Institute of Materials and Structure Science, HIgh Energy Accelerator Research Organization^* Intense Pulsed Neutron Source Division, Argonne National Laboratory, USA^** Graduate school of Engineering and Science, Ibaraki University, Japan^*** Research Reactor Institute, Kyoto University, Japan^**** Quantum Beam Science Directorate, Japan Atomic Energy Agency, Japan^***** Faculty of Engineering, Chiba Institute of Technology, Japan^******
○Fumihito Shikanai^* Keisuke Tomiyasu^* Ryoji Kiyanagi^** Masao Yonemura^*** Kenji Iwase^* Dyah Sulistyanintyas^* Tuerxun Wurnisha^* Kazuhiro Mori^**** Toru Ishigaki^***** Itaru Tsukushi^****** Susumu Ikeda^* Takashi Kamiyama^*

Hydrogen-bonded typed crystals of M₃X(YO₄)₂ have attracted much attention due to interesting phenomena in the high-temperature region. Most of the crystals undergo phase transition in the high-temperature, and show over 100 times higher electric conductivities than those at the room-temperature. It has been considered that the higher conductivities were due to the proton transfer in the crystals.
Crystal structures of protonic conductor K₃H(SeO₄)₂ in the phase I (conducting phase) and phase II (room-temperature phase) have been determined using a time-of-flight (TOF) neutron diffractometer VEGA. SeO₄ tetrahedra in the phase I were rotationally displaced with the occupancy 1/3 and the crystal structure in the phase II was remain locally. Proton distribution maps were obtained from the maximum entropy method (MEM) describe that the amount of the proton in a hydrogen bond were decline from 87.3 % to 21.4 % with increasing the temperature and 13.4 % of protons exist at inter-layer space. Incoherent quasi-elastic neutron scattering experiments performed by LAM80-ET spectrometer yield the QENS spectra of conducting protons. Proton diffusion constants are estimated as 1.9(1)×10^-10 m²/s at 393 K and 2.1(3)×10^-10 m²/s at 413 K respectively.