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41.
Volodymyr Pavlyuk Wojciech Ciesielski Beata Rozdzynska-Kielbik Grygoriy Dmytriv Helmut Ehrenberg 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(7):561-565
Binary and multicomponent intermetallic compounds based on lithium and p‐elements of Groups III–V of the Periodic Table are useful as modern electrode materials in lithium‐ion batteries. However, the interactions between the components in the Li–Ge–B ternary system have not been reported. The structure of tetralithium digermanium boride, Li4Ge2B, exhibits a new structure type, in the noncentrosymmetric space group R3m, in which all the Li, Ge and B atoms occupy sites with 3m symmetry. The title structure is closely related to the Mo2B5 and Li5Sn2 structure types, which crystallize in the centrosymmetric space group Rm. All the atoms in the title structure are coordinated by rhombic dodecahedra (coordination number = 14), similar to the atoms in related structures. According to electronic structure calculations using the tight‐binding–linear muffin‐tin orbital–atomic spheres approximation (TB–LMTO–ASA) method, strong covalent Ge—Ge and Ge—B interactions were established. 相似文献
42.
B/Nb and B/Nb2N bilayers and Nb/B/Nb trilayers of about 550 nm total thickness have been deposited on Si(100) wafers with 100 nm thermally
grown oxide. Nb and B layers were deposited by magnetron sputtering. Nb2N layers were prepared by nitridation of Nb films via rapid thermal processing (RTP). The samples were annealed subsequently
at temperatures between 600 and 1,200 °C in an RTP system under Ar or NH3 gas flow to study interdiffusion and reactivity of niobium, boron and nitrogen. Formation of phases was investigated by X-ray
diffraction (XRD); surface morphology and roughness were studied via scanning electron microscopy (SEM) and atomic force microscopy
(AFM), respectively. Elemental depth profiles of selected samples were recorded by secondary ion mass spectrometry (SIMS).
Annealing of the B/Nb bilayers and Nb/B/Nb trilayers under Ar leads to the formation of Nb3B2 at 1,200 °C at the B/Nb interface. At lower temperatures the high oxygen content in the boron layer is supposed to hinder
the formation of borides due to formation of glass-like boron oxides. In NH3 several niobium nitrides are formed but no boride phases. Here again the reactivity of boron with niobium is suppressed by
the high oxygen content and boron oxide formation. During annealing of the B/Nb2N bilayers no borides were formed indicating that well-formed Nb2N is an effective diffusion barrier for B. 相似文献
43.
Volodymyr Babizhetskyy Hansjürgen Mattausch Kurt Hiebl Régis Gautier 《Journal of solid state chemistry》2008,181(8):1882-1890
The ternary rare-earth metal boride carbides RE15B6C20 (RE=Pr, Nd) were synthesized by co-melting the elements. They exist above 1270 K. Their crystal structures were determined from single-crystal X-ray diffraction data. Both crystallize in the space group P1¯, Z=1, a=8.3431(8) Å, b=9.2492(9) Å, c=8.3581(8) Å, α=84.72(1)°, β=89.68(1)°, γ =84.23(1)° (R1=0.041 (wR2=0.10) for 3291 reflections with Io>2σ(Io)) for Pr15B6C20, and a=8.284(1) Å, b=9.228(1) Å, c=8.309(1) Å, α=84.74(1)°, β=89.68(1)°, γ=84.17(2)° (R1=0.033 (wR2=0.049) for 2970 reflections with Io>2σ(Io)) for Nd15B6C20. Their structure consists of a three-dimensional framework of rare-earth metal atoms resulting from the stacking of slightly corrugated and distorted square nets, leading to cavities filled with unprecedented B2C4 finite chains, disordered C3 entities and isolated carbon atoms, respectively. Structural and theoretical analyses suggest the ionic formulation (RE3+)15([B2C4]6−)3([C3]4−)2(C4−)2·11ē. Accordingly, density functional theory calculations indicate that the compounds are metallic. Both structural arguments as well as energy calculations on different boron vs. carbon distributions in the B2C4 chains support the presence of a CBCCBC unit. Pr15B6C18 exhibits antiferromagnetic order at TN=7.9 K, followed by a meta-magnetic transition above a critical external field B>0.03 T. On the other hand, Nd15B6C18 is a ferromagnet below TC≈40 K. 相似文献
44.
