The doping of ceria (CeO2) with aliovalent dopants is known to enhance the oxide ion conductivity of ceria, which is important for a number of applications such as fuel cells, oxygen sensors and catalysis. Samarium (Sm) and Gadolinium (Gd) doped ceria are known to display high oxide ion conductivity in the intermediate temperature range (600-800°C) which is desirable for applications. In most applications of doped ceria multi-crystalline materials are used, which contain extended defects such as surfaces and grain boundaries. It has been suggested that the interfaces in these materials can result in reduced oxide ion conductivity; however, the majority of studies consider only the average effect of the interface and not the possible effects of different specifically defined interfaces. Despite their importance, there is little information about the effects of specific interfaces which is amenable to molecular dynamics simulations. Here we employ an interatomic potential derived for a range of trivalent dopants in ceria from ab initio data, a dipole polarizable ionic model (DIPPIM). The DIPPIM allows for polarization effects resulting from induced dipoles, which is important in systems containing O2- due to the highly polarizable nature of the ion. We discuss the effect of the (111), (221) and (210) surfaces and their corresponding specific tilt grain boundaries (Σ3, Σ9 and Σ5) on the performance of SDC and GDC as oxide ion conductors. Segregation of the oxygen vacancies to the boundary is observed along with enhanced diffusion of the oxide ions parallel to the grain boundary, while it is restricted perpendicular to the boundary.

Interfaces and their influence on oxide ion diffusion in ceria

253rd National Meeting (2017)

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