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MM: Fachverband Metall- und Materialphysik

MM 32: Transport in Materials: Diffusion, Charge or Heat Conduction

MM 32.9: Vortrag

Donnerstag, 20. März 2025, 17:15–17:30, H22

Formation energies and charge transition levels of charged point defects in Hematite — •Hao Chen, Christoph Freysoldt, Mira Todorova, and Jörg Neugebauer — Max-Planck-Institut für Nachhaltige Materialien GmbH, Düsseldorf, Germany

Hematite (Fe₂O₃), an iron oxide fundamental to the process of iron ore reduction, exhibits rich defect physics and off-stoichiometric features, as iron can occur as either Fe³⁺ and Fe²⁺. Charged point defects and the associated Fe²⁺/Fe³⁺ transitions play an important role in phenomena such as thermodynamic stability, phase transitions between iron oxides, and electronic structure modulation. In order to correctly account for these effects in the prediction of defect equilibria, phase diagrams, diffusion, and related properties, a robust framework for understanding defect thermodynamics and constructing a comprehensive defect model at the ab initio level is essential. Here, we employ DFT+U as an efficient tool for studying strongly correlated systems. In view of the delocalization error of standard functionals, DFT+U is crucial to investigate Fe²⁺ ions as distinct species. Moreover, it systematically opens the band gap of the bulk iron oxides. Since Hubbard U parameter has a direct influence on the band structure and Fe-related defect states in the band gap, we investigate the impact of U values on the computed formation energies of vacancies and interstitials. Our results show that the defect formation energies have a surprisingly weak dependence on U, thus allowing reliable predictions. We analyze the electronic structures of the defects in detail to uncover the underlying physical mechanisms.

Keywords: iron oxide; DFT+U