Multiple tunneling channels order-disorder ferroelectric model and field-induced phase transition in relaxors

An improved eight-potential-well order-disorder ferroelectric model with isotropic distribution of random fields has been proposed and the field-induced phase transition and polarization behavior of relaxor ferroelectrics has been investigated. It was found that the type of phase transition, first order or second order, is independent of the random field width when the random field has an isotropic distribution. By introducing tunneling frequency between the nearest-neighbor wells, we observed a distinct threshold field and a corresponding nonzero phase transition temperature for field-induced phase transition, which is in good agreement with recent field-induced polarization measurement. Three kinds of dependence of polarization under an external electric field on temperature were demonstrated.