Studies on the effect of Li₂SO₄ on the structure of lithium borate glasses

Abstract

Thermal and spectroscopic investigations have been carried out on a number of glasses with a wide range of compositions in the pseudoternary glass system, Li₂SO₄-Li₂O-B₂O₃, to understand the role of sulfate ions in modifying the borate glass structure. Both nuclear magnetic resonance (NMR) and infrared (IR) spectroscopic results indicate that four-coordinate boron atoms are retained in the glass structure to a greater extent in sulfate-containing glasses than in pure lithium borate glasses. There seems to be some evidence for the existence of sulfoborate-type units in Raman spectra in the region of 800-960 cm^-1. These conclusions are supported by the observed behavior of glass transition temperatures and molar volumes. The possibility of formation of sulfoborate-type units is discussed from bonding and thermodynamic points of view.