National Institute Of Materials Physics - Romania

Publications

5781 articles found

4151. X-ray diffraction and microscopy investigations of structural inhomogeneities in NiMnSb crystallised from the melt

Authors: Monnereau, O; Guinneton, F; Tortet, L; Garnier, A; Notonier, R; Cernea, M; Manea, SA; Grigorescu, C

Published: NOV 2004, JOURNAL DE PHYSIQUE IV, 118, 350, DOI: 10.1051/jp4:2004118040

Our present work investigates the structural properties of bulk NiMnSb prepared by growth from the melt, using various thermal regimes. We studied the compositional behaviour of the polycrystalline material obtained from stoichiometric 1: 1:1 and respectively off-stoichiometric melts. The latter samples were grown with Mn excess up to 10% and respectively Ni deficiency between 2 and 10%. The X-ray diffraction and the Scanning electron microscopy complement each other in the characterisation of the phases occurring in the samples. The synthesis of NiMnSb starting from an initially stoichiometric mixture associated with a thermal treatment presenting plateaus gives the best results. Also, it seems that the presence of an excess of Mn is not sufficient to prevent the occurrence of the NiSb stray phase.

4152. X-ray diffraction on cyanide-hardened iron plates

Authors: Popescu, M; Hoyer, W; Stegarescu, M; Cornet, A; Broll, N

Published: NOV 2004, JOURNAL DE PHYSIQUE IV, 118, 353, DOI: 10.1051/jp4:2004118041

4153. Modeling of the amorphous diamond-like carbon

Authors: Popescu, M; Sava, F; Bradaczek, H

Published: NOV 2004, JOURNAL DE PHYSIQUE IV, 118, 96, DOI: 10.1051/jp4:2004118011

The atomic ordering of the amorphous diamond-like carbon at the scale larger than short-range order is directly related to the characteristics of the array of interstitial voids. The large interstitial voids are responsible for the first diffraction peak, while the smaller ones (second and third order size of the voids) are responsible especially for the intensity and position of the second peaks in the interference function (structure factor).

4154. Two-dimensional arrays of nanometre scale holes and nano-V-grooves in oxidized Si wafers for the selective growth of Ge dots or Ge/Si hetero-nanocrystals

Authors: Olzierski, A; Nassiopoulou, AG; Raptis, I; Stoica, T

Published: NOV 2004, NANOTECHNOLOGY, 15, 1700, DOI: 10.1088/0957-4484/15/11/056

Two-dimensional (2D) arrays of nanometre scale holes were opened in thin SiO2 layers on silicon by electron beam lithography and chemical etching. Oxidized silicon wafers with a 5 nm thick SiO2 layer on top were used in this respect. Pattern transfer involved either only removal of SiO2 or a two-step process of oxide removal and anisotropic silicon chemical etching to form nanometre scale silicon V-grooves. The size of the holes in the photoresist layer varied in the range 40-80 nm, depending on the exposure dose used. The smallest holes in the oxide were about 50 nm in diameter, while in V-grooves the smallest width was approximate to70 nm. 2D arrays of Ge dots or Ge/Si hetero-nanocrystals were selectively grown on these patterned silicon wafers. In small windows only one Ge island per hole was nucleated.

4155. Time-resolved photoluminescence analysis of distribution and migration of terbium ions in zeolites X

Authors: Tiseanu, C; Frunza, L; Kumke, M

Published: OCT 30 2004, PHYSICA B-CONDENSED MATTER, 352, 365, DOI: 10.1016/j.physb.2004.08.015

The photoluminescence (PL) dynamics of terbium-exchanged zeolites X was investigated upon laser excitation at 355 nm. The results evidenced the presence of at least two terbium main environments with PL lifetimes varying between 391-411 and 753-770 mus. The two-site nature of terbium distribution in zeolites X permitted a quantitative analysis of the migration process of terbium ions inside the pores and cavities upon dehydration in air at 200 degreesC. Besides the increase of the PL lifetimes with about 30% and 80% compared to those of the hydrated zeolite, a fraction of almost 30% of terbium ions was estimated to migrate from the supercages to the neighboring sodalites or hexagonal prisms. Our results evidenced for the first time the capability of time-resolved luminescence spectroscopy in quantitatively tracking for the intrazeolitic migration of lanthanides. (C) 2004 Elsevier B.V. All rights reserved.

