The stability of various point defects in NiAl(100) was investigated using first-principles calculations. For Al-rich surfaces, Ni vacancies within the first Al layer were energetically most favourable. For Ni-rich surfaces, so-called double defects, consisting of both Ni-antisite atom in the first Al layer and a Ni vacancy within the second Ni layer, form the configuration of lowest energy, superior to singular Ni antisites. An additional and significant energy gain was found in both cases by mutual lateral interaction of the defects, when they were arranged in the diagonal direction. Respective (√2 x 3√2)R45° ordered configurations were found as the most stable structures. A 50:50 mixture of both defect types turns out to be even lower in energy than the ideal Al-terminated NiAl(100) surface, proving the latter to be metastable only. This was in line with the frequently reported inability to prepare ideal NiAl(100) surfaces.

Point Defects in the NiAl(100) Surface. D.Lerch, K.Dössel, L.Hammer, S.Müller: Journal of Physics - Condensed Matter, 2009, 21[13], 134007 (6pp)