Structures of NiCd6+δ (−0.32 ≤ δ ≤ 0.35) – a γ-brass related phase, and NiCd1+δ (0 ≤ δ ≤ 0.05) – a Ti2Ni type phase in the nickel–cadmium system

Abstract

The crystal structures of the binary cadmium-rich complex metal alloys NiCd_6+δ (−0.32 ≤ δ ≤ 0.35) and NiCd_1+δ (0 ≤ δ ≤ 0.05) were studied by means of single crystal X-ray diffraction. The partitioning of the NiCd_6+δ structure into clusters grouped around all 16 high symmetry points of the face centered cubic cell leads to the identification of two partial structures forming replicas of two disjointed, interpenetrating, zinc blende-type nets. In one partial structure the nodes are NiTi₂-type Ni₄Cd₁₈ and bcc-type NiCd₂₆ clusters. This substructure is ordered and compositionally more or less invariant in the whole homogeneity range with the fixed composition Ni₅Cd₄₄. The complementary substructure varies in composition and exhibits vacancy, substitutional and positional disorders. The structure of NiCd_1+δ (0 ≤ δ ≤ 0.05) can be described by a 34-atom Ti₂Ni-type cluster.