DIFFUSE-SCATTERING IN THE ICOSAHEDRAL AL-LI-CU QUASI-CRYSTAL

Electron diffraction patterns of icosahedral quasicrystals frequently exhibit diffuse scattering features. We report a detailed analysis of diffuse scattering in Al6Li3Cu (T2) quasicrystalline samples. The samp les have been specifically heat-treated which allows to observe pronou nced diffuse effects. Diffuse streaks are observed along the 5-fold an d 2-fold symmetry axes and are elongated perpendicularly to these dire ctions. These streaks are due to discs in the 3-dimensional reciprocal space. The diffuse disc positions are only indexable in the 6-dimensi onal hyperspace but the disc intensities do not agree with the ones pr edicted by the Cut-and-Project method. The diffuse discs we observed s eem to be related to an original quasicrystalline phenomenon overlappi ng with the icosahedral phase.