STRUCTURE TRANSITION IN A ZNO GRAIN-BOUNDARY

The structure of a [0001]/31.5 degrees tilt boundary in ZnO has been i nvestigated using high-resolution electron microscopy. In some regions the interface structure is best described by reference to the periodi c dichromatic pattern corresponding to the misorientation [0001]132.5 degrees (Sigma = 13). These regions exhibit arrangements of periodic f acets with localized interfacial dislocations (having primitive Burger s vectors) superimposed upon them. Other regions are better described by reference to the dichromatic pattern corresponding to [0001]/30 deg rees which is periodic parallel to [0001] only. These segments of inte rface are parallel to (<0(1)over bar 10>) and (<11(2)over bar 0>) in t he adjacent crystals and their structure is incommensurate perpendicul ar to [0001]. No localized defects were found in such segments. A mode l is proposed for the progressive structural transition of interfaces in the misorientation range between the two singular values. It is sug gested that the observation presented is a composite of the two struct ural forms, one special and the other more general, corresponding to a n intermediate misorientation.