National Institute Of Materials Physics - Romania

Publications

911 articles found

891. 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.

892. 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.

893. 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

894. 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.

895. CURRENT-VOLTAGE CHARACTERISTICS OF HIGH-TEMPERATURE SUPERCONDUCTING CERAMICS WITH THE PEAK EFFECT IN THE MAGNETIC-FIELD DEPENDENCE OF THE TRANSPORT CRITICAL-CURRENT DENSITY

Authors: CRISAN, A

Published: APR 1995, JOURNAL OF SUPERCONDUCTIVITY, 8, 320, DOI: 10.1007/BF00732386

The experimentally determined current-voltage characteristics of high-T-c superconducting ceramics exhibiting the ''peak-effect'' in the magnetic field dependence of the transport critical-current density were described in terms of thermally activated flux creep at grain boundaries; taking into account the collective pinning of intergranular vortices. The peak effect was explained by considering the increase of the intergrain pinning potential at intermediate fields through the interaction of intergranular (Josephson type) vortices and intragranular (Abrikosov) vortices. The magnetic field dependences of the effective pinning potential and of the collective pinning exponent were experimentally determined, and the features of the I-V curves were explained through these dependences.

896. 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.

897. ON A MODIFIED KIM ANDERSON MODEL OF THE CURRENT-VOLTAGE CHARACTERISTICS OF HIGH-TEMPERATURE SUPERCONDUCTING CERAMICS

Authors: CRISAN, A

Published: AUG 1994, JOURNAL OF SUPERCONDUCTIVITY, 7, 691, DOI: 10.1007/BF00721648

In comparison with the ''classical'' Kim-Anderson model for the current-voltage characteristics of type-II superconductors, another model with a less sharp pinning potential is presented. In addition to the approximate solution, for currents close to the critical one, a complete solution of this model is derived, which better fits the experimentally obtained current-voltage characteristics.

898. HYPERFINE FIELDS AND MAGNETIC-ANISOTROPY IN FE100-XGDX THIN-FILMS AND FE80-XGDXB20 (0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-24) THIN-FILMS AND RIBBONS

Authors: KUNCSER, V; FILOTI, G; SERBANESCU, MD; JIANU, A; CRISTEA, L; DORMANN, JL; NOGUES, M; MAKNANI, J

Published: 1994, HYPERFINE INTERACTIONS, 94, 2326, DOI: 10.1007/BF02063782

Mossbauer measurements performed on Fe100-xGdx thin films and on Fe80-xGdxB20 both as thin films and ribbons show a dependence of the spins orientation and [H-hyp] versus temperature, Gd content and preparation conditions. Increasing the Gd content, the initial low anisotropy disappears and [H-hyp] decreases. A sharp increase of the anisotopy with temperature in ribbons with low Gd concentration is evidenced.

899. MAGNETIC-PROPERTIES OF FE100-XGDX THIN-FILMS AND FE80-XGDXB20 THIN-FILMS AND RIBBONS (0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-20)

Authors: FILOTI, G; KUNCSER, V; SERBANESCU, MD; JIANU, A; CRISTEA, L; NOGUES, M; DORMANN, JL; MAKNANI, J

Published: NOV 1993, IEEE TRANSACTIONS ON MAGNETICS, 29, 3125, DOI: 10.1109/20.280879

Magnetic and Mossbauer experiments were performed on Fe100-xGdx thin films and on Fe80-xGdxB20 both in thin films and ribbons for x less-than-or-equal-to 20. The ferrimagnetic order is perturbed by the presence of B and Fe-interactions are.different. For small Gd content, the low anisotropy is in the film plane, while for greater Gd the anisotropy goes out of the plane giving typical features of hysteresis loops and strong decrease of Mossbauer hyperfine fields.

900. DISSIPATION IN CURRENT-CARRYING HIGH-T(C) SUPERCONDUCTING CERAMICS IN APPLIED MAGNETIC-FIELD

Authors: MIU, L; POPA, S; CRISAN, A; ALDICA, G; JAKLOVSZKY, J

Published: AUG 1993, JOURNAL OF SUPERCONDUCTIVITY, 6, 284, DOI: 10.1007/BF00626270

The dissipation mechanism in high-T(c) superconducting ceramics was studied by analyzing the magnetic field dependence of the transport critical current and the form of the current-voltage characteristics. It was found that the actual magnetic field dependence of the transport critical current is significantly slower than that predicted by the weak-link-quenching model. The low-voltage-level current-voltage characteristics were described in terms of thermally activated flux creep at grain boundaries, taking into account collective pinning of intergranular Josephson vortices. For the investigated samples, a low-field, high-temperature mean pinning energy barrier of a few tens of meV was determined.