Quantitative Studies on Local Structure of Molten Binary Potassium Germanates

In situ high temperature Raman spectra of xK₂O-(100-x)GeO₂, samples containing 0, 5, 11.11, 20, 25, 33.3, 40, and 50 %mol K₂O, were measured. The structure units and a series of model clusters have been designed, optimized, and calculated by quantum chemistry ab initio calculations. The computational simulation in conjunction with the experiments put forward a novel method to correct the experimental Raman spectra of the melts. Deconvolution of the stretching vibrational bands of nonbridging oxygen of [GeO₄] tetrahedra of Raman spectra by Gaussian functions was carried out, and the quantitative distribution of different Q species in molten binary potassium germanates was obtained. The result on all molten samples show that four-fold coordinated germanium atoms occupy a dominant position in the melt and only four-fold coordinated exists in the melt when the K₂O content exceeds a certain amount. For melts with high GeO₂ content, with the increasing K₂O content, the structure of [GeO₄] tetrahedra gradually changes from a three-dimensional network consisting of both six-membered and three-membered rings to a three-dimensional network that presents all three-membered rings.