Structural evolution and dynamical properties of Al₂Ag and Al₂Cu liquids studied by experiments and ab initio molecular dynamics simulations

The structural evolution and dynamical properties of Al₂Ag and Al₂Cu liquids have been investigated in the temperature range of 943–1153 K by synchrotron X-ray diffraction and ab initio molecular dynamics simulations. It is demonstrated that the local atomic packing of Al₂Ag liquid has lower ordering than the Al₂Cu liquid, in which Al and Ag atoms are more randomly distributed while Al and Cu atoms tend to form pairs. With decreasing temperature, the bond-angle distributions of Ag[sbnd]Ag[sbnd]Ag and Ag[sbnd]Al[sbnd]Ag triplets shift to 60°, indicating that the local ordering transforms from the icosahedron-like to the hexagonal close-packed structure, while the Cu[sbnd]Cu[sbnd]Cu and Cu[sbnd]Al[sbnd]Cu triplets have the similar angles to those in the crystalline Al₂Cu compound. These are consistent with the major Voronoi polyhedrons in both liquids. The dynamic results reveal that Al and Ag atoms diffuse much easier in the Al₂Ag liquid than Al and Cu in the Al₂Cu liquid, making Al and Ag atoms more randomly distributed and thus reducing the local ordering in the Al₂Ag liquid.