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Sample records for cu nb ta

  1. 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.

  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. "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.

  4. 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

  5. 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.

  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. 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

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. 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

  3. 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

  4. 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.

  5. 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).

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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.

  17. Mechanical Properties of Cu-Cr-Nb Alloys

    NASA Technical Reports Server (NTRS)

    Ellis, David L.

    1997-01-01

    The chemical compositions of the alloys are listed. The alloying levels were near the values for stochiometric Cr2Nb. A slight excess of Cr was chosen for increased hydrogen embrittlement resistance. The microstructures of all Cu-Cr-Nb alloys were very similar. Two typical transmission electron microscope (TEM) micrographs are presented. The images show the presence of large mount of Cr2Nb precipitates in a nearly pure Cu matrix. The interactions between dislocations and precipitates are currently under investigations, but as the images demonstrates, the extremely fine (less then 15 nm) Cr2Nb are the primary strengtheners for the alloy.

  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. 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.

  20. 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.

  1. Microstructural variations in Cu/Nb and Al/Nb nanometallic multilayers

    SciTech Connect

    Polyakov, M. N.; Hodge, A. M.; Courtois-Manara, E.; Wang, D.; Kuebel, C.; Chakravadhanula, K.

    2013-06-17

    Miscible (Al/Nb) and immiscible (Cu/Nb) nanometallic multilayer systems were characterized by means of transmission electron microscopy techniques, primarily by automated crystallographic orientation mapping, which allows for the resolution of crystal structures and orientations at the nanoscale. By using this technique, distinctive Nb orientations in relation to the crystallographic state of the Al and Cu layer structures can be observed. Specifically, the Al and Cu layers were found to consist of amorphous, semi-amorphous, and crystalline regions, which affect the overall multilayer microstructure.

  2. 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

  3. On the Cu-Nb Phase Diagram and Solidified Microstructures

    NASA Technical Reports Server (NTRS)

    Li, D.; Robinson, M. B.; Rathz, T. J.; Williams, G.

    1998-01-01

    Container and containerless processing was employed to determine liquidus temperatures and to examine microstructural development in the Cu-Nb system. The Cu-Nb phase diagram of an S-shaped, near-horizontal liquidus, has been confirmed by both the temperature-time profiles and resultant microstructures with only Nb dendrites in a Cu matrix, which were obtained from crucible experiments under clean conditions. However, the microstructural pathways of Cu-Nb alloys are particularly sensitive to processing variables. By the addition of oxygen impurities or rapid solidification, droplet-shaped morphology was observed for some compositions, implying occurrence of a liquid-phase separation. The effects of impurities and cooling rates are analyzed in connection with a stable and metastable liquid miscibility gap, respectively.

  4. 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

  5. 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

  6. 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

  7. Supercoducting property of Zr-Cu-Al-Ni-Nb alloys

    NASA Astrophysics Data System (ADS)

    Okai, D.; Motoyama, G.; Kimura, H.; Inoue, A.

    The superconducting property of Zr55Cu(30-X)Al10Ni5NbX alloys prepared by arc melting and liquid quenching methods was investigated by magnetic susceptibility measurements. The crystalline alloys with X = 0∼25 at.% prepared by arc melting method exhibited superconductivity with maximum Tc,on of 10.1 K. The alloys (X = 10∼23 at.%) with crystalline particles embedded in an amorphous structure, which were fabricated by melt spinning method, showed superconductivity with Tc,on of less than 4.0 K. The superconducting property of the Zr-Cu-Al-Ni-Nb alloys was attributed to superconducting phases of Zr2Cu, Zr2Ni, Zr65Al10Nb25 and Zr-Nb contained in the Zr-Cu-Al-Ni-Nb alloys. The melt-spun Zr55Cu(30-X)Al10Ni5NbX (X = 10∼20 at.%) alloys exhibited glass transition at 718∼743 K and were found to be superconducting metallic glasses.

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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

  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. 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.

  15. 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

  16. 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.

  17. 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

  18. Mechanical and Thermal Properties of Two Cu-Cr-Nb Alloys and NARloy-Z

    NASA Technical Reports Server (NTRS)

    Ellis, David L.; Michal, Gary M.

    1996-01-01

    A series of creep tests were conducted on Cu-8 Cr-4 Nb (Cu-8 at.% Cr-4 at.% Nb), Cu-4 Cr-2 Nb (Cu-4 at.% Cr-2 at% Nb), and NARloy-Z (Cu-3 wt.% Ag-0.5 wt.% Zr) samples to determine their creep properties. In addition, a limited number of low cycle fatigue and thermal conductivity tests were conducted. The Cu-Cr-Nb alloys showed a clear advantage in creep life and sustainable load over the currently used NARloy-Z. Increases in life at a given stress were between 100% and 250% greater for the Cu-Cr-Nb alloys depending on the stress and temperature. For a given life, the Cu-Cr-Nb alloys could support a stress between 60% and 160% greater than NARloy-Z. Low cycle fatigue lives of the Cu-8 Cr-4 Nb alloy were equivalent to NARloy-Z at room temperature. At elevated temperatures (538 C and 650 C), the fatigue lives were 50% to 200% longer than NARloy-Z samples tested at 538 C. The thermal conductivities of the Cu-Cr-Nb alloys remained high, but were lower than NARloy-Z and pure Cu. The Cu-Cr-Nb thermal conductivities were between 72% and 96% that of pure Cu with the Cu-4 Cr-2 Nb alloy having a significant advantage in thermal conductivity over Cu-8 Cr4 Nb. In comparison, stainless steels with equivalent strengths would have thermal conductivities less than 25% the thermal conductivity of pure Cu. The combined results indicate that the Cu-Cr-Nb alloys offer an attractive alternative to current high temperature Cu-based alloys such as NARloy-Z.

  19. 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

  20. (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

  1. 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.

  2. [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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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)

  17. 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.

  18. 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.

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. High field performance of superconducting magnets using powder metallurgy processed Cu-Nb-Sn and Nb-Al

    SciTech Connect

    Zaleski, A.J.; Foner, S.

    1984-06-01

    Small superconducting magnets were fabricated with powder metallurgy processed Nb-Al wire and with powder metallurgy processed multistrand Cu-Nb--Sn wire with 19 tin cores. Tests in a background field of up to 15 T showed that short sample characteristics were achieved for three coils. Upper limits of resistivity were established for both powder metallurgy processed wires. The reacted wires in the magnets gave upper limits of resistivity at 10 T of less than 1.4 x 10/sup -14/ ..cap omega.. cm for the Nb/sub 3/Sn wire, and less than 9 x 10/sup -13/ ..cap omega.. cm for the Nb-Al wire.

  5. Stability of Cu-Nb layered nanocomposite from chemical bonding

    NASA Astrophysics Data System (ADS)

    Saikia, Ujjal; Sahariah, Munima B.; Pandey, Ravindra

    2016-07-01

    The potential use of layered metallic nanocomposites in radiation-resistant materials has been recognized with ultra-high mechanical strengths. Here we present results on layered Cu-Nb composite examining its stability in terms of chemical bond via charge density and transfer analysis, QTAIM, electron localization function and density of states using DFT. An intermediate character of bonding with a significant amount of charge transfer at the interface has been predicted. Shortening of intraplanar bond length is a good manifestation of their observed structural stability which may be due to electron promotion of 3 d → (4 s, 4 p) orbitals associated with the constituent atoms of the composite.

  6. 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.

  7. 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.

  8. 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

  9. The General Isothermal Oxidation Behavior of Cu-8Cr-4Nb

    NASA Technical Reports Server (NTRS)

    Thomas-Ogbuji, L. U.; Gray, Hugh R. (Technical Monitor)

    2002-01-01

    Oxidation kinetics of Cu-8Cr-4Nb was investigated by TGA (thermogravimetric) exposures between 500 and 900-C (at 25-50 C intervals) and the oxide scale morphologies examined by microscopy and micro-analysis. Because Cu-8Cr-4Nb is comprised of fine Cr2Nb precipitates in a Cu matrix, the results were interpreted by comparison with the behavior of copper (OFHC) and 'NARloy-Z' (a rival candidate material for thrust cell liner applications in advanced rocket engines) under the same conditions. While NARloy-Z and Cu exhibited identical oxidation behavior, Cu-8Cr-4Nb differed markedly in several respects: below approx. 700 C its oxidation rates were significantly lower than those of Cu; At higher temperatures its oxidation rates fell into two categories: an initial rate exceeding that of Cu, and a terminal rate comparable to that of Cu. Differences in oxide morphologies paralleled the kinetic differences at higher temperature: While NARloy-Z and Cu produced a uniform oxide scale of Cu2O inner layer and CuO outer layer, the inner (Cu2O) layer on Cu-8Cr-4Nb was stratified, with a highly porous/spongy inner stratum (responsible for the fast initial kinetics) and a dense/blocky outer stratum (corresponding to the slow terminal kinetics). Single and spinel oxides of Nb and Cr were found at the interface between the oxide scale and Cu-8Cr-4Nb substrate and it appears that these oxides were responsible for its suppressed oxidation rates at the intermediate temperatures. No difference was found between Cu-8Cr-4Nb oxidation in air and in oxygen at 1.0 atm.

  10. Vacuum Plasma Spray of Cu-8Cr-4Nb for Advanced Liquid-Fuel Combustion Chambers

    NASA Technical Reports Server (NTRS)

    Zimmerman, F.; Elam, S.; Ellis, D.; Miller, H.; McKechnie, T.; Hickman, R.

    2001-01-01

    Vacuum plasma spray (VPS) formed Cu-8Cr-4Nb alloy, with low oxygen, exhibits higher strength at room and elevated temperature than material formed by extrusion. The VPS formed material exhibits slightly lower ductility than the extruded material. VPS forming of Cu-8Cr-4Nb can be used to produce near net structures with mechanical properties comparable to current extruded material.

  11. 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

  12. 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.

  13. Tensile strain / transverse compressive stress effects in Nb{sub 3}Sn multifilamentary wires with CuNb reinforcing stabilizer

    SciTech Connect

    Katagiri, K.; Shoji, Y.; Noto, K.

    1997-06-01

    In order to improve the strain/stress characteristics of the critical current I{sub c}, the use of external CuNb reinforcing stabilizer, instead of the conventional Cu stabilizer, with bronze processed Nb{sub 3}Sn multifilamentary superconducting wires was examined up to the magnetic field of 14T and at a temperature of 4.2K. Although the axial tensile strain sensitivity of I{sub c} was not changed, the strain for peak I{sub c} as well as the reversible strain limit increased by 0.14% when the Cu stabilizer was replaced by the CuNb reinforcing stabilizer. On the other hand, the transverse compressive stress sensitivity of I{sub c} decreased and the reversible stress limit increased. An increase in both a bronze to Nb ratio and Sn content in bronze matrix resulted in a higher stress tolerance and, as a consequence, the contribution of the CuNb reinforcement became relatively small.

  14. 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.

  15. Trapping of Implanted He at Cu/Nb Interfaces Measured by Neutron Reflectometry

    SciTech Connect

    Wang, Peng; Zhernenkov, Mikhail; Kashinath, Abishek; Demkowicz, Michael; Baldwin, Jon K.; Majewski, Jaroslaw

    2012-06-20

    In single crystalline metals, He is insoluble and precipitates into bubbles. In contrast, Cu-Nb multilayers show no evidence of bubble formation below a critical concentration. The conclusions of this paper are: (1) He is trapped at Cu/Nb , Cu/Mo interfaces; (2) He is trapped interstitially; (3) The interface swells {approx} 10 times; and (4) The layered structure retains despite the swell of interfaces.

  16. Performance of a 14-T CuNb/Nb3Sn Rutherford coil with a 300 mm wide cold bore

    NASA Astrophysics Data System (ADS)

    Oguro, Hidetoshi; Watanabe, Kazuo; Awaji, Satoshi; Hanai, Satoshi; Ioka, Shigeru; Sugimoto, Masahiro; Tsubouchi, Hirokazu

    2016-08-01

    A large-bore 14-T CuNb/Nb3Sn Rutherford coil was developed for a 25 T cryogen-free superconducting magnet. The magnet consisted of a low-temperature superconducting (LTS) magnet of NbTi and Nb3Sn Rutherford coils, and a high-temperature superconducting magnet. The Nb3Sn Rutherford coil was fabricated by the react-and-wind method for the first time. The LTS magnet reached the designed operation current of 854 A without a training quench at a 1 h ramp rate. The central magnetic field generated by the LTS magnet was measured by a Hall sensor to be 14.0 T at 854 A in a 300 mm cold bore.

  17. 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

  18. A new type of Cu-Al-Ta shape memory alloy with high martensitic transformation temperature

    NASA Astrophysics Data System (ADS)

    Wang, C. P.; Su, Y.; Y Yang, S.; Shi, Z.; Liu, X. J.

    2014-02-01

    In this study, a new type of Cu-Al-Ta (Cu86Al12Ta2 wt%) shape memory alloy with high martensitic transformation temperature is explored. The microstructure, reversible martensitic transformation and shape memory properties are investigated by means of optical microscopy, back-scattered electron, electron probe microanalysis, x-ray diffraction, differential scanning calorimetry and tensile tests. It is proposed that Cu86Al12Ta2 alloy consists of a mixture of primarily {\\beta }_{1}^{\\prime} martensite and a little {\\gamma }_{1}^{\\prime} martensite and some different precipitates. The tiny thin-striped Ta2(Al,Cu)3 precipitate is predominant in the as-quenched condition, whereas the particle-shaped Cu(Al, Ta) precipitate is dominant after hot-rolling. Additionally, the dendritic-shaped γ1(Cu9Al4) phase begins to appear after hot-rolling, but it disappears when the sample is re-quenched. All studied samples have reversible martensitic transformation temperatures higher than 450 ° C. The results show that two-step martensitic transformation behavior is observed for Cu86Al12Ta2 alloy in all three different conditions due to the transformations between ({\\beta }_{1}^{\\prime}+{\\gamma }_{1}^{\\prime}) martensites and the austenite parent phase. The results further show that the recovery ratios are almost 100% when the pre-strains are ≤2.5%, then they gradually decrease with further increase of the pre-strains. The shape memory effects clearly increase as a result of increase of the pre-strains, up to a maximum value of 3.2%.

  19. Diffusion bonding titanium to stainless steel using Nb/Cu/Ni multi-interlayer

    SciTech Connect

    Li Peng; Li Jinglong; Xiong Jiangtao; Zhang Fusheng; Raza, Syed Hamid

    2012-06-15

    By using Nb/Cu/Ni structure as multi-interlayer, diffusion bonding titanium to austenitic stainless steel has been conducted. The effects of bonding temperature and bonding time on the interfacial microstructure were analyzed by scanning electron microscope equipped with energy dispersive spectroscope, and the joint strength was evaluated by tensile test. The results showed that Ni atoms aggregated at the Cu-Nb interface, which promoted Cu solution in Nb. This phenomenon forms a Cu-Nb solution strengthening effect. However, such effect would decay by using long bonding time that dilutes Ni atom aggregation, or be suppressed by using high bonding temperature that embrittles the Cu-Nb interface due to the formation of large grown intermetallic compounds. The sound joint was obtained by promoted parameters as 850 Degree-Sign C for 30-45 min, under which a bonding strength around 300 MPa could be obtained. - Highlights: Black-Right-Pointing-Pointer Titanium was diffusion bonded to stainless steel using Nb/Cu/Ni multi-interlayer. Black-Right-Pointing-Pointer The effects of bonding parameters on microstructure and joint strength were studied. Black-Right-Pointing-Pointer Nickel aggregation promotes Cu solution in Nb which can strengthen the joint. Black-Right-Pointing-Pointer The sound joint with strength of around 300 MPa was obtained by promoted parameters.

  20. Application of Al-Nb alloy film to metal capping layer on Cu

    NASA Astrophysics Data System (ADS)

    Takeyama, Mayumi B.; Noya, Atsushi

    2016-02-01

    An Al-Nb alloy film with the Al72Nb28 composition is applied as a candidate metal capping layer on Cu interconnects. In the Al72Nb28/Cu/SiO2/Si model system, the preferential oxidation of Al forming a thin surface Al2O3 layer occurs owing to oxidation in air for 1 h at temperatures up to ˜300 °C, resulting in the protection of the layers underneath from further oxidation, although a slight Cu intermixing into Al-Nb occurs. With increasing oxidation temperature up to 500 °C, the surface Al2O3 layer still grows by the preferential oxidation of Al and rejects Cu atoms from the surface oxidized layer. Although Nb atoms are left behind in the surface oxidized layer, they are in a metallic state owing to the high solubility of oxygen before forming an oxide. The extremely low solubility of Nb in Cu also protects Cu without excess intermixing. A good passivation characteristic of the Al72Nb28 alloy film on Cu is demonstrated.

  1. 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

  2. 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.

  3. A new Cu-8 Cr-4 Nb alloy for high temperature applications

    NASA Technical Reports Server (NTRS)

    Ellis, D. L.; Michal, G. M.; Dreshfield, R. L.

    1995-01-01

    Various applications exist where a high conductivity alloy with good strength and creep resistance are required. NASA LeRC has developed a Cu-8 at. percent Cr-4 at. percent Nb (Cu-8 Cr-4 Nb) alloy for these applications. The alloy is designed for use up to 700 C and shows exceptional strength, low cycle fatigue (LCF) resistance, and creep resistance. Cu-8 Cr-4 Nb also has a thermal conductivity of at least 72 percent that of pure Cu. Furthermore, the microstructure and mechanical properties of the alloy are very stable. In addition to the original application in combustion chambers, Cu-8 Cr-4 Nb shows promise for welding electrodes, brazing fixtures, and other applications requiring high conductivity and strength at elevated temperatures.

  4. Characteristics of Cu stabilized Nb3Al strands with low Cu ratio

    SciTech Connect

    Kikuchi, A.; Yamada, R.; Barzi, E.; Kobayashi, M.; Lamm, M.; Nakagawa, K.; Sasaki, K.; Takeuchi, T.; Turrioni, D.; Zlobin, A.V.; /NIMC, Tsukuba /Fermilab /Hitachi, Tsuchiura Works /KEK, Tsukuba

    2008-12-01

    Characteristics of recently developed F4-Nb{sub 3}Al strand with low Cu ratio are described. The overall J{sub c} of the Nb{sub 3}Al strand could be easily increased by decreasing of the Cu ratio. Although the quench of a pulse-like voltage generation is usually observed in superconducting unstable conductor, the F4 strand with a low Cu ratio of 0.61 exhibited an ordinary critical transition of gradual voltage generation. The F4 strand does not have magnetic instabilities at 4.2 K because of the tantalum interfilament matrix. The overall J{sub c} of the F4 strand achieved was 80-85% of the RRP strand. In the large mechanical stress above 100 MPa, the overall J{sub c} of the F4 strand might be comparable to that of high J{sub c} RRP-Nb{sub 3}Sn strands. The Rutherford cable with a high packing factor of 86.5% has been fabricated using F4 strands. The small racetrack magnet, SR07, was also fabricated by a 14 m F4 cable. The quench current, I{sub q}, of SR07 were obtained 22.4 kA at 4.5 K and 25.2 kA at 2.2 K. The tantalum matrix Nb{sub 3}Al strands are promising for the application of super-cooled high-field magnets as well as 4.2 K operation magnets.

  5. 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.

  6. Angular distributions of differential X-ray production cross sections for Cu and Ta in photoionization

    NASA Astrophysics Data System (ADS)

    Wang, Xing; Xu, Zhongfeng; Cheng, Lin

    2016-05-01

    The characteristic K-shell X-ray emission of Cu and L X-rays of Ta in photoionization has been measured at excitation energy of 15.9 keV. The differential X-ray production cross sections of Kα and Kβ for Cu and Lα, Lβ1, Lβ2, Lγ1 for Ta are derived at emission angles ranging from 100° to 150°. The ratio of Kβ and Kα X-ray production cross sections, Kβ/Kα, is calculated for Cu and it is found to be consistent with other work even at different incident energy. While the ratios of Lα/Lβ, Lα/Lγ1 and Lβ/Lγ1 for Ta are found to be different with other results at different excitation energy. The reasons giving rise to this discrepancy are clarified with thorough analysis.

  7. Cu diffusion in Nb3Sn internal tin superconductors during heat treatment

    NASA Astrophysics Data System (ADS)

    Pong, Ian; Oberli, Luc-Rene; Bottura, Luca

    2013-10-01

    Heat treatments and phase formation of Nb3Sn internal tin superconductors are more complicated than bronze route conductors due to the need to convert low melting/low decomposition temperature Sn-rich phases to higher temperature Cu-rich Cu-Sn phases. Conventionally, the Cu-Sn phase development in internal tin wires and hence heat treatment optimization and microstructure control are typically interpreted as a matter of outward Sn diffusion from the Sn core towards the Nb filaments, and Cu diffusion in the opposite direction is simply assumed. In this paper, we present a perspective of Cu diffusion, based on our investigation of phase development. We shall show that the conventional Sn diffusion perspective cannot explain some of our observations, in particular the subelement core phase development. We shall also show that the distribution of Kirkendall pores is opposite to that of the coarse Nb3Sn grains, thus establishing a direct relationship between copper diffusion and coarse Nb3Sn grain formation and distribution. We shall compare wires of different local Cu:Nb area ratio (LAR) and show how Cu diffusion appears to control the Cu-Sn phase formation across the subelement and the final Nb3Sn microstructure (and hence influences the critical current density). Drawing from what we learnt from our observation, we managed to modify a standard heat treatment and obtained up to over 20% improvement in critical current density in some of the wire designs we investigated.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  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. Conduction paths in Cu/amorphous-Ta{sub 2}O{sub 5}/Pt atomic switch: First-principles studies

    SciTech Connect

    Xiao, Bo Tada, Tomofumi; Watanabe, Satoshi; Gu, Tingkun

    2014-01-21

    We have examined the structure of Cu filaments in Cu/amorphous-Ta{sub 2}O{sub 5} (a-Ta{sub 2}O{sub 5})/Pt atomic switch from first principles. We have found that the Cu single atomic chains are unstable during the molecular dynamics (MD) simulation and thus cannot work as conduction paths. On the other hand, Cu nanowires with various diameters are stable and can form conductive paths. In this case, the Cu-Cu bonding mainly contributes to the conductive, delocalized defect state. These make a sharp contrast with the case of single Cu chains in crystalline Ta{sub 2}O{sub 5}, which can be conductive paths through the alternant Cu-Ta bonding structure. A series of MD simulations suggest that even Cu nanowires with a diameter of 0.24 nm can work as conduction paths. The calculations of the transport properties of Cu/a-Ta{sub 2}O{sub 5}/Pt heterostructures with Cu nanowires between two electrodes further confirm the conductive nature of the Cu nanowires in the a-Ta{sub 2}O{sub 5}.

  14. 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.

  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. Internal friction peaks observed in explosively deformed polycrystalline Mo, Nb, and Cu

    NASA Technical Reports Server (NTRS)

    Rieu, G. E.; Grimes, H. H.; Romain, J. P.; Defouquet, J.

    1974-01-01

    Explosive deformation (50 kbar range) induced, in Cu, Mo and Nb, internal friction peaks identical to those observed after large normal deformation. The variation of the peaks with pressure for Mo and Nb lead to an explanation of these processes in terms of double kink generation in screw and edge dislocations.

  17. In situ x-ray investigation of freestanding nanoscale Cu-Nb multilayers under tensile load.

    SciTech Connect

    Aydiner, C. C.; Misra, A.; Brown, D. W.; Mara, N. A.; Almer, J. D

    2009-01-01

    The yield behavior in a freestanding sputter-deposited Cu/Nb multilayer with 30 nm nominal individual layer thickness has been investigated with in situ synchrotron x-ray diffraction during tensile loading. A pronounced elastic-plastic transition is observed with the fraction of plastically yielded grains increasing gradually with strain. Near synchronous yielding is observed in the Cu and Nb grains. The gradual progression in yield behavior is interpreted in terms of residual stresses, and elastic and plastic anisotropy.

  18. In situ investigation of free-standing nanoscale Cu-Nb multylayers under tensile load.

    SciTech Connect

    Aydiner, C. C.; Misra, A.; Brown, D. W.; Mara, N. A.; Almer, J.; LANL

    2009-01-01

    The yield behavior in a freestanding sputter-deposited Cu/Nb multilayer with 30 nm nominal individual layer thickness has been investigated with in situ synchrotron x-ray diffraction during tensile loading. A pronounced elastic-plastic transition is observed with the fraction of plastically yielded grains increasing gradually with strain. Near synchronous yielding is observed in the Cu and Nb grains. The gradual progression in yield behavior is interpreted in terms of residual stresses, and elastic and plastic anisotropy.

  19. 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.

  20. 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

  1. 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.

  2. 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

  3. Creep Testing of High-Temperature Cu-8 Cr-4 Nb Alloy Completed

    NASA Technical Reports Server (NTRS)

    1995-01-01

    A Cu-8 at.% Cr-4 at.% Nb (Cu-8 Cr-4 Nb) alloy is under development for high-temperature, high heatflux applications, such as actively cooled, hypersonic vehicle heat exchangers and rocket engine combustion chambers. Cu-8 Cr-4 Nb offers a superior combination of strength and conductivity. It has also shown exceptional low-cycle fatigue properties. Following preliminary testing to determine the best processing route, a more detailed testing program was initiated to determine the creep lives and creep rates of Cu-8 Cr-4 Nb alloy specimens produced by extrusion. Testing was conducted at the NASA Lewis Research Center with constant-load vacuum creep units. Considering expected operating temperatures and mission lives, we developed a test matrix to accurately determine the creep properties of Cu-8 Cr-4 Nb between 500 and 800 C. Six bars of Cu-8 Cr-4 Nb were extruded. From these bars, 54 creep samples were machined and tested. The figure on the left shows the steady-state, or second-stage, creep rates for the samples. Comparison data for NARloy-Z (Cu-3 wt % Ag-0.5 wt % Zr), the alloy currently used in combustion chamber liners, were not unavailable. Therefore the steady-state creep rates for Cu at similar temperatures are presented. As expected, in comparison to pure Cu, the creep rates for Cu-8 Cr-4 Nb are much lower. The lives of the samples are presented in the figure on the right. As shown, Cu-8 Cr-4 Nb at 800 C is comparable to NARloy-Z at 648 C. At equivalent temperatures, Cu-8 Cr-4 Nb enjoys a 20 to 50 percent advantage in stress for a given life and 1 to 3 orders of magnitude greater life at a given stress. The improved properties allow for design tradeoffs and improvements in new and existing heat exchangers such as the next generation of combustion chamber liners. Average creep rates for Cu-8 Cr-4 Nb and pure Cu are shown. Average creep lives for Cu-8 Cr- 4 Nb and NARloy-Z are also shown. Currently, two companies are interested in the commercial usage of the Cu

  4. Confinement of electromigration induced void propagation in Cu interconnect by a buried Ta diffusion barrier layer

    NASA Astrophysics Data System (ADS)

    Yan, M. Y.; Tu, K. N.; Vairagar, A. V.; Mhaisalkar, S. G.; Krishnamoorthy, Ahila

    2005-12-01

    Direct observation, by means of in situ scanning electron microscopy, of void heterogeneous nucleation and migration controlled electromigration failure mechanism in Cu dual damascene interconnect structures has been recently reported [A. V. Vairagar, S. G. Mhaisalkar, A. Krishnamoorthy, K. N. Tu, A. M. Gusak, M. A. Meyer, and E. Zschech, Appl. Phys. Lett. 85, 2502 (2004)] In the present study, a dual damascene structure with an additional 25nm Ta diffusion barrier embedded into the upper Cu layer was fabricated. This thin layer of diffusion barrier blocked voids from propagating into the via, thus eliminating the previously reported failure mechanism. With this structure, a lifetime improvement of at least 40 times was achieved. Analysis on failed samples suggested that failures in samples with the embedded Ta barrier layer occurred at the bottom of the via, which were caused by void migration along the bottom of the Cu lines.

