Structure and dynamical properties of liquid Ni₆₄Zr₃₆ and Ni₆₅Hf₃₅ alloys: an ab initio molecular dynamics study

Ab initio molecular dynamics simulations are performed to investigate the atomic structures and dynamics of Ni₆₄Zr₃₆ and Ni₆₅Hf₃₅ metallic liquids in a temperature range of 1400-2500 K. Calculated results are in good agreement with recently reported high temperature experimental data. Local atomic structures are analyzed and compared for Ni₆₄Zr₃₆ and Ni₆₅Hf₃₅ metallic liquids in terms of average bond length, coordination number, Honey-Andersen index, Bond-orientation order, spatial correlation and Voronoi tessellation methods. It is found that Zr-Zr bonds have larger average length of 3.32 Å than 3.22 Å for Hf-Hf bonds, causing sluggish diffusion in Ni₆₅Hf₃₅ liquids. Zr and Hf atom-centered clusters with higher coordination numbers are inclined to aggregate with high-coordinated clusters, while Ni atom-centered clusters with lower coordination numbers prefer to avoiding to be the nearest neighbor with each other. Temperature dependent diffusion coefficients reveal the decoupled diffusion in both liquids, which are related with different spatial correlations for Ni- and Zr- (or Hf-) centered clusters.