BaTiO3(001) heterostructures and demonstrate the modulation of the magnetism and incidence of exchange bias in the ultrathin metallic Ni overlayer, depending on the ferroelectric state of the bottom layer. We establish that 5-nm-thick monocrystalline Ni film deposited on BaTiO3 with ferroelectric polarization pointing towards the surface (P+) favors the organization of Ni into uniform ferromagnetic domains. Ni grown on BaTiO3 with opposite ferroelectric polarization is featured by emerging exchange-bias coupling between the ferromagnetic Ni top layers and the antiferromagnetic reacted interface, as theoretically explained by first-principles calculations. We explicitly obtain the morphology of the magnetic domains of the crystalline Ni layer in atomic and magnetic force microscopy measurements (AFM/MFM). The resemblance of AFM and MFM images indicate that, although with radically different morphologies, in both cases all spins orient in the Ni plane. Consequently, the distinct signature of the ferroelectric-ferromagnetic coupling extracted from the magneto-optical Kerr effect measurements encodes all the information of sample magnetism. The peculiar magnetic coupling depending on the ferroelectric state indicates new ways of engineering the functionality of metal/ferroelectric interfaces.

36. Fish Bone Derived Bi-Phasic Calcium Phosphate Coatings Fabricated by Pulsed Laser Deposition for Biomedical Applications

Authors: Popescu-Pelin, G; Ristoscu, C; Duta, L; Pasuk, I; Stan, GE; Stan, MS; Popa, M; Chifiriuc, MC; Hapenciuc, C; Oktar, FN; Nicarel, A; Mihailescu, IN

Published: DEC 2020, MARINE DRUGS, 18, DOI: 10.3390/md18120623

We report on new biomaterials with promising bone and cartilage regeneration potential, from sustainable, cheap resources of fish origin. Thin films were fabricated from fish bone-derived bi-phasic calcium phosphate targets via pulsed laser deposition with a KrF * excimer laser source (lambda = 248 nm, tau(FWHM) <= 25 ns). Targets and deposited nanostructures were characterized by SEM and XRD, as well as by Energy Dispersive X-ray (EDX) and FTIR spectroscopy. Films were next assessed in vitro by dedicated cytocompatibility and antimicrobial assays. Films were Ca-deficient and contained a significant fraction of beta-tricalcium phosphate apart from hydroxyapatite, which could contribute to an increased solubility and an improved biocompatibility for bone regeneration applications. The deposited structures were biocompatible as confirmed by the lack of cytotoxicity on human gingival fibroblast cells, making them promising for fast osseointegration implants. Pulsed laser deposition (PLD) coatings inhibited the microbial adhesion and/or the subsequent biofilm development. A persistent protection against bacterial colonization (Escherichia coli) was demonstrated for at least 72 h, probably due to the release of the native trace elements (i.e., Na, Mg, Si, and/or S) from fish bones. Progress is therefore expected in the realm of multifunctional thin film biomaterials, combining antimicrobial, anti-inflammatory, and regenerative properties for advanced implant coatings and nosocomial infections prevention applications.

37. Magneto-functionalities of La 1-x A x MnO 3 (A = K; Ba) synthesized by flash combustion method

Authors: Bouzid, SA; Galca, AC; Sajieddine, M; Kuncser, V; Rostas, AM; Iacob, N; Enculescu, M; Amarande, L; Pasuk, I; Essoumhi, A

Published: OCT 25 2020, JOURNAL OF ALLOYS AND COMPOUNDS, 839, DOI: 10.1016/j.jallcom.2020.155546

38. Complex exchange coupling mechanisms in SRO/BFO/Fe heterostructures

Authors: Greculeasa, SG; Schinteie, G; Hrib, LM; Stancu, V; Pasuk, I; Kuncser, A; Kuncser, V

Published: JAN 30 2019, JOURNAL OF ALLOYS AND COMPOUNDS, 773, 345, DOI: 10.1016/j.jallcom.2018.09.208

Temperature dependent interfacial coupling mechanisms in SRO/BFO/Fe layered structures were investigated. The BFO/Fe heterostructures were prepared by PLD and sputtering, respectively, on the STO(0 0 1) substrate with a 20 nm SRO buffer layer. An annealing treatment in external magnetic field was further applied. Complex characterizations with X-ray diffraction, atomic force microscopy, Transmission Electron Microscopy, Mossbauer spectroscopy, magneto-optic Kerr effect and SQUID magnetometry were performed. Before annealing, the films show good crystallization and epitaxy of the SRO and BFO layers with smooth interfaces. Two coupling mechanisms of the ferromagnetic layers (top Fe and bottom SRO, respectively) to the epitaxial BFO film with mainly antiferromagnetic structure were evidenced in the as deposited samples at low temperatures. Negative exchange bias fields of up to 67(10) Oe and 37(5) Oe at low temperatures were observed for the two ferromagnetic components, respectively, depending on the thickness of the Fe layer. The field annealing treatments induce a specific morphology and magnetic spin structure at both interfaces of the BFO spacer layer, giving rise to a long range magnetostatic coupling between the two ferromagnetic films, in addition to the interfacial couplings. Moreover, the experimentally evidenced Fe clusters penetrating the BFO/Fe interface toward the BFO layer give support for this interaction. As an additional consequence, a considerable enhancement of both uniaxial and unidirectional anisotropies as well as an increased blocking temperature of exchange bias were obtained. The involved exchange coupling mechanisms were discussed in detail. (C) 2018 Elsevier B.V. All rights reserved.

39. Prototype Orthopedic Bone Plates 3D Printed by Laser Melting Deposition

Authors: Chioibasu, D; Achim, A; Popescu, C; Stan, GE; Pasuk, I; Enculescu, M; Iosub, S; Duta, L; Popescu, A

Published: MAR 19 2019, MATERIALS, 12, DOI: 10.3390/ma12060906

Laser melting deposition is a 3D printing method usually studied for the manufacturing of machine parts in the industry. However, for the medical sector, although feasible, applications and actual products taking advantage of this technique are only scarcely reported. Therefore, in this study, Ti6Al4V orthopedic implants in the form of plates were 3D printed by laser melting deposition. Tuning of the laser power, scanning speed and powder feed rate was conducted, in order to obtain a continuous deposition after a single laser pass and to diminish unwanted blown powder, stuck in the vicinity of the printed elements. The fabrication of bone plates is presented in detail, putting emphasis on the scanning direction, which had a decisive role in the 3D printing resolution. The printed material was investigated by optical microscopy and was found to be dense, with no visible pores or cracks. The metallographic investigations and X-ray diffraction data exposed an unusual biphasic alpha+beta structure. The energy dispersive X-ray spectroscopy revealed a composition very similar to the one of the starting powder material. The mapping of the surface showed a uniform distribution of elements, with no segregations or areas with deficient elemental distribution. The in vitro tests performed on the 3D printed Ti6Al4V samples in osteoblast-like cell cultures up to 7 days showed that the material deposited by laser melting is cytocompatible.

40. Bulks of Al-B-C obtained by reactively spark plasma sintering and impact properties by Split Hopkinson Pressure Bar

Authors: Vasylkiv, O; Borodianska, H; Demirskyi, D; Li, P; Suzuki, TS; Grigoroscuta, MA; Pasuk, I; Kuncser, A; Badica, P

Published: DEC 20 2019, SCIENTIFIC REPORTS, 9, DOI: 10.1038/s41598-019-55888-z

Mixtures of B4C, alpha-AlB12 and B powders were reactively spark plasma sintered at 1800 degrees C. Crystalline and amorphous boron powders were used. Samples were tested for their impact behavior by the Split Hopkinson Pressure Bar method. When the ratio R = B4C/alpha-AlB12 >= 1.3 for a constant B-amount, the major phase in the samples was the orthorhombic AlB24C4, and when R < 1 the amount of AlB24C4 significantly decreased. Predictions that AlB24C4 has the best mechanical impact properties since it is the most compact and close to the ideal cubic packing among the Al-B-C phases containing B-12-type icosahedra were partially confirmed. Namely, the highest values of the Vickers hardness (32.4 GPa), dynamic strength (1323 MPa), strain and toughness were determined for the samples with R = 1.3, i.e., for the samples with a high amount of AlB24C4. However, the existence of a maximum, detectable especially in the dynamic strength vs. R, indicated the additional influence of the phases and the composite's microstructure in the samples. The type of boron does not influence the dependencies of the indicated mechanical parameters with R, but the curves are shifted to slightly higher values for the samples in which amorphous boron was used.

41. Memcomputing and Nondestructive Reading in Functional Ferroelectric Heterostructures

Authors: Boni, GA; Filip, LD; Chirila, C; Iuga, A; Pasuk, I; Hrib, L; Trupina, L; Pintilie, I; Pintilie, L

Published: AUG 26 2019, PHYSICAL REVIEW APPLIED, 12, DOI: 10.1103/PhysRevApplied.12.024053

Multiple nonvolatile and well-separated capacitive states can be obtained in a two-terminal ferroelectric capacitor setup by fine tuning the polarization switching process. This approach allows for the implementation of memcomputing (same platform for storage and computing) capable ferroelectric structures. Digital and analog storage modes are exemplified in this work together with an algorithm for simple binary computation functions such as OR/NOR and AND/NAND for data processing on the same device. Results are obtained by controlling the polarization switching process in ferroelectric multi-layers such as Pb (Zr0.2Ti0.8)O-3/SrTiO3/Pb (Zr0.2Ti0.8)O-3 and Pb (Zr0.2Ti0.8)O-3/BaTiO3/Pb (Zr0.2Ti0.8)O-3. Besides memcomputing, these results can be used for nondestructive capacitive reading of information in simple ferroelectric capacitors or can open the way toward applications such as neuromorphic and chaotic circuits.

42. Structural, electric and pyroelectric properties of up and down graded PZT multilayers

Authors: Botea, M; Hrib, L; Pasuk, I; Iuga, A; Trupina, L; Negrea, R; Becherescu, N; Pintilie, L

Published: JUL 2019, CURRENT APPLIED PHYSICS, 19, 810, DOI: 10.1016/j.cap.2019.04.010

Multi-layered structures, composed of thin films from materials with different compositions or physical properties, represents a way to obtain enhanced properties or even new functionalities. In this work, lead zirconate titanate PbZrxTi1-xO3 (PZT; x = 0.20, 0.52, 0.80) multilayers were grown by pulsed laser deposition (PLD) on a single crystal strontium titanate (SrTiO3, STO) substrate, using a strontium ruthenate (SrRuO3, SRO) film as buffer layer for epitaxial growth, and also as back electrode. Up and down multi-layers were grown and their physical and structural properties were compared, up being the structure in which Zr concentration was varied from 20% near the STO substrate to 80% at the surface, while down is for the structure in which the Zr concentration starts with 80% near the substrate and ends with 20% at the surface. It was found that the electric and pyroelectric properties of the two graded structures are significantly different. The up structure presents electric properties that are comparable with those of single composition PZT films while the properties of the down structure are deteriorated, especially in terms of the leakage current magnitude. Pyroelectric signal could be measured only for the up structure. These differences were attributed to larger density of structural defects in the down structure compared to the up one. This is due to the different growth sequence: Lop structure starts with tetragonal PZT on cubic substrate (lower lattice mismatch, 1.1%) while down structure starts with rhombohedral PZT on cubic substrate (larger lattice mismatch, almost 5%).

43. Synthesis and thermal, emission and dielectric properties of liquid crystalline Eu(III), Sm(III) and Tb(III) complexes based on mesogenic 4-pyridone ligands functionalized with cyanobiphenyl groups

Authors: Chiriac, LF; Ganea, PC; Manaila-Maximean, D; Pasuk, I; Circu, V

Published: SEP 15 2019, JOURNAL OF MOLECULAR LIQUIDS, 290, DOI: 10.1016/j.molliq.2019.111184

New thermotropic lanthanidomesogens based on Eu(III), Sm(III) and Tb(III) with N-alkylated 4-pyridones mesogenic ligands, having two cyanobiphenyl groups attached via long alkoxy spacers, with 6, 9 and 10 carbons atoms in 3,5-positions of a benzyl unit, have been designed and investigated. The liquid crystal behavior was assessed by differential scanning calorimetry, the mesophases being assigned by polarized light microscopy based on their characteristic textures and confirmed by variable temperature X-ray powder diffraction analysis. The three N-alkylated 4-pyridones nematic ligands reacted with lanthanide nitrates to yield new lanthanidomesogens with a stable and reproducible smectic A phase up to 125 degrees C. The emission spectra of the complexes have shown the characteristic emission of the lanthanide trivalent ions, over the entire temperature range of SmA phase up to isotropic state. The dielectric spectroscopy measurements performed in the temperature range of existence of the liquid crystal phase, both in the low frequency (LF) domain 0.01-10 MHz and in the high frequency (HF) range, 1 MHz-3 GHz, revealed three dipolar relaxation processes. The characteristic times have been obtained by fitting the spectra of the dielectric loss with a two component Havriliak-Negami function. The activation constant/energy was determined from the Vogel-Fiilcher-Tammann law. (C) 2019 Elsevier B.V. All rights reserved.

44. Superconducting MgB2 textured bulk obtained by ex situ spark plasma sintering from green compacts processed by slip casting under a 12T magnetic field

Authors: Grigoroscuta, MA; Sandu, V; Kuncser, A; Pasuk, I; Aldica, G; Suzuki, TS; Vasylkiv, O; Badica, P

Published: DEC 2019, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 32, DOI: 10.1088/1361-6668/ab4620

MgB2 green bodies were prepared by magnetic field slip casting in ethyl alcohol with added polyethyleneimine dispersing agent under a high magnetic field, mu H-0(0) = 12 T. Samples were further processed by spark plasma sintering (SPS) and characterized for superconducting properties. Slip casting provides texturing of MgB2 (the degree of c-axis orientation is approximately 3.5%), which is further increased significantly (to about 21%) in the SPSed sample. The critical current density (J(c)) displays anisotropy relative to the orientation of the measuring magnetic field. Specific features of J(c)(H, T) and of the pinning force extracted from magnetic measurements with the field parallel and perpendicular to H-0 are discussed.

45. Ex Situ Spark Plasma Sintering of Short Powder-in-Tube MgB2 Tapes with Open and Closed Ends

Authors: Aldica, G; Burdusel, M; Popa, S; Pasuk, I; Ionescu, AM; Kuncser, A; Badica, P

Published: NOV 2018, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 31, 3432, DOI: 10.1007/s10948-018-4616-9

Short powder-in-tube tapes of MgB2 in the Fe sheath were fabricated by ex situ route from a commercial powder containing some free Mg and MgO impurity phases. The final heat treatment was performed by spark plasma sintering (SPS). Tapes were with open (OT) or closed (CT) endings. Closed endings were made by folding and pressing. The MgB2 core of the OT sample has shown a higher low-field critical current density, a higher maximum pinning force, a slightly higher disorder, smaller average MgB2 crystallite size, a weak contact between Fe and MgB2 core, and more macro-flux jumps. The upper and irreversibility fields were similar for OT and CT samples. In the center of the MgB2 cores, the detected impurity phase is MgO, while at the interface with Fe, MgB4 also occurs. Impurity phases found at interface, MgO and MgB4, are present in the center of the bulk SPSed samples. Reactions and pinning-force-related parameters are discussed with respect to Mg behavior influenced by condition of endings. It is inferred that the presence of free Mg in the raw MgB2 powder has an important contribution to observed differences, and its removal or control is recommended.

46. Cationic Substitutions in Hydroxyapatite: Current Status of the Derived Biofunctional Effects and Their In Vitro Interrogation Methods

Authors: Tite, T; Popa, AC; Balescu, LM; Bogdan, IM; Pasuk, I; Ferreira, JMF; Stan, GE

Published: NOV 2018, MATERIALS, 11, DOI: 10.3390/ma11112081

High-performance bioceramics are required for preventing failure and prolonging the life-time of bone grafting scaffolds and osseous implants. The proper identification and development of materials with extended functionalities addressing socio-economic needs and health problems constitute important and critical steps at the heart of clinical research. Recent findings in the realm of ion-substituted hydroxyapatite (HA) could pave the road towards significant developments in biomedicine, with an emphasis on a new generation of orthopaedic and dentistry applications, since such bioceramics are able to mimic the structural, compositional and mechanical properties of the bone mineral phase. In fact, the fascinating ability of the HA crystalline lattice to allow for the substitution of calcium ions with a plethora of cationic species has been widely explored in the recent period, with consequent modifications of its physical and chemical features, as well as its functional mechanical and in vitro and in vivo biological performance. A comprehensive inventory of the progresses achieved so far is both opportune and of paramount importance, in order to not only gather and summarize information, but to also allow fellow researchers to compare with ease and filter the best solutions for the cation substitution of HA-based materials and enable the development of multi-functional biomedical designs. The review surveys preparation and synthesis methods, pinpoints all the explored cation dopants, and discloses the full application range of substituted HA. Special attention is dedicated to the antimicrobial efficiency spectrum and cytotoxic trade-off concentration values for various cell lines, highlighting new prophylactic routes for the prevention of implant failure. Importantly, the current in vitro biological tests (widely employed to unveil the biological performance of HA-based materials), and their ability to mimic the in vivo biological interactions, are also critically assessed. Future perspectives are discussed, and a series of recommendations are underlined.