  5. Superconducting properties of Nb-Cu nano-composites and nano-alloys

    NASA Astrophysics Data System (ADS)

    Parab, Pradnya; Kumar, Sanjeev; Bhui, Prabhjyot; Bagwe, Vivas; Bose, Sangita

    2016-05-01

    The evolution of the superconducting transition temperature (Tc) in nano-composite and nano-alloys of Nb-Cu, grown by DC magnetron co-sputtering are investigated. Microstructure of these films depends less strongly on the ratio of Nb:Cu but more on the growth temperature. At higher growth temperature, phase separated granular films of Nb and Cu were formed which showed superconducting transition temperatures (Tc) of ~ 7.2±0.5K, irrespective of the composition. Our results show that this is primarily influenced by the microstructure of the films determined during growth which rules out the superconducting proximity effect expected in these systems. At room temperature growth, films with nano-scale alloying were obtained at the optimal compositional range of 45-70 atomic% (At%) of Nb. These were also superconducting with a Tc of 3.2K.

  6. Thermal and structural stability of cosputtered amorphous Ta(x)Cu(1-x) alloy thin films on GaAs

    NASA Technical Reports Server (NTRS)

    Oh, J. E.; Woolam, J. A.; Aylesworth, K. D.; Sellmyer, D. J.; Pouch, J. J.

    1986-01-01

    The characteristics of thin films of Ta-Cu, prepared over a wide range of compositions by cosputter deposition onto GaAs and fused quartz substrates, are studied by X-ray diffraction and van der Pauw resistivity measurement. Results show films to be amorphous over the range of 55-95 at. pct, and show Ta(93)Cu(7) barriers to be effective in preventing Au in-diffusion, with a 3000-A layer remaining unpenetrated after an annealing at 700 C for 20 min. Diffusion of Ga and/or As into amorphous 93 at. pct Ta is found to be more rapid than that of Au, and interfacial reactions were shown to form compounds including Ta3Au, CuAu, TaAs2, and Ga3Cu7 above 700 C.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Microstructure and Mechanical Properties of Vacuum Plasma Sprayed Cu-8Cr-4Nb

    NASA Technical Reports Server (NTRS)

    Holmes, Richard; Ellis, David; McKechnie, Timothy; Hickman, Robert

    1997-01-01

    This paper compares the tensile properties of Cu-8Cr-4Nb material produced by VPS to material previously produced by extrusion. The microstructure of the VPS material is also presented. The combustion chamber liner of rocket motors represents an extreme materials application. The liner hot wall is exposed to a 2760 C (5000 F) flame while the cold side is exposed to cryogenic hydrogen liquid. Materials for use in the combustion chamber liner require a combination of high temperature strength, creep resistance, and low cycle fatigue resistance along with high thermal conductivity. The hot side is also subject to localized cycles between reducing and oxidizing environments that degrade the liner by a process called blanching. A new Cu-8 at.% Cr-4 at% Nb (Cu-8Cr-4Nb) alloy has been developed at NASA Lewis Research Center as a replacement for the currently used alloy, NARloy-z (Cu-3 wt.% Ag-0.5 wt.% Zr). The alloy is strengthened by a fine dispersion of Cr2Nb particles. The alloy has better mechanical properties than NARloy-Z while retaining most of the thermal conductivity of pure copper. The alloy has been successfully consolidated by extrusion and hot isostatic pressing (HIPing). However, vacuum plasma spraying (VPS) offers several advantages over prior consolidation methods. VPS can produce a near net shape piece with the profile of the liner. In addition, oxidation resistant and thermal barrier coatings can be incorporated as an integral part of the liner hot wall during the VPS deposition. The low oxygen VPS Cu-8Cr-4Nb exhibits a higher strength than Cu-8Cr-4Nb produced by extrusion at elevated temperatures and a comparable strength at room temperature. Moduli and ductility were not significantly different. However, the ability to produce parts to near-net shape and maintain the good elevated temperature tensile properties of the extruded Cu-8Cr-4Nb makes VPS an attractive processing method for fabricating rocket engine combustion liners.

  14. 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

  15. 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.

  16. 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.

  17. Effects of Thermal and Mechanical Processing on Microstructures and Desired Properties of Particle-Strengthened Cu-Cr-Nb Alloys

    NASA Technical Reports Server (NTRS)

    Anderson, Kenneth Reed

    2000-01-01

    Ternary Cu-Cr-Nb alloys, particularly Cu-8 Cr-4 Nb (in at.%), have demonstrated good thermal stability as well as high strength and conductivity at elevated temperatures. The initial powder material has a bimodal size distribution of Cr2Nb precipitates. Primary Cr2Nb precipitates are approx. 1 micron, and secondary Cr2Nb particles are 30-200 nm. The particle coarsening was analyzed and found to follow LSW-type behavior, This study provides a detailed examination of the stability and strengthening effects of Cr2Nb particles. This investigation also revealed that the primary particles provide direct grain boundary pinning and indirect grain boundary strengthening but virtually no Orowan strengthening. The secondary particles found within grains do provide Orowan strengthening. For extruded material, grain bound-ary strengthening (Hall-Petch effect) accounts for two-thirds of the strength with Orowan effects contributing the remainder. The proven advantages of Cu-Cr-Nb were the motivation to improve these attributes via microstructural refinement. Mechanical milling (MM) of Cu- 4 Cr-2 Nb and Cu-8 Cr-2 Nb produced an increase in hot pressed Vickers hardness of 122% and 96%, respectively. The increase in hardness was more due to Cu grain-size refinement than to Cr,,Nb refinement. This study also demonstrated enhanced stability of MM Cu-4 Cr-2 Nb. Hot pressed 4 h milled Cu-4 Cr-2 Nb experienced only a 22% drop in hardness when annealed at 1273 K for 50 h versus a 30% drop for extruded Cu-8 Cr-4 Nb. The goal of improving the strength and stability of Cu-4 Cr-2 Nb to better than such properties for as- extruded Cu-8 Cr-4 Nb has been met. In addition, a figure-of-merit (FOM) coupling hardness and thermal conductivity was maximized for the case of 4 h milled Cu-4 Cr-2 Nb material. Overall, Cu-Cr-Nb alloys not only possess high strength, conductivity and thermal stability but also can be further developed to improve strength and stability.

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. Deformation behavior of Nb nanowires in TiNiCu shape memory alloy matrix

    SciTech Connect

    Jiang, Daqiang; Liu, Yinong; Yu, Cun; Liu, Weilong; Yang, Hong; Jiang, Xiaohua; Ren, Yang; Cui, Lishan

    2015-08-18

    An in-situ nanowire Nb/TiNiCu composite is fabricated based on the concept of strain under-matching between a phase transforming matrix and high strength nanomaterials. The deformation behavior of the Nb nanowire was investigated by means of in-situ synchrotron X-ray diffraction when the TiNiCu matrix underwent different deformation modes. The maximum lattice strain of the Nb nanowires was about 5% when the matrix deformed via martensitic transformation or 1% when deforming plastically by dislocation slip. As a result, the Nb nanowires showed a lattice strain of 3.5% when the matrix deformed in the mixed mode of plastic deformation and martensitic transformation, which means that the occurrence of plastic deformation does not impede load transfer from the matrix to the nanowires.

  3. Deformation behavior of Nb nanowires in TiNiCu shape memory alloy matrix

    DOE PAGESBeta

    Jiang, Daqiang; Liu, Yinong; Yu, Cun; Liu, Weilong; Yang, Hong; Jiang, Xiaohua; Ren, Yang; Cui, Lishan

    2015-08-18

    An in-situ nanowire Nb/TiNiCu composite is fabricated based on the concept of strain under-matching between a phase transforming matrix and high strength nanomaterials. The deformation behavior of the Nb nanowire was investigated by means of in-situ synchrotron X-ray diffraction when the TiNiCu matrix underwent different deformation modes. The maximum lattice strain of the Nb nanowires was about 5% when the matrix deformed via martensitic transformation or 1% when deforming plastically by dislocation slip. As a result, the Nb nanowires showed a lattice strain of 3.5% when the matrix deformed in the mixed mode of plastic deformation and martensitic transformation, whichmore » means that the occurrence of plastic deformation does not impede load transfer from the matrix to the nanowires.« less

  4. 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).

  5. 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.

  6. 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.

  7. 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.

  8. Structural and surface properties of semitransparent and antibacterial (Cu,Ti,Nb)Ox coating

    NASA Astrophysics Data System (ADS)

    Wojcieszak, D.; Mazur, M.; Kaczmarek, D.; Szponar, B.; Grobelny, M.; Kalisz, M.; Pelczarska, A.; Szczygiel, I.; Poniedzialek, A.; Osekowska, M.

    2016-09-01

    In this work structural and surface properties of oxide thin-film coating based on Cu, Ti and Nb prepared by reactive magnetron sputtering have been described. During the deposition process metallic Cu, Ti and Nb targets were sputtered in oxygen plasma. Structural characterization of the film microstructure has revealed that as-prepared coating was amorphous. Due to such structure and the content of Ti and Nb the hardness of the oxide film was about 3.6 GPa, which is 40% higher as compared to metallic Cu film. Moreover, the surface roughness was below 1 nm, what resulted in receiving of hydrophobic properties. The multioxide film was transparent at the level of 40%, but due to high Cu-content its optical absorption edge was about 450 nm and had bright orange color. Optical investigation has revealed that the energy band-gap of this film was 1.41 eV, which indicates on the presence of CuO form. Moreover, the studies of antimicrobial activity showed that as-prepared film had a strong bactericidal effect for Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus subtilis and Enterococcus hirae, while fungicidal effect for Candida albicans was not observed. The biological activity was related to the amount of copper ions released from the surface of (Cu,Ti Nb)Ox coating, which was equal to 0.041 ppm per day.

  9. 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.

  10. 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

  11. Development of Cu-Nb alloy microcomposite conductors for high field pulsed magnets. Final report

    SciTech Connect

    Pantsyrnyi, V.I.; Shikov, A.K.; Nikulin, A.D.; Belyiakov, N.M.; Potapenko, I.I.; Vorob`ova, A.E.; Silaev, A.G.; Kozlenkova, N.I.; Zinov`ev, V.G.; Drobyshev, V.A.

    1995-12-31

    Primary goal is to develop high strength-high conductivity composite wires with enhanced cross section. The following research areas were started: melting, deformation, TEM, SEM, and mechanical/electrical characterization of in-situ Cu-Nb microcomposites. Consumable arc melting using initial composite electrodes produced by cold deformation was chosen for preparing initial ingots of Cu-(16- 18)wt%Nb alloy. The deformation process including extrusion, drawing with intermediate heat treatments, and rolling was analyzed. Structure of Cu-Nb composite was investigated at all stages of its fabrication. Rebundling was successfully used to manufacture conductors with enhanced cross sections. Wire with 3x7mm{sup 2} cross section and 50m length was produced with UTS (20 C) = 1000 MPa and electroconductivity 70% IACS.

  12. Effect of hydrogen exposure on a Cu-8 Cr-4 Nb alloy

    NASA Technical Reports Server (NTRS)

    Ellis, David L.; Misra, Ajay K.; Dreshfield, Robert L.

    1993-01-01

    The advanced regeneratively cooled rocket thrust chamber may require new materials to achieve long life and improved performance. Current materials such as NARloy-Z (Cu-3 wt. percent Ag-0.5 wt. percent Zr), while highly conductive, do not have sufficient high temperature strength and creep resistance to meet the projected needs of advanced rocket motors. A Cu-8 at. percent Cr-4 at. percent Nb (Cu-8 Cr-4 Nb) alloy has been identified as a promising material for this application. However, hydrogen embrittlement is a concern given the presence of high pressure, high temperature hydrogen in regeneratively cooled rocket motors. Thermodynamic analysis of the reaction between Cr-rich Cr2Nb and H2 showed that there is a possibility of reaction at temperatures up to 323 K in a 35 MPa H2 environment. Above 323 K the pressure necessary to achieve reaction rapidly increased beyond the range experienced in rocket motors. Tensile specimens exposed in 34.5 MPa H2 at room temperatures and during cycling to 705 C did not show any degradation of properties. No evidence of reaction was observed for Cr2Nb precipitate observed on the fracture surfaces. Based on these results the Cu-8 Cr-4 Nb alloy was judged to be sufficiently stable for use in rocket motors.

  13. Excellent resistive memory characteristics and switching mechanism using a Ti nanolayer at the Cu/TaOx interface

    PubMed Central

    2012-01-01

    Excellent resistive switching memory characteristics were demonstrated for an Al/Cu/Ti/TaOx/W structure with a Ti nanolayer at the Cu/TaOx interface under low voltage operation of ± 1.5 V and a range of current compliances (CCs) from 0.1 to 500 μA. Oxygen accumulation at the Ti nanolayer and formation of a defective high-κ TaOx film were confirmed by high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, and X-ray photo-electron spectroscopy. The resistive switching memory characteristics of the Al/Cu/Ti/TaOx/W structure, such as HRS/LRS (approximately 104), stable switching cycle stability (>106) and multi-level operation, were improved compared with those of Al/Cu/TaOx/W devices. These results were attributed to the control of Cu migration/dissolution by the insertion of a Ti nanolayer at the Cu/TaOx interface. In contrast, CuOx formation at the Cu/TaOx interface was observed in an Al/Cu/TaOx/W structure, which hindered dissolution of the Cu filament and resulted in a small resistance ratio of approximately 10 at a CC of 500 μA. A high charge-trapping density of 6.9 × 1016 /cm2 was observed in the Al/Cu/Ti/TaOx/W structure from capacitance-voltage hysteresis characteristics, indicating the migration of Cu ions through defect sites. The switching mechanism was successfully explained for structures with and without the Ti nanolayer. By using a new approach, the nanoscale diameter of Cu filament decreased from 10.4 to 0.17 nm as the CC decreased from 500 to 0.1 μA, resulting in a large memory size of 7.6 T to 28 Pbit/sq in. Extrapolated 10-year data retention of the Ti nanolayer device was also obtained. The findings of this study will not only improve resistive switching memory performance but also aid future design of nanoscale nonvolatile memory. PMID:22734564

  14. 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

  15. 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

  16. Improved sensitivity of nonvolatile holographic storage in triply doped LiNbO(3):Zr,Cu,Ce.

    PubMed

    Liu, Fucai; Kong, Yongfa; Ge, Xinyu; Liu, Hongde; Liu, Shiguo; Chen, Shaolin; Rupp, Romano; Xu, Jingjun

    2010-03-15

    We have designed and grown triply doped LiNbO(3):Zr,Cu,Ce crystal and investigated its characteristics of nonvolatile holographic storage. It's observed that the photorefractive sensitivity of LiNbO(3):Zr,Cu,Ce has improved to 0.099 cm/J, which is about one order of magnitude larger than that of congruent LiNbO(3):Cu,Ce. And LiNbO(3):Zr,Cu,Ce also has high suppression to light-induced scattering. Our results indicated that triply doped LiNbO(3):Zr,Cu,Ce is an excellent candidate for nonvolatile holographic data storage. PMID:20389656

  17. 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

  18. 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. .

  19. Vacuum Plasma Spray of CuCrNb Alloy for Advanced Liquid - Fuel Combustion Chambers

    NASA Technical Reports Server (NTRS)

    Zimmerman, Frank

    2000-01-01

    The copper-8 atomic percent chromium-4 atomic percent niobium (CuCrNb) alloy was developed by Glenn Research Center (formally Lewis Research Center) as an improved alloy for combustion chamber liners. In comparison to NARloy-Z, the baseline (as in Space Shuttle Main Engine) alloy for such liners, CuCrNb demonstrates mechanical and thermophysical properties equivalent to NARloy-Z, but at temperatures 100 C to 150 C (180 F to 270 F) higher. Anticipated materials related benefits include decreasing the thrust cell liner weight 5% to 20%, increasing the service life at least two fold over current combustion chamber design, and increasing the safety margins available to designers. By adding an oxidation and thermal barrier coating to the liner, the combustion chamber can operate at even higher temperatures. For all these benefits, however, this alloy cannot be formed using conventional casting and forging methods because of the levels of chromium and niobium, which exceed their solubility limit in copper. Until recently, the only forming process that maintains the required microstructure of CrNb intermetallics is powder metallurgy formation of a billet from powder stock, followed by extrusion. This severely limits its usefulness in structural applications, particularly the complex shapes required for combustion chamber liners. Vacuum plasma spray (VPS) has been demonstrated as a method to form structural articles including small combustion chambers from the CuCrNb alloy. In addition, an oxidation and thermal barrier layer can be formed integrally on the hot wall of the liner that improve performance and extend service life. This paper discusses the metallurgy and thermomechanical properties of VPS formed CuCrNb versus the baseline powder metallurgy process, and the manufacturing of small combustion chamber liners at Marshall Space Flight Center using the VPS process. The benefits to advanced propulsion initiatives of using VPS to fabricate combustion chamber liners

  20. 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.

  1. 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

  2. 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

  3. 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

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. Chemical stability of highly (0001) textured Sm(CoCu)5 thin films with a thin Ta capping layer

    NASA Astrophysics Data System (ADS)

    Zhao, Haibao; Wang, Hao; Liu, Xiaoqi; Zhang, Tao; Wang, Jian-Ping

    2011-04-01

    With the highest magnetocrystalline anisotropy constant (Ku) among practical magnetic materials, SmCo5 could be a very attractive candidate for future high areal density magnetic recording. However, its corrosion resistance is always a concern in recording media applications. In this paper, the chemical stability and microstructures of highly (0001) textured Sm(CoCu)5 thin films with and without a 3 nm Ta capping layer were reported. For Sm(CoCu)5 thin films without a capping layer, the coercivity decreases significantly (from 8kOe to 1kOe) within one month. Sm(CoCu)5 thin films capped with a thin Ta layer (3 nm) behave differently. Even exposed to a laboratory environment (25 °C) over 3 years, the Ta-capped Sm(CoCu)5 thin films are stable in terms of structural and magnetic properties, i.e., there were no changes in X-ray diffraction peaks and vibrating sample magnetometer hysteresis loops. Microstructure of Ta-capped Sm(CoCu)5 thin films showed that Sm(CoCu)5 formed a domelike particle assembly structure on a smooth Ru underlayer and were well covered by partially oxidized Ta capping layer, as shown by TEM cross-section micrographs. Accelerated corrosion treatment (130 °C, 95% relative humidity, 6 h) was performed on Ta-capped Sm(CoCu)5 thin films. X-ray photoelectron spectroscopy (XPS) results showed that no Co was detected on the sample surface before the corrosion treatment, but strong XPS signals of CoOx and Co(OH)x were observed after treatment. Therefore, none of our Sm(CoCu)5 thin films can pass the accelerated corrosion test. Hcp-phased CoPt-alloys are proposed as better capping materials for Sm(CoCu)5 thin films in future high-density magnetic recording applications.

  10. 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.

  11. Skin effect suppression for Cu/CoZrNb multilayered inductor

    NASA Astrophysics Data System (ADS)

    Sato, Noriyuki; Endo, Yasushi; Yamaguchi, Masahiro

    2012-04-01

    The Cu/Co85Zr3Nb12 multilayer is studied as a conductor of a spiral inductor to suppress the skin effect at the 5 GHz range (matches IEEE 802.11 a standard) using negative-permeability in CoZrNb films beyond the ferromagnetic resonance frequency. The skin effect suppression becomes remarkable when the thickness of Cu in each period of the multilayer, tCu, is less than the skin depth of Cu at the targeting frequency. For the 5 GHz operation, tCu ≤ 750 nm. The resistance of the Cu/CoZrNb multilayered spiral inductor decreases as much as 8.7%, while keeping the same inductance of 1.1 nH as that of a similar air core. Accordingly, Q = 16. Therefore, the proposed method can contribute to realize a high-Q spiral inductor. We also study the potentially applicable frequency of this method. Given a soft magnetic material with Ms = 105 emu/cc and Hk = 5 Oe, the method can be applied at 700 MHz, the lowermost carrier frequency band for the 4th generation cellular phone system.

  12. Continuous high temperature gradient solidification of in situ Cu-Nb alloys for large scale development

    SciTech Connect

    LeHuy, H.; Fihey, J.L.; Foner, S.; Roberge, R.

    1982-01-01

    Several research groups are evaluating various scale-up approaches for the in situ technique of preparing multiply-connected Nb/sub 3/Sn composite superconducting wire. Previously, the authors developed an arrangement for continuous high temperature gradient solidification, and now have upgraded the process to permit the solidification of larger diameter (9.5 mm) rods in virtually unlimited lengths. The preparation, the microstructure, and the characteristics (solidification rate, dendrite branching, and dendrite size) are given for three directionally solidified in situ materials with a nominal composition of Cu-30 wt% Nb. Micrographs of variously extracted Nb filaments and various-order dendrites are provided. The HTGS technique offers several advantages over other scale-up production methods, such as the control over the microstructure, form, and size of the Nb dendrites. A critical current density of 10 kA/cm/sup 2/ at roughly 16.5 T has been measured for the fine dendrite materials.

  13. Enhanced magnetoimpedance and field sensitivity in microstructure controlled FeSiCuNbB ribbons

    NASA Astrophysics Data System (ADS)

    Sahoo, Trilochan; Chandra Mishra, Amaresh; Srinivas, V.; Nath, T. K.; Srinivas, M.; Majumdar, B.

    2011-10-01

    Fe73.5Si13.5Cu1Nb3B9 and Fe77.2Si11.2Cu0.8Nb3.3B7.5 nanocomposite materials consisting of nanocrystalline phase in an amorphous matrix were obtained by heat-treatment of their precursor amorphous ribbons. The influence of structural modifications induced during the heat-treatment on soft magnetic properties and magnetoimpedance (MI) effect have been studied. The structural investigations on both these ribbons revealed the presence of two phases, fine grained Fe3Si phase and a residual amorphous phase on heat-treatment. The maximum MI ratio obtained in the present study is 95% at f = 4 MHz, for the optimized heat-treated Fe77.2Si11.2Cu0.8Nb3.3B7.5 ribbon. This is ascribed to the increase in magnetic permeability and decrease in coercive force and intrinsic resistivity. Moreover, a maximum magnetic field sensitivity (ξ) of 8.3%/Oe at f = 2.5 MHz is obtained, for the optimized nanocrystalline Fe73.5Si13.5Cu1Nb3B9 ribbon. This suggests that tailoring of the nanocrystalline microstructures induced by optimum heat-treatment conditions can result in obtaining excellent combinations of the magnetic permeability and resistivity. Our results indicate that these Fe-based nanocrystalline materials can be ideally used for low magnetic field and high frequency sensor applications.

  14. Residual strain and texture in free-standing nanoscale Cu-Nb multilayers

    SciTech Connect

    Aydiner, C. C.; Brown, D. W.; Misra, A.; Mara, N. A.; Wang, Y.-C.; Wall, J. J.; Almer, J.

    2007-10-15

    We investigate the residual strains in a free-standing Cu/Nb multilayer of 30 nm nominal layer thickness with synchrotron x-rays. This material system is characterized by columnar grains of Cu and Nb with incoherent interfaces and a sharp physical-vapor-deposition texture. High energy x-rays were used with an area detector along with multiple sample rotations to yield diffraction strain components in a very large number of directions. Due to the texture and the elastic anisotropy of constituents, observed diffraction strains cannot be derived from a single strain tensor (also known as linear sin{sup 2} {psi}). Orientation-dependent diffraction strain modeling is utilized with a Vook-Witt micromechanical model. Obtained phase-resolved in-plane stress magnitudes are -515 MPa in Nb and +513 MPa in Cu, satisfying force equilibrium within experimental errors. The stresses of this magnitude will certainly influence the mechanical behavior of the multilayer upon further loading. The Vook-Witt model describes the Nb diffraction strains very well, and thereby provides information on the stress distribution in crystallites as a function of their orientation. On the other hand, the same level of agreement with the Vook-Witt model has not been achieved for Cu diffraction strains.

  15. Residual strain and texture in free-standing nanoscal Cu-Nb multilayers.

    SciTech Connect

    Aydiner, C. C.; Brown, D. W.; Misra, A.; Wang, Y. -C.; Wall, J.; Mara, N.; Almer, J.; LANL; National Cheng Kung Univ.

    2007-10-15

    We investigate the residual strains in a free-standing Cu/Nb multilayer of 30 nm nominal layer thickness with synchrotron x-rays. This material system is characterized by columnar grains of Cu and Nb with incoherent interfaces and a sharp physical-vapor-deposition texture. High energy x-rays were used with an area detector along with multiple sample rotations to yield diffraction strain components in a very large number of directions. Due to the texture and the elastic anisotropy of constituents, observed diffraction strains cannot be derived from a single strain tensor (also known as linear sin{sup 2} {psi}). Orientation-dependent diffraction strain modeling is utilized with a Vook-Witt micromechanical model. Obtained phase-resolved in-plane stress magnitudes are -515 MPa in Nb and +513 MPa in Cu, satisfying force equilibrium within experimental errors. The stresses of this magnitude will certainly influence the mechanical behavior of the multilayer upon further loading. The Vook-Witt model describes the Nb diffraction strains very well, and thereby provides information on the stress distribution in crystallites as a function of their orientation. On the other hand, the same level of agreement with the Vook-Witt model has not been achieved for Cu diffraction strains.

  16. 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.

