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Capable materials for solid oxide fuel cell cathodes have to provide high electrocatalytic activity for oxygen reduction as well as sufficient electronic conductivity and good ionic transport properties (1). This study compares the electrical transport properties and the oxygen exchange properties of two promising cathode materials for operating temperatures between 600 and 800°C: La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ and Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ . Both materials were synthesized by spray pyrolysis and characterised with respect to phase purity and to the element ratio by XRD and ICP-AES analysis. The sintering behaviour of the calcined powders and the coefficients of thermal expansion of dense sintered samples were studied by dilatometry. As important parameters for the oxygen exchange reaction the chemical surface exchange coefficients ( k ) and chemical diffusion coefficients ( D ) as well as the electrical conductivities are compared.

The thermally activated proton diffusion in BaZr 0.9 Y 0.1 O 3-d was studied with electrochemical impedance spectroscopy (IS) and quasi-elastic neutron scattering (QENS) in the temperature range 300-900 K. The diffusivities for the bulk material and the grain boundaries as obtained by IS obey an Arrhenius law with activation energies of 0.46 eV and 1.21 eV, respectively. The activation energies obtained by IS for the bulk are 0.26 eV above 700 K and 0.46 eV, below 700 K. The total diffusivity as obtained by IS is by one order of magnitude lower than the microscopic diffusivity as obtained by QENS. The activation energies obtained by QENS are 0.13 eV above 700 K and 0.04 eV, below 700 K. At about 700 K, the diffusion constants for IS and QENS have a remarkable crossover, suggesting two processes with different activation energies.

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This study compares the electrical transport and the oxygen exchange properties of two mixed conducting materials between 600 and 800°C, namely La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−␦ ͑LSCF͒ and Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−␦ ͑BSCF͒. Both materials were synthesized by spray pyrolysis and characterized by the electrical conductivity relaxation technique. LSCF has the higher electrical conductivity ͑257-412 S cm −1 between 450 and 900°C͒, while BSCF shows faster oxygen exchange kinetics and diffusion. The expansion of both materials between 600 and 800°C ͑BSCF = 27.3 ppm/K, LSCF = 15.5 ppm/K below 700°C up to 27.5 ppm/K at T Ͼ 800°C͒ does not match with the common electrolytes for solid oxide fuel cells.