Temperature-induced phase transitions in the rock-salt type SiC: A first-principles study.

The phase transitions in the rock-salt type SiC (B1-SiC) under decompression are studied in the framework of first-principles molecular dynamics simulations up to room temperature. The transformation pathways were determined based on an analysis of the symmetry and phonon spectra of high-symmetry transient structures identified in the simulations. The plausible pathways of the transformation of B1-SiC into the 3C-, 2H-, 4H-, 12R-SiC polytypes were suggested. The transformation paths were found to depend on both the availability of soft phonon modes in an unreconstructed phase and the initial conditions of the simulation. It is shown that an increase in cell volume at decompression leads to the condensation of a certain phonon mode. As a result, an intermediate state forms due to the atomic displacements and to subsequent strains related to this mode. All the decompressed structures were compressed back under pressure of 120-250 GPa depending on the type of the decompressed phase and simulation temperature that was in the range of 300-1200 K. The suggested scheme of structural identification can be used to determine the transition paths for the structural transformations of other similar structures under pressure.