Abstract
The structures of xSrO-(100 - x)TeO2 (x = 5, 7.5, 8.5 and 10 mol.%) glass, anti-glass 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 (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.
Highlights
Tellurite glasses are technologically important materials due to their unique physical properties such as high refractive index, excellent non-linear optical properties, low phonon energies, wide optical transmission window, semiconducting properties and low melting temperatures (Wang et al, 1994; Rivera & Manzani, 2017; Zhou et al, 2011; Manning, 2011)
The present study aims at the elucidation of the short-range structure of glass, anti-glass and crystalline samples of the xSrO–(100 À x)TeO2 system by high-energy X-ray diffraction (HEXRD)
The density of all the samples was determined by the Archimedes method using dibutyl phthalate (DBP) as the immersion fluid at laboratory temperature
Summary
Tellurite glasses are technologically important materials due to their unique physical properties such as high refractive index, excellent non-linear optical properties, low phonon energies, wide optical transmission window, semiconducting properties and low melting temperatures (Wang et al, 1994; Rivera & Manzani, 2017; Zhou et al, 2011; Manning, 2011). All the atoms are randomly distributed from their ideal positions causing large irregularities which result in apparently high temperature factors compared with those generated by the thermal motion of atoms This produces considerable vibrational disorder and results in broad phonon bands in the infrared and Raman spectra of these samples, similar to glasses (Gupta & Khanna, 2018; Gupta et al, 2019; Kaur, Khanna et al, 2018). The present study aims at the elucidation of the short-range structure of glass, anti-glass and crystalline samples of the xSrO–(100 À x)TeO2 system by high-energy X-ray diffraction (HEXRD). The samples were characterized by density measurements, Raman spectroscopy and differential scanning calorimetry (DSC)
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