Pressure-induced phase transition in ferrielectric CuInP2S6

We report the first observation of a pressure-induced phase transition in a lamellar chalcogenophosphate. Raman scattering measurements on the layered ferrielectric CuInP2S6 were performed at pressures of up to 17.5 GPa and room temperature. The recorded spectra indicate the onset of a transition at about 4.0 GPa which is inferred to be first-order. The significantly reduced number of bands observed at high pressure and reversibility of the transition are consistent with the conservation of the lamellar morphology and a possible ABC to AB chalcogen stacking change. A discussion is given of how compression might modify the potential for the off-center cations and the polar state of this material. (C) 1998 Elsevier Science Ltd. All rights reserved.