Electric field dependence of microwave losses in strontium titanate II

Electric field dependent microwave losses of an anharmonic pure strontium t itanate ferroelectric crystal is calculated in its paraelectric phase from the Silverman Joseph Hamiltonian augmented with fourth order phonon-coordin ates using double time Green's functions. The loss tangent consists of a co ntribution. which is quadratic in applied biasing plus a field independent contribution. The variation of tan delta with applied field is noticeable i n the vicinity of the Curie temperature. In the higher temperature region, the electric field effect ceases and the increase in loss arises mainly due to higher order anharmonic terms. In SrTiO3, loss tangent increases with t he increasing electric field.