New phase boundary and high-pressure thermoelasticity of ZnO

The phase transition of zinc oxide from B4 (hexagonal wurtzite structure) to B1 (cubic rocksalt structure) has been studied by energy-dispersive powder diffraction technique up to 11 GPa and 1273 K. Analysis of equation-of state (PVT) data for the rocksalt phase yields precise values Bf the bulk modulus and its temperature derivative. The previously accepted P-T phase diagram is shown to be incorrect. It is established that the B1 phase is not recoverable. The equilibrium transition pressure of the B4-to-B1 transformation is near 6 GPa (at ambient temperature) and the dP/dT lope close to zero. These new results are confirmed by using simultaneously three other different types of experiment (imaging, ultrasonic and X-ray, diffraction studies on single-crystal specimens).