Research progress of La₂Mo₂O₉-based oxide-ion conductor electrolyte materials

Recently, solid oxide-ion conductors have been receiving considerable attention owing to their potential applications in solid oxide fuel cells, oxygen sensors and so on. An innovative solid oxide-ion conductor, lanthanum–molybdenum oxide (La2Mo2O9), presents a reversible phase transformation at around 580°C from the low-temperature form α-La2Mo2O9 to the high-temperature form β-La2Mo2O9, leading to variation in the ionic conductivity. This paper reviews the research progress of lanthanum–molybdenum oxide and its doping systems; the structure and phase transition of the material, the conductivity of the oxide ion and the ionic conductivity and chemical stability of the material in a reducing atmosphere and at high temperatures are discussed. The research progress of the lanthanum–molybdenum oxide electrolyte was reviewed from four aspects – structure, conduction mechanism, preparation method and conductivity – and its future prospects assessed.