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We review results obtained from recent neutron scattering studies of thelead-oxide class of perovskite relaxors PMN and PZN. A ferroelectric soft modehas been identified in PMN at 1100 K that becomes overdamped near 620 K. Thisis the same temperature at which polar nanoregions (PNR) begin to form, denotedby Td, and suggests that a direct connection exists between the soft mode andthe PNR. The appearance of diffuse scattering intensity at Td reported byNaberezhnov et al. lends further support to this picture. At lower temperaturethe soft mode in PMN reappears close to Tc = 213 K (defined only for E > Ec).These results are provocative because the dynamics below Tc are characteristicof an ordered ferroelectric state, yet they occur in a system that remainscubic on average at all temperatures. We discuss a coupled-mode model thatsuccessfully describes these data as well as those from earlier latticedynamical studies of other perovskites such as BaTiO3.Comment: 10 pages, 7 figures, Conference - Fundamental Physics of  Ferroelectrics 200

Ferroelectric Dynamics in the Perovskite Relaxor PMN