Approximants to the icosahedral and decagonal phases in the Al–Cu–Cr system

A 1/1-type approximant to the AlCuCr icosahedral phase and approximants to a decagonal phase have been found in an as-cast Al₆₅Cu₂₀Cr₁₅ ingot. Selected area electron diffraction indicates that the 1/1-type approximant consists of Mackay icosahedra arranged on a bcc lattice, similar to the α-AlMnSi cubic phase. Ordering of the glue atoms produces a base-centered orthorhombic superstructure, making the overall structure monoclinic P2/m, with lattice parameters a = 12.6 Å, c = 17.92 Å, and α = 90°.