Electrical properties of ceria-carbonate composite electrolytes

Electrical conductivity and transport properties for composites consisting of samaria-doped ceria (SDC) and lithium-potassium carbonate were investigated at temperature of 450-550 deg. C. The conductivity at temperature above 500 deg. C as measured with ac impedance spectrum is 0.06-0.07 S cm{sup -1}, which is about one magnitude higher than that of SDC. The conductivity increases with carbonate content and is boosted to several times when the volume fraction of carbonate reaches 30%. An abrupt change in the electrical conductivity at 500 deg. C infers that superionic phase transition possibly occurs in the interface between SDC and carbonate. Negligible electronic conduction, {approx}10{sup -4} S cm{sup -1} at 500-550 deg. C, is observed with an ion-blocking cell. The dc transport numbers of carbonate ion and proton are determined by carbon dioxide and vapor concentration cells, respectively. Carbonate ionic transport number is about 0.67 above 500 deg. C whereas the protonic transport number is below 0.1. The oxygen ion transport number is calculated to be 0.23 at 550 deg. C and 0.31 at 500 deg. C.