EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

It has been believed that diffusion of a vacancy in metals becomes suppressed by hydrogen because of forming a stable hydrogen-vacancy complex. The fact that excess hydrogen can enhance greatly the self-diffusion of atoms in metals has been usually explained by the appearance of superabundant vacancies, because the vacancy formation energy decreases substantially with increasing H concentration, while individual vacancy diffusion is supposed to be slowed down. In addition, past computational and theoretical studies also suggest that the H impedes the diffusion of vacancy by increasing the energy barrier of vacancy jump. However, performing molecular dynamics simulation, first-principles grand canonical analysis, and theoretical activation energy computation for fcc Cu and Pd metals with H, we found that the diffusivity of vacancy is dramatically accelerated by H. The H acceleration effect is clearly explained by the newly developed theory of Gibbsian activation excess[J.-P. Du. et al., J. Phys. Chem. Lett., 11 (2020) 7015].