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**An improved calculation of the surface composition of binary solids and its application to the PtNi(110) case**

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W. Hofer and L.Z. Mezey^{*}

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Institut für Allgemeine Physik,
Technische Universität Wien, A-1040 Wien, Austria*

^{*}Institute of Physics, TU Budapest, H-1111 Budapest, Hungary
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*Vacuum 43 (1992) 601 - 604*

A new thermodynamic theory of interfaces [L.Z. Mezey, Surf. Sci. 162 (1985) 510]
states the conditions of the Thermodynamic Equilibrium State (TES) in a general
form, permitting -in principle- the calculation of the composition profile for
any number of components and sublayers, and that of the mixture's surface free
energy. In the MTCIP-1A (Modern Thermodynamic Calculation of Interface
Properties - First Approximation), for binary solids a simplified two-layer
case is treated, giving the topmost layer TES composition (and allowing for an
adsorbed overlayer of atoms forming surface chemical bonds). That approximate
calculation, used succesfully so far at least on a semi-quantitative level in
several cases (including the segregation of non-metallic interstitials), is
improved here.
Firstly, for pure chemical elements, the calculation of the surface free energies
of low-index planes and that of the molar surface area of a polycrystalline plane
are further developed for the fcc structure. Then a description of real mixture
effects for dilute binary solids is supplemented by a new calculation of lattice
distortion release at the surface.
With this improved method the Ni(Pt) (110) surface is investigated, showing Ni
segregation on (Pt)Ni (110), which is in agreement with the experimental
results.

Corresponding author: W. Hofer (hofer).