National Institute Of Materials Physics - Romania

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5840 articles found

5191. OPTICAL INDUCED MODIFICATIONS IN THIN-FILMS OF FE-PVA

Authors: FILOTI, G; KUNCSER, V; FRANKE, H; KARDINAL, T; MANIVANNAN, G

Published: MAR 1995, JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY-ARTICLES, 190, 320, DOI: 10.1007/BF02040006

The ferric chloride doped polymers change their refractive index under UV irradiation. The Fe:PVA is sensitive to ferric chloride concentration, molecular weight of PVA, and recording beam power. By Mossbauer investigations we tried to correlate the Fe2+ / Fe3+ ratio, as well as the temperature dependence of the energetical parameters with the assumed mechanisms which involve both the valence state of iron and a cross-linking reaction of PVA matrix.

5192. ARE MODULATIONS OF THE SCHOTTKY SURFACE-BARRIER THE ONLY EXPLANATION FOR THE GAS-SENSING EFFECTS IN SINTERED SNO2

Authors: IONESCU, R; MOISE, C; VANCU, A

Published: MAR 1995, APPLIED SURFACE SCIENCE, 84, 297, DOI: 10.1016/0169-4332(94)00544-3

Conductance transients of thick, sintered SnO2 films at step isothermal changes in oxygen partial pressure show exponential decays with time constants which cannot be explained in the frame of the usually accepted model of Schottky barriers at intergranular contacts dominating the conductance behavior. An alternative model, based on a linear relationship between conductance and the surface coverage by chemisorbed oxygen, accounts well for the experimental results. This model proposes the existence of a highly resistive sub-surface layer, isolating the surface from the bulk; it identifies the oxygen chemisorption sites with surface oxygen vacancies. The model is also supported by the temperature-variation of conductance in ''ramp'' experiments with increasing and decreasing temperature, and by the effects of prolonged heat treatments in oxygen upon the conductance and gas sensitivity.

5193. STRUCTURAL MODIFICATIONS IN IRON HYDRATED OXIDES INDUCED BY FOREIGN CATION

Authors: SPANU, V; TURCANU, CN; FILOTI, G

Published: MAR 1995, JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY-ARTICLES, 190, 380, DOI: 10.1007/BF02040015

The aqueous radioactive wastes are chemical systems as consequence of the variety of the contained cations. The chemical systems precipitated from FeSO4 and FeCl3 simulating the aqueous radioactive waste treatment have been investigated by Mossbauer spectroscopy. Mg2+, Ca2+ and Ba2+ were used as foreign cations, the calcium being among the main components of aqueous radioactive waste. The results showed the ion radius influence varying from Mg2+ and Ba2+ in the case of the precipitation from FeSO4. For the precipitation from ferric chloride the influences are not so evident.

5194. ANION INFLUENCE ON THE HYDRATED OXIDES FORMED BY FE3+ AND FE2+ PRECIPITATION

Authors: SPANU, V; TURCANU, CN

Published: MAR 1995, JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY-ARTICLES, 190, 374, DOI: 10.1007/BF02040014

The anion influence on the hydrated oxides formed by Fe3+ and Fe2+ precipitation simulating the aqueous radioactive waste treatment has been investigated by Mossbauer spectroscopy. Fe-3(SO4)(2), Fe(NO3)(3). FeCl3, FeSO4 and FeCl2 were used as iron sources and neutralized by NaOH. The obtained products contain several kinds of amorphous and/or poorly crystallized hydrated oxides, depending on the anion type which exists in solution and on the initial iron valence. The pH influence on the final precipitate is taken into account.

5195. AZIMUTHAL CORRELATION-FUNCTIONS AND THE ENERGY OF VANISHING FLOW IN NUCLEUS-NUCLEUS COLLISIONS

Authors: BUTA, A; ANGELIQUE, JC; AUGER, G; BIZARD, G; BROU, R; CABOT, C; CASSAGNOU, Y; CREMA, E; CUSSOL, D; ELMASRI, Y; EUDES, P; GONIN, M; HAGEL, K; HE, ZY; KERAMBRUN, A; LEBRUN, C; LEGRAIN, R; PATRY, JP; PEGHAIRE, A; PETER, J; POPESCU, R; REGIMBART, R; ROSATO, E; SAINTLAURENT, F; STECKMEYER, JC; TAMAIN, B; VIENT, E; WADA, R

Published: FEB 20 1995, NUCLEAR PHYSICS A, 584, 412, DOI: 10.1016/0375-9474(94)00520-W

A method is proposed for estimating the energy of vanishing flow (also called balance energy, E(bal)) without reconstructing the reaction plane. This method is based on the shapes of experimental particle-particle azimuthal correlation functions. It is used for determining E(bal) for three systems: Ar + Al, Zn + Ti, Zn + Ni. The results are compared with estimations using flow-parameter analysis and with theoretical expectations.

