Relationship between atomic structure and excellent glass forming ability in Pd42.5Ni7.5Cu30P20 metallic glass

To understand the relation of the glass-forming ability (GFA) to the local atomic configurations of a
Pd42.5Ni7.5Cu30P20 (PNCP) metallic glass having the best GFA at present, the local structures were investigated by
combining data obtained from anomalous X-ray scattering, X-ray and neutron diffraction, and applying reverse Monte Carlo modeling. By comparing the results of PNCP with Pd40Ni40P20 (PNP) and Pd40Cu40P20 (PCP) having a slightly and much worse GFAs, respectively, characteristic features were observed in the hyper-ordered atomic structures. Firstly, the concentration inhomogeneity of Ni/Cu in PNCP is larger than that of Ni in PNP and Cu in PCP. Secondly, a Voronoi tessellation showed that the fraction of pure icosahedral arrangements around the Cu atoms increases significantly in PNCP by adding icosahedral-preferred Ni atoms in PCP. Finally, a persistent homology (PH) analysis reveals the largest intermediate-size Cu PH rings in PNCP among the PH rings in these Pd-based BMGs. The structural heterogeneity for the excellent GFA of PNCP would be considered by an incompatible mixture of specific Pd-P configurations and icosahedral clusters around the secondary Ni and Cu metals.