Direct evidence of soft mode behavior near the Burns' temperature in   PbMg$_{1 / 3}$Nb$_{2 / 3}$O$_{3}$ (PMN) relaxor ferroectric
  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 the dielectric constant $\varepsilon $(T). The results are treated within the framework of the coupled SM and transverse optic (TO1) mode and the temperature dependence of the SM frequency at q=0.075 a* is determined. The parameters of the SM are consistent with the earlier estimates and the frequency exhibits a minimum near the Burns temperature ($\approx $ 650K) 
S. Vakhrushev (Ioffe Phys.-Tech. Institute, St. Peterburg, Russia) and   S. Shapiro (BNL, Upton, NY, USA)