Neutron powder diffraction study of protonic conductor K ₃H(SeO₄)₂

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 (QENS) 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.