ir reflectance spectra of ${\mathrm{Ti}}_2$${\mathrm{O}}_3$: Infrared-active phonons and Ti $3d$ electronic effects

The room-temperature reflectance of ${\mathrm{Ti}}_2$ ${\mathrm{O}}_3$ has been measured between 50 and 4000 ${\mathrm{cm}}^{-1\mathrm{}}$ for the two principal polarizations, $E$ perpendicular and $E$ parallel to the $c$ axis. An analysis of the data provides (i) the properties of the ir-active long-wavelength phonons—TO- and LO-phonon frequencies, oscillator strengths, and the damping; (ii) the values for the optical frequency ${\epsilon }_{\infty }$ and quasistatic ${\epsilon }_0$ dielectric constants, and (iii) information about electronic effects associated with the partially occupied Ti $3d$ states. The latter include the anisotropy in the free-carrier electronic conductivity $\frac{{\sigma }_{\perp }}{{\sigma }_{\parallel }}$ and the energy separation between the lowest-lying $d$ levels. Comparisons are made with the phonon properties of other $\alpha$-corundum structured sesquioxides $\alpha -{\mathrm{Al}}_2{\mathrm{O}}_3$ and ${\mathrm{Cr}}_2$ ${\mathrm{O}}_3$.