Electric conductivity and oxygen permeability of modified cerium oxides

Electrical conductivities of samarium (Sm), terbium (Tb), praseodymium (Pr) and zirconium (Zr) doped ceria membranes were measured in T = 600–900°C and pO₂ = 10^–22–0.21 atm. Doping Sm and Pr in CeO₂ respectively enhances the ionic conductivity and electron-hole conductivity of ceria. Sm-Pr doped ceria exhibits both n-type (at lower pO₂) and p-type (at high pO₂) electronic and ionic conductivity in the temperature range studied. Adding Tb in the Sm doped ceria causes a reduction in ionic conductivity. Zr-Pr doped ceria is an n-type electronic conductor at low and p-type electronic conductor at high pO₂. The ionic conductivity of Zr-Pr doped ceria is lower than Sm doped ceria but higher than pure ceria. Oxygen permeation flux through the Zr-Pr doped ceria membrane, dominated by the slow oxygen ionic conduction, is similar to the ytttria doped bismuth oxide membrane, and smaller, but close to that of perovskite-type lanthanum cobaltite membrane.