Structure model for the τ(μ) phase in Al-Cr-Si alloys deduced from the λ phase by the strong- reflections approach

There are very obvious common features in the electron diffraction patterns of the λ and τ(μ) phases in the Al–Cr–Si system. The positions of the strong reflections and their intensity distributions are similar for the two structures. The relation of the reciprocal lattices of the λ and τ(μ) phases is studied. By applying the strong-reflections approach, the structure factors of τ(μ) are deduced from the corresponding structure factors of the known λ phase. Rules for selecting reflections for the strong-reflections approach are described. Similar to that of λ, the structure of τ(μ) contains six layers stacked along the c axis in each unit cell. There are 752 atoms in each unit cell, 53 of them are unique. The corresponding composition of the τ(μ) model is Al3.82 − xCrSix. Simulated electron diffraction patterns from the structure model are in good agreement with the experimental ones. The arrangement of interpenetrated icosahedral clusters in the τ(μ) phase is discussed.