Part 2.: 125Te NMR study of M2O-TeO2 (M = Li, Na, K, Rb and Cs) glasses

The structure of TeO2 and M2O-TeO2 (M = Li, Na, K, Rb and Cs) glasses has been investigated by means of Te-125 static and magic-angle spinning (MAS) NMR spectroscopies. On the basis of the relationship between the local structures around Te atoms and the NMR parameters obtained by Te-125 NMR spectra of various tellurite crystals, the local structures around Te atoms in TeO2 and M2O-TeO2 glasses were examined. The spectral simulation of static NMR spectra enabled us to discriminate between TeO3 trigonal pyramid (tp) and TeO4 trigonal bipyramid (tbp) and to estimate the fractions of TeO3 tp (N-3) and TeO4 tbp (N-4) It was concluded that in TeO2 glass TeO4 tbps are connected by sharing their corners as in alpha-TeO2 crystal. N-3 increased and NS decreased with increasing M2O content. On the basis of a previous structural model, the fractions of TeO4 tbp without a non-bridging oxygen (NBO) atom, TeO4 tbp with an NBO atom, and TeO3 tp with two NBO atoms were calculated. A new model which presents the structural change for M2O-TeO2 glasses has been proposed. (C) 1999 Elsevier Science B.V. All rights reserved.