FINITE-SIZE EFFECTS ON THE PHASE-DIAGRAMS OF BINARY ALLOY-FILMS

The thermodynamics of ordering binary alloys with film geometry is stu died for the case of symmetry-preserving surfaces. In particular, we a nalyze the dependence of the phase diagrams on film thickness for the case of vanishing surface fields (ordinary transitions). We focus on t he interplay between ordering and segregation and its effects on the p hase equilibria of b.c.c.(1 1 0) films as well as on the low-temperatu re behavior of the critical curve. At T = 0 the critical curve of a b. c.c. ordering binary-alloy film ends at a finite concentration. It is shown that it is useful to interpret the zero temperature transitions as percolation-like transitions. Calculations by the cluster variation method in the pair and tetrahedron approximations are presented. (C) 1998 Elsevier Science Ltd. All rights reserved.