Complex metallic alloys in the Ce?Au?Sn system: a study of the atomic and electronic structures

We report the formation of a new stable quasicrystal approximant in the Ce–Au–Sn system. The crystalline structure of the Ce15Au65Sn20 compound is investigated by x-ray diffraction and is found to be of similar structure type to the Zn17Sc3 1/1 approximant. Large clusters with icosahedral symmetry are located at the node of the body-centred cubic (bcc) unit cell (a = 1.5190 nm) containing 161 atoms. We have used transmission electron microscopy to emphasize the relationship of this new compound with the icosahedral space group. The valence band has been investigated by photoemission spectroscopy and shows an indication of Van Hove singularities in the density of states, characteristic of quasicrystalline and related approximant phases. We expect similar 1/1 approximant and possibly icosahedral phases to be discovered in the new RE–Au–Sn systems (where RE is rare earth). We also found a hexagonal phase with a large unit cell possessing local icosahedral order, co-existing as a minority phase.