#
**A new surface segregation isotherm description and its application to binary alloys**

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

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

^{*}Institute of Physics, TU Budapest, H-1111 Budapest, Hungary
##
*Surf. Sci. 331-333 (1995) 799-804*

In previous years a new theory, modern thermodynamic calculation of
interface properties(MTCIP), was developed. Its general equations on the
thermodynamic
equilibrium were solved in a first approximation (MTCIP-1A) and applied to
several dilute binary alloy systems in good agreement with experimental results,
even in the case of surface reactions with the environment.
Here, first a more developed second approximation (MTCIP-2A) is shortly outlined,
allowing, among other new results, for any number of interface sublayers, and
being valid in the total compositional range of the bulk. Then, by some
simplifications, a new segregational isotherm is developed from it. Using the
two dilute limits as described by the MTCIP-2A, then even with a single surface
composition (measured at any bulk composition and temperature) this segregational
isotherm permits to obtain surface compositions over the total bulk compositional
range. Results are shown for the low-index surfaces of PtNi at temperatures of
about 1100 K, mostly in better agreement with experimental values than other
present theories.

Corresponding author: W. Hofer (hofer).