Synthesis and structural characterization of trimetallic perovskite-type oxides, LaFe_xCo_1-xO₃, by the thermal decomposition of cyano complexes, La[Fe_xCo_1-x(CN₆)]·nH₂O

Heteronuclear complexes in the series La[Fe_xCo_1-x(CN₆)]·nH₂O, with = 0 ∼ 1 were prepared. Some complexes consisted of a mixture of hexagonal and orthorhombic phases, due to the presence of different amounts of crystallization water molecules. The lattice constants estimated for the orthorhombic structures increased linearly with increasing Fe content, x. The formation of the perovskite-type oxides by the thermal decomposition of the complexes has been studied by simultaneous thermogravimetric and differential thermal analysis (TG/DTA), X-ray fluorescence (XRF), and X-ray diffraction (XRD). The thermal decomposition of the complexes caused the formation of a single perovskitic phase at different temperatures, depending on the Fe content. Orthorhombic LaFeO₃ and hexagonal LaCoO₃ were already obtained at about 600°C from the decomposition of the corresponding complexes. For the complexes containing both Fe and Co, the elemental analysis showed that the Fe content was always lower than the prescribed ratios. The single perovskitic phase was formed with increasing temperature as the prescribed ratios of Fe and Co became more similar, the maximum being for x = 0.5; at 1000°C, a single hexagonal phase was formed for x ≤ 0.35, and a single orthorhombic phase was formed for x ≤ 0.44, both being the measured Values.