Investigation of defect structures formed by doping tetravalent ions into inverse spinel-related iron oxides using atomistic simulation calculations

Abstract

Results from atomistic simulation calculations and X-ray photoelectron spectroscopy are used to refine the proposed defect structures of γ-Fe 2O 3 and Fe 3O 4 doped with tetravalent ions. These structures are of interest because of the effect of doping on the properties of the oxides. Calculations confirm that occupation by Sn 4+ and Ti 4+ of octahedral sites in Fe 3O 4 and γ-Fe 2O 3 is more favourable than occupation of tetrahedral sites and indicate that the M 4+ ions substitute on iron sites rather than occupy interstitial sites. For γ-Fe 2O 3, XPS results show that no reduction of Fe 3+ occurs.Of the possible remaining balncing defects, calculations indicate that vacancies on the iron sites with six nearest-neighbour iron atoms are favoured. In the case of Fe 3O 4 the results suggest that reduction of Fe 3+ to Fe 2+ is preferred and that reduction occurs on a site adjacent to M 4+. This small cluster localises the disruption to the crystal structure. These results suggest that the pattern of doping by tetravalent ions in spinel-related iron oxides differs from that in the corundum-related α-Fe 2O 3.