Fabrication of textured YBa 2 Cu 3 O x superconductor using directional growth
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Fabrication of textured YBa2Cu3O^ superconductor using directional growth Kwangsoo No, Dae-Shik Chung, and Jae-Myung Kim Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejon, Korea (Received 30 April 1990; accepted 30 July 1990)
Textured bulk YBa2Cu3Ox superconductor samples were fabricated using directional growth of superconductor grains reacted from Y2BaCuO5, BaCuC>2, and CuO powder mixtures. The samples consisted of several mm long grains aligned parallel to the growth direction. The microstructure observation and x-ray diffraction analysis showed that the grains have a preferred orientation to improve critical current density.
Since the rediscovery of the YBa2Cu3Ox (123) high temperature superconductor,1 tremendous research and development efforts have been made to apply this new ceramic material for practical use. Progress toward major applications of the bulk high temperature superconductor, however, has been hindered by low transport critical current densities (Jc) at the boiling point of liquid nitrogen and their severe degradation in weak magnetic fields because of the weak link problem in the sintered materials.2 Recently, Jin et al.3 and Murakami et a/.4 have succeeded in reducing the weak link problem in bulk samples by employing a melt and directional solidification process which enables the fabrication of well-textured samples with clean boundaries and large grains aligned in a preferred orientation. Those samples exhibited dramatically improved transport Jc values at the boiling point of liquid nitrogen of above 104 A/cm2 in zero magnetic field (H) and of above 103 A/cm2 at H = 1 T as compared to several hundred and about 1 A/cm2, respectively, for the samples without the texturing. A technique has been found for preparing 123 ceramics by reacting Y2BaCuO5 (211), BaCuO2 (Oil), and CuO (001) precursor powder mixture with the following reaction: Y2BaCuO5 + 3BaCuO2 + 2CuO -> 2YBa2Cu3O6 + \O2 f . (1) This reaction involves two melt forms, one beginning at -905 °C and one at -980 °C, representing 011 + 001 -» liquid and 211 + 011 -»• 202 + liquid,5 respectively. Those melt forms provide faster reaction than the reaction involving only interatomic diffusion in the solid state sintering technique. In this paper, we report a technique for texturing of bulk 123 ceramics by directional growth of 123 grains reacted from 211, 011, and 001 precursor powder mixtures.5 2610
http://journals.cambridge.org
J. Mater. Res., Vol. 5, No. 11, Nov 1990
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Y2BaCuO5 and BaCuO2 precursor powders were synthesized using solid state reactions of reagent grade Y2O3, BaCO3, and CuO powder mixtures. The processing conditions for the precursor powders were described in detail in Ref. 5. The mixtures of 211, 011, and 001 precursor powders were ground in an agate mortar and pestle for 1 h per each 10 grams, and bar samples of the powder mixture (approximately 0.3 x 0.1 x 3 cm in dimensions) were pressed in a steel mold. The bar samples were moved up thro
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