Orthorhombic Intermediate State in the Zinc Blende to Rocksalt Transformation Path of SiC at High Pressure

The mechanism of the $B3/B1$ phase transition of SiC has been investigated by periodic LCAO-DFT least-enthalpy calculations. A new transformation pathway, based on a $\mathrm{Pmm}2$ orthorhombic intermediate state with two SiC units per cell, is found to be energetically favored over the traditional $R3m$ mechanism. The computed activation enthalpy is 0.75 eV/SiC unit at the predicted transition pressure of 92 GPa ( $B3\mathrm{LYP}$ functional). Activation enthalpy and activation volume vs pressure are analyzed to characterize the kinetic aspects of the transformation.