Yb2Al15Pt6 − the most ordered variety of the Sc1.2Fe4Si9.8 aristotype

Abstract

The title compound was synthesized by reaction of the elemental components in a corundum crucible at 1450 ºC, and subsequent crystal growth using the Bridgman technique. The crystal structure of Yb 2 Al 15 Pt 6 was determined from X-ray single crystal diffraction data: space group Cmcm, Pearson symbol oS92, a = 12.7969(1) Å, b = 7.38813(7) Å, c = 16.3605(2) Å, R F = 0.036 for 1455 observed structure factors and 65 variable parameters. The title compound crystallizes in a new type of structure, which represents an ordered variety of the Sc 1.2 Fe 4 Si 9.8 aristotype. The structure can be described as an (ABB) 2 stacking of two trigonal layers with compositions Yb 4 Al 6 (A) and Pt 6 Al 12 (B). The layers A are almost planar and consist of ytterbium atoms arranged at the apexes of condensed hexagons centered by triangular Al 3 units. The slabs B may be considered as distorted hexagonal close-packed, similar to three adjacent layers I− − − −Cd− − − −I of the structure type CdI 2 (Al− − − −Pt− − − −Al). The structural particularities of Yb 2 Al 15 Pt 6 are discussed in comparison with the related structures of Y 2 Ga 9 Co 3 , Tb 2 Ge 3 Pt 9 , Yb 2 Ga 9 Pd 3 and Er 4 Al 24 Pt 9. A real-space analysis of the chemical bonding with the electron-localizability approach showed that the crystal structure of Yb 2 Al 15 Pt 6 consists of an anionic Al− − − −Pt framework, with Yb cations embedded in cavities. The Al− − − −Pt interactions within the framework are covalent polar, whereas ionic bonding is observed between ytterbium and the framework.

Magnetic Properties of the RE2Pt6X15 (RE = Y, La–Nd, Sm, Gd–Lu; X = Al, Ga) Series

“…The anomaly visible in the ZFC/FC measurements at T imp = 4.8(1) K has to be attributed to trace impurities with a so far unknown composition. The effective magnetic moment µ eff = 4.72(1) µ B proves that the Yb atoms are in the trivalent state, since the magnetic moment matches the calculated moment µ calc = 4.536 µ B well, in line with the investigations reported in the literature where the authors calculated a slightly reduced moment for the Yb atoms (Yb 4 f occupation of 13.3 electrons) . This is somehow unexpected, since Ca 2 Pt 6 Al 15 exists and Yb often is found in the divalent oxidation state, which is diamagnetic since it exhibits a 4 f 14 electron configuration.…”

U1.33T4Al8Si2 (T = Ni, Co): Complex Uranium Silicides Grown from Aluminum/Gallium Flux Mixtures

“…Additional variables that might induce ordering are synthesis procedure (stoichiometric synthesis, arc melting, flux growth), and heating profile (maximum temperature, cooling rate, annealing process). It is notable that the two ordered superstructures were found in compounds grown from reactions with high temperature annealing steps or very slow cooling rates. , This ordering effect can also be seen in two reports of Gd 4 Pt 9 Al 24 , a structurally related compound with similar layers of main group triangles and rare earth cations. In both cases the material was grown from an aluminum flux reaction, but one synthesis included a 300 h dwell at 850 °C (yielding a more ordered structure), and the other had a shorter reaction time (producing a disordered/averaged structure). , It is likely that modification of heating profile will enable control over the extent of ordering in the R 1.33 T 4 M 10 structure type, and potentially tuning of the magnetic properties of the lanthanides or actinides in this large family of materials.…”

“…The U 1.33 Co 4 Al 8 Si 2 phase exhibits greater evidence of supercell formation compared to the Ni analog, but the ordering was not sufficient to solve the structure in a supercell. In the many analogs of this structure type, two potential ordered supercells have been reported, an orthorhombic cell and a monoclinic cell. , The extent of ordering may be dependent on a number of parameters including atom size (as seen here). Further investigation of size effects will be facilitated by the flux growth of analogs with other actinides such as Th and Np.…”

Abrupt Europium Valence Change in Eu2Pt6Al15 around 45 K

“…During single crystal structure analysis, it rather quickly became evident that Eu 2 Pt 6 Al 15 crystallizes isostructurally to Sc 2 Pt 6 Al 15 in a commensurate modulated structure, which is a superstructure of the hexagonal RE 0.67 Pt 2 Al 5 compounds ( P 6 3 / mmc ; RE = Y, Ce, Gd–Tm; Sc 0.6 Fe 2 Si 4.9 type) and orthorhombic Yb 2 Pt 6 Al 15 ( Cmcm ) . As the refinement of Sc 2 Pt 6 Al 15 has been described before in great detail, the refinement of the title compounds will be handled rather quickly.…”

“…(Cmcm). 37 As the refinement of Sc 2 Pt 6 Al 15 has been described before in great detail, 38 the refinement of the title compounds will be handled rather quickly. The measured data was interpreted as orthorhombic C-centered lattice with q = 2/3 a* in superspace group Cmcm(α,0,0)0s0; a trilling was introduced to account for all measured reflections (Figure S1).…”