Atomistic Simulation of Subtle Microstructures in CeO2-Based Electrolyte for Design of the State-of-the-Art Fuel Cells

The research work of the microstructure of rare-earth-doped ceria as electrolyte in solid oxide fuel cell is introduced in this chapter. The results of subtle microstructures at atomic and nano scales including defect clusters and nano-sized domains studied by atomistic computer simulation combined with microstructure observation by transmission electron microscopy are focused on. These inhomogeneities are formed by aggregation of vacancies and dopants ions. The phase transformation from F-type structure to C-type structure in doped ceria is not a sudden change, but gradually takes place from clusters to domains, and then to C-type precipitates with increasing the doping concentration. Several stable cluster structures can be considered as unit structures for larger clusters. A unique dumbbell structure formed with six oxygen vacancies has been identified as the building block for defect cluster growth and sequentially for the evolution from F- to C-type structure. Furthermore, the results of various types of doped ceria suggest that the subtle microstructure change is a common phenomenon in rare-earth-doped ceria. The capability of the growth of defect cluster is affected by dopant type, which can explain the dopant type dependency of domain development with increasing doping concentration in heavily doped ceria. Then, an example of doped ceria sintered at different temperature shows that the ionic conductivity can be improved by controlling these subtle microstructures.