Grain boundaries in bulk YBCO

The problem of grain boundaries in high temperature superconductors is very important in determining the ability of these materials to carry supercurr ent. The success of fabricating polycrystalline bulk YBCO with high-angle g rain boundaries carrying high critical currents initiated microstructural s tudies of these boundaries in order to determine mechanism of current flow across them. TEM studies have been performed on grain boundaries with known J(c), followed by simulation of their atomic and electron structures as we ll as estimations of their superconducting order parameter. Using a model d eveloped to correlate grain boundary microstructure and superconducting pro perties, we have shown that coupling behavior of grain boundaries does not depend on misorientation characteristics alone. The grain boundary plane as well as the atomic ordering in the vicinity of grain boundary play an impo rtant role in the current carrying capabilities of these grain boundaries.