National Institute Of Materials Physics - Romania

Publications

903 articles found

871. Structural modifications of the superconducting phases on Bi system by electron beam irradiation

Authors: Aldica, G; Geru, II; Puscasu, BM; Constantinescu, F; Badica, P

Published: JUN 1996, JOURNAL OF SUPERCONDUCTIVITY, 9, 276, DOI: 10.1007/BF00727547

Superconducting samples of the Bi(Pb)-Sr-Ca-Cu-O system have been irradiated in transmission electron microscopy (TEM) to investigate the effect of a relative high fluence of electrons with 75 and 100 keV energy on the microstructure of the material. The diffraction pattern images show a dramatic change from very uniform lattice spots at ab crystalline planes to a circular pattern corresponding to damage and breaking of the materials in very small crystallites.

872. Temperature-dependent collective pinning exponent in Bi2Sr2Ca2Cu3O10+x tapes and bulk samples with preferential crystallite orientation

Authors: Crisan, A; Popa, S; Aldica, G; Jaklovszky, J

Published: JUN 1996, JOURNAL OF SUPERCONDUCTIVITY, 9, 291, DOI: 10.1007/BF00727550

The low-voltage-level current-voltage characteristics of Bi2Sr2Ca2Cu3O10+x tapes and bulk samples with preferential crystallite orientation were measured in applied magnetic fields both parallel and perpendicular to the samples' surfaces. The data were interpreted within the framework of the collective pinning model. The collective pinning exponent alpha changes from approximate to 1 to approximate to 0.5 (close to T-c), while in the case of unoriented samples it is constant (and equal to the theoretical value 1/2) as shown in an earlier paper. We suggest that this temperature dependence of alpha is due to the change of the dimensionality of the intragranular vortices.

873. Annealing effects in amorphous Fe77Gd3B20 ribbons

Authors: Mihalca, I; Ercuta, A; Zaharie, I; Jianu, A; Kuncser, V; Filoti, G

Published: MAY 1996, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 157, 162, DOI: 10.1016/0304-8853(95)01143-9

The crystallization kinetics of the amorphous alloy Fe77Gd3B20 were examined under isothermal flash annealing conditions both in air and in a vacuum. Magnetic measurements were used to determine the reaction order (n) and activation energy (E(a)), and Mossbauer spectroscopy (MS) was used to identify some resulting crystalline phases.

874. A new approach for the growth of high-T-c superconductors

Authors: Jaklovszky, J; Aldica, G; Rusu, C; Crisan, A

Published: APR 1996, APPLIED SUPERCONDUCTIVITY, 4, 194, DOI: 10.1016/S0964-1807(96)00023-3

In this paper we describe a modified liquid phase separation (double crucible) method for growth of superconducting Bi-Sr-Ca-Cu-O single crystals. We used alumina crucibles. The morphology and composition of as-grown crystals were investigated using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The stacking thin-plate single crystals of maximum 5 x 6 x 0.1 mm(3) were obtained. (C) 1997 Elsevier Science Ltd. All rights reserved.

875. Structural modifications of superconducting phases in Bi(Pb)-Sr-Ca-Cu-O system

Authors: Badica, P; Aldica, G; Alexeev, AF; Gridasova, TY; Morozov, VV

Published: MAR 1 1996, PHYSICA C, 259, 96, DOI: 10.1016/0921-4534(96)00021-4

Bi-Pb-Sr-Ca-Cu-O samples were produced by the spray-frozen, vacuum-freeze drying method from nitrate solutions. Structural modifications of crystallites during sintering were investigated in agreement with bulk density, phase structure of the samples, critical temperature T-c and critical current density j(c). A model for morphology changes of (2223) crystallites during sintering was proposed. Maximum j(c) in a zero magnetic field is reached on samples sintered for 200-250 h.

