Pressure Induced Phase Transitions in Spinel and Wurtzite Phases of ZnAl2S4Compound

Abstract

ZnAl2S4 single crystals with spinel (α-phase) and wurtzite (w-phase) structures have been studied by Raman spectroscopy under hydrostatic pressures of up to 300 kbar. Significant changes in the phonon spectrum of the α-phase have been observed at the critical pressure of 230 kbar, which are attributed to a reversible phase transition to a denser high-pressure phase, having a similar structure to that of calcium ferrite. In the pressure interval of 180 to 230 kbar, the two phases coexist. The irreversible disappearance of the Raman signal of w-ZnAl2S4 doped by Cd at pressures above 90 kbar was attributed to a phase transition to a rocksalt-type structure. This critical pressure is 40 kbar lower than that in undoped w-ZnAl2S4 and is explained on the basis of crystal structure quality. Different structures were realized upon removing the pressure, depending on the highest pressure previously reached, such as a mixture of wurtzite and spinel phases, a spinel quasi-crystalline structure, or a pressure-induced amorphous phase. The behavior of the quasi-crystalline spinel structure upon repeating the pressure cycle was found to be different from that of the α-phase single crystal.