Proton conduction mechanism and phase transition of (Rb,K)H(SeO)

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

The materials represented as MH(XO) (M=alkali metals, X=Se, S) are known to exhibit high protonic conductivities at relatively low temperature. Although the high protonic conductivity is considered to be due to the disorder of the hydrogen bonds in the materials, details have not been well understood. In addition, clarification of the phase transition to the high proton conducting phase is important in order to understand the realization of the high protonic conductivity. In this study, a high temperature neutron structural study was carried out on RbH(SeO), and the solid solution of RbKH(SeO) were also investigated by means of conductivity measurements and neutron structural studies. The high temperature neutron structure analyses revealed that the protons in the high proton conducting phase were two dimensionally distributed, which is considered to be the direct observation of the conducting protons. The solid solution exhibited non-linear decreases of the phase transition temperatures as the K concentration increased. The K ions were found to prefer to occupy one of two possible sites, of which occupancies apparently have close relationship with the phase transition temperature.