876. Influence of pyrolization temperature on final characteristics of BSCCO ceramic produced by spray-frozen, freeze drying method

Authors: Badica, P; Aldica, G; Alexeev, AF; Gridasova, TY; Morozov, VV

Published: FEB 1 1996, JOURNAL OF MATERIALS SCIENCE LETTERS, 15, 188, DOI: 10.1007/BF00274446

877. Ag-substituted Al-Cu-Fe icosahedral phases

Authors: Manaila, R; Macovei, D; Jianu, A; Popescu, R; Nicula, R; Zavaliche, F; Devenyi, A; Xie, Y; Hu, T

Published: FEB 1996, PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 193, 294, DOI: 10.1002/pssb.2221930202

The gradual substitution of Cu by Ag in the Al62Cu25.5-xAgxFe12.5 icosahedral phase (x less than or equal to 10) is investigated by X-ray diffraction from the viewpoint of the induced structural changes. The phonon and random phason disorders, estimated from diffraction linewidths, increase with x, the latter showing, however, an induction range of Ag concentrations. EXAFS results at the CuK and FeK edges show. for low Ag contents, and enhanced disorder in the first coordination sphere, partly relaxed for higher x values. The 6D hypercubic lattice parameter is found to be independent of the Ag content, despite the large diameter of monovalent Ag. The latter facts suggest a d-sp hybridization of the Ag bonds to the surrounding Al, taking place above a certain x value.

878. Corrosion behavior of some amorphous aluminium mixed-metal transition-metal alloys (Al-Mm-MT)

Authors: Ciolac, S; Calin, M; Roman, R; Jianu, A

Published: JAN 1996, REVISTA DE CHIMIE, 47, 66, DOI:

The results of the potentiostatic polarization studies taken on some Al-Mm-MT metallic glasses in reducing acid media are presented. The rest potentials development and the electrochemical parameters evaluated from the anodic and cathodic curves were correlated with the alloys composition, and related to those of the alloying components in crystalline state. Our results indicate that: alloying with rare earths does not affect interface processes; the transition metals interfere with the hydrogen reduction kinetics determining its acceleration by increasing Ni content in the alloy composition; substitution of Ni by Fe contributes to corrosion rate reduction, to passive state extension and stabilization, so that Al-Mm-Fe alloy behaves better than Al-Mm-(Fe, Ni) and Al-Mm-Ni alloys.

879. SINTERING TIME AND PROPERTIES OF YBA2CU3O-SIMILAR-TO-7 SUPERCONDUCTING CERAMICS

Authors: ALDICA, G; POPESCU, M; POPA, S; BUNESCU, MC; BADICA, P

Published: JUN 1995, JOURNAL OF SUPERCONDUCTIVITY, 8, 372, DOI: 10.1007/BF00728173

The effect of annealing duration in oxygen flow on the superconducting characteristics of YBa2Cu3Osimilar to 7 bulk ceramics was investigated by structural, electrical, magnetic, and electronic microscopy investigations. The long-time annealing is deleterious for the superconductivity in YBa2Cu3Osimilar to 7 ceramics. The optimum time interval for annealing is from 20 to 70 h at 950 degrees C, and within this range the maximum value of T-c is obtained.

880. AMORPHOUS-ALLOYS FOR DISCONTINUOUS CONCRETE REINFORCEMENT - CORROSION INVESTIGATION

Authors: CIOLAC, S; ROMAN, E; JIANU, A

Published: MAY 1995, REVUE ROUMAINE DE CHIMIE, 40, 418, DOI:

Electrochemical laboratory investigations were used as a screening tool for selection of metallic materials applicable to concrete reinforcement. Simultaneous examination of FeCrXP9C11 (X = 4; 7; 9), FeB13Si9, FeB13.5Si3.5C2 as compared to classical carbon steels aas conducted in simulated concrete corrosive electrolyte: Ca(OH)(2) sat. +/- NaCl +/- y Na2SO4 +/- CO2 sat. (x = 5; 50; 100 g/L, y = 1; 10 g/L). Indications are that FeCrXP9C11 amorphous alloys are highly resistant materials. Their resistance to the most aggressive media is 100-1000 times greater than of FeBSi(C) alloys and carbon steels.