Structure, microstructure, optical and magnetic properties of cobalt aluminate nanopowders obtained by sol-gel process

Abstract

The aim of this study was to detennine the effect of different complexing agents and of the annealing tem­perature on the structural, morphological and optical properties of the synthesized precursors. Thus, cobalt aluminate nanoparticles were prepared by the sol-gel method using polyacrylic acid, glycine or citric acid as complexing agents. The synthesis performed at 500°C for 5 hours led to dark green powders composed of solid solutions denoted Co2+ [Agci-x)Co????;i]O4 and of amorphous alumina (39.8wt%). Calcination at temperatures above 900°C caused the powder colour to change from dark green to blue. A direct spinel structure Co2+ [Al????+] 04 is all the more achieved as the annealing temperature is high. The powder obtained using polyacrylic acid as the complexing agent at 900°C for 5 hours revealed the best morphology; it consisted of agglomerates of primary particles with a quasi- spherical shape and a size in the range 20-40 nm.