Measurements of misorientation angles over a large distance in strongly coupled grain boundaries

Grain boundaries in polycrystalline melt-textured YBCO samples fabricated by the liquid phase removal method have been analyzed by transmission electron microscopy (TEM). These samples contain a number of grains separated by high-angle grain boundaries with lengths up to several millimeters and J/sub c/ values up to 18000 A/cm/sup 2/ at 77 K. The results of TEM studies show that the high misorientation angles of these boundaries are maintained over a large distance by certain intra-grain features such as platelet boundaries and low-angle grain boundaries. Measurements on adjacent platelets as well as at locations inside single grains show that the presence of these boundaries maintains the misorientation of the high-angle grain boundary in these samples within 6 degrees. This indicates that high-angle grain boundaries in these samples do not dissociate into low-angle grain boundaries and the high superconducting current is carried by the entire length of the boundary.