Basics of Calculating the Surface Properties of Solid Solutions Taking the Ordering of Components into Account

摘要

An approach for calculating the surface thermodynamic characteristics of solid solutions (alloys, salts, oxides, ferroelectrics, and nonstoichiometric compounds) with different degrees of ordering at the vapor-solid interface is formulated on the basis of the lattice gas model. This approach is the only one that makes it possible to describe the properties of phases and transition regions between equilibrium coexisting phases with equal accuracy. The model is constructed for the mixture components having comparable (but different) sizes with an arbitrary type of ordered structures in the bulk phase. The type of ordering is determined by some pattern formed by different sublattices periodically repeated in space. The transition region between the solid solution and vapor is a multilayered region with a variable density of components. Interatomic interaction potentials are taken into account in the approximation of pair contributions with preservation of direct correlation effects for several coordination spheres. A change of variables was used to reduce the equilibrium set of equations to component distributions, which allows one to reduce the problem to the dimensionality of the concentration profiles of components in the transition region. The case of nonequilibrium states of a solid solution and description of its evolution by kinetic equations are discussed. Finding the concentration profile of a solid solution allows one to evaluate the state of the interface roughness, the specific area of the rough surface, and the surface segregation of the solution components, and to analyze the effect of the surface segregation on the degree of ordering of the solution components in the transition region.