Relaxor behaviour in ferroelectric ceramics

The chapter shows the studies carried out on several relaxor ferroelectric ceramic materials, which have been developed by the present authors. Lanthanum modified lead zirconatetitanate ceramics will be evaluated considering different La³⁺ concentrations and Zr/Ti ratios. It will be discussed the dynamical behaviour of the PNRs taking into account a relaxation model, which considers a distribution function for the relaxation times. The influence of A or B vacancies on the relaxor behaviour will be also analyzed considering the decoupling effects of these defects in the Pb-O-Ti/Zr bounding. For the PZN-PT-BT system, the relaxor behaviour will be explained considering the presence of local compositional fluctuation on a macroscopic scale. Finally, the relaxor behaviour of Sr_0.50Ba_0.50Bi₂Nb₂O₉ ferroelectric ceramics, which belong to the Aurivillius family, will be discussed considering a positional disorder of cations on A or B sites of the perovskite blocks.