Secondary grain boundary dislocations in [001] twist boundaries in MgO II. Extrinsic structures

Abstract

Abstract Extrinsic secondary grain boundary dislocation (GBD) structures have been observed by weak-beam transmission electron microscopy in a variety of [001] twist boundaries in MgO. These structures were derived from segments of lattice dislocations embedded in the boundaries and could be interpreted as the result of the decomposition of the lattice dislocations into extrinsic GBDs and the subsequent interaction of the product GBDs with the intrinsic boundary structure. The results demonstrate that lattice dislocations in MgO are attracted to grain boundaries over a wide range of conditions and tend to remain embedded in the boundaries as extrinsic GBD structures. All observations could be rationalized on the basis of the CSL model for grain boundaries in cubic materials and were consistent with the intrinsic boundary structures described in Part I of the present work (Sun and Balluffi 1982). Furthermore, the results were similar in many respects to earlier results obtained with [001] twist boundaries in gold.