Statistical theory of forming structural vacancies in palladium hydride

Based on molecular-kinetic representations, the theory of forming structural vacancies and vacant-ordered superstructure of Cu₃Au type in palladium hydride is developed. Free energies of PdH and Pd₃VH₄ phases are calculated. The constitution diagram is constructed that determines ranges of temperature and concentration in which phases with A1 and L1₂ structures are formed and regions of two A1 + L1₂ phases are realized. Results of theoretical calculations are in agreement with the available experimental data.