Oxide Ion-Conducting Materials Containing Tetrahedral Moieties: Structures and Conduction Mechanisms

This Review presents an overview from the perspectiveof tetrahedralchemistry on various oxide ion-conducting materials containing tetrahedralmoieties which have received continuous growing attention as candidatesfor key components of various devices, including solid oxide fuelcells and oxygen sensors, due to the deformation and rotation flexibilityof tetrahedral units facilitating oxide ion transport. Emphasis isplaced on the structural and mechanistic features of various systemsranging from crystalline to amorphous materials, which include a varietyof gallates, silicates, germanates, molybdates, tungstates, vanadates,aluminates, niobate, titanates, indium oxides, and the newly reportedborates. They contain tetrahedral units in either isolated or linkedmanners forming different polyhedral dimensionality (0 to 3) withvarious defect properties and transport mechanisms. The developmentof oxide ion conductors containing tetrahedral moieties and the elucidationof the roles of tetrahedral units in oxide ion migration have demonstrateddiverse opportunities for discovering superior electrolytes for solidoxide fuel cells and other related devices and provided useful cluesfor uncovering the key factors directing fast oxide ion conduction.