A high-resolution transmission electron microscopic study was made of a 45 [100] twist grain boundary in a bi-crystalline specimen. This provided experimental evidence that the structure of quasi-periodic grain boundaries was controlled by the local atomic environment which existed at the boundary. The boundary which was investigated revealed certain special locations at which the local atomic environment favored step formation. These special locations were attributed to the existence of a dissimilar planar stacking, between (02¯2)1 and (020)2, across the boundary. This dissimilarity in stacking permitted the boundary to exhibit a close correspondence, for (02¯2)1 and (020)2, when the stacking ratio of the 2 planes approached 2. The boundary appeared to de-stabilize at such locations and to form steps in order to relax its structure.

M.Shamsuzzoha, P.A.Deymier, D.J.Smith: Scripta Materialia, 1996, 35[3], 327-31