Difference of hydrogen diffusivity in between amorphous and crystalline

Abstract

Amorphous alloys, showing somewhat higher hydrogen permeance than pure crystalline Pd, are perspective candidates for replacing the current Pd-based hydrogen selective membranes. As the origin of high permeability, they usually have much higher solubilities than crystalline alloys which originate from larger available spaces. However, their diffusivities are not consistently faster - sometimes higher and sometimes lower. We clarified this difference of hydrogen diffusivity in between amorphous and its counterpart crystalline with the aid of molecular dynamics simulation technique. In order to perform a simulation about the diffusion behavior of hydrogen in Cu-Zr amorphous alloys, the interatomic potential for the Cu-Zr-H ternary system have been developed based on the second nearest-neighbor modified embedded-atom method (2NN MEAM) formalism. A few first-principles calculations of physical properties for the Cu-H sub-binary system were carried out to supplement data necessary to optimize the potential parameters. The developed potential reproduced fundamental properties (structural, thermodynamic, defect and diffusion properties) mostly well for investigating the dynamic behavior of hydrogen. Then, through a series of diffusion simulations, the calculated diffusivity of hydrogen in the amorphous lattice is turned out to be lower than that in a bcc-based lattice, and to be higher than in a fcc-based lattice.