Local order in liquids forming quasicrystals and approximant phases

Neutron-scattering experiments were performed on liquid Al88.5(MnₓCr_1-x)11.5 alloys $(0<~x<~1),$ giving rise to equilibria with μ phase compounds whose structure is closely related to those of quasicrystalline phases. Assuming a Mn/Cr isomorphic substitution like the one existing in the μ phase, partial pair structure factors and corresponding correlation functions were determined in these liquids. The results show a strong (Mn-Cr)-Al chemical order where the average first coordination shell around transition-metal atoms appears to be in agreement with an icosahedral local order. Simulations based on liquid models containing icosahedral clusters like those existing in many Al-Mn-Cr intermetallic structures are found to reproduce the liquid total structure factors measured at large momentum transfer where the influence of local order is preponderant. Information on icosahedral local order is also obtained when such a simulation method is applied to other liquid alloys, Al92.3Mn7.7, Al₈₁Pd₁₉, and Al72.1Pd20.7Mn7.2, giving rise to approximant or quasicrystalline phases, but in which partial functions are not determined.