47. A Comparative Study of Ge-Based Organometallic Additions to MgB2

Authors: Batalu, D; Nakamura, T; Enculescu, M; Popa, S; Pasuk, I; Aldica, G; Ionescu, AM; Badica, P

Published: JUN 2018, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, 28, DOI: 10.1109/TASC.2018.2808366

Four Ge-based organometallic (OM = C6H10 Ge2O7) polymers with similar chemical composition were used as additions for MgB2. MgB2 (OM) 0.0014 dense samples with a relative density higher than 97% were obtained by ex situ spark plasma sintering. The critical current density and the irreversibility magnetic field of the added samples are slightly improved at high magnetic fields by repagermanium (Alfa Aesar) addition when compared to the pristine reference sample. Addition of Ge-straight-chain polymer shows some improvement of the maximum volume pinning force, F-p (max). There is no significant Ge substitution in the crystal lattice of MgB2, while C substitutes for B. Pinning mechanism is mainly of a point pinning type, with the grain boundary pinning mechanism strengthening at lower temperatures and when additives are not used. A relatively high amount of carbon in the samples washes out the Ge effects on pinning-force-related parameters. The structure and morphology of the polymer additive play an important role in dispersion when mixing, impacting the quality of the superconducting properties. The nanosize dimension of the pristine MgB2 powder shows also some drawbacks in mixing and sintering.

48. Polarization Orientation in Lead Zirconate Titanate (001) Thin Films Driven by the Interface with the Substrate

Authors: Tanase, LC; Abramiuc, LE; Popescu, DG; Trandafir, AM; Apostol, NG; Bucur, IC; Hrib, L; Pintilie, L; Pasuk, I; Trupina, L; Teodorescu, CM

Published: SEP 11 2018, PHYSICAL REVIEW APPLIED, 10, DOI: 10.1103/PhysRevApplied.10.034020

We investigate the effect of the nature of the substrate and the bottom interface on the out-of-plane polarization orientation of ultrathin (10-nm) lead zirconate titanate (PZT) thin films of (001) orientation by photoelectron spectroscopy of samples without surface contamination. The substrate nature is varied between insulator (strontium titanate, STO) and semiconductor (Nb-doped STO, STON) and finally to a metal with a work function lower than that of PZT (strontium ruthenate, SRO). Outward polarization is obtained for PZT/STON(001) and inward polarization is obtained for PZT/STO(001) and PZT/SRO(001). Explanations are given for all these typical cases, the main elements being charge accumulation for compensation of the depolarization field, self-doping of PZT films, and the interface electric field driving the orientation of the polarization of the ferroelectric films. We find p-type self-doping is correlated with the inward polarization, and the driving field is formed between a negatively charged region with negatively ionized acceptors near the interface with the substrate and the p-type degenerate region with holes accumulated inside, toward the surface. This mechanism may be reversed under the assumption of n-type self-doping, positively ionized donors near the interface, and accumulated electrons toward the surface in the case of an interface with a substrate with a higher work function, being in line with recent data (PZT/Pt or BaTiO3/SRO).

49. Dwell Time Influence on Spark Plasma-Sintered MgB2

Authors: Aldica, G; Popa, S; Enculescu, M; Pasuk, I; Ionescu, AM; Badica, P

Published: FEB 2018, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 31, 325, DOI: 10.1007/s10948-017-4236-9

Samples of MgB2 with relative density above 95% were obtained by spark plasma sintering (SPS) at 1150 A degrees C for a heating time of 100 A degrees C/min and a maximum pressure of 95 MPa. Dwell time was of 1, 4, 7, 10, and 20 min. Samples show that dwell time has a low influence on superconducting characteristics. However, small differences were observed and they are discussed from the viewpoint of density, structural, microstructural, critical current density, irreversibility field, and pinning type. The dominant contribution for all investigated samples is given by point and delta T (c) pinning.

50. Wide-Range Columnar and Lamellar Photoluminescent Liquid-Crystalline Lanthanide Complexes with Mesogenic 4-Pyridone Derivatives

Authors: Chiriac, LF; Pasuk, I; Secu, M; Micutz, M; Circu, V

Published: SEP 12 2018, CHEMISTRY-A EUROPEAN JOURNAL, 24, 13522, DOI: 10.1002/chem.201801781

A series of liquid crystals with various lanthanide ions (Eu-III, Sm-III, and Tb-III) was designed and prepared starting from the corresponding lanthanide nitrates and N-alkylated 4-pyridone derivatives bearing mesogenic 3,4,5-tris(alkyloxy)-benzyl moieties (alkyl=hexyl, octyl, decyl, dodecyl, tetradecyl, or hexadecyl). These new lanthanidomesogens were investigated for their mesogenic properties by a combination of differential scanning calorimetry, polarizing optical microscopy, and temperature-dependent powder X-ray diffraction (XRD). Their thermal stability was assessed by thermogravimetric analysis. All of these complexes show enantiotropic liquid-crystalline behavior with lamellar (SmA) phases in the case of shorter-chain complexes (C-6 and C-8) or hexagonal columnar phases (Col(h)) for complexes with longer alkyl chains (C-12, C-14, and C-16), which were assigned on the basis of their characteristic textures and XRD studies. For complexes with an intermediate number of carbon atoms in the side chains (C-10), both a lamellar phase at lower temperatures and a Col(h) phase at higher temperatures were evidenced. In the solid state, all these complexes show characteristic emissions assigned to the corresponding lanthanide ion. In addition, the luminescence decay curves showed single-exponential decays with characteristic times in the millisecond range (0.75-0.90 ms for Eu-III, 0.045-0.060 ms for Sm-III, and 0.75-1.05 ms for Tb-III).

51. Thermal analysis, microstructure and impurity phases evolution in Fe14Cr ferritic steel powders ball-milled in air and under an argon atmosphere

Authors: Mihalache, V; Mercioniu, I; Aldica, G; Pasuk, I

Published: OCT 2018, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 134, 474, DOI: 10.1007/s10973-018-7274-z

Refined structure of the ferritic phase induced by mechanical milling (under reducing atmosphere) and its thermal stability are required in various applications of nanostructured ferritic alloys. The impurification with nitrogen and oxygen uptaken from the air is very probable during ball-milling, especially at the long-time high-energy milling conditions. As a rule, these interstitial impurities in as-milled powders are in quantities under the sensibility limit of conventional measurement techniques, such as XRD and SEM/ EDS. To evidence the tendency for microstructure modification by impurities introduced during milling, the Fe-14Cr-3W-0.4Ti-0.25Y(2)O(3) (Fe14Cr) ferritic steel powders (re)loaded in air and milled up to 170 h with interruption of the milling process, and heated up to 1373 K were investigated by thermal analysis in correlation with X-ray diffraction and scanning electron microscopy. XRD failed to detect the impurities in powders milled up to 38 h in air although a consistent mass loss related to the degassing of N-2 was registered in thermogravimetric, TG, curves. (Fe,Cr)(4)N, fcc-c, (Fe, Cr)(2)O-3 impurity phases in powders milled over 38 h in air and (Fe,Cr)(2)O-4 formed upon heating were readily detected by XRD. The analysis of these results allowed to better understand the impurification process and to generalise it for any as-milled Fe-Cr-based alloy powder processed in any milling conditions irrespective of the milling atmosphere, duration and thus, of amounts of contaminants. The quality of three powders milled for 170 h in three different conditions was compared: in air, under an argon atmosphere with interruptions of the milling process and under an argon atmosphere without interruption of the milling process. The contamination of powder milled for 170 h under an argon atmosphere without interruption of the milling process is insignificant (corresponding to less than 0.5 mass% mass loss in TG) as compared to powders obtained in the other two milling conditions. New approaches for minimising the contamination from air are suggested.

52. Structural and magnetic properties of Ni nanofilms on Ge(001) by molecular beam epitaxy

Authors: Bocirnea, AE; Costescu, RM; Pasuk, I; Lungu, GA; Teodorescu, CM

Published: DEC 1 2017, APPLIED SURFACE SCIENCE, 424, DOI: 10.1016/j.apsusc.2017.03.034

Ni films of 20 nm nominal thickness were grown on Ge(001) substrates by molecular beam epitaxy at several different temperatures from room temperature up to 400 C. X-ray diffraction and X-ray photoelectron spectroscopy reveal the nucleation of Ni-Ge compounds (NiGe, Ni2Ge, Ni5Ge2) as well as a departure from the fcc Ni structure exhibited by the films at and beyond a temperature of 100 C. The binding energy of the Ni 2p peak increases from the RT value (852.7 eV) by 0.51.1 eV for the Ni/Ge(001) samples, while the Ge 2p binding energy changes by 0.60.7 eV after Ni growth compared to a clean Ge(001) substrate (there is only a +/- 0.15 eV shift among the samples grown on substrates at higher temperatures). By increasing substrate temperature, we obtained higher intermixing of Ni and Ge, but rather than both Ni and Ge interdiffusing, we find that Ni diffuses further into the germanium with higher substrate temperature, forming increasingly Ni-rich Ni-Ge compounds diluted into the Ge matrix. Based on Magneto-optic Kerr Effect measurements, Ni/Ge(001) grown on substrates at 100 and 200 C does not exhibit a hysteresis loop, while the samples on 300 and 400 C substrates show magnetic behavior, which we attribute to the magnetic character of hexagonal Ni5Ge2 (which is determined here for the first time to be a ferromagnetic phase). (c) 2017 Elsevier B.V. All rights reserved.

53. Intrinsic and extrinsic effects near orthorhombic-tetragonal phase transition in barium titanate ceramics doped with small amounts of zirconium

Authors: Amarande, L; Miclea, C; Cioangher, M; Pasuk, I; Iuga, A; Pintilie, I

Published: APR 15 2017, CERAMICS INTERNATIONAL, 43, 4925, DOI: 10.1016/j.ceramint.2016.12.143

Pure BT and BT doped with 1 and 2 mol% Zr, with orthorhombic-tetragonal (O-T) phase transitions near room temperature were prepared, with different grain sizes, by conventional ceramic method, at various sintering temperatures. Intrinsic and extrinsic effects of Zr addition on structural, dielectric, piezoelectric and ferroelectric properties of BT ceramics, near O-T phase transition were studied. In coarse grained ceramics, the intrinsic effects manifested in low field measurements (dielectric and piezoelectric constants), were reduced by Zr addition, while the extrinsic effects which control the high field response (remanent polarization and coercive field) were significantly enhanced. Instead, in fine grains ceramics, of either pure or doped BT, the extrinsic effects related to increased domain wall and grain boundaries density were dominant in both low and high field measurements, overlapping Zr effects. The results were explained in terms of crystal anisotropy correlated with grain size effects.

54. Multiple polarization states in symmetric ferroelectric heterostructures for multi-bit non-volatile memories

Authors: Boni, GA; Filip, LD; Chirila, C; Pasuk, I; Negrea, R; Pintilie, I; Pintilie, L

Published: DEC 28 2017, NANOSCALE, 9, 19278, DOI: 10.1039/c7nr06354g

Here we report a ferroelectric capacitor structure obtained by alternating ferroelectric and insulator thin-film layers which allows an increase of up to 2(n) polarization states, with n the number of ferroelectric layers. Four and up to eight distinct, stable and independently addressed polarization states are experimentally demonstrated in this work. The experimental findings are supported by a theoretical model based on the Landau-Ginzburg-Devonshire theory. The key parameter is the change in the strain conditions of ferroelectric layers induced by the insulating separator. Notably, the 2(n) increase in the storage capacity can be achieved without major changes in the present technology used for FeRAM devices. The test structures demonstrate very good memory characteristics such as retention and fatigue, opening the way towards the design of high density ferroelectric memories.

55. Synthesis and liquid crystalline properties of novel fluorinated N-benzoyl thiourea compounds. Effect of perfluoroalkyl chains on the thermal behavior and smectic phases stability

Authors: Ilis, M; Micutz, M; Pasuk, I; Staicu, T; Circu, V

Published: DEC 2017, JOURNAL OF FLUORINE CHEMISTRY, 204, 89, DOI: 10.1016/j.jfluchem.2017.10.008

A series of novel N-benzoyl-N'-aryl thiourea derivatives (BTU) bearing different number of alkoxy groups in terminal positions of benzoyl unit and a perfluorooctyl group on the other side have been designed and prepared. Their liquid crystalline properties were investigated by a combination of three techniques: polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and variable-temperature powder X-ray diffraction (XRD). Their thermal stability was studied by thermogravimetric analysis (TG). It was found that only the compounds which have only one alkoxy chain attached to benzoyl unit, 1a and 1b, show calamitic mesomorphic behavior, with smectic A and C phases being displayed. The type and stability of these mesophases are greatly influenced by the alkyl chain length as well as by the presence of perfluorooctyl group. The clearing and the mesophase ranges are significantly increased with the incorporation of perfluoroalkyl chains when compared to non-fluorinated analogues, with almost 40 degrees C. The attachment of additional alkoxy groups on the benzoyl moiety led to a significant decrease of the clearing points and suppression of the mesogenic character.

56. Tuning the liquid crystalline properties of palladium(II) metallomesogens: A study of rod-like to disc-like transition in cyclopalladated complexes with N-benzoyl thiourea derivatives

Authors: Micutz, M; Pasuk, I; Ilis, M

Published: OCT 2017, JOURNAL OF MOLECULAR LIQUIDS, 243, 156, DOI: 10.1016/j.molliq.2017.08.013

A new family of cyclometalated palladium(II) complexes with the non-symmetric dimeric liquid crystal Schiff base alpha-(4-cyanobipheny1-4'-yloxy)-omega-(4-n-decyloxyanilinebenzylidene-4'-oxy) hexane and alkoxysubstituted N-benzoyl thiourea (BTU) derivatives as auxiliary ligands was designed and prepared with the aim to study the influence of increasing the number of aliphatic chains on the molecular organization in the liquid crystal phase. The liquid crystalline behavior of these palladium(II) complexes was investigated by a combination of polarized optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction. A transition from the lamellar (complex 3a with two aliphatic chains on BTU ligand) to columnar organization (complexes 3b and 3c having three and four chains on BTU ligand, respectively) was evidenced for these palladium(II) complexes, which was correlated with the increase of the number of terminal chains at molecular periphery. (C) 2017 Elsevier B.V. All rights reserved.

57. Bis-imidazolium salts with alkyl sulfates as counterions: synthesis and liquid crystalline properties

Authors: Ilinca, TA; Pasuk, I; Circu, V

Published: OCT 7 2017, NEW JOURNAL OF CHEMISTRY, 41, 11124, DOI: 10.1039/c7nj02561k

A series of flexibly linked bis-imidazolium salts with alkyl sulfate anions having different chain lengths (10, 12, 14) was designed and prepared starting from 1,1'-(alpha,omega-alkanediyl)-bisimidazole and alkyl bromides (14 or 16 carbon atoms) followed by metathesis with the corresponding sodium salts. These compounds were investigated because of their liquid crystalline properties using a combination of differential scanning calorimetry (DSC), polarized optical microscopy (POM) and temperature dependent powder X-ray diffraction (XRD). All nine bis-imidazolium compounds with alkyl sulfate anions show liquid crystalline properties which were influenced by flexible spacer length, alkyl tail length and, finally, the length of alkyl chains attached to sulfate groups. Broader mesophase ranges were found for compounds with a shorter spacer (six carbon atoms), about 70 degrees C. For compounds with a spacer of ten carbon atoms, higher mesophase ranges and clearing temperatures were found for longer alkyl tails (sixteen carbon atoms). Increasing the length of alkyl chains attached to sulfate anions resulted in higher clearing temperatures for compounds with the longer spacer. The variation in the carbon atom number of the alkyl sulfate anion for bis-imidazolium compounds with the shorter spacer has almost no impact on their SmA phase stability.

58. Relationship between ferromagnetism and, structure and morphology in un-doped ZnO and Fe-doped ZnO powders prepared by hydrothermal route

Authors: Mihalache, V; Cernea, M; Pasuk, I

Published: AUG 2017, CURRENT APPLIED PHYSICS, 17, 1135, DOI: 10.1016/j.cap.2017.03.020

The magnetic properties, in the 5 K-350 K temperature range, were investigated in relationship with the structure and morphology of Zn1-xFexO (x = 0, 0.01, 0.03) powders prepared by hydrothermal route. The magnetization measurements reveal that all powders are ferromagnetic at room temperature, with Curie temperature TT, higher than 350 K. The coercivity Hc takes values between 58 Oe and 107 Oe at 300 K and, between 217 Oe and 613 Oe at 5 K. The weak magnetization of the un-doped ZnO powder is temperature independent and was associated with the high surface to volume ratio of the powder particles (or the number of surface defects). The saturation magnetization M-s, was substantially enhanced (up to a factor of about 20 at 300 K and of about 200 at 5 K) at all temperatures as Fe concentration increased, in spite of reduction of the surface to volume ratio of the powder particles. The Hc vs. Tand FC/ZFC curves for the un-doped ZnO show typical ferromagnetic behavior, whereas for the Fe doped powders exhibit Ruderman-Kittel-Kasuya-Yosida (RKKY) - like and spin-glass-like behavior. The observed magnetic phenomena in Fe doped ZnO can be explained on the basis of "donor defects concentration magnetic cations concentration" phase diagram for dilute magnetic semiconductors. (C) 2017 Elsevier B.V. All rights reserved.

59. Relation between domain structure and pyroelectric response in as-grown epitaxial Pb(Zr0.2Ti0.8)O-3 thin films on substrates with different resistivity

Authors: Pintilie, I; Trinca, L; Trupina, L; Pasuk, I; Pintilie, L

Published: SEP 2017, MATERIALS RESEARCH BULLETIN, 93, 207, DOI: 10.1016/j.materresbull.2017.04.054

Epitaxial Pb(Zr0.2Ti0.8)O-3 (PZT) thin films were grown by pulsed laser deposition on two slightly different types of single crystal substrates, namely SrTiO3 (STO) buffered with a thin layer of conductive SrRuO3 (SRO), and SrTiO3 doped with 0.5% Nb (STON). Although self-poling effect was expected in both cases, due to the compressive strain imposed by the substrate, it was found that the pyroelectric response of as grown samples is with about two orders of magnitude larger for the PZT film deposited on SRO/STO compared to the one deposited on STON substrate. In order to explain the finding, the electrical properties were investigated and it was found that the quantities involved in the equation giving the magnitude of the pyroelectric signal, namely dielectric constant and electrical resistivity, have about the same values Therefore, the different pyroelectric response in the as-grown samples was explained by different structure of ferroelectric domains induced by the different carrier concentration in the two substrates: 90 degrees domains for PZT on SRO/STO and 180 degrees domains for PZT on STON. It appears that the resistivity of the substrate and its ability to compensate the depolarization field affect the domain structure, with impact on the pyroelectric response, although the strain conditions are similar in both cases. The trying to increase the pyroelectric response for the PZT film deposited on STON substrate by applying a poling process was not successful, as the 180 degrees domain structure restores shortly after removing the poling field. (C) 2017 Elsevier Ltd. All rights reserved.

