Composition dependent gradient energy coefficient: How the asymmetric miscibility gap affects spinodal decomposition in Ag-Cu?

We report results for spinodal decomposition in Ag-Cu binary system. The asymmetric miscibility gap of any binary system necessarily means that the gradient energy coefficient κ is composition dependent. We demonstrate that while this composition dependence of κ does not modify the solubility curve and even the equilibrium interface profile hardly changes, the cutoff wavelength for spinodal decomposition does. Many calculations usually use composition independent gradient energy coefficient and the analytical expression for calculating the cutoff wavelength is valid also only for composition independent κ. We show that the κ-composition function can be calculated from the interaction energy V(c): κ=−1/12r02∂[(1−2c)V(c)]/∂c, where r0 is the interatomic distance. In this work we apply the Cahn-Hilliard theory and a 3D atomistic kinetic model, the Stochastic Kinetic Mean Field (SKMF), what we further developed purposefully. The improvement is not restricted to the Ag-Cu system, though, as the composition dependent interaction energy can be deduced e.g. from Redlich-Kister polynomials.