Surface oxide ion conduction of BaCe_0.5Pr_0.3Y_0.2O_3- thin film with complex mixed valence states

Solid oxide fuel cells (SOFCs), which operate in the medium temperature range from 300 degrees C to 500 C-degrees, 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-delta (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 similar to 6.7% by X-ray absorption spectroscopy and defect chemical analysis. The as-deposited film exhibited relatively high ionic conductivity (sigma T) of more than 10(-1) S center dot K cm(-1) and activation energy (E A) of similar to 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.