Strong Influence of the Diffuse Component on the Lattice Dynamics in Pb(Mg1/3Nb2/3)O3

The temperature and zone dependence of the lattice dynamics in Pb(Mg 1/3 Nb 2/3 )O 3 is characterized using neutron inelastic scattering. Through a detailed study of the phonon lineshape and a comparison of the structure factors to SrTiO 3 , we conclude that the coupling between the acoustic and optic modes is weak. However, based on a direct comparison between the (110) Brillouin zone where the diffuse scattering is strong to the (220) zone where the diffuse scattering is weak, a strong coupling between the diffuse component and low-energy acoustic phonon mode is observed. We conclude that the coupling to the diffuse component is the reason for several recent conflicting interpretations of the lattice dynamics based on data from zones with a strong diffuse component.