Thermal-Dependent Ferroelectric Cochran’s Frequency and Dielectric Properties in Arsenate-Type Family of KDP Crystal

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 in the earlier modified Ising type of pseudospin 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 theoretically in the vicinity of $T_{c}$. We have expressed the equation of Dyson and decoupled the correlation function with the consideration of Zuberav’s statistical article and two-time temperature-dependent Green’s function approach to deduce the theoretical derivation of the above ferroelectric parameter. The thermal variations of the order parameters $\left\langle {S^{x} } \right\rangle$ and $\left\langle {S^{z} } \right\rangle$ that characterize the first-order phase transition phenomenon are also introduced. A comparison of the theoretical findings has been made with the experimental findings reported by earlier authors. Good agreement is observed for the above-mentioned ferroelectric properties in CsH₂AsO₄, RbH₂AsO₄, and KH₂AsO₄ crystals.