Density Functional Theory Study of Iron-Oxygen Divacancies in Magnetite (FeO) and Hematite (FeO).

Density functional theory (DFT) calculations are employed to investigate the formation energies, charge redistribution, and binding energies of iron-oxygen divacancies in magnetite (FeO) and hematite (FeO). For magnetite, we focus on the low-temperature phase to explore variations with local environments. Building on previous DFT calculations of the variations in formation energies for oxygen vacancies with local charge and spin order in magnetite, we extend this analysis to include octahedral iron vacancies before analyzing the iron-oxygen divacancies. We also assessed the relative stability of iron-oxygen divacancies by comparing their formation energies with those of individual vacancies. Our findings reveal a significant energetic driving force for the formation of divacancy clusters, particularly in magnetite, where divacancies in the +1 charge state exhibit formation energies comparable to those of neutral iron vacancies under oxidizing conditions. In hematite, the results indicate a strong tendency for oxygen vacancies to bind to iron vacancies. These results highlight the significance of iron-oxygen vacancy complexes in the transport properties of iron oxides, with particular relevance to diffusion mechanisms under irradiation conditions.