Hyper-Raman scattering: New prospects for the description of the local structure of complex perovskites

Hyper-Raman scattering is used to investigate the vibrations in two prototypical relaxors, PbMg 1 / 3 Nb 2 / 3 O 3 and PbMg 1 / 3 Ta 2 / 3 O 3 (PMT). First-order scattering from polar modes is clearly observed. Most of the triply-degenerate cubic vibrations are split into doublets and their frequencies compare very well to that of PbTiO 3 in its tetragonal phase. Their shape and scattering intensities are sensitive to the local chemical ordering and ferroelectric distortions. For example, the tendency toward 1:1 local ordering on the B -site in PMT is clearly evidenced. These results demonstrate the strong potentiality of hyper-Raman scattering as structural probe of complex perovskites.