Surface oxide ion conduction of BaCe0.5Pr0.3Y0.2O3−δ thin film with complex mixed valence states

Abstract

Solid oxide fuel cells (SOFCs), which operate in the medium temperature range from 300 °C to 500 °C, are effective in shortening startup time and reducing fuel gas. In order to realize a practical electrolyte with high oxide ion conductivity, we have investigated the ionic conductivity of c-axis oriented BaCe0.5Pr0.3Y0.2O3−δ (BCPY) thin films with complex mixed valence states prepared on Al2O3 (0001) substrates by RF magnetron sputtering. The amount of oxygen vacancies on the surface in the as-deposited BCPY thin film was evaluated to be ∼6.7% by X-ray absorption spectroscopy and defect chemical analysis. The as-deposited film exhibited relatively high ionic conductivity (σT) of more than 10−1 S·K cm−1 and activation energy (E A) of ∼0.57 eV in the medium temperature range by thermal activation process on the surface. The energy separation between the top of the VB and the Fermi level was much larger than E A, indicating that the BCPY thin film is a pure oxide ion conductor without the contribution of electron or hole carriers. These results indicate that the c-axis oriented BCPY thin film can be applied to electrolyte of SOFC operating in the medium temperature range.