Abstract
Electron microscopy observations of the newly discovered icosahedral phase in the Al‐Cu‐Fe ternary system show a domain structure as expected from a group‐subgroup formal decomposition from a primitive six-dimensional (6D) hypercubic unit cell to a face‐centred one with twice the lattice parameter, as suggested by Ebalard and Spaepen. The structure of Al65Cu20Fe15 can be seen as an ordered F superstructure of the usual primitive quasilattice with, at least, two motifs in the 6D representation. The smoothness of the observed antiphase boundaries and the relative weak intensities of the superstructure reflections suggest that the ordered motifs should share many geometrical features. A possibility could be that at least one of the orbits of a given atomic species arranges in space according to a 6D primitive skeleton and chemical ordering occurs on the remaining orbits.