Twin boundaries parallel to the common-{111} plane in spinel

The structure of first-order twin boundaries in Mg-Al spinel has been examined using high-resolution transmission electron microscopy. Comparison of experimental images with computer calculated images of model twin boundaries, obtained using a multislice image simulation program, allow different twin structures to be identified. In addition to the interfaces which preserve the cation molarity ratio, it is shown that interfaces occur which do not intrinsically preserve the composition and which probably involve local cation rearrangement during their formation. Such observations thus emphasize the role of cation rearrangement at an internal interface in a ceramic material and suggests that such rearrangement permits formation of otherwise unstable configurations. © 1987 Taylor & Francis Group, LLC.