Synthesis of LaMO3 (M = Fe, Co, Ni) using nitrate or nitrite molten salts

Perovskite compound LaMO3 (M = Fe, Co, Ni) nanocrystals were successfully synthesized in molten nitrates or nitrites from a mixture of lanthanum nitrate and an M-containing nitrate for 2 h. The effect of the various process parameters on the phase purity, crystallite size, specific surface area and morphology of the synthesized nanocrystals were systematically studied by XRD, scanning electron microscopy (SEM), simultaneous TG/DSC and BET measurements. The results showed that salt medium, annealing temperatures (mainly 450–850 °C), oxidising properties and basicity of the melt played an important role in the synthesis of LaMO3. The addition of Na2O2 facilitated the reaction between La2O3 and NiO or Co3O4, leading to the formation of LaNiO3 and LaCoO3 at a much lower temperature of 450 °C. Pure hexagonal LaNiO3 nanocrystals were obtained in molten NaNO3–KNO3 eutectic with Na2O2 at 550–750 °C.

Research highlights▶ The molten salt, synthesis temperature, the oxidising properties, the basicity and oxidation states of the melt play an important role in LaMO3 synthesis. ▶ The system needs a careful optimisation of these parameters to obtain pure orthorhombic LaFeO3, hexagonal LaCoO3 and LaNiO3. Purely hexagonal LaNiO3 nanocrystals were successfully synthesized. ▶ SEM analyses were taken to investigate how the different parameters affect the microstructure of the samples. ▶ The specific surface area and crystallite size of LaMO3 show much difference in different system.