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, PbMg1/3 Nb2/3 O3 and PbMg1/3 Ta2/3 O3 (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 PbTiO3 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. [ABSTRACT FROM AUTHOR]