- Crystal Structure, Electrical Transport, and Magnetic Properties of Niobium Monophosphide
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Large single crystals of NbP have been prepared. A single-crystal X-ray diffraction study shows that it crystallizes in tetragonal symmetry with space group I41md (No. 109) and lattice parameters a = 3.3324(2) ?, = 11.3705-(7) ?, and Z = 4. A full matrix least-squares refinement based on a unique data set of 285 reflections (l > 2σ(I)) yielded R(F) = 0.017 and RwF2) = 0.046 for nine variables. The unit cell consists of one unique Nb and one P, each in trigonal prismatic coordination with the other element. There are two short and four long bond distances of Nb-P. The Nb-Nb bond distances are significantly shorter than Rc = 4.09 ?, the critical distance required for good Nb-Nb 4d orbital overlap for niobium metal-metal bonds. NbP shows metallic behavior with ρ = 4.5 × 10-5 Ω cm at room temperature. Magnetic susceptibility measurements on a collection of randomly oriented single crystals indicate very weak Pauli paramagnetism (~10-5 emu/mol). A discussion of the structure as well as the physical properties of NbP compared with those of previous results are presented. The band structure of NbP based on the extended Hückel (tight-binding) calculations is presented along with an analysis that reveals that the valence band is built up from three center bonds localized within Nbs triangles.
- Xu,Greenblatt,Emge,H?hn,Hughbanks,Tian
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- Synthesis, structure, and chemical vapor deposition studies of molecular precursors to NbP films
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Treatment of niobium pentachloride with cyclohexylphosphine and phenylphosphine in dichloromethane afforded octachlorotetrakis(cyclohexylphosphine)diniobium(IV) (85%) and octachlorotetrakis(phenylphosphine)diniobium-(IV) (88%), respectively, as brown-red and dark red crystalline solids. In addition, the phosphonium compound [P(C6H11)H3]2[NbCl6] was isolated in 68% yield from the same preparation of octachlorotetrakis(cyclohexylphosphine)diniobium(IV). Studies are described which demonstrate that the primary phosphine serves as the hydrogen atom source for the formation of the phosphonium salts. Octachlorotetrakis(cyclohexylphosphine)-diniobium(IV) can be prepared in 77% yield by addition of cyclohexylphosphine to NbCl4(THF)2 in toluene. The X-ray crystal structure determinations for two dimeric niobium(IV) complexes_ are described. Octachlorotetrakis-(cyclohexylphosphine)diniobium(IV) crystallizes in the triclinic space group Pī with a = 9.904(2) ?,b = 10.243-(2) ?, c = 10.642(1) ?, α = 76.33(2)°, β= 67.231(8)°, γ = 73.76(2)°, V = 945.7(3) ?3, and Z = 1. Octachlorotetrakis(phenylphosphine)diniobium(IV) crystallizes in the orthorhombic space group Pbca with a = 8.873(2) ?, b = 17.394(6) ?, c = 21.778(3) ?, V = 3361.1(9) ?3, and Z = 4. Octachlorotetrakis-(cyclohexylphosphine)diniobium(IV) and octachlorotetrakis(phenylphosphine)diniobium(IV) were evaluated as molecular precursors to niobium(III) phosphide (NbP) films in a chemical vapor deposition reactor. Octachlorotetrakis(phenylphosphine)diniobium(IV) was not volatile and was therefore not a useful precursor. However, octachlorotetrakis(cyclohexylphosphine)diniobium(IV) afforded specular, silver-colored films of NbP with substrate temperatures between 400 and 600 °C. The analysis of the films is presented.
- Scheper, Joseph T.
