Contribution of grain boundary planes to superconducting coupling in YBCO.

High-angle grain boundaries are considered to be the main obstacle for curr ent flow in polycrystalline bulk superconductors. In bicrystal YBCO thin fi lms, it has been shown that the current carrying behavior of grain boundari es is strongly dependent on misorientation angles. However, grain boundarie s formed by Liquid Phase Removal Method in bulk YBCO do not show such depen dence, where high-angle grain boundaries are found to be capable of carryin g high currents. To understand the mechanism by which current is carried by these high-angle grain boundaries, we performed TEM studies on two high-an gle boundaries whose Je varied considerably. The misorientation characteris tics and grain boundary planes for these grain boundaries were determined. Using a model developed to correlate grain boundary microstructure and supe rconducting properties, we have shown that the grain boundary planes as wel l as the atomic ordering in the vicinity of the grain boundary play importa nt roles in the current carrying capability of these grain boundaries.