X-Ray Absorption and Magnetic Resonance Spectroscopic Studies of LixV6Ol3.
NAVAL ACADEMY ANNAPOLIS MD
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Polycrystalline LixV6O13 samples, 0.5 or x or 6, were prepared by chemical intercalation in n-butyl lithium and investigated by various spectroscopic techniques, including x-ray absorption, electron paramagnetic resonance EPR, and 7Li solid state nuclear magnetic resonance NMR. The EPR results, which are sensitive to the total V4 concentration, are consistent with the expectation that the formal oxidation state of vanadium decreases monotonically with the addition of Li. This is confirmed by near-edge x-ray absorption fine structure spectra at the vanadium K-edge. The extended x-ray absorption fine structure shows that the local symmetry of the vanadium sites, as determined by the intensity of the first V-O peak in the radial distribution function, decreases with increasing x from 0or x or 1 and then increases with increasing x from 1 or x or 5. However, structural correlations beyond the nearest neighbor atoms rapidly decrease with increasing Li content above x1.5. A modest lattice expansion due to intercalated Li is inferred from the observed increase in the V-O radial distribution peak position, from 1.93 Angstroms at xO in agreement with x-ray diffraction results to 2.02 Angstroms at x5. Variable temperature 7Li NMR linewidth and spin-lattice relaxation measurements demonstrate that, at all concentrations studied 0.5 or x or 6 the Li ions are relatively immobile, even at 200 deg. Centigrade. At low Li concentrations up to x1.5 the Li ions tend to reside near V5 sites rather than paramagnetic V4 or V3 sites.
- Inorganic Chemistry
- Physical Chemistry
- Electricity and Magnetism
- Atomic and Molecular Physics and Spectroscopy