Browsing by Author "Burkhardt, U"

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    Cluster formation in the superconducting complex intermetallic compound Be21Pt5
    (American Chemical Society, 2018-01-09) Amon, A; Ormeci, A; Bobnar, M; Akselrud, LG; Avdeev, M; Gumeniuk, R; Burkhardt, U; Prots, Y; Hennig, C; Leithe-Jasper, A; Grin, Y
    Materials with the crystal structure of γ-brass type (Cu5Zn8 type) are typical representatives of intermetallic compounds. From the electronic point of view, they are often interpreted using the valence electron concentration approach of Hume–Rothery, developed previously for transition metals. The γ-brass-type phases of the main-group elements are rather rare. The intermetallic compound Be21Pt5, a new member of this family, was synthesized, and its crystal structure, chemical bonding, and physical properties were characterized. Be21Pt5 crystallizes in the cubic space group F4̅3m with lattice parameter a = 15.90417(3) Å and 416 atoms per unit cell. From the crystallographic point of view, the binary substance represents a special family of intermetallic compounds called complex metallic alloys (CMA). The crystal structure was solved by a combination of synchrotron and neutron powder diffraction data. Besides the large difference in the scattering power of the components, the structure solution was hampered by the systematic presence of very weak reflections mimicking wrong symmetry. The structural motif of Be21Pt5 is described as a 2 × 2 × 2 superstructure of the γ-brass structure (Cu5Zn8 type) or 6 × 6 × 6 superstructure of the simple bcc structural pattern with distinct distribution of defects. The main building elements of the crystal structure are four types of nested polyhedral units (clusters) with the compositions Be22Pt4 and Be20Pt6. Each cluster contains four shells (4 + 4 + 6 + 12 atoms). Clusters with different compositions reveal various occupation of the shells by platinum and beryllium. Polyhedral nested units with the same composition differ by the distance of the shell atoms to the cluster center. Analysis of chemical bonding was made applying the electron localizability approach, a quantum chemical technique operating in real space that is proven to be especially efficient for intermetallic compounds. Evaluations of the calculated electron density and electron localizability indicator (ELI-D) revealed multicenter bonding, being in accordance with the low valence electron count per atom in Be21Pt5. A new type of atomic interactions in intermetallic compounds, cluster bonds involving 8 or even 14 atoms, is found in the clusters with shorter distances between the shell atoms and the cluster centers. In the remaining clusters, four- and five-center bonds characterize the atomic interactions. Multicluster interactions within the polyhedral nested units and three-center polar intercluster bonds result in a three-dimensional framework resembling the structural pattern of NaCl. Be21Pt5 is a diamagnetic metal and one of rather rare CMA compounds revealing superconductivity (Tc = 2.06 K). © 2018 American Chemical Society
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    Superconductivity and magnetism in R4Be33Pt16 (R=Y, La–Nd, Sm–Lu ): a family of crystallographically complex noncentrosymmetric compounds
    (American Physical Society, 2021-07-14) Svanidze, E; Amon, A; Nicklas, M; Prots, Y; Juckel, M; Rosner, H; Burkhardt, U; Avdeev, M; Grin, Y; Leithe-Jasper, A
    Crystallographically complex compounds often possess peculiar physical properties, the evolution of which can be tracked by changing one of the constituent elements at a time. We report the discovery and synthesis of isotypic R4Be33Pt16 (R = Y, La–Nd, Sm–Lu) compounds, which crystallize with the noncentrosymmetric cubic pace group I¯43d. The lattice parameters vary from a=13.6682(4)Å for R = La to a=13.4366(3)Å for R = Lu. R4Be33Pt16 phases exhibit a wide range of ground states. R = Y, La, and Lu analogs display uperconductivity. their calculated electronic structures show nonzero density of states at the Fermi level, with the value of the Sommerfeld coefficient consistent with those obtained experimentally. The rest of the R4Be33Pt16 compounds exhibit magnetic ground states with ordering temperatures ranging from Tmag=0.4 K (R = Yb) to Tmag=40 K R r). The diversity of physical properties of R4Be33Pt16 compounds can likely be attributed to the nature of the ndividual rare-earth elements, structural noncentrosymmetry, the large number of atoms per unit cell (212), as well as the complex multicenter interactions within the Be-Pt framework. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license