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

A homogeneous wurtzite-to-rocksalt phase transformation in 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 SiC and GaN. SiC, 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 SiC, GaN, and AlN occur for roughly the same value of the enthalpy barrier. In contrast, 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.