The reinvestigation of the crystal structure of Ba8Ge43□3 (space group $Ia{\bar 3}d$, no. 230; a = 21.3123(5) Å; Z = 8; Pearson symbol cI408) shows a full ordering of the vacancies (□) in the germanium framework. This ordered crystal structure can be considered as a derivative of an ideal “Ba8Ge46” clathrate‐I type structure ($Pm{\bar 3}n$, a′ = a/2) in which three Ge vacancies (per formula unit) are allowed to order in a cubic superstructure with a doubled unit cell parameter (□ at the 24c site, space group $Ia{\bar 3}d$). In the resulting Ge framework, each vacancy □ is surrounded by four three‐bonded (3b)Ge‐ species. The ordering in crystals of as‐cast samples (cooled in argon atmosphere, non‐annealed) is partially disrupted. For the “as‐cast” crystals, a short‐range model is proposed based on the partial distribution of Ge on the 24c and 24d sites. From the electron balance, Ba8Ge43 can be considered as a metallic Zintl phase with four excess electrons per formula unit. The Ba8Ge43 phase is stable in the temperature range 770 ‐ 810 °C and exists in equilibrium with Ba6Ge25 and Ge. By decomposition of undercooled (metastable) Ba8Ge43, a new metastable binary BaGe˜5 phase is formed.
The europium-containing clathrate-I Eu(x)Ba(8-x)Cu(16)P(30) was synthesized from the elements. Powder X-ray diffraction in combination with energy dispersive X-ray absorption spectroscopy (EDXS) and metallographic studies showed the homogeneity range with x ≤ 1.5. Determination of the crystal structure confirmed the presence of an orthorhombic superstructure of clathrate-I and revealed that Eu atoms exclusively resided in small pentagonal-dodecahedral cages. Magnetic measurements together with X-ray absorption spectroscopy are consistent with a 4f(7) (Eu(2+)) ground state for Eu(x)Ba(8-x)Cu(16)P(30). Below 3 K the Eu moments order antiferromagnetically. Resistivity measurements revealed metallic behavior of the investigated clathrate, in line with the composition deviating from the Zintl counting scheme. Local vibrations of the guest atoms inside the cages are analyzed with the help of specific heat investigations.
A new phase, Sn(x)Pt4Sb(12-y)Sn(y), has been prepared from the elements. It exhibits a wide range of homogeneity with 0.3(2) < or = x < or = 1.0(2) and 4.2(2) < or = y < or = 7.0(2). The crystal structure and the composition were established by single-crystal and powder X-ray diffraction as well as wavelength-dispersive X-ray analysis measurements and were supported by nuclear magnetic resonance experiments. The compound is the first representative of the filled-skutterudite family with the filler atoms not located at the center of the cavity but covalently bonded to the cavity's wall, as confirmed by the analysis of chemical bonding with the electron localizability indicator. The Sn and Sb atoms share the framework site with different coordinate parameters caused by the difference in atomic size; additional tin atoms are located in the cavities of the framework. The material is a diamagnet in the whole composition range. In agreement with the calculated electronic density of states, the material reveals a metallic behavior in electronic transport. The absolute values of electrical resistivity vary with the tin-to-antimony ratio.
Introducing a Magnetic Guest to a Tetrel-Free Clathrate: Synthesis, Structure, and Properties of EuxBa8-xCu16P30 (0 ≤ x ≤ 1.5). -The title compounds are prepared by solid state reactions of the elements (1125 K, 360 h) and characterized by powder and single crystal XRD, XAS, electrical resistivity, specific heat, and magnetic susceptibility measurements. Eu1.5Ba6.5Cu16P30 crystallizes in the space group Pbcn with Z = 4 showing the same type of the clathrate I superstructure as the parent compound Ba8Cu16P30. The Eu atoms exclusively reside in small pentagonal-dodecahedral cages. Below 3 K the Eu moments order antiferromagnetically. Semiconducting behavior of the title clathrate as observed previously is not confirmed. Instead, all the samples show metal-like resistivity. -(KOVNIR*, K.; STOCKERT, U.; BUDNYK, S.; PROTS, Y.; BAITINGER, M.; PASCHEN, S.; SHEVELKOV, A. V.; GRIN, Y.; Inorg. Chem. 50 (2011) 20, 10387-10396, http://dx.doi.org/10.1021/ic201474h ; MPI Chem. Phys.
The new compound Yb2+3—xPd12—3+xP7 x = 0.40(4)) was synthesized by sintering of a mixture of elemental components at 1100 °C with subsequent annealing at 800 °C. The crystal structure of Yb2+3—xPd12—3+xP7 was solved and refined from X‐ray single‐crystal diffraction data: space group P6¯, a = 10.0094(4)Å, c = 3.9543(2)Å, Z = 1; R(F) = 0.022 for 814 observed unique reflections and 38 refined parameters. The atomic arrangement reproduces a structure motif of the hexagonal Zr2Fe12P7 type in which one of the transition metal positions is substituted predominantly by ytterbium (Yb : Pd = 0.86(1) : 0.14). The ytterbium atoms are embedded in the 3D polyanion formed by palladium and phosphorus atoms. Two different environments for ytterbium atoms are present in the structure. Magnetic susceptibility measurements and XAS spectroscopy at the Yb LIII edge show the presence of ytterbium in two electronic configurations, 4ƒ13 and 4ƒ14. The following model was derived. Ytterbium atoms in the 3k site are in the 4ƒ13 state, the two remaining positions contain ytterbium in intermediate‐valence states, giving totally 79 % ytterbium in the 4ƒ13 electronic configuration.
The antimonides Ce2Ir3Sb4, La2Ir3Sb4, and Ce2Rh3Sb4 were synthesized by solid state reaction from the elements. The crystal structures of these compounds were determined from single crystal X-ray diffraction data. Ce2Ir3Sb4 crystallises in a new structure type in the space group Pnma (no. 62) with a = 16.1510(8) Å, b = 4.5600(3) Å, c = 10.9463(5) Å. La2Ir3Sb4 and Ce2Rh3Sb4 crystallise in the Ce2Ir3Sb4 structure type as well with a = 16.2659(10) Å, b = 4.5896(3) Å, c = 10.9996(7) Å) and a = 16.2293(8) Å, b = 4.5604(2) Å, c = 10.9804(5) Å, respectively. The four- and five-bonded transition metal atoms and three- and four-bounded Sb atoms form a 3D-network with the rare-earth metal embedded in its cavities, resembling the topology of Ca in the CaBe2Ge2 or Th in ThCr2Si2 type. Magnetic susceptibility and X-ray absorption near edge spectroscopy data indicate a stable trivalent state for Ce in the Ce2Ir3Sb4 compound.
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