Incommensurately Modulated δ″-Au1+xCd2–x Formed by an Unquenchable Phase Transformation from the γ‑Brass δ′-Phase

The synthesis and structural determination of the compound δ″-Au1+xCd2–x (0.07 ≤ x ≤0.08) is reported. The structure may be formally derived from that of ξ-CoZn13, but elemental ordering causes an incommensurate modulation as determined by single-crystal X-ray diffraction at room temperature. The compound δ″-Au3.23Cd5.76 crystallizes in the monoclinic super space group C2/m(0β1/2)­00 with lattice parameters a = 14.790(2) Å, b = 8.251(1) Å, c = 12.744(1) Å, β = 115.182(9)° and a q-vector q = (0β1/2), β = 0.579b*. The δ″-phase is stable up to 652(1) K.