Fast Ionic Conduction in Solids

Abstract

Publisher Summary This chapter reviews the fast ionic conduction in solids. In a few solids, ionic conduction may approach a value typical of a molten salt or of proton conduction in a strong acid. Ionic conduction is an essential process in many solid-state reactions, and fast ionic conduction at low temperatures may offer a low-temperature synthetic route to compounds that are either metastable or unstable at normal sintering temperatures. A normal ionic conductor may be intrinsic or extrinsic. Most stoichiometric compounds are intrinsic conductors at low temperature; the ions are ordered so that they just fill sets of crystallographically equivalent sites, and mobile ions are created by exciting ions across an energy gap into interstitial positions. Solid electrolytes are used as thin-membrane separators of two reactants or of two products. These membranes must be dense, inert in their operational environment, without chemically reactive inhomogeneities, resistant to cracking under thermal or mechanical shock, and easily fabricated into large area sample. It is found that the disorder of the mobile ions results in partial occupancy of a set of sites that are energetically equivalent.