60. Cyclometalated palladium(II) metallomesogens with Schiff bases and N-benzoyl thiourea derivatives as co-ligands

Authors: Ilis, M; Batalu, D; Pasuk, I; Circu, V

Published: MAY 2017, JOURNAL OF MOLECULAR LIQUIDS, 233, 51, DOI: 10.1016/j.molliq.2017.02.114

Two series of cyclometalated palladium(II) complexes based on Schiff bases and N-benzoylthiourea (BTU) ligands having four alkoxy groups at their periphery, with different number of carbon atoms, have been designed and prepared. The liquid crystalline behavior of these palladium(II) complexes was investigated by a combination of polarized optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction while their thermal stability was studied by thermogravimetric analysis (TGA). The palladium(II) complexes are thermally stable on a broad temperature range up to 230 degrees C showing, depending on the alkoxy chain length, either monotropic or, for longest alkyl chain, enantiotropic smectic A and C phases. The luminescent properties of palladium(II) complexes were reported. These complexes show a yellow-orange solid-state emission at room temperature with two emission maxima at lambda(max) around 580 and 650 nm, respectively, with a shoulder around 710 nm, when the samples are irradiated in the 330-380 nm range. (C) 2017 Elsevier B.V. All rights reserved.

61. Structure, transition temperature, and magnetoresistance of titanium-doped lanthanum barium manganite epilayers onto STO 001 substrates

Authors: Galca, AC; Oumezzine, M; Leca, A; Chirila, CF; Kuncser, V; Kuncser, A; Ghica, C; Pasuk, I; Oumezzine, M

Published: OCT 30 2017, APPLIED PHYSICS LETTERS, 111, DOI: 10.1063/1.4998011

We have developed a thin film structure with a maximum magnetoresistance effect (MRE) at room temperature, which is one of the operating requirements for many applications. It is shown that La0.67Ba0.33Ti0.02Mn0.98O3 epilayers obtained by pulsed laser deposition onto (001) SrTiO3 single crystal substrates exhibit the highest MRE, Delta R/R(H) approximate to 150% or Delta R/R(0) approximate to 60% under 5 T, at 300 K, a temperature near to the corresponding Curie temperature (T-C). Both doping with a tiny amount of titanium and induced stress due to lattice mismatch between the thin film and the substrate contribute to a decrease in T-C as compared to the pristine compound and therefore to the decrease in the temperature where the highest MRE is recorded. Published by AIP Publishing.

62. Steplike Switching in Symmetric PbZr0.2Ti0.8O3/CoFeO4/PbZr0.2Ti0.8O3 Heterostructures for Multistate Ferroelectric Memory

Authors: Boni, AG; Chirila, C; Pasuk, I; Negrea, R; Pintilie, I; Pintilie, L

Published: SEP 28 2017, PHYSICAL REVIEW APPLIED, 8, DOI: 10.1103/PhysRevApplied.8.034035

A hysteresis loop with three polarization states is obtained in the case of a symmetric epitaxial ferroelectric-interlayer-ferroelectric structure with bottom and top SrRuO3 electrodes. The ferroelectric layers are of PbZr0.2Ti0.8O3, while the interlayer is CoFe2O4. It is shown that the three polarization states can be separately accessed, suggesting that this type of structure can be used as building element for a three-state nonvolatile ferroelectric random-access memory (FERAM). The presence of the three-state memory effect is explained through a simple phenomenological model based on Landau-Ginzburg-Devonshire theory. The findings of this study can pave the way to multistate all-oxide FERAM devices, resulting in a 50% increase in the storage density compared to actual nonvolatile memories.

63. Structural, magnetic and magnetocaloric effects in epitaxial La0.67Ba0.33Ti0.02Mn0.98O3 ferromagnetic thin films grown on 001-oriented SrTiO3 substrates

Authors: Oumezzine, M; Galca, AC; Pasuk, I; Chirila, CF; Leca, A; Kuncser, V; Tanase, LC; Kuncser, A; Ghica, C; Oumezzine, M

Published: 2016, DALTON TRANSACTIONS, 45, 15040, DOI: 10.1039/c6dt01914e

Epitaxial La0.67Ba0.33Ti0.02Mn0.98O3 (denoted as LBTMO hereafter) thin films of approximately 95 nm thickness were deposited by a pulsed laser deposition technique onto SrTiO3 (STO) (001) substrates. High-resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM) investigations revealed that the films are epilayers with a four-fold symmetry around the [001] direction. Cross-sectional TEM and the presence of Pendellosung fringes in the XRD profiles demonstrate smooth interfaces. The STO substrate induces an in-plane compressive strain, which leads to a slight tetragonality of the film structure. The epilayers exhibit paramagnetic-to-ferromagnetic phase transitions at the Curie temperature T-C (286 K), close to room temperature. The magnetization easy axis lies in the film plane along the [100] direction of the (001) substrate. The magnetic entropy change (Delta S-M) associated with the second-order magnetic phase transition was determined via magnetization measurements in the temperature range between 210 and 350 K under different magnetic fields. The relative cooling power (RCP) of this film is about 220 J kg(-1), somewhat lower than that of bulk Gd (410 J kg(-1)) for a 50 kOe field change, making the LBTMO ferromagnetic thin films a promising candidate for micro/nanomagnetic refrigeration around room temperature. The proposed universal curve provides a simple method for extrapolating Delta S-M in a wide range of fields and temperatures, thus confirming the order of the magnetic transition in this system. The magnetic entropy (Delta S-M)(max) around T-C is proportional to (mu H-0/T-C)(2/3) in agreement with the mean-field theory, indicating the existence of long-range ferromagnetic interactions in epitaxial LBTMO thin films.

64. Columnar bis(pyridinium) ionic liquid crystals derived from 4-hydroxypyridine: synthesis, mesomorphism and emission properties

Authors: Pana, A; Ilis, M; Staicu, T; Pasuk, I; Circu, V

Published: FEB 19 2016, LIQUID CRYSTALS, 43, 392, DOI: 10.1080/02678292.2015.1116630

A series of flexibly linked bis(pyridinium) salts with various counterions (Br-, PF6-, BF4- and OTf-) was designed and prepared starting from corresponding N-alkylated 4-pyridones precursors with mesogenic 3,4,5-tris(alkyloxy)benzyl moieties (alkyl=dodecyl or tetradecyl). These salts were investigated for their liquid crystalline properties by a combination of differential scanning calorimetry, polarising optical microscopy and temperature-dependent powder X-ray diffraction (XRD). Their thermal stability was checked by thermogravimetric analysis. All bis(pyridinium) salts, except the triflate salt with shorter terminal carbon chain, display an enantiotropic liquid crystalline behaviour with a hexagonal columnar (Col(h)) phase assigned on the basis of its characteristic texture and XRD studies. It was found that these luminescent bis(pyridinium) salts show weak emission in dichloromethane solutions at room temperature and a pronounced red-shifted emission in solid state. The emission properties of these bis(pyridinium) salts do not depend significantly on the nature of counterion employed.

65. Effects of vanadium doping on sintering conditions and functional properties of Nb-Li co-doped PZT ceramics. Comments on Li location

Authors: Amarande, L; Miclea, C; Cioangher, M; Grecu, MN; Pasuk, I

Published: NOV 15 2016, JOURNAL OF ALLOYS AND COMPOUNDS, 685, 166, DOI: 10.1016/j.jallcom.2016.05.266

The effect of 1 and 2 mol % V addition on sintering conditions, structural and functional properties of NbeLi co-doped PZT ceramics, prepared by conventional ceramic method, was systematically studied, by different experimental techniques. The reported results show that the increasing amount of vanadium, as a substitute for niobium, decreases the optimal sintering temperature with 100-150 degrees C, but slightly reduces the piezoelectric, ferroelectric, and electromechanical properties of these ceramics. In addition, the presence of vanadium increases the lattice tetragonality and grain size, promoting a harder piezoelectric behaviour, mostly in the absence of niobium. EPR spectra exhibit well-defined hyperfine splitting characteristics for V4+ state, dispersed in the lattice as VO2+ ion. Additionally, complex paramagnetic defects (charged oxygen vacancies and associated defects) are evidenced for 2 mol % vanadium addition. The results were explained by assuming that vanadium promotes the B-site Li substitution, compensated by oxygen vacancies, while niobium facilitates the A-site Li substitution with lead vacancies formation and partial reduction of V5+ to V4+. Thus, indirect information about lithium location is provided. (C) 2016 Elsevier B.V. All rights reserved.

66. Nematic ionic liquid crystals based on pyridinium salts derived from 4-hydroxypyridine

Authors: Pana, A; Pasuk, I; Micutz, M; Circu, V

Published: 2016, CRYSTENGCOMM, 18, 5069, DOI: 10.1039/c6ce00618c

A series of pyridinium salts with various counterions (Br-, NO3-, BF4-, PF6-, OTf- and SCN-) and different spacer chain lengths, which display a nematic phase, have been designed and prepared. They are derived from 4-hydroxypyridine and possess two mesogenic cyanobiphenyl groups attached to the pyridinium unit via a flexible long alkyl spacer (6, 9, 10). These salts exhibit solely a nematic phase with the thermal range influenced by the counterion employed and spacer length.

67. Reactive spark plasma sintering of MgB2 in nitrogen atmosphere for the enhancement of the high-field critical current density

Authors: Badica, P; Burdusel, M; Popa, S; Pasuk, I; Ivan, I; Borodianska, H; Vasylkiv, O; Kuncser, A; Ionescu, AM; Miu, L; Aldica, G

Published: OCT 2016, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 29, DOI: 10.1088/0953-2048/29/10/105020

High density bulks (97%-99%) of MgB2 were prepared by spark plasma sintering (SPS) in nitrogen (N-2) atmosphere for different heating rates (10, 20 and 100 degrees C min(-1)) and compared with reference samples processed in vacuum and Ar. N-2 reacts with MgB2 and forms MgB9N along the MgB2 grain boundaries. The high-field critical current density is enhanced for the sample processed in N-2 with a heating rate of 100 degrees C min(-1). At 2-35 K, this sample shows the strongest contribution of the grain boundary pinning (GBP). All samples are in the point pinning (PP) limit and by increasing temperature the GBP contribution decreases.

68. Spark plasma sintered MgB2 co-added with c-BN and C-60

Authors: Ionescu, AM; Aldica, G; Popa, S; Enculescu, M; Sandu, V; Pasuk, I; Kuncser, A; Miu, L; Badica, P

Published: FEB 15 2016, MATERIALS CHEMISTRY AND PHYSICS, 170, 209, DOI: 10.1016/j.matchemphys.2015.12.040

High density (above 92%) superconducting bulks of MgB2 co-added with cubic BN (c-BN) and fullerenes (C-60) were obtained by the ex-situ spark plasma sintering (SPS). Compositions were (MgB2)((1-x))(C)(x)(c-BN)(0.01), x = 0.0125, 0.025, 0.05, 0.075. The co-added sample (MgB2)(0.975)(C)(0.025)(c-BN)(0.01) shows a marginally higher critical current density J(c) at intermediate magnetic fields and below 15 K than for optimum samples added with c-BN or C-60. For this sample, pinning is in the point pinning limit and the delta T-c mechanism is dominant. At high magnetic fields co-added samples are inferior to samples added with one additive, but are superior to pristine sample. Co-addition of c-BN and C-60 is not effective for vortex pinning when compared with individual addition. The result is discussed based on phase formation aspects, microstructural details and residual strain. It was found that in the presence of C-60, c-BN consumption with formation of MgNB9 is intensified with implications on different elements that influence pinning. (C) 2015 Elsevier B.V. All rights reserved.

69. B4C in ex-situ spark plasma sintered MgB2

Authors: Burdusel, M; Aldica, G; Popa, S; Enculescu, M; Mihalache, V; Kuncser, A; Pasuk, I; Badica, P

Published: OCT 2015, CURRENT APPLIED PHYSICS, 15, 1270, DOI: 10.1016/j.cap.2015.07.017

Powder mixtures of MgB2 and B4C with composition ((MgB2) + (B4C) x, x = 0.005, 0.01, 0.03) were consolidated by Spark Plasma Sintering at 1150 degrees C for 3 min. The average particle size of B4C raw powder was relatively high of 4 mm. Despite this, it is shown that processing processes are fast and, as in the case of the in-situ routes, for our ex-situ method carbon substitutes for the boron in the crystal lattice of MgB2. Specifics of microstructure are discussed based on electron microscopy observations. Carbon substitution and microstructure contribute to enhancement of the critical current density J(c) at high magnetic fields and of the irreversibility field H-irr. Samples are shown to be in the point pinning limit with some tendency toward the grain boundary pinning depending on B4C doping amount and temperature. An optimum composition is found for x = 0.01: for this sample, at 20 K, a J(c) of 100 A/cm(2) is obtained at 5.35 T. This value is higher than for the pristine MgB2 sample and for an optimum ex-situ nano-SiC-doped sample obtained for the same SPS processing conditions. (C) 2015 Elsevier B.V. All rights reserved.

70. The influence of heating rate on superconducting characteristics of MgB2 obtained by spark plasma sintering technique

Authors: Aldica, G; Burdusel, M; Popa, S; Enculescu, M; Pasuk, I; Badica, P

Published: DEC 15 2015, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 519, 189, DOI: 10.1016/j.physc.2015.10.004

Superconducting bulks of MgB2 were obtained by the Spark Plasma Sintering (SPS) technique. Different heating rates of 20, 100, 235, 355, and 475 degrees C/min were used. Samples have high density, above 95%. The onset critical temperature T-c, is about 38.8 K. There is an optimum heating rate of similar to 100 degrees C/min to maximize the critical current density J(c0), the irreversibility field H-irr, the product (J(c0) x mu H-0(irr)), and to partially avoid formation of undesirable flux jumps at low temperatures. Significant microstructure differences were revealed for samples processed with low and high heating rates in respect to grain boundaries. (C) 2015 Elsevier B.V. All rights reserved.

71. Effect of counterion on the mesomorphic behavior and optical properties of columnar pyridinium ionic liquid crystals derived from 4-hydroxypyridine

Authors: Pana, A; Badea, FL; Ilis, M; Staicu, T; Micutz, M; Pasuk, I; Circu, V

Published: MAR 5 2015, JOURNAL OF MOLECULAR STRUCTURE, 1083, 251, DOI: 10.1016/j.molstruc.2014.11.059

A series of 3,4,5-tridodecyloxybenzyl pyridinium salts derived from 4-hydroxypyridine has been designed and prepared. The liquid crystalline properties of these compounds were investigated by polarized optical microscopy, differential scanning calorimetry and powder X-ray diffraction while their thermal stability was studied by thermogravimetric analysis. The N-3,4,5-tridodecyloxybenzyl-4-pyridone intermediate shows a monotropic columnar hexagonal mesophase ranging from 56 degrees C down to room temperature while the corresponding bromide dodecyl O-alkylated pyridinium salt shows one enantiotropic columnar mesophase and one additional monotropic columnar phase at lower temperatures. Replacing bromide ion (Br-) with other counterions (NO3-, BF4- and PF6-) resulted in mesophase suppression. These luminescent pyridinium salts show weak emission in dichloromethane solutions at room temperature and a pronounced red-shifted emission in solid state. Photoluminescent properties of the pyridinium salts do not depend significantly on the nature of counterion employed. (C) 2014 Elsevier B.V. All rights reserved.

72. Comparison between the ferroelectric/electric properties of the PbZr0.52Ti0.48O3 films grown on Si (100) and on STO (100) substrates

Authors: Chirila, C; Boni, AG; Pasuk, I; Negrea, R; Trupina, L; Le Rhun, G; Yin, S; Vilquin, B; Pintilie, I; Pintilie, L

Published: JUN 2015, JOURNAL OF MATERIALS SCIENCE, 50, 3894, DOI: 10.1007/s10853-015-8907-2

Ferroelectric/electric properties of PbZr0.52Ti0.48O3 (PZT) thin films grown by pulsed laser deposition (PLD) on two different substrates, Si (001) and SrTiO3 (STO) (001), were comparatively analyzed. The structural characterization has revealed the epitaxial relationship between the grown layers and the two types of substrates, with larger density of structural defects for the films deposited on Si (001) with buffer STO layer. The ferroelectric/electric properties are also different, with lower remnant polarization (about half of the value obtained on STO substrate), higher dielectric constant (about two times larger), and lower leakage current (about two orders of magnitude lower) for the PZT films deposited on Si (001) compared to those deposited on (001) STO substrates. Nevertheless, the results show that the use of a STO buffer layer on Si can be a solution to obtain good quality PZT capacitor structures without using expensive single-crystal oxide substrates. In this way, applications based on PZT capacitors (e.g. non-volatile memories, pyroelectric detectors, light switches, etc.) would be more easily integrated directly on Si wafers.

