Ionic conductivity in nano-scale CeO2/YSZ heterolayers

Abstract

CeO₂ based materials are promising candidates as solid oxide electrolytes within fuel cell systems. In this capacity, the oxygen anion conductivity is pivotal. Sata et al. [Nature, 2000, 408, 946–949] demonstrated the ability to ‘fine tune’ conductivities in BaF₂ and CaF₂ by generating BaF₂/CaF₂ heterolayers with different nanoscale film thicknesses. The resulting fluoride ion conductivities were found to be orders of magnitude higher compared with the component BaF₂ and CaF₂ materials. Similarly, it may be possible to fabricate CeO₂ thin films with tuneable conductivities. In this study, we explore this possibility using atomistic simulation. In particular, simulated amorphisation and recrystallisation was used to generate an atomistic model for a CeO₂/YSZ (yttrium stabilised zirconia) heterolayered system and, using this model, the ionic diffusivity, conductivity and associated activation energy barriers were calculated. However, in contrast to the BaF₂/CaF₂ system, the heterolayered CeO₂/YSZ system did not exhibit exemplary transport properties compared with the parent materials. This study describes a framework simulation procedure, which can be used in partnership with experiment, to explore a variety of microstructural features that may facilitate an increase in the ionic conductivity of heterolayered systems.