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

Comparative study of the short-range structure of α-V2O5, α-TeO2 and xV2O5-(100 - x)TeO2 glasses using X-ray diffraction, Rietveld analysis and reverse Monte Carlo simulations

Vanadium-tellurite glasses, tetragonal TeO₂ and orthorhombic V₂O₅ crystalline samples were characterized for their atomic structure properties by synchrotron X-ray diffraction, pair distribution function analysis, reverse Monte Carlo simulations (RMC) and Rietveld analysis. The pair correlation function, G(r), of V₂O₅ shows the first peak at 1.61 Å. G(r) of TeO₂ shows three peaks at 1.57, 2.13 and 2.88 Å due to Te-O linkages of three different lengths, whereas the Te-Te atomic pair correlation shows a peak at 3.85 Å. The average coordination number of V with O in crystalline V₂O₅ is 4.39 while that of Te with O in crystalline TeO₂ is 3.71. G(r) of the vanadium tellurite glass shows the first peak at 1.90 Å due to overlapping Te-O and V-O atomic pair correlations. The RMC analysis on diffraction data of glasses found that the V-O coordination number is in the range 5.27-5.59 and the Te-O coordination number is 5.39-5.67. However, it is found that these coordination numbers cannot be clearly defined due to short-range disorder.

Structure of lithium tellurite and vanadium lithium tellurite glasses by high-energy X-ray and neutron diffraction

xLi₂O-(100 - x)TeO₂ (x = 20 and 25 mol%) and xV₂O₅-(25 - x)Li₂O-75TeO₂ (x = 1, 2, 3, 4 and 5 mol%) glasses were prepared by melt-quenching and their thermal and structural properties were characterized by differential scanning calorimetry, Raman spectroscopy, high-energy X-ray diffraction and neutron diffraction and reverse Monte Carlo (RMC) simulations. The glass transition temperature increases steadily with an increase in V₂O₅ mol% in lithium tellurite glasses due to an increase in the average single bond energy of the glass network. The X-ray and neutron diffraction structure factors were modelled by RMC technique and the Te-O distributions show the first peak in the range 1.85-1.90 Å, with V-O = 1.75-1.95 Å, Li-O = 1.85-2.15 Å and O-O = 2.70-2.80 Å. The average Te-O coordination number decreases with an increase in Li₂O mol% in lithium tellurite glasses, and the V-O coordination decreases from 5.12 to 3.81 with an increase in V₂O₅ concentration in vanadium lithium tellurite glasses. The O-Te-O, O-V-O, O-Li-O and O-O-O linkages have maxima in the ranges 86°-89°, 82°-87°, 80°-85° and at 59^o, respectively. The structural analysis of tellurite glasses reveal significant short-range and medium-range disorder due to the existence of a wide range of Te-O and Te-Te distances in the first coordination shell.

In situ high pressure neutron diffraction and Raman spectroscopy of 20BaO-80TeO2 glass

The short-range structure of 20BaO–80TeO₂ glass was studied in situ by high pressure neutron diffraction and high pressure Raman spectroscopy. Neutron diffraction measurements were performed at the PEARL instrument of the ISIS spallation neutron source up to a maximum pressure of 9.0 ± 0.5 GPa. The diffraction data was analysed via reverse Monte Carlo simulations and the changes in the glass short-range structural properties, Ba–O, Te–O and O–O bond lengths and speciation were studied as a function of pressure. Te–O co-ordination increases from 3.51 ± 0.05 to 3.73 ± 0.05, Ba–O coordination from 6.24 ± 0.19 to 6.99 ± 0.34 and O–O coordination from 6.00 ± 0.05 to 6.69 ± 0.06 with an increase in pressure from ambient to 9.0 GPa. In situ high pressure Raman studies found that the ratio of intensities of the two bands at 668 cm⁻¹ and 724 cm⁻¹ increases from 0.99 to 1.18 on applying pressure up to 19.28 ± 0.01 GPa, and that these changes are due to the conversion of TeO₃ into TeO₄ structural units in the tellurite network. It is found that pressure causes densification of the tellurite network by the enhancement of co-ordination of cations, and an increase in distribution of Te–O and Ba–O bond lengths. The original glass structure is restored upon the release of pressure.

The short-range structure of 20BaO–80TeO₂ glass was studied in situ by high pressure neutron diffraction and high pressure Raman spectroscopy.