The results of atomistic simulation calculations and X-ray photo-electron spectroscopy were used to refine the structures of γ-Fe2O3 and Fe3O4 doped with tetravalent ions. Such structures were of interest because of the effect of doping upon the properties of the oxides. The calculations confirmed that occupation by Sn4+ and Ti4+ of the octahedral sites was more favourable than was occupation of the tetrahedral sites, and indicated that the M4+ ions were substituted at Fe sites rather than occupying interstitial sites. In the case of Fe2O3, X-ray photo-electron spectroscopic results showed that no reduction of Fe3+ occurred. As for potential balancing defects, the calculations indicated that vacancies on Fe sites, with 6 nearest-neighbour Fe atoms were favoured. In the case of Fe3O4, the results suggested that the reduction of Fe3+ to Fe2+ was preferred, and that reduction occurred on a site adjacent to M4+. Such small clusters localised disruption to the crystal structure.

Investigation of Defect Structures Formed by Doping Tetravalent Ions into Inverse Spinel-Related Iron Oxides using Atomistic Simulation Calculations. E.A.Moore, A.Bohórquez, F.J.Berry, O.Helgason, J.F.Marco: Journal of the Physics and Chemistry of Solids, 2001, 62[7], 1277-84