Structure of BaO-TeO2 glasses: A two-dimensional 125Te NMR spectroscopic study

The compositional evolution of the network structure of binary (BaO)x(TeO2)100 − x glasses (5 ≤ x ≤ 25) is studied using two-dimensional 125Te isotropic-anisotropic correlation nuclear magnetic resonance (NMR) spectroscopy. It is demonstrated that only a consideration of the full 125Te chemical shift tensor in combination with the composition dependent evolution of isotropic 125Te NMR line shape can yield a consistent structural model of these glasses in terms of the complex tellurium speciation. When taken together, the results indicate that the addition of the modifier BaO results in a progressive depolymerization of the network of corner- and edge-shared TeO4/2 trigonal bipyramids via their replacement with primarily a combination of negatively charged TeO3/2O trigonal bipyramids and TeO1/2O2 trigonal pyramids with one and two non-bridging oxygen, respectively.