NIMP| Alin IUGA, Author at NIMP

Publications

1. Structural, Frequency and Temperature Dependent Dielectric Properties of Zn2+ Substituted Ni-Co Based Spinel Ferrite (ZnxNi0.8-xCo0.2Fe2O4)

Authors: Oumezzine, M; Iuga, A; Enculescu, M; Galca, AC

Published: MAY 1 2023, ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY, 12, 053008, DOI: 10.1149/2162-8777/acd6bb

Zinc substituted nickel-cobalt ferrites, i.e., ZnxNi0.8-xCo0.2Fe2O4 (x = 0.0, 0.05, 0.10 and 0.20) with average crystallite size 100 nm were synthesized by citrate-gel auto-combustion method to investigate effects of Zn2+ substitution on the structural and dielectric properties. Both X-ray diffraction (XRD) and IR spectroscopy studies confirms the formation of pure cubic spinel structure. Variation of lattice parameter infers Vegard's law linear dependence with the addition of Zn2+ concentration. The temperature-dependent behavior of dielectric and modulus spectra has been studied within the frequency range 100 Hz-100 kHz for different temperatures between 100 K and 400 K. It was concluded that the dielectric responses of ZnxNi0.8-xCo0.2Fe2O4 are found to be frequency dependent and thermally activated. Also, In the Zn doped ferrites variations of dielectric loss (tan d) and the imaginary part of electric modulus (M") show the presence of the non-Debye type of dielectric relaxation. Rise in Zinc concentration leads to a decrease in dielectric constant (e (r)) due to the declining of Fe3+-O-M2+ conducting network (M is Co or Ni). Here, we report a low loss tangent factor of the order of 8x10-3 0.6Zn(0.2)Co(0.2)Fe(2)O(4) make this composition suitable for high frequency-applications at room temperature. The activation energy is calculated from electric modulus formalism and DC electrical conductivity and found to increase with further substitution of Zn2+ concentration.

2. Structural, Frequency and Temperature Dependent Dielectric Properties of Zn²⁺ Substituted Ni-Co Based Spinel Ferrite (Zn_xNi_0.8-xCo_0.2Fe₂O₄)

Authors: Oumezzine, M; Iuga, A; Enculescu, M; Galca, AC

Published: MAY 1 2023, ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY, 12, 053008, DOI: 10.1149/2162-8777/acd6bb

3. Ultrafast nondestructive pyroelectric reading of FeRAM memories

Authors: Iuga, AR; Lindfors-Vrejoiu, I; Boni, GA

Published: AUG 2021, INFRARED PHYSICS & TECHNOLOGY, 116, DOI: 10.1016/j.infrared.2021.103766

FeRAM memories constitute themselves as a robust counterpart to the mainstream NVRAM memories. Their unique properties, such as radiation resilience and low voltage operation, together with high speed writing and reading, high and long lasting remanence and very good endurance to cycling endorse them in the data storage domain. However price, poor scalability, the destructive way of reading and the necessary consequent re-writing represent technical drawbacks that diminish their practical value. This paper presents a new paradigm of completing previous efforts towards fast nondestructive reading of FeRAMs. An intermittent low intensity IR (infrared) laser diode generates a pyroelectric signal in the ferroelectric material. The amplitude and phase of this response depends on the state of polarisation of the ferroelectric. Comparing the phase of the electric response with the phase of the illuminating radiation (on/off), a decisive indication of the poling sense in the ferroelectric is given. Aiming to circumvent the notorious slowness of the pyroelectric response the array is continuously illuminated with the pulsating laser, which ensures a prompt answer from every bit of memory. The reading speed is, practically, limited by the electronics.

4. 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.

5. A nanoscale continuous transition from the monoclinic to ferroelectric orthorhombic phase inside HfO2 nanocrystals stabilized by HfO2 capping and self-controlled Ge doping

Authors: Palade, C; Lepadatu, AM; Slav, A; Cojocaru, O; Iuga, A; Maraloiu, VA; Moldovan, A; Dinescu, M; Teodorescu, VS; Stoica, T; Ciurea, ML

Published: SEP 28 2021, JOURNAL OF MATERIALS CHEMISTRY C, 9, 12366, DOI: 10.1039/d1tc02921e

Orthorhombic HfO2 exhibits nanoscale ferroelectricity that opens the perspective of ultra-scalable CMOS integration of ferroelectric memories. However, many aspects of the metastable orthorhombic crystallization mechanisms still need to be elucidated and new fabrication methods are of high interest. In this paper, the atomically resolved crystal structure of HfO2 is a 3-layer structure with a Ge-rich HfO2 intermediate layer capped by a top (cap) HfO2 layer and cladded by a bottom HfO2 layer. There is a continuity of crystal growth from the top and bottom HfO2 layers into the intermediate layer. A spatial transition from a monoclinic phase to an orthorhombic phase was revealed within a region of a few atomic layers at the interface between capped and intermediate HfO2 layers. This result suggests the mechanism of orthorhombic and monoclinic phase formation by a martensitic-like transformation of the initially grown tetragonal phase. The sample fabrication method we used involved magnetron sputtering deposition of the 3-layer structures, i.e. a stack of top HfO2/Ge-rich HfO2 intermediate/bottom HfO2 layers, followed by rapid thermal annealing. It results in self-optimized orthorhombic crystallization of HfO2 by Ge nanoparticle segregation in the intermediate layer. The ferroelectric effects are revealed by polarization-voltage hysteresis loops and piezoresponse force microscopy measurements. The atomistic computations performed by using the density functional theory support the experimental results by showing that the Ge doping of HfO2 leads to orthorhombic phase stabilization and increased Berry phase polarization.

