6533b7d9fe1ef96bd126cbc0

RESEARCH PRODUCT

Unmixing of binary alloys by a vacancy mechanism of diffusion: a computer simulation

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The initial stages of phase separation are studied for a model binary alloy (AB) with pairwise interactions e AA , e AB , e BB between nearest neighbors, assuming that there is no direct interchange of neighboring atoms possible, but only an indirect one mediated by vacancies (V) occurring in the system at a concentrationc v and which are strictly conserved, as are the concentrationsc A andc B of the two species.A-atoms may jump to vacant sites with jump rateГ A , B-atoms with jump rateГ B (in the absence of interactions). Particular attention is paid to the question to what extent nonuniform distribution of vacancies affects the unmixing kinetics. Our study focuses on the special caseГ A =Г B on a square lattice, considering three different choices of interactions with the same e=e AB − (e AA +e BB )/2: (i) e AB =e, e AA = e BB = 0; (ii) e AA = 0, e AA = e BB ; = ∓ e; (iii) e AB = e BB = 0, e AA = −2e. We obtain both the time evolution of the structure factorS(k,t) following a quench from infinite temperature to the considered temperature, and the timedependence of the mean cluster size and the various neighborhood probabilities of a vacancy. While in case (i) forc V ≦0.16 the distribution of vacancies in the system stays nearly random, in case (ii) the vacancies cluster in theA-B interfacial region, and in case (iii) they get nearly completely expelled from theA-rich regions. While phase separation proceeds in case (i) only slightly faster than in case (ii), a significant slowing down of the relaxation is observed for case (iii), which shows up in a strong reduction of the effective exponents describing the growth.