Shock-induced phase transitions among SiC polytypes

A series of recovery experiments was conducted using a propellant single-st age gun on starting materials of both alpha-SiC and beta-SiC. X-ray examina tion on the recovered samples indicated that obvious polytype transformatio ns among 3C, 6H, and 15R took place. To the alpha-SiC starting material, 15 R tends to increase and 6H tends to decrease, while a small amount of alpha -SiC form transforms to 3C type, along with increasing the shock temperatur e and pressure. X-ray diffraction analysis showed that the beta-SiC polytyp e is transformed into rhombohedral forms. From results of both types of SiC samples, rhombohedral polytypes seem to be the favored shock modification. The effects of shock pressure and shock temperature and their heterogeneou s distribution on these polytype transitions are discussed in detail. Analy sis showed that these polytype transitions resulted from the stacking seque nce changes of SiC atom layers. (C) 1998 Kluwer Academic Publishers.