γ-Brass type structures with I- and P-cell in the ternary Cu–Zn–In system

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Abstract γ-Brass type phases in Cu–Zn–In ternary system were synthesized from the highly pure elements by conventional solid-state synthesis and characterized by X-ray diffraction and EDX analysis. Diffraction analysis confirmed the existence of cubic γ-brass type phases with I- and P-cell having a significant homogeneity range in the ternary Cu–Zn–In system. The phase homogeneity is connected with structural disorder based on mixed site occupancies. Site specific In substitution was observed during single-crystal structure analysis. The γ-brass structures with body-centered cubic lattice (I 4 ‾ $‾{4}$ 3m) are viewed as 26-atom γ-clusters. Like Cu5Zn8, the inner tetrahedron (IT), outer tetrahedron (OT) and octahedron (OH) sites in the 26-atom clusters of γ-brass structures with I-cell are occupied by Zn, Cu, Cu, respectively. Indium substitution is restricted to the cuboctahedral (CO) site and the CO site is assumed to be mixed with In, Cu and Zn throughout the homogeneity range. The structures of cubic γ-brass type (P 4 ‾ $‾{4}$ 3m) phases with P-cell are built up with two independent 26‐atom γ‐clusters and centered at the special positions A (0, 0, 0) and B (½, ½, ½) of the unit cell. According to the single‐crystal X‐ray analyses, In substitutions are largely restricted to the cuboctahedral sited B clusters. In the cubic γ-phases with P-cell, site occupancy pattern of cluster positioned at A is similar to the γ-cluster in Cu5Zn8, whereas cluster B bears a close resemblance to Cu-poor γ-cluster (Cu14In12) of Cu9In4 (P 4 ‾ $‾{4}$ 3m). The vec values for cubic γ-brass type phases in the Cu–Zn–In ternary system ranges between 1.57 and 1.64.