Doping Dependence of the Critical Current and Irreversibility Field in   Y1-xCaxBa2Cu3O7-delta
  Critical current measurements were made on thin films of YBa2Cu3O7-delta and Y0.8Ca0.2Ba2Cu3O7-delta produced by sol-gel and pulsed laser deposition, respectively. Both samples have high critical currents at low temperatures and the critical current, Jc, is largest in the overdoped Y0.8Ca0.2Ba2Cu3O7-delta thin film. Annealing studies show a large increase in Jc with increasing hole concentration and suggests that the maximum Jc should occur for overdoped samples. The very overdoped region of the superconducting phase diagram was probed by studying bulk ceramic Y0.8Ca0.2Ba2Cu3O7-delta samples, where it was found that the irreversibility field systematically increases with increasing hole concentration when scaled by the reduced temperature (t = (1 - T/Tc)). 
Anita Semwal, N. M. Strickland, A. Bubendorfer, S. H. Naqib, Swee Kuan   Goh, G. V. M.Williams