Structure of TeO2 glass: Results from 2D 125Te NMR spectroscopy

Despite its chemical simplicity, a definitive description of the structure of TeO2 glass has remained elusive due to the complexity of the Te-O coordination environment. In this work we probe the Te-O coordination environment in glassy TeO2 using 2D Te-125 isotropic-anisotropic chemical shift correlation nuclear magnetic resonance (NMR) spectroscopy. The NMR results are consistent with the presence of two Te-O environments in this glass, characterized by their distinct set of Te-125 chemical shift parameters. The dominant environment (-89%) is a distorted trigonal bipyramidal TeO4 unit, reminiscent of that observed in crystalline gamma-TeO2. A second, minor (similar to 11%) component can be assigned, on the basis of its chemical shift parameters, to a TeO3 unit. The resulting average coordination number, n(TeO), measured by Te-125 NMR (n(TeO) approximate to 3.9) is higher than its previously reported value obtained using neutron diffraction (nTeO approximate to 3.7).