A simple construction of the AlCuLi quasicrystalline structure related to the (Al, Zn)49 Mg32 cubic structure type

Abstract

Both b.c.c. and icosahedral AlCuLi phases coexist following conventional ingot casting. Owing to a slight difference in their composition, they can be distinguished by a Z-contrast technique in a scanning electron microscope. Moreover, the existence of an orientation relationship between the b.c.c. and icosahedral (AlCuLi) phases is established by a transmission electron microscopic study of an ion-beam-thinned sample. It is therefore confirmed that a close structural relationship exists between both AlCuLi phases. A simple construction of the AlCuLi quasicrystalline structure is proposed on the basis of a modified illustration of the Bergman-Waugh-Pauling–type structure, Im3 (AlCuLi), isostructural with (Al,Zn)₄₉Mg₃₂, which reveals that triacontahedra—known to be the basic volume element of the three-dimensional Penrose tiling—exist in these cubic phases. A simple change of the coordination number between triacontahedra is considered to initiate the construction of the corresponding icosahedral phase.