Segregation and Ordering at a Ni-10 at.% Al Surface from First Principles
We have calculated the surface energy and work function of the (111) surface of Ni-10 at.% Al, as a function of the Al concentration in the first lattice plane, by means of the coherent potential approximation (CPA) for inhomogeneous systems, implemented within the layer Korringa-Kohn-Rostoker (LKKR) multiple scattering formalism. Our treatment includes the charge correlation ignored in the standard single-site implementation of the CPA. Temperature effects are accounted within the mean field approximation for the configurational entropy. We find that at 1000 K the surface concentration of Al is doubled with respect to its bulk nominal value, in agreement with the results of recent surface ion scattering experiments. Allowing the formation of an ordered L12 plane at the surface further lowers the free energy of the system.
KeywordsInterface Region Coherent Potential Approximation Random Alloy Binary Solid Solution Charge Correlation
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