Dynamical properties of an alkali chloride mixture in the glassy and liquid states

Molecular dynamics calculations have been carried out to reveal the dynamical properties of an alkali chloride mixture (50 mol% LiCl---40KCl---10CsCl) and pure LiCl in the liquid and glassy states. It is found that the mobility of Li⁺ ions in the mixture is significantly lower than that in LiCl, not only in liquid state but also in the glassy state. The partial dynamic structure factors, S_Li---Li (Q, ω) and S_{Cl---Cl (Q, ω)}, are evaluated to investigate the dynamical correlation between the Li⁺ and Cl⁻ ions. In LiCl glass, it is shown that the motions of the Li⁺ and Cl⁻ ions are highly correlated with each other, and both the acoustic and optic modes are spatially delocalized (Q < 1.8 Å⁻¹). On the other hand, in the mixture glass, the motion of the Li⁺ ions is almost independent of that of the Cl⁻ ions, and at small wavelengths there are the intense vibrations localized on single Li⁺ ions similar to an Einstein oscillation.