Synthesis and characterization of LaFeO3 powders prepared by a mixed mechanical/thermal processing route

Abstract

Lanthanum ferrite, LaFeO3 (LF), has raised considerable interest since it can be used in many applications such as solid-oxide fuel cell electrode, sensor material (H2O and ethanol) and catalyst. Since the conventional ceramic route of synthesis has some disadvantages, mainly related to an exaggerated grain growth, LF has been prepared by different methods including combustion synthesis, sol–gel, hydrothermal processes, polymerizable complex method and mechanochemistry. As concerns this last method, a problem occurs due to the moisture sensitivity of La2O3. To overcome the problem, we used lanthanum acetate sesquihydrate [La(CH3COO)3·1.5H2O] and iron (II) oxalate dehydrate [FeC2O4·2H2O] as precursors. The mechanism of the solid-state reactions in the mixtures has been studied by TG–DSC and XRPD. Synthesis of LaFeO3 has been realized by annealing the mechanically activated mixtures for 3 h at temperatures between 500 and 800 °C. While LF prepared at 500 °C < T < 600 °C has an amorphous character, LF obtained at T ≥ 600 °C is free from carbonaceous impurities as it is shown by FT-IR and TG measurements. The specific area of the LaFeO3 powders obtained starting from the mechanically activated mixture is decreasing by increasing the annealing temperature. On the contrary, the annealing on samples of physical mixture at temperatures up to 800 °C only yields a mixture of LaFeO3, La2O3 and Fe2O3.