Shock compression of 6H polytype SiC to 160 GPa

The Hugoniot compression curve for 6H polytype SiC has been determined to pressures of 160 GPa by a two-stage light-gas gun and an optical method which provides direct measurements of shock velocity and particle velocity of the shock compressed SiC. A phase transition has been detected at 105±{}4 GPa, with a volume reduction of 15±{}3 %. This volume change suggests that the high-pressure phase has sixfold coordination and most probably rocksalt structure. The transition of 6H SiC and the high-pressure behaviors of diamond structure Si and the other polytypes of SiC imply that the post-diamond phase of C may possess a sixfold-coordinated simple-cubic structure as predicted previously by a certain computer calculation.