Structure of the dielectric spectrum of relaxor ferroelectrics

Wide range dielectric response (10–1014Hz) 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 Tf, where extrapolated divergence of the mean relaxation time takes place; change of dielectric behaviour at the Burns temperature TB. Dynamics of polar nanoclusters, which appear below TB, 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 TB the fundamental dielectric contribution is due to polar phonons. Below TB the contributions caused by polar clusters dynamics prevail: both dipole reversal of polar cluster and fluctuations of their boundaries contribute to the dielectric response.