National Institute Of Materials Physics - Romania

Publications

5840 articles found

3811. Irreversible magnetization above critical temperature in superconducting Y0.47Pr0.53Ba2Cu3O7-delta

Authors: Sandu, V; Gyawali, P; Katuwal, T; Amasan, CC; Taylor, BJ; Maple, MB

Published: 2007, SIX INTERNATIONAL CONFERENCE OF THE BALKAN PHYSICAL UNION, 899, +, DOI:

Using magnetization measurements, we report the existence of an irreversibility in the magnetization in Y0.47Pr0.53Ba2Cu3O7-delta single crystals above the critical temperature (T-c = 13 K) that is visible up to 200 K. Magnetization vs temperature displays irreversibility up to an applied field of 500 Oe. We noticed a weak irreversibility at high temperatures and a stronger one at low temperatures. In the weak irreversibility regime, both zero-field- and field-cooled magnetization follow similar Curie-Weiss (C-W) dependences, with slightly different parameters. The C-W parameters, decrease fast with increasing field. The C-W temperature is negative, suggesting that the average interaction between spins is antiferromagnetic. All these data suggest that the paramagnetic state is in fact a free spin liquid containing floating antiferromagnetic clusters as well as superconducting phase fluctuations.

3812. High temperature thermolumineseence of BaFCl : EU2+ X-ray storage phosphor

Authors: Secu, CE; Secu, M; Predoi, D

Published: 2007, PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 4, NO 3, 4, +, DOI: 10.1002/pssc.200673736

Thermoluminescence (TL) of Eu2+-doped BaFCl polycrystalline powders X- ray irradiated at room temperature show several TL peaks at 364 K, 408 K, 470 K, 524 K and 646 K. Thermally activated recombination processes responsible for TL have been studied using complementary techniques as TL and its bleaching, diffuse reflectance, X-ray excited luminescence (XL) and photostimulated luminescence (PSL). Experimental results indicate that F(Cr) centres are the dominant electron trap centres, the Eu2+-trapped hole aggregate centres playing the role of recombination centres. The 470 K and 646 K TSL glow peaks are assigned to the recombination inside the triple aggregates (Eu2+ - hole centre - F(Cl-) centre). The remaining 408 K and 524 K TL peaks are tentatively assigned to recombination between F centres and double aggregates (Eu2+ - hole centre). (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

3813. Thermal treatments effects on microwave dielectric properties of Ba(Zn1/3Ta2/3)O-3 ceramics

Authors: Ioachim, A; Toacsan, MI; Nedelcu, L; Banciu, MG; Dutu, CA; Andronescu, E; Jinga, S

Published: 2007, ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY, 10, 268, DOI:

Ba(Zn1/3Ta2/3)O-3 dielectric materials were prepared by solid state reaction. The samples were sintered at temperatures in the range 1 400 divided by 1 600 degrees C for 4 h. Morphostructural characterization was performed by using SEM and XRD. The dielectric properties were measured in the microwave range (6 divided by 7 GHz). An additional annealing at 1 400 degrees C for 10 hours was performed in order to improve the dielectric parameters. The best parameters were achieved for the samples sintered at 1 600 degrees C with additional thermal treatment.

3814. The atomic scale modelling of nanomaterials

Authors: Popescu, M

Published: MAY-JUN 2007, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 68, 694, DOI: 10.1016/j.jpcs.2007.02.050

Atomic scale modelling of various nano-clusters has been pet-formed. Amorphous/crystalline transition has been modelled in phase change memory materials. The modelling gives the possibility to select the physically realistic configurations, to be prepared and applied in nano-devices. (c) 2007 Elsevier Ltd. All rights reserved.

3815. Small-signal circuit elements of MIS-type nanostructures

Authors: Racec, PN; Wulf, U

Published: 2007, NANOSCIENCE AND TECHNOLOGY, PTS 1 AND 2, 121-123, 552, DOI: 10.4028/www.scientific.net/SSP.121-123.549

Starting from a mean field calculation for the static capacitance of a MIS-nanostructure with a near back gate [P.N. Racec, E. R. Racec and U. Wulf, Phys. Rev. B 65, 193314, (2002)] we develop an approach to determine the equivalent small-signal circuit. The analyzed system has an open character, taken into account in the Landauer-Buttiker formalism. The Coulomb interaction is treated in Hartree approximation. Consistent with our static calculations we determine the charge-charge correlation function in the random phase approximation to find the ac-admittances. The small-signal circuit consists of a voltage-dependent capacitance and a resistance in series. Beyond a characteristic frequency v, they become frequency dependent. The characteristic frequency is given by the life time of specific resonance which develops in the system.

