Frequency and Temperature Response of the Polarization of Barium Titanate

Abstract

The frequency and temperature response of the polarization of BaTi${\mathrm{O}}_{3}$ from 1 to 1000 ${\mathrm{cm}}^{\ensuremath{-}1}$ and between 24 and 200\ifmmode^\circ\else\textdegree\fi{}C has been determined by transmission and reflectivity measurements on polarized single crystals. A single absorption band located at 491 ${\mathrm{cm}}^{\ensuremath{-}1}$ was observed in transmission, while in reflectivity a drop occurs from 10 to 80 ${\mathrm{cm}}^{\ensuremath{-}1}$ and absorption bands are located near 175 and 470 ${\mathrm{cm}}^{\ensuremath{-}1}$. These bands show temperature-dependent splittings caused by changes in crystal symmetry. Reflectivity analysis indicates that the dispersion of the polarization in single-domain BaTi${\mathrm{O}}_{3}$ consists of resonances at 12, 182, and 491 ${\mathrm{cm}}^{\ensuremath{-}1}$. The 12-${\mathrm{cm}}^{\ensuremath{-}1}$ resonance is highly damped and exhibits an unusual dispersion. The integrated intensity of the 12-${\mathrm{cm}}^{\ensuremath{-}1}$ resonance is very large, and above the Curie point decreases rapidly with increasing temperature. Its frequency remains between 6 and 22 ${\mathrm{cm}}^{\ensuremath{-}1}$ in the 24 to 200\ifmmode^\circ\else\textdegree\fi{}C range.