Intermediate transformation structures in silicon carbide

SUMMARY In order to examine the detailed structural origins of the confusing diffraction patterns often exhibited by partially transformed polytypic materials, HREM lattice imaging techniques have been used to examine directly the layer‐by‐layer stacking sequences in a range of samples of cubic (β) SiC partially transformed to α polytypes by high temperature annealing. A number of intermediate structures have been characterized, one of which provides the first direct evidence supporting an earlier model of the β→α transformation (Jagodzinski, 1971) in which three‐layer twins, separated by multiples of three layers, propagate through the cubic structure to produce a faulted haxagonal (6H) polytype. These observations, together with considerations of twin geometry, also suggest a means of co‐ordinating the sideways nucleation of 6H unit‐cell high steps, whose lengthways growth has been previously observed to effect the solid‐state β→α transformation (Jepps & Page, 1979).