A Heavily Disordered γ‐Brass Type Phase Ag _{5+ <i>δ</i>} Zn _{8‐ <i>δ</i>}

The γ‐brass type phase in the Ag–Zn system has been synthesized by a high‐temperature method, and the crystal structure has been determined by the single‐crystal X‐ray diffraction studies. The phase Ag 5+ δ Zn 8‐ δ adopts a cubic space group I 3 m with a cell parameter of ≈9.35 Å. Like the γ‐brass type phases, the structure can be seen as the combination of two similar 26 atom‐γ‐cluster present at (0, 0, 0) and (½, ½, ½) of the unit cell. Unlike the other members of the cubic I ‐centred γ‐brass/γ‐brass type phases, the structure of Ag 5+ δ Zn 8‐ δ is heavily disordered and accommodates substitutional disorder between Ag and Zn in all four crystallographic sites of the 26 atom‐γ‐cluster. The crystallographic work on the “coloring” of the Ag and Zn atoms among the different crystallographic sites of the Ag 5+ δ Zn 8‐ δ reveals that the site distribution pattern of Ag and Zn atoms is allied to the Cu 5 Zn 8 γ‐brass structures. This “coloring scheme” is rationalized by electronic structure calculations on the ordered model “Ag 5 Zn 8 ” from the experimentally determined structure of Ag 5+ δ Zn 8‐ δ . The pronounced pseudo‐gap near the Fermi level for Ag 5+ δ Zn 8‐ δ indicates that the phase is stabilized by the Fermi sphere‐Brillouin zone‐induced Hume–Rothery mechanism.