Grain boundary weak links in high-Tc superconductors

In this paper the transport critical current density (Jc) for high-Tc thin films, bicrystals, and bulk ceramics is shown to be determined by magnetic field penetration into the grain boundaries. The gross grain orientations may not in all cases be an important factor in determining this penetration. The parameter λG/λ J)2 can characterize the strength of the grain boundary coupling, which depends mainly on the crystal coherence and connectivity at the boundary area