STUDY OF PROTONIC MOBILITY IN CAHPO4-CENTER-DOT-2H(2)O (BRUSHITE) ANDCAHPO4 (MONETITE) BY INFRARED-SPECTROSCOPY AND NEUTRON-SCATTERING

We report the first quasi-elastic neutron scattering analysis of proto n mobility in the solid electrolyte CaHPO4 . 2H(2)O (brushite). We hav e studied this hydrated phosphate, in ponder state, from 190 to 520 K, using an incident wavelength of 5.12 Angstrom. The time of flight spe ctra are converted in S(Q, omega) structure factor and inelastic frequ ency distribution P(Q, omega) in the energy range 0-200 meV (0-1600 cm )(-1). 4 quasi-elastic contribution is clearly evidenced above room te mperature; it is fitted with a jump model, involving hydrogen bonds. T he 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 (E-a approxi mate to 0.145 eV). Above 450 K the dehydration of the compound is acco mpanied by the appearance of a long-range diffusive motion and by the disappearance of some low-frequency inelastic bands. (C) 1997 Academic Press.