First-Principles Theory of Hydrogen Diffusion in Aluminum

Ab initio molecular dynamics simulations are used to obtain the activation enthalpy and preexponential factor for the lattice diffusion of hydrogen in aluminum between the temperatures 650 and 850 K: $\Delta {\mathrm{H}}^{‡}=0.12\pm 0.02\mathrm{eV}$ and $D_0=1.8\times {10}^{-7}{\mathrm{m}}^2/\mathrm{s}$. Vacancies are found to significantly decrease the apparent diffusivity due to their ability to bind one, two, or even six hydrogen atoms, causing a strong composition dependence and non-Arrhenius behavior of the effective diffusion coefficient.