In the case of the B2 CoAl(100) surface, it was demonstrated that even slight deviations from the ideal stoichiometry of an ordered alloy in a sub-surface region or in the bulk could sharply affect its surface composition. By means of experimental surface analysis and first-principles calculations, it was shown that Co antisite atoms segregated right to the surface; driven by the same strong interactions which enforced order in the bulk. The findings were consistent with the lack of antisite segregation found earlier for the much weaker ordering FeAl(100), and resolved contradictory reports for NiAl(100).

Segregation in Strongly Ordering Compounds - a Key Role of Constitutional Defects. V.Blum, L.Hammer, C.Schmidt, W.Meier, O.Wieckhorst, S.Müller, K.Heinz: Physical Review Letters, 2002, 89[26], 266102 (4pp)