Progress in the development of oxygen ion and mixed conductors is responsible for innovations in the fields of gas sensors, fuel cells, oxygen permeation membranes, oxygen pumps and electrolyzers. Commercialization has been impeded by materials stability and compatibility issues, high costs of fabrication and inadequate understanding of the interfacial phenomena controlling the operation of these devices. In this text we assemble a unique group of experts whose articles straddle, for the first time, all the key topical areas ranging from fundamentals relating to (a) defects, electrochemical,...