FLUCTUATIONS AND SUSCEPTIBILITY DISPERSION IN FERROELECTRICS ON THE BASIS OF THE FOKKER-PLANCK EQUATION

The Fokker-Planck equation is used to calculate the dielectric susceptibility dispersion in ferroelectrics within the Landau-Ginzburg model. Equations for both the time-space correlation function and the susceptibility are obtained on the basis of subsequent consideration of fluctuations. Two cases are considered: 1. a small-size single domain ferroelectric and 2. an-infinite-size ferroelectric. Effects related to a switching of the system between two stable states due to fluctuations are investigated. The obtained results explain in general (without specific effects) both frequency and temperature dependence of the susceptibility (or permittivity) and the dielectric loss angle observed experimentally in ceramics and polycrystals (case 1) as well as in single ferroelectric crystals (case 2).