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

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The resistivity, ρ, and the critical current density at zeroapplied magnetic field, Jc, of ceramic Y1Ba2Cu3O7-δ samples with different average grain size, a (from 5 to14 µm), are reported. These results show that at a given temperatureJc depends only on the specific contact resistance of the average grainboundary junction, ρ□, so that the product Jcρ□is sample independent. The relevance of ρ□ and not of a onJc has been further tested on a subset of samples having very differentaverage grain size but similar ρ□ for which negligiblevariations of Jc are observed.