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 AgAgAg and AgAlAg triplets shift to 60°, indicating that the local ordering transforms from the icosahedron-like to the hexagonal close-packed structure, while the CuCuCu and CuAlCu 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.