Boron site preference in ternary Ta and Nb boron suicides

X-ray single crystal (XSC) and neutron powder diffraction data (NPD) were used to elucidate boron site preference for five ternary phases. Ta3Si1-xBx (x=0.112(4)) crystallizes with the Ti3P-type (space group P4(2)/n) with B-atoms sharing the 8g site with Si atoms. Ta5Si3-x (x=0.03(1); Cr5B3- type) crystallizes with space group 14/mcm, exhibiting a small amount of vacancies on the 4 alpha site. Both, Ta-5(Si1-xBx)(3), X=0.568(3), and Nb-5(Si1-xBx)(3), x=0.59(2), are part of solid solutions of M5Si3 with Cr5B3-type into the ternary M-Si-B systems (M=Nb or Ta) with B replacing Si on the 8h site. The D8(8)-phase in the Nb-Si-B system crystallizes with the Ti5Ga4-type revealing the formula Nb5Si3B1-x (x=0.292(3)) with B partially filling the voids in the 2b site of the Mn5Si3 parent type. (C) 2012 Elsevier Inc. All rights reserved.Higher Education Commission of Pakistan (HEC)Austrian OEADFAPESP (Sao Paulo, Brazil)FAPESP (Sao Paulo, Brazil) [97/06348-4]European Commission [RII3-CT-2003-505925]European Commissio

The system thorium-palladium-boron: A DFT study on the stability and properties of Th2Pd15B5

International audiencePhase relations in the Th-Pd-B system were determined via electron microprobe and X-ray powder diffraction analyses of similar to 20 ternary alloys. Phase equilibria are dominated by the two high-melting thorium borides ThB4, Th1-yB6 and one ternary compound, namely tau(1)-Th2Pd14+xB5, with a structure deriving from the Sc4Ni29B10-type. Th1-yB6 is the binary starting point of a continuous solid solution up to ThPd0.53B4.28 closely corresponding to the superconducting phase Th1-yPdxB6-2x (x <= 0.65; 0 <= y <= 0.22 at x = 0; T-C = 21 K), which was described by Zandbergen et al. in 1995 for x = 0.65 from high resolution electron microscopy. All thorium-rich palladium compounds from 0 to 75 at.% Pd form stable two-phase equilibria with ThB4 without any significant mutual solid solubilities. The solubility of Th in beta B has been determined for the first time from a single crystal X-ray study of ThB99 Th atoms occupy sites A1 (occ. = 13%), D (occ. = 11%), and a rather small amount of 2.9% resides in site 18f (D-d-hole). To shed light on the physical properties of the ternary compound, DFT (density functional theory) calculations were performed for two idealized representatives of the tau(1)-phase, namely for Th2Pd14B5 and Th2Pd15B4. The calculations cover ionic relaxation, electron density of states, band structure and Fermi surfaces, elastic constants (computed via the linear response method) and the phonon density of states. Furthermore the thermodynamic stability (energy of formation) as well as the phonon contribution of the thermodynamic properties, such as the specific heat have been calculated clearly indicating Th2Pd15B4 as the composition thermodynamically more stable than Th2Pd14B5. At the Fermi energy the Pd-d contribution is dominant for both structures, but the number of states is higher for Th2Pd15B4 with DOS(E-F) = 13 states/eV/f.u. than for Th2Pd14B5 with DOS(E-F) = 8.5 states/eV/f.u. The corresponding Sommerfeld constants, gamma(e) = DOS(E-F)kappa(B)pi(2)/3 = 30.55 mJ/molK(2) for Th(2)Pd(15)B(4 )and 19.98 mJ/molK(2) for Th2Pd14B5, clearly indicate metallic behavior of the tau(1)-phase. In addition, mechanical properties were measured for Th2Pd15B4 and compared with calculated values and data from the literature. Th2Pd15B4 on account of its high content of Pd is only slightly harder than the rather soft and almost ductile binary Pd-borides. (C) 2019 Elsevier B.V. All rights reserved