  17. 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

  18. Note: Resonance magnetoelectric interactions in laminate of FeCuNbSiB and multilayer piezoelectric stack for magnetic sensor.

    PubMed

    Li, Jianqiang; Lu, Caijiang; Xu, Changbao; Zhong, Ming

    2015-09-01

    This paper develops a simple miniature magnetoelectric (ME) laminate FeCuNbSiB/PZT-stack made up of magnetostrictive Fe73.5Cu1Nb3Si13.5B9 (FeCuNbSiB) foils and piezoelectric Pb(Zr, Ti)O3 (PZT) multilayer stack vibrator. Resonant ME interactions of FeCuNbSiB/PZT-stack with different layers of FeCuNbSiB foil (L) are investigated in detail. The experimental results show that the ME voltage coefficient reaches maximum value of 141.5 (V/cm Oe) for FeCuNbSiB/PZT-stack with L = 6. The AC-magnetic sensitivities can reach 524.29 mV/Oe and 1.8 mV/Oe under resonance 91.6 kHz and off-resonance 1 kHz, respectively. The FeCuNbSiB/PZT-stack can distinguish small dc-magnetic field of ∼9 nT. The results indicate that the proposed ME composites are very promising for the cheap room-temperature magnetic field sensing technology. PMID:26429496

  19. Note: Resonance magnetoelectric interactions in laminate of FeCuNbSiB and multilayer piezoelectric stack for magnetic sensor

    NASA Astrophysics Data System (ADS)

    Li, Jianqiang; Lu, Caijiang; Xu, Changbao; Zhong, Ming

    2015-09-01

    This paper develops a simple miniature magnetoelectric (ME) laminate FeCuNbSiB/PZT-stack made up of magnetostrictive Fe73.5Cu1Nb3Si13.5B9 (FeCuNbSiB) foils and piezoelectric Pb(Zr, Ti)O3 (PZT) multilayer stack vibrator. Resonant ME interactions of FeCuNbSiB/PZT-stack with different layers of FeCuNbSiB foil (L) are investigated in detail. The experimental results show that the ME voltage coefficient reaches maximum value of 141.5 (V/cm Oe) for FeCuNbSiB/PZT-stack with L = 6. The AC-magnetic sensitivities can reach 524.29 mV/Oe and 1.8 mV/Oe under resonance 91.6 kHz and off-resonance 1 kHz, respectively. The FeCuNbSiB/PZT-stack can distinguish small dc-magnetic field of ˜9 nT. The results indicate that the proposed ME composites are very promising for the cheap room-temperature magnetic field sensing technology.

  20. New hydrogen-evolution heteronanostructured photocatalysts: Pt-Nb3 O7 (OH) and Cu-Nb3 O7 (OH).

    PubMed

    Hmadeh, Mohamad; Hoepfner, Veronika; Larios, Eduardo; Liao, Kristine; Jia, Jia; Jose-Yacaman, Miguel; Ozin, Geoffrey A

    2014-08-01

    Nanorods of triniobium hydroxide heptaoxide, Nb3 O7 (OH), were synthesized by means of a hydrothermal method. Subsequently, Pt and CuO nanoparticles were introduced on the surface of Nb3 O7 (OH) nanorods by a microwave-assisted solvothermal nucleation and growth technique. The resulting Pt- and CuO-decorated Nb3 O7 (OH) nanorods demonstrated uniform particle dispersion and were fully characterized by X-ray diffraction, electron microscopy, and spectroscopic analysis. Furthermore, the solar-powered photocatalytic hydrogen production properties of these heteronanostructures were studied. The solar-driven H2 formation rate over Pt-Nb3 O7 (OH) was determined to be 710.4 ± 1.7 μmol g(-1) h(-1) with a quantum efficiency of ϕ=5.40% at λ=380 nm. Interestingly, the as-prepared CuO-Nb3 O7 (OH) heteronanostructure was found to be inactive under solar irradiation during an induction phase, whereupon it undergoes an in situ photoreduction process to form the photocatalytically active Cu-Nb3 O7 (OH). This restructuring process was monitored by an in situ measurement of the time-evolution of the optical absorption spectra. The solar-powered H2 production for the restructured compound was determined to be 290.3 ± 5.1 μmol g(-1) h(-1) . PMID:24942297

  1. Resistance and spin-direction memory loss at Nb/Cu interfaces

    NASA Astrophysics Data System (ADS)

    Baxter, David V.; Steenwyk, S. D.; Bass, J.; Pratt, W. P.

    1999-04-01

    A new method is described for measuring the loss of spin-direction memory (spin relaxation) in nonmagnetic materials and at nonmagnetic interfaces. The method involves inserting the material of interest into an exchange-biased spin valve and monitoring the associated reduction in the spin valve's magnetoresistance measured with the current perpendicular to the planes. This technique is tested by investigating spin relaxation near Nb/Cu interfaces. A surprisingly large loss per interface is found, between 15% and 25% with larger values being associated with thicker Nb layers.

  2. 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

  3. 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

  4. 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.

  5. Structure and microhardness of cu-ta joints produced by explosive welding.

    PubMed

    Maliutina, Iu N; Mali, V I; Bataev, I A; Bataev, A A; Esikov, M A; Smirnov, A I; Skorokhod, K A

    2013-01-01

    The structure and microhardness of Cu-Ta joints produced by explosive welding were studied. It was found that, during explosive welding, an intermediate layer 20⋯40  μ m thick with a finely dispersed heterophase structure, formed between the welded copper and tantalum plates. The structure of the layer was studied by scanning and transmission electron microscopy. Microvolumes with tantalum particles distributed in a copper matrix and microvolumes of copper particles in a tantalum matrix were detected. The tantalum particles in copper have a size of 5⋯500 nm, with a predominance of 5⋯50 nm particles. A mechanism for the formation of the finely dispersed heterophase structure in explosive welding is proposed. The microhardness of interlayers with the heterophase structure reaches 280 HV, which far exceeds the microhardness of copper (~130 HV) and tantalum (~160 HV). Many twins of deformation origin were found in the structure of the copper plate. The effect of heating temperature in the range from 100 to 900°C on the microhardness of copper, tantalum, and the Cu-Ta welded joint was studied. Upon heating to 900°C, the microhardness of the intermediate layer decreases from 280 to 150 HV. The reduction in the strength properties of the weld material is mainly due to structural transformations in copper. PMID:24453818

  6. Structure and Microhardness of Cu-Ta Joints Produced by Explosive Welding

    PubMed Central

    Maliutina, Iu. N.; Mali, V. I.; Bataev, I. A.; Bataev, A. A.; Esikov, M. A.; Smirnov, A. I.; Skorokhod, K. A.

    2013-01-01

    The structure and microhardness of Cu-Ta joints produced by explosive welding were studied. It was found that, during explosive welding, an intermediate layer 20⋯40 μm thick with a finely dispersed heterophase structure, formed between the welded copper and tantalum plates. The structure of the layer was studied by scanning and transmission electron microscopy. Microvolumes with tantalum particles distributed in a copper matrix and microvolumes of copper particles in a tantalum matrix were detected. The tantalum particles in copper have a size of 5⋯500 nm, with a predominance of 5⋯50 nm particles. A mechanism for the formation of the finely dispersed heterophase structure in explosive welding is proposed. The microhardness of interlayers with the heterophase structure reaches 280 HV, which far exceeds the microhardness of copper (~130 HV) and tantalum (~160 HV). Many twins of deformation origin were found in the structure of the copper plate. The effect of heating temperature in the range from 100 to 900°C on the microhardness of copper, tantalum, and the Cu-Ta welded joint was studied. Upon heating to 900°C, the microhardness of the intermediate layer decreases from 280 to 150 HV. The reduction in the strength properties of the weld material is mainly due to structural transformations in copper. PMID:24453818

  7. Film Deposition, Cryogenic RF Testing and Materials Analysis of a Nb/Cu Single Cell SRF Cavity

    SciTech Connect

    Zhao, Xin; Geng, Rongli; Palczerski, Ari; Li, Yongming

    2013-09-01

    In this study, we present preliminary results on using a cathodic-arc-discharge Nb plasma ion source to establish a Nb film-coated single-cell Cu cavity for SRF research. The polycrystalline Cu cavity was fabricated and mirror-surface-finished by a centrifugal barrel polishing (CBP) process at Jefferson Lab. Special pre-coating processes were conducted, in order to create a template-layer for follow-on Nb grain thickening. A sequence of cryogenic RF testing demonstrated that the Nb film does show superconductivity. But the quality factor of this Nb/Cu cavity is low as a result of high residual surface resistance. We are conducting a thorough materials characterization to explore if some microstructural defects or hydrogen impurities, led to such a low quality factor.

  8. Superconducting and ferromagnetic properties of NbN/NiCu and NbTiN/NiCu bilayer nanostructures for photon detection

    NASA Astrophysics Data System (ADS)

    Klimov, A.; Puźniak, R.; Aichner, B.; Lang, W.; Joon, E.; Stern, R.; Słysz, W.; Guziewicz, M.; Juchniewicz, M.; Borysiewicz, M. A.; Kruszka, R.; Wegrzecki, M.; Łaszcz, A.; Czerwinski, A.; Sobolewski, Roman

    2015-05-01

    Performance of superconducting single-photon detectors based on resistive hotspot formation in nanostripes upon optical photon absorption depends strongly on the critical current density JC of the fabricated nanostructure. Utilization of an ultrathin, weak-ferromagnet cap layer on the top of a superconducting film enhances of the structure's JC due to an extra flux pinning. We have fabricated a number of both NbN/NiCu and NbTiN/NiCu superconductor/ferromagnet (S/F) ultrathin bilayers and microbridges. NbN and NbTiN underlayers with thicknesses varying from 4 to 7 nm were grown using dc-magnetron sputtering on chemically cleaned sapphire single-crystal substrates. After rapid thermal annealing at high temperatures, the S films were coated with Ni0.54Cu0.46 overlayers with thicknesses of about 6 nm, using cosputtering. Compositions of the deposited films were confirmed by EDX spectroscopy analysis, while TEM studies demonstrated excellent epitaxial quality of our S layers with ~2-nm-thick F/S transition layer and atomically-sharp S/substrate interface. Magnetic properties of bilayers were studied using both the SQUID and Vibrating Sample Magnetometer techniques in low and high magnetic fields. Low-temperature tests confirmed that in all cases NiCu films were ferromagnetic with the Curie temperature of above 30 K. Below the bilayer critical temperature of approx. 12-13 K, the structures were fully proximitized with the strong superconducting signal. For superconducting transport properties characterization, we used bilayers patterned into 40-μm-long microbridges with the width varying from 0.4 μm to 2 μm. The same S/F nanostructures were also used to study their superconducting fluctuations. The temperature dependence of magnetoresistance demonstrated highly 2-dimensional character with an unusual negative region that extended almost to room temperature. In the S/F sample, the fluctuations were observed to be substantially below theoretical expectations.

  9. YBa2Cu3O(7-x)/Au/Nb device structures

    NASA Technical Reports Server (NTRS)

    Hunt, B. D.; Foote, M. C.; Bajuk, L.; Vasquez, R. P.

    1991-01-01

    Fabrication and testing of planar and edge geometry YBaCuO/Au/Nb superconductor/normal-metal/superconductor (SNS) device structures is described. Weak-link devices of this type serve as sensitive probes of the electrical quality of the YBaCuO/Au interface. The devices are fabricated using laser-ablated, in situ, c-axis-oriented YBaCuO thin films, with both annealed and unannealed YBaCuO/Au interfaces. The planar SNS structures are formed by sequential, in situ deposition of YBaCuO, Au, and Nb, followed by etching, planarization, and wiring electrode definition to produce junctions ranging from 5 to 20 micron on a side. Resulting RnA products are 1-10 x 10 to the -8th ohm-sq cm with critical current densities up to 5 kA/sq cm. For the edge geometry devices, the YBaCuO film edges are patterned using Ar ion milling, followed by a low energy ion cleaning step and in situ deposition of Au and Nb. Devices with areas in the 10 to the -7th to 10 to the -8th sq cm range have been fabricated with RnA products lower than 10 to the -8th ohm-sq cm and critical current densities up to 3kA/sq cm. Both types of devices show ac Josephson steps under microwave irradiation. The best results have been obtained with annealed YBaCuO/Au interfaces.

  10. Wetting and spontaneous infiltration: the case study of TaC/(Au, Al and Cu) compared to TiC/Cu

    NASA Astrophysics Data System (ADS)

    Aizenshtein, M.; Froumin, N.; Nafman, O.; Frage, N.

    2016-06-01

    Spontaneous infiltration of molten metals in to ceramic skeletons, in the course MMCs' production, is related to improved wetting of the ceramic by metals. TiC is considered a "metal-like" carbide and is supposed to be wetted well by metals through metallic bonding mechanism. Nevertheless, TiC/Cu exhibit an unusual behavior since spontaneous infiltration of molten Cu takes place, while TiC is partially wetted by Cu (θ=90°).In this work we studied the relation between wetting and spontaneous infiltration in the TaC/Au, Al and Cu systems. TaC is also considered a "metal-like" carbide and indeed no chemical interaction was observed at the interfaces of the studied systems.Sessile drop experiments showed almost perfect wetting in the three system but spontaneous infiltration occurred only in the first two (e.g. TaC/Au or Al). Thermodynamic calculation shows the difference between the systems which also has its' influence on the mechanical properties of the MMCs'. Further calculation clarifies the difference between TaC/Cu and TiC/Cu infiltration behavior, but is unable to explain the wetting results differences.Correlation between wetting and spontaneous infiltration in some cases is not straight forward and more studies and calculations on the atomistic level should be done in order to clarify this matter.

  11. Flux-mediated syntheses, structural characterization and low-temperature polymorphism of the p-type semiconductor Cu2Ta4O11

    NASA Astrophysics Data System (ADS)

    King, Nacole; Sullivan, Ian; Watkins-Curry, Pilanda; Chan, Julia Y.; Maggard, Paul A.

    2016-04-01

    A new low-temperature polymorph of the copper(I)-tantalate, α-Cu2Ta4O11, has been synthesized in a molten CuCl-flux reaction at 665 °C for 1 h and characterized by powder X-ray diffraction Rietveld refinements (space group Cc (#9), a=10.734(1) Å, b = 6.2506(3) Å, c=12.887(1) Å, β = 106.070(4)°). The α-Cu2Ta4O11 phase is a lower-symmetry monoclinic polymorph of the rhombohedral Cu2Ta4O11 structure (i.e., β-Cu2Ta4O11 space group R 3 ̅ c (#167), a = 6.2190(2) Å, c=37.107(1) Å), and related crystallographically by ahex=amono/√3, bhex=bmono, and chex=3cmonosinβmono. Its structure is similar to the rhombohedral β-Cu2Ta4O11 and is composed of single layers of highly-distorted and edge-shared TaO7 and TaO6 polyhedra alternating with layers of nearly linearly-coordinated Cu(I) cations and isolated TaO6 octahedra. Temperature dependent powder X-ray diffraction data show the α-Cu2Ta4O11 phase is relatively stable under vacuum at 223 K and 298 K, but reversibly transforms to β-Cu2Ta4O11 by at least 523 K and higher temperatures. The symmetry-lowering distortions from β-Cu2Ta4O11 to α-Cu2Ta4O11 arise from the out-of-center displacements of the Ta 5d0 cations in the TaO7 pentagonal bipyramids. The UV-vis diffuse reflectance spectrum of the monoclinic α-Cu2Ta4O11 shows an indirect bandgap transition of ∼2.6 eV, with the higher-energy direct transitions starting at ∼2.7 eV. Photoelectrochemical measurements on polycrystalline films of α-Cu2Ta4O11 show strong cathodic photocurrents of ∼1.5 mA/cm2 under AM 1.5 G solar irradiation.

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. Production and processing of Cu-Cr-Nb alloys

    NASA Technical Reports Server (NTRS)

    Ellis, David L.; Michal, Gary M.; Orth, Norman W.

    1990-01-01

    A new Cu-based alloy possessing high strength, high conductivity, and good stability at elevated temperatures was recently produced. This paper details the melting of the master alloys, production of rapidly solidified ribbon, and processing of the ribbon to sheet by hot pressing and hot rolling.

  17. Electrochemical characterization of surface complexes formed on Cu and Ta in succinic acid based solutions used for chemical mechanical planarization

    NASA Astrophysics Data System (ADS)

    Sulyma, Christopher M.; Roy, Dipankar

    2010-02-01

    Open-circuit potential measurements, cyclic voltammetry and Fourier transform impedance spectroscopy have been used to study pH dependent surface reactions of Cu and Ta rotating disc electrodes (RDEs) in aqueous solutions of succinic acid (SA, a complexing agent), hydrogen peroxide (an oxidizer), and ammonium dodecyl sulfate (ADS, a corrosion inhibitor for Cu). The surface chemistries of these systems are relevant for the development of a single-slurry approach to chemical mechanical planarization (CMP) of Cu lines and Ta barriers in the fabrication of semiconductor devices. It is shown that in non-alkaline solutions of H 2O 2, the SA-promoted surface complexes of Cu and Ta can potentially support chemically enhanced material removal in low-pressure CMP of surface topographies overlying fragile low-k dielectrics. ADS can suppress Cu dissolution without significantly affecting the surface chemistry of Ta. The data analysis steps are discussed in detail to demonstrate how the D.C. and A.C. electrochemical probes can be combined in the framework of the RDE technique to design and test CMP slurry solutions.

  18. INVESTIGATION OF Ta/Ni-Al INTEGRATED FILM USED AS A DIFFUSION BARRIER LAYER BETWEEN Cu AND Si

    NASA Astrophysics Data System (ADS)

    Yang, Lim; Wang, Shi Jie; Huo, Ji Chuan; Li, Xiao Hong; Guo, Jian Xin; Dai, Xiu Hong; Ma, Lian Xi; Zhang, Xiang Yi; Liu, Bao Ting

    2014-09-01

    Ta (3.3 nm)/Ni-Al (3.3 nm) integrated films deposited on Si substrates by magnetron sputtering, annealed at various temperatures in a ultra-high vacuum, have been studied as diffusion barrier layers between Cu and Si for application in Cu interconnection. The images of transmission electron microscopy (TEM) prove that the cross-sectional interfaces of Cu/Ta/Ni-Al/Si sample annealed at 600°C are clear and sharp. No Cu-silicide peaks can be found from the X-ray diffraction (XRD) patterns of the 850°C annealed sample, but the sheet resistance of the sample increases abruptly. Moreover, large grooves are found from the image of atomic force microscopy (AFM) for the 850°C annealed sample, implying the failure of the diffusion barrier. The integrated Ta/Ni-Al barrier layer retains thermally stable nature up to at least 800°C, indicating that the Ta/Ni-Al integrated film is an excellent diffusion barrier between Cu and Si.

  19. Fabrication and characterization of Na0.5K0.5NbO3-CuNb2O6 lead-free step-down piezoelectric transformers

    NASA Astrophysics Data System (ADS)

    Yang, Ming-Ru; Chu, Sheng-Yuan; Chan, I.-Hao; Huang, Sheng-Kai

    2011-08-01

    Lead-free (Na0.5K0.5)NbO3 (NKN) ceramics doped with 1 mol% CuNb2O6 (01CN) ceramics were prepared using the conventional mixed oxide method at a sintering temperature of 1075 °C. NKN + 1 mol% CuTa2O6 (NKN-01CN) ceramics sintered at 1075 °C exhibit excellent "hard" piezoelectric properties of kp = 40%, kt = 45%, and k33 = 57%, with ferroelectric property Ec = 23 kV/cm. The mechanical quality factor (Qm) is extraordinarily high (1933) and the temperature stability is excellent (Temperature coefficient of frequency (TCF) = -154 ppm/°C). The piezoelectric transformer (PT) was fabricated on NKN-01CN lead-free substrates, and the electrical characteristics were investigated. The devices were simplified into an equivalent circuit and analyzed using the MATLAB software package. The simulation results matched the experimental results. By reversing the input and the output, the step-down PT can be easily fabricated using a simple disk-type structure. A maximum efficiency of 93% with a voltage gain of 0.12 was measured, which was in good agreement with the simulation results (a maximum efficiency of 98.7% with a voltage gain of 0.13) for the step-down mode.

  20. 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

  1. 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.

  2. Residual stress, mechanical behavior and electrical properties of Cu/Nb thin-film multilayers

    SciTech Connect

    Griffin, A.J. Jr.; Hundley, M.F.; Jervis, T.R.; Kung, H.H.; Scarborough, W.K.; Walter, K.C.; Nastasi, M.; Embury, J.D.

    1995-09-01

    Effect of compositional wavelength (modulation) on residual stress, electrical resistivities and mechanical properties of Cu/Nb thin-film multilayers sputtered onto single-crystal Si substrates, was evaluated. Electrical resistivities were measured down to 4 K using a standard 4-point probe. Differential specimen curvature was used to determine residual stress, and a microprobe was used to obtain hardness and elastic modulus. Profilometry, ion-beam analysis and TEM were used. Hardness of the Cu-Nb multilayers increased with decreasing compositional wavelength so that the layered structures had hardness values in excess of either constituent and the hardness predicted by the rule of mixtures. A peak in net residual compressive stress of the multilayers was observed at a compositional wavelength of 100 nm. No resistivity plateau was observed within the composition wavelength range studied.

  3. Sandwich-Geometry YBa(2)Cu(3)O(7-delta)/Au/Nb SNS Devices

    NASA Technical Reports Server (NTRS)

    Foote, Marc C.; Hunt, Brian D.

    1993-01-01

    Superconductor/normal-conductor/superconductor (SNS) devices in which electronically active layers consist of high-temperature superconductor YBa(2)Cu(3)O(7-delta), normal conductor Au, and conventional superconductor Nb, fabricated in sandwich geometry. Devices and processes by which fabricated are part of continuing effort to develop SNS microbridges for use in superconducting quantum interference devices (SQUIDS's) or as mixers or local oscillators operating at frequencies of hundreds of gigahertz. Results show promise for manufacture of practical devices.

  4. Morphological stability of Cu-Nb nanocomposites under high-energy collision cascades

    SciTech Connect

    Zhang, Liang; Demkowicz, Michael J.

    2013-08-05

    We use molecular dynamics and phase field simulations to demonstrate that Cu-Nb multilayered nanocomposites with individual layer thicknesses above 2–4 nm remain morphologically stable when subjected to 100 keV collision cascades, characteristic of neutron or heavy ion irradiation. The probability of morphological instability rapidly increases as the layer thickness decreases to 1 nm, which we attribute to overlap of zones of liquid-like interdiffusion inside radiation-induced thermal spikes at neighboring interfaces in the multilayer.

  5. Relaxation process of Fe(CuNb)SiB amorphous alloys investigated by dynamical calorimetry

    SciTech Connect

    Zhu, J.; Clavaguera-Mora, M.T.; Clavaguera, N.

    1997-03-01

    Differential scanning calorimetry and dynamic differential scanning calorimetry were used to analyze the relaxation process of Fe(CuNb)SiB amorphous alloys. The Curie temperature (T{sub C}) evolution of the amorphous phase during relaxation as a function of heating rate, time and pre-annealing temperature were measured. Two distinct relaxation processes are observed, consequent with topological and chemical short range order changes. {copyright} {ital 1997 American Institute of Physics.}

  6. 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.

  7. 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

  8. 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

  9. 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.

  10. 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’.

  11. 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.

  12. 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

  13. Magnetic properties of nanocrystalline FeCuNb(Sb/W)SiB alloys

    SciTech Connect

    Degro, J.; Vojtanik, P.; Konc, M.; Zentko, A.; Csach, K.; Ocelik, V.

    1994-03-01

    The magnetic relaxation {Delta}r/r, the perminvar critical field H{sub CR}, the initial susceptibility {chi}{sub 10}, the coercive field H{sub c} as a function of annealing temperature in Fe{sub 73.5}Cu{sub 1}Nb{sub 2.95}Sb{sub 0.05}Si{sub 13.5}B{sub 9} and Fe{sub 73.5}Cu{sub 1}W{sub 3}Si{sub 13.5}B{sub 9} alloys were investigated. DSC measurements and thermomagnetic analyses were also done. The results using random anisotropy model can be explained.

  14. Critical current density and magnetization of proximity-effect-induced superconducting Cu in multifilamentary NbTi/Cu composite conductors

    NASA Astrophysics Data System (ADS)

    Kubota, Y.; Moriya, T.; Yasohama, K.

    2001-05-01

    The magnetization Mp of proximity-effect-induced superconducting Cu (PEISC) in multifilamentary NbTi/Cu composite conductors has been measured in transverse fields Be smaller than Bc1 of the NbTi filament at 4.2 K. The conductors were designed specifically to subtract out the magnetization of the NbTi filaments from magnetization of the conductors. The filament spacing is 1.38 μm and the width of the regular hexagonal filament is 7.60 μm. Twist pitches are 6.9, 13, 20, 94 and 189 mm. Mp was investigated as a function of the twist pitch lp and the field amplitude Bm. The first penetration field Bc1p of the magnetic flux, the decoupling field Bdp of the filament coupling, and the width of the Mp at a given field are directly proportional to the twist pitch. Mp magnetization loops intersect each other for Bc1p⩽ Bm⩽ Bdp and decrease suddenly at Bdp. The critical current density Jcp of PEISC is proportional to Be-2 and its value is 10 kA/m 2 at 7 mT.

  15. 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

  16. 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

  17. 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.

  18. 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.

  19. Hydroforming of Multi-Cell Niobium and NbCu-Clad Cavities

    SciTech Connect

    X. Singer, I. Jelezov, A. Matheisen, W. Singer, P. Kneisel

    2009-05-01

    Technological aspects of seamless tube fabrication and multi-cell cavity production by hydroforming will be discussed. Problems related to the fabrication of seamless cavities from bulk niobium are mainly solved. Several two cell- and three cell- niobium cavities have been produced by hydroforming at DESY. A 9-cell cavity of the TESLA shape has been completed from three sub-sections at company ZANON. The cavity was treated by electropolishing (EP) and successfully RF-tested. Two 3-cell units equipped with niobium beam pipes are being RF-tested after BCP surface treatment. The temperature mapping method with Jlab’s two-cell thermometry system is applied for performance analysis. It is of particular interest to compare the seamless cavity quench locations to those from standard cavities. The cryogenic test results and the T-mapping findings will be discussed. Of special interest is the combination of the seamless technique with NbCu cladding, i.e. the fabrication of cavity from bimetallic clad NbCu tube by hydroforming. Fabrication of single-cell and multi-cell NbCu clad cavities by hydroforming from bimetallic tubes is proven. Some test results will be presented.

