Rough interfaces in fcc and bcc alloys: Influence of the order of the bulk phase transition

Abstract

Using Monte Carlo simulations, we investigate the thermodynamical behavior of two different interfaces: the first one corresponds to an antiphase boundary in the ordered L12 phase on a fcc lattice and the second one corresponds to an antiphase boundary in the ordered DO₃ phase on a bcc lattice. We show that in both cases the interface undergoes a roughening transition at a temperature T_R below the bulk order-disorder transition. The temperature dependence of the interface profile near T_R is in good agreement with the Kosterlitz-Thouless theory. However, the two interfaces behave differently in the neighborhood of the bulk transitions. When the bulk transition is of the first order, the rough antiphase is wetted by the disordered phase and splits into two rough order-disorder interfaces. When the bulk transition is of the second order, the bulk correlation length becomes the only relevant length scale: the antiphase thickness diverges as ξ_b.