AN APPROACH OF THE STRUCTURE OF ICOSAHEDRAL AL6CULI3 BY MULTIPLE TWINNING OF A RHOMBOHEDRAL CRYSTAL

An analysis of the macroscopic morphology of slowly solidified Al6CuLi3 icosahedral quasicrystals, based on a multiple-twinning of a rhombohedral crystal nucleated on a 20 branded-star seed, is proposed. Consideration of dendrite growth by accretion of polyatomic clusters with icosahedral symmetry gives the key of the R3¯m twinned crystal structure. Its Fourier transform displays a pseudoicosahedral symmetry, with deviations from the perfect one in agreement with certain features of electron and X-rays diffraction patterns experimentally observed, as periodicities, symmetry dependent distortions and splitting of Bragg reflexions.