Low-angle tilt grain boundaries in YBa₂Cu₃O₇ superconductors

Abstract

The structure of low-angle tilt boundaries in YBa₂Cu₃O₇ superconductors was studied using high-resolution electron microscopy. The boundaries are shown to consist of arrays of triangular defects which have the spacing predicted by the Read-Shockley formula assuming them to be dislocations with a Burgers vector equal to 1·17 nm, the observed closure failure. It is shown that the structure of the dislocation cores changes as the grain boundary tilt angle is increased to 7·5°, starting out with a structure interpreted to be the result of the dissociation of a perfect || dislocation and at 7·5° having dislocation cores with an amorphous appearance. A stacking fault energy is estimated from the images of the dissociated dislocations to be 0·6-0·7 Jm-².