Raman Scattering in Paratellurite, TeO2

Abstract

Raman spectra of the tetragonal ${D_4}^4$ structure of Te${\mathrm{O}}_2$, paratellurite, have been obtained at temperatures of 85 and 295 °K. Frequencies and symmetry assignments for 18 of the 21 Raman-active optical branches are given with only one singlet-$A_1$ and two doublet-$E$ modes not observed. The measured LO-TO splittings of the six $E$ modes observed accounts for 63% of the total oscillator strength of the known ionic contribution to the ordinary-ray dielectric constant. Estimates for the positions of the LO and TO branches of the Raman-inactive, infrared-active, $A_2$ modes are made from the anisotropic frequency shifts of the oblique phonons in the extraordinary ray. In addition some weak, anomalous, polarization-selection-rule violations are reported.