Dynamical behavior ofSeO4tetrahedra in protonic conductorK3H(SeO4)2

Abstract

Neutron powder diffraction and inelastic neutron scattering experiments were performed to clarify the mechanism of phase transition and protonic conductivity of ${\text{K}}_{3}\text{H}{({\text{SeO}}_{4})}_{2}$. A rotational ${\text{SeO}}_{4}$ tetrahedra mode at the zone boundary $L$-point accounts for the symmetrical change in space group from $R\overline{3}m$ to $C2/c$. No significantly anomaly was observed in the transversal acoustic and under-damped optical modes, while a broad spectrum was observed around 0 meV at the $L$-point above ${T}_{C}$. The spectrum depends on the temperature and the dependence is represented by the soft mode due to an over-damped phonon both $Q$ and energy space. The rotational mode of tetrahedra drives the improper ferroelastic phase transition.