Raman spectroscopy study of the ferrielectric-paraelectric transition in layered CuInP2S6

The dynamics of the ferrielectric-paraelectric transition in lamellar CuInP2S6 is studied using Raman scattering. Band assignments for this system are established by comparison with published vibrational spectroscopy information on related chalcogenophosphates as well as with new data on SnP2S6 herein described. Relaxational rather than resonant behavior is indicated by the temperature dependence of the spectral characteristics, in agreement with the assumed order-disorder character of the transition. It is suggested that a coupling between P2S6 deformation modes and Cu-I vibrations enables the copper hopping motions which lead to the loss of polarity and the onset of ionic conductivity in this material. [S0163-1829(98)05334-X].