Raman scattering study of pressure-induced phase transitions in MIn2S4 spinels

MIn2S4 (M = Mn, Cd, Mg) spinels were investigated by Raman scattering spectroscopy under hydrostatic pressure up to 20 GPa. These compounds were found to undergo a reversible phase transition to a kaman-inactive defect NaCl-type structure. Transition pressures of 7.2, 9.3, and 12 GPa were found for M = Mn, Cd, and Mg, respectively. From the analysis of the pressure behaviour of Raman-active modes, it was concluded that the phase transition from spinel to NaCl-type structure is direct in MnIn2S4 and CdIn2S4, while it occurs via an intermediate LiVO2-type NaCl superstructure in MgIn2S4. The observed differences in pressure and path of the pressure-induced phase transition between these indium sulphide spinels are discussed.