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

W. Hofer and L.Z. Mezey*

Institut für Allgemeine Physik, Technische Universität Wien, A-1040 Wien, Austria
*Institute of Physics, TU Budapest, H-1111 Budapest, Hungary

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< encoded email address >).