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Sample records for nb ta solid

  1. Investigation of Local Structure and Cation Ordering in Dielectric Oxide Microwave Ceramics with stoichiometry A(Lix(Nb,Ta)y) O3 Using 7Li and 93Nb solid-state NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Kalfarisi, Rony

    The local structure and cation ordering in dielectric oxide microwave ceramics with stoichiometry A(Lix(Nb,Ta)y) O3 are investigated using 7Li and 93Nb solid-state NMR spectroscopy. For all samples, 7Li MAS NMR spectra show one strong and sharp resonance peak indicating one unique environment which corresponds to local lithium environment of nearest B-site neighbor (nBn) surrounded by 4 LiO6 octahedra and 2 NbO6 octahedra (TaO6 in some samples). In addition to this, 7Li MAS NMR spectrum of (Ca2/3La1/3) (Li1/3Nb2/3) O3 show one additional weak and broad resonance peak which can be assigned to nBn of 3 LiO6 octahedra and 3 NbO6 octahedra. 93Nb MAS NMR spectra of samples with niobium content, show a resonance peak with tail toward the low frequency limit, an evidence to the existence of chemical shifts and quadrupole couplings distributions. Both (Sr2/3La1/3) (Li1/3Nb2/3) O3 and Ca(Li1/4Nb3/4) O3 spectra show one broad resonance peak, which can be interpreted as one NbO6 octahedron nBn with many slight variations through out the sample. While (Ca2/3La1/3) (Li1/3Nb2/3) O3 spectra show four peaks correspond to four distinct NbO6 octahedra local nBn environments with the nBn configuration as: (i) 3 LiO6 and 3 NbO6; (ii) 2 LiO6 and 4 NbO6; (iii) 1 LiO6 and 5 NbO6; (iv) all 6 NbO6

  2. Reactions of laser-ablated Nb and Ta atoms with N2: experimental and theoretical study of M(NN)x (M = Nb, Ta; x = 1-4) in solid neon.

    PubMed

    Lu, Zhang-Hui; Jiang, Ling; Xu, Qiang

    2010-07-01

    Reactions of laser-ablated niobium and tantalum atoms with dinitrogen in solid neon have been investigated using matrix-isolation infrared spectroscopy. The Nb(NN)(x) and Ta(NN)(x) (x = 1-4) molecules formed during sample deposition or on annealing are the major products. The products are characterized on the basis of isotopic shifts, mixed isotopic splitting patterns, stepwise annealing, and change of reagent concentration and laser energy. Density functional theory calculations have been performed to understand the structures, ground electronic states, and bonding characteristics of niobium and tantalum dinitrogen complexes. The overall agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts supports the identification of these species from the matrix infrared spectra. The molecular orbital analyses and plausible reaction pathways for the formation of the products are also discussed. PMID:20527869

  3. First-principles calculation of phase equilibrium of V-Nb, V-Ta, and Nb-Ta alloys

    NASA Astrophysics Data System (ADS)

    Ravi, C.; Panigrahi, B. K.; Valsakumar, M. C.; van de Walle, Axel

    2012-02-01

    In this paper, we report the calculated phase diagrams of V-Nb, V-Ta, and Nb-Ta alloys computed by combining the total energies of 40-50 configurations for each system (obtained using density functional theory) with the cluster expansion and Monte Carlo techniques. For V-Nb alloys, the phase diagram computed with conventional cluster expansion shows a miscibility gap with consolute temperature Tc=1250 K. Including the constituent strain to the cluster expansion Hamiltonian does not alter the consolute temperature significantly, although it appears to influence the solubility of V- and Nb-rich alloys. The phonon contribution to the free energy lowers Tc to 950 K (about 25%). Our calculations thus predicts an appreciable miscibility gap for V-Nb alloys. For bcc V-Ta alloy, this calculation predicts a miscibility gap with Tc=1100 K. For this alloy, both the constituent strain and phonon contributions are found to be significant. The constituent strain increases the miscibility gap while the phonon entropy counteracts the effect of the constituent strain. In V-Ta alloys, an ordering transition occurs at 1583 K from bcc solid solution phase to the V2Ta Laves phase due to the dominant chemical interaction associated with the relatively large electronegativity difference. Since the current cluster expansion ignores the V2Ta phase, the associated chemical interaction appears to manifest in making the solid solution phase remain stable down to 1100 K. For the size-matched Nb-Ta alloys, our calculation predicts complete miscibility in agreement with experiment.

  4. Nb-Ta, Nb-Mo and Nb-V oxides prepared from hybrid organic-inorganic precursors

    SciTech Connect

    Deligne, N.; Bayot, D.; Degand, M.; Devillers, M.

    2007-07-15

    New hybrid organic-inorganic materials based on group 5 elements and a well-defined polymeric matrix have been prepared and used as precursors for Nb-Ta and Nb-Mo mixed oxides. In this non-conventional but easily accessible route to multimetallic oxides, a copolymer of N,N-diallyl-N-hexylamine and maleic acid was synthesised and used as matrix to stabilise inorganic species generated in solution from (NH{sub 4}){sub 6}Mo{sub 7}O{sub 24}.4H{sub 2}O, NH{sub 4}VO{sub 3} (gu){sub 3}[Nb(O{sub 2}){sub 4}] and (gu){sub 3}[Ta(O{sub 2}){sub 4}]. Solid-state studies indicate that the homogeneity of the blends can be kept up to about 0.5 mol Nb{sup V} and Ta{sup V} and 0.25 mol V{sup V} per mol of repeat units of the copolymer. The calcination conditions of these homogeneous hybrid precursors were optimised to produce Nb-Mo, Nb-Ta and Nb-V oxides. While the thermal treatment of the Nb-V hybrid blends led only to a mixture of different phases, the characterisation of the final phases by X-ray diffraction (XRD) proved the formation of pure Nb{sub 2}Mo{sub 3}O{sub 14} and showed that Nb-Ta oxides could be synthesised as single phases corresponding to a continuous series of solid solutions. - Graphical abstract: An alternative route based on hybrid organic-inorganic materials was implemented to synthesise Nb-Ta, Nb-Mo and Nb-V oxides. The hybrid materials were prepared by incorporation of inorganic salts based on Nb{sup V}, Ta{sup V}, V{sup V} and Mo{sup VI} in an organic polymer bearing cationic as well as anionic moieties. A thermal treatment of these hybrid blends has allowed the formation of multimetallic oxides.

  5. Biocompatibility of nanotube formed Ti-30Nb-7Ta alloys.

    PubMed

    Kim, Eun-Sil; Choe, Han-Cheol

    2014-11-01

    The purpose of this study was to investigate the biocompatibility of Ti-30Nb-7Ta alloy surface decorated with TiO2 nanotubes by anodization in an electrolyte containing 1 M H3PO4 and 0.8 wt.% NaF with an applied voltage of 10 V for 2 h. The anodization was carried out using a scanning potentiostat. The microstructures of alloys and morphology of the nanotubes were investigated by optical microscopy, field emission scanning electron microscopy, and X-ray diffractometry. In comparison to the Ti-30Nb-3Ta alloy, the Ti-30Nb-7Ta alloy contained a lower amount of α" phase, while the β phase was higher. In this study, we observed the formation of a spongy porous layer on the Ti-30Nb-7Ta alloy, while the Ti-30Nb and Ti-30Nb-3Ta alloys showed an absence of such a spongy layer. PMID:25958540

  6. Wear transition of solid-solution-strengthened Ti-29Nb-13Ta-4.6Zr alloys by interstitial oxygen for biomedical applications.

    PubMed

    Lee, Yoon-Seok; Niinomi, Mitsuo; Nakai, Masaaki; Narita, Kengo; Cho, Ken; Liu, Huihong

    2015-11-01

    In previous studies, it has been concluded that volume losses (V loss) of the Ti-29Nb-13Ta-4.6Zr (TNTZ) discs and balls are larger than those of the respective Ti-6Al-4V extra-low interstitial (Ti64) discs and balls, both in air and Ringer's solution. These results are related to severe subsurface deformation of TNTZ, which is caused by the lower resistance to plastic shearing of TNTZ than that of Ti64. Therefore, it is necessary to further increase the wear resistance of TNTZ to satisfy the requirements as a biomedical implant. From this viewpoint, interstitial oxygen was added to TNTZ to improve the plastic shear resistance via solid-solution strengthening. Thus, the wear behaviors of combinations comprised of a new titanium alloy, TNTZ with high oxygen content of 0.89 mass% (89O) and a conventional titanium alloy, Ti64 were investigated in air and Ringer's solution for biomedical implant applications. The worn surfaces, wear debris, and subsurface damage were analyzed using a scanning electron microscopy and an electron probe microanalysis. V loss of the 89O discs and balls are smaller than those of the respective TNTZ discs and balls in both air and Ringer's solution. It can be concluded that the solid-solution strengthening by oxygen effectively improves the wear resistance for TNTZ materials. However, the 89O disc/ball combination still exhibits higher V loss than the Ti64 disc/ball combination in both air and Ringer's solution. Moreover, V loss of the disc for the 89O disc/Ti64 ball combination significantly decreases in Ringer's solution compared to that in air. This decrease for the 89O disc/Ti64 ball combination in Ringer's solution can be explained by the transition in the wear mechanism from severe delamination wear to abrasive wear. PMID:26301568

  7. Boron site preference in ternary Ta and Nb boron silicides

    SciTech Connect

    Khan, Atta U.; Nunes, Carlos A.; Coelho, Gilberto C.; Suzuki, Paulo A.; Grytsiv, Andriy; Bourree, Francoise; Rogl, Peter F.

    2012-06-15

    X-ray single crystal (XSC) and neutron powder diffraction data (NPD) were used to elucidate boron site preference for five ternary phases. Ta{sub 3}Si{sub 1-x}B{sub x} (x=0.112(4)) crystallizes with the Ti{sub 3}P-type (space group P4{sub 2}/n) with B-atoms sharing the 8g site with Si atoms. Ta{sub 5}Si{sub 3-x} (x=0.03(1); Cr{sub 5}B{sub 3}- type) crystallizes with space group I4/mcm, exhibiting a small amount of vacancies on the 4a site. Both, Ta{sub 5}(Si{sub 1-x}B{sub x}){sub 3}, x=0.568(3), and Nb{sub 5}(Si{sub 1-x}B{sub x}){sub 3}, x=0.59(2), are part of solid solutions of M{sub 5}Si{sub 3} with Cr{sub 5}B{sub 3}-type into the ternary M-Si-B systems (M=Nb or Ta) with B replacing Si on the 8h site. The D8{sub 8}-phase in the Nb-Si-B system crystallizes with the Ti{sub 5}Ga{sub 4}-type revealing the formula Nb{sub 5}Si{sub 3}B{sub 1-x} (x=0.292(3)) with B partially filling the voids in the 2b site of the Mn{sub 5}Si{sub 3} parent type. - Graphical abstract: The crystal structures of a series of compounds have been solved from X-ray single crystal diffractometry revealing details on the boron incorporation. Highlights: Black-Right-Pointing-Pointer Structure of a series of compounds have been solved by X-ray single crystal diffractometry. Black-Right-Pointing-Pointer Ta{sub 3}(Si{sub 1-x}B{sub x}) (x=0.112) crystallizes with the Ti{sub 3}P-type, B and Si atoms randomly share the 8g site. Black-Right-Pointing-Pointer Structure of Nb{sub 5}Si{sub 3}B{sub 1-x} (x=0.292; Ti{sub 5}Ga{sub 4}-type) was solved from NPD.

  8. Structural studies of the metal-rich region in the ternary Ta-Nb-S system

    SciTech Connect

    Yao, Xiaoqiang.

    1991-10-07

    Six new solid solution type compounds have been prepared using high temperature techniques and characterized by means of single crystal x-ray techniques during a study of the metal-rich region of the ternary Ta-Nb-S system. The structures of Nb{sub x}Ta{sub 11-x}S{sub 4} are reminiscent of niobium-rich sulfides, rather than of tantalum-rich sulfides. The coordinations of sulfur are capped trigonal prismatic while the metal coordinations are capped distorted cubic prismatic for Nb{sub x}Ta{sub 11-x}S{sub 4}, and capped distorted cubic prismatic and pentagonal prismatic for Nb{sub 12-x}Ta{sub x}S{sub 4}. The structures of Nb{sub x}Ta{sub 5-x}S{sub 2} contain homoatomic layers sequenced S-M3-M2-M1-M2-M3-S (M is mixed Nb, Ta) generating six-layer sheets, respectively. Weak S-S interactions at 3.26 and 3.19{Angstrom} between sheets contrast with the M-M binding within and between the sheets in these two novel layered compounds. The former are presumably responsible for the observed graphitic slippage of the samples. Nb{sub 21-x}Ta{sub x}S{sub 8} and Nb{sub x}Ta{sub 2-x}S are isostructural with Nb{sub 21}S{sub 8} and Ta{sub 2}S, respectively. Extended Hueckel band calculations were carried out for two layered compounds, Nb{sub x}Ta{sub 5-x}S{sub 2} (x {approx} 1.72) and Nb{sub x}ta{sub 2-x}S (x {approx} 0.95). Based upon band calculations metallic properties can be expected for these two layered compounds. The relative preference of the metal sites for the two metal elements (Ta, Nb) in two layered compounds is explained by the results of the band calculations. 17 figs., 31 tabs., 80 refs.

  9. "Engineered dual NbTa barriers for higher Jc Nb3Sn superconductors"

    SciTech Connect

    Robert E. Barber; Karl T. Hartwig

    2012-07-07

    The tantalum (Ta) diffusion barrier in advanced Nb3Sn superconductors often develops a failure mode during wire drawing where the Nb and Ta layers deform non-uniformly leading to a rough interface with adjacent copper. The non-uniform deformation of these layers can lead to premature wire breakage and breaches in the barrier, and contamination of the copper stabilizer by tin (Sn). The objective of the proposed work was to demonstrate that a dual NbTa layer made from severely deformed Nb and Ta exhibits improved co-deformation behavior with pure Cu in advanced Nb3Sn superconductors. This phase I project demonstrated improved microstructural uniformity and superior mechanical property characteristics of equal channel angular extrusion (ECAE) processed and rolled Nb and Ta sheets. The results of this work point to a method for fabrication of higher field and lower cost superconducting magnets for high energy physics applications.

  10. Nb/Ta - Zr/Hf Fractionations during Subduction: Implications for the'Missing' Nb.

    NASA Astrophysics Data System (ADS)

    Zateslo, T.; Bizimis, M.; Salters, V. J.; Stern, C.; Taylor, R. N.

    2008-12-01

    Key differences between the chemical composition of terrestrial materials and those of meteorites have led to the suggestion that a 'hidden' high Nb/Ta reservoir exists in the Earth's mantle. In order to test this hypothesis we must identify the processes that can create such a reservoir. Here we report the first high precision HFSE data on products of the subduction processes thought to fractionate Nb from Ta: boninites (hydrous melting), adakites (slab melting), OIBs (Koolau, Walvis: plume with recycled oceanic crust), as well as kimberlites and lamproites. We developed a new method for the high precision determination of Nb, Ta, Zr, Hf concentrations based on a modified version of standard addition. All analyses were performed on a single collector ICPMS (ELEMENT 1), using Y and Yb as internal standards to correct for instrumental drift during the unspiked -spiked sample sequence. Concentrations are calculated using a York- type regression that accounts for all measured and propagated errors. Long-term reproducibility (multiple dissolutions and multiple spike solutions) for the standards BHVO-1, BIR-1 AGV-1 and BCR-1 are better than 0.8% (1s) for Nb/Ta and Zr/Hf ratios. The advantages of this method compared to previous methods are fast throughput, no column chemistry and low blanks. The Koolau and Walvis Ridge lavas have subchondritic Nb/Ta for a given Zr/Hf, overlapping other OIB suites and show no evidence for a recycled, high Nb/Ta reservoir in their source. OIB, considered as a group, have relatively constant Nb/Ta (15-16) but more variable Zr/Hf (35-50). In contrast, boninites (Chichi Jima) have significantly subchondritic Nb/Ta (4-12) at near constant Zr/Hf (35), while adakites (South Andes) extend to near chondritic Nb/Ta (13-19) at more variable Zr/Hf (30-40). The adakites showing the least evidence for crustal contamination have the highest Nb/Ta. The arc lavas cross the OIB trend at near right angle on a Nb/Ta vs. Zr/Hf plot having larger Nb/Ta

  11. Assessment of relative Ti, Ta, and Nb (TiTaN) enrichments in global ocean island basalts

    NASA Astrophysics Data System (ADS)

    Peters, B.; Day, J. M.

    2013-12-01

    The relative sensitivity of trace element concentrations to processes governing solid-melt and solid-fluid interactions has made them particularly useful for tracing the effects of partial melting, fractional crystallization, metasomatism and similar processes on the composition of a parental melt to a rock or mineral. Radiogenic and stable isotope compositions, in contrast, can provide information on the long-term history and provenance of magmas. Despite the distinct information derived from relative and absolute abundances of trace elements compared with isotopes, numerous studies of ocean island basalts (OIB) have attempted to use trace elements as diagnostic geochemical tracers to understand parental magma compositions. In particular, attempts have been made to correlate 'TiTaN' (Ti, Ta and Nb) anomalies to the He-Os isotopic compositions of OIB based on contributions from recycled eclogite, a theoretical high-TiTaN reservoir, and peridotite, a theoretical high-3He/4He reservoir (Jackson, et al., 2008 G-cubed). These authors have proposed that TiTaN anomalies can be used as independent indicators for recycled oceanic crust and lithospheric mantle in OIB sources, a distinction previously reserved for isotopic data. However, TiTaN anomalies appear uncorrelated to OIB mantle source composition for three reasons. First, a new geochemical compilation of global OIB shows a wide range of Ti (Ti/Ti* = 0.28 - 2.35), Ta (Ta/Ta* = 0.11 - 93.42) and Nb (Nb/Nb* = 0.13 - 17.79) anomalies that do not correlated with each other or noble gas systematics, indicating that: (i) TiTaN anomalies alone do not correspond to the primitive source traced by high-3He/4He or the solar neon component and (ii) Ti, Ta and Nb anomalies may each reflect distinct processes or origins, rather than tracing a single source or process together. Second, positive Ti anomalies can be generated by low-degree (1-10%), non-modal batch partial melting of garnet lherzolite at temperatures and pressures

  12. Mechanical Properties, Quantum Mechanical Calculations, and Crystallographic/Spectroscopic Characterization of GaNbO4, Ga(Ta,Nb)O4, and GaTaO4.

    PubMed

    Perfler, Lukas; Kahlenberg, Volker; Többens, Daniel; Schaur, Andreas; Tribus, Martina; Orlova, Maria; Kaindl, Reinhard

    2016-06-01

    Single crystals as well as polycrystalline samples of GaNbO4, Ga(Ta,Nb)O4, and GaTaO4 were grown from the melt and by solid-state reactions, respectively, at various temperatures between 1698 and 1983 K. The chemical composition of the crystals was confirmed by wavelength-dispersive electron microprobe analysis, and the crystal structures were determined by single-crystal X-ray diffraction. In addition, a high-P-T synthesis of GaNbO4 was performed at a pressure of 2 GPa and a temperature of 1273 K. Raman spectroscopy of all compounds as well as Rietveld refinement analysis of the powder X-ray diffraction pattern of GaNbO4 were carried out to complement the structural investigations. Density functional theory (DFT) calculations enabled the assignment of the Raman bands to specific vibrational modes within the structure of GaNbO4. To determine the hardness (H) and elastic moduli (E) of the compounds, nanoindentation experiments have been performed with a Berkovich diamond indenter tip. Analyses of the load-displacement curves resulted in a high hardness of H = 11.9 ± 0.6 GPa and a reduced elastic modulus of Er = 202 ± 9 GPa for GaTaO4. GaNbO4 showed a lower hardness of H = 9.6 ± 0.5 GPa and a reduced elastic modulus of Er = 168 ± 5 GPa. Spectroscopic ellipsometry of the polished GaTa0.5Nb0.5O4 ceramic sample was employed for the determination of the optical constants n and k. GaTa0.5Nb0.5O4 exhibits a high average refractive index of nD = 2.20, at λ = 589 nm. Furthermore, in situ high-temperature powder X-ray diffraction experiments enabled the study of the thermal expansion tensors of GaTaO4 and GaNbO4, as well as the ability to relate them with structural features. PMID:27175821

  13. Comparative Raman study of Weyl semimetals TaAs, NbAs, TaP and NbP.

    PubMed

    Liu, H W; Richard, P; Zhao, L X; Chen, G-F; Ding, H

    2016-07-27

    We report a comparative polarized Raman study of Weyl semimetals TaAs, NbAs, TaP and NbP. The evolution of the phonon frequencies with the sample composition allows us to determine experimentally which atoms are mainly involved for each vibration mode. Our results confirm previous first-principles calculations indicating that the A1, B1(2), E(2) and E(3) modes involve mainly the As(P) atoms, the B1(1) mode is mainly related to Ta(Nb) atoms, and the E(1) mode involves both kinds of atoms. By comparing the energy of the different modes, we establish that the B1(1), B1(2), E(2) and E(3) become harder with increasing chemical pressure. This behaviour differs from our observation on the A1 mode, which decreases in energy, in contrast to its behaviour under external pressure. PMID:27248581

  14. Comparative Raman study of Weyl semimetals TaAs, NbAs, TaP and NbP

    NASA Astrophysics Data System (ADS)

    Liu, H. W.; Richard, P.; Zhao, L. X.; Chen, G.-F.; Ding, H.

    2016-07-01

    We report a comparative polarized Raman study of Weyl semimetals TaAs, NbAs, TaP and NbP. The evolution of the phonon frequencies with the sample composition allows us to determine experimentally which atoms are mainly involved for each vibration mode. Our results confirm previous first-principles calculations indicating that the A1, B1(2), E(2) and E(3) modes involve mainly the As(P) atoms, the B1(1) mode is mainly related to Ta(Nb) atoms, and the E(1) mode involves both kinds of atoms. By comparing the energy of the different modes, we establish that the B1(1), B1(2), E(2) and E(3) become harder with increasing chemical pressure. This behaviour differs from our observation on the A1 mode, which decreases in energy, in contrast to its behaviour under external pressure.

  15. Characterization of multi-principal-element (TiZrNbHfTa)N and (TiZrNbHfTa)C coatings for biomedical applications.

    PubMed

    Braic, V; Balaceanu, M; Braic, M; Vladescu, A; Panseri, S; Russo, A

    2012-06-01

    Multi-principal-element (TiZrNbHfTa)N and (TiZrNbHfTa)C coatings were deposited on Ti6Al4V alloy by co-sputtering of Ti, Zr, Nb, Hf and Ta metallic targets in reactive atmosphere. The coatings were analyzed for elemental and phase compositions, crystalline structure, morphology, residual stress, hardness, friction performance, wear-corrosion resistance and cell viability. For all the films, only simple fcc solid solutions with (111) preferred orientations were found, with crystallite sizes in the range 7.2-13.5 nm. The coatings were subjected to compressive stress, with values ranging from 0.8 to 1.6 GPa. The carbide coating with the highest carbon content (carbon/metal ≈1.3) exhibited the highest hardness of about 31 GPa, the best friction behavior (μ = 0.12) and the highest wear resistance (wear rate K=0.2×10(-6)mm(3)N(-1)m(-1)), when testing in simulated body fluids (SBFs). Cell viability tests proved that the osteoblast cells were adherent to the coated substrates, and a very high percentage of live cells were observed on sample surfaces, after 72 h incubation time. PMID:22520431

  16. Microstructure and properties of simultaneously processed Nb-Ti and Nb-Ti-Ta superconducting wires

    SciTech Connect

    Taillard, R.; Florianova, E.; Bruzek, C.E.

    1997-06-01

    The evolution of the microstructure (sub-band size, {alpha} phase precipitation) of a Nb- 47.1wt%Ti and of a Nb-45 wt%Ti-15wt%Ta alloys is followed during their simultaneous thermomechanical processing. The effects of a Ta addition, cold work prestrain, and of the temperature and duration of heat treatments on the volume fraction, size, density and localization of the particles of {alpha} phase are especially documented. Widmanstatten {alpha} strengthens the NbTiTa alloy and exerts a deleterious influence on J{sub c}. Some solutions are proposed to these harmful effects. At last, the relationships describing the dependence of the {alpha} phase distribution on strain are also considered.

  17. Ordering Effects in NbC and TaC

    NASA Technical Reports Server (NTRS)

    Venables, J. D.; Meyerhoff, M. H.

    1972-01-01

    By means of transmission electron microscopy and electron diffraction, evidence has been obtained for the existence of long range carbon atom ordering in single-crystal niobium carbide that has a carbon-to-metal ratio close to the integral composition Nb6C5. The ordering, which gives rise to superlattice and domain structures similar to those observed in V6C5, appears, however, only in samples that have been cooled slowly through the order-disorder temperature of 1025 C. In TaC of similar composition, the ordering, although present, remains very imperfect even after the crystals are subjected to the same thermal treatment. The results are interpreted in terms of the electronic structure of the transition metal carbides as it is currently understood, and their relevance to the mechanical properties of NbC and TaC are discussed.

  18. Supporting data for senary refractory high-entropy alloy CrxMoNbTaVW

    PubMed Central

    Zhang, B.; Gao, M.C.; Zhang, Y.; Guo, S.M.

    2015-01-01

    This data article is related to the research paper entitled “senary refractory high-entropy alloy CrxMoNbTaVW [1]”. In this data article, the pseudo-binary Cr-MoNbTaVW phase diagram is presented to show the impact of Cr content to the senary Cr-MoNbTaVW alloy system; the sub-lattice site fractions are presented to show the disordered property of the Cr-MoNbTaVW BCC structures; the equilibrium and Scheil solidification results with the actual sample elemental compositions are presented to show the thermodynamic information of the melted/solidified CrxMoNbTaVW samples; and the raw EDS scan data of the arc-melted CrxMoNbTaVW samples are also provided. PMID:26693172

  19. Mesoporous Nb and Ta Oxides: Synthesis, Characterization and Applications in Heterogeneous Acid Catalysis

    NASA Astrophysics Data System (ADS)

    Rao, Yuxiang Tony

    In this work, a series of mesoporous Niobium and Tantalum oxides with different pore sizes (C6, C12, C18 , ranging from 12A to 30 A) were synthesized using the ligand-assisted templating approach and investigated for their activities in a wide range of catalytic applications including benzylation, alkylation and isomerization. The as-synthesized mesoporous materials were characterized by nitrogen adsorption, powder X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), and solid-state Nuclear magnetic resonance (NMR) techniques. In order to probe into the structural and coordination geometry of mesoporous Nb oxide and in efforts to make meaningful comparisons of mesoporous niobia prepared by the amine-templating method with the corresponding bulk sol-gel prepared Nb2O5 phase, 17O magic-angle-spinning solid-state NMR studies were conducted. The results showed a very high local order in the mesoporous sample. The oxygen atoms are coordinated only as ONb 2 in contrast with bulk phases in which the oxygen atoms are always present in a mixture of ONb2 and ONb3 coordination environments. To enhance their surface acidities and thus improve their performance as solid acid catalysts in the acid-catalyzed reactions mentioned above, pure mesoporous Nb and Ta oxides were further treated with 1M sulfuric acid or phosphoric acid. Their surface acidities before and after acid treatment were measured by Fourier transform infraRed (FT IR), amine titration and temperature programmed desorption of ammonia (NH3-TPD). Results obtained in this study showed that sulfated mesoporous Nb and Ta oxides materials possess relative high surface areas (up to 612 m 2/g) and amorphous wormhole structure. These mesoporous structures are thus quite stable to acid treatment. It was also found that Bronsted (1540 cm-1) and Lewis (1450 cm-1) acid sites coexist in a roughly 50:50 mixture

  20. Bond ionicity, lattice energy, bond energy and microwave dielectric properties of ZnZr(Nb1-xAx)2O8 (A = Ta, Sb) ceramics.

    PubMed

    Zhang, Ping; Zhao, Yonggui; Haitao, Wu

    2015-10-14

    The dependence of microwave dielectric properties on the structural characteristics of ZnZr(Nb1-xAx)2O8 (A = Ta, Sb) (0 ≤x≤ 0.10) ceramics is investigated. All the compounds were prepared by a conventional solid-state reaction method and analyzed via multiphase structure refinement. The diffraction patterns of ZnZr(Nb1-xAx)2O8 (A = Ta, Sb) show the monoclinic wolframite structure of ZrZrNb2O8 which consists of an oxygen octahedron, with the Nb ion in the center of the oxygen octahedron. For the ZnZr(Nb1-xAx)2O8 (A = Ta, Sb) ceramics, the dielectric constant (εr) decreased with the decrease in Nb-site bond ionicity. The quality factor (Q×f) of ZnZr(Nb1-xSbx)2O8 ceramics was found to be the highest (89 400 GHz), which is explained in terms of the average of the Nb-site lattice energy. With the decrease in the bond energy of the Nb-site, the temperature coefficient of resonant frequency (|τf|) value increased. The substitution of A(5+) (A = Ta, Sb) for Nb(5+) effectively influences the microstructure and microwave dielectric properties of ZrZrNb2O8 ceramics. PMID:26348992

  1. Synthesis and characterization of Ti-Ta-Nb-Mn foams.

    PubMed

    Aguilar, C; Guerra, C; Lascano, S; Guzman, D; Rojas, P A; Thirumurugan, M; Bejar, L; Medina, A

    2016-01-01

    The unprecedented increase in human life expectancy have produced profound changes in the prevailing patterns of disease, like the observed increased in degenerative disc diseases, which cause degradation of the bones. Ti-Nb-Ta alloys are promising materials to replace the damaged bone due to their excellent mechanical and corrosion resistance properties. In general metallic foams are widely used for medical application due to their lower elastic moduli compare to bulk materials. In this work we studied the synthesis of 34Nb-29Ta-xMn (x: 2, 4 and 6 wt.% Mn) alloy foams (50% v/v) using ammonium hydrogen carbonate as a space holder. Alloys were produced through mechanical alloying in a planetary mill for 50h. Green compacts were obtained by applying 430 MPa pressure. To remove the space holder from the matrix the green compacts were heated to 180 °C for 1.5h and after sintered at 1300 °C for 3h. Foams were characterized by x-ray diffraction, scanning, transmission electron microscopy and optical microscopy. The elastic modulus of the foam was measured as ~30 GPa, and the values are almost equal to the values predicted using various theoretical models. PMID:26478329

  2. Crystal Structure, Transformation Strain, and Superelastic Property of Ti-Nb-Zr and Ti-Nb-Ta Alloys

    NASA Astrophysics Data System (ADS)

    Kim, Hee Young; Fu, Jie; Tobe, Hirobumi; Kim, Jae Il; Miyazaki, Shuichi

    2015-06-01

    The composition dependences of transformation strain and shape memory, and superelastic properties were extensively investigated in Ti-Nb-Zr and Ti-Nb-Ta alloys in order to establish the guidelines for alloy design of biomedical superelastic alloys. The effects of composition on the crystal structure of the parent (β) phase and the martensite (α″) phase were also investigated. Results showed that not only transformation temperature but also transformation strain is tunable by alloy design, i.e., adjusting contents of Nb, Zr, and Ta. The lattice constant of the β phase increased linearly with increasing Zr content, while it was insensitive to Nb and Ta contents. On the other hand, the lattice constants of the α″ phase are mainly affected by Nb and Ta contents. The increase of Zr content exhibited a weaker impact on the transformation strain compared with Nb and Ta. The addition of Zr as a substitute of Nb with keeping superelasticity at room temperature significantly increased the transformation strain. On the other hand, the addition of Ta decreased the transformation strain at the compositions showing superelasticity. This study confirmed that the crystallography of martensitic transformation can be the main principal to guide the alloy design of biomedical superelastic alloys.

  3. Non-stoichiometry and Defects in the Weyl Semimetals TaAs, TaP, NbAs, and NbP

    NASA Astrophysics Data System (ADS)

    Besara, Tiglet; Rhodes, Daniel A.; Chen, Kuan-Wen; Zhang, Qui; Zheng, Bin; Xin, Yan; Balicas, Luis; Baumbach, Ryan E.; Siegrist, Theo

    We report on a structural study of the Weyl semimetals TaAs, TaP, NbAs, and NbP, utilizing diffraction techniques (single crystal x-ray diffraction and energy dispersive spectroscopy) and imaging techniques (transmission electron microscopy). We observe defects of various degrees, leading to non-stoichiometric single crystals of all four semimetals. While TaP displays a very large pnictide deficiency with composition TaP0 . 83 (3) and stacking faults accompanied by anti-site disorder and site vacancies, TaAs displays transition metal deficiency with composition Ta0 . 92 (2)As and a high density of stacking faults. NbP also displays pnictide deficiency, yielding composition NbP0 . 95 (2), and lastly, NbAs display very little deviation from a 1:1 composition, NbAs1 . 00 (3), and is therefore recommended to serve as the model compound for these semimetals. DOE-BES #DE-SC0008832 (TB & TS), NSF DMR-1157490 (NHMFL).

  4. Solid Collection Efforts: Ta Collimator Evaluation

    SciTech Connect

    Gostic, J M

    2011-11-21

    Ta collimator sets that were part of the gated x-ray detector diagnostic (GXD) at NIF were analyzed for debris distribution and damage in 2011. These disks (ranging in thickness from 250 to 750 {mu}m) were fielded approximately 10 cm from target chamber center (TCC) on various symcap, THD and re-emit shots. The nose cone holder and forward Ta collimator (facing target chamber center, TCC) from all shots show evidence of surface melt. Non-destructive analysis techniques such as optical microscopy, surface profilometry, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray fluorescence (XRF) were used to determine debris composition and degree of deformation associated with each Ta disk. Molten debris from the stainless steel nose cone contaminated the surface of the collimators along with other debris associated with the target assembly (Al, Si, Cu, Au and In). Surface elemental analysis of the forward collimator Ta disks indicates that Au hohlraum debris is less concentrated on these samples versus those fielded 50 cm from TCC in the wedge range filter (WRF) assembly. It is possible that the Au is distributed below or within the stainless steel melt layer covering the disk, as most of the foreign debris is captured in the melted coating. The other disks (fielded directly behind the forward collimator in a sandwiched configuration) have visible forms of deformation and warping. The degree of warping increases as the shock wave penetrates the assembly with the most damage sustained on the back collimator. In terms of developing a solid collection capability, the collimator analyses suggests that close proximity may cause more interference with capsule debris collection and more damage to the surface of the collector diagnostic. The analyses of the Ta collimators were presented to the Target and Laser Interaction Sphere (TaLIS) group; a representative presentation is attached to this document.

  5. A series of new phases in the alkali metal-Nb(V)/Ta(V)-Se(IV)/Te(IV)-O systems.

    PubMed

    Gu, Qian-Hua; Hu, Chun-Li; Zhang, Jian-Han; Mao, Jiang-Gao

    2011-03-21

    Six new phases in the alkali metal-Nb(V)/Ta(V)-Se(IV)/Te(IV)-O systems have been prepared by solid-state reactions at high-temperatures. Their structures were determined by single-crystal X-ray diffraction studies. AM(3)O(6)(QO(3))(2) (A = K, Rb, M = Nb, Ta, Q = Te; A = K, M = Nb, Q = Se) are isomorphous and their structures feature a 3D network with 1D 4- and 6-MRs tunnels along the a-axis which is composed of 2D layers of corner-sharing MO(6) octahedra bridged by QO(3) groups. The alkali metal ions are located at the above 1D tunnels of 6-MRs. The structure of Cs(3)Nb(9)O(18)(TeO(3))(2)(TeO(4))(2) features a thick Nb-Te-O layer built of corner-sharing NbO(6) octahedra, TeO(3) and TeO(4) groups. The 2D layer of the NbO(6) octahedra with 1D tunnels of 6-MRs along the c-axis are formed by 1D chains of NbO(6) chains along the c-axis and linear Nb(4)O(21) tetramers by corner-sharing. The TeO(3) and TeO(4) groups are grafted on both sides of the niobium-oxide layer via Nb-O-Te or/and Te-O-Te bridges. The caesium(i) ions are located at the above 1D tunnels of 6-MRs. TGA, UV-vis and infrared spectral measurements as well as electronic structure calculations have also been performed. PMID:21293821

  6. Fractionation of Nb/Ta and Zr/Hf in the Mantle-Crust Sytem

    NASA Astrophysics Data System (ADS)

    Mezger, K.; Weyer, S.; Muenker, C.

    2001-12-01

    The isovalent element pairs Zr/Hf and Nb/Ta have generally been regarded as behaving identical during most geologic processes. As a consequence, it was expected that the ratios of these elements pairs are more of less constant and chondritic in all reservoirs of the silicate Earth. However, recent measurements of Zr/Hf and Nb/Ta of higher precision have indicated that mantle-derived magmas in certain geochemical environments and tectonic settings are characterized by distinct variations in Zr/Hf and Nb/Ta ratios that deviate significantly from the chondritic values. In comparison to known analytical methods, the resolution of Nb/Ta and Zr/Hf measurements can be improved by nearly a factor of 10 by isotope dilution measurements using a mixed 180Ta-94Zr-180Hf-176Lu tracer. In order to establish the solar system ratios for Nb/Ta and Zr/Hf, chondrites and eucrites were analyzed. The mean Zr/Hf of all chondrites and eucrites investigated in this study is 34.2+/-0.3 (2 RSE) and is indistinguishable from the chondrite-only mean value, which is 34.1+/-0.6. This new mean Zr/Hf value is lower than the previous estimate for the Zr/Hf of 36.3, which was inferred from analyses of OIBs and the chondrite Orgueil (Jochum et al., 1986). The chondritic Nb/Ta of 17.6+/-1.0 determined in this study agrees with previously estimated values (Jochum et al. 2000). A comparison of basalts and peridotites reveals subchondritic Zr/Hf for depleted peridotites and basalts derived from the depleted mantle. Peridotites from the Balmuccia peridotite (Italy) have Zr/Hf as low as 10 and they show an excellent correlation with Zr-contents. Therefore it can be assumed that the lower Zr/Hf in the mantle relative to the chondritic value is a feature caused by melt extraction. Nb/Ta in the Balmuccia peridotites show a similar variation, but no correlation with Ta-contents and Zr/Hf can be observed. This decoupling is caused by the extremely incompatible behavior of Nb and Ta during mantle melting. Small

  7. Nb-Ta mobility and fractionation during exhumation of UHP eclogite from southwestern Tianshan, China

    NASA Astrophysics Data System (ADS)

    Zhang, Lijuan; Zhang, Lifei; Lü, Zeng; Bader, Thomas; Chen, Zhenyu

    2016-05-01

    In order to study the behavior of high field strength elements (HFSE) during retrograde overprint of ultrahigh-pressure (UHP) eclogites, analysis of Nb and Ta concentrations was carried out on bulk rock, rutile (in both veins and host rocks) and titanite in the host eclogite. The studied samples were collected from the UHP metamorphic belt of southwestern Tianshan, China. Petrographic observation and phase equilibria modeling show that the host eclogites have experienced UHP metamorphism and the rutile-bearing veins are thought to be originated from an internal fluid source, probably by lawsonite dehydration during exhumation. The presence of vein rutile indicates HFSE could be mobilized from host eclogites to veins, which is probably facilitated by complexation with dissolved Na-Al silicates and fluorine-rich fluids. Changes in fluid composition (e.g., F-1, X(CO2)) may trigger the precipitation of rutile. Rutile/fluid partitioning may be the key to fractionating Nb and Ta, with preference for Ta in the fluid, resulting in Nb/Ta ratio of rutile in the veins lower than that in the host eclogite. Besides, the transformation of rutile into titanite also might be an effective mechanism for fractionating Nb from Ta, resulting in the intra-grain Nb-Ta zonations in vein rutile. The Nb-Ta mobility and fractionation can happen during exhumation of the UHP eclogite, which should be very important for understanding the behavior of HFSE in subduction zone metamorphism.

  8. In vitro biocompatibility, mechanical properties, and corrosion resistance of Ti-Zr-Nb-Ta-Pd and Ti-Sn-Nb-Ta-Pd alloys.

    PubMed

    Ito, A; Okazaki, Y; Tateishi, T; Ito, Y

    1995-07-01

    There is much discussion about the toxic effect of vanadium and aluminum contained in Ti-6Al-4V alloy for prosthetic implants. The goal of the present investigation was to develop new titanium alloys with sufficient mechanical properties using more biocompatible alloying elements: zirconium, tin, niobium, tantalum, and palladium. The relative growth rates of L929 and MC3T3-E1 cells were significantly higher when cultured with the extraction of Ti-10Zr-8Nb-2Ta-0.2Pd or Ti-15Zr-4Nb-2Ta-0.2Pd alloys than when cultured with the extraction of Ti-6Al-4AV ELI alloy. The tensile strength, elongation, and reduction of area for Ti-15Sn-4Nb-2Ta-0.2Pd alloy were 989 MPa, 14.4%, and 49.3%, respectively, surpassing Ti-6Al-4V ELI alloy. (ASTM F138-84); those for Ti-15Zr-4Nb-2Ta-0.2Pd alloy were 725 MPa, 23.6% and 54.9%, respectively. More than 15% addition of tin as well as zirconium deteriorated the tensile properties. Titanium release into a 5% hydrochloric acid solution from the new titanium alloys was 20-50 micrograms/cm2 per day, though that from Ti-6Al-4V ELI alloy was 1300 micrograms/cm2 per day. The optimum alloy compositions are Ti-15Zr-4Nb-2Ta-0.2Pd and Ti-15Sn-4Nb-2Ta-0.2Pd, judging from cytocompatibility, corrosion resistance, and mechanical properties. The former is characterized by its higher level cytocompatibility and corrosion resistance, while the latter is characterized by mechanical properties. PMID:7593029

  9. Biocompatibility of new Ti-Nb-Ta base alloys.

    PubMed

    Hussein, Abdelrahman H; Gepreel, Mohamed A-H; Gouda, Mohamed K; Hefnawy, Ahmad M; Kandil, Sherif H

    2016-04-01

    β-type titanium alloys are promising materials in the field of medical implants. The effect of β-phase stability on the mechanical properties, corrosion resistance and cytotoxicity of a newly designed β-type (Ti77Nb17Ta6) biocompatible alloys are studied. The β-phase stability was controlled by the addition of small quantities of Fe and O. X-ray diffraction and microstructural analysis showed that the addition of O and Fe stabilized the β-phase in the treated solution condition. The strength and hardness have increased with the increase in β-phase stability while ductility and Young's modulus have decreased. The potentio-dynamic polarization tests showed that the corrosion resistance of the new alloys is better than Ti-6Al-4V alloy by at least ten times. Neutral red uptake assay cytotoxicity test showed cell viability of at least 95%. The new alloys are promising candidates for biomedical applications due to their high mechanical properties, corrosion resistance, and reduced cytotoxicity. PMID:26838885

  10. Differential Nb-Ta diffusion in rutile: disequilibrium formation of the continental crust

    NASA Astrophysics Data System (ADS)

    Marschall, H. R.; Dohmen, R.; Ludwig, T.

    2012-12-01

    Models for the differentiation of the crust-mantle system are guided by elemental abundances in these reservoirs. Elements are fractionated between coexisting phases during partial melting, and geochemical models have mostly been based on the assumption that trace-element equilibrium is established between the partial melts and the restitic minerals. Based on this assumption, experimentally determined mineral/melt element partition coefficients have been used to model the effects of crust-mantle differentiation. The element pair niobium and tantalum has been key for the distinction of different melting regimes involved in crustal differentiation, but equilibrium partition models have largely failed to reproduce the observed Nb/Ta patterns. Here we demonstrate that Nb and Ta are significantly fractionated kinetically by diffusion, and that Nb/Ta systematics of partial melts and restites will likely be influenced by kinetic factors. We employed two different experimental setups to determine diffusivities of Nb and Ta in rutile: (1) Thin film diffusion couples prepared by PLD [1] were annealed in gas mixing furnaces between 850 and \\unit{1150}{ȩlsius}. The resulting diffusion profiles were analysed by SIMS in depth profiling mode. (2) Rutile single crystals were placed in rutile-saturated Nb-Ta-doped basaltic melt at \\unit{1250}{ȩlsius} and lateral diffusion profiles were analysed by EPMA. Both sets of experiments demonstrate consistently and unequivocally that diffusion coefficients in rutile of Nb are 3 to 5 (!) times higher than those of Ta for the entire temperature range. The significantly higher mobility of Nb compared to Ta in rutile has direct consequences for their liquid-rock fractionation during partial melting events. We conclude that trace-element equilibrium cannot be expected for the natural range of grain sizes of rutile (the dominant mineral host of Nb and Ta in high-grade rocks) and the temperatures and time scales involved in partial melting of

  11. A new RHQT Nb3Al superconducting wire with a Ta/Cu/Ta three-layer filament-barrier structure

    NASA Astrophysics Data System (ADS)

    Takeuchi, Takao; Tsuchiya, Kiyosumi; Nakagawa, Kazuhiko; Nimori, Shigeki; Banno, Nobuya; Iijima, Yasuo; Kikuchi, Akihiro; Nakamoto, Tatsushi

    2012-06-01

    To suppress the low-magnetic-field instability (flux jumps in low magnetic fields) of a rapid-heating, quenching and transformation (RHQT) processed Nb3Al superconductor, we had previously modified the cross-sectional design of an RHQT Nb3Al by adopting a Ta filament-barrier structure. Unlike Nb barriers, Ta barriers are not superconducting in magnetic fields at 4.2 K so that they electromagnetically decouple filaments. However, small flux jumps still occurred at 1.8 K, which is a typical operating temperature for the magnets used in high-energy particle accelerators. Furthermore, poor bonding at the Ta/Ta interface between neighboring Ta-coated jelly-roll (JR) filaments frequently caused precursor wires to break during drawing. To overcome these problems, we fabricated a new RHQT Nb3Al wire with a Ta/Cu/Ta three-layer filament-barrier structure for which an internal stabilization technique (Cu rods encased in Ta are dispersed in the wire cross section) was extended. Removing the Ta/Ta interface in the interfilamentary barrier (JR filament/Ta/Cu/Ta/JR filament) allowed precursor wires to be drawn without breaking. Furthermore, the Cu filament barrier electromagnetically decoupled filaments to suppress flux jumps at 1.8 K. The ductile Cu layer also improved the bending strain tolerance of RHQT Nb3Al.

  12. Crystal structure and X-ray photoemission spectroscopic study of A{sub 2}LaMO{sub 6} [A=Ba, Ca; M=Nb, Ta

    SciTech Connect

    Dutta, Alo; Saha, Sujoy; Sinha, T.P.

    2015-09-15

    The X-ray photoemission spectroscopic (XPS) study of the double perovskite oxides A{sub 2}LaMO{sub 6} [A=Ba, Ca; M=Nb, Ta] synthesized by the solid-state reaction technique has been carried out to investigate the nature of the chemical state of the constituent ions and the bonding between them. The Rietveld refinement of the X-ray diffraction patterns suggests the monoclinic crystal structure of all the materials at room temperature. The negative and positive chemical shifts of the core level XPS spectrum of O-1s and Nb-3d{sub 3/2}/Ta-4f{sub 5/2} respectively suggest the covalent bonding between Nb/Ta cations and O ion. The change of the bonding strength between the anion and the cations from one material to another has been analyzed. The vibrational property of the materials is investigated using the room temperature Raman spectra. A large covalency of Ta-based compound than Nb compound is confirmed from the relative shifting of the Raman modes of the materials. - Graphical abstract: Crystal structure of two perovskite oxides CLN and CLT is investigated. XPS study confirms the two different co-ordination environments of Ca and covalent bonding between B-site cations and O-ion. - Highlights: • Ordered perovskite structure obtained by Rietveld refinement of XRD patterns. • Study of nature of chemical bonding by X-ray photoemission spectroscopy. • Opposite chemical shift of d-states of Nb/Ta with respect to O. • Covalent bonding between d-states of Nb/Ta and O. • Relative Raman shifts of CLN and CLT substantiate the more covalent character of Ta than Nb.

  13. Cell response to a newly developed Ti-10Ta-10Nb alloy and its sputtered nanoscale coating

    PubMed Central

    Kim, Young-Min; Vang, Mong-Sook; Yang, Hong-So; Lim, Hyun-Pil

    2009-01-01

    STATEMENT OF PROBLEM The success of titanium implants is due to osseointegration or the direct contact of the implant surface and bone without a fibrous connective tissue interface. PURPOSE The purpose of this study was to evaluate the osteoblast precursor response to titanium - 10 tantalum - 10 niobium (Ti-Ta-Nb) alloy and its sputtered coating. MATERIAL AND METHODS Ti-Ta-Nb coatings were sputtered onto the Ti-Ta-Nb disks. Ti6-Al-4V alloy disks were used as controls. An osteoblast precursor cell line, were used to evaluate the cell responses to the 3 groups. Cell attachment was measured using coulter counter and the cell morphology during attachment period was observed using fluorescent microscopy. Cell culture was performed at 4, 8, 12 and 16 days. RESULTS The sputtered Ti-Ta-Nb coatings consisted of dense nanoscale grains in the range of 30 to 100 nm with alpha-Ti crystal structure. The Ti-Ta-Nb disks and its sputtered nanoscale coatings exhibited greater hydrophilicity and rougher surfaces compared to the Ti-6Al-4V disks. The sputtered nanoscale Ti-Ta-Nb coatings exhibited significantly greater cell attachment compared to Ti-6Al-4V and Ti-Ta-Nb disks. Nanoscale Ti-Ta-Nb coatings exhibited significantly greater ALP specific activity and total protein production compared to the other 2 groups. CONCLUSIONS It was concluded that nanoscale Ti-Ta-Nb coatings enhance cell adhesion. In addition, Ti-Ta-Nb alloy and its nanoscale coatings enhanced osteoblast differentiation, but did not support osteoblast precursor proliferation compared to Ti-6Al-4V. These results indicate that the new developed Ti-Ta-Nb alloy and its nanoscale Ti-Ta-Nb coatings may be useful as an implant material. PMID:21165256

  14. Ferromagnetism in chemically reduced LiNbO3 and LiTaO3 crystals

    NASA Astrophysics Data System (ADS)

    Yan, Tao; Ye, Ning; Xu, Liuwei; Sang, Yuanhua; Chen, Yanxue; Song, Wei; Long, Xifa; Wang, Jiyang; Liu, Hong

    2016-05-01

    The ferromagnetism of bulk LiNbO3 and LiTaO3 at room temperature was investigated for the first time in the present work. The stoichiometric LiNbO3 is non-magnetic, while congruent LiNbO3 and LiTaO3 show very weak ferromagnetism. After chemical reduction in a mixture of zinc and lithium carbonate powders under flowing nitrogen, the ferromagnetic behavior of each sample became clear, with an increased value of magnetization. The saturation magnetization, the magnetic remanence and the coercive field of reduced congruent LiNbO3 are 7.0  ×  10‑3 emu g‑1, 0.65  ×  10‑3 emu g‑1 and 0.050 kOe, respectively. The ferromagnetism of chemically reduced LiNbO3 and LiTaO3 can be explained by considering the intrinsic Li vacancies, the appearance of Nb4+ (or Ta4+) on the surface with non-zero net spin and the oxygen vacancies at the surface.

  15. Ductility Characterization of U-6Nb and Ta-W Alloys

    SciTech Connect

    Sun, T; Cervantes, O

    2006-09-15

    We have previously evaluated the ductility behaviors of U-6Nb and pure Ta. One important observation was that both alloys have very stable necking ductility independent of test conditions. In contrast, uniform ductility varied significantly depending upon strain rates and temperatures. In general, higher strain rate and lower temperature reduce the uniform ductility. Using literature data, we have developed two dynamic ductility models to predict the ductility behaviors of pure-Ta and water-quenched U-6Nb respectively under extreme conditions. In this study we further evaluate the aging effect on U-6Nb and the W-addition effect on Ta. For U-6Nb, the objective is to determine whether or not the ductility degradation by low-temperature aging mostly measured in quasi-static condition can still be observed under dynamic loading (high strain rate) condition. For Ta-W alloys, the focus is to identify the key control parameter so that the optimal condition of high-strength/high-ductility of Ta-10W can be achieved for certain defense-related applications.

  16. Proposed long-range empirical potential to study the metallic glasses in the Ni-Nb-Ta system.

    PubMed

    Dai, Y; Li, J H; Che, X L; Liu, B X

    2009-05-21

    An n-body potential is constructed for the Ni-Nb-Ta ternary metal system in the newly proposed form of long-range empirical potential. The constructed Ni-Nb-Ta potential can well reproduce the lattice constants, cohesive energies, and elastic modulus of the metals and some compounds as well as the equations of state of the system. Applying the constructed Ni-Nb-Ta potential, molecular dynamics simulations and Voronoi tessellations are carried out to study the issues related to the Ni-Nb-Ta metallic glasses. It is found that increasing the Ni content can obviously improve the glass-forming ability of the binary Nb-Ta system, which features a isomorphous phase diagram unfavoring for forming glass, indicating that the Ni solute plays a decisive role in forming the Nb-based or Ta-based Ni-Nb-Ta metallic glasses. Concerning the atomic structure, the Voronoi cell volume and coordination number (CN) of Ta are generally larger than those of Ni in the binary Ni-Ta metallic glasses. With increasing the Ni concentration, the fraction of icosidihedron (CN=13) increases, while the fractions of icosihexahedron (CN=15) and icosioctahedron (CN=16) decrease. Meanwhile, with increasing the Ni concentration, the dominating coordination numbers of Ta atoms increase. Interestingly, similar feature in the atomic structure with variation of Ni concentration is also observed in the Ni-Nb metallic glasses. For the ternary Ni-Nb-Ta alloys, it is observed from the CN distributions that the structure of the metallic glasses is mostly affected by the Ni concentration. PMID:19438281

  17. Bone response to a novel Ti-Ta-Nb-Zr alloy.

    PubMed

    Stenlund, Patrik; Omar, Omar; Brohede, Ulrika; Norgren, Susanne; Norlindh, Birgitta; Johansson, Anna; Lausmaa, Jukka; Thomsen, Peter; Palmquist, Anders

    2015-07-01

    Commercially pure titanium (cp-Ti) is regarded as the state-of-the-art material for bone-anchored dental devices, whereas the mechanically stronger alloy (Ti-6Al-4V), made of titanium, aluminum (Al) and vanadium (V), is regarded as the material of choice for high-load applications. There is a call for the development of new alloys, not only to eliminate the potential toxic effect of Al and V but also to meet the challenges imposed on dental and maxillofacial reconstructive devices, for example. The present work evaluates a novel, dual-stage, acid-etched, Ti-Ta-Nb-Zr alloy implant, consisting of elements that create low toxicity, with the potential to promote osseointegration in vivo. The alloy implants (denoted Ti-Ta-Nb-Zr) were evaluated after 7 days and 28 days in a rat tibia model, with reference to commercially pure titanium grade 4 (denoted Ti). Analyses were performed with respect to removal torque, histomorphometry and gene expression. The Ti-Ta-Nb-Zr showed a significant increase in implant stability over time in contrast to the Ti. Further, the histological and gene expression analyses suggested faster healing around the Ti-Ta-Nb-Zr, as judged by the enhanced remodeling, and mineralization, of the early-formed woven bone and the multiple positive correlations between genes denoting inflammation, bone formation and remodeling. Based on the present experiments, it is concluded that the Ti-Ta-Nb-Zr alloy becomes osseointegrated to at least a similar degree to that of pure titanium implants. This alloy is therefore emerging as a novel implant material for clinical evaluation. PMID:25848727

  18. Color tone and interfacial microstructure of white oxide layer on commercially pure Ti and Ti-Nb-Ta-Zr alloys

    NASA Astrophysics Data System (ADS)

    Miura-Fujiwara, Eri; Mizushima, Keisuke; Watanabe, Yoshimi; Kasuga, Toshihiro; Niinomi, Mitsuo

    2014-11-01

    In this study, the relationships among oxidation condition, color tone, and the cross-sectional microstructure of the oxide layer on commercially pure (CP) Ti and Ti-36Nb-2Ta-3Zr-0.3O were investigated. “White metals” are ideal metallic materials having a white color with sufficient strength and ductility like a metal. Such materials have long been sought for in dentistry. We have found that the specific biomedical Ti alloys, such as CP Ti, Ti-36Nb-2Ta-3Zr-0.3O, and Ti-29Nb-13Ta-4.6Zr, form a bright yellowish-white oxide layer after a particular oxidation heat treatment. The brightness L* and yellowness +b* of the oxide layer on CP Ti and Ti-36Nb-2Ta-3Zr-0.3O increased with heating time and temperature. Microstructural observations indicated that the oxide layer on Ti-29Nb-13Ta-4.6Zr and Ti-36Nb-2Ta-3Zr-0.3O was dense and firm, whereas a piecrust-like layer was formed on CP Ti. The results obtained in this study suggest that oxide layer coating on Ti-36Nb-2Ta-3Zr-0.3O is an excellent technique for dental applications.

  19. Ferroelectric properties of RbNbO3 and RbTaO3

    NASA Astrophysics Data System (ADS)

    Lebedev, A. I.

    2015-02-01

    Phonon spectra of cubic rubidium niobate and rubidium tantalate with the perovskite structure are calculated from first principles within the density functional theory. Based on the analysis of unstable modes in phonon spectra, symmetries of possible distorted phases are determined, their energies are calculated, and it is shown that R3 m is the ground-state structure of RbNbO3. In RbTaO3, the ferroelectric instability is suppressed by zero-point lattice vibrations. For ferroelectric phases of RbNbO3, spontaneous polarization, piezoelectric, nonlinear optical, electro-optical, and other properties as well as the energy band gap in the LDA and GW approximations are calculated. The properties of rhombohedral RbNbO3 are compared with those of rhombohedral KNbO3, LiNbO3, and BaTiO3.

  20. Senary Refractory High-Entropy Alloy HfNbTaTiVZr

    NASA Astrophysics Data System (ADS)

    Gao, M. C.; Zhang, B.; Yang, S.; Guo, S. M.

    2016-07-01

    Discovery of new single-phase high-entropy alloys (HEAs) is important to understand HEA formation mechanisms. The present study reports computational design and experimental validation of a senary HEA, HfNbTaTiVZr, in a body-centered cubic structure. The phase diagrams and thermodynamic properties of this senary system were modeled using the CALPHAD method. Its atomic structure and diffusion constants were studied using ab initio molecular dynamics simulations. The microstructure of the as-cast HfNbTaTiVZr alloy was studied using X-ray diffraction and scanning electron microscopy, and the microsegregation in the as-cast state was found to qualitatively agree with the solidification predictions from CALPHAD. Supported by both simulation and experimental results, the HEA formation rules are discussed.

  1. Direct Electrolytic Reduction of Solid Ta2O5 to Ta with SOM Process

    NASA Astrophysics Data System (ADS)

    Chen, Chaoyi; Yang, Xiaqiong; Li, Junqi; Lu, Xionggang; Yang, Shufeng

    2016-06-01

    A process that uses the solid-oxide-oxygen-ion conducting membrane has been investigated to produce tantalum directly from solid Ta2O5 in molten CaCl2 or a molten mixture of 55.5MgF2-44.5CaF2 (in wt pct). The sintered porous Ta2O5 pellet was employed as the cathode, while the liquid copper alloy, saturated with graphite powder and encased in a one-end-closed yttria-stabilized-zirconia (YSZ) tube, acted as the anode. The electrolysis potential in this method is higher than that of the Fray-Farthing-Chen Cambridge process because the YSZ membrane tube blocks the melts to electrolyze, and only Ta2O5 is will be electrolyzed. The microstructures of reduced pellets and a cyclic voltammogram of solid Ta2O5 in molten CaCl2 were analyzed. In addition, the influence of particle size and porosity of the cathode pellets on metal-oxide-electrolyte, three-phase interlines was also discussed. The results demonstrate that the sintering temperature of cathode pellets and electrolytic temperature play important roles in the electrochemical process. Furthermore, this process can be used to produce Ta metal efficiently without the expensive cost of pre-electrolysis and generation of harmful by-products.

  2. Resistivity plateau and extremely large magnetoresistance in NbAs2 and TaAs2

    NASA Astrophysics Data System (ADS)

    Wang, Yi-Yan; Yu, Qiao-He; Guo, Peng-Jie; Liu, Kai; Xia, Tian-Long

    2016-07-01

    In topological insulators (TIs), metallic surface conductance saturates the insulating bulk resistance with decreasing temperature, resulting in resistivity plateau at low temperatures as a transport signature originating from metallic surface modes protected by time reversal symmetry (TRS). Such a characteristic has been found in several materials including Bi2Te2Se , SmB6 etc. Recently, similar behavior has been observed in metallic compound LaSb, accompanying an extremely large magnetoresistance (XMR). Shubnikov-de Hass (SdH) oscillation at low temperatures further confirms the metallic behavior of the plateau region under magnetic fields. LaSb [Tafti et al., Nat. Phys. 12, 272 (2015), 10.1038/nphys3581] has been proposed by the authors as a possible topological semimetal (TSM), while negative magnetoresistance is absent at this moment. Here, high quality single crystals of NbAs2/TaAs2 with inversion symmetry have been grown, and the resistivity under magnetic field is systematically investigated. Both of them exhibit metallic behavior under zero magnetic field, and a metal-to-insulator transition occurs when a nonzero magnetic field is applied, resulting in XMR (1.0 ×105% for NbAs2 and 7.3 ×105% for TaAs2 at 2.5 K and 14 T). With temperature decreased, a resistivity plateau emerges after the insulatorlike regime, and SdH oscillation has also been observed in NbAs2 and TaAs2.

  3. MRI-compatible Nb-60Ta-2Zr alloy for vascular stents: Electrochemical corrosion behavior in simulated plasma solution.

    PubMed

    Li, Hui-Zhe; Zhao, Xu; Xu, Jian

    2015-11-01

    Using revised simulated body fluid (r-SBF), the electrochemical corrosion behavior of an Nb-60Ta-2Zr alloy for MRI compatible vascular stents was characterized in vitro. As indicated by XPS analysis, the surface passive oxide film of approximately 1.3nm thickness was identified as a mixture of Nb2O5, Ta2O5 and ZrO2 after immersion in the r-SBF. The Nb-60Ta-2Zr alloy manifests a low corrosion rate and high polarization resistance similar to pure Nb and Ta, as shown by the potentiodynamic polarization curves and EIS. Unlike 316L stainless steel and the L605 Co-Cr alloy, no localized corrosion has been detected. Semiconducting property of passive film on the Nb-60Ta-2Zr alloy was identified as the n-type, with growth mechanism of high-field controlled growth. The excellent corrosion resistance in simulated human blood enviroment renders the Nb-60Ta-2Zr alloy promising as stent candidate material. PMID:26249582

  4. Synthesis and characterization of homo- and heterobimetallic niobium{sup v} and tantalum{sup v} peroxo-polyaminocarboxylato complexes and their use as single or multiple molecular precursors for Nb-Ta mixed oxides

    SciTech Connect

    Bayot, Daisy . E-mail: devillers@chim.ucl.ac.be

    2005-09-15

    New water-soluble bimetallic peroxo complexes of niobium{sup V} and/or tantalum{sup V} with high-denticity polyaminocarboxylate ligands have been prepared, characterized from the spectroscopic point of view, and used as molecular precursors for Nb-Ta mixed oxides. Four new homobimetallic complexes (gu){sub 3}[Nb{sub 2}(O{sub 2}){sub 4}(dtpaO{sub 3})].3H{sub 2}O 1 (gu){sub 3}[Ta{sub 2}(O{sub 2}){sub 4}(dtpaO{sub 3})].5H{sub 2}O 2 (gu){sub 3}[Nb{sub 2}(O{sub 2}){sub 4}(HtthaO{sub 4})].2H{sub 2}O 4 and (gu){sub 3}[Ta{sub 2}(O{sub 2}){sub 4}(HtthaO{sub 4})].3H{sub 2}O 5 and the corresponding heterometallic complexes (gu){sub 3}[NbTa(O{sub 2}){sub 4}(dtpaO{sub 3})].2.5H{sub 2}O 3 and (gu){sub 3}[NbTa(O{sub 2}){sub 4}(HtthaO{sub 4)}].2H{sub 2}O 6 have been obtained. In these compounds, the in situ oxidation of the nitrogen atoms of the PAC ligands into N-oxide groups has been evidenced by IR spectroscopy and mass spectrometry. The thermal treatment of the homonuclear complexes in air at 700 or 800 deg. C, depending on the Ta content, provided Nb{sub 2}O{sub 5} or Ta{sub 2}O{sub 5} while the heteronuclear compounds led to the solid solution TaNbO{sub 5}. BET and SEM measurements have been carried out and comparison of the morphology of the samples prepared from homo- and heterometallic precursors is discussed.

  5. Large magnetoresistance in compensated semimetals TaAs2 and NbAs2

    NASA Astrophysics Data System (ADS)

    Yuan, Zhujun; Lu, Hong; Liu, Yongjie; Wang, Junfeng; Jia, Shuang

    2016-05-01

    We report large magnetoresistance (MR) at low temperatures in single-crystalline nonmagnetic compounds TaAs2 and NbAs2. Both compounds exhibit parabolic-field-dependent MR larger than 5 ×103 in a magnetic field of 9 Tesla at 2 K. The MR starts to deviate from parabolic dependence above 10 T and intends to be saturated in 45 T for TaAs2 at 4.2 K. The Hall resistance measurements and band structure calculations reveal their compensated semimetal characteristics. Their large MR at low temperatures is ascribed to an effect for compensation of electrons and holes with large mobilities. After discussing the MR for different samples of TaAs2 and other semimetals, we found that the magnitudes of MR are strongly dependent on the samples' quality for different compounds.

  6. X-Ray and Ultraviolet Luminescence of Li 3Ta 1- xNb xO 4 Prepared by Flux Synthesis and Characterization of a New High Efficiency X-Ray Phosphor

    NASA Astrophysics Data System (ADS)

    Miao, C. R.; Torardi, C. C.

    1999-06-01

    The phase development and luminescence properties, under both X-ray and ultraviolet excitation, of the lithium orthotantalate-lithium orthoniobate system, Li3Ta1-xNbxO4 for x=0 to 1, were examined. Using a flux synthesis technique, it was found that the levels of Nb-doping in monoclinic Li3TaO4 and of Ta-doping in cubic Li3NbO4 are higher than previously reported. Under 30 kVp molybdenum X-ray excitation, Li3Ta1-xNb4O4 is an efficient blue-emitting phosphor with broadband emission, peaking in the range of 390 to 435 nm. For x=0 to 0.1, the overall luminescence efficiency is comparable to, or better than, a commercial calcium tungstate, CaWO4, Hi-Plus material. The composition Li3Ta0.995Nb0.005O4 demonstrates an overall luminescence efficiency that makes this phosphor 45% brighter than CaWO4 Hi-Plus, thereby making it a potentially attractive candidate for use in medical diagnostic imaging systems. Under ultraviolet excitation, broadband blue emission is also observed. For all the Li3Ta1-xNbxO4 (x>0) solid solutions, the emission peak maximums agree well with those seen under X-ray excitation and are the result of Nb5+ emission.

  7. HFSE Processing During Subduction and the Consequences for Nb/Ta and Zr/Hf Ratios in the Mantle

    NASA Astrophysics Data System (ADS)

    Pfänder, J. A.; Jung, S.; Münker, C.; Stracke, A.; Mezger, K.

    2008-12-01

    High-precision (MC-ICP-MS) Nb-Ta concentration ratios in Silicate Earth reservoirs (mantle and crust) are consistently sub-chondritic (<19.9; Münker et al., 2003). Various models have been proposed to explain this observation and include hidden reservoirs in the silicate Earth or Nb fractionation into the metal core. Nb becomes siderophile at high pressure and thus the core is a potential reservoir for the missing Nb (Wade & Wood, 2001). This model implies Nb depletion of the silicate portion of the Earth soon after, or even during accretion by a selective, pressure driven partitioning of Nb into the metal phase. As a consequence the bulk-silicate Earth acquired a Nb/Ta ratio of ~14 instead of ~20 as suggested by chondrites (Münker et al., 2003). In contrast, Zr/Hf likely remained chondritic (~35). As shown by the correlated Nb/Ta - Zr/Hf array (terrestrial fractionation array), subsequent second-order silicate differentiation that generated Earth's crust and mantle fractionated Nb/Ta concomitantly with Zr/Hf and produced complementary reservoirs with respect to Nb/Ta (crust ~12-13; mantle ~16). Although the mechanisms that fractionate Nb/Ta are poorly understood, a key role is attributed to the processes taking place during subduction of oceanic lithosphere, i.e. fractionation during dehydration and partial melting of eclogite or garnet amphibolite in the presence of Ti-phases with high D-values for the HFSE. Some hotspot lavas bear signatures of eclogite derived melts in that they have slightly higher Nb/Ta but lower Lu/Hf ratios than expected from melting of primitive mantle peridotite independent of whether rutile is present in the eclogitic residue or not. Eclogite melting, however, is not suitable to explain low Nb/Ta in the continental crust. Therefore, significant portions of the continental crust may have been produced early in Earth's history by amphibolite dominated melting in subduction zones or within thickened Archean mafic crust, as melts in

  8. Evidence of Nb-Ta mobility in high temperature F-rich fluids evidenced by the La Bosse quartz-Nb-ferberite stockwork (Echassières, French Massif Central).

    NASA Astrophysics Data System (ADS)

    Marignac, C.; Cuney, M.

    2012-04-01

    In the Echassières district (northern French Massif Central), the 310 Ma Beauvoir granite (a P-rich peraluminous RMG) overprints a quartz-ferberite stockwork. The 900 m-deep GPF1 scientific hole shows that the stockwork is split into two parts by the gently dipping Beauvoir intrusion: the upper section (~ 100m thick) occurs in the La Bosse quarry, , and the lower section (≥ 60 m thick) below the granite floor. The root of the stockwork (hypothetic La Bosse granite) has not been reached. The stockwork comprises flat-lying quartz veins (≤ 0.6 m thick) concordant to the regional schistosity of surrounding micaschists, and steep N10-N50°E quartz veins (≤ 0.2 m thick). The two sets result from hydraulic fracturing, and consistently display crack seal features. A family of aplites and aplo-pegmatites dikes follow the same set of fractures, being either later (with partial dissolution of pre-existing quartz veins) or earlier, than the quartz veins. There is no alteration, nor associated mineral other than ferberite, at the La Bosse quarry, whereas micaceous selvages are observed in the lower section. Ferberite display a trend of ferberite enrichment with increasing depth (0.71 to 0.95 Fb mole%). In the La Bosse quarry, three ferberite habitus are present: acicular, lanceolate and prismatic. Acicular crystals are typically nicely zoned, with alternating Nb-rich (4.95±0.94 % Nb2O5) and Nb-poor (1.57±0.38 % Nb2O5) growth bands. Ta (up to 0.30 Ta2O5), Ti and Sn are also enriched in the Nb-rich bands. Nb and Ta incorporation into the ferberite is in the form of columbite, as either true solid solution or nanoinclusions. Lanceolate crystals have a similarly zoned acicular core and a Nb-poor rim (1.08±0.66 % Nb2O5). Prismatic crystals are unzoned and Nb-poor (0.67±0.20 % Nb2O5). In the lower part of the stockwork, the Nb contents are lower (2.17 % Nb2O5 in the Nb-rich bands, 1.36 % in the Nb-poor bands, 0.08 % in the unzoned cortex, 0.15 % in the unzoned prisms

  9. Solid solution cermet: (Ti,Nb)(CN)-Ni cermet.

    PubMed

    Kwon, Hanjung; Jung, Sun-A

    2014-11-01

    Solid solution powders without W, (Ti,Nb)(CN) powders with a B1 structure (NaCl like), were synthesized by high energy milling and carbothermal reduction in nitrogen. The range of molar ratios of Ti/Nb for forming complete (Ti,Nb)(CN) phase was broader than that of Ti/W for the (Ti,W)(CN) phase because carbide or carbonitride of Nb had a B1 crystal structure identical to Ti(CN) while WC had a hexagonal crystal structure. The results revealed that the hardness of (Ti,Nb)(CN)-Ni cermets was higher than that of (Ti,W)(CN)-Ni cermets. The lower density of the (Ti,Nb)(CN) powder contributed to the higher hardness compared to (Ti,W)(CN) because the volumetric ratio of (Ti,Nb)(CN) in the (Ti,Nb)(CN)-Ni cermets was higher than that of (Ti,Nb)(CN) in the (Ti,W)(CN)-Ni cermets at the same weight ratio of Ni. Additionally, it was assumed that intrinsic the properties of (Ti,Nb)(CN) could also be the cause for the high hardness of the (Ti,Nb)(CN)-Ni cermets. PMID:25958611

  10. Homoatomic clustering in T4Ga5 (T = Ta, Nb, Ta/Mo): a story of reluctant intermetallics crystallizing in a new binary structure type.

    PubMed

    Fredrickson, Rie T; Kilduff, Brandon J; Fredrickson, Daniel C

    2015-02-01

    In the formation of binary compounds, heteroatomic interactions are generally expected to play the leading role in providing stability. In this Article, we present a series of gallides, T(4)Ga(5) (T = Ta, Nb, and Ta/Mo), which appear to defy this expectation. Their complex crystal structures represent a new binary structure type (to the best of our knowledge),, which can be visualized in terms of a host lattice of T@T(8) body centered cubic (bcc) clusters linked through face-capping Ga(2) dumbbells to form a primitive cubic framework. The cubic spaces that result are alternately filled by distorted T pentagonal dodecahedra (sharing atoms with the host lattice) and dimers of bcc fragments, leading to a √2 × √2 × 2 supercell of the host framework structure. Ga tetrahedra and icosahedral units fill the remaining void spaces. Underlying these structural features is a strong tendency for homoatomic clustering of Ta and Ga, which is evident in all of the coordination polyhedra. Electronic structure calculations using density functional theory (DFT) and DFT-calibrated Hückel models reveal possible origins for this elemental segregation and the factors stabilizing the structure as a whole. A deep pseudogap is present at the Fermi energy of Ta(4)Ga(5) (as well as at that of Nb(4)Ga(5)), corresponding to the near-optimization of Ta-Ta and Ta-Ga interactions. This pseudogap emerges as a result of the ability of extensive Ta-Ta bonding to provide local 18-electron configurations to the Ta atoms, despite the electron concentration being only 8.75 electrons per Ta atom. Support for these Ta-Ta interactions is provided by Ga bridging atoms, whose valence orbitals' low number of angular nodes confers preferential stabilization to Ta-Ta bonding functions over antibonding ones. The observed spatial separation of the structure into Ta and Ga domains occurs as a consequence of the Ga atoms being pushed toward the periphery of the Ta clusters to play this supporting role. PMID

  11. Single crystal structure and SHG of defect pyrochlores CsBVMoO6 (BV=Nb,Ta)

    NASA Astrophysics Data System (ADS)

    Fukina, D. G.; Suleimanov, E. V.; Yavetskiy, R. P.; Fukin, G. K.; Boryakov, A. V.; Borisov, E. N.; Borisov, E. V.; Surodin, S. I.; Saharov, N. V.

    2016-09-01

    The crystal structure and non-linear optical properties of CsNbMoO6 and CsTaMoO6 defect pyrochlores have been studied. The single crystals of these compounds grown by the flux method possess an octahedral faceting and reach up to 50 μm in size. The crystal structures of CsBVMoO6 (BV=Nb, Ta) were investigated by X-ray diffraction method. Both compounds crystallize in the cubic symmetry with noncentrosymmetric space group F-43m. The second harmonic generation of CsNbMoO6 and CsTaMoO6was found to be 1.6×10-2 and 8.5×10-4 of lithium niobate, correspondingly. It has been determined that distortions of [MO6] polyhedra (M=Nb, Ta, Mo) as well as polarizability and covalency of Nb-O and Ta-O bonds have a great effect on the second harmonic generation.

  12. [Research and Application of the ICP-MS Detection Technology for the Content of Nb and Ta in Geochemical Sample].

    PubMed

    Li, Zi-qiang; Li, Xiao-ying; Zhu, Kun; Xu, Xiao-xia; Yan, Zhi-yuan

    2015-08-01

    In order to provide the test analysis technology to support the exploration and development of niobium and tantalum resource, based on the special chemical properties of Nb and Ta in geochemical sample, we studied the detection methods for the content of Nb and Ta in geochemical sample by using inductively coupled plasma mass spectrometry (ICP-MS). The results show that the sample dissolution and instrumental parameter of ICP-MS, especially the former have significant influence? on detection results. Therefore, optimizing important parameters of sample dissolution is the key of the detection technology. The optimal parameters are that the weight of sample is 50 mg; the dosage of HF acid is 15 mL; the concentration of nitric acid and tartaric acid in the sample solution is 2% and 1.5%, respectively; the validity period of detection for sample solution ≤1 d. The detection method has been validated by the national geochemistry standard reference material. The precise and exaction of method meet the required of industry standards. The detection limits of method for Nb and Ta are 1.05 and 0.13 μg · g(-1), respectively. The experiment proved that the ICP-MS detection methods, which using certain preparation process of sample solutions, is suitable for accurate and rapid determination of Nb and Ta in geochemical sample, especially geochemical survey samples which with a large amount and low content of Nb and Ta. PMID:26672313

  13. The effect of microstructure and temperature on the oxidation behavior of two-phase Cr-Cr{sub 2}X (X = Nb, Ta) alloys

    SciTech Connect

    Brady, M.P.; Tortorelli, P.F.

    1998-11-01

    The oxidation behavior of Cr(X) solid solution (Cr{sub ss}) and Cr{sub 2}X Laves phases (X = Nb, Ta) was studied individually and in combination at 950--1,100 C in air. The Cr{sub ss} phase was significantly more oxidation resistant than the Cr{sub 2}X Laves phase. At 950 C, two-phase alloys of Cr-Cr{sub 2}Nb and Cr-Cr{sub 2}Ta exhibited in-situ internal oxidation, in which remnants of the Cr{sub 2}X Laves phase were incorporated into a growing chromia scale. At 1,100 C, the Cr-Cr{sub 2}Nb alloys continued to exhibit in-situ internal oxidation, which resulted in extensive O/N penetration into the alloy ahead of the alloy-scale interface and catastrophic failure during cyclic oxidation. IN contrast, the Cr-Cr{sub 2}Ta alloys exhibited a transition to selective Cr oxidation and the formation of a continuous chromia scale. The oxidation mechanism is interpreted in terms of multiphase oxidation theory.

  14. Synthesis and physical properties of the new layered ternary tellurides MIrTe 4 ( M = Nb, Ta), and the structure of NbIrTe 4

    NASA Astrophysics Data System (ADS)

    Mar, Arthur; Ibers, James A.

    1992-04-01

    Two new ternary transition-metal chalcogenides, niobium iridium tetratelluride (NbIrTe 4) and tantalum iridium tetratelluride (TaIrTe 4), have been prepared by reaction of the elemental powders at 1000°C. The structure of NbIrTe 4 has been determined by single-crystal X-ray diffraction methods. The compound crystallizes in space group C72 v- Pmn2 1 of the orthorhombic system with four formula units in a cell of dimensions a = 3.768(3), b = 12.486(10), c = 13.077(9) Å at 294 K. NbIrTe 4 is a layered compound with a structure closely related to those of WTe 2 and β-MoTe 2, variants of the CdI 2 structure type. The layers comprise buckled sheets of Te atoms, with the Nb and Ir atoms residing in distorted octahedral sites. Metal-metal bonding appears to be responsible for a close association of the Nb and Ir atoms. From Weissenberg photography, the compound TaIrTe 4 is found to be isostructural to NbIrTe 4, with cell dimensions a = 3.77(3), b = 12.37(6), c = 13.17(3) Å. Electrical resistivity measurements along the a axis of both compounds show that they are metallic: ϱ 298 = 8.1 × 10 -5and 1.2 × 10 -4 Ω cm for NbIrTe 4 and TaIrTe 4, respectively. Magnetic susceptibility measurements indicate essentially temperature-independent Pauli paramagnetism for both compounds: χm = 1.9 × 10 -3 and 8.9 × 10 -4 emu mol -1 for NbIrTe 4 and TaIrTe 4, respectively. The compounds NbIrTe 4 and TaIrTe 4 appear to belong to a larger class of compounds MM'Te 4 with M = Nb, Ta and M' = Ru, Os, Rh, Ir.

  15. Evidence of Nb-Ta mobility in high temperature F-rich fluids evidenced by the La Bosse quartz-Nb-ferberite stockwork (Echassières, French Massif Central).

    NASA Astrophysics Data System (ADS)

    Marignac, C.; Cuney, M.

    2012-04-01

    In the Echassières district (northern French Massif Central), the 310 Ma Beauvoir granite (a P-rich peraluminous RMG) overprints a quartz-ferberite stockwork. The 900 m-deep GPF1 scientific hole shows that the stockwork is split into two parts by the gently dipping Beauvoir intrusion: the upper section (~ 100m thick) occurs in the La Bosse quarry, , and the lower section (≥ 60 m thick) below the granite floor. The root of the stockwork (hypothetic La Bosse granite) has not been reached. The stockwork comprises flat-lying quartz veins (≤ 0.6 m thick) concordant to the regional schistosity of surrounding micaschists, and steep N10-N50°E quartz veins (≤ 0.2 m thick). The two sets result from hydraulic fracturing, and consistently display crack seal features. A family of aplites and aplo-pegmatites dikes follow the same set of fractures, being either later (with partial dissolution of pre-existing quartz veins) or earlier, than the quartz veins. There is no alteration, nor associated mineral other than ferberite, at the La Bosse quarry, whereas micaceous selvages are observed in the lower section. Ferberite display a trend of ferberite enrichment with increasing depth (0.71 to 0.95 Fb mole%). In the La Bosse quarry, three ferberite habitus are present: acicular, lanceolate and prismatic. Acicular crystals are typically nicely zoned, with alternating Nb-rich (4.95±0.94 % Nb2O5) and Nb-poor (1.57±0.38 % Nb2O5) growth bands. Ta (up to 0.30 Ta2O5), Ti and Sn are also enriched in the Nb-rich bands. Nb and Ta incorporation into the ferberite is in the form of columbite, as either true solid solution or nanoinclusions. Lanceolate crystals have a similarly zoned acicular core and a Nb-poor rim (1.08±0.66 % Nb2O5). Prismatic crystals are unzoned and Nb-poor (0.67±0.20 % Nb2O5). In the lower part of the stockwork, the Nb contents are lower (2.17 % Nb2O5 in the Nb-rich bands, 1.36 % in the Nb-poor bands, 0.08 % in the unzoned cortex, 0.15 % in the unzoned prisms

  16. Structural evolution in Ni-Nb and Ni-Nb-Ta liquids and glasses - A measure of liquid fragility?

    SciTech Connect

    Mauro, N. A.; Johnson, M. L.; Bendert, J. C.; Kelton, K. F.

    2013-01-07

    The structures of Ni59.5Nb40.5, Ni62Nb38, and Ni60Nb30Ta10 liquids and glasses were studied using synchrotron high-energy X-ray diffraction. To avoid reactions between the liquids and their containers and to deeply supercool them below their equilibrium liquidus temperatures, the liquids were processed without a container using the beamline electrostatic levitation (BESL) technique. The total static structure factor, S(q), and the total pair-correlation function, g(r), were obtained for all liquid compositions over a temperature range of approximately 250 °C; S(q) and g(r) were measured for the corresponding glasses at room temperature. All of the S(q)s have a shoulder on the high-q side of the second peak; this becomes more pronounced as the liquid is supercooled, and is most prominent in the glass. Based on a Honeycutt–Andersen analysis of the atomic configurations obtained from Reverse Monte Carlo fits to the total structure factors obtained from the scattering data, icosahedral short-range order (ISRO) is dominant in all liquids and becomes particularly pronounced in the glasses. No correlation is noted, however, between the amount of ISRO and easy glass formability. Structural features show evidence for an acceleration of ordering in the supercooled liquid above the glass transition temperature, consistent with the behavior expected for fragile liquids. This suggests that scattering data can provide a new method to assess liquid fragility, which is typically obtained from the temperature behavior of the viscosity near the glass transition temperature.

  17. The structural and electronic properties of cubic AgMO3 (M=Nb, Ta) by first principles calculations

    NASA Astrophysics Data System (ADS)

    Prasad, K. Ganga; Niranjan, Manish K.; Asthana, Saket

    2016-05-01

    We report the electronic structure of the AgMO3(M=Nb, Ta) within the frame work of density functional theory and calculations are performed within the generalized gradient approximation (GGA) by using ultrasoft pseudopotentials. The calculated equilibrium lattice parameters and volumes are extracted from fitting of Birch third order equation of state and which are reasonable agreement with the available experimental results. The density of states,band structure of Ag(Nb,Ta)O3 reveals that the valance bands mostly occupied with O-2p and O-2s states and whereas conduction band occupied with Nb (Ta) 4d(5d) states including less contribution from Ag 5s states.