3816. Fractal characteristics of metal clusters self-assembled in alkali halide matrices

Authors: Enculescu, M; Enculescu, I

Published: 2007, PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 4, NO 3, 4, +, DOI: 10.1002/pssc.200673716

Metal nanoclusters of Ag and An were obtained in alkali halide crystals (NaCl, KBr and KCl). The fractal character of the structures is proved by the fractal dimensions calculated using a home made computer program. The self aggregation of the metallic structures is governed in both cases (Ag and Au) by the DLA mechanism. This is proved by the values of the fractal dimension calculated using two methods, sandbox and box-counting, which are between 1.7 and 1.8 for Ag and for Au between 1.7 and 1.9. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

3817. Annealing effects on properties of Ba(Zn1/3Ta2/3)O-3 dielectric materials

Authors: Ioachim, A; Toacsan, MI; Banciu, MG; Nedelcu, L; Dutu, CA; Andronescu, E; Jinga, S

Published: 2007, 2006 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, +, DOI:

Ba(Zn1/3Ta2/3)O-3 dielectric materials were prepared by, solid state reaction. The samples were sintered at temperatures in the range 1400 divided by. 1600 degrees C for 4 h. Morphostructural characterization was performed by using SE l and XRD. The dielectric properties were measured in the microwave range (6 divided by 7 GHz). An additional annealing at 1400 degrees C for 10 hours was performed in order to improve the dielectric parameters. The best parameters were achieved for the samples sintered at 1600 degrees C with additional thermal treatment.

3818. Planar microwave bandpass filters with defected ground resonators

Authors: Militaru, N; Lojewski, G; Banciu, MG

Published: 2007, 2006 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, +, DOI:

In this paper a study of some planar microwave band pass filters composed of defected ground resonators is presented. Different kinds of couplings between two defected ground resonators are investigated: electric coupling, magnetic-coupling different mixed couplings. The values of the coupling and two coefficients are extracted from the simulation results, obtained by using a full-wave EM-field simulation software. On the basis of this study, some second-order coupled planar microwave bandpass Chebyshev of Chebyshev filters are designed. The simulated performances of these novel filter structures are very close to the filler requirements, validating this way the design method and its results.

3819. Influence of calcination temperature on the electrical signal of SnSe2 sensors

Authors: Tomescu, A; Simion, CE

Published: 2007, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 1, 121, DOI:

d The effect induced by the calcination temperature on gas sensing properties of thin SnSe2 layers exposed to reducing gas species, respectively CH4, CO and H2O, has been investigated. The sensor signal defined as the ratio between the electrical resistance in air and that in the test gas atmosphere has been used as monitoring parameter.

3820. Probing cellulose wettability by electron paramagnetic resonance

Authors: Ionita, G; Ghica, C; Ionita, P

Published: 2007, MATERIALS SCIENCE-POLAND, 25, 1017, DOI:

Carboxymethyl-cellu lose has been labelled with a stable free radical by reaction with 4-aminotempo in the presence of a coupling agent (EEDQ). The spin-labelled cellulose is highly stable, no leaking being noticed after months at room temperature. EPR spectroscopy was used as a main tool to study the wettability of such a material. The EPR spectrum of the dry spin-labelled cellulose shows the expected anisotropy, while addition of several solvents (acetone, ethyl acetate, DCM, methanol, toluene, PEG 200) induces the splitting of the spectrum into a two component system. Thus, the EPR spectrum is composed of a mobile component superimposed onto an immobilized one. Addition of water leads to a monocomponent isotropic spectrum. These data clearly indicate the presence of two types of sites to which the spin-label is attached. Variable temperature EPR spectra showed that an increase of temperature results in an increase in the mobility of the spin-label. Deposition of plain or spin-labelled gold nanoparticles on the cellulose fibres also affects the structure of the polymeric chain, as seen by changes in the EPR spectra.