Inelastic neutron scattering studies of the proton dynamics in bi-doped manganese oxides

The inelastic neutron scattering (ZNS) spectra from 16 to 4000 cm(-1) are p resented for lamellar-like manganese dioxides at 30 K: delta -MnO2 and chem ically modified Bi-delta -MnO2 at various reduction degrees (Bi-delta -MnO1 .96, Bi-delta -MnO1.88, Bi-delta -MnO1.78, Bi-delta -MnO1.70, and Bi-delta -MnO1.51). Three different types of protons are distinguished: water-like e ntities at 540 cm(-1), oxonium-like entities at 815 cm(-1), and free proton ic entities giving a continuum with constant intensity. The nonreduced samp les contain equimolecular mixtures of water-lace and oxonium-like entities, and there is no visible modification of the spectra attributable to the Bi entities. As the reduction degree increases, the band intensity at 540 cm( -1) decreases and that at 815 cm(-1) increases. Free protons are virtually unaffected. Even for the most reduced sample, there is no evidence for any feature specific to protons inserted in the [MnO6] layers. TRIO processes c an be distinguished: the removal of water molecules by the solvent on the o ne hand and the protonation of water-like entities on the other. (C) 2000 T he Electrochemical Society. S0013-4651(00)01-079-X. All rights reserved.