Chemically ordered structure and dynamics in Al80Ti20 liquids

We conducted ab initio molecular dynamics simulations to study the structural and dynamical properties in Al80Ti20 liquids. The prepeak that represents some chemically ordered structure, emerges in the partial static structure factors at low temperatures. By calculating coordination numbers, we found a preferred connection for Al-Ti pairs, which induces an excess Ti/Al concentration around the central Al/Ti atoms. An excess Ti concentration is even found in the second neighbour shells around Ti atoms, rationalizing the prepeak as the result of chemical concentration fluctuation in these neighbour shells. Concomitantly, slow structural relaxation occurs below 1400 K, exhibited as the second step relaxation in self-intermediate scattering function. The slow dynamics induces a non-Arrhenius transition for the temperature-dependent diffusivity and structural relaxation time, as well as the breakdown of the Stokes-Einstein relation. These results unveil the detailed ordering structure for the chemical interaction and the associated dynamical behaviour in Al80Ti20 liquids.