Abstract
The structures of three types of Σ = 3 incoherent twin boundary in β-SiC were studied by high-resolution electron microscopy (HREM) and theoretical calculations. Three types of Σ = 3 incoherent twin boundary consist of arrays of structural units composed of five-, six- and seven-membered rings, although the kinds of structural unit cell and the features of the structural units change according to the lengths or circumstances of the boundaries. At the boundary six {111} planes wide, the array consists of aligned symmetric structural units composed of five-, seven- and six-membered rings in that order and does not generate a rigid-body translation along the (111) direction. At the boundary 18 {111} planes wide, the array consists of both symmetric and asymmetric structural units, generating a translation along the (111) direction. At the boundary about 25 nm 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 asymmetric structural unit composed of five-seven-six-membered rings is lower than that of the symmetric structural unit; however, the difference between these is small. The observed results of HREM can be explained in terms of the theoretical results.
