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.