Thermal dependent ferroelectric Cochran’s frequency and dielectric properties in arsenate type family of KDP crystal

Abstract

Abstract Phonon anharmonic interactions up to the fourth order, and four body interaction terms, with the consideration of the extra spin-lattice term, direct spin-spin interaction terms, and four spin coupling are introduced into the earlier modified Ising type of pseudo-spin model Hamiltonian to account for the investigation of dielectric properties in arsenate type family of KDP crystals. Cochran’s mode frequency and other ferroelectric properties like energy shift, and width, electrical permittivity, spontaneous polarization, and loss tangent are investigated, in the vicinity of 𝑇𝑐. We have expressed the equation of Dyson and decoupled the correlation function with the consideration of Zubarev’s statistical article and two-time temperature-dependent Green’s function approach to deduct the theoretical derivation of the above ferroelectric parameter. Thermal variations of <𝑆𝑥> and <𝑆𝑧> order parameters are also introduced here, which is responsible for the first-order phase transition phenomenon. A comparison of theoretical findings has been made with experimental findings reported by earlier authors. Good agreement is observed for the investigation of the above ferroelectric properties in CsH2AsO4, RbH2AsO4, and KH2AsO4, crystals.