Hydrogen diffusion in quasicrystalline and amorphous ZrCuNiAl

We report on the direct determination of the hydrogen self-diffusion constant D in the hydrogen-storage Zr69.5Cu12Ni11Al7.5 alloy, prepared in both the icosahedral quasicrystalline and the bulk metallic glass phases, using the technique of NMR diffusion in a static fringe field of a superconducting magnet. The diffusion constant exhibits strong dependence on temperature and hydrogen concentration. D was found to obey classical Arrhenius thermally activated over-barrier hopping form, whereas the significant decrease of D with increasing hydrogen-to-metal concentration ratio H/M is a result of two effects – the increase of the activation energy for hydrogen jumps between interstitial sites due to lattice expansion upon hydrogenation and the decreasing number of available empty interstitials due to site blocking and creation of defects in the lattice during hydrogen loading. The actual alloy structure – the icosahedral, approximant or metallic glass – appears to be less important for the hydrogen diffusivity.