Frequency and Temperature Response of the Polarization of Barium Titanate

The frequency and temperature response of the polarization of BaTi${\mathrm{O}}_3$ from 1 to 1000 ${\mathrm{cm}}^{-1\mathrm{}}$ and between 24 and 200°C has been determined by transmission and reflectivity measurements on polarized single crystals. A single absorption band located at 491 ${\mathrm{cm}}^{-1\mathrm{}}$ was observed in transmission, while in reflectivity a drop occurs from 10 to 80 ${\mathrm{cm}}^{-1\mathrm{}}$ and absorption bands are located near 175 and 470 ${\mathrm{cm}}^{-1\mathrm{}}$. 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 ${\mathrm{cm}}^{-1\mathrm{}}$. The 12-${\mathrm{cm}}^{-1\mathrm{}}$ resonance is highly damped and exhibits an unusual dispersion. The integrated intensity of the 12-${\mathrm{cm}}^{-1\mathrm{}}$ resonance is very large, and above the Curie point decreases rapidly with increasing temperature. Its frequency remains between 6 and 22 ${\mathrm{cm}}^{-1\mathrm{}}$ in the 24 to 200°C range.