Structural relationship between an icosahedral phase and a 1/1 cubic crystalline approximant in an Al-Li-Cu alloy system, studied by atomic-scale observations of electron microscopy

We observed cubic R-phase and icosahedral I-phases in the Al-Li-Cu system by high-resolution transmission electron microscopy (HREM). The images of both the phases taken from three-fold axes showed the presence of the same kind of atom clusters, which are most likely to be the small triacontahedra. The R-phase was found to contain stacking faults along the {110} plane. This stacking fault is created by the insertion of extra atom units, which destroys the symmetry of the lattice, yet the symmetrical configuration of the facing clusters is well preserved.