Light scattering study of the coupled soft-optic and acoustic mode in hexagonal barium titanate.

Abstract

Low-frequency light scattering spectra of hexagonal barium titanate have been observed in the temperature region from 40 to 300 K. An intense central peak was observed near the phase transition temperature ${T}_{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}222\mathrm{K}$ and was assigned to be caused by the coupled soft-optic and acoustic mode. The coupled-mode model has been employed to fit experimental data and gives good agreement with the observed spectra. The ${\ensuremath{\omega}}_{0}^{2}/{\ensuremath{\gamma}}_{0}$ ratio of soft-optic-mode frequency ${\ensuremath{\omega}}_{0}$ and damping constant ${\ensuremath{\gamma}}_{0}$ and the bilinear coupling constant $A$ exhibit linear dependence on ${T\ensuremath{-}T}_{0}$ indicating mean-field behavior.