Phase diagram of a dilute binary alloy with annealed vacancies

Abstract

Phase diagram of a binary alloy with annealed impurities has been studied with Monte Carlo computer simulation technique. A combination of the traditional Metropolis method and the recently developed Swendsen-Wang technique are used to relax the system to the temperature of interest. For small vacancy concentrations “ v” the transition temperature, kT c/J , ( k is the Boltzmann constant, and J is the strength of interaction between nearest neighbours) decreases linearly with “ v”. This is consistent with earlier results on quenched binary systems. Below the coexistence curve the system phase separates into A-rich and B-rich 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 small islands of up (or down) spins. The tricritical point occurs at a temperature 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 tricritical 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.