Solid State Ionics, Vol.100, No.3-4, 183-191, 1997
Structure, Oxygen Stoichiometry and Electrical-Conductivity in the System Sr-Ce-Co-O
Mixed oxides in the system Sr-Ce-Co-O were prepared by solid state reaction and by freeze-drying of precursor compounds followed by thermal treatment. Two types of perovskite oxides exist in the system : Solid solutions of the type Sr1-yCeyCoO3-x and mixed oxides of the type (1-y)SrCeO3-ySrCoO(3-x). Microstructures and phase compositions were determined by electron microscopy and X-ray diffraction. SrCoO3-x forms a solid solution of ceria on the A-site in the strontium cobaltite lattice up to 0.15 mol Ce. This solid solution corresponds to the high-temperature structure of pure SrCoO3-x and is characterized by high oxygen exchange and electrical conductivity. The oxygen deficiency x was measured by solid electrolyte coulometry. The oxygen deficiency of solid solutions Sr1-yCeyCoO3-x increases with temperature and decreases with pO(2) in the ambient atmosphere and with increasing Ce dopant concentration. The pO(2)-T-x diagram of the solid solution was determined. The T, pO(2) and dopant concentration dependencies of electrical conductivity were measured by a four-point d.c. technique. By Ce doping strontium cobaltite becomes a stabilized high-conductive material (maximum conductivity : 500 S cm(-1) at 400 degrees C, E-a = 0.025 eV, p-type). Above this temperature the T-coefficient of the conductivity changes from positive (semiconducting) to negative values.
Keywords:PEROVSKITE;OXIDES