Osamu Izumi

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

Superconducting properties of Y-Ba-Cu-O compounds were investigated in relation to precipitation of second phases. Contour lines of Jc, Tc and diamagnetic signal intensities were presented in the YO1.5-BaO-CuO system. These superconducting properties decreased steeply with BaCuO2 precipitation, and the maximum Jc 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-Jc sample.

Superconductivity and Microstructural Observation of Er0.5Y0.5Ba2Cu3O7-y

The critical current density, Jc, of Er0.5Y0.5Ba2Cu3O7-y was investigated in relation to its microstructure. An increase was observed in the Jc of a sintered sample prepared from a mixture of YBa2Cu3O7-y and ErBa2Cu3O7-y with sintering time of up to 10 h at 930°C. The insufficiently sintered sample had a BaCuO2 network in the grain boundaries possibly caused by partial melting of the 1:2:3 compounds. This phase disappeared with increased sintering time, which relates to an endothermic reaction. It is considered that the increase in Jc is due to an increase in the degree of sintering and to the disappearance of the highly resistive phase from the grain boundary.