The characteristics of twins in polycrystals were investigated by using transmission electron microscopy. A simple wedge-shaped twin structure was observed and this was attributed to an absence of volume-change during the cubic to rhombohedral phase transition. In these polycrystals, (100) twins rather than (110) twins predominated; as in single crystals. In order to explain the origin of the predominance of (100) twins, strain tensors for the 2 twin geometries were calculated with the aid of phenomenological crystallography theory. It was found that the (100) twin had a lower strain after the transition than did the (110) twin. This confirmed that the (100) twin was more energetically favorable than the (110) twin.

Ferroelastic Twins in LaAlO3 Polycrystals. C.H.Kim, J.W.Jang, S.Y.Cho, I.T.Kim, K.S.Hong: Physica B, 1999, 262[3-4], 438-43