Recent experimental results concerning superionic conduction in zero-dimensional H-bonded crystals were presented, and a novel approach to the mechanism of proton conduction in the para-elastic phase was described. The key features of conduction in the high-temperature para-elastic (superionic) phase were 2 kinds of ionic state, H2XO4+e and XO4-e, which were formed by thermally breaking a H-bond, and H2XO4+e and XO4-e ionic states which moved coherently from an XO4 tetrahedron to a distant XO4 as a result of proton tunneling among the H bonds. It was shown that a characteristic feature of the band-like states, obtained from the itinerancy of H2XO4+e and XO4-e ionic states, was that of a Bethe lattice. That is, the appearance of a twin peak structure due to self-similarity. The calculated conductivity was of the order of 10-2S/cm, at and above the transition temperature. This was consistent with experiment.

On the Mechanism of Superionic Conduction in the Zero-Dimensional Hydrogen-Bonded Crystals M3H(XO4)2 with M = K, Rb, Cs and X = S, Se. H.Kamimura, Y.Matsuo, S.Ikehata, T.Ito, M.Komukae, T.Osaka: Physica Status Solidi B, 2004, 241[1], 61-8