Electronic structure studies of the spinel CoFe2O4 by X-ray photoelectron spectroscopy

The spinel CoFe2O4 has been synthesized by combustion reaction technique. X-ray photoelectron spectroscopy shows that samples are near-stoichiometric, and that the specimen surface both in the powder and bulk sample is most typically represented by the formula (Co0.4Fe0.6)[Co0.6Fe1.4]O4, where cations in parentheses occupy tetrahedral sites and those within square brackets in octahedral sites. The results demonstrate that most of the iron ions are trivalent, but some Fe2+ may be present in the powder sample. The Co 2p3/2 peak in powder sample composed three peaks with relative intensity of 45%, 40% and 15%, attributes to Co2+ in octahedral sites, tetrahedral sites and Co3+ in octahedral sites. The O 1s spectrum of the bulk sample is composed of two peaks: the main lattice peak at 529.90 eV, and a component at 531.53 eV, which is believed to be intrinsic to the sample surface. However, the vanishing of the O 1s shoulder peak of the powder specimen shows significant signs of decomposition.