6. Estimation of the pyroelectric coefficient for ceramic Pb(Zr,Ti)O-3 samples: Comparison of the results obtained by two easy to implement methods

Authors: Pintilie, L; Iuga, A; Stancu, V; Botea, M

Published: MAY 2020, INFRARED PHYSICS & TECHNOLOGY, 106, DOI: 10.1016/j.infrared.2020.103269

The pyroelectric coefficient of some Pb(Zr,Ti)O-3 type ceramics was estimated using two methods: a direct method, based on the temperature dependence of the charge/current generated by pyroelectric effect; an indirect method based on the frequency dependence of the pyroelectric signal generated by a pyroelectric element under modulated irradiation with infrared light. The purpose was to compare the results and to assess if the indirect method is enough accurate for rapid estimation of the pyroelectric coefficient of a material envisaged for infrared detection. The direct method is more accurate and requires accurate control of temperature and heating rate, while the indirect method is less accurate, with an error up to 20%, and requires the knowledge of quantities such as dielectric constant, electric conductance, and incident power. However, the indirect method can be more easily implemented and can provide a rapid assessment on the pyroelectric quality of a material with potential use in infrared detectors.

7. Comparison between dielectric and pyroelectric properties of PZFNT and BST type ceramics

Authors: Stancu, V; Amarande, L; Botea, M; Iuga, A; Leonat, LN; Tomulescu, AG; Cioangher, M; Balescu, LM; Pintilie, L

Published: 2019, PROCESSING AND APPLICATION OF CERAMICS, 13, 276, DOI: 10.2298/PAC1903269S

Ba0.75Sr0.25TiO3 (BST) and PbZr0.68Fe0.14Nb0.14Ti0.04O3 (PZFNT) ceramic pellets were obtained by ceramic technology and their structural, ferroelectric and pyroelectric properties were investigated. The relative density of BST and PZFNT is about 93% and 90%, respectively, with an average grain size of 102 mu m and 6.45 mu m. Both materials have similar room temperature dielectric constants (similar to 2000), but PZFNT shows higher remnant polarization (similar to 15 mu C/cm(2)) and better pyroelectric properties (similar to 1.69 . 10(-4) C/m(2)K), which recommend it for pyroelectric detectors, infrared radiation- and laser pulse energy-meters.

8. Carbon-based sprayed electrodes for pyroelectric applications

Authors: Chirila, C; Botea, M; Iuga, A; Tomulescu, AG; Balescu, L; Galca, AC; Boni, AG; Leonat, L; Pintilie, I; Pintilie, L

Published: AUG 15 2019, PLOS ONE, 14, DOI: 10.1371/journal.pone.0221108

A carbon-based layer was deposited by spraying on top of a ferroelectric layer grown by sol-gel on Si (001) substrate and its properties as electrode and absorber for pyroelectric detection were tested. It was found that the electric properties of the ferroelectric capacitor with top carbon-based sprayed electrode (CBSE) are comparable with those of the capacitors with standard top SrRuO3 (SRO)/Au electrode. Pyroelectric measurements show that the pyroelectric signal recorded on ferroelectric capacitors with top CBSE electrode is 2.5 times greater than for top SRO/Au electrode for low frequency range. The value of the pyroelectric coefficient was estimated to 9.73.10(-4) C/m(2)K for CBSE electrodes and 3.36.10(-4) C/m(2)K for SRO/Au respectively. The fabrication process of CBSE is of low cost, easy to implement and with high throughput making it attractive for manufacturing various devices like pyroelectric detector, thermal imaging, solar cells, etc.

9. STRUCTURAL, DIELECTRIC AND PYROELECTRIC PROPERTIES OF Nb AND Fe DOPED PZT CERAMICS

Authors: Stancu, V; Amarande, L; Botea, M; Cioangher, M; Tomulescu, A; Iuga, A; Pintilie, L

Published: JAN-MAR 2019, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 14, 230, DOI:

Lead zirconate titanate doped with iron and niobium (PZFNT) was prepared by conventional processing technique, solid state synthesis method. The influence of dopants on the microstructure, ferroelectric and pyroelectric properties was investigated. XRD data reveals a perovskite structure near to the lead zirconate phase. The relative density of PZFNT is approximate 90%, with average grains size of 6.45 mu m.

10. 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.

11. 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%).

12. Multiferroic (Nd,Fe)-doped PbTiO3 ceramics with coexistent ferroelectricity and magnetism at room temperature

Authors: Craciun, F; Cordero, F; Cernea, M; Fruth, V; Atkinson, I; Stanica, N; Vasile, BS; Trusca, R; Iuga, A; Galizia, P; Galassi, C

Published: MAY 2019, CERAMICS INTERNATIONAL, 45, 9396, DOI: 10.1016/j.ceramint.2018.08.147

We report the structural, dielectric, elastic, ferroelectric and ferromagnetic properties of multiferroic (Nd, Fe)doped PbTiO3 perovskite ceramics with composition (Pb-0.88 Nd-0.08 )(Ti-0.94 Fe-0 .04 Mn-0.02)O-3, prepared by different solid state reaction methods: the first one based on a single-stage calcination (Method I) and the second based on a double-stage calcination (Method II). Structural, dielectric and anelastic measurements evidenced a double phase transition for samples prepared by Method I, which has been attributed to phase separation. This phase separation has been confirmed also by TEM and HRTEM investigations. Samples prepared by Method II showed a single phase transition from paraelectric to ferroelectric phase. We found coexistent ferroelectric and ferromagnetic properties, also at room-temperature, but only for ceramics prepared by Method II. The crucial role of calcination process for avoiding phase separation and obtaining homogeneous structures with ferroelectric and ferromagnetic order is underlined.

