Crystal chemistry and properties of mixed ionic-electronic conductors

Oxides exhibiting mixed oxide-ion and electronic conducting (MIEC) properties have been attracting great interest in recent years due to their technological applications in solid-state electrochemical devices such as solid oxide fuel cells (SOFC), oxygen separation membranes, and electrochemical sensors. This article provides an overview of the composition-structure–property-performance relationships of several mixed conducting oxides: disordered ABO3 perovskite oxides, A-site ordered layered LnBaCo2O5+δ (Ln = lanthanide) perovskite oxides, Ruddlesden-Popper series of perovskite-based (La,Sr)n+1MnO3n+1 (n = 1–3 and M = Fe, Co, and Ni) intergrowth oxides, and hexagonal RBa(Co1-yMy)4O7 (R = rare earth or alkaline earth and M = Zn) oxides. Based on the available data, the role of chemical composition, crystal chemistry, and chemical bonding on the electrical and ionic transport, thermal, and electrochemical properties is discussed.