To the theory of phase transitions in relaxors

It is shown that the process of charge carrier localization on impurity cen ters is of importance. Localized carriers produce local electric fields, th ereby stimulating the appearance of an induced polarization near the phase transition point. The direction of this polarization is dictated by the spa tial distribution of the centers occupied by charge carriers. The temperatu re dependence of the dielectric constant is determined by the dynamics of t he local-center occupation with decreasing temperature. The dispersion of t he dielectric constant is determined by the vibrational characteristics of the local states forming near a localized charge. The phase transitions in relaxors are considered in the framework of the thermodynamic approach. (C) 2001 MAIK "Nauka/Interperiodica".