The energetics of substitutional cation impurities in the bulk, and at the Σ = 7 [¯10▪2] rhombohedral twin boundary, of alumina were studied by means of first-principles mixed-basis pseudopotential calculations that were based upon local density functional theory. An increased tendency to segregation was found for impurity cations of large ionic radius, where an enhanced overlap between impurity and O electronic states was observed. The effect of relaxation at the boundary was studied for Sc, Y and La. Segregation broke the screw-rotation symmetry of the pure unsegregated boundary and altered the interface-plane termination.

Substitutional Cation Impurities in α-Al2O3 – ab initio Case Study of Segregation to the Rhombohedral Twin Boundary. C.Elsässer, A.G.Marinopoulos: Acta Materialia, 2001, 49[15], 2951-9