  18. Excellent red phosphors of double perovskite Ca{sub 2}LaMO{sub 6}:Eu (M=Sb, Nb, Ta) with distorted coordination environment

    SciTech Connect

    Yin Xin; Wang Yaoming; Huang Fuqiang; Xia Yujuan; Wan Dongyun; Yao Jiyong

    2011-12-15

    Double perovskite Ca{sub 2}LaSbO{sub 6}, successfully synthesized by solid state reaction method, was identified by Rietveld refinements to crystallize in the monoclinic space group P2{sub 1}/n, which is isostructural to Ca{sub 2}LaMO{sub 6} (M=Nb, Ta). Excellent red luminescence of Eu-doped Ca{sub 2}LaMO{sub 6} (M=Sb, Nb, Ta) can be obtained and no luminescence quenching effect was observed when Eu-doping level reached 40%. For Ca{sub 2}La{sub 0.6}NbO{sub 6}:0.4Eu{sup 3+}, quantum efficiencies of 20.9% and 27.7% were reached to show high light conversion and bright red emission excited at 465 nm (blue light) and 534 nm (green light), respectively, comparable to the commercial phosphors. Through systemic investigation for the series of double perovskite compounds, the excellent red emission in Ca{sub 2}LaMO{sub 6} is attributed to highly distorted polyhedra of EuO{sub 8} (low tolerance factor of the pervoskite), and large bond distances of La-O (low crystal field effect of the activator). - Graphical Abstract: Eu{sup 3+} doped double-perovskite compounds A{sub 2}LnMO{sub 6} (A=Ca, Sr, Ba; Ln=La, Gd, Y; M=Sb, Nb, Ta) show the dependence of luminescence intensity on the crystal structure. Highlights: Black-Right-Pointing-Pointer A series of double perovskite compounds were synthesized by solid state reaction. Black-Right-Pointing-Pointer Eu{sup 3+} doped samples display intense red emission when excited by blue or green light. Black-Right-Pointing-Pointer High quantum efficiency was obtained, comparable to the commercial phosphors. Black-Right-Pointing-Pointer Luminescence properties were ascribed to crystal distortion and large Ln-O distance.

  19. Osseointegration behavior of novel Ti-Nb-Zr-Ta-Si alloy for dental implants: an in vivo study.

    PubMed

    Wang, Xiaona; Meng, Xing; Chu, Shunli; Xiang, Xingchen; Liu, Zhenzhen; Zhao, Jinghui; Zhou, Yanmin

    2016-09-01

    This study aimed to evaluate the effects of Ti-Nb-Zr-Ta-Si alloy implants on mineral apposition rate and new BIC contact in rabbits. Twelve Ti-Nb-Zr-Ta-Si alloy implants were fabricated and placed into the right femur sites in six rabbits, and commercially pure titanium implants were used as controls in the left femur. Tetracycline and alizarin red were administered 3 weeks and 1 week before euthanization, respectively. At 4 weeks and 8 weeks after implantation, animals were euthanized, respectively. Surface characterization and implant-bone contact surface analysis were performed by using a scanning electron microscope and an energy dispersive X-ray detector. Mineral apposition rate was evaluated using a confocal laser scanning microscope. Toluidine blue staining was performed on undecalcified sections for histology and histomorphology evaluation. Scanning electron microscope and histomorphology observation revealed a direct contact between implants and bone of all groups. After a healing period of 4 weeks, Ti-Nb-Zr-Ta-Si alloy implants showed significantly higher mineral apposition rate compared to commercially pure titanium implants (P < 0.05), whereas there was no significant difference between Ti-Nb-Zr-Ta-Si alloy implants and commercially pure titanium implants (P > 0.05) at 8 weeks. No significant difference of bone-to-implant contact was observed between Ti-Nb-Zr-Ta-Si alloy implants and commercially pure titanium implants implants after a healing period of 4 weeks and 8 weeks. This study showed that Ti-Nb-Zr-Ta-Si alloy implants could establish a close direct contact comparedto commercially pure titanium implants implants, improved mineral matrix apposition rate, and may someday be an alternative as a material for dental implants. PMID:27534399

  20. Icosahedral Gold Cage Clusters: M@Au₁₂⁻ (M = V, Nb, and Ta)

    SciTech Connect

    Zhai, Hua JIN.; Li, Jun; Wang, Lai S.

    2004-11-01

    We report the observation and characterization of a series of stable bimetallic 18-valence-electron clusters containing a highly symmetric 12-atom icosahedral Au cage with an encapsulated central heteroatom of group VB transition metals, M-Au??? (M = V, Nb, Ta). Electronic and structural properties of these clusters were probed by anion photoelectron spectroscopy and theoretical calculations. Characteristics of the M-Au??? species include their remarkably high binding energies and relatively simple spectral features, which reflect their high symmetry and stability. The adiabatic electronic binding energies of M-Au??? were measured to be 3.70 ? 0.03, 3.77 ? 0.03, and 3.76 ? 0.03 eV for M = V, Nb, and Ta, respectively. Comparison of density functional calculations with experimental data established the highly symmetric icosahedral structures for the 18-electron cluster anions, which may be promising building blocks for cluster-assembled nanomaterials in the form of stoichiometric [M-Au???]X? salts.

  1. Electronic band structures of AV(2) (A = Ta, Ti, Hf and Nb) Laves phase compounds.

    PubMed

    Charifi, Z; Reshak, Ali Hussain; Baaziz, H

    2009-01-14

    First-principles density functional calculations, using the all-electron full potential linearized augmented plane wave method, have been performed in order to investigate the structural and electronic properties for Laves phase AV(2) (A = Ta, Ti, Hf and Nb) compounds. The generalized gradient approximation and the Engel-Vosko-generalized gradient approximation were used. Our calculations show that these compounds are metallic with more bands cutting the Fermi energy (E(F)) as we move from Nb to Ta, Hf and Ti, consistent with the increase in the values of the density of states at the Fermi level N(E(F)). N(E(F)) is controlled by the overlapping of V-p/d, A-d and A-p states around the Fermi energy. The ground state properties of these compounds, such as equilibrium lattice constant, are calculated and compared with the available literature. There is a strong/weak hybridization between the states, V-s states are strongly hybridized with A-s states below and above E(F). Around the Fermi energy we notice that V-p shows strong hybridization with A-p states. PMID:21813979

  2. Effect of annealing on atomic ordering of amorphous ZrTaTiNbSi alloy

    NASA Astrophysics Data System (ADS)

    Yang, Tsung-Han; Huang, Rong-Tang; Wu, Cheng-An; Chen, Fu-Rong; Gan, Jon-Yiew; Yeh, Jien-Wei; Narayan, Jagdish

    2009-12-01

    In this letter, we have reported on initial stages of atomic ordering in ZrTaTiNbSi amorphous films during annealing. The atomic ordering and structure evolution were studied in Zr17Ta16Ti19Nb22Si26 amorphous films as a function of annealing temperature in the temperature range from 473 to 1173 K. Up to annealing temperature of 1173 K, the films retained amorphous structure, but the degree of disorder is increased with the increase in temperature. The formation of Si-M covalent bonds, which contributed to the local atomic arrangement, occurred in the initial stages of ordering. The bonding reactions between Si and other metal species explain the anomalous structural changes which were observed in x-ray diffraction and transmission electron microscopy. We discuss the stages of phase transformation for amorphous films as a function of annealing temperature. From these results, we propose that annealing leads to formation of random Si-M4 tetrahedron, and two observed rings, a first and second in the electron diffraction patterns compared to M-M and Si-M bond length, respectively.

  3. Microstructure and mechanical properties of Ti-35Nb-6Ta alloy after thermomechanical treatment

    SciTech Connect

    Malek, J.; Hnilica, F.; Vesely, J.; Smola, B.; Bartakova, S.; Vanek, J.

    2012-04-15

    The influence of thermo-mechanical treatment on microstructure and mechanical properties of T-35Nb-6Ta has been studied. The thermo-mechanical treatment was chosen to correspond to the production of wire with suitable mechanical properties for dental implants. After casting the alloy was hot forged (700-900 Degree-Sign C), solution treated (850 Degree-Sign C/30 min, water quenched) and cold swaged (reductions up to 91%). The annealing (700 Degree-Sign C/3 h/furnace) or aging (450 Degree-Sign C/8 h/furnace) was used as final heat treatment. The microstructure was studied by using light microscopy, scanning electron microscopy, transmission electron microscopy and XRD analysis. Cold swaging introduces microstructure consisting of highly deformed {beta}-phase grains with dislocation tangles and twins, which ensures high tensile strength about 820 MPa, low Young's modulus ({approx} 50 GPa) and good ductility {approx} 10%. Subsequent aging increases tensile strength (1000 MPa) as well as Young's modulus (75 GPa) without diminishing ductility. Annealing at 700 Degree-Sign C slightly decreases tensile strength (730 MPa) and increases the ductility and Young's modulus (17% and 62 GPa respectively). The mechanical properties attained recommend the thermo-mechanical treatment for production of wires for dental implants. - Highlights: Black-Right-Pointing-Pointer Ti35Nb6Ta alloy prepared via arc melting. Black-Right-Pointing-Pointer Thermo mechanical treatment. Black-Right-Pointing-Pointer Microstructural changes. Black-Right-Pointing-Pointer Mechanical properties.

  4. High Nb, Ta, and Al creep- and oxidation-resistant austenitic stainless steel

    DOEpatents

    Brady, Michael P [Oak Ridge, TN; Santella, Michael L [Knoxville, TN; Yamamoto, Yukinori [Oak Ridge, TN; Liu, Chain-tsuan [Oak Ridge, TN

    2010-07-13

    An austenitic stainless steel HTUPS alloy includes, in weight percent: 15 to 30 Ni; 10 to 15 Cr; 2 to 5 Al; 0.6 to 5 total of at least one of Nb and Ta; no more than 0.3 of combined Ti+V; up to 3 Mo; up to 3 Co; up to 1 W; up to 0.5 Cu; up to 4 Mn; up to 1 Si; 0.05 to 0.15 C; up to 0.15 B; up to 0.05 P; up to 1 total of at least one of Y, La, Ce, Hf, and Zr; less than 0.05 N; and base Fe, wherein the weight percent Fe is greater than the weight percent Ni wherein said alloy forms an external continuous scale comprising alumina, nanometer scale sized particles distributed throughout the microstructure, said particles comprising at least one composition selected from the group consisting of NbC and TaC, and a stable essentially single phase fcc austenitic matrix microstructure, said austenitic matrix being essentially delta-ferrite-free and essentially BCC-phase-free.

  5. Comparison of Nb- and Ta-doping of anatase TiO2 for transparent conductor applications

    NASA Astrophysics Data System (ADS)

    Anh Huy, Huynh; Aradi, Bálint; Frauenheim, Thomas; Deák, Peter

    2012-07-01

    Nb- or Ta-doped anatase TiO2 was shown to be a viable candidate for replacing indium-tin-oxide as a transparent conductive oxide. Calculating the electronic structures we find that Ta has the considerably higher solubility and lower optical effective mass of the two dopants. Our calculations also show that a reducing atmosphere is necessary for efficient dopant incorporation, and oxygen vacancies do not necessarily play a role in their activation.

  6. Quantifying the Electron Donor and Acceptor Abilities of the Ketimide Ligands in M(N═C(t)Bu2)4 (M = V, Nb, Ta).

    PubMed

    Damon, Peter L; Liss, Cameron J; Lewis, Richard A; Morochnik, Simona; Szpunar, David E; Telser, Joshua; Hayton, Trevor W

    2015-10-19

    Addition of 4 equiv of Li(N═C(t)Bu2) to VCl3 in THF, followed by addition of 0.5 equiv of I2, generates the homoleptic V(IV) ketimide complex, V(N═C(t)Bu2)4 (1), in 42% yield. Similarly, reaction of 4 equiv of Li(N═C(t)Bu2) with NbCl4(THF)2 in THF affords the homoleptic Nb(IV) ketimide complex, Nb(N═C(t)Bu2)4 (2), in 55% yield. Seeking to extend the series to the tantalum congener, a new Ta(IV) starting material, TaCl4(TMEDA) (3), was prepared via reduction of TaCl5 with Et3SiH, followed by addition of TMEDA. Reaction of 3 with 4 equiv of Li(N═C(t)Bu2) in THF results in the isolation of a Ta(V) ketimide complex, Ta(Cl)(N═C(t)Bu2)4 (5), which can be isolated in 32% yield. Reaction of 5 with Tl(OTf) yields Ta(OTf)(N═C(t)Bu2)4 (6) in 44% yield. Subsequent reduction of 6 with Cp*2Co in toluene generates the homoleptic Ta(IV) congener Ta(N═C(t)Bu2)4 (7), although the yields are poor. All three homoleptic group 5 ketimide complexes exhibit squashed tetrahedral geometries in the solid state, as determined by X-ray crystallography. This geometry leads to a d(x(2)-y(2))(1) ((2)B1 in D(2d)) ground state, as supported by DFT calculations. EPR spectroscopic analysis of 1 and 2, performed at X- and Q-band frequencies (∼9 and 35 GHz, respectively), further supports the (2)B1 ground-state assignment, whereas comparison of 1, 2, and 7 with related group 5 tetra(aryl), tetra(amido), and tetra(alkoxo) complexes shows a higher M-L covalency in the ketimide-metal interaction. In addition, a ligand field analysis of 1 and 2 demonstrates that the ketimide ligand is both a strong π-donor and strong π-acceptor, an unusual combination found in very few organometallic ligands. PMID:26419513

  7. Quantifying the electron donor and acceptor ability of the ketimide ligands in M(N=CtBu2)4 (M = V, Nb, Ta)

    PubMed Central

    Damon, Peter L.; Liss, Cameron J.; Lewis, Richard A.; Morochnik, Simona; Szpunar, David E.; Telser, Joshua; Hayton, Trevor W.

    2015-01-01

    Addition of 4 equiv of Li(N=CtBu2) to VCl3 in THF, followed by addition of 0.5 equiv I2, generates the homoleptic V(IV) ketimide complex, V(N=CtBu2)4 (1), in 42% yield. Similarly, reaction of 4 equiv of Li(N=CtBu2) with NbCl4(THF)2 in THF affords the homoleptic Nb(IV) ketimide complex, Nb(N=CtBu2)4 (2), in 55% yield. Seeking to extend the series to the tantalum congener, a new Ta(IV) starting material, TaCl4(TMEDA) (3), was prepared via reduction of TaCl5 with Et3SiH, followed by addition of TMEDA. Reaction of 3 with 4 equiv of Li(N=CtBu2) in THF results in a isolation of a Ta(V) ketimide complex, Ta(Cl)(N=CtBu2)4 (5), which can be isolated in 32% yield. Reaction of 5 with Tl(OTf) yields Ta(OTf)(N=CtBu2)4 (6) in 44% yield. Subsequent reduction of 6 with Cp*2Co in toluene generates the homoleptic Ta(IV) congener Ta(N=CtBu2)4 (7), although the yields are poor. All three homoleptic Group 5 ketimide complexes exhibit squashed tetrahedral geometries in the solid state, as determined by X-ray crystallography. This geometry leads to a dx2−y21 (2B1 in D2d) ground state, as supported by DFT calculations. EPR spectroscopic analysis of 1 and 2, performed at X- and Q-band frequencies (~9 and 35 GHz, respectively), further supports the 2B1 ground state assignment, while comparison of 1, 2, and 7 with related Group 5 tetra(aryl), tetra(amido) and tetra(alkoxo) complexes shows a higher M-L covalency in the ketimide-metal interaction. In addition, a ligand field analysis of 1 and 2 demonstrates that the ketimide ligand is both a strong π-donor and strong π-acceptor, an unusual combination found in very few organometallic ligands. PMID:26419513

  8. Photocatalytic removal of organic pollutants in aqueous solution by Bi(4)Nb(x)Ta((1-x))O(8)I.

    PubMed

    Hu, Xing-Yun; Fan, Jing; Zhang, Ke-Lei; Wang, Jian-Ji

    2012-06-01

    In this work, Bi(4)Nb(x)Ta((1-x))O(8)I photocatalysts have been synthesized by solid state reaction method and characterized by powder X-ray diffraction, scanning electron microscope and UV-Vis near infrared diffuse reflectance spectroscopy. The photocatalytic activity of these photocatalysts was evaluated by the degradation of methyl orange (MO) in aqueous solutions under visible light, UV light and solar irradiation. The effects of catalyst dosage, initial pH and MO concentration on the removal efficiency were studied, and the photocatalytic reaction kinetics of MO degradation as well. The results indicated that Bi(4)Nb(x)Ta((1-x))O(8)I exhibited high photocatalytic activity for the removal of MO in aqueous solutions. For example, the removal efficiency of MO by Bi(4)Nb(0.1)Ta(0.9)O(8)I was as high as 92% within 12 h visible light irradiation under the optimal conditions: initial MO concentration of 5-10 mg L(-1), catalyst dosage of 6 g L(-1) and natural pH (6-8), the MO molecules could be completely degradated by Bi(4)Nb(0.1)Ta(0.9)O(8)I within 40 min under UV light irradiation, and the photodegradation efficiency reaches to 60% after 7 h solar irradiation. Furthermore, the photocatalytic degradation of Bisphenol A (BPA) was also investigated under visible light irradiation. It is found that 99% BPA could be mineralized by Bi(4)Nb(0.1)Ta(0.9)O(8)I after 16 h visible light irradiation. Through HPLC/MS, BOD, TOC, UV-Vis measurements, we determined possible degradation products of MO and BPA. The results indicated that MO was degradated into products which are easier to be biodegradable and innocuous treated, and BPA could be mineralized completely. Furthermore, the possibility for the photosensitization effect in the degradation process of MO under visible light irradiation has been excluded. PMID:22386458

  9. Extraction of the fluoride-, chloride-, and bromide complexes of the elements Nb, Ta, Pa, and 105 into aliphatic amines

    NASA Astrophysics Data System (ADS)

    Paulus, W.; Kratz, J. V.; Strub, E.; Zauner, S.; Brüchle, W.; Pershina, V.; Schädel, M.; Schausten, B.; Adams, J. L.; Gregorich, K. E.; Hoffman, D. C.; Laue, C.; Lee, D. M.; McGrath, C. A.; Shaughnessy, D. K.; Strellis, D. A.; Sylwester, E. R.

    1999-01-01

    Previous studies of the halide complex formation of element 105 in HCl/HF mixtures and extractions into triisooctyl amine (TIOA) had been performed with the Automated Rapid Chemistry Apparatus, ARCA II. Element 105 was shown to be sorbed on the column from 12 M HCl/0.02 M HF together with its lighter homologues Nb, Ta and the pseudohomologue Pa. In elutions with 10 M HCl/0.025 M HF, 4 M HCl/0.02 M HF, and 0.5 M HCl/0.01 M HF, the extraction sequence Ta>Nb>105>Pa was observed and element 105 behaved very differently from its closest homologue Ta. As it is not possible within reasonable effort to model the many presumably mixed fluoride-chloride complexes involved in these studies, theoretical calculations were performed in the pure chloride system predicting a reversed sequence of extraction. To verify this experimentally, and in order to perform a systematic study of halide complexation of the group 5 elements, new batch extraction experiments for Nb, Ta, and Pa were performed with the quaternary ammonium salt Aliquat 336 in pure HF, HCl, and HBr solutions. Based on these results, new chromatographic column separations were elaborated to study separately the fluoride and chloride complexation of element 105 with ARCA II. In the system Aliquat 336/HF, after feeding of the activity onto the column in 0.5 M HF, element 105 did not elute in 4 M HF (Pa fraction) but showed a higher distribution coefficient close to that of Nb (and Ta). In the system Aliquat 336/HCl, after feeding onto the column in 10 M HCl, element 105 showed a distribution coefficient in 6 M HCl close to that of Nb establishing an extraction sequence Pa>Nb≥105>Ta which is theoretically predicted by considering the competition between hydrolysis and complex formation.

  10. Nb-Ta-Ti oxides fractionation in rare-metal granites: Krásno-Horní Slavkov ore district, Czech Republic

    NASA Astrophysics Data System (ADS)

    René, Miloš; Škoda, Radek

    2011-11-01

    Nb-Ta-Ti-bearing oxide minerals (Nb-Ta-bearing rutile, columbite-group minerals) represent the most common Nb-Ta host in topaz-albite granites and related rocks from the Krásno-Horní Slavkov ore district. Tungsten-bearing columbite-(Fe), W-bearing ixiolite, wodginite and tapiolite-(Fe) are extremely rare in these rocks. Rutile contains significant levels of Ta (up to 37 wt.% Ta2O5) and Nb (up to 24 wt.% Nb2O5), with Ta/(Ta + Nb) ratio ranging from 0.04 to 0.61. Columbite-group minerals are represented mostly by columbite-(Fe) and rarely by columbite-(Mn), with Mn/(Mn + Fe) ratio ranging from 0.23 to 0.94. The exceptionally rare Fe-rich, W-bearing ixiolite occurs only as inclusions in Nb-Ta-bearing rutile from quartz-free alkali-feldspar syenites (Vysoký Kámen stock). Wodginite was found only in the topaz-albite microgranite of gneissic breccia matrix that occurs in the upper most part of the Hub topaz-albite granite stock. In wodginite, the Mn/(Mn + Fe) ratio is 0.42-0.51, whereas the coexisting tapiolite-(Fe) has a distinctly lower Mn/(Mn + Fe) ratio close to 0.06.

  11. On the Structural and Luminescent Properties of the ScTa(1-x)Nb(x)O(4) System.

    ERIC Educational Resources Information Center

    Brixner, L. H.

    1980-01-01

    Diagrams and tables supplement textual information regarding the structure of ScNbo-4 and its observed and calculated d-values; excitation and emission spectra and cell constants for the ScTa(1-x)NB(x)O(4) system. (CS)

  12. A study on nuclear properties of Zr, Nb, and Ta nuclei used as structural material in fusion reactor

    NASA Astrophysics Data System (ADS)

    Sahan, Halide; Tel, Eyyup; Sahan, Muhittin; Aydin, Abdullah; Hakki Sarpun, Ismail; Kara, Ayhan; Doner, Mesut

    2015-07-01

    Fusion has a practically limitless fuel supply and is attractive as an energy source. The main goal of fusion research is to construct and operate an energy generating system. Fusion researches also contains fusion structural materials used fusion reactors. Material issues are very important for development of fusion reactors. Therefore, a wide range of fusion structural materials have been considered for fusion energy applications. Zirconium (Zr), Niobium (Nb) and Tantalum (Ta) containing alloys are important structural materials for fusion reactors and many other fields. Naturally Zr includes the 90Zr (%51.5), 91Zr (%11.2), 92Zr (%17.1), 94Zr (%17.4), 96Zr (%2.80) isotopes and 93Nb and 181Ta include the 93Nb (%100) and 181Ta (%99.98), respectively. In this study, the charge, mass, proton and neutron densities and the root-mean-square (rms) charge radii, rms nuclear mass radii, rms nuclear proton, and neutron radii have been calculated for 87-102Zr, 93Nb, 181Ta target nuclei isotopes by using the Hartree-Fock method with an effective Skyrme force with SKM*. The calculated results have been compared with those of the compiled experimental taken from Atomic Data and Nuclear Data Tables and theoretical values of other studies.

  13. On yield loci of HY80, HY100 steels and Ti-6Al-2Nb-1Ta-0. 8Mo

    SciTech Connect

    Chan, K.S.; Lindholm, U.S.; Wise, J.

    1984-11-01

    This paper extends other findings by examining the biaxial yield behavior of Ti-6A1-1Nb-1Ta-0.8Mo and HY 100 steel. The results of the study are compared with previous findings of HY80 steel to assess the effect of crystallography on the shape of the yield surface.

  14. Discovery of Weyl fermion semimetal and topological Fermi arc quasiparticles in TaAs, NbAs, NbP, TaP and related materials

    NASA Astrophysics Data System (ADS)

    Hasan, M. Zahid

    Topological matter can host Dirac, Majorana and Weyl fermions as quasiparticle modes on their boundaries. First, I briefly mention the basic theoretical concepts defining insulators and superconductors where topological surface state modes are robust only in the presence of a gap (Hasan & Kane; Rev. of Mod. Phys. 82, 3045 (2010)). In these systems topological protection is lost once the gap is closed turning the system into a trivial metal. A Weyl semimetal is the rare exception in this scheme which is a topologically robust metal (semimetal) whose low energy emergent excitations are Weyl fermions. In a Weyl fermion semimetal, the chiralities associated with the Weyl nodes can be understood as topological charges, leading to split monopoles and anti-monopoles of Berry curvature in momentum space. This gives a measure of the topological strength of the system. Due to this topology a Weyl semimetal is expected to exhibit 2D Fermi arc quasiparticles on its surface (Wan et.al., 2011). These arcs (``fractional'' Fermi surfaces) are discontinuous or disjoint segments of a two dimensional Fermi contour, which are terminated onto the projections of the Weyl fermion nodes on the surface we have observed experimentally in TaAs, NbAs, NbP class of materials (Xu, Belopolski et.al., Science 349, 613 (2015); Xu, Alidoust et.al., Nature Phys. (2015); Xu, Belopolski et.al., Science Adv. (2015), Belopolski, Xu et.al., arXiv (2015)) following our theoretical predictions (Huang, Xu, Belopolski et.al., Nature Commun. 6:7373 (2015), submitted in November 2014). Our theoretical predictions (Nature Commun. 2015) and experimental demonstrations (Science 2015, Nature Physics 2015, Science Advances 2015) reveal that these Fermi arc quasiparticles can only live on the boundary of a 3D crystal which collectively represents the realization of a new state of quantum matter beyond our earlier work on Fermi arcs in topological materials (Xu, Liu, Kushwaha et.al., Science 347, 294 (2015), adv

  15. Hemispherical emissivity of V, Nb, Ta, Mo, and W from 300 to 1000 K

    NASA Technical Reports Server (NTRS)

    Cheng, S. X.; Hanssen, L. M.; Riffe, D. M.; Sievers, A. J.; Cebe, P.

    1987-01-01

    The hemispherical emissivities of five transition elements, V, Nb, Ta, Mo, and W, have been measured from 300 to 1000 K, complementing earlier higher-temperature results. These low-temperature data, which are similar, are fitted to a Drude model in which the room-temperature parameters have been obtained from optical measurements and the temperature dependence of the dc resistivity is used as input to calculate the temperature dependence of the emissivity. A frequency-dependent free-carrier relaxation rate is found to have a similar magnitude for all these elements. For temperatures larger than 1200 K the calculated emissivity is always greater than the measured value, indicating that the high-temperature interband features of transition elements are much weaker than those determined from room-temperature measurements.

  16. High corrosion resistant Ti-5%Ta-1.8%Nb alloy for fuel reprocessing application

    NASA Astrophysics Data System (ADS)

    Kapoor, K.; Kain, Vivekanand; Gopalkrishna, T.; Sanyal, T.; De, P. K.

    2003-10-01

    The conventional low carbon austenitic stainless steels display good corrosion resistance behaviour in nitric acid media. However, they are sensitive to intergranular corrosion in boiling nitric acid media in the presence of oxidizing ions like hexavalent chromium, tetravalent iron and hexavalent plutonium. The Ti-5%Ta-1.8%Nb alloy was evaluated as a candidate material for such applications of nuclear fuel reprocessing. Extensive tests were carried out to establish the superior corrosion properties in comparison to the conventional stainless steel or nitric acid grade stainless steel. The fabricability of this new alloy to various shapes like rod, sheet, wire and its weldability, which is required for making vessels, was found to be good.

  17. The origin of hyper-ferroelectricity in Li BO3 (B=V, Nb, Ta, Os)

    NASA Astrophysics Data System (ADS)

    He, Lixin; Li, Pengfei; Ren, Xinguo; Guo, G.-C.

    The electronic and structural properties of Li BO3 (B=V, Nb, Ta, Os) are investigated via first-principles methods. We show that Li BO3 are belong to the recently proposed hyperferroelectrics, i.e., they all have unstable longitudinal optical phonon modes. Especially, the ferroelectric-like instability in the metal LiOsO3 is a limiting case of a hyperferroelectrics, whose optical dielectric constant goes to infinity. We further show via an effective Hamiltonian that in contrast to normal proper ferroelectricity, in which the ferroelectric instability usually comes from long range coulomb interactions, the hyperferroelectric instability is due to the structure instability driven by the short range interactions. This could happen in systems with large ion size mismatches, which therefore provides a useful guidance in searching for novel hyperferroelectrics.

  18. Study on ( n,t) Reactions of Zr, Nb and Ta Nuclei

    NASA Astrophysics Data System (ADS)

    Tel, E.; Yiğit, M.; Tanır, G.

    2012-04-01

    The world faces serious energy shortages in the near future. To meet the world energy demand, the nuclear fusion with safety, environmentally acceptability and economic is the best suited. Fusion is attractive as an energy source because of the virtually inexhaustible supply of fuel, the promise of minimal adverse environmental impact, and its inherent safety. Fusion will not produce CO2 or SO2 and thus will not contribute to global warming or acid rain. Furthermore, there are not radioactive nuclear waste problems in the fusion reactors. Although there have been significant research and development studies on the inertial and magnetic fusion reactor technology, there is still a long way to go to penetrate commercial fusion reactors to the energy market. Because, tritium self-sufficiency must be maintained for a commercial power plant. For self-sustaining (D-T) fusion driver tritium breeding ratio should be greater than 1.05. And also, the success of fusion power system is dependent on performance of the first wall, blanket or divertor systems. So, the performance of structural materials for fusion power systems, understanding nuclear properties systematic and working out of ( n,t) reaction cross sections are very important. Zirconium (Zr), Niobium (Nb) and Tantal (Ta) containing alloys are important structural materials for fusion reactors, accelerator-driven systems, and many other fields. In this study, ( n,t) reactions for some structural fusion materials such as 88,90,92,94,96Zr, 93,94,95Nb and 179,181Ta have been investigated. The calculated results are discussed andcompared with the experimental data taken from the literature.

  19. Pyrochlore formation, phase relations, and properties in the CaO-TiO{sub 2}-(Nb,Ta){sub 2}O{sub 5} systems

    SciTech Connect

    Roth, R.S.; Vanderah, T.A. Bordet, P.; Grey, I.E.; Mumme, W.G.; Cai, L.; Nino, J.C.

    2008-03-15

    Phase equilibria studies of the CaO:TiO{sub 2}:Nb{sub 2}O{sub 5} system confirmed the formation of six ternary phases: pyrochlore (A{sub 2}B{sub 2}O{sub 6}O'), and five members of the (110) perovskite-slab series Ca{sub n}(Ti,Nb){sub n}O{sub 3n+2}, with n=4.5, 5, 6, 7, and 8. Relations in the quasibinary Ca{sub 2}Nb{sub 2}O{sub 7}-CaTiO{sub 3} system, which contains the Ca{sub n}(Ti,Nb){sub n}O{sub 3n+2} phases, were determined in detail. CaTiO{sub 3} forms solid solutions with Ca{sub 2}Nb{sub 2}O{sub 7} as well as CaNb{sub 2}O{sub 6}, resulting in a triangular single-phase perovskite region with corners CaTiO{sub 3}-70Ca{sub 2}Ti{sub 2}O{sub 6}:30Ca{sub 2}Nb{sub 2}O{sub 7}-80CaTiO{sub 3}:20CaNb{sub 2}O{sub 6}. A pyrochlore solid solution forms approximately along a line from 42.7:42.7:14.6 to 42.2:40.8:17.0 CaO:TiO{sub 2}:Nb{sub 2}O{sub 5}, suggesting formulas ranging from Ca{sub 1.48}Ti{sub 1.48}Nb{sub 1.02}O{sub 7} to Ca{sub 1.41}Ti{sub 1.37}Nb{sub 1.14}O{sub 7} (assuming filled oxygen sites), respectively. Several compositions in the CaO:TiO{sub 2}:Ta{sub 2}O{sub 5} system were equilibrated to check its similarity to the niobia system in the pyrochlore region, which was confirmed. Structural refinements of the pyrochlores Ca{sub 1.46}Ti{sub 1.38}Nb{sub 1.11}O{sub 7} and Ca{sub 1.51}Ti{sub 1.32}V{sub 0.04}Ta{sub 1.10}O{sub 7} using single-crystal X-ray diffraction data are reported (Fd3m (no. 227), a=10.2301(2) A (Nb), a=10.2383(2) A (Ta)), with Ti mixing on the A-type Ca sites as well as the octahedral B-type sites. Identical displacive disorder was found for the niobate and tantalate pyrochlores: Ca occupies the ideal 16d position, but Ti is displaced 0.7 A to partially occupy a ring of six 96g sites, thereby reducing its coordination number from eight to five (distorted trigonal bipyramidal). The O' oxygens in both pyrochlores were displaced 0.48 A from the ideal 8b position to a tetrahedral cluster of 32e sites. The refinement results also suggested that

  20. Lattice dynamics and low-frequency excitations of transition-metal hydrides: NbDx, NbHx, and TaDx

    NASA Astrophysics Data System (ADS)

    Shapiro, S. M.; Richter, D.; Noda, Y.; Birnbaum, H.

    1981-02-01

    Phonon dispersion curves have been measured on single crystals of NbD0.85 along the [100], [011], and [111] directions. The dispersion curves of the α' phase of NbD0.85 at T=160°C were fit with a Born-von Kármán model of the interatomic force constants out to the seventh neighbors. From these constants the acoustic-phonon density of states is calculated. The results are compared with previous measurements on NbDx with x=0.45, x=0, and with the Nb-Mo system. A new dispersionless excitation is observed in NbD0.85 at ℏω=18.4 meV. A similar feature is observed in NbH0.82 at ℏω=19.0 meV and in TaD0.78 at ℏω=15.0 meV. The linewidth of this excitation in NbD0.85 decreases as the β phase is entered and its position shifts slightly to higher energies. A detailed examination of the dispersion curves within the β phase reveals interaction between the acoustic modes and this dispersionless excitation. Possible origins of this new feature are discussed. Also observed is an anomalous broadening of the [110] zone-boundary LA phonon with the α' phase.

  1. Lattice dynamics and low-frequency excitations of transition-metal hydrides:NbD/sub x/, NbH/sub x/, and TaD/sub x/

    SciTech Connect

    Shapiro, S.M.; Richter, D.; Noda, Y.; Birnbaum, H.

    1981-02-15

    Phonon dispersion curves have been measured on single crystals of NbD/sub 0.85/ along the (100), (011), and (111) directions. The dispersion curves of the ..cap alpha..' phase of NbD/sub 0.85/ at T=160 /sup 0/C were fit with a Born--von Karman model of the interatomic force constants out to the seventh neighbors. From these constants the acoustic-phonon density of states is calculated. The results are compared with previous measurements on NbD/sub x/ with x=0.45, x=0, and with the Nb-Mo system. A new dispersionless excitation is observed in NbD/sub 0.85/ at h..omega..=18.4 meV. A similar feature is observed in NbH/sub 0.82/ at h..omega..=19.0 meV and in TaD/sub 0.78/ at h..omega..=15.0 meV. The linewidth of this excitation in NbD/sub 0.85/ decreases as the ..beta.. phase is entered and its position shifts slightly to higher energies. A detailed examination of the dispersion curves within the ..beta.. phase reveals interaction between the acoustic modes and this dispersionless excitation. Possible origins of this new feature are discussed. Also observed is an anomalous broadening of the (110) zone-boundary LA phonon within the ..cap alpha..' phase.

  2. Fractionation of the geochemical twins Zr-Hf and Nb-Ta during scavenging from seawater by hydrogenetic ferromanganese crusts

    NASA Astrophysics Data System (ADS)

    Schmidt, Katja; Bau, Michael; Hein, James R.; Koschinsky, Andrea

    2014-09-01

    In contrast to igneous systems, the geochemical twins Zr and Hf are decoupled from each other in seawater, and specific Zr/Hf ratios appear to be characteristic of individual marine water masses. Hydrogenetic marine ferromanganese (Fe-Mn) crusts which accumulate trace metals from seawater may be an archive of Zr/Hf ratios that reveal changes in oceanic paleocirculation over millions of years. To verify whether Fe-Mn crusts truly reflect the Zr-Hf distribution in seawater, we studied these particle-reactive elements together with Nb and Ta (another geochemical twin pair) in bulk Fe-Mn crusts and their surface layers from different locations in the Atlantic and Pacific oceans. Zirconium (400-1000 mg kg-1), Hf (5-18 mg kg-1), Nb (42-83 mg kg-1) and Ta (0.5-1.5 mg kg-1) are significantly enriched in Fe-Mn crusts relative to the average continental crust, and their Zr/Hf and Nb/Ta ratios are super-chondritic (57-87 and 35-96, respectively), whereas the continental crust shows ratios close to those of chondrites. We emphasize that neither bulk Fe-Mn crusts nor their surface layers match the Zr/Hf or Nb/Ta ratios of modern deep seawater, but are lower and higher, respectively. The presence of aluminosilicate detritus cannot explain the different Zr/Hf ratios of crusts and ambient seawater, as potential detritus has much lower Zr and Hf concentrations. Consequently, these geochemical twins must be fractionated during their removal from seawater and their incorporation into Fe-Mn (oxyhydr)oxides. Hafnium is preferentially scavenged as shown by Zr/Hf ratios of crust surface layers (75-100) that are always below those of modern deep seawater (150-300). The decoupled behavior of geochemical twins during sorption, which is also observed for Nb-Ta, can be related to differences in the electron structures of these elements. Iron-normalized concentrations of Zr, Hf, Nb, and Ta increase with increasing size of the positive Ce anomaly (known to increase with decreasing growth rate

  3. Investigation of the structure stability and superelastic behavior of thermomechanically treated Ti-Nb-Zr and Ti-Nb-Ta shape-memory alloys

    NASA Astrophysics Data System (ADS)

    Sheremetyev, V. A.; Prokoshkin, S. D.; Brailovski, V.; Dubinskiy, S. M.; Korotitskiy, A. V.; Filonov, M. R.; Petrzhik, M. I.

    2015-04-01

    The superelastic parameters of Ti-Nb-Ta and Ti-Nb-Zr alloys, such as Young's modulus, residual strain, and transformation yield stress after thermomechanical treatment (TMT), were determined during cyclic mechanical tests using the tension-unloading scheme (maximum strain 2% per cycle, ten cycles). The superelastic parameters and the alloy structure have been studied by electron microscopy and X-ray diffraction analysis before and after testing and after holding for 40 days, as well as after retesting. The Young's modulus of the Ti-Nb-Ta alloy decreases from 30-40 to 20-25 GPa during mechanocycling after TMT by different modes; however, it returns to its original magnitude during subsequent holding for 40 days, and changes only a little during repeated mechanocycling. The Young's modulus of the Ti-Nb-Zr alloy changes insignificantly during mechanocycling, recovers during holding, and behaves stably upon repeated mechanocycling. Surface tensile stresses arise during mechanocycling, which facilitate the development of martensitic transformation under load, orient it, and thereby promote a decrease in the transformation yield stress and the residual strain. The enhancement of the level of initial strengthening stabilizes the superelastic behavior during mechanocycling.

  4. Residual stresses and clamped thermal expansion in LiNbO3 and LiTaO3 thin films

    NASA Astrophysics Data System (ADS)

    Bartasyte, A.; Plausinaitiene, V.; Abrutis, A.; Murauskas, T.; Boulet, P.; Margueron, S.; Gleize, J.; Robert, S.; Kubilius, V.; Saltyte, Z.

    2012-09-01

    Residual stresses in LiNbO3 and LiTaO3 epitaxial thin films were evaluated taking into account Li nonstoichiometry by means of Raman spectroscopy and x-ray diffraction. The epitaxial films were grown on C-cut sapphire substrates by pulsed injection metal organic chemical vapour deposition. Clamping of the epitaxial films by the substrate induced a transfer from the in plane thermal expansion to the out of plane component. The temperature of the phase transition of clamped LiTaO3 films was close to that expected for a bulk sample.

  5. Calibration graphs for Ti, Ta and Nb in sintered tungsten carbide by infrared laser ablation inductively coupled plasma atomic emission spectrometry.

    PubMed

    Kanický, V; Otruba, V; Mermet, J M

    2001-12-01

    Infrared laser ablation (IR-LA) has been studied as a sample introduction technique for the analysis of sintered cobalt-cemented tungsten carbide materials by inductively coupled plasma atomic emission spectrometry (ICP-AES). Fractionation of cobalt was observed. Linearity of calibration plots was verified at least up to 15% Ti, 8% Ta, and 3% Nb. Above 1% (m/m) Ti, Ta, and Nb, the repeatability of results was better than 3% R.S.D. The relative uncertainty at the centroid of the calibration line was in the range from +/- 3% to +/- 4% for Ti, Ta, and Nb with internal standardization by tungsten and up to +/- 5% without internal standardization. The limits of detection were 0.004% Ti, 0.001% Ta, and 0.004% Nb. Elimination of the cemented hardmetal dissolution procedure is the main advantage of this method. PMID:11769803

  6. Diffusion control of an ion by another in LiNbO3 and LiTaO3 crystals

    PubMed Central

    Zhang, De-Long; Zhang, Qun; Qiu, Cong-Xian; Wong, Wing-Han; Yu, Dao-Yin; Yue-Bun Pun, Edwin

    2015-01-01

    Diffusion-doping is an effective, practical method to improve material properties and widen material application. Here, we demonstrate a new physical phenomenon: diffusion control of an ion by another in LiNbO3 and LiTaO3 crystals. We exemplify Ti4+/Xn+ (Xn+ = Sc3+, Zr4+, Er3+) co-diffusion in the widely studied LiNbO3 and LiTaO3 crystals. Some Ti4+/Xn+-co-doped LiNbO3 and LiTaO3 plates were prepared by co-diffusion of stacked Ti-metal and Er-metal (Sc2O3 or ZrO2) films coated onto LiNbO3 or LiTaO3 substrates. The Ti4+/Xn+-co-diffusion characteristics were studied by secondary ion mass spectrometry. In the Xn+-only diffusion case, the Xn+ diffuses considerably slower than the Ti4+. In the Ti4+/Xn+ co-diffusion case, the faster Ti4+ controls the diffusion of the slower Xn+. The Xn+ diffusivity increases linearly with the initial Ti-metal thickness and the increase depends on the Xn+ species. The phenomenon is ascribed to the generation of additional defects induced by the diffusion of faster Ti4+ ions, which favors and assists the subsequent diffusion of slower Xn+ ion. For the diffusion system studied here, it can be utilized to substantially shorten device fabrication period, improve device performance and produce new materials. PMID:25941037

  7. Dielectric and piezoelectric properties in the lead-free system Na0.5K0.5NbO3-BiScO3-LiTaO3.

    PubMed

    Zhu, Fangyuan; Ward, Michael B; Comyn, Tim P; Bell, Andrew J; Milne, Steven J

    2011-09-01

    Phase relations, dielectric and piezoelectric properties are reported for the ternary system 98%[(1 - x) (Na(0.5)K(0.5)NbO(3))-x(LiTaO(3))]-2%[BiScO(3)] for compositions x ≤ 10 mol% LiTaO(3). The phase content at room-temperature changed from mixed phase, monoclinic + tetragonal, for unmodified 98%(Na(0.5)K(0.5)NbO(3))-2%(BiScO(3)), to tetragonal phase for compositions >2 mol% LiTaO(3). Curie peaks at 360 to 370°C were observed for all compositions, but peaks became diffuse at x ≥ 3 mol%, and two dielectric peaks, at 370 and 470°C, were observed for 5 mol% LiTaO(3). Phase segregation, and finite size affects associated with the core-shell structure, account for the occurrence of two dielectric peaks in 5 mol% LiTaO(3), and diffuse dielectric behavior. The value of d(33) piezoelectric charge coefficient increased from ~160 pC/N for 0 mol% LiTaO(3) to 205 to 214 pC/N for 1 to 2 mol% LiTaO3 solid solutions, before falling sharply at 3 mol% LiTaO(3). TEM-EDX analysis revealed core-shell grain structures with segregation of Bi, Sc, and Ta in the outer ~100-nm shell of the 5 mol% LT sample. PMID:21937312

  8. Morphology of nanotube arrays grown on Ti-35Nb-2Ta-3Zr alloys with different deformations

    NASA Astrophysics Data System (ADS)

    Wang, Pei; Li, Hua; Zhang, Yangyang; Liu, Hezhou; Guo, Yiping; Liu, Zhongtang; Zhao, Shichang; Yin, Jimin; Guo, Yanjie

    2014-01-01

    Nanotubes on Ti-35Nb-2Ta-3Zr alloy with different degrees of deformations in thickness were fabricated by anodization method. The effect of deformations on the morphology, crystal phase and grain size of nanotubes was investigated. Nanotube arrays with uniform diameter were achieved by using ethylene glycol (EG)/NH4F organic electrolyte, indicating the electrolyte composition will influence the arrangement of TiO2 nanotube arrays. With the increasing degree of deformation, the corrosion potential Ecorr of the alloys had a positive displacement, which suggested an enhanced anticorrosion ability and resulted in nanotubes with smaller diameter. After heat treatment, anatase TiO2 was obtained. Due to the existence of lattice distortion, the grain size of TiO2 nanotubes prepared by Ti-35Nb-2Ta-3Zr alloy with deformations was smaller than that of with no deformation. However, when the reductions of alloy increased, there was a tendency to make the grain size larger, which was probably caused by the restriction of the wall thickness of nanotubes. The study about the nanotubes formed on Ti-35Nb-2Ta-3Zr alloy with different deformations provides a basis for its application on the drug-loading by Ti alloy prosthesis artificial joint.

  9. Characterization of the Ti-10Nb-10Zr-5Ta Alloy for Biomedical Applications. Part 2: Wettability, Tribological Performance and Biocompatibility

    NASA Astrophysics Data System (ADS)

    Braic, V.; Balaceanu, M.; Braic, M.; Vitelaru, C.; Titorencu, I.; Pruna, V.; Parau, A. C.; Fanara, C.; Vladescu, A.

    2014-01-01

    The Ti-10Nb-10Zr-5Ta alloy, prepared in a levitation melting furnace, was investigated as a possible candidate for replacing Ti6Al4V alloy in medical applications. The sessile drop method, pin-on-disc and in vitro tests were used to analyze wettability, wear resistance, and biocompatibility of the new alloy. The characteristics of the Ti-10Nb-10Zr-5Ta alloy were assessed in comparison to those of the Ti6Al4V alloy. The Ti-10Nb-10Zr-5Ta system was found to have hydrophilic characteristics with similar contact angle as the Ti6Al4V alloy. In all environments (deionized water, simulated body fluid and Fusayama Meyer artificial saliva), the friction coefficient showed a stable evolution versus sliding distance, being similar for both alloys. On overall, the wear resistance of Ti-10Nb-10Zr-5Ta alloy was lower than that of Ti6Al4V for all testing environments. The Ti-10Nb-10Zr-5Ta alloy exhibited good biocompatibility characteristics at in vitro test compared to Ti6Al4V alloy. The cell viability on Ti-10Nb-10Zr-5Ta surfaces was higher than the one observed on Ti6Al4V samples, regardless the number of days spent in osteoblast-like cells culture. A high degree of cell attachment and spreading was observed on both alloys.

  10. Mechanism of the ferroelectric phase transitions in LiNbO3 and LiTaO3

    NASA Astrophysics Data System (ADS)

    Ohkubo, Y.; Murakami, Y.; Saito, T.; Yokoyama, A.; Uehara, S.; Kawase, Y.

    2002-02-01

    The temperature dependences of the nuclear-electric-quadrupole frequency ωQ of 117In doped in LiTaO3 (TC=938 K) and Li1-xInx/3TaO3 with x=0.2 (TC=818 K) show that the order-disorder of the Li ions is not the driving mechanism for the ferroelectric instability in LiNbO3 and LiTaO3 systems, and imply that the oxygen order-disorder is the driving mechanism. The significantly different temperature dependences of ωQ of 111Cd in these materials compared, to those of 117In, demonstrate that this order-disorder is of dynamic character.

  11. Electrochemical and spectroscopic studies of the chloro and oxochloro complex formation of Nb(V) and Ta(V) in NaCl-AlCl3 melts.

    PubMed

    von Barner, J H; Bjerrum, N J

    2005-12-26

    The equilibrium constant for the chloro complex formation of Nb(V) NbCl6-<--->NbCl5+Cl- (i) in NaCl-AlCl3 melts at 175 degrees C was found to be pKi = 2.86(5). The oxochloro complex formation of Nb(V) and Ta(V) in NaCl-AlCl3 melts at 175 degrees C could be explained by the following equilibria: MOCl4- <-->MOCl3+Cl- (ii) MOCl3<-->MOCl2(+)+Cl- (iii) where M = Nb and Ta. The equilibrium constants determined by potentiometric measurements with chlorine-chloride electrodes were, for M = Nb, pKii = 2.21(4) and pKiii = 3.95(5) and, for M = Ta, pKii = 2.743(15) and pKiii = 4.521(13). NbCl6- has two bands in the UV-vis region, a strong one at 34.7 x 10(3) cm-1 and a weaker one at 41.6 x 10(3) cm-1. The MOCl4- complexes showed in the case of Nb(V) absorption bands at 32.7 and 42.9 x 10(3) cm-1 and in the case of Ta(V) at 38.6 and 48.1 x 10(3) cm-1. PMID:16363855

  12. The luminescence of trigonal bipyramidal NbO/sup 5 -//sub 5/ and TaO/sup 5 -//sub 5/ and a comparison with other niobates and tantalates

    SciTech Connect

    Blasse, G.; Lammers, J.J.; Torardi, C.C.; Verhaar, M.C.G.

    1985-11-15

    The luminescence of La/sub 3/NbO/sub 4/Cl/sub 6/ with trigonal bipyramidal NbO/sup 5 -//sub 5/ groups is reported. The Nb/sup 5 +/ coordination does not seem to influence the niobate emission. The luminescence and Raman spectrum of La/sub 3/TaO/sub 4/Cl/sub 6/ are also reported. Finally, differences in luminescence of the M and M' modifications of YTaO/sub 4/ are discussed.

  13. Constraints on Lu-Hf and Nb-Ta systematics in globally subducted oceanic crust from a survey of orogenic eclogites and amphibolites

    NASA Astrophysics Data System (ADS)

    Zirakparvar, N. Alex

    2016-04-01

    To further understand Lu-Hf and Nb-Ta systematics in globally subducted oceanic crust, this paper evaluates all available Lu-Hf garnet isochron ages and initial ɛHf values in conjunction with present-day bulk-rock Lu-Hf isotope and trace element (K, Nb, Ta, Zr, and Ti in addition to Lu-Hf) data from the world's orogenic eclogites and amphibolites (OEAs). Approximately half of OEAs exhibit Lu-Hf and Nb-Ta systematics mimicking those of unsubducted oceanic crust whereas the rest exhibit variability in one or both systems. For the Lu-Hf system, mixing calculations demonstrate that subduction-related phase transformations, in conjunction with open system behavior, can shift subducted oceanic crust toward higher Lu/Hf, or toward lower Lu/Hf that can also be associated with unradiogenic ɛHf values. However, evaluation of potential mechanisms for fractionating Nb from Ta is more complicated because many of the OEAs have Nb-Ta systematics that are decoupled from Lu-Hf and the behavior of K, Zr, and Ti. Nonetheless, the global data set demonstrates that the association between unradiogenic ɛHf and elevated Nb/Ta observed in some kimberlitic eclogite xenoliths can be inherited from processes that occurred during subduction of their oceanic crustal protoliths. This allows for a geologically based estimate of the Nb concentration in a reservoir composed of deeply subducted oceanic crust. However, mass balance calculations confirm that such a reservoir, when considered as a whole, likely has a Nb concentration similar to unsubducted oceanic crust and is therefore not the solution to the problem of the Earth's "missing" Nb.

  14. Effect of crystal structure on microwave dielectric properties of Li{sub 2}SrTa{sub 2(1−x)}Nb{sub 2x}O{sub 7} compounds

    SciTech Connect

    Singh, Santosh Kumar; Murthy, V.R.K

    2015-10-15

    Highlights: • Synthesis of orthorhombic Li{sub 2}SrTa{sub 2(1−x)}Nb{sub 2x}O{sub 7} compounds • The mechanism for enhancement of quality factor by bond strength. • Deviation of τ{sub ƒ} with octahedral distortion of the compound. - Abstract: The Li{sub 2}SrTa{sub 2(1−x)}Nb{sub 2x}O{sub 7} (x = 0–1.0) with layered-perovskite type structure were synthesized by conventional solid state reaction method. The X-ray diffraction reveals that all these compounds possess orthorhombic crystal structure with Cmcm space group. B-site bond strength and B-site octahedral distortion of these compounds were calculated using bond lengths obtained from Rietveld refinement. The dielectric constant (ϵ{sub r}) decreased from 24.2 to 15.2 with increase in the Nb concentration, which was due to decrease in dielectric polarizability of compound. The non-monotonic variation in quality factor (Q × ƒ) was observed with Nb concentration. This variation of quality factor was correlated with the B-site bond strength. The B-site octahedral distortion was found to increase with Nb content, which was the major factor for increase in temperature coefficient of resonant frequency (τ{sub f}) of these compounds.

  15. Ti-Nb-(Zr,Ta) superelastic alloys for medical implants: Thermomechanical processing, structure, phase transformations and functional properties

    NASA Astrophysics Data System (ADS)

    Dubinskiy, Sergey

    The aim of this project is to develop a new class of orthopaedic implant materials that combine the excellent biocompatibility of pure titanium with the outstanding biomechanical compatibility of Ti-Ni-based shape memory alloys. The most suitable candidates for such a role are Ti-Nb-Zr and Ti-Nb-Ta near-beta shape memory alloys. Since this class of materials was developed quite recently, the influence of thermomechanical treatment on their structure and functional properties has not as yet been the subject of any comprehensive study. Consequently, this project is focused on the interrelations between the composition, the microstructure and the functional properties of superelastic Ti-Nb-Zr and Ti-Nb-Ta alloys for biomedical application. The principal objective is to improve the functional properties of these alloys, more specifically their superelastic properties and fatigue resistance, through optimization of the alloys' composition and thermomechanical processing. It is shown in this thesis that the structure and functional properties of Ti-Nb-based shape memory alloys can be effectively controlled by thermomechanical processing including cold deformation with post-deformation annealing and ageing. It is also shown that the formation of nanosubgrain substructure leads to a significant improvement of superelasticity and fatigue resistance in these alloys. The influence of ageing on the ω-phase precipitation kinetics and, consequently, on the functional properties of Ti-Nb-Zr and Ti-Nb-Ta alloys is also observed. Based on the results obtained, optimized regimes of thermomechanical treatment resulting in a best combination of functional properties are recommended for each alloy, from the orthopaedic implant materials standpoint. An original tensile stage for a low-temperature chamber of an X-ray diffractometer is developed and used in this project. A unique low-temperature (-150...+100°C) comparative in situ X-ray study of the transformations' features and crystal

  16. Blue Phosphorene/MS2 (M = Nb, Ta) Heterostructures As Promising Flexible Anodes for Lithium-Ion Batteries.

    PubMed

    Peng, Qiong; Wang, Zhenyu; Sa, Baisheng; Wu, Bo; Sun, Zhimei

    2016-06-01

    The idea of forming van der Waals (vdW) heterostructures by integrating various two-dimensional materials breaks the limitation of the restricted properties of single material systems. In this work, the electronic structure modulation, stability, entire stress response and the Li adsorption properties of heterostructures by combining blue phosphorene (BlueP) and MS2 (M = Nb, Ta) together were systematically investigated using first-principles calculations based on vdW corrected density functional theory. We revealed that BlueP/MS2 vdW heterostructures possess good structural stability with negative formation energy, enhanced electrical conductivity, improved mechanical flexibility (ultimate strain >17%) and high-capacity (528.257 mAhg(-1) for BlueP/NbS2). The results suggest that BlueP/NbS2 and BlueP/TaS2 heterostructures are ideal candidates used as promising flexible electrode for high recycling rate and portable lithium-ion batteries, which satisfy the requirement of next-generation flexible energy storage and conversion devices. PMID:27165567

  17. Electronic structures of transition metal dipnictides X P n2 (X =Ta , Nb; P n =P , As, Sb)

    NASA Astrophysics Data System (ADS)

    Xu, Chenchao; Chen, Jia; Zhi, Guo-Xiang; Li, Yuke; Dai, Jianhui; Cao, Chao

    2016-05-01

    The electronic structures and topological properties of transition metal dipnictides X P n2 (X =Ta , Nb; P n =P , As, Sb) have been systematically studied using first-principles calculations. In addition to small bulk Fermi surfaces, the band anticrossing features near the Fermi level can be identified from band structures without spin-orbit coupling, leading to nodal lines in all these compounds. Inclusion of spin-orbit coupling gaps out these nodal lines, leaving only a pair of disentangled electron/hole bands crossing the Fermi level. Therefore, the low-energy physics can be in general captured by the corresponding two-band model with several isolated small Fermi pockets. Detailed analysis of the Fermi surfaces suggests that the arsenides and NbSb2 are nearly compensated semimetals while the phosphorides and TaSb2 are not. Based on the calculated band parities, the electron and hole bands are found to be weakly topological nontrivial, giving rise to surface states. As an example, we presented the surface-direction-dependent band structure of the surfaces states in TaSb2.

  18. Development of Ta-matrix Nb3Al Strand and Cable for High-Field Accelerator Magnet

    SciTech Connect

    Tsuchiya, K.; Ghosh, A.; Kikuchi, A.; Takeuchi, T.; Banno, N.; Iijima, Y.; Nimori, S.; Takigawa, H.; Terashima, A.; Nakamoto, T.; Kuroda, Y.; Maruyama, M.; Takao, T.; Tanaka, K.; Nakagawa, K.; Barzi, E.; Yamada, R.; Zlobin, A.

    2011-08-03

    Research and development of Nb{sub 3}Al strands and cables for a high field accelerator magnet is ongoing under the framework of the CERN-KEK collaboration. In this program, new Ta-matrix Nb{sub 3}Al strands were developed and their mechanical properties and superconducting properties were studied. The non-Cu J{sub c} values of these strands were 750 {approx} 800 A/mm{sup 2} at 15 T and 4.2 K. Using these strands, test fabrication of 27-strand Rutherford cable was carried out in collaboration with NIMS and Fermilab. The properties of the strands extracted from the cable were examined and it was found that there was no degradation of the superconducting properties of the strands. In this paper, we report the fabrication of the strands and the cable in brief and present some of the results obtained by studying their properties.

  19. Loparite, a rare-earth ore (Ce, Na, Sr, Ca)(Ti, Nb, Ta, Fe+3)O3

    USGS Publications Warehouse

    Hedrick, J.B.; Sinha, S.P.; Kosynkin, V.D.

    1997-01-01

    The mineral loparite (Ce, NA, Sr, Ca)(Ti, Nb, Ta, Fe+3)O3 is the principal ore of the light-group rare-earth elements (LREE) in Russia. The complex oxide has a perovskite (ABO3) structure with coupled substitutions, polymorphism, defect chemistry and a tendency to become metamict. The A site generally contains weakly bonded, easily exchanged cations of the LREE, Na and Ca. The B site generally contains smaller, highly charged cations of Ti, Nb or Fe+3. Mine production is from Russia's Kola Peninsula. Ore is beneficiated to produce a 95% loparite concentrate containing 30% rare-earth oxides. Loparite concentrate is refined by either a chlorination process or acid decomposition process to recover rare-earths, titanium, niobium and tantalum. Rare-earths are separated by solvent extraction and selective precipitation/dissolution. The concentrate is processed at plants in Russia, Estonia and Kazakstan.

  20. Nonlinear optical properties of different types of proton-exchanged LiNbO3 and LiTaO3 waveguides

    NASA Astrophysics Data System (ADS)

    Korkishko, Yuri N.; Fedorov, Vyacheslav A.; Kostritskii, Sergey M.; Alkaev, Alexander N.; Maslennikov, Evgeny I.; Laurell, Fredrik

    2003-04-01

    Reflection second-harmonic generation (SHG) from the polished waveguide end face is used to investigate the second-order nonlinear optical properties of different types of PE LiNbO3 and LiTaO3 waveguides in different HxLi1-xNbO3 and HxLi1-xTaO3 phases: as-exchanged and annealed proton-exchanged (APE) waveguides, high-temperature proton-exchanged (HTPE) waveguides, as well as reverse proton exchanged (RPE) waveguides. A detailed correlation is done between the nonlinear properties, the processing conditions, crystal structure parameters, the refractive index changes and the optical losses of the waveguides. The intensity of reflected SH signal, strongly reduced after the initial proton exchange in both LiNbO3 and LiTaO3, is found to be restored and even increased after annealing. However, this apparent increase of the nonlinearity is accompanied by high scattering and a strong degradation of the quality of the SHG reflected beam in the region of initial step-like PE waveguides. The recently proposed HTPE technique has been shown to produce high-quality alpha-phase PE LiNbO3 or PE LiTaO3 waveguides with essentially undegraded nonlinear optical properties. It has been also shown that the nonlinear properties of annealed proton exchanged LiNbO3 and LiTaO3 waveguides can be effectively recovered by the reverse proton exchange technique.

  1. Preparation and visible-light photocatalytic properties of BiNbO₄ and BiTaO₄ by a citrate method

    SciTech Connect

    Zhai, Hai-Fa; Li, Ai-Dong; Kong, Ji-Zhou; Li, Xue-Fei; Zhao, Jie; Guo, Bing-Lei; Yin, Jiang; Li, Zhao-Sheng; Wu, Di

    2013-06-01

    Visible-light photcatalysts of BiNbO₄ and BiTaO₄ powders have been successfully synthesized by a citrate method. The formation of pure triclinic phase of BiNbO₄ and BiTaO₄ at low temperature of 700 °C can be attributed to the advantage of the citrate method. The photocatalytic activity and possible mechanism were investigated deeply. For BiNbO₄ particles, the mechanism of methyl violet (MV) degradation under visible light irradiation involves photocatalytic and photosensitization pathways and the catalyst specific surface area has dominant influence. While for BiTaO₄ particles, the dominant mechanism arises from photosensitization pathways and a trade off between high specific surface area and good crystallinity is achieved. BiNbO₄ powder calcined at 700 °C shows the best photocatalytic efficiency among these catalysts, which is ascribed to its large surface area and more positive conduction band level. The optimal catalyst loading, additive H₂O₂ concentration and pH value is around 1 g/L, 2 mmol/L and 8 mmol/L, respectively. - Graphical abstract: Photodegradation performance and adsorption ability of BiNbO₄ and BiTaO₄ powders, respectively. BNO700 with the best photocatalytic efficiency is ascribed to its large surface area and more positive conduction band level. Highlights: • Pure BiNbO₄ and BiTaO₄ powders were prepared by a citrate method. • Excellent performance of visible-light degradation of MV was observed. • Different MV degradation mechanism for BiNbO₄ and BiTaO₄ powders was proposed. • BNO700 has large surface area and more positive conduction band level.

  2. Effect of deformation on corrosion behavior of Ti-23Nb-0.7Ta-2Zr-O alloy

    SciTech Connect

    Guo, W.Y.; Sun, J. Wu, J.S.

    2009-03-15

    The influence of deformation on the corrosion behavior of a newly developed multifunctional beta titanium alloy Ti-23Nb-0.7Ta-2Zr-O (mol%) in Ringer's solution at 310 K was evaluated using an electron backscatter diffraction technique and electrochemical measurements. The results showed that the effect of deformation on the corrosion resistance of the beta titanium alloy is complicated. Small levels of plastic deformation are detrimental to the corrosion resistance, whereas large deformations tend to eliminate this detrimental effect.

  3. Significant enhancement of compositional and superconducting homogeneity in Ti rather than Ta-doped Nb3Sn

    NASA Astrophysics Data System (ADS)

    Tarantini, C.; Sung, Z.-H.; Lee, P. J.; Ghosh, A. K.; Larbalestier, D. C.

    2016-01-01

    Nb3Sn wire is now very close to its final optimization, but despite its classical nature, a detailed understanding of the role of Ta and Ti doping in the A15 is not fully developed. Long thought to be essentially equivalent in their influence on Hc2, they were interchangeably applied. Here, we show that Ti produces significantly more homogeneous chemical and superconducting properties. Despite Ta-doped samples having a slightly higher Tc onset in zero-field, they always have a wider Tc-distribution. In particular, whereas the Ta-doped A15 has a Tc-distribution extending from 18 down to 5-6 K (the lowest expected Tc for the binary A15 phase), the Ti-doped samples have no A15 phase with Tc below ˜12 K. The much narrower Tc distribution in the Ti-doped samples has a positive effect on their in-field Tc-distribution too, leading to an extrapolated μ0Hc2(0) 2 T larger than the Ta-doped wire. Ti-doping also appears to be very homogeneous even when the Sn content is reduced in order to inhibit breakdown of the diffusion barriers in very high Jc conductors. The enhanced homogeneity of the Ti-doped samples appears to result from its assistance of rapid diffusion of Sn into the filaments and by its incorporation into the A15 phase interchangeably with Sn on the Sn sites of the A15 phase.

  4. Influence of Ta substitution for Nb in Zn3Nb2O8 and the impact on the crystal structure and microwave dielectric properties.

    PubMed

    Zhao, Yonggui; Zhang, Ping

    2016-08-01

    Zn3(Nb1-xTax)2O8 (x = 0.02-0.10) ceramics were prepared via a solid-state reaction route and the dependence of their microwave dielectric properties on their structural characteristics were investigated. XRD patterns show that a single Zn3Nb2O8 phase with layered crystal structures was formed in ceramic samples with 0.02 ≤x≤ 0.10. The Raman spectrum was used for the first time to analyze the vibrational phonon modes of the Zn3Nb2O8 samples. Based on P-V-L dielectric theory, the intrinsic factors that influence the microwave dielectric properties were systematically investigated. According to the calculated results, the experimental dielectric constant had a close relationship with the theoretical dielectric constant. The Nb-site lattice energy was found to be a vital factor in explaining the change of the Q×f values. While the Nb-site bond energy increases, the |τf| value decreases which indicates that higher bond energy would result in a more stable system. This work presents a novel method to investigate the intrinsic factors that influence microwave dielectric properties. PMID:27362863

  5. Nb and Ta layer doping effects on the interfacial energetics and electronic properties of LaAlO3/SrTiO3 heterostructure: first-principles analysis.

    PubMed

    Nazir, Safdar; Behtash, Maziar; Cheng, Jianli; Luo, Jian; Yang, Kesong

    2016-01-28

    The two-dimensional electron gas (2DEG) formed at the n-type (LaO)(+1)/(TiO2)(0) interface in the polar/nonpolar LaAlO3/SrTiO3 (LAO/STO) heterostructure (HS) has emerged as a prominent research area because of its great potential for nanoelectronic applications. Due to its practical implementation in devices, desired physical properties such as high charge carrier density and mobility are vital. In this respect, 4d and 5d transition metal doping near the interfacial region is expected to tailor electronic properties of the LAO/STO HS system effectively. Herein, we studied Nb and Ta-doping effects on the energetics, electronic structure, interfacial charge carrier density, magnetic moment, and the charge confinements of the 2DEG at the n-type (LaO)(+1)/(TiO2)(0) interface of LAO/STO HS using first-principles density functional theory calculations. We found that the substitutional doping of Nb(Ta) at Ti [Nb(Ta)@Ti] and Al [Nb(Ta)@Al] sites is energetically more favorable than that at La [Nb(Ta)@La] and Sr [Nb(Ta)@Sr] sites, and under appropriate thermodynamic conditions, the changes in the interfacial energy of HS systems upon Nb(Ta)@Ti and Nb(Ta)@Al doping are negative, implying that the formation of these structures is energetically favored. Our calculations also showed that Nb(Ta)@Ti and Nb(Ta)@Al doping significantly improve the interfacial charge carrier density with respect to that of the undoped system, which is because the Nb(Ta) dopant introduces excess free electrons into the system, and these free electrons reside mainly on the Nb(Ta) ions and interfacial Ti ions. Hence, along with the Ti 3d orbitals, the Nb 4d and Ta 5d orbitals also contribute to the interfacial metallic states; accordingly, the magnetic moments on the interfacial Ti ions increase significantly. As expected, the Nb@Al and Ta@Al doped LAO/STO HS systems show higher interfacial charge carrier density than the undoped and other doped systems. In contrast, Nb@Ti and Ta@Ti doped systems may

  6. Characterization of the Ti-10Nb-10Zr-5Ta Alloy for Biomedical Applications. Part 1: Microstructure, Mechanical Properties, and Corrosion Resistance

    NASA Astrophysics Data System (ADS)

    Vladescu, A.; Braic, V.; Balaceanu, M.; Braic, M.; Parau, A. C.; Ivanescu, S.; Fanara, C.

    2013-08-01

    Ti-10Nb-10Zr-5Ta alloy was investigated as possible material candidate for replacing Ti6Al4V in medical applications. The alloy was prepared in a levitation melting furnace and characterized in terms of elemental and phase composition, microstructure, mechanical properties, and corrosion resistance in simulated body fluid and Fusayama Meyer artificial saliva solutions. The characteristics of the new alloy were compared to those of the Ti6Al4V alloy. The Ti-10Nb-10Zr-5Ta system was found to posses of a polyhedral structure consisting in α' and β phases. X-ray structural analysis revealed a mixture of hexagonal α' martensite (main phase, with grain size of about 21 nm) and β bcc phase. The Ti-10Nb-10Zr-5Ta alloy exhibited some better mechanical properties (Young modulus, tensile properties) and corrosion resistance (polarization resistance, corrosion current density, and corrosion rate), as compared to Ti6Al4V alloy.

  7. Violation of Kohler's rule in Ta2PdTe6 and absence of same in Nb2PdS5: A high field magneto transport study

    NASA Astrophysics Data System (ADS)

    Goyal, Reena; Jha, Rajveer; Awana, V. P. S.

    2016-05-01

    Here, we present the comparative study of magnetotransport properties of recently discovered Ta2PdTe6 and Nb2PdS5 superconductors. The XRD and magnetotransport measurements are performed on these samples to investigate structure and superconducting properties as well as normal state transport properties of these compounds. Both the compounds are crystallized in monoclinic structure within space group C 2/m. Here, we observe superconductivity in both the compounds Ta2PdTe6 (Tc =4.4 K) and Nb2PdS5 (Tc =6.6 K). We see a linear magnetoresistance in Ta2PdTe6 as well as violation of Kohler's rule in same compound. On the other hand, we find the absence of same in Nb2PdS5 compound.

  8. Molten salt synthesis, characterization, and luminescence properties of GdNbO{sub 4}/LuTaO{sub 4}:Eu{sup 3+} phosphors

    SciTech Connect

    Lin, Jintai; Zhou, Zhan; Wang, Qianming

    2013-08-01

    Graphical abstract: Well crystallized GdNbO4:Eu3{sup +} and LuTaO{sub 4}:Eu3{sup +} in the presence of fluxes were formed under reduced temperature in contrast to conventional method and their photophysical properties were studied. - Highlights: • Molten salt method was used to assemble two phosphors. • Both GdNbO{sub 4}:Eu{sup 3+} and LuTaO{sub 4}:Eu{sup 3+} could be red emissive. • The two powders were well dispersed as nano-particles. - Abstract: GdNbO{sub 4}:Eu{sup 3+} and LuTaO{sub 4}:Eu{sup 3+} have been successfully prepared with different fluxes (NaCl, KCl, NaCl and KCl) by the molten salt method. X-ray diffraction (XRD) patterns illustrated that well crystallized GdNbO{sub 4}:Eu{sup 3+} and LuTaO{sub 4}:Eu{sup 3+} in the presence of fluxes were formed under reduced temperature (900 °C) in contrast to conventional method (GdNbO{sub 4}:Eu{sup 3+}: around 1200 °C; LuTaO{sub 4}:Eu{sup 3+}: around 1500 °C). Scanning electron microscope (SEM) images revealed that well dispersed particles were achieved (granular or rod-like structures). Meanwhile, the photo-luminescent studies demonstrated that both niobate and tantalate are efficient hosts to sensitize europium red emissions. The results indicated that GdNbO{sub 4}:Eu{sup 3+} using NaCl as the flux gave much enhanced red emission whereas LuTaO{sub 4}:Eu{sup 3+} synthesized with the assistance of mixed salts (NaCl–KCl) achieved the best luminescence.

  9. (Ag,Cu)-Ta-O ternaries as high-temperature solid-lubricant coatings.

    PubMed

    Gao, Hongyu; Otero-de-la-Roza, Alberto; Gu, Jingjing; Stone, D'Arcy; Aouadi, Samir M; Johnson, Erin R; Martini, Ashlie

    2015-07-22

    Ternary oxides have gained increasing attention due to their potential use as solid lubricants at elevated temperatures. In this work, the tribological properties of three ternary oxides-AgTaO3, CuTaO3, and CuTa2O6-were studied using a combination of density-functional theory (DFT), molecular dynamics (MD) simulations with newly developed empirical potential parameters, and experimental measurements (AgTaO3 and CuTa2O6 only). Our results show that the MD-predicted friction force follows the trend AgTaO3 < CuTaO3 < CuTa2O6, which is consistent with the experimentally measured coefficients of friction. The wear performance from both MD and experiment exhibits the opposite trend, with CuTa2O6 providing the best resistance to wear. The sliding mechanisms are investigated using experimental characterization of the film composition after sliding, quantification of Ag or Cu cluster formation at the interface during the evolution of the film in MD, and DFT energy barriers for atom migration on the material surface. All our observations are consistent with the hypothesis that the formation of metal (or metal oxide) clusters on the surface are responsible for the friction and wear behavior of these materials. PMID:26106877

  10. Magnetic torque study of Weyl semimetal compounds TaP and NbP up to 45 Tesla

    NASA Astrophysics Data System (ADS)

    Li, Gang; Asaba, Tomoya; Tinsman, Colin; Yu, Fan; Lawson, Benjamin; Chen, Yulin; Li, Lu

    Weyl semimetal is a recently proposed new state in condensed matter physics, in which the bulk bands could have three dimensional linear dispersion but the degeneracy at the cross point is lifted into a pair of Weyl points with opposite chirality. Among the predicted candidates, Tantalum monophorspide (TaP) and Niobium monophorspide (NbP) have the simplest composition and do not require extrinsic tuning. Photoemission data is accumulating and the unique Fermi-arc surface state is observed. Magnetotransport experiments has shown highly anisotropic magnetoresistance and quantum oscillations has been observed. Because both linear dispersive bands and conventional bands exist in these materials, a detailed study of the electronic strucuture of the bulk is highly desirable. We use torque magnetometry to study quantum oscillations of TaP and NbP down to 300 mK, and up to 45 Tesla, with focus on the angular dependence of oscillation frequencies. Our comparison shows clear difference in geometry of different bulk bands in these materials. Besides, a discussion will be made on high field torque data since 45 Tesla is high enough to push several of the bands into quantum limit.

  11. Th-REE- and Nb-Ta-accessory minerals in post-collisional Ediacaran felsic rocks from the Katerina Ring Complex (S. Sinai, Egypt): An assessment for the fractionation of Y/Nb, Th/Nb, La/Nb and Ce/Pb in highly evolved A-type granites

    NASA Astrophysics Data System (ADS)

    Moreno, J. A.; Molina, J. F.; Bea, F.; Abu Anbar, M.; Montero, P.

    2016-08-01

    The relationships of Y/Nb, Th/Nb, La/Nb and Ce/Pb ratios in A-type felsic rocks from the Ediacaran Katerina Ring Complex, northernmost Arabian-Nubian Shield (ANS; S. Sinai, Egypt), are investigated in this work to understand their behavior during generation of highly evolved granitic magmas and to explore the nature of magma sources. Textural and compositional relationships of cognate Th-REE- and Nb-Ta-accessory minerals in Katerina felsic rocks show that chevkinite-group minerals (CGM), monazite, thorite, allanite and xenotime formed from residual liquids in quartz syenite porphyries, quartz monzonites and peralkaline granites, whereas in aluminous granites, allanite and monazite crystallized early, and thorite and columbite formed from residual liquids. Relationships of Y/Nb, Th/Nb, La/Nb and Ce/Pb ratios with Zr/Hf ratios in the aluminous granites and with Be abundances in the peralkaline granites suggest a decrease in La/Nb and Ce/Pb ratios in the former, and in Y/Nb and La/Nb ratios in the latter with crystallization progress. This contrasts with absence of systematic variations of Th/Nb and Ce/Pb ratios in the peralkaline compositions and of Y/Nb ratio in the aluminous ones. In this latter, Th/Nb ratio can present a significant decrease only in highly evolved compositions. An analysis of Y/Nb, Th/Nb, La/Nb and Ce/Pb relationships in worldwide OIB and subduction-related magmatic suites reveals that A-type felsic rocks with (Th/Nb)N < 1.3, (La/Nb)N < 1.3, and (Ce/Pb)N > 1 may have A1-type affinity, and those with (Th/Nb)N > 2, (La/Nb)N > 2, and (Ce/Pb)N < 1 tend to present A2-type affinity. The crystal fractionation of Th-LREE- and Nb-Ta-accessory minerals and mixing of components derived from the two granite groups may cause deviations from these compositional limits that can be evaluated using constraints imposed by Th/Nb-La/Nb, Ce/Pb-Th/Nb and Ce/Pb-La/Nb relationships in OIB and subduction-related magmatic suites. Three mantle sources might have been

  12. Geochemical evolution of micas and Sn-, Nb-, Ta- mineralization associated with the rare metal pegmatite in Angwan Doka, central Nigeria

    NASA Astrophysics Data System (ADS)

    Akoh, Juliet U.; Ogunleye, Paul O.; Ibrahim, Aliyu A.

    2015-12-01

    The pegmatites in Angwan Doka, north central Nigeria are genetically related to the basement granites formed during the Pan-African orogeny, 550-530 Ma ago. They occur as sharply discordant dykes in the granitic and metasedimentary basement rocks. The pegmatite population comprises of mineralogically simple and complexly zoned types that are characterized by LCT (Li, Cs and Ta) geochemical signature. The host granitoids range in composition from hornblende, titanite-bearing to biotite-muscovite granodiorites. Analysis of geochemical data of whole rock and muscovite from the different zones reveals compositional variations and evolution across the pegmatite body from border zone to the lepidolite-quartz core zone. Fractionation of Rb, Cs, Sr, Li, F, B, Be Sn, Zn, Ta, Nb and Mn which increases from host granitoids, through the border zone to the central core, with decrease in Fe, Mg, Ti, Ba content, is typical and marks the magmatic crystallization trend of the pegmatites. Other distinctive attribute of the pegmatites is occurrence of cassiterite believed to have formed as a consequence of greisenization, albitization and late-stage metasomatism, which led to enrichment in Sn (up to 886 ppm) in the intermediate zone. Chemical composition of muscovite from the different zones of the pegmatite reveals high concentration of primary magmatic columbite-Fe (ferrocolumbite and ferrotantalite) in the border zone and tantalite-Mn (manganocolumbite and manganotantalite) in the core zone. Ta predominates (352 ppm) in the most evolved lepidolite (Li- and F-rich) zone while Nb was enriched (up to 714 ppm) in the border zone. These geochemical features are ascribed to undercooling of the melt and crystallization in boundary layers accompanied with increased accumulation of incompatible and fluxing components. With increasing fractionation, Nb/Ta and Fe/Mn ratio decreased and is accompanied with increase in Rb, Cs, Li, F and Be typical of crystallization from magmatic process. The

  13. Nb-Ta-Ti-W-Sn-oxide minerals as indicators of a peraluminous P- and F-rich granitic system evolution: Podlesí, Czech Republic

    NASA Astrophysics Data System (ADS)

    Breiter, K.; Škoda, R.; Uher, P.

    2007-11-01

    The strongly peraluminous, P- and F-rich granitic system at Podlesí in the Krušné Hory Mountains, Czech Republic, resembles the zonation of rare element pegmatites in its magmatic evolution (biotite → protolithionite → zinnwaldite granites). All granite types contain disseminated Nb-Ta-Ti-W-Sn minerals that crystallized in the following succession: rutile + cassiterite (in biotite granite), rutile + cassiterite → ferrocolumbite (in protolithionite granite) and ferrocolumbite → ixiolite → ferberite (in zinnwaldite granite). Textural features of Nb-Ta-Ti-W minerals indicate a pre-dominantly magmatic origin with only minor post-magmatic replacement phenomena. HFSE remained in the residual melt during the fractionation of the biotite granite. An effective separation of Nb + Ta into the melt and Sn into fluid took place during subsequent fractionation of the protolithionite granite, and the tin-bearing fluid escaped into the exocontact. To the contrast, W contents are similar in both protolithionite and zinnwaldite granites. Although the system was F-rich, only limited Mn-Fe and Ta-Nb fractionation appeared. Enrichment of Mn and Ta was suppressed due to foregoing crystallization of Mn-rich apatite and relatively low Li content, respectively. The content of W in columbite increases during fractionation and enrichment in P and F in the melt. Ixiolite (up to 1 apfu W) instead of columbite crystallized from the most fluxes-enriched portions of the melt (unidirectional solidification textures, late breccia).

  14. Ultrahigh temperature Bi3Ti0.96Sc0.02Ta0.02NbO9-based piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Gai, Zhi-Gang; Wang, Jin-Feng; Sun, Wen-bin; Wang, Chun-Ming; Zhao, Ming-Lei; Sun, Shang-Qian; Ming, Bao-Quan; Qi, Peng; Zheng, Li-mei; Du, Juan; Zhang, Shujun; Shrout, Thomas R.

    2008-07-01

    The effect of (Sc,Ta,Ce) doping on the properties of Bi3TiNbO9 (BTNO)-based ceramics was investigated. The cerium modification greatly improves the piezoelectric activity of Bi3(Ti0.96Sc0.02Ta0.02)NbO9-based ceramics and significantly decreases the dielectric dissipation. The d33 of Bi3Ti0.96Sc0.02Ta0.02NbO9+x wt %CeO2 (x =0.35) was found to be 18 pC/N, the highest value among the BTNO-based ceramics and almost three times as much as the reported d33 values of the pure BTNO ceramics (˜6 pC/N). The modification increased the resistivity ρ of the samples extremely, resolving the low resistivity problem for high temperature applications. The dielectric spectroscopy shows that the TC for all the ceramics is higher than 900 °C. The mechanical quality factor Q and planar coupling factors kp and kt of Bi3Ti0.96Sc0.02Ta0.02NbO9+0.35 wt %CeO2 ceramic were found to be 2835, 9%, and 23%, respectively, and it has high TC and stable piezoelectric properties, demonstrating that the (Sc,Ta,Ce) modified BTNO-based material is a wonderful candidate for high temperature applications.

  15. Syntheses and structures of six compounds in the A{sub 2}LiMS{sub 4} (A=K, Rb, Cs; M=V, Nb, Ta) family

    SciTech Connect

    Huang Fuqiang; Deng Bin; Ibers, James A. . E-mail: ibers@chem.northwestern.edu

    2005-01-15

    Six new compounds in the A{sub 2}LiMS{sub 4} (A=K, Rb, Cs; M=V, Nb, Ta) family, namely K{sub 2}LiVS{sub 4}, Rb{sub 2}LiVS{sub 4}, Cs{sub 2}LiVS{sub 4}, Rb{sub 2}LiNbS{sub 4}, Cs{sub 2}LiNbS{sub 4}, and Rb{sub 2}LiTaS{sub 4}, have been synthesized by the reactions of the elements in Li{sub 2}S/S/A{sub 2}S{sub 3} (A=K, Rb, Cs) fluxes at 773K. The A and M atoms play a role in the coordination environment of the Li atoms, leading to different crystal structures. Coordination numbers of Li atoms are five in K{sub 2}LiVS{sub 4}, four in A{sub 2}LiVS{sub 4} (A=Rb, Cs) and Cs{sub 2}LiNbS{sub 4}, and both four and five in Rb{sub 2}LiMS{sub 4} (M=Nb, Ta). The A{sub 2}LiVS{sub 4} (A=Rb, Cs) structure comprises one-dimensional chains of {sub {infinity}}{sup 1}[LiVS{sub 4}] tetrahedra. The Rb{sub 2}LiMS{sub 4} (M=Nb, Ta) structure is composed of two-dimensional {sub {infinity}}{sup 2}[LiMS{sub 4}] layers. The Cs{sub 2}LiNbS{sub 4} structure contains one-dimensional {sub {infinity}}{sup 1}[LiNbS{sub 4}] chains that are related to the Rb{sub 2}LiMS{sub 4} layers. The K{sub 2}LiVS{sub 4} structure contains a different kind of {sub {infinity}}{sup 1}[LiVS{sub 4}] layer.

