Grain boundary structure in hexagonal materials

The structure of grain boundaries in hexagonal materials has been studied using transmission electron microscopy. On the basis of these observations, boundaries are classified as low-angle, special or general. Low-angle boundaries are composed of crystal dislocation networks, similar to observations in materials exhibiting other crystal symmetries. Special boundaries contained interfacial dislocation networks accommodating deviations from singular reference structures. Evidence that reference structures are based on 3-D, 2-D and 1-D periodic configurations has been obtained, but further work is required on this topic. An observation of a transition between two structural forms which are characteristic of 3-D and 1-D reference structures is also presented. In the 1-D case, the interfacial structure is incommensurate in one direction, and hence resembles a general boundary in some respects.