13. Composite BNT-BT0.08/CoFe2O4 with core-shell nanostructure for piezoelectric and ferromagnetic applications

Authors: Cernea, M; Vasile, BS; Ciuchi, IV; Surdu, VA; Bartha, C; Iuga, A; Galizia, P; Galassi, C

Published: JAN 2019, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 240, 15, DOI: 10.1016/j.mseb.2019.01.001

In this work, we report on the synthesis and characterization of BNT-BT0.08/CoFe2O4 biphasic composite with core-shell structure. This artificial core (BNT-BT0.08/shell (CoFe2O4) heterostructure was prepared by sol-gel method and the resulting composite was characterized in term of microstructure, dielectric, piezoelectric and magnetic properties. BNT-BT0.08/CoFe2O4 sintered ceramic shows high permittivity (epsilon' >= 30) and high dielectric losses (tan delta >= 10) in the low frequency range (nu <= 10(4) Hz), remnant polarization (Pr) of similar to 7.7 mu C/cm(2) and, remanent magnetization (Mr) of 24 emu/g at 5 K and of 14 emu/g, at room temperature. The present study reveals that the ferroelectric, piezoelectric and magnetic properties of this new architectured composite depend on the amount of each component and, can be tailored by adjusting their synthesis conditions. BNT-BT0.08/CoFe2O4 core-shell material investigated in this work provides a novel way to exploit new applications for the multifunctional composite, such as piezoelectric sensor, magnetoelectronic sensors and data storage devices.

14. Synthesis and characterization of novel ferrite-piezoelectric multiferroic core-shell-type structure

Authors: Cernea, M; Vasile, BS; Ciuchi, IV; Surdu, VA; Bartha, C; Iuga, A; Galizia, P; Galassi, C

Published: JUL 2018, JOURNAL OF MATERIALS SCIENCE, 53, 9661, DOI: 10.1007/s10853-018-2264-x

Hybrid ferromagnetic/piezoelectric core-shell nanoparticles and ceramics have potential for a wide range of applications due to their tunability, electronic and magnetic properties. In this study, we designed a core-shell-type nanostructure of composition CoFe2O4/BNT-BT0.08, where BNT-BT0.08 is the abbreviation of bismuth, sodium titanate (Bi0.5Na0.5TiO3, BNT) doped with 8 mol% barium titanate (BaTiO3, BT). This multiferroic composite was prepared by covering CoFe2O4 nanoparticles with a shell of BNT-BT0.08 using the sol-gel technique. Scanning and transmission electron microscopy confirmed formation of a core-shell structure. The results of microstructure, dielectric, piezoelectric and magnetic investigations demonstrated that this heterostructure shows simultaneously electrical and magnetic behavior, at room temperature. XRD pattern of core-shell composite CoFe2O4/BNT-BT0.08 powder reveals only cubic CoFe2O4 and rhombohedral Bi0.5Na0.5TiO3 phases. CoFe2O4/BNT-BT0.08 core-shell nanostructure sample shows high values of permittivity (epsilon >= 600) together with high dielectric losses (tan delta >= 1) in the low-frequency range (nu <= 10(4) Hz). PFM and polarization hysteresis indicated a ferroelectric domains structure and remnant polarization of similar to 2.6 A mu C/cm(2) for the ceramics pellets samples of CoFe2O4/BNT-BT0.08. The present study reveals the possibility of coating nanoparticles onto nanometer-sized core particles, using controlled sol-gel process, in order to prepare multifunctional core-shell composites for piezoelectric and magnetoelectronic sensors.

15. Millimeter wave and Terahertz investigations on some dielectric materials

Authors: Banciu, MG; Furuya, T; Geambasu, DC; Nedelcu, L; Pantelica, D; Dracea, MD; Ionescu, P; Iuga, A; Chirila, C; Hrib, L; Trupina, L; Tani, M

Published: 2018, CAS 2018 PROCEEDINGS: 2018 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 290, DOI:

Investigations of barium strontium titanate (BST) layers deposited on MgO and Si substrates are presented. Since the Sr content determines the dielectric and optical properties of the BST layers at room temperature, accurate compositional analysis was performed by using Rutherford Backscattering technique at 3.041 Mev.

16. Effect of in-plane ordering on dielectric properties of highly {111}-oriented bismuth-zinc-niobate thin films

Authors: Le Febvrier, A; Deputier, S; Demange, V; Bouquet, V; Galca, AC; Iuga, A; Pintilie, L; Guilloux-Viry, M

Published: OCT 2017, JOURNAL OF MATERIALS SCIENCE, 52, 11313, DOI: 10.1007/s10853-017-1297-x

Bi1.5-xZn0.92-yNb1.5O6.92-delta (BZN) thin films were grown by pulsed laser deposition on two different Pt-covered substrates, namely textured {111} Pt/TiO2/SiO2/(100) Si substrate (Pt/Si) and epitaxial {111} Pt/R-plane sapphire substrate (Pt/sapphire). In both cases, the BZN films present {111} and {100} out-of-plane orientations, in relative ratios of 65: 35 on Pt/Si and 80: 20 on Pt/sapphire, respectively. The film grown on Pt/Si is textured, while the film deposited on Pt/sapphire presents epitaxial-like relationships with the substrate, for both out-of-plane orientations. Dielectric measurements were taken on both types of thin films, using Pt/BZN/Pt planar capacitor structures. The BZN/Pt/sapphire film presents higher dielectric constant (245 at 100 kHz) and higher tunability (12% at 600 kV/cm) than the BZN/Pt/Si film (200; 6%), while the dielectric losses values are nearly same (similar to 0.05).

