Synthesis and thermal analysis of the strontium and iron-doped lanthanum cobaltite nano-powder precursors

Powders of perovskite-type oxides, with the general formula La _0.8Sr_0.2Co_1-x:Fe_xO₃ (0.0<x<1.0), were synthesized by the amorphous citrate method, and chemical reactions in such a synthesis process were systematically investigated via thermal analysis. A series of decompositions of citric acid derivatives occurred at 575-750 K, and the subsequent oxidation of metal-organic amorphous compounds to perovskite-type oxides occurred at 650-850 K. The apparent activation energies for those processes in La_0.8Sr _0.2Co_0.5Fe_0.5O₃ (x= 0.5) were determined to be 101-105 and 45-49 kJ/mol, respectively, using a non-isothermal technique based on the Kissinger approach. The exothermic peaks of those reactions were temperature-dependent on Fe content (x), and they increased with increasing x, reaching a maximum at x = 0.7-0.8, and then decreased. An X-ray diffraction analysis of samples heat-treated at 873 K for 2 h revealed that they have a single-phase perovskite structure for all compositions, with their unit cell volume increasing with Fe content (x). The obtained oxides were nanoparticles with diameters of 10 to 20 nm, which increased with Fe content (x). The amorphous citrate route was found to give excellent starting gel precursors for the low-temperature synthesis of La_0.8Sr _0.2Co_1-xFe_xO₃ nanoparticles.