Ionic conduction and microstructure of the ceria-strontia system

Abstract

Ionic conduction of oxygen in the ceria-strontia system, (CeO 2) 1- x (SrO) x , was investigated as a function of temperature, partial pressure of oxygen, and oxide composition, together with its crystal structure, density and microstructure. Undoped ceria and its solid solution of strontia have the cubic fluorite structure. Samples above the solubility limit of strontia ( x>0.08) were mixtures of 0.92CeO 2·0.08SrO and SrCeO 3. The ionic conductivity was greatly enhanced with an addition of small amount of strontia to ceria. The conductivity of ceria-strontia system at 0.05⩽ x⩽0.40 was much higher than that of calcia-stabilized zirconia. At this composition range, the ionic transference number was nearly unity even at 600°C. It was found that the excellent ionic conductivity was little affected by the presence of the second phase of SrCeO 3 at 0.1< x<0.4. Further increase in strontia content leads to a decrease in conductivity at x=0.5. The (CeO 2) 0.90(SrO) 0.10 sample is regarded as a pure ionic conductor at P O 2 >10 −11 atm (900°C), where the conductivity is a constant versus P O 2 . The n-type electronic conductivity increased with a decrease in P O 2 and became dominant below P O 2 =10 −11 atm.