Point defects in the NiAl(100) surface

Abstract

The stability of various point defects in NiAl(100) has been investigated by first-principlescalculations. For Al-rich surfaces, Ni vacancies within the first Al layer are energeticallymost favourable. For Ni-rich surfaces, so-called double defects, consisting of both Ni-antisiteatom in the first Al layer and a Ni vacancy within the second Ni layer, form theconfiguration of lowest energy, superior to singular Ni antisites. An additional andsignificant energy gain is found in both cases by mutual lateral interaction of the defects,when they are arranged in the diagonal direction. Respective ordered configurations were found as the most stable structures. A 50:50 mixture of bothdefect 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 is in line with the often reportedinability in experiments to prepare ideal NiAl(100) surfaces.