5196. TEMPERATURE-DEPENDENCE OF SURFACE-TENSION OF LIQUID-CRYSTALS AT THE PHASE-TRANSITION

Authors: MOLDOVAN, R; TINTARU, M; BEICA, T; FRUNZA, S; STOENESCU, DN

Published: FEB 20 1995, MODERN PHYSICS LETTERS B, 9, 242, DOI: 10.1142/S0217984995000231

The surface tension is calculated as the excess of the free energy per unit area, due to the presence of a surface layer, using Landau-de Gennes expansions, in the hypothesis of a first order transition in the bulk and taking into account the dependence of the surface free energy from the surface tilt angle. The surface order parameter is calculated and surface-ordered phase above the phase transition temperature has been found. A variety of calculated surface tension versus temperature curves with a jump at the phase transition, with positive or negative slope, well describing the experimental data from literature, have been attained.

5197. COLLECTIVE PINNING BEHAVIOR OF INTERGRANULAR JOSEPHSON VORTICES AND THE INTERGRANULAR IRREVERSIBILITY LINE OF HIGH-T-C SUPERCONDUCTING CERAMICS

Authors: MIU, L

Published: FEB 1995, JOURNAL OF SUPERCONDUCTIVITY, 8, 146, DOI: 10.1007/BF00732256

The supercurrent-transport properties of YBa(2)Cu(3)O(similar to)7 (Y: 123) polycrystalline hulk sintered samples with random grain orientation were thoroughly investigated. The dissipation process in these materials occurs due to intergranular flux motion, rather than by weak-link quenching. It was found that the model which takes into consideration collective creep of intergranular vortices is self-consistent in describing the low-voltage-level current-voltage characteristics and the intergranular irreversibility line of high-T-c superconducting ceramics.

5198. FE-57 MOSSBAUER STUDY OF GD(2)FE(14-X)M(X)C COMPOUNDS WITH M=NI, SI, CU, V

Authors: MORARIU, M; ROGALSKI, M; VALEANU, M; PLUGARU, N; BURZO, E

Published: FEB 1995, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 140, 1002, DOI: 10.1016/0304-8853(94)01499-X

Gd(2)Fe(14-x)M(x)C compounds, with M = Ni, Si, Cu or V and x less than or equal to 1.5 were investigated by Fe-57 Mossbauer spectroscopy. A preferential substitution of iron sites by the M elements is evidenced. The hyperfine parameters are discussed in correlation with the data obtained by magnetic measurements.

5199. EFFECT OF INTERGROWTH DEFECTS ON THE X-RAY-DIFFRACTION PATTERN .2. A CASE-STUDY OF BI-BASED SUPERCONDUCTORS

Authors: MALIS, O; MANCIU, M; MANAILA, R; DEVENYI, A

Published: FEB 1995, PHYSICA STATUS SOLIDI A-APPLIED RESEARCH, 147, 333, DOI: 10.1002/pssa.2211470204

In Part I a general equation was derived for the intensity diffracted by a matrix phase containing intergrowths. It was applied to the case of Bi2Sr2Can-1CunOy phases (n = 2, 3) with stacking defects (''wrong'' number n of Cu-O planes in a half-cell). A least-squares program based on this equation yields the nature, concentration, and short-range order of the defect intergrowths. The program uses the peak shifts which are induced by the presence of defects. The analysis is exemplified on several BSCCO samples, whose defect state informs about the formation steps of the superconducting phases.

5200. EFFECT OF INTERGROWTH DEFECTS ON THE X-RAY-DIFFRACTION PATTERN

Authors: MANAILA, R; MALIS, O; MANCIU, M; DEVENYI, A

Published: JAN 16 1995, PHYSICA STATUS SOLIDI A-APPLIED RESEARCH, 147, 43, DOI: 10.1002/pssa.2211470104

The presence of intergrowth with a different spacing inside a layered phase causes significant alterations in the X-ray diffraction pattern, concerning both line positions and widths. An analysis of these changes, based on a Hendricks-Teller-type formalism yields estimates about the defect nature, concentration and short-range order. The procedure was exemplified by simulation of XRD patterns for Bi-based oxidic superconductors, in which intergrowths of related phases are often present inside the matrix phase.