  20. Atomistic modeling of defect-induced plasticity in CuNb nanocomposites

    NASA Astrophysics Data System (ADS)

    Martínez, Enrique; Caro, Alfredo; Beyerlein, Irene J.

    2014-08-01

    CuNb nanocomposites have proven stable under light-ion irradiation, although their response to heavy-ion bombardment and subsequent loading is still uncertain. In this paper we analyze the change in mechanical properties of model CuNb nanocomposites in vacancy supersaturated environments, mimicking certain effects introduced by heavy-ion irradiation. We have performed compression tests using molecular dynamics for different defect contents. The presence of defects substantially modifies the system response upon external loading. The dislocation nucleation mechanism changes with the interface atomic density. Stacking fault tetrahedra in the Cu layer may act as dislocation sources to lower significantly the yield stress and the same applies for voids present in the Nb layer. We have analyzed in detail the dislocation-interface interaction mechanisms under different conditions, showing how dislocations react with the misfit dislocations present at the interface to modify the atomic structure of the boundary, which suggests that the interface could be designed to optimize its defect healing properties. We conclude that heavy-ion irradiation softens the multilayer nanocomposites and that interfaces help in recovering these materials as they absorb the dislocations created from irradiation-induced defects.

  1. Monolithic Cu-Cr-Nb Alloys for High Temperature, High Heat Flux Applications

    NASA Technical Reports Server (NTRS)

    Ellis, David L.; Locci, Ivan E.; Michal, Gary M.; Humphrey, Derek M.

    1999-01-01

    Work during the prior four years of this grant has resulted in significant advances in the development of Cu-8 Cr4 Nb and related Cu-Cr-Nb alloys. The alloys are nearing commercial use in the Reusable Launch Vehicle (RLV) where they are candidate materials for the thrust cell liners of the aerospike engines being developed by Rocketdyne. During the fifth and final year of the grant, it is proposed to complete development of the design level database of mechanical and thermophysical properties and transfer it to NASA Glenn Research Center and Rocketdyne. The database development work will be divided into three main areas: Thermophysical Database Augmentation, Mechanical Testing and Metallography and Fractography. In addition to the database development, work will continue that is focussed on the production of alternatives to the powder metallurgy alloys currently used. Exploration of alternative alloys will be aimed at both the development of lower cost materials and higher performance materials. A key element of this effort will be the use of Thermo-Calc software to survey the solubility behavior of a wide range of alloying elements in a copper matrix. The ultimate goals would be to define suitable alloy compositions and processing routes to produce thin sheets of the material at either a lower cost, or, with improved mechanical and thermal properties compared to the current Cu-Cr-Nb powder metallurgy alloys.

  2. Combinatorial Investigations of High Temperature CuNb Oxide Phases for Photoelectrochemical Water Splitting.

    PubMed

    Skorupska, Katarzyna; Maggard, Paul A; Eichberger, Rainer; Schwarzburg, Klaus; Shahbazi, Paria; Zoellner, Brandon; Parkinson, Bruce A

    2015-12-14

    High-throughput combinatorial methods have been useful in identifying new oxide semiconductors with the potential to be applied to solar water splitting. Most of these techniques have been limited to producing and screening oxide phases formed at temperatures below approximately 550 °C. We report the development of a combinatorial approach to discover and optimize high temperature phases for photoelectrochemical water splitting. As a demonstration material, we chose to produce thin films of high temperature CuNb oxide phases by inkjet printing on two different substrates: fluorine-doped tin oxide and crystalline Si, which required different sample pyrolysis procedures. The selection of pyrolysis parameters, such as temperature/time programs, and the use of oxidizing, nonreactive or reducing atmospheres determines the composition of the thin film materials and their photoelectrochemical performance. XPS, XRD, and SEM analyses were used to determine the composition and oxidation states within the copper niobium oxide phases and to then guide the production of target Cu(1+)Nb(5+)-oxide phases. The charge carrier dynamics of the thin films produced by the inkjet printing are compared with pure CuNbO3 microcrystalline material obtained from inorganic bulk synthesis. PMID:26505910

  3. 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.

  4. 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

  5. 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

  6. 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.

  7. 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

  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. 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.

  10. 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.

  11. Mechanical Failure of Thin Ta and Cu/Ta Layers on Polyimide Substrates: A Synchrotron-Based Technique for In Situ Characterization

    SciTech Connect

    Frank, Stephan; Olliges, Sven; Spolenak, Ralph; Handge, Ulrich A.

    2009-06-18

    In situ synchrotron radiation diffraction and confocal light microscopy is used to study fragmentation and buckling of thin brittle Ta layers with thicknesses of 50 nm, 100 nm and 200 nm on polyimide substrates. Synchrotron-based stress measurements confirm that cracking leads to relaxation of tensile stress. Simultaneously, compressive stress arises in transverse direction, which finally leads to buckling. This behavior can be explained quantitatively by a two-dimensional shear lag model. It is well established that the properties of the coating-substrate interface determine the processes of coating fragmentation and delamination. A possible approach for influencing and controlling these processes is given by the incorporation of a ductile interlayer. It can be observed that the presence of Cu interlayers with thicknesses of 5 nm, 20 nm and 50 nm reduces the fracture strength of brittle Ta coatings on polyimide substrates, whereas the resistance to buckling is increased significantly.

  12. 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.

  13. All-YBa2Cu3O7 trilayer tunnel junctions with Sr2AlTaO6 barrier

    NASA Astrophysics Data System (ADS)

    Ying, Q. Y.; Hilbert, Claude

    1994-12-01

    A new barrier material, Sr2AlTaO6, was employed in fabricating all-YBa2Cu3O7 trilayer tunnel junctions using in situ coevaporation and sputtering deposition. It was found that the superior material properties of Sr2AlTaO6 allow the use of a very thin barrier layer. A dramatic increase in the quasiparticle density of states at the YBa2Cu3O7 superconductive gap was observed for the first time from thin-film all-YBa2Cu3O7 devices. Well-defined gap structures were observed at temperatures up to 47 K. The tunneling characteristics are consistent with the typical superconductor-insulator-superconductor behavior. The temperature dependence of the superconductive gap is compared with the BCS theory.

  14. 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

  15. 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.

  16. High plastic Zr-Cu-Fe-Al-Nb bulk metallic glasses for biomedical applications

    NASA Astrophysics Data System (ADS)

    Wang, Shu-shen; Wang, Yun-liang; Wu, Yi-dong; Wang, Tan; Hui, Xi-dong

    2015-06-01

    Four Zr-Cu-Fe-Al-based bulk metallic glasses (BMGs) with Zr contents greater than 65at% and minor additions of Nb were designed and prepared. The glass forming abilities, thermal stabilities, mechanical properties, and corrosion resistance properties of the prepared BMGs were investigated. These BMGs exhibit moderate glass forming abilities along with superior fracture and yield strengths compared to previously reported Zr-Cu-Fe-Al BMGs. Specifically, the addition of Nb into this quaternary system remarkably increases the plastic strain to 27.5%, which is related to the high Poisson's ratio and low Young's and shear moduli. The Nb-bearing BMGs also exhibit a lower corrosion current density by about one order of magnitude and a wider passive region than 316L steel in phosphate buffer solution (PBS, pH 7.4). The combination of the optimized composition with high deformation ability, low Young's modulus, and excellent corrosion resistance properties indicates that this kind of BMG is promising for biomedical applications.

  17. Interaction of small mobile stacking fault tetrahedra with free surfaces, dislocations, and interfaces in Cu and Cu-Nb

    NASA Astrophysics Data System (ADS)

    Martínez, Enrique; Uberuaga, Blas P.; Beyerlein, Irene J.

    2016-02-01

    The presence of stacking fault tetrahedra (SFTs) in face-centered-cubic metals substantially modifies the material response to external loading. These defects are extremely stable with increasing energetic stability as they grow in size. At the sizes visible within a transmission electron microscope, they appear nearly immobile. We have recently shown that these defects might indeed migrate, with defective SFTs exhibiting particularly high mobilities. In this paper, using molecular dynamics, we show how mobile SFTs interact with various types of extended defects, including free surfaces, dislocations, and interfaces in Cu and Cu-Nb systems. We observe a direct relation between the energetics of a single vacancy interacting with each external defect and the propensity for the SFT to be absorbed. Finally, using mesoscale modeling, we show how the fact that SFTs can migrate influences the system evolution and potentially important observables of interest such as the void denuded zones around defect sinks.

  18. 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

  19. 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.

  20. 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.

  1. 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

  2. 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

  3. Structural evolution and the kinetics of Cu clustering in the amorphous phase of Fe-Cu-Nb-Si-B alloy

    NASA Astrophysics Data System (ADS)

    Gupta, P.; Gupta, A.; Shukla, A.; Ganguli, Tapas; Sinha, A. K.; Principi, G.; Maddalena, A.

    2011-08-01

    An attempt has been made to investigate the evolution of the structure of the amorphous phase of Fe73.9 Cu0.9 Nb3.1 Si13.2 B8.9 (finemet) alloy by a combination of wide-angle x-ray scattering, small angle x-ray scattering (SAXS), Mössbauer spectroscopy and X-ray absorption near edge spectroscopy on the supposition that they would provide complementary information. Before the onset of nanocrystallization, the amorphous phase undergoes a structural relaxation resulting in small increase in the hyperfine field and a decrease in the width of the first diffraction maxima. There is an increase in the topological ordering in the system, though chemical inhomogeneity sets-in due to the clustering of Cu atoms in the pure amorphous state of this alloy. Annealing at 400 °C (well below the crystallization temperature) for different time durations results in occurrence of Cu clusters having fcc structure. Kinetics of Cu clustering is studied using SAXS. The incubation time for the clustering at 400 °C is ˜120 min. With further annealing, the average cluster size gradually increases from the initial value of ˜0.4 nm, reaching a value of ˜0.6 nm after annealing for 720 min. Cluster size exhibits a t1/2 dependence, suggesting a diffusion controlled growth.

  4. Comparison of the Crystallization Behavior of Fe-Si-B-Cu and Fe-Si-B-Cu-Nb-Based Amorphous Soft Magnetic Alloys

    NASA Astrophysics Data System (ADS)

    Smith, Casey; Katakam, Shravana; Nag, Soumya; Zhang, Y. R.; Law, J. Y.; Ramanujan, Raju V.; Dahotre, Narendra B.; Banerjee, Rajarshi

    2014-06-01

    The role of the solute elements, copper, and niobium, on the different stages of de-vitrification or crystallization of two amorphous soft magnetic alloys, Fe73.5Si13.5B9Nb3Cu1, also referred to as FINEMET, and a Fe76.5Si13.5B9Cu1 alloy, a model composition without Nb, has been investigated in detail by coupling atom probe tomography and transmission electron microscopy. The effects of copper clustering and niobium pile-up at the propagating interface between the α-Fe3Si nanocrystals and the amorphous matrix, on the nucleation and growth kinetics have been addressed. The results demonstrate that while Cu clustering takes place in both alloys in the early stages, the added presence of Nb in FINEMET severely restricts the diffusivity of solute elements such as Cu, Si, and B. Therefore, the kinetics of solute partitioning and mobility of the nanocrystal/amorphous matrix interface is substantially slower in FINEMET as compared to the Fe76.5Si13.5B9Cu1 alloy. Consequently, the presence of Nb limits the growth rate of the α-Fe3Si nanocrystals in FINEMET and results in the activation of a larger no. of nucleation sites, leading to a substantially more refined microstructure as compared to the Fe76.5Si13.5B9Cu1 alloy.

  5. Unusual multiferroicity in Cu{sub 3}Nb{sub 2}O{sub 8}

    SciTech Connect

    Sharma, G. Saha, J. Patnaik, S.

    2014-04-24

    Cu{sub 3}Nb{sub 2}O{sub 8} is an anti-ferromagnetic - ferroelectric material in which the non-collinear spin alignment leads to breaking of spatial inversion symmetry. We confirm that the ferroelectricity and magnetic anomaly both occur at T{sub N1} = 25K. The emergence of ferroelectricity due to complex spin ordering is investigated by the temperature dependent low temperature measurements of magnetization, dielectric constant and electric polarization. The microscopic origin to explain magneto-electric coupling in this compound is based on a model based on ferroaxial coupling rather than inverse Dzyalonshkii-Moria interaction.

  6. 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.

  7. 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.

  8. Cu-Cr-Nb-Zr Alloy for Rocket Engines and Other High-Heat- Flux Applications

    NASA Technical Reports Server (NTRS)

    Ellis, David L.

    2013-01-01

    Rocket-engine main combustion chamber liners are used to contain the burning of fuel and oxidizer and provide a stream of high-velocity gas for propulsion. The liners in engines such as the Space Shuttle Main Engine are regeneratively cooled by flowing fuel, e.g., cryogenic hydrogen, through cooling channels in the back side of the liner. The heat gained by the liner from the flame and compression of the gas in the throat section is transferred to the fuel by the liner. As a result, the liner must either have a very high thermal conductivity or a very high operating temperature. In addition to the large heat flux (>10 MW/sq m), the liners experience a very large thermal gradient, typically more than 500 C over 1 mm. The gradient produces thermally induced stresses and strains that cause low cycle fatigue (LCF). Typically, a liner will experience a strain differential in excess of 1% between the cooling channel and the hot wall. Each time the engine is fired, the liner undergoes an LCF cycle. The number of cycles can be as few as one for an expendable booster engine, to as many as several thousand for a reusable launch vehicle or reaction control system. Finally, the liners undergo creep and a form of mechanical degradation called thermal ratcheting that results in the bowing out of the cooling channel into the combustion chamber, and eventual failure of the liner. GRCop-84, a Cu-Cr-Nb alloy, is generally recognized as the best liner material available at the time of this reporting. The alloy consists of 14% Cr2Nb precipitates in a pure copper matrix. Through experimental work, it has been established that the Zr will not participate in the formation of Laves phase precipitates with Cr and Nb, but will instead react with Cu to form the desired Cu-Zr compounds. It is believed that significant improvements in the mechanical properties of GRCop-84 will be realized by adding Zr. The innovation is a Cu-Cr-Nb-Zr alloy covering the composition range of 0.8 to 8.1 weight

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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}.

  14. 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

  15. A rate theory study of helium bubble formation and retention in Cu-Nb nanocomposites

    NASA Astrophysics Data System (ADS)

    Dunn, A. Y.; McPhie, M. G.; Capolungo, L.; Martinez, E.; Cherkaoui, M.

    2013-04-01

    A spatially dependent rate theory model for helium migration, clustering, and trapping on interfaces between Cu and Nb layers is introduced to predict the evolution of the concentrations of He clusters of various sizes during implantation and early annealing. Migration and binding energies of point defects and small clusters in bulk Cu and Nb are found using conjugate gradient minimization and the nudged elastic band method. This model is implemented in a three-dimensional framework and used to predict the relationship between helium bubble formation and the nano-composite microstructure, including interfacial free volume, grain size, and layer thickness. Interstitial and vacancy-like migration of helium is considered. The effects of changing layer thickness and interfacial misfit dislocation density on the threshold for helium bubble nucleation are found to match experiments. Accelerated helium release due to interfaces and grain boundaries is shown to occur only when diffusion rates on interfaces and grain boundaries are greatly increased relative to the bulk material.

  16. Oxidation Behavior of GRCop-84 (Cu-8Cr-4Nb) at Intermediate and High Temperatures

    NASA Technical Reports Server (NTRS)

    Thomas-Ogbuji, Linus U.; Humphrey, Donald L.; Greenbauer-Seng, Leslie (Technical Monitor)

    2000-01-01

    The oxidation behavior of GRCop-84 (Cu-8 at %Cr-4 at %Nb) has been investigated in air and in oxygen, for durations of 0.5 to 50 hours and temperatures ranging from 500 to 900 C. For comparison, data was also obtained for the oxidation of Cu and NARloy-Z (Cu-3 wt% Ag-0.5 wt% Zr) under the same conditions. Arrhenius plots of those data showed that all three materials had similar oxidation rates at high temperatures (> 750 C). However, at intermediate temperatures (500 to 750 C) GRCop exhibited significantly higher oxidation resistance than Cu and NARloy-Z. The oxidation kinetics of GRCop-84 exhibited a sharp and discontinuous jump between the two regimes. Also, in the high temperature regime GRCop-84 oxidation rate was found to change from a high initial value to a significantly smaller terminal value at each temperature, with progress of oxidation; the two different oxidation rates were found to correlate with a porous intial oxide and a dense final oxide, respectively.

  17. 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.

  18. 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

  19. 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

  20. 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

  1. 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

  2. LETTER TO THE EDITOR: Observations of distinct atomic packings in Cu Nb metallic glasses synthesized by ion beam mixing

    NASA Astrophysics Data System (ADS)

    Tai, K. P.; Wang, T. L.; Li, J. H.; Liu, B. X.

    2006-09-01

    The structural transformation and disordered atomic packing of metallic glasses in a selected immiscible system at equilibrium, i.e. the Cu-Nb system characterized by a positive heat of formation, are studied using ion beam mixing far from equilibrium. The experimental results indicate that the Cu-Nb metallic glasses could be formed in a composition range from 30 to 85 at.% of Nb and that the Cu-Nb metallic glasses are formed through two different structural phase transition routes, i.e. from the Nb-based body centred cubic and face centred cubic solid solutions, in which the two distinct predominant atomic packings have icosahedral and icositetrahedral orderings, respectively, revealed by the respective diffraction patterns. These observations not only help in formulating a general atomic structural spectrum for the binary metallic glasses, but also suggest an important concept of structural heredity: that the crystalline structure of the constituent metals plays a decisive role in determining the atomic structure of the resultant metallic glasses.

  3. 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

  4. Effect of Nb and Cu on the high temperature creep properties of a high Mn–N austenitic stainless steel

    SciTech Connect

    Lee, Kyu-Ho; Suh, Jin-Yoo; Huh, Joo-Youl; Park, Dae-Bum; Hong, Sung-Min; Shim, Jae-Hyeok; Jung, Woo-Sang

    2013-09-15

    The effect of Nb and Cu addition on the creep properties of a high Mn–N austenitic stainless steel was investigated at 600 and 650 °C. In the original high Mn–N steel, which was initially precipitate-free, the precipitation of M{sub 23}C{sub 6} (M = Cr, Fe) and Cr{sub 2}N took place mostly on grain boudaries during creep deformation. On the other hand, the minor addition of Nb resulted in high number density of Z-phases (CrNbN) and MX (M = Nb; X = C, N) carbonitrides inside grains by combining with a high content of N, while suppressing the formation of Cr{sub 2}N. The addition of Cu gave rise to the independent precipitation of nanometer-sized metallic Cu particles. The combination of the different precipitate-forming mechanisms associated with Z-phase, MX and Cu-rich precipitates turned out to improve the creep-resistance significantly. The thermodynamics and kinetics of the precipitation were discussed using thermo-kinetic simulations. - Highlights: • The creep rupture life was improved by Nb and Cu addition. • The creep resistance of the steel A2 in this study was comparable to that of TP347HFG. • The size of Z-phase and MX carbonitride did not change significantly after creep test. • The nanometer sized Cu-rich precipitate was observed after creep. • The predicted size of precipitates by MatCalc agreed well with measured size.

  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. Humidity effects on the redox reactions and ionic transport in a Cu/Ta2O5/Pt atomic switch structure

    NASA Astrophysics Data System (ADS)

    Tsuruoka, Tohru; Valov, Ilia; Mannequin, Cedric; Hasegawa, Tsuyoshi; Waser, Rainer; Aono, Masakazu

    2016-06-01

    Redox reactions at the Cu/Ta2O5 interface and subsequent Cu ion transport in a Ta2O5 film have been investigated by means of cyclic voltammetry (CV) measurements. Under positive bias to the Cu electrode, Cu is preferentially oxidized to Cu2+ and then to Cu+. Subsequent negative bias causes a reduction of the oxidized Cu ions at the interface. It was found that CV curves change drastically with varied relative humidity levels from 5 to 85%. At higher humidity levels, the ion concentrations and diffusion coefficients, estimated from the CV curves, suggest increased redox reaction rates and a significant contribution of proton conduction to the ionic transport. The results indicate that the redox reactions of moisture are rate-limiting and highlight the importance of water uptake by the matrix oxide film in understanding and controlling the resistive switching behavior of oxide-based atomic switches.

  7. 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.

  8. A study of the superconducting properties of YBa2Cu(9-x)Nb(x)O(y) thin films

    NASA Technical Reports Server (NTRS)

    Srinivas, S.; Bhatnagar, A. K.; Pinto, R.; Pai, S. P.; Apte, P. R.; Purandare, S. C.; Dsousa, C. P.

    1995-01-01

    Effect of Niobium substitution at the copper site in YBa2Cu3O(7-x) was studied in thin film form. The films were deposited by laser ablation technique using the targets of the YBa2Cu(3-x)Nb(x)O(y) where x = 0.0, 0.025, 0.05, 0.1, 0.2, 0.4, 0.8 and 1.0 under identical deposition conditions on SrTiO3 (100) substrates. Films were characterized by XRD, resistivity, I-V and J(sub c) measurements. Films made from x = 0.025 and 0.05 concentrations of Nb substituted targets showed relatively improved superconducting properties compared to that of undoped films. the best J(sub c) realized for x - 0.025 Nb concentration was 1.8 x 10(exp 6) A/sq cm and for 0.05 Nb concentration it was 3.2 x 10(exp 6) A/sq cm at 77 K. However, degradation of the superconducting properties, with the increase of x is greater than or equal to 0.1 Nb concentration and drastic suppression and complete loss of superconductivity was noticed for x is greater than or equal to 0.4. The growth of impurity phase YBa2NbO6 for x = 0.1 and above of Nb concentration was noted from XRD (X-Ray Diffraction) patterns. However, the site occupancy of Nb could not be confirmed from these studies.

  9. 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

  10. 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.

  11. Novel Josephson junction geometries in NbCu bilayers fabricated by focused ion beam microscope

    NASA Astrophysics Data System (ADS)

    Hadfield, R. H.; Burnell, G.; Grimes, P. K.; Kang, D.-J.; Blamire, M. G.

    2002-02-01

    We explore novel junction configurations as an extension of our established focused ion beam-based low Tc SNS junction fabrication technique [1]. By milling a circular trench (diameter 1 μm, width 50 nm) in a 125 nm Nb 75 nm Cu bilayer we define a superconducting island connected to the bulk of the film by a normal metal barrier and entirely enclosed in-plane by the superconducting film. The properties of this Corbino geometry Josephson junction can be probed by depositing an insulating layer over the device and drilling a 0.3 μm diameter hole down to the island to allow a Nb via to be deposited. Behavior of such devices has been studied in a Helium bath at 4.2 K. An SNS-like current-voltage characteristic and Shapiro steps are observed. It is in terms of magnetic field behavior that the device exhibits novel characteristics: as the device is entirely enclosed in type II superconductor, when a magnetic field is applied perpendicular to the plane of the film, only quantized flux can enter the junction. Hence as applied magnetic field is increased the junction critical current is unchanged, then abruptly suppressed as soon as a flux quantum enters.

  12. Annealing effects on the microwave linewidth broadening of FeCuNbSiB ferromagnetic films

    SciTech Connect

    Alves, M. J. P.; Gonzalez-Chavez, D. E.; Sommer, R. L.; Bohn, F.

    2015-03-28

    We systematically investigate the annealing effects on the microwave linewidth broadening of FeCuNbSiB ferromagnetic films with thickness of 100 nm. We correlate the non-uniform residual stress obtained from grazing incidence x-ray diffraction measurements with the ferromagnetic resonance (FMR) linewidth due to effective field inhomogeneities measured from broadband ferromagnetic resonance absorption measurements. We also estimate the annealing temperature effect on the Gilbert and two-magnon scattering contributions to the total ferromagnetic resonance FMR linewidth. We show that the effective field inhomogeneities constitute the main contribution to the microwave linewidth, while this contribution is related to the non-uniform residual stress in the films which is reduced by thermal annealing.

  13. Surface Acoustic Wave Duplexer Composed of SiO2/Cu Electrode/LiNbO3 Structure Having Convex and Concave Portions

    NASA Astrophysics Data System (ADS)

    Nakai, Yasuharu; Nakao, Takeshi; Nishiyama, Kenji; Kadota, Michio

    2009-07-01

    The transition bandwidth of 20 MHz between the transmission (Tx: 1850-1910 MHz) and the receiving (Rx: 1930-1990 MHz) bands of personal communication service (PCS) handy phones in the United States (US) is very narrow compared with those of other systems. We have already realized surface acoustic wave (SAW) duplexers with sizes of 5.0×5.0×1.7 and 3.0×2.5×1.2 mm3 for PCS handy phones in the US with an excellent temperature coefficient of frequency (TCF) by using a shear horizontal (SH) wave on a flattened SiO2/Cu electrode/36-48° YX-LiTaO3 structure and a Rayleigh wave on a SiO2/Cu electrode/120-128° YX-LiNbO3 structure. Although the surface of the above-mentioned structures is flattened SiO2, we have also studied the shape of the SiO2 surface. As a result, in addition to increasing the stop-band width, which corresponds to the reflection coefficient, the TCF and power durability have been improved by forming convex portions on the surface of the SiO2 over the interdigital transducer (IDT) gaps.

  14. 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

  15. 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

  16. 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

  17. 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.

  18. Influence of surface coating on the performance of V-Cu, V-Ti, and Ta membranes for hydrogen separation

    SciTech Connect

    Paglieri, S. N.; Pesiri, D. R.; Dye, R. C.; Tewell, C. R.; Snow, R. C.; Smith, F. M.; Birdsell, S. A.

    2004-01-01

    Foils of V{sub 0.95}Ti{sub 0.05}, V{sub 1-x}Cu{sub x} (x = 0.01-0.12, atom fraction) and Ta coated with thin films of Pd or Pd alloys (Pd-Cu or Pd-Ag), and other metal interlayers were fabricated and tested for hydrogen permeability and stability at temperatures from 320-450 C. Vanadium-alloy or Ta foils were ion-milled and coatings between 30 and 250 nm thick were applied to both sides in-situ via electron beam evaporation. Membranes were between 40 and 75 {mu}m thick and were completely permselective for hydrogen. Pt or Ni surface coatings on VTi{sub 5} foils reduced the permeability by at least an order of magnitude while the membrane coated with the thinnest Pd layer (30 nm) exhibited the fastest hydrogen flux decline at 450 C. The hydrogen flux through a 75 {mu}m thick Pd/V{sub 0.99}Cu{sub 0.01}/Pd composite membrane with 100 nm Pd per side was 0.66 mol (STP)/m{sup 2} {center_dot} s at 350 C and a transmembrane pressure differential ({Delta}P) of 3.5 atm compared to 0.44 mol (STP)/m{sup 2} {center_dot} s for a 71 {mu}m thick Pd/V{sub 0.88}Cu{sub 0.12}/Pd membrane at the same conditions. Foils of Ta were coated with layers of Ti, Mo and Pd to increase the hydrogen flux stability during operation above 400 C. Although the hydrogen flux through the coated Ta foils was generally an order of magnitude less than through the vanadium-alloy membranes, the hydrogen flux stability was greater. Metallic interdiffusion at different temperatures between various surface coatings and foils was characterized with AES depth profiles. Methods are being developed for welding the thin foil membranes into modules for testing.

