- A new ternary Al 2 CuIr 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 Al 2 CuIr 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%, RB= 3.69% and R f= 2.41%.