National Institute Of Materials Physics - Romania

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5781 articles found

2471. Morphological, optical and electrical properties of samarium oxide thin films

Authors: Constantinescu, C; Ion, V; Galca, AC; Dinescu, M

Published: AUG 1 2012, THIN SOLID FILMS, 520, 6397, DOI: 10.1016/j.tsf.2012.06.049

We present here results on samarium oxide thin films, obtained by pulsed laser deposition and by radio frequency assisted pulsed laser deposition. Three different substrate types were used: silicon, platinum covered silicon and titanium covered silicon. The influence of the deposition parameters (oxygen pressure and laser fluence) on the structure and morphology of the thin films was studied. The substrate-thin film interface zone was investigated; the optical and electrical properties (the losses, dielectric constant and leakage currents) were also determined. (C) 2012 Elsevier B.V. All rights reserved.

2472. Elastic strain and stress determination by Rietveld refinement: generalized treatment for textured polycrystals for all Laue classes. Corrigenda

Authors: Popa, NC; Balzar, D

Published: AUG 2012, JOURNAL OF APPLIED CRYSTALLOGRAPHY, 45, 839, DOI: 10.1107/S0021889812024879

Errors in the article by Popa & Balzar [], caused by an equation from literature used without checking, are corrected. It is expected that other published papers will have been affected as the source error is in a reference book.

2473. Structural, dielectric, and piezoelectric properties of fine-grained NBT-BT0.11 ceramic derived from gel precursor

Authors: Cernea, M; Galassi, C; Vasile, BS; Capiani, C; Berbecaru, C; Pintilie, I; Pintilie, L

Published: AUG 2012, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 32, 2397, DOI: 10.1016/j.jeurceramsoc.2012.02.021

(Na1/2Bi1/2)TiO3 doped in situ with 11 inol% BaTiO3 (NBT-BT0.11) powders were synthesized by a sol-gel method, and the electrical properties of the resulting ceramics were investigated. The powders consisting of uniform and fine preliminary particles of about 50 nm were prepared by calcining the gel precursor at 700 degrees C. (Na1/2Bi1/2)(0.89)Ba0.11TiO3 ceramics, sintered at temperatures up to 1150 degrees C have a rhombohedral symmetry while the ceramic sintered at 1200 degrees C exhibits a tetragonal crystalline structure. The ceramics show high dielectric constant (epsilon(r) similar to 5456), dielectric loss of 0.02, depolarization temperature T-d similar to 110 degrees C and temperature corresponding to the maximum value of dielectric constant T-m similar to 262 degrees C. The dielectric constant (epsilon(33)) and the piezoelectric constant (d(33)) attain the maximum values of 924 and 13 pC/N, respectively, while the electromechanical coupling factor (k(p)) value is 0.035. The NBT-BT0.11 ceramics derived from sol-gel present high mechanical quality factor (Q(m) similar to 860). The dielectric and piezoelectric properties values of NBT-BT0.11 ceramics derived from sol-gel are smaller than those of samples produced by the conventional solid state reaction method, due to the grains size and oxygen vacancies that generate dipolar defects. (C) 2012 Elsevier Ltd. All rights reserved.

2474. A Simple Fabrication of FeSe Superconductors with High Upper Critical Field

Authors: Zhao, PH; Yan, W; Yang, JY; Han, YL; Aldica, G; Sandu, V; Badica, P; Nie, JC

Published: AUG 2012, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 25, 1785, DOI: 10.1007/s10948-012-1540-2

A simple and reproducible fabrication process for the synthesis of FeSe superconductors has been developed. The properties were characterized by X-ray diffraction, scanning electron microscope, superconductivity quantum interference device, and physical property measurement system. It showed a zero resistance superconducting critical temperature of similar to 7.9 K and an onset critical temperature of similar to 13.9 K. The upper critical magnetic field at zero temperature was estimated to be 31 T. The growth mechanism of FeSe flakes was also discussed.

2475. Effect of Tritium Loading on the Superconducting Properties of Niobium and Tantalum

Authors: Sandu, V; Popa, S; Nicolescu, MS; Enachescu, M; Sandu, E

Published: AUG 2012, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 25, 1804, DOI: 10.1007/s10948-012-1551-z

Niobium and tantalum sheets were loaded with tritium and their superconducting properties were investigated. Superconductivity is rather robust in both materials though they belong to different types of superconductors. The critical temperature does not change in the case of Nb at low field but decreases slightly in the case of Ta. The tritium-loaded Nb shows a higher remanent magnetization which we attribute to the subsurface accumulation of defects, but the high field irreversible magnetization is smaller than for the bare sample. In the case of Ta, both the remanent magnetization and the irreversible magnetization are slightly reduced after tritiation.

