Magnetization and Critical Current Density Measurements of Textured Bulk Y-Ba-Cu-O Superconductor (酸化物超伝導体の材料プロセスと特性評価<特集>)

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Strongly textured high Tc bulk YBCO was prepared with rapid solidification (RS) and directional annealing (DA) processes. It was found that the 123 crystallites grow with their c-axes perpendicular to the sample traveling direction. We have obtained transport Jc of 2, 000 A/cm2 by pulse current and 1.150A/cm2 by dc current at 77K in a 15T field. It has been found that the Jc values measured by pulse and dc methods are essentially equal in high magnetic fields (8T to 15T) and Jc measured by pulse current is larger than that measured by dc current in magnetic fields below 8T. Flux creep rate was same for field-cooled(fc) or zero field-cooled (zfc) conditions. This indicates that flux does not easily penetrate the sample along non-superconducting grain boundaries. The orientation-dependent shape of the dc magnetic hysteresis loops proved the anisotropic nature of the flux line structure and the flux pinning. Dislocations with a density of-5x109/cm2 were found in the 123 crystals and they were found to lie on the a-b plane. The enhancement of Jc is probably due to flux pinning by the dislocations, the preferred orientation of the crystallites with the a-b plane parallel to the sample traveling direction and the strong grain couplings.
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