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 ob served 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.