Influence of codoping on the conductivity of Sc-doped zirconia by first-principles calculations and experiments

Abstract

Doped zirconia is a promising electrolyte candidate for Solid Oxide Fuel Cells (SOFCs). The effects of dopants and their interactions with oxygen vacancies on the conduction properties have been systematically investigated by density functional theory (DFT) calculations and experiments. The influences of dopants' valences and radii on the defect formation energies and defect binding energies are discussed. Our results show that, for Scandia stabilized zirconia (ScSZ) co-doped with In3+, Yb3+, or Bi3+, the defect formation energy differences and binding energy differences of different sites are low, which indicates that for these co-doping cases the oxygen vacancies distribute more randomly, and are more beneficial for improving the oxygen vacancy diffusing efficiency. The inner influence mechanisms of the co-dopants are discussed from the aspects of elastic and electrostatic effects. Oxygen diffusion barriers in ScSZ co-doped with various elements are also calculated by the saddle point method. The calculated results indicate that the diffusion barrier orders for different edges are ESc-Zr < EZr-Zr < ESc-M for RM > RZr and ESc-Zr ≈ ESc-M < EZr-Zr for RM < RZr. Furthermore, relative experiments are carried out to verify the theoretical results.