Charged vacancy diffusion in chromium oxide crystal: DFT and DFT+U predictions

Abstract

In this work, we computationally studied the lattice diffusion through the ion-vacancy exchange mechanism in α-Cr2O3 crystal using the first-principles density functional theory (DFT) and DFT+U calculation methods. For both O and Cr vacancies, we have identified four elementary diffusion paths in α-Cr2O3 crystal. Our DFT+U calculations predict that the O vacancy with charge +2 (VO2+) is stable when Fermi energy is near to valence band maximum, whereas the Cr vacancy with charge −3 (VCr3−) is stable when Fermi energy is close to conduction band minimum. Moreover, the DFT+U calculations predict that the migration energy for VO2+ diffusion varies from 1.18 to 2.98 eV, whereas that for VCr3− diffusion varies from 2.02 to 2.59 eV, close to experimental data. Both DFT and DFT+U results indicate that the migration energy of neutral vacancies (VO0 and VCr0) is higher than that of the charged vacancies (VO2+ and VCr3−) along any diffusive path. Importantly, it is found that the DFT+U method describes α-Cr2O3 crystal better in terms of the magnetism, band gap, charge state of vacancies, and migration energies for charged vacancy diffusion as compared to the DFT method.