Phase Relationship between 3C‐ and 6H‐Silicon Carbide at High Pressure and High Temperature

The phase relationship between 3C‐ and 6H‐SiC is investigated in the pressure range 2.5–6.5 GPa and the temperature range 400°–2500°C, by analyzing recovered samples, using X‐ray diffractometry and Raman‐scattering techniques. The phase transition from 3C‐ to 6H‐SiC occurs at 2200°C and 2.5 GPa. In the pressure range >4.5 GPa, 6H‐SiC transforms to 3C‐SiC at 2500°C, via an intermediate state, as indicated by broadening peaks in the X‐ray diffraction profile. Thermodynamically, 3C‐SiC appears to be the low‐temperature stable form, and the temperature of transition to 6H‐SiC, which is stable at high temperature, appears to increase with pressure.