  19. 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.

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Cu-Cr Literature Review

    SciTech Connect

    Need, Ryan F.

    2012-08-09

    Cu-Cr alloys are part of a class of face-centered cubic (FCC)-body-centered cubic (BCC) composites that includes similar alloys, such as Cu-Nb and Cu-Ta. When heavily deformed, these FCC-BCC materials create 'in situ' composites with a characteristic structure-nanoscale BCC filaments in a ductile FCC matrix. The strength of these composites is vastly greater than predicted by the rule of mixtures, and has been shown to be inversely proportional to the filament spacing. Lower raw materials costs suggest that Cu-Cr alloys may offer more economical solution to high-strength, high-conductivity wire than either their Nb or Ta counterparts. However, Cr is also more brittle and soluble in Cu than Nb or Ta. These qualities necessitate thermal treatments to remove solute atoms from the Cu matrix, improve conductivity, and maintain the ductility of the Cr filaments. Through the use of different thermomechanical processing routes or the addition of select dopants, alloys with strength in excess of 1 GPa at 70% IACS have been achieved. To date, previous research on Cu-Cr alloys has focused on a relatively small number of alloy compositions and processing methods while the effects of dopants and ageing treatments have only been studied independently. Consequently, there remains considerable opportunity for the development and optimization of these alloys as a leading high-strength, high-conductivity material.

  9. Complex permeability spectra of PbO and Ta2O5 added nanocrystalline MgCuZn ferrites

    NASA Astrophysics Data System (ADS)

    V, Seetha Rama Raju

    2015-05-01

    PbO and Ta2O5 added MgCuZn ferrites are prepared by the Microwave-Hydrothermal (M-H) processing. The nanocrystalline ferrites are sintered to a temperature of 900 °C/4 h. SEM pictures reveal that, the addition of PbO causes a small amount of grain growth, whereas the addition of Ta2O5 causes a fine-grained microstructure. The complex permeability spectra (μ*=μ‧-iμ″) of the prepared samples were measured in the frequency range from 1 MHz to 1.8 GHz, the μ* spectra are analyzed into two magnetization processes with focus on the particle size of ferrite samples. In addition to the spin rotation relaxation in 130-200 MHz, it is initially identified the contribution from reversible domain wall bowing rising at 6-40 MHz. The magnetic state of the ferrite is also influenced by the addition of PbO and Ta2O5. The spin rotation mechanism of the present ferrites is enhanced by the preparation of nanocrystalline samples.

  10. Optimization of the microstructure and properties of Co-substituted Fe-Si-B-Nb-Cu nanocrystalline soft magnetic alloys

    NASA Astrophysics Data System (ADS)

    Ohnuma, M.; Ping, D. H.; Abe, T.; Onodera, H.; Hono, K.; Yoshizawa, Y.

    2003-06-01

    The effect of Co replacement for Fe on the microstructure and soft magnetic properties of Fe78.8-xCoxNb2.6Si9B9Cu0.6 (x=5-60) nanocrystalline alloys has been studied for improving the soft magnetic properties of Fe-Si-B-Nb-Cu type alloys at a high frequency range. The magnetic anisotropy constant increases with x, but the coercivity increases when x exceeds 20, indicating that magnetic softness is degraded by replacing Fe with Co. Three-dimensional atom-probe observations have revealed that the number density of Cu-enriched clusters decreases with x, thereby decreasing the number density of the heterogeneous nucleation sites for bcc-Fe primary crystals. In addition, differential scanning calorimetry measurements show that the Cu clustering temperature shifts to a higher temperature with increasing x, suggesting that the kinetics for the Cu clustering decreases as Co content. These experimental results are discussed from the thermodynamical point of view, and the optimized Cu composition to achieve a low coercivity with 40 at % Co has been found. 2003 American Institute of Physics.

  11. 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.

  12. 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

  13. 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.

  14. 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

  15. The problem of intermixing of metals possessing no mutual solubility upon explosion welding (Cu-Ta, Fe-Ag, Al-Ta)

    SciTech Connect

    Greenberg, B.A.; Ivanov, M.A.; Rybin, V.V.; Elkina, O.A.; Antonova, O.V.; Patselov, A.M.; Inozemtsev, A.V.; Plotnikov, A.V.; Volkova, A.Yu.; Besshaposhnikov, Yu.P.

    2013-01-15

    On the basis of the results obtained for joints of dissimilar metals such as copper-tantalum and iron-silver, the reason of immiscible suspensions mixing upon explosion welding has been cleared out. It has been found that the interface (plain or wavy) is not smooth and contains inhomogeneities, namely, cusps and local melting zones. The role of granulating fragmentation providing partitioning of initial materials as a main channel of input energy dissipation has been revealed. It has been shown that in joints of metals possessing normal solubility the local melting zones are true solutions, but if metals possess no mutual solubility the local melting zones are colloidal solutions. Realization of either emulsion or suspension variant takes place. The results can be used in the development of new joints of metals possessing no mutual solubility. - Highlights: Black-Right-Pointing-Pointer Immiscible pairs Ta/Cu and Fe/Ag are welded successfully by explosive welding. Black-Right-Pointing-Pointer Fragmentation provides for partitioning as the main energy dissipation channel. Black-Right-Pointing-Pointer Immiscible metals form colloidal solid solutions during solidification. Black-Right-Pointing-Pointer Melting and boiling temperatures ratio determines the colloidal solution type. Black-Right-Pointing-Pointer Local melting zones being in suspension form enhance welds hardening.

  16. Compliance current induced non-reversible transition from unipolar to bipolar resistive switching in a Cu/TaOx/Pt structure

    NASA Astrophysics Data System (ADS)

    Kurnia, F.; Jung, C. U.; Lee, B. W.; Liu, Chunli

    2015-08-01

    Unipolar resistive switching (URS) as well as bipolar resistive switching (BRS) behaviors in a Cu/TaOx/Pt structure were investigated. Upon increasing the compliance current (Ic), the current-voltage characteristics of the Cu/TaOx/Pt structure showed a URS behavior at Ic = 0.1 mA then experienced a non-reversible transition from the URS to a BRS mode at Ic = 10 mA. Through a detailed analysis of the electrical properties in each resistance state of URS and BRS, we revealed that the permanent transition from the URS to the BRS mode was induced by the formation of stronger Cu metal conductive filaments within the TaOx thin film. More interestingly, both URS and BRS modes were governed by the formation and rupture of conductive filaments, whereas the rupture of these filamentary paths in BRS was proposed due to both Joule heating and electric field effects.

  17. Properties of the Ti40Zr10Cu36Pd14 BMG Modified by Sn and Nb Additions

    NASA Astrophysics Data System (ADS)

    Sypien, Anna; Stoica, Mihail; Czeppe, Tomasz

    2016-03-01

    The results of investigation of the influence of additions of 2 and 3 at.% of Sn and simultaneously of Sn and 3 at.% Nb on microstructure and properties of the bulk metallic glasses of composition (Ti40Cu36- x Zr10Pd14Sn x )100- y Nb y are reported. It was found that the additions of Sn increased the temperatures of glass transition (T g), primary crystallization (T x ), melting, and liquidus as well as supercooled liquid range (Δ T) and glass forming ability (GFA). The nanohardness and elastic modulus decreased in alloys with 2 and 3 at.% Sn additions, revealing similar values. The 3 at.% Nb addition to the Sn-containing amorphous phase decreased as well all the T g, T x , T L, and T m temperatures as Δ T and GFA; however, relatively larger values of this parameters in alloys containing larger Sn content were preserved. In difference to the previously published results, in the case of the amorphous alloys containing small Nb and Sn additions, a noticeable amount of the quenched-in crystalline phases was not confirmed, at least of the micrometric sizes. In the case of the alloys containing Sn or both Sn and Nb, two slightly different amorphous phase compositions were detected, suggesting separation in the liquid phase. Phase composition of the alloys determined after amorphous phase crystallization was similar for all compositions. The phases Cu8Zr3, CuTiZr, and Pd3Zr were mainly identified in the proportions dependent on the alloy compositions.

  18. Kinetics of phase growth in the Cu-Sn system and application to composite Nb3Sn strands

    SciTech Connect

    Emanuela Barzi et al.1

    2002-11-18

    Nb{sub 3}Sn is the superconductor most used in the R and D of high field accelerator magnets by either the wind and react or the react and wind technique. In order to program the low temperature steps of the heat treatment, the growth kinetics of Cu-Sn intermetallics was investigated as a function of duration and temperature. The diffusion constants of {eta}, {var_epsilon} and {delta} phases between 150 and 550 C were evaluated using Cu-Sn model samples. Statistical and systematic errors were thoroughly evaluated for an accurate data analysis. Next the behavior of Internal Tin and Modified Jelly Roll Nb{sub 3}Sn composites was compared with the model predictions.

  19. Production and Precipitation Hardening of Beta-Type Ti-35Nb-10Cu Alloy Foam for Implant Applications

    NASA Astrophysics Data System (ADS)

    Mutlu, Ilven; Yeniyol, Sinem; Oktay, Enver

    2016-04-01

    In this study, beta-type Ti-35Nb-10Cu alloy foams were produced by powder metallurgy method for dental implant applications. 35% Nb was added to stabilize the beta-Ti phase with low Young's modulus. Cu addition enhanced sinterability and gave precipitation hardening capacity to the alloy. Sintered specimens were precipitation hardened in order to enhance the mechanical properties. Electrochemical corrosion behavior of the specimens was examined by electrochemical impedance spectroscopy in artificial saliva. Electrochemical impedance spectroscopy results indicated that the oxide film on the surface of foam is a bi-layer structure consisting of outer porous layer and inner barrier layer. Impedance values of barrier layer were higher than porous layer. Corrosion resistance of specimens decreased at high fluoride concentrations and at low pH of artificial saliva. Corrosion resistance of alloys was slightly decreased with aging. Mechanical properties, microstructure, and surface roughness of the specimens were also examined.

  20. Probing off-Hugoniot states in Ta, Cu, and Al to 1000 GPa compression with magnetically driven liner implosions

    DOE PAGESBeta

    Lemke, R. W.; Dolan, D. H.; Dalton, D. G.; Brown, J. L.; Tomlinson, K.; Robertson, G. R.; Knudson, M. D.; Harding, E.; Mattsson, A. E.; Carpenter, J. H.; et al

    2016-01-07

    We report on a new technique for obtaining off-Hugoniot pressure vs. density data for solid metals compressed to extreme pressure by a magnetically driven liner implosion on the Z-machine (Z) at Sandia National Laboratories. In our experiments, the liner comprises inner and outer metal tubes. The inner tube is composed of a sample material (e.g., Ta and Cu) whose compressed state is to be inferred. The outer tube is composed of Al and serves as the current carrying cathode. Another aluminum liner at much larger radius serves as the anode. A shaped current pulse quasi-isentropically compresses the sample as itmore » implodes. The iterative method used to infer pressure vs. density requires two velocity measurements. Photonic Doppler velocimetry probes measure the implosion velocity of the free (inner) surface of the sample material and the explosion velocity of the anode free (outer) surface. These two velocities are used in conjunction with magnetohydrodynamic simulation and mathematical optimization to obtain the current driving the liner implosion, and to infer pressure and density in the sample through maximum compression. This new equation of state calibration technique is illustrated using a simulated experiment with a Cu sample. Monte Carlo uncertainty quantification of synthetic data establishes convergence criteria for experiments. Results are presented from experiments with Al/Ta, Al/Cu, and Al liners. Symmetric liner implosion with quasi-isentropic compression to peak pressure ~1000 GPa is achieved in all cases. Lastly, these experiments exhibit unexpectedly softer behavior above 200 GPa, which we conjecture is related to differences in the actual and modeled properties of aluminum.« less

  1. Probing off-Hugoniot states in Ta, Cu, and Al to 1000 GPa compression with magnetically driven liner implosions

    NASA Astrophysics Data System (ADS)

    Lemke, R. W.; Dolan, D. H.; Dalton, D. G.; Brown, J. L.; Tomlinson, K.; Robertson, G. R.; Knudson, M. D.; Harding, E.; Mattsson, A. E.; Carpenter, J. H.; Drake, R. R.; Cochrane, K.; Blue, B. E.; Robinson, A. C.; Mattsson, T. R.

    2016-01-01

    We report on a new technique for obtaining off-Hugoniot pressure vs. density data for solid metals compressed to extreme pressure by a magnetically driven liner implosion on the Z-machine (Z) at Sandia National Laboratories. In our experiments, the liner comprises inner and outer metal tubes. The inner tube is composed of a sample material (e.g., Ta and Cu) whose compressed state is to be inferred. The outer tube is composed of Al and serves as the current carrying cathode. Another aluminum liner at much larger radius serves as the anode. A shaped current pulse quasi-isentropically compresses the sample as it implodes. The iterative method used to infer pressure vs. density requires two velocity measurements. Photonic Doppler velocimetry probes measure the implosion velocity of the free (inner) surface of the sample material and the explosion velocity of the anode free (outer) surface. These two velocities are used in conjunction with magnetohydrodynamic simulation and mathematical optimization to obtain the current driving the liner implosion, and to infer pressure and density in the sample through maximum compression. This new equation of state calibration technique is illustrated using a simulated experiment with a Cu sample. Monte Carlo uncertainty quantification of synthetic data establishes convergence criteria for experiments. Results are presented from experiments with Al/Ta, Al/Cu, and Al liners. Symmetric liner implosion with quasi-isentropic compression to peak pressure ˜1000 GPa is achieved in all cases. These experiments exhibit unexpectedly softer behavior above 200 GPa, which we conjecture is related to differences in the actual and modeled properties of aluminum.

  2. Effects of cold-treatment and strain-rate on mechanical properties of NbTi/Cu superconducting composite wires.

    PubMed

    Guan, Mingzhi; Wang, Xingzhe; Zhou, Youhe

    2015-01-01

    During design and winding of superconducting magnets at room temperature, a pre-tension under different rate is always applied to improve the mechanical stability of the magnets. However, an inconsistency rises for superconductors usually being sensitive to strain and oversized pre-stress which results in degradation of the superconducting composites' critical performance at low temperature. The present study focused on the effects of the cold-treatment and strain-rate of tension deformation on mechanical properties of NbTi/Cu superconducting composite wires. The samples were immersed in a liquid nitrogen (LN2) cryostat for the adiabatic cold-treatment, respectively with 18-hour, 20-hour, 22-hour and 24-hour. A universal testing machine was utilized for tension tests of the NbTi/Cu superconducting composite wires at room temperature; a small-scale extensometer was used to measure strain of samples with variable strain-rate. The strength, elongation at fracture and yield strength of pre-cold-treatment NbTi/Cu composite wires were drawn. It was shown that, the mechanical properties of the superconducting wires are linearly dependent on the holding time of cold-treatment at lower tensile strain-rate, while they exhibit notable nonlinear features at higher strain-rate. The cold-treatment in advance and the strain-rate of pre-tension demonstrate remarkable influences on the mechanical property of the superconducting composite wires. PMID:25713767

  3. 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.

  4. 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.

  5. 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

  6. Phase Selection in a Laser Surface Melted Zr-Cu-Ni-Al-Nb Alloy

    NASA Astrophysics Data System (ADS)

    Welk, Brian A.; Fraser, Hamish L.; Dixit, Vikas; Williams, Tim; Gibson, Mark A.

    2014-04-01

    The present work explores the use of the LENS™ (laser engineered net shaping) powder deposition technique in combination with laser surface melting to evaluate the formation-properties-production of bulk metallic glass-forming systems. A model Zr-Cu-Ni-Al-Nb alloy was subjected to a number of laser surface melting experiments to remelt and rapidly solidify a thin surface layer (the laser power varied from 150 W to 450 W and the travel speed of the substrate surface relative to the laser beam varied from 8 mm/s to 170 mm/s). Detailed SEM/TEM evaluation of the microstructure formed under selected laser surface melting conditions was conducted. A marked transition in the microstructure was observed as a result of phase selection, driven by the undercooling manifest under the different imposed solidification conditions. It is considered that such a technique provides valuable insight into the scope for microstructure manipulation through the precise control of the processing variables. The control of the microstructural length scale and the tuning of the intrinsic elastic constants of the constituent phases have been identified as being paramount, for example, in the alloy design of amorphous matrix composites.

  7. Residual Stresses in Thermal Barrier Coatings for a Cu-8Cr-4Nb Substrate System

    NASA Technical Reports Server (NTRS)

    Ghosn, Louis J.; Raj, Sai V.

    2002-01-01

    Analytical calculations were conducted to determine the thermal stresses developed in a coated copper-based alloy, Cu-8%(at.%)Cr-4%Nb (designated as GRCop-84), after plasma spraying and during heat-up in a simulated rocket engine environment. Finite element analyses were conducted for two coating systems consisting of a metallic top coat, a pure copper bond coat and the GRCop-84. The through thickness temperature variations were determined as a function of coating thickness for two metallic coatings, a Ni-17%(wt%)Cr-6%Al-0.5%Y alloy and a Ni-50%(at.%)Al alloy. The residual stresses after low-pressure plasma spraying of the NiCrAlY and NiAl coatings on GRCop-84 substrate were also evaluated. These analyses took into consideration a 50.8 mm copper bond coat and the effects of an interface coating roughness. The through the thickness thermal stresses developed in coated liners were also calculated after 15 minutes of exposure in a rocket environment with and without an interfacial roughness.

  8. 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.

  9. 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.

  10. Mirroring the dynamic magnetic behavior of magnetostrictive Co/(Ag,Cu,Ta) multilayers grown onto rigid and flexible substrates

    NASA Astrophysics Data System (ADS)

    Agra, K.; Gomes, R. R.; Della Pace, R. D.; Dorneles, L. S.; Bohn, F.; Corrêa, M. A.

    2015-11-01

    We investigate the magnetoimpedance effect in a wide frequency range in magnetostrictive Co/(Ag,Cu,Ta) multilayers grown onto rigid and flexible substrates. We observe a direct correlation between structural and quasi-static magnetic properties and the magnetoimpedance effect, since they are directly dependent on the nature of the spacer material. Moreover, we verify that all these properties are insensitive to the kind of employed substrate. We compare the magnetoimpedance results measured for multilayers in rigid and flexible substrates and discuss them in terms of different mechanisms that govern the impedances changes, magnetic anisotropy, structural character, and of numerical calculation results found in the literature. The fact that magnetostrictive multilayers can be reproduced in distinct kinds of substrates corresponds to an important advance for their applicability. The results place multilayers grown onto flexible substrates as attractive candidates for application as probe element in the development of MI-based sensor devices.

  11. 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.

  12. 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.

  13. Synthesis and characterization of particulate reinforced Zr[sub 57]Nb[sub 5]Al[sub 10]Cu[sub 15. 4]Ni[sub 12. 6] bulk metallic glass composites

    SciTech Connect

    Choi-Yim, H.; Busch, R.; Johnson, W.L. . W.M. Keck Lab. of Engineering Materials); Koester, U. . Dept. of Chemical Engineering)

    1999-06-22

    The Zr[sub 57]Nb[sub 5]Al[sub 10]Cu[sub 15.4]Ni[sub 12.6] bulk metallic glass forming liquid is reinforced with WC, SiC, W, or Ta particles. Structure, microstructure and thermal stability of the composites are studied by X-ray diffraction, optical microscopy and differential scanning calorimetry. The metallic glass matrix remains amorphous after adding up to 20 vol.% of particles. The reactions at the interfaces between the matrix and the different reinforcing materials are investigated with scanning electron microscopy, transmission electron microscopy and electron microprobe. The mechanical properties of the composites are studied in compression and tension. The influence of the introduced particles on the thermal stability of the matrix as well as on the mechanical properties is discussed.

  14. Soft magnetic behaviour in amorphous and nanocrystalline Fe 73.5-xMn xSi 13.5B 9Nb 3Cu 1 ( x=1, 3, 5) alloys

    NASA Astrophysics Data System (ADS)

    Tho, N. D.; Chau, N.; Yu, S. C.; Lee, H. B.; Tuan, L. A.; Hoa, N. Q.

    2006-09-01

    Amorphous ribbons Fe 73.5-xMn xSi 13.5Nb 3Cu 1 ( x=1, 3, 5) were prepared by rapid quenching on a single rotated copper wheel. The X-ray patterns show that the as-cast samples are amorphous. The measurements of thermomagnetic curves indicated that the Curie temperature of the amorphous phase of the samples decreased with increasing Mn content. The optimal heat treatment was performed at Ta=535 °C for 1 h and showed that the ultrasoft magnetic properties of nanocomposite materials were obtained. The frequency dependence of magnetoimpedance was measured in the frequency range of 1-10 MHz and at a fixed current of 10 mA. The correlation between the MI effect and the soft magnetic properties is discussed.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. Interface and defect structures in YBa2Cu3O7-δ and Nb : SrTiO3 heterojunction

    NASA Astrophysics Data System (ADS)

    Fu, L. F.; Browning, N. D.; Ramadan, W.; Ogale, S. B.; Kundaliya, D. C.; Venkatesan, T.

    2007-01-01

    YBa2Cu3O7-δ thin films grown on a Nb-doped SrTiO3 substrate by a pulsed laser deposition method have been fully characterized by scanning transmission electron microscopy Z-contrast imaging and electron energy loss spectroscopy techniques. The Nb distribution was found to be uniform and unchanged across the interface, ensuring a high quality p-n junction heterointerface. We first observed the coexistence of 124 and 125 YBCO defect structure phases, appearing as planar defects in a YBCO thin film. Dispersive Y2O3 nanoparticles have also been observed in the thin film. The interaction of these defect structures and Y2O3 nanoparticles is thought to be beneficial for pinning flux through the entire film thickness.

  5. Phase selection and nanocrystallization in Cu-free soft magnetic FeSiNbB amorphous alloy upon rapid annealing

    NASA Astrophysics Data System (ADS)

    Morsdorf, L.; Pradeep, K. G.; Herzer, G.; Kovács, A.; Dunin-Borkowski, R. E.; Povstugar, I.; Konygin, G.; Choi, P.; Raabe, D.

    2016-03-01

    Nucleation of soft magnetic Fe3Si nanocrystals in Cu-free Fe74.5Si15.5Nb3B7 alloy, upon rapid (10 s) and conventional (30 min) annealing, was investigated using x-ray diffraction, transmission electron microscopy, Mössbauer spectroscopy, and atom probe tomography. By employing rapid annealing, preferential nucleation of Fe3Si nanocrystals was achieved, whereas otherwise there is simultaneous nucleation of both Fe3Si and undesired Fe-B compound phases. Analysis revealed that the enhanced Nb diffusivity, achieved during rapid annealing, facilitates homogeneous nucleation of Fe3Si nanocrystals while shifting the secondary Fe-B crystallization to higher temperatures resulting in pure soft magnetic nanocrystallization with very low coercivities of ˜10 A/m.

  6. 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

  7. 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}.

  8. STRUCTURE AND MAGNETIC PROPERTIES OF NANOCRYSTALLINE (Fe50Co50)73.5Cu1Nb3Si13.5B9 ALLOYS

    NASA Astrophysics Data System (ADS)

    Wang, Yuxin; Ju, Ying; Lu, Wei; Yan, Biao; Gao, Wei

    2013-07-01

    (Fe50Co50)73.5Cu1Nb3Si13.5B9 amorphous ribbons, a type of Co doped Finemet alloy, were prepared by melt-spinning and annealed at 440-560°C for 30 min. Influences of heat treatment and Co content on the crystallization were analyzed through differential scanning calorimetric (DSC) and X-ray diffractometry (XRD). The microstructure was analyzed by atomic force microscopy (AFM). The magnetic properties of (Fe50Co50)73.5Cu1Nb3Si13.5B9 and Finemet ribbons were tested by an alternating current soft magnetic properties measurement system. A comparative study of frequency dispersion properties between (Fe50Co50)73.5Cu1Nb3Si13.5B9 and Finemet was conducted. Results indicate that the optimal magnetic property has been achieved when (Fe50Co50)73.5Cu1Nb3Si13.5B9 ribbons were annealed at the temperature range of 480°C-520°C, after which the grain size became between 10 nm and 20 nm. Although the permeability of (Fe50Co50)73.5Cu1Nb3Si13.5B9 is not as high as that of Finemet, this Co-doped Finemet amorphous alloy presents better high frequency properties, and therefore is a promising candidate for the high frequency field applications.

  9. Precipitation strengthened high strength, high conductivity Cu-Cr-Nb alloys produced by chill block melt spinning. Final Report Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Ellis, David L.; Michal, Gary M.

    1989-01-01

    A series of Cu-based alloys containing 2 to 10 a/o Cr and 1 to 5 a/o Nb were produced by chill block melt spinning (CBMS). The melt spun ribbons were consolidated and hot rolled to sheet to produce a supersaturated Cu-Cr-Nb solid solution from which the high melting point intermetallic compound Cr2Nb could be precipitated to strengthen the Cu matrix. The results show that the materials possess electrical conductivities in excess of 90 percent that of pure Cu at 200 C and above. The strengths of the Cu-Cr-Nb alloys were much greater than Cu, Cu-0.6 Cr, NARloy-A, and NARloy-Z in the as-melt spun condition. The strengths of the consolidated materials were less than Cu-Cr and Cu-Cr-Zr below 500 C and 600 C respectively, but were significantly better above these temperatures. The strengths of the consolidated materials were greater than NARloy-Z, at all temperatures. The GLIDCOP possessed similar strength levels up to 750 C when the strength of the Cu-Cr-Nb alloys begins to degrade. The long term stability of the Cu-Cr-Nb alloys was measured by the microhardness of aged samples and the growth of precipitates. The microhardness measurements indicate that the alloys overage rapidly, but do not suffer much loss in strength between 10 and 100 hours which confirms the results of the electrical resistivity measurements taken during the aging of the alloys at 500 C. The loss in strength from peak strength levels is significant, but the strength remains exceptionally good. Transmission electron microscopy (TEM) of the as-melt spun samples revealed that Cr2Nb precipitates formed in the liquid Cu during the chill block melt spinning, indicating a very strong driving force for the formation of the precipitates. The TEM of the aged and consolidated materials indicates that the precipitates coarsen considerably, but remain in the submicron range.

