Polytypes in SiC

Figure 1.6 The three most common polytypes in SiC viewed in the [1120] plane. From left to right, 4H-SiC, 6H-SiC, and 3C-SiC k and h denote crystal symmetry points that are cubic and hexagonal, respectively.

Up to now, more than 140 SiC polytypes have been reported, but their number seems to be unlimited. Improvements in structural analysis have revealed new polytypes that differ from each other by the number of layers and order in the unit cell. For instance, polytype 1200R has parameter c = 301.56 nm. It is found that the presence of different polytypes in SiC and other materials is caused by solid-state transformations caused by internal and external sources of strain. Phase transformations of this type are observed for many types of matter, and as shown by investigations polytypism is comparatively widely distributed in nature. The most important physical-chemical parameters of the main SiC polytype structures are shown in Table 1. It is clearly seen from the table that there is a linear correlation with the hexagonality for most of the parameters. 

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