Vibrational spectroscopy at very high pressures—XX Raman and far-IR study of the phase transition in paratellurite

Raman and far-IR spectra have been obtained up to ca. 45 kbar [4.5 GPa] for paratellurite (Te0₂) in a diamond anvil cell. At the D₄⁴ to D₂⁴ phase transition ca. 9 kbar an E symmetry mode initially at 122cm^?1 was found to split into two components in both IR and Raman spectra: their coincidence in both types of spectra shows that one component in the Raman spectrum cannot be an LO mode. No other E modes were seen to split. A further phase transition claimed ca. 30 kbar was not confirmed.Paratellurite is exceptionally sensitive to the presence of non-hydrostatic stresses, which greatly influence the phonon frequencies. This behaviour is illustrated by Raman spectra obtained under varying degrees of shear stress.