Critical Current Densities in Superconducting Y-Ba-Cu-O Prepared by the Quench-and-Melt Growth Technique

Abstract

The critical current characteristic of a Y-Ba-Cu-O specimen prepared by the quench-and-melt growth (QMG) technique was investigated by the ac-inductive method. It was found that there were two kinds of currents. The bulk critical current density is 1.0×10 8 A/m 2 at 77 K and 0.12 T. This value is comparable to a previous estimate from dc-magnetization measurements. The local current density amounts to 3.2×10 10 A/m 2 under the same conditions. Appearance of two kinds of currents seems to be caused by nonsuperconducting second-phase layers formed along the direction of grain growth, which disturb uniform current.