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

In this work, we computationally studied the lattice diffusion through the ion-vacancy exchange mechanism in alpha-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 alpha-Cr2O3 crystal. Our DFT+U calculations predict that the O vacancy with charge +2 (V-O(2+)) is stable when Fermi energy is near to valence band maximum, whereas the Cr vacancy with charge 3(V-Cr(3-)) is stable when Fermi energy is close to conduction band minimum. Moreover, the DFT+U calculations predict that the migration energy for V-O(2+) diffusion varies from 1.18 to 2.98 eV, whereas that for V-Cr(3-) 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 (V-O(0) and V-Cr(0)) is higher than that of the charged vacancies (V-O(2+) and V-Cr(3+)) along any diffusive path. Importantly, it is found that the DFT+U method describes alpha-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. Published by AIP Publishing.