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

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 ofB1-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.

Ab initio molecular dynamics simulation of a pressure induced zinc blende to rocksalt phase transition in SiC

The high-pressure induced phase transformation from the zinc blende to rocksalt structure in SiC has been studied by the ab initio molecular dynamics method. The simulations showed that SiC passes through a tetragonal intermediate state before transforming to a monoclinic phase at 160 GPa. The mechanism for this phase transformation agrees well with recent ab initio MD simulations, in which the applied pressure was as high as ∼600 GPa, but in the present study the transformation occurs at much lower pressure.

Universal transition state for high-pressure zinc blende to rocksalt phase transitions

First-principles density functional calculations show that the high-pressure transitions of different semiconductors from zinc blende to rocksalt go through a transition state, which is universal in the sense that its position along the path and the corresponding geometry is independent of the chemical components of the semiconductor. This is explained using a Landau-like model expansion of the free energy in cosine functions of atomic position.