Hopping models for ion conduction in noncrystals

TL;DR

This paper explores ion conduction in noncrystals using hopping models, emphasizing the role of percolation and the random barrier model in explaining universal conductivity behaviors across different disordered materials.

Contribution

It demonstrates how percolation theory and the random barrier model explain universal ac conductivity and temperature dependence in ion conduction of noncrystalline materials.

Findings

Random barrier model reproduces time-temperature superposition in ac conductivity.

Percolation is fundamental to understanding ion conduction universality.

Temperature dependence of dc conductivity is linked to percolation phenomena.

Abstract

Ion conduction in noncrystals (glasses, polymers, etc) has a number of properties in common. In fact, from a purely phenomenological point of view, these properties are even more widely observed: ion conduction behaves much like electronic conduction in disordered materials (e.g., amorphous semiconductors). These universalities are subject of much current interest, for instance interpreted in the context of simple hopping models. In the present paper we first discuss the temperature dependence of the dc conductivity in hopping models and the importance of the percolation phenomenon. Next, the experimental (quasi)universality of the ac conductivity is discussed. It is shown the random barrier model is able to reproduce the experimental finding that the response obeys time-temperature superposition, while at the same time a broad range of activation energies is involved in the conduction process. Again, percolation is the key to understanding what is going on. Finally, some open problems in the field are listed.