Infrared Study of the Lattice Vibrations in LiTaO3

Polarized infrared reflectivity measurements have been made on single-crystal LiTa${\mathrm{O}}_3$ in the frequency range 20 - 10 000 ${\mathrm{cm}}^{-1\mathrm{}}$ at 300 °K. Kramers-Kronig and classical-oscillator dispersion-theory analyses of these data have yielded values for the frequency, strength, and linewidth of the infrared-active transverse optic modes and longitudinal optic modes. Analysis of the far-infrared interference spectrum yields values of 41 and 40 for the ordinary and extra-ordinary clamped dielectric constants, as well as values for their temperature dependence and dispersion. A calculation is made of the spontaneous polarization in LiTa${\mathrm{O}}_3$ and LiNb${\mathrm{O}}_3$ using the x-ray ion displacements.