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- Ternary early-transition-metal palladium pnictides Zr3Pd4P3, Hf3Pd4P3, HfPdSb, and Nb5Pd4P4
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Several ternary palladium pnictides of the early transition metals have been prepared by arc-melting of the elemental metals and the binary pnictides ZrP, HfP, HfSb2, or NbP, and their structures have been determined by X-ray diffraction methods. The phosphides M3Pd4P3 (M = Zr, Hf) adopt a new structure type (Pearson symbol oP40), crystallizing in the orthorhombic space group Pnma with Z = 4 and unit cell parameters of a = 16.387(2), b = 3.8258(5), and c = 9.979(1) A for Zr3Pd4P3 and a = 16.340(2), b = 3.7867(3), and c = 9.954(1) A for Hf3Pd4P3. The antimonide HfPdSb was identified by powder X-ray diffraction (orthorhombic, Pnma, Z = 4, a = 6.754(1) A, b = 4.204(1) A, and c = 7.701(2) A) and confirmed to be isostructural to ZrPdSb, which adopts the TiNiSi-type structure. The phosphide Nb5Pd4P4 adopts the Nb5Cu4Si4-type structure, crystallizing in the tetragonal space group I4/m with Z = 2, a = 10.306(1) A, and c = 3.6372(5) A. Coordination geometries of pentacapped pentagonal prisms for the early transition metal, tetracapped distorted tetragonal prisms for Pd, and tricapped trigonal prisms for the pnicogen are found in the three structures; tetracapped tetragonal prisms for Nb are also found in Nb5-Pd4P4. In common with many metal-rich compounds whose metal-to-nonmetal ratio is equal or close to 2:1, the variety of structures formed by these ternary palladium pnictides arises from the differing connectivity of pnicogen-filled trigonal prisms. Pnicogen-pnicogen bonds are absent in these structures, but metal-metal bonds (in addition to metal-pnicogen bonds) are important interactions, as verified by extended Huckel band structure calculations on Zr3Pd4P3.
- Wang,McDonald,Mar
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- Effect of magnetic field on the hydrogen evolution activity using non-magnetic Weyl semimetal catalysts
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An external switch to control the kinetics of the reaction by manipulating the participating electrons could be interesting as it can alter the rate of the reaction without affecting the reaction pathway. The magnetic field, like a switch, is non-invasive
- Felser, Claudia,Gupta, Uttam,Kumar, Nitesh,Li, Guowei,Rajamathi, Catherine R.,Rao, C. N. R.,Shekhar, Chandra,Sun, Yan
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- Preparation of Al, Cr, Nb, Mo, and W monophosphides from a lithium metaphosphate melt
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Synthesis of a series of phosphides (AlP, CrP, NbP, MoP, and WP) by reactions of powdered metals with a melt of lithium metaphosphate LiPO3 was studied. Thermodynamic parameters (ΔH2980, ΔS2980, ΔG2980, and ΔG12730) of the reactions were calculated and their temperature modes were optimized on the basis of the standard thermodynamic characteristics of the initial substances and the reaction products. X-ray patterns of the powders of the obtained compounds are presented.
- Lesnyak,Stratiichuk,Sudavtsova,Slobodyanik
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- A Series of MAX Phases with MA-Triangular-Prism Bilayers and Elastic Properties
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We report a new type of MAX phase (M=transition metals, A=main group elements, and X=C/N), Nb3As2C, designated as 321 phase. It differs from all the previous Mn+1AXn phases in that it consists of an alternate stacking of one MX layer and two MA layers in its unit cell, while only one MA layer is allowed in usual MAX phases. The new 321 phase exhibits a bulk modulus of Nb3As2C up to 225(3) GPa as determined by high-pressure synchrotron X-ray diffraction, one of the highest values among MAX phases. Isostructural 321 phases V3As2C, Nb3P2C, and Ta3P2C are also found to exist. First-principles calculations reveal the outstanding elastic stiffness in 321 phases. Among all 321 phases, Nb3P2C is predicted to have the highest elastic properties. These 321 phases, represented by a chemical formula Mn+1AnX, were added as new members to the MAX family and their other properties deserve future investigations.
