STRUCTURE OF THE ALPHA-CR2O3(0001) SURFACE - AN AB-INITIO TOTAL-ENERGY STUDY

The structure of the basal plane of the alpha phase of Cr2O3 has been investigated using periodic ab initio Hartree-Fock theory. The Cr-term inated surface, which is nonpolar but is charged, is found to be stabl e. However, a large-scale relaxation of the surface layer away from th e ideal bulk-terminated structure has been found. The top layer Cr3+ i ons move inward toward the second-layer O2- ions by nearly 50% of thei r original interlayer spacing. This results in a slight lowering of th e Cr ionicity in the surface layer, but no large-scale changes in bond character have been found. We therefore propose that the mechanism be hind this dramatic reconstruction is purely electrostatic in origin.