STRUCTURE OF SOLID SOLUTIONS RCo 2-x Li x Si 2 (R = Gd, Dy)
Анотація
A search for quaternary alumogermanides was carried out in the system R–Ni–Al–Ge. Ten alloys of nominal composition R 3 NiAl 3 Ge 2 (R = Y, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were synthesized from high-purity metals by arc-melting and annealed at 600°C for 1800 h. Phase and structural analyses were performed based on X-ray powder diffraction data. The structural parameters were refined by the Rietveld method. All of the alloys appeared to be single-phase. The existence of two known (with Y and Er)mand eight new (with Sm, Gd, Tb, Dy, Ho, Tm, Yb, and Lu) quaternary R 3 NiAl 3 Ge 2 compounds wasmestablished. The compounds are isotypic and their crystal structures belong to the type Y 3 NiAl 3 Ge 2 (Pearson symbol hP9, space group P-62m). As expected, the cell parameters decrease with decreasingnradius of the rare-earth metal, from Sm to Lu, with the exception of the Yb-containing compound due to the valence of Yb (Yb II ).
The hexagonal structure type Y 3 NiAl 3 Ge 2 (Z = 1) is a quaternary variant of the binary type Fe 2 P (Z = 3) and the ternary types β 1 -K 2 UF 6 , Lu 3 CoGa 5 , Zr 3 Cu 4 Si 2 , and ZrNiAl. It belongs to a family of structures with trigonal prismatic coordination of the small atoms (Ni and Ge). The Ni- and Ge- centered trigonal prisms form infinite columns via common triangular faces. The columns of Gecentered prisms (GeY 6 ) share prism edges and form a three-dimensional framework with six-membered rings in the (001) plane, whereas the columns of Ni-centered prisms (NiAl 6 ) are isolated and located in the channels of the framework.
Key words: quaternary alumogermanide, X-ray powder diffraction, crystal structure, isotypic compounds.
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