ATOMIC-STRUCTURE OF THE ICOSAHEDRAL AL-LI-CU QUASI-CRYSTAL

Using both powder and single crystal samples, neutron and x-ray diffraction data were obtained with quasicrystals of the AlLiCu system. Isotopic substitution on the Li and Cu atomic sites allowed amplitudes and phase shift of the partial structure factors to be determined. Using a high-dimensional crystallography approach results in the phases to be reconstructed and atomic densities were calculated. The six-dimensional periodic structure appeared as a primitive hypercubic lattice with mid-edge and vertex Al/Cu atomic surfaces plus a Li bodycentre site. The major drawbacks of the experimental approach are then bypassed by modelling details of the six-dimensional structure, still in agreement with diffraction data. The related three-dimensional quasiperiodic structure can be described in terms of connected clusters or, alternatively, families of atomic planes. Comparison with the structure of the crystalline R-phase is of interest.