High-resolution transmission electron microscopy was used to study the atomic structure of a  = 7 grain boundary. This boundary had a misorientation of [01•1]/180. The grain boundary plane was (01•2)1||(01•2)2. Four possible unrelaxed grain boundary structures could be constructed from the constrained coincidence-site lattice patterns. The atomic structure of the boundary was deduced from a through-focus series of high-resolution images and computer image simulations. A DSC dislocation in the  = 7 grain boundary was identified. The Burgers vector of this dislocation was 1/14[05•2], and it was a pure edge dislocation. Most of the boundary had a structure which comprised O terminating layers with an identical width of 0.135nm. This was referred to as the -domain. There were no unsaturated Al-O bonds in the boundary core of the  domain, but the Al-O bonds were slightly elongated. The coexistence of 2 interfacial domains,  and , was observed. The  domain had the same atomic structure as that of the  domain, but the width of the interfacial layers was 0.17nm. These 2 interfacial structures produced differing contrasts in high-resolution images, and were separated by partial DSC dislocations in the  = 7 (01•2) grain boundary. The Burgers vector of the partial-DSC dislocations could be determined by reference to the interfacial structures, constrained coincidence-site patterns, step vector and closure failure of the Burgers circuit. The partial-DSC dislocations in the  = 7 (01•2) grain boundary always appeared as a pair which resembled a stacking fault in the bulk of the crystal.

F.R.Chen, C.C.Chu, J.Y.Wang, L.Chang: Philosophical Magazine A, 1995, 72[3], 529-44