In order to clarify the mechanism of high proton conductivity (σH+) for

superprotonic ionic conductors, MHXO4, where M = Cs and Rb, X = S and Se,

muon-spin rotation and relaxation (μ+SR) and quasi-elastic neutron scattering

measurements were performed at temperatures mainly in the vicinity of Tc, at

which MHXO4 undergoes a structural phase transition from a low-T orthorhombic

phase (Phase II) to a high-T tetragonal phase (Phase I). The μ+SR experiment

showed the presence of muonium (Mu) state even in Phase I only for CsHSO4,

while no Mu state was found in Phase I of CsHSeO4. Considering the fact that the

σH+ in Phase I of CsHSO4 was more than 10 times larger that of CHSe, this implied

a relationship between the presence of the atomic hydrogen (Mu) state and high σH+

in Phase I of CsHSO4. According to the quasi-elastic neutron scattering

measurements using a single crystal of CsHSeO4, line shapes of the energy spectra

along three crystallographic directions were found to be slightly anisotropic in

Phase I, in contrast to the isotropic conductivity reported by AC conductivity

measurements.

Study of Hydrogen Diffusion in Superprotonic Ionic Conductors, MHXO4, by Μ+SR

and QENS. Y.Ikedo, H.Nozaki, M.Harada, J.Sugiyama, T.J.Sato, Y.Matsuo,

K.Nishiyama, J.S.Lord, Y.Qiu, J.R.D.Copley: Nuclear Instruments and Methods in

Physics Research A, 2009, 600[1], 316-8