Phase transitions in H-bonded deuterated Rochelle salt crystal

Abstract

The modified two-sublattice pseudospin lattice coupled mode model Hamiltonian is extended by adding third- and fourth-order phonon anharmonic interactions, extra spin–lattice interactions, direct spin–spin interaction and an applied electric field terms considered for the study of deuterated Rochelle salt crystal. The double-time thermal-dependent Green function, Dyson equation and symmetric decoupling scheme have been used to derive the expressions for energy shift, line width, ferroelectric soft mode frequency, dielectric constant, dielectric tangent loss and spontaneous polarization. Model values of various physical parameters are fitted in the obtained expressions; the thermal variations of ferroelectric soft mode frequency, dielectric constant, loss tangent and spontaneous polarization have been calculated for deuterated Rochelle salt crystal. Theoretical results with model values compare well with experimental data reported by others for deuterated Rochelle salt. Our expressions contain all possible interactions as compared to the earlier authors.