Relaxor ferroelectricity is observed in many strongly disordered ferroelectric solids. However, the atomistic mechanism of the phenomenon, particularly at high temperatures, is not well understood. In this Letter we show the local lattice dynamics as the origin of relaxor ferroelectricity through the first use of the dynamic pair-density function determined by pulsed neutron inelastic scattering. For a prototypical relaxor ferroelectric, $\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_3$, we demonstrate that the dynamic local polarization sets in around the so-called Burns temperature through the interaction of off-centered Pb ions with soft phonons, and the slowing down of local polarization with decreasing temperature produces the polar nanoregions and the relaxor behavior below room temperature.

• Received 12 December 2007

DOI:https://doi.org/10.1103/PhysRevLett.100.137602