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Diffraction Studies of Nanocrystals: Theory and Experiment

100%

Palosz B., Grzanka E., Gierlotka S., Stel'makh S., Pielaszek R., Bismayer U., Neuefeind J., Weber H., Palosz W.

Acta Physica Polonica A

2002

vol. 102

issue 1

57-82

Based on theoretical calculations of powder diffraction data it is shown that the assumption of the infinite crystal lattice for small particles is not justified, leads to significant changes of the diffraction patterns, and may lead to erroneous interpretation of the experimental results. An alternate evaluation of diffraction data of nanoparticles, based on the so-called "apparent lattice parameter", alp, is proposed.

Time Dependent Changes in Ag Doped YBCO Superconductors

100%

Volochová D., Antal V., Diko P., Šefčiková M., Zmorayová K., Kováč J., Weber H., Chaud X.

issue 5

1047-1048

Magnetization measurements at 77 K were conducted on the single-crystalline samples of YBCO superconductor doped with Ag prepared by the top-seeded melt-growth process. The single-grain samples had a nominal composition Y_{1.5}Ba_2(Cu,Ag)_3O_{y}. Magnetization measurements on the samples, oxygenated by two different processes: by standard oxygenation and by high pressure oxygenation, repeated after 24 months, revealed time dependent changes in magnetization behaviour and critical transition temperatures, T_{c}, which could be associated with redistribution of oxygen vacancies and their interaction with Ag dopant atoms.

Nanostructural Superconducting Materials for Fault Current Limiters and Cryogenic Electrical Machines

53%

Prikhna T., Gawalek W., Savchuk Y., Sergienko N., Moshchil V., Sokolovsky V., Vajda J., Tkach V., Karau F., Weber H., Eisterer M., Joulain A., Rabier J., Chaud X., Wendt M., Dellith J., Danilenko N., Habisreuther T., Dub S., Meerovich V., Litzkendorf D., Nagorny P., Kovalev L., Schmidt C., Melnikov V., Shapovalov A., Kozyrev A., Sverdun V., Kosa J., Vlasenko A.

issue 1

7-14

Materials of the Y-Ba-Cu-O (melt-textured YBa_{2}Cu_{3}O_{7-δ}-based materials or MT-YBCO) and Mg-B-O (MgB_{2}-based materials) systems with high superconducting performance, which can be attained due to the formation of regularly distributed nanostructural defects and inhomogeneities in their structure can be effectively used in cryogenic technique, in particular in fault current limiters and electrical machines (electromotors, generators, pumps for liquid gases, etc.). The developed processes of high-temperature (900-800°C) oxygenation under elevated pressure (16 MPa) of MT-YBCO and high-pressure (2 GPa) synthesis of MgB_{2}-based materials allowed us to attain high superconductive (critical current densities, upper critical fields, fields of irreversibility, trapped magnetic fields) and mechanical (hardness, fracture toughness, Young modulus) characteristics. It has been shown that the effect of materials properties improvement in the case of MT-YBCO was attained due to the formation of high twin density (20-22 μm^{-1}), prevention of macrocracking and reduction (by a factor of 4.5) of microcrack density, and in the case of MgB_{2}-based materials due to the formation of oxygen-enriched as compared to the matrix phase fine-dispersed Mg-B-O inhomogeneities as well as inclusions of higher borides with near-MgB_{12} stoichiometry in the Mg-B-O matrix (with 15-37 nm average grain sizes). The possibility is shown to obtain the rather high T_{c} (37 K) and critical current densities in materials with MgB_{12} matrix (with 95% of shielding fraction as calculated from the resistant curve).

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Diffraction Studies of Nanocrystals: Theory and Experiment

Time Dependent Changes in Ag Doped YBCO Superconductors

Nanostructural Superconducting Materials for Fault Current Limiters and Cryogenic Electrical Machines