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.