Coarsening in the Ising model with vacancy dynamics

We simulate coarsening in an alloy at 50% concentration using the Ising model, under either Kawasaki (K-) or vacancy (V-) dynamics, on three different lattices (sc, fee, bcc) at five different temperatures. At times t greater than 2000 MCS the first zero R of the spherically averaged pair correlation function obeys R approximate to R-0+(lambda t)(1/3) where R-0, lambda are constants. As the temperature falls, lambda(K) (the value of lambda for K-dynamics) falls but lambda(V) rises, so that at low temperatures lambda(V) much greater than lambda(K). The ratio lambda(K)/lambda(V) is approximately proportional to the equilibrium concentration of minority atoms in either phase. For the various lattices, the values of lambda are roughly proportional to the diffusivities and, therefore, to the squared nearest-neigbour distances, i.e., lambda(sc) : lambda(bcc) : lambda(fcc) x 4:3:2. At T = 0.9T(c), Ro is between 2 and 3 for both types of dynamics and all three lattices, as the temperature falls, Ro remains near 2 for K-dynamics but falls, very roughly in proportion to the temperature, for V-dynamics. (C) 2000 Elsevier Science B.V. All rights reserved.