Dynamics of mobile ions in solid electrolytes – conductivity spectra and the concept of mismatch and relaxation

Abstract

Experimental conductivity spectra σ( ν) of solid electrolytes with disordered structures, both crystalline and glassy, exhibit surprisingly similar overall characteristics. On closer inspection, however, differences become apparent as well. These include slightly different shapes of the frequency-dependent functions σ( ν) and, in the low-frequency limit, the observation of either Arrhenius or non-Arrhenius temperature dependences. The empirical features of conductivity spectra, both the common and the more specific ones, are now well reproduced with the help of two coupled rate equations describing the evolution of the ion dynamics with time in a very general fashion. The present treatment, which is based on the jump relaxation model, is called the concept of mismatch and relaxation (CMR). From the CMR, realistic spectra σ( ν) are derived for crystalline and glassy ion conductors at different temperatures. Characteristic features in the spectra are traced back to their dynamic origins.