  16. Theoretical and experimental insights into applicability of solid-state 93Nb NMR in catalysis.

    PubMed

    Papulovskiy, Evgeniy; Shubin, Alexandre A; Terskikh, Victor V; Pickard, Chris J; Lapina, Olga B

    2013-04-14

    Ab initio DFT calculations of (93)Nb NMR parameters using the NMR-CASTEP code were performed for a series of over fifty individual niobates, and a good agreement has been found with experimental NMR parameters. New experimental and calculated (93)Nb NMR data were obtained for several compounds, AlNbO4, VNb9O25, K8Nb6O19 and Cs3NbO8, which are of particular interest for catalysis. Several interesting trends have been identified between (93)Nb NMR parameters and the specifics of niobium site environments in niobates. These trends may serve as useful guidelines in interpreting (93)Nb NMR spectra of complex niobium oxide systems, including amorphous samples and niobium-based multicomponent heterogeneous catalysts. Potential applications of (93)Nb NMR to study solid polyoxoniobates are discussed. PMID:23450163

  17. Effects of WO3 and Ta2O5 Dopants on the Structure, Microstructure, and Microwave Dielectric Properties of Ca5Nb4TiO17 Ceramics

    NASA Astrophysics Data System (ADS)

    Wang, Sea-Fue; Hsu, Yung-Fu; Chen, Chun-Ya

    2016-06-01

    Ca5Nb4TiO17 ceramics were doped with WO3 and Ta2O5 to improve their microwave dielectric properties. The substitution of W6+ into Nb5+/Ti4+ sites resulted in the reduction of the sintering temperatures of the Ca5Nb4-1.2 x W x TiO17 ceramics to 1450°C for x > 0.3 due to the formation of a second phase, CaWO4. In addition, the densification temperatures of the Ca5Nb4- x Ta x TiO17 ceramics increased with Ta5+ content. Some irregular grains of CaWO4 were observed in the microstructures with plate-like grains, which increased with increasing W6+ content in the Ca5Nb4-1.2 x W x TiO17 ceramics. All the Ca5Nb4- x Ta x TiO17 samples exhibited dense microstructures with closely packed plate-like grains and a few pores. The dielectric constant (ɛ r ) of the Ca5Nb4-1.2 x W x TiO17 ceramics decreased with increasing W6+ content from 45.0 for x = 0 to 36.4 for x = 0.9. This decrease occurred because the more highly polarizable Nb5+ ions were replaced by less polarizable W6+ ions at B-sites, and the formation of the CaWO4 second phase diluted ɛ r . The quality factor ( Q × f) reached a maximum of 26,478 GHz for x = 0.3 because of the cation distribution and decrease in the volume of cation sites as well as the increase in the average grain size. The CaWO4 second phase caused the temperature coefficient of the resonant frequency (τ f ) of the Ca5Nb4-1.2 x W x TiO17 ceramics to move in the positive direction. For the Ca5Nb4- x Ta x TiO17 ceramics, ɛ r decreased almost linearly with increasing Ta5+ content from 45.2 for x = 0 to 36.2 for x = 2.5 because of the dampening of the ionic mobility and decrease in the molecular polarizability. The Q × f and τ f values decreased with increasing x value.

  18. Signatures of Fermi Arcs in the Quasiparticle Interferences of the Weyl Semimetals TaAs and NbP

    NASA Astrophysics Data System (ADS)

    Chang, Guoqing; Xu, Su-Yang; Zheng, Hao; Lee, Chi-Cheng; Huang, Shin-Ming; Belopolski, Ilya; Sanchez, Daniel S.; Bian, Guang; Alidoust, Nasser; Chang, Tay-Rong; Hsu, Chuang-Han; Jeng, Horng-Tay; Bansil, Arun; Lin, Hsin; Hasan, M. Zahid

    2016-02-01

    The recent discovery of the first Weyl semimetal in TaAs provides the first observation of a Weyl fermion in nature. Such a topological semimetal features a novel type of anomalous surface state, the Fermi arc, which connects a pair of Weyl nodes through the boundary of the crystal. Here, we present theoretical calculations of the quasiparticle interference (QPI) patterns that arise from the surface states including the topological Fermi arcs in the Weyl semimetals TaAs and NbP. Most importantly, we discover that the QPI exhibits termination points that are fingerprints of the Weyl nodes in the interference pattern. Our results, for the first time, propose a universal interference signature of the topological Fermi arcs in TaAs, which is fundamental for scanning tunneling microscope (STM) measurements on this prototypical Weyl semimetal compound. More generally, our work provides critical guideline and methodology for STM studies on new Weyl semimetals. Further, the scattering channels revealed by our QPIs are broadly relevant to surface transport and device applications based on Weyl semimetals.

  19. Signatures of Fermi Arcs in the Quasiparticle Interferences of the Weyl Semimetals TaAs and NbP.

    PubMed

    Chang, Guoqing; Xu, Su-Yang; Zheng, Hao; Lee, Chi-Cheng; Huang, Shin-Ming; Belopolski, Ilya; Sanchez, Daniel S; Bian, Guang; Alidoust, Nasser; Chang, Tay-Rong; Hsu, Chuang-Han; Jeng, Horng-Tay; Bansil, Arun; Lin, Hsin; Hasan, M Zahid

    2016-02-12

    The recent discovery of the first Weyl semimetal in TaAs provides the first observation of a Weyl fermion in nature. Such a topological semimetal features a novel type of anomalous surface state, the Fermi arc, which connects a pair of Weyl nodes through the boundary of the crystal. Here, we present theoretical calculations of the quasiparticle interference (QPI) patterns that arise from the surface states including the topological Fermi arcs in the Weyl semimetals TaAs and NbP. Most importantly, we discover that the QPI exhibits termination points that are fingerprints of the Weyl nodes in the interference pattern. Our results, for the first time, propose a universal interference signature of the topological Fermi arcs in TaAs, which is fundamental for scanning tunneling microscope (STM) measurements on this prototypical Weyl semimetal compound. More generally, our work provides critical guideline and methodology for STM studies on new Weyl semimetals. Further, the scattering channels revealed by our QPIs are broadly relevant to surface transport and device applications based on Weyl semimetals. PMID:26919003

  20. Influence of the B-site ordering on the magnetic properties of the new La{sub 3}Co{sub 2}MO{sub 9} double perovskites with M = Nb or Ta

    SciTech Connect

    Fuertes, V.C.; Blanco, M.C.; Franco, D.G.; De Paoli, J.M.; Sanchez, R.D.; Carbonio, R.E.

    2011-01-15

    Double perovskites La{sub 3}Co{sub 2}NbO{sub 9} and La{sub 3}Co{sub 2}TaO{sub 9} have been prepared by both solid state and sol-gel synthesis. The crystal structures have been studied from X-ray and neutron powder diffraction data. Rietveld refinements show that the crystal structure is monoclinic (P2{sub 1}/n), with different degrees of ordering of B' and B'' cations, with octahedra tilted according to the Glazer notation a{sup -}b{sup -}c{sup +}. Occupancy refinements show that the solid state materials are more B-site ordered than the sol-gel ones. Magnetization measurements show that these perovskites show two magnetic contributions, one with spontaneous magnetization and other with linear behaviour with the magnetic field associated to antiferromagnetic correlations. In the samples synthesized by solid state the spontaneous magnetization is more important than those synthesized by the sol-gel and present T{sub C} of 62 K for Nb and 72 K for Ta. On the other hand, materials prepared by sol-gel have T{sub C} 20 K for Nb and 40 K for Ta, respectively and major presence of the antiferromagnetic contribution. The competition between these magnetic behaviours is interpreted, by a microscopic point of view, as to be due to the different degrees of Co{sup 2+} ions disorder on the B site of the double perovskite structure. This disorder affects the ratio between the antiferromagnetic Co{sup 2+}-O-Co{sup 2+} and the ferromagnetic Co{sup 2+}-O-M{sup 5+}-O-Co{sup 2+} couplings proposed for the system.

  1. Nanoindentation, High-Temperature Behavior, and Crystallographic/Spectroscopic Characterization of the High-Refractive-Index Materials TiTa2O7 and TiNb2O7.

    PubMed

    Perfler, Lukas; Kahlenberg, Volker; Wikete, Christoph; Schmidmair, Daniela; Tribus, Martina; Kaindl, Reinhard

    2015-07-20

    Colorless single crystals, as well as polycrystalline samples of TiTa2O7 and TiNb2O7, were grown directly from the melt and prepared by solid-state reactions, respectively, at various temperatures between 1598 K and 1983 K. The chemical composition of the crystals was confirmed by wavelength-dispersive X-ray spectroscopy, and the crystal structures were determined using single-crystal X-ray diffraction. Structural investigations of the isostructural compounds resulted in the following basic crystallographic data: monoclinic symmetry, space group I2/m (No. 12), a = 17.6624(12) Å, b = 3.8012(3) Å, c = 11.8290(9) Å, β = 95.135(7)°, V = 790.99(10) Å(3) for TiTa2O7 and a = 17.6719(13) Å, b = 3.8006(2) Å, c = 11.8924(9) Å, β = 95.295(7)°, V = 795.33(10) Å(3), respectively, for TiNb2O7, Z = 6. Rietveld refinement analyses of the powder X-ray diffraction patterns and Raman spectroscopy were carried out to complement the structural investigations. In addition, in situ high-temperature powder X-ray diffraction experiments over the temperature range of 323-1323 K enabled the study of the thermal expansion tensors of TiTa2O7 and TiNb2O7. To determine the hardness (H), and elastic moduli (E) of the chemical compounds, nanoindentation experiments have been performed with a Berkovich diamond indenter tip. Analyses of the load-displacement curves resulted in a hardness of H = 9.0 ± 0.5 GPa and a reduced elastic modulus of Er = 170 ± 7 GPa for TiTa2O7. TiNb2O7 showed a slightly lower hardness of H = 8.7 ± 0.3 GPa and a reduced elastic modulus of Er = 159 ± 4 GPa. Spectroscopic ellipsometry of the polished specimens was employed for the determination of the optical constants n and k. TiNb2O7 as well as TiTa2O7 exhibit a very high average refractive index of nD = 2.37 and nD = 2.29, respectively, at λ = 589 nm, similar to that of diamond (nD = 2.42). PMID:26132138

  2. Influence of heating rates on in situ resistance measurements of a bronze route Nb Sn Cu Ta multifilamentary conductor

    NASA Astrophysics Data System (ADS)

    Tan, K. S.; Hopkins, S. C.; Glowacki, B. A.

    2004-11-01

    The superconducting properties of a bronze process multifilamentary conductor are controlled by the structure, dimensions and composition of the intermetallic layers, which are strongly influenced by the details of the heat treatments applied to the conductor. It has previously been reported that the electrical resistivity of a Vacuumschmelze bronze process conductor varies during heat treatment, and that analysis of the conductor as a set of parallel resistors allows the features of the resistivity variation to be assigned to the progress of Nb 3Sn intermetallic phase formation. The behaviour of NSP2 Nb-Sn-Cu-Ta bronze process multifilamentary conductors (Imperial Metal Industries) is now reported as a function of the heating rate, in preparation for more complex non-isothermal heat treatment procedures. It is shown that the resistance of the wire measured in situ by an alternating current (AC) technique can be used to observe the progress of the formation of Nb 3Sn, and that the comparison of resistometric measurements at different heating rates can give an indication of other processes (such as recovery and recrystallisation) occurring at lower temperatures during the heating up process prior to isothermal annealing. In addition, this wire containing only about 1% of copper was carefully chosen because of the broken tantalum barriers around individual copper filaments. Therefore, the resistometric measurements were used to attempt to detect the diffusion of tin from the bronze matrix into the copper filaments at lower temperatures without noticeable influence on Nb 3Sn phase formation. Treating the NSP2 wire as a set of parallel resistors also permits estimates to be made of the intermetallic layer thicknesses from resistometric measurements, and these are shown to be in good agreement with estimates from scanning electron microscopy. The difference in critical temperature, Tc, between wires heated at different rates, with the presence of the bronze matrix and

  3. Significant enhancement of compositional and superconducting homogeneity in Ti rather than Ta-doped Nb3Sn

    DOE PAGESBeta

    Tarantini, C.; Sung, Z. -H.; Lee, P. J.; Ghosh, A. K.; Larbalestier, D. C.

    2016-01-25

    Nb3Sn wires are now very close to their final optimization but despite its classical nature, detailed understanding of the role of Ta and Ti doping in the A15 is not fully understood. Long thought to be essentially equivalent in their influence on Hc2, they were interchangeably applied. Here we show that Ti produces significantly more homogeneous chemical and superconducting properties. Despite Ta-doped samples having a slightly higher Tc onset in zero-field, they always have a wider Tc-distribution. In particular, whereas the Ta-doped A15 has a Tc-distribution extending from 18 down to 5-6 K (the lowest expected Tc for the binarymore » A15 phase), the Ti-doped samples have no A15 phase with Tc below ~12 K. The much narrower Tc distribution in the Ti-doped samples has a positive effect on their in-field Tc-distribution too, leading to an extrapolated μ0Hc2(0) 2 Tesla larger than the Ta-doped one. Ti-doping also appears to be very homogeneous even when the Sn content is reduced in order to inhibit breakdown of the diffusion barriers in very high Jc conductors. As a result, the enhanced homogeneity of the Ti-doped samples appears to result from its assistance of rapid diffusion of Sn into the filaments and by its incorporation into the A15 phase interchangeably with Sn on the Sn sites of the A15 phase.« less

  4. Fast Ion Conduction in Li7-xLa3(Zr2-xMx)O12 (m = Ta5+, Nb5+, X = 0, 0.25) Garnets

    NASA Astrophysics Data System (ADS)

    Adams, Stefan; Gu, Wenyi; Rao, R. Prasada

    2013-07-01

    Due to their high ionic conductivity and stability versus metallic Li, garnet-related Li7La3Zr2O12 (LLZ) are of interest as Li solid electrolytes for all-solid state batteries or Li-Air batteries. The correlation between structure and ion mobility in undoped, Ta5+, Nb5+ or Al3+ doped LLZ is studied combining Molecular Dynamics (MD) simulations, bond valence (BV) studies and experimental characterisation. In-situ XRD and neutron powder diffraction are employed to monitor the phase transition and to analyze the Li and dopant distribution. Simulations reproduce static and dynamic characteristics of the material. In LLZ the site occupancy of tetrahedral sites increases only gradually with temperature from 1/3 near room temperature to a maximum value of 0.56 that can be understood from mutual site blocking. Pentavalent doping enhances ionic conductivity by increasing the vacancy concentration and reducing local Li ordering. Trivalent doping on the Li site is slightly less effective in enhancing conductivity. The simulated diffusion coefficient and its activation energy closely match the experimental conductivities.

  5. Bone bonding bioactivity of Ti metal and Ti-Zr-Nb-Ta alloys with Ca ions incorporated on their surfaces by simple chemical and heat treatments.

    PubMed

    Fukuda, A; Takemoto, M; Saito, T; Fujibayashi, S; Neo, M; Yamaguchi, S; Kizuki, T; Matsushita, T; Niinomi, M; Kokubo, T; Nakamura, T

    2011-03-01

    Ti15Zr4Nb4Ta and Ti29Nb13Ta4.6Zr, which do not contain the potentially cytotoxic elements V and Al, represent a new generation of alloys with improved corrosion resistance, mechanical properties, and cytocompatibility. Recently it has become possible for the apatite forming ability of these alloys to be ascertained by treatment with alkali, CaCl2, heat, and water (ACaHW). In order to confirm the actual in vivo bioactivity of commercially pure titanium (cp-Ti) and these alloys after subjecting them to ACaHW treatment at different temperatures, the bone bonding strength of implants made from these materials was evaluated. The failure load between implant and bone was measured for treated and untreated plates at 4, 8, 16, and 26 weeks after implantation in rabbit tibia. The untreated implants showed almost no bonding, whereas all treated implants showed successful bonding by 4 weeks, and the failure load subsequently increased with time. This suggests that a simple and economical ACaHW treatment could successfully be used to impart bone bonding bioactivity to Ti metal and Ti-Zr-Nb-Ta alloys in vivo. In particular, implants heat treated at 700 °C exhibited significantly greater bone bonding strength, as well as augmented in vitro apatite formation, in comparison with those treated at 600 °C. Thus, with this improved bioactive treatment process these advantageous Ti-Zr-Nb-Ta alloys can serve as useful candidates for orthopedic devices. PMID:20883837

  6. Development of Low Cost Membranes (Ta, Nb & Cellulose Acetate) for H2/CO2 Separation in WGS Reactors

    SciTech Connect

    Seetala, Naidu; Siriwardane, Upali

    2011-12-15

    The main aim of this work is to synthesize low temperature bimetallic nanocatalysts for Water Gas Shift reaction (WGS) for hydrogen production from CO and steam mixture; and develop low-cost metal (Nb/Ta)/ceramic membranes for H2 separation and Cellulose Acetate membranes for CO2 separation. .

  7. Elastic, Electronic and Thermodynamic Properties of Rh3X(X = Zr, Nb and Ta) Intermetallic Compounds

    NASA Astrophysics Data System (ADS)

    Ould Kada, M.; Seddik, T.; Sayede, A.; Khenata, R.; Bouhemadou, A.; Deligoz, E.; Alahmed, Z. A.; Bin Omran, S.; Rached, D.

    2014-11-01

    Structural, electronic, elastic and thermodynamic properties of Rh3X(X = Zr, Nb, Ta) intermetallic compounds are investigated in the framework of density functional theory (DFT). The exchange-correlation (XC) potential is treated with the generalized gradient approximation (GGA) and local density approximation (LDA). The computed ground state properties agree well with the available theoretical and experimental values. The elastic constants are obtained by calculating the total energy versus volume conserving strains using Mehl model. The electronic and bonding properties are discussed from the calculations of band structures (BSs), densities of states and electron charge densities. The volume and bulk modulus at high pressure and temperature are investigated. Additionally, thermodynamic properties such as the heat capacity, thermal expansion and Debye temperature at high pressures and temperatures are also analyzed.

  8. Phonon and thermal expansion properties in Weyl semimetals MX (M = Nb, Ta; X = P, As): ab initio studies.

    PubMed

    Chang, Dahu; Liu, Yaming; Rao, Fengfei; Wang, Fei; Sun, Qiang; Jia, Yu

    2016-06-01

    Weyl semimetal (WSM) is a new type of topological quantum material for future spintronic devices. Using the first-principles density functional theory, we systematically investigated the thermal expansion properties, and the temperature dependence of isovolume heat capacity and bulk modulus in WSMs MX (M = Nb, Ta; X = P, As). We also presented the phonon dispersion curves and its variation under stress in MX and the anisotropic thermal expansion properties due to the anisotropic crystal structure in WSMs have been predicted in our calculations. Intriguing, we found that the heat capacities increase more rapidly with increasing temperature in the low temperature region for all MX. Furthermore, our results showed that the thermal expansion properties are determined mainly by the isovolume heat capacity at low temperatures, while the bulk modulus has the major effect at high temperatures. These results are useful for applications of WSMs in electronic and spintronic devices. PMID:27174542

  9. A new mineral species rossovskyite, (Fe3+,Ta)(Nb,Ti)O4: crystal chemistry and physical properties

    NASA Astrophysics Data System (ADS)

    Konovalenko, Sergey I.; Ananyev, Sergey A.; Chukanov, Nikita V.; Rastsvetaeva, Ramiza K.; Aksenov, Sergey M.; Baeva, Anna A.; Gainov, Ramil R.; Vagizov, Farit G.; Lopatin, Oleg N.; Nebera, Tatiana S.

    2015-11-01

    A new mineral rossovskyite named after L.N. Rossovsky was discovered in granite pegmatites of the Bulgut occurrence, Altai Mts., Western Mongolia. Associated minerals are microcline, muscovite, quartz, albite, garnet of the almandine-spessartine series, beryl, apatite, triplite, zircon, pyrite, yttrobetafite-(Y) and schorl. Rossovskyite forms flattened anhedral grains up to 6 × 6 × 2 cm. The color of the mineral is black, and the streak is black as well. The luster is semi-metallic, dull. Mohs hardness is 6. No cleavage or parting is observed. Rossovskyite is brittle, with uneven fracture. The density measured by the hydrostatic weighing method is 6.06 g/cm2, and the density calculated from the empirical formula is 6.302 g/cm3. Rossovskyite is biaxial, and the color in reflection is gray to dark gray. The IR spectrum contains strong band at 567 cm-1 (with shoulders at 500 and 600 cm-1) corresponding to cation-oxygen stretching vibrations and weak bands at 1093 and 1185 cm-1 assigned as overtones. The reflection spectrum in visible range is obtained. According to the Mössbauer spectrum, the ratio Fe2+:Fe3+ is 35.6:64.4. The chemical composition is as follows (electron microprobe, Fe apportioned between FeO and Fe2O3 based on Mössbauer data, wt%): MnO 1.68, FeO 5.92, Fe2O3 14.66, TiO2 7.69, Nb2O5 26.59, Ta2O5 37.51, WO3 5.61, total 99.66. The empirical formula calculated on four O atoms is: {{Mn}}_{0.06}^{2 + } {{Fe}}_{0.21}^{2 + } {{Fe}}_{0.47}^{3 + } Ti0.25Nb0.51Ta0.43W0.06O4. The crystal structure was determined using single-crystal X-ray diffraction data. The new mineral is monoclinic, space group P2/ c, a = 4.668(1), b = 5.659(1), c = 5.061(1) Å, β = 90.21(1)º; V = 133.70(4) Å3, Z = 2. Topologically, the structure of rossovskyite is analogous to that of wolframite-group minerals. The crystal-chemical formula of rossovskyite is [(Fe3+, Fe2+, Mn)0.57Ta0.32Nb0.11][Nb0.40Ti0.25Fe0.18Ta0.11W0.06]O4. The strongest lines of the powder X-ray diffraction pattern

  10. Bioactive surface modification of Ti-29Nb-13Ta-4.6Zr alloy through alkali solution treatments.

    PubMed

    Takematsu, E; Katsumata, K; Okada, K; Niinomi, M; Matsushita, N

    2016-05-01

    Bioactive surface modification of Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) was performed through three different alkali solution treatments, including the electrochemical (E), hydrothermal (H), and hydrothermal-electrochemical (HE) processes; all of the processes lead to the formation of sodium-contained amorphous titanium oxide layers on TNTZ samples. The TNTZ samples subjected to the E, H, and HE processes exhibit a flat surface, smooth and fine mesh-like structure surface, and rough mesh-like structure surface, respectively. In the bioactive test, namely, simulated body fluid test, apatite inductivity increases as the surface morphology becomes rough. The order of inductivity for the three processes was HE>H>E. The surface chemical composition also affects the apatite induction ability. The surface with fewer niobium species exhibits better apatite inductivity. PMID:26952470

  11. Recrystallization temperature influence upon texture evolution of a SPD processed Ti-Nb-Ta-Zr-O alloy

    NASA Astrophysics Data System (ADS)

    Cojocaru, V. D.; Raducanu, D.; Gordin, D. M.; Cinca, I.; Thibon, I.; Caprarescu, A.

    2014-08-01

    The present study investigates the texture features occurred during recrystallization of a Ti-29Nb-9Ta-10Zr-0.2O (wt.%) alloy processed by multi-pass cold-rolling, up to 90% thickness reduction. Data concerning alloy component phases and the lattice parameters of identified phases were obtained and analysed for all thermo-mechanical processing stages. Crystallographic texture changes occurred during alloy thermo-mechanical processing (coldrolling and recrystallization), were investigated using X-ray diffraction; by acquiring the pole figures data of the main β-Ti phase. Data concerning observed texture components and texture fibers was analysed using phi1 - Φ - phi2 Bunge system in phi2 = 0° and 45° sections. The γ textural fiber was analysed for all thermo-mechanical processing stages.

  12. Effect of oxygen on the microstructure and mechanical properties of Ti-23Nb-0.7Ta-2Zr alloy

    NASA Astrophysics Data System (ADS)

    Duan, Hui-ping; Xu, Hong-xia; Su, Wen-huang; Ke, Yu-bin; Liu, Zeng-qian; Song, Hong-hai

    2012-12-01

    The influence of oxygen content on the microstructure and mechanical properties of Ti-23Nb-0.7Ta-2Zr (at%) alloy in as-cast and cold-rolled states was investigated systematically in this paper. It is found that the alloy containing oxygen element is only composed of a single β phase, while the alloy without oxygen element consisted of β and α″ phases. Although the grain size becomes larger, the elastic deformation ratio, strength, and hardness of the alloy are all increased with an increase of oxygen content. The as-cast alloy has excellent plastic deformation ability, but the cold-rolled alloy containing oxygen element exhibits brittle characteristics. A conclusion can be drawn that oxygen element can stabilize β phase, inhibit the phase transformation from β to α″, and furthermore help to increase the strength and elastic deformation ability of the alloy.

  13. Newly developed Ti-Nb-Zr-Ta-Si-Fe biomedical beta titanium alloys with increased strength and enhanced biocompatibility.

    PubMed

    Kopova, Ivana; Stráský, Josef; Harcuba, Petr; Landa, Michal; Janeček, Miloš; Bačákova, Lucie

    2016-03-01

    Beta titanium alloys are promising materials for load-bearing orthopaedic implants due to their excellent corrosion resistance and biocompatibility, low elastic modulus and moderate strength. Metastable beta-Ti alloys can be hardened via precipitation of the alpha phase; however, this has an adverse effect on the elastic modulus. Small amounts of Fe (0-2 wt.%) and Si (0-1 wt.%) were added to Ti-35Nb-7Zr-6Ta (TNZT) biocompatible alloy to increase its strength in beta solution treated condition. Fe and Si additions were shown to cause a significant increase in tensile strength and also in the elastic modulus (from 65 GPa to 85 GPa). However, the elastic modulus of TNZT alloy with Fe and Si additions is still much lower than that of widely used Ti-6Al-4V alloy (115 GPa), and thus closer to that of the bone (10-30 GPa). Si decreases the elongation to failure, whereas Fe increases the uniform elongation thanks to increased work hardening. Primary human osteoblasts cultivated for 21 days on TNZT with 0.5Si+2Fe (wt.%) reached a significantly higher cell population density and significantly higher collagen I production than cells cultured on the standard Ti-6Al-4V alloy. In conclusion, the Ti-35Nb-7Zr-6Ta-2Fe-0.5Si alloy proves to be the best combination of elastic modulus, strength and also biological properties, which makes it a viable candidate for use in load-bearing implants. PMID:26706526

  14. Corrosion Behaviour of Nitrogen-Implantation Ti-Ta-Nb Alloy in Physiological Solutions Simulating Real Conditions from Human Body

    NASA Astrophysics Data System (ADS)

    Drob, Silviu Iulian; Vasilescu, Cora; Drob, Paula; Vasilescu, Ecaterina; Gordin, Doina Margareta; Gloriant, Thierry

    2015-04-01

    We applied a new nitrogen-implantation technique (trademark Hardion+) using a source of nitrogen ions, electron cyclotron resonance that assures higher energy and deeper implantation than the conventional techniques. The N-implantation surface of the new Ti-25Ta-25Nb alloy was analyzed as follows: for the phase identification by x-ray diffraction (XRD) in a glancing geometry (1°); for the hardness by the nano-indentation method; for the corrosion behaviour in Ringer solutions of different pH values (simulating the real conditions from the human body) by cyclic and linear polarization, electrochemical impedance spectroscopy and the monitoring of the open circuit potentials and corresponding potential gradients. XRD pattern was indexed with face-centred cubic TiN compound partially substituted with TaN and NbN. The hardness increased about 2 times for the N-implantation alloy. The implantation layer had a protection effect, increasing the corrosion and passivation potentials and decreasing the tendency to passivation and passive current density, due to its compactness, reinforcement action. The corrosion current density and rate decreased by about 10 times and the polarization resistance increased by about 2 times, indicative of a more resistant nitride layer. The porosity was much reduced and the protection efficiency had values closed to 90%, namely the implantation treatment led to the formation of a dense, resistant layer. Impedance spectra showed that the capacitive behaviour of the N-implantation alloy was more insulating and protective. An electric equivalent circuit with two times constants was modelled.

  15. New insights into magma source compositions: constraints from combined Zr/Hf and Nb/Ta systematics

    NASA Astrophysics Data System (ADS)

    Bennett, S.; Elliott, T.; Blundy, J.

    2003-04-01

    Knowledge of the behaviour of trace elements in the mantle is a pre-requisite for the modelling and ultimately, understanding of mantle processes. As new, improved analytical techniques are developed additional groups of elements can be exploited to this end. One such group are the High Field Strength Elements (HFSE). Conventional wisdom suggests that the HFSE pairs Zr-Hf and Nb-Ta should behave as "geochemical twins" retaining chondritic ratios during petrogenetic processes such as melt generation and fractional crystallisation. However, precise measurements of these elements using Isotope Dilution (ID)- Plasma Ionisation Multi-collector Mass Spectrometry (PIMMS) are able to demonstrate that Zr/Hf and Nb/Ta show considerable variation between samples [1,2,3]. We have also developed new high precision separation and measurement techniques for the HFSE to specifically investigate the origin of the "garnet signature" in MORB and OIB [4,5,6]. Experiments carried out in simple synthetic systems by van Westrenen et al [7] suggest that DZr < DHf for pyropic garnets, such as those found in garnet peridotite, but the reverse, DZr > DHf is true of grossular rich garnets as would be present in a eclogitic source component of recycled crustal origin. This suggests that the HFSE have the potential to distinguish between these two garnet-bearing mantle sources. We will present data on a range of mantle derived melts with variable "garnet signatures" in order to address this issue. [1]Weyer et al. (2003), EPSL 205, 309-324. [2]Büchl et al. (2002), Goldschmidt Abstracts, A108. [3]David et al. (2000), EPSL 178, 285-301. [4]Hirschmann and Stolper (1996), CMP 124, 185-208. [5]Hirschmann (1996), Nature 384, 215-217. [6]Stracke et al. (1999), G-cubed, 1. [7]van Westrenen et al. (1999), Am. Min 84, 838-847.

  16. Crystal Structure Refinement of Mg 5Nb 4O 15and Mg 5Ta 4O 15by Rietveld Analysis of Neutron Powder Diffraction Data

    NASA Astrophysics Data System (ADS)

    Pagola, S.; Carbonio, R. E.; Fernández-Díaz, M. T.; Alonso, J. A.

    1998-05-01

    The crystal structure of the isomorphous phases Mg5Nb4O15and Mg5Ta4O15was refined from neutron powder diffraction data. These compounds are isostructural with pseudobrookite, Fe2TiO5. The two kinds of metal sites of this structure are randomly occupied by Mg(II) and Nb(V) or Ta(V). The structure consists of double chains of (Mg,M)O6units (whereM=Nb or Ta), sharing edges on thebcplane, interconnected through common oxygens along theaaxis to give a three-dimensional array. The (Mg,M)O6polyhedra at both metal positions can be described as very distorted octahedra, with (Mg,M)-O distances ranging from 1.93 to 2.22 Å. The crystallographic formulas can be written as (Mg0.73(2)Nb0.27(2))4c(Mg0.94(2)Nb1.06(2))8fO5and (Mg0.66(2)Ta0.34(2))4c(Mg1.01(2)Ta0.99(2))8fO5respectively, where 4c and 8f are the Wyckoff sites of the two metal positions of the structure. The space group is Cmcm (orthorhombic) andZ=4. Unit cell parameters, cell volume,RwpandRIvalues obtained werea=3.8068(1) Å,b=10.0561(1) Å,c=10.2566(1) Å,V=392.64(2) Å3, and 6.72% and 2.94% for the niobium compound; anda=3.81884(6) Å,b=10.0574(2) Å,c=10.2343(2) Å,V=393.07(2) Å3, and 4.46%, and 2.36% for the tantalum compound.

  17. Tailoring the magnetic properties of new Fe-Ni-Co-Al-(Ta,Nb)-B superelastic rapidly quenched microwires

    SciTech Connect

    Borza, F. Lupu, N.; Dobrea, V.; Chiriac, H.

    2015-05-07

    Ferromagnetic Fe-Ni-Co-Al-(Ta,Nb)-B microwires with diameters from 170 μm to 50 μm, which possess both superelastic and good magnetic properties, have been prepared by rapid quenching from the melt using the in rotating water spinning technique followed by cold-drawing and ageing. The cold-drawing and annealing processes lead to the initialization of premartensitic phases as confirmed by the X-ray diffraction and scanning transmission electron microscopic investigations, more significantly in the 50 μm cold-drawn microwires. An increase in the coercive field and in the saturation magnetization has been obtained by annealing, more importantly in the case of Nb-containing alloy. Ageing by thermal or current annealing led to the initialization of the superelastic effect. High values of strain of up to 1.8%, very good repeatability under successive loading, and values of superelastic effect of up to 1.2% have been achieved. The structural analysis coupled with the stress-strain data suggests that these materials annealed at 800 °C have superelastic potential at reduced ageing times. The magnetic behavior was found to be easily tailored through both thermal and thermomagnetic treatments with changes in the magnetic parameters which can be contactless detected. The results are important for future applications where both mechanical and magnetic properties matter, i.e., sensing/actuating systems.

  18. Structural and ferroelectric properties of (K,Na,Li)(Nb,Ta)O3 — CaZrO3 thick films by aerosol deposition

    NASA Astrophysics Data System (ADS)

    Lee, Jungkeun; Lee, Soohwan; Choi, Min-Geun; Kang, Soo-Bin; Lim, Ji-Ho; Kim, Hwee-Jong; Jeong, Dae-Yong; Kong, Young-Min; Lee, Jong-Pil

    2015-04-01

    Ferroelectric (1- x)(K0.51Na0.47Li0.02)(Nb0.8Ta0.2)O3 — paraelectric xCaZrO3 solid solution films were deposited on Pt-coated Si substrates by using an aerosol deposition method. The hysteresis and the dielectric properties changed significantly even with small changes in the content of paraelectric CaZrO3. With increasing CaZrO3 content, the ferroelectric phase transformed gradually to a paraelectric phase. With the addition of 3.0 mol% CaZrO3, the dielectric constant was highest; ɛ 33 ~1100 at 1 kHz with a ferroelectric hysteresis loop. Although the 5.0 mol% of CaZrO3 added film revealed a higher remanent polarization, saturated polarization and coercive field than the 3.0 mol% CaZrO3 added film, the former exhibited an asymmetric polarization — electric field hysteresis loop. The X-ray diffraction confirmed that the ferroelectric to paraelectric phase transition occurred at approximately 3.0 mol% CaZrO3.

  19. Prediction and Confirmation of Phases Formed in the Diffusion Zone of Ti-5Ta-2Nb/304L SS Explosive Clads

    NASA Astrophysics Data System (ADS)

    Prasanthi, T. N.; Sudha, Cheruvathur; Parida, P. K.; Dasgupta, A.; Saroja, S.

    2015-04-01

    Explosive cladding, a solid-state welding technique was used to fabricate dissimilar joints between Ti-5Ta-2Nb alloy and 304L austenitic stainless steel. To remove the residual stresses and improve the ductility of the `as clad' joints, further heat treatments were carried out in the temperature range of 873 K to 1073 K (600 °C to 800 °C) for varying durations. Systematic change in the interface microstructure and microchemistry due to thermally activated interdiffusion of alloying elements was studied. This information together with that of the thermal stability of non-equilibrium phases in base materials was used to evaluate the probability of formation of various phases across the explosive clad interface using JMatPro®, a materials modeling software. In the clad heat treated at 1073 K (800 °C) for 20 hours, evidence was obtained for the presence of different phases (predicted to form) in the diffusion zone by transmission electron microscopy on site-specific specimens prepared by focused ion beam milling. An attempt to understand the specific influence of the type of phase, their relative mole fraction, and microchemistry on the mechanical property of the joint has also been made based on both experimental and computational study.

  20. Crystal structures, electronic properties, and pressure-induced superconductivity of the tetrahedral cluster compounds GaNb(4)S(8), GaNb(4)Se(8), and GaTa(4)Se(8).

    PubMed

    Pocha, Regina; Johrendt, Dirk; Ni, Bingfang; Abd-Elmeguid, Mohsen M

    2005-06-22

    The crystal structures of the tetrahedral cluster compounds GaNb(4)S(8) and GaTa(4)Se(8) were determined by single-crystal X-ray diffraction. They crystallize in the cubic GaMo(4)S(8) structure type (F3m), which can be derived from the spinel type by shifting the metal atoms off the centers of the chalcogen octahedra along [111]. Electrical resistivity and magnetic susceptibility measurements show that the electronic conduction originates from hopping of localized unpaired electrons (S = (1)/(2)) among widely separated Nb(4) or Ta(4) clusters, and thus these materials represent a new class of Mott insulators. Under high pressure we find that GaNb(4)S(8) undergoes a transition from the Mott insulating to a superconducting state with T(C) up to 4 K at 23 GPa, similar to GaNb(4)Se(8) and GaTa(4)Se(8). High-pressure single-crystal X-ray studies of GaTa(4)Se(8) reveal that the superconducting transition is connected with a gradual decrease of the octahedral distortion with increasing pressure. DFT band structure calculations show that weakly coupled cluster orbitals are responsible for a high density of states at the Fermi level. The correct insulating magnetic ground state for GaNb(4)S(8) with mu(eff) = 1.73 mu(B) is for the first time achieved by the LDA+U method using U = 6 eV and rhombohedral symmetry. PMID:15954779

  1. Processing, physical metallurgy and creep of NiAl + Ta and NiAl + Nb alloys. Ph.D. Thesis. Final Contractor Report

    NASA Technical Reports Server (NTRS)

    Pathare, Viren M.

    1988-01-01

    Powder processed NiAl + Ta alloys containing 1, 2, and 4.5 at percent tantalum and NiAl + Nb alloys containing 1 and 2 at percent niobium were developed for improved creep properties. In addition, a cast alloy with 5 at percent tantalum was also studied. Hot extrusion parameters for processing alloys with 1 and 2 at percent of tantalum or niobium were designed. The NiAl + 4.5 at percent Ta alloy could be vacuum hot pressed successfully, even though it could not be extruded. All the phases in the multiphase alloys were identified and the phase transformations studied. The Ni2AlTa in NiAl + 4.5 at percent Ta alloy transforms into a liquid phase above 1700 K. Solutionizing and annealing below this temperature gives rise to a uniform distribution of fine second phase precipitates. Compressive creep properties were evaluated at 1300 K using constant load and constant velocity tests. In the higher strain rate region single phase NiAl + 1 at percent Ta and NiAl + 1 at percent Nb alloys exhibit a stress exponent of 5 characteristic of climb controlled dislocation creep. In slower strain rate regime diffusional creep becomes important. The two phase alloys containing 2 to 5 at percent Ta and 2 at percent Nb show considerable improvement over binary NiAl and single phase alloys. Loose dislocation networks and tangles stabilized by the precipitates were found in the as crept microstructure. The cast alloy which has larger grains and a distribution of fine precipitates shows the maximum improvement over binary NiAl.

  2. Effect of isovalent substitution on microstructure and phase transition of LaNb{sub 1−x}M{sub x}O{sub 4} (M=Sb, V or Ta; x=0.05–0.3)

    SciTech Connect

    Wachowski, S.; Gazda, M.

    2014-11-15

    LaNb{sub 1−x}M{sub x}O{sub 4} oxides with pentavalent elements of different ionic sizes (M=Sb, Ta and V, x=0.05–0.3) were synthesized by the solid state reaction method. Special interest was devoted to the antimony substituted lanthanum niobate which is a new material in this group. Rietveld analysis of the X-ray diffraction patterns was used to determine the influence of the material composition on unit cell parameters. On the basis of dilatometric measurements phase transition temperatures and thermal expansion coefficients of the studied materials were determined. It was shown that with increasing concentration of Sb the phase transition temperature decreases. Thermal expansion coefficient of the antimony substituted samples above the transition temperature is in the range from 8.1 to 9.1×10{sup −6} 1/K, whereas below the transition temperature the TEC value is between 14 and 17.3×10{sup −6} 1/K. Influence of Ta, V and Sb substitutions on the microstructure and grain size was studied. - Graphical abstract: Substitution of niobium by other pentavalent elements in LaNbO{sub 4} leads to change in phase transition temperature. In case of Sb substituent a shift of phase transition into the lower temperature region is observed. LaNb{sub 0.7}Sb{sub 0.3}O{sub 4} substitution allows to achieve material with tetragonal crystal structure at room temperature and no phase transition up to 1000 °C. - Highlights: • Antimony doped lanthanum niobate was successfully synthesized by solid state synthesis method. • The structural properties have been investigated by XRD and SEM. • The influence of doping on phase transition temperature has been studied.

  3. Forced polarization of α-sapphire induced by coated LiNbO3 and LiTaO3 films

    NASA Astrophysics Data System (ADS)

    Yang, X.; Wu, X. L.; Feng, Y.; Li, J.; Jiang, M.

    2004-04-01

    We have investigated the formation mechanism of the interfacial electric field in LiNbO3(or LiTaO3)/α-sapphire crystal structures, which is important in understanding the photoluminescence properties of this kind of ferroelectric film-coated crystal material. It is revealed that the interfacial electric field arises from the interfacial polarization charge generated during poling of LiNbO3(or LiTaO3) film near Curie temperature, which induces forced polarization of the α-sapphire crystal. As a result, lattice distortions of the α-sapphire crystal change the crystal field of Cr3+ ion in the sapphire crystal and therefore lead to intensity enhancement of R-line luminescence from Cr3+ centers.

  4. Nb/Ta, Zr/Hf and REE in the depleted mantle: implications for the differentiation history of the crust-mantle system

    NASA Astrophysics Data System (ADS)

    Weyer, Stefan; Münker, Carsten; Mezger, Klaus

    2003-01-01

    High-precision Nb, Ta, Zr, Hf, Sm, Nd and Lu concentration data of depleted mantle rocks from the Balmuccia peridotite complex (Ivrea Zone, Italian Alps) were determined by isotope dilution using multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS) and thermal ionisation mass spectrometry (TIMS). The Zr/Hf ratios of all investigated samples from the Balmuccia peridotite complex are significantly lower than the chondritic value of 34.2, and the most depleted samples have Zr/Hf ratios as low as 10. Correlated Zr/Hf ratios and Zr abundances of the lherzolites preserve the trend of a mantle residue that has been depleted by fractional melting. This trend confirms experimental studies that predict Hf to behave more compatibly than Zr during mantle melting. Experimentally determined partition coefficients imply that the major Zr and Hf depletion most likely occurred in the spinel stability field, with ( DZr/ DHf) cpx≈0.5, and not in the garnet stability field, where ( DZr/ DHf) grt is probably close to one. However, minor amounts of melting must have also occurred in a garnet facies mantle, as indicated by low Sm/Lu ratios in the Balmuccia peridotites. The Nb/Ta ratios of most lherzolites are subchondritic and vary only from 7 to 10, with the exception of three samples that have higher Nb/Ta ratios (18-24). The overall low Nb/Ta ratios of most depleted mantle rocks confirm a higher compatibility of Ta in the mantle. The uniform Nb/Ta ratios in most samples imply that even in 'depleted' mantle domains the budget of the highly incompatible Nb and Ta is controlled by enrichment processes. Such a model is supported by the positive correlation of Zr/Nb with the Zr concentration. However, the overall enrichment was weak and did barely affect the moderately incompatible elements Zr and Hf. The new constraints from the partitioning behaviour of Zr-Hf and Nb-Ta provide important insights into processes that formed the Earth's major silicate reservoirs. The

  5. Enhanced photoluminescence from Cr3+ centers in α-sapphire coated with LiNbO3(:Fe) and LiTaO3 films

    NASA Astrophysics Data System (ADS)

    Yang, X.; Wu, X. L.; Siu, G. G.; Kong, F.; Qiu, T.

    2004-12-01

    A LiNbO3(:Fe) or LiTaO3 film is sandwiched between a (012)-oriented α-sapphire wafer and an amorphous Al2O3 or SiO2 film using pulsed laser deposition. After annealing at 1000 °C in O2, the film becomes a c-oriented single-domain ferroelectric. This sandwich structure shows an enhanced photoluminescence from trace amounts of Cr3+ centers in the host α-sapphire (R-line emission at 691 nm). Spectral analyses suggest that both strong space-charge and photorefractive effects of the LiNbO3(:Fe) or LiTaO3 film cause a change in the crystal field of the host α-sapphire, which increases the transition probability of Cr3+ and thus leads to an enhancement of the R-line intensity. The result has prospective applications in laser and optical integrated devices.

  6. Simultaneous holographic and photocurrent studies of the photorefractive effect in LiTaO3 and LiNbO3

    NASA Technical Reports Server (NTRS)

    Spinhirne, J. M.; Ang, D.; Joiner, C. S.; Estle, T. L.

    1977-01-01

    In reduced LiNbO3:Mn both the photorefractive sensitivity and the simultaneously measured photocurrent result from drift with a polarization-dependent effective 'internal field' of about 6 kV/cm. In reduced undoped LiTaO3 the observed difference in applied fields of the minimum photorefractive sensitivity and zero photocurrent imply charge transport is by a mechanism that cannot be completely described by diffusion and drift in an electric field. The direct measurement of the harmonic content of phase gratings written in several LiNbO3 and LiTaO3 crystals shows termination of charge-transport results from the space-charge field of the hologram.

  7. Structural and electrical properties of Na{sub 2}Pb{sub 2}Eu{sub 2}W{sub 2}Ti{sub 4}X{sub 4}O{sub 30} (X = Nb, Ta) ferroelectric ceramics

    SciTech Connect

    Das, Piyush R.; Biswal, L.; Behera, Banarji; Choudhary, R.N.P.

    2009-06-03

    A new group of tungsten bronze family Na{sub 2}Pb{sub 2}Eu{sub 2}W{sub 2}Ti{sub 4}X{sub 4}O{sub 30} (X = Nb, Ta) having all the valence elements (I-VI) were prepared by a high-temperature solid-state reaction technique. The formations of the compounds were confirmed by X-ray diffraction technique with an orthorhombic structure. Surface morphology of the compounds was studied by scanning electron microscope (SEM). Studies of dielectric properties ({epsilon}{sub r} and tan {delta}) of the above compounds at different frequencies in a wide temperature range (300-700 K) with an impedance analyzer exhibit a ferroelectric phase transition at 580 and 394 K for Na{sub 2}Pb{sub 2}Eu{sub 2}W{sub 2}Ti{sub 4}Nb{sub 4}O{sub 30} and Na{sub 2}Pb{sub 2}Eu{sub 2}W{sub 2}Ti{sub 4}Ta{sub 4}O{sub 30}, respectively. Ferroelectric properties of these compounds were confirmed with polarization (hysteresis) study.

  8. Differences and Commonalities in the Gas-Phase Reactions of Closed-Shell Metal Dioxide Clusters [MO2 ](+) (M=V, Nb, and Ta) with Methane.

    PubMed

    Zhou, Shaodong; Li, Jilai; Schlangen, Maria; Schwarz, Helmut

    2016-05-17

    High-level electronic structure calculations, in combination with Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometric studies, permit the mechanism by which closed-shell, "naked" [TaO2 ](+) brings about C-H bond activation of methane to be revealed. These studies also help to understand why the lighter congeners of [MO2 ](+) (M=V, Nb) are unreactive under ambient conditions. PMID:27062433

  9. Thermoelectric Properties of Fe2VAl and Fe2V0.75M0.25Al (M = Mo, Nb, Ta) Alloys: First-Principles Calculations

    NASA Astrophysics Data System (ADS)

    Al-Yamani, H.; Hamad, B.

    2016-02-01

    Ab initio investigations of the structural, electronic, and thermoelectric properties of stoichiometric Fe2VAl full-Heusler alloy and Fe2V0.75M0.25Al (M = Mo, Nb, Ta) nonstoichiometric alloys have been performed using density functional theory on the basis of the full-potential linearized augmented plane wave method with the generalized gradient approximation. The thermoelectric properties are calculated using semiclassical Boltzmann transport theory within the constant-relaxation-time approximation. Fe2VAl, Fe2V0.75Nb0.25Al, and Fe2V0.75Ta0.25Al alloys are found to exhibit a semimetallic behavior, while Fe2V0.75Mo0.25Al acts as a metal. We found that Fe2VAl has a pseudogap of about -0.13 eV, whereas Fe2V0.75Nb0.25Al and Fe2V0.75Ta0.25Al are characterized by a zero energy gap around the Fermi level. Thermoelectric calculations showed that Fe2VAl has both p- and n-type thermoelectric properties, where the p-type thermopower values are found to be higher than those of n-type. The Seebeck coefficient S has maximum values from 20 μV K-1 to 125 μV K-1 and from 19 μV K-1 to 90 μV K-1 in the temperature range of 100 K to 800 K for p- and n-type, respectively. The maximum thermoelectric properties can be obtained at carrier concentration of the order of 1020 cm-3 for p- or n-type doping. Substitution of Nb and Ta atoms enhanced the thermoelectric properties to 150 μV K-1 at 800 K. The optimum concentrations for the three partially substituted alloys were found to be between 1020 cm-3 and 1021 cm-3.

  10. Isotropic plasticity of β-type Ti-29Nb-13Ta-4.6Zr alloy single crystals for the development of single crystalline β-Ti implants.

    PubMed

    Hagihara, Koji; Nakano, Takayoshi; Maki, Hideaki; Umakoshi, Yukichi; Niinomi, Mitsuo

    2016-01-01

    β-type Ti-29Nb-13Ta-4.6Zr alloy is a promising novel material for biomedical applications. We have proposed a 'single crystalline β-Ti implant' as new hard tissue replacements for suppressing the stress shielding by achieving a drastic reduction in the Young's modulus. To develop this, the orientation dependence of the plastic deformation behavior of the Ti-29Nb-13Ta-4.6Zr single crystal was first clarified. Dislocation slip with a Burgers vector parallel to <111> was the predominant deformation mode in the wide loading orientation. The orientation dependence of the yield stress due to <111> dislocations was small, in contrast to other β-Ti alloys. In addition, {332} twin was found to be operative at the loading orientation around [001]. The asymmetric features of the {332} twin formation depending on the loading orientation could be roughly anticipated by their Schmid factors. However, the critical resolved shear stress for the {332} twins appeared to show orientation dependence. The simultaneous operation of <111> slip and {332} twin were found to be the origin of the good mechanical properties with excellent strength and ductility. It was clarified that the Ti-29Nb-13Ta-4.6Zr alloy single crystal shows the "plastically almost-isotropic and elastically highly-anisotropic" nature, that is desirable for the development of 'single crystalline β-Ti implant'. PMID:27417073

  11. High resolution transmission electron microscopy study of the hardening mechanism through phase separation in a beta-Ti-35Nb-7Zr-5Ta alloy for implant applications.

    PubMed

    Afonso, Conrado R M; Ferrandini, Peterson L; Ramirez, Antonio J; Caram, Rubens

    2010-04-01

    beta-Ti alloys are highly attractive metallic materials for biomedical applications due to their high specific strength, high corrosion resistance and excellent biocompatibility, including low elastic modulus. This work aims to clarify the hardening mechanism of a beta-Ti-Nb-Zr-Ta alloy using different characterization techniques. Ingots (50 g) of Ti-35Nb-7Zr-5Ta (wt.%) alloy were arc furnace melted in an Ar((g)) atmosphere, homogenized, hot rolled, solubilized and finally aged at several temperatures from 200 to 700 degrees C for 4 h. Microstructure characterization was performed using X-ray diffraction, optical microscopy, scanning and high resolution transmission electron microscopy (HR-TEM). The 4 h aging showed that the highest hardness values were found when aged at 400 degrees C and the HR-TEM images confirmed splitting of spots on the Fourier space map, which indicated the presence of a coherent interface between separated phases (beta and beta') and explains the hardening mechanism of the alloy. Through geometric phase analysis analysis, using the HR-TEM image, the localized strain map showed 5-10 nm domains of the beta and beta' phases. The combination of suitable values of yield strength, hardness and low Young's modulus makes Ti-35Nb-7Zr-5Ta alloy suitable for medical applications as a metallic orthopedic implant. PMID:19913645

  12. DFT simulation on the temperature-dependent electronic transition of V (Nb or Ta) substituted NiMn2O4

    NASA Astrophysics Data System (ADS)

    Li, Hai-Long; Bian, Liang; Chang, Ai-Ming; Jian, Ji-Kang; Hou, Wen-Ping; Gao, Lei; Zhang, Xiao-Yan; Wang, Lei; Ren, Wei; Song, Mian-Xin; Dong, Fa-Qin

    2016-07-01

    Previously, we reported that the d-p (Mn-3d-O-2p) orbital hybridization induces Mn valence change (Mn3+→Mn4+) in the octahedron. The electron transfer mechanism can be controlled by modifying the Mn-3d orbital in the octahedron. Here, we used the density functional theory (DFT) with generalized gradient approximation (GGA) and two-dimensional correlation analysis (2D-CA) techniques to calculate the electron transfer mechanism of the V (Nb or Ta) substituted NiMn2O4 (NMO) in the temperature range of 50-1500 K. The results show that the heat accumulation accelerates the O-2p4 orbital splitting, inducing charge disproportionation. The V-3d3 substituted Mn increases the intensity and of the partial density of state (PDOS) at conduction band (1-3 eV), this enhances the V-3d3-O-2p4 p-d σ∗ orbital. The Nb-4d3/Ta-5d3 substituted Mn reduces the intensity of the PDOS at conduction band (1-5 eV), this weakens the Nb-4d3/Ta-5d3-O-2p4 p-d σ∗ orbital. This study effectively analyzes the microscopic changes of the electron transfer caused by the heat accumulation, provides a theoretical basis for the design of NMO-based negative temperature coefficient (NTC) thermistors.

  13. Isotropic plasticity of β-type Ti-29Nb-13Ta-4.6Zr alloy single crystals for the development of single crystalline β-Ti implants

    NASA Astrophysics Data System (ADS)

    Hagihara, Koji; Nakano, Takayoshi; Maki, Hideaki; Umakoshi, Yukichi; Niinomi, Mitsuo

    2016-07-01

    β-type Ti-29Nb-13Ta-4.6Zr alloy is a promising novel material for biomedical applications. We have proposed a ‘single crystalline β-Ti implant’ as new hard tissue replacements for suppressing the stress shielding by achieving a drastic reduction in the Young’s modulus. To develop this, the orientation dependence of the plastic deformation behavior of the Ti-29Nb-13Ta-4.6Zr single crystal was first clarified. Dislocation slip with a Burgers vector parallel to <111> was the predominant deformation mode in the wide loading orientation. The orientation dependence of the yield stress due to <111> dislocations was small, in contrast to other β-Ti alloys. In addition, {332} twin was found to be operative at the loading orientation around [001]. The asymmetric features of the {332} twin formation depending on the loading orientation could be roughly anticipated by their Schmid factors. However, the critical resolved shear stress for the {332} twins appeared to show orientation dependence. The simultaneous operation of <111> slip and {332} twin were found to be the origin of the good mechanical properties with excellent strength and ductility. It was clarified that the Ti-29Nb-13Ta-4.6Zr alloy single crystal shows the “plastically almost-isotropic and elastically highly-anisotropic” nature, that is desirable for the development of ‘single crystalline β-Ti implant’.

  14. Anion Exchange Behavior Of Ti, Zr, Hf, Nb And Ta As Homologues Of Rf And Db In Mixed HF--Acetone Solutions

    SciTech Connect

    Aksenov, N. V.; Bozhikov, G. A.; Starodub, G. Ya.; Dmitriev, S. N.; Filosofov, D. V.; Sun Jin, Jon; Radchenko, V. I.; Lebedev, N. A.; Novgorodov, A. F.

    2010-04-30

    We studied in detail the sorption behavior of Ti, Zr, Hf, Nb and Ta on AG 1 anion exchange resin in HF-acetone mixed solutions as a function of organic cosolvent and acid concentrations. Anion exchange behavior was found to be strongly acetone concentration dependent. The distribution coefficients of Ti, Zr, Hf and Nb increased and those of Ta decreased with increasing content of acetone in HF solutions. With increasing HF concentration anion exchange equilibrium analysis indicated the formation of fluoride complexes of group 4 elements with charge-3 and Ta---2. For Nb the slope of-2 increased up to-5. Optimal conditions for separation of the elements using AIX chromatography were found. Group 4 elements formed MF{sub 7}{sup 3-} (M = Ti, Zr, Hf) complexes whose sorption decreased Ti>Hf>Zr in reverse order of complex stability. This fact is of particular interest for studying ion exchange behavior of Rf compared to Ti. The advantages of studying chemical properties of Rf and Db in aqueous HF solutions mixed with organic solvents are briefly discussed.

  15. Isotropic plasticity of β-type Ti-29Nb-13Ta-4.6Zr alloy single crystals for the development of single crystalline β-Ti implants

    PubMed Central

    Hagihara, Koji; Nakano, Takayoshi; Maki, Hideaki; Umakoshi, Yukichi; Niinomi, Mitsuo

    2016-01-01

    β-type Ti-29Nb-13Ta-4.6Zr alloy is a promising novel material for biomedical applications. We have proposed a ‘single crystalline β-Ti implant’ as new hard tissue replacements for suppressing the stress shielding by achieving a drastic reduction in the Young’s modulus. To develop this, the orientation dependence of the plastic deformation behavior of the Ti-29Nb-13Ta-4.6Zr single crystal was first clarified. Dislocation slip with a Burgers vector parallel to <111> was the predominant deformation mode in the wide loading orientation. The orientation dependence of the yield stress due to <111> dislocations was small, in contrast to other β-Ti alloys. In addition, {332} twin was found to be operative at the loading orientation around [001]. The asymmetric features of the {332} twin formation depending on the loading orientation could be roughly anticipated by their Schmid factors. However, the critical resolved shear stress for the {332} twins appeared to show orientation dependence. The simultaneous operation of <111> slip and {332} twin were found to be the origin of the good mechanical properties with excellent strength and ductility. It was clarified that the Ti-29Nb-13Ta-4.6Zr alloy single crystal shows the “plastically almost-isotropic and elastically highly-anisotropic” nature, that is desirable for the development of ‘single crystalline β-Ti implant’. PMID:27417073

  16. Fatigue characteristics of bioactive glass-ceramic-coated Ti-29Nb-13Ta-4.6Zr for biomedical application.

    PubMed

    Li, S J; Niinomi, M; Akahori, T; Kasuga, T; Yang, R; Hao, Y L

    2004-08-01

    A new surface-coating method by which CaP invert glass is used to improve the bioactivity of titanium alloys has been developed recently. In this method, the powder of CaP invert glass (CaO-P2O5-TiO2-Na2O) is coated on the surface of titanium alloy samples and heated between 1073 and 1123 K. With this treatment, a calcium phosphate layer mainly containing beta-Ca3(PO4)2 phase can be coated easily on titanium alloy samples. In the present study, the effect of this coating process on the fatigue properties of Ti-29Nb-13Ta-4.6Zr, a new metastable beta alloy for biomedical applications, has been investigated. The fatigue endurance limit of the coated alloy was found to be about 15% higher than that of uncoated alloy, as a result of the formation of a hard (alpha + beta) layer and a small amount of the omega phase during the coating process. The coating exhibits excellent adhesion to the substrate during the tensile and fatigue tests. Subsequent ageing at 673 K for 259.2 ks greatly improves the fatigue resistance of the coated alloy due to isothermal omega phase precipitation, and does not have obvious detrimental effect on the coating properties. PMID:15020109

  17. Deformation-induced ω phase in modified Ti-29Nb-13Ta-4.6Zr alloy by Cr addition.

    PubMed

    Li, Qiang; Niinomi, Mitsuo; Hieda, Junko; Nakai, Masaaki; Cho, Ken

    2013-08-01

    For spinal-fixation applications, implants should have a high Young's modulus to reduce springback during operations, though a low Young's modulus is required to prevent stress shielding for patients after surgeries. In the present study, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) with a low Young's modulus was modified by adding Cr to obtain a higher deformation-induced Young's modulus in order to satisfy these contradictory requirements. Two newly designed alloys, TNTZ-8Ti-2Cr and TNTZ-16Ti-4Cr, possess more stable β phases than TNTZ. These alloys consist of single β phases and exhibit relatively low Young's moduli of <65GPa after solution treatment. However, after cold rolling, they exhibit higher Young's moduli owing to a deformation-induced ω-phase transformation. These modified TNTZ alloys show significantly less springback than the original TNTZ alloy based on tensile and bending loading-unloading tests. Thus, the Cr-added TNTZ alloys are beneficial for spinal-fixation applications. PMID:23624220

  18. High-Temperature Deformation Characteristics of a β-Type Ti-29Nb-13Ta-4.6Zr Alloy

    NASA Astrophysics Data System (ADS)

    Ghanbari, E.; Zarei-Hanzaki, A.; Farghadany, E.; Abedi, H. R.; Khoddam, Sh.

    2016-04-01

    The hot deformation behavior of a biomedical β-type Ti-Nb-Ta-Zr alloy has been studied through applying hot compression tests over a wide range of temperatures and strain rates (600-900 °C and 0.003-0.3 s-1). The main microstructural feature of the specimens, which were deformed at 900 °C, is the pancaked primary grains decorated by the serrated boundaries. The latter may well imply to the occurrence of dynamic recovery. The dynamic recrystallization however is considered as the main restoration mechanism in the specimens, which were deformed at 800 °C under all strain rates. The sizes of the new recrystallized grains well follow the serration amplitude of the primary grain boundaries. At lower deformation temperatures (600 and 700 °C), the strain rate sensitivity is suddenly decreased and ended to the strain localization in the form of macro shear band. The higher accumulated energy within the shear band zones appears to stimulate the occurrence of dynamic recrystallization. To further clarify the high-temperature flow behavior of the experimental alloy, a quantitative approach has been also employed. The observed flow hardening and softening has been justified considering the evolved microstructural features.

  19. XAFS Studies of Ni Ta and Nb Chlorides in the Ionic Liquid 1-Ethyl-3-Methyl Imidazolium Chloride / Aluminum Chloride

    SciTech Connect

    W OGrady; D Roeper; K Pandya; G Cheek

    2011-12-31

    The structures of anhydrous nickel, niobium, and tantalum chlorides have been investigated in situ in acidic and basic ionic liquids (ILs) of 1-methyl-3-ethylimidazolium chloride (EMIC)/AlCl{sub 3} with X-ray absorption spectroscopy (XAS). The coordination of NiCl{sub 2} changes from tetrahedral in basic solution to octahedral in acidic solution. The NiCl{sub 2} is a strong Lewis acid in that it can induce the AlCl{sub 3} to share its chlorides in the highly acidic IL, forming a structure with six near Cl{sup -} ions and eight further distant Al ions which share the chloride ions surrounding the Ni{sup 2+}. When Nb{sub 2}Cl{sub 10}, a dimer, is added to the acidic or basic solution, the dimer breaks apart and forms two species. In the acid solution, two trigonal bipyramids are formed with five equal chloride distances, while in the basic solution, a square pyramid with four chlorides forming a square base and one shorter axial chloride bond. Ta{sub 2}Cl{sub 10} is also a dimer and divides into half in the acidic solution and forms two trigonal bipyramids. In the basic solution, the dimer breaks apart but the species formed is sufficiently acidic that it attracts two additional chloride ions and forms a seven coordinated tantalum species.

  20. Fluid-mediated alteration of (Y,REE,U,Th)-(Nb,Ta,Ti) oxide minerals in granitic pegmatite from the Evje-Iveland district, southern Norway

    NASA Astrophysics Data System (ADS)

    Duran, Charley J.; Seydoux-Guillaume, Anne-Magali; Bingen, Bernard; Gouy, Sophie; de Parseval, Philippe; Ingrin, Jannick; Guillaume, Damien

    2016-02-01

    We document the textural relations and chemical composition of (Y,REE,U,Th)-(Nb,Ta,Ti) oxide minerals in a granitic pegmatite from the Evje-Iveland district, southern Norway, using a combination of scanning and transmission electron microscopy, electron probe micro-analysis and infrared absorption spectroscopy. The (Y,REE,U,Th)-(Nb,Ta,Ti) oxide mineral is euxenite, which is strongly radiation damaged and surrounded by radial fractures. Within euxenite grains, three domains of distinct composition comprising unaltered, intermediate and altered euxenite, have been identified. In most cases pyrochlore occurs as corroded grain boundaries around euxenite and within relict fractures. Intermediate and altered euxenite are depleted in U, Pb, Ti, Nb, and Y, but enriched in Si and Ca relative to unaltered euxenite. Pyrochlore is also enriched in Fe, Pb, Zr and LREE relative to all euxenite phases. Altered domains of euxenite have deficient analytical totals and contain O-H. These domains are metamict and contain nanopores and nanodomains enriched in U and Ca. We suggest that as radiation damage accumulated in euxenite, radial fractures developed around the euxenite grains, thus allowing fluid infiltration. In the presence of fluid, euxenite was replaced by secondary euxenite then pyrochlore, owing to dissolution-precipitation and diffusion reactions. During alteration, U and the strategic metals Nb, Ti, and REE were mobilized at both the nanoscale and the scale of the pegmatite.

  1. Microstructure characteristics and mechanical properties of laser-TIG hybrid welded dissimilar joints of Ti-22Al-27Nb and TA15

    NASA Astrophysics Data System (ADS)

    Zhang, Kezhao; Lei, Zhenglong; Chen, Yanbin; Liu, Ming; Liu, Yang

    2015-10-01

    Laser-TIG-hybrid-welding (TIG - tungsten inert gas) process was successfully applied to investigate the microstructure and tensile properties of Ti-22Al-27Nb/TA15 dissimilar joints. The HAZ of the arc zone in Ti-22Al-27Nb was characterized by three different regions: single B2, B2+α2 and B2+α2+O, while the single B2 phase region was absent in the HAZ of the laser zone. As for the HAZ in TA15 alloy, the microstructure mainly contained acicular α‧ martensites near the fusion line and partially remained the lamellar structure near the base metal. The fusion zone consisted of B2 phase due to the relatively high content of β phase stabilizing elements and fast cooling rate during the welding process. The tensile strength of the welds was higher than that of TA15 alloy because of the fully B2 microstructure in the fusion zone, and the fracture preferentially occurred on the base metal of TA15 alloy during the tensile tests at room temperature and 650 °C.

  2. NbF{sub 5} and TaF{sub 5}: Assignment of {sup 19}F NMR resonances and chemical bond analysis from GIPAW calculations

    SciTech Connect

    Biswal, Mamata; Body, Monique; Legein, Christophe; Sadoc, Aymeric; Boucher, Florent

    2013-11-15

    The {sup 19}F isotropic chemical shifts (δ{sub iso}) of two isomorphic compounds, NbF{sub 5} and TaF{sub 5}, which involve six nonequivalent fluorine sites, have been experimentally determined from the reconstruction of 1D {sup 19}F MAS NMR spectra. In parallel, the corresponding {sup 19}F chemical shielding tensors have been calculated using the GIPAW method for both experimental and DFT-optimized structures. Furthermore, the [M{sub 4}F{sub 20}] units of NbF{sub 5} and TaF{sub 5} being held together by van der Waals interactions, the relevance of Grimme corrections to the DFT optimization processes has been evaluated. However, the semi-empirical dispersion correction term introduced by such a method does not show any significant improvement. Nonetheless, a complete and convincing assignment of the {sup 19}F NMR lines of NbF{sub 5} and TaF{sub 5} is obtained, ensured by the linearity between experimental {sup 19}F δ{sub iso} values and calculated {sup 19}F isotropic chemical shielding σ{sub iso} values. The effects of the geometry optimizations have been carefully analyzed, confirming among other matters, the inaccuracy of the experimental structure of NbF{sub 5}. The relationships between the fluorine chemical shifts, the nature of the fluorine atoms (bridging or terminal), the position of the terminal ones (opposite or perpendicular to the bridging ones), the fluorine charges, the ionicity and the length of the M–F bonds have been established. Additionally, for three of the {sup 19}F NMR lines of NbF{sub 5}, distorted multiplets, arising from {sup 1}J-coupling and residual dipolar coupling between the {sup 19}F and {sup 93}Nb nuclei, were simulated yielding to values of {sup 93}Nb–{sup 19}F {sup 1}J-coupling for the corresponding fluorine sites. - Graphical abstract: The complete assignment of the {sup 19}F NMR lines of NbF{sub 5} and TaF{sub 5} allow establishing relationships between the {sup 19}F δ{sub iso} values, the nature of the fluorine atoms

  3. Direct solid-state precipitation-processed A15 /Nb3Al/ superconducting material

    NASA Astrophysics Data System (ADS)

    Hong, M.; Morris, J. W., Jr.

    1980-12-01

    A 'solid-state precipitation' process was used to prepare superconducting tapes containing Nb3Al in a niobium matrix. Small ingots of Nb-(17-19 at. %)Al were prepared by arc melting, homogenizing, quenching, warm rolling into tape, and aging at 750-900 C to precipitate the A15 phase. Transmission electron microscopy studies revealed Nb3Al precipitation in fine particles which formed a semicontinuous network over subgrain boundaries formed by the recovery of deformation-induced dislocations. Promising high-field critical currents were obtained (current density approximately 10 thousand A/sq cm in a field of 14 T at 4.2 K).

  4. Crystallographic shear in the Nb/sub 2/O/sub 5/-WO/sub 3/ and Ta/sub 2/O/sub 5/-WO/sub 3/ systems

    SciTech Connect

    England, P.J.; Booth, J.; Tilley, R.J.D.; Ekstrom, T.

    1982-08-01

    Crystallographic shear (CS) phases occurring in the Nb/sub 2/O/sub 5/-WO/sub 3/ and Ta/sub 2/O/sub 5/-WO/sub 3/ systems near to WO/sub 3/ were characterized by X-ray diffraction and high-resolution transmission electron microscopy. The Nb/sub 2/O/sub 5/-WO/sub 3/ samples were heated at 1600K. They contained ordered )104) and )001) CS planes and wavy CS which were composed of intergrowths of )104) and )001) CS segments. The compsition range over which the )104) CS series extended was from (Nb, W)O/sub 2.954/ i.e., (Nb,W)/sub 65/O/sub 192/, i.e., (Nb,W)/sub 52/O/sub 153/. The composition range over which the )001)CS series extended was from (Nb,W)O/sub 2.9375/, i.e., (Nb,W)/sub 16/O/sub 47/ to (Nb,W)O/sub 2.875/, i.e., (Nb,W)/sub 8/O/sub 23/.The Ta/sub 2/O/sub 5/-WO/sub 3/ samples were prepared at 1593, 1623, and 1672K. At lower temperatures ordered )103) CS phases were found, with a composition range extending between (Ta,W)O/sub 2.960/, i.e., (Ta,W)/sub 50/O/sub 148/, to (Ta,W)O/sub 2.944/, i.e., (Ta,W)/sub 36/O/sub 106/. At 1673K ordered )103) CS phases occurred, as did wavy CS composed of intergrowths of )103) and )104) CS segments.

  5. Structural and magnetic study of Yb{sup 3+} in the perovskites Sr{sub 2}YbMO{sub 6} (M=Nb, Ta, Sb)

    SciTech Connect

    Coomer, Fiona C.; Campbell, John; Giordano, Nico; Collins, Oonagh M.; Cussen, Edmund J.

    2015-01-15

    The compounds Sr{sub 2}YbNbO{sub 6}, Sr{sub 2}YbTaO{sub 6} and Sr{sub 2}YbSbO{sub 6} have been prepared using solid state methods by heating pelleted reagents in air at temperatures up to 1400 °C. Rietveld refinement against room temperature neutron powder diffraction data show that all three compounds crystallise with a cation-ordered variant of the perovskite structure in the P2{sub 1}/n space group. Complete cation ordering occurs between M{sup 5+} and Yb{sup 3+} over two octahedrally-coordinated sites in the structure and all compounds are stoichiometric in oxygen. The Sb–O bond lengths are similar to related perovskite compounds but differ slightly from those indicated by bond valence sums. Magnetic susceptibility data resemble Curie–Weiss paramagnetic behaviour, but can be better understood as arising from the effect of the octahedral crystal field on the {sup 2}F{sub 5/2} ground state of Yb{sup 3+} leading to a temperature dependent magnetic moment on this ion below 100 K. - Graphical abstract: The magnetic susceptibility of the face-centred cubic Yb{sup 3+} lattice is dominated by the temperature dependent single-ion moment below 100 K. - Highlights: • Cation-ordered perovskites are studied using neutron diffraction and magnetometry. • Yb{sup 3+} cations form a pseudo face centred cubic lattice in a distorted structure. • Sb{sup 5+} cation is slightly overbonded as observed in related perovskites. • Crystal field splitting of 4f{sup 13} Yb{sup 3+} giving a temperature dependent moment. • Magnetic susceptibility reproduces theoretical predictions below 100 K.

  6. A co-precipitation technique to prepare BiNbO{sub 4}, MgTiO{sub 3} and Mg{sub 4}Ta{sub 2}O{sub 9} powders

    SciTech Connect

    Gaikwad, A.B.; Navale, S.C.; Samuel, V.; Murugan, A.V.; Ravi, V. . E-mail: ravi@ems.ncl.res.in

    2006-02-02

    A simple co-precipitation technique has been used successfully for the preparation of pure, ultrafine, single phase BiNbO{sub 4} (BN), MgTiO{sub 3} and Mg{sub 4}Ta{sub 2}O{sub 9}. An aqueous sodium hydroxide or ammonium hydroxide and ammonium carbonate solution was used to precipitate these cations as hydroxides and carbonates simultaneously under basic conditions. These precursors on heating at 750 deg. C, produce the respective powders. For comparison, these compounds were also prepared by the traditional solid state method. The phase purity and lattice parameters were studied by powder X-ray diffraction (XRD). Particle size and morphology was studied by transmission electron spectroscopy (TEM)

  7. Low-loss Ca{sub 5-x}Sr{sub x}A{sub 2}TiO{sub 12} [A=Nb,Ta] ceramics: Microwave dielectric properties and vibrational spectroscopic analysis

    SciTech Connect

    Bijumon, Pazhoor Varghese; Sebastian, Mailadil Thomas; Dias, Anderson; Moreira, Roberto Luiz; Mohanan, Pezholil

    2005-05-15

    Complex perovskite-type Ca{sub 5-x}Sr{sub x}A{sub 2}TiO{sub 12} [A=Nb,Ta] (0{<=}x{<=}5) ceramics were prepared by conventional solid-state ceramic route. The crystal structure, microwave dielectric properties, and vibrational spectroscopic characteristics of these materials are reported. The structure and microstructure were investigated by x-ray diffraction and scanning electron microscopy techniques. The microwave dielectric properties were measured in the 3-5-GHz frequency range by the resonance method. Structural evolutions from orthorhombic to an averaged pseudocubic phase, with associated changes in dielectric properties, were observed as a function of composition. The structure-property relationships in these ceramics were established using Raman and Fourier transform infrared spectroscopic techniques. Raman analysis showed characteristic bands of ordered perovskite materials, with variation in both intensity and frequency as a function of composition.

  8. Dielectric, ferroelectrics properties and impedance spectroscopy analysis of the [(Na0.535K0.480)0.966Li0.058](Nb0.90Ta0.10)O3-based lead-free ceramics

    NASA Astrophysics Data System (ADS)

    Saidi, M.; Chaouchi, A.; D'Astorg, S.; Rguiti, M.; Courtois, C.

    2015-04-01

    Polycrystalline of [(Na0.535K0.480)0.966Li0.058](Nb0.90Ta0.10)O3 samples were prepared using the high-temperature solid-state reaction technique. X-ray diffraction (XRD) analysis indicates the formation of a single-phase with orthorhombic structure. AC impedance plots were used as tool to analyze the electrical behavior of the sample as a function of frequency at different temperatures. The AC impedance studies revealed the presence of grain effect, from 425°C onwards. Complex impedance analysis indicated non-Debye type dielectric relaxation. The Nyquist plot showed the negative temperature coefficient of resistance (NTCR) characteristic of NKLNT. The AC conductivity results were used to correlate with the barrier hopping (CBH) model to evaluate the binding energy (Wm), the minimum hopping distance (Rmin), the density of states at Fermi level (N(Ef)), and the activation energy of the compound.

  9. Nb Ta (Ti Sn) oxide mineral chemistry as tracer of rare-element granitic pegmatite fractionation in the Borborema Province, Northeastern Brazil

    NASA Astrophysics Data System (ADS)

    Beurlen, Hartmut; da Silva, Marcelo R. R.; Thomas, Rainer; Soares, Dwight R.; Olivier, Patrick

    2008-02-01

    The Borborema Pegmatitic Province (BPP), northeastern Brazil, is historically important for tantalum mining and also famous for top-quality specimens of exotic Nb Ta oxides and, more recently, for the production of gem quality, turquoise blue, ‘Paraíba Elbaite.’ With more than 750 registered mineralized rare-element granitic pegmatites, the BPP extends over an area of about 75 by 150 km in the eastern part of the Neoproterozoic Seridó Belt. The Late Cambrian pegmatites are mostly hosted by a sequence of Neoproterozoic cordierite sillimanite biotite schists of the Seridó Formation and quartzites and metaconglomerates of the Equador Formation. The trace-element ratios in feldspar and micas allow to classify most pegmatites as belonging to the beryl columbite phosphate subtype. Electron microprobe analyses (EMPA) of columbite, tapiolite, niobian tantalian rutile, ixiolite and wodginite group minerals from 28 pegmatites in the BPP are used to evaluate the effectiveness of Nb Ta oxide chemistry as a possible exploration tool, to trace the degree of pegmatite fractionation and to classify the pegmatites. The columbite group mineral composition allows to establish a compositional trend from manganoan ferrocolumbite to manganocolumbite and on to manganotantalite. This trend is typical of complex spodumene- and/or lepidolite-subtype pegmatites. It clearly contrasts with another trend, from ferrocolumbite through ferrotantalite to ferrowodginite and ferrotapiolite compositions, typical of pegmatites of the beryl columbite phosphate subtype. Large scatter and anomalous trends in zoned crystals partially overlap and conceal the two main evolution patterns. This indicates that a large representative data set of heavy mineral concentrate samples, collected systematically along cross-sections, would be necessary to predict the metallogenetic potential of individual pegmatites. Other mineral species, e.g. garnets and/or tourmaline, with a more regular distribution than Nb

  10. Synthesis, properties and phase transitions of pyrochlore- and fluorite-like Ln{sub 2}RMO{sub 7} (Ln = Sm, Ho; R = Lu, Sc; M = Nb, Ta)

    SciTech Connect

    Shlyakhtina, A.V.; Belov, D.A.; Pigalskiy, K.S.; Shchegolikhin, A.N.; Kolbanev, I.V.; Karyagina, O.K.

    2014-01-01

    Graphical abstract: Temperature dependences of bulk conductivity for Sm{sub 2}ScTaO{sub 7} pyrochlore prepared at (1) 1400 °C, 20 h; and (2) 1200 °C, 40 h. - Highlights: • The phase formation of Ln{sub 2}RMO{sub 7} (Ln = Sm, Ho; R = Lu, Sc; M = Nb, Ta) at 1200–1600 °C. • The bulk conductivity and magnetic susceptibility were measured. • The bulk conductivity of Sm{sub 2}ScTaO{sub 7} has oxygen ion type at T ≥ 750 °C. • The first-order structural phase transition was observed in Sm{sub 2}ScTaO{sub 7} at ∼650–700 °C. • This phase transformation is not typical for defect fluorites. - Abstract: We have studied the new compounds with fluorite-like (Ho{sub 2}RNbO{sub 7} (R = Lu, Sc)) and pyrochlore-like (Sm{sub 2}ScTaO{sub 7}) structure as potential oxide ion conductors. The phase formation process (from 1200 to 1600 °C) and physical properties (electrical, thermo mechanical, and magnetic) for these compounds were investigated. Among the niobate materials the highest bulk conductivity is offered by the fluorite-like Ho{sub 2}ScNbO{sub 7} synthesized at 1600 °C: 3.8 × 10{sup −5} S/cm at 750 °C, whereas in Sm system the highest bulk conductivity, 7.3 × 10{sup −6} S/cm at 750 °C, is offered by the pyrochlore Sm{sub 2}ScTaO{sub 7} synthesized at 1400 °C. In Sm{sub 2}ScTaO{sub 7} pyrochlore we have observed the first-order phase transformation at ∼650–700 °C is related to rearrangement process in the oxygen sublattice of the pyrochlore structure containing B-site cations in different valence state and actually is absent in the defect fluorites. The two holmium niobates show Curie–Weiss paramagnetic behavior, with the prevalence of antiferromagnetic coupling. The magnetic susceptibility of Sm{sub 2}ScTaO{sub 7} is a weak function of temperature, corresponding to Van Vleck paramagnetism.

  11. Low Temperature Elastic Constants and Piezoelectric Coefficients of LiNbO3 and LiTaO3: Resonant Ultrasound Spectroscopy Measurement and Lattice Dynamics Analysis

    NASA Astrophysics Data System (ADS)

    Tarumi, Ryuichi; Matsuhisa, Tomohiro; Shibutani, Yoji

    2012-07-01

    The complete sets of elastic constants Cij and piezoelectric coefficients eij for LiNbO3 and LiTaO3 single crystals have been determined by resonant ultrasound spectroscopy (RUS) from ambient temperature to 6 K. Both Cij(T) and eij(T) of the two crystals monotonically increased as the temperature decreased. The Einstein temperature estimated from Varshni's equation revealed that e15 and e22 of LiNbO3 have remarkably low values compared with the acoustic Debye temperature. In addition, the lattice anharmonicity of these piezoelectric coefficients was also extraordinarily low. An analysis based on the group theory and lattice dynamics revealed that both LiNbO3 and LiTaO3 crystals have three types of internal displacement modes: A1, A2, and E, and only the E mode affects e15 and e22. Therefore, it is reasonable to suppose that the E mode internal displacement is responsible for the unusual behaviors of the tow piezoelectric coefficients.

  12. Temperature-dependent Raman scattering study of the defect pyrochlores RbNbWO6 and CsTaWO6.

    PubMed

    Mączka, M; Knyazev, A V; Majchrowski, A; Hanuza, J; Kojima, S

    2012-05-16

    Lattice dynamics calculations and temperature-dependent Raman scattering experiments were performed on RbNbWO(6) and CsTaWO(6) pyrochlore oxides. The observed bands were assigned to the respective motions of atoms in the unit cell. The spectra showed the presence of additional Raman bands not allowed for by the [Formula: see text] cubic structure. We have shown that these bands appear due to both substitutional disorder in the 16c sites and displacive disorder of the A ions. Raman studies also revealed the presence of an additional 80 cm(-1) band at room temperature for RbNbWO(6), not observed for CsTaWO(6). The presence of this band has been attributed to off-center displacement of the Nb and W ions due to structural phase transition into a tetragonal ferroelectric phase. The temperature evolution of the 80 cm(-1) band intensity revealed that it disappeared at a much higher temperature (about 650 K) than the reported phase transition temperature (about 360 K). This behavior is reminiscent of chemically disordered perovskite ferroelectrics, including relaxor ferroelectrics, and was attributed to the presence of small polar regions with local tetragonal distortion embedded in the paraelectric matrix of the [Formula: see text] structure. PMID:22517168

  13. Effect of dopants on the soft magnetic properties and high frequency characteristics of FeCoBM (M = Ti, Nb, Hf, and Ta) thin films.

    PubMed

    Hsieh, C C; Lin, T H; Chang, H W; Chang, C W; Chang, W C; Yang, C C

    2011-03-01

    Effect of dopants on the soft magnetic properties and high frequency characteristics of FeCoBM thin films (M = Ti, Nb, Hf, and Ta) have been studied. For (Fe0.55Co0.45)(100-x)B(x) (x = 5-15) thin films, with the increase of B content, the resistivity was increased because B could decrease the crystallinity of the films. The (Fe0.55Co0.45)90B10 thin film showed the optimum properties, where 4piM(s) = 16.1 kG, H(ce) = 64.2 Oe, H(ch) = 13.5 Oe, H(k) = 310 Oe and p = 338 microomega-cm. To reduce the coercivity of the film, the elements M, including Ti, Nb, Hf, and Ta, were selected to substitute for B in the FeCoB films. It was found that (Fe0.55Co0.45)90B6Ti2Nb2 thin film after annealing at a temperature of 200 degrees C for 30 min showed the optimal properties, where 4piM(s) = 15.8 kG, H(ce) = 4.8 Oe, H(ch) = 3.6 Oe, H(k) = 224 Oe and p = 290 microomega-cm. The theoretically calculated ferromagnetic resonance frequency of the developed films can be higher than 5 GHz. PMID:21449469

  14. Effect of Zr, V, Nb, Mo, and Ta substitutions on magnetic properties and microstructure of melt-spun SmCo5 magnets

    PubMed Central

    Fukuzaki, Tomokazu; Iwane, Hiroaki; Abe, Kazutomo; Doi, Toshihiro; Tamura, Ryuji; Oikawa, Tadaaki

    2014-01-01

    We have investigated effects of metal substitutions on the magnetic properties and microstructure of melt-spun Sm-Co-Cu-Fe-M (M = Zr, V, Nb, Mo, Ta) magnets. We prepared melt-spun ribbons with compositions of Sm(Co1−xCux)5Fe0.54−yMy (x = 0.1–0.5, y = 0–0.43, M = Zr, V, Nb, Mo, Ta). For compositions of Sm(Co1−xCux)5Fe0.54 (x = 0.1–0.5), coercivity increased with increasing of annealing temperature, and a high coercivity of 17.6 kOe was obtained at a Cu content of x = 0.3. The coercivity was found to increase with increasing melting point of the substitution element. A high coercivity of 24.5 kOe was obtained for a composition of Sm(Co0.7Cu0.3)5Fe0.34Ta0.2. PMID:24753631

  15. Effect of Zr, V, Nb, Mo, and Ta substitutions on magnetic properties and microstructure of melt-spun SmCo5 magnets.

    PubMed

    Fukuzaki, Tomokazu; Iwane, Hiroaki; Abe, Kazutomo; Doi, Toshihiro; Tamura, Ryuji; Oikawa, Tadaaki

    2014-05-01

    We have investigated effects of metal substitutions on the magnetic properties and microstructure of melt-spun Sm-Co-Cu-Fe-M (M = Zr, V, Nb, Mo, Ta) magnets. We prepared melt-spun ribbons with compositions of Sm(Co1- x Cu x )5Fe0.54- y M y (x = 0.1-0.5, y = 0-0.43, M = Zr, V, Nb, Mo, Ta). For compositions of Sm(Co1- x Cu x )5Fe0.54 (x = 0.1-0.5), coercivity increased with increasing of annealing temperature, and a high coercivity of 17.6 kOe was obtained at a Cu content of x = 0.3. The coercivity was found to increase with increasing melting point of the substitution element. A high coercivity of 24.5 kOe was obtained for a composition of Sm(Co0.7Cu0.3)5Fe0.34Ta0.2. PMID:24753631

  16. Fabrication of Nb3Al superconducting wires by utilizing the mechanically alloyed Nb(Al)ss supersaturated solid-solution with low-temperature annealing

    NASA Astrophysics Data System (ADS)

    Pan, X. F.; Yan, G.; Qi, M.; Cui, L. J.; Chen, Y. L.; Zhao, Y.; Li, C. S.; Liu, X. H.; Feng, Y.; Zhang, P. X.; Liu, H. J.; Li, L. F.

