Structure analysis and phase transition of super protonic conductor RbKH(SeO)

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

The materials represented as MH(XO) are known to exhibit super protonic conductivity at rather low temperature, but the mechanism of the super protonic phase transition and the protonic conduction have not been clarified. In this study, a mixed material, RbKH(SeO), was investigated by means of conductivity measurements and neutron diffraction. The neutron diffraction experiments were conducted on BL18 at J-PARC/MLF. The conductivity measurements revealed that the phase transition temperature significantly changes below x=2. Meanwhile, the neutron structure analyses revealed that K atoms exclusively occupy one of two non-equivalent sites for M atoms below x=2. These observations are indicative of the close relationship between the phase transition and the internal atomic arrangement.