Order-disorder phase transition and dielectric mechanism in relaxor ferroelectrics

An overview is presented on the order-disorder structural transitions and the dielectric mechanism in the complex-perovskite type relaxor ferroelectrics, i.e., the relaxors. Emphasis is put on the theoretical understanding of the structural transitions, the macroscopic dielectric properties, and the relationship between them. The influences of the composition, the temperature, and the atomic interactions on the order-disorder microstructures can be well understood in the cluster-variation-method calculations. The criterion drawn from theoretical analysis is successful in predicting the order-disorder structure of relaxors. Among various physical models about relaxors, the dipole glassy model that described the dielectric response as the thermally activated flips of the local spontaneous polarization under random interactions is discussed in details. The Monte Carlo simulation results of this model are consistent with the linear and nonlinear experiments of relaxors.