First-principles study of the wurtzite-to-rocksalt phase transition in zinc oxide

Wurtzite (B4) compounds commonly undergo a structural transition to the rocksalt (B1) phase under high pressure. The underlying transition mechanism, or the so-called transition path, has been extensively investigated in recent years. Two different transition paths have been proposed for the B4-B1 phase transition, that is the 'hexagonal' path and the 'tetragonal' path. In this work, taking zinc oxide (ZnO) as an example, we have made a comparative study of these two paths from first-principles. The calculated results lead to the conclusion that the tetragonal path is more favourable under lower pressure but the hexagonal path is more favourable under higher pressure, which indicates a competition between these two paths in the ZnO case. We have also investigated the evolution of structural and electronic properties along the two different paths; the axial ratio c/a is suggested as a good indicator in experiments to identify the transition path.