Insights into the Fe³⁺ Doping Effects on the Structure and Electron Distribution of Cr₂O₃ Nanoparticles

Herein, we carefully investigated the Fe³⁺ doping effects on the structure and electron distribution of Cr₂O₃ nanoparticles using X-ray diffraction analysis (XRD), maximum entropy method (MEM), and density functional theory (DFT) calculations. We showed that increasing the Fe doping induces an enlargement in the axial ratio of c/a, which is associated with an anisotropic expansion of the unit cell. We found that as Fe³⁺ replaces Cr in the Cr₂O₃ lattice, it caused a higher interaction between the metal 3d states and the oxygen 2p states, which led to a slight increase in the Cr/Fe-O1 bond length followed by an opposite effect for the Cr/Fe-O2 bonds. Our results also suggest that the excitations characterize a well-localized bandgap region from occupied Cr d to unoccupied Fe d states. The Cr₂O₃ and Fe-doped Cr₂O₃ nanoparticles behave as Mott-Hubbard insulators due to their band gap being in the d-d gap, and Cr 3d orbitals dominate the conduction band. These findings suggest that the magnitude and the character of the electronic density near the O atom bonds in Cr₂O₃ nanoparticles are modulated by the Cr-Cr distances until its stabilization at the induced quasi-equilibrium of the Cr₂O₃ lattice when the Fe³⁺ doping values reaches the saturation level range.