Proton Conduction Path in Rb₃H(SeO₄)₂Studied by High Temperature Neutron Single Crystal Diffraction

Abstract

A superprotonic conductor, Rb 3 H(SeO 4) 2 , was structurally investigated by means of neutron single crystal diffraction. The hydrogen bond length was found to gradually elongate as the temperature approaches the superprotonic phase transition temperature and jumps to a much longer value upon the transition. The structure of SeO 4 tetrahedron remains unchanged below the transition temperature and becomes more distorted upon the transition with disordered apical oxygen forming three disordered hydrogen bonds. Consequently, the hydrogen atoms (protons) in the hydrogen bonds are significantly delocalized 2-dimensionally being indicative of the proton migration. In the proton distribution map, there found small bumps between the adjacent hydrogen bonds. They may be interstitial sites for the conducting protons corresponding to a monomer state of [HSeO 4 ]- .

Phase Transition and Internal Crystal Structure of Superprotonic Conductor, Rb3−xKxH(SeO4)2

“…The two XO 4 tetrahedrons are connected with a hydrogen bond, and the hydrogen bond is isolated within the dimer in the room temperature phase. The superprotonic phase emerges upon a structural phase transition where the hydrogen bonds become disordered and build a 2-dimensional network [11]. In this phase the apical oxygen atom of XO 4 tetrahedron, which participates in the hydrogen bond, also become disordered partially occupying three equivalent sites.…”