Pressure-induced phase transition in SiC

X-ray diffraction studies have been made of cubic (3C) and hexagonal (6H) polytypes of SiC under pressures to 105 and 95 GPa, respectively, using a diamond-anvil cell and an imaging plate technique. 3C-SiC undergoes a phase transition into the rocksalt-type structure at 100 GPa or higher accompanied by a volume reduction of 20.3%. The 6H polytype of SiC remains stable to the highest pressure studied, with a premonition of a phase transition above 90 GPa. Equation-of-state data for the two polytypes have been found to be essentially the same to 95 GPa, yielding the bulk modulus 260(9) GPa and its pressure derivative 2.9(0.3).