Electronic structure of Pd_42.5Ni_7.5Cu₃₀P₂₀, an excellent bulk metallic glass former: Comparison to the Pd₄₀Ni₄₀P₂₀ reference glass

In-house photoemission and inverse-photoemission spectra (PES and IPES) were measured on Pd_42.5Ni_7.5Cu₃₀P₂₀ and Pd₄₀Ni₄₀P₂₀ bulk metallic glasses in order to clarify the origin of excellent glass-forming ability from the viewpoint of electronic structure. Minima are observed for both the metallic glasses at a slightly higher energy than the Fermi level. Incident photon-energy dependent PES spectra were obtained using synchrotron radiation and the Pd 4d partial density of states (DOS) was estimated from the PES data. Soft X-ray emission spectra were also measured near the Ni and Cu 2p_3/2 absorption edges to evaluate, respectively, the Ni and Cu 3d partial DOS in the valence band. The Pd 4d and the Ni and Cu 3d partials in the conduction band were obtained from X-ray absorption spectra around the Pd 3p_3/2 and Ni and Cu 2p_3/2 absorption edges, respectively. It was found that the Pd 4d partial DOS near the Fermi energy largely decreases and becomes localized by replacing the Ni atoms with the Cu atoms, which may be closely related to the excellent glass-forming ability of the Pd_42.5Ni_7.5Cu₃₀P₂₀ bulk metallic glass due to a selective formation of Pd-P covalent bonds.