Vibrational spectroscopy and density of K2O-B2O3-GeO2 glasses with variable B/Ge ratio.

Glasses of the K2O-B2O3-GeO2 system were studied by means of Raman and IR spectroscopy. The density of the samples was measured and the dependence of the molar volume and atomic density on composition was calculated. Curve-fitting of Raman spectra was applied to obtain a definition of the main structural units formed in the system. The conditions for highly-coordinated boron and germanium atoms were obtained. It was shown that potassium cations remain connected to germanate structural units at a B/Ge ratio of up to 1, whereas the explicit redistribution of borate and germanate structural groupings becomes most noticeable only at a B/Ge ratio > 2.