Spectroscopic investigation of structure transformation in wavellite |
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| Authors: | G S Nazarova V P Lutoev T A Denisova |
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| Institution: | 1. Institute of Geology, Komi Science Centre of the Ural Division of the Academy of Sciences of the USSR, 54 Pervomajskaja st, 167610, Syktyvkar, USSR
2. Institute of Chemistry, Ural Department of the Academy of Sciences of the USSR, Sverdlovsk, USSR
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| Abstract: | The Electron Spin Resonance of VO2+, and the Infrared and Nuclear Magnetic Resonance of protons were studied in wavellite. Interpretation of1H NMR by shape function calculation allows us to determine the distribution of protons between molecular water, OH-groups, the three-spin magnetic configuration H3O+ and to ascertain the characteristic distances between protons. The spin-Hamiltonian parameters, Fermi contact interaction parameters and dipolar hyperfine coupling parameterPK were calculated. Three types of VO2+ complexes were detected in wavellite. It is found that VO2+(1)- and VO2+(2)-centres disappear and a new VO2+(3)-centre appears during annealing. VO2+(1) is more stable than VO2+(2). The parameters of the VO2+(3) complex change in the process of annealing. The transformation of VO2+(1) is connected with the destruction of acidic H3O+-groups, and the transformation of VO2+(2) correlates with the loss of weakly-bonded water molecules in the wavellite structure. ThePK parameter and Δg?Δg ⊥ ratio can be used as markers of disorder in the wavellite structure. |
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