EFFECT OF THE VACANCY INTERACTION ON ANTIPHASE DOMAIN GROWTH IN A 2-DIMENSIONAL BINARY ALLOY

We have performed a Monte Carlo simulation of the influence of diffusi ng vacancies on the antiphase domain growth process in a binary alloy after a quench through an order-disorder transition. The problem has b een modeled by means of a Blume-Emery-Griffiths Hamiltonian whose biqu adratic coupling parameter K controls the microscopic interactions bet ween vacancies. The asymmetric term L has been taken as L=0 and the or dering dynamics has been studied at very low temperature as a function of K inside the range -0.5 less than or equal to K/J less than or equ al to 1.40 (with J>0 being the ordering energy). The system evolves ac cording to the Kawasaki dynamics so that the alloy concentration is co nserved while the order parameter is not. The simulations have been pe rformed on a two-dimensional square lattice and the concentration has been taken so that the system corresponds to a stoichiometric alloy wi th a small concentration of vacancies. We find that, independently of K, the vacancies exhibit a tendency to concentrate at the antiphase bo undaries. This effect gives rise, via the vacancy-vacancy interaction (described by K), to an effective interaction between bulk diffusing v acancies and moving interfaces that turns out to strongly influence th e domain growth process. One distinguishes three different behaviors: (i) For K/J<1 the growth process of ordered domains is anisotropic and can be described by algebraic laws with effective exponents lower tha n 1/2; (ii) K/J similar or equal to 1 corresponds to the standard Alle n-Cahn growth; (iii) for K/J>1 we found that, although the motion of t he interface is curvature driven, the repulsive effective interaction between both the vacancies in the bulk and those at the interfaces slo ws down the growth.