73. Polarization induced self-doping in epitaxial Pb(Zr0.20Ti0.80)O-3 thin films

Authors: Pintilie, L; Ghica, C; Teodorescu, CM; Pintilie, I; Chirila, C; Pasuk, I; Trupina, L; Hrib, L; Boni, AG; Apostol, NG; Abramiuc, LE; Negrea, R; Stefan, M; Ghica, D

Published: OCT 8 2015, SCIENTIFIC REPORTS, 5, DOI: 10.1038/srep14974

The compensation of the depolarization field in ferroelectric layers requires the presence of a suitable amount of charges able to follow any variation of the ferroelectric polarization. These can be free carriers or charged defects located in the ferroelectric material or free carriers coming from the electrodes. Here we show that a self-doping phenomenon occurs in epitaxial, tetragonal ferroelectric films of Pb(Zr0.2Ti0.8)O-3, consisting in generation of point defects (vacancies) acting as donors/acceptors. These are introducing free carriers that partly compensate the depolarization field occurring in the film. It is found that the concentration of the free carriers introduced by selfdoping increases with decreasing the thickness of the ferroelectric layer, reaching values of the order of 10(26) m(-3) for 10 nm thick films. One the other hand, microscopic investigations show that, for thicknesses higher than 50 nm, the 2O/(Ti+Zr+Pb) atomic ratio increases with the thickness of the layers. These results suggest that the ratio between the oxygen and cation vacancies varies with the thickness of the layer in such a way that the net free carrier density is sufficient to efficiently compensate the depolarization field and to preserve the outward direction of the polarization.

74. HETEROSTRUCTURES BASED ON SMALL MOLECULES ORGANIC COMPOUNDS

Authors: Socol, M; Rasoga, O; Breazu, C; Socol, G; Preda, N; Pasuk, I; Visan, D; Stavarache, I; Gherendi, F; Girtan, M; Sidwaba, U

Published: OCT-DEC 2015, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 10, 1392, DOI:

Heterostructures with layers from small molecules organic compounds were deposited on ITO/glass substrate by thermal vacuum evaporation (TVE) technique. Structural, optical and morphological investigations were carried out on the realised layers (zinc phthalocyanine-ZnPc, fullerene-C60 and 1,4,5,8-naphthalene-tetracarboxylic dianhydride-NTCDA). The films are polycrystalline keeping the morphological features characteristic to these materials. The prepared heterostructures reveal a large absorption domain in the visible domain. The current-voltage (I-V) characteristics of the investigated structures, recorded in dark, present an improvement in the current value (similar to one order of magnitude) for the standard structure (ITO/PEDOT: PSS/ZnPc/C60/NTCDA/Al) with a supplimentary layer of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS). For the inverted structure (Al/NTCDA/C60/ZnPc/ITO) was also noticed an increased curent value in comparasion with that observed for the standard structure.

75. Ge-Added MgB2 Superconductor Obtained by Ex Situ Spark Plasma Sintering

Authors: Batalu, D; Aldica, G; Burdusel, M; Popa, S; Enculescu, M; Pasuk, I; Miu, D; Badica, P

Published: FEB 2015, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 28, 534, DOI: 10.1007/s10948-014-2705-y

Spark plasma sintering (SPS) was applied for fabrication of dense (relative density > 97 %) bulk MgB2 samples added with Ge. Mixtures of MgB2 and Ge powders with starting compositions (MgB2) Ge (x) , x=0.005, 0.01, and 0.03 were used. Added samples show enhancement of the critical current density at high magnetic fields when compared to a pristine reference sample. The optimum composition is for x=0.005 and for this sample J (c)(20 K) =10(2)A/cm (2) is obtained at 5 T, while for the reference sample is obtained at 3.9 T. Ge does not substitute in the crystal lattice of MgB2 and T (c,onset) or T (c,midpoint) from magnetization measurements scatter within 0.15 or 0.3 K, respectively.

76. A new class of thermotropic lanthanidomesogens: Eu(III) nitrate complexes with mesogenic 4-pyridone ligands

Authors: Pana, A; Chiriac, FL; Secu, M; Pasuk, I; Ferbinteanu, M; Micutz, M; Circu, V

Published: 2015, DALTON TRANSACTIONS, 44, 14199, DOI: 10.1039/c5dt01197c

A new class of thermotropic lanthanidomesogens has been designed and prepared. They are based on 4-pyridone ligands that possess mesogenic cyanobiphenyl groups attached to the 4-pyridone unit via a flexible long alkyl spacer and show a very high thermal stability (decomposition temperatures near 300 degrees C). Depending on the alkyl length spacer, these complexes exhibit a SmA phase with transition temperatures influenced by the number of mesogenic groups employed and the spacer length.

77. Electrode interface controlled electrical properties in epitaxial Pb(Zr0.52Ti0.48)O-3 films grown on Si substrates with SrTiO3 buffer layer

Authors: Boni, AG; Chirila, C; Pasuk, I; Negrea, R; Trupina, L; Le Rhun, G; Vilquin, B; Pintilie, I; Pintilie, L

Published: OCT 30 2015, THIN SOLID FILMS, 593, 130, DOI: 10.1016/j.tsf.2015.09.028

Electrical properties of ferroelectric capacitors based on PbZr0.52Ti0.48O3 thin films grown by pulsed laser deposition on silicon substrate with SrTiO3 buffer layer grown by molecular beam epitaxy were studied. A SrRuO3 layer was deposited as bottom electrode also by pulse laser deposition and Pt, Ir, Ru, SrRuO3 were used as top contacts. Electrical characterization comprised hysteresis and capacitance-voltage measurements in the temperature range from 150 K to 400 K. It was found that the macroscopic electrical properties are affected by the electrode interface, by the choice of the top electrode. However, even for metals with very different work functions (e.g. Pt and SrRuO3) the properties of the top and bottom electrode interfaces remain fairly symmetric suggesting a strong influence from the bound polarization charges located near the interface. (C) 2015 Elsevier B.V. All rights reserved.

78. Influence of hole depletion and depolarizing field on the BaTiO3/La0.6Sr0.4MnO3 interface electronic structure revealed by photoelectron spectroscopy and first-principles calculations

Authors: Popescu, DG; Barrett, N; Chirila, C; Pasuk, I; Husanu, MA

Published: DEC 28 2015, PHYSICAL REVIEW B, 92, DOI: 10.1103/PhysRevB.92.235442

The effects of the bonding mechanism and band alignment in a ferroelectric (FE) BaTiO3/ferromagnetic La0.6Sr0.4MnO3 heterostructure are studied using x-ray photoelectron spectroscopy and first-principles calculations. The band lineup at the interface is determined by a combination of band bending and polarization-induced modification of core-hole screening. A Schottky barrier height for electrons of 1.22 +/- 0.17 eV is obtained in the case of downwards FE polarization of the top layer. The symmetry of the bonding states is emphasized by integrating the local density of states +/- 0.2 eV around the Fermi level, and strong dependence on the FE polarization is found: upwards, polarization stabilizes Ti t(2g) (xy) orbitals, while downwards, polarization favors Ti t(2g) (yz) symmetry. It is predicted that the abrupt (La, Sr)vertical bar TiO2 interface is magnetoelectrically active, leading to a A-type antiferromagnetic coupling of the first TiO2 interface layer with the underlying manganite layer through a superexchange mechanism.

79. Polarization-Control of the Potential Barrier at the Electrode Interfaces in Epitaxial Ferroelectric Thin Films

Authors: Pintilie, I; Teodorescu, CM; Ghica, C; Chirila, C; Boni, AG; Hrib, L; Pasuk, I; Negrea, R; Apostol, N; Pintilie, L

Published: FEB 26 2014, ACS APPLIED MATERIALS & INTERFACES, 6, 2939, DOI: 10.1021/am405508k

Electrode interface is a key element in controlling the macroscopic electrical properties of the ferroelectric capacitors based on thin films. In the case of epitaxial ferroelectrics, the electrode interface is essential in controlling the leakage current and the polarization switching, two important elements in the read/write processes of nonvolatile memories. However, the relation between the polarization bound charges and the electronic properties of the electrode interfaces is not yet well understood. Here we show that polarization charges are controlling the height of the potential barriers at the electrode interfaces in the case of Pb(Zr,Ti)O-3 and BaTiO3 epitaxial films. The results suggest that the height is set to a value allowing rapid compensation of the depolarization field during the polarization switching, being almost independent of the metals used for electrodes. This general behavior open a new perspective in engineering interface properties and designing new devices based on epitaxial ferroelectrics.

80. Significant enhancement of the critical current density for cubic BN addition into ex situ spark plasma sintered MgB2

Authors: Badica, P; Aldica, G; Burdusel, M; Popa, S; Negrea, RF; Enculescu, M; Pasuk, I; Miu, L

Published: SEP 2014, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 27, DOI: 10.1088/0953-2048/27/9/095013

High density (above 93%) superconducting bulks of MgB2 with addition of hexagonal BN (h-BN) and cubic BN (c-BN) with compositions ((MgB2) + (BN)(x), x = 0.01, 0.03, 0.05) were obtained by ex situ spark plasma sintering. All the investigated samples have the critical temperature T-c = 38.8 K. The variation of the critical current density J(c) with the external magnetic field H for h-BN added sample is almost overlapping the J(c)(H) dependence for the pristine MgB2 sample. On the other hand, J(c) for the samples added with c-BN is larger at high magnetic fields, while the decrease of J(c) at low H is very small. At T = 20 K, a J(c) of 10(2) A cm(-2) is determined for the sample with x(c-BN) = 0.005 at H = 58 kOe, and for the sample with x(c-BN) = 0.01 at 54 kOe. Magnetic relaxation measurements indicate a significant flux pinning enhancement in MgB2 samples added with c-BN. It is proposed that the disorder at the interface caused by the convenient lattice matching relationship between the lateral plane of the MgB2 crystal prism and the face of the c-BN crystal cube is responsible for the observed vortex pinning increase.

81. Synthesis and Raman scattering of multiferroic Fe-Pb(Zr0.2Ti0.8)O-3 core-shell wire arrays

Authors: Baibarac, M; Sima, M; Matei, E; Pasuk, I; Mihut, L

Published: JAN 2014, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 211, 205, DOI: 10.1002/pssa.201330062

A new method to fabricate an Fe-PZT core-shell wire arrays developed in three steps is reported in this paper. This involves the electrochemical growth of an iron wire array by template method, deposition by spin coating of the PZT precursor prepared by sol-gel technique on the iron wires surface and annealing treatment to obtain Fe-PZT core-shell structures. The structure of the Fe-PZT core-shell wire array was characterized by scanning electron microscopy (SEM) and Raman scattering. Raman lines situated at 372 and 575cm(-1) indicate the formation of the FeO particles on the Fe wires surface as a result of the use of an aqueous solution for electrochemical synthesis. An upshift of Raman lines of Fe decorated with FeO wires was observed after formation of Fe-PZT core-shell structure. The annealing treatment of this structure involves a partial transformation of the FeO into Fe2O3 particles both with structure rhombohedral and cubic that were evidenced by Raman lines peaked at 243 and 497cm(-1), respectively. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

82. Origin of the stabilization of the metastable tetragonal high-pressure phase in SrCuO2 thin films grown on SrTiO3 substrates by pulsed laser deposition

Authors: Mihailescu, CN; Pasuk, I; Straticiuc, M; Nita, CR; Pantelica, D; Giapintzakis, J

Published: NOV 30 2014, APPLIED SURFACE SCIENCE, 320, 857, DOI: 10.1016/j.apsusc.2014.09.116

In this work we have systematically investigated the evolution of structure and stoichiometry in SrCuO2 films grown on TiO2-terminated SrTiO3 substrates as a function of the substrate temperature. Depending on the growth temperature SrCuO2/SrTiO3 films can exhibit either a pure tetragonal high-pressure phase, or a pure orthorhombic low-pressure phase, or a mixed phase. Our results indicate that at low substrate temperatures the non-equilibrium state of the growth process is responsible for the stabilization of the metastable tetragonal high-pressure structure in SrCuO2 thin films grown on ( 0 01) SrTiO3 substrates, whose lattice matches the metastable structure. In addition, at higher substrate temperatures thermodynamics become dominant over other factors and the SrCuO2 thin films are stabilized in the thermodynamically stable orthorhombic phase. (C) 2014 Elsevier B.V. All rights reserved.

83. Enhancement of smectic C mesophase stability by using branched alkyl chains in the auxiliary ligands of luminescent Pt(II) and Pd(II) complexes

Authors: Ilis, M; Micutz, M; Dumitrascu, F; Pasuk, I; Molard, Y; Roisnel, T; Circu, V

Published: FEB 17 2014, POLYHEDRON, 69, 39, DOI: 10.1016/j.poly.2013.11.015

A novel series of Pd(II) and Pt(II) complexes based on cyclometallated imine ligands and N-benzoylthiourea (BTU) derivatives as auxiliary ligands has been prepared and their liquid crystalline properties as well as photophysical properties have been investigated. The crystal structure of one cyclometallated Pt(II) complex with N-(p-F-phenyl)-N'-benzoylthiourea as a co-ligand has been solved. The liquid crystalline properties have been investigated by a combination of DSC, POM and variable temperature powder X-ray diffraction. These new metallomesogens display either a monotropic SmC phase or both SmA and SmC phases, depending on the number of alkoxy groups attached to the imine ligand, alkyl chain length or the use of branched alkoxy terminal groups. We found that the introduction of branched alkoxy terminal groups lead to lower transition temperatures and stabilization of the SmC phase in both the Pd(II) and Pt(II) complexes. While the Pd(II) complexes display no emission, the Pt(II) complexes show good emission properties in solution, in the solid state and as a PMMA film at room temperature, and their investigation is reported. (C) 2013 Elsevier Ltd. All rights reserved.

84. General equivalent circuit derived from capacitance and impedance measurements performed on epitaxial ferroelectric thin films

Authors: Pintilie, L; Hrib, L; Pasuk, I; Ghica, C; Iuga, A; Pintilie, I

Published: JUL 28 2014, JOURNAL OF APPLIED PHYSICS, 116, DOI: 10.1063/1.4891255

Voltage and frequency dependent capacitance measurements were performed on epitaxial BaTiO3 and Pb(Zr0.2Ti0.8)O-3 thin films deposited on single crystal SrTiO3 substrates with (001) and (111) orientations. The measured capacitors have common bottom SrRuO3 contact and different metals as top electrodes: SrRuO3, Pt, Cu, Al, and Au. The capacitance-voltage characteristics were used to extract information regarding the density of the free carriers and the linear contribution to the static dielectric constant. The frequency dependent impedance was used to develop a suitable equivalent circuit for the epitaxial ferroelectric capacitors. It was found that the frequency dependence of the imaginary part of the impedance can be well simulated, in all cases, using a circuit composed of Schottky-type capacitance related to electrode interfaces, contact resistance, and the R-C parallel connection related to the ferroelectric volume of the film. Values for the components of the equivalent circuit were obtained by fitting the experimental data with the simulated curves. These were then used to extract quantities such as dielectric constant in the ferroelectric volume, the width of the depletion layers, and the apparent built-in potential. It was found that, although the investigated capacitors are of different ferroelectric materials, grown on substrates with different orientations, and having different metals as top electrodes, the values for the capacitance associated with the Schottky contacts and the apparent built-in potential are not very different. The results suggest a strong influence of ferroelectric polarization on the electrode interface properties in the case of epitaxial ferroelectric films. (C) 2014 AIP Publishing LLC.

85. Electrical properties related to the structure of GeSi nanostructured films

Authors: Ciurea, ML; Stavarache, I; Lepadatu, AM; Pasuk, I; Teodorescu, VS

Published: JUL 2014, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 251, 1346, DOI: 10.1002/pssb.201350112

GeSi nanostructured films were obtained by cosputtering from two Ge and Si targets and subsequent annealing in furnace in N-2 for 5 h at 700, 800 and 900 degrees C, with the aim to show the correlation between electrical properties and crystalline structure of the films. The as-deposited films are amorphous, have a Ge: Si composition of 55: 45 and 185 nm thickness. The film structure was investigated by XRD and TEM, and the electrical behaviour was studied by measuring current-voltage (I-V) and current-temperature (I-T) characteristics and by discussing them in correlation with the structure. Different electrical behaviours of GeSi films corresponding to different structures have been evidenced. The 700 degrees C annealed GeSi films are formed of nanocrystals (7-15 nm) separated by amorphous regions (1-2 nm). These films present a superlinear I-V characteristic typical of high field-assisted tunnelling through potential barriers (amorphous regions) between nanocrystals. The I-T characteristic at low temperature follows a T-1/2 law showing a thermally activated tunnelling of carriers between neighboring GeSi nanocrystals. The films annealed at 800 and 900 degrees C have a like behavior, they are completely crystallized and present linear I-V and Arrhenius I-T dependences reflecting the polycrystalline behaviour. [GRAPHICS] . (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

86. High magnetic field enhancement of the critical current density by Ge, GeO2 and Ge2C6H10O7 additions to MgB2

Authors: Batalu, D; Aldica, G; Popa, S; Miu, L; Enculescu, M; Negrea, RF; Pasuk, I; Badica, P

Published: JUL 1 2014, SCRIPTA MATERIALIA, 82, 64, DOI: 10.1016/j.scriptamat.2014.03.024

Ge, GeO2 and Ge2C6H10O7 additions to MgB2 obtained by ex situ spark plasma sintering significantly enhance the critical current density J(c) in high magnetic fields. A J(c)(T = 20 K) of 102 A cm(-2) is obtained at 3.9 T in the pristine sample and at 5.8 T in the MgB2(Ge2C6H10O7)(0.0014) sample. The decrease in the critical temperature for added samples is less than 1 K and T-c(20 K, H = 0) shows a small decrease from 5.5 x 10(5) A cm(-2) in the pristine sample to 3.9 x 10(5) A cm(-2) in MgB2(Ge2C6H10O7)(0.0014) sample. Ge does not substitute into the MgB2 lattice. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

87. Luminescent liquid crystalline materials based on palladium(II) imine derivatives containing the 2-phenylpyridine core

Authors: Micutz, M; Ilis, M; Staicu, T; Dumitrascu, F; Pasuk, I; Molard, Y; Roisnel, T; Circu, V

Published: 2014, DALTON TRANSACTIONS, 43, 1161, DOI: 10.1039/c3dt52137k

In this work we report our studies concerning the synthesis and characterisation of a series of imine derivatives that incorporate the 2-phenylpyridine (2-ppy) core. These derivatives were used in the cyclo-metalating reactions of platinum(II) or palladium(II) in order to prepare several complexes with liquid crystalline properties. Depending on the starting materials used as well as the solvents employed, different metal complexes were obtained, some of them showing both liquid crystalline behaviour and luminescence properties at room temperature. It was found that, even if there are two competing coordination sites, the cyclometalation process takes place always at the 2-ppy core with (for Pt) or without (for Pd) the imine bond cleavage. We successfully showed that it is possible to prepare emissive room temperature liquid crystalline materials based on double cyclopalladated heteroleptic complexes by varying the volume fraction of the long flexible alkyl tails on the ancillary benzoylthiourea (BTU) ligands.

