National Institute Of Materials Physics - Romania

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867 articles found

11. Paving the Way to the Fuel of the Future-Nanostructured Complex Hydrides

Authors: Comanescu, C

Published: JAN 2023, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 24, 143, DOI: 10.3390/ijms24010143

Hydrides have emerged as strong candidates for energy storage applications and their study has attracted wide interest in both the academic and industry sectors. With clear advantages due to the solid-state storage of hydrogen, hydrides and in particular complex hydrides have the ability to tackle environmental pollution by offering the alternative of a clean energy source: hydrogen. However, several drawbacks have detracted this material from going mainstream, and some of these shortcomings have been addressed by nanostructuring/nanoconfinement strategies. With the enhancement of thermodynamic and/or kinetic behavior, nanosized complex hydrides (borohydrides and alanates) have recently conquered new estate in the hydrogen storage field. The current review aims to present the most recent results, many of which illustrate the feasibility of using complex hydrides for the generation of molecular hydrogen in conditions suitable for vehicular and stationary applications. Nanostructuring strategies, either in the pristine or nanoconfined state, coupled with a proper catalyst and the choice of host material can potentially yield a robust nanocomposite to reliably produce H-2 in a reversible manner. The key element to tackle for current and future research efforts remains the reproducible means to store H-2, which will build up towards a viable hydrogen economy goal. The most recent trends and future prospects will be presented herein.

12. Measurements of Surface Impedance in MgB2 in DC Magnetic Fields: Insights in Flux-Flow Resistivity

Authors: Alimenti, A; Torokhtii, K; Garcia, PV; Silva, E; Grigoroscuta, MA; Badica, P; Crisan, A; Pompeo, N

Published: JAN 2023, MATERIALS, 16, 205, DOI: 10.3390/ma16010205

We present the multifrequency measurements of the surface resistance of spark-plasma-sintered MgB2 performed through a dielectric loaded resonator operating at 16.5 and 26.7 GHz. By normally applying magnetic fields <= 1.2 T to the sample surface, we drove it in the mixed state. By means of data-rooted analysis, we found that the sample vortex dynamics could be fully described within a single-component approach. Pinning phenomena were present and characterized by a depinning frequency smaller than the measurement ones. The multiband nature of the superconductor emerged in the flux-flow resistivity, whose field dependence could be interpreted well within theoretical models. By exploiting them, the upper critical field was extracted in the low-temperature range, which exhibited a consistent temperature trend with the values obtained at the onset of the resistive transition near Tc, and was well in line with literature data on other polycrystalline samples.

13. Structural and transport properties of Cu2CoSnS4 films prepared by spray pyrolysis

Authors: El Khouja, O; Assahsahi, I; Nouneh, K; Touhami, ME; Secu, M; Talbi, A; Khaaissa, Y; Matei, E; Stancu, V; Galatanu, A; Galca, AC

Published: NOV 1 2022, CERAMICS INTERNATIONAL, 48, DOI: 10.1016/j.ceramint.2022.07.185

In the present work, stannite Cu2CoSnS4 (CCTS) films were elaborated using spray pyrolysis method on soda-lime glass, at different deposition temperatures (T-d = 250, 300, and 350 degrees C), followed by different chosen sulfurization temperatures (T-s = 450, 500, and 550 degrees C). X-ray diffraction (XRD) revealed the nearly single-phase formation of CCTS films at 300 degrees C deposition temperature. After sulfurization in argon flow, the XRD lines become narrower, the average crystallite size expanding above 70 nm. The Raman spectroscopy analysis confirmed the stannite structure formation, as well as the presence CoS2 secondary phases, which reduces at higher sulfurization temperature (550 degrees C). The energy dispersive spectroscopy results indicated atomic ratios of Cu/Co/Sn/S close to the ideal stoichiometric ratio 2:1:1:4. The room temperature photoluminescence emission is recorded with maximum in the 1.35-1.40 eV range. Thermoelectric properties are measured up to 130 degrees C, the films show poor power factor as a result of small positive Seebeck coefficients 10-45 Of K -1 and low electrical conductivity despite of having relatively high carrier concentration (similar to 10(20) cm(-3)).

