Possible Existence of Intrinsic Geometrical Boundaries for the Critical Currents inside YBa2Cu307-δ

The irreversible magnetization of YBa2Cu307-δ crystals of different sizes have been measured and compared to other results published in the literature. We conclude that even the superconducting crystals contain normal barriers or weak links which strongly limit the spatial scale of supercurrents. These barriers are not the twin boundaries but could be related to a possible secondary decomposition of the off-stoichiometric crystals in high and low oxygen concentration regions. Supercurrents of about 4.106 A/cm2 at 4 K would be contained inside regions into the crystals having a perimeter of about 1 mm if the Beam model can be applied