POLYTYPE DISTRIBUTION IN SILICON-CARBIDE

Silicon carbide is a candidate material for high-performance applications. It exists as a composite of many structurally distinct but related polytypes with differing physical properties. It is well known, for example, that the flexural strength of formed SiC composites is strongly dependent on the relative amounts of the various polytypes present in the composite. X-ray powder diffraction is the method of choice to determine polytype distribution. Each of the SiC polytypes gives a unique diffraction pattern; unfortunately, the patterns for the various polytypes superimpose in part, making interpretation difficult. The authors have developed a method to separate the superimposed patterns to give quantitative information on the distribution of the polytypes in the composite. This approach provides a useful tool in relating preparation conditions to performance properties.