Insights into the Fe 3+ Doping Effects on the Structure and Electron Distribution of Cr 2 O 3 Nanoparticles.

Herein, we carefully investigated the Fe 3+ doping effects on the structure and electron distribution of Cr 2 O 3 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 Fe 3+ replaces Cr in the Cr 2 O 3 lattice, it caused a higher interaction between the metal 3 d states and the oxygen 2 p 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 Cr 2 O 3 and Fe-doped Cr 2 O 3 nanoparticles behave as Mott-Hubbard insulators due to their band gap being in the d - d gap, and Cr 3 d orbitals dominate the conduction band. These findings suggest that the magnitude and the character of the electronic density near the O atom bonds in Cr 2 O 3 nanoparticles are modulated by the Cr-Cr distances until its stabilization at the induced quasi-equilibrium of the Cr 2 O 3 lattice when the Fe 3+ doping values reaches the saturation level range.