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

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