Structural properties and electrochemical characteristics of Ba _0.5Sr_0.5 Co_1-x Fe_x O _3-δ Phases in Different Atmospheres

Ba_0.5Sr_0.5Co_1-xFe_x O _3-δ (0.2<x<0.8) powders were synthesized using a wet chemical procedure starting from nitrates as precursors and citric acid and ethylenediaminetetraacetic acid as complexing agents. The structural properties and the electrochemical behavior of the materials were investigated as a function of temperature (T), atmosphere (air, oxygen, and hydrogen), and Fe content (x) using simultaneous thermogravimetric and differential thermal analysis, X-ray diffraction analysis, and electrochemical impedance spectroscopy measurements. Significant differences were observed in the crystalline structure of the Ba_0.5Sr_0.5Co_1-xFe_x O_3-δ samples when they were fired in different atmospheres (inert and air; oxidizing and reducing). The formation of a cubic-type single phase in the 0.2 and 0.8 Fe content (x) range was confirmed under oxidizing conditions. The unit cell volume increased with decreasing (x) and in more oxidizing atmospheres. Further structural transformation with the collapse of the cubic structure was observed with increasing Fe content (x) under reducing conditions. The cubic-type Ba_0.5Sr_0.5Co _1-xFe_x O_3-δ solid solutions were tested as electrodes on Ce_0.8Sm_0.2 O_2-x pellets in symmetrical cells. The lowest obtained values of area specific resistance were 0.56 for Ba0.5 Sr0.5 Co0.2 Fe0.8 O3-δ in air and 0.25 cm² for Ba_0.5Sr_0.5Co_1-xFe_x O _3-δ in oxygen atmosphere at 1073 K.