Structural and electronic properties of ZnO under high pressure

We theoretically study the electronic properties and pressure-induced solid-solid phase transitions of ZnO by using the first-principles pseudopotential method. The wurtzite (B4), rocksalt (B1), zinc blende (B3) and CsCl (B2) crystal structures of ZnO have been considered. It has been shown that the B3 phase is not a stable phase in ZnO over the pressure range of 0-300 GPa. The sequence of these phases is B4 → B1 → B2 with the transition pressure is found to be 8.8 and 263 GPa, respectively. The detailed volume changes during the phase transformation were analyzed. Moreover, the analysis of the electronic properties indicates that the bandgap of B4-ZnO is direct, while B1 and B2 phases become indirect under high pressure. The mechanism of these changes of band structures was analyzed.