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Ternary Aluminides with the Ideal Composition A 2 Pt 6 Al 15 ( A = Y, Gd—Tm, Zr)
Author(s) -
Niermann Jens,
Jeitschko Wolfgang
Publication year - 2004
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.200300336
Subject(s) - diffractometer , crystallography , yttrium , crystal structure , ternary operation , materials science , superstructure , single crystal , lattice constant , chemistry , diffraction , physics , metallurgy , optics , computer science , programming language , thermodynamics , oxide
Ternary rare earth platinum aluminides were prepared by arc‐melting of the elemental components followed by annealing in a high‐frequency furnace. Their crystal structure was determined for the yttrium compound from four‐circle X‐ray diffractometer data. It has hexagonal symmetry with a = 428.1(1) pm, c = 1638.3(3) pm, space group P 6 3 / mmc , and was refined to a conventional residual of R = 0.018 for 325 F values and 19 variable parameters. Of the five crystallographic positions, the yttrium position and one of the three aluminum positions show partial occupancies corresponding to the composition Y 1.357(3) Pt 4 Al 9.99(2) with the Pearson symbol hP 20 — 4.65. These partially occupied sites are that close to each other that at best only one can be fully occupied. A model for an ordered distribution of occupied and unoccupied Y and Al sites requires a √3 larger a axis with the Pearson symbol hP 20 — 4.67 for the subcell, very close to the experimental result. Corresponding superstructure reflections could be observed on an image‐plate single‐crystal diffractometer only in the form of diffuse streaks. The compound has the ideal composition Y 2 Pt 6 Al 15 with Z = 2 for the superstructure. This corresponds to the formula Y 1.33 Pt 4 Al 10 with Z = 1 for the subcell. The compounds A 1.33 Pt 4 Al 10 with A = Gd, Tb, Dy, Ho, Er, Tm were found to be isotypic with that of the yttrium compound. This structure is closely related to or isotypic with, respectively, those of Yb 2 Fe 4 Si 9 , Sc 1.2 Fe 4 Si 9.8 , Ce 1.2 Pt 4 Ga 9.8 , Ce 2 Pt 6 Ga 15 , Tb 0.67 Ni 2 Ga 5— x Si x , RE 0.67 Ni 2 Ga 5— x Ge x > (with RE = Y, Sm, Ho), and Gd 0.67 Pt 2 Al 5 , reported in earlier investigations. The new compound Zr 1.00(1) Pt 4 Al 10.22(3) has nearly the same hexagonal structure with a = 426.1(1) pm and c = 1622.8(3) pm. It was refined from four‐circle diffractometer data to a residual of R = 0.021 for 288 structure factors and 19 variable parameters.