Influence of internal electric and elastic fields on characteristics of heterogeneous ferroelectric materials

Dielectric properties of polycrystalline ferroelectric ceramics and ferroelectrics with compensated impurities were investigated. Electric fields at the boundaries between crystallites and the fields created by a random distribution of impurities were calculated. It was shown, that the influence of these fields leads to an increase in the effective dielectric constant and to a displacement of the phase transition temperature in these ferroelectrics to lower temperatures. These effects are associated with an asymmetric nonlinear dependence of the thermodynamic potential near to the equilibrium value of spontaneous polarization vector. The asymmetry of this dependence in the random electric and elastic fields with a zero mean value reduces the length of the spontaneous polarization vector. The polarization reduced by the indicated fields lies in a region with less curvature of the thermodynamic potential that effectively means growth the value of dielectric constant of the studied system.