The concept of a crystallographic index was applied to the design of ceria-based electrolytes which maximized the oxide ionic conductivity. The suggested index considered the fluorite structure, and combined the expected O vacancy level with the ionic radius mismatch between host and dopant cations. By using this approach, the oxide-ion conductivity of Sm- or La-doped CeO2-based system was optimized. In observations of the microstructure at the atomic scale, both Sm-doped CeO2 and La-doped CeO2 electrolytes had large micro-domains of over 10nm in the lattice. On the other hand, Sm or La and alkaline-earth co-doped CeO2-based electrolytes with a high effective index had small micro-domains of around 1 to 3nm in the microstructure. The large micro-domains could prevent oxide ions from passing through the lattice. It was concluded that the improvement in ionic conductivity was reflected by changes in the microstructure at the atomic scale.

Oxide Ionic Conductivity and Microstructures of Sm- or La-Doped CeO2-Based Systems. T.Mori, J.Drennan, J.H.Lee, J.G.Li, T.Ikegami: Solid State Ionics, 2002, 154-155, 461-6