Structural influences on the hydroxyl spectra of barium gallogermanate glasses

Abstract

The infrared absorption of hydroxyl in three series of barium gallogermanate glasses — 10 mol% Ga 2O 3, 60 mol% GeO 2, and BaO/Ga 2O 3 = 1 — have been measured. Four separate bands associated with the OH stretching vibration dominate the absorption spectra of these glasses between 4000 and 1500 cm −1. Two of these bands are attributed to hydroxyl with vibrational frequencies perturbed by hydrogen bonds between the hydroxyl and adjacent non-bridging oxygens. The other two bands arise from the vibration of ‘free’ hydroxyl ions associated with either germanium or gallium tetrahedra. Hydrogen-bonded hydroxyl absorptions are present in the spectra of all compositions. This observation leads to a modification of the previously proposed structural model for these glasses. In addition, the relative concentration of various types of hydroxyl is correlated to the changes in structure associated with changes in composition. Specifically, the fraction of hydrogen-bonded hydroxyl increases at the expense of ‘free’ hydroxyl when the number of non-bridging oxygens in the glass increases.