Photoemission investigation of the electronic-structure changes in Zr-Ni-Cu metallic glasses upon hydrogenation

The electronic density of states (DOS) in the valence band of Zr₅₀Ni_50-xCuₓ metallic glasses (x=10, 15, 17, and 20) and their hydrides was investigated by means of ultraviolet photoemission spectroscopy (UPS). In the spectra, one could distinguish Cu-, Ni-, and Zr-derived states both before and after hydrogenation. It was found that hydrogen markedly modified the states mainly in the region of Cu-derived states whereas the Ni- and Zr-derived states were affected to a lesser extent or in a different way by hydrogen. The effect of hydrogenation on the Cu-derived $3d$ valence-band states was ascribed to a hydrogen-induced phase separation as a result of which the Zr-Ni-Cu metallic glass transformed into a nanoscale mixture of Cu-rich clusters and copper-depleted Zr-Ni-Cu-H glassy hydride regions.