Stacking fault energy and planar defects on the basal plane in the beta-alumina system

Commercial forms of beta alumina have been examined using transmission electron microscopy. Measurements of the stacking fault energy on the basal plane have been made from the separation of partial dislocations and the equilibrium separation of partials at dislocation nodes, and estimated as 0.6 to 1.65×10^–3 Jm^–2. The structure of two- and three-block beta-alumina has been discussed and their relationship and transformation examined. It has been shown that transformation from two- to three-block beta-alumina cannot be accomplished by a simple shear. Structures generated by the passage of partial dislocations on the glide plane are discussed, and simple twining on the basal plane is examined and shown to be possible in the three-block, but not in the two-block material.