Polytetrahedral order and chemical short-range order in metallic melts

The reasons are investigated for the prepeak and the asymmetry of the second peak in the structure factor curve that are observed in a variety of metallic melts. The prepeak is observed as an additional maximum in the left wing of the main peak of the structure factor for multicomponent melts and is attributed to their chemical short-range order (CSRO). The asymmetry of the second peak in the structure factor, which is usually explained by the icosahedral (polytetrahedral) order in the melt, is observed both for multicomponent systems and for pure metals. However, some aluminum alloys with transition metals exhibit the two features simultaneously, which requires an explanation. An X-ray diffraction study of the liquid ternary Al66.6Mn16.7Co16.7 alloy is performed at 1393 K and that of liquid copper at 1353 K, 1403 K, and 1553 K. The reverse Monte Carlo (RMC) method is used to derive structural models of these and other melts. Structural analysis of these melts is conducted using Delaunay simplices. A theoretical simulation of CSRO is performed in the model of liquid aluminum, the structure factor of which does not have these features. It is discussed that CSRO can exist in a melt regardless of the presence of the polytetrahedral order.