中性子回折・散乱から見たプロトン伝導体Ｋ３Ｈ（ＳｅＯ４）２

Abstract

Neutron powder diffraction, quasi elastic and inelastic scattering measurements were performed to examine the mechanism of phase transition and protonic conduction of K3H (SeO4) 2. SeO4 tetrahedra in the high-temperature phase (phase I) were rotationally displaced with the occupancy 1/3 and the crystal structure in the room temperature phase (phase II) remained locally. Proton distribution maps obtained from MEM describe that 13.4% of protons exist at inter-layer space. Proton diffusion constants were estimated as 1.9 (1) × 10-10 m2/s at 393 K and 2.1 (3) × 10-10 m2/s at 413 K respectively. A rotational mode of SeO4 tetrahedra causes change from R3m to C2/c. No soft mode was observed both of transversal acoustic and zone boundary optical modes, however, a diffusive spectrum was observed around 0 meV at the L-point (0.5 2 0) above Tc as an over-dumped phonon mode. The rotational mode of SeO4 tetrahedra drives the improper ferroelastic phase transition, and assists the disconnection and reconstruction of hydrogen bonds in the phase I.