Crystal structures of two very similar 2 × 2 × 2 superstructures of γ-brass-related phases in ternary Ir–Cd–Cu system

Abstract

A binary phase Ir8Cd41 in the Ir–Cd binary system and novel ternary phases in the Ir–Cd–Cu system have been synthesized from the constituent elements using high-temperature solid-state synthesis. The structure of previously reported Ir8Cd41 and newly found ternary phases in the Ir–Cd–Cu system have been characterized by single crystal X-ray diffraction and EDS analysis. The structural analysis reveals that Ir8Cd41 adopts V8Ga41-type structure and ternary Ir–Cd–Cu phases adopt two 2 × 2 × 2-superstructures of the γ-brass-related phase. The structures of ternary Ir–Cd–Cu phases are associated with structural disorder (vacancies as well as mixed site occupancies). The crystal structures of the ternary phases are viewed using layer description and cluster concept. The 2 × 2 × 2-superstructure of γ-brass-related phases in the Cu-poor region are not isostructural with the phases in the Cu-rich region, and they are consistent with the absence of a continuous phase region between two 2 × 2 × 2-superstructures of γ-brass-related phases. In the Cu-poor region, the structures contain ∼404 atoms per unit cell, whereas in the Cu-rich phases the structures contain ∼411 atoms in their respective unit cells. The crystal structures in the Cu-poor region represent a new type in the 2 × 2 × 2-superstructure of γ-brass-related phases in view of the combination of constituent cluster types, whereas the structures in the Cu-rich region adopt the Rh7Mg44 structure type.