Electrical characterisation of single grain boundaries in DyBa2Cu3Ox ceramics

Single grain boundaries in polycrystalline DyBa2Cu3Ox bulk were isolated. Measurements of their electrical properties show, that they act as Josephson junctions and that their properties can be described by the RSJ model. The current distribution inside the junction is inhomogeneous and there is evidence for small areas with high current density. A model for calculating Ic(T) taking into account a depression of the order parameter Δ at the superconductor insulator interface is introduced. Calculations using a distinct depression of Δ are fitting the experimental data very well. Finally, it is shown that the grain boundaries also exhibit the AC-Josephson effect. (orig.)