Hyper‐Raman scattering study of the soft mode in relaxor ferroelectric (Ba_0.8Sr_0.2)_0.925Bi_0.05Ti_0.95(Zn_1/3Nb_2/3)_0.05O₃

Abstract

We report hyper-Raman scattering measurements of the lowest transverse optic (TO) phonon branch in the relaxor Bi 0.05 -BSTZN in the paraelectric phase from 300 to 973 K. The results evidence a displacive-like behavior from a highly damped soft mode at high temperature to an overdamped (quasi-elastic-like) component on cooling close to T c . A fit with a mean field law ω 0 T ð Þ¼ C ffiffiffiffiffiffiffiffiffiffiffiffiffi ffi T À T 0 p gives a temperature T 0 = 102 K significantly lower than T 0 = 188 K found by dielectric measurements. Reconciling the two experiments likely deserves considering a coupled modes analysis involving a second mode at slightly higher wavenumber. This behavior is very similar to that previously observed in PMN. Considering the rather complex chemical composition of the present compound as compared with PMN, these results emphasize a universal low-wavenumber dynamics of ferroelectric relaxors.