The structures of 3 types of Σ = 3 incoherent twin boundary in the β-phase were studied by means of high-resolution electron microscopy and theoretical calculations. The 3 types of Σ = 3 incoherent twin boundary consisted of arrays of structural units which comprised 5-, 6- and 7-membered rings. The types of structural unit cell, and the features of the structural units, changed according to the length or situation of the boundary. At a boundary which was six {111}-planes wide, the array consisted of aligned symmetrical structural units which comprised 5-, 7- and 6-membered rings (in that order) and did not generate a rigid-body translation along the <111> direction. At a boundary which was 18 {111}-planes wide, the array consisted of both symmetrical and asymmetrical structural units; generating a translation along the <111> direction. At the boundary which was about 25nm long and the inclined boundary, the array consists of zigzag or obliquely distributed symmetric structural units. It is known from the tight-binding calculations that the grain-boundary energy becomes lower when the Si site is reconstructed than when the C site is reconstructed. The grain-boundary energy of the asymmetrical structural unit which comprised 5-, 7- or 6-membered rings was lower than that of the symmetrical structural unit. However, the difference between these is small. The observed results of HREM can be explained in terms of the theoretical results.

Experimental and Theoretical Study of Σ=3 Incoherent Twin Boundary in β-SiC. K.Tanaka, M.Kohyama: Philosophical Magazine Letters, 2002, 82[2], 215-29