Structure, chemical stability and electrical conductivity of perovskite La_0.6Sr_0.4M_0.3Fe_0.7O_3-δ (M = Co, Ti) oxides

The perovskite La_0.6Sr_0.4M_0.3Fe_0.7O_3-δ (M = Co, Ti) powders have been synthesized by the citrate gel method. The structural and chemical stability of the La_0.6Sr_0.4M_0.3Fe_0.7O_3-δ (M = Co, Ti) oxides were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) techniques. The electrical conductivities of the sintered La_0.6Sr_0.4M_0.3Fe_0.7O_3-δ (M = Co, Ti) ceramics were measured. The results demonstrate the chemical stability in H₂/helium (He) atmosphere of the La_0.6Sr_0.4Ti_0.3Fe_0.7O_3-δ oxide is improved significantly compared to that of the La_0.6Sr_0.4Co_0.3Fe_0.7O_3-δ oxide. The incorporation of Ti^3+/4+ ions in the perovskite structure can significantly stabilize the neighboring oxygen octahedral due to the stronger bonding strength, leading to the enhanced structural and chemical stability of the La_0.6Sr_0.4Ti_0.3Fe_0.7O_3-δ. In addition, the perovskite La_0.6Sr_0.4M_0.3Fe_0.7O_3-δ (M = Co, Ti) oxides possess much higher chemical stability in CO₂/He atmosphere than that of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ oxide, in which the perovskite structure is destroyed completely in a flowing CO₂-containing atmosphere.