Structure of the dielectric spectrum of relaxor ferroelectrics

Wide range dielectric response (10-10(14)Hz) of three relaxor ferroelectric s: PMN, PLZT and PST is analyzed. The common features are: low phonon contr ibution to the high static permittivity; dielectric relaxation in a wide fr equency range; widening of the relaxation times distribution with decreasin g temperature down to the freezing temperature T-f, where extrapolated dive rgence of the mean relaxation time takes place; change of dielectric behavi our at the Burns temperature T-B. Dynamics of polar nanoclusters, which app ear below T-B, is considered to be responsible for the relaxor behaviour. I t enables us to define the general structure of the dielectric spectrum of relaxor ferroelectrics. Only above T-B the fundamental dielectric contribut ion is due to polar phonons. Below T-B the contributions caused by polar cl usters dynamics prevail: both dipole reversal of polar cluster and fluctuat ions of their boundaries contribute to the dielectric response. (C) 2001 El sevier Science Ltd. All rights reserved.