A variety of 1,1-diacetates have been chemoselectively and efficiently deprotected to the corresponding aldehydes as well as deprotected and concomitantly reduced to the corresponding alcohols in high yields at ambient temperature with nickel boride generated in situ using different molar ratios of sodium borohydride and nickel (II) chloride in methanol at room temperature. Deprotection and reduction of a variety of aromatic, aliphatic and heterocyclic acylals have been achieved efficiently. Mild reaction conditions, easy work-up, high yields and chemoselectivity demonstrate the efficiency of this new method. 相似文献
45.
The structural, electronic, and mechanical properties of ReB and ReC have been studied by use of the density functional theory. For each compound, six structures are considered, i.e., hexagonal WC, NiAs, wurtzite, cubic NaCl, CsCl, and zinc-blende type structures. The results indicate that for ReB and ReC, WC type structure is energetically the most stable among the considered structures, followed by NiAs type structure. ReB-WC (i.e., ReB in WC type structure) and ReB-NiAs are both thermodynamically and mechanically stable. ReC-WC and ReC-NiAs are mechanically stable and becomes thermodynamically stable above 35 and 55 GPa, respectively. The estimated hardness from shear modulus is 34 GPa for ReB-WC, 28 GPa for ReB-NiAs, 35 GPa for ReC-WC and 37 GPa for ReC-NiAs, indicating that they are potential candidates to be ultra-incompressible and hard materials. 相似文献
46.
47.
Volodymyr Babizhetskyy Arndt Simon Kurt Hiebl 《Journal of solid state chemistry》2010,183(10):2343-2351
The ternary rare-earth boride carbides R15B4C14 (R=Y, Gd-Lu) were prepared from the elements by arc-melting followed by annealing in silica tubes at 1270 K for 1 month. The crystal structures of Tb15B4C14 and Er15B4C14 were determined from single crystal X-ray diffraction data. They crystallize in a new structure type in space group P4/mnc (Tb15B4C14: a=8.1251(5) Å, c=15.861(1) Å, Z=2, R1=0.041 (wR2=0.088) for 1023 reflections with Io>2σ(Io); Er15B4C14: a=7.932(1) Å, c=15.685(2) Å, Z=2, R1=0.037 (wR2=0.094) for 1022 reflections with Io>2σ(Io)). The crystal structure contains discrete carbon atoms and bent CBC units in octahedra and distorted bicapped square antiprisms, respectively. In both structures the same type of disorder exists. One R atom position needs to be refined as split atom position with a ratio 9:1 indicative of a 10% substitution of the neighboring C4− by C24−. The actual composition has then to be described as R15B4C14.2. The isoelectronic substitution does not change the electron partition of R15B4C14 which can be written as (R3+)15(C4−)6(CBC5−)4•e−. The electronic structure was studied with the extended Hückel method. The investigated compounds Tb15B4C14, Dy15B4C14 and Er15B4C14 are hard ferromagnets with Curie temperatures TC=145, 120 and 50 K, respectively. The coercive field BC=3.15 T for Dy15B4C14 is quite remarkable. 相似文献
48.
Codeposition of Ca and B on various single crystal substrates was carried out by MBE technique. A new calcium boride CaB3 was epitaxially grown on Al2O3(0001) with substrate temperature . Structural characterization by RHEED and X-ray diffraction indicated that CaB3 has a hexagonal cell with lattice parameters and . No evidence for superconductivity was found down to 2 K. 相似文献
49.
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