Infrared-Absorption Studies on Barium Titanate and Related Materials

TLDR

The authors measured the infrared absorption of BaTiO₃ in thin crystals and powder, tracking the 495 cm⁻¹ band across temperatures and estimating a 225 cm⁻¹ Ba–TiO₃ vibration from specific‑heat analysis. The study identified TiO₃‑related absorption bands at 495 and ~340 cm⁻¹, observed symmetry‑induced band splitting during phase transitions, and found that BaTiO₃’s spectra and band intensities closely resemble those of related perovskite titanates and niobates, with minor shifts attributable to unit‑cell size and symmetry.

Abstract

The infrared-absorption spectrum of BaTi${\mathrm{O}}_{3}$ has been measured for thin single crystals and for powder samples dispersed in pressed KBr disks. Absorption bands for single-crystal samples occur at 495 ${\mathrm{cm}}^{\ensuremath{-}1}$ and at ca 340 ${\mathrm{cm}}^{\ensuremath{-}1}$, arising from normal vibrations of the Ti${\mathrm{O}}_{3}$ group. A third vibration, a motion of Ba against the Ti${\mathrm{O}}_{3}$ group, occurs below the experimentally accessible range. A frequency of about 225 ${\mathrm{cm}}^{\ensuremath{-}1}$ is expected for this vibration on the basis of a comparison of the specific heat contributions of the observed bands with the measured low-temperature specific heat. Measurements were made on the 495-${\mathrm{cm}}^{\ensuremath{-}1}$ band over a wide temperature range. As the crystal changes from the cubic to the tetragonal, orthorhombic, and rhombohedral structures, there occurs band splitting which can be related to the change of crystal symmetry. The spectra of the perovskite titanates, SrTi${\mathrm{O}}_{3}$, PbTi${\mathrm{O}}_{3}$, and CaTi${\mathrm{O}}_{3}$, and the perovskite niobates, KNb${\mathrm{O}}_{3}$ and NaNb${\mathrm{O}}_{3}$, have been found to be similar, in general features, to that of BaTi${\mathrm{O}}_{3}$. The slight differences in band frequency and structure can be related to differences in unit-cell size and symmetry. Integrated band intensities have been found to be in reasonable agreement with measurements on other oxide systems that have vibrations in this spectral region.