Correlation between nonbridging oxygens and the thermal and optical properties of the TeO2-Li2O-MoO3 glassy system

In this work, the correlation between the number of nonbridging oxygen (NBO) atoms and the thermal and optical properties of TeO2-Li2O-MoO3 glasses was studied. Samples containing (100 - x)TeO2-x(Li2O-MoO3) with x = 10, 15, 20, and 25 mol% were investigated by Raman and Fourier transform infrared (FTIR) spectroscopies. From the optical absorption measurements, the band gap energies were determined. The Raman and FTIR results showed that with increasing x, the TeO4 units transform into TeO3+1 units and then into TeO3 units, while the Mo coordination changes from 4 -> 6. This transformation corresponds to a decrease in the total number of NBO with increasing x in this glass matrix. The decrease in the NBO is also confirmed by the increase in band gap energies and the decrease in the optical basicity, indicating a more polymerized network with increasing x.