Hrem analysis of a cubic-hexagonal (ZrB-ZrB2) interface using the coincidence approach

The structure of a cubic-hexagonal ZrB-ZrB2 interface has been investigated using high resolution electron microscopy and image processing. The interface is in an unusual and complex orientation relationship with an exact parallelism of the (01 (1) over bar)(ZrB),(0001)(ZrB2) planes and a misorientation of 3 degrees between the (111)(ZrB) and (1 (1) over bar 00)(ZrB2), planes. Apparently flat al a low magnification, the mean plane of the interface is lying parallel to a high index plane for the two crystals. A structural analysis al an atomic scale of the interface reveals that the interface is in fact built up over two types of facets, one is characterised by a low atomic density and a small misfit whereas the other one is characterised by a high atomic density and a large misfit. An analysis based on the coincidence approach relates the complex structure of this interface to an energetically favourable configuration due to a compromise between elastic strain minimisation and misfit accommodation. (C) 1997 Acta Metallurgica Inc.