The structure of low-angle tilt boundaries in YBa2Cu3O7 superconductors was studied using high-resolution electron microscopy. The boundaries were shown to consist of arrays of triangular defects which had the spacing predicted by the Read-Shockley formula, assuming them to be dislocations having a Burgers vector equal to 1.17nm; the observed closure failure. It was shown that the structure of the dislocation cores changed as the grain-boundary tilt angle was increased to 7·5°. Starting with a structure that was interpreted as being the result of the dissociation of a perfect |c| dislocation and, at 7.5°, having dislocation cores with an amorphous appearance. The stacking-fault energy was estimated, from the images of dissociated dislocations, to be 600 to 700mJ/m2.

Low-Angle Tilt Grain Boundaries in YBa2Cu3O7 Superconductors. M.F.C.Hisholm, D.A.Smith: Philosophical Magazine A, 1989, 59[2], 181-97