Partial structure of Pd₄₂:5Ni₇:5Cu₃₀P ₂₀ bulk metallic glass

In order to study local structure in Pd_42.5Ni _7.5Cu₃₀P₂₀ excellent bulk metallic glass-former, an anomalous x-ray scattering (AXS) experiment was performed at energies close to the Pd, Ni and Cu K absorption edges together with the reference Pd₄₀Ni₄₀P₂₀ and Pd ₄₀Cu₄₀P₂₀ glasses at the beamline BM02 of the ESRF. The differential structure factors, Δ_iS(Q), were obtained with a good statistical quality. A small shoulder observed at about 19 nm ^-1 in S(Q) becomes prominent in Δ_PdS(Q), indicating a Pd-Pd atomic correlation of 0.32 nm. This pre-shoulder was not observed in Pd₄₀Ni₄₀P₂₀ bulk glass having a slightly worse critical-cooling-rate, but in Pd₄₀Cu₄₀P₂₀ glass ribbon available by only ultrafast quenching. It is suggested that covalently bonded Pd-P-Pd connection with an almost right bond angle would be formed by replacing the Ni with the Cu atoms. From the obtaining differential pair distribution function around the Pd K edge, Δ_Pdg(r), the first peak position in Pd_42.5Ni_7.5Cu₃₀P₂₀ shows a longest atomic distance among the glasses and the width of the first peak is slightly narrower than that in Pd₄₀Cu₄₀P ₂₀. Thus, a more uniform atomic arrangement around Pd atoms with a loose packing, i.e., a longer and uniform Pd sublattice, is expected for Pd _42.5Ni_7.5Cu₃₀P₂₀ compared to the other two reference glasses.