  10. Selective photocatalytic reduction of CO2 to methanol in CuO-loaded NaTaO3 nanocubes in isopropanol

    PubMed Central

    Xiang, Tianyu; Chen, Jingshuai; Wang, Yuwen; Yin, Xiaohong; Shao, Xiao

    2016-01-01

    Summary A series of NaTaO3 photocatalysts were prepared with Ta2O5 and NaOH via a hydrothermal method. CuO was loaded onto the surface of NaTaO3 as a cocatalyst by successive impregnation and calcination. The obtained photocatalysts were characterized by XRD, SEM, UV–vis, EDS and XPS and used to photocatalytically reduce CO2 in isopropanol. This worked to both absorb CO2 and as a sacrificial reagent to harvest CO2 and donate electrons. Methanol and acetone were generated as the reduction product of CO2 and the oxidation product of isopropanol, respectively. NaTaO3 nanocubes loaded with 2 wt % CuO and synthesized in 2 mol/L NaOH solution showed the best activity. The methanol and acetone yields were 137.48 μmol/(g·h) and 335.93 μmol/(g·h), respectively, after 6 h of irradiation. Such high activity could be attributed to the good crystallinity, morphology and proper amount of CuO loading, which functioned as reductive sites for selective formation of methanol. The reaction mechanism was also proposed and explained by band theory. PMID:27335766

  11. 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

  12. Citrate sol gel synthesis, phase formation, optical-properties and TEM analysis of nanocrystalline TaSr2SmCu2O8 materials

    NASA Astrophysics Data System (ADS)

    Balamurugan, S.; George, Jincymol; Parthiban, P.

    2016-05-01

    We report the citrate sol gel (CSG) derived synthesis of nanocrystalline tantalo-cuprate, TaSr2SmCu2O8 (Ta1212Sm) materials and studied the thermal, phase formation, photoluminescence (PL) and photo-catalytic properties and TEM analysis. Like Ta1212Eu phase, the present Ta1212Sm phase is also successfully crystallized in tetragonal symmetry with lattice parameter, a = 0.3875(1) nm and c = 1.1690(5) nm with average crystalline size of ~61.5 nm upon subsequent annealing of the combustion product at 1100°C for 24 h under O2 atmosphere. The room temperature PL emission spectrum of nanocrystalline Ta1212Sm materials exhibits an emission peak at ~605 nm under excitation wavelength of 404 nm. The photo-degradation (~89 %) of methyl orange (MO) by the Ta1212Sm catalyst in the presence of H2O2 is explored. The TEM micro-images reveal that the particles are in nano-scale and irregular morphology.

  13. Reduced losses in rolled Fe73.5Si15.5Nb3B7Cu1 nanocrystalline ribbon

    NASA Astrophysics Data System (ADS)

    Kernion, S. J.; Lucas, M. S.; Horwath, J.; Turgut, Z.; Michel, E.; Keylin, V.; Huth, J. F.; Leary, A. M.; Shen, S.; McHenry, M. E.

    2013-05-01

    Eddy currents in magnetic components undergoing high frequency switching can be mitigated by reducing the thickness of the component. Planar flow cast Fe73.5Si15.5Nb3B7Cu1 ribbon was plastically deformed by cold rolling, resulting in a thickness reduction of 38%. Shear band formation was seen and the coercivity was dramatically higher in the rolled ribbon. After crystallization, the hysteresis loop of the rolled ribbon was nearly identical to a non-rolled ribbon and losses were lower in the rolled ribbon above 25 kHz. Reductions in thickness by this method can lead to increases in operating frequency for power conversion applications.

  14. Cryostatic influence of formvar coatings on sizing of the stabilizer in composite NbTi-Cu superconductors. [for magnets

    NASA Technical Reports Server (NTRS)

    Caspi, S.; Lee, J. Y.; Kim, Y. I.; Frederking, T. H. K.

    1978-01-01

    Often undesirable low energy densities are associated with extreme safety measures (e.g. cryostatic stability) in large superconducting magnets. Therefore, a medium-sized, formvar-coated composite NbTi alloy, Cu-stabilized, has been studied (48 filaments, approximately square cross section about 1/5 cm thickness). Thermal quench behavior (caused by heating) was investigated in various fluid states of He4, including pressurized and superfluid He4. The data obtained support existence of a particular coating thickness ('limiting' thickness) with the property that thermal boundary conditions of uncoated superconductors at a quench are not deteriorated.

  15. A novel 3D Cu(I) coordination polymer based on Cu6Br2 and Cu2(CN)2 SBUs: in situ ligand formation and use as a naked-eye colorimetric sensor for NB and 2-NT.

    PubMed

    Song, Jiang-Feng; Li, Yang; Zhou, Rui-Sha; Hu, Tuo-Ping; Wen, Yan-Liang; Shao, Jia; Cui, Xiao-Bing

    2016-01-14

    A novel coordination polymer with the chemical formula [Cu4Br(CN)(mtz)2]n (mtz = 5-methyl tetrazole) (), has been synthesized under solvothermal conditions and characterized by elemental analysis, infrared (IR) spectroscopy, thermal gravimetric analysis, powder X-ray diffraction and single-crystal X-ray diffraction. Interestingly, the Cu(i), CN(-) and mtz(-) in compound are all generated from an in situ translation of the original precursors: Cu(2+), acetonitrile and 1-methyl-5-mercapto-1,2,3,4-tetrazole (Hmnt). The in situ ring-to-ring conversion of Hmnt into mtz(-) was found for the first time. Structural analysis reveals that compound is a novel 3D tetrazole-based Cu(i) coordination polymer, containing both metal halide cluster Cu6Br2 and metal pseudohalide cluster Cu2(CN)2 secondary building units (SBUs), which shows an unprecedented (3,6,10)-connected topology. Notably, a pseudo-porphyrin structure with 16-membered rings constructed by four mtz(-) anions and four copper(i) ions was observed in compound . The fluorescence properties of compound were investigated in the solid state and in various solvent emulsions, the results show that compound is a highly sensitive naked-eye colorimetric sensor for NB and 2-NT (NB = nitrobenzene and 2-NT = 2-nitrotoluene). PMID:26600452

  16. A transmission electron microscopy study of the effect of interfaces on bubble formation in He-implanted Cu-Nb multilayers.

    PubMed

    Bhattacharyya, D; Demkowicz, M J; Wang, Y-Q; Baumer, R E; Nastasi, M; Misra, A

    2012-02-01

    Magnetron sputtered thin films of Cu, Nb, and Cu-Nb multilayers with 2.5 and 5 nm nominal layer thickness were deposited on Si and implanted with 4He+ and 3He+ ions. Secondary ion mass spectroscopy and nuclear reaction analysis, respectively, were used to measure the 4He+ and 3He+ concentration profile with depth inside the films. Cross-sectional transmission electron microscopy was used to characterize the helium bubbles. Analysis of the contrast from helium bubbles in defocused transmission electron microscope images showed a minimum bubble diameter of 1.25 nm. While pure Cu and Nb films showed bubble contrast over the entire range of helium implantation, the multilayers exhibited bubbles only above a critical He concentration that increased almost linearly with decreasing layer thickness. The work shows that large amounts of helium can be trapped at incoherent interfaces in the form of stable, nanometer-size bubbles. PMID:22258724

  17. 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

  18. YBa2Cu3O(7-delta)/Au/Nb sandwich geometry SNS weak links on c-axis oriented YBa2Cu3O(7-delta)

    NASA Technical Reports Server (NTRS)

    Foote, M. C.; Hunt, B. D.; Bajuk, L. J.

    1991-01-01

    Sandwich geometry superconductor/normal metal/superconductor structures have been fabricated on LaAlO3 and cubic zirconia with laser-ablated, c-axis-oriented YBa2Cu3O(7-delta) base electrodes, 100-600 A of Au, and Nb counter electrodes, all formed in situ without breaking vacuum. Junctions range in size from 5 to 50 micron on a side. Four probe I-V measurements at 4.2 K show RnA products as low as 6 x 10 to the -9th sq cm and critical current densities up to 5.2 kA/sq cm. AC Josephson steps were observed with the application of 10-GHz radiation. The temperature dependence of Jc and the observation of the AC Josephson effect suggest that true supercurrents are present and that they do indeed represent the characteristics of the YBa2Cu3O(7-delta)/Au/Nb structure. The best results were obtained when the devices were annealed at about 450 C in O2 for 30 min after Au deposition.

  19. Ni-free Zr-Cu-Al-Nb-Pd bulk metallic glasses with different Zr/Cu ratios for biomedical applications.

    PubMed

    Huang, Lu; Yokoyama, Yoshihiko; Wu, Wei; Liaw, Peter K; Pang, Shujie; Inoue, Akihisa; Zhang, Tao; He, Wei

    2012-08-01

    Zr-based bulk metallic glasses (BMGs) possess attractive properties for prospective biomedical applications. The present study designs Ni-free Zr-Cu-Al-Nb-Pd BMGs and investigates their in vitro biocompatibility by studying mechanical properties, bio-corrosion resistance, and cellular responses. The Ti-6Al-4V alloy is used as a reference material. It is found that the Zr-based BMGs exhibit good mechanical properties, including high strengths above 1600 MPa, high hardness over 4700 MPa, and low elastic moduli of 85-90 GPa. The Zr-based BMGs are corrosion resistant in a simulated body environment, as revealed by wide passive regions, low passive current densities, and high pitting overpotentials. The formation of ZrO(2)-rich surface passive films of the Zr-based BMGs contributes to their high corrosion resistance, whereas their pitting corrosion in the phosphate buffered saline solution can be attributed to the sensitivity of the ZrO(2) films to the chloride ion. The general biosafety of the Zr-based BMGs is revealed by normal cell adhesions and cell morphologies. Moreover, the Zr/Cu content ratio in the alloy composition affects the biocompatibility of the Zr-based BMGs, by increasing their corrosion resistance and surface wettability with the increase of the Zr/Cu ratio. Effects of Zr/Cu ratios can be used to guide the future design of biocompatible Zr-based BMGs. PMID:22689253

  20. 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.

  1. 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

  2. Vortex phase diagram of the layered superconductor Cu0.03TaS2 for H is parallel to c.

    PubMed

    Zhu, X D; Lu, J C; Sun, Y P; Pi, L; Qu, Z; Ling, L S; Yang, Z R; Zhang, Y H

    2010-12-22

    The magnetization and anisotropic electrical transport properties have been measured in high quality Cu(0.03)TaS(2) single crystals. A pronounced peak effect has been observed, indicating that high quality and homogeneity are vital to the peak effect. A kink has been observed in the magnetic field, H, dependence of the in-plane resistivity ρ(ab) for H is parallel to c, which corresponds to a transition from activated to diffusive behavior of the vortex liquid phase. In the diffusive regime of the vortex liquid phase, the in-plane resistivity ρ(ab) is proportional to H(0.3), which does not follow the Bardeen-Stephen law for free flux flow. Finally, a simplified vortex phase diagram of Cu(0.03)TaS(2) for H is parallel to c is given. PMID:21406807

  3. Strain-Rate Dependence of Material Strength: Large-Scale Atomistic Simulations of Defective Cu and Ta Crystals

    NASA Astrophysics Data System (ADS)

    Abeywardhana, M.; Vasquez, A.; Gaglione, J.; Germann, T. C.; Ravelo, R.

    2015-06-01

    Large-Scale molecular dynamics (MD) simulations are used to model shock wave (SW) and quasi-isentropic compression (QIC) in defective copper and tantalum crystals. The atomic interactions were modeled employing embedded-atom method (EAM) potentials. In the QIC simulations, the MD equations of motion are modified by incorporating a collective strain rate function in the positions and velocities equations, so that the change in internal energy equals the PV work on the system. We examined the deformation mechanisms and material strength for strain rates in the 109-1012 s-1 range For both Cu and Ta defective crystals, we find that the strain rate dependence of the flow stress in this strain rate regime, follows a power law with an exponent close to 0.40. This work was supported by the Air Force Office of Scientific Research under AFOSR Award No. FA9550-12-1-0476. Work at Los Alamos was performed under the auspices of the U.S. Department of Energy (DOE) under Contract No. DE-AC52-06NA25396.

  4. Probing off-Hugoniot states in Ta, Cu, and Al to 10 Mbar compression with magnetically driven liner implosions

    NASA Astrophysics Data System (ADS)

    Mattsson, T. R.; Lemke, R. W.; Dolan, D. H.; Dalton, D. G.; Brown, J. L.; Robertson, G. R.; Knudson, M. D.; Harding, E.; Mattsson, A. E.; Carpenter, J. H.; Drake, R. R.; Cochrane, K.; Robinson, A. C.; Tomlinson, K.; Blue, B. E.

    We report on a technique for obtaining off-Hugoniot equation of state data on solid metals by a magnetically driven cylindrical liner implosion on Sandia's Z-machine (Z). The sample material is in an inner tube with an outer tube composed of Al that serves as the current carrying cathode. A shaped current pulse quasi-isentropically compresses the sample as it implodes. Photonic Doppler velocimetry measures the implosion velocity of the free inner surface of the sample material, and the explosion velocity of the return current anode free outer surface. The velocimetry measurements are used in conjunction with magnetohydrodynamic simulations and optimization to infer pressure and density in the sample. Results are presented for experiments on the Z-machine in which Ta, Cu, and Al samples were compressed to peak pressure 10 Mbar. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  5. 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.

  6. 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.

  7. Recoil studies of photonuclear reactions on natCu, natAg, natTa, and 197Au at intermediate energies

    NASA Astrophysics Data System (ADS)

    Fujiwara, I.; Haba, H.; Matsumura, H.; Sakamoto, K.; Miyamoto, Y.; Oura, Y.; Shibata, S.; Furukawa, M.

    1999-01-01

    The recoil properties of nuclides produced in the photonuclear reactions on natCu, natAg, natTa, and 197Au induced by bremsstrahlung of end-point energies (E o) of 250 to 1000 MeV have been investigated using the thick-target thick-catcher method. The obtained mean ranges of produced nuclides smoothly increase with an increase of the mass difference (ΔA) between products and target, and show E 0-independence at E 0≥600 MeV, reflecting the limiting behavior above (3, 3) resonance region. The mean kinetic energies, T, deduced from the mean ranges show the following two components; (1) (γ, xn) products by giant-resonance and/or quasi-deuteron resonance absorption, (2) (γ, xnyp) products by mainly (3, 3) resonance absorption. Slightly rapid increase of T was found around ΔA=15, 18, 24, and 25 for natCu, natAg, natTa and 197Au, respectively, reflecting a change in mechanism. Kinematic properties of the product nuclei were calculated by using the PICA (Photon-Induced Intranuclear Cascade Analysis) code. The T calculated by the PICA code at E 0=400 MeV well reproduced the experimental results of natCu, but the same calculation for natAg, natTa, and 197Au gave lower mean kinetic energies than the experimental results.

  8. Recoil studies of photonuclear reactions on natCu, natAg, natTa, and 197Au at intermediate energies

    NASA Astrophysics Data System (ADS)

    Fujiwara, I.; Haba, H.; Matsumura, H.; Sakamoto, K.; Miyamoto, Y.; Oura, Y.; Shibata, S.; Furukawa, M.

    1999-01-01

    The recoil properties of nuclides produced in the photonuclear reactions on natCu, natAg, natTa, and 197Au induced by bremsstrahlung of end-point energies ( E o) of 250 to 1000 MeV have been investigated using the thick-target thick-catcher method. The obtained mean ranges of produced nuclides smoothly increase with an increase of the mass difference (ΔA) between products and target, and show E 0-independence at E 0≥600 MeV, reflecting the limiting behavior above (3, 3) resonance region. The mean kinetic energies, T, deduced from the mean ranges show the following two components; (1) (γ, xn) products by giant-resonance and/or quasi-deuteron resonance absorption, (2) (γ, xnyp) products by mainly (3, 3) resonance absorption. Slightly rapid increase of T was found around ΔA=15, 18, 24, and 25 for natCu, natAg, natTa and 197Au, respectively, reflecting a change in mechanism. Kinematic properties of the product nuclei were calculated by using the PICA (Photon-Induced Intranuclear Cascade Analysis) code. The T calculated by the PICA code at E 0=400 MeV well reproduced the experimental results of natCu, but the same calculation for natAg, natTa, and 197Au gave lower mean kinetic energies than the experimental results.

  9. ECR Nb Films Grown on Amorphous and Crystalline Cu Substrates: Influence of Ion Energy

    SciTech Connect

    Valente, Anne-Marie; Eremeev, Grigory V.; Spradlin, Joshua K.; Phillips, H. Lawrence; Reece, Charles E.; Cao, C.; Proslier, Thomas; Tao, T.

    2014-02-01

    In the pursuit of niobium (Nb) films with similar performance with the commonly used bulk Nb surfaces for Superconducting RF (SRF) applications, significant progress has been made with the development of energetic condensation deposition techniques. Using energetic condensation of ions extracted from plasma generated by Electron Cyclotron Resonance, it has been demonstrated that Nb films with good structural properties and RRR comparable to bulk values can be produced on metallic substrates. The controlled incoming ion energy enables a number of processes such as desorption of adsorbed species, enhanced mobility of surface atoms and sub-implantation of impinging ions, thus producing improved film structures at lower process temperatures. Particular attention is given to the nucleation conditions to create a favourable template for growing the final surface exposed to SRF fields. The influence of the deposition energy on film growth on copper substrates is investigated with the characterization of the film surface, structure, superconducting properties and RF performance.

  10. Microstructural evolution of Fe{sub 3}B/Nd{sub 2}Fe{sub 14}B nanocomposite magnets microalloyed with Cu and Nb

    SciTech Connect

    Ping, D.H.; Hono, K.; Kanekiyo, H.; Hirosawa, S.

    1999-12-10

    The microalloying effect of Cu and Nb on the microstructure and magnetic properties of an Fe{sub 3}B Nd{sub 2}Fe{sub 14}B nanocomposite permanent magnet has been studied by transmission electron microscopy (TEM) and atom probe field ion microscopy (APFIM). Additions of Cu are effective in refining the nanocomposite microstructure and the temperature range of the heat treatment to optimize the hard magnetic properties is significantly extended compared with that of the ternary alloy. Combined addition of Cu and Nb is further effective in reducing the grain size. Optimum magnetic properties obtained by annealing a melt-spun Nd{sub 4.5}Fe{sub 75.8}B{sub 18.5}Cu{sub 0.2}Nb{sub 1} amorphous ribbon at 660 C for 6 min are B{sub r} = 1.25 T, H{sub cJ} = 273 kA/m and (BH){sub max} = 125 kJ/m{sup 3}. The soft magnetic Fe{sub 23}B{sub 6} phase coexists with the Fe{sub 3}B and Nd{sub 2}Fe{sub 14}B phases in the optimum microstructure of the Cu and Nb containing quinternary alloy. Three-dimensional atom probe (3DAP) results show that the finer microstructure is due to the formation of a high number density of Cu clusters prior to the crystallization reaction, which promote the nucleation of the Fe{sub 3}B phase. The Nb atoms appear to induce the formation of the Fe{sub 23}B{sub 6} phase when the remaining amorphous phase is crystallized.

  11. 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.

  12. Atomic scale study of CU clustering and pseudo-homogeneous Fe-Si nanocrystallization in soft magnetic FeSiNbB(CU) alloys.

    PubMed

    Pradeep, K G; Herzer, G; Raabe, D

    2015-12-01

    A local electrode atom probe has been employed to trace the onset of Cu clustering followed by their coarsening and subsequent growth upon rapid (10s) annealing of an amorphous Fe73.5Si15.5Cu1Nb3B7 alloy. It has been found that the clustering of Cu atoms introduces heterogeneities in the amorphous matrix, leading to the formation of Fe rich regions which crystallizes pseudo-homogeneously into Fe-Si nanocrystals upon annealing. In this paper, we present the data treatment method that allows for the visualization of these different phases and to understand their morphology while still quantifying them in terms of their size, number density and volume fraction. The crystallite size of Fe-Si nanocrystals as estimated from the atom probe data are found to be in good agreement with other complementary techniques like XRD and TEM, emphasizing the importance of this approach towards accurate structural analysis. In addition, a composition driven data segmentation approach has been attempted to determine and distinguish nanocrystalline regions from the remaining amorphous matrix. Such an analysis introduces the possibility of retrieving crystallographic information from extremely fine (2-4 nm sized) nanocrystalline regions of very low volume fraction (< 5 Vol%) thereby providing crucial in-sights into the chemical heterogeneity induced crystallization process of amorphous materials. PMID:25907803

  13. 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.

  14. The giant magnetoelectric effect in Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites

    NASA Astrophysics Data System (ADS)

    Qiu, Jing; Wen, Yumei; Li, Ping; Chen, Hengjia

    2015-05-01

    The Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites with excellent magnetoelectric (ME) coupling effect were synthesized by electrostatic spray depositing. The ME coupling characteristics of Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites were investigated. It is found that the appropriate thickness ratio between magnetostrictive layers and piezoelectric layers (tm/tp) will be favorable to raise the resonance ME field output performance. The resonance frequency of ME field coefficient can be tuned by controlling tm/tp. The optimum resonance ME field coefficient of Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites achieves 259.2 V/cm Oe at mechanical resonance frequency at 11.5 kHz with the dc bias magnetic field is 60 Oe. Remarkably, the proposed composites exhibit a giant ME effect and a higher ME voltage coefficient than the previous Terfenol-D/PZT laminated composites. It indicates that the mentioned Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites have great potential for the application of highly sensitive magnetic field sensing and vibration energy harvesting.

  15. 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.

  16. 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.

  17. A study on the superconducting properties of YBa{sub 2}Cu{sub 9-x}Nb{sub x}O{sup y} thin films

    SciTech Connect

    Srinivas, S.; Bhatnagar, A.K.; Pinto, R.

    1994-12-31

    Effect of niobium substitution at the copper site in YBa{sub 2}Cu{sub 9}O{sub 7-x} was studied in thin film form. The films were deposited by laser ablation technique using the targets of the YBa{sub 2}Cu{sub 3-x}Nb{sub x}O{sub y} where x = 0.0, 0.025, 0.05, 0.1, 0.2, 0.4, 0.8 and 1.0 under identical deposition conditions on SrTiO{sub 9} <100> substrates. Films were characterized by XRD, resistivity, I-V and J{sub c} measurements. Films made from x = 0.025 and 0.05 concentrations of Nb substituted targets showed relatively improved superconducting properties compared to that of undoped films. The best 7 realized for x = 0.025 Nb concentration was 1.8 x 10{sup {sigma}} A/cm{sup 2} and for 0.05 Nb concentration it was 3.2x10{sup {sigma}} A/cm{sup 2} at 77K. However, degradation of the superconducting properties, with the increase of x {ge} 0.1 Nb concentration and drastic suppression and complete loss of superconductivity was noticed for x {ge} 0.4. The growth of impurity phase YBa{sub 2}NbO{sub 6} for x = 0.1 and above of Nb concentration was noticed from XRD patterns. However, the site occupancy of Nb could not be confirmed from these studies.

  18. Angle-integrated photoemission studies of ruthocuprate Eu_2-xCe_xRuSr_2Cu_2O_10, Gd_2RuSr_2Cu_2O_10 and Eu_1.5Nb_1-xRu_xCu_2O_10 systems

    NASA Astrophysics Data System (ADS)

    Frazer, B.; Hirai, Y.; Rast, Simon; Felner, I.; Asaf, U.; Onellion, M.

    2000-03-01

    We report on both resonant photoemission and fixed photon energy studies of the conduction band and core levels for several ruthocuprate systems. The pure Ru-containing compounds exhibit ferromagnetic order, with metallic behavior and superconductivity depending on the rare earth and oxygen content. We report on as-prepared, hydrogen loaded, and oxygen-annealed polycrystalline samples. The Nb-Ru series changes from purely superconducting to both ferromagnetic and superconducting (Ru). The resonant photoemission measurements of the conduction band across the Ru4p, Cu3p, and Eu4d core levels allow us to determine the location and contribution of Ru, Cu and rare earth related states in the conduction band. The O1s, Cu2p, Ru3p, Ce4d, and Gd4d and several Nb core levels allow us to determine the valence of Ru and Nb, and the metallicity of the Ru/Nb, rare earth, and CuO2 planes.

  19. Cryostatic influence of Formvar coatings on sizing of the stabilizer in superconductive NbTi-Cu - Conductor bundle effects

    NASA Technical Reports Server (NTRS)

    Caspi, S.; Lee, J. Y.; Kim, Y. I.; Chuang, C.; Allen, R. J.; Frederking, T. H. K.

    1979-01-01

    In continuation of single-conductor studies, quench onset data of quasi-steady operation are reported for a Formvar-coated composite (Nb48Ti/Cu) in bundle geometry (conductor thickness about 0.2 cm, approximately square cross section). Overall thermal conductances of the heater simulation technique applied are of the order 0.1 W/(sq cm-K), comparable to single-specimen results, around 4 K and below the lambda transition in agreement with model predictions. Considerable deterioration, however, occurs below 3 K and down to the lambda temperature during operation in near-saturated He I. Consequences for magnets of intermediate energy density are discussed with emphasis on the modifications necessitated by coatings.

