Synthesis and Study of (Sr,La)2FeCo0.5Mo0.5O6- δ Oxides with Double Perovskite Structure

Complex oxides Sr2 - xLaxFeCo0.5Mo0.5O6 - delta, (x = 0.2, 0.4; delta approximate to 0.03-0.15) have been first synthesized by the sol-gel method. Their crystal structures have been refined by the Rietveld method; the refinement showed that the complex oxides have the structure of cubic double perovskite (a approximate to 2a(per), space group Fm3m) with partial ordering of Fe(Co) and Mo in the B positions. Based on the Fe-57 Mossbauer measurements, the average formal oxidation state of iron has been found to decrease from +3.20 (x = 0.0) to +3.04 (x = 0.4). Our study of the behavior of perovskites in a reducing Ar/H-2 atmosphere (8%) revealed a decrease in the reduction resistance with decreasing La content (x = 0.4 -> 0). The combination of the properties studied, namely chemical stability with respect to the reaction with Ce1 - xGdxO2 - x/2 and Zr1 - xYxO2 - x/2, high-temperature thermal expansion, and electrical conductivity in air and Ar/H-2, shows that Sr1.6La0.4Fe-Co0.5Mo0.5O6 - delta (delta approximate to 0.03) perovskite is more attractive as an electrode material for medium-temperature symmetric solid oxide fuel cells than Sr2FeCo0.5Mo0.5O6 - delta.