11B MAS NMR spectra of BO3/2-TeO2 glasses

Abstract

11B Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectra of BO3/2-TeO2 glasses have been used to determine the compositional dependence of the fraction of 4-coordinated boron atoms, N4 = BO4/(BO3+BO4). In 1 BO3/2 ∙ 99 TeO2 (mol%) glass, almost all boron atoms form BO4 tetrahedra. The fraction N4 decreases with increase of BO3/2 content. The authors propose a glass structural model in which the TeO3 trigonal pyramids formed by a part of the tellurium atoms are connected with the BO4 tetrahedra by vertex-sharing. An excess and a deficiency of local charges of a TeO3 trigonal pyramid and a BO4 tetrahedron compensate each other. The conversion of a BO3 triangle to a BO4 tetrahedron is concurrent with the formation of a TeO3 trigonal pyramid.