Atomic and electronic structure analysis of Σ = 3 incoherent twin boundaries in β-SiC

The structures of Σ = 3 incoherent twin boundaries in β-SiC were studied by high-resolution electron microscopy (HREM), electron energy-loss spectroscopy (EELS), and theoretical calculation. Especially, the existence of the variety of structures of Σ = 3 incoherent twin boundaries was found by HREM. All the observed Σ = 3 incoherent twin boundaries consist of arrays of structural units composed of five-, six-, and seven-membered rings, although the kinds or features of structural units change according to the lengths or circumstances of the boundaries. It is shown from the tight-binding calculations that the grain boundary energy becomes lower when the reconstructed 〈011〉 bonds are occupied by Si-Si bonds than C-C bonds. The grain boundary energy of the symmetrical structural unit composed of five-seven-six-membered rings is lower than that of the asymmetric one, however, the difference between those is small. EELS analysis indicated that C atoms exist at grain boundaries on the similar condition of grain interior. The observed results of HREM and EELS can be explained by the theoretical results.