Temperature dependence of Raman spectra of the quartz- and rutile-types of GeO2

The temperature dependence (at ambient pressure) of the Raman spectra of both the quartz- and rutile-types of GeO₂ has been studied from 109 to 874?K. All spectra were corrected for the effects of temperature and are presented in their reduced form to allow a direct comparison of intensities at all temperatures. In the quartz-type GeO₂, the Raman bands above 400?cm^?1 exhibited relatively larger temperature dependences and at least four of the bands in this region vary nonlinearly with increasing temperature. Deconvolution of the most intense Raman band at 700?cm^?1 in the rutile-type GeO₂ revealed the presence of a previously unreported band at 684?cm^?1 at 298?K which may arise from splitting of the A_1g mode. A nonlinear temperature dependence was observed for all the Raman bands above 600?cm^?1 in the rutile-type GeO₂ with the new band at 684?cm^?1 exhibiting the largest curvature. In common with previous studies of rutile-type oxides, the B_1g mode at 171?cm^?1 showed anomalous behaviour by increasing linearly in frequency with increasing temperature. In a separate experiment, the oxidation of metallic germanium in air demonstrated that the quartz-type GeO₂ is the preferred form of germanium oxide at temperatures above 745?K at atmospheric pressure. Thermodynamic calculations predict that the rutile-form of GeO₂ should be the stable species under these conditions. This suggests that atmospheric gases may have a marked effect on the kinetics and stability of the quartz and rutile forms of GeO₂.