  20. Significant change of spin transport property in Cu/Nb bilayer due to superconducting transition

    PubMed Central

    Ohnishi, Kohei; Ono, Yuma; Nomura, Tatsuya; Kimura, Takashi

    2014-01-01

    The combination between the spin-dependent and super-conducting (SC) transports is expected to provide intriguing properties such as crossed Andreev reflection and spin-triplet superconductivity. This may be able to open a new avenue in the field of spintronics, namely superconducting spintronics because a superconductor itself has great potential for future nanoelectronic applications. To observe such SC spin transports, the suppression of the extrinsic effects originating from the heating and Oersted field due to the electric current is a crucial role. Pure spin current without accompanying the charge current is known as a powerful mean for preventing such extrinsic effects. However, non-negligible heat flow is found to exist even in a conventional pure spin current device based on laterally-configured spin valve because of the heating around the spin injector. Here, we develop a nanopillar-based lateral spin valve, which significantly reduces the heat generation, on a superconducting Nb film. By using this ideal platform, we found that the spin absorption is strongly suppressed by the SC transition of Nb. This demonstration is the clear evidence that the super-conducting Nb is an insulator for the pure spin current. PMID:25179118

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. Kinetic analysis of the non-isothermal crystallization process, magnetic and mechanical properties of FeCoBSiNb and FeCoBSiNbCu bulk metallic glasses

    NASA Astrophysics Data System (ADS)

    Ramasamy, Parthiban; Stoica, Mihai; Taghvaei, A. H.; Prashanth, K. G.; Ravi Kumar, Eckert, Jürgen

    2016-02-01

    The crystallization kinetics of [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 and {[(Fe0.5Co0.5)0.75B0.2Si0.05]0.96Nb0.04}99.5Cu0.5 bulk metallic glasses were evaluated using differential scanning calorimetry under non-isothermal condition. The fully glassy rods with diameters up to 2 mm were obtained by copper mold injection casting. Both glasses show good thermal stability, but the addition of only 0.5% Cu completely changes the crystallization behavior. The average activation energy required for crystallization decreases from 645 kJ/mol to 425 kJ/mol after Cu addition. Upon heating, the Cu-free alloy forms only the metastable Fe23B6 phase. In contrast, two well-separated exothermic events are observed for the Cu-added bulk glassy samples. First, the (Fe,Co) phase nucleates and then (Fe,Co)2B and/or (Fe,Co)3B crystallize from the remaining glassy matrix. The Cu-added alloy exhibits a lower coercivity and a higher magnetic saturation than the base alloy, both in as-cast as well as in annealed condition. Besides, the Cu-added glassy sample with 2 mm diameter exhibits a maximum compressive fracture strength of 3913 MPa together with a plastic strain of 0.6%, which is highest plastic strain ever reported for 2 mm diameter ferromagnetic bulk metallic glass sample. Although Cu addition improves the magnetic and mechanical properties of the glass, it affects the glass-forming ability of the base alloy.

  7. The effects of shockwave profile shape and shock obliquity on spallation in Cu and Ta: kinetic and stress-state effects on damage evolution(u)

    SciTech Connect

    Gray, George T

    2010-12-14

    Widespread research over the past five decades has provided a wealth of experimental data and insight concerning shock hardening and the spallation response of materials subjected to square-topped shock-wave loading profiles. Less quantitative data have been gathered on the effect of direct, in-contact, high explosive (HE)-driven Taylor wave (or triangular-wave) loading profile shock loading on the shock hardening, damage evolution, or spallation response of materials. Explosive loading induces an impulse dubbed a 'Taylor Wave'. This is a significantly different loading history than that achieved by a square-topped impulse in terms of both the pulse duration at a fixed peak pressure, and a different unloading strain rate from the peak Hugoniot state achieved. The goal of this research is to quantify the influence of shockwave obliquity on the spallation response of copper and tantalum by subjecting plates of each material to HE-driven sweeping detonation-wave loading and quantify both the wave propagation and the post-mortem damage evolution. This talk will summarize our current understanding of damage evolution during sweeping detonation-wave spallation loading in Cu and Ta and show comparisons to modeling simulations. The spallation responses of Cu and Ta are both shown to be critically dependent on the shockwave profile and the stress-state of the shock. Based on variations in the specifics of the shock drive (pulse shape, peak stress, shock obliquity) and sample geometry in Cu and Ta, 'spall strength' varies by over a factor of two and the details of the mechanisms of the damage evolution is seen to vary. Simplistic models of spallation, such as P{sub min} based on 1-D square-top shock data lack the physics to capture the influence of kinetics on damage evolution such as that operative during sweeping detonation loading. Such considerations are important for the development of predictive models of damage evolution and spallation in metals and alloys.

  8. 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.

  9. In situ Growth of NixCu1-x Alloy Nanocatalysts on Redox-reversible Rutile (Nb,Ti)O4 Towards High-Temperature Carbon Dioxide Electrolysis

    NASA Astrophysics Data System (ADS)

    Wei, Haoshan; Xie, Kui; Zhang, Jun; Zhang, Yong; Wang, Yan; Qin, Yongqiang; Cui, Jiewu; Yan, Jian; Wu, Yucheng

    2014-06-01

    In this paper, we report the in situ growth of NixCu1-x (x = 0, 0.25, 0.50, 0.75 and 1.0) alloy catalysts to anchor and decorate a redox-reversible Nb1.33Ti0.67O4 ceramic substrate with the aim of tailoring the electrocatalytic activity of the composite materials through direct exsolution of metal particles from the crystal lattice of a ceramic oxide in a reducing atmosphere at high temperatures. Combined analysis using XRD, SEM, EDS, TGA, TEM and XPS confirmed the completely reversible exsolution/dissolution of the NixCu1-x alloy particles during the redox cycling treatments. TEM results revealed that the alloy particles were exsolved to anchor onto the surface of highly electronically conducting Nb1.33Ti0.67O4 in the form of heterojunctions. The electrical properties of the nanosized NixCu1-x/Nb1.33Ti0.67O4 were systematically investigated and correlated to the electrochemical performance of the composite electrodes. A strong dependence of the improved electrode activity on the alloy compositions was observed in reducing atmospheres at high temperatures. Direct electrolysis of CO2 at the NixCu1-x/Nb1.33Ti0.67O4 composite cathodes was investigated in solid-oxide electrolysers. The CO2 splitting rates were observed to be positively correlated with the Ni composition; however, the Ni0.75Cu0.25 combined the advantages of metallic nickel and copper and therefore maximised the current efficiencies.

  10. In situ growth of Ni(x)Cu(1-x) alloy nanocatalysts on redox-reversible rutile (Nb,Ti)O₄ towards high-temperature carbon dioxide electrolysis.

    PubMed

    Wei, Haoshan; Xie, Kui; Zhang, Jun; Zhang, Yong; Wang, Yan; Qin, Yongqiang; Cui, Jiewu; Yan, Jian; Wu, Yucheng

    2014-01-01

    In this paper, we report the in situ growth of Ni(x)Cu(1-x) (x = 0, 0.25, 0.50, 0.75 and 1.0) alloy catalysts to anchor and decorate a redox-reversible Nb1.33Ti0.67O4 ceramic substrate with the aim of tailoring the electrocatalytic activity of the composite materials through direct exsolution of metal particles from the crystal lattice of a ceramic oxide in a reducing atmosphere at high temperatures. Combined analysis using XRD, SEM, EDS, TGA, TEM and XPS confirmed the completely reversible exsolution/dissolution of the Ni(x)Cu(1-x) alloy particles during the redox cycling treatments. TEM results revealed that the alloy particles were exsolved to anchor onto the surface of highly electronically conducting Nb1.33Ti0.67O4 in the form of heterojunctions. The electrical properties of the nanosized Ni(x)Cu(1-x)/Nb1.33Ti0.67O4 were systematically investigated and correlated to the electrochemical performance of the composite electrodes. A strong dependence of the improved electrode activity on the alloy compositions was observed in reducing atmospheres at high temperatures. Direct electrolysis of CO2 at the Ni(x)Cu(1-x)/Nb1.33Ti0.67O4 composite cathodes was investigated in solid-oxide electrolysers. The CO2 splitting rates were observed to be positively correlated with the Ni composition; however, the Ni0.75Cu0.25 combined the advantages of metallic nickel and copper and therefore maximised the current efficiencies. PMID:24889679

  11. In situ Growth of NixCu1-x Alloy Nanocatalysts on Redox-reversible Rutile (Nb,Ti)O4 Towards High-Temperature Carbon Dioxide Electrolysis

    PubMed Central

    Wei, Haoshan; Xie, Kui; Zhang, Jun; Zhang, Yong; Wang, Yan; Qin, Yongqiang; Cui, Jiewu; Yan, Jian; Wu, Yucheng

    2014-01-01

    In this paper, we report the in situ growth of NixCu1-x (x = 0, 0.25, 0.50, 0.75 and 1.0) alloy catalysts to anchor and decorate a redox-reversible Nb1.33Ti0.67O4 ceramic substrate with the aim of tailoring the electrocatalytic activity of the composite materials through direct exsolution of metal particles from the crystal lattice of a ceramic oxide in a reducing atmosphere at high temperatures. Combined analysis using XRD, SEM, EDS, TGA, TEM and XPS confirmed the completely reversible exsolution/dissolution of the NixCu1-x alloy particles during the redox cycling treatments. TEM results revealed that the alloy particles were exsolved to anchor onto the surface of highly electronically conducting Nb1.33Ti0.67O4 in the form of heterojunctions. The electrical properties of the nanosized NixCu1-x/Nb1.33Ti0.67O4 were systematically investigated and correlated to the electrochemical performance of the composite electrodes. A strong dependence of the improved electrode activity on the alloy compositions was observed in reducing atmospheres at high temperatures. Direct electrolysis of CO2 at the NixCu1-x/Nb1.33Ti0.67O4 composite cathodes was investigated in solid-oxide electrolysers. The CO2 splitting rates were observed to be positively correlated with the Ni composition; however, the Ni0.75Cu0.25 combined the advantages of metallic nickel and copper and therefore maximised the current efficiencies. PMID:24889679

  12. 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

  13. Effect of In3+ concentration on the photorefraction and scattering properties in In:Fe:CU:LiNbO3 crystals at 532 nm wavelength

    NASA Astrophysics Data System (ADS)

    Luo, Suhua; Meng, Qingxin; Wang, Jian; Sun, Xiudong

    2016-01-01

    The LiNbO3 crystals doped with Fe2O3, CuO and various In2O3, respectively, have been grown by the Czochralski method in air atmosphere. The photorefractive properties at 532 nm wavelength were measured by using the typical two-wave coupling experiments. Meanwhile, the incident exposure energy flux threshold for the light-induced scattering was characterized to investigate the scattering properties of the crystals. The results show that the response time shortens, the recording sensitivity improves, and the light-induced scattering decreases with the increasing In3+ ions concentration. However, the doping of In3+ ions leads to the decrease of the diffraction efficiency and the gain coefficient. So, the appropriate In3+ ions concentration should be doping in In:Fe:Cu:LiNbO3 crystals to adapt our practical application in the green light region photorefractive holographic recording.

  14. Temperature dependence of the magnetostriction and the induced anisotropy in nanocrystalline FeCuNbSiB alloys, and their fluxgate properties

    SciTech Connect

    Nielsen, O.V.; Petersen, J.R.; Herzer, G.

    1994-03-01

    Making use of the stress induced magnetic anisotropy in some iron-rich FeCuNbSiD nanocrystalline materials the authors studied the thermal dependence of their magnetostriction which becomes zero below the Curie temperature. The choice of a suitable composition and annealing temperature results in materials with zero magnetostriction at room temperature. Due to the low magnetostriction these materials have very promising fluxgate properties which were studied as well.

  15. Magnetic properties of Fe73.5Cu1Nb3-xUxSi13.5B9 (x = 1, 2, 3) nanocrystalline alloys

    NASA Astrophysics Data System (ADS)

    Kollár, P.; Füzer, J.; Matta, P.; Švec, T.; Konč, M.

    1996-05-01

    The influence of uranium content and annealing on the magnetic properties and Hall effect of Fe73.5Cu1Nb3-xUxSi13.5B9 (x = 1, 2, 3) nanocrystalline alloys prepared by melt spinning were investigated. Measurements of magnetic properties of surface layers confirmed higher concentration of uranium in the air-side surface layers than in the wheel-side layers.

  16. Fracture behavior under fatigue loading at room temperature and its influence on critical current of Nb-Ti/Cu composite wire

    NASA Astrophysics Data System (ADS)

    Hojo, Masaki; Iwasaki, Naoya; Sekino, Fumiaki; Ochiai, Shojiro; Sakai, Shuji; Watanabe, Kazuo

    1999-11-01

    Fracture behavior under fatigue loading at room temperature and its influence on critical superconducting current at 4.2 K were investigated for Nb-Ti/Cu multifilamentary composite wire with a copper ratio of 7.83 and an overall diameter of 0.504 mm in which 24 Nb-Ti filaments were embedded. There was a knee in the relation between the applied maximum stress and the number of cycles to failure ( S- N relations). The fracture mechanism below and above this knee was different. When the maximum stress in the fatigue test was high, extensive multiple necking of the Nb-Ti filament occurred, and this was responsible for the final fracture of the composite wire. On the other hand, when the maximum stress in the fatigue tests was low, the fatigue crack nucleated in the copper, which grew and caused the fracture of the Nb-Ti filaments. The critical current was insensitive to fatigue loading when the maximum stress was low. When the maximum stress was high, the critical current after fatigue loading was lower than that after static loading. This was due to severe multiple necking during fatigue loading. Extracted Nb-Ti filaments were also fatigued using a specially designed fatigue testing machine. The S- N curve of filaments agreed well with the stress component of the filament calculated from the S- N relation of the composite wire.

  17. Influence of Ta2O5-Co2O3 co-doping on the magnetic property of NiMgCuZn ferrites

    NASA Astrophysics Data System (ADS)

    Sun, Ke; Wang, Juntao; Yang, Yan; Li, Yao; Yu, Zhong; Lan, Zhongwen; Jiang, Xiaona; Guo, Rongdi; Wu, Chuanjian

    2015-11-01

    NiMgCuZn ferrites co-doped with Ta2O5 and Co2O3 additives have been prepared by a solid-state reaction method. The influence of Ta2O5-Co2O3 (TC) additives on the microstructure, static magnetic properties and core losses (Pcv) at high frequency of NiMgCuZn ferrites has been investigated by scanning electron microscope (SEM), LCR meter and B-H analyzer. The results revealed that the composite additives reduce the sintering density via inhibiting the grain growth. According to Zagg's report, the average grain sizes are smaller than 2.4 μm for different TC contents, hence all the samples have single domain structures. In addition, the saturation induction and initial permeability of the samples reduce monotonously with the increase of TC contents. While the coercivity and cutoff frequency show an opposite trend. For the samples with different TC contents, the core losses at high frequency have been discussed.

  18. Operating experience with the heat-resistant material 15 NiCuMoNb 5 in conventional power plants

    SciTech Connect

    Adamsky, F.J.; Teichmann, H.; Tolksdorf, E.

    1998-07-01

    The forerunners of the material 15 NiCuMoNb 5 (WB 36), known as CuNi steels for boiler drums, allowed operating pressures to exceed 100 bar for the first time in the 30s, thereby creating the basis for power station to achieve high performance and efficiency levels. Even present day steel developments for the thick walled components used in nuclear technology have almost reached the level of this steel with regard to the high temperature limit of elasticity as a design value up to temperatures of 400 C, but have not exceeded it. In the mid-60s, extensive investigations were carried out into these materials following a few spectacular cases of serious damage, basically manifesting themselves in two ways: as cracks in the area of the downpipe bores and brittle fractures revealed by pressure testing. The cracks were recognized as stress/strain-induced corrosion and this was counteracted internally by improving the quality of the water, particularly with regard to its oxygen content. The inadequate toughness characteristics, responsible for the fractures occurring during the pressure test, were improved by specific alloying measures and in particular by reducing the sulphur content. Particular attention was paid to welding work. Reporting on operating experience means reporting the results of investigations into damage to components made from heat-resistant materials and providing a critical evaluation. A few examples are summarized below for this purpose. Some are current examples and others go back a few years, but are still the subject of discussion in the sector because of the fundamental knowledge to be gained from them.

  19. 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.

  20. 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.

  1. Glass transition, crystallization kinetics and pressure effect on crystallization of ZrNbCuNiBe bulk metallic glass

    NASA Astrophysics Data System (ADS)

    Xing, P. F.; Zhuang, Y. X.; Wang, W. H.; Gerward, L.; Jiang, J. Z.

    2002-04-01

    The glass transition behavior and crystallization kinetics of Zr48Nb8Cu14Ni12Be18 bulk metallic glass have been investigated by differential scanning calorimetry and x-ray powder diffraction (XRD). The activation energies of both glass transition and crystallization events have been obtained using the Kissinger method. Results indicate that this glass crystallizes by a three-stage reaction: (1) phase separation and primary crystallization of glass, (2) formation of intermetallic compounds, and (3) decomposition of intermetallic compounds and crystallization of residual amorphous phase. The pressure effect on crystallization is studied by in situ high-pressure and high-temperature XRD using synchrotron radiation. Two crystallization temperatures, observed by in-situ XRD, behave differently with varying pressure. The onset crystallization temperature increases with pressure with a slope of 9.5 K/GPa in the range of 0 to 4.4 GPa, while the another crystallization temperature keeps almost unchanged in the applied pressure range. The results are attributed to the competing processes between the thermodynamic potential barrier and the diffusion activation energy under pressure.

  2. The huge influence of nanograins on the magnetic properties of iron-based Fe Cu Nb B nanocrystalline alloys

    NASA Astrophysics Data System (ADS)

    Bremers, H.; Hupe, O.; Hofmeister, C. E.; Michele, O.; Hesse, J.

    2005-06-01

    In 1995 Skorvanek and O'Handley presented the first experimental evidence for a huge influence of nanograins on the magnetization of a nanostructured alloy. In this contribution experiments are described, performed on as-cast amorphous and nanostructured Fe79Cu1Nb7B13 alloys. In order to get nanostructured samples with different nanograin contents the samples were annealed at different properly chosen temperatures in vacuum. This led to the formation of nanograins embedded in a residual amorphous matrix. These nanograins consist of pure bcc Fe of about 5-6 nm in diameter. Their content can be enhanced without markedly changing their size when annealing at slightly higher temperatures. So an alloy series with the same nominal composition but different nanograin contents and residual amorphous matrices, i.e. a series of nanostructured alloys, was obtained. Our aim was to study the influence of increasing nanograin concentration on the magnetic properties of the coupled system amorphous matrix plus nanograins. We describe magnetization measurements over a wide temperature range, below and above the Curie temperature of the initial amorphous matrix. In a next step these measurements are evaluated in a molecular field approach assuming two different coupled ferromagnetic systems assigned to the amorphous matrix and the nanograins.

  3. Role of interfaces on the trapping of He in 2D and 3D Cu-Nb nanocomposites

    NASA Astrophysics Data System (ADS)

    Lach, Timothy G.; Ekiz, Elvan H.; Averback, Robert S.; Mara, Nathan A.; Bellon, Pascal

    2015-11-01

    The role of interface structure on the trapping of He in Cu-Nb nanocomposites was investigated by comparing He bubble formation in nano-multilayers grown by PVD, nanolaminates fabricated by accumulative roll bonding (ARB), and 3D nanocomposites obtained by high pressure torsion (HPT). All samples were implanted with 1 MeV He ions at room temperature and characterized by cross section transmission electron microscopy (TEM). The critical He concentration leading to bubble formation was determined by correlating the He bubble depth distribution detected by TEM with the implanted He depth profile obtained by SRIM. The critical He dose per unit interfacial area for bubble formation was largest for the PVD multilayers, lower by a factor of ∼1.4 in the HPT nanocomposites annealed at 500 °C, and lower by a factor of ∼4.6 in the ARB nanolaminates relative to the PVD multilayers. The results indicate that the (111)FCC||(110)BCC Kurdjumov-Sachs (KS) interfaces predominant in PVD and annealed HPT samples provide more effective traps than the (112)KS interfaces predominant in ARB nanolaminates; however, the good trapping efficiency and high interface area of 3D HPT structures make them most attractive for applications.

  4. 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.

  5. 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)

  6. 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

  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. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Switching of saturation magnetization by carrier injection in YBa2Cu3O7-δ/α-Fe2O3/Nb-SrTiO3 junctions

    NASA Astrophysics Data System (ADS)

    Chen, Yuansha; Lian, Guijun; Xiong, Guangcheng; Venkatesan, T.

    2011-06-01

    Ferromagnetic (FM) α-Fe2O3 layers were deposited on n-type oxide semiconductor substrates of Nb-doped SrTiO3 (NSTO) to form YBa2Cu3O7-δ/α-Fe2O3/NSTO junctions. Multilevel resistance switching behavior was observed in YBa2Cu3O7-δ/α-Fe2O3/NSTO junctions with stable resistive states. The saturation magnetization MS of the YBa2Cu3O7-δ/α-Fe2O3/NSTO junctions was modulated by carrier injection and correlated with the conductivity of the switched state. This is the first report of simultaneous modulation of intrinsic magnetic and transport properties for FM oxide devices by using carrier injection.

  15. Effect of Nb2O5 and V2O5 addition on the superconducting properties of YBa2Cu3O(y) thin films

    NASA Technical Reports Server (NTRS)

    Srinivas, S.; Bhatnagar, A. K.; Pinto, R.; Pai, S. P.; Apte, P. R.; Purandare, S. C.; Souza, C. P. D.

    1995-01-01

    The effect of Nb2O5 and V2O5 addition on the superconducting properties and microstructure of YBa2Cu3O(y) has been studied in thin films. Polycrystalline targets for laser ablation were prepared by mixing high purity V2O5 or Nb2O5 powders with a well characterized YBa2Cu3O(y) powder in the range 0 to 4 wt percent by solid state reaction method. Thin films (approximately 1500 A thickness) of the above targets were grown on (100) SrTiO3 (STO) and (100) LaAlO3 (LAO) substrates at 700 C temperature by pulsed laser deposition (PLD) technique. In the case of Nb2O5 addition we have noticed an increase in J(sub c) up to 0.5 wt percent and higher additive concentration (greater than 0.5 wt percent) have degraded the superconducting properties. However, in the case of V2O3 addition, there is an improvement in current density and microstructural properties up to 1 wt percent and the superconducting properties degrade for concentrations greater than 1 wt percent. The best J(sub c) for 0.5 wt percent of Nb2O5 added YBCO thin film is 1.6 x 10(exp 6) A/sq cm and for that of V2O5 added sample is 3.4 x 10(exp 6) A/sq cm at 77 K as compared to the pure YBa2Cu3O(y) (YBCO) film J(sub c) (1.2 x 10(exp 6) A/sq cm) observed on STO substrates. The reason for improvement in J(sub c) and microstructural properties in the case of V2O5 addition could be due to the low melting of V2O5 (690 C) which can act as a very good surfactant during deposition. Over all, we have realized that Nb2O5 addition or V2O5 addition to YBCO have shown significant improvement over the undoped YBa2Cu3O(7-x) films grown under identical conditions.

  16. Photoelectrochemistry, Electronic Structure, and Bandgap Sizes of Semiconducting Cu(I)-Niobates and Cu(I)-Tantalates

    SciTech Connect

    Maggard, Paul A.

    2013-11-14

    Semiconducting metal-oxides have remained of intense research interest owing to their potential for achieving efficient solar-driven photocatalytic reactions in aqueous solutions that occur as a result of their bandgap excitation. The photocatalytic reduction of water or carbon dioxide to generate hydrogen or hydrocarbon fuels, respectively, can be driven on p-type (photocathodic) electrodes with suitable band energies. However, metal-oxide semiconductors are typically difficult to dope as p-type with a high mobility of carriers. The supported research led to the discovery of new p-type Cu(I)-niobate and Cu(I)-tantalate film electrodes that can be prepared on FTO glass. New high-purity flux syntheses and the full structural determination of several Cu(I)-containing niobates and tantalates have been completed, as well as new investigations of their optical and photoelectrochemical properties and electronic structures via density-functional theory calculations. For example, CuNbO3, Cu5Ta11O30 and CuNb3O8 were prepared in high purity and their structures were characterized by both single-crystal and powder X-ray diffraction techniques. These two classes of Cu(I)-containing compounds exhibit optical bandgap sizes ranging from ~1.3 eV to ~2.6 eV. Photoelectrochemical measurements of these compounds show strong photon-driven cathodic currents that confirm the p-type semiconductor behavior of CuNbO3, CuNb3O8, and Cu5Ta11O30. Incident-photon-to-current efficiencies are measured that approach greater than ~1%. Electronic-structure calculations based on density functional theory reveal the visible-light absorption stems from a nearly-direct bandgap transition involving a copper-to-niobium or tantalum (d10 to d0) charge-transfer excitations.

  17. Preparation of Sr2AlTaO6 Insulating Films on YBa2Cu3O7-δ by Metalorganic Chemical Vapor Deposition with Purified Sr Source

    NASA Astrophysics Data System (ADS)

    Takahashi, Yoshihiro; Zama, Hideaki; Ishimaru, Yoshihiro; Inoue, Nobuyoshi; Wu, Yuan; Morishita, Tadataka; Tanabe, Keiichi

    2002-02-01

    200-nm-thick Sr2AlTaO6 (SAT) insulating films were prepared on 10-μm-thick superconducting YBa2Cu3O7-δ (YBCO) films by metalorganic chemical vapor deposition (MOCVD). By employing a purified Sr(thd)2 metalorganic source, instead of Sr(thd)2-2tetraene, and a higher evaporation temperature, we could reproducibly obtain stoichiometric SAT films with high crystallinity as revealed by the full-width at half maximum value of the SAT (004) X-ray rocking curve which was as small as 0.2°. Moreover, a 200-nm-thick c-axis-oriented YBCO film with a Tc of 90 K and a Jc higher than 107 A/cm2 below 60 K could be grown on the SAT film. These results confirm that the SAT films prepared by MOCVD are suitable for use as insulating layers in high-Tc multilayer electronic devices.

  18. Development of 100kVA AC superconducting coil using NbTi cables with a CuSi alloy matrix

    SciTech Connect

    Kasahara, H.; Akita, S.; Torii, S.; Sugimoto, M.; Matsumoto, K.; Tanaka, Y.; Tachikawa, K.

    1996-07-01

    For implementation of AC superconducting equipment, it is imperative to develop low loss cables having highly stable characteristics. Here, newly developed NbTi superconducting cables using a CuSi alloy matrix are of low loss and are very promising as cables for practical application. However, since the CuSi alloy is a new material as a matrix for NbTi superconducting cables, many unknown factors as regards to optimum conditions for the manufacture of long cables, as well as superconducting characteristics are involved. For this new superconducting cable, a long strand (km class) was manufactured as a step for practical application, and a primary twisted cable was fabricated. Using this cable, a coil of the 100kVA class was fabricated for trial, and its performance characteristic with transport current was evaluated. This coil had no training phenomenon and had high stabilities. Furthermore, it permitted full AC current transmission of up to DCIc. Upon analysis of the coil loss, the hysteresis loss was smaller than coupling loss, and there was little increase of loss due to the current flow to the coil. consequently, by using CuSi alloy matrix superconducting cables, it was possible to provide an AC coil of low loss and high stability, and the present cable was found to be promising as a new AC superconducting cable in the future.

  19. 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.

