Mössbauer spectra for a variety of analysed spinel phases, representing a very wide range in both total iron content and Fe3+/(Fe2++Fe3+) ratio, indicate an essentially ordered arrangement of iron atoms in the crystal structures of natural chromite and Cr-bearing spinels. All of the Mössbauer spectra have been rationalised by fitting just two doublets, assigned to Fe2+ in the tetrahedral (T) cation site and Fe3+ in the octahedral (M) site, using initial Mössbauer parameters for synthetic end-member compositions. Calculated Fe3+ to Fe2+ ratios agree well with wet chemical data. This ideal Fe2+ (T site) -Fe3+ (M site) ordering scheme has been disregarded in recent Mössbauer studies on chromite, and complex fits and explanations have been proposed. However, we find no evidence in the Mössbauer spectra of the spinels investigated in this study of T site Fe3+ and M site Fe2+ or of electron delocalization (or chargehopping) effects.
ASJC Scopus subject areas
- Geochemistry and Petrology