Crystal structure determination of the Γ2 phase in the Fe–Zn–Al system by single-crystal synchrotron X-ray diffraction combined with scanning transmission electron microscopy

Abstract

The crystal structure of the Γ2 phase in the Fe–Zn–Al ternary system has been determined by single-crystal synchrotron X-ray diffraction combined with scanning transmission electron microscopy. The Γ2 phase possesses the γ′-brass structure with the space group of F4¯3m, similarly to the Γ1 phase in the Fe–Zn binary system. However, the Γ1 and Γ2 phases are not isostructural with each other because the constituent cluster types are different when described by the nested cluster model. Moreover, the crystal structure of the Γ2 phase can be classified into a new type of the γ′-brass structure since it comprises a nested cluster (the Ti2Ni type with a cluster centre (CC) atom) which does not exist in any of the γ′-brass structures ever reported. The unit cell of the Γ2 phase contains 32 Fe, 16 Al and 348 Zn atoms so that the compound is expressed with the chemical formula of Fe8Zn87Al4, and comprises Fe-centred Zn12 and Zn9Al3 icosahedra, Zn-centred Zn10 polyhedra and tetrapods consisting of split sites of Zn atoms with partial occupancies.