Structural stability, phase transition, and hydrogen diffusion of PdCu phases with additions of Nb and Cr

Ab initio calculation shows that both Nb and Cr are energetically more favorable to substitute the Cu atoms in Pd8Cu8 phases, and decrease H stability in Pd8Cu8, which seems good to the process of dehydrogenation of PdCu membranes. Calculation also reveals that the addition of Nb, Cr, and H in PdCu would make it easier for the phase transition of BCC → FCC to take place along the Bain path. In addition, it is discovered that both Nb and Cr should have an important effect to increase the energy barrier of hydrogen diffusion, which is adverse to the hydrogen permeation of PdCu membranes. The derived findings are in nice agreement with similar results from experiments, and could provide a fundamental understanding to the influence of Cr and Nb on various properties of Pd8Cu8 phases.