Investigation of precursors in the preparation of nanostructured La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ via a modified combined complexing method

A complexing precursor of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ was synthesized through a modified combined complexing method to prepare homogenous La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ nanopowders with high yield at very low pH values. Precursors of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ compound with single chelator and of individual La, Sr, Co, Fe cations with combined chelators were also prepared and characterized. Fourier transform infrared spectroscopy results indicated EDTA could incorporate the Co, Fe cations into soluble complex under pH < 1. Using the citric acid-EDTA in this process could ensure the complexation of all cations and the best molar ratio of EDTA to metal cations was 0.5:1. Calcination of the combined complex precursor, according to XRD patterns, resulted in the crystallization of single phase LSCF by 700 °C. FESEM and BET analysis showed the calcined powder was homogenous and consisted of particles having sizes of approximately 70 nm. It is found that the sample of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ sintered at 1200 °C has a higher conductivity than at 1100 °C or 1300 °C, and the highest conductivity reaches 284 S cm^-1 at 700 °C.