Infrared dielectric response of relaxor ferroelectrics

In the article we discuss the dielectric response of relaxor-type complex perovskites in the phonon-frequency region on the basis of a rich collection of experimental data accumulated in our laboratory by numerous infrared spectroscopy investigations over the past decade. The effect of the cation occupational disorder and of the nanoscopic inhomogeneous polarisation on the infrared response is considered in the framework of the factor-group symmetry analysis and the effective-medium approach. Polar mode assignment and comparison of the mode parameters of different materials is facilitated by systematic evaluation of mode-plasma frequencies. Whenever possible, the results are presented in form of tables convenient for further analysis or by comparison with results of other techniques, including ab-initio calculations. Infrared properties of other non-perovskite relaxors are briefly mentioned.