Marco, José F.; Gancedo, J. Ramón; Gracia, Mercedes; Gautier, Juan Luis; Rios, Edmundo I.; Palmer, Helen M.; Greaves, Colin and Berry, Frank J.
Cation distribution and magnetic structure of the ferrimagnetic spinel NiCo2O4.
Journal of Materials Chemistry, 11(12) pp. 3087–3093.
The compound NiCo2O4, with spinel-related structure, has been prepared by thermal decomposition of metal nitrates and its bulk structural properties examined by means of magnetic measurements, neutron diffraction, X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The results suggest a delocalised electron distribution on the octahedral sites with average oxidation states of +3.5 and +2.5 for nickel and cobalt, respectively, and lead to a cation distribution for NiCo2O4 of (tet)[Ni0.93.5+Co1.12.5+](oct)O-4. This electronic configuration is consistent with magnetisation measurements if applied magnetic fields cause a charge redistribution on the octahedral sites to favour Co3+ and Ni3+. The surface of NiCo2O4 was examined by X-ray photoelectron spectroscopy (XPS) and found to have a different composition containing Co2+, Co3+, Ni2+, Ni3+ and, probably, Ni4+.
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