Characterization of LaCoO_3 powders obtained by water-based sol-gel method with citric acid

摘要

LaCoO_3-based materials are studied because they exhibit interesting, electrical, magnetic and catalytic properties. In this contribution, LaCoO_3 powders were synthesized by sol-gel method in aqueous medium starting from metal nitrates or acetates, and citric acid as the chelating agent at room temperature. The relation between the reactions in solution, crystallization pathway and morphology is discussed. The dried powders were amorphous. Their thermal decomposition occurs stepwise upon heating to 400 deg C for nitrate or 500 deg C for acetate-based precursors, respectively. Pure perovskite LaCoO_3 phase is formed after heating at 600 deg C in the case of nitrates while in the case of acetates separation of phases occurs when 2 mol of citric acid are used. The choice of the precursor influences the morphology of the powders heated at 600 deg C. The nitrate-based powders are composed of agglomerates of fine particles while the acetate-based powders mainly consist of gel fragments. Some preliminary electrical and catalytic properties are also presented.