    2014-07-01

    High-performance Nb3Al superconducting wire is a promising candidate to the application of high-field magnets. However, due to the production problem of km-grade wires that are free from low magnetic field instability, the Nb3Al wires made by rapid heating, quenching and transformation (RHQT) are still not available to the large-scale engineering application. In this paper, we reported the properties of the in situ powder-in-tube (PIT) Nb3Al superconducting wires, which were made by using the mechanically alloyed Nb(Al)ss supersaturated solid solution, as well as the low temperature heat-treatment at 800 °C for 10 h. The results show that Nb3Al superconductors in this method possess very fine grains and well superconducting properties, though a little of Nb2Al and Nb impurities still keep being existence at present work. At the Nb3Al with a nominal 26 at.% Al content, the onset Tc reaches 15.8 K. Furthermore, a series of Nb3Al wires and tapes with various sizes have been fabricated; for the 1.0 mm-diameter wire, the Jc at 4.2 K, 10 T and 14 T have achieved 12,700 and 6900 A/cm2, respectively. This work suggests it is possible to develop high-performance Cu-matrix Nb3Al superconducting wires by directly using the Nb(Al)ss supersaturated solid-solution without the complex RHQT heat-treatment process.

  17. Crystallisation of magmatic topaz and implications for Nb-Ta-W mineralisation in F-rich silicic melts - The Ary-Bulak ongonite massif

    NASA Astrophysics Data System (ADS)

    Agangi, Andrea; Kamenetsky, Vadim S.; Hofmann, Axel; Przybyłowicz, Wojciech; Vladykin, Nikolay V.

    2014-08-01

    Textural, mineralogical and geochemical data on F-rich rhyolite (ongonite) from the Ary-Bulak massif of eastern Transbaikalia help constrain the formation of magmatic topaz. In these rocks, topaz occurs as phenocrysts, thus providing compelling evidence for crystallisation at the orthomagmatic stage. Cathodoluminescence images of topaz and quartz reveal growth textures with multiple truncation events in single grains, indicative of a dynamic system that shifted from saturated to undersaturated conditions with respect to topaz and quartz. Electron microprobe and Raman analyses of topaz indicate near-pure F composition [Al2SiO4F2], with very limited OH replacement. Laser ablation ICP-MS traverses revealed the presence of a large number of trace elements present at sub-ppm to hundreds of ppm levels. The chemical zoning of topaz records trace element fluctuations in the coexisting melt. Concentrations of some trace elements (Li, Ga, Nb, Ta and W) are correlated with cathodoluminescence intensity, thus suggesting that some of these elements act as CL activators in topaz. The study of melt inclusions indicates that melts with different F contents were trapped at different stages during formation of quartz and topaz phenocrysts, respectively. Electron microprobe analyses of glass in subhedral quartz-hosted melt inclusions indicate F ≤ 1.2 wt.%, whereas irregular-shaped melt inclusions hosted in both topaz and quartz have F ≤ 9 wt.%. Cryolithionite [Na3Li3Al2F12] coexists with glass in irregular inclusions, implying high Li contents in the melt. The very high F contents would have increased the solubility of Nb, Ta and W in the melt, thus allowing progressive concentration of these elements during magma evolution. Crystallisation of Nb-Ta-W-oxides (W-ixiolite and tantalite-columbite) may have been triggered by separation of cryolithionite, which would have caused F and Li depletion and consequent drop in the solubility of these elements.

  18. Cooperative phenomena induced by Nb admixture in K1- xLixTaO3

    NASA Astrophysics Data System (ADS)

    Giulotto, E.; Galinetto, P.; Camagni, P.; Samoggia, G.; Trepakov, V. A.; Jastrabik, L.; Syrnikov, P. P.

    2000-07-01

    Raman scattering observations were performed on samples of K1-xLixTa1- yNbyO3, with x in the range 0.6-1.0 mol% and y in the range 0.2-0.3 mol%. Concentrations of Li and Nb, determined by analytical methods, were below the known thresholds at which these substituents can separately induce a ferroelectric transition in the quantum paraelectric KTaO3. The temperature evolution of TO1 and TO4 spectra was monitored. The results show a critical behaviour below 50 K, characterized by an abrupt increase of first-order scattering strengths and by spontaneous splitting of the non-softening TO1 mode. From our data, we infer the occurrence of a ferroelectric phase transition of order-disorder character. This proves that small additions of Nb enhance the tendency of the Li subsystem towards cooperative ordering in the KTaO3 matrix.

  19. Photocatalytic properties of CoOx-loaded nano-crystalline perovskite oxynitrides ABO2N (A = Ca, Sr, Ba, La; B = Nb, Ta)

    NASA Astrophysics Data System (ADS)

    Oehler, Florian; Ebbinghaus, Stefan G.

    2016-04-01

    Highly crystalline niobium- and tantalum-based oxynitride perovskite nanoparticles were obtained from hydrothermally synthesized oxide precursors by thermal ammonolysis at different temperatures. The samples were studied with respect to their morphological, optical and thermal properties as well as their photocatalytic activity in the decomposition of methyl orange. Phase pure oxynitrides were obtained at rather low ammonolysis temperatures between 740 °C (CaNbO2N) and 1000 °C (BaTaO2N). Particle sizes were found to be in the range 27 nm-146 nm and large specific surface areas up to 37 m2 g-1 were observed. High photocatalytic activities were found for CaNbO2N and SrNbO2N prepared at low ammonolysis temperatures. CoOx as co-catalyst was loaded on the oxynitride particles resulting in a strong increase of the photocatalytic activities up to 30% methyl orange degradation within 3 h for SrNbO2N:CoOx.

  20. Lattice structure transformation and change in surface hardness of Ni3Nb and Ni3Ta intermetallic compounds induced by energetic ion beam irradiation

    NASA Astrophysics Data System (ADS)

    Kojima, H.; Yoshizaki, H.; Kaneno, Y.; Semboshi, S.; Hori, F.; Saitoh, Y.; Okamoto, Y.; Iwase, A.

    2016-04-01

    Ni3Nb and Ni3Ta intermetallic compounds, which show the complicated lattice structures were irradiated with 16 MeV Au5+ ions at room temperature. The X-ray diffraction measurement revealed that the lattice structure of these intermetallic compounds changed from the ordered structures to the amorphous state by the ion irradiation. The irradiation-induced amorphization caused the increase in Vickers hardness. The result was compared with our previous results for Ni3Al and Ni3V, and was discussed in terms of the intrinsic lattice structures of the samples.

  1. Synthesis and Luminescence Properties of LnM(v)O4 (M = Nb, Ta):RE3+ (RE = Eu, Tb) Nanophosphors.

    PubMed

    Huo, Jiansheng; Wang, Qianming

    2015-01-01

    A group of LnM(v)O4 (M = Nb, Ta):RE3+ (RE = Eu3+, Tb3+) phosphors have been synthesized by pretreatments with a special reactor (supersonic microwave co-assistance (SMC) machine). Powder characteristics were studied by X-ray Diffraction, photoluminescence, fluorescence microscope and scanning electronic microscope. Results showed the samples can exhibit green or red emissions upon the ultra-violet excitations. The influence of SMC method on the physical properties has been investigated in detail. PMID:26328400

  2. Deformation Mechanisms and Biocompatibility of the Superelastic Ti-23Nb-0.7Ta-2Zr-0.5N Alloy

    NASA Astrophysics Data System (ADS)

    Castany, P.; Gordin, D. M.; Drob, S. I.; Vasilescu, C.; Mitran, V.; Cimpean, A.; Gloriant, T.

    2016-03-01

    In this study, we have synthesized a new Ti-23Nb-0.7Ta-2Zr-0.5N alloy composition with the aim to obtain useful mechanical properties to be used in medicine such as high strength, good superelastic property, low modulus, and large ductility. Thus, mechanical properties including superelasticity and plasticity were investigated in relation with the different deformation mechanisms observed (stress-induced martensitic transformation, twinning and dislocation slip). On the other hand, the corrosion resistance in simulated body fluid (Ringer solution) and the in vitro cell behavior (MG63 human osteoblasts) of such biomedical alloy were also evaluated in order to assess its biocompatibility.

  3. Dielectric properties of some MM'O{sub 4} and MTiM'O{sub 6} (M=Cr, Fe, Ga; M'=Nb, Ta, Sb) rutile-type oxides

    SciTech Connect

    Mani, Rohini; Achary, S.N.; Chakraborty, Keka R.; Deshpande, S.K.; Joy, Joby E.; Nag, Abanti; Gopalakrishnan, J.; Tyagi, A.K.

    2010-06-15

    We describe an investigation of the structure and dielectric properties of MM'O{sub 4} and MTiM'O{sub 6} rutile-type oxides for M=Cr, Fe, Ga and M'=Nb, Ta and Sb. All the oxides adopt a disordered rutile structure (P4{sub 2}/mnm) at ambient temperature. A partial ordered trirutile-type structure is confirmed for FeTaO{sub 4} from the low temperature (17 K) neutron diffraction studies. While both the MM'O{sub 4} oxides (CrTaO{sub 4} and FeTaO{sub 4}) investigated show a normal dielectric property MTiM'O{sub 6} oxides for M=Fe, Cr and M'=Nb/Ta/Sb display a distinct relaxor/relaxor-like response. Significantly the corresponding gallium analogs, GaTiNbO{sub 6} and GaTiTaO{sub 6}, do not show a relaxor response at T<500 K. - Graphical abstract: Dielectric response of FeTiNbO{sub 6}.

  4. Ternary borides Nb7Fe3B8 and Ta7Fe3B8 with Kagome-type iron framework.

    PubMed

    Zheng, Qiang; Gumeniuk, Roman; Borrmann, Horst; Schnelle, Walter; Tsirlin, Alexander A; Rosner, Helge; Burkhardt, Ulrich; Reissner, Michael; Grin, Yuri; Leithe-Jasper, Andreas

    2016-06-21

    Two new ternary borides TM7Fe3B8 (TM = Nb, Ta) were synthesized by high-temperature thermal treatment of samples obtained by arc-melting. This new type of structure with space group P6/mmm, comprises TM slabs containing isolated planar hexagonal [B6] rings and iron centered TM columns in a Kagome type of arrangement. Chemical bonding analysis in Nb7Fe3B8 by means of the electron localizability approach reveals two-center interactions forming the Kagome net of Fe and embedded B, while weaker multicenter bonding present between this net and Nb atoms. Magnetic susceptibility measurements reveal antiferromagnetic order below TN = 240 K for Nb7Fe3B8 and TN = 265 K for Ta7Fe3B8. Small remnant magnetization below 0.01μB per f.u. is observed in the antiferromagnetic state. The bulk nature of the magnetic transistions was confirmed by the hyperfine splitting of the Mössbauer spectra, the sizable anomalies in the specific heat capacity, and the kinks in the resistivity curves. The high-field paramagnetic susceptibilities fitted by the Curie-Weiss law show effective paramagnetic moments μeff≈ 3.1μB/Fe in both compounds. The temperature dependence of the electrical resistivity also reveals metallic character of both compounds. Density functional calculations corroborate the metallic behaviour of both compounds and demonstrate the formation of a sizable local magnetic moment on the Fe-sites. They indicate the presence of both antiferro- and ferrromagnetic interactions. PMID:27216270

  5. Screened coulomb hybrid DFT investigation of band gap and optical absorption predictions of CuVO3, CuNbO3 and Cu5Ta11O30 materials.

    PubMed

    Harb, Moussab; Masih, Dilshad; Takanabe, Kazuhiro

    2014-09-14

    We present a joint theoretical and experimental investigation of the optoelectronic properties of CuVO3, CuNbO3 and Cu5Ta11O30 materials for potential photocatalytic and solar cell applications. In addition to the experimental results obtained by powder X-ray diffraction and UV-Vis spectroscopy of the materials synthesized under flowing N2 gas at atmospheric pressure via solid-state reactions, the electronic structure and the UV-Vis optical absorption coefficient of these compounds are predicted with high accuracy using advanced first-principles quantum methods based on DFT (including the perturbation theory approach DFPT) within the screened coulomb hybrid HSE06 exchange-correlation formalism. The calculated density of states are found to be in agreement with the UV-Vis diffuse reflectance spectra, predicting a small indirect band gap of 1.4 eV for CuVO3, a direct band gap of 2.6 eV for CuNbO3, and an indirect (direct) band gap of 2.1 (2.6) eV for Cu5Ta11O30. It is confirmed that the Cu(I)-based multi-metal oxides possess a strong contribution of filled Cu(I) states in the valence band and of empty d(0) metal states in the conduction band. Interestingly, CuVO3 with its predicted small indirect band gap of 1.4 eV shows the highest absorption coefficient in the visible range with a broad absorption edge extending to 886 nm. This novel result offers a great opportunity for this material to be an excellent candidate for solar cell applications. PMID:25055167

  6. Conduction processes in metal–insulator–metal diodes with Ta{sub 2}O{sub 5} and Nb{sub 2}O{sub 5} insulators deposited by atomic layer deposition

    SciTech Connect

    Alimardani, Nasir; McGlone, John M.; Wager, John F.; Conley, John F.

    2014-01-15

    Metal–insulator–metal diodes with Nb{sub 2}O{sub 5} and Ta{sub 2}O{sub 5} insulators deposited via atomic layer deposition are investigated. For both Nb{sub 2}O{sub 5} and Ta{sub 2}O{sub 5}, the dominant conduction process is established as Schottky emission at small biases and Frenkel–Poole emission at large biases. Fowler–Nordheim tunneling is not found to play a role in determining current versus voltage asymmetry. The dynamic dielectric constants are extracted from conduction plots and found to be in agreement with measured optical dielectric constants. Trap energy levels at ϕ{sub T} ≈ 0.62 and 0.53 eV below the conduction band minimum are estimated for Nb{sub 2}O{sub 5} and Ta{sub 2}O{sub 5}, respectively.

  7. Biological Behaviour and Enhanced Anticorrosive Performance of the Nitrided Superelastic Ti-23Nb-0.7Ta-2Zr-0.5N Alloy

    PubMed Central

    Mitran, Valentina; Vasilescu, Cora; Drob, Silviu Iulian; Osiceanu, Petre; Calderon-Moreno, Jose Maria; Tabirca, Mariana-Cristina; Gordin, Doina-Margareta; Gloriant, Thierry; Cimpean, Anisoara

    2015-01-01

    The influence of gas nitriding surface treatment on the superelastic Ti-23Nb-0.7Ta-2Zr-0.5N alloy was evaluated. A thorough characterization of bare and nitrided Ti-based alloy and pure Ti was performed in terms of surface film composition and morphology, electrochemical behaviour, and short term osteoblast response. XPS analysis showed that the nitriding treatment strongly influenced the composition (nitrides and oxynitrides) and surface properties both of the substrate and of the bulk alloy. SEM images revealed that the nitrided surface appears as a similar dotted pattern caused by the formation of N-rich domains coexisting with less nitrided domains, while before treatment only topographical features could be observed. All the electrochemical results confirmed the high chemical stability of the nitride and oxynitride coating and the superiority of the applied treatment. The values of the corrosion parameters ascertained the excellent corrosion resistance of the coated alloy in the real functional conditions from the human body. Cell culture experiments with MG63 osteoblasts demonstrated that the studied biomaterials do not elicit any toxic effects and support cell adhesion and enhanced cell proliferation. Altogether, these data indicate that the nitrided Ti-23Nb-0.7Ta-2Zr-0.5N alloy is the most suitable substrate for application in bone implantology. PMID:26583096

  8. Realization of ultrasmooth surface with atomic scale step structure on LiNbO3 and LiTaO3 substrates.

    PubMed

    Lee, G

    2002-07-01

    Z-cut (C-plane), X-cut (M-plane), Y-cut (A-plane) LiNbO3 and LiTaO3 substrates were annealed at high temperature over 1000 degrees C in air. On all annealed substrates, atomic scale step structures with uniform height were observed, which demonstrates that the surfaces of the substrates become atomically smooth. The step height on Z-cut substrates was 0.25 +/-0.02 nm, which was well accordance with the distance between oxygen layers along the c-axis of the hexagonal unit cell of LiNbO3 and LiTaO3 crystals. The step heights on X-cut and on Y-cut substrates were 0.45 +/- 0.04 nm and 0.50 +/- 0.05 nm, respectively, which corresponded well with the distances between A-planes and M-planes in the unit cell. PMID:19436397

  9. Biological Behaviour and Enhanced Anticorrosive Performance of the Nitrided Superelastic Ti-23Nb-0.7Ta-2Zr-0.5N Alloy.

    PubMed

    Mitran, Valentina; Vasilescu, Cora; Drob, Silviu Iulian; Osiceanu, Petre; Calderon-Moreno, Jose Maria; Tabirca, Mariana-Cristina; Gordin, Doina-Margareta; Gloriant, Thierry; Cimpean, Anisoara

    2015-01-01

    The influence of gas nitriding surface treatment on the superelastic Ti-23Nb-0.7Ta-2Zr-0.5N alloy was evaluated. A thorough characterization of bare and nitrided Ti-based alloy and pure Ti was performed in terms of surface film composition and morphology, electrochemical behaviour, and short term osteoblast response. XPS analysis showed that the nitriding treatment strongly influenced the composition (nitrides and oxynitrides) and surface properties both of the substrate and of the bulk alloy. SEM images revealed that the nitrided surface appears as a similar dotted pattern caused by the formation of N-rich domains coexisting with less nitrided domains, while before treatment only topographical features could be observed. All the electrochemical results confirmed the high chemical stability of the nitride and oxynitride coating and the superiority of the applied treatment. The values of the corrosion parameters ascertained the excellent corrosion resistance of the coated alloy in the real functional conditions from the human body. Cell culture experiments with MG63 osteoblasts demonstrated that the studied biomaterials do not elicit any toxic effects and support cell adhesion and enhanced cell proliferation. Altogether, these data indicate that the nitrided Ti-23Nb-0.7Ta-2Zr-0.5N alloy is the most suitable substrate for application in bone implantology. PMID:26583096

  10. An aqueous route to [Ta6O19]8- and solid-state studies of isostructural niobium and tantalum oxide complexes.

    PubMed

    Anderson, Travis M; Rodriguez, Mark A; Bonhomme, François; Bixler, Joel N; Alam, Todd M; Nyman, May

    2007-10-28

    A new soft chemical route to [Ta6O19]8- has been developed by the dissolution of [Ta(O2)4]3- in conditions alkaline enough to arrest formation of Ta2O5, followed by [VO4]3--catalyzed decomposition of the peroxide ligands and crystallization of the salt. An average of bond lengths and angles from isostructural salts of [Ta6O19]8- and [Nb6O19]8- indicate there is an increase in terminal M(eta=O) bond lengths and M-micro2-O-M angles and a decrease in bridging micro2-O-M bond lengths in [Ta6O19]8-, although the central micro6-O-M bond lengths are identical within experimental error. Two new structures of Na7[HNb6O19].15H2O () and Na8[Ta6O19].15H2O () are exemplary of the fact that protonated micro2-OH are observed exclusively in the niobates. In these structures, the metal-oxide framework, seven sodium atoms, and all fifteen water molecules are located in identical unit cell positions, but in an eighth charge-balancing sodium is located in close proximity to the protonated micro2-OH in . Differences in the basicity of Nb(v)- and Ta(v)-bound oxygen atoms are also manifested at the surfaces of 17O-enriched powders of Nb2O5 and Ta2O5. Oxygen exchange at the surface of these materials readily takes place at both terminal and bridging sites in Nb2O5 but only at terminal sites in Ta2O5. PMID:17928908

  11. A pseudo-tetragonal tungsten bronze superstructure: a combined solution of the crystal structure of K6.4(Nb,Ta)(36.3)O94 with advanced transmission electron microscopy and neutron diffraction.

    PubMed

    Paria Sena, Robert; Babaryk, Artem A; Khainakov, Sergiy; Garcia-Granda, Santiago; Slobodyanik, Nikolay S; Van Tendeloo, Gustaaf; Abakumov, Artem M; Hadermann, Joke

    2016-01-21

    The crystal structure of the K6.4Nb28.2Ta8.1O94 pseudo-tetragonal tungsten bronze-type oxide was determined using a combination of X-ray powder diffraction, neutron diffraction and transmission electron microscopy techniques, including electron diffraction, high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), annular bright field STEM (ABF-STEM) and energy-dispersive X-ray compositional mapping (STEM-EDX). The compound crystallizes in the space group Pbam with unit cell parameters a = 37.468(9) Å, b = 12.493(3) Å, c = 3.95333(15) Å. The structure consists of corner sharing (Nb,Ta)O6 octahedra forming trigonal, tetragonal and pentagonal tunnels. All tetragonal tunnels are occupied by K(+) ions, while 1/3 of the pentagonal tunnels are preferentially occupied by Nb(5+)/Ta(5+) and 2/3 are occupied by K(+) in a regular pattern. A fractional substitution of K(+) in the pentagonal tunnels by Nb(5+)/Ta(5+) is suggested by the analysis of the HAADF-STEM images. In contrast to similar structures, such as K2Nb8O21, also parts of the trigonal tunnels are fractionally occupied by K(+) cations. PMID:26646168

  12. Microstructure and Mechanical Properties of Laser-Welded Joints of Ti-22Al-25Nb/TA15 Dissimilar Titanium Alloys

    NASA Astrophysics Data System (ADS)

    Li, Dalong; Hu, Shengsun; Shen, Junqi; Zhang, Hao; Bu, Xianzheng

    2016-05-01

    Laser beam welding (LBW) was applied to join 1-mm-thick dissimilar titanium alloys, Ti-22Al-25Nb (at.%) and TA15, and the microstructure and mechanical properties of the welded joints were systematically analyzed. Defect-free joints were obtained, and the fusion zone mainly consisted of B2 and martensitic α' phases because of the uneven distribution of the β phase stabilizer and rapid cooling rate of LBW. The phase compositions of the heat-affected zone varied with the different thermal cycles during the welding process. The different microstructures of the dissimilar titanium alloys led to an unsymmetrical hardness profile, with the welded seam exhibiting the lowest value of 271 HV. In room-temperature tensile tests, the fractures all occurred preferentially in the fusion zone. The strengths of the joints were close to those of the base metal but with prominently decreasing ductility. In tensile tests performed at 550 °C, all the joints fractured in the TA15 base metal, and the strength and plasticity of the welds were equivalent to those of the TA15 base metal.

  13. Y,REE,Nb,Ta,Ti-oxide (AB 2O 6) minerals from REL-REE euxenite-subtype pegmatites of the Třebíč Pluton, Czech Republic; substitutions and fractionation trends

    NASA Astrophysics Data System (ADS)

    Škoda, Radek; Novák, Milan

    2007-04-01

    Aeschynite-group minerals (AGM) and euxenite-group minerals (EGM) occur in REL-REE euxenite-subtype pegmatites from the Třebíč Pluton, Czech Republic. They form strongly metamictized, light brown to black, equigranular to needle-like, subhedral to anhedral grains enclosed in blocky K-feldspar and less commonly in albite, and blocky quartz, and in the graphic unit (quartz and K-feldspar). Both AGM and EGM are homogeneous to slightly heterogeneous in BSE images. They are not commonly associated with the other primary Y,REE,Ti,Nb-bearing minerals, i.e. allanite-(Ce), monazite-(Ce), titanite, and ilmenite, which occur within the same textural-paragenetic unit. Aeschynite-(Y), aeschynite-(Ce), aeschynite-(Nd), nioboaeschynite-(Ce), tantalaeschynite-(Ce), vigezzite and polycrase-(Y) were identified using EMP and canonical discrimination analysis [Ercit, T.S., 2005a. Identification and alteration trends of granitic-pegmatite-hosted (Y,REE,U,Th)-(Nb,Ta,Ti) oxide minerals: a statistical approach. Can. Mineral. 43, 4 1291-1303.]. The exchange vector ACa B(Nb,Ta) A(Y,REE) - 1 BTi - 1 or its combination with the exchange vector ACa 2B(Nb,Ta) 3A(U,Th) - 1 A(Y,REE) - 1 BTi - 3 have been elucidated for the AGM. The exchange vector ACa A(U,Th) A(Y,REE) - 2 is predominant in the EGM. The AGM are enriched in HREE, whereas LREE are concentrated in the EGM. Weak to none-existent geochemical fractionations, as expressed by the U/(U + Th), Y/(Y + REE), Ta/(Ta + Nb) and (Nb + Ta)/(Ti + Nb + Ta) ratios, were noted for single grains from both the AGM and EGM, as well as in grains of polycrase-(Y) from four different textural-paragenetic units located in the Vladislav pegmatite. Simultaneous increase of U/(U + Th) and Y/(Y + REE) in the AGM during fractionation is typical. The Ta/(Ta + Nb) fractionation is usually weak and contradicts the Y/(Y + REE) and U/(U + Th) fractionation trends. This unusual behavior of Nb and Ta may be controlled by associated Ti-rich minerals (titanite

  14. Raman scattering and far-infrared reflectivity of Ba5Ta4O15-x and Ba5Nb4O15-x (0.0

    NASA Astrophysics Data System (ADS)

    Massa, Nestor E.; Pagola, Silvina; Carbonio, Raul E.; Alonso, Jose A.; Rasines, Isidoro; Polla, Griselda; Leyva, Gabriela

    1996-06-01

    Quite often the literature cites superconductors with high critical temperature as having an anharmonic lattice close to a structural phase transition. It is then of interest to find materials, with distorted perovskite structure, that reveal bare phonon behavior expected for such an environment. Here we discuss layered Ba5Nb4O15 and Ba5Ta4O15-x (0.0 less than or equal to x less than or equal to 0.56) that have four Nb/Ta ions per formula unit. This implies that there is an empty octahedra that in the lattice avoids direct face sharing of the (Nb/Ta)O6 sublattice. As consequence, one expects strong anharmonicities that translate into several subtle anomalous shapes and wide phonon band profiles in the low temperature Raman and infrared spectra. We see that while a centrosymmetric D3d3- P3m1 space group is deduced for both compounds from neutron diffraction measurements, narrow splits of a symmetric stretching Raman mode hint small local departures of that symmetry in Ba5Nb4O15. Weaker structure on the band lower frequency side suggests that in their understanding one has to consider arguments that indicate that the anharmonic contributions to the lattice potential energy are so large that they cannot be treated only by perturbation theory, i.e., there is a lifting of the degeneracy of phonon transitions in the harmonic approximation. Defect induced modes, that are Raman active in Ba5Nb4O15, are understood as local modes due to unrelaxed portions of the lattice that may be related to changes of the phonon damping in infrared reflectivity spectra. It is also noteworthy to point out that the replacement Nb by Ta induces a hardening of most phonons. This is reflected in an increase of frequencies in spite of a heavier Ta ion.

  15. Comprehensive investigation of elastic and electrical properties of Li/Ta-modified (K,Na)NbO3 lead-free piezoceramics

    NASA Astrophysics Data System (ADS)

    Yao, Fang-Zhou; Wang, Ke; Li, Jing-Feng

    2013-05-01

    A full set of elastic and electrical coefficients of (K,Na)NbO3-based lead-free piezoceramics with a nominal composition of Li0.03(K0.48Na0.52)0.97(Nb0.8Ta0.2)O3 (abbreviated as KNNLT) was evaluated by the standard resonance method, and compared to those of K4CuNb8O23 doped (K0.45Na0.55)NbO3 (KNN-KCN) as well as typical Pb(Zr,Ti)O3-based piezoceramics PZT5A. The measurement of intermediate elastic stiffness and compliance coefficients of KNNLT indicated that KNNLT is elastically "softer" than KNN-KCN but "harder" than PZT5A. An extremely high piezoelectric stiffness coefficient h33 = 68.8 × 108 V/m was obtained, due to an especially low clamped dielectric constant ɛ33S of 361. And a large longitudinal electromechanical coupling factor k33 = 57% was observed in the KNNLT system. Furthermore, the piezoelectric coefficient d33 of KNNLT was characterized via three distinctive methods: the resonance method, the Berlincourt method, and the converse piezoelectric strain measurement; while these three techniques yielded values of 174 pC/N, 195 pC/N, and 308 pm/V, respectively. The difference in d33 values determined by the three methods may be attributed to different measurement frequencies and extrinsic piezoelectric contributions related to domain wall vibration and domain switching. Besides, the piezoelectric performances of KNNLT piezoceramics were found insensitive to frequency but susceptible to temperature and electric field cycling.

  16. The contrasting effect of the Ta/Nb ratio in (111)-layered B-site deficient hexagonal perovskite Ba5Nb4-xTaxO15 crystals on visible-light-induced photocatalytic water oxidation activity of their oxynitride derivatives.

    PubMed

    Hojamberdiev, Mirabbos; Bekheet, Maged F; Zahedi, Ehsan; Wagata, Hajime; Vequizo, Junie Jhon M; Yamakata, Akira; Yubuta, Kunio; Gurlo, Aleksander; Domen, Kazunari; Teshima, Katsuya

    2016-08-01

    The effect of the Ta/Nb ratio in the (111)-layered B-site deficient hexagonal perovskite Ba5Nb4-xTaxO15 (0 ≤ x ≤ 4) crystals grown by a KCl flux method on visible-light-induced photocatalytic water oxidation activity of their oxynitride derivatives BaNb1-xTaxO2N (0 ≤ x ≤ 1) was investigated. The Rietveld refinement of X-ray data revealed that all Ba5Nb4-xTaxO15 samples were well crystallized in the space group P3[combining macron]m1 (no. 164). Phase-pure BaNb1-xTaxO2N (0 ≤ x ≤ 1) porous structures were obtained by nitridation of the flux-grown oxide crystals at 950 °C for 20, 25, 30, 35, and 40 h, respectively. The absorption edge of BaNb1-xTaxO2N (0 ≤ x ≤ 1) was slightly shifted from 720 to 690 nm with the increasing Ta/Nb ratio. The O2 evolution rate gradually progressed and reached the highest value (127.24 μmol in the first 2 h) with the Ta content up to 50 mol% but decreased at 75 and 100 mol% presumably due to the reduced specific surface area and high density of structural defects, such as grain boundaries acting as recombination centers, originated from high-temperature nitridation for prolonged periods. Transient absorption spectroscopy provided evidence for the effect of the Ta/Nb ratio on the behavior and energy states of photogenerated charge carriers, indicating a direct correlation with photocatalytic water oxidation activity of BaNb1-xTaxO2N. PMID:27437784

  17. Crystal Structure, Electronic Structure, and Photocatalytic Activity of Oxysulfides: La2Ta2ZrS2O8, La2Ta2TiS2O8, and La2Nb2TiS2O8.

    PubMed

    Goto, Yosuke; Seo, Jeongsuk; Kumamoto, Kazunori; Hisatomi, Takashi; Mizuguchi, Yoshikazu; Kamihara, Yoichi; Katayama, Masao; Minegishi, Tsutomu; Domen, Kazunari

    2016-04-01

    The novel oxysulfides La2Ta2ZrS2O8 (LTZSO), La2Ta2TiS2O8 (LTTSO), and La2Nb2TiS2O8 (LNTSO) were synthesized, and their crystal structures, electronic structures, and photocatalytic activities for water splitting under visible light were investigated. Density functional theory calculations showed that these compounds are direct-band-gap semiconductors. Close to the conduction band minimum, the main contribution to the band structure comes from the d orbitals of Zr or Ti ions, while the region near the valence band maximum is associated with the 3p orbitals of S ions. The absorption-edge wavelength was determined to be 540 nm for LTZSO and 700 nm for LTTSO and LNTSO. An analysis of the crystal structure using synchrotron X-ray diffraction revealed that these compounds contained antisite defects at transition metal ion sites, and these were considered to be the origin of the broad absorption at wavelengths longer than that corresponding to band-gap excitation. LTZSO was revealed to be active in the oxygen evolution reaction from aqueous solution containing a sacrificial electron acceptor under visible-light illumination. This result was supported by the band alignment and flat-band potential determined by photoelectron spectroscopy and Mott-Schottky plots. PMID:27008368

  18. A15 superconductors through direct solid-state precipitation: V3Ga and Nb3Al

    NASA Astrophysics Data System (ADS)

    Hong, M.

    1980-09-01

    The use of a solid-state precipitation process to prepare superconducting tapes containing an A15 phase, V3Ga or Nb3Al in a ductile niobium or vanadium containing BCC matrix is discussed. Ingots were prepared by arc-melting, homogenized, quenched, warm-rolled over 99% into tape and aged at temperatures in the range 600 C - 1000 C to precipitate the superconducting A15 phase. In the V-Ga system, transmission electron microscopy (TEM) studies revealed the A15 precipitates in an elongated form. However, for the Nb-Al samples deformed and aged at 750 C, TEM studies revealed A15 precipitation in fine equi-axed particles which formed as a semicontinuous network over sub-grain boundaries formed by the recovery of deformation-induced dislocations. In the V-Ga system, the maximum critical transition temperature (15 K) was found in materials aged at temperatures of 750 C or below. At these aging temperatures the T sub C initially increased with aging time and passed through a distinct maximum. In the Nb-Al system and T sub C increased with aging time to a plateau and then increased again to a second plateau. The maximum T sub C measured was 17 K. Promising high-field overall critical currents were obtained in the Nb-Al system.

  19. Phase diagram and structure-property relationships in the lead-free piezoelectric system: Na0.5K0.5NbO3-LiTaO3.

    PubMed

    Skidmore, Thomas A; Comyn, Timothy P; Bell, Andrew J; Zhu, Fangyuan; Milne, Steven J

    2011-09-01

    A phase-diagram for the Na(0.5)K(0.5)NbO(3)-LiTaO(3) solid solution series (NKN-LT) is presented for compositions ≤ 10 mol% LT, based on the combined results of temperaturevariable X-ray powder diffraction and dielectric measurements. In addition to the reported orthorhombic and tetragonal polymorphs of NKN-LT, a monoclinic phase is revealed. Changes to electrical properties as a function of LT substitution are correlated to phase content. Increasing the LT content from 5 to 7 mol% LT led to improved temperature stability of piezoelectric properties because of the avoidance of the monoclinic-tetragonal polymorphic phase transition during thermal cycling (at >25°C). For 7 mol% LT samples: d(33) = 200 pC/N; T(c) = 440°C; ε(r) = 550 and tan δ = 0.02 (at 20°C). Modification of this composition by solid solution with BiScO(3) led to a decrease in d(33) values. Transmission electron microscopy of a sample of 0.95[0.93 NKN-0.07LT]-0.05BiScO(3) indicated a core-shell grain structure which led to temperature-stable dielectric properties. PMID:21937313

  20. Microwave dielectric properties of (A2+(1/3)B5+(2/3))0.5Ti0(0.5)O2 (A2+ = Zn, Mg, B5+ = Nb, Ta) ceramics.

    PubMed

    Kim, E S; Kang, D H

    2008-05-01

    Dielectric properties of (A(2+)(1/3)B(5+)(2/3))(0.5)Ti0(0.5)O(2) (A(2+) = Zn, Mg, B(5+) = Nb, Ta) ceramics were investigated at microwave frequencies. A single phase with tetragonal rutile structure was obtained through the entire compositions. Dielectric properties were strongly dependent on the structural characteristics. The specimens with B(5+) = Nb showed a larger dielectric constant than those with B(5+) = Ta due to the decrease of bond valence. Quality factors (Qf) of the specimens with B(5+) = Ta were larger than those with B(5+) = Nb. Temperature coefficient of the resonant frequencies (TCF) of (Zn(1/3)Nb(2/3) )0(0.5)Ti0(0.5)O(2) was larger than that of (Mg(1/3)Ta(2/3))0(0.5)Ti0(0.5)O(2). These results could be attributed to the changes of the temperature coefficient of dielectric constant and the degree of oxygen octahedral distortion. PMID:18519214

  1. Diffusion of oxygen in amorphous Al{sub 2}O{sub 3}, Ta{sub 2}O{sub 5}, and Nb{sub 2}O{sub 5}

    SciTech Connect

    Nakamura, R. Tsukui, S.; Toda, T.; Tane, M.; Suzuki, T.; Ishimaru, M.; Nakajima, H.

    2014-07-21

    The self-diffusivity of oxygen in amorphous Al{sub 2}O{sub 3} (a-Al{sub 2}O{sub 3}), a-Ta{sub 2}O{sub 5}, and a-Nb{sub 2}O{sub 5} was investigated along with structural analysis in terms of pair distribution function (PDF). The low activation energy, ∼1.2 eV, for diffusion in the oxides suggests a single atomic jump of oxygen ions mediated via vacancy-like defects. However, the pre-exponential factor for a-Ta{sub 2}O{sub 5} and a-Nb{sub 2}O{sub 5} with lower bond energy was two orders of magnitude larger than that for a-Al{sub 2}O{sub 3} with higher bond energy. PDF analyses revealed that the short-range configuration in a-Ta{sub 2}O{sub 5} and a-Nb{sub 2}O{sub 5} was more broadly distributed than that in a-Al{sub 2}O{sub 3}. Due to the larger variety of atomic configurations of a-Ta{sub 2}O{sub 5} and a-Nb{sub 2}O{sub 5}, these oxides have a higher activation entropy for diffusion than a-Al{sub 2}O{sub 3}. The entropy term for diffusion associated with short-range structures was shown to be a dominant factor for diffusion in amorphous oxides.

  2. Role of the (Ta/Nb)O{sub x}/Al{sub 2}O{sub 3} interface on the flatband voltage shift for Al{sub 2}O{sub 3}/(Ta/Nb)O{sub x}/Al{sub 2}O{sub 3} multilayer charge trap capacitors

    SciTech Connect

    Nabatame, Toshihide; Ohi, Akihiko; Ito, Kazuhiro; Takahashi, Makoto; Chikyo, Toyohiro

    2015-01-15

    The authors studied the characteristics of Si/Al{sub 2}O{sub 3}/(Ta/Nb)O{sub x}/Al{sub 2}O{sub 3}/SiO{sub 2}/Pt charge trap capacitors fabricated by atomic layer deposition and postmetallization annealing at 400 °C. Al{sub 2}O{sub 3} and (Ta/Nb)O{sub x} films are amorphous and have negligible fixed charges. In program mode, a flatband voltage (V{sub fb}) drastically shifts toward the positive direction at a short program time of 10{sup −4} s. A large V{sub fb} shift of approximately 4 V arises after programming at 1 mC/cm{sup 2} because there is a large difference in the conduction band offset between the (Ta/Nb)O{sub x}-charge trapping layer (TNO-CTL) and the Al{sub 2}O{sub 3}-blocking layer (AlO-BL) (1.8 eV). In the retention mode, most of the trapped electrons in the TNO-CTL transfers across the Al{sub 2}O{sub 3}-tunneling layer (AlO-TL) rather than the AlO-BL. The thickness of the AlO-TL affects the V{sub fb} shift degradation behavior in the retention mode. The injected electrons are dominantly located at the TNO-CTL/ALO-BL interface, determined from the thickness dependence of the TNO-CTL on the V{sub fb} shift.

  3. Elevated-temperature flow strength, creep resistance and diffusion welding characteristics of Ti-gAl-2Nb-1Ta-0.8Mo

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.; Moore, T. J.

    1977-01-01

    A study of the flow strength, creep resistance and diffusion welding characteristics of the titanium alloy Ti-6Al-2Nb-1Ta-0.8Mo was conducted. Two mill-processed forms of this alloy were examined. The forged material was essentially processed above the beta transus while the rolled form was subjected to considerable work below the beta transus. Between 1150 and 1250 K, the forged material was stronger and more creep resistant than the rolled alloy. Both forms exhibit superplastic characteristics in this temperature range. Strain measurements during diffusion welding experiments at 1200 K reveal that weld interfaces have no measurable effect on the overall creep deformation. Significant deformation appears to be necessary to produce a quality diffusion weld between superplastic materials. A 'soft' interlayer inserted between faying surfaces would seemingly allow manufacture of quality diffusion welds with little overall deformation.

  4. First-principles prediction of kink-pair activation enthalpy on screw dislocations in bcc transition metals: V, Nb, Ta, Mo, W, and Fe

    NASA Astrophysics Data System (ADS)

    Dezerald, L.; Proville, L.; Ventelon, Lisa; Willaime, F.; Rodney, D.

    2015-03-01

    The atomistic study of kink pairs on screw dislocations in body-centered cubic (bcc) metals is challenging because interatomic potentials in bcc metals still lack accuracy and kink pairs require too many atoms to be modeled by first principles. Here, we circumvent this difficulty using a one-dimensional line tension model whose parameters, namely the line tension and Peierls barrier, are reachable to density functional theory calculations. The model parameterized in V, Nb, Ta, Mo, W, and Fe, is used to study the kink-pair activation enthalpy and spatial extension. Interestingly, we find that the atomistic line tension is more than twice the usual elastic estimates. The calculations also show interesting group tendencies with the line tension and kink-pair width larger in group V than in group VI elements. Finally, the present kink-pair activation energies are shown to compare qualitatively with experimental data and potential origins of quantitative discrepancies are discussed.

  5. The behaviour of the extended HFSE group (Nb, Ta, Zr, Hf, W, Mo) during the petrogenesis of mafic K-rich lavas: The Eastern Mediterranean case

    NASA Astrophysics Data System (ADS)

    Kirchenbaur, M.; Münker, C.

    2015-09-01

    In arc lavas, elements of the extended high field strength element group (HFSE; Nb, Ta, Zr, Hf, W, and Mo) are valuable tracers to unravel magma source processes. These elements can also help to identify residual mineral assemblages in subducting slabs and in the mantle. Most high-precision studies on HFSE behaviour to date only focused on intra-oceanic arc suites and data for mafic lavas of the K-rich series (medium-K, high-K and shoshonitic) are scarce. Arguably, K-rich series are the most incompatible element-rich end-members of subduction zone magmatism, and they often record sediment recycling into the mantle. Understanding HFSE fractionation in K-rich lavas can therefore provide important insight into the global HFSE budget. Here we present a comprehensive extended HFSE dataset obtained by isotope dilution on well-characterised K-rich lavas from the Eastern Mediterranean, also including subducting sediment samples drilled during DSDP Leg 13 and ODP Leg 160 South and West of Crete. The volcanic samples include mafic calc-alkaline lavas from the active Aegean Island arc (Santorini) and post-collisional Tertiary lavas from SE Bulgaria. The Santorini lavas record a hydrous sediment melt-mediated source overprint of a depleted mantle source by components from the subducting African plate. The Bulgarian lavas tap lithospheric mantle sources that were overprinted by fluid- and melt-like subduction components during Eocene subduction of the African Plate. The sediments in this study comprise silts/sands, marl oozes, limestones and clay-rich debris flows and approximate the bulk sediment subducted beneath the Hellenic arc. The marked enrichment of all HFSE in the lavas is controlled by the composition of the subducted sediments as shown by low 176Lu/177Hf (0.008630-0.02433) and Zr/Nb (11.3-29.4), combined with variable εHf (-3 to +11) and elevated W contents (up to 2.45 ppm) in the lavas. Nevertheless, the lavas display unfractionated ratios of Nb/Ta and Zr/Hf of 12

  6. Electronic structure of the LiAA‧O6 (A = Nb, Ta, and A‧ = W, Mo) ceramics by modified Becke-Johnson potential

    NASA Astrophysics Data System (ADS)

    Ali, Zahid; Khan, Imad; Rahman, Mazhar; Ahmad, Rashid; Ahmad, Iftikhar

    2016-08-01

    DFT is used to study various transition metal based ceramics LiAA‧O6 (A = Nb, Ta, and A‧ = W, Mo) in tetragonal phase with space group 421 m (No. 113). The calculated structural and geometrical parameters are found in closed agreement with the experiments. Electronic clouds explain the chemical bonding and reveal that Li atom occupy central position and form ionic bond. Other bonds in these compounds are significantly covalent due to the sharing of electrons between O and A/A‧. The electronic properties demonstrate that these compounds are wide bandgap semiconductors in the energy range of 2.18-2.60 eV. These bandgap energies confirm the suitability of these oxides in optoelectronic devices operating in the visible range of the electromagnetic spectrum.

  7. Elevated temperature flow strength, creep resistance and diffusion welding characteristics of Ti-6Al-2Nb-1Ta-0.8Mo

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.; Moore, T. J.

    1979-01-01

    A study of the flow strength, creep resistance and diffusion welding characteristics of the titanium alloy Ti-6Al-2Nb-1Ta-0.8Mo has been conducted. Two mill-processed forms of this alloy were examined. The forged material had been processed above the beta transus (approximately 1275 K) while the rolled form had been subjected to work below the beta transus. Between 1150 and 1250 K, the forged material was stronger and more creep resistant than the rolled alloy. Both forms exhibit superplastic characteristics in this temperature range. Strain measurements during diffusion welding experiments at 1200 K reveal that weld interfaces have no measurable effect on the overall creep deformation. Significant deformation appears to be necessary to produce a quality diffusion weld between superplastic materials. A 'soft' interlayer inserted between faying surfaces would seemingly allow manufacture of quality diffusion welds with little overall deformation.

  8. Atomic Control of Conductivity Versus Ferromagnetism in Wide-Gap Oxides Via Selective Doping: V, Nb, Ta in Anatase TiO2

    NASA Astrophysics Data System (ADS)

    Osorio-Guillén, Jorge; Lany, Stephan; Zunger, Alex

    2008-01-01

    We identify two general types of electronic behaviors for transition-metal impurities that introduce excess electrons in oxides. (i) The dopants introduce resonant states inside the host conduction band and produce free electrons; (ii) the dopants introduce a deep gap state that carries a magnetic moment. By combining electronic structure calculations, thermodynamic simulations, and percolation theory, we quantify these behaviors for the case of column V-B dopants in anatase TiO2. Showing behavior (i), Nb and Ta dopants can convert the insulator TiO2 into a transparent conductor. Showing behavior (ii), V dopants could convert nonmagnetic TiO2 into a ferromagnet. Whether a dopant shows behavior (i) or (ii) is encoded in its atomic d orbital energy.

  9. First-principles investigation of the stability of MN and CrMN precipitates under coherency strains in α-Fe (M = V, Nb, Ta)

    NASA Astrophysics Data System (ADS)

    Fors, Dan H. R.; Wahnström, Göran

    2011-06-01

    We perform a systematic ab initio study of the interface energetics of thin coherent rocksalt (nacl) structured MN and tetragonal CrMN films in bcc Fe (M = V, Nb, Ta), motivated by the vital role of MN and CrMN precipitates for the long-term creep resistance in 9%-12%Cr steels. The similarities and differences in the work of separations and the elastic costs for the coherency strains are identified, and the possibility for formation of coherent films are discussed. Our findings provide valuable information of the interface energetics, which in continuation can be combined with thermodynamical modeling to obtain a better understanding of the initial nucleation stage of the MN and CrMN precipitates, and their influence on the long-term microstructural evolution in 9%-12%Cr steels.

  10. Room-Temperature Magnetocapacitance in Fe-Doped K0.5Na0.5Nb0.95Ta0.05O3 Ceramics

    NASA Astrophysics Data System (ADS)

    Li, Huan; Yang, Wenlong; Li, Yu; Meng, Qingxin; Zhou, Zhongxiang

    2012-10-01

    Ferroelectric and magnetic properties of Fe-doped potassium-sodium tantalate niobate (K0.5Na0.5(Nb0.95Ta0.05)1-xFexO3-x; x = 0 and 0.01) ceramics prepared by the conventional sintering method were investigated. In comparison with pure ceramics, the 0.01 Fe-doped ceramics show magnetic and ferroelectric properties simultaneously at room temperature. The relative dielectric constant significantly decreases after applying a magnetic field for the Fe-doped ceramics, indicating the coupling between ferroelectric and ferromagnetic orders. Magnetocapacitance of -0.77% was observed at room temperature and 50 kHz by the application of a magnetic field of 5000 Oe.

  11. Modelling potential photovoltaic absorbers Cu3 MCh 4 (M  =  V, Nb, Ta; Ch  =  S, Se, Te) using density functional theory

    NASA Astrophysics Data System (ADS)

    Kehoe, Aoife B.; Scanlon, David O.; Watson, Graeme W.

    2016-05-01

    The geometric and electronic properties of a series of potential photovoltaic materials, the sulvanite structured \\text{C}{{\\text{u}}3}MC{{h}4} (M  =  V, Nb, Ta; Ch  =  S, Se, Te), have been computationally examined using both PBEsol+U and HSE06 methods to assess the materials’ suitability for solar cell application and to compare the predictions of the two theoretical approaches. The lattice parameters, electronic density of states, and band gaps of the compounds have been calculated to ascertain the experimental agreement obtained by each method and to determine if any of the systems have an optical band gap appropriate for photovoltaic absorber materials. The PBEsol+U results are shown to achieve better agreement with experiment than HSE06 in terms of both lattice constants and band gaps, demonstrating that higher level theoretical methods do not automatically result in a greater level of accuracy than their computationally less expensive counterparts. The PBEsol+U calculated optical band gaps of five materials suggest potential suitability as photovoltaic absorbers, with values of 1.72 eV, 1.49 eV, 1.19 eV, 1.46 eV, and 1.69 eV for Cu3VS4, Cu3VSe4, Cu3VTe4, Cu3NbTe4, and Cu3TaTe4, respectively, although it should be noted that all fundamental band gaps are indirect in nature, which could lower the open-circuit voltage and hence the efficiency of prospective devices.

  12. Peculiarities of hydrogen permeation through Zr-1%Nb alloy and evaluation of terminal solid solubility

    NASA Astrophysics Data System (ADS)

    Denisov, E. A.; Kompaniets, M. V.; Kompaniets, T. N.; Bobkova, I. S.

    2016-04-01

    Hydrogen permeation through Zr-1%Nb alloy was studied at the temperature below the temperature of α-β transition. Analysis of the transient permeation curves from a closed volume in a surface limited regime allowed to determine total and mobile hydrogen concentrations. At the mobile hydrogen concentration of 4.3 at% a part of the absorbed hydrogen is cut out of permeation process. Increase of the mobile hydrogen concentration in α-phase of Zr-1%Nb alloy is ceasing at the concentration of (5.5 ± 0.3) at%, which is the maximum possible concentration of the mobile hydrogen in α-phase of the studied alloy. From this moment on all absorbed hydrogen is spent on hydride formation. The obtained results are compared with those obtained by means of traditional techniques for terminal solid solubility determination.

  13. Systematic study on the electronic structure and mechanical properties of X2BC (X = Mo, Ti, V, Zr, Nb, Hf, Ta and W)

    NASA Astrophysics Data System (ADS)

    Bolvardi, H.; Emmerlich, J.; Baben, M. to; Music, D.; von Appen, J.; Dronskowski, R.; Schneider, J. M.

    2013-01-01

    In this work the electronic structure and mechanical properties of the phases X2BC with X =Ti, V, Zr, Nb, Mo, Hf, Ta, W (Mo2BC-prototype) were studied using ab initio calculations. As the valence electron concentration (VEC) per atom is increased by substitution of the transition metal X, the six very strong bonds between the transition metal and the carbon shift to lower energies relative to the Fermi level, thereby increasing the bulk modulus to values of up to 350 GPa, which corresponds to 93% of the value reported for c-BN. Systems with higher VEC appear to be ductile as inferred from both the more positive Cauchy pressure and the larger value of the bulk to shear modulus ratio (B/G). The more ductile behavior is a result of the more delocalized interatomic interactions due to larger orbital overlap in smaller unit cells. The calculated phase stabilities show an increasing trend as the VEC is decreased. This rather unusual combination of high stiffness and moderate ductility renders X2BC compounds with X = Ta, Mo and W as promising candidates for protection of cutting and forming tools.

  14. Computational study on the molecular structures and photoelectron spectra of bimetallic oxide clusters MW2O9(-/0) (M=V, Nb, Ta).

    PubMed

    Chen, Wen-Jie; Zhang, Chang-Fu; Zhang, Xian-Hui; Zhang, Yong-Fan; Huang, Xin

    2013-05-15

    Density functional theory (DFT) and coupled cluster theory (CCSD(T)) calculations are carried out to investigate the electronic and structural properties of a series of bimetallic oxide clusters MW2O9(-/0) (M=V, Nb, Ta). Generalized Koopmans' theorem is applied to predict the vertical detachment energies (VDEs) and simulate the photoelectron spectra (PES). Theoretical calculations at the B3LYP level yield singlet and doublet ground states for the bimetallic anionic and neutral clusters, respectively. All the clusters present the six-membered ring structures with different symmetries, except that the TaW2O9(-) cluster shows a chained style with a penta-coordinated tantalum atom. Spin density analyses reveal oxygen radical species in all neutral clusters, consistent with their structural characteristics. Moreover, additional calculations are performed to study the oxidation reaction of CO molecule with the W3O9(+) cation and the isoelectronic VW2O9 cluster, and results indicate that the introduction of vanadium at tungsten site can efficiently improve the oxidation reactivity. PMID:23523755

  15. Computational study on the molecular structures and photoelectron spectra of bimetallic oxide clusters MWO9-/0 (M = V, Nb, Ta)

    NASA Astrophysics Data System (ADS)

    Chen, Wen-Jie; Zhang, Chang-Fu; Zhang, Xian-Hui; Zhang, Yong-Fan; Huang, Xin

    2013-05-01

    Density functional theory (DFT) and coupled cluster theory (CCSD(T)) calculations are carried out to investigate the electronic and structural properties of a series of bimetallic oxide clusters MWO9-/0 (M = V, Nb, Ta). Generalized Koopmans' theorem is applied to predict the vertical detachment energies (VDEs) and simulate the photoelectron spectra (PES). Theoretical calculations at the B3LYP level yield singlet and doublet ground states for the bimetallic anionic and neutral clusters, respectively. All the clusters present the six-membered ring structures with different symmetries, except that the TaWO9- cluster shows a chained style with a penta-coordinated tantalum atom. Spin density analyses reveal oxygen radical species in all neutral clusters, consistent with their structural characteristics. Moreover, additional calculations are performed to study the oxidation reaction of CO molecule with the WO9+ cation and the isoelectronic VW2O9 cluster, and results indicate that the introduction of vanadium at tungsten site can efficiently improve the oxidation reactivity.

  16. X-ray Structure Refinements and Strain Analysis of Substituted Cubic Lead Pyrochlores Pb 2( M2- yPb y)O 7- δ(0.0< y<0.8; M=Nb or Ta)

    NASA Astrophysics Data System (ADS)

    Nalini, G.; Somashekar, R.; Guru Row, T. N.

    2001-01-01

    The phase diagrams in the PbO-Nb2O5 system and the PbO-Ta2O5 system depict pyrochlore structure at certain molar ratios. Compositions Pb2Nb1.51Pb0.49O6.30 (1), Pb2Ta1.4Pb0.6O6.21 (2), and Pb2Ta1.25Pb0.75O6.57 (3) belonging to this family, are refined in the cubic space group Fdoverline3m (Z=8; lattice parameter a=10.762(1), 10.744(1), 10.757(5) Å, respectively) using the Rietveld refinement approach. The analyses suggest that the B-site is partially occupied by Pb leading to the general formula Pb2(M2-yPby)O7-δ(0.0Nb or Ta). There is an overall broadening observed in the X-ray peak widths in 1, 2, and 3 compared to the Pb-deficient parent phases. It is observed that the X-ray peak widths of 2 is broad, while 3 displays narrow peak widths. It is found via strain analysis that the line broadening observed correlates with the strain in the lattice.

  17. Transport and thermoelectric properties of Sr{sub 3}(Ti{sub 0.95}R{sub 0.05}){sub 2}O{sub 7} (R = Ta, Nb, W) oxides

    SciTech Connect

    Sun, R. R.; Qin, X. Y.; Li, L. L.; Li, D.; Wang, N. N.; Zhang, J.; Wang, Q. Q.

    2012-12-15

    The Sr{sub 3}(Ti{sub 0.95}R{sub 0.05}){sub 2}O{sub 7} (R = Ta, Nb, W) polycrystalline compounds were fabricated, and their transport and thermoelectric properties were investigated. The results indicate that at T > 300 K electrical resistivity {rho} for all the doped compounds increases monotonically with temperature, and basically can be described by a relation {rho}{proportional_to}T{sup M} at T > {approx}650 K, with M = 1.39, 1.66, and 1.77 for R = Ta, Nb, and W, respectively, implying that at the high temperatures the acoustic phonon scattering dominates the scattering process. Although the resistivity {rho} of Sr{sub 3}(Ti{sub 0.95}Ta{sub 0.05}){sub 2}O{sub 7} exhibits a metallic-like behavior at the temperature as low as 5 K, a transition from metallic state (d{rho}/dT > 0) to semiconductor-like state (d{rho}/dT < 0) was observed at a critical low temperature {approx}41 K and {approx}79 K for R = Nb and W, respectively. At T < {approx}22 K, {approx}57 K, and {approx}80 K, a relation of {sigma}{proportional_to}T{sup 1/2} (here conductivity {sigma} = 1/{rho}) holds for the doped compounds with R = Nb, Ta, and W, respectively, suggesting that at the low temperatures the main transport mechanism is electron-electron interaction due to the presence of disorder induced by the dopants. The thermoelectric figure of merit (ZT) for Ta-doped compound increases more steeply with increasing temperature among the three compounds and reaches 0.066 at 1000 K.

  18. The in vitro and in vivo performance of a strontium-containing coating on the low-modulus Ti35Nb2Ta3Zr alloy formed by micro-arc oxidation.

    PubMed

    Liu, Wei; Cheng, Mengqi; Wahafu, Tuerhongjiang; Zhao, Yaochao; Qin, Hui; Wang, Jiaxing; Zhang, Xianlong; Wang, Liqiang

    2015-07-01

    The β-titanium alloy is thought to be a promising alloy using as orthopedic or dental implants owing to its characteristics, which contains low elastic modulus, high corrosion resistance and well biocompatibility. Our previous study has reported that a new β-titanium alloy Ti35Nb2Ta3Zr showed low modulus close to human bone, equal tissue compatibility to a traditional implant alloy Ti6Al4V. In this study, micro-arc oxidation (MAO) was applied on the Ti35Nb2Ta3Zr alloy to enhance its surface characteristics and biocompatibility and osseointegration ability. Two different coatings were formed, TiO2 doped with calcium-phosphate coating (Ca-P) and calcium-phosphate-strontium coating (Ca-P-Sr). Then we evaluated the effects of the MAO coatings on the Ti35Nb2Ta3Zr alloy through in vitro and in vivo tests. As to the characteristics of the coatings, the morphology, chemical composition, surface roughness and contact angle of MAO coatings were tested by scanning electron microscopy, energy dispersive spectroscopy, atomic force microscopy, and video contact-angle measurement system respectively. Besides, we performed MTT assay, ALP test and cell morphology-adhesion test on materials to evaluate the MAOed coating materials' biocompatibility in vitro. The in vivo experiment was performed through rabbit model. Alloys were implanted into rabbits' femur shafts, then we performed micro-CT, histological and sequential fluorescent labeling analysis to evaluate implants' osseointegration ability in vivo. Finally, the Ca-P specimens and Ca-P-Sr specimens exhibited a significant enhancement in surface roughness, hydrophilicity, cell proliferation, cell adhesion. More new bone was found around the Ca-P-Sr coated alloy than Ca-P coated alloy and Ti35Nb2Ta3Zr alloy. In conclusion, the MAO treatment improved in vitro and in vivo performance of Ti35Nb2Ta3Zr alloy. The Ca-P-Sr coating may be a promising modified surface formed by MAO for the novel β-titanium alloy Ti35Nb2Ta3Zr. PMID

  19. Kinetics and mechanisms of ligand substitution reactions of the vanadium triad metals. Syntheses and reactivities of (. eta. sup 5 -C sub 5 H sub 5 )M(CO) sub 3 (C sub 4 H sub 8 E) (M = Nb, E = S, Se, Te; M = Ta, E = S)

    SciTech Connect

    Freeman, J.W.; Basolo, F. )

    1991-01-01

    Kinetic studies were performed for CO substitution reactions of CpM(CO){sub 4} (M = Nb, Ta) and for dialkylchalcogenide substitution reactions of CpM(CO){sub 3}(C{sub 4}H{sub 8}E) (M = V, E = S; M = Nb, E = O, S, Se, Te; M = Ta, E = O, S) with phosphines. The syntheses and characterization of the new compounds CpM(CO){sub 3}(C{sub 4}H{sub 8}E) (M = Nb, E = S, Se, Te; M = Ta, E = S) are reported. Both CpM(CO){sub 4} and CpM(CO){sub 3}(C{sub 4}H{sub 8}E) were found to react by the same mechanism. For M = V, a dissociative mechanism was observed, while for M = Nb, Ta both dissociative and associative mechanisms were observed. This change in mechanism is attributed to the larger size of the Nb and Ta centers. The reactivity of the compounds was found to increase in the order V > Nb > Ta. The higher reactivity of the V compounds compared to the Nb compounds is unusual when compared to other triads, where the second-row metal usually forms the most reactive compound. The reactivity of the CpM(CO){sub 3}(C{sub 4}H{sub 8}E) compounds was found to increase in the order Te < Se < S < O, indicating that the heavier chalcogenides form more stable complexes than the higher chalcogenides.

  20. Improved Piezoelectric Properties of LiTaO3 Family Solid Solution Ceramics with Modified Composition

    NASA Astrophysics Data System (ADS)

    Bamba, Noriko; Takaoka, Junpei; Chino, Takashi; Fukami, Tatsuo; Elouadi, Brahim

    2006-09-01

    Nonstoichiometric LiTaO3 ceramics doped with 15 mol % CaTiO3 have been prepared to improve the piezoelectricity of LiTaO3 ceramics and iron doping has been investigated to obtain a high mechanical quality factor, Qm. By increasing the ratio of B sites (Ta and Ti) from 49.5 to 52.0 mol %, crack generation was suppressed and resonance frequency in the radial vibration mode shifted. (Li0.84Ca0.15)(Ta0.86Ti0.15)O3 ceramics whose A and B site ratios were 49.5 and 50.5 mol %, respectively, caused a higher resonance frequency and a high piezoelectric activity than the stoichiometric LiTaO3. The optimum composition for the piezoelectric properties was obtained from the nonstoichiometric LiTaO3 expressed as (Li0.832Ca0.158)(Ta0.856Ti0.15Fe0.004)O3; the phase shift was 73° and the quality factor Qm was 7872 in the radial vibration mode. Although the phase shift is still not sufficiently high, it is expected to approach 90° by fixing it under better poling conditions. One of the possible applications of this material is as an oscillator element for signal processing circuits.

  1. β-NbPO 5 and β-TaPO 5: Bronzoïds, second members of the monophosphate tungsten bronze series (PO 2) 4(WO 3) 2 m

    NASA Astrophysics Data System (ADS)

    Chahboun, H.; Groult, D.; Hervieu, M.; Raveau, B.

    1986-12-01

    The oxides β-NbPO 5 and β-TaPO 5 have been studied by X-ray diffraction and high resolution electron microscopy. They exhibit different supercells based on an orthorhombic subcell with the parameters a0 = 11.27 Å, b0 = 5.28 Å, c0 = 6.62 Å. It is shown that their framework corresponds to the member m = 2 of the series of monophosphate tungsten bronzes (PO 2) 4(WO 3) 2 m with pentagonal tunnels (MPTB P). The structure can thus be described as built up from ReO 3-type slabs which are two octahedra wide and connected through phosphate planes. The stability of these bronzoïds is discussed with respect to that of the MPTB P compounds. The relationships between the structures of the α and β forms of NbPO 5 and TaPO 5 are studied.

  2. The effect of boron addition on microstructure and mechanical properties of biomedical Ti35Nb6Ta alloy

    SciTech Connect

    Málek, Jaroslav; Hnilica, František; Veselý, Jaroslav; Smola, Bohumil; Březina, Vítězslav

    2014-10-15

    The beta-titanium alloys are promising materials for bioapplications but their processing via melting is difficult. Coarse grains have been observed in as-cast specimens. Subsequent thermo-mechanical processing seems to be necessary in order to obtain fine-grained microstructure with better mechanical properties. The grain size can be decreased significantly by addition of small boron amount. In this work Ti–35Nb–6Ta alloy with various B additions (0, 0.05, 0.1, 0.3 and 0.5 wt.%) has been studied. Even the smallest amount of B leads to significant grain refinement in Ti–35Nb–6Ta alloy (from 1300 to about 350 μm). Slight grain refinement has been observed also after hot forging and solution treatment. TiB particles emerged in specimens due to B addition. These particles contribute to changes in mechanical properties not only in hot forged and solution treated specimens (hardness increase from 140 to 180 HV10), but also in cold swaged specimens (hardness from 230 to 250 HV10, tensile strength from 800 to 920 MPa). The hardness values can be increased up to 370 HV10 during aging at 400 °C (specimen with 0.5 wt.% B). It has been observed that specimens with low boron addition 0.05 wt.% possess no cytotoxicity. On the other hand in specimens with 0.1 wt.% B or more slight adverse effect on cytotoxicity has been observed. - Highlights: • The influence of boron on microstructure and mechanical properties has been studied. • Beta-transus temperature has been determined. • Cytotoxicity depending on boron content has been evaluated. • Possibility of final heat treatment has been determined.

  3. Investigation on transition behavior and electrical properties of (K{sub 0.5}Na{sub 0.5}){sub 1-x}Li{sub x}Nb{sub 0.84}Ta{sub 0.1}Sb{sub 0.06}O{sub 3} around polymorphic phase transition region

    SciTech Connect

    Zhu, Chen; Wang, Wenchao; Shi, Honglin; Wang, Fangyu; Cao, Yongge; Huang, Jiquan; Wang, Chong; Tang, Fei; Yuan, Xuanyi; Liu, Yang

    2014-01-15

    (K{sub 0.5}Na{sub 0.5}){sub 1-x}Li{sub x}Nb{sub 0.84}Ta{sub 0.1}Sb{sub 0.06}O{sub 3} (KNLNTS) lead free ceramics with different Li concentration were fabricated by conventional solid-state reaction method. By increasing Li ions in KNLNTS, the grains grow up and the crystal structure changes from orthorhombic to tetragonal. When 0.03 ≤ x ≤ 0.05, the ceramics structure lays in PPT region. Polarization versus electric field (P-E) hysteresis loops at room temperature show good ferroelectric properties and the remnant polarization decreases by increasing Li content while coercive electric keeps almost unchanged. In PPT region, taking x = 0.04 as an example, the sample shows excellent dielectric properties: the dielectric constant is 1159 and loss tangent is 0.04, while the piezoelectric constant d{sub 33} is 245 pC/N and kp is 0.44 at room temperature, it is promising for (K{sub 0.5}Na{sub 0.5}){sub 1-x}Li{sub x}Nb{sub 0.84}Ta{sub 0.1}Sb{sub 0.06}O{sub 3} with 4 at. % Li to substitute PZT.

  4. Synthesis and structural characterization of AMV2O8 (A = K, Rb, Tl, Cs; M = Nb, Ta) vanadates: a structural comparison of A(+)M(5+)V2O8 vanadates and A(+)M(5+)P2O8 phosphates.

    PubMed

    Paidi, Anil Kumar; Devi, R Nandini; Vidyasagar, Kanamaluru

    2015-10-21

    Eight new quaternary vanadates of niobium and tantalum, AMV2O8 (A = K, Rb, Tl, Cs; M = Nb, Ta), have been prepared by solid state reactions and structurally characterized by single crystal and powder X-ray diffraction (XRD) techniques. The two cesium compounds, unlike the known CsSbV2O8 with a layered yavapaiite structure, have a new three-dimensional structure and the other six compounds possess the known KSbV2O8 structure type. The three types of [(MV2O8)(-)]∞ anionic frameworks of twelve A(+)M(5+)V2O8 (A = K, Rb, Tl, Cs; M = Nb, Ta, Sb) vanadates could be conceived to be built by different connectivity patterns of M2V4O18 ribbons, which contain MO6 octahedra and VO4 tetrahedra. A structural comparison of these twelve vanadates and the nineteen A(+)M(5+)P2O8 phosphates has been made. The spectroscopic studies of these eight new quaternary vanadates are presented. PMID:26390384

  5. M4Se 16Br 2 ( M = Nb, Ta), a new chain-like structure from progressive condensation of ( M2Se 4) groups

    NASA Astrophysics Data System (ADS)

    Grenouilleau, P.; Meerschaut, A.; Guemas, L.; Rouxel, J.

    1987-02-01

    Nb 4Se 16Br 2 and Ta 4Se 16Br 2 crystallize in the monoclinic system, space group {P2 1}/{c} with a = 12.862(3)Å, b = 13.862(3) Å, c = 16.029(3) Å, β = 127.70(1)°, Z = 4 and a = 12.844(2) Å, b = 13.875(2) Å, c = 16.018(4) Å, β = 127.57(1)°, Z = 4, respectively. The structures were solved from 3182 and 2784 reflections, respectively, collected on a NONIUS CAD4 automatic diffractometer (Mo Kα radiation). The final R indexes are 0.030 and 0.033. The common structural type is based on the presence of four chains running in a direction parallel to the a axis. Along the chains four metal atoms are found; short and long M- M distances alternate in the sequence of three consecutive short bonds ( overlined(M-M) ˜- 3.1 Å) and one long ( overlined(M … M) ˜- 3.7 Å). The shortest bonds are associated with [ M4Se 12] groups built up from the condensation of three [ M2Se 4] units.

  6. Large pinning forces and matching effects in YBa2Cu3O7-δ thin films with Ba2Y(Nb/Ta)O6 nano-precipitates

    PubMed Central

    Opherden, Lars; Sieger, Max; Pahlke, Patrick; Hühne, Ruben; Schultz, Ludwig; Meledin, Alexander; Van Tendeloo, Gustaaf; Nast, Rainer; Holzapfel, Bernhard; Bianchetti, Marco; MacManus-Driscoll, Judith L.; Hänisch, Jens

    2016-01-01

    The addition of mixed double perovskite Ba2Y(Nb/Ta)O6 (BYNTO) to YBa2Cu3O7−δ (YBCO) thin films leads to a large improvement of the in-field current carrying capability. For low deposition rates, BYNTO grows as well-oriented, densely distributed nanocolumns. We achieved a pinning force density of 25 GN/m3 at 77 K at a matching field of 2.3 T, which is among the highest values reported for YBCO. The anisotropy of the critical current density shows a complex behavior whereby additional maxima are developed at field dependent angles. This is caused by a matching effect of the magnetic fields c-axis component. The exponent N of the current-voltage characteristics (inversely proportional to the creep rate S) allows the depinning mechanism to be determined. It changes from a double-kink excitation below the matching field to pinning-potential-determined creep above it. PMID:26887291

  7. Multiphoton photoluminescence contrast in switched Mg:LiNbO{sub 3} and Mg:LiTaO{sub 3} single crystals

    SciTech Connect

    Reichenbach, P. Kämpfe, T.; Thiessen, A.; Haußmann, A.; Eng, L. M.; Woike, T.

    2014-09-22

    We observed a multiphoton luminescence contrast between virgin and single-switched domains in Mg-doped LiNbO{sub 3} (LNO) and LiTaO{sub 3} (LTO) single crystals with different doping levels of 0–7 mol. % and 0–8 mol. %, respectively. A luminescence contrast in the range of 3% was measured between as-grown and electrically inverted domain areas in Mg:LNO samples, while the contrast reaches values of up to 30% for the Mg:LTO case. Under annealing, an exponential decay of the domain contrast was observed. The activation energy of about 1 eV being determined for the decay allowed a comparison with reported activation energies of associated defects, clearly illustrating a strong connection between thermal contrast decay and the H{sup +} and Li{sup +}-ion mobility. Finally, performing similar experiments on oxidized samples undoubtedly demonstrated that the origin of the reported luminescence contrast is strongly connected with lithium ions.

  8. Influence of the A/B nonstoichiometry, composition modifiers, and preparation methods on properties of Li- and Ta-modified (K,Na)NbO3 ceramics

    NASA Astrophysics Data System (ADS)

    Morozov, Maxim I.; Hoffmann, Michael J.; Benkert, Katrin; Schuh, Carsten

    2012-12-01

    Properties of Li- and Ta- modified (K,Na)NbO3 piezoceramics with the base composition near the orthorhombic-tetragonal phase boundary have been investigated with respect to variation of temperature, stoichiometry, compositional homogeneity, atmosphere of thermal treatment, and dopants (Ba, Mn). Although the influence of the most of the abovementioned factors has already been reported in the literature, the paper focuses on several aspects of the composition—property relationships that still remain controversial or poorly elucidated. In particular, we show that improvement of compositional homogeniety in these ceramics emphasizes the instability of piezoelectric response with respect to variation of temperature in the vicinity of the orthorhombic-tetragonal phase transition. Ba dopant is shown to suppress conductivity in ceramics sintered in air, though it makes conductivity more sensitive to variation of the oxygen partial pressure. Mn dopant is shown to suppress conductivity and strongly reduce the influence of the oxygen partial pressure on conductivity of the ceramics. Finally, we show that chemical modifications to the ceramic composition, such as Mn dopant or variation of nonstoichiometry affect the piezoelectric response mainly by the shift of the orthorhombic-tetragonal phase transition temperature.

  9. Large pinning forces and matching effects in YBa2Cu3O(7-δ) thin films with Ba2Y(Nb/Ta)O6 nano-precipitates.

    PubMed

    Opherden, Lars; Sieger, Max; Pahlke, Patrick; Hühne, Ruben; Schultz, Ludwig; Meledin, Alexander; Van Tendeloo, Gustaaf; Nast, Rainer; Holzapfel, Bernhard; Bianchetti, Marco; MacManus-Driscoll, Judith L; Hänisch, Jens

    2016-01-01

    The addition of mixed double perovskite Ba2Y(Nb/Ta)O6 (BYNTO) to YBa2Cu3O(7-δ) (YBCO) thin films leads to a large improvement of the in-field current carrying capability. For low deposition rates, BYNTO grows as well-oriented, densely distributed nanocolumns. We achieved a pinning force density of 25 GN/m(3) at 77 K at a matching field of 2.3 T, which is among the highest values reported for YBCO. The anisotropy of the critical current density shows a complex behavior whereby additional maxima are developed at field dependent angles. This is caused by a matching effect of the magnetic fields c-axis component. The exponent N of the current-voltage characteristics (inversely proportional to the creep rate S) allows the depinning mechanism to be determined. It changes from a double-kink excitation below the matching field to pinning-potential-determined creep above it. PMID:26887291

  10. Surface Modification and In Vitro Characterization of Cp-Ti and Ti-5Al-2Nb-1Ta Alloy in Simulated Body Fluid

    NASA Astrophysics Data System (ADS)

    Sasikumar, Y.; Rajendran, N.

    2012-10-01

    Ti and its alloys are widely used in manufacturing orthopedic implants as prostheses for joint replacement because of their high corrosion resistance and excellent biocompatibility. However, they lack in bone-bonding ability and leads to higher rate of osteolysis and subsequent loosening of implants. In order to enhance the bone-bonding ability of these alloys, various surface-modification techniques are generally employed. The present investigation is mainly concerned with the surface modification of Cp-Ti and Ti-5Al-2Nb-1Ta alloy using a mixture of alkali and hydrogen peroxide followed by subsequent heat treatment to produce a porous gel layer with anatase structure, which enhances osseointegration. The morphological behavior was examined by x-ray diffractometer (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) coupled with energy dispersive x-ray analysis (EDX). The in vitro characterization of all the specimens was evaluated by immersing the specimens in simulated body fluid solution to assess the apatite formation over the metal surface. The apatite formation was confirmed by XRD, SEM-EDX, and Fourier transform infrared spectroscopy (FT-IR). Further, the electrochemical corrosion behaviors of both the untreated and treated specimens were evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy. The results revealed that the surface-modified and heat-treated specimens exhibited higher corrosion resistance and excellent biocompatibility when compared to the chemical and untreated specimens.

  11. Enhancement of adhesive strength of hydroxyapatite films on Ti-29Nb-13Ta-4.6Zr by surface morphology control.

    PubMed

    Hieda, Junko; Niinomi, Mitsuo; Nakai, Masaaki; Cho, Ken; Gozawa, Tatsuya; Katsui, Hirokazu; Tu, Rong; Goto, Takashi

    2013-02-01

    Hydroxyapatite (HAp) films were deposited on a β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ), by metal organic chemical vapor deposition (MOCVD) in order to improve its hard-tissue compatibility. The surface morphologies of TNTZ substrates were changed by acid treatments and mechanical polishing prior to the HAp film deposition. The adhesive strength of the HAp films formed on TNTZ substrates treated with an HF solution increased to twice that of the HAp film deposited on a TNTZ substrate with a mirror-like finish. Complex microstructures with deeply etched grain boundaries, formed on the TNTZ substrates after immersion in the HF solution, were responsible for the increase in the adhesive strength of the HAp film caused by an interlocking effect. The HAp films on TNTZ substrates treated with a H(2)SO(4) solution exhibited lower adhesive strength than HAp films on TNTZ substrates treated with HF solution, regardless of the surface roughness of the substrates. Additionally, acid treatments using HNO(3) and H(2)O(2) solutions did not change the surface morphologies of the TNTZ substrates. The complex microstructures with deeply etched grain boundaries and nanosized asperities formed on the TNTZ substrates are important factors in the improvement of the adhesive strengths of HAp films deposited on TNTZ substrates. PMID:23274485

  12. Microstructures and wear properties of surface treated Ti-36Nb-2Ta-3Zr-0.35O alloy by electron beam melting (EBM)

    NASA Astrophysics Data System (ADS)

    Chen, Zijin; Liu, Yong; Wu, Hong; Zhang, Weidong; Guo, Wei; Tang, Huiping; Liu, Nan

    2015-12-01

    Ti-36Nb-2Ta-3Zr-0.35O (wt.%) (TNTZO, also called gum metal) alloy was surface treated by electron beam melting (EBM), in order to improve wear properties. The microstructures and phase constitutions of the treated surface were characterized by optical microscopy (OM), scanning electron microscopy (SEM), grazing incidence X-ray diffraction (GIXD) and electron backscattered diffraction (EBSD). The results showed that the martensitic phase and dendrites were formed from the β phase alloy after the EBM treatment, and microstructures in the surface changed with the processing parameters. Compared with the untreated TNTZO alloy, the surface modified TNTZO alloys exhibited higher nano-hardness, 8.0 GPa, and the wear loss was also decreased apparently. The samples treated at a scanning speed of 0.5 m/s exhibited the highest wear resistance due to the fast cooling rate and the precipitation of acicular α″ phase. The relationship between the wear property and the surface microstructure of TNTZO alloy was discussed.

  13. Large pinning forces and matching effects in YBa2Cu3O7-δ thin films with Ba2Y(Nb/Ta)O6 nano-precipitates

    NASA Astrophysics Data System (ADS)

    Opherden, Lars; Sieger, Max; Pahlke, Patrick; Hühne, Ruben; Schultz, Ludwig; Meledin, Alexander; van Tendeloo, Gustaaf; Nast, Rainer; Holzapfel, Bernhard; Bianchetti, Marco; MacManus-Driscoll, Judith L.; Hänisch, Jens

    2016-02-01

    The addition of mixed double perovskite Ba2Y(Nb/Ta)O6 (BYNTO) to YBa2Cu3O7-δ (YBCO) thin films leads to a large improvement of the in-field current carrying capability. For low deposition rates, BYNTO grows as well-oriented, densely distributed nanocolumns. We achieved a pinning force density of 25 GN/m3 at 77 K at a matching field of 2.3 T, which is among the highest values reported for YBCO. The anisotropy of the critical current density shows a complex behavior whereby additional maxima are developed at field dependent angles. This is caused by a matching effect of the magnetic fields c-axis component. The exponent N of the current-voltage characteristics (inversely proportional to the creep rate S) allows the depinning mechanism to be determined. It changes from a double-kink excitation below the matching field to pinning-potential-determined creep above it.

  14. Enhanced 77 K vortex-pinning in Y Ba2Cu3O7-x films with Ba2Y TaO6 and mixed Ba2Y TaO6 + Ba2Y NbO6 nano-columnar inclusions with irreversibility field to 11 T

    NASA Astrophysics Data System (ADS)

    Rizzo, F.; Augieri, A.; Angrisani Armenio, A.; Galluzzi, V.; Mancini, A.; Pinto, V.; Rufoloni, A.; Vannozzi, A.; Bianchetti, M.; Kursumovic, A.; MacManus-Driscoll, J. L.; Meledin, A.; Van Tendeloo, G.; Celentano, G.

    2016-06-01

    Pulsed laser deposited thin Y Ba2Cu3O7-x (YBCO) films with pinning additions of 5 at. % Ba2Y TaO6 (BYTO) were compared to films with 2.5 at. % Ba2Y TaO6 + 2.5 at. % Ba2Y NbO6 (BYNTO) additions. Excellent magnetic flux-pinning at 77 K was obtained with remarkably high irreversibility fields greater than 10 T (YBCO-BYTO) and 11 T (YBCO-BYNTO), representing the highest ever achieved values in YBCO films.

  15. Variation of Nb-Ta, Zr-Hf, Th-U and K-Cs in two diabase-granophyre suites

    USGS Publications Warehouse

    Gottfried, D.; Greenland, L.P.; Campbell, E.Y.

    1968-01-01

    Concentrations of Nb, Ta, Zr, Hf, Th, U and Cs have been determined in samples of igneous rocks representing the diabase-granophyre suites from Dillsburg, Pennsylvania, and Great Lake, Tasmania. Niobium and tantalum have a three to fourfold increase with differentiation in each of the suites. The chilled margin of the Great Lake intrusion contains half the niobium and tantalum content (5.3 ppm and 0.4 ppm, respectively) of the chilled basalt from Dillsburg (10 ppm and 0.9 ppm, respectively). The twofold difference between the suites is correlated with differences in their titanium content. The average Nb Ta ratios for each suite are similar: 13.5 for the Great Lake suite, and 14.4 for the Dillsburg suite. The zirconium content of the two suites is essentially the same and increases from 50 to 60 ppm in the chilled margins to 240-300 ppm in the granophyres. Hafnium is low in the early formed rocks (0.5 -1.5 ppm and achieves a maximum in the granophyres (5-8 ppm). The Zr Hfratio decreases from 68 to 33 with progressive differentiation. In the Dillsburg suite thorium and uranium increase from 2.6 ppm and 0.6 ppm, respectively, in the chilled samples to 11.8 ppm and 3.1 ppm in the granophyres. The chilled margin of the Great Lake suite contains 3.2 ppm thorium and 9.8 ppm uranium; the granophyre contains 11.2 ppm thorium and 2.8 ppm uranium. The average Th U ratios of the Dillsburg and Great Lake suites are nearly the same-4.1 and 4.4, respectively. Within each suite the Th U ratio remains quite constant. Cesium and the K Cs ratio do not vary systematically in the Dillsburg suite possibly because of redistribution or loss of cesium by complex geologic processes. Except for the chilled margin of the Great Lake suite, the variation of Cs and the K Cs ratio are in accord with theoretical considerations. Cesium increases from about 0.6 ppm in the lower zone to 3.5 ppm in the granophyre; the K Cs ratio varies from 10 ?? 103 in the lower zone to 6 ?? 103 in the granophyre. A

  16. Bi{sub 4}LnNb{sub 3}O{sub 15} (Ln = La, Pr, Nd) and Bi{sub 4}LaTa{sub 3}O{sub 15}: New intergrowth Aurivillius related phases

    SciTech Connect

    Mandal, Tapas Kumar; Augustine, Saji; Gopalakrishnan, J. . E-mail: gopal@sscu.iisc.ernet.in; Boullay, Ph.

    2005-06-15

    We describe the synthesis and characterization of new intergrowth Aurivillius related phases, Bi{sub 4}LnNb{sub 3}O{sub 15} (Ln = La, Pr, Nd) and Bi{sub 4}LaTa{sub 3}O{sub 15}. Both powder X-ray diffraction and electron microscopy investigations show that the compounds adopt orthorhombic structures with the cell parameters a {approx} 5.5 A, b {approx} 5.5 A and c {approx} 20.9 A, suggesting an ordered intergrowth structure that consists of n = 1 [Bi{sub 2}NbO{sub 6}]{sup -} and n = 2 [Bi{sub 2}LnNb{sub 2}O{sub 9}]{sup +} Aurivillius fragments which are stacked alternately along the c-axis. The oxides do not show a second harmonic generation (SHG) response toward 1064 nm laser radiation; they do not show a ferroelectric-paraelectric transition either between 30 and 900 deg. C in dielectric measurements, indicating a centrosymmetric structure. Optical absorption studies show that the intergrowth phases possess considerably smaller band gaps than the parent Nb{sub 2}O{sub 5} and Ta{sub 2}O{sub 5}.