88. Influence of co-dopants average valence on microstructural and electromechanical properties of lead titanate ceramics

Authors: Amarande, L; Miclea, C; Cioangher, M; Grecu, MN; Pasuk, I; Negrea, RF

Published: MAY 2014, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 34, 1200, DOI: 10.1016/j.jeurceramsoc.2013.12.002

Effects of Ni, Nb and Mn co-doping on microstructural, dielectric and electromechanical properties of lead titanate (PT) dense ceramics, obtained as a result of decreasing lattice anisotropy with increasing amount of co-dopants, were investigated. Different values of the average valence (AV) of Ni-Nb co-dopants were obtained by mutual valence compensation between these acceptor donor ions of various relative concentrations. Significantly higher amounts of Mn2+ (resulted by reduction of Mn4+ in presence of donor co-dopants) were found in materials with Ni-Nb AV >4+. These materials show higher coupling factors, correlated with higher mechanical quality factors, compared to the rest of materials. Hard-like piezoelectric behavior was manifested in materials with Ni-Nb AV <4+, whereas ceramics with Ni-Nb AV >4+, and without manganese, turned out to have a soft-like behavior. Electromechanical properties of PT ceramics are discussed in terms of average valence of Ni-Nb co-dopants and multivalence state of manganese. (C) 2013 Elsevier Ltd. All rights reserved.

89. Liquid crystals based on silver carbene complexes derived from dimeric bis(imidazolium) bromide salts

Authors: Pana, A; Ilis, M; Micutz, M; Dumitrascu, F; Pasuk, I; Circu, V

Published: 2014, RSC ADVANCES, 4, 59497, DOI: 10.1039/c4ra11023d

A series of bis(imidazolium) salts with different mesogenic groups (cyanobiphenyl or cholesteryl) and their silver carbene complexes with Br- anion has been designed and prepared. The liquid crystalline behaviour of these ionic liquids and their corresponding silver-carbene complexes was investigated by polarised optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction while their thermal stability was studied by thermogravimetric analysis (TGA). The silver complexes are thermally stable on a broad temperature range with accessible transition temperatures close to ambient temperature. The compounds with cholesteryl groups show higher transition temperatures than the compounds possessing cyanobiphenyl mesogenic groups, but their thermal stability is limited by a slight decomposition before reaching the isotropic state. Interestingly, the bis(imidazolium) salt with two cyanobiphenyl groups at each side shows an enantiotropic nematic phase on a short range, being one of the few examples of ILC displaying nematic phase.

90. Influence of a hydrophobin underlayer on the structuring and antimicrobial properties of ZnO films

Authors: Popescu, AC; Stan, GE; Duta, L; Dorcioman, G; Iordache, O; Dumitrescu, I; Pasuk, I; Mihailescu, IN

Published: DEC 2013, JOURNAL OF MATERIALS SCIENCE, 48, 8336, DOI: 10.1007/s10853-013-7646-5

Adhesion to substrate and antimicrobial efficiency of pulsed laser-deposited ZnO nanostructures were significantly increased by interposing a buffer nano-layer of hydrophobin. The hydrophobin interlayer increased by eight times the ZnO film resilience to wash in water, while in alkaline or acidic artificial sweat, it increased by 2 and 1.2 times, respectively, as compared to textiles covered with ZnO films only. Hydrophobin boosted the biocide effect of ZnO nanostructured films in case of Candida albicans and mold mix inoculum cultures by 50 and 30 %, respectively. An interpretation of these phenomena is advanced based upon the results of the structural investigations.

91. Structural properties of silver doped hydroxyapatite and their biocompatibility

Authors: Ciobanu, CS; Iconaru, SL; Pasuk, I; Vasile, BS; Lupu, AR; Hermenean, A; Dinischiotu, A; Predoi, D

Published: APR 1 2013, MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS, 33, 1402, DOI: 10.1016/j.msec.2012.12.042

The aim of this study was to obtain a novel hydroxyapatite-based material with high biocompatibility. The structural properties of the samples were well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). The X-ray diffraction studies revealed the characteristic peaks of hydroxyapatite in each sample. Other phases or impurities were not observed. The scanning electron microscopy observations suggest that the doping components have no influence on the surface morphology of the samples, which reveals a homogeneous aspect of the synthesized particles for all samples. The presence of calcium (Ca), phosphor (P), oxygen (O) and silver (Ag) in the Ag:HAp is confirmed by energy dispersive X-ray (EDAX) and X-ray Photoelectron Spectroscopy analyses. Nanocrystalline silver doped HAp stimulated viability and potentiated the activation of murine macrophages. (C) 2012 Elsevier B.V. All rights reserved.

92. Wireless AlN sensor for condition based monitoring of industrial equipment

Authors: Ionescu, G; Ionescu, O; Popovici, S; Costea, S; Dumitru, V; Brezeanu, M; Stan, GE; Pasuk, I

Published: 2013, 2013 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1-2, 58, DOI:

This paper reports on the experimental realization and characterization of a wireless sensing system for machine-tool condition based monitoring. The system comprises a vibration sensor, an ARDUINO Leonardo development board and an RM 42 Blue tooth module. The sensing principle is based on a vibration sensor which includes a piezoelectric AlN layer deposited by sputtering on a flexible stainless steel foil. The functional testing of the sensor using a test stand for asynchronous engines equipped with frequency convertors is demonstrated.

93. MgB2 with Addition of Bi2O3 Obtained by Spark Plasma Sintering Technique

Authors: Burdusel, M; Aldica, G; Popa, S; Enculescu, M; Pasuk, I; Badica, P

Published: MAY 2013, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 26, 1556, DOI: 10.1007/s10948-012-2015-1

Bi2O3 and Bi-metal powders were mixed with MgB2 powder. Starting compositions were (MgB2)(Bi2O3) x, x = 0.0025, 0.005, 0.015, and (MgB2)(Bi)(y), y = 0.01. Mixtures were processed by Spark Plasma Sintering (SPS) technique. As obtained composite samples show high density, above 94 % of the theoretical density. Samples with Bi2O3 for x = 0.0025 and 0.005 show higher critical current densities, J(c), at high fields and at 20 K than for the pristine sample. Their irreversibility field, H-irr, is also higher. On the other hand, sample added with Bi-metal has lower J(c) and H-irr at any temperature than for the pristine sample.

94. Growth and structural characterization of orthorhombic and tetragonal SrCuO2 thin films

Authors: Mihailescu, CN; Pasuk, I; Athanasopoulos, GI; Luculescu, C; Socol, M; Saint-Martin, R; Revcolevschi, A; Giapintzakis, J

Published: AUG 1 2013, APPLIED SURFACE SCIENCE, 278, 135, DOI: 10.1016/j.apsusc.2012.12.029

Epitaxial SrCuO2 thin films were grown on (0 0 1) SrTiO3 substrates by pulsed laser deposition using a stoichiometric target. X-ray diffraction indicated that the SrCuO2 films undergo a structural phase transition as a function of the substrate temperature. Films deposited at temperatures below 600 degrees C exhibit a tetragonal phase with the c-axis oriented along the growth direction while films deposited at temperatures above 700 degrees C exhibit an orthorhombic phase with the b-axis oriented along the growth direction. Atomic force microscopy indicated that the as-grown film surfaces are rather smooth and the roughness increases with increasing substrate temperature. Energy dispersive X-ray spectroscopy in agreement with X-ray diffraction intensity ratio data revealed that all films are non-stoichiometric and contain Sr vacancies (Sr/Cu similar to 0.8). The influence of film-substrate lattice matching and substrate temperature on the structural phase transition is discussed. (C) 2012 Elsevier B.V. All rights reserved.

95. Preparation by sol-gel and solid state reaction methods and properties investigation of double perovskite Sr2FeMoO6

Authors: Cernea, M; Vasiliu, F; Plapcianu, C; Bartha, C; Mercioniu, I; Pasuk, I; Lowndes, R; Trusca, R; Aldica, GV; Pintilie, L

Published: NOV 2013, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 33, 2490, DOI: 10.1016/j.jeurceramsoc.2013.03.026

Double perovskite Sr2FeMoO6 was prepared by two ways consisting in sol gel technique and solid-state reaction method. The resulting powders from gel and mixed oxides precursors showed microstructures consisting of very fine grains (0.5-0.8 mu m) and a crystalline perovskite structure. The structural and microstructural properties of the double perovskite Sr2FeMoO6 powders as-prepared and ceramics were compared. Tetragonal Sr2FeMoO6 pellets were prepared from the two powders by spark plasma sintering at: 1000, 1100 and 1200 degrees C and then annealing at 1200 degrees C, 2 h in 5%H-2/Ar. The pellets presented different magnetic characteristics. The saturation magnetization of the samples prepared by sol-gel is close to those prepared by conventional synthesis method. (C) 2013 Elsevier Ltd. All rights reserved.

96. BNT-BT0.08 wires derived from sol-gel precursor and their piezoelectric behavior

Authors: Cernea, M; Pintilie, L; Trupina, L; Vasile, BS; Chirila, C; Pasuk, I

Published: MAY 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1668-4

Lead-free piezoelectric (Bi0.5Na0.5)(0.92)Ba0.08TiO3, (abbreviated as BNT-BT0.08) wires were prepared using its corresponding precursor sol and, a polycarbonate template membrane. The polycarbonate membrane used has a thickness of 30 mu m and pore diameter of 300 nm. Uniform surface morphology of the wires with average diameter of 145 nm and a length of about 20 mu m was obtained when the concentration of the sol was 0.3 M. The ferroelectric and piezoelectric properties of an individual BNT-BT0.08 wire were investigated using the PFM technique. The hysteresis loops between the PFM phase and DC bias and, the characteristic butterfly loops of the PFM amplitude versus DC bias, indicated a ferroelectric and piezoelectric behavior of as-obtained BNT-BT0.08 wires.

97. Structural, electric and magnetic properties of Pb(Zr0.2Ti0.8)O-3-CoFe2O4 heterostructures

Authors: Chirila, C; Ibanescu, G; Hrib, L; Negrea, R; Pasuk, I; Kuncser, V; Pintilie, I; Pintilie, L

Published: OCT 31 2013, THIN SOLID FILMS, 545, 7, DOI: 10.1016/j.tsf.2013.06.033

Electric and magnetic properties of symmetric and asymmetric Pb(Zr-0.2 Ti-0.8)O-3-CoFe2O4 (PZT/CFO) heterostructures, grown by pulsed laser deposition on SrTiO3 (100) substrates with a 25 nm SrRuO3 (SRO) buffer layer as bottom electrode, were investigated by using hysteresis and capacitance measurements. X-ray diffraction, and transmission electron microscopy investigations reveal the high quality crystalline structure and the epitaxial relationship between SRO, PZT and CFO. The electric polarization-voltage hysteresis reveals that the remnant polarization and the coercive field are significantly affected by the CFO layer. The frequency dependence of capacitance suggests a Maxwell-Wagner type relaxation at low frequencies and is also affected by the presence of the PZT/CFO interface(s). The magnetic hysteresis measurements infer the possible presence of another spinel phase (Co3O4) in the CFO film, due to the lattice mismatch at the PZT/CFO interfaces, and with direct influence on the magnetic response of the structure. According to the electric and magnetic characterization, better room temperature multiferroic properties would be expected for the symmetric heterostructure. (C) 2013 Published by Elsevier B. V.

98. Multi-layer haemocompatible diamond-like carbon coatings obtained by combined radio frequency plasma enhanced chemical vapor deposition and magnetron sputtering

Authors: Popa, AC; Stan, GE; Husanu, MA; Pasuk, I; Popescu, ID; Popescu, AC; Mihailescu, IN

Published: DEC 2013, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 24, 2707, DOI: 10.1007/s10856-013-5026-y

Radio-frequency Plasma Enhanced Chemical Vapour Deposition (in different methane dilutions) was used to synthesize adherent and haemocompatible diamond-like carbon (DLC) films on medical grade titanium substrates. The improvement of the adherence has been achieved by interposing a functional buffer layer with graded composition TixTiC1-x (x = 0-1) synthesized by magnetron co-sputtering. Bonding strength values of up to similar to 67 MPa have been measured by pull-out tests. Films with different sp(3)/sp(2) ratio have been obtained by changing the methane concentration in the deposition chamber. Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction were employed for the physical-chemical characterization of the samples. The highest concentration of sp(3)-C (similar to 87 %), corresponding to a lower DLC surface energy (28.7 mJ/m(2) ), was deposited in a pure methane atmosphere. The biological response of the DLC films was assayed by a state-of-the-art biological analysis method (surface enhanced laser desorption/ionization-time of flight mass spectroscopy), in conjunction with other dedicated testing techniques: Western blot and partial thromboplastin time. The data support a cause-effect relationship between sp(3)-C content, surface energy and coagulation time, as well as between platelet-surface adherence properties and protein adsorption profiles.

99. Electrode interface control of the Schottky diode-like behavior in epitaxial Pb(Zr0.2Ti0.8)O-3 thin films: A critical analysis

Authors: Hrib, LM; Boni, AG; Chirila, C; Pasuk, I; Pintilie, I; Pintilie, L

Published: JUN 7 2013, JOURNAL OF APPLIED PHYSICS, 113, DOI: 10.1063/1.4808464

Metal-ferroelectric-metal structures based on epitaxial Pb(Zr0.2Ti0.8)O-3 thin films are prepared by pulsed laser deposition on single crystal SrTiO3 substrates ((001) orientation) with buffer SrRuO3 layer as bottom electrode. Pt, Cu, and SrRuO3 are used as top contacts. The current-voltage (I-V) measurements reveal a strong influence of the top electrode interface on the magnitude of the leakage current and the shape of the I-V characteristics. The lowest current values are obtained for top Cu and the highest for top Pt. Diode-like behavior is obtained for top Cu and Pt, but the forward and reverse biases are opposite in sign. Contrary to the case of BiFeO3 layers deposited on the same type of substrates, it was found that the diode-like behavior is not switchable with the polarization reversal although the polarization values are comparable. It is also shown that the metal-ferroelectric-metal (MFM) structure based on Pb(Zr,Ti)O-3 (PZT) can be simulated and modeled as a back-to-back connection of two Schottky diodes. The diode-like behavior of the MFM structure can be induced by a slight asymmetry of the potential barriers at the electrode interfaces behaving as Schottky contacts. The study ends with a critical discussion of the MFM structures based on PZT and BiFeO3 (BFO) layers. It is shown that the switchable diode-like behavior is not uniquely determined by the polarization reversal and is not a general characteristic for MFM structures. Such behavior may be present only if the polarization induced band-bending at the interface is generating an accumulation layer at the interface. This could be possible in BiFeO3 based MFM structures due to the lower band gap compared to Pb(Zr0.2Ti0.8)O-3 thin films. (C) 2013 AIP Publishing LLC.

100. Casimir effect demonstrated by Raman spectroscopy on trilayer graphene intercalated into stiff layered structures of surfactant

Authors: Baibarac, M; Baltog, I; Mihut, L; Pasuk, I; Lefrant, S

Published: JAN 2013, CARBON, 51, 142, DOI: 10.1016/j.carbon.2012.08.021

Polarized Raman scattering studies on stiff layered structure of surfactant intercalated with trilayer graphene were performed at different intensities and excitation wavelengths. The D and 2D Raman bands reach the highest and lowest intensity when the polarization of laser excitation light is oriented along and perpendicular on the edges. The 2D band discloses two lorentzian components, separated by similar to 40 cm(-1), which result from the action of interplanar forces, of Casimir nature. The value of similar to 40 cm(-1) is close to the energy value associated with E-2g interplanar layer shear mode evidenced so far only by neutron spectrometry. A new result regards the opposite variation of the intensities of D and 2D bands with the increase of the wavelength of the excitation light. This originates in the different origin of the D and 2D bands; the former is dependent on disorder including also the graphene edges while the latter, results from in a double resonant mechanism combined with a Casimir effect. One demonstrates that the magnitude of Casimir force, which activates interlayer vibration modes, depends on the carrier density on the graphene sheets which can be varied both by the intensity and the wavelength of the excitation laser light. (C) 2012 Elsevier Ltd. All rights reserved.

