中性子回折・散乱から見たプロトン伝導体K_3H (SeO_4)_2 Structure and Dynamics of Protonic Conductor K_3H (SeO_4)_2 Studied by Neutron Diffraction and Scattering
Neutron powder diffraction, quasi elastic and inelastic scattering measurements were performed to examine the mechanism of phase transition and protonic conduction of K<SUB>3</SUB>H (SeO<SUB>4</SUB>) <SUB>2</SUB>. SeO<SUB>4</SUB> 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<SUP>-10</SUP> m<SUP>2</SUP>/s at 393 K and 2.1 (3) × 10<SUP>-10</SUP> m<SUP>2</SUP>/s at 413 K respectively. A rotational mode of SeO<SUB>4</SUB> tetrahedra causes change from <I>R</I>3<I>m</I> to <I>C</I>2/<I>c</I>. 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 <I>T</I><I><SUB>c</SUB></I> as an over-dumped phonon mode. The rotational mode of SeO<SUB>4</SUB> tetrahedra drives the improper ferroelastic phase transition, and assists the disconnection and reconstruction of hydrogen bonds in the phase I.
日本結晶学会誌 50(3), 224-230, 2008-06-30
The Crystallographic Society of Japan