Structure and Properties of γ-Brass-Type Pt2Zn11—δ (0.2 < δ < 0.3)

Abstract

The γ-brass type phase Pt 2 Zn 11Ϫδ (0.2 < δ < 0.3) was prepared by reaction of the elements in evacuated silica ampoules. The structures of crystals grown in the presence of excess zinc or alternatively excess platinum were determined from single crystal X-ray diffraction intensities and confirmed by Rietveld profile fits. Pt 2 Zn 10.72(1) crystallizes in the space group I43m, a ϭ 908.55(4) pm, Z ϭ 4. The structure refinement converged at R F ϭ 0.0302 for I o > 2σ (I o ) for 293 symmetrically independent intensities and 19 variables. The structure consists of a 26 atom cluster which is comprised of four crystallographically distinct atoms. The Struktur und Eigenschaften von Pt 2 Zn 11؊δ (0.2 < δ < 0.3) vom γ-Messing-TypInhaltsübersicht. Die Phase Pt 2 Zn 11-δ (0.2< δ < 0.3) vom γ-Messing-Typ wurde durch Umsetzung der Elemente in Quarzglasampullen sowohl einphasig als auch im Phasengemenge in Koexistenz mit den Nachbarphasen hergestellt. Die Strukturen von zwei Kristallen wurden aus Röntgen-Beugungsintensitäten bestimmt und durch quantitative Auswertung eines Pulver-Röntgen-Diffraktogramms nach Rietveld bestätigt. Pt 2 Zn 10.72(1) kristallisiert in der Raumgruppe I43m, a ϭ 908.55(4) pm, Z ϭ 4. Die Strukturverfeinerung konvergierte bei R F ϭ 0.0302 mit I o > 2σ (I o ), 293 symmetrisch unabhängigen Reflexen und 19 Variablen.atoms Zn(1), Pt(1), Zn(2) and Zn(3) form an inner tetrahedron IT, an outer tetrahedron OT, an octahedron OH, and a distorted cuboctahedron CO respectively. About 14 % of the Zn(1) sites are unoccupied. Pt 2 Zn 10.73 melts at 1136(2) K. It is a moderate metallic conductor (ρ 298 ϭ 0.2Ϫ0.9 mΩ cm) whose magnetic properties (χ mol ϭ Ϫ4.6 10 Ϫ10 to Ϫ5.4 10 Ϫ10 m 3 mol Ϫ1 ) are dominated by the core diamagnetism of its components.

Pt29Zn49, a complex defective AlB2-type derivative structure

“…The temperature independent molar susceptibility was calculated from the slope of a linear plot χ mol T versus T. The value −1.3 × 10 10 m 3 mol −1 refers to an average atom of the compound. Although slightly less negative, the value compares well with the molar susceptibilities measured for other Zn-rich Pt-Zn phases [7][8][9].…”

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

“…This approach of describing the γ‐brass structure is robust and useful for direct comparisons with other γ‐brass structures in different systems so as to increase our understanding of site preferences for different elements in these phases. For instance, in the γ‐ T 2 Zn 11 systems ( T = Ni,37 Pd,9 Pt,12 Rh,10 and Ir11), the OT position is exclusively occupied by the minority component T . In addition, cubic γ‐brass structures have also been reported in the binary Pd‐Zn and Au‐Zn, respectively, as Pd 2+ x Zn 11– x and Au 5 Zn 8 .…”

“…To calculate these vec values, only the valence s and p electrons are used. The observed γ‐brass phases in binary and ternary systems adopt one of four different Bravais lattices, namely, primitive cubic ( P ‐cell),5–7 body‐centered cubic ( I ‐cell),8–12 face‐centered cubic ( F ‐cell; a superstructure ofγ‐brass),13–16 and rhombohedral ( R ‐cell) 17–21. Furthermore, the e – /atom ratios for these different structure types are nearly the same, so there are no guidelines explaining the existence of a specific structure type as a function of vec , except for the R ‐cell.…”

Pd0.213Cd0.787 and Pd0.235Cd0.765 Structures: Their Long c Axis and Composite Crystals, Chemical Twinning, and Atomic Site Preferences

“…These phases prove to be variants of the g-brass structure, and as such they add to the already rich field of gbrass structural variants. [35,57,[79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95][96][97] But they do more than just add another structure or two to the overall picture of gbrass variants. Previous views of g-brass focused on the polyhedral nature of the structure, [76,98] the fact that the gbrass unit cell is a 3 3 3 defective bcc lattice, the rhombohedral [83,89,[99][100][101] or primitive [88,90,96,102] variants, or the 2 2 2 superstructures of g-brass.…”