Two-component lattice-gas model with a liquid–vapor phase transition in both pure components

Abstract
A two‐component decorated lattice‐gas model is presented that possesses a liquid–vapor phase transition in both pure components with a coexistence surface and critical curve which extend smoothly from one pure component to the other. The model is exactly soluble in terms of the simple one‐component lattice gas of Yang and Lee (spin‐1/2 Ising model) and exhibits nonclassical critical exponents. It can produce azeotropy and critical azeotropic points, and is used to analyze the vicinity of the critical azeotrope. For sufficiently repulsive interactions between primary and secondary cell occupants the model exhibits multiple phase transitions and a phenomenon analogous to saddle‐point azeotropy.