STRUCTURE OF LITHIUM, SODIUM AND POTASSIUM GERMANATE GLASSES, STUDIED BY RAMAN-SCATTERING

Polarized and depolarized Raman spectra of alkali germanate glasses are given, together with Raman powder spectra of the crystalline compounds Li2O · 2 GeO2; 3 Li2O · 8 GeO2; 2 Li2O· 9 GeO2; Li2O · 7 GeO2; 2 Na2O · 9 GeO2; K2O · 2 GeO2; K2O · 4 GeO2 and K2O · 8 GeO2. The alkali germanate glasses: xA2O (1-x) GeO2 are studied in the composition range 0 < x < 0.333. The vibrational modes observed in the high energy range of the Raman spectra of the crystalline compounds are interpreted in terms of symmetrical and antisymmetrical O-Ge-O and Ge-O- stretch vibrations. The molecular structure of the germanate glasses is deduced from a comparison of the Raman spectra of the glasses with those of the crystalline compounds, together with a study of the polarization properties of the glass spectra. It is observed that 6-coordinated Ge atoms occur in a network structure which resembles the structures occurring in the crystalline compounds 2 Li2O · 9 GeO2 and 2 Na2O · 9 GeO2. In the region of 0.18 < x < 0.33 it is found that tetrahedra with one non-bridging oxygen atom are formed. These tetrahedra are probably present in a network as occurs in the crystalline digermanates Li2O · 2 GeO2 and K2O · 2 GeO2. © 1979.