Emergent ionic conduction in aliovalently-doped fast ion conductors

Abstract

Fast-ion conducting materials are an important class of materials commonly used in all-solid-state fuel cells and electrolyzers. The material structure contains diverse dopant-rich to dopant-lean cation arrangements that individually contribute to the overall ionic current. This makes it both challenging and fascinating to understand the ion conduction behavior. Ionic conductivity relations in terms of microscopic ion hopping for these moderately to heavily doped oxide materials, typically needed for materials design and optimization, are not available. We examine the oxygen ordering and movement in yttria stabilized zirconia (YSZ), a popular fast ion conductor used in high temperature fuel cells, as a function of the applied electric field E and show that the emergent current density j(E) can be written as . This expression contains contributions from at least 22 different local cation arrangements. The reduced complexity model provides a fundamental understanding of the competing local driving forces and a connection to the observed macroscopic ionic conductivity and Ohm's law behavior.