Relaxation processes and ultrasonic attenuation in KDP type ferroelectrics

Abstract

The anharmonic four - particle cluster model Hamiltonian for stochastic motion H2PO4 - of groups has been used to study the physical properties of KDP type ferroelectrics. Using Green’s function method and Dyson’s equation the renormalized frequency of the coupled system and collective wave half width have been evaluated with the help of model Hamiltonian by considering the anharmonicity upto fourth order. The higher order correlations have been decoupled using symmetric decoupling scheme at the later stage after applying the Dyson’s treatment and have been evaluated using the renormalized Hamiltonian. The relaxational behaviour and ultrasonic attenuation have been related to the width of collective mode. The temperature dependence of ultrasonic attenuation coefficient, dielectric constant and loss tangent has been discussed in terms of a relaxational soft mode.