Characterization of the Nickel Cobaltite, NiCo2O4, Prepared by Several Methods: An XRD, XANES, EXAFS, and XPS Study
✍ Scribed by J.F. Marco; J.R. Gancedo; M. Gracia; J.L. Gautier; E. Rı́os; F.J. Berry
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- English
- Weight
- 201 KB
- Volume
- 153
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
The bulk structural properties of the nickel cobaltite, NiCo 2 O 4 , prepared by the thermal decomposition of carbonates, sol+gel methods, and the decomposition of hydroxides, have been examined by X-ray powder di4raction (XRD) and X-ray absorption spectroscopy (EXAFS and XANES). The results indicate, as expected, that Ni occupies the octahedral sites of the spinel structure while Co occupies both tetrahedral and octahedral sites. The XANES and EXAFS data are compatible with the existence of Ni 2؉ and Ni 3؉ . The structural data indicate that Co is present as Co 2؉ and Co 3؉ .The bulk cation distribution appears to be dependent on the synthesis procedure. The results of the surface examination by X-ray photoelectron spectroscopy (XPS) show that the surface composition is di4erent from the nominal bulk composition and also varies with the preparative method. All the XP spectra indicate the presence of Ni 2؉ and Ni 3؉ , their relative concentrations being noticeably dependent upon the synthesis method used. In contrast, the Co XP spectra recorded from all samples are very similar and indicate the presence of both Co 2؉ and Co 3؉ .