ON THE LIMITING FACTORS OF THE CRITICAL CURRENT-DENSITY IN HIGH-TC SUPERCONDUCTING CERAMICS

The temperature dependence of the critical current density at high temperatures and in weak applied magnetic field for YBa2Cu3O7-y ceramic samples with a pronounced granular character is analyzed. The experimental results can be explained in terms of thermally activated motion of the intergrain Josephson vortices at grain boundaries, which may be an indication that the actual limiting factor for the critical current density in ceramic samples results from a weak pinning force density for the intergrain vortices rather than from the weak-link quenching.