SMALL-SIGNAL DIELECTRIC-RELAXATION IN THE DISORDERED PEROVSKITE PB(MG1/3NB2/3)O3

Decay-current and conventional dielectric measurements have been performed on single-crystal samples of the disordered perovskite Pb(Mg1/3Nb2/3)O3 (PMN). Low-frequency dielectric data of Colla and co-workers on the same system are critically reanalysed and compared to our results. In contrast to previously proposed spin-glass or master-plot approaches, we suggest a phenomenological description in terms of alpha- and beta-relaxations: a relatively high-frequency beta-process takes over when the characteristic alpha-relaxation time becomes extremely long. The continuous slowing down of polar motion distinguishes PMN from related compounds such as Pb(Zn1/3Nb2/3)O3, for which, in contrast to PMN, there is evidence of a structural phase transition.