Dynamic and structural heterogeneity in undercooled miscible and immiscible metallic liquid

Molecular dynamics computer simulations are performed to study the structure and dynamic relaxation of the metallic alloys Cu50Ag50 and Cu50Zr50 with and without miscibility gap, respectively. The interactions between the particles are modeled by an effective potential of the modified embedded atom method (MEAM). Cu50Zr50 undercooled liquid shows negative mixing enthalpy; the stronger interaction of heterogeneous atom pairs than that of homogeneous atom pairs, the longer the α-relaxation time and the lower the diffusion coefficient than that of the Cu50Ag50 liquid. Dynamic relaxation is related to the structural heterogeneity: the amount of five-fold symmetry (icosahedron-like) clusters is predominant in Cu50Zr50 melts, which hinders the movement of atoms and increases the dynamic relaxation time. The amount of non-five-fold symmetry (crystal-like) clusters is more pronounced in Cu50Ag50 melts, which leads to shorter dynamic relaxation time and enhanced crystallization of the Cu50Ag50 melt. The quantitative relationship between the five-fold symmetry parameter W and the diffusion coefficient D, as well as the α-relaxation time τ α , is obtained in the two distinct undercooled liquids. The present work provides an understanding of the atomic-scale structure and the dynamic properties in the miscible and immiscible liquid mixtures.