17. 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.

18. TEMPERATURE INFLUENCE ON THE CAPACITANCE-VOLTAGE HYSTERESIS OF TRANSPARENT a-IGZO/PZT/FTO MFS-HETEROSTRUCTURE

Authors: Trinca, LM; Besleaga, C; Stancu, V; Radu, R; Iuga, A; Boni, AG; Galca, AC; Pintilie, L

Published: 2017, ROMANIAN REPORTS IN PHYSICS, 69, DOI:

Capacitance-voltage (C-V) hysteresis of metal-ferroelectric-semiconductor (MFS) structure based on a-In2GaZnO5.5 and Pb0.2Zr0.8TiO3 layers are recorded in the 350-470 K range. The structure is grown on FTO/glass to obtain a transparent MFS. The memory functionality of the heterostructure is proved through C-V and P-V characteristics. The memory window is dependent on the temperature, the largest value of 2.5 V being obtained at 470 K, where the contribution of the ferroelectric-semiconductor interface defect states is minimized. The direction of C-V hysteresis is clockwise at 350 K, and it turns counterclockwise at higher temperatures where the ferroelectric polarization has the main contribution.

19. Novel multiferroic (Pb-1 (-) Nd-3x/2(x))(Ti-0.98 (-) yFeyMn0.02)O-3 ceramics with coexisting ferroelectricity and ferromagnetism at ambient temperature

Authors: Craciun, F; Cernea, M; Fruth, V; Zaharescu, M; Atkinson, I; Stanica, N; Tanase, LC; Diamandescu, L; Iuga, A; Galassi, C

Published: NOV 15 2016, MATERIALS & DESIGN, 110, 704, DOI: 10.1016/j.matdes.2016.08.046

We report the evolution of structural, dielectric, ferroelectric and ferromagnetic properties in novel (Pb1 - 3x/2Ndx) (Ti0.98 - yFeyMn0.02)O-3 perovskite ceramics (x = 0.08, 0 < y < 0.05). We found room-temperature ferroelectric polarization and ferromagnetism for higher amount of iron ions(y >= 0.04). The paraelectric-ferroelectric phase transition occurred between 650 and 670 K for 0 <= y <= 0.05. Ferromagnetic hysteresis was measured at different temperatures on samples with y >= 0.04. Detailed structural analysis evidenced the variation of unit cell parameters with y increasing, confirming the substitution of the iron element in the lattice. Fe-57 Mtissbauer spectroscopy evidenced that iron ions occupy Ti positions in the perovskite lattice, with the oxidation state Fe3+ and two coordination types. X-ray photoelectron spectroscopy confirmed the presence of iron only as Fe3+ and, moreover, evidenced the presence of a substantial amount of Ti3+ ions in the structure. The presence of both Fe3+ (spin 5/2) in different coordinations as well as Ti3+ (spin 1/2) magnetic ions in B-site positions drives the occurrence of magnetic properties from low temperature to above room temperature, through superexchange Fe3+-O-Fe3+, Fe3+-O-Ti3+ and Ti3+-O-Ti3+ interactions. The finding of coexistent ferroelectric and ferromagnetic properties in these compounds ground the route to facile synthesis of multiferroics by simply doping a classical perovskite ferroelectric material like PbTiO3 with an adequate amount of transition magnetic ions. (C) 2016 Elsevier Ltd. All rights reserved.

20. Intrinsic pyroelectric properties of thick, coarse grained Ba1-xSrxTiO3 ceramics

Authors: Ianculescu, A; Pintilie, I; Vasilescu, CA; Botea, M; Iuga, A; Melinescu, A; Dragan, N; Pintilie, L

Published: JUN 2016, CERAMICS INTERNATIONAL, 42, 10348, DOI: 10.1016/j.ceramint.2016.03.152

The intrinsic pyroelectric properties of thick, coarse grained Ba1-xSrxTiO3 (BST) ceramics were studied in relation with Sr content. The intrinsic values of the pyroelectric coefficient were determined directly from the frequency dependence of the measured pyroelectric signal by adapting the formalism developed for thin films deposited on thick substrates to thick and non-uniformly heated ceramics with uniform composition. Ceramic pellets, of about 1 mm thickness, with relative density of 89-95% were prepared using powder synthesized by the sol gel method. It was found that the intrinsic pyroelectric properties are enhanced by increasing the Sr content, while other features (e.g. tetragonality, grain size, polarization, transition temperature) decrease. The best intrinsic pyroelectric properties were obtained for 30% Sr content. The present results open the possibility to use large and thick BST ceramic pellets for manufacturing detectors useful for monitoring high power lasers. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

21. Synthesis, Structural and Electrical Properties of BNT-BTCe@SiO2 Core-Shell Heterostructure

Authors: Cernea, M; Vasile, BS; Ciuchi, IV; Iuga, A; Alexandrescu, E; Pintea, J; Galassi, C

Published: NOV 2015, SCIENCE OF ADVANCED MATERIALS, 7, 2305, DOI: 10.1166/sam.2015.2287

