Central peak in the vibrational spectrum of the relaxor ferroelectric lead scandotantalate

A low-frequency region of the vibrational spectrum of relaxor ferroelectric lead scandotantalate PbSc1/2Ta1/2O3 (PST) was studied by Raman and micro-Brillouin scattering in the temperature interval from 80 to 500 K. It is shown that light scattering spectra have a quasielastic contribution referred to sometimes as the central peak consisting of two components: wide (full width at half maximum (FWHM)∼30 cm−1) and narrow (FWHM∼0.5 cm−1). Temperature dependencies of the central peak intensity and width exhibit a broad anomaly corresponding to the dielectric response maximum and a narrow anomaly in the vicinity of 290 K. Mechanisms responsible for the temperature evolution of the central peak are discussed.