X-ray diffraction study of the structure of Al-Ni melts

The structures of Al-Ni melts with 0, 10, 18, 25, 28, 32, 40, 75, 90, and 100 at % Ni are studied by X-ray diffraction. The structural models of the melts, which were analyzed by the Voronoi-Delaunay transformation method, are reconstructed by a procedure that is inverse to the Monte Carlo method using experimental structure-factor curves. The parameters characterizing atomic ordering at short and longer distances are determined to change nonmonotonically in the range 10–40 at % Ni with an extreme in the vicinity of the melt containing 28 at % Ni. In this concentration range, nickel atoms are predominantly located in the pentagonal rings of polytetrahedral clusters of the icosahedral type; these atoms are ～4.1 Å from each other. Such clusters generate a prepeak in the structure-factor curves of the melts in the range 10–40 at % Ni.