Ab initiosimulations of the structural phase transformation of2H‐SiCat high pressure

Abstract

We study the pressure-induced phase transition in the $2H\text{\penalty1000-\hskip0pt}\mathrm{Si}\mathrm{C}$ (wurtzite) using a constant-pressure ab initio technique. A first-order phase transition from the wurtzite structure to a rocksalt structure at $600.0--700.0\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ is predicted in the constant-pressure simulations. The transformation consists of two successive processes. First, the wurtzite crystal transforms into a fivefold coordinated hexagonal structure with space group $P{6}_{3}∕mmc$ due to a compression in the direction of the $c$ axis. Second, the hexagonal phase becomes unstable with respect to shear deformation and converts to first a fivefold coordinated orthorhombic intermediate state within the $Cmcm$ symmetry, and then a rocksalt state. We also study the wurtzite-to-rocksalt and zinc-blende-to-rocksalt phase transformations of SiC from the enthalpy calculations and find that both zinc-blende and wurtzite SiC polytypes show nearly similar equation of state and transforms to a rocksalt structure about $100.0\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, in excellent agreement with experiments.