In situ Raman spectroscopy of K2O-GeO2 melts

Raman spectra of potassium germanate melts K2O-GeO2, containing 10, 20, 30 and 40 mol.% K2O were measured. Based on a comparison of melts and glasses spectra we were able to determine the basic structural units formed in the system and to reveal the structural features of potassium-germanate melts during vitrification. It was shown that in melts, in contrast to glasses, an increase of the K2O content leads to a monotonic decrease of the fraction of germanium atoms in the octahedral coordination and the formation of [GeO4] tetrahedra with one and two non-bridging oxygen atoms. During cooling of germanate melts and their glass transition, an increase of the coordination number of germanium atoms and an increase of the degree of polymerisation of the network occur due to the formation of Ge-O-Ge bridging bonds.