CORRELATION OF CRITICAL CURRENT DENSITY WITH Cu3+ CONCENTRATION AND DENSITY IN YBa2Cu3O7−x

Abstract

Superconducting YBa 2 Cu 3 O 7 wires and tapes were fabricated by cold drawing, rolling and extrusion processes. It was found that the critical current density, after O 2 equilibration, correlates both with density and Cu 3+ concentration. Full density was achieved by using a special heat treatment, but the critical current density was low owing to the low Cu 3+ concentration present in this heavily twinned material. The best critical current density results were obtained for material with density of 92–95% of the theoretical value. The low critical current density of the porous specimens is attributed not only to a poor connectivity between grains but also to a low Cu 3+ concentration due to the instability of Cu 3+ at crystallite surfaces which increase in area with specimen porosity.