101. TILT c AXIS CRYSTALLITE GROWTH OF ALUMINIUM NITRIDE FILMS BY REACTIVE RF-MAGNETRON SPUTTERING

Authors: Stan, GE; Pasuk, I; Trinca, LM; Galca, AC; Enculescu, M; Miculescu, F

Published: JAN-MAR 2012, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 7, 50, DOI:

The article reports on the tilted growth of textured aluminium nitride thin films obtained by radio-frequency magnetron sputtering onto 50 mm diameter Si (111) wafers, in reactive atmosphere, in a planar sputtering system without tilting the substrate and with no additional sputtering geometry alterations. The films were investigated using, X-ray diffraction, spectroscopic ellipsometry and scanning electronic microscopy, done by local measurements on the wafer surface, at different distances from the centre. A progressive increase of the tilt angle when moving away from the sample centre has been found. The maximum tilt angle of the columnar AlN crystallites, obtained near the edges of the wafer, is about 7 degrees. The results showed also that tilting is associated with smaller thickness and larger dispersion of the c axis orientation. Synthesizing inclined c axis AlN films should allow the fabrication of surface acoustic wave devices based on shear waves for liquid sensor applications.

102. The impact of the Pb(Zr,Ti)O-3-ZnO interface quality on the hysteretic properties of a metal-ferroelectric-semiconductor structure

Authors: Pintilie, I; Pasuk, I; Ibanescu, GA; Negrea, R; Chirila, C; Vasile, E; Pintilie, L

Published: NOV 15 2012, JOURNAL OF APPLIED PHYSICS, 112, DOI: 10.1063/1.4765723

The hysteretic properties of metal-ferroelectric-semiconductor (MFS) structures based on Pb(Zr0.2Ti0.8)O-3 (PZT) and ZnO films were studied with respect of the quality of the PZT-ZnO interface. The films were grown by pulsed laser deposition (PLD) on platinized silicon (Pt/Si) substrate and on single crystal, (001) oriented SrTiO3 (STO) substrates. The structural analysis has revealed that the PZT-ZnO stack grown on single crystal STO is epitaxial, while the structure grown on Pt/Si has columnar texture. The temperature change of the capacitance-voltage (C-V) hysteresis direction, from clockwise at low temperatures to counter clockwise at high temperatures, was observed at around 300K in the case of the MFS structure grown by PLD on Pt/Si substrate. This temperature is lower than the one reported for the case of the PZT-ZnO structure grown by sol-gel on Pt/Si substrate (Pintilie et al., Appl. Phys. Lett. 96, 012903 (2010)). In the fully epitaxial structures the C-V hysteresis is counter clockwise even at 100K. These findings strongly points out that the quality of the PZT-ZnO interface is essential for having a C-V hysteresis of ferroelectric nature, with negligible influence from the part of the interface states and with a memory window of about 5V at room temperature. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4765723]

103. Pulsed laser deposition of highly textured La5Ca9Cu24O41 films on SrLaAlO4 (100) and Gd3Ga5O12 (100) substrates

Authors: Pervolaraki, M; Pasuk, I; Stan, GE; Giapintzakis, J

Published: SEP 15 2012, APPLIED SURFACE SCIENCE, 258, 9479, DOI: 10.1016/j.apsusc.2012.02.145

The growth of La5Ca9Cu24O41 thin films on SrLaAlO4 (1 0 0) and Gd3Ga5O12 (1 0 0) substrates by pulsed laser deposition is reported in this paper. The influence of deposition process parameters, such as oxygen pressure, substrate temperature, and laser repetition rate, on the crystallinity, orientation and microstructure of the films has been investigated. X-ray diffraction and atomic force microscopy studies showed a clear dependence of the film crystallographic orientation and morphology (grain size) on the substrate temperature and the oxygen pressure used in the deposition process. (c) 2012 Elsevier B.V. All rights reserved.

104. Photoluminescence and Raman evidence for mechanico-chemical interaction of polyaniline-emeraldine base with ZnS in cubic and hexagonal phase

Authors: Scocioreanu, M; Baibarac, M; Baltog, I; Pasuk, I; Velula, T

Published: FEB 2012, JOURNAL OF SOLID STATE CHEMISTRY, 186, 223, DOI: 10.1016/j.jssc.2011.12.012

The mechanico-chemical interaction of a polyaniline-emeraldine base (PANI-EB) with ZnS in the cubic and wurtzite phases is studied by Raman spectroscopy and photoluminescence (PL). The results demonstrate that such an interaction leads to the formation of a PANI-salt and metallic Zn. Regardless of the structural form of the ZnS, the formation PANI-salt is indicated by a band in the Raman spectrum that shifts from 1162 to 1176 cm(-1) and the appearance of a new band at 1330 cm(-1) that indicates the protonated structure of a PANI-salt. The presence of the second product is determined by comparative PL studies performed on ZnS that has interacted mechanico-chemically with PANI-EB and metallic Zn powder. The variations of the PL spectra and their associated excitation spectra are explained as resulting from the charge collection processes that occur in the composite materials produced by the mechanico-chemical interaction between ZnS and PANI-EB or metallic Zn. (C) 2011 Elsevier Inc. All rights reserved.

105. The effect of the top electrode interface on the hysteretic behavior of epitaxial ferroelectric Pb(Zr,Ti)O-3 thin films with bottom SrRuO3 electrode

Authors: Pintilie, L; Pasuk, I; Negrea, R; Filip, LD; Pintilie, I

Published: SEP 15 2012, JOURNAL OF APPLIED PHYSICS, 112, DOI: 10.1063/1.4754318

The hysteretic behavior of the epitaxial Pb(Zr,Ti)O-3 thin films with different top metal electrodes is studied, with emphasis on the influence of the leakage current and trap generation current on the shape of the loop as well as on the magnitude of the measured polarization. Cu, Pt, and SrRuO3 were used as top contacts and important differences were observed for measurements performed in both dynamic and static modes, although the contacts were deposited on the same epitaxial Pb(Zr,Ti)O-3 film grown on SrRuO3/SrTiO3 substrate. A peculiar behavior was observed especially for the static hysteresis loops where, depending of the top contact, the loop is influenced mainly by the leakage current (Pt) or by the trap generation current (Cu and SrRuO3). The last one can contribute with an additive charge, having a linear dependence on the applied voltage, as suggested by the simple model developed to explain the abnormally high values of the dielectric constant extracted from the linear part of the static hysteresis loop. It is concluded that the properties of the top electrode interface can significantly impact the hysteretic behavior of the ferroelectric films. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4754318]

106. Structure and Magnetic Properties of Nanosized Magnetite Obtained by Glass Recrystallization

Authors: Sandu, V; Nicolescu, MS; Kuncser, V; Popa, S; Pasuk, I; Ghica, C; Sandu, E

Published: JUN 2012, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 12, 5050, DOI: 10.1166/jnn.2012.4943

We present the preparation, structural and magnetic properties of nanosized magnetite obtained by the crystallization of a series of Fe-containing borosilicate glasses. Several compositions with the ratio Fe2O3/SiO2 spanning from 0.37 to 0.67 were investigated as a function of two nucleators Cr2O3 and P2O5, respectively, and modifiers and intermediates (Al2O3 and MgO). Mossbauer spectroscopy revealed the degree, the type and the location of disorder induced by a specific composition and nucleators. In addition to magnetite, it was also revealed the presence of large amounts of Fe-rich paramagnetic phases. The magnetic response is analysed in relation with the amount of Fe ions which remain dispersed in the glassy matrix as noninteracting (paramagnetic) ions. We discuss the role of the nucleators on the disorder in both tetrahedral and octahedral sites of the magnetite.

107. Spark plasma sintering of MgB2 in the two-temperature route

Authors: Aldica, G; Batalu, D; Popa, S; Ivan, I; Nita, P; Sakka, Y; Vasylkiv, O; Miu, L; Pasuk, I; Badica, P

Published: JUL 2012, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 477, 50, DOI: 10.1016/j.physc.2012.01.023

Superconducting bulks of MgB2 were obtained by an ex-situ two-temperature route applied to spark plasma sintering (SPS). Processing of samples was performed at lower temperatures than previously reported. Samples produced by the two-temperature route show a higher morphological uniformity, a higher density (above 98%), a higher Vickers hardness, and undesirable stronger microscale flux jumps, as indicated by magnetic relaxation measurements when compared to a sample obtained by the one-temperature route (95.3% relative density). At the same time, all sintered samples show approximately constant crystallite size, critical current density, irreversibility field, critical temperature, weight fraction of impurity phases (MgB4 and MgO), and the amount of carbon accidentally introduced during SPS processing. (C) 2012 Elsevier B.V. All rights reserved.

108. INFLUENCE OF ANNEALING TREATMENT OF NANO-HYDROXYAPATITE BIOCERAMICS ON THE VIBRATIONAL PROPERTIES

Authors: Ciobanu, CS; Andronescu, E; Stoicu, A; Florea, O; Le Coustumer, P; Galaup, S; Djouadi, A; Mevellec, JY; Musa, I; Massuyeau, F; Prodan, AM; Lafdi, K; Trusca, R; Pasuk, I; Predoi, D

Published: APR-JUN 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 624, DOI:

Nano-hydroxyapatite bio-ceramics were synthesized by sol-gel method. The gel was dried at 80 degrees C for 96 h. The dried gels were individually heated at a rate of 5 degrees C/min up to 600 degrees C, 800 degrees C, and 1000 degrees C. X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used for to characterize the composition, morphology and particle size of samples. At 800 degrees C a small amount of CaO (about 0.3 wt%) was detected in which increased after annealing at 1000 degrees C (about 1.1 wt%). The crystallites are elongated along the c crystallographic axis, but the size anisotropy decreases with increasing temperature above 800 degrees C. The size along the elongation axis increased from 43 nm at 80 degrees C to about 143 nm at 1000 degrees C, as determined by XRD, and from 120 to 280 nm, as measured by TEM. The functional groups were analyzed using Fourier transform infrared (FTIR) and Raman spectroscopies confirming the presence of various and PO43 and OH- bands in the samples. After calcination at 1000 degrees C the bands are more intense which indicates an increase in the cristallynity. The photoluminescence (PL) of HAp treated at various temperatures (80, 600, 800, 1000 degrees C) was also studied. hFOB 1.19 osteoblats cells were used to determine cell proliferation, viability and citotoxicity after interaction with the prepared bioceramics. To evaluate cell proliferation rate quantitative by the hFOB 1.19 cells on HAp samples were cultured to 4 days. Cellular morphology was investigated using FESEM to obtain qualitative information of osteoblast cells on HAp samples. The number of hFOB 1.19 cells on control HAp_80, HAp_600, HAp_800 and HAp_1000 was 400 +/- 30, 360 +/- 25, 350 +/- 21, 320 +/- 16 and 300 +/- 10 after 4 days. Our results proved that the HAp sintered at 1000 degrees C promoted osteoblast cell attachment and adhesion.

109. PREPARATION AND ELECTRICAL CHARACTERIZATION OF SiGe NANOSTRUCTURES

Authors: Stavarache, I; Lepadatu, AM; Pasuk, I; Teodorescu, VS; Ciurea, ML

Published: 2011, 2011 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS 2011), 34TH EDITION, VOLS 1 AND 2, 52, DOI:

This paper presents the preparation and investigation of structure and electrical properties of nanostructures consisting of Si1-xGex nanocrystals. Nanostructures were prepared by RF magnetron sputtering, followed by thermal annealing. X-ray diffraction, TEM, high resolution TEM and SAED measurements were performed. Current-voltage and current-temperature characteristics were taken. Nanostructures have different electrical behavior. Current-voltage curves are linear, while current-temperature curves are dependent on the annealing temperature. In films annealed at 650 degrees C, electrical transport is controlled by quantum confinement effect and localized states (current-temperature characteristics), while in films annealed at 900 degrees C it is controlled by tunneling of thermally activated carriers between neighboring nanocrystals.

110. Radical modification of the wetting behavior of textiles coated with ZnO thin films and nanoparticles when changing the ambient pressure in the pulsed laser deposition process

Authors: Popescu, AC; Duta, L; Dorcioman, G; Mihailescu, IN; Stan, GE; Pasuk, I; Zgura, I; Beica, T; Enculescu, I; Ianculescu, A; Dumitrescu, I

Published: SEP 15 2011, JOURNAL OF APPLIED PHYSICS, 110, DOI: 10.1063/1.3639297

Cotton/polyester woven fabrics were functionalized with ZnO thin films or nanoparticles by pulsed laser deposition, using a KrF* excimer laser source. Depending on the number of applied laser pulses, well-separated nanoparticles (for 10 pulses) or compact thin films (for 100 pulses) were deposited. The synthesized nanostructures were evaluated morphologically by scanning electron microscopy and atomic force microscopy, physico-chemically by x-ray diffraction and functionally by the contact angle method. By modifying the ambient gas nature and pressure in the deposition chamber, hydrophilic or hydrophobic surfaces were obtained. When using an oxygen flux, both the deposited thin films and nanoparticles were hydrophilic. After deposition in vacuum, the nanoparticles were hydrophobic, but the thin films were super-hydrophobic. This radical modification of wetting behavior was assigned to the differences in microstructure features and surface electrical charging in the two cases. (C) 2011 American Institute of Physics. [doi:10.1063/1.3639297]

111. Grain growth, microstructure and surface modification of textured CeO2 thin films on Ni substrate

Authors: Mihalache, V; Pasuk, I

Published: JUL 2011, ACTA MATERIALIA, 59, 4885, DOI: 10.1016/j.actamat.2011.04.029

CeO2 films were prepared from solutions of different concentrations (0.05-1.0 M) on textured Ni substrates. Homogeneous nucleation and growth of CeO2 nanocrystals <8 nm occurs upon calcination at 350-500 degrees C. At the heating and sintering stage, the homogeneous growth is inhibited in favor of the development of grains with (0 0 1) texture. The grain growth normal to the film surface is well described by a stretched exponential function with a relaxation time of up to 60 min and with Kohlrausch exponent values of less than unity. The increase in grain size is accompanied by the relaxation of the microstrain. During the relaxation time, the grain coarsening is controlled by surface diffusion characterized by an activation energy as low as 0.6 eV. At the relaxation time, the surface morphology is strongly concentration dependent. The surface morphology changes from separated (agglomerated) grains to a continuous grain configuration as the concentration increases from 0.05 M to 0.8 M. After the relaxation time, both the grain size normal to the film surface and the lateral grain size continue to grow, and the grain configuration continues to change. These processes are concentration dependent. In the films with a nominal thickness >170 nm (>0.8 M), the transition to classical curvature-driven grain-growth kinetics is evident (at 1000 degrees C, below the literature value of 1100 degrees C). The decrease in the Kohlrausch exponent for these thick films suggests that the grain coarsening through grain boundary migration is responsible for the stretched regime of grain-size relaxation. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

112. Synthesis and dielectric characterization of Ba0.6Sr0.4TiO3 ferroelectric ceramics

Authors: Nedelcu, L; Ioachim, A; Toacsan, M; Banciu, MG; Pasuk, I; Berbecaru, C; Alexandru, HV

Published: JUN 30 2011, THIN SOLID FILMS, 519, 5815, DOI: 10.1016/j.tsf.2010.12.191

Ferroelectric ceramics Ba0.6Sr0.4TiO3 (BST 40) were prepared, by solid-state reaction in the temperature range 1210-1450 degrees C. Maximum values of the ceramic densities were around 94% of their theoretical value. X-ray diffraction techniques (XRD) and scanning electron spectroscopy (SEM) were used to analyze the structure and the surface morphology of ceramics. Rounded, well defined or abnormal granular growth was observed in the SEM images, vs. sintering conditions and purity of the raw materials. In all samples, BST 40 ceramic is the major phase, but there are also present small amounts of secondary phases, as revealed in XRD diffraction patterns. Permittivity and dielectric loss measurements were performed in the temperature range - 150 to + 150 degrees C, and 150 Hz-5 MHz frequency values. Permittivity values rising from 1200 to 12,500, with increasing sintering temperatures, were recorded. Narrow and well defined transition peaks were noticed at higher sintering temperatures. Curie temperature was around 2 degrees C, for samples with the mentioned composition. Permittivity and losses vs. frequency show different behavior whether BST ceramics are in polar or non-polar state and with the distance toward phase transition. Microwave measurements performed at room temperature have shown lower values of permittivity, compared with similar data at low frequency, and dielectric losses lower than 1% at 0.7 GHz. The sintering conditions (temperatures, sintering time, etc.) and purity of the raw materials lead to important changes of transition temperatures in the polymorphic diagram, which we have built-for the other Ba1 - xSrxTiO(3) compositions (x = 0.25-0.90) sintered at 1260 degrees C for 2 h. (C) 2011 Elsevier B.V. All rights reserved.

113. Highly adherent bioactive glass thin films synthetized by magnetron sputtering at low temperature

Authors: Stan, GE; Pasuk, I; Husanu, MA; Enculescu, I; Pina, S; Lemos, AF; Tulyaganov, DU; El Mabrouk, K; Ferreira, JMF

Published: DEC 2011, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 22, 2710, DOI: 10.1007/s10856-011-4441-1

Thin (380-510 nm) films of a low silica content bioglass with MgO, B2O3, and CaF2 as additives were deposited at low-temperature (150A degrees C) by radio-frequency magnetron sputtering onto titanium substrates. The influence of sputtering conditions on morphology, structure, composition, bonding strength and in vitro bioactivity of sputtered bioglass films was investigated. Excellent pull-out adherence (similar to 73 MPa) was obtained when using a 0.3 Pa argon sputtering pressure (BG-a). The adherence declined (similar to 46 MPa) upon increasing the working pressure to 0.4 Pa (BG-b) or when using a reactive gas mixture (similar to 50 MPa). The SBF tests clearly demonstrated strong biomineralization features for all bioglass sputtered films. The biomineralization rate increased from BG-a to BG-b, and yet more for BG-c. A well-crystallized calcium hydrogen phosphate-like phase was observed after 3 and 15 days of immersion in SBF in all bioglass layers, which transformed monotonously into hydroxyapatite under prolonged SBF immersion. Alkali and alkali-earth salts (NaCl, KCl and CaCO3) were also found at the surface of samples soaked in SBF for 30 days. The study indicated that features such as composition, structure, adherence and bioactivity of bioglass films can be tailored simply by altering the magnetron sputtering working conditions, proving that this less explored technique is a promising alternative for preparing implant-type coatings.

