Critical current density versus normal-state resistivity in granular high-temperature superconductors with different average grain size

The resistivity, rho, and the critical current density at zero applied magnetic field, J(c), of ceramic Y1Ba2Cu3O7-delta samples with different average grain size, a (from 5 to 14 mu m), are reported. These results show that at a given temperature J(c) depends only on the specific contact resistance of the average grain boundary junction, rho square, so that the product J(c)rho square is sample independent. The relevance of rho square and not of a on J(c) has been further tested on a subset of samples having very different average grain size but similar rho square for which negligible variations of J(c) are observed.