Signatures of structural differences in Pt-P- and Pd-P-based bulk glass-forming liquids

The structural differences between the compositionally related Pt-P- and Pd-P-based bulk glass-forming liquids are investigated in synchrotron X-ray scattering experiments. Although Pt and Pd are considered to be topologically equivalent in structural models, we show that drastic changes in the total structure factor and in the reduced pair distribution function are observed upon gradual substitution. These variations indicate the existence of significant structural differences on the short- (SRO) and medium-range order (MRO) length scale. The structural data suggest that the distribution of the dominant polyhedra and the distribution of their connection schemes gradually change from Pt-P- to Pd-P-based alloys, which is likely connected to the different sensitivities to annealing or cooling rate induced embrittlement. The evolution of the total structure factor and the reduced pair distribution function with increasing temperature indicate the (partial) dissolution of both, the MRO and the SRO, which reflects the thermodynamic properties of the liquids.