EVOLUTION OF DISORDERING IN SIC UPON SINTERING - PHASE-ANALYSIS OF SIC BY RIETVELD METHOD WITH APPLICATION OF NEUTRON AND X-RAY-DIFFRACTION

Neutron and X-ray diffraction patterns of a and 6 powders as well as of sintered SiC were analysed by a multiphase Rietveld method. It is shown that structural models combined of large period polytypes can be used to approximate the disordering of these polytype structures. The hexagonality of the samples could be terminated with reproducibility 1-2% using different combinations of large-period polytypes. It follows that the usual classification into alpha and beta SiC is an oversimplification. The polytype behaviour of SiC powders and the role of twinning of cubic layer stackings is discussed. Distribution functions of stacking sequences of different length in a and phases are derived.