X-ray diffraction and transmission electron microscopy study of extremely large-period polytypes in SiC

Extremely large-period polytypes in SiC have been investigated by single-crystal X-ray diffraction and direct lattice imaging by electron microscopy, which has been found to be a more suitable technique for studying structures of extremely large periodicities. Some crystals giving rise to a diffuse streaking along h0.l reciprocal lattice rows when studied by X-ray diffraction, showed the presence of extremely long- period polytypes when investigated by electron microscopy. The c periodicity of such SiC structures (having periodicities of more than 1000 Å) has been determined by this technique and the super-period block spacing is found to contain block spacings of 6H, 15R, 4H and 21R polytypes.