The influence of SiO2 layer in a core-shell BNT-BTCe@SiO2 heterostructure on the electrical properties of the BNT-BTCe core ceramic was investigated. The core-shell composite was prepared by coating BNT-BTCe powder with silica layer by a chemical process. BNT-BTCe grain-core was a solid solution of (Bi0.5Na0.5)TiO3 (BNT) and Ba0.95Ce0.05TiO3 (BTCe) with 92: 8 molar ratio. The thickness of the amorphous silica shell was about 128 nm and the size of the grain core was about 250 nm. The structure, microstructure, dielectric, ferroelectric and piezoelectric properties of BNT-BTCe@SiO2 core-shell powder and sintered ceramic were investigated and compared with those of the BNT-BTCe base material. We found that the values of permittivity (epsilon(r)) and dielectric losses of core-shell ceramic are lower and higher, respectively, than those of BNT-BTCe ceramic indicating that the SiO2 does not improve the dielectric properties of BNT-BTCe ceramic. For the BNT-BTCe@SiO2 composite, the silica layer leads to the increase of diffuseness degree of the phase transition and to a better ferroelectric relaxor. The sintered BNT-BTCe@SiO2 heterostructure shows higher remnant polarization P-r, higher coercive field E-c and higher piezoelectric constants (k(t), d(33), g(33), c(33)(E) and S-11(E)) than BNT-BTCe ceramic. The results of our study suggest that BNT-BTCe@SiO2 core-shell material could be interesting for applications in the ferroelectric and piezoelectric domains.

22. 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.

23. Electric-field-induced transformations in epitaxial relaxor ferroelectric PbMg1/3Nb2/3O3 films

Authors: Tyunina, M; Pintilie, I; Iuga, A; Pintilie, L

Published: MAR 24 2014, PHYSICAL REVIEW B, 89, DOI: 10.1103/PhysRevB.89.094106

Electric-field-induced transformations are studied experimentally in cube-on-cube-type epitaxial film of relaxor ferroelectric (FE) PbMg1/3Nb2/3O3 grown on (001) MgO substrate. The dielectric response, polarization, and current are measured along the out-of-plane < 100 > direction of the film and analyzed as a function of temperature, frequency, and applied field. Compared to the < 100 > crystal, transformation of the low-temperature relaxor state to a new state in the (001) film takes place at considerably lower temperatures and larger fields. Based on the found bisigmoidal shape and the two scaling regimes of the current-voltage curves, the two corresponding electric-field-induced processes are suggested to be dipolar flips and flow of a phase boundary in the film. The field-induced state in the film is dynamic and unstable, and it differs from the field-induced FE state in the crystal. The robustness of the relaxor state to electric field in the film is discussed in relation to spatial anisotropy of the dipolar system in the (001) film.

24. Frustration of ferroelectricity in epitaxial film of relaxor ferroelectric PbSc1/2Nb1/2O3

Authors: Tyunina, M; Pintilie, I; Iuga, A; Stratulat, MS; Pintilie, L

Published: AUG 13 2014, JOURNAL OF PHYSICS-CONDENSED MATTER, 26, DOI: 10.1088/0953-8984/26/32/325901

Relaxor-to-ferroelectric transformations induced by varying electric fields and temperatures are studied experimentally in acube-on-cubetype epitaxial PbSc1/2Nb1/2O3 film grown on La1/2Sr1/2CoO3/MgO(001). Dielectric response, quasi-static and dynamic polarization, and dynamic current-voltage characteristics evidence the absence of spontaneous relaxor-to-ferroelectric transition. The electricfield-induced transformation from a glass-like relaxor state to a new dynamic polar state is detected at low temperatures below 100 K only. The frustration of ferroelectricity is discussed in relation to orientational anisotropy of the dipolar system in the epitaxial (001) film.

25. Synthesis, structural characterization and dielectric properties of Nb doped BaTiO3/SiO2 core-shell heterostructure

Authors: Cernea, M; Vasile, BS; Boni, A; Iuga, A

Published: FEB 25 2014, JOURNAL OF ALLOYS AND COMPOUNDS, 587, 559, DOI: 10.1016/j.jallcom.2013.10.228

Perovskite complex ceramic oxides, BaTiO3 doped with 0.5 mol% Nb2O5 and then nanocoated with SiO2 (abbreviated as BT-Nb-0.005/SiO2) was successful prepared using conventional sol-gel processing. Phase composition, particle morphology, structure, and electric properties of BT-Nb-0.005 core and BT-Nb-0.005/SiO2 core-shell were examined and compared, using X-ray diffraction, transmission electron microscopy and, dielectric and ferroelectric measurements. Core-shell composite with well-defined perovskite tetragonal phase of BaTiO3 was achieved. Furthermore, single crystalline BT-Nb-0.005/SiO2 core-nanoshell heterostructure with similar to 34 nm shell thick was prepared, which is a novelty in ferroelectrics field. The ferroelectric quality of BT-Nb-0.005 has suffered an alteration when the (BT-Nb-0.005)/SiO2 core-shell heterostructure was realized. One-dimensional BT-Nb-0.005/SiO2 core-shell heterostructure exhibits an improvement of dielectric losses and a decrease of dielectric constant, compared to uncoated BT-Nb-0.005. The (BT-Nb-0.005)/SiO2 core-shell material could be interesting for application in the composite capacitors. (C) 2013 Elsevier B.V. All rights reserved.

