Doping dependence of the critical current and irreversibility field inY1−xCaxBa2Cu3O7−δ

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Critical current measurements were made on thin films ofY Ba2Cu3O7−δ and Y0.8Ca0.2Ba2Cu3O7−δ produced by sol–gel and pulsed laser deposition, respectively. Both sampleshave high critical currents at low temperatures and the critical current,Jc, is largest inthe overdoped Y0.8Ca0.2Ba2Cu3O7−δ thin film. Annealing studies show a large increase inJc with increasing hole concentration and suggests that the maximumJc should occur for overdoped samples. The very overdoped region of thesuperconducting phase diagram was probed by studying bulk ceramicY0.8Ca0.2Ba2Cu3O7−δ samples, where it was found that the irreversibility field systematically increaseswith increasing hole concentration when scaled by the reduced temperature(τ = (1−T/Tc)).