The electric field dependent microwave losses of anharmonic pure PbTi03 and KNb03 ferroelectric perovskites have been calculated in paraelectric phase from the Silverman-Joseph Hamiltonian augmented with fourth order phonon coordinates using double time Green's function. The loss tangent consists of a contribution which is quadratic in applied biasing plus a field independent contribution. The variation of tanδ with applied electric field is noticeable in 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 both the crystals, loss tangent increases with the increasing electric field.
Green's function, Hamiltonian, Microwave losses, Anharmonicity, Perovskites