14. Damage threshold of CuCrFeTiV high entropy alloys for nuclear fusion reactors

Authors: Dias, M; Magalha, S; Antao, F; da Silva, RC; Gonsalves, AP; Carvalho, PA; Correia, JB; Galatanu, A; Alves, E

Published: OCT 15 2022, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 529, DOI: 10.1016/j.nimb.2022.09.003

A CuCrFeTiV high entropy alloy was prepared and irradiated with swift heavy ions in order to check its adequacy for use as a thermal barrier in future nuclear fusion reactors. The alloy was prepared from the elemental powders by ball milling, followed by consolidation by spark plasma sintering at 1178 K and 65 MPa. The samples were then irradiated at room temperature with 300 keV Ar+ ions with fluences in the 3 x 1015 to 3 x 1018 Ar+/cm2 range to mimic neutron-induced damage accumulation during a duty cycle of a fusion reactor. Structural changes were investigated by X-ray diffraction, and scanning electron microscopy and scanning transmission electron microscopy, both coupled with X-ray energy dispersive spectroscopy. Surface irradiation damage was detected for high fluences (3 x 1018 Ar+/cm2) with formation of blisters of up to 1 mu m in diameter. Cross-sectional scanning transmission electron microscopy showed the presence of intergranular cavities only in the sample irradiated with 3 x 1018 Ar+/cm2, while all irradiation experiments produced intragranular nanometric-sized bubbles with increased density for higher Ar+ fluence. The Williamson-Hall method revealed a decrease in the average crystallite size and an increase in residual strain with increasing fluence, consistent with the formation of Ar+ bubbles at the irradiated surface.

15. New superdielectric materials: (1-x) SrFe12O19 - x BNT-BT nanocomposites

Authors: Greculeasa, SG; Comanescu, C; Iacob, N; Kuncser, A; Smaranda, I; Amarande, L; Cioangher, M; Burdusel, M; Teodorescu, V

Published: OCT 1 2022, PHYSICA B-CONDENSED MATTER, 642, 414139, DOI: 10.1016/j.physb.2022.414139

Novel (1-x) SrFe12O19 - x BNT-BT0.08 (x = 0; 0.5; 0.8; 1) nanocomposites were explored in this study. The samples were produced by sol-gel method and compacted by conventional sintering. The composition, morphology, local structure, dielectric and magnetic properties were investigated by X-ray diffraction, Transmission Electron Microscopy, Impedance Analysis, Mossbauer spectroscopy, and SQUID magnetometry. The desired composition and the presence of the magnetoplumbite SrFe12O19 and perovskite BNT-BT structures were verified by X-ray diffraction. Irregular morphology and large size distributions are evidenced in the electron microscopy micrographs. The reported room temperature dielectric constants in this study are the highest values obtained in multiferroic composites at room temperature: giant dielectric constants (similar to 1.3 x 10(6)) were obtained, relative to 0.13 x 10(4) in BNT-BT. The hyperfine parameters allowed the identification of the Wyckoff positions of the Fe ions corresponding closely to the theoretical case. The hard magnetic character of the SrFe12O19 phase is evidenced from the magnetic measurements. For the first time in multifermic composites, superdielectric characteristics are evidenced at room temperature.

16. Influence of erbium doping on the structural, magnetic and optical properties of hematite (?-Fe(2)O( )3) nanorods

Authors: Popov, N; Ristic, M; Kuncser, V; Zadro, K; Velinov, N; Badica, P; Alexandru-Dinu, A; Iacob, N; Krehula, LK; Music, S; Krehula, S

Published: OCT 2022, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 169, 110857, DOI: 10.1016/j.jpcs.2022.110857

Pure and Er-doped hematite (alpha-Fe2O3) nanorods were prepared by a two-step method involving hydrothermal synthesis and calcination of pure and Er-doped goethite (alpha-FeOOH) nanorods. Substitution of Fe3+ by Er3+ in the crystal structure of hematite caused morpho-structural changes such as expansion of the unit cell and gradual shortening and rounding of hematite nanorods towards formation of nanoellipsoids. These changes induced modification of magnetic and optical properties suggesting the possibility of a systematic control of physical properties via rare earth substitution. A decrease in the hyperfine magnetic field, coercive field and Morin transition temperature, as well as an increase of the magnetic susceptibility and a narrowing of the optical band gap were observed by substitution. Intimate mechanisms related to the formation of more and more defect-like hematite phases with decreased temperatures for the transition to the low temperature antiferromagnetic phase at increased doping level were evidenced via temperature dependent Mo center dot ssbauer spectroscopy.

