TRANSMISSION ELECTRON-MICROSCOPY STUDIES OF LOW-ANGLE GRAIN-BOUNDARY INTERACTIONS IN MELT-TEXTURED YBA2CU3O7-X

The low-angle grain boundaries and their intersections in melt-texture d YBa2Cu3O7-x have been characterized by TEM. Grain boundaries are fou nd to contain both tilt and twist components and consist of dislocatio n arrays, These boundaries are also observed to interact and at the re gions of interaction the ab-planes alignment of the grains is maintain ed by varying the values and directions of the twist and tilt angles, and is also accompanied by changes in the grain boundary plane. These changes seem to influence the effectiveness of pinning of grain bounda ry dislocations. The dislocation structure of these grain boundaries i s discussed in connection with their possible coupling properties. Bas ed on this analysis, most of these boundaries are found to be strongly coupled, but short pieces of these boundaries can be weakly coupled. However, the influence of these pieces on the J(c) of the total bounda ry is negligible.