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 Qn 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.