Ab initio total energy studies of the α-Cr2O3 (0001) and (01(1)over-bar-2) surfaces

The surface structure of the basal plane and of the thermodynamically most stable facet of the alpha phase of Cr2O3 has been studied using periodic ab initio Hartree-Fock theory. The Cr-terminated (0001) surface, which is nonpolar but charged, is found to be stable. However, a large scale relaxation of the surface layer away from the ideal bulk-terminated structure has been found. The outermost layer of Cr3+ ions moves inward toward the second layer of O2- ions by nearly 50% of their original interlayer spacing. The (01(1) over bar 2) surface, which is oxygen-terminated, is also nonpolar, and stable. Again an appreciable relaxation, with the top layer moving outward compared with the ideal bulk structure, is found. The driving force behind both effects is presumed to be mainly electrostatic.