114. Bioactive glass thin films deposited by magnetron sputtering technique: The role of working pressure

Authors: Stan, GE; Marcov, DA; Pasuk, I; Miculescu, F; Pina, S; Tulyaganov, DU; Ferreira, JMF

Published: SEP 15 2010, APPLIED SURFACE SCIENCE, 256, 7110, DOI: 10.1016/j.apsusc.2010.05.035

Bioglass coatings were prepared by radio frequency magnetron sputtering deposition at low temperature (150 degrees C) onto silicon substrates. The influence of argon pressure values used during deposition (0.2 Pa, 0.3 Pa and 0.4 Pa) on the short-range structure and biomineralization potential of the bioglass coatings was studied. The biomineralization capability was evaluated after 30 days of immersion in simulated body fluid. SEM-EDS, XRD and FTIR measurements were performed. The tests clearly showed strong biomineralization features for the bioglass films. The thickness of the chemically grown hydroxyapatite layers was more than twice greater for the BG films deposited at the highest working pressure, in comparison to those grown on the films obtained at lower working pressures. The paper attempts to explain this experimental fact based on structural and compositional considerations. (C) 2010 Elsevier B.V. All rights reserved.

115. First stages of bioactivity of glass-ceramics thin films prepared by magnetron sputtering technique

Authors: Berbecaru, C; Alexandru, HV; Stan, GE; Marcov, DA; Pasuk, I; Ianculescu, A

Published: MAY 25 2010, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 169, 105, DOI: 10.1016/j.mseb.2010.01.007

Implant type coatings were prepared by magnetron sputtering (MS) technique onto medical grade Ti6Al4V alloy substrates starting from biological 45S5 glass system powders. The as-deposited thin layers were annealed 2 h at 700 degrees C in ambient air, followed by a slow cooling (2 degrees C/min) in order to induce crystallization. The behavior of the coatings was investigated by soaking the samples in simulated body fluids (SBF) and extracting them after 24 and 72 h. The changes in the films' structure were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) analysis and by Fourier transform infrared spectroscopy (FTIR). A pitched, pore free microstructure with 6 mu m agglomerates of submicron grains in a continuous matrix was revealed by the SEM images of the annealed samples. Complex silicates as Na(4)Ca(4)Si(6)O(18)-combeite and phosphates NaCaPO(4) as crystalline phases were identified in the XRD diffraction patterns. In-growths after 24 h show the enrichment in Si-O (s) non-bonding oxygen (NBO). The polymerization reaction in the surface layer appears for the sample immersed 72 h in SBF. No crystalline hydroxyapatite (HA) was evidenced for those samples. Subsequent dissolution processes of the surface layers were noticed from XRD patterns and SEM images. (c) 2010 Elsevier B.V. All rights reserved.

116. Biomineralization capability of adherent bio-glass films prepared by magnetron sputtering

Authors: Stan, GE; Pina, S; Tulyaganov, DU; Ferreira, JMF; Pasuk, I; Morosanu, CO

Published: APR 2010, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 21, 1055, DOI: 10.1007/s10856-009-3940-9

Radiofrequency magnetron sputtering deposition at low temperature (150A degrees C) was used to deposit bioactive glass coatings onto titanium substrates. Three different working atmospheres were used: Ar 100%, Ar + 7%O(2), and Ar + 20%O(2). The preliminary adhesion tests (pull-out) produced excellent adhesion values (similar to 75 MPa) for the as-deposited bio-glass films. Bioactivity tests in simulated body fluid were carried out for 30 days. SEM-EDS, XRD and FTIR measurements were performed. The tests clearly showed strong bioactive features for all the prepared films. The best biomineralization capability, expressed by the thickest chemically grown carbonated hydroxyapatite layer, was obtained for the bio-glass coating sputtered in a reactive atmosphere with 7% O(2).

117. Biomineralization capability of adherent bio-glass films prepared by magnetron sputtering (vol 21, pg 1047, 2010)

Authors: Stan, GE; Pina, S; Tulyaganov, DU; Ferreira, JMF; Pasuk, I; Morosanu, CO

Published: OCT 2010, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 21, 2899, DOI: 10.1007/s10856-010-4040-6

118. PHYSICO-CHEMICAL PROPERTIES OF NANO-SIZED HEXAGONAL HYDROXYAPATITE POWDER SYNTHESIZED BY SOL-GEL

Authors: Costescu, A; Pasuk, I; Ungureanu, F; Dinischiotu, A; Costache, M; Huneau, F; Galaup, S; Le Coustumer, P; Predoi, D

Published: OCT-DEC 2010, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 5, 1000, DOI:

Calcium phosphate ceramic powders were synthesized via sol-gel method. The powders were sintered at 600 and 1000 degrees C and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron microscopy (SEM and TEM), elemental microanalysis (EDS), infrared spectroscopy (FTIR), and thermal analysis (TGA and DTA). The XRD analysis revealed a well crystallized hydroxyapatite (HAp) structure at all temperatures. At 1000 degrees C a small amount of CaO (about 1.2 %) was detected. The average crystallite size increased from 19 nm at 80 degrees C to about 125 nm at 1000 degrees C. FTIR spectra showed the presence of various PO43- and OH- groups present in the powders. In order to verify the biocompatibility of HAP powders with hFOB 1.19 osteoblasts cells, an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test was applied. It was noticed that the ceramics obtained at 1000 degrees C, increased the cell viability with 10%, 40% and 55% after 6, 12 respectively 24 h, whereas that obtained at 600 degrees C was less effective. Our results proved the high biocompatibility of calcium phosphate ceramic powders obtained by sol-gel and sintered at 1000 degrees C.

119. HIGHLY TEXTURED (001) AlN NANOSTRUCTURED THIN FILMS SYNTHESIZED BY REACTIVE MAGNETRON SPUTTERING FOR SAW AND FBAR APPLICATIONS

Authors: Stan, GE; Pasuk, I; Galca, AC; Dinescu, A

Published: OCT-DEC 2010, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 5, 1054, DOI:

Highly oriented (001) AlN (wurtzite type) thin films have been successfully deposited on silicon, platinized silicon and glass substrates by reactive radio-frequency magnetron sputtering at low temperature (150 degrees C). X-ray diffraction, spectroscopic ellipsometry and scanning electron microscopy techniques have been employed to asses the structural characteristics of the AlN films. We have investigated both the influence of AlN film's thickness and of the substrate nature on crystallinity. The thicker films present a better c axis alignment, a minimum orientation dispersion of 3.5. being reached for 1 mu m AlN on silicon. The micro-and macrostrain of the AlN lattice relaxes as the film thickness increases. The film deposited onto platinum has the maximum value of tensile strain along c axis. The film on glass exhibited the poorest texturing and the highest defect concentration. From an optical point of view the film deposited on Pt is the denser one and that deposited on glass is the most rarefied. One can conclude that when using a low deposition temperature and a base pressure of similar to 10(-4) Pa the increase of film thickness leads to improved AlN structure on Si or Pt supports.

120. INFLUENCE OF PREPARATION METHOD ON STRUCTURAL PROPERTIES OF GeSiO NANOSYSTEMS

Authors: Stavarache, I; Lepadatu, AM; Teodorescu, V; Stoica, T; Pasuk, I; Stan, G; Iancu, V; Ciurea, ML

Published: 2010, 2010 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 80, DOI: 10.1109/SMICND.2010.5650255

GeSiO nanosystems were obtained using two different preparation methods, sol-gel and magnetron-sputtering. Transmission electron microscopy measurements were performed to investigate the films structure. Amorphous and crystalline Ge dots embedded in amorphous silicon dioxide were observed. The Ge concentration in the GeSiO films was by Energy-dispersive X-ray spectroscopy.

121. ZnO particles of wurtzite structure as a component in ZnO/carbon nanotube composite

Authors: Baibarac, M; Baltog, I; Velula, T; Pasuk, I; Lefrant, S; Gautier, N

Published: NOV 4 2009, JOURNAL OF PHYSICS-CONDENSED MATTER, 21, DOI: 10.1088/0953-8984/21/44/445801

Composites based on carbon nanotubes and ZnO particles with needle shapes were prepared for applications in energy storage. Depending on the temperature (85 or 25 degrees C) at which the reaction between NaOH and ZnCl(2) was carried out, particles with two different morphologies: needle-shaped (NS) and double-pyramid-shaped (DPS), respectively, are obtained. Scanning electron microscopy, photoluminescence, UV-Vis absorption spectroscopy, x-ray diffraction and Raman light scattering studies reveal that the NS and DPS particles belong to ZnO with wurtzite (WZ) structure and epsilon-Zn(OH)(2) as precursors of ZnO, respectively. Using the ZnO/carbon nanotube composite as a negative electrode and an electrolytic solution containing LiPF(6), the charge-discharge characteristics of rechargeable lithium ions cells were determined. Additional information concerning the electrochemical reactions at the interface of the two electrodes was obtained by cyclic voltammetry.

122. Effect of annealing upon the structure and adhesion properties of sputtered bio-glass/titanium coatings (vol 255, pg 9132, 2009)

Authors: Stan, GE; Morosanu, CO; Marcov, DA; Pasuk, I; Miculescu, F; Reumont, G

Published: DEC 15 2009, APPLIED SURFACE SCIENCE, 256, 1617, DOI: 10.1016/j.apsusc.2009.08.083

123. Effect of Nickel-Niobium Co-Doping on Structural, Electromechanical, and Dielectric Properties of Lead Titanate Ceramics

Authors: Amarande, L; Miclea, C; Tanasoiu, T; Iuga, A; Cioangher, MC; Trupina, L; Grecu, MN; Pasuk, I

Published: SEP 2009, IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL, 56, 1798, DOI: 10.1109/TUFFC.2009.1251

Lead titanate (PT) ceramics co-doped with 8 to 13 mol% Ni-Nb, by substituting titanium ions, were prepared by conventional ceramic method and the influence of Ni-Nb doping level on their mopho-structural, electromechanical and dielectric properties was investigated. Dense tetragonal PT ceramics were obtained for 8 to 12 mol% Ni-Nb co-doping. Lattice anisotropy decreased from 1.053 to 1.046 with increasing doping level. Large thickness coupling factors of 0.4 were obtained for 8, 11, and 12 mol% Ni-Nb. Large electromechanical anisotropy of 10 was obtained for 8 mol% Ni-Nb. It was found that Ni-Nb co-doping has both softening and hardening effects as a function of donor or acceptor behavior of different amounts of Ni-Nb. For 13 mol% Ni-Nb, segregation of a small amount of a secondary phase occurs, lattice constants and tetragonality significantly decrease and the resulting ceramic becomes very hard.

124. STRUCTURAL AND OPTICAL PROPERTIES OF SOL-GEL DERIVED HYDROXYAPATITE FILMS IN DIFFERENT STAGES OF CRYSTALLIZATION AND DENSIFICATION PROCESSES

Authors: Tionica, S; Gartner, M; Ianculescu, A; Anastasescu, M; Slav, A; Pasuk, I; Stoica, T; Zaharescu, M

Published: 2009, NANOSTRUCTURED MATERIALS AND NANOTECHNOLOGY II, 29, +, DOI:

Hydroxyapatite (HAp) films, widely used as a biocompatible material for hard tissues repairing. are studied in this paper for a better control and understanding of the crystallization and densification of sol-gel deposited layers. Calcium nitrate and triethyl phosphite diluted in alcohols were used as calcium and phosphorus precursors. HAp coatings were obtained by spinning method, followed by drying and annealing in the range 130-750 degrees C. Specific temperatures of the chemical reactions of HAp formation have been revealed by thermogravimetric analysis (TG-DTA). Structural. chemical and optical characterizations of the films were performed by Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Analysis (EDX) facilities, X-ray diffraction (XRD). Fourier Transform Infrared Spectroscopy (FTIR) and Spectral Ellipsometry (SE). The film crystallinity increases with file annealing temperature above 550 degrees C. XRD lines of HAp crystallographic planes become narrow at 750 degrees. and correspond to a single crystallographic phase. The Film morphology depends not only on annealing history but also on the synthesis parameters. Thus. layers with large grains of well sinterized HAp nano-crystals can be obtained. Using EDX measurements, the Ca/P ratio was found close to the stoichiometric value in the well sinterized HAp grain regions and slightly increased 1.82 for boundary regions between grains. The density of pores usually observed in sol-gel derived films was estimated for different samples using modeling of SE data.

125. Nanostructured Ferrite Formation in Borosilicate Glass

Authors: Sandu, V; Popa, S; Pasuk, I; Enculescu, I; Nicolescu, MS; Radicescu, S

Published: 2009, MULTI-FUNCTIONAL MATERIALS AND STRUCTURES II, PTS 1 AND 2, 79-82, +, DOI: 10.4028/www.scientific.net/AMR.79-82.445

We present the preparation, structural, and magnetic properties of a series of Fe-containing borosilicate glasses as a function of the ratio SiO2/Fe2O3 which is ranging from 1.49 to 2.68. The role of nucleators (Cr2O3 and P2O5) was also investigated. X-Ray diffraction has revealed the formation of magnetite as the major or unique crystalline phase. As SEM micrographs have revealed, the addition of P2O5 give rise to a finer structure as compared with Cr2O3. In addition, the same oxide decreases the temperature of structural transition with almost 100 degrees C. The magnetization data reveal a two step transition at low temperatures: a high temperature transition at T-v = 128 K, which we attribute to the Verwey transition, and a low temperature transition at T-s = 48 K which, most likely, is the result of change in the dynamic of the domain motion.

126. Effect of annealing upon the structure and adhesion properties of sputtered bio-glass/titanium coatings

Authors: Stan, GE; Morosanu, CO; Marcov, DA; Pasuk, I; Miculescu, F; Reumont, G

Published: AUG 30 2009, APPLIED SURFACE SCIENCE, 255, 9138, DOI: 10.1016/j.apsusc.2009.06.117

Bio-glass films were deposited by radio-frequency magnetron sputtering technique onto medical grade Ti6Al7Nb alloy substrates from prepared silica based bio-glass target. A low deposition temperature was used (150 degrees C) and three different working pressures, followed by annealing in air at 550 and 750 degrees C. A quasi-stoichiometric target to substrate atomic transfer was found for Si, Ca and P, along with strong enrichment in Na and depletion in K and Mg, as evidenced by the energy dispersive microanalysis. The best results, taking into account stoichiometry and surface roughness, were obtained for the BG layers deposited at 0.3 Pa argon working pressure. The infrared spectroscopy of the as-sputtered and of the annealed films evidenced the characteristic molecular vibrations of silicate, phosphate and carbonate functional groups. The as-deposited films are amorphous and became partly crystalline after annealing at 750 degrees C, as evidenced by X-ray diffraction. The pull-out measurements, performed with a certified pull-test machine, gave very strong film-substrate adhesion strength values. For the non-crystalline layers, the pull-out strength is higher than 85 MPa, and decreases after annealing at 750 degrees C to 72.9 +/- 7.1 MPa. The main objective of this work was to establish the influence of the working pressure upon the composition and morphology of the as-deposited films, and of the annealing temperature upon structure and film substrate adhesion. (C) 2009 Elsevier B. V. All rights reserved.

127. Titanium oxide thin films produced by pulsed laser deposition

Authors: Sima, C; Grigoriu, C; Viespe, C; Pasuk, I; Matei, E

Published: JUN 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 830, DOI:

The structural peculiarities of titanium oxide films formed by pulsed laser deposition have been investigated. A pure titanium target was irradiated by a Nd:YAG laser (355 and 532 nm). The work studied the influence of the beam wavelength, and oxygen pressure (20, 40, 80, and 160 mTorr) upon the layer structure. The films deposited at room temperature were partly crystalline. The crystalline fraction was a mixture of titanium sub-oxides. The 532 nm wavelength seems to favour the oxidation of titanium leading to TiO(2) formation even at room temperature. After annealing, crystalline TiO(2-) anatase formed at both irradiation wavelengths, but only at low oxygen pressures (20 and 40 mTorr). The best crystallization occurs in the layers deposited at the lowest oxygen pressure (20 mTorr), at both laser beam wavelengths; most anatase formed in the sample obtained at 20 mTorr, 532 nm. At 20 mTorr the films were compact, for both wavelengths, but also tilted or randomly distributed columnar grains were observed at higher pressure. The films deposited with 355 nm, were thinner than those with 532 nm; at 355 nm the thickness decreased at higher pressure, while at 532 nm the dependence was opposite.

128. An Optimized Method for Electroless Pd Deposition onto Alumina Substrates

Authors: Petica, A; Anicai, L; Pasuk, I

Published: DEC 2008, REVISTA DE CHIMIE, 59, 1381, DOI:

An optimized electroless deposition procedure to form Pd membranes onto ceramic substrates involving the thermal decomposition of a Pd complex compound ([Pd (NH3)(4)] [PdCl4]) is discussed. This allowed a reaction efficiency of about 90-95%. The proposed method significantly diminishes the Pd wastes as compared with the classical procedure involving hydrazine based reduction step. A Pd layer of about 3-5 mu m has been uniformly deposited on the inner surface of the alpha-Al2O3 based substrate, being characterized by a very good adherence and light grey metallic appearance. Homogeneous films of Pd were obtained by annealing the deposited Pd layers at temperatures higher than 500 degrees C in a hydrogen atmosphere. XRD and laser confocal microscopy techniques have been proved to be suitable to characterize the composition, thickness and uniformity of the formed Pd membranes.

