MICROSCOPIC MODELS FOR CONDUCTIVITY IN SOLID ELECTROLYTES

We discuss microscopic models for ionic conductivity with emphasis on material independent general results. Correlated motion of particles can be experimentally investigated by studying the frequency dependent conductivity σ(ω). We start the discussion with the simplest single particle jump diffusion model and then proceed to more advanced descriptions. All models which derive σ(ω) from the equilibrium transition rates contain no memory effects by construction. It can be shown that the correlated motion of interacting particles with no memory effects is always backward and [dσ(ω)]/dω ≥ 0. Experimentally [dσ(ω)/dω < 0 is found in Ag+ and Cu+ conductors and we discuss a model which allows for memory effects by coupling between diffusion and long lived vibrational fluctuations. © 1979.