Interfacial Tension of Two-Component Two-Phase Ordered Cubic Solid Systems

A numerical analysis of the thermodynamic determination of interfacial tension (IT) between two ordered phases of a solid body as an excess value of free energy ΔF for two-phase system with and without taking into account the presence of the phase boundary has been carried out. The interface between ordered phases is considered within the framework of this domain geometry as a set of cubic monolayers with a variable density of components, including the cubic shape of the separating surface. A microscopic analysis of the generalization of the Gibbs thermodynamic approach, which introduces interfacial tension on the mathematical phase interface, is given for the case of a complex cubic boundary shape containing cube corner regions with local interfacial tensions for faces, edges, and face vertices. The calculation was carried out in the simplest version of the lattice gas model, taking into account the interaction of nearest neighbors in the quasi-chemical approximation. Each site of a two-component mixture on a rigid lattice can be occupied by mixture components A + B and vacancies V. Two main methods of calculating IT are compared, which are expressed in terms of different partial contributions 
 into excess free energy ΔF (Here i = A, B; V are vacancies; and 1 ≤ f ≤ t, t is the number of types of nodes of different types, depending on the position of the node inside the corner regions of the cube). An ambiguity of IT values is obtained depending on the type of functions 
 for the dependence of the IT on the domain size at a fixed temperature. The role of vacancies as the main mechanical characteristic of a two-component mixture in the lattice-gas model is discussed under the condition of strict phase equilibrium in three partial equilibria (mechanical, thermal, and chemical). It is shown that, if IT calculations are carried out for two dense separating phases, neglecting the allowance for vacancies, then this distorts the real value of the IT.