Drivers of chemical diffusion of hydrogen in the thin transition metallic glass V80Zr20

We demonstrate the feasibility of using optical transmission to determine concentration-dependent hydrogen diffusion coefficients and activation energies of thin metallic glass films over a wide range of temperatures and concentrations. The hydrogen concentration's temporal and spatial profiles are simultaneously extracted without requiring a metal-insulator transition or hydride formation. The concentration-dependent activation energy is extracted and is found to exhibit similar concentration dependence as hydrogen in the disordered bulk alpha-phase of vanadium. The activation energy is in stark contrast, however, to the activation energy found in epitaxial vanadium films of similar thickness. The chemical diffusion increases with hydrogen concentration in the glass, whereas it decreases in the crystalline case owing to the differences in the thermodynamic factors. This technique provides detailed insight into the concentration dependence of hydrogen diffusion and constrains theories treating correlated motion of hydrogen and short-range hydrogen-hydrogen interaction. The method can be applied to other materials that show an optical response to hydrogen uptake.