Phase Compatibility and Superconductivity of Y-Ba-Cu-O Compounds

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Superconducting properties of Y-Ba-Cu-O compounds were investigated in relation to precipitation of second phases. Contour lines of J c, T c and diamagnetic signal intensities were presented in the YO1.5-BaO-CuO system. These superconducting properties decreased steeply with BaCuO2 precipitation, and the maximum J c was obtained in the yttrium-rich composition of Y1.2Ba2Cu3O7-y . It is considered, therefore, that the BaCuO2 precipitating around the YBa2Cu3O7-y grains interrupt the superconducting current pass at the grain boundary. Yttrium-rich composition, which inhibits BaCuO2 precipitation, is effective for the preparation of the high-J c sample.