Abstract
We report the first quasi-elastic neutron scattering analysis of proton mobility in the solid electrolyte CaHPO4·2H2O (brushite). We have studied this hydrated phosphate, in powder state, from 190 to 520 K, using an incident wavelength of 5.12 Å. The time of flight spectra are converted inS(Q,ω) structure factor and inelastic frequency distributionP(Q,ω) in the energy range 0–200 meV (0–1600 cm)−1. A quasi-elastic contribution is clearly evidenced above room temperature; it is fitted with a jump model, involving hydrogen bonds. The quasi-elastic and inelastic scattering data are compared with FTIR results. Two kinds of motions are determined: jumps of acidic protons on hydrogen bonds and vibrations of lattice water molecules associated with the motion of their hydrogen atom on hydrogen bonds (Ea≈0.145 eV). Above 450 K the dehydration of the compound is accompanied by the appearance of a long-range diffusive motion and by the disappearance of some low-frequency inelastic bands.
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