Kaindl, R.; Többens, D.M.; Penner, S.; Bielz, T.; Soisuwan, S.; Klötzer, B.: Quantum mechanical calculations of the vibrational spectra of quartz- and rutile-type GeO2. Physics and Chemistry of Minerals 39 (2012), p. 47-55
10.1007/s00269-011-0458-8

Abstract:
Heat-treatment and stepwise cooling of as-delivered, water-containing quartz-type GeO2 powder resulted in transformation into a water-free form. A rutiletype modification could be prepared by impregnation of the quartz-type phase with RbOH solutions, drying and annealing. Raman- and FTIR-absorption spectra of quartz and rutile-type GeO2 were measured and compared to quantum-mechanical ab initio calculations based on a hybrid functional using the Perdew–Burke–Ernzerhof correlation functional with 16.7% Hartree–Fock exchange density functional. Maximum and mean deviations between measured spectral bands and assigned vibrational modes are 14 and ±8 cm-1 for the quartz-type and 30 and ±13 cm-1 for the rutile-type polymorphic form. Water is incorporated into GeO4 entities of quartz-type GeO2; a water-free and structurally stable form can be prepared by a heating up to 1425 K, tempering at 1323 K and stepwise cooling. Spectral bands not explained by the calculations suggest defects and distortions in both quartz- and rutile type structures, in case of the quartz-type one by incomplete transformation into an ideal structure after removing the water, whereas the rutile-type modification most probably incorporates Rb during its synthesis.