17. Morpho-Structural Investigations and Carbon Nanoclustering Effects in Cr-Al-C Intermetallic Alloys

Authors: Crisan, AD; Crisan, O

Published: SEP 2022, NANOMATERIALS, 12, 3225, DOI: 10.3390/nano12183225

Intermetallic Cr-Al-C thin films from the 211 class of MAX phases were fabricated via ion beam deposition and structural investigations were undertaken to obtain information about morpho-structural effects propelled by carbon excess in the stoichiometry of the films. In order to promote the occurrence of the Cr2AlC MAX phase, the stoichiometric thin films were subsequently annealed at two temperature values: 650 degrees C and 700 degrees C in UHV conditions for 30 min. The morpho-structural effects in both as-deposited and annealed films were monitored using scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. XRD analysis showed that the as-deposited sample was almost completely crystallized in the hexagonal Cr2AlC structure, with a remaining amorphous fraction of about 17%, most probably rich in carbon. Raman analysis allowed the identification of three spectral regions, two of them encompassing the Raman optical modes belonging to the Cr2AlC 211 MAX phase, while the third one gave strong evidence of highly intense and large D- and G-bands of carbon. Structural parameters such as the crystal lattice parameters as well as the volume of the crystal unit cell were found to decrease upon annealing; this decrease is attributed to the grain growth. The average crystallite dimension was proven to increase after annealing, while the lattice micro-strain lowered to approximately 63% in the annealed thin film compared to the as-deposited one. Well-formed and intense Raman peaks attributed to D- and G-bands of carbon were also observed and, corroborated with the structural data, seemed to indicate an overall increased level of crystal ordering as well as potential carbon nanoclustering after thermal treatments with thin Cr2AlC films. This observed phenomenon concords with previously documented reports on ab initio modelling of possible Cr2AlC structures with carbon excess.

18. Magnetic Properties of Nanosized Fe and FeCo Systems on Trenched Mo Templates

Authors: Stanciu, AE; Schinteie, G; Kuncser, AC; Locovei, C; Trupina, L; Iacob, N; Leca, A; Borca, B; Kuncser, V

Published: SEP 2022, COATINGS, 12, 1366, DOI: 10.3390/coatings12091366

The manipulation of magnetic anisotropy represents the fundamental prerequisite for the application of magnetic materials. Here we present the vectorial magnetic properties of nanostructured systems and thin films of Fe and FeCo prepared on linearly trenched Mo templates with thermally controlled periodicity. The magnetic properties of the nanosystems are engineered by tuning the shape, size, thickness, and composition parameters of the thin films. Thus, we control coercivity, magnetization, orientation of the easy axis of magnetization, and the long-range magnetic order of the system in the function of the temperature. We distinguish magnetic components that emerge from the complex morpho-structural features of the undulating Fe or FeCo nanostructured films on trenched Mo templates: (i) assembly of magnetic nanowires and (ii) assembly of magnetic islands/clusters. Uniaxial anisotropy at room temperature was proven, characterized, and explained in the case of all systems. Our work contributes to the understanding of magnetic properties necessary for possible further applications of linear systems and undulated thin films.

19. Magnetic Nanoparticles: Current Advances in Nanomedicine, Drug Delivery and MRI

Authors: Comanescu, C

Published: SEP 2022, CHEMISTRY-SWITZERLAND, 4, DOI: 10.3390/chemistry4030063

Magnetic nanoparticles (MNPs) have evolved tremendously during recent years, in part due to the rapid expansion of nanotechnology and to their active magnetic core with a high surface-to-volume ratio, while their surface functionalization opened the door to a plethora of drug, gene and bioactive molecule immobilization. Taming the high reactivity of the magnetic core was achieved by various functionalization techniques, producing MNPs tailored for the diagnosis and treatment of cardiovascular or neurological disease, tumors and cancer. Superparamagnetic iron oxide nanoparticles (SPIONs) are established at the core of drug-delivery systems and could act as efficient agents for MFH (magnetic fluid hyperthermia). Depending on the functionalization molecule and intrinsic morphological features, MNPs now cover a broad scope which the current review aims to overview. Considering the exponential expansion of the field, the current review will be limited to roughly the past three years.

20. Dielectric, piezoelectric and magnetic behavior of CoFe2O4/BNT-BT0.08 monolayer thin films composites

Authors: Cernea, M; Radu, R; Craciun, F; Gavrila, R; Surdu, VA; Trusca, R; Mihalache, V

Published: AUG 2022, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 282, 115770, DOI: 10.1016/j.mseb.2022.115770

We report in this paper on the monolayer composites thin films that have the magnetic spinel CoFe2O4 and the piezoelectric perovskite BNT-BT0.08 as constituent phases. Composite thin films of CoFe2O4 and BNT-BT0.08, with molar ratios of 0.5:1, 1:1 and 1.5:1, have been deposited by spin coating method from a sol precursor, mixture type, of CoFe2O4 and BNT-BT0.08. The monolayer thin films, deposited on Si/SiO2/TiO2/Pt substrate, were characterized using selected methods, such as: X-ray diffraction, scanning electron microscopy, atomic force microscopy/piezoelectric force microscopy, dielectric spectroscopy, and vibrating sample magnetometer. X-ray diffraction demonstrated the two phases: cubic CoFe2O4 and rhombohedral BNT-BT0.08. Furthermore, the Si/ SiO2/TiO2/Pt/BNT-BT0.08/CoFe2O4 monolayers show a simultaneous enhancement of both the magnetization and coercivity with the increase of the magnetic phase, accompanied by a decrease of the dielectric constant. The obtained results reveal that the investigated monolayer structures present superior properties compared to those of bilayer composites.

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