The apparent ’five-fold’ nature of large T2 (AI6Li3Cu) crystals

LargeT ₂ (Al₆Li₃Cu) crystals which display apparent five-fold symmetry have been studied using several different electron microscopy techniques. Electron microprobe X-ray analysis was used to determine the phases present in two different alloys cast with bulk compositions close to stoi-chiometricT ₂. Convergent beam electron diffraction (CBED) of these crystals indicates that they do not display five-fold rotational symmetry, and TEM images and selected area diffraction from thin foil specimens indicate a microcrystalline or twinned structure is responsible for the apparent five-fold symmetry ofT ₂. Microdiffraction patterns obtained from the thinnest regions of the crystals are consistent with a cubic structure having a lattice parameter of ≈0.40 nm.