CRITICAL-CURRENT DENSITY OF LA1.85SR0.15CU1-YVYO4-DELTA CERAMICS

The J(ct) value of 89 A cm(-2) obtained for the base composition La1.8 5ST0.15CUO4-delta at 7.5 K is greater than previously reported values, indicating a reduced contribution from intergranular weak links. A re duction in J(ct) observed with increasing vanadium concentration over the range gamma less than or equal to 0.05 is considered to be a conse quence of the decrease in superconducting transition temperature, from 34 to 20 K, rather than an increase in the weak link contribution the absence of a distinct drop in J(ct) at a temperature intermediate bet ween 7.5 K and T-c confirms that these ceramics do not exhibit flux la ttice melting. The J(ct) of the samples declines steeply, to less than half the zero-field value, when measured in an applied field of 20 mT and thereafter decreases at a very much lower rate to a limiting valu e as the field is increased to 0.5 T. The initial steep drop in the fi eld dependence of J(ct) is accentuated with increasing vanadium concen tration, indicating that the critical field uw for the penetration of the weak link regions is sensitive to increasing vanadium concentratio n, in accordance with the known compositional dependence of H-c1 in th ese ceramics. As the J(ct) of the vanadium solid solutions all decline s to a common limiting value with increasing applied magnetic fields, the weak link contribution to J(ct)(W) is also considered to be indepe ndent of the specific vanadium concentration these solid solutions.