Direct evidence of soft mode behavior near the Burns temperature in thePbMg1/3Nb2/3O3relaxor ferroelectric

Inelastic neutron scattering measurements of the relaxor ferroelectric PbMg 1 / 3 Nb 2 / 3 O 3 (PMN) in the temperature range 490 K<T<880 K directly observe the soft mode (SM) associated with the Curie-Weiss behavior of thedielectric constant e(T). The results are treated within the framework of the coupled SM and transverse optic (TO1) mode and the temperature dependence of the SM frequency at q=0.075a* is determined. The parameters of the SM are consistent with the earlier estimates and the frequency exhibits a minimum near the Burns temperature (650 K).