The anomalous X-ray scattering (AXS) measurements have been made to determine the local ordering structures around Ni and Cu in Pd40Ni10Cu30P20 and Pd40Ni40P20 alloys in both the liquid and amorphous state using the synchrotron radiation at incident X-ray energies close to the K-absorption edges of Ni and Cu. A characteristic small hump was clearly found at r=0.37 nm in the environmental radial distribution function (RDF) around Cu in liquid and amorphous Pd40Ni10Cu30P20 alloy. Such peak was not detected in the environmental RDF around Ni, and the local atomic arrangement around Ni was found to be similar to the Pd40Ni40P20 case. These experimental facts can be described when considering the trigonal prismatic packing related to Ni and the tetragonal dodecahedral packing related to Cu. This is in a sense a necessary condition at best, although it might not be the sufficient condition. However, the effect of elemental substitution with Cu for Ni in the Pd-Ni-Cu-P alloy is thought to induce the particular atomic association related to Cu, which is an important factor for exhibiting its wide supercooled liquid region and high reduced glass transition temperature.
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