Pressure-induced structural changes in ZnS

We report detailed data on the structural parameters and equations of state of high-density ZnS obtained by x-ray diffraction using synchrotron radiation for pressures below 96 GPa. It is shown that initial room condition phases of ZnS, zinc blende and wurtzite, transform unambiguously to the rocksalt structure at 12 GPa and at room temperature. Our data hence rule out the existence of an intermediate phase of the cinnabar type in ZnS. The initial zinc-blende and wurtzite phases present quantitatively similar equations of state parametrized by B-0 = 79.5 GPa and B'(0) = 4, and B-0 = 80.1 GPa and B'(0) = 4, respectively. As compared to the initial phases, the rocksalt phase, adopted at higher pressure, is denser and less compressible with B-0 = 117.6 GPa and B'(0) = 4. The high-pressure rocksalt structure is also shown to be unstable for pressures in excess of 65 GPa, leading to a transition to the Cmcm structure, an orthorhombic distortion, without a significant change in volume. The occurrence of the Cmcm structure in dense ZnS is inline with the observed dense phases in other zinc chalcogenides.