Frequency-dependent conductivity of ionic liquids and superionic conductors

Abstract

The frequency-dependent ionic conductivities of molten AgCl, AgBr and AgI have been measured in the far-infrared (15-300 cm^-1). The results can be satisfactorily described by a simple phenomenological model which is based on the memory-function approach. Qualitative agreement is found between our experiments on molten silver halides and computer experiments on molten alkali halides. In the solid superionic conductor alpha -AgI a pronounced restrahl resonance was found. Remnants of this resonance still exist in the liquid state, but oscillation and diffusion occur on the same timescale. Superionic conductors of the AgI type thus occupy an intermediate position between an ordered ionic solid and an ionic liquid.