Critical current density of la 1.85 sr 0.15 cu 1 –y vyo4_ceramics

The Jct value of 89 A cm-2 obtained for the base composition Lai.8sSro.isCu04_j at 7.5 K is greater than previously reported values, indicating a reduced contribution from intergranular weak links. A reduction in observed with increasing vanadium concentration over the range y < 0.05 is considered to be a consequence 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 at a temperature intermediate between 7.5 K and Tc confirms that these ceramics do not exhibit flux lattice melting. The Jct 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 value as the field is increased to 0.5 T. The initial steep drop in the field dependence of Ja is accentuated with increasing vanadium concentration, indicating that the critical field for the penetration of the weak link regions is sensitive to increasing vanadium concentration, in accordance with the known compositional dependence of Hc1 in these ceramics. As the Ja of the vanadium solid solutions all declines to a common limiting value with increasing applied magnetic fields, the weak link contribution to is also considered to be independent of the specific vanadium concentration these solid solutions.