Theoretical investigation of superabundant vacancy formation

Formation of superabundant vacancies in metallic alloys associated with the absorption of hydrogen has been attracting broad interests. The key to understand this phenomenon is that the formation of vacancy is assisted by the trapping effect of hydrogen atoms absorbed in interstitial sites. The framework of the statistical mechanics study has been proposed by Fukai and coworkers based on Bragg-Williams approximation. In the present study, Cluster Variation Method is employed to formulate the phase equilibria within the square approximation on a two-dimensional square lattice.