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

Abstract

Complex oxides Sr_{2 − x}La_xFeCo_0.5Mo_0.5O_{6 − δ}, (x = 0.2, 0.4; δ ≈ 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 ≈ 2a_per, space group Fm3̄m) with partial ordering of Fe(Co) and Mo in the B positions. Based on the ⁵⁷Fe Mössbauer 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/H₂ 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 Ce_{1 − x}Gd_xO_{2 − x/2} and Zr_{1 − x}Y_xO_{2 − x/2}, high-temperature thermal expansion, and electrical conductivity in air and Ar/H₂, shows that Sr_1.6La_0.4Fe-Co_0.5Mo_0.5O_{6 − δ} (δ ≈ 0.03) perovskite is more attractive as an electrode material for medium-temperature symmetric solid oxide fuel cells than Sr₂FeCo_0.5Mo_0.5O_{6 − δ}.