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

Grain boundaries in polycrystalline melt-textured YBCO samples fabricated b y the Liquid Phase Removal Method have been analyzed by Transmission Electr on Microscopy (TEM). These samples contain a number of grains separated by high-angle grain boundaries with lengths up to several millimeters and Je v alues up to 18 000 A/cm(2) at 77 K, The results of TEM studies show that th e high misorientation angles of these boundaries are maintained over a larg e distance by certain intra-grain features such as platelet boundaries and low-angle grain boundaries. Measurements on adjacent platelets as well as a t locations inside single grains show that the presence of these boundaries maintains the misorientation of the high-angle grain boundary in these sam ples within 6 degrees. This indicates that high-angle grain boundaries in t hese samples do not dissociate into low-angle grain boundaries and the high superconducting current is carried by the entire length of the boundary.