- Chen, Hongxiang,Yang, Dongliang,Zhang, Qinghua,Jin, Shifeng,Guo, Liwei,Deng, Jun,Li, Xiaodong,Chen, Xiaolong
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- Evolution of the Fermi surface of Weyl semimetals in the transition metal pnictide family
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Topological Weyl semimetals (TWSs) represent a novel state of topological quantum matter which not only possesses Weyl fermions (massless chiral particles that can be viewed as magnetic monopoles in momentum space) in the bulk and unique Fermi arcs generated by topological surface states, but also exhibits appealing physical properties such as extremely large magnetoresistance and ultra-high carrier mobility. Here, by performing angle-resolved photoemission spectroscopy (ARPES) on NbP and TaP, we directly observed their band structures with characteristic Fermi arcs of TWSs. Furthermore, by systematically investigating NbP, TaP and TaAs from the same transition metal monopnictide family, we discovered their Fermiology evolution with spin-orbit coupling (SOC) strength. Our experimental findings not only reveal the mechanism to realize and fine-tune the electronic structures of TWSs, but also provide a rich material base for exploring many exotic physical phenomena (for example, chiral magnetic effects, negative magnetoresistance, and the quantum anomalous Hall effect) and novel future applications.
- Liu,Yang,Sun,Zhang,Peng,Yang,Chen,Zhang,Guo,Prabhakaran,Schmidt,Hussain,Mo,Felser,Yan,Chen
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- BaGa2Pn2 (Pn = P, As): New semiconducting phosphides and arsenides with layered structures
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Reported are the synthesis, the structural characterization, and the electronic band structures of two new Zintl phases: BaGa2P 2 and BaGa2As2. Both compounds are isoelectronic and isotypic and crystallize in a monoclinic system with a new structure type (Pearson symbol mP20). The structures have been established by single-crystal X-ray diffraction, space group P21/c (Z = 4), with lattice parameters as follows: a = 7.3363(13)/7.495(5) A; b = 9.6648(17)/9.901(6) A; c = 7.4261(13)/7.643(5) A; β = 115.373(2)°/115.381(8)° for BaGa2P2/BaGa 2As2, respectively. The atomic arrangements in both cases are devoid of disorder and are best rationalized as polyanionic layers, ∞2[Ga2Pn2]2- (Pn = P, As), with Ba2+ cations separating them. The layers, in turn, can be viewed as the result of condensation of Ga2Pn6 units, which are isosteric with the ethane molecule in its staggered conformation. Structural parallels with other known Zintl phases are presented. The electronic structures, computed using the tight-binding linear muffin-tin orbital methods (TB-LMTO), are discussed as well.
- He, Hua,Stearrett, Ryan,Nowak, Edmund R.,Bobev, Svilen
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- Novel quaternary metal-rich phosphides: Stabilization by differential fractional site occupancies and polar intermetallic bonding
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The new phosphide Hf5Nb5Ni3P5 has been prepared by arc-melting of a pressed stoichiometric mixture of HfP, N-b, and Ni. Single crystals suitable for the structure determination were obtained after annealing in an induction furnace at 1350 °C. Hf5Nb5Ni3P5 crystallizes in the hexagonal space group P6?2m (No. 189). The early transition metal atoms Hf and Nb are found on three crystallographically different sites, with refined occupancies of 100% Hf for the M1, 59.5(4)% Hf and 40.5(4)% Nb for the M2, and 13.1(6)% Hf and 86.9(6)% Nb for the M3 site. Small variations of the Hf to Nb ratio are possible, occurring with significantly different lattice parameters. The early transition elements form a three-dimensional framework with numerous M- M (M = Hf, Nb) interactions, including Ni and P in its trigonal prismatic voids. The differential fractional site occupancies can be understood on the basis of the different preferences of Hf and Nb to form M-M, M-Ni, and M-P bonds. The metallic character is confirmed by the Pauli paramagnetism experimentally obtained.
- Kleinke, Holger,Franzen, Hugo F.
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- Interaction of Group VB Transition Metals with Uranium Monophosphide
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The character and extent of interaction of Group VB transition metals with uranium monophosphide at 1073-2273 K is studied. The interaction products are solid solutions; VP, NbP. and TaP monophosphides; and at high temperatures, liquid phases of the eutectic type. The kinetic constants for the growth of monophosphide layers are determined. In all cases, small quantities of uranium dissolve in the resulting monophosphides. A comparison of the kinetic constants for phosphidization of the transition metals is made.
- Panov
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p. 490 - 493
(2008/10/08)
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