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 _ x)TeO2 (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 A ˚ 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 (NTe–O) for 5SrO–95TeO2 glass is 3.93 which decreases to 3.59 on increasing the SrO concentration to 10 mol.%. The changes in NTe–O revealed that the glass network predominantly contains TeO4 units with a small amount of TeO3 units and there is a structural transformation TeO4 ! TeO3 with an increase in SrO concentration. The O—Te—O bond angle distributions have a peak at 79_ and reveal that the Oequatorial—Te—Oequatorial 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 SrTe5O11 and the disordered monoclinic SrTeO3 phases, whereas the crystalline samples contain monoclinic SrTeO3 and the orthorhombic TeO2 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.