Fast ion transport in oxide glasses

The discovery of fast ion transport in solids has in recent years stimulated much interest in the scientific community both with regard to obtaining improved understanding of the phenomenon and applying such materials in advanced battery systems. More recently the phenomenon of fast ion transport has also been observed to occur in increasing numbers of amorphous systems. In this paper we review recent transport data obtained in over 100 glasses which appear to exhibit exceptionally high Ag, Li, Na and F ion conductivities at temperatures far from the melting points. We also include results recently obtained in our laboratory for glasses in the lithium borate system. Common characteristics of these glasses are summarized and are compared with predictions of classical diffusion theory. Relatively low and composition-independent values of σ₀ indicate poor agreement with a simple isolated-ion diffusion model, while composition-dependent activation energies are related to structural changes. Some glasses share similar properties with their crystalline counterparts while others do not. This is discussed in terms of the relative disorder already existing within the crystals. The need for improved characterization of glasses is also discussed.