Structure of Icosahedral Al-Cu-Li

It is found by x-ray-absorption fine-structure measurements that the Cu sites in the stable icosahedral phase ($T2\mathrm{}$ phase) and the $R$ phase of Al-Cu-Li alloys are nearly identical. We infer that the structural unit in the $T2\mathrm{}$ phase is a truncated icosahedron composed of 105 atoms. We speculate that the $T2\mathrm{}$ phase and icosahedral Al-Mn-Si have the same structure except for a different structural unit. This is supported by recent x-ray diffraction measurements of both diffraction-peak positions and widths of the $T2\mathrm{}$ phase.