Structure of zinc and niobium tellurite glasses by neutron and x-ray diffraction**Some of these results have already been presented in thesis work: Yousef E 2003 Astudy of some physical properties of tellurite glass (Al-Azhar University, AssiutEgypt).

Abstract

Neutron and x-ray diffraction experiments of high resolving power with neutrons from aspallation source and high-energy photons from a synchrotron have been performed oncompositional series of binary Zn, Nb and on mixed Zn/Nb tellurite glasses. The Te–O,Zn–O and Nb–O coordination numbers are determined by Gaussian fitting of thefirst-neighbour peaks in the neutron and x-ray data simultaneously. The transition ofTeO4 toTeO3 units with increasing fraction of a second component is indicated by decreasing total Te–Ocoordination numbers. This transition appears different for glasses with ZnO orNb2O5 additions. Details of the Te–O peaks suggest there are two species of Te–O bonds withlengths of and nm. The change of their fractions shows excellent agreement with the existence ofTeO4 trigonalbipyramids and TeO3 trigonal pyramids. All oxygen atoms from ZnO andNb2O5 areused for rupture of Te–O–Te bridges, which is accompanied with a change of nearly all participatingTeO4 toTeO3 groups. The tendency for a change decreases for glasses of higher second component content which is accompanied by the occurrenceof TeO4 groups with non-bridging oxygens. The Nb tellurite glasses show transition tonetwork-forming behaviour with the formation of Nb–O–Nb bridges. The fractions ofTeO3 unitsof ternary Zn/Nb tellurite glasses agree with an additivity behaviour of the modifying effects of ZnOand Nb2O5 additions.