4156. Evidence for vortices in the pseudogap region of Y1-xPrxBa2Cu3O7 from angular magnetoresistivity measurements

Authors: Sandu, V; Cimpoiasu, E; Katuwal, T; Li, S; Maple, MB; Almasan, CC

Published: OCT 22 2004, PHYSICAL REVIEW LETTERS, 93, DOI: 10.1103/PhysRevLett.93.177005

In-plane angular magnetoresistivity Deltarho(ab)(anis) measurements were made on Y1-xPrxBa2Cu3O7-delta single crystals in the pseudogap region. For xgreater than or equal to0.2 single crystals, Deltarho(ab)(anis)(theta) displays a deviation from the typical quasiparticle contribution (proportional tosin(2)theta) for temperatures smaller than a certain value T-phi in the pseudogap region. This deviation is consistent with a flux-flow type contribution to angular magnetoresistivity, indicating the presence of vortexlike excitations above the zero-field critical temperature in the pseudogap region.

4157. Influence of the SMCo5 hard magnetic phase on the magnetoresistive properties of Cu-Fe ribbons

Authors: Larde, R; Le Breton, JM; Richomme, F; Teillet, J; Hauet, A; Maignan, A; Crisan, O

Published: OCT 20 2004, JOURNAL OF PHYSICS-CONDENSED MATTER, 16, 7492, DOI: 10.1088/0953-8984/16/41/026

The SmCo5 hard magnetic phase was added to magnetoresistive granular Cu-Fe alloys in order to investigate the influence of the presence of a hard magnetic phase on the magnetoresistive properties of a granular alloy that contains a soft magnetic phase. Cu-80(Sm0.17Co0.83)(x)Fe20-x ribbons, with x = 20, 15, 10, 5, obtained by melt spinning, were investigated. The ribbons are composed of magnetic Fe, SmCo5, and Co precipitates embedded in a Cu matrix. In the as-quenched state, the magnetic interactions between magnetic precipitates lead to the formation of magnetic coherent regions and the magnetoresistance effect is only observed at high field (>1T). After annealing, the strength of interactions decreases and a magnetoresistance effect is observed at low field (<1T). The largest magnetoresistance effect (16%) is observed at 5K for the Cu-80(Sm0.17Co0.83)(10)Fe-10 alloy annealed at 450degreesC.

4158. An exactly solvable model for a ternary solution with three-body interactions and orientationally dependent bonding

Authors: Buzatu, FD; Lungu, RP; Huckaby, DA

Published: OCT 1 2004, JOURNAL OF CHEMICAL PHYSICS, 121, 6206, DOI: 10.1063/1.1788633

A model is considered in which the bonds of a honeycomb lattice are covered by rodlike molecules of types AA, BB, and AB. Neighboring molecular ends have three-body and orientation-dependent interactions. The model is shown to be equivalent to a spin-1/2 Ising model on the same lattice with a field, but with only pairwise interactions. Symmetric and asymmetric coexistence surfaces for the separation into an AA-rich and a BB-rich phase are calculated exactly. (C) 2004 American Institute of Physics.

4159. alpha-Fe2O3-In2O3 mixed oxide nanoparticles synthesized under hydrothermal supercritical conditions

Authors: Sorescu, M; Diamandescu, L; Tarabasanu-Mihaila, D

Published: OCT 2004, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 65, 1725, DOI: 10.1016/j.jpcs.2004.05.002

alpha-Fe2O3-In2O3 mixed oxide nanoparticles system has been synthesized by hydrothermal supercritical and postannealing route, starting with (1-x)Fe(NO3)(3)(.)9H(2)O(.)xIn(NO3)(3)(.)5H(2)O aqueous solution (x = 0-1). X-ray diffraction and Mossbauer spectroscopy have been used to study the phase structure and substitutions in the nanosized samples. The concentration regions for the existence of the solid solutions in the alpha-Fe2O3-In2O3 nanoparticle system together with the solubility limits of In3+ ions in the hematite lattice and of Fe3+ ions in the cubic In2O3 structure have been evidenced. In general, the substitution level is considerably lower than the nominal concentration x. A justification of the processes leading to the formation of iron and indium phases in the investigated supercritical hydrothermal system has been given. (C) 2004 Elsevier Ltd. All rights reserved.

4160. Nano-sized barium zirconate powders obtained by the sol-gel method

Authors: Dediu, OG; Crisan, M; Aldica, G; Zaharescu, M

Published: OCT 2004, REVUE ROUMAINE DE CHIMIE, 49, 817, DOI:

Nanoparticles of barium zirconate were obtained by the sol-gel method starting from different barium sources and zirconium n-butoxide in butanol. The intermediate wet gels were obtained by hydrolysis of the precursors with water excess, at room temperature. The dried gels were characterized by DTA and IR techniques and were thermally treated in air to obtain crystalline products. XRD and TEM methods proved the formation of barium zirconate nanopowders. According to XRD and TEM data, better results were obtained when starting with barium nitrate than with barium acetate precursors.