Quasielastic thermal neutron scattering experiment on the proton conductor SrCe_0.95Yb_0.05H_0.02O_2.985

On the basis of a QENS experiment using thermal neutrons on the proton conductor SrCe_0.95Yb_0.05H_0.02O_2.985 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 representing protons trapped on energetically lowered sites (nearby an Yb³⁺ ion on a Ce⁴⁺ site; trapped state); into this model we integrate a very fast localized motion taking place in the free state as a reorientation of the OH^.. ions. This motion is visible as a broad quasielastic component in the neutron energy spectra and exhibits a very low activation energy.