La2Pd3Ge5 and Nd2Pd3Ge5 Compounds: Chemical Bonding and Physical Properties

The two La2Pd3Ge5 and Nd2Pd3Ge5 compounds, crystallizing in the oI40-U2Co3Ge5 crystal structure, were targeted for analysis of their chemical bonding and physical properties. The compounds of interest were obtained by arc melting and characterized by differential thermal analysis, scanning electron microscopy, and X-ray diffraction both on powder and on a single crystal (for the La analogue), to ensure the high quality of the samples and accurate crystallographic data. Chemical bonding was studied by analyzing the electronic structure and effective QTAIM charges of La2Pd3Ge5. A significant charge transfer mainly occurs from La to Pd so that Ge species assume tiny negative charges. This result, together with the -(I)COHP analysis, suggests that, in addition to the expected homopolar Ge bonds within zigzag chains, heteropolar interactions between Ge and the surrounding La and Pd occur with multicenter character. Covalent La-Pd interactions increase the complexity of chemical bonding, which could not be adequately described by the simplified, formally obeyed, Zintl-Klemm scheme. Electric resistivity, specific heat, magnetization, and magnetic susceptibility as a function of temperature indicate for both compounds a metallic-like behavior. For Nd2Pd3Ge5, two low-temperature phase transitions are detected, leading to an antiferromagnetic ground state

Yb9+xCuMg4-x (x = 0.034): A \u3ba-Phase Formed by Lanthanoids

Atom order in the crystal structures of Yb2Cu2-xMg (x = 0.17; Mo2FeB2-type; P4/mbm; a = 0.75592(2) nm; c = 0.40282(1) nm) and Yb9+xCuMg4-x (x = 0.034; Hf9Mo4B-type; P63/mmc; a = 1.0169(5) nm; c = 1.0290(5) nm) was determined from powder and X-ray single-crystal counter data analyses supported by electron probe microanalyses. Among the group of the so-called \u3ba-phases, Yb9+xCuMg4-x is the first representative formed by a lanthanoid element. The structure of this \u3ba-phase can be viewed as a typical network of corner-connected empty Yb6-octahedra, which encompass Yb6Mg6-icosahedra (filled by a mix of Mg/Yb atoms) and Yb6-trigonal prisms centered by Cu atoms to complete the three-dimensional metal framework. From another point of view, the same structure is considered as built from infinite polyicosahedral columns of Yb9Mg4 composition with Cu atoms located in trigonal prismatic interstices, highlighting similarities with other Yb-rich Yb-Cu-Mg phases. Density functional theory (DFT) calculations classify Yb9CuMg4 as a polar intermetallic. Metallic-like behavior is inferred from the Sommerfeld constant, \u3b3 = 49.2 mJ/mol\ub7K(2), derived from the electronic density of states, calculated at the Fermi level. DFT integration of the f-density of states indicates almost completely filled f-states, revealing 13.6 and 13.7 electrons in the valence band for Yb1 and Yb2 atoms, respectively, close to the Yb(2+) ground state ((1)S0) for both Yb atoms. Magnetic susceptibility data recorded on the same compound are consistent with a nonmagnetic divalent Yb(2+) state. Temperature-dependent heat capacity data display a metallic behavior characterized by a small Sommerfeld constant \u3b3 = 64.8 mJ/mol\ub7K(2) and a rather low Debye temperature \u398D = 140 K as typical for soft materials

Yb_9+<i>x</i>CuMg_4–<i>x</i> (<i>x</i> = 0.034): A κ‑Phase Formed by Lanthanoids

Atom order in the crystal structures of Yb₂Cu_2–<i>x</i>Mg (<i>x</i> = 0.17; Mo₂FeB₂-type; <i>P</i>4/<i>mbm</i>; <i>a</i> = 0.75592(2) nm; <i>c</i> = 0.40282(1) nm) and Yb_9+<i>x</i>CuMg_4–<i>x</i> (<i>x</i> = 0.034; Hf₉Mo₄B-type; <i>P</i>6₃/<i>mmc;</i> <i>a</i> = 1.0169(5) nm; <i>c</i> = 1.0290(5) nm) was determined from powder and X-ray single-crystal counter data analyses supported by electron probe microanalyses. Among the group of the so-called κ-phases, Yb_9+<i>x</i>CuMg_4–<i>x</i> is the first representative formed by a lanthanoid element. The structure of this κ-phase can be viewed as a typical network of corner-connected empty Yb₆-octahedra, which encompass Yb₆Mg₆-icosahedra (filled by a mix of Mg/Yb atoms) and Yb₆-trigonal prisms centered by Cu atoms to complete the three-dimensional metal framework. From another point of view, the same structure is considered as built from infinite polyicosahedral columns of Yb₉Mg₄ composition with Cu atoms located in trigonal prismatic interstices, highlighting similarities with other Yb-rich Yb–Cu–Mg phases. Density functional theory (DFT) calculations classify Yb₉CuMg₄ as a polar intermetallic. Metallic-like behavior is inferred from the Sommerfeld constant, γ = 49.2 mJ/mol·K², derived from the electronic density of states, calculated at the Fermi level. DFT integration of the f-density of states indicates almost completely filled f-states, revealing 13.6 and 13.7 electrons in the valence band for Yb1 and Yb2 atoms, respectively, close to the Yb²⁺ ground state (¹S₀) for both Yb atoms. Magnetic susceptibility data recorded on the same compound are consistent with a nonmagnetic divalent Yb²⁺ state. Temperature-dependent heat capacity data display a metallic behavior characterized by a small Sommerfeld constant γ = 64.8 mJ/mol·K² and a rather low Debye temperature Θ_D = 140 K as typical for soft materials

