Monte carlo study of the phase diagrams of binary alloys with face centered cubic lattice structure

Abstract

We describe the results of Monte Carlo computations of the coherent phase diagram (in the temperature-composition plane) of ordering binary alloys on an f.c.c. lattice. Results on long- and short-range order parameters as well as ordering energies are also given. We consider the system with nearest neighbor interaction in the grand-canonical ensemble (equivalent to an Ising antiferromagnet in a magnetic field) as well as in the canonical ensemble (fixed composition). The close agreement between both approaches serves as a severe test of the good accuracy obtained, and so does the fact that differences between results for lattices with 2048 sites and with 16384 sites are found to be negligibly small. Results with next-nearest neighbor interaction are also given, and for both models a comparison with other available predictions is made, particularly with the cluster-variation method. While the latter is found to be quite accurate at stoichiometric composition, it appears to do less well in the more general case. The tetrahedral approximation of the cluster variation method predicts a topology of the phase diagram, in the case of nearest neighbor interaction different from the computer simulations. Some consequences for the interpretation of the behavior of copper-gold alloys are indicated.