Transport critical currents in field-oriented Y1Ba2Cu3Oy polycrystals

Abstract

Field-orientedY1Ba2Cu3Oy samples with various values of the transport critical current density, Jc, have been prepared with various heat treatments. The Jc increased rapidly with an increase in relative sintered density of the oriented samples. The field-oriented samples with higher Jc had grains of larger sizes and better connections between the neighboring grains than the low Jc samples. The maximum values of Jc at a magnetic field of 7 T were 370 A/cm2 at 4.2 K and 24 A/cm2 at 77 K. The hysteresis in the Jc-H curves at 4.2 K decreased with an increase in Jc both for an applied field H∥ab plane and for H∥c axis. The critical currents of the samples with higher Jc were less degraded by aging in the air for 1 year than those of the low Jc samples. The relation between the field-cooled Jc-H curves and the zero-field-cooled ones for an oriented sample with low Jc is qualitatively interpreted by the effect of the intragrain currents on the intergrain fields.