Effect of glycine concentration on the properties of LaCoO3 perovskite prepared by the glycine-nitrate process

摘要

LaCoO3 nanocrystals have been prepared by the glycine-nitrate process. The effect of glycine content in the synthesis solution on various properties of LaCoO3 has been studied in the glycine-to-nitrate molar ratio between 0.75 and 2.0. The samples are characterized by X-ray diffraction for phase purity and particle size, by transmission electron microscopy for particle size, by BET for surface area and by temperature-programmed reduction for reducibility of Co~(n+). XRD reflections show the presence of impurities in the as-prepared samples while only rhombohedral phase could be identified in the samples after calcination at 700 °C. For all the glycine-to-nitrate ratios tested, the particle size estimated from XRD data ranges from 58-69 nm, which are systematically lower than those determined by BET which ranged from 97-118 nm. TPR profiles of the samples show two major peaks; one due to the reduction of Co~(3+) to Co~(2+) and the other due to the reduction of Co~(2+) to Co0. The samples prepared under fuel-deficient and fuel-rich conditions show higher reducibility as compared to that of the sample prepared under stoichiometric conditions.