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

Abstract

The aim of this study was to determine 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+[Al3+2(1-x)Co3+2x]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+[Al3+2]O4 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.