Raman Spectrum of Single-Domain BaTiO3

Abstract

Room-temperature Raman spectra of high-quality single-domain BaTi${\mathrm{O}}_{3}$ crystals are reported. The frequencies of the Raman-active long-wavelength optical phonons are determined and shown to be in reasonable agreement with the Lyddane-Sachs-Teller (LST) relation as well as infrared reflectivity data. The effects of mode damping on the Raman line shape are discussed using a classical lattice-polarization-fluctuation model for the Raman scattering process. Based on this model, it is shown that the soft $E$ mode is overdamped, and at 25\ifmmode^\circ\else\textdegree\fi{}C has an undamped mode frequency ${\ensuremath{\omega}}_{\mathrm{TO}}$ of 36\ifmmode\pm\else\textpm\fi{}3 ${\mathrm{cm}}^{\ensuremath{-}1}$ and a damping constant $\ensuremath{\Gamma}$ of 1.1\ifmmode\pm\else\textpm\fi{}0.1. The temperature dependence of ${\ensuremath{\omega}}_{\mathrm{TO}}$ is given and found to be consistent with the LST relation. The soft ${A}_{1}$ mode is not observed, but is estimated from the LST relation and infrared reflectivity data to be heavily damped ($\ensuremath{\Gamma}\ensuremath{\approx}0.5$) and to have an undamped mode frequency of 180\ifmmode\pm\else\textpm\fi{}10 ${\mathrm{cm}}^{\ensuremath{-}1}$.