Consideration of Lattice Vibrations in the Incommensurate Phase of Thiourea

Abstract

On the basis of a simple model thermodynamic potential of the Landau-Lifshitz type which reproduces the successive phase transitions—first into an incommensurate phase and then into a commensurate phase—in thiourea, several fundamental aspects of lattice vibrations in the incommensurate phase of this material are clarified. The results are discussed in time relationship with Raman and infrared data so far reported.