26. Enhancement of pyroelectric signal by continuous ultraviolet illumination of epitaxial Pb(Zr0.2Ti0.8)O-3 films

Authors: Pintilie, L; Botea, M; Iuga, A

Published: SEP 29 2014, APPLIED PHYSICS LETTERS, 105, DOI: 10.1063/1.4896855

The pyroelectric signal generated by an epitaxial Pb(Zr0.2Ti0.8)O-3 film can be enhanced by continuous illumination with ultraviolet (UV) light. The measured signal increases more than 2 times at low modulation frequencies of the incident infrared (IR) radiation (similar to 10 Hz) and at wavelengths where the short-circuit photocurrent presents the maximum value (similar to 280-300 nm). The tentative explanation is that the changes in polarization induced by the temperature variation under modulated IR illumination are generating a variable internal electric field, able to collect the photogenerated carriers produced under continuous UV illumination leading to an additional signal in phase with the pyroelectric one. This finding could be exploited for designing pyroelectric detectors with enhanced characteristics by combining both UV and IR responses. (C) 2014 AIP Publishing LLC.

27. Giant pyroelectric coefficient determined from the frequency dependence of the pyroelectric signal generated by epitaxial Pb(Zr0.2Ti0.8)O-3 layers grown on single crystal SrTiO3 substrates

Authors: Botea, M; Iuga, A; Pintilie, L

Published: DEC 2 2013, APPLIED PHYSICS LETTERS, 103, DOI: 10.1063/1.4838035

Epitaxial Pb(Zr0.2Ti0.8)O-3 layers of good structural quality were grown on single crystal SrTiO3 substrates. The pyroelectric coefficient was estimated from the signal generated by the ferroelectric film working as a pyroelectric detector in the voltage mode, without pre-poling procedure. The obtained value is as high as 1.9 x 10(-3) C/m(2) K. The large value is attributed to the presence of 90 degrees ferroelectric domains and to the compressive misfit strain, leading to an enhanced ferroelectric polarization. (C) 2013 AIP Publishing LLC.

28. BEHAVIOR OF THE MAIN PROPETIES OF HARD AND SOFT TYPE PIEZOCERAMICS WITH TEMPERATURE FROM 2 TO 600 K

Authors: Miclea, C; Tanasoiu, T; Miclea, CF; Amarande, L; Cioangher, M; Trupina, L; Iuga, A; Spanulescu, I; Miclea, CT; David, C; Susu, M

Published: 2010, 2010 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 304, DOI:

The application area of piezoceramic materials and devices based on such materials is continuously extended. The working conditions for such devices and structures may be sometimes very hard such as low and high temperatures, nuclear radiation, high pressure and so on. Such conditions may affect to some extent the transducer performances due to the changes of the basic properties of piezoceramic materials used as sensors. In this regard we have investigated the changes of the main piezoelectric properties of two typically hard and soft piezoceramics within a large temperature range from 2 to 600 K. All parameters measured showed a rather steady increase or decrease with increasing temperature. The results were discussed in terms of intrinsic and domain wall contribution to the dielectric and piezoelectric response of materials.

29. Soft type PZT material used to fabricate a high intensity air siren

Authors: Miclea, C; Iuga, A; Tanasoiu, C; Trupina, L; Cioangher, M; Miclea, CT; Malczanek, V; Susu, M; Voicu, I

Published: FEB 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 281, DOI:

A high quality soft type PZT material was designed and produced in order to be used as sensor for a high intensity air siren, Two thin disks from this material were assembled into a parallel bimorph type sensor with an intermediate metallic plate for the siren. This assembly behaves like an acoustic resonator in the high frequency audio range. This structure transforms the radial mode of vibration into a flexural one, with a much lower frequency. A mechanical impedance adapter was used in order to assure a good match between the oscillating ceramic and the surrounding air. A theoretical approach was outlined, which allows the evaluation of the resonance frequency for the working transducer. The theoretical and experimental data agree to a satisfactory degree up to the input errors assumed by the model. Acoustical and impedance measurements were made in order to appreciate the influence of the metallic plate on the frequency. The bimorph necessary for making the siren was designed as a parallel structure and the corresponding transducer was measured and evaluated. In order to increase the acoustic emission a frontal cardboard horn was added to the resonator.

30. 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.

31. A HIGH PERFORMANCE PZT TYPE MATERIAL USED AS SENSOR FOR AN AUDIO HIGH FREQUENCY PIEZOELECTRIC SIREN

Authors: Miclea, C; Tanasoiu, C; Iuga, A; Spanulescu, I; Miclea, CF; Plavitu, C; Amarande, L; Cioangher, M; Trupina, L; Miclea, CT; Tanasoiu, T

Published: 2008, CAS: 2008 INTERNATIONAL SEMICONDUCTOR CONFERENCE, PROCEEDINGS, +, DOI: 10.1109/SMICND.2008.4703364

A high quality PZT type material was designed and produced in order to be used as sensor for a high internsity siren. Two disks from this materials were assembled into a parallel bimorph type transducer with an intermediate metallic plate. This assembly behaves like an acoustic resonator in the high frequency audio range. The fundamental of the flexural mode for a free resonator is taken into account Its frequency dependence on the geometry of the system and on its material properties is computed using the results for a circular plate with clamped edges and an observation on the equivalence between the movement of a particular part of a resonator in a stationary state and the movement of that pari separated from the resonator but with the same border conditions. Acoustical and impedance measurements were made in order to appreciate the influence of the metallic plate on the frequency. In order to increase the acoustic emission a frontal cardboard horn was added to the resonator.

