Abstract

Considering third- and fourth-order phonon anharmonic interactions terms in the four particle cluster model Hamiltonian proposed by Blinc et al 1982 J Phys C15 4661 for the stochastic motion of 4 H2PO groups for KDP KH2PO4 type ferroelectrics expressions for soft mode frequency and loss tangent are evaluated For the calculations method of double time temperature dependent Green s function has been used By fitting model values of physical quantities the dielectric loss in paraelectric phase of KDP KH2PO4 crystal at 9 2 GHz for field along the a-axis tan a and c-axis tan c have been calculated which compare well with experimental results of Kaminow et al 1963Phy Rev 129 1562 A good agreement has been found In the microwave frequency rage an increase in frequency is followed by an increase in transverse and longitudinal dielectric loss tangent The loss decreases with increase in temperature for KDP KH2PO4 crystal in their paraelectric phase This shows Curie-Weiss type behavior of the dielectric loss tangent