High-density phases of ZnO: Structural and compressive parameters

Dense ZnO phases, obtained by static compression at room temperature, are s tudied by x-ray diffraction using synchrotron radiation. The initial wurtzi te structure of ZnO is observed to transform to the rocksalt structure at 9 .1 +/- 0.2 GPa with a large volume collapse of 16.7% on increasing pressure . Accurately determined structural and compressive parameters over a large pressure range for both phases are presented. We report the following value s for the null compression bulk moduli and their pressure derivatives: 142. 6 GPa and 3.6 and 202.5 GPa and 3.54, for the: wurtzite and the rocksalt ph ases, respectively. From a comparison between the present results and calcu lated ones, it is inferred that Hartree-Fock calculations yield the best es timation of the compressive parameters in dense ZnO. Furthermore, we show t hat the ideal relationship between the c/a axial ratio and the u oxygen pos itional parameter is preserved as the wurtzite lattice becomes denser while approaching the structural transition pressure. [S0163-1829(98)04945-5].