Synthesis And Characterization Of Perovskite Compound

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℃), 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℃. Pure hexagonal LaNiO3 nanocrystals were obtained in molten NaNO3-KNO3 eutectic with Na2O2 at 550-750℃. Pure perovskite compound SrFeO3 nanocrystals were successfully synthesized in molten NaNO3-KNO3 eutectic with Na2O2 from a mixture of strontium nitrate and ferric nitrate. It was found that metal nitrates is the suitable precursors and NaNO3-KNO3 eutectic with Na2O2 is the suitable salt medium, which results in the formation of pure SrFeO3 nanocrystals at a much lower temperature of 400℃.Perovskite compound LaFeO3 was prepared by solution combustion synthesis using lanthanum nitrate and ferric nitrate as oxidants, citric acid as organic fuel and ammonia and NaOH solution as pH regulator. The results showed that the pH regulator and the pH value of precursor solution had significant effect on the phase composition, crystallite size and morphology of LaFeO3. When the pH value of precursor solution was adjusted to 5,7 and 9 by ammonia, pure phase LaFeO3 could be obtained by solution combustion method and had a crystallite size of 29.4,37.2 and 32.3 nm, respectively, while a mixture of amorphous phase and Fe2O3 was obtained at pH=13. In contrast to this, NaOH solution as pH regulator, pure phase LaFeO3 could be obtained in the pH range of 5 to 13, and the LaFeO3 nanocrystals prepared at pH=7 had a net-like porous structure with the largest crystallite size of 30.5 nm. However, under the acidic and basic conditions, the obtained LaFeO3 products were an aggregate of irregular particles. Cubic LaMnO3 nanocrystals appeared in SEM photography when the product was prepared at pH=13 and using KOH as pH regulator. The LaMnO3 nanocrystals prepared at pH=10 and using ammonia as pH regulator had a net-like porous structure. With other pH regulators, the products were an aggregate of irregular particles.