Short- and medium-range orders in Al-Mn melts

Abstract

The structures of Al-Mn melts with 14.3, 20, 26.7, 40, 50, and 70 at % Mn are studied by X-ray diffraction at a temperature 50°C above the liquidus temperature. The reverse Monte Carlo simulation and experimental structure-factor curves are used to construct structural models for liquid Al, Mn, and their binary melts. The character of atomic ordering on short- and medium-range scales is studied by dividing model configurations into Voronoi polyhedra and Delaunay simplexes. A nonmonotonic dependence of structural parameters is found in the region with a high aluminum content. The structural parameters have extremum values in an Al6Mn melt. The prepeak in the structure-factor curves in the diffraction vector range 9–25 nm−1 is shown to be caused by a chemical atomic order in polytetrahedral clusters.