Calculation of native defect energies in α-A1₂O₃ and α-Cr₂O₃ using a modified Matsui potential

Alumina and chromia are very important materials in the surface coatings industry, e.g. for corrosion protection and as catalyst supports. The type of defects and the associated formation energy in these materials are of direct relevance to the surface stability and reaction kinetics. In the present work, a modified Matsui potential is applied to calculate the native point defect energies in α-Al₂O₃ and α-Cr₂O₃ based on the Mott-Littleton theory. Particular attention is paid to the convergence of the defect energies with the number of atoms surrounding the defect. The results show that the relative values of the defect formation energies are such that the Schottky energy is smaller than either of the Frenkel energies, which is in agreement with experimental data and recent results of first-principles calculations. The implications of these findings for diffusion mechanisms and the associated reaction kinetics are discussed briefly.