A single microscopic approach for ionic transport in glassy and polymer electrolytes

Abstract

A micro-structural model is developed for non crystalline materials presenting a glass transition phenomenon. A singled expression of the conductivity temperature relationship, both below and above the glass transition temperature, is obtained while the electrical behaviour of such materials is usually described by different relationships depending on the temperature domain. In this model, below and above T g, the charge carrier formation results from the partial dissociation of ionic pairs as it is the case for the formation of the Frenkel defects. In the solid state, the defect migration proceeds from an indirect interstitial mechanism, while in the super-cooled state, a cooperative mechanism involving the neighbouring atoms is superposed to the first one, justifying a deviation from an Arrhnius law to the so called “free volume” behaviour. This approach allows numerical fits of experimental data in the whole temperature range which leads to accurate determinations of the main thermodynamic parameters of the ionic transport: the ideal glass transition temperature and both the formation and migration enthalpies.