Temperature dependence of microwave loss in ADP-type crystals

Abstract

By using four sublattice pseudospin lattice coupled mode model along with third and fourth-order phonon anharmonic interaction terms for ADP-type crystals, expressions for shift, width, renormalized soft mode frequency, dielectric constant and loss have been evaluated. The method of double-time thermal Green's function has been used for calculation. Fitting the values of model parameters in expressions, the temperature dependences of soft mode frequency and loss have been calculated. In the microwave frequency range, an increase in frequency is followed by increase in loss. The loss decreases with increase in temperature for ADP crystal in its paraelectric phase. This shows Curie-Weiss behaviour of the dielectric tangent loss. Theoretical results are compared with experimental results of Nagamiya [Progr Theor Phys, 7 (1952) 275] and Busch, Helv Phys Acta, 11 (1938) 269]. A good agreement has been found.