Complete miscibility between different crystallographic structures:: Monte Carlo simulations of Cu-Ag deposited on Cu(001)

Monte Carlo simulations of an AgcCu1-c monolayer deposited onto Cu(001) show that complete miscibility of two elements adopting different crystallographic structures can be observed in the surface, while experimental bulk phase diagrams preclude a similar phenomenon in the bulk. While the deposited pure Ag monolayer is pseudohexagonal and the pure Cu monolayer is square and pseudomorphic, for intermediate concentrations at sufficiently high temperatures a disordered state appears in which square and hexagonal environments, respectively due to Cu and Ag, coexist. As a result, the surface phase diagram does not present any miscibility gap at 650 K.