Crystal Structures and Stabilities of γ‐ and γ′‐Brass Phases in Pd2–xAuxZn11 (x = 0.2–0.8): Vacancies vs. Valence Electron Concentration

Abstract

AbstractTo probe the effect of valence electron concentration (vec or e–/atom) on γ‐Pd2+xZn11–x phases a series of compoundsPd2–xAuxZn11 (x = 0.3–0.8; e–/atom = 1.70–1.75) was synthesized and structurally characterized. The gold‐substituted γ‐brass type phase was observed for x ≤ 0.3, having a refined composition of Pd1.93Au0.27(1)Zn10.80(1) (space group I$\bar{4}$3m; a = 9.0953 (2) Å). Further addition of gold (0.4 ≤ x ≤ 0.8) leads to a 2 × 2 × 2 superstructure of theγ‐brass type phase (denoted as the γ′‐phase), with noticeable phase width (F$\bar{4}$3m; 18.1827(4)–18.1799(4) Å). The γ′‐phase consists of four independent 26‐atoms clusters, which are arranged around four distinct high symmetry points. The structural stability and phase width ofγ′‐phase are primarily controlled by two of these clusters, both of which show mixed occupancies and occurrence of non‐stoichiometric vacancies. Amongst all the observed γ′‐phases in the Pd‐Au‐Zn system, the vacancy concentration increases with increasing values of gold substitution. The vec of all observed γ′‐phases fall between 1.636 and 1.654 e–/atom values, which are greatly influenced by the nonstoichiometric vacancies present in the structure.