X-ray diffraction from a SiC crystal undergoing the 3c–6h solid state transformation by non-random microtwinning

Abstract

Recent high resolution electron microscope studies of the 3C-6H transformation in SiC have shown that the transformation occurs by a process of non-random microtwinning. A theoretical model is developed for the transformation assuming that the twin faults occur preferentially at three layer spacings with a probability (β) which is greater than the probability (α) of their occurrence at larger separations. Then a corresponds to the probability of random nucleation of the 6H phase in the 3C matrix and β to the growth of the 6H nuclei. The probability of microtwinning at less than three-layer separations is assumed t o be negligible. On the basis of such a model the X-ray diffraction effects are predicted from a partially transformed crystal. The peak broadening and peak shifts of the 3C and 6H reflections are computed for various values of a and β. The proposed mechanism of transformation can be experimentally verified by recording the intensity profiles from electron diffraction patterns or by single crystal diffractometry of a partially transformed crystal.