Study of Ferroelectric Phase Transitions in the Rochelle Salt with the Pseudo-Spin-Lattice Coupled Mode Model

Abstract

Statistical Green's function theory has been successfully applied to study the ferroelectric phase transitions in the Rochelle Salt and its deuterated form with two sub-lattice pseudo-spin model containing spin-phonon interaction terms. The Blinc-de Gennes model parameters have been calculated for both of the salts. A phenomenological explanation of the isotope and the impurity dependence of the transition temperatures has also been sought from our calculations. The origin of non-logarithmic behaviour of the heat capacity has been attributed to the strong proton-phonon and anharmonic interactions. Finally, renormalized phonon frequency and the temperature dependence of the soft mode frequency have been studied theoretically. The present study suggests that phase transitions for the Rochelle Salt and its deuterated variety can be understood by a displacive mechanism.