  17. Grain Boundary Wetting by a Second Solid Phase in the Zr-Nb Alloys

    NASA Astrophysics Data System (ADS)

    Straumal, B. B.; Gornakova, A. S.; Kucheev, Y. O.; Baretzky, B.; Nekrasov, A. N.

    2012-05-01

    Zr-Nb alloys play the important role in the energy production being the main material for the cladding of nuclear fuel in the nuclear power plants. The thermo-mechanical treatment of these alloys proceeds in the (αZr) + (βZr, Nb) two-phase area of the Zr-Nb phase diagram. Therefore, the morphology and the mutual arrangement of the (Zr) and (Nb) phases play an extremely important role. The microstructure of binary Zr-Nb alloys with 2.5, 4, and 8 wt.% Nb after long anneals (720 h) was studied between 660 and 810 °C in the two-phase (αZr) + (βZr, Nb) area of the Zr-Nb phase diagram. (βZr, Nb)/(βZr, Nb) grain boundaries (GBs) completely or incompletely wetted by the αZr phase were observed. The portion of the completely wetted (βZr, Nb)/(βZr, Nb) GBs increases from 10% (at 660 °C) to 60% close to the upper border of the (αZr) + (βZr, Nb) two-phase area of the Zr-Nb phase diagram (850 °C). The temperature of the beginning of the GB wetting phase transition of (βZr, Nb)/(βZr, Nb) GBs by the αZr phase is T ws = 630 ± 10 °C. The αZr/αZr GBs completely wetted by a layer of (βZr, Nb) phase were not observed in the studied samples.

  18. Assessing the performance and longevity of Nb, Pt, Ta, Ti, Zr, and ZrO₂-sputtered Havar foils for the high-power production of reactive [18F]F by proton irradiation of [18O]H2O.

    PubMed

    Gagnon, K; Wilson, J S; Sant, E; Backhouse, C J; McQuarrie, S A

    2011-10-01

    As water-soluble ionic contaminants, which arise following proton irradiation of [18O]H2O have been associated with decreased [18F]FDG yields, the minimization of these contaminants is an asset in improving the [18F]F reactivity. To this end, we have previously demonstrated that the use of Nb-sputtered Havar foils results in decreased radionuclidic and chemical impurities in proton irradiated [18O]H2O, improved [18F]FDG yields, and improved [18F]FDG yield consistency when compared with non-sputtered Havar. Resulting from the highly reactive chemical microenvironment within the target however, this niobium layer is observed to degrade over time. To find a material that displays increased longevity with regards to maintaining high [18F]F reactivity, this project extensively investigated and compared Havar foils sputtered with Nb, Pt, Ta, Ti, Zr and ZrO₂. Of the materials investigated, the results of this study suggest that Ta-sputtered Havar foil is the preferred choice. For similar integrated currents (~1,000,000 μA min), when comparing the Ta-sputtered Havar with Nb-sputtered Havar we observed: (i) greater than an order of magnitude decrease in radionuclidic impurities, (ii) a 6.4 percent increase (p=0.0025) in the average TracerLab MX [18F]FDG yield, and (iii) an overall improvement in the FDG yield consistency. Excellent performance of the Ta-sputtered foil was maintained throughout its ~1,500,000 μA min lifetime. PMID:21782460

  19. Extreme high field strength element (HFSE) depletion and near-chondritic Nb/Ta ratios in Central Andean adakite-like lavas (~ 28°S, ~ 68°W)

    NASA Astrophysics Data System (ADS)

    Goss, A. R.; Kay, S. M.

    2009-03-01

    The eruption of andesites with steep REE patterns and high Sr concentrations (adakite-like) in the northernmost Chilean flatslab region of the Central Andes spatially and temporally corresponds with the appearance of a marked HFSE (high field strength element) depletion in these lavas (La/Ta up to 95). Known as the Dos Hermanos and Pircas Negras andesites, these lavas erupted at the beginning (˜ 8 Ma), during (7-3 Ma), and immediately following (3-2 Ma) a period of tectonic instability characterized by eastward migration of the frontal volcanic arc. ICP-MS analyses of the HFSE reveal a range of chondritic (20-18) to subchondritic (18-11) Nb/Ta ratios in these lavas. Evident temporal trace element trends support a change from a rutile-bearing to an amphibole-bearing eclogitic residual assemblage in equilibrium with the mafic precursor magmas of these andesites. This change in residual mineralogy is contemporaneous with the onset of frontal arc migration in the region. Potential eclogitic sources for the Dos Hermanos and Pircas Negras adakitic andesites include mafic Andean lower crust and an additional flux of forearc crust transported to the sub-arc mantle via subduction erosion during the height of arc migration and Pircas Negras magmatism. Batch melting models of rutile- or amphibole-bearing eclogitic arc basalt in tandem with magma mixing calculations generate the observed adakitic signatures and near-chondritic Nb/Ta ratios of these Central Andean andesites.

  20. Vortex Matter in Highly Strained Nb_{75} Zr_{25} : Analogy with Viscous Flow of Disordered Solids

    NASA Astrophysics Data System (ADS)

    Chandra, Jagdish; Manekar, Meghmalhar; Sharma, V. K.; Mondal, Puspen; Tiwari, Pragya; Roy, S. B.

    2016-06-01

    We present the results of magnetization and magneto-transport measurements in the superconducting state of an as-cast Nb_{75} Zr_{25} alloy. We also report the microstructure of our sample at various length scales by using optical, scanning electron and transmission electron microscopies. The information of microstructure is used to understand the flux pinning properties in the superconducting state within the framework of collective pinning. The magneto-transport measurements show a non-Arrhenius behaviour of the temperature- and field-dependent resistivity across the resistive transition and is understood in terms of a model for viscous flow of disordered solids which is popularly known as the `shoving model'. The activation energy for flux flow is assumed to be mainly the elastic energy stored in the flux-line lattice. The scaling of pinning force density indicates the presence of two pinning mechanisms of different origins. The elastic constants of the flux-line lattice are used to estimate the length scale of vortex lattice movement, or the volume displaced by the flux-line lattice. It appears that the vortex lattice displacement estimated from elastic energy considerations is of the same order of magnitude as that of the flux bundle hopping length during flux flow. Our results could provide possible directions for establishing a framework where vortex matter and glass-forming liquids or amorphous solids can be treated in a similar manner for understanding the phenomenon of viscous flow in disordered solids or more generally the pinning and depinning properties of elastic manifolds in random media. It is likely that the vortex molasses scenario is more suited to explain the vortex dynamics in conventional low-T_C superconductors.

  1. Enhancement of photoelectrochemical activity of SnS thin-film photoelectrodes using TiO2, Nb2O5, and Ta2O5 metal oxide layers

    NASA Astrophysics Data System (ADS)

    Vequizo, Junie Jhon M.; Yokoyama, Masanori; Ichimura, Masaya; Yamakata, Akira

    2016-06-01

    Tin sulfide (SnS) fine photoelectrodes fabricated by three-step pulsed electrodeposition were active for H2 evolution. The incident-photon-conversion-efficiency increases from 900 nm and offers a good fit with the absorption spectrum. The activity was enhanced by 3.4, 3.0, and 1.8 times compared to bare SnS by loading Nb2O5, TiO2, and Ta2O5, respectively. Nb2O5 was most efficient because its conduction band is low enough to facilitate effective electron transfer from SnS; it also has sufficiently high potential for H2 evolution. The overall activity is determined by the competitive interfacial electron transfer between SnS/metal-oxide and metal-oxide/water. Therefore, constructing appropriate heterojunctions is necessary for further improving photoelectrochemical systems.

  2. Ferroelectric and electrical properties of lead-free (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3 thin films

    NASA Astrophysics Data System (ADS)

    Kim, Ju Sung; Ahn, Chang Won; Ullah, Amir; Chae, Song A.; Kim, Ill Won

    2016-06-01

    The Li, Ta, and Sb-substituted lead-free (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3 (KNLNTS) thin films were fabricated on Pt(111)/TiO2/SiO2/Si substrates using the radio frequency (RF) magnetron sputtering method. The KNLNTS thin films were annealed at 750 °C for 1 h in an oxygen ambient. The film with a thickness of 350 nm exhibited a typical ferroelectric P - E hysteresis loop without fatigue even after 1010 pulses. The KNLNTS thin film exhibited a relatively low leakage current density of ~10 -7 A/cm2 even up to an applied electric field of 142 kV/cm. A well-saturated piezoelectric hysteresis loop was obtained with a piezoelectric coefficient d 33 of 21 pm/V.

  3. Photolysis of CpRe(CO){sub 3} and CpM(CO){sub 4}, where M = Nb and Ta, in nujol matrices and supercritical ethylene. An unexpected ethylene polymerization catalyst

    SciTech Connect

    Bitterwolf, T.E.; Bays, J.T.; Gallagher, S.; Linehan, J.C.; Yonker, C.R.

    1997-12-31

    Nujol matrix photochemical studies of CpRe(CO){sub 3} establish the primary photochemical event to be loss of carbon monoxide to form an electron deficient species. CpM(CO){sub 4}, where M = Nb or Ta, give both CpM(CO){sub 3} and CpM(CO){sub 2} species upon photolysis in the Nujol matrix. Upon photolysis of these compounds in supercritical ethylene, IR bands associated with CpM(CO){sub n-1}(ethylene) are observed as well as bands associated with CpM(CO){sub n-2}(ethylene){sub 2}. White precipitate, formed under photochemical conditions, has been shown to be polyethylene.

  4. Aqueous Synthesis and Structural Comparison of Rare Earth Niobates and Tantalates: (La,K,[vacancy])[subscript 2]Nb[subscript 2]O[subscript 7-x](OH)[subscript 2] and Ln2Ta2O7(OH)2 ([vacancy] = vacancy; Ln = La-Sm)

    SciTech Connect

    Nyman, May; Rodriguez, Mark A.; Alam, Todd M.; Anderson, Travis M.; Ambrosini, Andrea

    2009-06-30

    Rare-earth niobates and tantalates are functional materials that are exploited as photocatalysts, host lattices for phosphors, and ion conductors. These phases are extremely challenging to synthesize by methods other than solid-state processing, which limits expansion of this useful class of materials. Hydrothermal processing in particular is hampered by the incompatibility of base-soluble tantalate or niobate with acid-soluble rare-earth oxides. Furthermore, an added challenge with tantalates is they are especially inert and insoluble. We present here a general hydrothermal process that has produced a range of rare-earth niobate/tantalate materials; including new phases, (La,K,{sub {open_square}}){sub 2}Nb{sub 2}O{sub 7-x}(OH){sub 2} (1) and Ln{sub 2}Ta{sub 2}O{sub 7}(OH){sub 2} (2) ({open_square} = vacancy, Ln = La-Sm -- excluding radioactive promethium). The structures of 1 and the La-analogue of 2 were determined from powder X-ray diffraction data collected at the APS 11-BM line and corroborated by compositional analyses, infrared spectroscopy, {sup 139}La and {sup 1}H MAS NMR, and thermogravimetric analyses. The synthesis and characterization studies reveal that the tantalate (2) is compositionally pure with no vacancies or dopants, while the niobate (1) formed under identical conditions has both vacancies and potassium dopants. We attribute these features to the greater flexibility of Nb{sup 5+} in oxide lattices to accommodate distorted and lower coordination geometries, whereas Ta{sup 5+} is found predominantly in octahedral environments. Other differences in aqueous niobate and tantalate chemistry are noted by the different phases that form as a function of the Ln{sup 3+} radius.

  5. Electronic structures of anatase (TiO2)1-x(TaON)x solid solutions: a first-principles study.

    PubMed

    Dang, Wenqiang; Chen, Hungru; Umezawa, Naoto; Zhang, Junying

    2015-07-21

    Sensitizing wide band gap photo-functional materials under visible-light irradiation is an important task for efficient solar energy conversion. Although nitrogen doping into anatase TiO2 has been extensively studied for this purpose, it is hard to increase the nitrogen content in anatase TiO2 because of the aliovalent nitrogen substituted for oxygen, leading to the formation of secondary phases or defects that hamper the migration of photoexcited charge carriers. In this paper, electronic structures of (TiO2)1-x(TaON)x (0 ≤ x ≤ 1) solid solutions, in which the stoichiometry is satisfied with the co-substitution of Ti for Ta along with O for N, are investigated within the anatase crystal structure using first-principles calculations. Our computational results show that the solid solutions have substantially narrower band gaps than TiO2, without introducing any localized energy states in the forbidden gap. In addition, in comparison with the pristine TiO2, the solid solution has a direct band gap when the content of TaON exceeds 0.25, which is advantageous to light absorption. The valence band maximum (VBM) of the solid solutions, which is mainly composed of N 2p states hybridized with O 2p, Ti 3d or Ta 5d orbitals, is higher in energy than that of pristine anatase TiO2 consisting of non-bonding O 2p states. On the other hand, incorporating TaON into TiO2 causes the formation of d-d bonding states through π interactions and substantially lowers the conduction band minimum (CBM) because of the shortened distance between some metal atoms. As a result, the anatase (TiO2)1-x(TaON)x is expected to become a promising visible-light absorber. In addition, some atomic configurations are found to possess exceptionally narrow band gaps. PMID:26096698

  6. First Principles Investigation of the Elastic, Optoelectronic and Thermal Properties of XRuSb: (X = V, Nb, Ta) Semi-Heusler Compounds Using the mBJ Exchange Potential

    NASA Astrophysics Data System (ADS)

    Bencherif, K.; Yakoubi, A.; Della, N.; Miloud Abid, O.; Khachai, H.; Ahmed, R.; Khenata, R.; Bin Omran, S.; Gupta, S. K.; Murtaza, G.

    2016-07-01

    Semi-Heusler materials are intensively investigated due to their potential use in diverse applications, such as in spintronics and green energy applications. In this work, we employ the density functional theory to calculate the structural, electronic, elastic, thermal and optical properties of the VRuSb, NbRuSb and TaRuSb semi-Heusler compounds. The calculated results for the lattice constants, bulk moduli and their corresponding pressure derivative values are in fairly good agreement with previous works. In addition, besides the local density approximation, the modified Becke-Johnson exchange potential is also used to improve the value of the band gaps. The bonding nature reveals a mixture of covalent and ionic bonding character of the VRuSb, NbRuSb and TaRuSb compounds. Furthermore, the elastic constants ( C ij) and the related elastic moduli confirm their stability in the cubic phase and demonstrate their ductile nature. We also analyze the influence of the pressure and temperature on the primitive cell volume, heat capacity, volume expansion coefficient, and Debye temperature of the semi-Heusler compounds. Additionally, we investigate the optical properties, such as the complex dielectric function, refractive index, reflectivity, and the energy loss function.

  7. First Principles Investigation of the Elastic, Optoelectronic and Thermal Properties of XRuSb: (X = V, Nb, Ta) Semi-Heusler Compounds Using the mBJ Exchange Potential

    NASA Astrophysics Data System (ADS)

    Bencherif, K.; Yakoubi, A.; Della, N.; Miloud Abid, O.; Khachai, H.; Ahmed, R.; Khenata, R.; Bin Omran, S.; Gupta, S. K.; Murtaza, G.

    2016-04-01

    Semi-Heusler materials are intensively investigated due to their potential use in diverse applications, such as in spintronics and green energy applications. In this work, we employ the density functional theory to calculate the structural, electronic, elastic, thermal and optical properties of the VRuSb, NbRuSb and TaRuSb semi-Heusler compounds. The calculated results for the lattice constants, bulk moduli and their corresponding pressure derivative values are in fairly good agreement with previous works. In addition, besides the local density approximation, the modified Becke-Johnson exchange potential is also used to improve the value of the band gaps. The bonding nature reveals a mixture of covalent and ionic bonding character of the VRuSb, NbRuSb and TaRuSb compounds. Furthermore, the elastic constants (C ij) and the related elastic moduli confirm their stability in the cubic phase and demonstrate their ductile nature. We also analyze the influence of the pressure and temperature on the primitive cell volume, heat capacity, volume expansion coefficient, and Debye temperature of the semi-Heusler compounds. Additionally, we investigate the optical properties, such as the complex dielectric function, refractive index, reflectivity, and the energy loss function.

  8. Influence of boron vacancies on phase stability, bonding and structure of MB 2 (M  =  Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W) with AlB2 type structure

    NASA Astrophysics Data System (ADS)

    Dahlqvist, Martin; Jansson, Ulf; Rosen, Johanna

    2015-11-01

    Transition metal diborides in hexagonal AlB2 type structure typically form stable MB 2 phases for group IV elements (M  =  Ti, Zr, Hf). For group V (M  =  V, Nb, Ta) and group VI (M  =  Cr, Mo, W) the stability is reduced and an alternative hexagonal rhombohedral MB 2 structure becomes more stable. In this work we investigate the effect of vacancies on the B-site in hexagonal MB 2 and its influence on the phase stability and the structure for TiB2, ZrB2, HfB2, VB2, NbB2, TaB2, CrB2, MoB2, and WB2 using first-principles calculations. Selected phases are also analyzed with respect to electronic and bonding properties. We identify trends showing that MB 2 with M from group V and IV are stabilized when introducing B-vacancies, consistent with a decrease in the number of states at the Fermi level and by strengthening of the B-M interaction. The stabilization upon vacancy formation also increases when going from M in period 4 to period 6. For TiB2, ZrB2, and HfB2, introduction of B-vacancies have a destabilizing effect due to occupation of B-B antibonding orbitals close to the Fermi level and an increase in states at the Fermi level.

  9. Influence of boron vacancies on phase stability, bonding and structure of MB₂ (M  =  Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W) with AlB₂ type structure.

    PubMed

    Dahlqvist, Martin; Jansson, Ulf; Rosen, Johanna

    2015-11-01

    Transition metal diborides in hexagonal AlB2 type structure typically form stable MB2 phases for group IV elements (M  =  Ti, Zr, Hf). For group V (M  =  V, Nb, Ta) and group VI (M  =  Cr, Mo, W) the stability is reduced and an alternative hexagonal rhombohedral MB2 structure becomes more stable. In this work we investigate the effect of vacancies on the B-site in hexagonal MB2 and its influence on the phase stability and the structure for TiB2, ZrB2, HfB2, VB2, NbB2, TaB2, CrB2, MoB2, and WB2 using first-principles calculations. Selected phases are also analyzed with respect to electronic and bonding properties. We identify trends showing that MB2 with M from group V and IV are stabilized when introducing B-vacancies, consistent with a decrease in the number of states at the Fermi level and by strengthening of the B-M interaction. The stabilization upon vacancy formation also increases when going from M in period 4 to period 6. For TiB2, ZrB2, and HfB2, introduction of B-vacancies have a destabilizing effect due to occupation of B-B antibonding orbitals close to the Fermi level and an increase in states at the Fermi level. PMID:26445165

  10. A15 superconductors through direct solid-state precipitation: V/sub 3/Ga and Nb/sub 3/Al

    SciTech Connect

    Hong, M.

    1980-09-01

    A solid-state precipitation process was used to prepare superconducting tapes containing an A15 phase, V/sub 3/Ga or Nb/sub 3/Al, in a ductile niobium or vanadium containing BCC matrix. Ingots weighing as large as 30 to 50 gms of V-(14 approx. 19 at. %) Ga and Nb-(13 approx. 22 at. %) Al were prepared by arc-melting, homogenized, quenched, warm-rolled over 99% into tape, and aged at temperatures in the range 600/sup 0/C to 1000/sup 0/C to precipitate the superconducting A15 phase. The features demonstrated by the process are very attractive for practical applications. In the V-Ga system, transmission electron microscopy (TEM) studies revealed the A15 precipitates in an elongated form. However, for the Nb-Al samples, deformed and aged at 750/sup 0/C, TEM studies revealed A15 precipitation in fine equi-axed particles which formed as a semi-continuous network over sub-grain boundaries formed by the recovery of deformation-induced dislocations. In the V-Ga system, the maximum critical transition temperature (approx. 15 K) was found in materials aged at temperatures of 750/sup 0/C or below. At these aging temperatures the T/sub c/ initially increased with aging time and passed through a distinct maximum. The source of the exceptionally high T/sub c/ is discussed. In the Nb-Al system, the aging response of the T/sub c/ of the tested samples was somewhat different; the T/sub c/ increased with aging time to a plateau, and then increased again to a second plateau. The maximum T/sub c/ measured was approx. 17 K. Promising high-field overall critical currents were obtained in the Nb-Al system (overall J/sub c/ approx. 10/sup 4/ A/cm/sup 2/ in a magnetic field of 140 KG at 4.2 K).

  11. Heterogeneous structure and mechanical hardness of biomedical β-type Ti-29Nb-13Ta-4.6Zr subjected to high-pressure torsion.

    PubMed

    Yilmazer, H; Niinomi, M; Nakai, M; Hieda, J; Todaka, Y; Akahori, T; Miyazaki, T

    2012-06-01

    A novel β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ), has been developed as a candidate for biomedical applications. TNTZ exhibits non-toxicity and a low Young's modulus close to that of bone (10-30 GPa). Such a low Young's modulus of this alloy is achieved by comprising a single metastable β phase. Greater mechanical biocompatibility, which implies higher mechanical strength and hardness while maintaining a low Young's modulus, has been aimed for TNTZ. Therefore, strengthening by grain refinement and increasing dislocation density is expected to provide TNTZ high mechanical strength while keeping a low Young's modulus because they keep the original β phase. In this case, high-pressure torsion (HPT) processing is one of the effective ways to obtain these properties simultaneously in TNTZ. Thus, in this study, the effect of HPT processing on the microstructure and mechanical hardness of TNTZ was systematically investigated at rotation numbers (N) of 1 to 20 under a pressure of around 1.25 GPa at room temperature. On the cross sections of TNTZ subjected to HPT processing (TNTZ(HPT)) after cold rolling (TNTZ(CR)) at any rotation number, a heterogeneous microstructure consisting of a matrix and a non-etched band, which is not corroded by etching solution, can be observed. The thickness of non-etched band increases as rotation number and distance from specimen center increase. Both matrix and non-etched band comprise a single β phase, but their grain geometries are different each other. Equiaxed grains and elongated grains are observed in the matrix and the non-etched band, respectively. The equiaxed grain diameter, which is ranged from 155 nm to 44 nm, in the matrix decreases with increasing rotation number. Contrastingly, the elongated grains with a length of around 300 nm and a width of 30 nm, which are nearly constant with rotation number, are observed in the non-etched band. The mechanical hardness of TNTZ(HPT) is consistently much higher than that of

  12. Synthesis and characterization of perovskite-type (Li,Sr)(Zr,Nb)O3 quaternary solid electrolyte for all-solid-state batteries

    NASA Astrophysics Data System (ADS)

    Yu, Ran; Du, Qing-Xia; Zou, Bang-Kun; Wen, Zhao-Yin; Chen, Chun-Hua

    2016-02-01

    Stable solid electrolytes with high lithium ionic conductivity are crucial for all-solid-state lithium ion batteries. The compatibility with electrodes require a sintering temperature around 1000 °C. A perovskite-type (Li,Sr)(Zr,Nb)O3 system with A-site vacancy is designed and synthesized by a solid-state reaction route. Four compositions with different concentrations of A-site vacancy and several sintering temperatures between 1100 and 1300 °C are selected to find an optimal composition. X-ray diffraction and scanning electron microscope are employed to analyze the crystalline phases and the microstructure of the sintered samples. The ionic conductivities of the materials are measured by AC impedance spectroscopy. For the sample with the optimal composition Li3/8Sr7/16Zr1/4Nb3/4O3 and sintered at 1200 °C, its total ionic conductivity is 2.00×10-5 and 1.65×10-4 Scm-1 at 30 and 100 °C, respectively. Its activation energy for lithium ion conduction is 0.26 eV.

  13. A-SITE-AND/OR B-SITE-MODIFIED PBZRTIO3 MATERIALS AND (PB, SR, CA, BA, MG) (ZR, TI,NB, TA)O3 FILMS HAVING UTILITY IN FERROELECTRIC RANDOM ACCESS MEMORIES AND HIGH PERFORMANCE THIN FILM MICROACTUATORS

    NASA Technical Reports Server (NTRS)

    Roeder, Jeffrey F. (Inventor); Chen, Ing-Shin (Inventor); Bilodeau, Steven (Inventor); Baum, Thomas H. (Inventor)

    2004-01-01

    A modified PbZrTiO.sub.3 perovskite crystal material thin film, wherein the PbZrTiO.sub.3 perovskite crystal material includes crystal lattice A-sites and B-sites at least one of which is modified by the presence of a substituent selected from the group consisting of (i) A-site substituents consisting of Sr, Ca, Ba and Mg, and (ii) B-site substituents selected from the group consisting of Nb and Ta. The perovskite crystal thin film material may be formed by liquid delivery MOCVD from metalorganic precursors of the metal components of the thin film, to form PZT and PSZT, and other piezoelectric and ferroelectric thin film materials. The thin films of the invention have utility in non-volatile ferroelectric memory devices (NV-FeRAMs), and in microelectromechanical systems (MEMS) as sensor and/or actuator elements, e.g., high speed digital system actuators requiring low input power levels.

  14. Shape-controlled crystal growth of Sr3NbGa3Si2O14 and Sr3TaGa3Si2O14 piezoelectric crystals by the micro-pulling-down method.

    PubMed

    Yokota, Yuui; Sato, Masato; Futami, Yoshisuke; Tota, Kazushige; Onodera, Ko; Yanagida, Takayuki; Yoshikawa, Akira

    2012-09-01

    We grew column-shaped Sr(3)NbGa(3)Si(2)O(14) (SNGS) and Sr(3)TaGa(3)Si(2)O(14) (STGS) langasite-type piezoelectric single crystals by the micro-pulling-down (μ-PD) method. 3-mm-diameter SNGS and STGS crystals were grown using a Pt-Rh crucible with a 3-mm-diameter columnar die. According to X-ray rocking curve measurements, the grown crystals had crystallinity equivalent to that of crystals grown by the Czochralski (Cz) method. The crystals were single-phase materials with langasite-type crystal structure. The lattice parameters of the grown crystals were almost consistent with those of crystals grown by the Cz method. PMID:23007751

  15. Structure, bonding and stability of semi-carbides M2C and sub-carbides M4C (M=V, Cr, Nb, Mo, Ta, W): A first principles investigation

    NASA Astrophysics Data System (ADS)

    Abderrahim, F. Z.; Faraoun, H. I.; Ouahrani, T.

    2012-09-01

    Density functional theory within the generalized gradient approximation (GGA) is used to investigate the electronic structure and formation energies of semi-carbides M2C and sub-carbides M4C (where M=V, Cr, Nb, Mo, Ta and W). Our results show that M2C carbides are more stable than M4C. Total and partial densities of states were obtained and analyzed systematically for these phases. Moreover, the bonding nature of M2C polymorphs is studied from the point of view of the Quantum Theory of Atoms in Molecules (QTAIM). It is found that inter-atomic interactions in these carbides are of mixed type including ionic, covalent and metallic components.

  16. Structure and dielectric properties of solid solutions Bi7Ti4 + x W x Ta1-2 x O21 ( x = 0-0.5)

    NASA Astrophysics Data System (ADS)

    Zubkov, S. V.; Vlasenko, V. G.; Shuvaeva, V. A.; Shevtsova, S. I.

    2016-01-01

    A number of solid solutions Bi7Ti4 + x W x Ta1-2 x O21 ( x = 0-0.5) have been synthesized from oxides by solid-phase reaction. The crystal structure, the electrophysical characteristics, and the microstructure of the prepared ceramic samples have been studied. According to X-ray powder diffraction, all the compounds are single-phase with the structure of mixed-layer Aurivillius phases ( m = 2.5) with the orthorhombic crystal lattice (space group I2 cm, Z = 2). Temperature dependences of the relative permittivity ɛ( T) of the compound have been measured, from which it has been found that the Curie temperature T C of perovskite-like oxides Bi7Ti4 + x W x Ta1-2 x O21 ( x = 0-0.5) decreases linearly as substitution parameter x decreases. The activation energies of charge carriers have been found in different temperature ranges.

  17. Importance of cluster distortions in the tetrahedral cluster compounds GaM{sub 4}X{sub 8} (M=Mo,V,Nb,Ta; X=S,Se): Ab initio investigations

    SciTech Connect

    Sieberer, M.; Turnovszky, S.; Redinger, J.; Mohn, P.

    2007-12-01

    In this paper, we study the structural properties of selected representatives of the so-called molybdenum cluster compounds. Belonging to this family are the GaM{sub 4}X{sub 8} compounds with M=Mo as a group VIB element and V, Nb, or Ta as a group VB element. X denotes either S or Se. These compounds are known to exhibit semiconducting behavior in the electrical resistivity, caused by hopping of electrons between well-separated metal clusters. The large separation of the tetrahedral metal (M{sub 4}) clusters is believed to be the origin of strong correlations. We show that recent calculations neglected an important type of structural distortion, namely, those happening only within the M{sub 4} unit at a fixed angle {alpha}=60 deg. of the trigonal (fcc-like) cell. These internal distortions gain a significant amount of energy compared to the cubic cell and they are--to our knowledge--almost undetectable with powder x-ray diffraction experiments. However, they strongly influence the band-structure by opening up a gap at the Fermi-energy. This, however, puts into question whether all compounds of this family are really Mott insulators as stated elsewhere. In particular, ferromagnetic GaMo{sub 4}S{sub 8} and GaV{sub 4}S{sub 8} are well described within density functional theory. Only the Nb- and Ta-based representatives require a large effort due to the lack of magnetic long-range order caused by frustrated antiferromagnetic M-M interactions.

  18. Unique LaTaO[subscript 4] Polymorph for Multiple Energy Applications

    SciTech Connect

    Nyman, May; Rodriguez, Mark A.; Rohwer, Lauren E.S.; Martin, James E.; Waller, Mollie; Osterloh, Frank E.

    2009-11-04

    Rare-earth niobate and tantalate (RE-Nb/Ta) materials are of considerable interest in environmental and energy-related applications that include phosphors for solid-state lighting, photocatalysts for both contaminant degeneration and H{sub 2} generation, chemically robust hosts for nuclear materials and wastes, and ion conductors for lithium batteries or solid-oxide fuel cells. However, the chemically inert nature limits the synthetic routes available to obtain these materials, which in turn hampers the discovery and development of new RE-Nb/Ta phases. Of the simple orthotantalate, LaTaO{sub 4}, there were three polymorphs known prior. With this paper, we present the structural characterization (from high-resolution X-ray powder diffraction data collected at the APS 11-BM line) of a fourth polymorph. It is obtained only from dehydration of La{sub 2}Ta{sub 2}O{sub 7}(OH){sub 2}, which is in turn synthesized hydrothermally. The structure of the new LaTaO{sub 4} polymorph is distinctive from the others in the arrangement of the alternating La-O polyhedra layers and TaO{sub 6} octahedra layers. Luminescence measurements (Eu-doped) and photocatalysis studies of the new LaTaO{sub 4} polymorph, and comparison to the performance of a previously described LaTaO{sub 4} polymorph reveals enhanced performance of the new polymorph in both applications. This study illustrates the relevance of form-function relationships in solid-state materials, as well as the important role of synthesis in the development of advanced functional materials.

  19. Effect of La2O3 modified on pyroelectric properties of 0.69Pb(Mg1/3Nb2/3)O3-0.31PbTiO3 solid solutions

    NASA Astrophysics Data System (ADS)

    Hyun, June Won; Kim, Yeon Jung; Lee, Ju Ho; Lee, Ky Am

    2012-12-01

    The pyroelectric and polarization properties of La2O3 modified 0.69Pb(Mg1/3Nb2/3)O3-0.31PbTiO3 solid solution systems were examined by the static technique as a function of temperature. The peak temperature of the pyroelectric coefficient maxima was decreased by La2O3. From the pyroelectric data, two major anomalies corresponding to the rhombohedral → tetragonal → cubic phase transitions were observed. This suggests that the successive transition of 0.69Pb(Mg1/3Nb2/3)O3-0.31PbTiO3 systems appeared not to be affected by La2O3. The optimum conditions for obtaining compositions with improved pyroelectric properties ( p }~ 0.013 C/m2K at 126°C, P s }~ 0.197 C/m2 at 25°C) are a sintering temperature of 1250°C and the nominal addition of 0.03 wt. % La2O3. The figures of merit ( F v }~ 0.034 m2/C, F d }~ 0.357 × 10-4 Pa1/2) of the composition 0.69Pb(Mg1/3Nb2/3)O3-0.31PbTiO3-0.03 wt. % La2O3 are comparable to that of TGS and LiTaO3. Also, the piezoelectric constant ( d 33) and the electromechanical coupling factor ( k p ) were found to be about 379-422 × 10-12 C/N and 0.274-0.342 for 0.69PMN-0.31PT- xLa systems, respectively.

  20. Stiffness and toughness prediction of Co-Fe-Ta-B metallic glasses, alloyed with Y, Zr, Nb, Mo, Hf, W, C, N and O by ab initio molecular dynamics

    NASA Astrophysics Data System (ADS)

    Schnabel, Volker; Evertz, Simon; Rueß, Holger; Music, Denis; Schneider, Jochen M.

    2015-03-01

    Ab initio molecular dynamics simulations are used to systematically explore the influence of alloying on the stiffness and plasticity of Co-Fe-Ta-B metallic glasses. The Co43.5Ta6.1B50.4 metallic glass studied in this work, with a Young's modulus of 295 GPa, is the stiffest metallic glass known in literature. From the analysis of the density of the states it is suggested that the very large stiffness is due to strong covalent metal to boron bonding. Furthermore it has been observed that by alloying with Y, Zr, Nb, Mo, Hf, W, C, N and O the bulk to shear modulus ratio can be varied from 2.08 to 2.82. As noted by Lewandowski et al (2005 Phil. Mag. Lett. 85 77) a brittle to plastic transition for metallic glasses can be identified in the range of 2.33 to 2.44. Hence, it is evident that the whole range from brittle to plastic behaviour can be covered, with the systems studied in this work. This evolution from brittle to plastic behaviour can be attributed to a change from predominately covalent to predominately metallic bond character.

  1. Electrically tunable microwave properties in NiFeTa/[Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32(011) magnetoelectric heterostructures

    NASA Astrophysics Data System (ADS)

    Phuoc, Nguyen N.; Ong, C. K.

    2015-02-01

    The studied magnetoelectric heterostructure consisting of a NiFeTa thin film grown onto a [Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32(011) (PMN-PT) substrate was prepared by using gradient-composition sputtering technique. A shorted micro-strip transmission-line perturbation method using a vector network analyzer was employed to study the electrical field modulation of microwave properties of the NiFeTa/PMN-PT heterostructure. It was found that the resonance frequency of the sample can be tuned from 1.72 GHz to 2.05 GHz when the applied electrical field is varied from -6 kV/cm to 6 kV/cm. Moreover, we experimentally observed a quasi-linear relationship between the resonance frequency and the electrical field in a wide range of electrical field from 0 kV/cm to 6 kV/cm in the heterostructure, which is suggested to be useful for applications. All the results are discussed taking into account the reverse magnetostrictive effect and the reverse piezoelectric effect.

  2. Properties of K1-xLixTaO3 Solid Solutions; First-Principles Computations and Comparison with Experiments

    NASA Astrophysics Data System (ADS)

    Prosandeev, Serguei A.; Cockayne, Eric; Burton, Benjamin; Trepakov, Vladimir; Kapphan, Siegmar; Savinov, Maxim; Jastrabik, Lubomir

    2002-11-01

    Experiments on K0.957Li0.043TaO3 samples indicate two different relaxation processes (π and π/2). First-principles computations clarify the natures of these relaxations, and yield good agreement with experiment.

  3. Ion beam and defect-related research in the Solid State Division. [LiNbO/sub 3/, Al/sub 2/O/sub 3/

    SciTech Connect

    Roberto, J.B.

    1986-08-05

    This paper contains viewgraphs on the topic of radiation effects of solid state materials. In particular, it elaborates on ion beam deposition of thin film structures, ion implantation damage in crystals of Al/sub 2/O/sub 3/, and ion implanted optical waveguides in LiNbO/sub 3/. (LSP)

  4. Preparation and crystal structure of H-BaTa{sub 2}O{sub 6}-type K{sub 1.83}Ba{sub 4.17}Nb{sub 12.18}O{sub 36} and dielectric properties of the related compounds

    SciTech Connect

    Zhang, W.; Kumada, N. . E-mail: kumada@yamanashi.ac.jp; Takei, T.; Yamanaka, J.; Kinomura, N.

    2005-07-12

    Single crystal of a novel compound, K{sub 1.83}Ba{sub 4.17}Nb{sub 12.18}O{sub 36}, has been synthesized in the course of investigation on the K{sub 2}O-BaO-Nb{sub 2}O{sub 5} system. The crystal structure was determined by single crystal X-ray diffraction data. The space group of this compound was found to be P6/mmm (no. 191) with the lattice parameters of a=21.109(4) and c=3.967(1)A. The final R-factors were R=0.039 and R{sub w}=0.042 for unique 508 reflections. The crystal structure had the same tunnel structure as that of hexagonal BaTa{sub 2}O{sub 6} (H-BaTa{sub 2}O{sub 6}), which is the high temperature form in three modifications of BaTa{sub 2}O{sub 6}. The chemical composition of K{sub 1.83}Ba{sub 4.17}Nb{sub 12.18}O{sub 36} was close to that of the tetragonal tungsten bronze (TTB) type KBa{sub 2}Nb{sub 5}O{sub 15} and the powder samples within this composition were prepared so as to clarify the boundary between H-BaTa{sub 2}O{sub 6} and TTB-type structures. The H-BaTa{sub 2}O{sub 6}-type structure appears in (K+Ba)/Nb-bar 0.500 and the TTB-type structure is in (K+Ba)/Nb>=0.575. The dielectric constants of these samples were measured from room temperature to 500deg. C for sintered body. The TTB-type compounds exhibited ferroelectric temperature dependence with the Curie points of 284-372deg. C and the H-BaTa{sub 2}O{sub 6}-type compounds were not ferroelectrics as predicted from the crystal structure analysis.

  5. Polarisation-independent electrooptical switch based on LiNbO{sub 3} and LiTaO{sub 3} crystals

    SciTech Connect

    Davydov, B L; Krylov, Aleksandr A; Yagodkin, D I

    2007-05-31

    Two electrooptical switches for nonpolarised narrow beams from fibre laser and luminescent sources are considered. Requirements for crystals, the accuracy of their thermal stabilisation, and tolerances for their manufacturing and adjustment are estimated from the point of view of the maximum switching contrast. A switch based on two LiNbO{sub 3} crystals with a control half-wave voltage of {approx}270 V, connected with an isotropic single-mode fibre, is tested. It is shown that errors in the adjustment and manufacturing of crystal phase elements can be compensated by a weak controllable heating of one of the crystals. (laser devices and elements)

  6. History-dependent thermal expansion in NbO{sub 2}F

    SciTech Connect

    Wilkinson, Angus P.; Josefsberg, Ryan E.; Gallington, Leighanne C.; Morelock, Cody R.; Monaco, Christopher M.

    2014-05-01

    Materials with cubic ReO{sub 3}-type structures are of interest for their low or negative thermal expansion characteristics. TaO{sub 2}F is known to display almost zero thermal expansion over a wide temperature range. On heating NbO{sub 2}F, its volume coefficient of thermal expansion decreases from ∼+45 ppm K{sup −1} at 100 K to almost zero at 400 K. NbO{sub 2}F is cubic between 100 and 500 K. Samples of “NbO{sub 2}F” prepared by the digestion of Nb{sub 2}O{sub 5} in aqueous HF followed by mild drying contain hydroxyl defects and metal vacancies. On heating, they can undergo irreversible chemical changes while maintaining a cubic ReO{sub 3}-type structure. The possibility of hydroxyl defect incorporation should be considered when preparing oxyfluorides for evaluation as battery materials. - Graphical abstract: “NbO{sub 2}F” prepared by the digestion of Nb{sub 2}O{sub 5} in HF contains cation vacancies and hydroxyl groups. It undergoes irreversible changes on heating to low temperatures, unlike NbO{sub 2}F prepared by the solid state reaction of Nb{sub 2}O{sub 5} and NbF{sub 5}. - Highlights: • The digestion of Nb{sub 2}O{sub 5} in aqueous HF followed by mild drying does not produce NbO{sub 2}F. • The ReO{sub 3}-type product from the HF digestion of Nb{sub 2}O{sub 5} contains metal vacancies and hydroxyl. • The thermal expansion coefficient of NbO{sub 2}F decreases on heating and approaches zero at ∼400 K.

  7. Solid-state synthesis of Ti2Nb10O29/reduced graphene oxide composites with enhanced lithium storage capability

    NASA Astrophysics Data System (ADS)

    Wang, Wan Lin; Oh, Byeong-Yun; Park, Ju-Young; Ki, Hangil; Jang, Jaewon; Lee, Gab-Yong; Gu, Hal-Bon; Ham, Moon-Ho

    2015-12-01

    Owing to their multiple redox couples, titanium-niobium-based oxides are still considered promising candidates for use as anodes for safe, rechargeable lithium ion batteries with high energy and power densities. Titanium-niobium-based oxide electrodes have, however, exhibited relatively poor cycling performance as a result of pulverization. In this study, we report on a simple two-step solid-state reaction route for producing hybrid composites of Ti2Nb10O29 (TNO) anchored on reduced graphene oxide (RGO), and the electrochemical performance of the resulting TNO/RGO composites. Solid-state reactions enable both the formation of TNO and the uniform distribution of RGO in the TNO/RGO composites. The TNO/RGO composites exhibited discharge and charge capacities of 261 and 256 mAh g-1, respectively, with much better cycling performance (182 mAh g-1 after the 50th cycles) and rate capability (165 mAh g-1 at a current density of 500 mA g-1) compared to the pure TNO.

  8. Structural characterization and electrical conductivity of the Ca0.01La0.99-xSmxNbO4-δ solid series

    NASA Astrophysics Data System (ADS)

    Cao, Yong; Duan, Nanqi; Yan, Dong

    2016-05-01

    Ca0.01La0.99-xSmxNbO4-δ (x=0, 0.1, 0.2, 0.4, 0.6, 0.8, 0.99) is prepared by using a solid reaction route, and single phase is achieved. Structural and phase transformation of Ca0.01La0.99-xSmxNbO4-δ have been characterized by high temperature X-ray diffraction. The lattice parameters a, b, c decrease and γ increases with increasing x, at both room and high temperature. The phase transformation temperature increases linearly with increasing x for Ca0.01La0.99-xSmxNbO4-δ. The electrical conductivity of Ca0.01La0.99-xSmxNbO4-δ is measured in wet air. A clear relationship between the structural, phase transformation and electrical conductivity of Ca0.01La0.99-xSmxNbO4-δ is built, which will provide a guideline to tailor the electrical conductivity.

  9. Experimental Study and Computer Simulation on Multicomponent Diffusion in Multiphase Dispersions During Solid Carburizing of HP40Nb and KHR45A Alloys

    NASA Astrophysics Data System (ADS)

    Zhao, Yanping; Gong, Jianming; Wang, Xiaowei; Shen, Limin; Li, Qingnan

    2015-10-01

    To simulate solid carburizing processes of HP40Nb and KHR45A alloys at 1273 K and 1373 K (1000 °C and 1100 °C), Thermo-Calc (Thermo-Calc Software, Inc., Stockholm, Sweden) and DICTRA (Thermo-Calc Software, Inc.) software analyses were performed. A model to treat multicomponent diffusion in multiphase dispersions was applied, where carbides are assumed to be distributed in face-centered cubic matrix and diffusion only occurs in the matrix. The time-dependent carbon flux determined by weight gain measurement was used as boundary condition in diffusion simulations. The calculated carbides are NbC, M23C6, and M7C3 ("M" stands for metal atoms), where M23C6 first precipitates, then M7C3 appears as carbon increases, and NbC covers the largest area of carbon content. The results show that carburization resistance is much better for KHR45A than HP40Nb due to the addition of elements (Si, Cr, Ni, and Nb). Microhardness measurements were also conducted to obtain the carburized case depths, and the results agreed well with the predicted calculations.

  10. Formation and Characteristics of Anatase-Type Titania Solid Solution Nanoparticles Doped with Nb5+ M (M = Ga3+, Al3+, Sc3+)

    NASA Astrophysics Data System (ADS)

    Hirano, Masanori; Ito, Takaharu

    2011-10-01

    Anatase-type titania solid solutions co-doped with Nb5+ and cation M (M = Ga3+, Al3+, Sc3+) with composition Ti1-2XNbXMXO2 were directly formed as nanoparticles from precursor solutions of TiOSO4, NbCl5, and metal salts (Ga(SO4)3, Al(NO3)3, and Sc(NO3)3) under mild hydrothermal conditions at 180 °C for 5 h using the hydrolysis of urea. The effect of co-doped cation M on the formation and properties of anatase-type titania solid solutions was investigated. The region of anatse-type solid solution depended on the co-doped cation M. The composition range of anatase-type titania solid solution in the case of M = Sc3+ was much wider than that in the case of M = Ga3+ and Al3+. The increase in the amount of co-doped cation M = Ga3+, Al3+ enhanced the crystallite growth of anatase solid solutions under the hydrothermal conditions. The solid solutions co-doped with M = Al3+ showed the most improved photocatalytic activity in the three cations. The anatase-to-rutile phase transformation of solid solutions was promoted at lower temperature via the presence of co-doped cation M = Ga3+.

  11. Synthesis and characterization of compounds Sr{sub 2}{ital RM}Cu{sub 2}O{sub 8{minus}{delta}} ({ital R}=Pr, Nd, Sm, Eu, Gd; {ital M}=Nb, Ta)

    SciTech Connect

    Vybornov, M.; Perthold, W.; Michor, H.; Holubar, T.; Hilscher, G.; Rogl, P.; Fischer, P.; Divis, M.

    1995-07-01

    Although traces of superconductivity ({lt}0.2%) have been detected in Ba{sub 2}La{ital M}{sub 1{minus}{ital x}}W{sub {ital x}}Cu{sub 2}O{sub 8{minus}{delta}} ({ital x}{similar_to}0.3,{ital M}=Nb,Ta) below 30 K, the superconducting impurity phase could not be resolved. The antiferromagnetic (AF) order of the rare-earth sublattice in this {ital R}-2112 system (e.g., {ital T}{sub {ital N}}{sup Gd}=2.18 K) appears to be similar to that of the {ital R}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} series (e.g., {ital T}{sub {ital N}}{sup Gd}=2.29 K); however, the exceptional high AF order of Pr in Pr-123 (with 17 K) is reduced to below 2.3 K for Sr{sub 2}Pr{ital M} Cu{sub 2}O{sub 8{minus}{delta}}. The temperature and field dependence of the specific heat and the susceptibility is discussed in terms of crystal field splitting derived from the {ital R}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} compounds. Overall crystal field splitting in the title compounds is comparable with that of the {ital R}-123 compounds.

  12. Electrochemical characterization of a low modulus Ti-35.5Nb-7.3Zr-5.7Ta alloy in a simulated body fluid using EIS for biomedical applications

    SciTech Connect

    Bhola, R.; Bhola, S. M.; Mishra, B.; Ayers, R. A.; Olson, D. L.

    2011-06-23

    Electrochemical characterization of the low modulus Ti-35.5Nb-7.3Zr-5.7Ta beta alloy (TNZT) has been performed in phosphate buffer saline solution at 37 deg. C using the non destructive electrochemical impedance spectroscopy technique. Measurements were performed at various immersion intervals at the open circuit potential (OCP), which was also monitored with time. Results obtained for TNZT alloy have been compared with those for the commercially used Ti-6Al-4V mixed alloy (Ti64) and the commercially pure titanium (Ti2) alpha alloy. Potentiodynamic polarization was performed to supplement the data obtained from EIS analysis. The TNZT alloy exhibits a two time constant impedance response, whereas the Ti64 and Ti2 alloys display a one time constant behavior. Human fetal osteoblast cells show a better adhesion and a higher cell count for the TNZT alloy compared to the other two alloys. The present investigation is an effort to understand the correlation between the electrochemical, morphological and cellular characteristics of titanium alloys to qualify them for implant applications.

  13. Bending springback behavior related to deformation-induced phase transformations in Ti-12Cr and Ti-29Nb-13Ta-4.6Zr alloys for spinal fixation applications.

    PubMed

    Liu, Huihong; Niinomi, Mitsuo; Nakai, Masaaki; Hieda, Junko; Cho, Ken

    2014-06-01

    The springback behavior of Ti-12Cr and Ti-29Nb-13Ta-4.6Zr (TNTZ) during deformation by bending was investigated; and the microstructures of the non-deformed and deformed parts of both alloys were systematically examined to clarify the relationship between microstructure and springback behavior. For the deformed Ti-12Cr alloy, deformation-induced ω-phase transformation occurs in both the areas of compression and tension within the deformed part, which increases the Young׳s modulus. With the deformed TNTZ alloy, deformation-induced ω-phase transformation is observed in the area of compression within the deformed part; while a deformation-induced α″ martensite transformation occurs in the area under tension, which is likely to be associated with the pseudoelasticity of TNTZ. Among these two alloys, Ti-12Cr exhibits a smaller springback and a much greater bending strength when compared with TNTZ; making Ti-12Cr the more advantageous for spinal fixation applications. PMID:24561725

  14. Scanning tunneling microscopy study of nano-structured polyatom-substituted H4PW11M1O40 Keggin and H7P2W17M1O62 (M = Nb, Ta) Wells-Dawson heteropolyacid catalysts.

    PubMed

    Choi, Jung Ho; Park, Dong Ryul; Park, Sunyoung; Song, In Kyu

    2012-07-01

    Polyatom-substituted H4PW11M1O40 Keggin and H7P2W17M1O62 (M = Nb, Ta) Wells-Dawson heteropolyacid (HPA) catalysts were investigated by scanning tunneling microscopy (STM) and tunneling spectroscopy to elucidate their redox property and oxidation catalysis. STM images clearly showed that HPAs formed nano-structured monolayer arrays on graphite surface. In tunneling spectroscopy, HPAs exhibited a distinctive current-voltage behavior called negative differential resistance (NDR). NDR peak voltage of the HPAs was then correlated with reduction potential determined by electrochemical method in solution. NDR peak voltage of the HPAs appeared at less negative voltage with increasing reduction potential. Vapor-phase oxidative dehydrogenation of isobutyraldehyde to methacrolein was also carried out as a model reaction to probe oxidation catalysis of the HPAs. NDR peak voltage of the HPAs appeared at less negative voltage with increasing yield for methacrolein. NDR peak voltage could be utilized as a correlating parameter for the reduction potential and as a probe of oxidation catalysis in the oxidative dehydrogenation of isobutyraldehyde. PMID:22966671

  15. Coordination complexes of NbX5 (X = F, Cl) with (N,O)- and (O,O)-donor ligands and the first X-ray characterization of a neutral NbF5 adduct.

    PubMed

    Bortoluzzi, Marco; Marchetti, Fabio; Pampaloni, Guido; Pucino, Margherita; Zacchini, Stefano

    2013-09-28

    A variety of fairly air-stable complexes were prepared by straightforward reactions of NbX5 (X = F, Cl) with a series of potential bidentate (N,O)- and (O,O)-donor ligands in CH2Cl2. NbF5 reacted with equimolar amounts of 2-[(2,6-diisopropylphenyl)iminomethyl]phenol (dpimpH) and 2-benzoyl-6-hydroxy-6-phenylpentafulvene (bhpfH) to afford the mononuclear complexes NbF5[κ(1)(O)-OC6H4CH=NHC6H3(CHMe2)2], 2, and NbF5[κ(1)(O)-bhpfH], 7, respectively. The 1:1 reactions of NbF5 with salicylaldehyde oxime (saoH2) and 2-phenylaminoethanol gave the hexafluoroniobato salts [NbF4{κ(1)(O)-ON(H)=CHC6H4OH}2][NbF6], 3, and [NbF4{κ(1)(O)-OCH2CH2NH2Ph}2][NbF6], 6, respectively. The syntheses of 2, 3 and 6 are accompanied by oxygen to nitrogen intramolecular H migration, leading to the formation of metal-alkoxide moieties. The parallel chemistry of NbCl5 is characterised by HCl release. The 1:1 reactions with dpimpH, saoH2 and bhpfH yielded, respectively, the ionic complex [NbCl2{κ(1)(N):κ(1)(O)-dpimp}2][NbCl6], 4a, the neutral-dinuclear Nb2Cl7[κ(1)(O)-saoH][κ(2)(O)-sao], 5, and the mononuclear NbCl4[κ(2)(O)-bhpf], 8. The tantalum species [TaCl2{κ(1)(N):κ(1)(O)-dpimp}2][TaCl6], 4b, was prepared from TaCl5/dpimpH. The new products 2-8 were fully characterized by analytical and spectroscopic techniques. Moreover the solid state structures of 2 and 8 were ascertained by X-ray diffraction studies; the structure of 2 exhibits an intramolecular bifurcated N-H···(O,F) hydrogen bond. DFT calculations were carried out in order to predict the lowest energy structures in the distinct cases, showing generally good agreement with the experimental data. PMID:23873411

  16. Low temperature synthesis and characterization of BiNbO{sub 4} powders

    SciTech Connect

    Radha, R.; Muthurajan, H.; Koteswara Rao, N.; Pradhan, Sivaram; Gupta, U.N.; Jha, R.K.; Mirji, S.A.; Ravi, V.

    2008-08-15

    BiNbO{sub 4} powders, a potential microwave dielectric ceramic were prepared by both co-precipitation and solid state techniques. In the former method, an aqueous ammonium hydroxide was used to precipitate Bi{sup 3+} and Ta{sup 5+} cations as hydroxides simultaneously under basic conditions. It is observed that the co-precipitation produces BiNbO{sub 4} phase on heating at 600 deg. C, whereas complete phase formation occurs only at 800 deg. C in the case of solid state method. The phase contents and lattice parameters were studied by powder X-ray diffraction. The sequence of the reaction and phase evolution of BiNbO{sub 4} were also studied by the X-ray diffraction. The samples were characterized by the differential-thermal/thermo-gravimetric analyses and scanning electron microscopy techniques.

  17. Dielectric properties of Ba0.6Sr0.4TiO3-Sr(Ga0.5Ta0.5)O3 solid solutions.

    PubMed

    Xu, Yebin; Liu, Ting; He, Yanyan; Yuan, Xiao

    2008-11-01

    Ba(0.6)Sr(0.4)TiO(3)-Sr(Ga(0.5)Ta(0.5))O(3) solid solutions are prepared by a solid-state reaction method, and their dielectric and tunable characteristics are investigated. The solid solutions with cubic perovskite structures are obtained for compositions of 10-50 mol% Sr(Ga(0.5)Ta(0.5))O(3). It is observed that the addition of Sr(Ga(0.5)Ta(0.5))O(3) into Ba(0.6)Sr(0.4)TiO(3) causes a shift in the phase transition peak to a lower temperature. Ba(0.6)Sr(0.4)TiO(3)-Sr(Ga(0.5)Ta(0.5))O(3) solid solutions exhibit depressed and broadened phase transition peaks, resulting in decreased dielectric constants and dielectric losses at room temperature. With the increase of Sr(Ga(0.5)Ta(0.5))O(3) content, the dielectric constant, loss tangent, and tunability are decreased. 0.9Ba(0.6)Sr(0.4)TiO(3)-0.1Sr(Ga(0.5)Ta(0.5))O(3) has a dielectric constant epsilon = 534 and a tunability of 16% at 100 kHz under 2.63 kV/mm. The dielectric characteristics of Ba(0.6)Sr(0.4)TiO(3)-Sr(Ga(0.5)Ta(0.5))O(3) ceramics at microwave frequencies are also evaluated. PMID:19049916

  18. Phase Stability and Electrical Conductivity of Ca-doped LaNb1-xTaxO4- high temperature proton conductors

    SciTech Connect

    Bi, Zhonghe; Kim, Jung-Hyun; Bridges, Craig A; Huq, Ashfia; Paranthaman, Mariappan Parans

    2011-01-01

    The electrical conductivity, phase structure and stability of La0.99Ca0.01Nb1-xTaxO4- (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5, =0.005) a potential candidate for proton conductor for Solid Oxide Fuel Cells (SOFCs) have been investigated using AC impedance technique and in-situ X-ray powder diffraction. Partially substituting Nb with Ta elevates the phase transition temperature (from monoclinic to a tetragonal structure at high temperature) from ~520 C for x=0 to near 800 C for x=0.4. AC conductivity of the La0.99Ca0.01Nb1-xTaxO4- both in dry and wet air decreased slightly with increase of Ta content above 750 C, while below 500 C, it decreased one order of magnitude. It was also found that the activation energy for the total conductivity increases with increasing Ta content from 0.50 eV (x=0) to 0.58 eV (x=0.3) for the tetragonal phase, however, it decreases with increasing Ta content from 1.18 eV (x=0) to 1.08 eV (x=0.4) for the monoclinic phase. By removing the detrimental high temperature phase transition out of intermediate temperature range, partial substitution of Nb with Ta brings this class of material closer to its application in intermediate-temperature SOFCs.

  19. Solid state {sup 31}P MAS NMR spectroscopy and conductivity measurements on NbOPO{sub 4} and H{sub 3}PO{sub 4} composite materials

    SciTech Connect

    Risskov Sørensen, Daniel; Nielsen, Ulla Gro; Skou, Eivind M.

    2014-11-15

    A systematic study of composite powders of niobium oxide phosphate (NbOPO{sub 4}) and phosphoric acid (H{sub 3}PO{sub 4}) has been performed in order to characterize the material's ability to perform as an electrolyte material in medium temperature fuel cells and electrolyzers. Powders of H{sub 3}PO{sub 4} contents between 13.1 and 74.2 M% were produced and characterized with powder X-ray diffraction, {sup 31}P MAS NMR and impedance spectroscopy. NMR revealed that a significant degree of dehydration and vaporization of H{sub 3}PO{sub 4} takes place above 200 °C, and increases with temperature. At 500 °C the NbOPO{sub 4} and H{sub 3}PO{sub 4} has reacted to form niobium pyrophosphate (Nb{sub 2}P{sub 4}O{sub 15}). Impedance spectroscopy showed an increase in conductivity with increasing acid concentration, whereas the conductivity decreased slightly with increasing temperature. The highest conductivity measured was 2.5·10{sup −3} S/cm for a sample containing 74.2 M% of H{sub 3}PO{sub 4}. Lastly, it was shown that NbOPO{sub 4} has no significant conductivity of its own. - Graphical abstract: Conductivity of NbOPO{sub 4}/H{sub 3}PO{sub 4} composites as a function of equivalent P{sub 2}O{sub 5} content. The conductivity is insignificant for pure NbOPO{sub 4}. - Highlights: • Composites have been made from NbOPO{sub 4} and H{sub 3}PO{sub 4}. • The composites composition has been investigated with solid state NMR. • The composites have shown clear signs of acid dehydration upon heating. • The conductivity of the composites increases for increasing acid content. • NbOPO{sub 4} has no significant conductivity of its own.

  20. Mechanistic investigations of CO-photoextrusion and oxidative addition reactions of early transition-metal carbonyls: (η(5)-C5H5)M(CO)4 (M = V, Nb, Ta).

    PubMed

    Su, Shih-Hao; Su, Ming-Der

    2016-06-28

    The mechanisms for the photochemical Si-H bond activation reaction are studied theoretically using a model system of the group 5 organometallic compounds, η(5)-CpM(CO)4 (M = V, Nb, and Ta), with the M06-2X method and the Def2-SVPD basis set. Three types of reaction pathways that lead to final insertion products are identified. The structures of the intersystem crossings, which play a central role in these photo-activation reactions, are determined. The intermediates and transitional structures in either the singlet or triplet states are also calculated to provide a mechanistic explanation of the reaction pathways. All of the potential energy surfaces for the group 5 η(5)-CpM(CO)4 complexes are quite similar. In particular, the theoretical evidence suggests that after irradiation using light, η(5)-CpM(CO)4 quickly loses one CO ligand to yield two tricarbonyls, in either the singlet or the triplet states. The triplet tricarbonyl 16-electron intermediates, ([η(5)-CpM(CO)3](3)), play a key role in the formation of the final oxidative addition product, η(5)-CpM(CO)3(H)(SiMe3). However, the singlet counterparts, ([η(5)-CpM(CO)3](1)), play no role in the formation of the final product molecule, but their singlet metal centers interact weakly with solvent molecules ((Me3)SiH) to produce alkyl-solvated organometallic complexes, which are observable experimentally. This theoretical evidence is in accordance with the available experimental observations. PMID:27265245

  1. Synthesis of luminescent nanocrystals and solid solutions in the YNbO{sub 4}–EuNbO{sub 4} system via hydrothermal route

    SciTech Connect

    Hirano, Masanori Dozono, Hayato

    2014-02-01

    Highlights: • Nanocrystals: YNbO{sub 4}:Eu{sup 3+} were directly formed under hydrothermal conditions at 240 °C. • The nanocrystals (10–20 nm) were luminescent and had ellipsoidal morphology. • The complete solid solutions in the YNbO{sub 4}–EuNbO{sub 4} system were also directly formed. • The PL intensity and R/O intensity ratio changed depending on heating temperature. - Abstract: Luminescent nanocrystals having distinctive ellipsoidal morphology and the complete solid solution of monoclinic phase in the YNbO{sub 4}–EuNbO{sub 4} system were hydrothermally formed under weakly basic conditions at 180–240 °C for 5 h. The excitation spectra of the Y{sub 1−x}Eu{sub x}NbO{sub 4} nanocrystals, which consisted of the charge transfer (CT) band around 240–270 nm due to [NbO{sub 4}]{sup 3−}–Eu{sup 3+} interaction and several sharp bands corresponding to the f–f transitions of Eu{sup 3+}, e.g. the most intense absorption band at 395 nm ({sup 7}F{sub 0}→{sup 5}L{sub 6}), showed that the compounds could be excited by both ultraviolet and visible light. A dominant red emission at 610 nm and a weak orange emission at 590 nm assigned to {sup 5}D{sub 0}→{sup 7}F{sub 2} and {sup 5}D{sub 0}→{sup 7}F{sub 1} transitions of Eu{sup 3+}, respectively were observed in the as-prepared nanocrystals containing europium under excitation at 395 nm. The heat treatment at temperatures more than 1000 °C in air was effective for the improvement in the photoluminescence intensity of the as-prepared solid solutions. By the enhancement in the crystallinity and crystallite growth of the monoclinic phase through heat treatment at 1300 °C in air, the luminescence intensity of the as-prepared solid solution, Y{sub 0.75}Eu{sub 0.25}NbO{sub 4} (x = 0.25), which showed the most significant photoluminescence, became more than 5 times as strong as that before the heat treatment.

  2. Achieving high capacity in bulk-type solid-state lithium ion battery based on Li6.75La3Zr1.75Ta0.25O12 electrolyte: Interfacial resistance

    NASA Astrophysics Data System (ADS)

    Liu, Ting; Ren, Yaoyu; Shen, Yang; Zhao, Shi-Xi; Lin, Yuanhua; Nan, Ce-Wen

    2016-08-01

    A bulk-type all-solid-state lithium ion battery based on Ta-doped Li6.75La3Zr1.75Ta0.25O12 (LLZ-Ta) is prepared by a simple solid state process with high capacity of 279.0 μAh cm-2 at 80 °C. However, severe polarization is discovered during charging/discharging cycles at room temperature (RT) for battery with a higher active cathode loading. Large interfacial resistance due to the poor contact at the interfaces between cathode and LLZ-Ta solid electrolyte and at the interfaces within the composite cathode layer is proven to be the main reason for the poor electrochemical performance of the battery at RT. The polarization could be suppressed at elevated temperature, which is attributed to the decreased interfacial resistance as indicated by the results of impedance measurements and gives rise to much enhanced performance of the all-solid-state battery.

  3. Evaluation of phase equilibria in the Nb-rich portion of Nb-B system

    SciTech Connect

    Tang, Zhihong; Kramer, M.; Akinc, M.

    2007-12-19

    The phase equilibria in the Nb-rich portion of Nb-B system have been evaluated experimentally using metallographic analysis, differential thermal analysis (DTA) and X-ray diffraction. It showed that Nb{sub ss} (solid solution) and NbB are the only two primary phases in the 0-40 at.% B composition range, and the eutectic reaction L{leftrightarrow}Nb{sub ss}+NbB exists, instead of the generally accepted reaction L{leftrightarrow}Nb{sub ss}+Nb{sub 3}B{sub 2}, as indicated in the Nb-B phase diagram. The Nb{sub 3}B{sub 2} phase, however, forms by the peritectoid reaction Nb{sub ss}+NbB{leftrightarrow}Nb{sub 3}B{sub 2}. DTA tests were conducted on annealed Nb-14B, Nb-16B, Nb-18B and Nb-40B alloys, and temperature and heat of phase transition were determined. The eutectic reaction (L{leftrightarrow}Nb{sub ss}+NbB) temperature was determined to be 2104 {+-} 5 C, and the heat of phase transition was estimated as 22-30 kJ/mol, depending on the method of calibration used. The thermal event associated with peritectoid reactions was not observed in DTA curves due to sluggish solid state transformation, but the thermal annealing experiments show that peritectoid temperature is above 1900 C.

  4. The exchange interactions and the state of manganese atoms in the solid solutions in Bi3NbO7 of cubic and tetragonal modifications

    NASA Astrophysics Data System (ADS)

    Chezhina, N. V.; Zhuk, N. A.; Korolev, D. A.

    2016-01-01

    The comparative analysis of magnetic behavior of manganese-containing solid solutions Bi3Nb1-xMnxO7-δ (x=0.01-0.10) of cubic and tetragonal modifications was performed. Based on the results of magnetic susceptibility studies paramagnetic manganese atoms in solid solutions of cubic and tetragonal modifications were found to be in the form of Mn(III), Mn(IV) monomers and exchange-coupled dimers of Mn(III)-O-Mn(III), Mn(IV)-O-Mn(IV), Mn(III)-O-Mn(IV). The exchange parameters and the distribution of monomers and dimers in solid solutions as a function of the content of paramagnetic atoms were calculated.

  5. Synthesis and characterization of Ti{sub 1-2} {sub x} Nb {sub x} Ni {sub x} O{sub 2-} {sub x} {sub /2} solid solutions

    SciTech Connect

    Martos, Monica Julian, Beatriz Dehouli, Hakim; Gourier, Didier Cordoncillo, Eloisa Escribano, Purificacion

    2007-02-15

    Doped-rutile has been traditionally used in ceramic pigments for its intense optical properties. In this paper, we compare the classical ceramic synthesis of Ti{sub 1-2} {sub x} Nb {sub x} Ni {sub x} O{sub 2-} {sub x} {sub /2} system with the sol-gel methodology, which allows a reduction of the anatase-rutile transformation temperature. The composition was optimised in order to obtain a unique rutile phase with the minimum amount of pollutant Ni(II) and enhanced chromatic coordinates. Incorporation of the doping ions in the rutile structure was corroborated by XRD and Rietveld refinements. The species responsible for the colour mechanism were studied by different techniques. UV-VIS spectroscopy showed the characteristic features of Ni{sup 2+} ions, whose existence was corroborated by EPR and magnetic measurements. From these results, (Ni,Nb)doped-TiO{sub 2} powder samples can be now shaped as thin films, monoliths, etc. by using sol-gel methodology without modifying their properties. This study introduces new possibilities of coloured TiO{sub 2}-based solid solutions in new combined advanced applications (colouring agent and photocatalyst, etc.). - Graphical abstract: The synthesis and characterization of the Ti{sub 1-2} {sub x} Nb {sub x} Ni {sub x} O{sub 2-} {sub x} {sub /2} system prepared by traditional solid-state and sol-gel methodologies is reported. The incorporation of the doping ions in the rutile structure by Rietveld refinements and the magnetic response are discussed. The similarity found by both procedures introduces new possibilities of coloured TiO{sub 2}-based solid solutions.

  6. Simulation of solidly mounted plate wave resonator with wide bandwidth using 0-th shear horizontal mode in LiNbO3 plate

    NASA Astrophysics Data System (ADS)

    Kadota, Michio; Tanaka, Shuji

    2015-07-01

    A cognitive radio system using a vacant frequency band of digital TV channels (TV white space) requires a tunable filter with wide tunable ranges of center frequency and bandwidth. An ultra-wideband resonator is a key device to implement the tunable filter, because the tunable range is limited by the bandwidth (BW) of the resonators. A 0-th shear horizontal (SH0) mode plate wave resonator using an ultra-thin LiNbO3 plate is known to have a large electromechanical coupling factor, i.e., a large BW, but the structural fragility of the ultra-thin LiNbO3 plate is problematic. In this study, the feasibility of solidly mounted resonator type SH0 mode plate wave resonator was investigated systematically by finite element method simulation. The design parameters including the Euler angle, thickness of a LiNbO3 plate, and the material and thickness of an interdigital transducer were optimized. With the best design, a BW as wide as 26% is obtained.

  7. TA Collaborations

    ERIC Educational Resources Information Center

    Diefendorf, Martha

    2010-01-01

    This paper highlights several current collaborative activities of the National Early Childhood Technical Assistance Center (NECTAC). There are many specific examples of TA (Technical Assistance) collaborations that take place on a regular basis; the seven examples presented here were selected to represent different types of collaboration. The…

  8. Temperature- and Frequency-Dependent Dielectric Properties of Sol-Gel-Derived BaTiO3-NaNbO3 Solid Solutions

    NASA Astrophysics Data System (ADS)

    Kwon, Do-Kyun; Goh, Yumin; Son, Dongsu; Kim, Baek-Hyun; Bae, Hyunjeong; Perini, Steve; Lanagan, Michael

    2016-01-01

    A sol-gel-derived powder synthesis method has been used to prepare BaTiO3-NaNbO3 (BT-NN) solid-solution ceramic samples with various compositions. Fine and homogeneous complex perovskite ceramics were obtained at lower processing temperatures than used in conventional solid-state processing. The ferroelectric and relaxor ferroelectric properties of the sol-gel-synthesized (1 - x)BaTiO3- xNaNbO3 [(1 - x)BT- xNN] ceramics in the wide composition range of 0 < x ≤ 0.7 were extensively studied. Structural and dielectric characterization results revealed that a low level of NN addition ( x = 0.04) to BT is sufficient to cause a continuous relaxor-to-ferroelectric transition, and the relaxor behavior was consistently observed at compositions with high NN content up to x = 0.7. A number of relaxor parameters including the Curie temperature, Burns temperature, freezing temperature, γ, diffuseness parameter ( δ), and activation energy were determined from the temperature and frequency dependency of the real part of the dielectric permittivity for various BT-NN compositions using the Curie-Weiss law and Vögel-Fulcher relationship. The systematic changes of these parameters with respect to composition indicate that a continuous crossover between BT-based relaxor and NN-based relaxor occurs at a composition near x = 0.4.

  9. Multi-component solid solution alloys having high mixing entropy

    SciTech Connect

    Bei, Hongbin

    2015-10-06

    A multi-component high-entropy alloy includes a composition selected from the following group: VNbTaTiMoWRe, VNbTaTiMoW, VNbTaTiMoRe, VNbTaTiWRe, VNbTaMoWRe, VNbTiMoWRe, VTaTiMoWRe, NbTaTiMoWRe, VNbTaTiMo, VNbTaTiW, VNbTaMoW, VNbTiMoW, VTaTiMoW, NbTaTiMoW, VNbTaTiRe, VNbTaMoRe, VNbTiMoRe, VTaTiMoRe, NbTaTiMoRe, VNbTaWRe, VNbTiWRe, VTaTiWRe, NbTaTiWRe, VNbMoWRe, VTaMoWRe, NbTaMoWRe, VTiMoWRe, NbTiMoWRe, TaTiMoWRe, wherein relative amounts of each element vary by no more than .+-.15 atomic %.

  10. Phase stability and site substitution in Nb-Al compounds

    SciTech Connect

    Sluiter, M.; Takahashi, M.; Kawazoe, Y.

    1995-07-01

    The site preferences of Ta, Mo, and W in A15 Nb{sub 3}Al, the phase stability of off-stoichiometric A15 Nb{sub 3}Al, and the atomic order of the Nb{sub 2}Al D8{sub b} ({sigma}) phase are investigated by performing electronic structure calculations based on the local density approximation. Mo, W, and Ta ale found to have a preference for the Nb sublattice. Ta has the strongest site preference. It was shown that some recently proposed ground states for off-stoichiometric A15 phases are unlikely to occur in the Nb-Al system. Moreover, it was shown that the atomic order in the D8{sub b} Nb{sub 2}Al phase contributes significantly to its stability.

  11. Dielectric spectroscopy of Pb1- x Ba x (Mg1/3Nb2/3) m (Zn1/3Nb2/3) y (Ni1/3Nb2/3) n Ti z O3 solid solutions in a wide temperature interval

    NASA Astrophysics Data System (ADS)

    Talanov, M. V.; Kubrin, S. P.; Pavelko, A. A.; Reznichenko, L. A.

    2016-06-01

    The dielectric spectra of Pb1- x Ba x (Mg1/3Nb2/3) m (Zn1/3Nb2/3) y (Ni1/3Nb2/3) n Ti z O3 ( x = 0-0.15, m = 0.4541, y = 0.0982, n = 0.1477, and z = 0.3) ceramic samples have been studied in wide intervals of temperature (10-873 K) and frequency of the measurement electric field (0.1-1000 kHz). It has been found that an increase in the Ba2+( x) content leads to a reduction in the phase transition temperature (from 418 K at x = 0 to 256 K at x = 0.15), to the transition from the normal ferroelectric state to the relaxor ferroelectric one (at x ≥ 0.025), and to the disappearance of temperature hysteresis of dependences of the relative dielectric permittivity. It has been hypothesized that a tricritical point is present near x ˜ 0.125 in the x-T phase diagram of the studied solid solutions.

  12. Structure and dielectric properties of solid solutions Bi7Ti4 + x W x Nb1 - 2 x O21 ( x = 0-0.5)

    NASA Astrophysics Data System (ADS)

    Vlasenko, V. G.; Zubkov, S. V.; Shuvaeva, V. A.

    2015-05-01

    The structural and electrophysical characteristics of a series of solid solutions of layered perovskite-type oxides Bi7Ti4 + x W x Nb1 - 2 x O21 ( x = 0-0.5) have been investigated. According to X-ray powder dif- fraction data, all the studied compounds are single-phase and have the structure of Aurivillius phases ( m = 2.5) with an orthorhombic crystal lattice (space group I2 cm, Z = 2). The changes in the tetragonal and orthorhombic distortions of perovskite-like layers in the compounds have been considered depending on their chemical composition. The temperature dependences of the relative permittivity ɛ( T) have been measured. It has been shown that the Curie temperature T C of the perovskite-type oxides Bi7Ti4 + x W x Nb1 - 2 x O21 ( x = 0-0.5) decreases linearly with an increase in the parameter x. The activation energies of charge carriers have been obtained in different temperature ranges. It has been found that there are three temperature regions with very different activation energies due to different natures of charge carriers in the studied compounds.

  13. Tantalum-niobium alloy diffusion barriers for superconducting Nb{sub 3}Sn wires in fusion applications

    SciTech Connect

    McKinnell, J.C.; O`Larey, P.M.; Siddall, M.B.

    1997-06-01

    Fusion magnets using cable in conduit conductors require Nb{sub 3}Sn wires having high residual resistivity ratio (RRR) to ensure adequate stability. The diffusion barrier in Nb{sub 3}Sn composite wire is one of the key factors controlling the RRR of the wire. Ta40wt.% Nb diffusion barriers have been investigated for application to fusion type wires. Ta40wt.% Nb diffusion barriers exhibit excellent fabricability in the wire drawing process and yield residual resistivity ratio values in excess of 300 (bare wire surface) and 150 (Cr plated wire surface). The hysteresis loss due to the A15 formed as a layer on the Ta40wt.% Nb diffusion barrier is minimal. Comparisons of Ta40wt.% Nb diffusion barriers to barriers made of V, Nb and Ta are also performed.

  14. Lithium ion diffusion measurements on a garnet-type solid conductor Li6.6La3Zr1.6Ta0.4O12 by using a pulsed-gradient spin-echo NMR method.

    PubMed

    Hayamizu, Kikuko; Matsuda, Yasuaki; Matsui, Masaki; Imanishi, Nobuyuki

    2015-09-01

    The garnet-type solid conductor Li7-xLa3Zr2-xTaxO12 is known to have high ionic conductivity. We synthesized a series of compositions of this conductor and found that cubic Li6.6La3Zr1.6Ta0.4O12 (LLZO-Ta) has a high ionic conductivity of 3.7×10(-4)Scm(-1) at room temperature. The (7)Li NMR spectrum of LLZO-Ta was composed of narrow and broad components, and the linewidth of the narrow component varied from 0.69kHz (300K) to 0.32kHz (400K). We carried out lithium ion diffusion measurements using pulsed-field spin-echo (PGSE) NMR spectroscopy and found that echo signals were observed at T≥313K with reasonable sensitivity. The lithium diffusion behavior was measured by varying the observation time and pulsed-field gradient (PFG) strength between 313 and 384K. We found that lithium diffusion depended significantly on the observation time and strength of the PFG, which is quite different from lithium ion diffusion in liquids. It was shown that lithium ion migration in the solid conductor was distributed widely in both time and space. PMID:26051010

  15. A-site- and/or B-site-modified PbZrTiO3 materials and (Pb, Sr, Ca, Ba, Mg) (Zr, Ti, Nb, Ta)O3 films having utility in ferroelectric random access memories and high performance thin film microactuators

    NASA Technical Reports Server (NTRS)

    Roeder, Jeffrey F. (Inventor); Chen, Ing-Shin (Inventor); Bilodeau, Steven (Inventor); Baum, Thomas H. (Inventor)

    2001-01-01

    A modified PbZrTiO.sub.3 perovskite crystal material thin film, wherein the PbZrTiO.sub.3 perovskite crystal material includes crystal lattice A-sites and B-sites at least one of which is modified by the presence of a substituent selected from the group consisting of (i) A-site substituents consisting of Sr, Ca, Ba and Mg, and (ii) B-site substituents selected from the group consisting of Nb and Ta. The perovskite crystal thin film material may be formed by liquid delivery MOCVD from metalorganic precursors of the metal components of the thin film, to form PZT and PSZT, and other piezoelectric and ferroelectric thin film materials. The thin films of the invention have utility in non-volatile ferroelectric memory devices (NV-FeRAMs), and in microelectromechanical systems (MEMS) as sensor and/or actuator elements, e.g., high speed digital system actuators requiring low input power levels.

  16. Trends in electronic structures and structural properties of MAX phases: a first-principles study on M(2)AlC (M = Sc, Ti, Cr, Zr, Nb, Mo, Hf, or Ta), M(2)AlN, and hypothetical M(2)AlB phases.

    PubMed

    Khazaei, Mohammad; Arai, Masao; Sasaki, Taizo; Estili, Mehdi; Sakka, Yoshio

    2014-12-17

    MAX phases are a large family of layered ceramics with many potential structural applications. A set of first-principles calculations was performed for M(2)AlC and M(2)AlN (M = Sc, Ti, Cr, Zr, Nb, Mo, Hf, or Ta) MAX phases as well as for hypothetical M(2)AlB to investigate trends in their electronic structures, formation energies, and various mechanical properties. Analysis of the calculated data is used to extend the idea that the elastic properties of MAX phases can be controlled according to the valence electron concentration. The valence electron concentrationcan be tuned through the various combinations of transition metal and nonmetal elements. PMID:25419878

  17. Dielectric Properties Of Pb(In{sub 1/2}Nb{sub 1/2})O{sub 3}-PbTiO{sub 3} Solid Solution Synthesized By Solid State Reaction Route

    SciTech Connect

    Ramesh, G.; Subramanian, V.; Aruna, G.

    2011-07-15

    Phase pure (1-x)Pb(In{sub 1/2}Nb{sub 1/2})O{sub 3}-x PbTiO{sub 3} ceramics near morphotrophic phase boundary (x = 0.35) are prepared by conventional solid state reaction route, by adding 2 mol.% MgO. The dielectric properties of lead indium niobate-lead titanate ceramic are studied as a function of both temperature and frequency. For this composition the dielectric constant for 100 Hz increases from 1944 at room temperature to 1510 at Curie temperature(304 deg. C). The saturation polarization, measured at room temperature, is found to be 23.9 {mu}C/cm{sup 2} for 40 kV/cm.

  18. Effect of Li addition on crystal structure and phase separation of highly defective (La,Li)TaO 3 solid electrolytes

    NASA Astrophysics Data System (ADS)

    Sun, Chien-Ying; Fung, Kuan-Zong

    2002-08-01

    La 1/3TaO 3 was found to exhibit a perovskite structure in which two-thirds of A-cation sites are vacant. An ordered arrangement of vacancies causes the formation of a superstructure with doubled c-axis compared with a perovskite subcell. With small amount of Li addition, a superstructure with vacancies located at the (002) plane was still present. When Li ions were added into more than 20% of A-cation sites, the superstructure disappeared and the perovskite structure also changed from tetragonal to near cubic. When more than 60% of A-cation sites were incorporated by Li ions, a phase separation of cubic La 0.166Li 0.5TaO 3 perovskite and rhombohedral LiTaO 3 was observed. The phase separation was caused by the big difference of ionic radius between La and Li ions. The microstructure and microchemical analysis of (La,Li)TaO 3 were examined using scanning electron microscopy and EDX.

  19. Graphene-Modified Interface Controls Transition from VCM to ECM Switching Modes in Ta/TaOx Based Memristive Devices.

    PubMed

    Lübben, Michael; Karakolis, Panagiotis; Ioannou-Sougleridis, Vassilios; Normand, Pascal; Dimitrakis, Panagiotis; Valov, Ilia

    2015-10-28

    By modification of the electrode-solid-electrolyte interface with graphene, transit from valence change memories (VCM) to electrochemical metallization memories (ECM) in the cell Ta(C)/Ta2 O5 /Pt is demonstrated, thus, bridging both mechanisms. The ECM operation is discussed in the light of Ta-cation mobility in TaOx . The crucial role of electrochemical processes and moisture in the resistive switching process is also highlighted. PMID:26456484

  20. The solid state structure and reactivity of NbCl(5) x (N,N'-dicyclohexylurea) in solution: evidence for co-ordinated urea dehydration to the relevant carbodiimide.

    PubMed

    Aresta, Michele; Dibenedetto, Angela; Stufano, Paolo; Aresta, Brunella Maria; Maggi, Sabino; Pápai, Imre; Rokob, Tibor András; Gabriele, Bartolo

    2010-08-14

    NbCl(5) x (N,N'-dicyclohexylurea) 1a owns a distorted octahedral structure due to intramolecular NH...Cl bonding. The unit cell contains four units which are intermolecularly NH...Cl and NH...N bonded. An extended intramolecular network of H-bonding (N-H...Cl, CH...Cl, CH...N) causes the 3D self assembling of the units. Upon addition of base, the HCl release from 1a is observed with the transfer to Nb of the O-atom of the carbonylic function of the starting urea which is converted into the relevant carbodiimide CyN=C=NCy 4. The latter is quantitatively released by adding an excess of NEt(3) at 308 K (py and DBU are less efficient) with formation of the known NbOCl(3)(NEt(3))(2), isolated in quantitative yield. Increasing the temperature leads to a loss in selectivity as the formed DCC undergoes further reactions. At 350 K, the isocyanate CyN=C=O has been isolated in 60% yield besides a mixture of Nb-complexes. DFT calculations have been coupled to IR and NMR experiments for characterizing possible reaction intermediates and the behaviour of 1a. Several other MCl(x) species (ScCl(3), YCl(3), LaCl(3), TiCl(4), TaCl(5), AlCl(3), SnCl(4)) have been shown to be able to co-ordinate DCU but not all of them promote the conversion of urea into DCC. PMID:20544121

  1. X-Ray diffraction characteristics of Ti /SUB 1-x/ Nb /SUB x/ C /SUB o. 5/ N /SUB 0. 5/ solid solutions

    SciTech Connect

    Ordan'yan, S.S.; Maskhuliya, L.G.; Panteleev, I.B.; Pavlyuk, E.G.; Persinin, S.A.

    1986-05-01

    A study of the influence of production factors (temperature and length of synthesis, method of addition of the components, repeated refinement and homogenization) on the parameters of the structure of phases of variable composition was made. The solid solutions were synthesized from titanium and niobium carbide and nitride powders, and the carbonitride of the composition Ti /SUB 0.77/ Nb /SUB 0.23/ C /SUB 0.5/ N /SUB 0.5/ , by the carbothermal method. X-ray diffraction was taken by a DRON-3 diffractometer controlled by an SM-1 computer. The lattice parameter, the characteristics of the fine crystal structure and the residual macrostresses were determined. It was concluded that the nature of the original components does not influence the character of the concentration relationship of the microstructural parameters, a change in which occurs only under the influence of synethesis temperature and is accompanied by effects of diffusion perfection of the structure of the phases of variable composition.

  2. Development of Ta-based Superconducting Tunnel Junction X-ray Detectors for Fluorescence XAS

    SciTech Connect

    Friedrich, S; Drury, O; Hall, J; Cantor, R

    2009-09-23

    We are developing superconducting tunnel junction (STJ) soft X-ray detectors for chemical analysis of dilute samples by fluorescence-detected X-ray absorption spectroscopy (XAS). Our 36-pixel Nb-based STJ spectrometer covers a solid angle {Omega}/4{pi} {approx} 10{sup -3}, offers an energy resolution of {approx}10-20 eV FWHM for energies up to {approx}1 keV, and can be operated at total count rates of {approx}10{sup 6} counts/s. For increased quantum efficiency and cleaner response function, we have now started the development of Ta-based STJ detector arrays. Initial devices modeled after our Nb-based STJs have an energy resolution below 10 eV FWHM for X-ray energies below 1 keV, and pulse rise time discrimination can be used to improve their response function for energies up to several keV. We discuss the performance of the Ta-STJs and outline steps towards the next-generation of large STJ detector arrays with higher sensitivity.

