Structural analysis of WO3-TeO2 glasses by neutron, high energy X-ray diffraction, reverse Monte Carlo simulations and XANES

Abstract

The structure of WO3-TeO2 glasses containing 15, 20 and 25 mol% WO3 are studied by neutron diffraction (ND), high energy X-ray diffraction (XRD) and X-ray Absorption Near Edge spectroscopy (XANES). The short-range structural properties of glasses i.e. TeO and WO speciation, coordination number distributions, bond-lengths, and the OTeO, OWO and OOO bond angle distributions in the glass network are determined by the Reverse Monte Carlo (RMC) simulations of the ND and XRD data. RMC technique successfully determined all partial pair correlation functions and the coordination number distributions revealed that glass network consists predominantly of TeO4 and WO4 units with small amounts of triangular, penta and hexa co-ordinated units. The average WO and TeO bond lengths are in the ranges: 1.69–1.75 ± 0.01 Å and 1.99–2.00 ± 0.01 Å respectively. Both WO and TeO correlation peaks are asymmetrical, that indicate a distribution of their bond lengths in the respective structural units. The O-Te-O bond angle distribution has a peak at 107 ± 2°. Similarly the O-W-O bond angle distribution has a peak at 108 ± 5°. On increasing the WO3 concentration from 15 to 25 mol%, the average TeO coordination number decreases from 3.80 to 3.61 ± 0.02 due to the structural transformation: TeO4 → TeO3, similarly the WO coordination also decreases and is in the range: 3.79–3.67 ± 0.02. XANES studies found that the oxidation state of Te and W ions in the glasses are 4+ and 6+ respectively.