Superstructure of Eu4Cd25:: A quasicrystal approximant

The quasicrystal approximant Eu4Cd25, formerly designated EuCd6, was synthesized and characterized by means of single-crystal X-ray diffraction. Superstructure reflections corresponding to an F-centered cubic unit cell with a doubled cell-parameter relative to the I-centered cubic sub-cell could be observed in the diffraction data. This gives the largest cubic unit cell reported to date among binary alloys. ne superstructure exhibits structural features that are found in all the RE-Cd-6 approximants as well as a further ordering between vacant/occupied Cd-8 cubes and oriented Cd-4 tetrahedra, which causes the superstructure. A reversible high-temperature phase-transition was observed at 782 K by means of DSC.