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On the Structural Chemistry of γ‐Brasses: Two Different Interpenetrating Networks in Ternary F ‐Cell Pd–Zn–Al Phases
Author(s) -
Thimmaiah Srinivasa,
Miller Gordon J.
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200903300
Subject(s) - crystallography , ternary operation , atom (system on chip) , crystal structure , chemistry , superstructure , cluster (spacecraft) , tetrahedron , pseudogap , phase (matter) , phase diagram , octahedron , physics , doping , condensed matter physics , thermodynamics , cuprate , computer science , embedded system , programming language , organic chemistry
Novel ternary phases, (Pd 1− x Zn x ) 18 (Zn 1− y Al y ) 86− δ (0≤ x ≤0.162, 0.056≤ y ≤0.088, 0≤ δ ≤4), which adopt a superstructure of the γ‐brass type (called γ′‐brass), have been synthesized from the elements at 1120 K. Single‐crystal X‐ray structural analysis reveals a phase width ( F $\bar 4$ 3 m , a =18.0700(3)–18.1600(2) Å, Pearson symbols cF 400– cF 416), 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 γ‐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 Pd 4 Zn 22 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 γ′‐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 γ‐brasses, in general.