Yb_9+<i>x</i>CuMg_4–<i>x</i> (<i>x</i> = 0.034): A κ‑Phase Formed by Lanthanoids

Atom order in the crystal structures of Yb₂Cu_2–<i>x</i>Mg (<i>x</i> = 0.17; Mo₂FeB₂-type; <i>P</i>4/<i>mbm</i>; <i>a</i> = 0.75592(2) nm; <i>c</i> = 0.40282(1) nm) and Yb_9+<i>x</i>CuMg_4–<i>x</i> (<i>x</i> = 0.034; Hf₉Mo₄B-type; <i>P</i>6₃/<i>mmc;</i> <i>a</i> = 1.0169(5) nm; <i>c</i> = 1.0290(5) nm) was determined from powder and X-ray single-crystal counter data analyses supported by electron probe microanalyses. Among the group of the so-called κ-phases, Yb_9+<i>x</i>CuMg_4–<i>x</i> is the first representative formed by a lanthanoid element. The structure of this κ-phase can be viewed as a typical network of corner-connected empty Yb₆-octahedra, which encompass Yb₆Mg₆-icosahedra (filled by a mix of Mg/Yb atoms) and Yb₆-trigonal prisms centered by Cu atoms to complete the three-dimensional metal framework. From another point of view, the same structure is considered as built from infinite polyicosahedral columns of Yb₉Mg₄ composition with Cu atoms located in trigonal prismatic interstices, highlighting similarities with other Yb-rich Yb–Cu–Mg phases. Density functional theory (DFT) calculations classify Yb₉CuMg₄ as a polar intermetallic. Metallic-like behavior is inferred from the Sommerfeld constant, γ = 49.2 mJ/mol·K², derived from the electronic density of states, calculated at the Fermi level. DFT integration of the f-density of states indicates almost completely filled f-states, revealing 13.6 and 13.7 electrons in the valence band for Yb1 and Yb2 atoms, respectively, close to the Yb²⁺ ground state (¹S₀) for both Yb atoms. Magnetic susceptibility data recorded on the same compound are consistent with a nonmagnetic divalent Yb²⁺ state. Temperature-dependent heat capacity data display a metallic behavior characterized by a small Sommerfeld constant γ = 64.8 mJ/mol·K² and a rather low Debye temperature Θ_D = 140 K as typical for soft materials

On the boron rich phases in the Yb-B system

The final publication is available via https://doi.org/10.1016/j.jssc.2017.08.007.Two boron rich phases were successfully synthesized by borothermal reduction of Yb oxide under vacuum. For the new boron-poorer phase, the single phase was established at around [B]/[Yb]=43.3 at 1500 °C (Pbam space group; YB50-type; a=16.5811(5) Å, b=17.5950(5) Å, c=9.4647(3) Å; powder X-ray diffraction; Rietveld refinement). The crystal structure of the boron-richer phase ([B]/[Yb]=56.0) has been elucidated by single crystal X-ray diffraction ( space group; YB66-type; a=23.3587(6) Å). Powder X-ray diffraction data of the alloy YbB~70 annealed at 1825 °C yielded, along with the YB66-type compound (a=23.3691(2) Å), β-rh B as a secondary phase ( space group, a=10.9298(3) Å, c=23.875(1) Å), for which the solubility of Yb was found to be below 1 at.%. Both YbB43.3 and YbB56.0 feature complicated boron atom frameworks which exhibit shorter B-B separations both within and between boron clusters as compared to those observed for prototype structures.Austrian Science Funds (FWF