Phase transition of ZnO under high pressure and temperature

Pressure induced B4 (wurtzite) -B1(rocksalt) transition of ZnO was investigated by energy dispersive X-ray diffraction method up to 12GPa and 1000°C. The phase boundary between the B4 and B1 phases can be described by a straight line with P/GPa=6.1-0.0012*T/°C. Under non-hydrostatic condition, the phase transition at 27°C is reversible with a large hysteresis about±4.0GPa, and the high pressure phase with the B1 structure is unquenchable at ambient condition. On the other hand, the B1 type high pressure phase is quenchable under hydrostatic condition. The unit cell parameter of the B1 phase at 0.1MPa and 27°C is determined to be a=4.2783(3)Å. Bulk moduli of the B4 and B1 phases at 27°C are determined to be 128.4±0.9GPa and 197±3GPa, respectively. Furthermore, an anisotropic compression behavior of the B4 type ZnO is observed, in which the c axis of the B4 type structure is slightly more compressible than that of the a axis.