By means of first principles simulations we demonstrate that tiny deviations from stoichiometry in the bulk composition of the NiPt-L1₀ ordered alloy have a great impact on the atomic configuration of the (111) surface. We predict that at T=600 K the (111) surface of the Ni₅₁Pt₄₉ and Ni₅₀Pt₅₀ alloys corresponds to the (111) truncation of the bulk L1₀ ordered structure. However, the (111) surface of the nickel deficient Ni₄₉Pt₅₁ alloy is strongly enriched by Pt and should exhibit the pattern of the 2×2 structure. Such a drastic change in the segregation behavior is due to the presence of different antisite defects in the Ni- and Pt-rich alloys and is a manifestation of the so-called off-stoichiometric effect.
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Pourovskii et al. (2003) studied this question.
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