32. A PZT type piezoceramic material with high planar coupling factor used for a miniature bimorph ventilator

Authors: Miclea, C; Iuga, A; Tanasoiu, C; Amarande, L; Cioangher, M; Miclea, CT

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1515, DOI:

New PZT type ceramic materials, doped with Ni, were prepared by the usual solid state reaction. The best composition proved to be the one containing 6% atomic Ni and having the following chemical formula: Pb0.95Bi0.03Nb0.02Zr0.51 Ti0.43Ni0.06O3. Rectangular samples of this powder were pressed and sintered at 1200 OC for 4 hours and then it was cut in thin slices used to construct an efficient bimorph type ventilator to be used in miniaturized devices for cooling. Miniature ventilators made of PZT ceramics are preferred due to their smallness, high electromechanical efficiency and lack of rotating parts and last but not least of contiguous electrical contacts. We made such a device by using two thin ceramic PZT plates of the material with the best piezoelectric properties, assembled in a flexural oscillator through a proper bimorph association. The emerging doublet behaves itself very much like a bimetal system and possesses a good developed flexural mode. Attaching a metallic elastic plate to the bimorph produces a highly efficient miniature ventilator. A theoretical quantitative study of this flexural bimorph system with elastic plate attached was proposed.

33. Structural and dielectric investigations of donor-acceptor substituted PZT ceramics

Authors: Dimitriu, E; Iuga, A; Ramer, R; Sandu, I; Cernea, M

Published: 2007, FERROELECTRICS, 353, 582, DOI: 10.1080/00150190701368091

Scanning electron microscopy (SEM) and energy dispersive X-ray measurements reveal inhomogeneities in the distribution of elements in W-, Li- doped PZT materials with the composition PbZr0.51 Ti0.49-2.5x W1.5xLixO3 (x = 0.03 and 0.05). Increasing the tungsten concentration leads to an increase of inhomegenities number in the PZT matrix. The high sintering temperature and Li+ concentration contribute to the vitreous aspect Of the materials. X-ray diffraction patterns revealed the Presence of both rhombohedral and tetragonal phases in the two materials. Considering the materials as composites with a 0-3 connectivity pattern, a mathematical approach is proposed. This was used to calculate the contribution of the agglomerations to the experimental dielectric constant.

34. Effect of lead content on the structure and piezoelectric properties of hard type lead titanate-zirconate ceramics

Authors: Miclea, C; Tanasoiu, C; Miclea, CF; Amarande, L; Gheorghiu, A; Spanulescu, I; Plavitu, C; Miclea, CT; Cioangher, MC; Trupina, L; Iuga, A

Published: 2007, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 27, 4059, DOI: 10.1016/J.jeurceramsoc.2007.02.094

In the present investigation we studied the effect of lead content on a hard type ceramics starting from lack to excess PbO. Specimens of Pb-x(Mn0.017Sb0.033Zr0.48Ti0.47)O-3 with 0.96 <= x <= 1.06 were prepared by conventional oxide mixing technique and sintered at temperatures between 1280 and 1350 degrees C. In samples with lower Ph concentration the pyrochlore phase appeared, while in those with higher Pb an excess of PbO phase was detected. These phases proved detrimental for the properties of sintered ceramics. The highest values of piezoelectric properties were observed only for samples with an excess lead of about 2% sintered at 1340 degrees C, indicating that it represents the optimum amount of PbO. For such samples, the density p was 7.77 g/cm (3). the remnant polarization P, was 37 mu C/cm(3) the planar coupling coefficient k(P) was 0.57 and the charge constant d(33) was 340 C-P/N. (c) 2007 Elsevier Ltd. All rights reserved.

35. Piezoelectric material for high efficiency ultrasonic siren

Authors: Dimitriu, E; Iuga, A

Published: 2006, ADVANCED MATERIALS FORUM III, PTS 1 AND 2, 514-516, 229, DOI: 10.4028/www.scientific.net/MSF.514-516.225

A PZT-type material, doped with niobium and lithium was prepared by the ceramic technique. The microstructure of the sintered material at 1280 degrees C was performed by scanning electron microscopy (SEM), transmission electron microscopy and by X-ray diffraction. Dielectric and piezoelectric properties were measured. The good planar properties of the material made it possible to obtain ceramic disks with a strong radial mode. Two such disks, glued together, with opposed polarisation constitute a bimorf element, which successfully converts the radial mode into a flexural one. At the center of the bimorf a conical acoustical impedance adapter is fixed in order to increase the frontal acoustical emission of the device. This ultrasonic device provides a broad band, high acoustical emission, and is suitable to work as a high efficiency ultrasonic siren. It can be used in intruder alarm devices, ultrasonic telemeters.

36. PZT-type materials with improved radial piezoelectric properties

Authors: Dimitriu, E; Iuga, A; Ciupina, V; Prodan, G; Ramer, R

Published: 2005, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 25, 2404, DOI: 10.1016/j.jeurceramsoc.2005.03.070

The goal of this work is to prepare doped PZT-type materials with improved radial piezoelectric properties. Ceramic materials were obtained by solid-state reaction at different sintering temperatures. SAED, bright field TEM and HRTEM methods were used for the microstructure studies. The influence of the composition and nanostructure on the dielectric and piezoelectric properties of the materials is discussed. One of the materials with high coupling constant was used in the construction of a miniature flexural ventilator. Designated to function at an emf of 220 V/50 Hz, this device is characterized by high efficiency, reliability and low energy consumption. (c) 2005 Elsevier Ltd. All rights reserved.

