Protonic and electronic conductivities of terbium doped strontium cerates

Electronic and protonic conductivities of Tb doped SrCeO₃ were measured in a hydrogen containing and hydrogen-free atmosphere of the same oxygen partial pressure in 500-900 °C. In a H₂ containing atmosphere, the material exhibits mixed electronic and proton-conductivity and, for SrCe_0.95Tb_0.05O_3-δ, the proton transfer number increases with decreasing temperature, from about 0.4 at 900 °C to about 0.8 at 500 °C. The total conductivity for SrCe_0.95Tb_0.05O_3-δ decreases from about 3 × 10^{- 3} S/cm in the reducing atmosphere to 4 × 10^{- 5} S/cm in air at 900 °C with an activation energy respectively of 39 kJ/mol and 76 kJ/mol for protonic and n-type electronic conduction. Results of XRD analysis show a decrease in the lattice volume of the SrCe_1-xTb _xO_3-δ with increasing Tb concentration. SrCe_1-xTb _xO_3-δ exhibits negligible proton-conductivity with x smaller than 0.005. At 800 °C under a reducing atmosphere, SrCe_1-xTb_xO_3-δ, with x > 0.005, are mixed electronic and proton conductors with a maximum proton-conductivity of about 3 × 10^{- 3} S/cm at x = 0.025 and proton transfer number of about 0.7 for x in the range of 0.005-0.125.