Solid-state NMR and XANES studies of lithium and silver silicate gels synthesized by the sol-gel route

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The objective of this study is to understand the effect of low temperature sol-gel synthesis on the microstructural properties of lithium [xLi2O-(1-x)SiO2; x=0.1-0.8 in steps of 0.1] and silver [xAg2O-(1-x)SiO2; x=0.1-0.8 in steps of 0.1] silicate xerogels via solid state nuclear magnetic resonance (NMR) and X-ray absorption near edge structure (XANES) techniques. The Li silicate xerogels were analyzed with solid-state 7Li and 29Si NMR and the Ag silicate xerogels were studied with Ag XANES. At high Li loading, 7Li NMR shows quadrupolar satellite transitions attributed to LiNO3, a phase also found with X-ray diffraction (XRD). At low Li loading, both NMR and XRD results show an amorphous xerogel. The silicate network is monitored with 29Si NMR and shows evidence of Li incorporation. For the Ag silicate xerogels, Ag-L-III XANES spectral studies show a local environment similar to AgNO3 for low Ag loading levels, and an increased Ag oxidation for higher Ag loading levels. Si K edge spectra show only an amorphous phase, with no evidence of a crystalline quartz phase. The electrical conductivity of the lithium silicates was estimated from impedance data and the highest conductivity is exhibited by the 0.3Li2O-0.7SiO2 composition xerogel. The conductivity dependence on loading level strongly suggests that the observed conductivity is due to Li+ mobility. However, further experimental studies are needed to rule out the possibility that the conductivity is, at least in part, due to H+ mobility. Variation in conductivity is explained qualitatively using existing theoretical models. © 2002 Elsevier Science B.V. All rights reserved.

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Journal of Non-Crystalline Solids

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