NMR Investigations of the Protonic Transport Mechanism in Composed Materials on the Basis of Cesium Acid Sulfates and Phosphates |
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Authors: | Alexander V Chernyak Vitaly I Volkov |
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Institution: | 1. Institute of Problems of Chemical Physics, Russian Academy of Sciences, Prospekt academika Semenova, 1, Chernogolovka, Russia
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Abstract: | The composite materials Cs(HSO4)1?x (H2PO4) x were investigated by X-ray phase analysis, differential scanning calorimetry, nuclear magnetic resonance (NMR) relaxation, pulsed field gradient NMR (PFG-NMR) and impedance spectroscopy. Three composite materials types x = 0.1 ÷ 0.3 mixture CsHSO4, α-Cs3(HSO4)2(H2PO4), β-Cs3(HSO4)2.5(H2PO4)0.5—compositions of area I; x = 0.4 ÷ 0.5 mixture α-Cs3(HSO4)2(H2PO4) and Cs2(HSO4)(H2PO4)—compositions of area II; x = 0.6 ÷ 0.9 mixture Cs2(HSO4)(H2PO4) and CsH2PO4—compositions of area III, were synthesized. The phase transition temperature from the low-to-high conductive phase for obtained composite materials is notably below (about 100 °C) than that for the individual components. The proton self-diffusion coefficients measured by PFG-NMR are lower than the diffusion coefficients calculated from proton conductivities data. The correlation times τ d controlling the 31P–1H magnetic dipole–dipole interaction were calculated according to data of the spin–lattice relaxation on 31P nuclei. The self-diffusion coefficients estimated from the Einstein equation are in good agreement with the experimental self-diffusion coefficients measured by PFG-NMR. It confirms the fact that the proton mobility is caused by the rotation of PO4 anion tetrahedra. |
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