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 ¹²⁵Te 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 ¹²⁵Te 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 (N₃) and TeO₄ tbp (N₄). It was concluded that in TeO₂ glass TeO₄ tbps are connected by sharing their corners as in α-TeO₂ crystal. N₃ increased and N₄ 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.