Crystal structure of the Al₂CuIr phase

A new ternary Al₂CuIr phase was revealed in the Al-Cu-Ir system. It is formed below 1063 °C from the β-phase (CsCl-type structure) extending at elevated temperatures from AlIr. The crystal structure of the Al₂CuIr phase was determined using a combination of precession electron diffraction and X-ray powder diffraction techniques. The phase has an orthorhombic C-centered unit cell with lattice parameters a = 8.1196(7) Å, b = 5.0646(2) Å and c = 5.18513(3) Å; its crystal symmetry can be described by the Cmme (no. 67) space group (Pearson symbol oC16). The unit cell of the new phase contains 8 Al, 4 Cu and 4 Ir atoms and exhibits a new structure type. The reliability factors characterizing the Rietveld refinement procedure are: R_p = 4.45%, R_wp = 6.45%, R_B = 3.69% and R_f = 2.41%.