QUASI-ELASTIC THERMAL-NEUTRON SCATTERING EXPERIMENT ON THE PROTON CONDUCTOR SRCE0.95YB0.05H0.02O2.985

On the basis of a QENS experiment using thermal neutrons on the proton conductor SrCe0.95Yb0.05H0.02O2.985 we extend our two-state model for the proton diffusion in this compound. This model was developed from a recent high resolution QENS experiment using cold neutrons, with the first state representing free diffusion of the protons (jumping from oxygen to oxygen forming OH-; free state) and the second state represe nting protons trapped on energetically lowered sites (nearby an Yb3+ i on on a Ce4+ site; trapped state); into this model we integrate a very fast localized motion taking place in the free state as a reorientati on of the OH- ions. This motion is visible as a broad quasielastic com ponent in the neutron energy spectra and exhibits a very low activatio n energy.