Raman and Infrared Structural Investigation of xRb2O·(1 − x)GeO2 Glasses

Abstract

Infrared reflectance and Raman spectra of rubidium germanate glasses, xRb2O·(1 − x)GeO2, have been measured and studied as a function of Rb2O mole fraction in the range 0 ≤x ≤ 0.60. The spectra of corresponding crystalline germanate phases, GeO2-quartz, GeO2-rutile, Rb2Ge4O9, K4Ge9O20, K2Ge2O5, and K2GeO3, have been also measured for a better understanding of the glass spectra. At very low content (x ≤ 0.01) Rb2O was found to induce a redistribution of GeO4 tetrahedra in rings smaller than those encountered in quartz- and glassy GeO2. The spectral manifestations of this trend are the frequency increase of the Raman active symmetric stretching vibration of Ge−O−Ge bridges and the parallel decrease of the infrared frequency of the asymmetric stretching of Ge−O−Ge bridges. Beyond the composition x = 0.01 and up to x ≈ 0.15−0.20, the predominant modification mechanism involves the transformation of GeO4 tetrahedra into GeO6 octahedra, with characteristic Raman scattering at 315, 590, and 630 cm-1. At higher a...