Structural study of solid solution of protonic conductors RbKH(SeO) by single crystal neutron diffraction

Kiyanagi, Ryoji  ; Matsuo, Yasumitsu*; Ohara, Takashi   ; Kawasaki, Takuro   ; Oikawa, Kenichi   ; Kaneko, Koji   ; Tamura, Itaru  ; Hanashima, Takayasu*; Munakata, Koji*; Nakao, Akiko*; Kawakita, Yukinobu  

The materials represented as MH(XO) is known to exhibit a super protonic conductivity at rather low temperature. The protonic conductivity emerges upon a structural phase transition, and the phase transition temperature varies depending on the elements at M and X. In addition, the protonic conductivity also varies depending on the elements, but the origin has not been uncovered. In order to clarify the relation between the structure and the protonic conductivity including the phase transition mechanism, Solid solutions of super protonic conductors, RbKH(SeO) (x=0, 1, 2, 3), were structurally investigated by single crystal neutron diffraction. The structure analyses showed evident linear relation between the lattice parameters and x. Meanwhile, K was found to preferably reside at one of the two M sites. A apparent relation between the occupancy of K at one site and the transition temperature and the hydrogen-bond length were demonstrated.