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

Decay-current and conventional dielectric measurements have been perfo rmed on single-crystal samples of the disordered perovskite Pb(Mg1/3Nb 2/3)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 approac hes, 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 rel ated compounds such as Pb(Zn1/3Nb2/3)O3, for which, in contrast to PMN , there is evidence of a structural phase transition.