  3. Development of Ta-based Superconducting Tunnel Junction X-ray Detectors for Fluorescence XAS

    SciTech Connect

    Friedrich, Stephan; Drury, Owen B.; Hall, John; Cantor, Robin

    2010-06-23

    We are developing superconducting tunnel junction (STJ) soft X-ray detectors for chemical analysis of dilute samples by fluorescence-detected X-ray absorption spectroscopy (XAS). Our 36-pixel Nb-based STJ spectrometer covers a solid angle {Omega}/4{pi}{approx_equal}10{sup -3}, offers an energy resolution of {approx}10-20 eV FWHM for energies up to {approx}1 keV, and can be operated at total count rates of {approx}10{sup 6} counts/s. For increased quantum efficiency and cleaner response function, we have now started the development of Ta-based STJ detector arrays. Initial devices modeled after our Nb-based STJs have an energy resolution below 10 eV FWHM for X-ray energies below 1 keV, and pulse rise time discrimination can be used to improve their response function for energies up to several keV. We discuss the performance of the Ta-STJs and outline steps towards the next-generation of large STJ detector arrays with higher sensitivity.

  4. 93Nb NMR chemical shift scale for niobia systems.

    PubMed

    Lapina, Olga B; Khabibulin, Dzhalil F; Romanenko, Konstantin V; Gan, Zhehong; Zuev, Mikhail G; Krasil'nikov, Vladimir N; Fedorov, Vladimir E

    2005-09-01

    93Nb solid-state NMR spectra of a series of inorganic niobates with Nb in different oxygen coordination environments were measured. For all studied compounds the chemical shielding and quadrupole tensor parameters were determined using conventional and ultrahigh field NMR facilities, ultrahigh speed MAS, DQ STMAS, solid-echo and computer modeling. It has been demonstrated that the 93Nb isotropic chemical shift is sensitive to the coordination number of Nb sites. For the first time the 93Nb NMR chemical shift scale for NbOx polyhedra in solid materials has been proposed: for four-coordinated Nb sites, the isotropic shifts occur from -650 to -950 ppm; five-coordinated Nb sites have the isotropic shifts in the range of -900 to -980 ppm; for six-coordinated Nb sites the isotropic shifts vary from -900 to -1360 ppm; the shifts from -1200 to -1600 ppm are typical for seven-coordinated Nb sites; for eight-coordinated Nb sites the shifts are higher than -1400 ppm. The possible correlation between the value of the isotropic chemical shift and the ionic character of the NbOx-MOy polyhedra association has been suggested. The magnitude of the 93Nb quadrupole coupling constant depends on the local symmetry of Nb sites and may vary from hundreds of kHz to hundreds of MHz. PMID:16216475

  5. Quench tests of Nb3Al small racetrack magnets

    SciTech Connect

    Yamada, R.; Kikuchi, A.; Tartaglia, Michael Albert; Ambrosio, G.; Andreev, N.; Barzi, E.; Carcagno, R.; Feher, S.; Kashikhin, V.V.; Kotelnikov, S.; Lamm, Michael J.; /Fermilab /NIMC, Tsukuba /KEK, Tsukuba

    2007-08-01

    Two Cu stabilized Nb3Al strands, F1 (Nb matrixed) and F3 (Ta matrixed), have been made at NIMS and their Rutherford cables were made at Fermilab in collaboration with NIMS. A Small Race-track magnet using F1 Rutherford cable, the first Nb3Al dipole magnet in the world, was constructed and tested to full current at Fermilab. This magnet was tested extensively to full short sample data and its quench characteristics were studied and reported. The 3-D magnetic field calculation was done with ANSYS to find the peak field. The quench characteristics of the magnet are explained with the characteristics of the Nb3Al strand and Rutherford cable. The other Small Race-track magnet using Ta matrixed F3 strand was constructed and will be tested in the near future. The advantages and disadvantages of these Nb3Al cables are discussed.

  6. Multinuclear Solid-State NMR Investigation of Hexaniobate and Hexatantalate Compounds.

    PubMed

    Deblonde, Gauthier J-P; Coelho-Diogo, Cristina; Chagnes, Alexandre; Cote, Gérard; Smith, Mark E; Hanna, John V; Iuga, Dinu; Bonhomme, Christian

    2016-06-20

    This work determines the potential of solid-state NMR techniques to probe proton, alkali, and niobium environments in Lindqvist salts. Na7HNb6O19·15H2O (1), K8Nb6O19·16H2O (2), and Na8Ta6O19·24.5H2O (3) have been studied by solid-state static and magic angle spinning (MAS) NMR at high and ultrahigh magnetic field (16.4 and 19.9 T). (1)H MAS NMR was found to be a convenient and straightforward tool to discriminate between protonated and nonprotonated clusters AxH8-xM6O19·nH2O (A = alkali ion; M = Nb, Ta). (93)Nb MAS NMR studies at different fields and MAS rotation frequencies have been performed on 1. For the first time, the contributions of NbO5Oμ2H sites were clearly distinguished from those assigned to NbO6 sites in the hexaniobate cluster. The strong broadening of the resonances obtained under MAS was interpreted by combining chemical shift anisotropy (CSA) with quadrupolar effects and by using extensive fitting of the line shapes. In order to obtain the highest accuracy for all NMR parameters (CSA and quadrupolar), (93)Nb WURST QCPMG spectra in the static mode were recorded at 16.4 T for sample 1. The (93)Nb NMR spectra were interpreted in connection with the XRD data available in the literature (i.e., fractional occupancies of the NbO5Oμ2H sites). 1D (23)Na MAS and 2D (23)Na 3QMAS NMR studies of 1 revealed several distinct sodium sites. The multiplicity of the sites was again compared to structural details previously obtained by single-crystal X-ray diffraction (XRD) studies. The (23)Na MAS NMR study of 3 confirmed the presence of a much larger distribution of sodium sites in accordance with the 10 sodium sites predicted by XRD. Finally, the effect of Nb/Ta substitutions in 1 was also probed by multinuclear MAS NMR ((1)H, (23)Na, and (93)Nb). PMID:27245403

  7. Microstructural and weldability evaluation of 310TaN

    SciTech Connect

    Lundin, C.D.; Qiao, C.Y.P.; Swindeman, R.W.

    1996-08-01

    Excellent weldability and good microstructural stability of 310TaN, in terms of the formation and growth of secondary phases at elevated temperature, was revealed in this investigation. The interganular stress corrosion resistance of 310TaN is superior to modified 800H and 310HCbN evaluated previously due to the fact that TaC, TaN and Ta(C,N) particles are more stable compared to Nb-rich or Ti-rich carbides, nitrides and carbonitrides presented in the other advanced alloys. Using resistance spot welding technique for which extremely fast cooling is a characteristic, it was found that a very minor amount of gain boundary liquation takes place during welding thermal cycling. The limited grain boundary liquation is of the eutectic type i.e., a low tendency to weld HAZ hot cracking.

  8. The reactivity of 1,1-dialkoxyalkanes with niobium and tantalum pentahalides. Formation of coordination compounds, C-H and C-C bond activation and the X-ray structure of the stable carboxonium species [Me(2)C=CHC(=OMe)Me][NbCl(5)(OMe)].

    PubMed

    Marchetti, Fabio; Pampaloni, Guido; Zacchini, Stefano

    2009-10-14

    The reactions of the pentahalides NbX5 (X = Cl, Br) with the 1,1-dialkoxyalkanes CHR'(OEt)2 or 1,3-dioxolane yield the coordination adducts NbX5[kappa1-(OEt)CHR'(OEt)] (X = Cl, R' = H, 2a; X = Br, R' = H, 2b; X = Cl, R' = Me, 2c; X = Br, R' = Me, 2d) or NbCl5(kappa1-right angle OCH2OCH2C right angle H2), 3, respectively. Compounds 2a-c and 3 are stable at room temperature, while 2d slowly converts into the alkoxide NbBr4[OCH(Me)OEt], 4. Room-temperature fragmentations are observed upon reacting CH2(OMe)2, CHMe(OMe)2 and CMe2(OMe)2 with MX5 (M = Nb, Ta; X = Cl, Br). The complexes MX5[O(Me)(CH2X)], 5, and [MX3(OMe)2]2, 6, form selectively from MX5/CH2(OMe)2 (M = Nb, Ta; X = Cl, Br), while mixtures of [NbX4(OMe)]2 (X = Cl, 8a; X = Br, 8b) and organic halides are obtained from NbX5/CHMe(OMe)2. Instead, the reaction of NbCl5 with CMe2(OMe)2 affords the stable carboxonium species [Me2C=CHC(=OMe)Me][NbCl5(OMe)], 7, as prevalent product. Furthermore, 1,1-dialkoxyalkanes are generally activated by MF5 (M = Nb, Ta) at room temperature: according to the cases, alcohols, ethers, esters and ketones have been detected in the reaction mixtures after hydrolysis. In agreement with NMR data, the carboxonium ion [Me2C=CHC(=OMe)Me]+ is produced from NbF5/CMe2(OMe)2. The complexes NbF5[OEt(Me)], 9a, and NbF5[O=CH(OEt)], 9b, obtained by addition of CH2(OEt)2 to NbF5, have been characterised by NMR spectroscopy. Trimethyl formate, CH(OMe)3, reacts with NbX5 (X = Cl, Br) with formation of the alkoxides 6 and 8, in admixture with NbX5[O=CH(OMe)] and MeX; otherwise, MF5[O=CH(OMe)] and MF5(OMe2) have been synthesised from MF5/CH(OMe)3 (M = Nb, Ta). Complete screening of the organic fragments produced in the distinct reactions has been carried out by both GC-MS and NMR analyses on the reaction mixtures, after treatment with water. The solid state structures of the mixed halo-alkoxy complexes [TaX3(OMe)(mu-OMe)]2 (X = Cl, 6c; X = Br, 6d) and of the stable alkylated ketone containing species 7

  9. Search for solid conductors of Na(+) and K(+) ions: Five new conductors

    NASA Technical Reports Server (NTRS)

    Singer, J.; Kautz, H.; Fielder, W. L.; Fordyce, J.

    1975-01-01

    Five conductors of three structure types were discovered which, as solids, can transport Na(+) or K(+) ions with conductivities of approximately .00001/(omega cm) at 300 K. These compounds are: (1) the pyrochlores NaTaWO6 and NaTa2O5F, both with an activation energy for conduction delta E of 21 kJ/mole; (2) the bodycentered cubic form of NaSbO3, with delta E = 42 kJ/mole; and (3) the niobates 2Na2O with 3Nb2O5 and 2K2O with 3Nb2O5, with the alkali ions probably in open layers of the incompletely determined structure; delta E = 17 kJ/mole. On the basis of approximately 40 structure types, some generalizations were made regarding the relation between structure and ionic transport.

  10. A new insight into high-strength Ti62Nb12.2Fe13.6Co6.4Al5.8 alloys with bimodal microstructure fabricated by semi-solid sintering.

    PubMed

    Liu, L H; Yang, C; Kang, L M; Qu, S G; Li, X Q; Zhang, W W; Chen, W P; Li, Y Y; Li, P J; Zhang, L C

    2016-01-01

    It is well known that semi-solid forming could only obtain coarse-grained microstructure in a few alloy systems with a low melting point, such as aluminum and magnesium alloys. This work presents that semi-solid forming could also produce novel bimodal microstructure composed of nanostructured matrix and micro-sized (CoFe)Ti2 twins in a titanium alloy, Ti62Nb12.2Fe13.6Co6.4Al5.8. The semi-solid sintering induced by eutectic transformation to form a bimodal microstructure in Ti62Nb12.2Fe13.6Co6.4Al5.8 alloy is a fundamentally different approach from other known methods. The fabricated alloy exhibits high yield strength of 1790 MPa and plastic strain of 15.5%. The novel idea provides a new insight into obtaining nano-grain or bimodal microstructure in alloy systems with high melting point by semi-solid forming and into fabricating high-performance metallic alloys in structural applications. PMID:27029858

  11. A new insight into high-strength Ti62Nb12.2Fe13.6Co6.4Al5.8 alloys with bimodal microstructure fabricated by semi-solid sintering

    PubMed Central

    Liu, L. H.; Yang, C.; Kang, L. M.; Qu, S. G.; Li, X. Q.; Zhang, W. W.; Chen, W. P.; Li, Y. Y.; Li, P. J.; Zhang, L. C.

    2016-01-01

    It is well known that semi-solid forming could only obtain coarse-grained microstructure in a few alloy systems with a low melting point, such as aluminum and magnesium alloys. This work presents that semi-solid forming could also produce novel bimodal microstructure composed of nanostructured matrix and micro-sized (CoFe)Ti2 twins in a titanium alloy, Ti62Nb12.2Fe13.6Co6.4Al5.8. The semi-solid sintering induced by eutectic transformation to form a bimodal microstructure in Ti62Nb12.2Fe13.6Co6.4Al5.8 alloy is a fundamentally different approach from other known methods. The fabricated alloy exhibits high yield strength of 1790 MPa and plastic strain of 15.5%. The novel idea provides a new insight into obtaining nano-grain or bimodal microstructure in alloy systems with high melting point by semi-solid forming and into fabricating high-performance metallic alloys in structural applications. PMID:27029858

  12. A new insight into high-strength Ti62Nb12.2Fe13.6Co6.4Al5.8 alloys with bimodal microstructure fabricated by semi-solid sintering

    NASA Astrophysics Data System (ADS)

    Liu, L. H.; Yang, C.; Kang, L. M.; Qu, S. G.; Li, X. Q.; Zhang, W. W.; Chen, W. P.; Li, Y. Y.; Li, P. J.; Zhang, L. C.

    2016-03-01

    It is well known that semi-solid forming could only obtain coarse-grained microstructure in a few alloy systems with a low melting point, such as aluminum and magnesium alloys. This work presents that semi-solid forming could also produce novel bimodal microstructure composed of nanostructured matrix and micro-sized (CoFe)Ti2 twins in a titanium alloy, Ti62Nb12.2Fe13.6Co6.4Al5.8. The semi-solid sintering induced by eutectic transformation to form a bimodal microstructure in Ti62Nb12.2Fe13.6Co6.4Al5.8 alloy is a fundamentally different approach from other known methods. The fabricated alloy exhibits high yield strength of 1790 MPa and plastic strain of 15.5%. The novel idea provides a new insight into obtaining nano-grain or bimodal microstructure in alloy systems with high melting point by semi-solid forming and into fabricating high-performance metallic alloys in structural applications.

  13. An aqueous route to [Ta6O19]8- and solid-state studies of isostructural niobium and tantalum oxide complexes.

    SciTech Connect

    Nyman, May D.; Anderson, Travis Mark; Alam, Todd M.; Rodriguez, Mark Andrew; Joel N. Bixler; Francois Bonhomme

    2007-10-01

    Tantalate materials play a vital role in our high technology society: tantalum capacitors are found in virtually every cell phone. Furthermore, electronic characteristics and the incredibly inert nature of tantalates renders them ideal for applications such as biomedical implants, nuclear waste forms, ferroelectrics, piezoelectrics, photocatalysts and optical coatings. The inert and insoluble nature of tantalates is not fundamentally understood; and furthermore poor solubility renders fabrication of novel or optimized tantalates very difficult. We have developed a soft chemical route to water-soluble tantalum oxide clusters that can serve as both precursors for novel tantalate materials and ideal models for experimental and computational approaches to understanding the unusually inert behavior of tantalates. The water soluble cluster, [Ta6O19]8- is small, highly symmetric, and contains the representative oxygen types of a metal oxide surface, and thus ideally mimics a complex tantalate surface in a simplistic form that can be studied unambiguously. Furthermore; in aqueous solution, these highly charged and super-basic clusters orchestrate surprising acid-base behavior that most likely plays an important role in the inertness of related oxide surfaces. Our unique synthetic approach to the [Ta6O19]8- cluster allowed for unprecedented enrichment with isotopic labels (17O), enabling detailed kinetic and mechanistic studies of the behavior of cluster oxygens, as well as their acid-base behavior. This SAND report is a collection of two publications that resulted from these efforts.

  14. Er3+ diffusion in LiTaO3 crystal

    NASA Astrophysics Data System (ADS)

    Zhang, De-Long; Zhang, Qun; Wong, Wing-Han; Pun, Edwin Yue-Bun

    2015-12-01

    Some Er3+-doped LiTaO3 plates were prepared by in-diffusion of Er-metal film locally coated onto congruent Z-cut substrate in air at a wide temperature range from 1000 to 1500 °C. After diffusion, Er3+-doping effect on LiTaO3 refractive index and Li2O out-diffusion arising from Er3+ in-diffusion were studied at first. Refractive indices at the doped and undoped surface parts were measured by prism coupling technique and the surface composition was estimated. The results show that Er3+ dopant has small contribution to the LiTaO3 index. Li2O out-diffusion is slight (Li2O content loss <0.3 mol%) for the temperature below 1300 °C while is moderate (Li2O content loss <0.6 mol%) for the temperature above 1400 °C. The Er3+ profile was studied by secondary ion mass spectrometry. The study shows that the diffused Er3+ ions follow either a complementary error function or a Gaussian profile. Characteristic parameters including diffusivity, diffusion constant, activation energy, solubility, solubility constant and heat of solution were obtained and compared with the LiNbO3 case. The comparison shows that the diffusivity and solubility in LiTaO3 are considerably smaller than in LiNbO3 because of the difference of Ta and Nb in atomic weight.

  15. Anion photoelectron spectroscopy of germanium and tin clusters containing a transition- or lanthanide-metal atom; MGe(n)- (n = 8-20) and MSn(n)- (n = 15-17) (M = Sc-V, Y-Nb, and Lu-Ta).

    PubMed

    Atobe, Junko; Koyasu, Kiichirou; Furuse, Shunsuke; Nakajima, Atsushi

    2012-07-14

    The electronic properties of germanium and tin clusters containing a transition- or lanthanide-metal atom from group 3, 4, or 5, MGe(n) (M = Sc, Ti, V, Y, Zr, Nb, Lu, Hf, and Ta) and MSn(n) (M = Sc, Ti, Y. Zr, and Hf), were investigated by anion photoelectron spectroscopy at 213 nm. In the case of the group 3 elements Sc, Y, and Lu, the threshold energy of electron detachment of MGe(n)(-) exhibits local maxima at n = 10 and 16, while in the case of the group 4 elements Ti, Zr, and Hf, it exhibits a local minimum only at n = 16, associated with the presence of a small bump in the spectrum. A similar behavior is observed for MSn(n)(-) around n = 16, and these electronic characteristics of MGe(n) and MSn(n) are closely related to those of MSi(n). Compared to MSi(n), however, the larger cavity size of a Ge(n) cage allows metal atom encapsulation at a smaller size n. A cooperative effect between the electronic and geometric structures of clusters with a large cavity of Ge(16) or Sn(16) is discussed together with the results of experiments that probe their geometric stability via their reactivity to H(2)O adsorption. PMID:22333909

  16. Effect of Ta doped on microstructure of sodium potassium niobate single crystal grown by flux method

    NASA Astrophysics Data System (ADS)

    Saravanan, R.; Rajesh, D.; Rajasekaran, S. V.; Perumal, R.; Chitra, M.; Jayavel, R.

    2013-06-01

    Single crystals of sodium potassium niobate (K0.5Na0.5)NbO3 (KNN) and 0.5mol%, 1mol% and 1.5 mol% tantalum oxide Ta2O5 doped KNN were grown by flux method. The formation of microstructure and domain structure was investigated for both pure and Ta doped KNN single crystals. The partial substitution of the B-site ion Nb5+ by the Ta5+ ion in the KNN single crystal results show that the decrease in the domain size and increase in the surface roughness with increasing concentration of dopants.

  17. New insights into the initial stages of Ta oxide nanotube formation on polycrystalline Ta electrodes.

    PubMed

    El-Sayed, Hany A; Horwood, Corie A; Abhayawardhana, Anusha D; Birss, Viola I

    2013-02-21

    Ta oxide nanotubes (NTs) were formed by the anodization of Ta at 15 V in a solution of concentrated sulfuric acid containing 0.8-1.0 M hydrofluoric acid. To study the initial stages of NT formation, FESEM images of samples anodized for very short times were obtained. The results contradict the existing explanation of the current-time data collected during anodization, which has persisted in the literature for more than two decades. In addition to providing a first-time morphological study of Ta oxide NT formation at very early stages of anodization, we also propose a new interpretation of the i-t response, showing that pores are already present in the first few milliseconds of anodization and that NTs are formed well before present models predict. This behaviour may also extend to the anodization of other valve metals, such as Al, Ti, Zr, W, and Nb. PMID:23338813

  18. Mechanical properties and microstructures of dental cast Ti-6Nb-4Cu, Ti-18Nb-2Cu, and Ti-24Nb-1Cu alloys.

    PubMed

    Takahashi, Masatoshi; Kikuchi, Masafumi; Takada, Yukyo

    2016-01-01

    The mechanical properties -tensile strength, yield strength, elongation after fracture, and Vickers hardness- and alloy phases of the dental cast alloys Ti-6%Nb-4%Cu, Ti-18%Nb-2%Cu, and Ti-24%Nb-1%Cu were investigated. Ti-6%Nb-4%Cu consisted of a single α-phase, while Ti-18%Nb-2%Cu and Ti-24%Nb-1%Cu consisted of α- and β-phases. The tensile strengths, yield strengths, and hardnesses of these alloys were higher than those of Ti-5%Cu and Ti-30%Nb; however, their breaking elongations were smaller. These differences in the mechanical properties are attributable to solid-solution strengthening or to precipitation strengthening by the dual-phase (α+β) structure. Thus, Ti-Nb-Cu alloys are suitable for use in high-strength dental prostheses, such as implantretained superstructures and narrow-diameter implants. PMID:27477221

  19. Synthesis, properties and structures of NbOF3 complexes and comparisons with NbOCl3 analogues.

    PubMed

    Levason, William; Reid, Gillian; Trayer, Jonathan; Zhang, Wenjian

    2014-03-01

    The first series of complexes of niobium(v) oxide trifluoride, [NbOF3(OPR3)2] (R = Me or Ph), [NbOF3(dppmO2)] (dppmO2 = Ph2P(O)CH2P(O)Ph2), [NbOF3(dmso)2], [NbOF3(tmeda)] (tmeda = Me2N(CH2)2NMe2) and [NbOF3(diimine)] (diimine = 2,2'-bipy, 1,10-phen) have been prepared, either by reaction of the corresponding complexes of NbF5 and hexamethyldisiloxane (HMDSO) in CH2Cl2-MeCN solution, or directly from NbF5, ligand and HMDSO. They were characterised by IR, (1)H, (31)P{(1)H} and (19)F{(1)H} NMR spectroscopy, and X-ray crystal structures are reported for [NbOF3(OPR3)2] (R = Me or Ph) and [NbOF3(dppmO2)]. Complexes of NbOCl3, [NbOCl3(OPPh3)2], [NbOCl3(dppmO2)], [NbOCl3(dppeO2)] (dppeO2 = Ph2P(O)(CH2)2P(O)Ph2), [NbOCl3(tmeda)] and [NbOCl3(diimine)] were made from NbCl5 and HMDSO in MeCN (which forms [NbOCl3(MeCN)2] in situ), followed by addition of the neutral ligand. Their properties are compared with the oxide fluoride analogues. X-ray structures are reported for [NbOCl3(dppmO2)], [NbOCl3(dppeO2)], [NbOCl3(tmeda)] and [NbOCl3(2,2'-bipy)]. The synthesis and spectroscopic characterisation of [MF5L] (M = Nb or Ta; L = OPR3, OAsPh3) and [MF4(diimine)2][MF6] are also described, and the key properties of the four series of complexes compared. PMID:24413623

  20. Solid state 31P MAS NMR spectroscopy and conductivity measurements on NbOPO4 and H3PO4 composite materials

    NASA Astrophysics Data System (ADS)

    Risskov Sørensen, Daniel; Nielsen, Ulla Gro; Skou, Eivind M.

    2014-11-01

    A systematic study of composite powders of niobium oxide phosphate (NbOPO4) and phosphoric acid (H3PO4) has been performed in order to characterize the material's ability to perform as an electrolyte material in medium temperature fuel cells and electrolyzers. Powders of H3PO4 contents between 13.1 and 74.2 M% were produced and characterized with powder X-ray diffraction, 31P MAS NMR and impedance spectroscopy. NMR revealed that a significant degree of dehydration and vaporization of H3PO4 takes place above 200 °C, and increases with temperature. At 500 °C the NbOPO4 and H3PO4 has reacted to form niobium pyrophosphate (Nb2P4O15). Impedance spectroscopy showed an increase in conductivity with increasing acid concentration, whereas the conductivity decreased slightly with increasing temperature. The highest conductivity measured was 2.5·10-3 S/cm for a sample containing 74.2 M% of H3PO4. Lastly, it was shown that NbOPO4 has no significant conductivity of its own.

  1. FAST TRACK COMMUNICATION: Re-entrant-like relaxor behaviour in the new 0.99BaTiO3 0.01AgNbO3 solid solution

    NASA Astrophysics Data System (ADS)

    Lei, Chao; Ye, Zuo-Guang

    2008-06-01

    A new solid solution of 0.99BaTiO3-0.01AgNbO3 was prepared by a solid state reaction. Its structural, dielectric and ferroelectric properties were investigated. Besides the three phase transitions associated with pure BaTiO3, the dielectric permittivity shows an additional peak around 100 °C. This peak exhibits a dielectric relaxation satisfying the Vogel-Fulcher law, indicating typical relaxor behaviour. The relaxor state occurs after the paraelectric to ferroelectric phase transition upon cooling, i.e., inside the ferroelectric phase, indicating a re-entrant-like phenomenon. This unusual phase transition sequence has never been reported in canonical lead-based ferroelectrics. Moreover, the relaxor state arises from a tetragonal phase rather than from a cubic phase as observed in conventional complex perovskite relaxors.

  2. Interpretation of Polar Orders Based on Electric Characterizations: Example of Pb(Yb_{1/2} Nb_{1/2} )O_3 -PbTiO_3 Solid Solution

    NASA Astrophysics Data System (ADS)

    Cochard, Charlotte; Bril, Xavier; Guedes, Orland; Janolin, Pierre-Eymeric

    2016-07-01

    Characterizing the polar order is a fundamental step in the understanding of a material and a necessity for application purposes since each polar order is associated with specific functionalities. Here, using the Pb(Yb_{1/2} Nb_{1/2} )O_3 -PbTiO_3 (PYN-PT) solid solution as an example, we propose to differentiate the polar order based on two simple electrical characterization methods: measurement of the dielectric constant and hysteresis loops. Comparing the dielectric constant measured in high and low electric field conditions, we show that the polarization-electric field measurements may induce out-of-equilibrium phases. The better understanding of the effect of the measuring conditions on the polar order has led us to propose a new sequence of equilibrium polar orders in the PYN-PT solid solution at room temperature.

  3. Phase diagram of the system of (1- x)BiFeO3- x PbFe0.5Nb0.5O3 solid solutions at room temperature

    NASA Astrophysics Data System (ADS)

    Shilkina, L. A.; Pavlenko, A. V.; Reznitchenko, L. A.; Verbenko, I. A.

    2016-03-01

    Experimental samples of solid solutions of the (1- x)BiFeO3- x PbFe0.5Nb0.5O3 (0.00 ≤ x ≤ 1.00, Δ x = 0.025-0.05) system have been prepared according to the conventional ceramic technology. Their structural and dielectric characteristics have been studied. A phase diagram of the system at room temperature has been plotted taking into account the crystallochemical specificity, spatial inhomogeneity, and structural imperfection of the samples. This diagram is characterized by the presence of solid substitutional and interstitial solutions; the formation of concentration ranges with a dominant role of BiFeO3 and PbFe0.5Nb0.5O3; the presence of five single-phase regions, two regions of coexistence of phase states, and three morphotropic regions; and the formation of six regions with a constant experimental unit-cell volume. Correlations between the structural characteristics and dielectric properties of the ceramics under study have been established.

  4. Landau-Ginzburg description of anomalous properties of novel room temperature multiferroics Pb(Fe1/2Ta1/2)x(Zr0.53Ti0.47)1-xO3 and Pb(Fe1/2Nb1/2)x(Zr0.53Ti0.47)1-xO3

    NASA Astrophysics Data System (ADS)

    Glinchuk, Maya D.; Eliseev, Eugene A.; Morozovska, Anna N.

    2016-01-01

    Landau-Ginzburg thermodynamic formalism is used for the description of the anomalous ferroelectric, ferromagnetic, and magnetoelectric properties of Pb(Fe1/2Ta1/2)x(Zr0.53Ti0.47)1-xO3 and Pb(Fe1/2Nb1/2)x(Zr0.53Ti0.47)1-xO3 micro-ceramics. We calculated temperature, composition, and external field dependences of ferroelectric, ferromagnetic, and antiferromagnetic phases transition temperatures, remanent polarization, magnetization, hysteresis loops, dielectric permittivity, and magnetoelectric coupling. Special attention was paid to the comparison of developed theory with experiments. It appeared possible to describe adequately main experimental results including a reasonable agreement between the shape of calculated and measured hysteresis loops and remnant polarization. Since Landau-Ginzburg thermodynamic formalism appertains to single domain properties of a ferroic, we did not aim to describe quantitatively the coercive field under the presence of realistic poly-domain switching. Information about linear and nonlinear magnetoelectric coupling coefficients was extracted from the experimental data. From the fitting of experimental data with theoretical formula, we obtained the composition dependence of Curie-Weiss constant that is known to be inversely proportional to harmonic (linear) dielectric stiffness, as well as the strong nonlinear dependence of anharmonic parameters in free energy. Keeping in mind the essential influence of these parameters on multiferroic properties, the obtained results open the way to govern practically all the material properties with the help of suitable composition choice. A forecast of the strong enough influence of antiferrodistortive order parameter on the transition temperatures and so on the phase diagrams and properties of multiferroics are made on the basis of the developed theory.

  5. In situ high-temperature high-pressure Raman spectroscopy on single-crystal relaxor ferroelectrics PbSc1/2Ta1/2O3 and PbSc1/2Nb1/2O3

    NASA Astrophysics Data System (ADS)

    Waeselmann, N.; Mihailova, B.; Gospodinov, M.; Bismayer, U.

    2013-04-01

    The effect of temperature on the pressure-induced structural changes in perovskite-type (ABO3) relaxor ferroelectrics is studied by in situ high-temperature high-pressure Raman spectroscopy on single crystals of PbSc1/2Ta1/2O3 (PST) and PbSc1/2Nb1/2O3 (PSN), which allowed us to elucidate the interplay between the polar and antiferrodistortive order coexisting on the mesoscopic scale at ambient conditions. High-pressure experiments were carried out at elevated temperatures below and above the characteristic intermediate temperature T*. The results were compared with those obtained at room temperature, which for PST is just above the paraelectric-ferroelectric phase transition TC, whereas for PSN is below TC. It is shown that the first critical pressure pc1, at which a transition from a relaxor to a non-polar rhombohedral state with antiphase octahedral tilt ordering occurs, decreases at elevated temperatures due to the weakening of the polar coupling, which in turn facilitates the evolution of the preexisting medium-range antiferrodistortive order into a long-range order. The critical pressure pc2 of the second phase transition, involving a change in the type of the antiferrodistortive order, is not affected by temperature, i.e. it is independent of the state of polar coupling and is mainly related to the initial correlation length of antiferrodistortive order. The strong influence of temperature on pc1, which occurs only when the mesoscopic polar order is suppressed, emphasizes the importance of coexisting ferroelectric and antiferrodistortive coupling for the occurrence of the relaxor states.

  6. Weyl semimetal state in TaP: experimental discovery

    NASA Astrophysics Data System (ADS)

    Shibayev, Pavel; Hasan Research Group Team

    Despite their extreme rareness in nature, Weyl semimetals provide the first realization of Weyl fermions. After families of tantalum-based (TaAs, TaP) and niobium-based (NbAs, NbP) compounds were recently predicted as Weyl semimetal candidates, our group experimentally realized the Weyl semimetal state in TaP. Angle-resolved photoemission spectroscopy (ARPES) was used to probe the surface features of TaP. Weyl fermion cones and nodes were directly observed in the bulk, and Fermi arcs were observed on the surface. The surface states were found to possess a rich structure, containing topological Fermi arcs and topologically trivial closed contours in the neighborhood of Weyl points. This finding opens up possibilities to study the relationship between trivial and topological surface states on the surface of a Weyl semimetal. By determining the number of chiral edge modes on a closed path enclosing the Weyl node, bulk-boundary correspondence was demonstrated, leading to the establishment of a topologically nontrivial nature of the Weyl semimetal state in TaP. The work at Princeton and Princeton-led ARPES measurements were supported by the Gordon and Betty Moore Foundations EPiQS Initiative through Grant GBMF4547 (Hasan) and by U.S. Department of Energy DE-FG-02-05ER46200.

  7. Preparation and properties of all-solid-state inorganic thin film glass/ITO/WO3/LiNbO3/NiOx/ITO electrochromic device

    NASA Astrophysics Data System (ADS)

    Wu, Zhonghou; Diao, Xungang; Dong, Guobo

    2016-01-01

    The all-thin-film inorganic electrochromic device (ECD) with LiNbO3 as the ion conductor layer was prepared. The ECD was fabricated monolithically in a same vacuum chamber layer by layer using DC reactive sputtering for WO3, NiOx and ITO, and radio frequency (RF) sputtering for LiNbO3. The properties and performance of WO3 thin film and the ECD were studied through X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet-visible spectrometry. WO3 thin film has more than 60% optical modulation with porous amorphous structure. The visible transmittance modulation of the ECD is more than 65%, and the response time of coloring and bleaching are 45 s and 25 s, respectively.

  8. Growth and holographic storage properties of Mg:Fe:LiTaO3 crystal

    NASA Astrophysics Data System (ADS)

    Zhao, Yequan; Fang, Shuangquan; Xu, Wusheng; Xu, Yuheng

    2003-04-01

    Mg:Fe:LiTaO3 crystals were first grown by Czochralski method, and Fe:LiTaO3 crystals, Fe:LiNbO3 and Mg:Fe:LiNbO3 crystals were also grown at the same time. The holographic storage properties of these crystals, such as the exponential gain coefficient, the diffraction efficiency and the response time, were measured by the two-wave coupling method. It was found that the response speed of Mg:Fe:LiTaO3 crystal was five times faster than that of Fe:LiTaO3. The light scattering resistance ability was also measured, and that of Mg:Fe:LiTaO3 crystal was two orders of magnitude higher than that of Fe:LiTaO3 as well as higher than that of Mg:Fe:LiNbO3. The enhancement mechanism of the photorefractive properties for Mg:Fe:LiTaO3 crystal was discussed for the first time.

  9. Releasing metal catalysts via phase transition: (NiO)0.05-(SrTi0.8Nb0.2O3)0.95 as a redox stable anode material for solid oxide fuel cells.

    PubMed

    Xiao, Guoliang; Wang, Siwei; Lin, Ye; Zhang, Yanxiang; An, Ke; Chen, Fanglin

    2014-11-26

    Donor-doped perovskite-type SrTiO3 experiences stoichiometric changes at high temperatures in different Po2 involving the formation of Sr or Ti-rich impurities. NiO is incorporated into the stoichiometric strontium titanate, SrTi0.8Nb0.2O3-δ (STN), to form an A-site deficient perovskite material, (NiO)0.05-(SrTi0.8Nb0.2O3)0.95 (Ni-STN), for balancing the phase transition. Metallic Ni nanoparticles can be released upon reduction instead of forming undesired secondary phases. This material design introduces a simple catalytic modification method with good compositional control of the ceramic backbones, by which transport property and durability of solid oxide fuel cell anodes are largely determined. Using Ni-STN as anodes for solid oxide fuel cells, enhanced catalytic activity and remarkable stability in redox cycling have been achieved. Electrolyte-supported cells with the cell configuration of Ni-STN-SDC anode, La0.8Sr0.2Ga0.87Mg0.13O3 (LSGM) electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode produce peak power densities of 612, 794, and 922 mW cm(-2) at 800, 850, and 900 °C, respectively, using H2 as the fuel and air as the oxidant. Minor degradation in fuel cell performance resulted from redox cycling can be recovered upon operating the fuel cells in H2. Such property makes Ni-STN a promising regenerative anode candidate for solid oxide fuel cells. PMID:25333295

  10. Characterization of SrCo0.7Fe0.2Nb0.1O3-δ cathode materials for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Lü, Shiquan; Yu, Bo; Meng, Xiangwei; Zhao, Xiaoyu; Ji, Yuan; Fu, Chengwei; Zhang, Yongjun; Yang, Lili; Fan, Hougang; Yang, Jinghai

    2015-01-01

    A new cubic perovskite oxide, SrCo0.7Fe0.2Nb0.1O3-δ (SCFN), is investigated as a cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). XRD results show that there are no serious reactions between SCFN and Sm0.2Ce0.8O1.9 (SDC) except a slight peak shift. XPS analysis shows that the transition-metal cations in the SCFN exist in two different valence states, i.e., [Sr2+][Co3+/Co4+]0.7[Fe3+/Fe4+]0.2[Nb4+/Nb5+]0.1O3-δ. The electrical conductivity of the SCFN sample reaches a maximum 304 S cm-1 at 350 °C in air. In order to optimize thermal expansion coefficients (TECs) and electrochemical performance of the SCFN cathode, we fabricate SCFN-xSDC (x = 0, 20, 30, 40, 50, 60, wt%) composite cathodes. The thermal expansion behavior shows that the TECs value of SCFN cathode decreases greatly with SDC addition. The SDC addition reduces the polarization resistance, and the lowest polarization resistance 0.0255 Ω cm2 is achieved at 800 °C for SCFN-50SDC composite cathode. For SCFN-xSDC (x = 0, 40, 50, 60) composites, the maximum power densities of single-cells with SCFN-xSDC cathodes on 300 μm thick SDC electrolyte achieve 417, 557, 630 and 517 mW cm-2 at 800 °C, respectively. These results indicate that SCFN-50SDC composite is a potential cathode material for application in IT-SOFCs.

  11. Characterization of solid-phase welds between Ti-6Al-2Sn-4Zr-2Mo-0. 01Si and Ti-13. 5A1-21. 5Nb titanium aluminide

    SciTech Connect

    Baeslack, W.A. III; Juhas, M.; Fraser, H.L. ); Broderick, T.F. . Materials Directorate)

    1994-12-01

    Dissimilar-alloy welds have been produced between Ti-6Al-2Sn-4Zr-2Mo-0.1Si (wt.%) and Ti-13.5Al-21.5Nb (wt.%) titanium aluminide using three different solid-phase welding processes that create significantly different thermo-mechanical conditions at the weld interface. Exposure to supertransus temperatures, appreciable deformation and rapid cooling of the weld interface region during linear-friction welding promote dynamic recrystallization of beta grains and beta decomposition to fine martensitic products. In contrast, diffusion welding at temperatures below the base metal beta transus temperatures and at relatively low pressures minimizes deformation and microstructural variations in the weld interface region relative to the unaffected base metal. During capacitor-discharge resistance spot welding, extremely rapid heating of the weld interface region to near-solidus temperatures, and subsequent rapid cooling, result in the formation of a metastable, ordered-beta microstructure in the Ti-13.5ASl-21.5Nb and fine alpha-prime martensite in the Ti-6Al-2Sn-4Zr-2Mo-0.1Si.

  12. Solid-state NMR characterization of the structure and thermal stability of hybrid organic-inorganic compounds based on a HLaNb2O7 Dion-Jacobson layered perovskite.

    PubMed

    Cattaneo, Alice S; Ferrara, Chiara; Marculescu, Adriana Mossuto; Giannici, Francesco; Martorana, Antonino; Mustarelli, Piercarlo; Tealdi, Cristina

    2016-08-01

    Dion-Jacobson phases, like MLaNb2O7, are an interesting class of ion-exchangeable layered perovskites possessing electronic and photocatalytic properties. Their protonated and organo-modified homologues, in particular, have already been indicated as promising catalysts. However, the structural analysis of these highly tailorable materials is still incomplete, and both the intercalation process and thermal stability of the included organic moieties are far from being completely understood. In this study, we present a thorough solid-state NMR characterization of HLaNb2O7·xH2O intercalated with different amounts of octylamine, or with decylamine. Samples were analyzed as prepared, and after thermal treatment at different temperatures up to 220 °C. The substitution of pristine proton ions was followed via(1)H MAS NMR spectroscopy, whereas the alkyl chains were monitored through (13)C((1)H) CP MAS experiments. The interactions in the interlayer space were explored using (13)C((1)H) 2D heteronuclear correlation experiments. We demonstrate that some of the protons are involved in the functionalization reaction, and some of them are in close proximity to the alkyl ammonium chains. Heating of the hybrid materials leads first to a rearrangement of the alkyl chains and then to their degradation. The spatial arrangement of the chains, their interactions and the thermal behavior of the materials depend on the extent of the functionalization, and on the nature of the intercalated alkyl ammonium ions. PMID:27440133

  13. Structural and kinetic investigation of the hydride composite Ca(BH4)2 + MgH2 system doped with NbF5 for solid-state hydrogen storage.

    PubMed

    Karimi, Fahim; Pranzas, P Klaus; Pistidda, Claudio; Puszkiel, Julián A; Milanese, Chiara; Vainio, Ulla; Paskevicius, Mark; Emmler, Thomas; Santoru, Antonio; Utke, Rapee; Tolkiehn, Martin; Minella, Christian B; Chaudhary, Anna-Lisa; Boerries, Stefan; Buckley, Craig E; Enzo, Stefano; Schreyer, Andreas; Klassen, Thomas; Dornheim, Martin

    2015-11-01

    Designing safe, compact and high capacity hydrogen storage systems is the key step towards introducing a pollutant free hydrogen technology into a broad field of applications. Due to the chemical bonds of hydrogen-metal atoms, metal hydrides provide high energy density in safe hydrogen storage media. Reactive hydride composites (RHCs) are a promising class of high capacity solid state hydrogen storage systems. Ca(BH4)2 + MgH2 with a hydrogen content of 8.4 wt% is one of the most promising members of the RHCs. However, its relatively high desorption temperature of ∼350 °C is a major drawback to meeting the requirements for practical application. In this work, by using NbF5 as an additive, the dehydrogenation temperature of this RHC was significantly decreased. To elucidate the role of NbF5 in enhancing the desorption properties of the Ca(BH4)2 + MgH2 (Ca-RHC), a comprehensive investigation was carried out via manometric measurements, mass spectrometry, Differential Scanning Calorimetry (DSC), in situ Synchrotron Radiation-Powder X-ray Diffraction (SR-PXD), X-ray Absorption Spectroscopy (XAS), Anomalous Small-Angle X-ray Scattering (ASAXS), Scanning and Transmission Electron Microscopy (SEM, TEM) and Nuclear Magnetic Resonance (NMR) techniques. PMID:26418174

  14. Relaxor Behavior and Dielectric Relaxation in Lead-Free Solid Solutions of (1 - x)(Bi0.5Na0.5TiO3)- x(SrNb2O6)

    NASA Astrophysics Data System (ADS)

    Bajpai, P. K.; Singh, K. N.; Tamrakar, Preeti

    2016-02-01

    Lead-free compositions (1 - x) (Bi0.5Na0.5TiO3)- x(SrNb2O6) (BNT-SN) are synthesized by a simple solid state reaction route. SN diffuse in distorted perovskite BNT for low concentrations of SN ( x ≤ 0.03) and are stabilized in rhombohedral perovskite phase with experimentally observed relative density of the ceramics >92%. A temperature-dependent dielectric response exhibits a broad dielectric peak that shows frequency-dependent shifts towards higher temperatures reflecting typical relaxor behavior. Modified Curie-Weiss law and Lorentz-type empirical relationships are used to fit the dielectric data that exhibit almost complete diffuse phase transition characteristics. In addition, significant dielectric dispersion is observed in a low-frequency regime in both components of the dielectric response and a small dielectric relaxation peak is observed. Cole-Cole plots indicate the poly-dispersive nature of the dielectric relaxation.

  15. Structural, dielectric and magnetic properties of (Pb1-xCax)(Fe0.5Nb0.5)O3 solid solution ceramics

    NASA Astrophysics Data System (ADS)

    Puri, Maalti; Bahel, Shalini; Raevski, I. P.; Narang, Sukhleen Bindra

    2016-06-01

    Ceramic samples of (Pb1-xCax)(Fe0.5Nb0.5)O3 with x=0.0, 0.20, 0.40, 0.45, 0.50, 0.55, 0.60 and 1.0 were fabricated by columbite precursor method. All the synthesized samples have a perovskite structure and unit cell volume decreases with increasing Ca content. The substitution of Ca for Pb has been found to have a pronounced effect on structural, dielectric and magnetic properties. Saturated magnetic loops were observed at room temperature for compositions with x≥0.40. The observed maximal magnetization at room temperature is rather small and varies non-monotonically with increasing Ca contents. It is supposed that room-temperature magnetic properties of (Pb1-xCax)(Fe0.5Nb0.5)O3 ceramics might be due to the presence of ferromagnetic impurity, presumably PbFe12O19 and/or CaFe12O19.

  16. Formation of perovskite solid solutions and lithium-ion conductivity in the compositions, Li 2 xSr 1-2 xM III0.5- xTa 0.5+ xO 3 (M = Cr, Fe, Co, Al, Ga, In, Y)

    NASA Astrophysics Data System (ADS)

    Watanabe, Hiroyuki; Kuwano, Jun

    Formation of solid solutions with perovskite structure and ionic conductivity have been investigated in the systems Li 2 xSr 1-2 xM III0.5- xTa 0.5+ xO 3 (M = Cr, Fe, Co, Al, Ga, In, Y). Perovskite solid solutions formed in ranges of x ≤ 0.25 for M = Fe, Cr, x < 0.22 for Ga and x < ˜ 0.16 for M = Co, In. No single-phase samples of perovskite solid solution were prepared for M = Al, Y. The solid solutions Li 0.5Sr 0.5M III0.25Ta 0.75O 3 (M = Fe, Cr; x = 0.25) had high bulk conductivities of 1.0 × 10 -4 S cm -1 and 6.0 × 10 -5 S cm -1 at room temperature, respectively. The former value was the highest of those reported to date for lithium electrolytes based on tantalates. They were simple cubic perovskites (space group: Pm3 m; a = 396.39 pm for Fe, a = 395.03 pm for Cr), indicating that the Li and Sr ions, and the M (Fe or Cr) and Ta ions are randomly distributed over the A-sites and B-sites, respectively. Frame emission analysis for Li in both sintered pellets revealed that the loss of the Li content took place during sintering. The high conductivity is probably attributed to an A-site deficient perovskite phase resulting from the loss. The perovskite solid solutions in the other systems exhibited conductivities as low as 10 -7-10 -8 S cm -1. The Fe- and Cr-containing solid solutions are the first of tantalate-based perovskites with high Li-ion conductivity.

  17. Development of High Resolution Resonance Ionization Mass Spectrometry for Neutron Dosimetry Technique with93Nb(n,n')93mNb Reaction

    NASA Astrophysics Data System (ADS)

    Tomita, Hideki; Takatsuka, Takaaki; Takamatsu, Takahide; Adachi, Yoshitaka; Furuta, Yujin; Noto, Takuma; Iguchi, Tetsuo; Sonnenschein, Volker; Wendt, Klaus; Ito, Chikara; Maeda, Shigetaka

    2016-02-01

    We have proposed an advanced technique to measure the 93mNb yield precisely by Resonance Ionization Mass Spectrometry, instead of conventional characteristic X-ray spectroscopy. 93mNb-selective resonance ionization is achievable by distinguishing the hyperfine splitting of the atomic energy levels between 93Nb and 93mNb at high resolution. In advance of 93mNb detection, we could successfully demonstrate high resolution resonant ionization spectroscopy of stable 93Nb using an all solid-state, narrow-band and tunable Ti:Sapphire laser system operated at 1 kHz repetition rate.

  18. Determination of Activities of Niobium in Cu-Nb Melts Containing Dilute Nb

    NASA Astrophysics Data System (ADS)

    Wang, Daya; Yan, Baijun; Sichen, Du

    2015-04-01

    The activity coefficients of niobium in Cu-Nb melts were measured by equilibrating solid NbO2 with liquid copper under controlled oxygen potentials in the temperature range of 1773 K to 1898 K (1500 °C to 1625 °C). Either CO-CO2 gas mixture or H2-CO2 gas mixture was employed to obtain the desired oxygen partial pressures. Cu-Nb system was found to follow Henry's law in the composition range studied. The temperature dependence of Henry's constant in the Cu-Nb melts could be expressed as follows: The partial molar excess Gibbs energy change of niobium in Cu-Nb melts can be expressed as follows:

  19. High-field Nb{sub 3}Sn superconductors prepared through a new route

    SciTech Connect

    Tachikawa, K.; Natsuume, M.; Tomori, H.; Kuroda, Y.

    1997-06-01

    Nb{sub 3}Sn superconductors have been prepared through Nb{sub 6}Sn{sub 5} compound powder synthesized by a melt diffusion process from Nb and Sn powders. The Nb{sub 6}Sn{sub 5} powder was mixed with Nb powder in a ball mill. The resulting mixed powder was encased in a Ta tube, and fabricated into a tape. The mechanical mixing of Nb{sub 6}Sn{sub 5} and Nb powder promotes the formation of A15 Nb{sub 3}Sn phase in the subsequent heat treatment, and improves superconducting performance. The Nb{sub 3}Sn tape shows an upper critical field B{sub c2} of nearly 25T at 4.2K after the reaction at 900{degrees}C. The B{sub c2} is still increased by Ti doping. A small amount of Cu addition decreases the optimum reaction temperature to 850{degrees}C. Present Nb{sub 3}Sn specimen exhibits considerably larger normal state resistivity than that of bronze-processed Nb{sub 3}Sn, which may be the origin of enhanced B{sub c2} in the present Nb{sub 3}Sn specimen.

  20. Pressure dependence of the monoclinic phase in (1–x)Pb(Mg1/3Nb2/3)O3-xPbTiO₃ solid solutions

    SciTech Connect

    Ahart, Muhtar; Sinogeikin, Stanislav; Shebanova, Olga; Ikuta, Daijo; Ye, Zuo-Guang; Mao, Ho-kwang; Cohen, R. E.; Hemley, Russell J.

    2012-12-26

    We combine high-pressure x-ray diffraction, high-pressure Raman scattering, and optical microscopy to investigate a series of (1–x)Pb(Mg1/3Nb2/3)O3-xPbTiO₃ (PMN-xPT) solid solutions (x=0.2, 0.3, 0.33, 0.35, 0.37, 0.4) in diamond anvil cells up to 20 GPa at 300 K. The Raman spectra show a peak centered at 380 cm⁻¹ starting above 6 GPa for all samples, in agreement with previous observations. X-ray diffraction measurements are consistent with this spectral change indicating a structural phase transition; we find that the triplet at the pseudocubic (220) Bragg peak merges into a doublet above 6 GPa. Our results indicate that the morphotropic phase boundary region (x=0.33–0.37) with the presence of monoclinic symmetry persists up to 7 GPa. The pressure dependence of ferroelectric domains in PMN-0.32PT single crystals was observed using a polarizing optical microscope. The domain wall density decreases with pressure and the domains disappear at a modest pressure of 3 GPa. We propose a pressure-composition phase diagram for PMN-xPT solid solutions.

  1. Pressure dependence of the monoclinic phase in (1–x)Pb(Mg1/3Nb2/3)O3-xPbTiO₃ solid solutions

    DOE PAGESBeta

    Ahart, Muhtar; Sinogeikin, Stanislav; Shebanova, Olga; Ikuta, Daijo; Ye, Zuo-Guang; Mao, Ho-kwang; Cohen, R. E.; Hemley, Russell J.

    2012-12-26

    We combine high-pressure x-ray diffraction, high-pressure Raman scattering, and optical microscopy to investigate a series of (1–x)Pb(Mg1/3Nb2/3)O3-xPbTiO₃ (PMN-xPT) solid solutions (x=0.2, 0.3, 0.33, 0.35, 0.37, 0.4) in diamond anvil cells up to 20 GPa at 300 K. The Raman spectra show a peak centered at 380 cm⁻¹ starting above 6 GPa for all samples, in agreement with previous observations. X-ray diffraction measurements are consistent with this spectral change indicating a structural phase transition; we find that the triplet at the pseudocubic (220) Bragg peak merges into a doublet above 6 GPa. Our results indicate that the morphotropic phase boundary regionmore » (x=0.33–0.37) with the presence of monoclinic symmetry persists up to 7 GPa. The pressure dependence of ferroelectric domains in PMN-0.32PT single crystals was observed using a polarizing optical microscope. The domain wall density decreases with pressure and the domains disappear at a modest pressure of 3 GPa. We propose a pressure-composition phase diagram for PMN-xPT solid solutions.« less

  2. Study of Sr2Mg(Mo0.8Nb0.2)O6-δ as anode material for solid oxide fuel cells using hydrocarbons as fuel

    NASA Astrophysics Data System (ADS)

    Escudero, M. J.; Gómez de Parada, I.; Fuerte, A.; Daza, L.

    2013-12-01

    Sr2Mg(Mo0.8Nb0.2)O6-δ (SMMNb) was investigated as potential anode material of solid oxide fuel cells (SOFCs) for direct oxidation of methane. The compound was prepared by solid state reaction, followed by annealing under reducing atmosphere of 10% H2/N2 at 900 °C. The structural and morphological properties of fresh and reduced material were characterized by XRD, XPS and SEM. Additionally, catalytic properties towards oxidation of methane, electrical properties in reducing atmosphere as well as thermal and chemical compatibility with common SOFC electrolytes were investigated. These results reveal a double perovskite single phase in the fresh and reduced compound and, after reduction, a change in the niobium valence was observed. SMMNb shows a good activity for methane partial oxidation as well as combined reforming reaction. The material presents a semiconductor behaviour with n-type electronic conduction and an excellent thermal compatibility with SOFC electrolytes such as SDC, GDC and LSGM, based on similarity of values of TEC. However, this material reacts with zirconia-based electrolytes (YSZ and ScSZ). Although, a low electrochemical activity for H2 and CH4 oxidation was found, SMMNb demonstrates high tolerance to carbon deposition when the anode is exposed to methane.

  3. Room temperature neutron diffraction and magnetic studies of multiferroic Pb0.9Bi0.1Fe0.55Nb0.45O3 solid solution

    NASA Astrophysics Data System (ADS)

    Dadami, S. T.; Matteppanavar, S.; Shivaraja, I.; Rayaprol, S.; Deshpande, S. K.; Angadi, B.

    2016-05-01

    The Pb0.9Bi0.1Fe0.55Nb0.45O3 (PBFNO) solid solution was synthesized by single step solid state reaction method and the optimized parameters are 700°C for 2hr (calcination) and 800°C for 3hr (sintering). The formation of desired material was confirmed using X-Ray Diffraction (XRD) and Neutron Diffraction (ND) studies. The structural and magnetic properties of the sintered pellets were investigated at room temperature (RT) through XRD, ND and Magnetic (M-H) studies. The structural analysis was carried out by Rietveld refinement through the Full Prof program. Rietveld refined XRD and ND patterns confirms the monoclinic structure with Cm space group and obtained cell parameters from the ND data are a = 5.651(2) Å, b = 5.658(2) Å, c = 4.005(1) Å and α = 90°, β = 89.98(1)°, γ = 90°. RT M-H curve studies have been carried out. It shows the clear opening of hysteresis (M-H) loop, is evidenced as the existence of weak ferromagnetism at RT. The M-H data shows existence weak ferromagnetism embedded in an antiferromagnetic matrix structure. The dielectric constant with frequency shows the formation of barrier layers at the grain and grain boundary interfaces gives rise to interfacial space charge polarization.

  4. Investigation of the growth and the holographic storage properties of Fe:LiTaO3 crystal

    NASA Astrophysics Data System (ADS)

    Liu, Caixia; Zhang, Tao; Zhao, Shouzhi

    2005-01-01

    The LiTaO3 crystal doped with 0.03 wt% Fe2O3 was grown in a diameter-controlled Czochraski equipment using Si-Mo bar heater furnace. The photo-damage resistance ability, exponential gain coefficient, diffraction efficiency and response time of Fe:LiTaO3 and Fe:LiNbO3 crystals were measured. The measured results showed that the photo-damage resistance ability of Fe:LiTaO3 crystal was as much as 5 times higher than that of Fe:LiNbO3, the response speed of Fe:LiTaO3 crystal was improved one order of magnitude than that of Fe:LiNbO3, and the exponential gain coefficient and diffraction efficient of Fe:LiTaO3 crystal were smaller than that of Fe:LiNbO3, respectively. Using Fe:LiTaO3 crystal as recording medium, the obtained image was clear and complete in the holographic associative memory experiment using self-pump phase conjugate reflector.

  5. Synthesis of a 12R-type hexagonal perovskite solid solution Sr3NdNb(3-x)Ti(x)O(12-δ) and the influence of acceptor doping on electrical properties.

    PubMed

    Chinelatto, Adilson L; Boulahya, Khalid; Pérez-Coll, Domingo; Amador, Ulises; Tabacaru, Corina; Nicholls, Simon; Hoelzel, Markus; Sinclair, Derek C; Mather, Glenn C

    2015-04-28

    A solid solution forms for Sr3NdNb(3-x)Ti(x)O(12-δ) with approximate limits 0 ≤ x ≤ 0.06. The system crystallizes with a 12R-type hexagonal perovskite structure in the space group R3, as determined by neutron diffraction and selected area electron diffraction. The electrical properties of the end members have been investigated by impedance spectroscopy in the temperature range 550-800 °C under various gas atmospheres and as a function of oxygen and water-vapour partial pressure. Proton transport dominates under wet oxidising conditions in the temperature range 550-700 °C, as confirmed by the H(+)/D(+) isotope effect. Acceptor doping considerably enhances proton conductivity with a value of 3.3 × 10(-6) S cm(-1) for the bulk response of x = 0.06 at 700 °C in moistened air. The presence of a -¼ slope for both doped and undoped samples in the range 10(-19) ≤ pO2 ≤ 10(-8) atm at 900 °C indicates n-type transport under reducing conditions following the extrinsic model attributable to acceptor centres. The conductivity is essentially independent of pO2 at 600 °C under dry oxidising conditions, consistent with oxide-ion transport; a positive power-law dependence at higher temperature indicates extrinsic behaviour and a significant electron-hole contribution. The dielectric constant at RT of nominally stoichiometric Sr3NdNb3O12 is εr ∼ 37, with a moderately high quality factor of Q × f ∼ 16,400 GHz at fr ∼ 6.4 GHz. The temperature coefficient of resonant frequency of x = 0 is τf ∼ 12 ppm °C(-1), which lowers to -3 ppm °C(-1) for the Ti-doped phase x = 0.06. PMID:25811695

  6. Sodium niobate adsorbents doped with tantalum (TaV) for the removal of bivalent radioactive ions in waste waters.

    PubMed

    Paul, Blain; Yang, Dongjiang; Martens, Wayde N; Frost, Ray L

    2011-04-01

    Sodium niobates doped with different amounts of tantalum (Ta(V)) were prepared via a thermal reaction process. It was found that pure nanofibrils and bar like solids can be obtained when tantalum is introduced into the reaction system. For the well crystallized fibril solids, the Na(+) ions are difficult to exchange, and the radioactive ions such as Sr(2+) and Ra(2+) just deposit on the surface of the fibers during the sorption process, resulting in lower sorption capacity and distribution coefficients (K(d)). However, the bar like solids are poorly crystallized and have many exchangeable Na(+) ions. They are able to remove highly hazardous bivalent radioactive isotopes such as Sr(2+) and Ra(2+) ions. Even in the presence of many Na(+) ions, they also have higher K(d). More importantly, such sorption finally intelligently triggers considerable collapse of the structure, resulting in permanent entrapment of the toxic bivalent cations in the solids, so that they can be safely disposed of. This study highlights new opportunities for the preparation of Nb-based adsorbents to efficiently remove toxic radioactive ions from contaminated water. PMID:21266294

  7. Growth and optical properties of Mg, Fe Co-doped LiTaO3 crystal

    NASA Astrophysics Data System (ADS)

    Fang, Shuangquan; Ma, Decai; Zhang, Tao; Ling, Furi; Wang, Biao

    2006-02-01

    Mg, Fe double-doped LiTaO3 and LiNbO3 crystals have been grown by Czochralski method. The optical properties were measured by two-beam coupling experiments and transmitted facula distortion method. The results showed that the photorefractive response speed of Mg:Fe:LiTaO3 was about three times faster than that of Fe:LiTaO3, whereas the photo-damage resistance was two orders of magnitude higher than that of Fe:LiTaO3. In this paper, site occupation mechanism of impurities was also discussed to explain the high photo-damage resistance and fast response speed in Mg:Fe:LiTaO3 crystal.

  8. Magnetotransport of single crystalline NbAs

    DOE PAGESBeta

    Ghimire, N. J.; Luo, Yongkang; Neupane, M.; Williams, D. J.; Bauer, E. D.; Ronning, F.

    2015-03-27

    We report transport measurement in zero and applied magnetic field on a single crystal of NbAs. Transverse and longitudinal magnetoresistance in the plane of this tetragonal structure does not saturate up to 9 T. In the transverse configuration (H ∥ c, I ⊥ c) it is 230,000% at 2 K. The Hall coefficient changes sign from hole-like at room temperature to electron-like below ~150 K. The electron carrier density and mobility calculated at 2 K based on a single band approximation are 1.8 × 1019 cm-3 and 3.5 × 105 cm2/Vs, respectively. These values are similar to reported values formore » TaAs and NbP, and further emphasize that this class of noncentrosymmetric, transition-metal monopnictides is a promising family to explore the properties of Weyl semimetals and the consequences of their novel electronic structure.« less

  9. Strategy for stabilization of the antiferroelectric phase (Pbma) over the metastable ferroelectric phase (P2{sub 1}ma) to establish double loop hysteresis in lead-free (1−x)NaNbO{sub 3}-xSrZrO{sub 3} solid solution

    SciTech Connect

    Guo, Hanzheng Randall, Clive A.; Shimizu, Hiroyuki; Mizuno, Youichi

    2015-06-07

    A new lead-free antiferroelectric solid solution system, (1−x)NaNbO{sub 3}-xSrZrO{sub 3}, was rationalized through noting the crystal chemistry trend, of decreasing the tolerance factor and an increase in the average electronegativity of the system. The SrZrO{sub 3} doping was found to effectively stabilize the antiferroelectric (P) phase in NaNbO{sub 3} without changing its crystal symmetry. Preliminary electron diffraction and polarization measurements were presented which verified the enhanced antiferroelectricity. In view of our recent report of another lead-free antiferroelectric system (1−x)NaNbO{sub 3}-xCaZrO{sub 3} [H. Shimizu et al. “Lead-free antiferroelectric: xCaZrO{sub 3} - (1−x)NaNbO{sub 3} system (0 ≤ x ≤ 0.10),” Dalton Trans. (published online)], the present results point to a general strategy of utilizing tolerance factor to develop a broad family of new lead-free antiferroelectrics with double polarization hysteresis loops. We also speculate on a broad family of possible solid solutions that could be identified and tested for this important type of dielectric.

  10. Atomic and electronic structure of Ni-Nb metallic glasses

    SciTech Connect

    Yuan, C. C.; Yang, Y.-F. Xi, X. K.

    2013-12-07

    Solid state {sup 93}Nb nuclear magnetic resonance spectroscopy has been employed to investigate the atomic and electronic structures in Ni-Nb based metallic glass (MG) model system. {sup 93}Nb nuclear magnetic resonance (NMR) isotropic metallic shift of Ni{sub 60}Nb{sub 35}Sn{sub 5} has been found to be ∼100 ppm lower than that of Ni{sub 60}Nb{sub 35}Zr{sub 5} MG, which is correlated with their intrinsic fracture toughness. The evolution of {sup 93}Nb NMR isotropic metallic shifts upon alloying is clearly an electronic origin, as revealed by both local hyperfine fields analysis and first-principle computations. This preliminary result indicates that, in addition to geometrical considerations, atomic form factors should be taken into a description of atomic structures for better understanding the mechanical behaviors of MGs.

  11. Abnormal alloying behaviour observed in an immiscible Zr Nb system

    NASA Astrophysics Data System (ADS)

    Wang, T. L.; Liang, S. H.; Li, J. H.; Tai, K. P.; Liu, B. X.

    2008-05-01

    For the immiscible Zr-Nb system characterized by a positive heat of formation (+6 kJ mol-1), thermodynamic calculation showed that the Gibbs free energy of the properly designed Zr-Nb multilayered films could be elevated to a higher level than that of the corresponding amorphous phase as well as the supersaturated solid solutions. Accordingly, nano-sized Zr-Nb multilayered films were prepared and then irradiated by 200 keV xenon ions. It was found that amorphous phases could be obtained within a composition range 12-92 at% of Nb. Also, two metastable crystalline phases of fcc structures with different lattice parameters were also obtained. Molecular dynamic simulation was carried out, based on a proven realistic Zr-Nb potential, to reveal the atomistic mechanism of the solid-state crystal-to-amorphous transition. A brief discussion on the formation of the two metastable crystalline phases is presented.

  12. Solidification modeling of Nb bearing superalloys

    SciTech Connect

    DuPont, J.N.; Marder, A.R.; Robino, C.V.

    1997-08-01

    The solidification behavior of experimental Ni base and Fe base superalloys containing Nb, Si, and C was studied using differential thermal analysis (DTA) and microstructural characterization techniques. The solidification reaction sequences responsible for microstructural development were found to be similar to those expected in the Ni-Nb-C ternary system, where the solute-rich interdendritic liquid exhibited two eutectic-type reactions at the terminal stages of solidification: L {yields} ({gamma} + NbC) and L {yields} ({gamma} + Laves). A pseudo ternary {gamma}-Nb-C approach was developed to provide a quantitative description of solidification behavior for these experimental alloys. Solute redistribution calculations in the model are based on a previous approach developed by Mehrabian and Flemings, with modifications made to account for the high diffusion rate of C in the solid. Solidification parameters for Nb and C were determined through DTA and electron probe microanalysis techniques and used as inputs to the model. Reasonable agreement is found between calculated volume fractions of the {gamma}/NbC and {gamma}/Laves constituents and those measured experimentally. The modeling results permit detailed descriptions of the relation between alloy composition and microstructural evolution during solidification.

  13. High temperature coarsening of Cr2Nb precipitates in Cu-8 Cr-4 Nb alloy

    NASA Technical Reports Server (NTRS)

    Anderson, Kenneth Reed

    1996-01-01

    A new high-temperature-strength, high-conductivity Cu-Cr-Nb alloy with a CrNb ratio of 2:1 was developed to achieve improved performance and durability. The Cu-8 Cr4 Nb alloy studied has demonstrated remarkable thermal and microstructural stability after long exposures at temperatures up to 0.98 T(sub m). This stability was mainly attributed to the slow coarsening kinetics of the Cr2Nb precipitates present in the alloy. At all temperatures, the microstructure consists of a bimodal and sometimes trimodal distribution of strengthening Cr2Nb precipitates, depending on precipitation condition, i.e. from liquid or solid solution, and cooling rates. These precipitates remain in the same size range, i.e. large precipitates of approximately I pm, and small precipitates less dm 300 nm, and effectively pin the grain boundaries thus retaining a fine grain size of 2.7 micro-m after 100 h at 1323 K. (A relatively small number of Cr-rich and Nb-rich particles were also present.) This grain boundary pinning and sluggish coarsening of Cr2Nb particles explain the retention of good mechanical properties after prolonged holding at very high temperatures, e.g., 75% of the original hardness after aging for 100 h at 1273 K. Application of LSW-based coarsening models indicated that the coarsening kinetics of the large precipitates are most likely governed by grain boundary diffsion and, to a lesser extent, volume diffusion mechanisms.

  14. Efficient and stable iron based perovskite La0.9Ca0.1Fe0.9Nb0.1O3-δ anode material for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Kong, Xiaowei; Zhou, Xiaoliang; Tian, Yu; Wu, Xiaoyan; Zhang, Jun; Zuo, Wei; Gong, Xiaobo; Guo, Zhanhu

    2016-06-01

    A novel La0.9Ca0.1Fe0.9Nb0.1O3-δ (LCFNb) perovskite for solid oxide fuel cells (SOFCs) anode is prepared by means of the citrate-nitrate route and composited with Ce0.8Sm0.2O1.9 (SDC) by impregnation method to form nano-scaled LCFNb/SDC anode catalytic layers. The single cells with LCFNb and LCFNb/SDC impregnated anodes both achieve relatively high power output with maximum power densities (MPDs) reaching up to 610, 823 mW·cm-2 in H2 at 800 °C, respectively, presenting a high potential of LCFNb for use as SOFCs anode. The power outputs of the single cells with LCFNb/SDC composite anode in CO and syngas (COsbnd H2 mixture) are almost identical to that in H2 at each testing temperature. This composite anode also presents excellent durability in both H2 and CO for as long as 50 h, showing desirable anti-reduction and carbon deposition resistance abilities. Besides, the cell output is stable in 100 ppm H2Ssbnd H2 atmospheres for 20 h at a current density of 600 mA·cm-2 with negligible sulfur accumulation on the anode surface. Hence, a novel iron based perovskite LCFNb anode with remarkable cell performance, carbon deposition resistance and sulfur poisoning tolerance for SOFCs is successfully obtained.

  15. Room-temperature paramagnetoelectric effect in magnetoelectric multiferroics Pb(Fe1/2Nb1/2)O3 and its solid solution with PbTiO3

    NASA Astrophysics Data System (ADS)

    Laguta, V. V.; Morozovska, A. N.; Eliseev, E. A.; Raevski, I. P.; Raevskaya, S. I.; Sitalo, E. I.; Prosandeev, S. A.; Bellaiche, L.

    2016-06-01

    We have observed the magnetoelectric response at room temperature and above in high-resistive ceramics made of multiferroic Pb(Fe1/2Nb1/2)O3 (PFN) and PFN-based solid solution 0.91PFN-0.09PbTiO3 (PFN-PT). The value of the paramagnetoelectric (PME) coefficient shows a pronounced maximum near the ferroelectric-to-paraelectric phase transition temperature, T_C, and then decreases sharply to zero for T>T_C. The maximal PME coefficient in PFN is about 4x10(-18) s/A. The theoretical description of the PME effect, within the framework of a Landau theory of phase transitions allowing for realistic temperature dependences of spontaneous polarization, dielectric and magnetic susceptibilities, qualitatively reproduces well the temperature dependence of the PME coefficient. In particular, the Landau theory predicts the significant increase of the PME effect at low temperatures and near the temperature of the paraelectric-to-ferroelectric phase transition, since the PME coefficient is equal to the product of the spontaneous polarization, dielectric permittivity, square of magnetic susceptibility and the coefficient quantifying the strength of the biquadratic magnetoelectric coupling

  16. Efficient and stable iron based perovskite La0.9Ca0.1Fe0.9Nb0.1O3-δ anode material for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Kong, Xiaowei; Zhou, Xiaoliang; Tian, Yu; Wu, Xiaoyan; Zhang, Jun; Zuo, Wei; Gong, Xiaobo; Guo, Zhanhu

    2016-06-01

    A novel La0.9Ca0.1Fe0.9Nb0.1O3-δ (LCFNb) perovskite for solid oxide fuel cells (SOFCs) anode is prepared by means of the citrate-nitrate route and composited with Ce0.8Sm0.2O1.9 (SDC) by impregnation method to form nano-scaled LCFNb/SDC anode catalytic layers. The single cells with LCFNb and LCFNb/SDC impregnated anodes both achieve relatively high power output with maximum power densities (MPDs) reaching up to 610, 823 mW·cm-2 in H2 at 800 °C, respectively, presenting a high potential of LCFNb for use as SOFCs anode. The power outputs of the single cells with LCFNb/SDC composite anode in CO and syngas (COsbnd H2 mixture) are almost identical to that in H2 at each testing temperature. This composite anode also presents excellent durability in both H2 and CO for as long as 50 h, showing desirable anti-reduction and carbon deposition resistance abilities. Besides, the cell output is stable in 100 ppm H2Ssbnd H2 atmospheres for 20 h at a current density of 600 mA·cm-2 with negligible sulfur accumulation on the anode surface. Hence, a novel iron based perovskite LCFNb anode with remarkable cell performance, carbon deposition resistance and sulfur poisoning tolerance for SOFCs is successfully obtained.

  17. Quench tests and FEM analysis of Nb3Al Rutherford cables and small racetrack magnets

    SciTech Connect

    Yamada, R.; Kikuchi, A.; Chlachidze, G.; Ambrosio, G.; Andreev, N.; Barzi, E.; Carcagno, R.; Kashikin, V.V.; Kotelnikov, S.; Lamm, M.; Novitski, I.; /Fermilab /Tsukuba Magnet Lab. /KEK, Tsukuba

    2008-12-01

    In collaboration between NIMS and Fermilab, we have made copper stabilized Nb{sub 3}Al Rutherford cables, using Nb-matrixed and Ta-matrixed strands. First these cables were investigated at high current in low self field using a flux pump. Using these Rutherford cables, we built and tested small racetrack magnets. The magnet made with the Nb-matrixed strand showed the flux jump instability in low field. The small racetrack magnet wound with the Ta-matrixed Nb{sub 3}Al Rutherford cable was very stable at 4.5 K operation without any instability, as well as at 2.2 K operation. With the successful operation of the small racetrack magnet up to its short sample data, the feasibility of the Nb{sub 3}Al strand and its Rutherford cable for their application to high field magnets is established. The characteristics of Nb{sub 3}Al Rutherford cable is compared with that of the Nb{sub 3}Sn Rutherford cable and the advantages of Nb{sub 3}Al Rutherford cable are discussed.

  18. Redetermination of tantalum penta­bromide, (TaBr5)2

    PubMed Central

    Habermehl, Katja; Pantenburg, Ingo; Meyer, Gerd

    2010-01-01

    Crystals of di-μ-bromido-bis­[tetra­bromidotantalum(V)], (TaBr5)2, were obtained by recrystallization at 773 K. A first crystal structure study of (TaBr5)2 was reported by Rolsten [J. Am. Chem. Soc. (1958) ▶, 80, 2952–2953], who analysed the powder diffraction pattern and came to the conclusion that it crystallizes isotypically with (NbBr5)2 in a primitive ortho­rhom­bic cell. These findings are not in agreement with our current results of a monoclinic C-centred structure. (TaBr5)2 is isotypic with α-(NbCl5)2. The crystal structure contains [TaBr6] octa­hedra sharing common edges forming [TaBr5]2 dimers. Two crystallographically independent dimers with symmetries m and 2/m and Ta⋯Ta distances of 4.1574 (11) and 4.1551 (15) Å, respectively, are present in the structure. PMID:21588474

  19. The role of Fe on the solubility of Nb in α-Zr

    NASA Astrophysics Data System (ADS)

    Woo, O. T.; Griffiths, M.

    2009-01-01

    The solid solubility of Nb in α-Zr is an important parameter that has a potential impact on the corrosion properties of Zr-Nb alloys at reactor operating temperatures, i.e. below the monotectoid temperature. Work on dilute Zr-Nb alloys has shown that Fe is a common impurity that confounds the assessment of the solid solubility limit for Nb in Zr. This is because Fe has a very low solubility limit and it forms precipitates with both Nb and Zr. To assess the effect of Fe on the phases formed in the binary Zr-Nb alloy system, alloys containing 0.1-0.7 wt% Nb and <11 to 470 wt ppm Fe were heat-treated at temperatures between 575 °C and 600 °C and examined by transmission electron microscopy. Results indicate that, even at a concentration ⩽ 24 ppm, Fe readily combines with Nb to form precipitates in the alloys with Nb contents in the range of 0.20 to 0.29 wt%. However, β-Nb particles were not observed for these same alloys and were only seen when the Nb content was ⩾ 0.49 wt%. Because β-Nb particles were not found in the 0.29 wt% Nb alloy and the precipitation was estimated to have a negligible effect on the amount of Nb remaining in solution (reduced by <0.001 wt%), it is proposed that the solubility limit of Nb in a true binary Zr-Nb alloy would be between 0.29 and 0.49 wt%.

  20. Influence of temperature on luminescence of terbium ions in LiNbO{sub 3}

    SciTech Connect

    Ryba-Romanowski, W.; Golab, S.; Dominiak-Dzik, G.; Palatnikov, M. N.; Sidorov, N. V.

    2001-06-04

    Single crystals of LiNbO{sub 3} doped with terbium were grown by the Czochralski method and their optical properties were examined. It has been found that, in contrast to isostructural LiTaO{sub 3}:Tb, the terbium ions in LiNbO{sub 3} exhibit intense luminescence at low temperatures only, up to about 150 K. At this temperature, a luminescence quenching mechanism with activation energy of 0.22 eV is switched on. As a consequence, the luminescence of LiNbO{sub 3}:Tb is reduced to a negligible level at room temperature. {copyright} 2001 American Institute of Physics.

  1. Evaluation of pulsed laser deposited SrNb0.1Co0.9O3-δ thin films as promising cathodes for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Chen, Dengjie; Chen, Chi; Gao, Yang; Zhang, Zhenbao; Shao, Zongping; Ciucci, Francesco

    2015-11-01

    SrNb0.1Co0.9O3-δ (SNC) thin films prepared on single-crystal yttria-stabilized zirconia (YSZ) electrolytes are evaluated as promising cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Geometrically well-defined polycrystalline SNC thin films with low surface roughness and high surface oxygen vacancy concentration are successfully fabricated by pulsed laser deposition. The thin films are characterized by basic techniques, e.g., X-ray diffraction for phase structure identification, scanning electron microscopy and atomic force microscopy for microstructures measurement, and X-ray photoelectron spectroscopy for elements quantification. Electrochemical impedance spectroscopy (EIS) is used to investigate oxygen reduction reaction activities of SNC thin films in symmetric electrochemical cells. Current collectors (Ag paste, Ag strip, and Au strip) are found to have negligible impact on polarization resistances. A slight decrease of the electrode polarization resistances is observed after adding a samarium doped ceria (SDC) buffer layer between SNC and YSZ. SNC thin-film electrodes exhibit low electrode polarization resistances, e.g., 0.237 Ω cm2 (SNC/SDC/YSZ/SDC/SNC) and 0.274 Ω cm2 (SNC/YSZ/SNC) at 700 °C and 0.21 atm, demonstrating the promise of SNC materials for IT-SOFCs. An oxygen reduction reaction mechanism of SNC thin films is also derived by analyzing EIS at temperature of 550-700 °C under oxygen partial pressure range of 0.04-1 atm.

  2. Superconducting properties of (Nb,Ti)/sub 3/Sn wires fabricated by the bronze process

    SciTech Connect

    Suenaga, M.; Okuda, S.; Sabatini, R.; Itoh, K.; Luhman, T.S.

    1981-01-01

    A study was made of the influence of the alloying addition of Ti in the Nb core on the superconducting critical properties since (1) Ti is less expensive than Nb or Ta, (2) Ti has a lower melting temperature than Ta and Nb, thus making the alloy fabrication easier, (3) Ti-Nb alloys are also known to be easily fabricated in composite wires with Cu, and finally (4) it appears that an increased normal-state resistivity rho/sub n/, and therefore the upper critical field H/sub c2/, will lead to enhanced J/sub c/ at high fields. It is expected that the addition of Ti will increase the rho/sub n/ of the Nb/sub 3/Sn. As shown in preliminary results, small additions of Ti to the Nb can significantly enhance critical-current densities of Nb/sub 3/Sn at high magnetic fields (H > 12 T). A detailed account of this study is given.

  3. Magnetization, Low Field Instability and Quench of RHQT Nb(3)Al Strands

    SciTech Connect

    Yamada, R.; Wake, M.; Kikuchi, A.; Velev, V.; /Fermilab

    2009-01-01

    Since 2005, we made and tested three RHQT Nb{sub 3}Al strands, one with Nb matrix and two with Ta matrix, which are fully stabilized with Cu electroplating. We observed anomalously large magnetization curves extending beyond 1 to 1.5 Tesla with the F1 Nb matrix strand at 4.2 K, when we measured its magnetization with a balanced coil magnetometer. This problem was eliminated with the Ta matrix strands operating at 4.2 K. But with these strands a similar but smaller anomalous magnetization was observed at 1.9 K. We studied these phenomena with FEM. With the F1 Nb matrix strand, it is explained that at low external field, inter-filamentary coupling currents in the outer layers of sub-elements create a shielding effect. It reduces the inside field, keeps the inside Nb matrix superconductive, and stands against a higher outside field beyond the Hc of Nb. At an even higher external field, the superconductivity of the whole Nb matrix collapses and releases a large amount of energy, which may cause a big quench. Depending on the size of the energy in the strand or the cable, a magnet could quench, causing the low field instability. Some attempt to analyze the anomaly with FEM is presented.

  4. Efficient Room-Temperature Activation of Methane by TaN(+) under C-N Coupling.

    PubMed

    Zhou, Shaodong; Li, Jilai; Schlangen, Maria; Schwarz, Helmut

    2016-09-12

    The thermal reaction of diatomic tantalum nitride cation [TaN](+) with methane has been explored using FT-ICR mass spectrometry complemented by high-level quantum chemical calculation; based on this combined experimental/computational approach, mechanistic aspects of this novel, highly efficient C-N coupling process have been uncovered. In distinct contrast to [TaN](+) , its lighter congeners [VN](+) and [NbN](+) are inert towards methane under ambient conditions, and the origins of the remarkably variable efficiencies of the three metal nitrides are uncovered by CCSD(T) calculations. PMID:27510819

  5. Structural and electronic investigations of PbTa4O11 and BiTa7O19 constructed from α-U3O8 types of layers

    NASA Astrophysics Data System (ADS)

    Boltersdorf, Jonathan; Maggard, Paul A.

    2015-09-01

    The PbTa4O11 and BiTa7O19 phases were prepared by ion-exchange and solid-state methods, respectively, and their structures were characterized by neutron time-of-flight diffraction and Rietveld refinement methods (PbTa4O11, R 3 (No. 146), a=6.23700(2) Å, c=36.8613(1) Å; BiTa7O19, P 6 bar c 2 (No. 188), a=6.2197(2) Å, c=20.02981(9) Å). Their structures are comprised of layers of TaO6 octahedra surrounded by three 7-coordinate Pb(II) cations or two 8-coordinate Bi(III) cations. These layers alternate down the c-axis with α-U3O8 types of single and double TaO7 pentagonal bipyramid layers. In contrast to earlier studies, both phases are found to crystallize in noncentrosymmetric structures. Symmetry-lowering structural distortions within PbTa4O11, i.e. R 3 bar c →R3, are found to be a result of the displacement of the Ta atoms within the TaO7 and TaO6 polyhedra, towards the apical and facial oxygen atoms, respectively. In BiTa7O19, relatively lower reaction temperatures leads to an ordering of the Bi/Ta cations within a lower-symmetry structure, i.e., P63/mcm→ P 6 bar c 2 . In the absence of Bi/Ta site disorder, the Ta-O-Ta bond angles decrease and the Ta-O bond distances increase within the TaO7 double layers. Scanning electron microscopy images reveal two particle morphologies for PbTa4O11, hexagonal rods and finer irregularly-shaped particles, while BiTa7O19 forms as aggregates of irregularly-shaped particles. Electronic-structure calculations confirm the highest-energy valence band states are comprised of O 2p-orbitals and the respective Pb 6s-orbital and Bi 6s-orbital contributions. The lowest-energy conduction band states are composed of Ta 5d-orbital contributions that are delocalized over the TaO6 octahedra and layers of TaO7 pentagonal bipyramids. The symmetry-lowering distortions in the PbTa4O11 structure, and the resulting effects on its electronic structure, lead to its relatively higher photocatalytic activity compared to similar structures without

  6. INRAD work at TA-55

    SciTech Connect

    Kleinschmidt, Phillip D; Lacy, Keith A; Hahn, Wendy K; Shonrock, Clinton O

    2011-01-18

    The INRAD Facility at TA-55 is described. Safety considerations in operating the facility are described in the Detailed Operating Procedure (DOP) format. Other considerations on the future operation of the facility are discussed.

