Structural investigations of tungsten silver phosphate glasses by solid state NMR, vibrational and X-ray absorption near edge spectroscopies |
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Authors: | Silvia H. Santagneli Matthias T. Rinke Younes Messaddeq Hellmut Eckert |
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Affiliation: | a Institute of Chemistry, São Paulo State University, UNESP,CP 355, Araraquara-SP,14801-970, Brazilb Institute of Science and Technology, Universidade Federal de Alfenas, Campus de Poços de Caldas, Alfenas-MG, Brazilc Institut für Physikalische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstr. 30, D-48149 Münster, Germanyd Centre of Optics Photonics and Lasers, Laval University, Québec, Canada G1VOA6 |
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Abstract: | Glasses were prepared in the pseudo-binary system (1 − x)AgPO3-xWO3 (0≤ × ≤ 0.6 mol%). The structural evolution of the vitreous network was studied as a function of composition by thermal analysis, Fourier Transform Infrared spectroscopy (FTIR), Raman scattering, high resolution 31P solid state NMR and XANES at the W-L1 absorption edge. For compositions with x ranging from 0 to 0.5 a pronounced increase in the glass transition temperature is observed, suggesting a significant increase in the glass network connectivity. At the same time Raman spectra indicate that tungsten atoms are linked to non-bridging oxygen atoms (W-O- or W=O bonded species) whereas the 31P MAS-NMR spectra indicate the successive formation of new P-O-W linkages. The formation of some anionic tungsten sites (if these are revealed by the presence of W-O terminal bonds) implies an increase in the average degree of polymerization of the phosphate network, which is consistent with the compositional evolution of the 31P MAS-NMR spectra at low x values. For higher x-values, the Raman spectra indicate the presence of W-O-W linkages. W-L1 XANES data indicate that at least 90% of tungsten atoms are octahedrally coordinated. |
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Keywords: | Tungstate glasses Glass structure Solid state NMR Raman XANES |
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