Oxide ion conduction in ytterbium-doped strontium cerate

Abstract

The perovskite compound SrCe 0.95 Yb 0.05 O 2.975 , reported to be a high-temperature protonic conductor, has been studied in atmospheres of N 2 /O 2 and N 2 /H 2 using impedance spectroscopy and concentration cell techniques. Below 600°C, the compound exhibited higher conductivity in N 2 :5% H 2 than in air, though the activation energies in each case were found to be similar, 0.59 and 0.65 eV respectively. At 600°C, the conductivity in both atmospheres attained a value of ≈2×10 −3 Ω −1 cm −1 , while in oxygen-rich atmospheres, it followed a positive P O 2 dependence, demonstrating that the compound is a mixed oxide ion/p-type electronic conductor, with ionic transport numbers of 0.97 in air, and 0.76 in oxygen. EMF measurements on oxygen concentration cells at 800°C indicated mixed oxide ion/electronic conduction with ionic transport numbers of 0.60 to 0.67, while measurements on a hydrogen concentration cell indicated mixed electronic/ionic conduction with an ionic transport number identical to that in oxygen. The results suggest that ionic conduction in the perovskite is dominated by oxide ion transport, and that any protonic transport occurring in hydrogen-rich atmospheres is coupled to oxide ion transport.