  7. Metabolism of triiodothyroacetic acid (TA3) in rat liver. I. Deiodination of TA3 and TA3 sulfate by microsomes.

    PubMed

    Rutgers, M; Heusdens, F A; Visser, T J

    1989-07-01

    The deiodination of the acetic acid side-chain analogs of T3 as well as 3,3'-diiodothyronine (3,3'-T2) was investigated by incubating 125I-labeled 3,3',5-triiodothyroacetic acid (TA3) and 3,3'-diiodothyroacetic acid (3,3'-TA2) with rat liver microsomes at 37 C and pH 7.2 in the presence of 5 mM dithiothreitol. TA3 sulfate (TA3S) and 3,3'-TA2S were also tested as substrate since sulfation is known to accelerate T3 and 3,3'-T2 conversion. Reaction products were analyzed on Sephadex LH-20 and HPLC. TA3 underwent only inner ring deiodination (IRD), but 3,3'-TA2 was equally converted by IRD and outer ring deiodination (ORD). TA3S was metabolized very rapidly by IRD to 3,3'-TA2S which was only observed transiently due to its rapid deiodination predominantly in the outer ring. Kinetic studies under initial reaction rate conditions yielded apparent Michaelis-Menten (Km) values (micromolar) of 1.8 for TA3, 0.8 for 3,3'-TA2, and 0.004 for TA3S, and 0.02 for 3,3'-TA2S and Vmax values (picomoles per min/mg protein) of 174 for TA3, 49 for 3,3'-TA2, 21 for TA3S, and 63 for 3,3'-TA2S. The Vmax/Km ratios for the IRD of TA3 and TA3S were 16 and 930 times higher, respectively, relative to T3. Deiodinations were sensitive to propylthiouracil inhibition, indicating the involvement of the type I iodothyronine deiodinase. Furthermore, the iodothyroacetic acid derivatives competitively inhibited the ORD of rT3 with apparent inhibition constant (Ki) values (0.45 microM for TA3, 4 nM for TA3S, and 0.04 microM for 3,3'-TA2S) in agreement with corresponding Km values. We conclude that 1) TA3 and 3,3'-TA2 are better substrates than T3 and 3,3'-T2 for the type I deiodinase of rat liver; 2) the IRD of TA3 and ORD of 3,3'-TA2 are markedly enhanced by sulfation similar to the parent iodothyronines; and 3) TA3S in the best known substrate for IRD due to its very high affinity for the type I deiodinase. PMID:2737156

  8. Correlation of crystal structure and microwave dielectric properties of Nd1.02(Nb1-xTax)0.988O4 ceramic.

    PubMed

    Zhang, Ping; Zhao, Yonggui; Liu, Jian; Song, Zhenkun; Xiao, Mi; Wang, Xiuyu

    2015-03-21

    The phase structures of Nd1.02(Nb1-xTax)0.988O4 ceramics were analyzed via multiphase structure refinement. The X-ray diffraction patterns of Nd1.02(Nb1-xTax)0.988O4 showed that the monoclinic fergusonite structure of NdNbO4 and a second phase NdTa7O19 were obtained. The oxygen octahedron distortion was investigated according to the supercell of the NdNbO4 ceramic. The correlations between packing fractions, bond valences and microwave dielectric properties were discussed. For the main phase NdNbO4, as the polarizabilities increased, the ε increased. The Q × f value was mainly attributed to the packing fraction. With the increase of bond valence of the B-site and the oxygen octahedron distortion, the τf value decreased. The substitution of Ta(5+) for Nb(5+) effectively influenced the microstructure and the microwave dielectric properties of NdNbO4 ceramics. Optimal microwave dielectric properties can be obtained for Nd1.02(Nb0.94Ta0.06)0.988O4 ceramics at x = 0.06. PMID:25698378

  9. A Review of the Properties of Nb3Sn and Their Variation with A15Composition, Morphology and Strain State

    SciTech Connect

    Godeke, Arno

    2006-03-27

    Significant efforts can be found throughout the literature to optimize the current carrying capacity of Nb{sub 3}Sn superconducting wires. The achievable transport current density in wires depends on the A15 composition, morphology and strain state. The A15 sections in wires contain, due to compositional inhomogeneities resulting from solid state diffusion A15 formation reactions, a distribution of superconducting properties. The A15 grain size can be different from wire to wire and is also not necessarily homogeneous across the A15 regions. Strain is always present in composite wires, and the strain state changes as a result of thermal contraction differences and Lorentz forces in magnet systems. To optimize the transport properties it is thus required to identify how composition, grain size and strain state influence the superconducting properties. This is not accurately possible in inhomogeneous and spatially complex systems such as wires. This article therefore gives an overview of the available literature on simplified, well defined(quasi--)homogeneous laboratory samples. After more than 50 years of research on superconductivity in Nb{sub 3}Sn, a significant amount of results are available, but these are scattered over a multitude of publications. Two reviews exist on the basic properties of A15 materials in general, but no specific review for Nb{sub 3}Sn is available. This article is intended to provide such an overview. It starts with a basic description of the Niobium--Tin intermetallic. After this it maps the influence of Sn content on the electron--phonon interaction strength and on the field-temperature phase boundary. The literature on the influence of Cu, Ti and Ta additions will then be briefly summarized.This is followed by a review on the effects of grain size and strain. The article is concluded with a summary of the main results.

  10. Catalytic efficiency of Nb and Nb oxides for hydrogen dissociation

    SciTech Connect

    Isobe, Shigehito; Kudoh, Katsuhiro; Hino, Satoshi; Hashimoto, Naoyuki; Ohnuki, Somei; Hara, Kenji

    2015-08-24

    In this letter, catalytic efficiency of Nb, NbO, Nb{sub 2}O{sub 3}, NbO{sub 2}, and Nb{sub 2}O{sub 5} for dissociation and recombination of hydrogen were experimentally investigated. On the surface of Nb and Nb oxides in a gas mixture of H{sub 2} and D{sub 2}, H{sub 2} and D{sub 2} molecules can be dissociated to H and D atoms; then, H{sub 2}, D{sub 2}, and HD molecules can be produced according to the law of probability. With increase of frequency of the dissociation and recombination, HD ratio increases. The ratio of H{sub 2} and HD gas was analyzed by quadrupole mass spectrometry. As a result, NbO showed the highest catalytic activity towards hydrogen dissociation and recombination.

  11. Crystal Structures of U(Ta,W) 5O 16and U(Ta,W) 2O 8Revealed by High-Resolution Transmission Electron Microscopy

    NASA Astrophysics Data System (ADS)

    Askeljung, Charlotta; Sundberg, Margareta

    1999-04-01

    Two new phases, U(Ta,W)5O16and U(Ta,W)2O8, were formed by solid state reaction of the binary oxides (U3O8, Ta2O5, and WO3) and Ta metal powder. They were characterized by high-resolution transmission electron microscopy and X-ray powder diffraction techniques. The phases are orthorhombic with the following unit cell dimensions: U(Ta,W)5O16,a=10.052(1),b=7.3207(5), andc=7.9600(4) Å; and U(Ta,W)2O8,a= 20.232(2),b=7.4520(4), andc=4.0652(2) Å. Both structures are built up of (Ta,W)O6-octahedra arranged as ReO3-type slabs two octahedra wide. In U(Ta,W)5O16these slabs are connected by a thin lamella consisting of hexagonal UO8-bipyramids and (Ta,W)O6-octahedra alternating along both thebandcaxes. EDS analysis indicated a composition of UTa1.5W3.5O16. The structure is related to UMo5O16, but with every other layer displaced through {1}/{2}b. The second phase, U(Ta,W)2O8, is isotypic with the orthorhombic modification of UMo2O8, in which the ReO3-type slabs are intergrown with lamellas of edge-sharing pentagonal UO7-bipyramids. The composition UTa0.5W1.5O8was obtained by EDS analysis. Some defects in terms of three-octahedra-wide ReO3-type slabs have been observed in U(Ta,W)5O16crystals. EDS analyses of such crystals showed a high-tungsten and a low-tantalum content.

  12. Precipitates in Nb and Nb-V microalloyed X80 pipeline steel.

    PubMed

    Li, Zhongyi; Liu, Delu; Zhang, Jianping; Tian, Wenhuai

    2013-08-01

    Precipitates in two X80 pipeline steels were studied by transmission electron microscopy equipped with an energy filtering system. The steels are microalloyed with niobium and niobium-vanadium (Nb-V), respectively, and produced by continuous hot rolling. Besides the precipitates TiN and (Ti, Nb) (C, N), which were 10-100 nm in size, a large number of precipitates smaller than 10 nm distributed in the two steels have been observed. In the Nb-V microalloyed steel, only a few titanium nitrides covered by vanadium compounds on the surface have been observed. It is inferred that the vanadium exists mainly in the matrix as a solid solution element. The fact has been accepted that there was no contribution to the precipitation strengthening of the X80 steel by adding 0.04-0.06% vanadium under the present production process. By contrast, the toughness of the Nb-V steel is deteriorated. Therefore, a better toughness property of the Nb microalloyed X80 results from the optimum microalloying composition design and the suitable accelerating cooling after hot rolling. PMID:23920176

  13. Explorations of New SHG Materials in the Alkali-Metal-Nb(5+)-Selenite System.

    PubMed

    Cao, Xue-Li; Hu, Chun-Li; Kong, Fang; Mao, Jiang-Gao

    2015-11-16

    Standard high-temperature solid-state reactions of NaCl, Nb2O5, and SeO2 resulted in two new sodium selenites containing a second-order Jahn-Teller (SOJT) distorted Nb(5+) cation, namely, Na2Nb4O7(SeO3)4 (P1̅; 1) and NaNbO(SeO3)2 (Cmc21; 2). Compound 1 exhibits an unusual 3D [Nb4O7(SeO3)4](2-) anionic network composed of 2D [Nb4O11(SeO3)2](6-) layers which are further bridged by additional SeO3(2-) anions via corner sharing; the 2D [Nb4O11(SeO3)2](6-) layer is formed by unusual quadruple [Nb4O17](14-) niobium oxide chains of corner-sharing NbO6 octahedra being further interconnected by selenite anions via Nb-O-Se bridges. The polar compound 2 features a 1D [NbO(SeO3)2](-) anionic chain in which two neighboring Nb(5+) cations are bridged by one oxo and two selenite anions. The alignments of the polarizations from the NbO6 octahedra in 2 led to a strong SHG response of ∼7.8 × KDP (∼360 × α-SiO2), which is the largest among all phases found in metal-Nb(5+)-Se(4+)/metal-Nb(5+)-Te(4+)-O systems. Furthermore, the material is also type I phase matchable. The above experimental results are consistent with those based on DFT theoretical calculations. Thermal stabilities and optical properties for both compounds are also reported. PMID:26513233

  14. A New Niobium Cluster Oxychloride Built from Interconnected Nb 6Cl 12O 6 Units: Na 0.21Nb 6Cl 10.5O 3

    NASA Astrophysics Data System (ADS)

    Gulo, Fakhili; Perrin, Christiane

    2002-01-01

    The new Na0.21Nb6Cl10.5O3 oxychloride was synthesized by a solid state route, from NaCl, Nb2O5, NbCl5, and Nb, heated at 680°C for 2 weeks. The structure was determined by single-crystal X-ray diffraction. It crystallizes in the trigonal system (Roverline3c space group, a=11.5048(1) Å, c=44.9446(7) Å, V=5151.88(10) Å3, Z=12). The structure is built from [(Nb6Cli9Oi3) Oa3Cla3] units, which share their inner and apical oxygens forming pseudolayers with short Nb-Nb intercluster distances (3.399 Å). Along the c axis, these layers are interconnected by apical-apical chlorines. The sodium atoms are randomly distributed in the voids arranged between two adjacent layers, in a deformed chlorine prismatic coordination. The developed formula Na0.21 [(Nb6Cli9Oi-a3/2)Oa-i3/2Cla-a3/2] leads to a number of valence electrons per cluster close to 14. This oxychloride will be compared to CsNb6Cl12O2 which we have previously isolated and which was the first example of a Nb6 oxyhalide involving Oi-a, Oa-i interunit connections.

  15. Microstructural Investigations On Ni-Ta-Al Ternary Alloys

    SciTech Connect

    Negache, M.; Souami, N.

    2010-01-05

    The Ni-Al-Ta ternary alloys in the Ni-rich part present complex microstructures. They are composed of multiple phases that are formed according to the nominal composition of the alloy, primary Ni(gamma), Ni{sub 3}Al(gamma'), Ni{sub 6}AlTa(tau{sub 3}), Ni{sub 3}Ta(delta) or in equilibrium: two solid phases (gamma'-tau{sub 3}), (tau{sub 3}-delta), (tau{sub 3}-gamma), (gamma-delta) or three solid phases (gamma'-tau{sub 3}-delta). The nature and the volume fraction of these phases give these alloys very interesting properties at high temperature, and this makes them attractive for specific applications. We have developed a series of ternary alloys in electric arc furnace, determining their solidification sequences using Differential Thermal Analysis (DTA), characterized by SEM-EDS, X-ray diffraction and by a microhardness tests. The follow-up results made it possible to make a correlation between the nature of the formed phases and their solidifying way into the Ni{sub 75}Al{sub x}Ta{sub y} (x+y = 25at.%) system, which are varied and complex. In addition to the solid solution Ni (gamma), the formed intermetallics compounds (gamma', tau{sub 3} and delta) has been identified and correlated with a complex balance between phases.We noticed that the hardness increases with the tantalum which has a hardening effect and though the compound Ni{sub 3}Ta(delta) is the hardest. The below results provide a better understanding of the complex microstructure of these alloys.

  16. EUSO-TA prototype telescope

    NASA Astrophysics Data System (ADS)

    Bisconti, Francesca

    2016-07-01

    EUSO-TA is one of the prototypes developed for the JEM-EUSO project, a space-based large field-of-view telescope to observe the fluorescence light emitted by cosmic ray air showers in the atmosphere. EUSO-TA is a ground-based prototype located at the Telescope Array (TA) site in Utah, USA, where an Electron Light Source and a Central Laser Facility are installed. The purpose of the EUSO-TA project is to calibrate the prototype with the TA fluorescence detector in presence of well-known light sources and cosmic ray air showers. In 2015, the detector started the first measurements and tests using the mentioned light sources have been performed successfully. A first cosmic ray candidate has been observed, as well as stars of different magnitude and color index. Since Silicon Photo-Multipliers (SiPMs) are very promising for fluorescence telescopes of next generation, they are under consideration for the realization of a new prototype of EUSO Photo Detector Module (PDM). The response of this sensor type is under investigation through simulations and laboratory experimentation.

  17. Phase relation and microstructure of NbCr{sub 2} Laves intermetallics in ternary Nb-Cr-X alloy systems

    SciTech Connect

    Yoshida, M.; Takasugi, T.

    1997-12-31

    The isothermal phase diagrams of ternary alloy systems Nb-Cr-V and Nb-Cr-Mo are determined by metallography, X-ray diffraction (XRD) and transmission electron microscopy (TEM) equipped with energy dispersive X-ray (EDX). In two alloy systems, the C15 NbCr{sub 2} Laves phases are equilibrated directly with bcc solid solution without forming any intermediate phases. Relatively large amount of ternary elements V and Mo are soluble in the C15 NbCr{sub 2} Laves phases. It is shown that the C15 Laves phases extend along directions so that V occupies Cr site while Mo occupies Nb site. Also, characteristic structure containing micro twins and stacking faults is observed in the C15 Laves phase alloyed with Mo. Bcc phase has a wider solid solution range in the X(=V and Mo)-rich side than the Nb-rich and Cr-rich sides. A variety of duplex microstructures are observed depending on alloy system and alloy composition.

  18. High dielectric constant observed in (1 − x)Ba(Zr{sub 0.07}Ti{sub 0.93})O{sub 3}–xBa(Fe{sub 0.5}Nb{sub 0.5})O{sub 3} binary solid-solution

    SciTech Connect

    Kruea-In, Chatchai; Eitssayeam, Sukum; Pengpat, Kamonpan; Rujijanagul, Gobwute

    2012-10-15

    Binary solid-solutions of the (1 − x)Ba(Zr{sub 0.07}Ti{sub 0.93})O{sub 3}–xBa(Fe{sub 0.5}Nb{sub 0.5}O{sub 3}) system, with 0.1 ≤ x ≤ 0.9,were fabricated via a solid-state processing technique. X-ray diffraction analysis revealed that all samples exhibited a single perovskite phase. The BaFe{sub 0.5}Nb{sub 0.5}O{sub 3} also promoted densification and grain growth of the system. Dielectric measurements showed that all samples displayed a relaxor like behavior. The x = 0.1 sample presented a dielectric-frequency and temperature with low loss tangent (<0.07 at 10 kHz). For x > 0.2 samples, the dielectric data showed a broad dielectric constant–temperature curve with a giant dielectric characteristic. In addition, a high dielectric constant > 50,000 (at 10 kHz and temperature > 150 °C) was observed for the x = 0.9 sample.

  19. Magnetotransport of single crystalline NbAs

    SciTech Connect

    Ghimire, N. J.; Luo, Yongkang; Neupane, M.; Williams, D. J.; Bauer, E. D.; Ronning, F.

    2015-03-27

    We report transport measurement in zero and applied magnetic field on a single crystal of NbAs. Transverse and longitudinal magnetoresistance in the plane of this tetragonal structure does not saturate up to 9 T. In the transverse configuration (H ∥ c, I ⊥ c) it is 230,000% at 2 K. The Hall coefficient changes sign from hole-like at room temperature to electron-like below ~150 K. The electron carrier density and mobility calculated at 2 K based on a single band approximation are 1.8 × 1019 cm-3 and 3.5 × 105 cm2/Vs, respectively. These values are similar to reported values for TaAs and NbP, and further emphasize that this class of noncentrosymmetric, transition-metal monopnictides is a promising family to explore the properties of Weyl semimetals and the consequences of their novel electronic structure.

  20. The Crystallization Clinic-A TA Orientation Exercise

    NASA Astrophysics Data System (ADS)

    Kandel, Marjorie

    1999-01-01

    Our orientation exercise for TAs in the organic laboratories is a Crystallization Clinic, and the main feature is a contest. Each TA has a different unknown solid to recrystallize. The products are judged by the students in the organic lab courses. Beauty of the crystals is the single criterion. The contest serves to refresh the TAs' technique and to give them empathy with the beginning students.

  1. Correlation between microstructure and corrosion behavior of Zr-Nb binary alloy

    NASA Astrophysics Data System (ADS)

    Jeong, Yong Hwan; Lee, Kyoung Ok; Kim, Hyun Gil

    2002-04-01

    To investigate the correlation between microstructure and corrosion characteristics of Zr-Nb alloy, the microstructural observation and corrosion test with the change of cooling rate from beta temperature and the variation of Nb content were performed. The oxide characterization was also carried out by synchrotron XRD and TEM. When the Nb is contained less than solid solution limit (0.6 wt%) in Zr matrix, the difference of corrosion rate was not observed in spite of showing the significant changes of microstructures with cooling rate. While, when the Nb content in the alloy is more than 0.6 wt%, the corrosion properties were deteriorated with increasing the supersaturated Nb concentration in matrix and increasing the area fraction of β Zr. Also it was observed that the supersaturated Nb in matrix was more effective to decrease the corrosion resistance than the β Zr phase in the same Nb containing alloy, while the equilibrium Nb concentration below solubility limit in the matrix played an important role to enhance the corrosion resistance. During the corrosion testing in steam at 400 °C, the formation of β Nb phase in water-quenched specimen would result in the reduction of Nb concentration in matrix. Thus, the corrosion resistance is enhanced with the formation of β Nb phase. It is suggested from this study that the equilibrium Nb concentration below solubility limit in α matrix would be a more dominant factor in the enhancement of corrosion resistance than β phase (β Nb or β Zr), supersaturated Nb, precipitate, and internal microstructure such as twin, dislocation and plate.

  2. TA-55 change control manual

    SciTech Connect

    Blum, T.W.; Selvage, R.D.; Courtney, K.H.

    1997-11-01

    This manual is the guide for initiating change at the Plutonium Facility, which handles the processing of plutonium as well as research on plutonium metallurgy. It describes the change and work control processes employed at TA-55 to ensure that all proposed changes are properly identified, reviewed, approved, implemented, tested, and documented so that operations are maintained within the approved safety envelope. All Laboratory groups, their contractors, and subcontractors doing work at TA-55 follow requirements set forth herein. This manual applies to all new and modified processes and experiments inside the TA-55 Plutonium Facility; general plant project (GPP) and line item funded construction projects at TA-55; temporary and permanent changes that directly or indirectly affect structures, systems, or components (SSCs) as described in the safety analysis, including Facility Control System (FCS) software; and major modifications to procedures. This manual does not apply to maintenance performed on process equipment or facility SSCs or the replacement of SSCs or equipment with documented approved equivalents.

  3. Fabrication of Nb3Al superconducting bulks by mechanical alloying method

    NASA Astrophysics Data System (ADS)

    Qi, Ming; Pan, Xi Feng; Zhang, Ping Xiang; Cui, Li Jun; Li, Cheng Shan; Yan, Guo; Chen, Yong Liang; Zhao, Yong

    2014-06-01

    Since it can directly prepare the Nb-Al supersaturated solid solution, mechanical alloying is thought as a promising method to make high-performance Nb3Al superconductors at a low temperature annealing condition, without the complicated rapid heating, quenching and transformation (RHQT) process. In this paper, we investigate the effects of milling time, the content of Al and annealing temperature on phase formation and superconducting properties of mechanical alloying Nb3Al bulks in detail. The study results show that Nb-Al supersaturated solid solution could be obtained by high energy ball milling, as long as the Nb-Al blended powder is ball milled for 1 h, even the amorphous phase appears with the ball milling time prolonging to 10 h, the Nb-Al intermetalics do not come out either. Amorphous phase is hardly beneficial to synthesizing the Nb3Al phase, instead, it will make the products impurity. By optimizing the milling time, elements composition and annealing temperature , pure Nb3Al phase is obtained and the highest onset superconducting transition temperature (Tc-onset) reaches 15.8 K and the critical current density (Jc) 106 A/cm2 at 8 K without outer field. This paper also discusses the main reasons that affect the superconducting properties of mechanical alloying Nb3Al superconductor.

  4. Nioboaeschynite-(Ce), Ce(NbTi)O6

    PubMed Central

    Morrison, Shaunna M.; Downs, Robert T.; Domanik, Kenneth J.; Yang, Hexiong; Doell, Donald

    2012-01-01

    Nioboaeschynite-(Ce), ideally Ce(NbTi)O6 [cerium(III) niobium(V) titanium(IV) hexa­oxide; refined formula of the natural sample is Ca0.25Ce0.79(Nb1.14Ti0.86)O6], belongs to the aeschynite mineral group which is characterized by the general formula AB 2(O,OH)6, where eight-coordinated A is a rare earth element, Ca, Th or Fe, and six-coordinated B is Ti, Nb, Ta or W. The general structural feature of nioboaeschynite-(Ce) resembles that of the other members of the aeschynite group. It is characterized by edge-sharing dimers of [(Nb,Ti)O6] octa­hedra which share corners to form a three-dimensional framework, with the A sites located in channels parallel to the b axis. The average A—O and B—O bond lengths in nioboaeschynite-(Ce) are 2.471 and 1.993 Å, respectively. Moreover, another eight-coordinated site, designated as the C site, is also located in the channels and is partially occupied by A-type cations. Additionally, the refinement revealed a splitting of the A site, with Ca displaced slightly from Ce (0.266 Å apart), presumably resulting from the crystal-chemical differences between the Ce3+ and Ca2+ cations. PMID:22904701

  5. Nb(x)Ti(1-x)N Superconducting-Nanowire Single-Photon Detectors

    NASA Technical Reports Server (NTRS)

    Stern, Jeffrey A.; Farr, William H.; Leduc, Henry G.; Bumble, Bruce

    2008-01-01

    Superconducting-nanowire single-photon detectors (SNSPDs) in which Nb(x)Ti(1-x)N (where x<1) films serve as the superconducting materials have shown promise as superior alternatives to previously developed SNSPDs in which NbN films serve as the superconducting materials. SNSPDs have potential utility in optical communications and quantum cryptography. Nb(x)Ti(1-x)N is a solid solution of NbN and TiN, and has many properties similar to those of NbN. It has been found to be generally easier to stabilize Nb(x)Ti(1-x)N in the high-superconducting-transition temperature phase than it is to so stabilize NbN. In addition, the resistivity and penetration depth of polycrystalline films of Nb(x)Ti(1-x)N have been found to be much smaller than those of films of NbN. These differences have been hypothesized to be attributable to better coupling at grain boundaries within Nb(x)Ti(1-x)N films.

  6. Study of Structural Phase Transitions in Na1-xSrx/2NbO3

    NASA Astrophysics Data System (ADS)

    Bahuguna, Rajni; Wankhede, M. G.; Mishra, S. K.; Shinde, A. B.; Krishna, P. S. R.

    2015-02-01

    The solid solution Na1-xSrx/2NbO3 is prepared by solid state reaction method. Detailed analyses of powder x-ray diffraction data clearly suggest a change of structure from ABO3 perovskite (NaNbO3 like) to complicated Tungsten Bronze SrNb2O6 like. The presence of additional reflections clearly suggests that cell multiplicity for x>=0.20 is different to that of pure NaNbO3. For composition x>=0.20, the lattice parameters are related with pseudocubic perovskite cell parameters as follows: Ao= 4ap, Bo= 3bp Co= 5cp. The lattice parameters and volume increases monotonically with increasing concentration of Sr2+ in NaNbO3 matrix.

  7. Processing of High-Performance Nb3Sn Wires Through a New Diffusion Reaction Using sn Based Alloys

    NASA Astrophysics Data System (ADS)

    Tachikawa, K.; Sasaki, H.; Yamaguchi, M.; Hayashi, Y.; Nakata, K.; Takeuchi, T.

    2010-04-01

    Tightly consolidated Sn-Ta and Sn-B based alloys have been prepared by the reaction among constituent metal powders at 750-775° C. Sn-Ta and Sn-B based alloys exhibit quite similar microstructures. A small amount of Ti addition seems to improve the bonding between Ta or B particles and Sn matrix. Nb3Sn wires have been fabricated by the Jelly Roll (JR) and Multi-rod (MR) process using Sn based alloy sheet and rod, respectively. Thick Nb3Sn layers with nearly stoichiometric A15 composition are synthesized through a new diffusion mechanism between Nb and Sn based alloy. Bc2 (4.2 K)'s of 26.9 T (mid) and 26.5 T (mid) have been obtained in the JR and MR processed wires, respectively, using Sn-Ta based alloy. These wires exhibit enough non-Cu Jc to be used above 20 T and 4.2 K. Tc of JR wires using Sn-B based sheet is 18.14 K (offset) which is slightly higher than that of wires using Sn-Ta based sheet.

  8. Wetting, spreading and reactions at liquid/solid interfaces

    NASA Astrophysics Data System (ADS)

    Pask, J. A.; Tomsia, A. P.

    1980-07-01

    Chemical reactions of glass metal interfaces are investigated. Chemical (thermodynamic) stable equilibrium at glass metal interfaces is established when the liquid glass becomes saturated with the low valence oxide of the metal. Stable or metastable equilibrium conditions at glass metal interfaces result in a constant contact angle in a sessile drop experiment. If chemical equilibrium is absent, then a driving force exists for the occurrence of a reaction to attain equilibrium. All reactions that take place contribute to the maintenance of the necessary saturation of the liquid and solid at the interface with the solid substrate oxide in order to realize chemical bonding across the interface. Spreading always occurs when the solid metal is an active participant in these reactions. Examples showing the development of these principles are based on systems of sodium disilicate with Fe, Co, Ni, Fe-Ni alloys, Pt, Ag, Au, Cu, Ta, W, Mo, Nb, Zr and Cr. The final structure and composition of the glass metal interfacial zone are determined by the kinetics and thermodynamics of the reactions that occur.

  9. Superconductivity in the T2 phase of the Ta-Ge-B system

    NASA Astrophysics Data System (ADS)

    Correa, Lucas Eduardo; Nunes, Carlos; Coelho, Gilberto; Silva, Antonio Augusto; Fisk, Zack; Jefferson Machado, Antonio

    2012-02-01

    In the Ta-Ge system the αTa5Ge3 phase is not superconductor. Considering the high solubility of this phase for boron, in this work it has been evaluated the effect of boron doping in αTa5Ge3 on the electrical, heat capacity and magnetic properties of the produced materials. It has been shown that boron doping promoted superconductivity for some specific composition. The Ta5GeB2, also named T2 phase, crystallizes in the tetragonal symmetry with Cr5B3 prototype structure. In this composition the sample presented the maximum superconducting critical temperature (3.4 K). Others systems that exhibit the existence of the T2 phase present superconductivity such as Mo5SiB2 (Tc ˜5.5 K), Nb5Si3-xBx (Tcmax ˜7.8 K) and W5SiB2 (Tc ˜5.5 K). Thus, Ta5GeB2 is more one example.

  10. Comparison of low-voltage field emission from TaC and tungsten fiber arrays

    SciTech Connect

    Cochran, J.K.; Lee, K.J.; Hill, D.N.

    1988-01-01

    Field emitter array (FEA) devices were constructed using thin-film fabrication techniques based on in situ eutectic composites containing either TaC or NbC fibers in a NiCr alloy matrix. The emission characteristics of the TaC devices were measured and compared to those of W--ZrO/sub 2/ FEA's. Both devices produced the linear Fowler--Nordheim plots common to all field emission devices; however, the array current density of the TaC FEA's was more than two orders of magnitude lower than that of the W--ZrO/sub 2/ FEA's. This was primarily due to the lower fiber density and lower field enhancement of the carbide fiber devices. If it were possible to produce cathode geometries comparable to those of the W--ZrO/sub 2/ FEA's, a theoretical analysis indicates that emission performance of the TaC devices would be superior because of the lower work function of TaC. However, post-emission observations indicated that the carbide fiber emitters failed more readily than the tungsten emitters under comparable operating conditions.

  11. Effect of A Site and Oxygen Vacancies on the Structural and Electronic Properties of Lead-Free KTa0.5Nb0.5O3 Crystal

    NASA Astrophysics Data System (ADS)

    Yang, Wenlong; Wang, Li; Lin, Jiaqi; Li, Xiaokang; Xiu, Hanjiang; Shen, Yanqing

    2016-04-01

    The structural and electronic properties of lead-free potassium tantalite niobate KTa0.5Nb0.5O3 (KTN) with A site vacancies V_{{K}}0 , V_{{K}}^{1 - } and oxygen vacancies V_{{O}}0 , V_{{O}}^{2 + } , were investigated by first-principles calculations, which indicated that A site vacancies V_{{K}}0 are likely to form in the KTN compared with V_{{K}}^{1 - } , and oxygen vacancies V_{{O}}^{2 + } are likely to form compared with V_{{O}}0 in the KTN according to the investigation of formation energy. The results show that K and O vacancies have significant influence on the atomic interactions of the atoms and the electronic performance of the materials. And Ta atoms are more easily influenced by the K and O vacancies than the Nb atoms from the atomic displacements in KTN with K and O vacancies. The investigation of density of state indicates that the compensation of electrons in KTN with vacancies make the hybridization become stronger among Ta d, Nb d and O p orbitals. Besides, Mulliken population of all the Ta and Nb atoms in KTN with charged vacancies are influenced by complement electrons. The strength of the Nb-O bond is stronger than Ta-O based on the changes of bond lengths and Mulliken population.

  12. Effect of A Site and Oxygen Vacancies on the Structural and Electronic Properties of Lead-Free KTa0.5Nb0.5O3 Crystal

    NASA Astrophysics Data System (ADS)

    Yang, Wenlong; Wang, Li; Lin, Jiaqi; Li, Xiaokang; Xiu, Hanjiang; Shen, Yanqing

    2016-07-01

    The structural and electronic properties of lead-free potassium tantalite niobate KTa0.5Nb0.5O3 (KTN) with A site vacancies V_{{K}}0 , V_{{K}}^{1 - } and oxygen vacancies V_{{O}}0 , V_{{O}}^{2 + } , were investigated by first-principles calculations, which indicated that A site vacancies V_{{K}}0 are likely to form in the KTN compared with V_{{K}}^{1 - } , and oxygen vacancies V_{{O}}^{2 + } are likely to form compared with V_{{O}}0 in the KTN according to the investigation of formation energy. The results show that K and O vacancies have significant influence on the atomic interactions of the atoms and the electronic performance of the materials. And Ta atoms are more easily influenced by the K and O vacancies than the Nb atoms from the atomic displacements in KTN with K and O vacancies. The investigation of density of state indicates that the compensation of electrons in KTN with vacancies make the hybridization become stronger among Ta d, Nb d and O p orbitals. Besides, Mulliken population of all the Ta and Nb atoms in KTN with charged vacancies are influenced by complement electrons. The strength of the Nb-O bond is stronger than Ta-O based on the changes of bond lengths and Mulliken population.

  13. Calculations of electron stopping powers for 41 elemental solids over the 50 eV to 30 keV range with the full Penn algorithm

    NASA Astrophysics Data System (ADS)

    Shinotsuka, H.; Tanuma, S.; Powell, C. J.; Penn, D. R.

    2012-01-01

    We present mass collision electron stopping powers (SPs) for 41 elemental solids (Li, Be, graphite, diamond, glassy C, Na, Mg, Al, Si, K, Sc, Ti, V, Cr, Fe, Co, Ni, Cu, Ge, Y, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Cs, Gd, Tb, Dy, Hf, Ta, W, Re, Os, Ir, Pt, Au, and Bi) that were calculated from experimental energy-loss-function data with the full Penn algorithm for electron energies between 50 eV and 30 keV. Improved sets of energy-loss functions were used for 19 solids. Comparisons were made of these SPs with SPs calculated with the single-pole approximation, previous SP calculations, and experimental SPs. Generally satisfactory agreement was found with SPs from the single-pole approximation for energies above 100 eV, with other calculated SPs, and with measured SPs.

  14. Ultrasonic transducers based on undoped lead-free (K0.5Na0.5)NbO3 ceramics.

    PubMed

    Bah, Micka; Giovannelli, Fabien; Schoenstein, Frederic; Brosseau, Christophe; Deschamps, Jean-Robert; Dorvaux, Frédéric; Haumesser, Lionel; Le Clezio, Emmanuel; Monot-Laffez, Isabelle

    2015-12-01

    Lead zirconate titanate (PZT) ceramics are the dominant piezoelectric elements for non-destructive evaluation (NDE) and ultrasonic transducers devices. However, the presence of lead content may impose the scientific community to develop lead-free ceramics, concerning human health and environmental safety. During the past ten years, many contributions have highlighted the potential properties of complex compositions like LiNbO3, LiTaO3 and LiSbO3 in the lead-free (K0.5Na0.5)NbO3 KNN system. In this context, for the first time, the practical applications and the effectiveness of simply undoped (K0.5Na0.5)NbO3 (KNN) ceramics are investigated. KNN powder is prepared by conventional solid state mixed oxide route. Ceramics of this material are prepared using conventional sintering (CS) and spark plasma sintering (SPS). Thickness coupling factor kt of 44-46%, planar coupling factor kp of 29-45%, relative permittivity at constant strain ε33,r(S) of 125-243 and acoustic impedance Z of 23-30 MRay are obtained for these two kinds of undoped KNN ceramics. Both ceramics are used to build single-element ultrasonic transducers. Relative bandwidth of 49-78% and insertion loss of -27 and -51dB are obtained for SPS and CS transducers, respectively. These results are suitable for use in non-destructive evaluation. The effectiveness of undoped KNN is evaluated using the KLM model, and compared to standard PZT based probe. Finally, chemical aging test of undoped KNN has demonstrated its stability in water. PMID:26117145

  15. Investigation of a terahertz-wave parametric oscillator using LiTaO3 with the pump-wavelength tuning method

    NASA Astrophysics Data System (ADS)

    Sun, Bo; Bai, Xianpeng; Liu, Jinsong; Yao, Jianquan

    2014-03-01

    We investigate theoretically the performance of a terahertz parametric oscillator (TPO) using LiTaO3 (LT) with the pump-wavelength tuning method. The frequency tuning accuracy of the LT-TPO is potentially superior to that of a TPO using LiNbO3 (LN) under the same conditions. The variation of the radiation angle of THz waves coupled from the Si prism of the LT-TPO is up to about 20° lower than that for the LN-TPO for a pump-wavelength tuning range of 0.4-1.6 μm. Although the THz-wave parametric gain characteristics of LiTaO3 are somewhat unsatisfactory compared with those of LiNbO3, the LT-TPO with pump-wavelength tuning can still show potential for high-performance operation, with the excellent optical properties of the LiTaO3.

  16. Two phase diagrams of Pb(Ti0.485Zr0.515)0.98(Nb0.5Bi0.5)0.02O3 solid solution in the temperature range 20 ≤ t ≤ 600°C

    NASA Astrophysics Data System (ADS)

    Shilkina, L. A.; Pavlenko, A. V.; Reznichenko, L. A.; Dudkina, S. I.

    2014-09-01

    A high-temperature analysis of Pb(Ti0.485Zr0.515)0.98(Nb0.5Bi0.5)0.02O3 solid solution has been carried out in the temperature range 20 ≤ t ≤ 600°C by X-ray powder diffraction. Two different phase diagrams are plotted: one is based on the change in the diffraction pattern of main reflections, while the other is based on the diffraction pattern of real (defect) structure. A transition to the cubic phase can be observed at t ≥ 360°C (in the former diagram) and t ≥ 450°C (in the latter diagram). The nonmonotonic (with inflection points) behavior of the temperature dependence of the cell volume in the cubic phase is explained.

  17. Thermal conductivity of K1-xLixTaO3 and KTa1-xNbxO3

    NASA Astrophysics Data System (ADS)

    Tachibana, Makoto

    2015-11-01

    Thermal conductivity data between 1.8 and 300 K are reported for K1-xLixTaO3 (0≤x≤0.03) and KTa1-xNbxO3 (0≤x≤0.16) single crystals. Whereas lightly Li- and Nb-doped crystals exhibit relaxor-like behavior in dielectric susceptibility, they do not show the glasslike thermal transport found in conventional relaxors such as PbMg1/3Nb2/3O3 and Na1/2Bi1/2TiO3. The lack of glasslike behavior in K1-xLixTaO3 and KTa1-xNbxO3 is confirmed by the absence of temperature-linear contribution in heat capacity.

  18. Metastable bcc phase formation in the Nb-Cr system

    SciTech Connect

    Thoma, D.J.; Schwarz, R.B.; Perepezko, J.H.; Plantz, D.H.

    1993-08-01

    Extended metastable bcc solid solutions of Nb-Xat.%Cr (X = 35, 50, 57, 77, 82, and 94) were synthesized by two-anvil splat-quenching. In addition, bcc (Nb-67at.%Cr) was prepared by mechanically alloying mixtures of niobium and chromium powders. The lattice parameters were measured by X-ray diffraction and the Young`s moduli were measured by low-load microindentation. The composition dependence of the lattice parameters and elastic moduli show a positive deviation with respect to a rule of mixtures. During continuous heating at 15C/min., the metastable precursor bcc phases decomposed at temperatures above 750C to uniformly refined microstructures.

  19. Facile synthesis and characterization of hexagonal NbSe{sub 2} nanoplates

    SciTech Connect

    Zhang, Xianghua; Zhang, Du; Tang, Hua; Ji, Xiaorui; Zhang, Yi; Tang, Guogang; Li, Changsheng

    2014-05-01

    Graphical abstract: - Highlights: • Uniform hexagonal NbSe{sub 2} nanoplates were prepared by a simple solid state reaction. • The possible formation mechanism of the NbSe{sub 2} nanoplates was discussed. • The formation of NbSe{sub 2} nanoplates undergoes a series of phase transition. - Abstract: The NbSe{sub 2} nanoplates with hexagonal morphology have been successfully prepared by a facile, environmentally friendly reaction in closed reactor at moderate temperature. The thermal (750 °C) solid-state reaction between the ball-milled mixture of micro-sized Nb and Se yielded a high yield of NbSe{sub 2} nanoplates. The as-prepared products were characterized by XRD, EDS, and SEM. The results showed that the as-prepared products were hexagonal phase NbSe{sub 2} nanoplates with uniform sizes and the formation of NbSe{sub 2} nanoplates underwent a series of phase transition. On the basis of experimental results obtained at different temperatures, a reasonable reaction process and a formation mechanism were proposed. Moreover, the ball milling time played a crucial role in acquiring the homogeneous distribution nanoplates.

  20. Ba5{V,Nb}12Sb19+x, novel variants of the Ba5Ti12Sb19+x-type: crystal structure and physical properties.

    PubMed

    Failamani, F; Grytsiv, A; Giester, G; Polt, G; Heinrich, P; Michor, H; Bauer, E; Zehetbauer, M; Rogl, P

    2015-10-01

    The novel compounds Ba5{V,Nb}12Sb19+x, initially found in diffusion zone experiments between Ba-filled skutterudite Ba0.3Co4Sb12 and group V transition metals (V,Nb,Ta), were synthesized via solid state reaction and were characterized by means of X-ray (single crystal and powder) diffraction, electron probe microanalysis (EPMA), and physical (transport and mechanical) properties measurements. Ba5V12Sb19.41 (a = 1.21230(1) nm, space group P4[combining overline]3m; RF(2) = 0.0189) and Ba5Nb12Sb19.14 (a = 1.24979(2) nm, space group P4[combining overline]3m; RF(2) = 0.0219) are the first representatives of the Ba5Ti12Sb19+x-type, however, in contrast to the aristotype, the structure of Ba5V12Sb19.41 shows additional atom disorder. Temperature dependent ADPs and specific heat of Ba5V12Sb19.41 confirmed the rattling behaviour of Ba1,2 and Sb7 atoms within the framework built by V and Sb atoms. Electrical resistivity of both compounds show an upturn at low temperature, and a change from p- to n-type conductivity above 300 K in Ba4.9Nb12Sb19.4. As expected from the complex crystal structure and the presence of defects and disorder, the thermal conductivity is suppressed and lattice thermal conductivity of ∼0.43 W m(-1) K(-1) is near values typical for amorphous systems. Vicker's hardness of (3.8 ± 0.1) GPa (vanadium compound) and (3.5 ± 0.2) GPa (niobium compound) are comparable to Sb-based filled skutterudites. However, the Young's moduli measured by nanoindentation for these compounds EI(Ba4.9V12Sb19.0) = (85 ± 2) GPa and EI(Ba4.9Nb12Sb19.4) = (79 ± 5) GPa are significantly smaller than those of skutterudites, which range from about 130 to 145 GPa. PMID:26327293

  1. TA-2 water boiler reactor decommissioning (Phase 1)

    SciTech Connect

    Elder, J.C.; Knoell, C.L.

    1986-12-01

    Removal of external structures and underground piping associated with the gaseous effluent (stack) line from the TA-2 Water Boiler Reactor was performed as Phase I of reactor decommissioning. Six concrete structures were dismantled and 435 ft of contaminated underground piping was removed. Extensive soil contamination by /sup 137/Cs was encountered around structure TA-2-48 and in a suspected leach field near the stream flowing through Los Alamos Canyon. Efforts to remove all contaminated soil were hampered by infiltrating ground water and heavy rains. Methods, cleanup guidelines, and ALARA decisions used to successfully restore the area are described. The cost of the project was approximately $320K; 970 m/sup 3/ of low-level solid radioactive waste resulted from the cleanup operations.

  2. Theoretical study of the electronic states of Nb4, Nb5 clusters and their anions (Nb4?, Nb5?)

    SciTech Connect

    Balasubramanian, K; Majumdar, D

    2004-05-06

    Geometries and energy separations of the various low-lying electronic states of Nb{sub n} and Nb{sub n}{sup -} (n = 4, 5) clusters with various structural arrangements have been investigated. The complete active space multi-configuration self-consistent field (CASMCSCF) method followed by multi-reference singles and doubles configuration interaction (MRSDCI) calculations that included up to 52 million configuration spin functions have been used to compute several electronic states of these clusters. The ground states of both Nb{sub 4} ({sup 1}A', pyramidal) and Nb{sub 4}{sup -} ({sup 2}B{sub 3g}, rhombus) are low-spin states at the MRSDCI level. The ground state of Nb{sub 5} cluster is a doublet with a distorted trigonal bipyramid (DTB) structure. The anionic cluster of Nb{sub 5} has two competitive ground states with singlet and triplet multiplicities (DTB). The low-lying electronic states of these clusters have been found to be distorted due to Jahn-Teller effect. On the basis of the energy separations of our computed electronic states of Nb{sub 4} and Nb{sub 5}, we have assigned the observed photoelectron spectrum of Nb{sub n}{sup -}(n = 4, 5) clusters. We have also compared our MRSDCI results with density functional calculations. The electron affinity, ionization potential, dissociation and atomization energies of Nb{sub 4} and Nb{sub 5} have been calculated and the results have been found to be in excellent agreement with the experiment.

  3. Nb(x)Ti(1-x)N Superconducting-Nanowire Single-Photon Detectors

    NASA Technical Reports Server (NTRS)

    Stem, Jeffrey A.; Farr, William H.; Leduc, Henry G.; Bumble, Bruce

    2008-01-01

    Superconducting-nanowire singlephoton detectors (SNSPDs) in which Nb(x)Ti(1-x)N (where x<1) films serve as the superconducting materials have shown promise as superior alternatives to previously developed SNSPDs in which NbN films serve as the superconducting materials. SNSPDs have potential utility in optical communications and quantum cryptography. Nb(x)Ti(1-x)N is a solid solution of NbN and TiN, and has many properties similar to those of NbN. It has been found to be generally easier to stabilize NbxTi1 xN in the high-superconducting-transitiontemperature phase than it is to so stabilize NbN. In addition, the resistivity and penetration depth of polycrystalline films of Nb(x)Ti(1-x)N have been found to be much smaller than those of films of NbN. These differences have been hypothesized to be attributable to better coupling at grain boundaries within Nb(x)Ti(1-x)N films.

  4. Resistance of Ta/PtMn/Ta thin films

    NASA Astrophysics Data System (ADS)

    Boekelheide, Z. A.; Checkelsky, J. G.; Eckert, J. C.; Sparks, P. D.; Carey, M. J.

    2004-03-01

    Anomalous electrical resistance as a function of temperature has been observed for IrMn exchange-biased spin valves and Ti/IrMn/Ti trilayers (1). We have followed up with a study of Pt_50Mn_50 thin films with structure Ta/PtMn/Ta. In the past, resistance of PtMn alloys has been studied by Sarkissian (2) and Kastner (3) with Mn concentration ranging from 0.05-18%. These studies have found resistance minima, which vary depending on Mn concentration. We have found similar resistance curves for the PtMn structures, which depend on the thickness of the film and whether the film has been annealed. This work was supported by the Parsons Foundation, The Office of Naval Research, and the Harvey Mudd College Faculty Research Committee. References: (1) J. C. Eckert, N. P. Stern, D. S. Snowden, and P. D. Sparks, J. Appl. Phys. 93, 6608 (2003) (2) B. V. B. Sarkissian and R. H. Taylor, J. Phys. F 4, L243 (1974) (3) J. Kastner, E. F. Wassermann, K. Matho, and J. L. Tholence, J. Phys. F 8, 103 (1974)

  5. Measurements of the cross section for the (182)W(n,p)(182(m+g))Ta and (184)(n,p)(184)Ta reactions in the 14MeV energy range using the activation technique.

    PubMed

    Song, Yueli; Zhou, Fengqun; Tian, Mingli; Li, Yong; Yuan, Shuqing; Lan, Changlin

    2015-04-01

    The cross section for the (182)W(n,p)(182(m+g))Ta and (184)W(n,p)(184)Ta reactions has been measured in the neutron energy range of 13.5-14.7MeV using the activation technique and a coaxial HPGe γ-ray detector. In our experiment, the fast neutrons were produced by the T(d,n)(4)He reaction at the ZF-300-II Intense Neutron Generator at Lanzhou University. Natural wolfram foils of 99.9% purity were used as target materials. The neutron flux was determined using the monitor reaction (93)Nb(n,2n)(92m)Nb and the neutron energies were determined using the method of cross-section ratio measurements employing the (90)Zr(n,2n)(89)Zr to (93)Nb(n,2n)(92m)Nb reactions. The results of this work are compared with experimental data found in the literature and the estimates obtained from a published empirical formula based on the statistical model with Q-value dependence and odd-even effects taken into consideration. PMID:25617709

  6. Fabrication of fine-grain tantalum diffusion barrier tube for Nb3Sn conductors

    NASA Astrophysics Data System (ADS)

    Hartwig, K. T.; Balachandran, S.; Mezyenski, R.; Seymour, N.; Robinson, J.; Barber, R. E.

    2014-01-01

    Diffusion barriers used in Nb3Sn wire are often fabricated by wrapping Ta sheet into a tube with an overlap seam. A common result of such practice is non-uniform deformation in the Ta sheet as it thins by wire drawing because of non-uniform grain size and texture in the original Ta sheet. Seamless Ta tube with a fine-grain and uniform microstructure would be much better for the diffusion barrier application, but such material is expensive and difficult to manufacture. This report presents results on a new fabrication strategy for Ta tube that shows promise for manufacture of less costly tube with an improved microstructure. The fabrication method begins with seam-welded tube but gives a fine-grain uniform microstructure with little difference between the longitudinal seam weld region and the parent metal after post-weld processing. Severe plastic deformation processing (SPD) applied by area reduction extrusion and tube equal channel angular extrusion (tECAE) are used to refine and homogenize the microstructure. Microstructure and mechanical property results are presented for Ta tubes fabricated by this new processing strategy.

  7. Fabrication of fine-grain tantalum diffusion barrier tube for Nb{sub 3}Sn conductors

    SciTech Connect

    Hartwig, K. T.; Balachandran, S.; Mezyenski, R.; Seymour, N.; Robinson, J.; Barber, R. E.

    2014-01-27

    Diffusion barriers used in Nb{sub 3}Sn wire are often fabricated by wrapping Ta sheet into a tube with an overlap seam. A common result of such practice is non-uniform deformation in the Ta sheet as it thins by wire drawing because of non-uniform grain size and texture in the original Ta sheet. Seamless Ta tube with a fine-grain and uniform microstructure would be much better for the diffusion barrier application, but such material is expensive and difficult to manufacture. This report presents results on a new fabrication strategy for Ta tube that shows promise for manufacture of less costly tube with an improved microstructure. The fabrication method begins with seam-welded tube but gives a fine-grain uniform microstructure with little difference between the longitudinal seam weld region and the parent metal after post-weld processing. Severe plastic deformation processing (SPD) applied by area reduction extrusion and tube equal channel angular extrusion (tECAE) are used to refine and homogenize the microstructure. Microstructure and mechanical property results are presented for Ta tubes fabricated by this new processing strategy.

  8. 78 FR 28627 - TA-W-80,340; TA-W-80,340A; TA-W-80,340B

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-05-15

    ... Employment and Training Administration TA-W-80,340; TA-W-80,340A; TA-W-80,340B] Bush Industries, Inc., Mason... (TA-W-80,340) and Bush Industries, Inc., Allen Street Facility, Jamestown, New York (TA-W- 80,340A... the subject firm's Erie, Pennsylvania facility. The amended notice applicable to TA-W-80,340 is...

  9. Direct evidence on Ta-Metal Phases Igniting Resistive Switching in TaOx Thin Film

    PubMed Central

    Kyu Yang, Min; Ju, Hyunsu; Hwan Kim, Gun; Lee, Jeon-Kook; Ryu, Han-Cheol

    2015-01-01

    A Ta/TaOx/Pt stacked capacitor-like device for resistive switching was fabricated and examined. The tested device demonstrated stable resistive switching characteristics including uniform distribution of resistive switching operational parameters, highly promising endurance, and retention properties. To reveal the resistive switching mechanism of the device, micro structure analysis using high-resolution transmission electron microscope (HR-TEM) was performed. From the observation results, two different phases of Ta-metal clusters of cubic α-Ta and tetragonal β-Ta were founded in the amorphous TaOx mother-matrix after the device was switched from high resistance state (HRS) to low resistance state (LRS) by externally applied voltage bias. The observed Ta metal clusters unveiled the origin of the electric conduction paths in the TaOx thin film at the LRS. PMID:26365532

  10. Elastic and Acoustic Properties of Hexagonal Cr2Nb Compound

    NASA Astrophysics Data System (ADS)

    Yadawa, Pramod Kumar

    2013-01-01

    The ultrasonic properties like ultrasonic sound velocity in the hexagonal structured Cr2Nb compound have been studied along unique axis at room temperature. The second- and third-order elastic constants (SOECs and TOECs) have been calculated for this compound using Lennard-Jones potential. The velocities VL and VS1 have minima and maxima respectively with 45° with unique axis of the crystal, while VS2 increases with the angle from unique axis. Debye average sound velocities of Cr2Nb have been found to be increasing with the angle and has maximum at 55° with unique axis at room temperature. Hence, when a sound wave travels at 55° with unique axis of this material, then the average sound velocity is found to be maximum. The inconsistent behavior of angle dependent velocities is associated to the action of SOECs. The ultrasonic properties are discussed in correlation with elastic, thermal and electrical properties. It has been found that the thermal conductivity is the main contributor to the behavior of ultrasonic attenuation and the cause of attenuation is phonon-phonon interaction. The mechanical properties of Cr2Nb are better than other chromium-based alloys (Cr2Ta, Cr2Zr and Cr2Hf) at room temperature, because it has high ultrasonic velocity and low ultrasonic attenuation.

  11. Synthesis of Ti-Ta alloys with dual structure by incomplete diffusion between elemental powders.

    PubMed

    Liu, Yong; Li, Kaiyang; Wu, Hong; Song, Min; Wang, Wen; Li, Nianfeng; Tang, Huiping

    2015-11-01

    In this work, powder metallurgical (PM) Ti-Ta alloys were sintered using blended elemental powders. A dual structure, consisting of Ti-rich and Ta-rich zones, was formed due to the insufficient diffusion between Ti and Ta powders. The microstructure, mechanical properties and in vitro biological properties of the alloys were studied. Results indicated that the alloys have inhomogenous microstructures and compositions, but the grain structures were continuous from the Ti-rich zone to the Ta-rich zone. The Ta-rich zone exhibited a much finer grain size than the Ti-rich zone. The alloys had a high relative density in the range of 95-98%, with the porosity increasing with the content of Ta due to the increased difficulty in sintering and the formation of Kirkendall pores. The alloys had a good combination of low elastic modulus and high tensile strength. The strength of alloys was almost doubled compared to that of the ingot metallurgy alloys with the same compositions. The low elastic modulus was due to the residual pores and the alloying effect of Ta, while the high tensile strength resulted from the strengthening effects of solid solution, fine grain size and α phase. The alloys had a high biocompatibility due to the addition of Ta, and were suitable for the attachment of cells due to the surface porosity. It was also indicated that PM Ti-(20-30)Ta alloys are promising for biomedical applications after the evaluations of both the mechanical and the biological properties. PMID:26275506

  12. Electro-optic MZI modulators, utilizing different phases in proton-exchanged LiTaO3 waveguides

    NASA Astrophysics Data System (ADS)

    Kostritskii, S. M.; Korkishko, Yu. N.; Fedorov, V. A.; Tavlykaev, R. F.; Ramaswamy, R. V.

    2005-09-01

    Electro-optic Mach-Zehnder interferometric (MZI) modulators have been fabricated by proton exchange in LiTaO3. Electro-optic efficiency of these modulators has been found to be depending on phase composition of HxLi1-xTaO3 waveguide in full accordance with the data of Raman scattering spectroscopy on microscopic contributions in electro-optic effect for the different HxLi1-xTaO3 phases. These spectroscopy data were used to found an appropriate phase composition and, thus, optimize MZI modulators. The experimental samples of MZI modulator fabricated at the optimal technological conditions exhibit the improved electro-optical efficiency with far superior photorefractive resistance compared to the LiNbO3 waveguides and modulators.

  13. The influence of hydrogen charging on the glassy low temperature properties of a polycrystalline NbTi-alloy

    NASA Astrophysics Data System (ADS)

    Abens, S.; Gladun, A.; Jäckel, M.; Lipp, D.; Sahling, S.

    1999-03-01

    We measured the thermal conductivity, specific heat and heat release of polycrystalline Nb 37Ti 63 at low temperatures. Further we charged our samples with hydrogen and investigated the influence of different charging concentrations on these thermal properties. All physical features show low temperature behaviour similar to amorphous solids. The distribution parameter P¯ and the coupling constant γ, extracted from the experimental data, indicate two different tunneling systems in NbTi and hydrogen charged NbTi. In hydrogen charged NbTi the distribution parameter varies nearly proportional to the hydrogen concentration.

  14. Electron paramagnetic resonance of Cr3+ in near-stoichiometric LiTaO3

    NASA Astrophysics Data System (ADS)

    Loyo-Menoyo, M.; Keeble, D. J.; Furukawa, Y.; Kitamura, K.

    2005-06-01

    Electron-paramagnetic-resonance (EPR) experiments on the dominant Cr3+ center in near-stoichiometric LiTaO3 crystals, grown by the double crucible Czochralski method, are reported. A near complete roadmap of EPR positions was obtained allowing an accurate determination of the spin-Hamiltonian parameters. Newman superposition model calculations of zero-field splitting term were performed and support the model of Cr3+ incorporation within the Li octahedron. Calculations were also made for Cr3+ in LiNbO3, again good agreement with a Li site model was obtained for the main EPR center. The temperature dependence of the zero-field splitting parameter for Cr3+ in LiTaO3 was found to show anomalous behavior in the region of 40 K, suggesting the presence local structural instability at the ion site.

  15. Helicity-protected ultrahigh mobility Weyl fermions in NbP

    NASA Astrophysics Data System (ADS)

    Wang, Zhen; Zheng, Yi; Shen, Zhixuan; Lu, Yunhao; Fang, Hanyan; Sheng, Feng; Zhou, Yi; Yang, Xiaojun; Li, Yupeng; Feng, Chunmu; Xu, Zhu-An

    2016-03-01

    Noncentrosymmetric transition-metal monopnictides, including TaAs, TaP, NbAs, and NbP, are emergent topological Weyl semimetals (WSMs) hosting exotic relativistic Weyl fermions. In this Rapid Communication, we elucidate the physical origin of the unprecedented charge carrier mobility of NbP, which can reach 1 ×107cm2V-1s-1 at 1.5 K. Angle- and temperature-dependent quantum oscillations, supported by density function theory calculations, reveal that NbP has the coexistence of p - and n -type WSM pockets in the kz=1.16 π /c plane (W1-WSM) and in the kz=0 plane near the high symmetry points Σ (W2-WSM), respectively. Uniquely, each W2-WSM pocket forms a large dumbbell-shaped Fermi surface enclosing two neighboring Weyl nodes with the opposite chirality. The magnetotransport in NbP is dominated by these highly anisotropic W2-WSM pockets, in which Weyl fermions are well protected from defect backscattering by real spin conservation associated to the chiral nodes. However, with a minimal doping of ˜1 % Cr, the mobility of NbP is degraded by more than two orders of magnitude, due to the invalidity of helicity protection to magnetic impurities. Helicity protected Weyl fermion transport is also manifested in chiral anomaly induced negative magnetoresistance, controlled by the W1-WSM states. In the quantum regime below 10 K, the intervalley scattering time by impurities becomes a large constant, producing the sharp and nearly identical conductivity enhancement at low magnetic field.

  16. Designing polar and magnetic oxides: Zn2FeTaO6--in search of multiferroics.

    PubMed

    Li, Man-Rong; Stephens, Peter W; Retuerto, Maria; Sarkar, Tapati; Grams, Christoph P; Hemberger, Joachim; Croft, Mark C; Walker, David; Greenblatt, Martha

    2014-06-18

    Polar oxides are technically of great interest but difficult to prepare. Our recent discoveries predicted that polar oxides can be synthesized in the corundum-derivative A2BB'O6 family with unusually small cations at the A-site and a d(0) electron configuration ion at B'-site. When magnetic transition-metal ions are incorporated more interesting polar magnetic oxides can form. In this work we experimentally verified this prediction and prepared LiNbO3 (LN)-type polar magnetic Zn2FeTaO6 via high pressure and temperature synthesis. The crystal structure analysis indicates highly distorted ZnO6 and (Fe/Ta)O6 octahedra, and an estimated spontaneous polarization (PS) of ∼50 μC/cm(2) along the c-axis was obtained from point charge model calculations. Zn2Fe(3+)Ta(5+)O6 has a lower magnetic transition temperature (TN ∼ 22 K) than the Mn2FeTaO6 analogue but is less conductive. The dielectric and polarization measurements indicate a potentially switchable component. PMID:24841411

  17. On the Nb-Ge Binary System

    NASA Astrophysics Data System (ADS)

    Papadimitriou, Ioannis; Utton, Claire; Tsakiropoulos, Panos

    2015-12-01

    First-principles calculations were used to study intermetallic compounds in the Nb-Ge system, to gain a better understanding of the phase diagram and resolve conflicts reported in the literature. The enthalpy of formation with regard to temperature was calculated for all the intermetallic compounds, to investigate phase stabilities and phase equilibria at low and elevated temperatures. These results, combined with the electronic DOS, suggest that the tI32 (W5Si3-type) Nb5Ge3 and NbGe2 compounds are stable over the whole temperature range. The stoichiometric cP8 Nb3Ge becomes stable close to its melting temperature. Regarding different compositions of the cP8 Nb3Ge, the calculations suggest the (Nb)0.75(Nb,Ge)0.25 model for the Nb3Ge phase instead of the proposed model, (Nb)0.75(Nb,Ge,Va)0.25, where Va represents vacancy. The calculations show that the tI32 (Cr5B3-type) Nb5Ge3, hP16 (Mn5Si3-type) Nb5Ge3 and Nb10Ge7 compounds should be considered metastable. The elastic constants, bulk, shear, and Young's modulus, Poisson's ratio, and Debye temperature of the Nb, Ge, cP8 Nb3Ge, tP32 Nb3Ge, tI32 (Cr5B3-type) Nb5Ge3, tI32 (W5Si3-type) Nb5Ge3, hP16 (Mn5Si3-type) Nb5Ge3, Nb10Ge7 and NbGe2 were calculated. These phases were found to be mechanically stable. Using the Cauchy pressure, Pugh's index of ductility, and the Poisson's ratio as criteria, the calculations suggest that the tI32 (Cr5B3-type) Nb5Ge3 and NbGe2 intermetallics should be brittle (with the latter being the most brittle) and the cP8 Nb3Ge, tP32 Nb3Ge, hP16 Nb5Si3 and Nb10Ge7 ductile (with cP8 Nb3Ge being the most ductile).

  18. Nb1.30Cr0.70S5: a layered ternary mixed-metal sulfide

    PubMed Central

    Yun, Hoseop; Kim, Gangbeom

    2009-01-01

    The new layered ternary sulfide, Nb1.30Cr0.70S5, niobium chromium penta­sulfide, is isostructural with the solid solution Nb1+xV1−xS5 and belongs to the FeNb3Se10 structure type. Each layer is composed of two unique chains of face-sharing [NbS8] bicapped trigonal prisms (m symmetry) and edge-sharing [MS6] (M= Nb, Cr) octa­hedra (m symmetry). One of the two metal sites is occupied by statistically disordered Nb and Cr atoms, with 0.3 and 0.7 occupancy, respectively. The chains are connected along the c axis, forming two-dimensional layers, which then stack on top of each other to complete the three dimensional structure. As a result, an undulating van der Waals gap is found between the layers. PMID:21581463

  19. Syntheses, optical properties and electronic structures of copper(I) tantalates: Cu{sub 5}Ta{sub 11}O{sub 30} and Cu{sub 3}Ta{sub 7}O{sub 19}

    SciTech Connect

    Palasyuk, Olena; Palasyuk, Andriy; Maggard, Paul A.

    2010-04-15

    Two copper tantalates, Cu{sub 5}Ta{sub 11}O{sub 30} (1) and Cu{sub 3}Ta{sub 7}O{sub 19} (2), were synthesized by solid-state and flux synthetic methods, respectively. A synthetic route yielding 2 in high purity was found using a CuCl flux at 800deg. C and its structure was characterized using powder X-ray diffraction (XRD) data (P6{sub 3}/m (no. 176), Z=2, a=6.2278(1) A, and c=20.1467(3) A). The solid-state synthesis of 1 was performed using excess Cu{sub 2}O that helped to facilitate the growth of single crystals and their characterization by XRD (P6-bar2c (no. 190), Z=2, a=6.2252(1) A, and c=32.516(1) A). The atomic structures of both copper tantalates consist of alternating single and double layers of TaO{sub 7} pentagonal bipyramids that are bridged by a single layer of isolated TaO{sub 6} octahedra and linearly-coordinated Cu{sup +}. Measured optical bandgap sizes of {approx}2.59 and {approx}2.47 eV for 1 and 2 were located well within visible-light energies and were consistent with their orange-yellow colours. Each also exhibits optical absorption coefficients at the band edge of {approx}700 and {approx}275 cm{sup -1}, respectively, and which were significantly smaller than that for NaTaO{sub 3} of {approx}1450 cm{sup -1}. Results of LMTO calculations indicate that their visible-light absorption is attributable mainly to indirect bandgap transitions between Cu 3d{sup 10} and Ta 5d{sup 0} orbitals within the TaO{sub 7} pentagonal bipyramids. - Graphical abstract: The copper(I) tantalates, Cu{sub 5}Ta{sub 11}O{sub 30} and Cu{sub 3}Ta{sub 7}O{sub 19}, were synthesized by high-temperature solid-state reactions and by a new CuCl flux method, respectively. Their structures consist of single and double layers of TaO{sub 7} pentagonal bipyramids separated by isolated TaO{sub 6} octahedra and Cu atoms. UV-vis spectra show visible-light bandgap sizes of {approx}2.5-2.6 eV, which LMTO calculations show arise primarily from indirect transitions between the filled Cu 3d

  20. STUDY ON SYNTHESIS AND EVOLUTION OF NANOCRYSTALLINE Mg4Ta2O9 BY AQUEOUS SOL-GEL PROCESS

    NASA Astrophysics Data System (ADS)

    Wu, H. T.; Yang, C. H.; Wu, W. B.; Yue, Y. L.

    2012-06-01

    Nanosized and highly reactive Mg4Ta2O9 were successfully synthesized by aqueous sol-gel method compared with conventional solid-state method. Ta-Mg-citric acid solution was first formed and then evaporated resulting in a dry gel for calcination in the temperature ranging from 600°C to 800°C for crystallization in oxygen atmosphere. The crystallization process from the gel to crystalline Mg4Ta2O9 was identified by thermal analysis and phase evolution of powders was studied using X-ray diffraction (XRD) technique during calcinations. Particle size and morphology were examined by transmission electron microscopy (TEM) and high resolution scanning electron microscopy (HR-SEM). The results revealed that sol-gel process showed great advantages over conventional solid-state method and Mg4Ta2O9 nanopowders with the size of 20-30 nm were obtained at 800°C.

  1. Preparation, characterization and photocatalytic property of nanosized K-Ta mixed oxides via a sol-gel method

    SciTech Connect

    Zhang, Gaoke; Jiang, Wei; Yu, Shujie

    2010-11-15

    Pyrochlore-type K{sub 2}Ta{sub 2}O{sub 6} compound cannot be obtained by a conventional solid-state reaction. Here, we report the synthesis of K{sub 2}Ta{sub 2}O{sub 6} and tetragonal tungsten bronze (TTB)-type K{sub 6}Ta{sub 10.8}O{sub 30} nanopowders using a facile and low-cost sol-gel method at low temperature. The as-prepared samples were characterized by XRD, TG-DSC, FESEM, UV-vis diffuse reflectance spectrum and XPS. The compound K{sub 2}Ta{sub 2}O{sub 6} was formed at 700 {sup o}C and reached complete crystallization at 750 {sup o}C, and decomposed into pure K{sub 6}Ta{sub 10.8}O{sub 30} with the volatilization of K{sub 2}O at 900 {sup o}C. The transformation of K{sub 2}Ta{sub 2}O{sub 6} to K{sub 6}Ta{sub 10.8}O{sub 30} is reported for the first time. The band gap of the pure K{sub 2}Ta{sub 2}O{sub 6} and K{sub 6}Ta{sub 10.8}O{sub 30} samples was found to be about 4.16 and 3.63 eV, respectively. The as-prepared K{sub 2}Ta{sub 2}O{sub 6} sample exhibited an efficient photocatalytic activity for the decomposition of azo dye acid red G (ARG) and 4-nitrophenol (4-NP, a typical persistent organic pollutant) solution under UV irradiation. According to the experimental results, the mechanism of the photocatalytic reaction over K{sub 2}Ta{sub 2}O{sub 6} was discussed.

  2. Evidence for weak ferromagnetism, isostructural phase transition, and linear magnetoelectric coupling in the multiferroic Bi0.8Pb0.2Fe0.9Nb0.1O3 solid solution

    NASA Astrophysics Data System (ADS)

    Patel, Jay Prakash; Senyshyn, Anatoliy; Fuess, Hartmut; Pandey, Dhananjai

    2013-09-01

    Magnetization, dielectric, and calorimetric studies on Bi0.8 Pb0.2 Fe0.9 Nb0.1O3 (BF-0.2PFN) reveal very weak ferromagnetism but strong dielectric anomaly at the antiferromagnetic transition temperature (TN) characteristic of magnetoelectric coupling. We correlate these results with nuclear and magnetic structure studies using x-ray and neutron powder diffraction techniques, respectively. Rietveld refinements using x-ray powder diffraction data in the temperature range 300 to 673 K reveal pronounced anomalies in the unit cell parameters at TN, indicating strong magnetoelastic coupling. The nuclear and magnetic structures of BF-0.2PFN were determined from neutron powder diffraction data using a representation theory approach. They show the occurrence of a first-order isostructural phase transition (IPT) accompanying the magnetic ordering below TN˜566 K, leading to significant discontinuous change in the ionic polarization (ΔPz˜1.6(3) μC/cm2) and octahedral tilt angle (˜0.3°) at TN. The ionic polarization obtained from refined positional coordinates of the nuclear structure and Born effective charges is shown to scale linearly with sublattice magnetization, confirming the presence of linear magnetoelectric coupling in BF-0.2PFN at the atomic level, despite the very low value of remanent magnetization (Mr).

  3. Polar behavior of double perovskite (Bi,Pb)ZnNbO6 and (Bi,Sr)ZnNbO6: Density functional calculations

    SciTech Connect

    Takagi, Shigeyuki M; Subedi, Alaska P; Singh, David J; Cooper, Valentino R

    2010-01-01

    The polar behavior of double perovskite (Bi,Pb)ZnNbO{sub 6} and (Bi,Sr)ZnNbO{sub 6} was investigated using first principles density functional calculations within the local density approximation. These materials have both A-site size disorder and ions with sterochemical activity. We found a strong ferroelectric distortion in both materials. The polarization of the Pb material is >80 muCcm{sup 2} along the rhombohedral direction and the Sr based material is only slightly inferior. The high polarization results mainly from a large off-centering of Bi and the large Born effective charge of Nb, which yields a large contribution polarization although the Nb off-centers by a smaller amount. Neither of these materials favors a tetragonal state, and therefore solid solutions with PbTiO{sub 3} may show morphotoropic phase boundaries.

  4. Cr{sub 2}Nb-based alloy development

    SciTech Connect

    Liu, C.T.; Tortorelli, P.F.; Horton, J.A.

    1995-06-01

    The objective of this task is to develop a new generation of structural materials based on intermetallic alloys for use as critical hot components in advanced fossil energy conversion systems. The intermetallic phase, Cr{sub 2}Nb, with a complex cubic structure (C-15) has been selected for this development because of its high melting point (1770{degrees}C), relatively low material density (7.7 g/cm{sup 2}), excellent high-temperature strength (at 1000 to 1250{degrees}C), and potential resistance to oxidation and corrosion. This intermetallic phase, like many other Laves phases, has a wide range of compositional homogeneity suggesting the possibility of improving its mechanical and metallurgical properties by alloying additions. The major engineering concern with Cr{sub 2}Nb and other A{sub 2}B Laves phases is their poor fracture toughness and fracture resistance at ambient temperatures. The single-phase Cr{sub 2}Nb is very hard ({approximately}800 DPH) and brittle at room temperature. Because of this brittleness, the development effort has concentrated on two-phase structures containing the hard intermetallic phase Cr{sub 2}Nb and the softer Cr-rich solid solution phase. Potential applications of Cr-Cr{sub 2}Nb alloys include hot components (for example, air heat exchangers and turbine blades) in advanced energy conversion systems and heat engines, wear-resistant parts in coal handling systems (e.g., nozzles), drill bits for oil/gas wells, and valve guides in diesel engines. Current studies are focuses on enhancement of fracture resistance in tension at ambient temperatures and oxidation resistance above 1000{degrees}C. This report summarizes recent progress on controlling microstructure and improving the mechanical and metallurgical properties and the high-temperature corrosion behavior of Cr-Cr{sub 2}Nb alloys through alloying conditions, material processing, and heat treatment.

  5. Protective interlayer for high temperature solid electrolyte electrochemical cells

    DOEpatents

    Singh, Prabhakar; Vasilow, Theodore R.; Richards, Von L.

    1996-01-01

    The invention comprises of an electrically conducting doped or admixed cerium oxide composition with niobium oxide and/or tantalum oxide for electrochemical devices, characterized by the general formula: Nb.sub.x Ta.sub.y Ce.sub.1-x-y O.sub.2 where x is about 0.0 to 0.05, y is about 0.0 to 0.05, and x+y is about 0.02 to 0.05, and where x is preferably about 0.02 to 0.05 and y is 0, and a method of making the same. This novel composition is particularly applicable in forming a protective interlayer of a high temperature, solid electrolyte electrochemical cell (10), characterized by a first electrode (12); an electrically conductive interlayer (14) of niobium and/or tantalum doped cerium oxide deposited over at least a first portion (R) of the first electrode; an interconnect (16) deposited over the interlayer; a solid electrolyte (18) deposited over a second portion of the first electrode, the first portion being discontinuous from the second portion; and, a second electrode (20) deposited over the solid electrolyte. The interlayer (14) is characterized as being porous and selected from the group consisting of niobium doped cerium oxide, tantalum doped cerium oxide, and niobium and tantalum doped cerium oxide or admixtures of the same. The first electrode (12), an air electrode, is a porous layer of doped lanthanum manganite, the solid electrolyte layer (18) is a dense yttria stabilized zirconium oxide, the interconnect layer (16) is a dense, doped lanthanum chromite, and the second electrode (20), a fuel electrode, is a porous layer of nickel-zirconium oxide cermet. The electrochemical cell (10) can take on a plurality of shapes such as annular, planar, etc. and can be connected to a plurality of electrochemical cells in series and/or in parallel to generate electrical energy.

  6. Protective interlayer for high temperature solid electrolyte electrochemical cells

    DOEpatents

    Singh, P.; Vasilow, T.R.; Richards, V.L.

    1996-05-14

    The invention is comprised of an electrically conducting doped or admixed cerium oxide composition with niobium oxide and/or tantalum oxide for electrochemical devices, characterized by the general formula: Nb{sub x}Ta{sub y}Ce{sub 1{minus}x{minus}y}O{sub 2} where x is about 0.0 to 0.05, y is about 0.0 to 0.05, and x+y is about 0.02 to 0.05, and where x is preferably about 0.02 to 0.05 and y is 0, and a method of making the same is also described. This novel composition is particularly applicable in forming a protective interlayer of a high temperature, solid electrolyte electrochemical cell, characterized by a first electrode; an electrically conductive interlayer of niobium and/or tantalum doped cerium oxide deposited over at least a first portion of the first electrode; an interconnect deposited over the interlayer; a solid electrolyte deposited over a second portion of the first electrode, the first portion being discontinuous from the second portion; and, a second electrode deposited over the solid electrolyte. The interlayer is characterized as being porous and selected from the group consisting of niobium doped cerium oxide, tantalum doped cerium oxide, and niobium and tantalum doped cerium oxide or admixtures of the same. The first electrode, an air electrode, is a porous layer of doped lanthanum manganite, the solid electrolyte layer is a dense yttria stabilized zirconium oxide, the interconnect layer is a dense, doped lanthanum chromite, and the second electrode, a fuel electrode, is a porous layer of nickel-zirconium oxide cermet. The electrochemical cell can take on a plurality of shapes such as annular, planar, etc. and can be connected to a plurality of electrochemical cells in series and/or in parallel to generate electrical energy. 5 figs.

  7. Synthesis of superconducting Nb3Sn coatings on Nb substrates

    DOE PAGESBeta

    Barzi, E.; Franz, S.; Reginato, F.; Turrioni, D.; Bestetti, M.

    2015-12-01

    In the present work the electrochemical and thermal syntheses of superconductive Nb3Sn films are investigated. The Nb3Sn phase is obtained by electrodeposition of Sn layers and Cu intermediate layers onto Nb substrates followed by high temperature diffusion in inert atmosphere. Electrodeposition was performed from aqueous solutions at current densities in the 20 to 50 mA/cm2 range and at temperatures between 40 and 50°C. Subsequent thermal treatments were realized to obtain the Nb3Sn superconductive phase. Glow discharge optical emission spectrometry (GDOES) demonstrated that after thermal treatment interdiffusion of Nb and Sn occurred across a thickness of about 13 μm. Scanning Electronmore » Microscopy (SEM) allowed accurately measuring the thickness of the Nb3Sn phase, whose average for the various types of film samples was between 5.7 and 8.0 μm. X-ray diffraction (XRD) patterns confirmed the presence of a cubic Nb3Sn phase (A15 structure) having (210) preferred orientation. The maximum obtained Tc was 17.68 K and the Bc20 ranged between 22.5 T and 23.8 T. With the procedure described in the present paper, coating complex shapes cost-effectively becomes possible, which is typical of electrochemical techniques. Furthermore, this approach can be implemented in classical wire processes such as "Jelly Roll" or "Rod in Tube", or directly used for producing superconducting surfaces. In conclusion, the potential of this method for Superconducting Radiofrequency (SRF) structures is also outlined.« less

  8. Synthesis of superconducting Nb3Sn coatings on Nb substrates

    NASA Astrophysics Data System (ADS)

    Barzi, E.; Bestetti, M.; Reginato, F.; Turrioni, D.; Franz, S.

    2016-01-01

    In the present work the electrochemical and thermal syntheses of superconducting Nb3Sn films are investigated. The Nb3Sn phase is obtained by electrodeposition of Sn layers and Cu intermediate layers onto Nb substrates followed by high temperature diffusion in inert atmosphere. Electrodeposition was performed from aqueous solutions at current densities in the 20-50 mA cm-2 range and at temperatures between 40 °C and 50 °C. Subsequent thermal treatments were realized to obtain the Nb3Sn superconductive phase. Glow discharge optical emission spectrometry demonstrated that after thermal treatment interdiffusion of Nb and Sn occurred across a thickness of about 13 μm. Scanning electron microscopy allowed accurately measuring the thickness of the Nb3Sn phase, whose average for the various types of film samples was between 5.7 and 8.0 μm. X-ray diffraction patterns confirmed the presence of a cubic Nb3Sn phase (A15 structure) having (210) preferred orientation. The maximum obtained T c was 17.68 K and the B c20 ranged between 22.5 and 23.8 T. With the procedure described in the present paper, coating complex shapes cost-effectively becomes possible, which is typical of electrochemical techniques. Furthermore, this approach can be implemented in classical wire processes such as ‘jelly roll’ or ‘rod in tube’, or directly used for producing superconducting surfaces. The potential of this method for superconducting radiofrequency structures is also outlined.

  9. Safety assessment for TA-48 radiochemical operations

    SciTech Connect

    1994-08-01

    The purpose of this report is to document an assessment performed to evaluate the safety of the radiochemical operations conducted at the Los Alamos National Laboratory operations area designated as TA-48. This Safety Assessment for the TA-48 radiochemical operations was prepared to fulfill the requirements of US Department of Energy (DOE) Order 5481.1B, ``Safety Analysis and Review System.`` The area designated as TA-48 is operated by the Chemical Science and Technology (CST) Division and is involved with radiochemical operations associated with nuclear weapons testing, evaluation of samples collected from a variety of environmental sources, and nuclear medicine activities. This report documents a systematic evaluation of the hazards associated with the radiochemical operations that are conducted at TA-48. The accident analyses are limited to evaluation of the expected consequences associated with a few bounding accident scenarios that are selected as part of the hazard analysis. Section 2 of this report presents an executive summary and conclusions, Section 3 presents pertinent information concerning the TA-48 site and surrounding area, Section 4 presents a description of the TA-48 radiochemical operations, and Section 5 presents a description of the individual facilities. Section 6 of the report presents an evaluation of the hazards that are associated with the TA-48 operations and Section 7 presents a detailed analysis of selected accident scenarios.

  10. Magneto-optic measurements of the Weyl semimetal NbAs

    NASA Astrophysics Data System (ADS)

    Armstrong, Nathan; Shao, Yinming; Yuan, Zhujun; Jia, Shuang; Basov, D. N.; Timusk, Thomas

    NbAs is among the newly discovered Weyl semimetals that are of great interest because they have the potential to confirm the chiral anomaly predicted by particle physics. It has been theorized that two separated Weyl nodes of opposite chirality can have a chiral current flow between them with the application electric and magnetic fields parallel to the displacement of the nodes. Indeed, magnetoresistance measurements on TaAs and NbAs found a negative magnetoresistance with these fields. ARPES and band structure calculations show that NbAs has two different groups of Weyl nodes with all the node splittings in kx -ky planes. In addition to the Weyl nodes there are other trivial bands that create Fermi pockets elsewhere in the BZ that are also observed in reflectance measurements. We will present magneto-optics results from far infrared optical data of NbAs in Voigt geometry up to 8 Tesla. In the far infrared at large fields there are two strong features that show an 11% and 3% change of reflectance in field at 60 and 480 cm-1 , respectively. We evaluate these data with comparison to the above mentioned band structure of NbAs.

  11. Josephson Coupling in Nb/SmB6/Nb Junctions

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaohang; Lee, Seunghun; Drisko, Jasper; Cumings, John; Greene, Richard; Takeuchi, Ichiro

    Josephson coupling of superconductors through a topological surface has attracted considerable attention because it may provide device applications of topological insulators with implications for Majorana fermions. However, the results of previous Josephson junction studies on topological insulators have not been fully understood due to complications arising from the conducting bulk and the non-pristine nature of the surfaces/interfaces of the topological insulator materials used. In this work, SmB6 thin films with a highly insulating bulk were adopted to minimize the influence of the bulk carriers while in-situ deposition of Nb film on SmB6 surface was used to ensure the interface quality. The bilayer structure was then patterned into Nb/SmB6/Nb lateral junctions by e-beam lithography and ion milling. The Nb electrodes in our junctions had a typical width of ~1 μm and the gap between the two Nb electrodes was varied from 50 nm to 200 nm. A critical current up to 40 μA has been observed in junctions with a gap around 50 nm at 2.0 K. In this talk, I will discuss the implication of our results to the desired Josephson coupling through topological surface states. This work was supported by NSF under Grant No. DMR-1410665 and conducted at CNAM and at the Maryland NanoCenter.

  12. Shallow levels and photoconductivity in K1-xLixTaO3

    NASA Astrophysics Data System (ADS)

    Galinetto, P.; Giulotto, E.; Sangalli, P.; Camagni, P.; Samoggia, G.

    1999-11-01

    We present the results of experiments performed on K1-xLixTaO3 as well as on Nb-doped and nominally pure KTaO3 single crystals, in which we compared observations of thermally stimulated currents and photoconductivity. In the Li-doped compounds, the large enhancement of conductivity caused by ultraviolet excitation at low temperature was found to correlate with the filling of shallow trapping centres, giving intense charge release below 30-40 K. No sign of a corresponding release was shown by pure or Nb-doped KTaO3, consistently with a very low yield of photocurrent which one observes in these cases. The depth of the trapping levels in K1-xLixTaO3 crystals was found to be between 50 and 70 meV. On the basis of past models and recent calculations, these levels can be identified with hole traps, originating from the perturbation of O2- states at the top of the valence band. They are a plausible source of enhanced photoconductivity, via the quenching of electron-hole recombination.

  13. Site Change of Hydrogen in Niobium on Alloying with Oversized Ta Atoms

    NASA Astrophysics Data System (ADS)

    Yagi, Eiichi; Yoshii, Motoyasu; Okada, Yoshinori; Matsuba, Hiroshi; Miyahara, Kazuya; Koike, Shigetoshi; Sugawara, Takamasa; Shishido, Toetsu; Ogiwara, Kiyoshi

    2009-06-01

    In order to clarify a difference in hydrogen interaction with oversized solute atoms and with undersized solute atoms in bcc metals in the low solute concentration region, the site occupancy of hydrogen in Nb alloyed with 5 at. % of oversized Ta atoms has been studied at room temperature for hydrogen concentrations of 0.018 and 0.025 at the hydrogen-to-metal-atom ratio (CH=[H]/[M]) by the channelling method utilizing a nuclear reaction 1H(11B,α)αα with a 11B beam of an energy of 2.03 MeV. Clearly different from the result on hydrogen in Nb alloyed with undersized Mo atoms, in both specimens H atoms are distributed over tetrahedral (T) sites and the displaced-T sites (d-T sites) which are displaced from T sites by about 0.25 Å towards their nearest neighbour octahedral (O) sites. The T site is more favourable for hydrogen occupancy, but the number of available T sites is limited, and excess H atoms occupy the d-T sites. Therefore, in contrast to a strong attractive interaction between hydrogen and undersized Mo atoms (trapping), there exists no such a strong attractive interaction between hydrogen and oversized Ta atoms. It is considered that the trapping of hydrogen by undersized solute atoms is effective to the large enhancement of the terminal solubility of hydrogen (TSH) on alloying with undersized solute atoms, at least, in the low solute concentration region.

  14. Electrical and optical properties of Ta-Si-N thin films deposited by reactive magnetron sputtering

    SciTech Connect

    Oezer, D.; Sanjines, R.; Ramirez, G.; Rodil, S. E.

