Structure refinement of the δ1p phase in the Fe-Zn system by single-crystal X-ray diffraction combined with scanning transmission electron microscopy

The structure of the delta(1p) phase in the iron-zinc system has been refined by single-crystal synchrotron X-ray diffraction combined with scanning transmission electron microscopy. The large hexagonal unit cell of the delta(1p) phase with the space group of P6(3)/mmc comprises more or less regular (normal) Zn-12 icosahedra, disordered Zn-12 icosahedra, Zn-16 icosioctahedra and dangling Zn atoms that do not constitute any polyhedra. The unit cell contains 52 Fe and 504 Zn atoms so that the compound is expressed with the chemical formula of Fe13Zn126. All Fe atoms exclusively occupy the centre of normal and disordered icosahedra. Iron-centred normal icosahedra are linked to one another by face-and vertex-sharing forming two types of basal slabs, which are bridged with each other by face-sharing with icosioctahedra, whereas disordered icosahedra with positional disorder at their vertex sites are isolated from other polyhedra. The bonding features in the delta(1p) phase are discussed in comparison with those in the Gamma and zeta phases in the iron-zinc system.