Microwave dielectric tangent losses in KDP and DKDP crystals

By adding cubic and quartic phonon anharmionic interactions in the pseudospin lattice coupled mode (PLCM) model for KDP-type crystals and using double-time temperature dependent Green's function method, expressions for soft mode frequency, dielectric constant and dielectric tangent loss are obtained. Using model parameters given by Ganguli et al [9] the dielectric losses are calculated for KDP and DKDP crystals. In the microwave frequency range an increase in frequency (1-35 GHz) is followed by an increase in dielectric tangent loss (1-35) at 98 K and (1-15) x 10(-2) at 333 K for KDP and DKDP crystals respectively. The dielectric tangent loss decreases from 0.052 to 0.042 for KDP crystals with increase in temperature from 130 to 170 K and for DKDP crystals it decreases from 0.0166 to 0.0074 with an increase in temperature from 230-343 K in their paraelectric phases at 10 GHz. This shows Curie-Weiss behavior of the dielectric tangent loss.