Frequency and Temperature Response of the Polarization of Barium Titanate

The frequency and temperature response of the polarization of BaTiO₃ from 1 to 1000 cm^-1 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 cm^-1 was observed in transmission, while in reflectivity a drop occurs from 10 to 80 cm^-1 and absorption bands are located near 175 and 470 cm^-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 BaTiO₃ consists of resonances at 12, 182, and 491 cm^-1. The 12-cm^-1 resonance is highly damped and exhibits an unusual dispersion. The integrated intensity of the 12-cm^-1 resonance is very large, and above the Curie point decreases rapidly with increasing temperature. Its frequency remains between 6 and 22 cm^-1 in the 24 to 200^∘{}C range.