Neutron powder diffraction study on the high-temperature phase of K3H(SeO4)2

Neutron powder diffraction measurements were carried out on K3H(SeO4)2 at 413 K in the protonic conducting phase (phase I) and at 298 K in the room-temperature phase (phase II) using a time-of-flight (TOF) neutron diffractometer VEGA. The crystal structures and nuclear density distribution maps were obtained by the Rietveld method and maximum entropy method (MEM). In the phase I, a proton in the hydrogen bond is disordered and SeO4 tetrahedron is rotationally displaced. The structure in the phase II locally remains even in the phase I. The amount of the proton in the hydrogen bond region varies from 87% for the phase II to 21% for the phase I. In the phase I, the proton densities were also obtained in the inter SeO4 layers space with the amount of 13%.