PHASE-DIAGRAM OF A DILUTE BINARY ALLOY WITH ANNEALED VACANCIES

Phase diagram of a binary alloy with annealed impurities has been stud ied with Monte Carlo computer simulation technique. A combination of t he traditional Metropolis method and the recently developed Swendsen-W ang technique are used to relax the system to the temperature of inter est. For small vacancy concentrations ''v'' the transition temperature , KT(c)/J, (k is the Boltzmann constant, and J is the strength of inte raction between nearest neighbours) decreases linearly with ''v''. Thi s is consistent with earlier results on quenched binary systems. Below the coexistence curve the system phase separates into A-rich and B-ri ch regions with vacancies randomly distributed amongst them. At lower temperatures the vacancies also phase separate out. At higher vacancy concentrations the spins representing atoms A and B separate into smal l islands of up (or down) spins. The tricritical point occurs at a tem perature kT/J=0.65+/-0.02 and a vacancy concentration of 0.38+/-0.01. Because of a change in the nature of the phase transition at the tricr itical point the region around this point is difficult to explore. The phase boundary corresponding to phase separation of vacancies for v < 0.38 and those of spins for v > 0.38 is located by the abrupt changes in the vacancy concentration as a function of the field strength.