PHASE-DIAGRAM OF A 2-DIMENSIONAL DILUTE BINARY ALLOY

Phase diagrams of two-dimensional binary alloy with vacancies (ABV) is studied with pairwise interaction epsilon(AA), epsilon(BB), and epsil on(AB) between the nearest neighbors. Attention is focussed on the cas e where the vacancies are annealed and epsilon(BA) = epsilon, epsilon( AA) = epsilon(BB) = 0. For vacancy concentrations c(upsilon) < 0.2, th e critical temperature decreases linearly with c(upsilon). The vacanci es remain randomly distributed within the A and B phase separated regi ons. For c(upsilon) > 0.2 the critical temperature no longer shows thi s linear trend and falls to zero very sharply at c(upsilon) = 0.39. Th is critical vacancy concentration is slightly lower than the one expec ted for quenched vacancies, where the percolation threshold of atomic species is 0.59 (c(upsilon) = 0.41). The mobility of vacancies and the nature of atomic interactions makes it energetically favorable for th e vacancies to occupy the boundary layers between A and B phase separa ted regions, thus making the process of phase separation difficult. Th is lowers the critical temperature below that of the case where the va cancies are quenched. Salient features of the phase diagram are discus sed by comparison with previously studied similar systems with differe nt interaction energies.