    2012-12-01

    consistent description of the evolution of the Ta-Si-N system from a solid solution to a nanocomposite material due to the addition of Si atoms.

  15. Structural evolution in a hydrothermal reaction between Nb2O5 and NaOH solution: from Nb2O5 grains to microporous Na2Nb2O6.2/3H2O fibers and NaNbO3 cubes.

    PubMed

    Zhu, Huaiyong; Zheng, Zhanfeng; Gao, Xueping; Huang, Yining; Yan, Zhimin; Zou, Jin; Yin, Hongming; Zou, Qingdi; Kable, Scott H; Zhao, Jincai; Xi, Yunfei; Martens, Wayde N; Frost, Ray L

    2006-02-22

    Niobium pentoxide reacts actively with concentrate NaOH solution under hydrothermal conditions at as low as 120 degrees C. The reaction ruptures the corner-sharing of NbO(7) decahedra and NbO(6) octahedra in the reactant Nb(2)O(5), yielding various niobates, and the structure and composition of the niobates depend on the reaction temperature and time. The morphological evolution of the solid products in the reaction at 180 degrees C is monitored via SEM: the fine Nb(2)O(5) powder aggregates first to irregular bars, and then niobate fibers with an aspect ratio of hundreds form. The fibers are microporous molecular sieve with a monoclinic lattice, Na(2)Nb(2)O(6).(2)/(3)H(2)O. The fibers are a metastable intermediate of this reaction, and they completely convert to the final product NaNbO(3) cubes in the prolonged reaction of 1 h. This study demonstrates that by carefully optimizing the reaction condition, we can selectively fabricate niobate structures of high purity, including the delicate microporous fibers, through a direct reaction between concentrated NaOH solution and Nb(2)O(5). This synthesis route is simple and suitable for the large-scale production of the fibers. The reaction first yields poorly crystallized niobates consisting of edge-sharing NbO(6) octahedra, and then the microporous fibers crystallize and grow by assembling NbO(6) octahedra or clusters of NbO(6) octahedra and NaO(6) units. Thus, the selection of the fibril or cubic product is achieved by control of reaction kinetics. Finally, niobates with different structures exhibit remarkable differences in light absorption and photoluminescence properties. Therefore, this study is of importance for developing new functional materials by the wet-chemistry process. PMID:16478193

  16. Search for solid conductors of Na/+/ and K/+/ ions - Five new conductors

    NASA Technical Reports Server (NTRS)

    Singer, J.; Kautz, H.; Fielder, W.; Fordyce, J.

    1975-01-01

    Five new conductors of positive Na and K ions, for use as separators in high energy secondary batteries, have been discovered. They include: (1) the pyrochlores NaTaWO6 and NaTa2O5F; (2) the bcc form of NaSbO3; and (3) the niobates 2Na2O-3Nb2O5 and 2K2O-3Nb2O5, with the alkali ions probably in open layers of the completely determined structure. On the basis of approximately 40 structure types, generalizations have been made regarding the relation between structure and ionic transport.

  17. Field investigations of soils at TA-19, TA-26, TA-73 and TA-0, SWMU aggregate 0-D and 016

    SciTech Connect

    McFadden, L.D.

    1995-03-01

    Field based investigations of the general soil-geomorphic characteristics were carried out at TA-19, -26, -73, -0, Aggregate 0-D and -016 in order to provide information for utilization in ongoing and anticipated LANL ERP (Environmental Restoration Project) activities at these sites. These investigations show that soils exhibiting diverse morphologic character, varying ages, and relations to landforms characterize these sites. A review of recent and ongoing soils studies also shows that soil textural, chemical, and mineralogical characteristics may profoundly influence the migration and/or retardation of a variety of potential contaminants initially placed in direct contact with soils, or that encounter soils during subsurface percolation or discharge. Soil-geomorphic relations also provide important insights into recent site erosion, deposition or other surficial processes that must, be considered as part of environmental assessment of a given site and remediation; and, the planned geomorphic mapping activities at each site, as well as other associated activities (e.g, geophysical survey, site sampling) are accordingly appropriate and necessary with respect to identification of significant soil relations at each site. Specific and general recommendations in consideration of important findings regarding the possible impacts of soil development of the nature of contaminant behavior at various sites are provided to help guide sampling and analysis activities during ERP investigations outlined in the RFI Work Plan for Operational Unit-1071.

  18. Preparation and investigation of the quaternary alloy CuTaInSe{sub 3}

    SciTech Connect

    Grima-Gallardo, P. Munoz, M.; Duran, S.; Delgado, G.E.; Quintero, M.; Ruiz, J.

    2007-12-04

    Polycrystalline samples of the quaternary alloy CuTaInSe{sub 3} were prepared by the usual melt and anneal technique. The analysis of the diffraction pattern indicates a single phase which indexes as a tetragonal chalcopyrite-like structure with lattice parameters a = 5.7837 {+-} 0.0002 A; c = 11.6208 {+-} 0.0007 A and V = 389 {+-} 1 A{sup 3}. Differential thermal analysis shows that the melting transition of CuTaInSe{sub 3} is incongruent with large liquid + solids regions.

  19. Room-Temperature Magnetism Realized by Doping Fe into Ferroelectric LiTaO3

    NASA Astrophysics Data System (ADS)

    Song, Ying-Jie; Zhang, Qing-Hua; Shen, Xi; Ni, Xiao-Dong; Yao, Yuan; Yu, Ri-Cheng

    2014-01-01

    We synthesize LiTa1-xFexO3-σ (LTFO) ceramics by the conventional solid-state reaction method. The samples remain single phase up to x = 0.09. The magnetic measurements show that the doping of Fe successfully realizes ferromagnetism of LTFO at room temperature. The dielectric measurements indicate that LTFO is ferroelectric, similarly to LiTaO3 (LTO), but its ferroelectric Curie temperature seems to decrease with the increasing Fe content. By means of doping Fe ions into LTO, the coexistence of spontaneous electric polarization and spontaneous magnetic moment is realized at room temperature.

  20. Photoelectron Spectroscopy Study of [Ta2B6]-: a Hexagonal Bipyramdial Cluster

    NASA Astrophysics Data System (ADS)

    Jian, Tian; Li, Weili; Romanescu, Constantin; Wang, Lai-Sheng

    2014-06-01

    It has been a long-sought goal in cluster science to discover stable atomic clusters as building blocks for cluster-assembled nanomaterials, as exemplified by the fullerenes and their subsequent bulk syntheses.[1,2] Clusters have also been considered as models to understand bulk properties, providing a bridge between molecular and solid-state chemistry.[3] Herein we report a joint photoelectron spectroscopy and theoretical study on the [Ta2B6]- and [Ta2B6] clusters.[4] The photoelectron spectrum of [Ta2B6]- displays a simple spectral pattern and a large HOMO-LUMO gap, suggesting its high symmetry. Theoretical calculations show that both the neutral and anion are D6h pyramidal. The chemical bonding analyses for [Ta2B6] revealed the nature of the B6 and Ta interactions and uncovered strong covalent bonding between B6 and Ta. The D6h-[TaB6Ta] gaseous cluster is reminiscent of the structural pattern in the ReB6X6Re core in the [(Cp*Re)2B6H4Cl2] and the TiB6Ti motif in the newly synthesized Ti7Rh4Ir2B8 solid-state compound.[5,6] The current work provides an intrinsic link between a gaseous cluster and motifs for solid materials. Continued investigations of the transition-metal boron clusters may lead to the discovery of new structural motifs involving pure boron clusters for the design of novel boride materials. Reference [1] H.W. Kroto, J. R. Heath, S. C. OBrien, R. F. Curl, R. E. Smalley, Nature 1985, 318, 162 - 163. [2] W. Krtschmer, L. D. Lamb, K. Fostiropoulos, D. R. Huffman, Nature 1990, 347, 354 - 358. [3] T. P. Fehlner, J.-F. Halet, J.-Y. Saillard, Molecular Clusters: A Bridge to Solid-State Chemitry, Cambridge University Press, UK, 2007. [4] W. L. Li, L. Xie, T. Jian, C. Romanescu, X. Huang, L.-S. Wang, Angew. Chem. Int. Ed. 2014, 126, 1312 - 1316. [5] B. Le Guennic, H. Jiao, S. Kahlal, J.-Y. Saillard, J.-F. Halet, S. Ghosh, M. Shang, A. M. Beatty, A. L. Rheingold, T. P. Fehlner, J. Am. Chem. Soc. 2004, 126, 3203 - 3217. [6] B. P. T. Fokwa, M. Hermus, Angew

  1. Ge{sub x}NbSe{sub 2} and Ge{sub x}NbS{sub 2} intercalation compounds

    SciTech Connect

    Kars, Mohammed; Gomez-Herrero, A.; Rebbah, Allaoua; Otero-Diaz, L.C.

    2009-07-01

    The structures of two intercalation compounds, Ge{sub {approx}0.2}NbSe{sub 2} and Ge{sub {approx}0.3}NbS{sub 2} were investigated by single crystal X-ray diffraction and electron microscopy (selected area electron diffraction (SAED), high resolution electron microscopy (HRTEM) and X-ray microanalysis by energy dispersive spectroscopy (XEDS)). Crystal structure determinations of the average structure of the intercalation compounds 2H-Ge{sub 0.217}NbSe{sub 2} and 4H-Ge{sub 0.288}NbS{sub 2} are reported: the selenide compound crystallizes in the space group P6{sub 3}/mmc with a = 3.4560(9) A and c = 12.966(3) A and adopts the 2H-NbSe{sub 2} structure-type, while the sulfide compound crystallizes in the P6{sub 3}mc space group, with a = 3.3392(9) A and c = 25.404(7) A with a structure-type 4H{sub c}-NbS{sub 2} which it is known for TaSe{sub 2}. In both structures the germanium atoms are located in the empty octahedral positions of the van der Waals gap between the NbX{sub 2} (X = S, Se) layers. Electron diffraction patterns from several Ge{sub x}NbSe{sub 2} crystal flakes show different superstructures and exhibit diffracted diffuse intensity: weak satellites corresponding to a{sub 0}{radical}(3)xa{sub 0}{radical}(3) and 2a{sub 0} x 2a{sub 0} superstructures were observed for x {approx} 0.15 (a{sub 0} is the basal lattice parameter of the host structure). For x {approx} 0.25-0.33, the same type of satellite is observed with a stronger intensity. For x {approx} 0.5 only satellites corresponding to the a{sub 0}{radical}(3)xa{sub 0}{radical}(3) superstructure were present. In the case of Ge{sub x}NbS{sub 2}, with 0.10 < x < 0.25, the germanium atoms are ordered in domains with an a{sub 0}{radical}(3)xa{sub 0}{radical}(3) superstructure. In some crystals disorder along the c-axis has been observed.

  2. Electric Field Gradient at Nb Site in the Intermetallic Compounds Nb3X (X = AI, In, Si, Ge, Sn) Measured by PAC

    NASA Astrophysics Data System (ADS)

    Junqueira, A. C.; Carbonari, A. W.; Filho, J. Mestnik; Saxena, R. N.

    2000-02-01

    The electric field gradient (efg) at the Nb site in the intermetallic compounds Nb3X (X = Al, In, Si, Ge, Sn) was measured by the Perturbed Angular Correlation (PAC) method using the well-known gamma-gamma cascade of 133 -482 keV in 181Ta from the β- decay of 181Hf, substituting approximately 0.1 atom percent of Nb. The PAC results show that Vzz drops by nearly 40% when X changes from Al to In, and by about 25% when X changes from Si to Ge and Sn. This behavior is most probably related to the change in the degree of sp hybridization in these compounds. The Vzz values of the studied compounds do not follow the well known universal correlation for the efg's in non-cubic metals but the observed trend is well reproduced by results of ab-initio electronic structure calculations. In the case of Nb3 Al a linear temperature dependence of the quadrupole frequencies was observed in the temperature range of 6.5 to 1210 K.

  3. Synthesis and morphology of CVD diamond on Ta and TaC film

    NASA Astrophysics Data System (ADS)

    Togashi, Fumitaka; Kobayashi, Ken; Mitsuhashi, Masahiko; Karasawa, Shiro; Ohya, Seishiro; Watanabe, Takeshi

    1993-03-01

    Synthetic diamond films have been deposited on the Si(111) surface, polycrystalline Ta plate, TaC/Si, and TaC/Ta substrates using an electron assisted chemical vapor deposition (EACVD) method. The effects of substrate pretreatment and existence of carbide layer on the diamond nucleation, subsequent growth and morphology have been studied. The substrate pretreatment, scratching by diamond powder, affects nucleation behavior, subsequent growth and morphology of diamond. Existence of carbide layer and formation of carbide on the substrate affects nucleation density, growth rate and morphology of diamond.

  4. Improvement of critical current density of bronze processed Nb{sub 3}Sn superconducting wire

    SciTech Connect

    Miyazaki, T.; Fukumoto, Y.; Matsukura, N.

    1997-06-01

    Effects of tantalum addition to niobium filaments and tin contents in bronze matrix on the critical current density (J{sub c}) of Nb{sub 3}Sn superconducting wires manufactured by the bronze process were investigated in order to improve the J{sub c} in the high magnetic fields. In the results using the bronze composition of Cu-13wt.%Sn-0.3wt.%Ti, the J{sub c} shows a peak for 1 wt.% of tantalum content in the niobium filament. On the other hand, J{sub c} of samples with Cu-14wt.%Sn-0.3wt.%Ti is almost 1.7 times higher than that with Cu-13wt.%Sn-0.3wt.%Ti. From these findings, the authors manufactured a multifilamentary prototype (Nb,Ti,Ta){sub 3}Sn conductor made of Nb-1.0wt.%Ta and Cu-14wt.%Sn.0.3wt.%Ti. The non Cu J{sub c} of the conductor was 701 A/mm{sup 2} at 12 T and 51 A/mm{sup 2} at 21 T for the heat treatment temperature of 650{degrees} C.

  5. Highly flexible, mechanically robust superconducting wire consisting of NbN-carbon-nanotube nanofibril composites

    NASA Astrophysics Data System (ADS)

    Kim, Jeong-Gyun; Kang, Haeyong; Kim, Joonggyu; Lee, Young Hee; Suh, Dongseok

    A flexible superconducting fiber is prepared by twisting carbon nanotube (CNT) sheets coated with sputter-deposited niobium nitride (NbN) layer to form the shape of yarn. Twisted CNT yarn, which has been extensively studied due to its high flexibility as well as excellent mechanical properties, and NbN, which is a superconducting material with high transition temperature (Tc) and critical magnetic field (Hc), are combined together by the deposition of NbN layer on free-standing CNT-sheet substrate followed by the biscrolling process. We tried many experimental conditions to investigate the superconducting properties of NbN-CNT yarn as a function of NbN thickness and number of CNT-sheet layers, and found out that the superconducting property of NbN on CNT-sheet can be comparable to that of NbN thin film on the normal solid substrate. In addition, the superconducting property survived even under the condition of severe mechanical deformation such as knotting. These results show the potential application of this technology as a large-scale fabrication method of flexible, mechanically robust, high performance superconducting wire. This work is supported by the Institute for Basic Science (IBS-R011-D1), and by the National Research Foundation (BSR-2013R1A1A1076063) funded by the Ministry of Science, ICT & Future Planning, Republic of Korea.

  6. Fracture toughness and fatigue crack growth in rapidly quenched Nb-Cr-Ti in situ composites

    SciTech Connect

    Chan, K.S.; Davidson, D.L.; Anton, D.L.

    1997-09-01

    In situ composites based on the Nb-Cr-Ti ternary system were processed by rapid solidification in order to reduce the size of the reinforcing intermetallic phase. Two-phase microstructures with small Cr{sub 2}Nb particles in a Nb(Cr, Ti) solid solution alloy matrix were produced for several compositions that previous work showed to produce high toughness composites in cast materials. The fracture and fatigue behaviors of these composites were characterized at ambient temperature. The results indicate that the fracture resistance increases with a decreasing volume of Cr{sub 2}Nb particles. Fracture toughnesses of the rapidly solidified materials with their smaller particle sizes were lower than for conventionally processed composites with larger particles of the intermetallic compound. The fatigue crack growth rate curves exhibit steep slopes and a low critical stress intensity factor at fracture. The lack of fracture and fatigue resistance is attributed to the continguity of the intermetallic particles and the absence of plastic flow in the Nb solid solution matrix. The matrix alloy appears to be embrittled by (1) the rapid solidification processing that prevented plastic relaxation of residual stresses, (2) a high oxygen content, and (3) the constraint caused by the hard Cr{sub 2}Nb particles.

  7. The effect of solid metal composition on solid metal/ liquid metal partitioning of trace elements

    NASA Astrophysics Data System (ADS)

    Rai, N.; van Westrenen, W.

    2010-12-01

    Fundamental understanding of the partitioning behaviour of elements between different core and/or mantle phases is needed to constrain processes of planetary differentiation and evolution. The partitioning behaviour of elements between solid metal and liquid metal in the Fe-S system, of relevance to core crystallisation in planetesimals and the terrestrial planets, has been investigated by several workers [1-6], most of whom [1-5] conclude that variations in partition coefficients can be explained by variations in melt composition. However, recently Stewart et al. [6] showed that the crystal-lattice strain model commonly used to describe silicate mineral - silicate melt partitioning can be applied to partially molten metallic systems. This suggests the structure of the solid metal also plays a role in determining solid metal / molten metal partitioning. Here, we investigate the effect of the structure of the solid metal in the Fe-S system on solid/liquid metal partitioning by obtaining new element partitioning data at pressures between 0.5 and 3 GPa. The effect of the solid metal is isolated from pressure-temperature-melt composition effects by performing experiments at constant P and T with two Fe-S bulk compositions on either side of the eutectic composition. In addition to the effect of solid metal composition we investigate the effects of pressure and S content on trace element partitioning behaviour and the application of the lattice strain model to our results. Starting mixtures were doped with several hundred ppm levels of trace elements Ni, Co, W, Mo, V, Nb, Ta, Sn, Cu, Pb, Zn, Cr, Mn, P, Ge,. Experiments were performed using a QUICKPress piston cylinder apparatus at the VU University, Amsterdam using alumina capsules. Experiments were heated to 1073 K at pressure and allowed to sinter for a duration of 10 hours before the temperature was raised at a rate of 50 K / min to the target value. Preliminary EPMA data for a 1 GPa experiment with FeS as the solid

  8. The synthesis of NbSi{sub 2} by mechanical alloying

    SciTech Connect

    Lou, T.; Fan, G.; Ding, B.; Hu, Z.

    1997-05-01

    The stoichiometric intermetallic compound NbSi{sub 2} has been synthesized by mechanical alloying (MA) elemental Nb and Si powders. The alloying process has been investigated by means of x-ray diffraction (XRD) and differential scanning calorimetry (DSC). It was found that the formation of the Nb{sub 2}Si intermetallic compound occurs abruptly after 65 min of milling without any interruptions during the alloying process. However, short interruptions at a 5 min interval during ball milling result in a gradual reaction for the formation of the NbSi{sub 2} compound as well as a new metastable bcc structured solid solution. We conclude that the temperature rise during mechanical alloying plays an important role in initiating the abrupt reaction after an incubation milling time. {copyright} {ital 1997 Materials Research Society.}

  9. Giant semiclassical magnetoresistance in high mobility TaAs2 semimetal

    NASA Astrophysics Data System (ADS)

    Wu, Desheng; Liao, Jian; Yi, Wei; Wang, Xia; Li, Peigang; Weng, Hongming; Shi, Youguo; Li, Yongqing; Luo, Jianlin; Dai, Xi; Fang, Zhong

    2016-01-01

    We report the observation of colossal positive magnetoresistance (MR) in single crystalline, high mobility TaAs2 semimetal. The excellent fit of MR by a single quadratic function of the magnetic field B over a wide temperature range (T = 2-300 K) suggests the semiclassical nature of the MR. The measurements of Hall effect and Shubnikov-de Haas oscillations, as well as band structure calculations, suggest that the giant MR originates from the nearly perfectly compensated electrons and holes in TaAs2. The quadratic MR can even exceed 1 200 000% at B = 9 T and T = 2 K, which is one of the largest values among those of all known semi-metallic compounds, including the very recently discovered WTe2 and NbSb2. The giant positive magnetoresistance in TaAs2 not only has a fundamentally different origin from the negative colossal MR observed in magnetic systems but also provides a nice complemental system that will be beneficial for applications in magnetoelectronic devices.

  10. Geologic setting and mineralization of the Kougarok Sn(Ta-Nb) deposit, seaward peninsula, Alaska

    SciTech Connect

    Puchner, C.C.

    1985-01-01

    The Kougarok tin (tantalum-niobium) deposit is located in the north-central Seward Peninsula, roughly 130 kilometers north of Nome, Alaska. Tin and tantalum-niobium mineralization occur within granitic dikes, subhorizontal sheets, plugs, and in schists adjacent to the granite bodies. Rb/Sr and K/Ar age determinations indicate the granites at Kougarok are late Cretaceous in age and coeval with other tin granites of the Seward Peninsula. The host rock to the granites at Kougarok is polydeformed pelitic schists of possible Precambrian age. Known mineralization occurs in four geologic settings: 1) within steep cylindrical pipes of greisenized granite; 2) in greisenized dikes; 3) in greisen along the roof zone of a subhorizontal granite sheet; and 4) as stringer zones in schists. Tin mineralization is known in all the above geologic environments and occurs dominantly as disseminated cassiterite in quartz+/-tourmaline+/-topaz greisen. Grades of significant tin mineralization range from 0.1 to 15 percent tin and average approximately 0.5 percent tin. Tantalum-niobium mineralization is confined to the roof greisen environment. Tantalite-columbite occurs as disseminated grains in white mica altered granite lateral to tin-bearing quartz-tourmaline greisen. Grades for both tantalum and niobium range from 0.02 to 0.05 percent.

  11. Nb K- and L3-edges XAFS study on the structure of supported Nb carbide catalyst

    NASA Astrophysics Data System (ADS)

    Ichikuni, N.; Yanagase, F.; Mitsuhara, K.; Hara, T.; Shimazu, S.

    2016-05-01

    Mesoporous silica SBA-15 supported NbC catalysts were prepared under reduced pressure of CH4-H2 gas in a closed circulating system. Nb K- and L 3-edges XAFS measurements revealed that small NbC cluster formed on SBA-15 support and gradual carburization process by lengthening the carburization temperature-maintaining period. Carburization degree of Nb species was clearly explained by using threshold energy shift of Nb L 3-edge XANES profile.

  12. Effects of annealing on antiwear and antibacteria behaviors of TaN-Cu nanocomposite thin films

    SciTech Connect

    Hsieh, J. H.; Cheng, M. K.; Chang, Y. K.; Li, C.; Chang, C. L.; Liu, P. C.

    2008-07-15

    TaN-Cu nanocomposite films were deposited by reactive cosputtering on Si and tool steel substrates. The films were then annealed using rapid thermal annealing (RTA) at 400 deg. C for 2, 4, and 8 min, respectively, to induce the nucleation and growth of Cu particles in TaN matrix and on film surface. Field emission scanning electron microscopy was applied to characterize Cu nanoparticles emerged on the surface of TaN-Cu thin films. The effects of annealing on the antiwear and antibacterial properties of these films were studied. The results reveal that annealing by RTA can cause Cu nanoparticles to form on the TaN surface. Consequently, the tribological behaviors, as well as the antibacterial behavior may vary depending on particle size, particle distribution, and total exposed Cu amount. For the samples with large Cu particles, the reduction of averaged friction and wear rate is obvious. Apparently, it is due to the smeared Cu particles adhered onto the wear tracks. This Cu layer may act as a solid lubricant. From the antibacterial testing results, it is found that both Cu particle size and total exposed Cu amount are critical in making short-term antibacterial effect. Overall, all the annealed TaN-Cu samples can reach >99% antibacterial efficiency in 24 h, with respect to uncoated Si substrate.

  13. Microstructural Characterization of U-Nb-Zr, U-Mo-Nb, and U-Mo-Ti Alloys via Electron Microscopy

    SciTech Connect

    A. Ewh; D. D. Keiser, Jr.; Y. H. Sohn

    2010-06-01

    Ternary uranium molybdenum alloys are currently being investigated for use as dispersion and monolithic nuclear fuels in research reactors. In this study, two such ternary alloys, with compositions U-8Mo-3Nb and U-7Mo-3Ti in wt.%, were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM) with high angle annular dark field (HAADF) imaging via scanning transmission electron microscopy (STEM) to identify phase constituents. These alloys were homogenized at 950°C for 96 hours and were expected to be single-phase bcc-!-U. However, upon examination, it was determined that despite homogenization, each of the alloys contained a small volume fraction precipitate phase. Through SEM and XRD, it was confirmed that the matrix retained the bcc-!-U phase, but the precipitate phases could not be identified using these methods. TEM specimens were prepared using site-specific focused ion beam (FIB) in situ lift out (INLO) technique to include at least one precipitate from each alloy. By electron diffraction, the precipitate phases for the U- 8Mo-3Nb and U-7Mo-3Ti alloys were identified as bcc-(Mo,Nb) solid solution and bcc- (Mo,Ti) solid solution, respectively.

  14. Compressive creep behavior of Nb{sub 5}Si{sub 3}

    SciTech Connect

    Subramanian, P.R.; Parthasarathy, T.A.; Mendiratta, M.G.; Dimiduk, D.M.

    1995-04-15

    Advanced intermetallic materials, such as refractory silicides, exhibit high melting points, high stiffness, low densities, and good strength retention at elevated temperatures. Further, some of these silicides are in equilibrium with terminal refractory solid solution (beta) phases, and therefore, offer the potential for ductile phase toughening. Studies were conducted to elucidate the compressive creep behavior of monolithic Nb{sub 5}Si{sub 3} and to generate the constitutive creep law. This, in turn, is required for modeling the creep behavior of the Nb/Nb{sub 5}Si{sub 3} two-phase system. Nb{sub 5}Si{sub 3} has the ordered tetragonal structure with 32 atoms/cell in both its allotropic forms: {alpha}Nb{sub 5}Si{sub 3} (D8{sub l} Cr{sub 5}Si{sub 3}-type; a {approximately} 0.656 nm; c = 1.187 nm) and {beta}Nb{sub 5}Si{sub 3} (D8{sub m} W{sub 5}Si{sub 3}-type; a = 1.000 nm; c = 0.507 nm). {alpha}Nb{sub 5}Si{sub 3} is stable below 1,935 C, while {beta}Nb{sub 5}Si{sub 3} is stable above 1,645 C. The large lattice parameters as well as the large number of atoms in the unit cell suggest that dislocation creep is unlikely to occur in Nb{sub 5}Si{sub 3}, because large Burgers vectors and complex dislocation core structures are expected in this material.

  15. EDITORIAL: TaCoNa-Photonics 2008 TaCoNa-Photonics 2008

    NASA Astrophysics Data System (ADS)

    Chigrin, Dmitry N.; Busch, Kurt; Lavrinenko, Andrei V.

    2009-11-01

    intensify theoretical discussions and to put them on `solid' ground it was decided to invite world-leading experts in experimental photonics for plenary talks. Over three days, the workshop has brought together more than 70 specialists in theoretical and computational nano-photonics. The workshop took place in the historical `Physikzentrum Bad Honnef', whose unique atmosphere supported a multitude of highly interesting debates and discussions that often lasted until midnight and beyond. Different theoretical and numerical aspects of light generation, control and detection in general inhomogeneous media, photonic crystals, plasmonic structures, metamaterials and integrated optical systems were covered in 15 invited talks and 52 contributed oral and posters presentations. The plenary talks were given by Professor M Wegener (metamaterials) and Professor W Barnes (plasmonics). This special section is a cross-sectional selection of papers which were submitted by the authors of invited and contributed oral presentations. It also includes two papers of the winners of the Best Poster Awards. We hope that these papers will enhance the interest of the scientific community regarding nano-photonics in general and regarding the TaCoNa-Photonics workshop series in particular. It is our distinct pleasure to acknowledge the generous financial support of our sponsors: Karlsruhe School of Optics & Photonics (KSOP) (Germany), U.S. Army International Technology Center-Atlantic, Research Division (USA), and the Office of Naval Research Global (USA). Without the organizational assistance from the International Department of the Universität Karlsruhe GmbH (Germany) this event would simply have been impossible.

  16. High field properties of NbN conductors on practical substrates

    SciTech Connect

    Kampwirth, R.T.; Capone, D.W. II; Gray, K.E.; Ho, H.; Chumbley, S.

    1987-01-01

    A new UHV, oil free, two gun magnetron sputtering system has been developed to allow continuous production of NbN conductors. A scaling rule relating film properties to preparation conditions was successfully used to predict the preparation conditions necessary to achieve the best NbN film properties in the two gun system. Comparison of high field J/sub c/ results between the new two gun system and a diffusion pumped one gun system show similar results for NbN on sapphire substrates, suggesting no effect from oil backstreaming. Short sections of double side coated Ti tapes 25 ..mu..m thick with approx. = ..mu..m of NbN have J/sub c/ = 1 x 10/sup 4/ A/cm/sup 2/ at 18T with H/sub c2/(4.2K) of 22.5 to 23 T. Ta wires made under the same conditions with approx. =2.7 ..mu..m of NbN had J/sub c/(18T) a factor of two lower. An 11 turn coil with a 2.5 cm bending radius has been made by coating one side of a moving tape 1.3 m long with approx. =3..mu..m of NbN. The best section had a J/sub c/approx. = 1 x 10/sup 4/ A/cm/sup 2/ at 18T and J/sub c/approx. =4 x 10/sup 3/ A/cm/sub 2/ at 20T.

  17. Microstructure Evolution and Wear Behavior of the Laser Cladded CoFeNi2V0.5Nb0.75 and CoFeNi2V0.5Nb High-Entropy Alloy Coatings

    NASA Astrophysics Data System (ADS)

    Jiang, Li; Wu, Wei; Cao, Zhiqiang; Deng, Dewei; Li, Tingju

    2016-04-01

    The high-entropy alloy (HEA) coatings have received considerable attentions owing to their unique structures and properties caused by the quick solidification. In this work, the CoFeNi2V0.5Nb0.75 and CoFeNi2V0.5Nb HEAs which show fully eutectic and hypereutectic microstructures in their casting samples were laser cladded on 304 stainless steel substrate with laser power of 1400, 1600, and 1800 W. Results show that the HEA coatings are composed of the FCC solid solution phase and the Fe2Nb-type Laves phase. The cladding zones of the CoFeNi2V0.5Nb0.75 and CoFeNi2V0.5Nb coatings show cellular dendritic crystals, while the bonding zones show directional columnar crystals. Compared to the 304 stainless steel substrate, the HEA coatings show better wear resistance because of the combination of the hard Fe2Nb-type Laves phase and the ductile FCC solid solution matrix. Moreover, the HEA coatings with power of 1600 W show the best wear resistance attributing to the maximum volume fraction of the hard Fe2Nb-type Laves phase.

  18. Paramagnetic Meissner effect in Nb

    SciTech Connect

    Kostic, P.; Veal, B.; Paulikas, A.P.; Welp, U.; Todt, V.R.; Gu, C.; Geiser, U.; Williams, J.M.; Carlson, K.D.; Klemm, R.A.

    1996-01-01

    The paramagnetic Meissner effect (PME), or Wohlleben effect, in which the field-cooled magnetization of superconducting samples is paramagnetic below {ital T}{sub {ital c}}, has been reported to occur in some samples of a variety of high-{ital T}{sub {ital c}} cuprate superconductors. It has been proposed that the effect arose in granular hole-doped cuprates from current loops with {pi} phase shifts of the superconducting order parameter at some grain-boundary junctions. It is argued that such behavior would be expected to occur in a {ital d}-wave superconductor, but not in a conventional {ital s}-wave superconductor. To test this hypothesis, we have searched for the occurrence of the effect in Nb, and have confirmed a recent report by Minhaj {ital et} {ital al}. of its occurrence in some Nb samples. For these studies, the effects of stray fields and field gradients in the measurement volume of the superconducting quantum interference device magnetometer have been carefully considered to rule out the possibility that measurement artifacts might be responsible for the apparent paramagnetic behavior in Nb. The {ital M}({ital T}) and {ital M}({ital H}) curves obtained in Nb samples that show the PME also show remarkably strong resemblance to those curves reported for the cuprate materials exhibiting the PME. Evidence is presented that the effect arises from inhomogeneously trapped flux, and is strongly influenced by sample geometry and surface effects. These results suggest that, for the effect to be observable, {ital T}{sub {ital c}} on the sample surface must be different from the bulk {ital T}{sub {ital c}}. The occurrence of the PME in Nb strongly suggests that the observation of this effect is unrelated to {ital d}-wave superconductivity. {copyright} {ital 1996 The American Physical Society.}

  19. Thermally stable perpendicular magnetic anisotropy features of Ta/TaO{sub x}/Ta/CoFeB/MgO/W stacks via TaO{sub x} underlayer insertion

    SciTech Connect

    Yang, SeungMo; Lee, JaBin; An, GwangGuk; Kim, JaeHong; Chung, WooSeong; Hong, JinPyo

    2014-09-21

    We report that a TaO{sub x} underlayer enhances the stability of perpendicular magnetic anisotropy (PMA) in TaO{sub x}/Ta/CoFeB/MgO stacks during annealing; control of oxygen content in the TaO{sub x} layer is critical. X-ray photoelectron spectroscopy observations revealed clear suppression of Ta atom diffusion towards the CoFeB/MgO interface or MgO regions. The TaO{sub x} underlayer possibly served as a diffusion sponge, permitting some thermally activated Ta atoms to impregnate the TaO{sub x} underlayer via a diffusion path, such as grain boundaries. We propose a possible mechanism for enhanced PMA stability based on diffusion of thermally activated Ta atoms.

  20. Effects of Solute Nb Atoms and Nb Precipitates on Isothermal Transformation Kinetics from Austenite to Ferrite

    NASA Astrophysics Data System (ADS)

    Wang, Li; Parker, Sally; Rose, Andrew; West, Geoff; Thomson, Rachel

    2016-05-01

    Nb is a very important micro-alloying element in low-carbon steels, for grain size refinement and precipitation strengthening, and even a low content of Nb can result in a significant effect on phase transformation kinetics from austenite to ferrite. Solute Nb atoms and Nb precipitates may have different effects on transformation behaviors, and these effects have not yet been fully characterized. This paper examines in detail the effects of solute Nb atoms and Nb precipitates on isothermal transformation kinetics from austenite to ferrite. The mechanisms of the effects have been analyzed using various microscopy techniques. Many solute Nb atoms were found to be segregated at the austenite/ferrite interface and apply a solute drag effect. It has been found that solute Nb atoms have a retardation effect on ferrite nucleation rate and ferrite grain growth rate. The particle pinning effect caused by Nb precipitates is much weaker than the solute drag effect.

  1. Effects of Solute Nb Atoms and Nb Precipitates on Isothermal Transformation Kinetics from Austenite to Ferrite

    NASA Astrophysics Data System (ADS)

    Wang, Li; Parker, Sally; Rose, Andrew; West, Geoff; Thomson, Rachel

    2016-07-01

    Nb is a very important micro-alloying element in low-carbon steels, for grain size refinement and precipitation strengthening, and even a low content of Nb can result in a significant effect on phase transformation kinetics from austenite to ferrite. Solute Nb atoms and Nb precipitates may have different effects on transformation behaviors, and these effects have not yet been fully characterized. This paper examines in detail the effects of solute Nb atoms and Nb precipitates on isothermal transformation kinetics from austenite to ferrite. The mechanisms of the effects have been analyzed using various microscopy techniques. Many solute Nb atoms were found to be segregated at the austenite/ferrite interface and apply a solute drag effect. It has been found that solute Nb atoms have a retardation effect on ferrite nucleation rate and ferrite grain growth rate. The particle pinning effect caused by Nb precipitates is much weaker than the solute drag effect.

  2. Studies of the local geometry for Fe3 in LiTaO3 crystal from EPR data

    NASA Astrophysics Data System (ADS)

    Wen-Chen, Z.

    The EPR zero-field splitting D for Fe3+ in LiTaO3 crystal has been calculated from the microscopic spin-orbit coupling mechanism and the empirical superposition model. It is found that to reach the good fit between the calculated and observed values of D, the Fe3+ ion does not occupy the exact Li+ site, but is required to move about 0.24±0.11 Å in the direction of the -c axis in LiTaO3 crystal. The result is very similar to that for Fe3+ in the isomorphous LiNbO3 crystal obtained from the X-ray standing waves experiment. The reasonableness of the Fe3+ displacement is discussed.

  3. Structure and physical properties of EuTa{sub 2}O{sub 6} tungsten bronze polymorph

    SciTech Connect

    Kolodiazhnyi, T. Sakurai, H.; Vasylkiv, O.; Borodianska, H.; Forbes, S.; Mozharivskyj, Y.

    2014-08-11

    A tetragonal tungsten bronze (TTB) polymorph of EuTa{sub 2}O{sub 6} was prepared and analyzed. EuTa{sub 2}O{sub 6} crystallizes in the centrosymmetric Pnam space group (with unit cell: a = 12.3693, b = 12.4254, and c = 7.7228 Å) isomorphous with orthorhombic β-SrTa{sub 2}O{sub 6}. In contrast to early reports, we see no evidence of deviation from paramagnetic Curie-Weiss behavior among the Eu{sup 2+} 4f{sup 7}spins in EuTa{sub 2}O{sub 6} down to 2 K. Dielectric constant shows a broad peak at ca. 50 K with dielectric dispersion resembling diffuse phase transition. The relaxation time, however, follows a simple (non-freezing) thermally activated process with an activation energy of 92 meV and an attempt frequency of f{sub 0} = 5.79 × 10{sup 12 }Hz. A thermal conductivity of EuTa{sub 2}O{sub 6} shows a low-temperature (T ≈ 30 K) “plateau” region reminiscent of a glass-like behaviour in Nb-based TTB compounds. This behaviour can be attributed to the loosely bound Eu{sup 2+} ions occupying large tricapped trigonal prismatic sites in the EuTa{sub 2}O{sub 6} structure.

  4. Vibrational analysis of Ba{sub 5-x}Sr{sub x}Nb{sub 4}O{sub 15} microwave dielectric ceramic resonators

    SciTech Connect

    Ratheesh, R.; Sreemoolanadhan, H.; Sebastian, M.T.

    1997-06-01

    The Ba{sub 5-x}Sr{sub x}Nb{sub 4}O{sub 15} ceramics have been prepared and characterised using XRD, Raman, FTIR, and microwave dielectric property measurements. The measured dielectric properties show smooth variation with Sr content. The spectroscopic studies show that the symmetry of the NbO{sub 6} octahedra increases with increase in strontium content, maintaining the hexagonal structure. Hence, the possibility of a monoclinic structure for Sr{sub 5}Nb{sub 4}O{sub 15} seems to be inappropriate. The observed symmetric stretching bands of NbO{sub 6} octahedra confirm the existence of corner connected octahedra in all the solid solution compounds. The behavior of the dielectric constant of (Ba{sub 5-x}Sr{sub x})Nb{sub 4}O{sub 15} system can be correlated to the variation of symmetric stretching vibrations of NbO{sub 6} octahedra.

  5. First-principles studies of Ni-Ta intermetallic compounds

    SciTech Connect

    Zhou Yi; Wen Bin; Ma Yunqing; Melnik, Roderick; Liu Xingjun

    2012-03-15

    The structural properties, heats of formation, elastic properties, and electronic structures of Ni-Ta intermetallic compounds are investigated in detail based on density functional theory. Our results indicate that all Ni-Ta intermetallic compounds calculated here are mechanically stable except for P21/m-Ni{sub 3}Ta and hc-NiTa{sub 2}. Furthermore, we found that Pmmn-Ni{sub 3}Ta is the ground state stable phase of Ni{sub 3}Ta polymorphs. The polycrystalline elastic modulus has been deduced by using the Voigt-Reuss-Hill approximation. All Ni-Ta intermetallic compounds in our study, except for NiTa, are ductile materials by corresponding G/K values and poisson's ratio. The calculated heats of formation demonstrated that Ni{sub 2}Ta are thermodynamically unstable. Our results also indicated that all Ni-Ta intermetallic compounds analyzed here are conductors. The density of state demonstrated the structure stability increases with the Ta concentration. - Graphical abstract: Mechanical properties and formation heats of Ni-Ta intermetallic compounds are discussed in detail in this paper. Highlights: Black-Right-Pointing-Pointer Ni-Ta intermetallic compounds are investigated by first principle calculations. Black-Right-Pointing-Pointer P21/m-Ni{sub 3}Ta and hc-NiTa{sub 2} are mechanically unstable phases. Black-Right-Pointing-Pointer Pmmn-Ni{sub 3}Ta is ground stable phase of Ni{sub 3}Ta polymorphs. Black-Right-Pointing-Pointer All Ni-Ta intermetallic compounds are conducting materials.

  6. Low-Temperature Aging Kinetics of a 15-Year Old Water-Quenched U-6wt.% Nb Alloy

    SciTech Connect

    Hsiung, L; Zhou, J

    2007-10-30

    It is well known that U-6wt.% Nb (U-14at.% Nb) alloy has a microstructure containing martensitic phases supersaturated with Nb that can be obtained by rapid quenching the alloy from {gamma} (bcc)-field solid solution to room temperature. The high cooling rate forces the {gamma}-phase solid solution to transform to variants of the low-temperature {alpha} (orthorhombic) phase in which Nb is forced to retain in the supersaturated solid solution. However, the crystal lattice of supersaturated solution formed by rapid quenching is in unstable conditions and is severely distorted since the solubility of Nb in the {alpha} phase at room temperature is nearly zero under an equilibrium condition. Two variant phases, a monoclinic distortion of {alpha} phase that is designated as {alpha}{double_prime} martensite and a tetragonal distortion of {gamma} phase that is designated as {gamma}{sup o} phase, can form in the as-quenched alloy, as shown in Fig. 1. We have learned from our previous TEM studies on the low-temperature aging of a water-quenched U6Nb (WQ-U6Nb) alloy that there are two possible transformation pathways for phase decomposition of the alloy supersaturated with 14 at.% of Nb upon aging at temperatures below 200 C, i.e., (1) supersaturated solid solution {alpha}{double_prime} {yields} spinodal decomposition {yields} {alpha}{sub 1} (Nb-lean) + {alpha}{sub 2} (Nb-rich) at 200 C and (2) supersaturated solid solution {alpha}{double_prime} {yields} spinodal ordering {yields}{alpha}{double_prime}{sub po} (partially ordered phase) {yields} phase decomposition and precipitation {yields} {alpha} (U) + {alpha}{sub o} (U{sub 3}Nb) at ambient temperatures [1]. The mechanisms for the spinodal transformation occurred at 200 C and the spinodal ordering occurred at ambient temperatures are quite similar; both are caused by the composition modulation of Nb except that the wavelength ({lambda} {approx} 3 nm) of modulation for spinodal decomposition is larger than that ({lambda

  7. Materials Analysis of CED Nb Films Being Coated on Bulk Nb Single Cell SRF Cavities

    SciTech Connect

    Zhao, Xin; Reece, Charles; Palczewski, Ari; Ciovati, Gianluigi; Krishnan, Mahadevan; James, Colt; Irfan, Irfan

    2013-09-01

    This study is an on-going research on depositing a Nb film on the internal wall of bulk Nb single cell SRF cavities, via a cathodic arc Nb plasma ions source, an coaxial energetic condensation (CED) facility at AASC company. The motivation is to firstly create a homoepitaxy-like Nb/Nb film in a scale of a ~1.5GHz RF single cell cavity. Next, through SRF measurement and materials analysis, it might reveal the baseline properties of the CED-type homoepitaxy Nb films. Literally, a top-surface layer of Nb films which sustains SRF function, always grows up in homo-epitaxy mode, on top of a Nb nucleation layer. Homo-epitaxy growth of Nb must be the final stage (a crystal thickening process) of any coatings of Nb film on alternative cavity structure materials. Such knowledge of Nb-Nb homo-epitaxy is useful to create future realistic SRF cavity film coatings, such as hetero-epitaxy Nb/Cu Films, or template-layer-mitigated Nb films. One large-grain, and three fine grain bulk Nb cavities were coated. They went through cryogenic RF measurement. Preliminary results show that the Q0 of a Nb film could be as same as the pre-coated bulk Nb surface (which received a chemically-buffered polishing plus a light electro-polishing); but quality factor of two tested cavities dropped quickly. We are investigating if the severe Q-slope is caused by hydrogen incorporation before deposition, or is determined by some structural defects during Nb film growth.

  8. Icositetrahedral and icosahedral atomic configurations observed in the Nb-Ag metallic glasses synthesized by ion beam mixing

    SciTech Connect

    Tai, K. P.; Gao, N.; Dai, X. D.; Li, J. H.; Lai, W. S.; Liu, B. X.

    2006-08-28

    Metallic glasses are obtained in an immiscible Nb-Ag system by ion beam mixing and an atomic configuration in the amorphous structure is discovered, i.e., an icositetrahedral ordering, which, together with an icosahedral ordering also observed in the Nb-Ag metallic glasses and in some previously reported systems, helps in formulating a structural spectrum of the amorphous solids. The experimental characterization and atomistic modeling with an ab initio derived Nb-Ag potential demonstrate the significance of structural heredity, i.e., the crystalline structures of the constituent metals play a decisive role in determining the atomic structure of the metallic glasses in the system.

  9. Submillimeter SIS Mixers Using High Current Density Nb/AIN/Nb Tunnel Junctions and NbTiN Films

    NASA Astrophysics Data System (ADS)

    Kawamura, J.; Miller, D.; Chen, J.; Kooi, J.; Zmuidzinas, J.; Bumble, B.; Leduc, H.; Stern, J.

    1999-03-01

    We are currently exploring ways to improve the performance of SIS mixers above 700 GHz. One approach is to use NbTiN in place of Nb for all or some of the mixer circuitry. With its high gap frequency and low losses demonstrated up to 800 GHz, it should be possible to fabricate an all-NbTiN SIS mixer with near quantum-limited noise performance up to 1.2 THz. Using a quasioptical twin-slot two-junction mixer with NbTiN ground plane and wiring and hybrid Nb/A1N/NbTiN junctions, we measured an uncorrected receiver noise temperature of TRx ~ 500 K across 790-850 GHz at 4.2 K bath temperature. Our second approach is to reduce the RC product of the mixer by employing very high current density Nb/A1N/Nb junctions. By using these we will greatly relax the requirement on tuning circuits, which is where substantial losses occur in mixers operating above the Nb gap frequency. These junctions have resistance-area products of R_N*A ~ 5.6 Ohm um2, good subgap to normal resistance ratios, R_sg/R_N ~ 10, and good run-to-run reproducibility. From FTS measurements we infer that omega*R_N*C = 1 at 270 GHz in these junctions. This is a substantial improvement over that available using Nb/Al0x/Nb technology. The sensitivity of a receiver incorporating these high current density mixers is T_Rx = 110 K at 533 GHz using a design for lower J_c mixers, which is close to the best we have measured with lower J_c Nb/Al0x/Nb mixers.

  10. Thermoelectric properties in the series Ti{sub 1-x}Ta{sub x}S{sub 2}

    SciTech Connect

    Beaumale, M.; Barbier, T.; Bréard, Y.; Hébert, S.; Guilmeau, E.; Kinemuchi, Y.

    2014-01-28

    Polycrystalline samples in the series Ti{sub 1-x}Ta{sub x}S{sub 2} with x varying from 0 to 1 were prepared using solid-liquid-vapor reaction and spark plasma sintering. Rietveld refinements of X-ray diffraction data are consistent with the existence of a full solid solution for x ≤ 0.4. Transport measurements reveal that tantalum can act as electron donor when substituted in the Ti sites. As a consequence, the electrical resistivity and the absolute value of the Seebeck coefficient decrease with Ta content due to an increase in the carrier concentration. The lattice thermal conductivity being reduced due to mass fluctuation effect, the ZT values in Ti{sub 0.95}Ta{sub 0.05}S{sub 2} is slightly increased as compared to TiS{sub 2}.

  11. TaRAR1 and TaSGT1 associate with TaHsp90 to function in bread wheat (Triticum aestivum L.) seedling growth and stripe rust resistance.

    PubMed

    Wang, Guan-Feng; Fan, Renchun; Wang, Xianping; Wang, Daowen; Zhang, Xiangqi

    2015-04-01

    RAR1 and SGT1 are important co-chaperones of Hsp90. We previously showed that TaHsp90.1 is required for wheat seedling growth, and that TaHsp90.2 and TaHsp90.3 are essential for resistance (R) gene mediated resistance to stripe rust fungus. Here, we report the characterization of TaRAR1 and TaSGT1 genes in bread wheat. TaRAR1 and TaSGT1 each had three homoeologs, which were located on wheat groups 2 and 3 chromosomes, respectively. Strong inhibition of seedling growth was observed after silencing TaSGT1 but not TaRAR1. In contrast, decreasing the expression of TaRAR1 or TaSGT1 could all compromise R gene mediated resistance to stripe rust fungus infection. Protein-protein interactions were found among TaRAR1, TaSGT1 and TaHsp90. The N-terminus of TaHsp90, the CHORD-I and CHORD-II domains of TaRAR1 and the CS domain of TaSGT1 may be instrumental for the interactions among the three proteins. Based on this work and our previous study on TaHsp90, we speculate that the TaSGT1-TaHsp90.1 interaction is important for maintaining bread wheat seedling growth. The TaRAR1-TaSGT1-TaHsp90.2 and TaRAR1-TaSGT1-TaHsp90.3 interactions are involved in controlling the resistance to stripe rust disease. The new information obtained here should aid further functional investigations of TaRAR1-TaSGT1-TaHsp90 complexes in regulating bread wheat growth and disease resistance. PMID:25697954

  12. Team one (GA/MCA) effort of the DOE 12 Tesla Coil Development Program. 12 Tesla ETF toroidal field coil helium bath cooled NbTi alloy concept

    SciTech Connect

    Not Available

    1980-07-01

    This report presents the conceptual design of an ETF compatible toroidal field coil, employing helium bath cooled NbTi alloy conductor. The ten TF-coil array generates a peak field of 11-1/2 tesla at 2.87 m radius, corresponding to a major axis field of 6.1 tesla. The 10 kA conductor is an uninsulated, unsoldered Rutherford cable, employing NbTiTa ally as developed in Phase I of this effort. The conductor is encased within a four element frame of stainless steel strips to provide hoop and bearing load support.

  13. Containerless processing of Nb-Ge alloys in a long drop tube

    NASA Technical Reports Server (NTRS)

    Bayuzick, R. J.

    1982-01-01

    The thirty-two meter drop tube at the Marshall Space Flight Center was used to study the effect of zero gravity containerless processing on the structure and properties of materials. The concept involves the suppression of heterogeneous nucleation of solid in liquid and, therefore, solidification accompanied by large degrees of undercooling. Under these conditions metastable phases can be formed or, at the very least, unique nonequilibrium microstructures (containing equilibrium phases) with unique properties can be produced. The drop tube solidification was applied to niobium base alloys with emphasis on the Nb-Ge binary system in an effort to produce metastable phases with high superconducting transition temperatures in bulk specimens. In the past, only lower Ge alloys (Nb-13 a/o, Nb-18 a/o, and Nb-22 a/o) could be undercooled. Higher Ge alloys (e.g., Nb-25 a/o Ge and Nb-27 a/o Ge) can now be undercooled on a routine basis.

  14. Softening Kinetics in High Al and High Al-Nb-Microalloyed Steels

    NASA Astrophysics Data System (ADS)

    Pereda, B.; Aretxabaleta, Z.; López, B.

    2015-03-01

    Double-hit torsion tests were performed in order to study the effect of high Al levels (up to 2 wt.%) and Nb microalloying (up to 0.07 wt.%) on the static softening kinetics of 0.2%C-2%Mn steels. The addition of 1%Al leads to a delay in the softening kinetics due to solute-drag effect, equivalent to that exerted by 0.027%Nb. For the 2%Al steels, at temperatures below 1000 °C, γ → α phase transformation occurs after deformation, resulting in a larger retardation of the softening kinetics. At temperatures higher than 1000 °C, Nb in solid solution also contributes to the retardation of the static softening kinetics, and at lower temperatures NbC strain-induced precipitation leads to incomplete softening for the 1%Al steel, and to a complex interaction between softening, phase transformation, and NbC strain-induced precipitation for the 2%Al-Nb steels. The effect of Al on the static softening kinetics was quantified and introduced in a model developed in previous works for the prediction of the austenite microstructural evolution. In order to validate the results of the model, multipass torsion tests were carried out at conditions representative of hot strip and plate rolling mills. Model predictions show reasonable agreement with the results obtained at different deformation conditions.

  15. Second order incommensurate phase transition in 25L-Ta{sub 2}O{sub 5}

    SciTech Connect

    Audier, M.; Chenevier, B.; Roussel, H.; Lintanf Salauen, A.

    2010-09-15

    A new structural state 25L-Ta{sub 2}O{sub 5}, obtained from sintering and annealing treatments of a Ta{sub 2}O{sub 5} powder, is identified both by electron diffraction and high resolution imaging on a transmission electron microscope (TEM). According to general rules for the different L-Ta{sub 2}O{sub 5} structures proposed by Grey et al. (J. Solid State Chem. 178 (2005) 3308), a structural model is derived from their crystallographic data on 19L-Ta{sub 2}O{sub 5}. This model yields simulated images in agreement with high resolution TEM observations of the structure oriented along its [001] zone axis, but only for a very thin crystal thickness of less than 1.2 nm. Such a limitation is shown to be due to a modulation of the structure along its [001] axis. Actually, from an analysis of a diffuse scattering and of its evolution into satellites reflections as a function of the cooling rate, a second order incommensurate phase transition can be assumed to occur in this compound. The property of single phase samples observed by TEM is also verified by X-ray powder diffraction. In a discussion about studies performed by different authors on incommensurate structures in the system Ta{sub 2}O{sub 5}-WO{sub 3}, it is noticed that TEM results, similar to ours, indicate that phase transitions could be expected in these structures. - Graphical Abstract: Electron diffraction patterns of [100] zone axis, showing a structural change of the 25L-Ta{sub 2}O{sub 5} phase through a variation of the cooling rate from 1000 {sup o}C.

  16. Engineering Mathematics Assessment Using "MapleTA"

    ERIC Educational Resources Information Center

    Jones, Ian S.

    2008-01-01

    The assessment of degree level engineering mathematics students using the computer-aided assessment package MapleTA is discussed. Experience of academic and practical issues for both online coursework and examination assessments is presented, hopefully benefiting other academics in this novel area of activity. (Contains 6 figures and 1 table.)

  17. Preliminary analysis of EUSO—TA data

    NASA Astrophysics Data System (ADS)

    Fenu, F.; Piotrowski, L. W.; Shin, H.; Jung, A.; Bacholle, S.; Bisconti, F.; Capel, F.; Eser, J.; Kawasaki, Y.; Kuznetsov, E.; Larsson, O.; Mackovjak, S.; Miyamoto, H.; Plebaniak, Z.; Prevot, G.; Putis, M.; Shinozaki, K.; Adams, J.; Bertaina, M.; Bobik, P.; Casolino, M.; Matthews, J. N.; Ricci, M.; Wiencke, L.; EUSO-TA Collaboration

    2016-05-01

    The EUSO-TA detector is a pathfinder for the JEM-EUSO project and is currently installed in Black Rock Mesa (Utah) on the site of the Telescope Array fluorescence detectors. Aim of this experiment is to validate the observation principle of JEM-EUSO on air showers measured from ground. The experiment gets data in coincidence with the TA triggers to increase the likelihood of cosmic ray detection. In this framework the collaboration is also testing the detector response with respect to several test events from lasers and LED flashers. Moreover, another aim of the project is the validation of the stability of the data acquisition chain in real sky condition and the optimization of the trigger scheme for the rejection of background. Data analysis is ongoing to identify cosmic ray events in coincidence with the TA detector. In this contribution we will show the response of the EUSO-TA detector to all the different typologies of events and we will show some preliminary results on the trigger optimization performed on such data.

  18. Kinetic behavior of WO3-doped Nb2O5 electrochromic thin films

    NASA Astrophysics Data System (ADS)

    Melo, Luciana O.; Dragunski, Douglas C.; Avellaneda, Cesar O.; Pawlicka, Agnieszka

    2003-07-01

    An electrochromic material (EC) reversibly changes its optical characteristics response, coloring and bleaching states when a small voltage or current is passed through it. This phenomenon is used to develop electrochromic devices like smart windows, which control the amount of heat and light entering in a building and optimize energy consumption. The change of the transparency of these devices involves the injection and extraction of small cations and electrons into the EC material and study of the kinetics of ions injection implies on operation understanding of these devices. Pure and doped niobium oxides (Nb2O5) are promising cathodic electrochromic materials and their electrooptical performance depends strongly of its structural morphology. The sol-gel process allows for facile fabrication of large area coatings at a low cost and offers advantages of controlling the composition and microstructure of the films. In order to study the solid sate diffusion of lithium into Nb2O5, Nb2O5:Li+ and Nb2O5:WO3, two electroanalytical techniques have been used i.e. galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS). GITT have been applied in order to obtain the chemical diffusion coefficient of Lix in Nb2O5 doped and undoped films, where the values approaching were of the 2.5x10-11 cm2s-1 at x=0,83, 7.4x10-13 cm2s-1 at x=1.65 and 1.6x10-10 cm2s-1 at x=0.33 for Nb2O5, Nb2O5:Li+ and Nb2O5-WO3 respectively. From these measurements it was also observed that within each film, D increases as x increases.

  19. Roles of TaON and Ta(3)N(5) in the visible-Fenton-like degradation of atrazine.

    PubMed

    Du, Yingxun; Zhao, Lu; Zhang, Yuanyuan

    2014-02-28

    In this study, the roles of TaON and Ta3N5 in the degradation of atrazine by the visible-Fenton-like system were examined in detail. The TaON and Ta3N5 samples prepared by the nitridation of Ta2O5 and characterized by XRD, DRS, BET and PL analyses. The results showed that the TaON sample had weaker absorption in the visible region but higher specific surface area than the Ta3N5 sample. The degradation rate of atrazine in visible-TaON-Fenton-like system was 2.64 times than that in visible-Ta3N5-Fenton-like system. Both Fe(2+) and H2O2 could be reduced by eCB (electrons in the conduction band) in TaON or Ta3N5, while atrazine could not be oxidized by hVB (holes in the valance band). OH is the active species for the degradation of atrazine in visible-TaON/Ta3N5-Fenton-like systems. Majority of OH originated from Fenton reaction. After Fe(3+) was reduced by eCB to Fe(2+), Fe(2+) reacted quickly with H2O2 to generate OH. In addition, by capturing eCB, a little of H2O2 was reduced to yield OH, which contributed a small fraction of atrazine degradation. Based on the experimental results, the roles of TaON and Ta3N5 in the visible-Fenton-like system were proposed. And the higher photocatalytic activity of TaON than Ta3N5 was suggested to be due to the higher separation efficiency of electrons and holes, which may be related to the larger specific surface area. PMID:24413052

  20. Phase stability of ScN-based solid solutions for thermoelectric applications from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Kerdsongpanya, Sit; Alling, Björn; Eklund, Per

    2013-08-01

    We have used first-principles calculations to investigate the trends in mixing thermodynamics of ScN-based solid solutions in the cubic B1 structure. 13 different Sc1-xMxN (M = Y, La, Ti, Zr, Hf, V, Nb, Ta, Gd, Lu, Al, Ga, In) and three different ScN1-xAx (A = P, As, Sb) solid solutions are investigated and their trends for forming disordered or ordered solid solutions or to phase separate are revealed. The results are used to discuss suitable candidate materials for different strategies to reduce the high thermal conductivity in ScN-based systems, a material having otherwise promising thermoelectric properties for medium and high temperature applications. Our results indicate that at a temperature of T = 800 °C, Sc1-xYxN; Sc1-xLaxN; Sc1-xGdxN, Sc1-xGaxN, and Sc1-xInxN; and ScN1-xPx, ScN1-xAsx, and ScN1-xSbx solid solutions have phase separation tendency, and thus, can be used for forming nano-inclusion or superlattices, as they are not intermixing at high temperature. On the other hand, Sc1-xTixN, Sc1-xZrxN, Sc1-xHfxN, and Sc1-xLuxN favor disordered solid solutions at T = 800 °C. Thus, the Sc1-xLuxN system is suggested for a solid solution strategy for phonon scattering as Lu has the same valence as Sc and much larger atomic mass.

  1. Synthesis and Optical Characterization of Red-Emitting BaTa2O6:Eu(3+) Phosphors.

    PubMed

    İlhan, Mustafa; Ekmekçi, Mete Kaan; Mergen, Ayhan; Yaman, Cemalettin

    2016-09-01

    Undoped and Eu(3+) doped BaTa2O6 phosphors were synthesized via solid state reaction method and characterized by using XRD, SEM-EDS and photoluminescence (PL) analyses. The XRD results revealed that the crystal structure of BaTa2O6 allowed up to 10 mol% levels of Eu(3+) ions due to the TTB characteristic network of adjacent octahedrals. SEM-EDS analyses confirmed the formation of BaTa2O6 structure and EuTaO4 secondary phase. BaTa2O6:Eu(3+) phosphors exhibited orange and red emissions at 592.2 nm and 615.7 nm in the visible region respectively. The Commission Internationale d'Eclairage (CIE) chromaticity coordinates of the BaTa2O6:Eu(3+) phosphors that excited at λ ex = 400 nm ranged from orangish-red to pinkish-red depending on increasing Eu(3+) concentration. PMID:27325113

  2. Synthesis, structure and photoluminescence properties of Ho3+ doped TTB-BaTa2O6 phosphors

    NASA Astrophysics Data System (ADS)

    İlhan, Mustafa

    2014-12-01

    Ho3+ doped TTB-BaTa2O6 phosphors were produced by the solid state reaction method. XRD analysis confirmed the formation of BaTa2O6 single phase which was accomplished by heat treatment at 1425 °C for 20 h. The crystal structure of TTB-BaTa2O6 allowed doping concentration of Ho3+ ions up to 10 mol%, maintaining a single phase composition. A second phase of HoTaO4 begins to appear at 15 mol%. The lattice structure and the crystallite sizes changed with the concentration of Ho3+. In SEM analysis, it was also shown that BaTa2O6 grain sizes changed with the concentration of Ho3+. EDS analysis revealed that the Ta/Ba ratio increased on the grains depending on Ho3+ concentration. Charge balance of the structure was formulated through the EDS results. In fluorometer analysis, a strong green emission (λem = 546.9 nm) was observed in the visible spectral region. The emission increased with the doping concentration of up to 2.5 mol%, and above this level decreased due to concentration quenching.

  3. Crystal structure and optical properties of high-index LiTaO3 otical waveguides prepared by nonisovalent ion exchange

    NASA Astrophysics Data System (ADS)

    Morozova, Tamara V.; Korkishko, Yuri N.; Fedorov, Vyacheslav A.

    1995-03-01

    The optical properties and both unstrained lattice constants in the high-index zinc-substituted lithium tantalate waveguides are determined depending on exchange and annealing conditions. The LiTaO3-ZnTa2O6 system clearly exhibits a complex structural chemistry. The two distinct phases have been observed. The dependences of the extraordinary and ordinary indices change on the lattice parameters of the unstrained single crystalline Li1-xZnx/2TaO3 solid solutions in both observed phases were obtained.

  4. On the effect of Ta on improved oxidation resistance of Ti-Al-Ta-N coatings

    SciTech Connect

    Pfeiler, M.; Scheu, C.; Hutter, H.; Schnoeller, J.; Michotte, C.; Mitterer, C.; Kathrein, M.

    2009-05-15

    Formation of protective oxide scales is the main reason for the high oxidation resistance of TiAlN based coatings. Here the authors report on further improvement in the oxidation resistance of TiAlN by Ta alloying. An industrial-scale cathodic arc evaporation facility was used to deposit Ti-Al-Ta-N coatings from powder metallurgically produced Ti{sub 38}Al{sub 57}Ta{sub 5} targets. After oxidation in ambient air, a significantly reduced oxide layer thickness in comparison to unalloyed TiAlN reference material was observed. Energy-dispersive x-ray spectroscopy line scans and secondary ion mass spectroscopy depth profiling showed that the oxide scale consists of an Al-rich top layer without detectable amount of Ta and a Ti-Ta-rich sublayer. Transmission electron microscopy investigations revealed {alpha}-Al{sub 2}O{sub 3}, rutile-type TiO{sub 2}, and anatase-type TiO{sub 2} as the scale forming oxides. Furthermore, the Ti-Ta-rich sublayer consists of a porous layer at the oxide-nitride interface but appears dense toward the Al-rich top layer. The improved oxidation resistance is explained by doping the TiO{sub 2} lattice by replacing Ti{sup 4+} with Ta{sup 5+} in the rutile lattice, which decreases the oxygen mass transport. This leads to reduced oxidation of Ti under formation of TiO{sub 2} at the oxide-nitride interface and is the reason for the excellent oxidation behavior of Ti-Al-Ta-N coatings.

  5. Spin Seebeck Effect vs. Anomalous Nernst Effect in Ta/CoFeB /Ta Structures

    NASA Astrophysics Data System (ADS)

    Yang, Bowen; Xu, Yadong; Schneider, Mike; Shi, Jing; Univ of California-Riverside Team; Everspin Technologies Inc. Team

    2014-03-01

    We have studied the spin Seebeck effect (SSE) and anomalous Nernst effect (ANE) in a vertical trilayer structure under a vertical temperature gradient. The structure consists of a 3nm CoFeB layer sandwiched by β-phase tantalum (Ta) layers. The samples are deposited by magnetron sputtering. The existence of Ta β-phase is verified by the resistivity and its negative temperature coefficient of resistance(TCR). Under a fixed vertical temperature gradient, the measured transverse thermoelectric voltage is linearly proportional to the total sample resistance when the Ta thickness exceeds 2 nm, which can be explained by a shunting resistor model. When the Ta thickness is below 2 nm, the voltage deviates from the linear resistance dependence and merges to the ANE voltage of the CoFeB single layer, due to a weakened inverse spin Hall effect (ISHE) in Ta thinner than the spin diffusion length. In the linear regime, the slope contains both a varying SSE and a fixed ANE responses, thus the SSE contribution could be quantitatively separated out from the ANE of CoFeB. Our results indicate a large SSE from the β-phase Ta due to its large Spin Hall Angle. This work was supported by CNN/DMEA and DOE.

  6. Direct evidence on Ta-Metal Phases Igniting Resistive Switching in TaO(x) Thin Film.

    PubMed

    Yang, Min Kyu; Ju, Hyunsu; Kim, Gun Hwan; Lee, Jeon-Kook; Ryu, Han-Cheol

    2015-01-01

    A Ta/TaOx/Pt stacked capacitor-like device for resistive switching was fabricated and examined. The tested device demonstrated stable resistive switching characteristics including uniform distribution of resistive switching operational parameters, highly promising endurance, and retention properties. To reveal the resistive switching mechanism of the device, micro structure analysis using high-resolution transmission electron microscope (HR-TEM) was performed. From the observation results, two different phases of Ta-metal clusters of cubic α-Ta and tetragonal β-Ta were founded in the amorphous TaOx mother-matrix after the device was switched from high resistance state (HRS) to low resistance state (LRS) by externally applied voltage bias. The observed Ta metal clusters unveiled the origin of the electric conduction paths in the TaOx thin film at the LRS. PMID:26365532

  7. Low-temperature deposition of TaB and TaB 2 by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Motojima, Seiji; Kito, Kazuhito; Sugiyama, Kohzo

    1982-02-01

    Tantalum borides were deposited on a copper substrate from a gas phase TaCl 5-BCl 3-H 2-Ar in the temperature range of 540-800°C. TaB 2 (single-phase) was deposited at a source gas flow ratio (BCl 3/TaCl 5) of six and a temperature above 600°C. On the other hand, TaB (single-phase) was deposited at BCl 3/TaCl 5 = 2-4 and 600-700°C. The microhardness of TaB and TaB 2 were 3250 and 3150 kg/mm 2, respectively. The TaB layer was stable to oxidation below 700° C and to acid corrosion.

  8. Garnet-type solid-state fast Li ion conductors for Li batteries: critical review.

    PubMed

    Thangadurai, Venkataraman; Narayanan, Sumaletha; Pinzaru, Dana

    2014-07-01

    Batteries are electrochemical devices that store electrical energy in the form of chemical energy. Among known batteries, Li ion batteries (LiBs) provide the highest gravimetric and volumetric energy densities, making them ideal candidates for use in portable electronics and plug-in hybrid and electric vehicles. Conventional LiBs use an organic polymer electrolyte, which exhibits several safety issues including leakage, poor chemical stability and flammability. The use of a solid-state (ceramic) electrolyte to produce all-solid-state LiBs can overcome all of the above issues. Also, solid-state Li batteries can operate at high voltage, thus, producing high power density. Various types of solid Li-ion electrolytes have been reported; this review is focused on the most promising solid Li-ion electrolytes based on garnet-type metal oxides. The first studied Li-stuffed garnet-type compounds are Li5La3M2O12 (M = Nb, Ta), which show a Li-ion conductivity of ∼10(-6) at 25 °C. La and M sites can be substituted by various metal ions leading to Li-rich garnet-type electrolytes, such as Li6ALa2M2O12, (A = Mg, Ca, Sr, Ba, Sr0.5Ba0.5) and Li7La3C2O12 (C = Zr, Sn). Among the known Li-stuffed garnets, Li6.4La3Zr1.4Ta0.6O12 exhibits the highest bulk Li-ion conductivity of 10(-3) S cm(-1) at 25 °C with an activation energy of 0.35 eV, which is an order of magnitude lower than that of the currently used polymer, but is chemically stable at higher temperatures and voltages compared to polymer electrolytes. Here, we discuss the chemical composition-structure-ionic conductivity relationship of the Li-stuffed garnet-type oxides, as well as the Li ion conduction mechanism. PMID:24681593

  9. New substitutions and novel derivatives of the Aurivillius phases, Bi{sub 5}TiNbWO{sub 15} and Bi{sub 4}Ti{sub 3}O{sub 12}

    SciTech Connect

    Tripathy, Mamata; Mani, Rohini; Gopalakrishnan, J. . E-mail: gopal@sscu.iisc.ernet.in

    2007-05-03

    We investigated isomorphous substitution of several metal atoms in the Aurivillius structures, Bi{sub 5}TiNbWO{sub 15} and Bi{sub 4}Ti{sub 3}O{sub 12}, in an effort to understand structure-property correlations. Our investigations have led to the synthesis of new derivatives, Bi{sub 4}LnTiMWO{sub 15} (Ln = La, Pr; M = Nb, Ta), as well as Bi{sub 4}PbNb{sub 2}WO{sub 15} and Bi{sub 3}LaPbNb{sub 2}WO{sub 15}, that largely retain the Aurivillius (n = 1) + (n = 2) intergrowth structure of the parent oxide Bi{sub 5}TiNbWO{sub 15}, but characteristically tend toward a centrosymmetric/tetragonal structure for the Ln-substituted derivatives. On the other hand, coupled substitution, 2Ti{sup IV} {sup {yields}} M{sup V} + Fe{sup III} in Bi{sub 4}Ti{sub 3}O{sub 12}, yields new Aurivillius phases, Bi{sub 4}Ti{sub 3-2x}Nb {sub x}Fe {sub x}O{sub 12} (x = 0.25, 0.50) and Bi{sub 4}Ti{sub 3-2x}Ta {sub x}Fe {sub x}O{sub 12} (x = 0.25) that retain the orthorhombic noncentrosymmetric structure of the parent Bi{sub 4}Ti{sub 3}O{sub 12}. Two new members of this family, Bi{sub 2}Sr{sub 2}Nb{sub 2}RuO{sub 12} and Bi{sub 2}SrNaNb{sub 2}RuO{sub 12} that are analogous to Bi{sub 2}Sr{sub 2}Nb{sub 2}TiO{sub 12}, possessing tetragonal (I4/mmm) Aurivillius structure have also been synthesized.

  10. RbCa2Nb3O10 from X-ray powder data

    PubMed Central

    Liang, Zhen-Hua; Tang, Kai-Bin; Chen, Qian-Wang; Zheng, Hua-Gui

    2009-01-01

    Rubidium dicalcium triniobate(V), RbCa2Nb3O10, has been synthesized by solid-state reaction and its crystal structure refined from X-ray powder diffraction data using Rietveld analysis. The compound is a three-layer perovskite Dion–Jacobson phase with the perovskite-like slabs derived by termination of the three-dimensional CaNbO3 perovskite structure along the ab plane. The rubidium ions (4/mmm symmetry) are located in the inter­stitial space. PMID:21582979

  11. Synthesis of MgNb{sub 2}O{sub 6} by coprecipitation

    SciTech Connect

    Navale, S.C.; Gaikwad, A.B.; Ravi, V. . E-mail: ravi@ems.ncl.res.in

    2006-07-13

    A simple coprecipitation technique was used successfully to synthesize fine powders of MgNb{sub 2}O{sub 6} (MN) phase. An aqueous mixture of ammonium carbonate and ammonium hydroxide was used to precipitate Mg{sup 2+} and Nb{sup 5+} cations as carbonate and hydroxide respectively under basic conditions. This precipitate on heating at 750 deg. C produced MN powders. For comparison MN powders were prepared by the traditional solid state method. The phase content and the lattice parameters were studied by powder X-ray diffraction (XRD). Particle size and morphology of the particles were studied by scanning electron microscopy (SEM)

  12. Structural, dielectric and magnetic studies of Ba and Nb codoped BiFeO3 multiferroics

    NASA Astrophysics Data System (ADS)

    Jangra, Sandhaya; Sanghi, Sujata; Agarwal, Ashish; Kaswan, Kavita; Rangi, Manisha; Singh, Ompal

    2016-05-01

    Polycrystalline materials with composition Bi0.8Ba0.2Fe1-xNbxO3 (x= 0.07, 0.10) were prepared via solid state reaction method. Preliminary analysis of structure was performed by XRD technique and confirmed formation of single phase crystalline materials. Rietveld refinement reveled that these materials have rhombohedral phase with R3c space group. Dielectric constant increased with temperature and Nb concentration. Ba and Nb co-doping suppress the spiral spin structure and produce net magnetization.

  13. Dielectric and Electrical Properties of BiFeO3-LiTaO3 Systems

    NASA Astrophysics Data System (ADS)

    Mohanty, Suchismita; Choudhary, R. N. P.

    2015-07-01

    Materials of general formula (Bi1- x Li x )(Fe1- x Ta x )O3 ( x = 0.0, 0.5) were prepared from polycrystalline BiFeO3 and LiTaO3 by solid-state reaction. Analysis of the basic structural properties of the materials by room-temperature x-ray diffraction revealed the formation of single-phase tetragonal crystals for (Bi0.5Li0.5)(Fe0.5Ta0.5)O3. Scanning electron micrographs confirmed the polycrystalline nature of the materials. The microstructure of the materials comprised uniformly distributed grains of unequal size. Studies of the temperature-frequency dependence of dielectric did not reveal any dielectric anomaly or phase transition in the temperature range studied. The presence of hysteresis loops at room temperature confirmed the known ferroelectricity of BiFeO3 and (Bi0.5Li0.5)(Fe0.5Ta0.5)O3. Complex impedance spectroscopic analysis revealed the materials had negative temperature coefficient of resistance (NTCR)-type behavior. The electrical conductivity and relaxation characteristics of the materials suggested the presence of a thermally activated process, and their values suggested the materials had similar types of conductivity and relaxation species. The frequency dependence of the ac conductivity obeyed Jonscher's universal power law.

  14. Enhancement of the superconducting critical temperature in Nb/Py/Nb trilayers

    NASA Astrophysics Data System (ADS)

    Ilyina, E. A.; Hernàndez, J. M.; García-Santiago, A.; Cirillo, C.; Attanasio, C.

    2012-09-01

    Superconducting critical temperature, Tc, have been measured in a series of Nb/Py/Nb (here Py = Ni80Fe20) trilayers having constant Py thickness, dPy = 432 nm, and variable Nb thickness, dNb, in the range 20-30 nm. We have observed that, for dNb between 23 and 27 nm, resistive transitions shift towards higher temperature if stripe domains are present in the Py layer. We relate those observations to the non-homogeneous magnetization in the Py layer due to the presence of stripe domain structures.

  15. Atomically engineering Cu/Ta interfaces.

    SciTech Connect

    Webb, Edmund Blackburn, III; Zhou, Xiao Wang

    2007-09-01

    This report summarizes the major research and development accomplishments for the late start LDRD project (investment area: Enable Predictive Simulation) entitled 'Atomically Engineering Cu/Ta Interfaces'. Two ultimate goals of the project are: (a) use atomistic simulation to explore important atomistic assembly mechanisms during growth of Cu/Ta multilayers; and (b) develop a non-continuum model that has sufficient fidelity and computational efficiency for use as a design tool. Chapters 2 and 3 are essentially two papers that address respectively these two goals. In chapter 2, molecular dynamics simulations were used to study the growth of Cu films on (010) bcc Ta and Cu{sub x}Ta{sub 1-x} alloy films on (111) fcc Cu. The results indicated that fcc crystalline Cu films with a (111) texture are always formed when Cu is grown on Ta. The Cu films are always polycrystalline even when the Ta substrate is single crystalline. These polycrystalline films are composed of grains with only two different orientations, which are separated by either orientational grain boundaries or misfit dislocations. Periodic misfit dislocations and stacking fault bands are observed. The Cu film surface roughness was found to decrease with increasing adatom energy. Due to a Cu surface segregation effect, the Cu{sub x}Ta{sub 1-x} films deposited on Cu always have a higher Cu composition than that used in the vapor mixture. When Cu and Ta compositions in the films are comparable, amorphous structures may form. The fundamental origins for all these phenomena have been studied in terms of crystallography and interatomic interactions. In chapter 3, a simplified computational method, diffusional Monte Carlo (dMC) method, was developed to address long time kinetic processes of materials. Long time kinetic processes usually involve material transport by diffusion. The corresponding microstructural evolution of materials can be analyzed by kinetic Monte Carlo simulation methods, which essentially

  16. High-throughput exploration of thermoelectric and mechanical properties of amorphous NbO2 with transition metal additions

    NASA Astrophysics Data System (ADS)

    Music, Denis; Geyer, Richard W.; Hans, Marcus

    2016-07-01

    To increase the thermoelectric efficiency and reduce the thermal fatigue upon cyclic heat loading, alloying of amorphous NbO2 with all 3d and 5d transition metals has systematically been investigated using density functional theory. It was found that Ta fulfills the key design criteria, namely, enhancement of the Seebeck coefficient and positive Cauchy pressure (ductility gauge). These quantum mechanical predictions were validated by assessing the thermoelectric and elastic properties on combinatorial thin films, which is a high-throughput approach. The maximum power factor is 2813 μW m-1 K-2 for the Ta/Nb ratio of 0.25, which is a hundredfold increment compared to pure NbO2 and exceeds many oxide thermoelectrics. Based on the elasticity measurements, the consistency between theory and experiment for the Cauchy pressure was attained within 2%. On the basis of the electronic structure analysis, these configurations can be perceived as metallic, which is consistent with low electrical resistivity and ductile behavior. Furthermore, a pronounced quantum confinement effect occurs, which is identified as the physical origin for the Seebeck coefficient enhancement.

  17. Oxygen Atom Adsorption on and Diffusion into Nb(110) and Nb(100) from First Principles

    SciTech Connect

    Tafen, De Nyago; Gao, Michael C

    2013-11-01

    In order to understand the dynamics of oxidation of Nb, we examine the adsorption, absorption, and diffusion of an oxygen atom on, in, and into Nb(110) and Nb(100) surfaces, respectively, using density functional theory. Our calculations predict that the oxygen atom adsorbs on the threefold site on Nb(110) and the fourfold hollow site on Nb(100), and the adsorption energy is -5.08 and -5.18 eV respectively. We find the long and short bridge sites to be transition states for O diffusion on Nb(110), while the on top site is a rank-2 saddle point. In the subsurface region, the oxygen atom prefers the octahedral site, as in bulk niobium. Our results also show that the O atom is more stable on Nb(110) subsurface than on Nb(100) subsurface. The diffusion of oxygen atoms into niobium surfaces passes through transition states where the oxygen atom is coordinated to four niobium atoms. The diffusion barriers of the oxygen atom into Nb(110) and Nb(100) are 1.81 and 2.05 eV, respectively. Analysis of the electronic density of states reveals the emergence of well localized electronic states below the lowest states of clean Nb surfaces due to d-p orbital hybridization.

  18. Optimization of Ta thickness for perpendicular magnetic tunnel junction applications in the MgO-FeCoB-Ta system

    NASA Astrophysics Data System (ADS)

    Sokalski, Vincent; Moneck, Matthew T.; Yang, En; Zhu, Jian-Gang

    2012-08-01

    The impact of Ta thickness on magnetic anisotropy and interlayer magnetic coupling is evaluated for the Ta-FeCoB-MgO thin film system commonly used in magnetic tunnel junctions. It is shown that there exists a window of Ta thickness where strong magnetic coupling of FeCoB with another magnetic layer is achievable through Ta while still maintaining properties required for use in a perpendicular magnetic tunnel junction. We also expand on existing knowledge about the role of annealing temperature, film composition, and seedlayer sequence on magnetic anisotropy in Ta/FeCoB/MgO tri-layers of varying FeCoB thickness.

  19. Syntheses and Properties of Homoleptic Carbonyl and Trifluorophosphane Niobates: [Nb(CO)(6)](-), [Nb(PF(3))(6)](-) and [Nb(CO)(5)](3)(-) (,)(1).

    PubMed

    Barybin, Mikhail V.; Ellis, John E.; Pomije, Marie K.; Tinkham, Mary L.; Warnock, Garry F.

    1998-12-14

    Reductive carbonylations of NbCl(4)(THF)(2), THF = tetrahydrofuran, mediated by sodium naphthalene in 1,2-dimethoxyethane, DME, or sodium anthracene in THF, provide [Nb(CO)(6)](-) as the tetraethylammonium salt in 60% or 70% isolated yields, respectively, the highest known for atmospheric pressure syntheses of this metal carbonyl. Corresponding reductions involving PF(3) give about 40% yields of [Et(4)N][Nb(PF(3))(6)], which in the past was only accessible by a photochemical route. Electrochemical data for [Nb(CO)(6)](-) and [Nb(PF(3))(6)](-) are compared and show that the PF(3) complex is almost 1 V more difficult to oxidize than the CO analogue. Protonation of [Nb(PF(3))(6)](-) by concentrated sulfuric acid yields a volatile, thermally unstable species, which has been shown by (1)H NMR and mass spectral studies to be the new niobium hydride, Nb(PF(3))(6)H. Previously unpublished (93)Nb and (13)C NMR studies corroborate prior claims that the sodium metal reduction of [Nb(CO)(6)](-) in liquid ammonia affords [Nb(CO)(5)](3)(-), the only known Nb(III-) species. The first details of this synthesis and those of [Nb(CO)(5)H](2)(-), [Nb(CO)(5)SnPh(3)](2)(-), [Nb(CO)(5)NH(3)](-), and [Nb(CO)(5)(CNtBu)](-) are presented. PMID:11670773

  20. Fergusonite-type CeNbO{sub 4+δ}: Single crystal growth, symmetry revision and conductivity

    SciTech Connect

    Bayliss, Ryan D.; Pramana, Stevin S.; An, Tao; Wei, Fengxia; Kloc, Christian L.; White, Andrew J.P.; Skinner, Stephen J.; White, Timothy J.; Baikie, Tom

    2013-08-15

    Large fergusonite-type (ABO{sub 4}, A=Ce, B=Nb) oxide crystals, a prototype electrolyte composition for solid oxide fuel cells (SOFC), were prepared for the first time in a floating zone mirror furnace under air or argon atmospheres. While CeNbO{sub 4} grown in air contained CeNbO{sub 4.08} as a minor impurity that compromised structural analysis, the argon atmosphere yielded a single phase crystal of monoclinic CeNbO{sub 4}, as confirmed by selected area electron diffraction, powder and single crystal X-ray diffraction. The structure was determined in the standard space group setting C12/c1 (No. 15), rather than the commonly adopted I12/a1. AC impedance spectroscopy conducted under argon found that stoichiometric CeNbO{sub 4} single crystals showed lower conductivity compared to CeNbO{sub 4+δ} confirming interstitial oxygen can penetrate through fergusonite and is responsible for the higher conductivity associated with these oxides. - Graphical abstract: Large fergusonite-type CeNbO{sub 4} crystals were prepared for the first time in a floating zone mirror furnace. Crystal growth in an argon atmosphere yielded a single phase monoclinic CeNbO4, as confirmed by selected area electron diffraction, powder and single crystal X-ray diffraction. The structure was determined in the standard space group setting C12/c1 (No. 15), rather than the commonly adopted I12/a1. AC impedance spectroscopy found CeNbO{sub 4} single crystals showed lower conductivity compared to CeNbO{sub 4+δ} confirming interstitial oxygen can penetrate through fergusonite and is responsible for the higher conductivity associated with these oxides. Highlights: • Preparation of single crystals of CeNbO{sub 4} using a floating zone mirror furnace. • Correction to the crystal symmetry of the monoclinic form of CeNbO{sub 4}. • Report the conductivity of a single crystal of CeNbO{sub 4}.