129. Calcium phosphate ceramics for biomedical applications

Authors: Predoi, D; Vatasescu-Balcan, RA; Pasuk, I; Trusca, R; Costache, M

Published: AUG 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2155, DOI:

Calcium phosphate compounds have been studied for biomedical applications due to chemical and structural similarity to the mineral phase of bone and tooth. The composition, physico-chemical properties, crystal size and morphology of synthetic apatite are extremely sensitive to preparative conditions and sometimes it resulted into non-stoichiometric calcium deficient hydroxyapatite (HAp) powders. The present paper describes the synthesis of calcium phosphate ceramics powders via a sol-gel method, The powders were sintered at 600 and 800 degrees C. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDXS) were used for characterization and evaluation of the phase composition, morphology and particle size of samples, The functional group of the coatings were analyzed using Fourier transform infrared (FTIR). The XRD analysis revealed a well crystallized HA structure at both temperatures. At 800 degrees C a small amount of CaO (about 0.4%) was detected. The mean crystallite size, determined from the breadth of the diffraction lines, increases from 30 nm at 600 degrees C to about 110 nm at 800 degrees C. FTIR spectra showed the presence of various PO43- and OH- groups present in the powders. Osteoblast cells were used to determine cell proliferation, viability and citotoxicity after interaction with the prepared bioceramics, by MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, a tetrazole) assay. We note that the viability of HAp-600 starts to decrease after 12h, while the viability of HAp-800 decreases after 6h.

130. PLD and RF-PLD synthesis of Ba0.6Sr0.4TiO3 ferroelectric thin films for electrically controlled devices

Authors: Nedelcu, L; Ioachim, A; Toacsan, MI; Banciu, MG; Pasuk, I; Buda, M; Scarisoreanu, N; Ion, V; Dinescu, M

Published: NOV 2008, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 93, 679, DOI: 10.1007/s00339-008-4694-9

Ba0.6Sr0.4TiO3 (BST) bulk ceramic synthesized by solid state reaction was used as target for thin films grown by pulsed laser deposition (PLD) and radiofrequency beam assisted PLD (RF-PLD). The X-ray diffraction patterns indicate that the films exhibit a polycrystalline cubic structure with a distorted unit cell. Scanning Electron Microscopy investigations showed a columnar microstructure with size of spherical grains up to 150 nm. The capacitance-voltage (C-V) characteristics of the BST films were performed by applying a DC voltage up to 5 V. A value of 280 for dielectric constant and 12.5% electrical tunability of the BST capacitor have been measured at room temperature.

131. Thickness dependence of crystallization process for hydroxyapatite thin films

Authors: Mercioniu, I; Ciuca, S; Pasuk, I; Slav, A; Morosanu, C; Bercu, M

Published: AUG 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 2538, DOI:

Hydroxyapatite (HAP) thin films (0.2 pm, 0.3 pm and 1.2 mu m thickness) were grown by RF magnetron sputtering in argon atmosphere onto silicon substrates at high deposition rates (0.6 mu m/h). Crystalline HAP films were obtained using a low temperature (100 degrees C) followed by post-deposition annealing at 300 degrees C, 450 degrees C, 500 degrees C and 550 degrees C in environmental air for 1 hour. An important influence of the films thickness upon the crystallization degree was noticed at intermediate annealing temperatures, as obtained from XRD measurements. For low and high temperatures similar values were obtained with a better crystallization degree for the thinner films. FTIR absorption led to the same conclusion considering the shape of stretching and bending PO4 lines. This suggests that the crystallization process has a diffusion component besides usual thermal activation process.

132. Micro-structure and magnetic properties of Fe-Cu nanocomposites for anisotropic permanent magnets

Authors: Kuncser, V; Valeanu, M; Lifei, F; Predoi, D; Jianu, A; Kappel, W; Codescu, M; Patroi, E; Pasuk, I; Bulinski, M; Filoti, G

Published: MAY 31 2005, JOURNAL OF ALLOYS AND COMPOUNDS, 395, 6, DOI: 10.1016/j.jallcom.2004.11.059

Melt spun ribbons of FexCu100-x were obtained by different procedures, in order to maximize the dispersion of the Fe atoms in the Cu matrix. Subsequent thermal and mechanical treatments were used for a controlled crystallization process of the soft magnetic phase. A detailed analysis of structural aspects and crystallization dynamics and their relation with the magnetic behavior of the Fe-Cu ribbons has been obtained via Mossbauer spectroscopy, X-ray diffraction (XRD) and magnetic measurements. In order to obtain composite permanent magnets with shape anisotropy, the optimal conditions and the suitable processing were established. &COPY; 2004 Elsevier B.V. All rights reserved.

133. Chemical growth of calcium phosphate layers on magnetron sputtered HA films

Authors: Verestiuc, L; Morosanu, C; Bercu, M; Pasuk, I; Mihailescu, IN

Published: MAR 15 2004, JOURNAL OF CRYSTAL GROWTH, 264, 491, DOI: 10.1016/j.jcrysgro.2004.01.015

Chemical growth of calcium phosphate films on top of apatite structures is an essential step for promoting implants integration in human bones. We used for chemical growth silicon wafers either covered with crystalline and amorphous hydroxyapatite films or uncoated. To promote growing, the structures have been immersed in simulated body fluids for 21 days at 37degreesC. The growth stages were monitored by atomic spectroscopy of Ca and P ions in solution. The calcium phosphate deposits were investigated by X-ray diffraction, optical and atomic force microscopy and FTIR spectroscopy. The grown structures onto sputtered hydroxyapatite were amorphous and smooth. The depositions performed directly on silicon substrates are mild. (C) 2004 Elsevier B.V. All rights reserved.

134. FexCu1-x alloys for permanent magnets

Authors: Kappel, W; Codescu, MM; Pasuk, I; Patroi, E; Kuncser, V; Valeanu, M; Predoi, D; Filoti, G

Published: SEP 2004, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 6, 978, DOI:

New magnetic composite materials, ribbon samples, with nominal compositions FexCu1-x (x=0.2; 0.5; 0.8) were obtained by the melt spinning technique. Various information was provided via X-ray diffraction, Mossbauer and magnetic measurements. The structural aspects: phase composition, size and texture effects, have been corroborated with magnetic properties. Finally, the possibility to choose the adequate composition and the suitable processing in order to obtain desired anisotropic magnetic materials were presented.

135. Preparation of BaTi4O9 from oxalates

Authors: Cernea, M; Chirtop, E; Neacsu, D; Pasuk, I; Iordanescu, S

Published: FEB 2002, JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 85, 503, DOI:

A barium titanate precursor with a barium:titanium ratio of 1:4 was prepared by controlled coprecipitation of mixed barium and titanium species with an ammonium oxalate aqueous solution at pH 7. The results of thermal analysis and IR measurement show that the obtained precursor is a mixture of BaC2O4.0.5H(2)O and TiO(OH)(2).1.5H(2)O in a molar ratio of 1:4. Crystallized BaTi4O9 was obtained by the thermal decomposition of a precipitate precursor at 1300degreesC for 2 h in air. The dimensions of the powder calcined at 1000degreesC are between 100 and 300 nm. The grain dimensions of the sintered sample for 2 h at 1300degreesC are of the order of 10 to 30 mum. Dielectric properties of disk-shaped sintered specimens in the microwave frequency region were measured using the TE011 mode. Excellent microwave characteristics for BaTi4O9-epsilon = 38 +/- 0.5, Q = 3800-4000 at 6-7 GHz and tau(f) = 11 +/- 0.7 ppm/degreesC-were found.

136. MICROSTRUCTURE, MAGNETIC AND MAGNETOSTRICTIVE BEHAVIOUR IN RAPIDLY QUENCHED OFF-STOICHIOMETRIC Ni-Mn-Ga FERROMAGNETIC SHAPE MEMORY ALLOYS

Authors: Sofronie, M; Tolea, F; Enculescu, M; Pasuk, I; Popescu, B

Published: , ROMANIAN REPORTS IN PHYSICS, 2022, DOI: 503

Dr. Iuliana PASUK

Scientific Researcher III

Publications

1. Physico-chemical characterization and in vitro biological study of manganese doped β-tricalcium phosphate-based ceramics for bone regeneration applications

2. Experimental Band Structure of Pb(Zr,Ti)O-3: Mechanism of Ferroelectric Stabilization

3. Experimental Band Structure of Pb(Zr,Ti)O-3: Mechanism of Ferroelectric Stabilization

4. Influence of on-off pulsed current pattern on processes during spark plasma sintering of MgB2 superconductor

5. Physico-chemical characterization and in vitro biological study of manganese doped beta-tricalcium phosphate-based ceramics for bone regeneration applications

6. Experimental Band Structure of Pb(Zr,Ti)O3: Mechanism of Ferroelectric Stabilization

7. Columnar Liquid Crystals of Copper(I) Complexes with Ionic Conductivity and Solid State Emission

8. Ferroelectricity modulates polaronic coupling at multiferroic interfaces

9. Negative Capacitance and Switching Dynamics Control Via Non-Ferroelectric Elements

10. MICROSTRUCTURE, MAGNETIC AND MAGNETOSTRICTIVE BEHAVIOUR IN RAPIDLY QUENCHED OFF-STOICHIOMETRIC Ni-Mn-Ga FERROMAGNETIC SHAPE MEMORY ALLOYS

11. Controlling polarization direction in epitaxial Pb(Zr0.2Ti0.8)O-3 films through Nb (n-type) and Fe (p-type) doping

12. Effect of the supersaturation with nitrogen on the structure refinement and magnetic properties of mechanically alloyed and heated Fe14Cr ferritic alloys

13. MgB2 with Addition of Cubic BN and Ge2C6H10O7 Obtained by Spark Plasma Sintering Technique

14. Full Length Article Towards high degree of c-axis orientation in MgB2 bulks

15. Sr and Mg Doped Bi-Phasic Calcium Phosphate Macroporous Bone Graft Substitutes Fabricated by Robocasting: A Structural and Cytocompatibility Assessment

16. Evidence of Counterion Size Effect on the Stability of Columnar Phase of Ionic Liquid Crystals Based on Pyridinium Salts Derived from N-3,4,5-Tri(alkyloxy)-benzyl-4-pyridones

17. Effect of disubstitution pattern of the terminal alkyl chains on the mesophase of liquid crystals based on lanthanide(III) complexes: A study of the thermal, emission and dielectric behavior

18. Sintered and 3D-Printed Bulks of MgB2-Based Materials with Antimicrobial Properties

19. Accidental Impurities in Epitaxial Pb(Zr0.2Ti0.8)O-3 Thin Films Grown by Pulsed Laser Deposition and Their Impact on the Macroscopic Electric Properties

20. MgB2 powders and bioevaluation of their interaction with planktonic microbes, biofilms, and tumor cells

21. Hard/soft effects of multivalence co-dopants in correlation with their location in PZT ceramics

22. Effect of strain and stoichiometry on the ferroelectric and pyroelectric properties of the epitaxial Pb(Zr0.2Ti0.8)O-3 films deposited on Si wafers

23. Partially-oriented MgB2 superconducting bulks with addition of B4C and cubic BN obtained by slip casting under high magnetic field and spark plasma sintering

24. Structural Details of BaTiO3 Nano-Powders Deduced from the Anisotropic XRD Peak Broadening

25. The Physico-Chemical Properties and Exploratory Real-Time Cell Analysis of Hydroxyapatite Nanopowders Substituted with Ce, Mg, Sr, and Zn (0.5-5 at.%)

26. New superconductor/ferromagnet heterostructure formed by YBa2Cu3O7-x and CaRuO3

27. Influence of Thickness on the Magnetic and Magnetotransport Properties of Epitaxial La0.7Sr0.3MnO3 Films Deposited on STO (001)

28. Tetragonal-Cubic Phase Transition and Low-Field Dielectric Properties of CH3NH3PbI3 Crystals

29. Antimicrobial and Cytocompatible Bovine Hydroxyapatite-Alumina-Zeolite Composite Coatings Synthesized by Pulsed Laser Deposition from Low-Cost Sustainable Natural Resources

30. Effect of the processing parameters on surface, physico-chemical and mechanical features of bioceramics synthesized from abundant carp fish bones

31. High magnetic shielding properties of an MgB2 cup obtained by machining a spark-plasma-sintered bulk cylinder

32. Enhanced critical current density at high magnetic fields in MgB2 with Ga/In acetylacetonate processed by spark plasma sintering

33. Reproducibility of small Ge2C6H10O7-added MgB2 bulks fabricated by ex situ Spark Plasma Sintering used in compound bulk magnets with a trapped magnetic field above 5T

34. Polarized emission and dielectric studies of novel lanthanidomesogens based on 4-pyridone ligands

35. Polarization-dependent magnetism of the Ni/BaTiO3 interface

36. Fish Bone Derived Bi-Phasic Calcium Phosphate Coatings Fabricated by Pulsed Laser Deposition for Biomedical Applications

37. Magneto-functionalities of La 1-x A x MnO 3 (A = K; Ba) synthesized by flash combustion method

38. Complex exchange coupling mechanisms in SRO/BFO/Fe heterostructures

39. Prototype Orthopedic Bone Plates 3D Printed by Laser Melting Deposition

40. Bulks of Al-B-C obtained by reactively spark plasma sintering and impact properties by Split Hopkinson Pressure Bar

41. Memcomputing and Nondestructive Reading in Functional Ferroelectric Heterostructures

42. Structural, electric and pyroelectric properties of up and down graded PZT multilayers

43. Synthesis and thermal, emission and dielectric properties of liquid crystalline Eu(III), Sm(III) and Tb(III) complexes based on mesogenic 4-pyridone ligands functionalized with cyanobiphenyl groups

44. Superconducting MgB2 textured bulk obtained by ex situ spark plasma sintering from green compacts processed by slip casting under a 12T magnetic field

45. Ex Situ Spark Plasma Sintering of Short Powder-in-Tube MgB2 Tapes with Open and Closed Ends

46. Cationic Substitutions in Hydroxyapatite: Current Status of the Derived Biofunctional Effects and Their In Vitro Interrogation Methods

47. A Comparative Study of Ge-Based Organometallic Additions to MgB2

48. Polarization Orientation in Lead Zirconate Titanate (001) Thin Films Driven by the Interface with the Substrate

49. Dwell Time Influence on Spark Plasma-Sintered MgB2

50. Wide-Range Columnar and Lamellar Photoluminescent Liquid-Crystalline Lanthanide Complexes with Mesogenic 4-Pyridone Derivatives

51. Thermal analysis, microstructure and impurity phases evolution in Fe14Cr ferritic steel powders ball-milled in air and under an argon atmosphere

52. Structural and magnetic properties of Ni nanofilms on Ge(001) by molecular beam epitaxy

53. Intrinsic and extrinsic effects near orthorhombic-tetragonal phase transition in barium titanate ceramics doped with small amounts of zirconium

54. Multiple polarization states in symmetric ferroelectric heterostructures for multi-bit non-volatile memories

55. Synthesis and liquid crystalline properties of novel fluorinated N-benzoyl thiourea compounds. Effect of perfluoroalkyl chains on the thermal behavior and smectic phases stability

56. Tuning the liquid crystalline properties of palladium(II) metallomesogens: A study of rod-like to disc-like transition in cyclopalladated complexes with N-benzoyl thiourea derivatives

57. Bis-imidazolium salts with alkyl sulfates as counterions: synthesis and liquid crystalline properties

58. Relationship between ferromagnetism and, structure and morphology in un-doped ZnO and Fe-doped ZnO powders prepared by hydrothermal route

59. Relation between domain structure and pyroelectric response in as-grown epitaxial Pb(Zr0.2Ti0.8)O-3 thin films on substrates with different resistivity

60. Cyclometalated palladium(II) metallomesogens with Schiff bases and N-benzoyl thiourea derivatives as co-ligands

61. Structure, transition temperature, and magnetoresistance of titanium-doped lanthanum barium manganite epilayers onto STO 001 substrates

62. Steplike Switching in Symmetric PbZr0.2Ti0.8O3/CoFeO4/PbZr0.2Ti0.8O3 Heterostructures for Multistate Ferroelectric Memory

63. Structural, magnetic and magnetocaloric effects in epitaxial La0.67Ba0.33Ti0.02Mn0.98O3 ferromagnetic thin films grown on 001-oriented SrTiO3 substrates

64. Columnar bis(pyridinium) ionic liquid crystals derived from 4-hydroxypyridine: synthesis, mesomorphism and emission properties

65. Effects of vanadium doping on sintering conditions and functional properties of Nb-Li co-doped PZT ceramics. Comments on Li location

66. Nematic ionic liquid crystals based on pyridinium salts derived from 4-hydroxypyridine

67. Reactive spark plasma sintering of MgB2 in nitrogen atmosphere for the enhancement of the high-field critical current density

68. Spark plasma sintered MgB2 co-added with c-BN and C-60

69. B4C in ex-situ spark plasma sintered MgB2

70. The influence of heating rate on superconducting characteristics of MgB2 obtained by spark plasma sintering technique

71. Effect of counterion on the mesomorphic behavior and optical properties of columnar pyridinium ionic liquid crystals derived from 4-hydroxypyridine

72. Comparison between the ferroelectric/electric properties of the PbZr0.52Ti0.48O3 films grown on Si (100) and on STO (100) substrates

73. Polarization induced self-doping in epitaxial Pb(Zr0.20Ti0.80)O-3 thin films

74. HETEROSTRUCTURES BASED ON SMALL MOLECULES ORGANIC COMPOUNDS

75. Ge-Added MgB2 Superconductor Obtained by Ex Situ Spark Plasma Sintering

76. A new class of thermotropic lanthanidomesogens: Eu(III) nitrate complexes with mesogenic 4-pyridone ligands

77. Electrode interface controlled electrical properties in epitaxial Pb(Zr0.52Ti0.48)O-3 films grown on Si substrates with SrTiO3 buffer layer

6. Experimental Band Structure of Pb(Zr,Ti)O₃: Mechanism of Ferroelectric Stabilization