Structure of strontium tellurite glass, anti-glass and crystalline phases by high-energy X-ray diffraction, reverse Monte Carlo and Rietveld analysis

Abstract

The structures of xSrO-(100 À x)TeO 2 (x = 5, 7.5, 8.5 and 10 mol.%) glass, antiglass and crystalline samples were studied by high-energy X-ray diffraction (HEXRD), reverse Monte Carlo (RMC) simulations, atomic pair distribution function analysis and Fullprof Rietveld refinement. The atomic pair distributions show the first peak at 1.90 Å due to the Te-O equatorial bonds and the Te-O peak is asymmetrical due to the range of Te-O bond lengths in glass, anti-glass and crystalline samples. The short-range structural properties of glasses such as Te-O bond lengths, Te-O speciation, Te-Te distances and O-Te-O bond angle distributions were determined by RMC simulations. The average Te-O coordination number (N Te-O ) for 5SrO-95TeO 2 glass is 3.93 which decreases to 3.59 on increasing the SrO concentration to 10 mol.%. The changes in N Te-O revealed that the glass network predominantly contains TeO 4 units with a small amount of TeO 3 units and there is a structural transformation TeO 4 ! TeO 3 with an increase in SrO concentration. The O-Te-O bond angle distributions have a peak at 79 and reveal that the O equatorial -Te-O equatorial bonds are the most abundant linkages in the tellurite network.Two glass samples containing 7.5 and 8.5 mol.% of SrO were annealed at 350 C for 1 h to produce anti-glass phases; they were further annealed at 450 C for 4 h to transform them into crystalline phases. The anti-glass samples are disordered cubic SrTe 5 O 11 and the disordered monoclinic SrTeO 3 phases, whereas the crystalline samples contain monoclinic SrTeO 3 and the orthorhombic TeO 2 phases. The unit-cell parameters of the anti-glass and crystalline structures were determined by Fullprof Rietveld refinement. Thermal studies found that the glass transition temperature increases with an increase in SrO mol.% and the results on the short-range structure of glasses from Raman spectroscopy are in agreement with the RMC findings.

In situhigh pressure neutron diffraction and Raman spectroscopy of 20BaO–80TeO2glass

“…30 It is well known from the ambient pressure X-ray diffraction, neutron diffraction and Raman spectroscopy studies that the average Te-O coordination number in the tellurite network decreases steadily upon adding network modier oxides due to the structural transformation: TeO 4 / TeO 3 + NBO. [34][35][36][37][38][39] Neutron and X-ray diffraction, infrared and Raman spectroscopy are excellent techniques for investigating in situ changes in the glass shortrange structure under extreme conditions of high pressures and high temperatures. 13,[40][41][42] The binary xBaO-(100 À x)TeO 2 glasses are of interest due to their positive, negative and zero-stress optical coefficients.…”