Dielectric constants are calculated forPb_xSr_1-xTiO₃single crystals in para-electric phase. In our calculations, double time temperature-dependent Green's function technique along with a modified Hamiltonian for the crystalsis used which includes anharmonicity up to the fourth order due to the interactions of the soft mode. Fourier transformation and Dyson’s equation treatment is used in arriving the result. In this paper, temperature and composition dependent dielectric constants of Pb_xSr_1-xTiO₃ have been studied. Dielectric constant increases with increase in the composition x at constant temperature and decreases with increasing temperature at constant value of x.

Keywords: Dielectric Constant, Perovskites, Anharmonicity, Retarted Green's Function, Hamiltonian, Fourier Transform, Dyson’s Equation.