The Crystal Structures of U2Cu3 Al and UCUAl2, and their Relationship with Some Other Phases in the System U-Cu-Al

Abstract

X-ray investigations of a great number of samples along the specifically chosen tie-lines in the isothermal sections of the system U-Cu-Al (800 °C) indicated the existence of two new ordered ternary phases, i.e. U2Cu3Al and UCuAl2. The first one is hexagonal (S. G. P63/mmc, MgZn2-type), with a = 5.065 ± 0.005 Å, c = 8.307 ± 0.005 Å and c/a = 1.640. The ordered atomic arrangement of all atoms, as confirmed by trial and error method is consistent with a rather uncommon superstructure of the MgZn2-type. UCuAl2 is tetragonal, a = 3.857 ± 0.005 A, c = 8.736 ± 0.005 A, c/a = 2.265, probable space group is I4/mmm, and represents an ordered ternary structure variant of the TiAl3 type. The crystal structures of these two new phases were correlated, in terms of stacking sequences, with those which were identified in this system previously.