First-principles study of the wurtzite-to-rocksalt homogeneous transformation inZnO: A case of a low-transformation barrier

A homogeneous wurtzite-to-rocksalt phase transformation in $\mathrm{ZnO}$ is studied using a first-principles pseudopotential method. The calculated transformation enthalpy barrier at the phase equilibrium transition pressure is much lower than the barriers previously studied in $\mathrm{SiC}$ and $\mathrm{GaN}$. $\mathrm{SiC}$, $\mathrm{GaN}$, and AlN are found experimentally to transform at a pressure significantly higher than their respective phase equilibrium transition pressures. Interestingly we note that the experimentally observed transition pressure in $\mathrm{SiC}$, $\mathrm{GaN}$, and AlN occur for roughly the same value of the enthalpy barrier. In contrast, $\mathrm{ZnO}$ readily transforms at the phase equilibrium transition pressure consistent with the fact that its enthalpy barrier at that pressure is well below this critical barrier value.