Abstract
The lattice dynamics of both as-charged and room-temperature-aged, hydrogenated bulk metallic glasses (BMGs) with the stoichiometry of (Zr 55 Cu 30 Ni 5 Al 10 ) 99 Y 1 have been investigated by inelastic neutron scattering at 4 K. The vibrational density of states of dissolved hydrogen atoms in the as-charged BMG shows a broad band maximized at ∼135 meV. Three months of room-temperature aging caused this band to narrow somewhat, losing intensity at both lower and higher energies. The results suggest that hydrogen atoms preferably occupy the interstitial tetrahedral-like t sites comprised of four Zr atoms, with a local atomic arrangement similar to that of δ-zirconium hydride. At higher hydrogen loadings, hydrogen atoms can also occupy octahedral-like and/or more Zr-deficient tetrahedral-like o sites. The spectral differences between the as-charged and aged specimens and accompanying Vickers hardness measurements suggested that around two-thirds of the hydrogen atoms in the as-charged specimen were trapped in the strongly binding t sites and relatively immobile at room temperature, while the remaining one-third occupied the more weakly binding o-sites and disappeared from the specimen upon aging. These latter sites most likely play a crucial role in the diffusion of hydrogen in BMGs at room temperature. © 2011 American Physical Society.