Optical, thermal, and structural properties of Nb2O5-TeO2 and WO3-TeO2 glasses

Glass samples from two systems, Nb2O5-TeO2 and WO3-TeO2, were prepared at two melt quenching rates and characterized by density, DSC, UV-visible, and Raman spectroscopy. Addition of Nb2O5 decreased the density while increase in the WO3 concentration increased the density. Glasses prepared at higher quenching rates had smaller densities than glasses of the same composition prepared at lower quenching rate although the short-range structure of both glasses were identical, as revealed by Raman spectroscopy. Optical studies found an intense absorption band just below the absorption edge in both the glass series. This band was attributed to electronic transitions of Nb5+ and W6+ ions and a lone pair of electrons on Te atoms. Glass transition temperature increased with increase in Nb2O5 and WO3 mol% due to the increase in average bond strength in the glass network. Raman spectroscopy showed that the concentration of TeO4 units decreased with the increase in Nb2O5 and WO3 concentrations.