Investigation of the particular features of the structure factor of liquid Al-based alloys

We study the structure of liquid binary and ternary alloys of aluminum with transition metals (Al-TM) obtained by Reverse Monte Carlo (RMC) and Molecular Dynamics (MD) simulation methods. Two distinctive features of their structure factor are discussed: the shoulder on the second peak and the prepeak on the left side of the main peak. The quadruples of mutually neighboring atoms (Delaunay simplexes) with a shape close to a regular tetrahedron's (quasi-regular tetrahedra) have been selected in the models and examined. They combine into clusters of different morphology (polytetrahedra) forming a polytetrahedral order (PTO), and there are no compact clusters of these tetrahedra similar to icosahedron in our alloys. It is discussed that the second peak feature of the structure factor is associated with PTO, and does not require for its explanation the presence of icosahedral short-range order (ISRO) in the liquid alloys. The prepeak is caused by the chemical short-range order (CSRO). In our models it is observed mainly on the subsystem of atoms which is complementary to the subsystem of the polytetrahedra. Simulation of the CSRO was performed on a model of monatomic liquid. A new length scale responsible for the prepeak has been obtained in this simulation.