| The fundamental origins of the stability of the (Pd-Ni)80P 20 bulk metallic glasses (BMGs), a prototype for a whole class of BMG formers, were explored. While much of the properties of their BMGs have been characterized, their glass-stability have not been explained in terms of the atomic and electronic structure. The local structure around all three constituent atoms was obtained, in a complementary way, using extended X-ray absorption fine structure (EXAFS), to probe the nearest neighbor environment of the metals, and extended energy loss fine structure (EXELFS), to investigate the environment around P. The occupied electronic structure was investigated using X-ray photoelectron spectroscopy (XPS). The (Pd-Ni)80P20 BMGs receive their stability from cumulative, and interrelated, effects of both atomic and electronic origin. The stability of the (Pd-Ni)80P20 BMGs can be explained in terms of the stability of Pd60Ni20P 20 and Pd30Ni50P20, glasses at the end of BMG formation, The atomic structure in these alloys is very similar to those of the binary phosphide crystals near x = 0 and x = 80, which are trigonal prisms of Pd or Ni atoms surrounding P atoms. Such structures are known to exist in dense, randomly-packed systems. The structure of the best glass former in this series, Pd40Ni40P20 is further described by a weighted average of those of Pd30Ni 50P20 and Pd60Ni20P20. Bonding states present only in the ternary alloys were found and point to a further stabilization of the system through a negative heat of mixing between Pd and Ni atoms, The Nagel and Tauc criterion, correlating a decrease in the density of states at the Fermi level with an increase in the glass stability, was consistent with greater stability of the PdxNi (80−x)P20 glasses with respect to the binary alloys of P. A valence electron concentration of 1.8 e/a, which ensures the superpositioning of the first peak in the structure factor with twice the Fermi momentum, was used to calculate the interatomic potential of these alloys. The importance of Pd to the stability of the alloys is evidenced by the fact that replacing Ni with Pd places the nearest neighbor distances at more attractive positions in this potential. |
