First-Principles Calculated Structures and Carbon Binding Energies of Σ11 {10(1)over-bar1}/{10(1)over-bar(1)over-bar} Tilt Grain Boundaries in Corundum Structured Metal Oxides

To give a basic understanding of the experimentally observed difference between Cr2O3 and Al2O3 scales on carbon permeation, we employed the first-principles calculation methods to predict atomistic structures, formation energies, and carbon binding energies of Sigma 11 {10 (1) over bar1}/{10 (1) over bar(1) over bar} tilt grain boundaries (GB) in both alpha-Al2O3 and alpha-Cr2O3 with a corundum structure. Owing to different surface terminations, we predicted two distinct kinds of stable atomistic structures for the GB: one with measurable voids and high formation energy, and the other with a compact interface and low formation energy. The predicted GB structures agree with experimental images. No significant structural difference was found for the same GB in alpha-Al2O3 and alpha-Cr2O3. Moreover, we predicted that atomic carbon would bind to the Sigma 11 {10 (1) over bar1}/10 (1) over bar(1) over bar} GB in alpha-Cr2O3 appreciably more strongly than in alpha-Al2O3. Therefore, our computational results suggest that chemical affinity rather than geometric structure of the GBs is related to different carbon permeation behaviors in Al2O3 and Cr2O3 scales. [GRAPHICS] .