Influence of calcination temperature on phase formation and local structure of Co0.6Zn0.4Fe1.6Cr0.4O4 nanoparticles

Abstract

In this work, Co0.6Zn0.4Fe1.6Cr0.4O4 nanoparticles were synthesized by the solid state combustion technique and calcined at various temperatures from 700 to 900 °C. The phase formation, morphology and local structure of the calcined samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray absorption near edge structure (XANES) techniques. The XRD analysis revealed existence of the single-phase cubic spinel structure in the samples calcined at 900 °C. The average crystallite sizes increased as the calcination temperature increased. The XANES spectra allowed the valence states of Co2+, Cr3+, Fe3+ and Zn2+ ions in all calcined samples to be established. The clear agreement between measured and ab initio theoretical XANES spectra was the strongest evidence of Cr3+ and Zn2+ ions substituting for Co2+ and Fe3+, respectively, in CoFe2O4 inverse spinel structure. XANES results also suggested that the site occupancy of Co2+, Cr3+, Fe3+ and Zn2+ ions was mixed, with the majority Co2+ and Cr3+ ions occupying octahedral sites and the majority of Fe3+ ions occupying tetrahedral sites, while the Zn2+ ions equally occupied octahedral and tetrahedral sites in a ratio of 50:50.