37. Piezoelectric and optical properties of Sr-doped PT-PZ-Pb(Mg1/3Nb2/3)O-3 ceramics

Authors: Dimitriu, E; Ramer, R; Ghica, C; Iuga, A; Ghiordanescu, V

Published: 2004, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 24, 1708, DOI: 10.1016/S0955-2219(03)00478-3

Ceramics in the ternary system (Pb,Sr)TiO3-PbZrO3-Pb(Mg1/3Nb2/3)O-3, in the ratio 85.976/5.817/8.207 mol%, was prepared by mixed oxide route. With about 13.98 at % Sr+2, as isovalent substitution in A-position of the lead titanate, high-density samples were obtained for the sintering temperatures of about 1220 and 1230 degreesC. Tetragonal phases were identified both by XRD method and selected area electron diffraction pattern (SAED). The lattice parameter ratio, c/a, of about 1.017 indicated a decrease of tetragonal distortion. The typical TEM micrographs showed domains of about 50 nm wide. The reflection spectra were recorded to prove the presence of the transition Ti+4 to Ti+3. The principal mechanical, electrical and electromechanical properties were discussed as a function of the sintering temperature. The variation of the relative constant with the temperature and frequency evidenced a relaxation-like behavior of this ternary system. By combining the ferroelectric and relaxor end member we tried to improve the piezoelectric properties of a ceramic with a high content of lead titanate, and to achieve a material with both piezoelectric and relaxor-like properties. (C) 2003 Elsevier Ltd. All rights reserved.

38. Influence of microstructure on physical properties of PT porous ceramics

Authors: Dimitriu, E; Bunescu, CM; Iuga, A; Ramer, R

Published: 2002, FERROELECTRICS, 270, 1236, DOI:

The electromechanical and piezoelectric properties of PT-type ceramics can be modified both by A or B site substitution in the perovskite, and by varying the porosity of the material. In this work rare earth modified lead titanate material with the general formula (Pb(0.88)Nd(0.036)Dy(0.044))(Ti(0.98)Mn(0.02))O(3), was prepared by the ceramic technique. Sintering was carried out at 1260degreesC and 1170degreesC, for 5 hours. The microstructural analysis was performed on fresh fracture surface, in order to observe the true porosity of the material and morphology and dimensions of grains. A scanning electron microscope equipped with wavelength dispersive X-ray spectrometer and energy dispersive X-ray spectrometer was used. Materials with round shaped and agglomerated particles, smaller than 1 m, and pores with the maximum diameter of about 7 m were obtained. The effect of the pores on the values of electromechanical and piezoelectric properties is discussed.

39. Preparation and characterization of Ce-doped BaTiO3 thin films by r.f. sputtering

Authors: Cernea, M; Matei, I; Iuga, A; Logofatu, C

Published: OCT 2001, JOURNAL OF MATERIALS SCIENCE, 36, 5030, DOI: 10.1023/A:1011858319581

Ce-doped BaTiO3 thin films prepared on silicon-platinium by r.f. sputtering has been investigated. BaTiO3 doped with 5.5 mol%CeO2 thin film was deposited at 550 degreesC substrate temperature in an Ar atmosfere. The crystal structure and shape were examined by X-ray diffraction and scanning electron microscopy with EDAX. Analysis by X-ray diffraction patterns show that the crystalline film with a cubic structure of BaTiO3, was obtained. The surface morphology (roughness, the grain size and the droplet size) of the thin film surface was examined by atomic force microscopy (AFM). The grain size is about 160 nm, the droplet size is about 0.675 mum and the roughness is 36.88 nm. EDAX analysis established a composition of the film to be identical with that of the target (BaTiO3 doped with 5.5 mol%CeO2). The broad peak in the capacitance versus temperature curve at the Curie point indicate that the r.f. sputtered Ce-doped BaTiO3 film is ferroelectric. The values of the capacitance of the thin film at 1 KHz were found to be 86 pF and the loss dielectric was tan delta = 0.0875. The film exibits a dielectric anomaly peak at 23 degreesC showing ferroelectric to paraelectric phase transition. (C) 2001 Kluwer Academic Publishers.

40. Preparation and properties of Ce-doped BaTiO3 thin films by r. f. sputtering

Authors: Cernea, M; Iliescu, M; Matei, I; Iuga, A; Logofatu, C

Published: 2000, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 2, 692, DOI:

Ce-doped BaTiO3 thin films prepared on silicon-platinium by r.f. sputtering has been investigated. BaTiO3 doped with 5.5 mol.%CeO2 thin film was deposited at 550 degreesC substrate temperature in Ar atmosfere. The crystal structure and shape were examined by X-ray diffraction and scanning electron microscopy with EDAX. Analysis by X-ray diffraction patterns show that the crystalline film with a cubic structure of BaTiO3, was obtained. The surface morphology (roughness, the grain size and the droplet size) of the thin film surface was examined by atomic force microscopy (AFM). The grain size is about 160 nm, the droplet size is about 0.675 mum and the roughness is 36.88 nm. EDAX analyse established a composition of the film identicaly with that of target (BaTiO3 doped with 5.5 mol.%CeO2). The broad peak in the capacitance versus temperature curve at Curie point indicate that the r.f. sputtered Ce-doped BaTiO3 film is ferroelectric. The values of the capacitance of the thin film at 1 KWz were found to be 86 pF and the loss dielectric was tan delta =0.0875. The film have presented dielectric anomaly peak at 23 degreesC showing ferroelectric to paraelectric phase transition.

41. A nanoscale continuous transition from the monoclinic to ferroelectric orthorhombic phase inside HfO2 nanocrystals stabilized by HfO2 capping and self-controlled Ge doping