Structure of the dielectric spectrum of relaxor ferroelectrics

Wide range dielectric response (10–10 14 Hz) of three relaxor ferroelectrics: PMN, PLZT and PST is analyzed. The common features are: low phonon contribution to the high static permittivity; dielectric relaxation in a wide frequency range; widening of the relaxation times distribution with decreasing temperature down to the freezing temperature T f , where extrapolated divergence of the mean relaxation time takes place; change of dielectric behaviour at the Burns temperature T B . Dynamics of polar nanoclusters, which appear below T B , is considered to be responsible for the relaxor behaviour. It enables us to define the general structure of the dielectric spectrum of relaxor ferroelectrics. Only above T B the fundamental dielectric contribution is due to polar phonons. Below T B the contributions caused by polar clusters dynamics prevail: both dipole reversal of polar cluster and fluctuations of their boundaries contribute to the dielectric response.