2476. Effects of ZnO Nanoparticles on the Wet Scrub Resistance and Photocatalytic Properties of Acrylic Coatings

Authors: Vaja, F; Comanescu, C; Oprea, O; Ficai, D; Guran, C

Published: JUL 2012, REVISTA DE CHIMIE, 63, 726, DOI:

In this work zinc oxide, ZnO, nanopowders were synthesized by co-precipitation method from a zinc acetate, Zn(CH3COO)(2), solution. The obtained nanoparticles were morphologically and structurally characterized by XRD diffraction, SEM, IR and UV-Vis spectroscopy. The new obtained material was investigated as an additive in coatings for improving wet scrub resistance, self-cleaning properties etc. The XRD pattern of the ZnO nanoparticles highlights the wurtzite hexagonal structure and also proves its purity. The correlations made based on their crystallization planes identified ZnO as the sole product. ZnO nanoparticles obtained by co-precipitation method have been introduced by strong shaking in the coating system; this has positively influenced the surface properties of the films.

2477. Structure and electrical transport in films of Ge nanoparticles embedded in SiO2 matrix

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

Published: JUL 2012, JOURNAL OF NANOPARTICLE RESEARCH, 14, DOI: 10.1007/s11051-012-0930-5

The films containing Ge nanoparticles embedded in SiO2 matrix were prepared by RF magnetron sputtering and subsequently by thermal annealing. Their structure was investigated by conventional transmission electron microscopy and high resolution transmission electron microscopy together with energy-dispersive X-ray spectroscopy. The electrical behavior of films was studied by measuring current-temperature and current-voltage characteristics. The structure investigation reveals two kinds of features: a low density of big Ge nanoparticles with sizes from 20 to 50 nm and a network of small amorphous Ge nanoregions/nanoparticles (5 nm size or less) with high density, both being embedded in amorphous SiO2 matrix. The electrical transport was shown to take place through the network of amorphous Ge nanoregions. At low temperature, the T-1/4 dependence of the current was evidenced, while at high temperature, the T-1 Arrhenius dependence was found. At both low and high temperatures, the conductivity is nearly constant. The behavior at low temperature was explained by the hopping mechanism on localized states located in a band near the Fermi energy, while at high temperature by the charge excitation to the extended states.

2478. Grain boundary diffusion driven spark plasma sintering of nanocrystalline zirconia

Authors: Borodianska, H; Demirskyi, D; Sakka, Y; Badica, P; Vasylkiv, O

Published: JUL 2012, CERAMICS INTERNATIONAL, 38, 4389, DOI: 10.1016/j.ceramint.2011.12.064

A methodology is proposed to investigate in detail shrinkage kinetics under isothermal spark plasma sintering (SPS) conditions applied to ceramic nano powders such as Y2O3 stabilized ZrO2. To do so, mild SPS conditions were used (low temperatures and pressure, long dwell times). The extracted experimental activation energy has the value of 246 +/- 37 kJ mol(-1) and the slope of the curves on the intense densification stage is around 0.33. Results are in agreement with densification by a grain-boundary diffusion mechanism as for conventional sintering and the contribution from the specific pressure-assisted mechanisms as for hot pressing is insignificant. This result suggests that exploration of mild SPS might prove rewarding in separation and control of the sintering mechanisms leading to production of specific ceramic with new or improved functionality. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

2479. Preparation and properties of nanocrystalline BNT- BTx piezoelectric ceramics by sol-gel and spark plasma sintering

Authors: Cernea, M; Poli, G; Aldica, GV; Berbecaru, C; Vasile, BS; Galassi, C

Published: JUL 2012, CURRENT APPLIED PHYSICS, 12, 1105, DOI: 10.1016/j.cap.2012.01.016

(Bi0.5Na0.5)TiO3 was doped in situ with 5, 8, and 11 mol% BaTiO3 (BNT-BTx; x = 0.05, 0.08 and 0.11) using a sol-gel technique. The resulting powders from gel precursors showed microstructures consisting of nano-sized grains and crystalline perovskite structure. Spark plasma sintering (SPS) technique was used to prepare high densified (98-99%rho(theor)) BNT-BTx ceramics from these nanopowders. The results confirm the spark plasma sintering method applied to nano-scale powders, obtained by sol-gel, as a viable route in producing nanostructured ceramics. The evolution of the structure and electrical properties of the ceramics with BaTiO3 concentration (x) was investigated. The permittivity of BNT-BT0.08 ceramic is higher (epsilon(r) = 2090, at 100 kHz) than that for x = 0.05 (epsilon(r) = 1350) and x = 0.11 (epsilon(r) = 1800). BNT-BT0.08 ceramic shows maximum values for the frequency constants (N-p, N-t), piezoelectric charge coefficient (d(31)) and piezoelectric voltage coefficient (g(31)), and minimum values for the electromechanical coupling factor (k(p)) and piezoelectric charge coefficient (d(33)). The electrical properties of these ceramics are influenced by grains size, oxygen deficiency and non-uniform internal stresses due to these oxygen deficiencies. BNT-BTx ceramics sintered by SPS seem to be good ceramic resonators with high mechanical quality factor (Q(m)). Crown Copyright (C) 2012 Published by Elsevier B. V. All rights reserved.

2480. 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.