Superfast ion diffusion in mixed conductors

Materials that conduct both electrons and ions are important technologically for use in electrodes, permeation membranes, sensors and catalysts. They often consist of two or more components in a composite, with each mode of conduction catered for separately. This paper shows that a composite of the ‘super-ionic’ conductor rubidium silver iodide (RbAg₄I₅) and the electronic conductor graphite exhibits extremely fast diffusion of silver ions at the interface between the two materials, generating both a silver excess and a silver deficiency, analogous to single-phase mixed conductors, even though such behaviour is not possible in the individual phases.