Correlation of grain boundary defect structure with boundary orientation in Ba2YCu3O7−x

Abstract

Correlations between observed defect structures and the orientation of planes involved in grain boundary formation in single phase, nearly ideal density Ba₂YCu₃O_7−x are presented. Three types of grain boundary structures are observed: (1) coherent boundaries with only a low‐energy network of dislocations at the interface, which are associated with boundaries not involving a basal plane face, (2) semicoherent boundaries surrounded by a 50–1500 Å wide band of dislocation loops on the c‐axis side of the basal‐plane‐faced boundary, and (3) incoherent boundaries where severe local strain has produced substantial plastic deformation and generation of small voids, again associated with basal‐plane‐faced boundaries. These results are interpreted using a model for local stress based on the known highly anisotropic thermal contraction of the material during cooling from sintering temperatures.