Pressure-induced phase transitions in chromium thiospinels

The pressure and temperature dependence of the structure of CoCr₂S₄ and Co_0.65Ni_0.35Cr₂S₄ have been studied by in situ time-of-flight powder neutron diffraction. While the thiospinel CoCr₂S₄ transforms to a defect NiAs-type phase at 1.3 GPa and 800 °C, the nickel-doped thiospinel undergoes this phase change at 0.4 GPa and 750 °C. Quenching of the hexagonal high-temperature and high-pressure phase resulted in a transition to a monoclinic Cr₃S₄ phase, due to the ordering of the metal vacancies in every second layer. Moreover, the spinel CoCr₂S₄ transforms at room temperature and 8.6 GPa to a phase which does not exhibit a NiAs-type structure.