On the Structural Chemistry of gamma-Brasses: Two Different Interpenetrating Networks in Ternary F-Cell Pd-Zn-Al Phases

TitleOn the Structural Chemistry of gamma-Brasses: Two Different Interpenetrating Networks in Ternary F-Cell Pd-Zn-Al Phases
Publication TypeJournal Article
Year of Publication2010
AuthorsThimmaiah S, Miller GJ
Journal TitleChemistry-A European Journal
Volume16
Pages5461-5471
ISBN Number0947-6539
Accession NumberISI:000277988900028
Keywordsapproximants, cluster compounds, crystal-structure, CU5ZN8, delta-phase, gamma brasses, hume-rothery compounds, hume-rothery phase, quasi-crystal, superstructure, system, ternary phases, x-ray, x-ray diffraction, ZINC
Abstract

Novel ternary phases, (Pd1-xZnx)(18)(Zn1-yAly)(86-delta) (0 <= x <= 0.162, 0.056 <= y <= 0.088, 0 <=delta <= 4), which adopt a superstructure of the gamma-brass type (called gamma'-brass), have been synthesized from the elements at 11120 K. Single-crystal X-ray structural analysis reveals a phase width (F (4) over bar 3m, a = 18.0700(3)-18.1600(2) angstrom, Pearson symbols cF400-cF416), which is associated with structural disorder based on both vacancies as well as mixed site occupancies. These structures are constructed of four independent 26-atom gamma-clusters per primitive unit cells and centered at the four special positions A (0, 0, 0), B (1/4, 1/4. 1/4), C (1/2, 1/2, 1/2) and D (3/4, 3/4, 3/4). Two of these, centered at B and C. are completely ordered Pd4Zn22 clusters, whereas the other two, centered at A and D, contain all structural disorder in the system. According to our single-crystal X-ray results, Al substitutions are restricted to the A- and D-centered clusters. Moreover, the outer tetrahedron (OT) site of the 26-atom cluster at D is completely vacant at the Al-rich boundary of these phases. Electronic structure calculations, using the tight-binding linear muffin-tin orbital atomic-spheres approximation (TB-LMTO-ASA) method, on models of these new. ternary gamma'-brass phases indicate that the observed chemical compositions and atomic distributions lead to the presence of a pseudogap at the Fermi level in the electronic density of states curves, which is consistent with the Hume-Rothery interpretation of gamma-brasses. in general.

URL<Go to ISI>://000277988900028
DOIDoi 10.1002/Chem.200903300