Dielectric Behaviour of Ba_xSr_1–xTiO₃ Perovskites

Using the method of double - time thermal Green's functions and Kubo formalism, a general expression is derived for the complex dielectric constant of Ba_xSr_1-xTiO₃ ferroelectric crystal in the paraelectric phase taking into account the change of mass as well as harmonic force constant between impurity atom and host lattice atoms. The results are used to obtain an expression for the frequency dependence of the dielectric constant of Ba_xSr_1-xTiO₃ due to impurity and anharmonic scattering. To a first order approximation of the defect parameters the Curie temperature shift is found to depend only on the harmonic force constant changes between the impurity and host lattice atoms, and is proportional to the concentration of defects. The dielectric constant of ceramic SrTiO₃ can be enhanced by the addition of cation impurities like lead, barium, zirconium etc.

doi:10.4038/sljp.v3i0.186

Sri Lankan Journal of Physics, Vol.3 (2002) 63-73