BOND-ORIENTATIONAL ORDER IN LIQUID ALUMINIUM80-TRANSITION METAL20 ALLOYS

The structures of liquid Al80Mn20 and Al80Ni20 are simulated by molecu lar dynamics using interatomic potentials derived from neutron diffrac tion data. For these two alloys, the generated three dimensional parti cle configurations are consistent with the experimental partial pair c orrelation functions. The characterization of the local symmetries by both the construction of the Voronoi polyhedra and the calculation of the second-order invariants of spherical harmonics allows us to confir m the existence of a local icosahedral order in the quasicrystal-formi ng liquid Al80Mn20 and its absence in liquid Al80Ni20 about 70 K above the liquidus line. Molecular dynamics simulations of the correspondin g supercooled liquids show that this order increases strongly for A180 Mn20 and starts to develop for Al80Ni20. An improvement of the agreeme nt between the experimental and calculated pair correlation functions by the reverse Monte Carlo method yields liquid configurations charact erized by the same most frequently observed Voronoi polyhedra as those obtained in the molecular dynamics configurations, but with lower per centages.