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M: Metallphysik
M 21: Intermetallische Phasen II
M 21.4: Talk
Saturday, March 5, 2005, 11:45–12:00, TU H2038
On the broken-bond model and the pair-potential modelling of alloy surfaces — •Ralf Drautz1,2 and Manfred Fähnle1 — 1Max-Planck-Institut für Metallforschung, Heisenbergstraße 3, 70569 Stuttgart, Germany — 2Department of Materials, University of Oxford, OX1 3PH, UK
The existence of a surface breaks the symmetry of the bulk material leading in general to an ordering behaviour at the surface which is different from the one of the bulk. We discuss the theoretical modelling of this situation with the cluster-expansion (CE) method [1] and with the many-body potential expansion [2], and we apply these calculational techniques to the system Ni90Al10(110) [1]. It is shown that a broken-bond model which discards the contributions to the CE of clusters with bonds pointing out of the surface and assumes bulk values for the contributions of the remaining clusters may fail badly to describe surface segregation and ordering. The tendency of a minority atom to segregate to the surface of a diluted binary alloy is discussed by use of pair potentials. It is shown that perfectly transferable and hence environment-independent pair potentials [2] in general cannot describe the situation adequately.
[1] R. Drautz, H. Reichert, M. Fähnle, H. Dosch, and J. M. Sanchez, Phys. Rev. Lett. 87, 236102 (2001)
[2] R. Drautz, M. Fähnle, and J. M. Sanchez, J. Phys.: Condensed Matter 16, 3843 (2004)