Muon dynamics in superprotonic conductors

Abstract

Abstract In order to clarify the mechanism of high proton conductivity ( σ H + ) for superprotonic conductors, MHXO 4 , where M = Cs and Rb, X = S and Se, μ + SR experiments have been performed in the temperature range between 250 and 450 K using single crystal samples. Here, MHXO 4 exhibits extraordinary high σ H + at T above its structural phase transition ( T c = 414 K for CsHSO 4 ) from a low- T monoclinic phase (Phase II) to a high- T tetragonal phase (Phase I). Since the asymmetry of weak transverse field (wTF) spectrum does not reach its maximum at ambient T , muonium (Mu) state is found to exist in both CsHSO 4 and CsHSeO 4 . The Mu fraction in wTF spectrum for CsHSO 4 is still a finite value even in Phase I, while the Mu state disappears in Phase I of CsHSeO 4 . The longitudinal field μ + SR measurements for observing the Mu state and its dynamics in CsHSO 4 , show fast Mu diffusion and the conversion from Mu to diamagnetic μ + in whole T range measured. Considering the fact that the σ H + in Phase I of CsHSO 4 is about 10 times larger than that of CsHSeO 4 , the Mu formation in Phase I implies the presence of the atomic hydrogen state and play a possible crucial role for the high σ H + in Phase I of CsHSO 4 .