Unconventional superconducting granularity of the Y1-xPrxBa2Cu3O7-δ compound

We report on fluctuation magnetoconductivity and magnetic irreversibility of Y1-xPrxBa2Cu3O7-delta single crystals and a polycrystalline sample. Although our samples are all single phase (orthorhombic) and the single crystals show no sign of structural inhomogeneity, all the samples exhibit two close and sharp genuine superconducting transitions. On the other hand, while the resistive transition of the polycrystalline sample exhibits in addition a coherence transition characteristic of a granular superconductor and the magnetic irreversibility displays the signature of the intergrain flux dynamics, the single crystals show no sign of these features. In view of these facts, we conclude that the well characterized split superconducting transition must result from a peculiar phase separation related with oxygen doping.