  20. High sensitivity zero-biased magnetic field sensor based on multiphase laminate heterostructures with FeCuNbSiB nanocrystalline soft magnetic alloy

    NASA Astrophysics Data System (ADS)

    Qiu, Jing; Wen, Yumei; Li, Ping; Chen, Hengjia

    2016-05-01

    In this paper, a high sensitivity zero-biased magnetic field sensor based on multiphase laminate heterostructures consisting of FeCuNbSiB/Terfenol-D (Tb1-xDyxFe2)/PZT (Pb(Zr1-x,Tix)O3)/Terfenol-D/PZT/Ternol-D/FeCuNbSiB (FMPMPMF) is presented, whose ME coupling characteristics and sensing performances have been investigated. Compared to traditional Terfenol-D/PZT/Terfenol-D (MPM) and Terfenol-D/PZT/Terfenol-D/PZT/Terfenol-D (MPMPM) sensors, the zero-biased ME coupling characteristics of FMPMPMF sensor were significantly improved, owing to a build-in magnetic field in FeCuNbSiB/Terfenol-D layers. The optimum zero-biased resonant ME voltage coefficient of 3.02 V/Oe is achieved, which is 1.65 times as great as that of MPMPM and 2.51 times of MPM sensors. The mean value of low-frequency ME field coefficient of FMPMPMF reaches 122.53 mV/cm Oe, which is 2.39 times as great as that of MPMPM and 1.79 times of MPM sensors. Meanwhile, the induced zero-biased ME voltage of FMPMPMF sensor shows an excellent linear relationship to ac magnetic field both at the low frequency (1 kHz) and the resonant frequency (106.6 kHz). Remarkably, it indicates that the proposed zero-biased magnetic field sensor give the prospect of being able to applied to the field of highly sensitive ac magnetic field sensing.

  1. 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)

  2. DC bias immune nanocrystalline magnetic cores made of Fe73Nb3Cu1B7Si16 ribbon with induced transverse magnetic anisotropy.

    PubMed

    Nosenko, Anton; Rudenko, Olexandr; Mika, Taras; Yevlash, Igor; Semyrga, Olexandr; Nosenko, Viktor

    2016-12-01

    The comparative analysis of magnetic properties of cut cores made of nanocrystalline Fe73Nb3Cu1B7Si16 alloy ribbon and cores made of the same ribbon with preliminary tension-induced transverse magnetic anisotropy was carried out. The possibility of improving magnetic properties of cut cores, decreasing loss, and increasing DC bias immunity of reversible magnetic permeability is presented. The influence of induced magnetic anisotropy on DC bias immunity of reversible magnetic permeability was investigated. The advantages and disadvantages of new cores (made of ribbon heated under tensile stress) over cut ones were determined. PMID:26847696

  3. DC bias immune nanocrystalline magnetic cores made of Fe73Nb3Cu1B7Si16 ribbon with induced transverse magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Nosenko, Anton; Rudenko, Olexandr; Mika, Taras; Yevlash, Igor; Semyrga, Olexandr; Nosenko, Viktor

    2016-02-01

    The comparative analysis of magnetic properties of cut cores made of nanocrystalline Fe73Nb3Cu1B7Si16 alloy ribbon and cores made of the same ribbon with preliminary tension-induced transverse magnetic anisotropy was carried out. The possibility of improving magnetic properties of cut cores, decreasing loss, and increasing DC bias immunity of reversible magnetic permeability is presented. The influence of induced magnetic anisotropy on DC bias immunity of reversible magnetic permeability was investigated. The advantages and disadvantages of new cores (made of ribbon heated under tensile stress) over cut ones were determined.

  4. Influence of uranium content on magnetostriction of Fe73.5Cu1Nb3-xUxSi13.5B9 alloys

    NASA Astrophysics Data System (ADS)

    Pavlík, G.; Sovák, P.

    2006-09-01

    The aim of this work was to study the influence of annealing treatment on structure, magnetic properties and magnetostriction of the Fe73.5Cu1Nb3-xUxSi13.5B9 nanocrystalline alloys. The results confirmed the nanocrystalline character of these alloys in the temperature range 550- 650C. The influence of the uranium content on the structural stability has been observed for annealing treatment at higher temperature, i.e. at about 700C. The coercivity and the magnetostriction strongly depended both on the annealing temperature and on the uranium content.

  5. Effect of Nb doping on superconducting and magnetic properties of RuSr 2(Gd 1.5- yEu yCe 0.5)Cu 2O z

    NASA Astrophysics Data System (ADS)

    Lee, H. K.; Williams, G. V. M.

    2004-11-01

    We performed resistivity and magnetization measurements on the ruthenocuprates (Ru 1- xNb x)Sr 2(Gd 1.4Ce 0.6)Cu 2O z ( x = 0-0.5) and (Ru 0.5Nb 0.5)Sr 2(Gd 1.5- yEu yCe 0.5)Cu 2O z ( y = 0-1.5). It is found that the Nb substitution for Ru depresses superconductivity only slightly from Tc = 27 K for x = 0 to Tc = 24 K for x = 0.5, but significantly reduces the ferromagnetic component. In contrast to the Nb-free sample, a partial evolution of the Meissner state followed by a reentrance of the magnetization is observed in the field-cooled magnetization measurements of the Nb-doped samples. The magnetization measurements on the (Ru 0.5Nb 0.5)Sr 2(Gd 1.5- yEu yCe 0.5)Cu 2O z system indicate that the reentrant behavior of the magnetization below Tc is caused by the paramagnetic contribution of the Gd 3+ ions and the Meissner effect can be seen more clearly after suppressing the paramagnetic response of the sublattice of Gd 3+ ions.

  6. Devitrification of Mechanically Alloyed Zr-Ti-Nb-Cu-Ni-Al Glassy Powders Studied by Time-Resolved X-ray Diffraction

    SciTech Connect

    Scudino, S.; Sordelet, D.J.; Eckert, J.

    2009-04-13

    The crystallization of mechanically alloyed Zr{sub 67}Ti{sub 6.14}Nb{sub 1.92}Cu{sub 10.67}Ni{sub 8.52}Al{sub 5.75} glassy powder is investigated by time-resolved X-ray diffraction. The powder displays a multi-step crystallization behavior characterized by the formation of a metastable nanoscale quasicrystalline phase during the first stage of the crystallization process. At higher temperatures, coinciding with the second crystallization event, the amorphous-to-quasicrystalline transformation is followed by the precipitation of the tetragonal Zr{sub 2}Cu phase (space group I4/mmm) and the tetragonal Zr{sub 2}Ni phase (space group I4/mcm). The transformations are gradual and the quasicrystals and the subsequent phases coexist over a temperature interval of about 25K.

  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. 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

  9. 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.

  10. 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

  11. 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

  12. O 2-annealing effects on dielectric properties of Sr 2AlTaO 6/YBa 2Cu 3O y films

    NASA Astrophysics Data System (ADS)

    Takahashi, Yoshihiro; Zama, Hideaki; Morishita, Tadataka; Tanabe, Keiichi

    2001-08-01

    Approximately 160-nm-thick Sr 2AlTaO 6 (SAT) thin films were prepared by metalorganic chemical vapor deposition on liquid phase epitaxy-grown 60-μm-thick YBa 2Cu 3O 7- δ (YBCO) films. The effects of oxygen postannealing on the dielectric properties of SAT and the superconducting properties of YBCO were investigated. The c-axis length of YBCO decreased from 11.82 to 11.70 Å and its Tc of 90 K was observed after oxidation for 250 h at 500°C in 1 atm O 2 atmosphere, indicating that YBCO is almost fully oxygenated through SAT. Postannealed samples showed reasonably low dielectric constants for SAT of approximately 24 and low conductance of 10 -8 S at 10 5 Hz which corresponds to a loss tangent of 5×10 -4. On the other hand, the SAT films without postannealing exhibited an order of magnitude larger conductance. The improved dielectric properties of the annealed samples are probably attributed to compensation of oxygen defects at the SAT grain boundaries as well as oxidation of the lower YBCO film.

  13. Enhancement of the thermoelectric figure of merit in n-type Cu0.008Bi2Te2.7Se0.3 by using Nb doping

    NASA Astrophysics Data System (ADS)

    Lee, Kyu Hyoung; Ryu, Byungki; Park, Hee Jung; Lee, Kimoon; Roh, Jong Wook; Kim, Sang Il; Hwang, Sungwoo; Choi, Soon-Mok; Kim, Jong-Young; Lee, Jeong Hoon; Lim, Jae-Hong; Kim, Sung Wng

    2016-01-01

    Doping with foreign atom has been shown to be an effective way to enhance the dimensionless figure of merit ZT of Bi2Te3-based thermoelectric raw materials. Herein, we report that doping with Nb is effective in enhancing the Seebeck coefficient of n-type Cu0.008Bi2Te2.7Se0.3 polycrystalline bulks. Considering compensation of the Seebeck coefficient due to decrease of the electrical conductivity in Nb-doped compositions, the absolute value of Seebeck coefficient rather increased benefiting from an enhancement of the density of states (DOS) effective mass m* from 1.09 m 0 (Cu0.008Bi2Te2.7Se0.3) to 1.21 m 0 - 1.27 m 0 (Cu0.008Bi2- x Nb x Te2.7Se0.3) due to a DOS engineering effect. The values of ZT were 0.84 at 300 K and 0.86 at 320 K for Cu0.008Bi1.99Nb0.01Te2.7Se0.3. This compositional tuning approach highlights the possibility of further enhancement of ZT for n-type Bi2Te3-based compounds by using a combination of nanostructuring technologies to reduce the thermal conductivity.

  14. Investigation of Trimetallic Ligand-Pillared Oxyfluorides: Ag2Cu(pzc)2MOxF6-x (M = Mo, Nb, and W)

    SciTech Connect

    Lin, Haisheng; Maggard, Paul A.

    2011-06-12

    Three new ligand-pillared hybrid solids, Ag₂Cu(pzc)₂MOx F6-x (I, M = Mo, x = 2; II, M = W, x = 2; III, M = Nb, x = 1) (pzc = pyrazine-2-carboxylate) were synthesized via hydrothermal reactions at 150 °C, and their structures were determined by single-crystal X-ray diffraction (P2₁/n (No. 14), Z = 2; a = 7.2302(1), 7.2124(2), 7.2715(2) Å; b = 7.9460(1), 7.9270(2), 7.98436(3) Å; c = 13.9173(2), 13.8959(4), 13.8226(5) Å, for I, II, and III, respectively). All three are isostructural and contain unusual trimetallic (Ag₂CuMOx F6-x )2+ layers that consist of [Ag₂O₂F₂]n and [CuMOx F6-x ]n chains that alternate within the layers. Each structure also contains [MOx F6-x ]2- octahedra with fully disordered O/F positions and with an inversion center on the M{sup n+} sites, i.e., Mo6+, W6+ and Nb5+. Magnetic susceptibility measurements can be fitted to the Curie–Weiss law with a Curie constant consistent with a single non-interacting Cu(II) (S = ½) site per formula unit. Thermogravimetric analyses indicate that these hybrid compounds are stable up to ~280 °C, with each exhibiting a single weight-loss step beginning at ~300 °C that corresponds to the loss of all pyrazine-2-carboxylate ligands and additional O/F atoms via oxidation of the ligand during its removal. UV–Vis diffuse reflectance measurements show that each exhibits an optical bandgap size of ~2.8 eV, and which electronic-structure calculations show arise from excitations between the Cu(II)-based valence orbitals and the M 5+/6+-based conduction band orbitals.

  15. Glass Formation, Chemical Properties and Surface Analysis of Cu-Based Bulk Metallic Glasses

    PubMed Central

    Qin, Chunling; Zhao, Weimin; Inoue, Akihisa

    2011-01-01

    This paper reviews the influence of alloying elements Mo, Nb, Ta and Ni on glass formation and corrosion resistance of Cu-based bulk metallic glasses (BMGs). In order to obtain basic knowledge for application to the industry, corrosion resistance of the Cu–Hf–Ti–(Mo, Nb, Ta, Ni) and Cu–Zr–Ag–Al–(Nb) bulk glassy alloy systems in various solutions are reported in this work. Moreover, X-ray photoelectron spectroscopy (XPS) analysis is performed to clarify the surface-related chemical characteristics of the alloy before and after immersion in the solutions; this has lead to a better understanding of the correlation between the surface composition and the corrosion resistance. PMID:21731441

  16. Frequency dependence of the magnetoimpedance in nanocrystalline FeCuNbSiB with high transverse stress-induced magnetic anisotropy

    SciTech Connect

    Vazquez, M.; Kurlyandskaya, G.V.; Garcia-Beneytez, J.M.; Sinnecker, J.P.; Barandiaran, J.M.; Lukshina, V.A.; Potapov, A.P.

    1999-09-01

    Stress-annealed nanocrystalline FeCuNbSiB ribbons show correlation between induced magnetic anisotropy and magnetoimpedance. Two types of crystallization process were used in order to induce a transverse magnetic anisotropy: the first one was performed submitting the original amorphous samples to an applied tensile stress of {sigma} = 150 MPa. In the second one, samples are nanocrystallized in a first stage and submitted to stress annealing at {sigma} = 290 MPa afterwards. The maximum of the magnetoimpedance can be obtained for dc fields larger than the anisotropy field of the sample of close to the irreversibility field. This behavior can be explained based in the simultaneous switching of two different magnetization processes taking place in the samples with high transverse magnetic anisotropy.

  17. 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

  18. Micro-structural, thermal, optical and physical properties nanocrystalline NbSr2Pr1.5Ce0.5Cu2O10-δ material synthesized by mechano-thermal method

    NASA Astrophysics Data System (ADS)

    Parthiban, P.; Balamurugan, S.; Satya, A. T.; Janaki, J.

    2015-06-01

    We have prepared nanocrystalline NbSr2Pr1.5Ce0.5Cu2O10-δ (Nb1222Pr) material by annealing the ball milled powder at 1000°C for 24h and studied by various characterization techniques such as TG-DTA, XRD, FT-IR, NIR, SEM-EDX, magnetization and electrical resistivity. Significant difference is seen in the TG-DTA curves of the as-milled powder due to ball milling. The annealed Nb1222Pr material is crystallized in tetragonal symmetry with lattice parameters, a = 0.3887(3) nm and c = 2.878(2) nm with reduced average particle size of ˜42.67 nm. Agglomeration of fine spherical particle sizes in the range of ˜180 - 280 nm is seen through SEM micro-image. The variation in the crystalline sizes of the Nb1222Pr phase obtained from XRD and SEM image indicate the polycrystalline characteristic of fine nanocrystalline particles. Neither superconductivity nor magnetic ordering is seen for the Nb1222Pr phase down to 5 K under 100 Oe. The four probe resistivity measurement reveals the semiconducting behavior of the Nb1222Pr phase.

  19. Study of the effects of MeV Ag, Cu, Au, and Sn implantation on the optical properties of LiNbO3

    NASA Technical Reports Server (NTRS)

    Williams, E. K.; Ila, D.; Sarkisov, S.; Curley, M.; Poker, D. B.; Hensley, D. K.; Borel, C.

    1998-01-01

    The authors present the results of characterization of linear absorption and nonlinear refractive index of Au, Ag, Cu and Sn ion implantation into LiNbO3. Ag was implanted at 1.5 MeV to fluences of 2 to 17 x 17(exp 16)/sq cm at room temperature. Au and Cu were implanted to fluences of 5 to 20 x 10(exp 16)/sq cm at an energy of 2.0 MeV. Sn was implanted to a fluence of 1.6 x 10(exp 17)/sq cm at 160 kV. Optical absorption spectrometry indicated an absorption peak for the Au implanted samples after heat treatment at 1,000 C at approx. 620 nm. The Ag implanted samples absorption peaks shifted from approx. 450 nm before heat treatment to 550 nm after 500 C for 1h. Heat treatment at 800 C returned the Ag implanted crystals to a clear state. Cu nanocluster absorption peaks disappears at 500 C. No Sn clusters were observed by optical absorption or XRD. The size of the Ag and Au clusters as a function of heat treatment were determined from the absorption peaks. The Ag clusters did not change appreciably in size with heat treatment. The Au clusters increased from 3 to 9 nm diameter upon heat treatment at 1000 C. TEM analysis performed on a Au implanted crystal indicated the formation of Au nanocrystals with facets normal to the c-axis. Measurements of the nonlinear refractive indices were carried out using the Z-scan method with a tunable dye laser pumped by a frequency doubled mode-locked Nd:YAG laser. The dye laser had a 4.5 ps pulse duration time and 76 MHz pulse repetition rate (575 nm).

  20. Temperature dependent properties and poling effect of K4CuNb8O23 modified (Na0.5K0.5)NbO3 lead free piezoceramics

    NASA Astrophysics Data System (ADS)

    Chen, Qiang; Chen, Yu; Peng, Zhihang; Wu, Jiagang; Liu, Hong; Xiao, Dingquan; Yu, Ping; Zhu, Jiliang; Zhu, Jianguo

    2015-03-01

    Lead free piezoelectric ceramics (Na0.5K0.5)NbO3 modified by 4% mol. K4CuNb8O23 (abbreviated NKN:4KCN hereinafter) contain moderate piezoelectric constant d33 ˜ 100 pC N-1 and large mechanical quality factor Qm > 1000, showing possible replacement of the lead-based ones (Chen et al., J Appl. Phys. 102, 104109 (2007)). In terms of practical use, however, the temperature stability of NKN:4KCN is not clear to date. We made a systematic investigation on the properties versus temperature of NKN:4KCN to evaluate whether it can be practically used. In the range from room temperature (RT ˜ 25 °C) to 100 °C, the ferroelectricity of poled NKN:4KCN material is nearly temperature independent, remanent polarization Pr is about 27.6 ±1 μC cm-2. When the as-studied NKN:4KCN ceramics were thermal depolarized in temperature range from RT to 450 °C, piezoelectric constant d33 changed little, retaining about 99 pC N-1, 77 ± 3 pC N-1, from RT to 150 °C, 200 °C to 350 °C, respectively. The poled NKN:4KCN material showed higher orthorhombic to tetragonal phase transition temperature (TO-T ˜ 200 °C) compared to unpoled sample (TO-T ˜ 194 °C). Moreover, this kind of lead free material displayed negative temperature coefficient of frequency (TCF) and positive TCF in orthorhombic and tetragonal phase state, respectively. The TCF was about -360 ppm K-1 in the range from RT to 125 °C, close to some lead-based commercial ones. The significance of this work lies in evaluating whether such a material can be practically used or not. We believe such a material might be the most promising candidate for replacing lead-based ones in some areas in the future.

  1. Structure and dielectric properties of Ba{sub 5}NdCu{sub 1.5}Nb{sub 8.5}O{sub 30−δ} tungsten bronze ceramics

    SciTech Connect

    Tan, Yan-Qing; Yu, Yuan; Hao, Yong-Mei; Dong, Su-Ying; Yang, Yi-Wen

    2013-05-15

    Highlights: ► Tetragonal tungsten bronze ceramic Ba{sub 5}NdCu{sub 1.5}Nb{sub 8.5}O{sub 30−δ} was prepared. ► Titanium was replaced by copper in M{sub 5}RTi{sub 3}Nb{sub 7}O{sub 30} for the first time. ► Detailed structural information was retrieved by Rietveld refinement. ► An obvious relaxor-like dielectric behavior was observed in this ceramic, ion disorders in A1 and B sites contribute to this behavior. - Abstract: A new type of tungsten bronze ceramic Ba{sub 5}NdCu{sub 1.5}Nb{sub 8.5}O{sub 30−δ} has been prepared by a conventional solid-state reaction technique. Its structural, dielectric properties were investigated. Rietveld analysis shows that Ba{sub 5}NdCu{sub 1.5}Nb{sub 8.5}O{sub 30−δ} has a single-phase tetragonal (space group P4bm and lattice constants a = b = 12.4961(4) Å, c = 3.9426(8) Å, V = 615.66(4) Å{sup 3}) tungsten bronze structure. The occupations of sites A and B are quite interesting. A1 sites are fully disordered occupied by Ba ions and Nd ions and A2 sites for Ba ions only, while B-sites are equal for both Cu and Nb ions to occupy. This material exhibits an obvious relaxation behavior in the 213–573 K temperature range. The dielectric constants have been fitted by the modified Curie–Weiss law and all the estimated γ values are close to 2, confirming the typical relaxor ferroelectric behavior. The disorders of Ba{sup 2+} or Nd{sup 3+} in A1 sites and Nb{sup 5+}, Cu{sup 2+} in B sites induced by the oxygen vacancies may contribute to this dielectric behavior.

  2. Magnetic microstructure in a stress-annealed Fe73.5Si15.5B7Nb3Cu1 soft magnetic alloy observed using off-axis electron holography and Lorentz microscopy

    NASA Astrophysics Data System (ADS)

    Kovács, A.; Pradeep, K. G.; Herzer, G.; Raabe, D.; Dunin-Borkowski, R. E.

    2016-05-01

    Fe-Si-B-Nb-Cu alloys are attractive for high frequency applications due to their low coercivity and high saturation magnetization. Here, we study the effect of stress annealing on magnetic microstructure in Fe73.5Si15.5B7Nb3Cu1 using off-axis electron holography and the Fresnel mode of Lorentz transmission electron microscopy. A stress of 50 MPa was applied to selected samples during rapid annealing for 4 s, resulting in uniaxial anisotropy perpendicular to the stress direction. The examination of focused ion beam milled lamellae prepared from each sample revealed a random magnetic domain pattern in the sample that had been rapidly annealed in the absence of stress, whereas a highly regular domain pattern was observed in the stress-annealed sample. We also measured a decrease in domain wall width from ˜ 94 nm in the sample annealed without stress to ˜ 80 nm in the stress-annealed sample.

  3. 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…

  4. Partitioning behavior of Al in a nanocrystalline Fe{sub 71.5}Si{sub 13.5}B{sub 9}Nb{sub 3}Cu{sub 1}Al{sub 2} alloy

    SciTech Connect

    Warren, P.J.; Todd, I.; Davies, H.A.; Cerezo, A.; Gibbs, M.R.J.; Kendall, D.; Major, R.V.

    1999-11-05

    The nanocrystalline Fe-Si-B-Nb-Cu alloy, known as FINEMET, is now a well established commercial soft magnetic material exhibiting excellent permeability while maintaining a high saturation magnetization. It is produced by melt-spinning to form a ribbon with an amorphous structure. The purpose of this investigation was to use 3-dimensional atom probe microanalysis to experimentally quantify the local phase chemistries of this nanocomposite microstructure, with particular reference to the partitioning behavior of the Al.

  5. Microalloying effect of Cu and Nb on the microstructure and magnetic properties of Fe{sub 3}B/Nd{sub 2}Fe{sub 14}B nanocomposite permanent magnets

    SciTech Connect

    Ping, D.H.; Hono, K.; Kanekiyo, H.; Hirosawa, S.

    1999-09-01

    This paper reports the microalloying effect of Cu and Nb on the microstructure and magnetic properties of a Fe{sub 3}B/Nd{sub 2}Fe{sub 14}B nanocomposite permanent magnet. Optimum magnetic properties with B{sub r} = 1.25 T, H{sub cJ} = 273 kA/m and (BH){sub max} = 125 kJ/m{sup 3} were obtained by annealing a melt-spun Nd{sub 4.5}Fe{sub 75.8}B{sub 18.5}Cu{sub 0.2}Nb{sub 1} amorphous ribbon at 660 C for 6 min. Compared with a ternary Nd{sub 4.5}Fe{sub 77}B{sub 18.5} alloy, the grain size is much finer in the optimum microstructure of the Cu and Nb containing alloys, and the temperature range of the heat-treatment for obtaining optimum hard magnetic properties was significantly extended. The soft magnetic Fe{sub 23}B{sub 6} phase coexists with Fe{sub 3}B and Nd{sub 2}Fe{sub 14}B phases in the optimum microstructure. Three-dimensional atom probe (3DAP) analysis results have revealed that the finer microstructure is due to the formation of a high number density of Cu clusters, which promote the nucleation of the Fe{sub 3}B phase. The Nb atoms appear to induce the formation of the Fe{sub 23}B{sub 6} phase and stabilize it by partitioning into this phase.

  6. High frequency properties of Fe73.5Cu1Nb3Si13.5B9/Zn0.5Ni0.5Fe2O4 soft magnetic composite with micro-cellular structure

    NASA Astrophysics Data System (ADS)

    Liu, Tong; Wang, MingGang; Zhao, ZhanKui

    2012-12-01

    Soft magnetic composite with micro-cellular structure was prepared by spark plasma sintering (SPS) process with Fe73.5Cu1Nb3Si13.5B9 micron-powders clad by 5wt% Zn0.5Ni0.5Fe2O4 nano-particles. The effect of SPS on the micro structure of the Finemet powder and the micro structure of the composite were studied. It has been found that the as-prepared composite consists of Fe73.5Cu1Nb3Si13.5B9 cells and the cell-wall composed of nano Zn0.5Ni0.5Fe2O4 particles distributing around Fe73.5Cu1Nb3Si13.5B9 cell-body. The composite exhibits low eddy-current loss which is to be resulted by high resistivity of the Zn0.5Ni0.5Fe2O4 cell-wall. The sintered samples were annealed at different temperature and the magnetic properties at different frequency of the annealed samples were measured. It shows that the Zn0.5Ni0.5Fe2O4 cell-wall possesses good thermostability.

  7. Calorimetric Investigation of Thermal Stability of 304H Cu (Fe-17.7Cr-9.3Ni-2.95Cu-0.91Mn-0.58Nb-0.24Si-0.1C-0.12N-Wt Pct) Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Tripathy, Haraprasanna; Subramanian, Raju; Hajra, Raj Narayan; Rai, Arun Kumar; Rengachari, Mythili; Saibaba, Saroja; Jayakumar, Tammana

    2016-05-01

    The sequence of phase instabilities that take place in a Fe-17.7Cr-9.3Ni-0.58Nb-2.95Cu-0.12N (wt pct) austenitic stainless steel (304H Cu grade) as a function of temperature has been investigated using dynamic calorimetry. The results obtained from this investigation are supplemented by Thermocalc-based equilibrium and Scheil-Gulliver nonequilibrium solidification simulation. The following phase transformation sequence is found upon slow cooling from liquid: L → L + γ → L + γ + MX → γ + MX + δ → γ +MX + M23C6 → γ + MX + M23C6 + Cu. Under slow cooling, the solidification follows austenite + ferrite (AF) mode, which is in accordance with Thermocalc prediction and Scheil-Gulliver simulation. However, higher cooling rates result in skeletal δ-ferrite formation, due to increased segregation tendency of Nb and Cr to segregate to interdendritic liquid. The solidification mode is found to depend on combined Nb + Cu content. Experimental estimates of enthalpy change associated with melting and secondary phase precipitation are also obtained. In addition a semi-quantitative study on the dissolution kinetics of M23C6 type carbides has also been investigated. The standard solution treatment at 1413 K (1140 °C) is found to be adequate to dissolve both Cu and M23C6 into γ-austenite; but the complete dissolution of MX type carbonitrides occurs near the melting region.

  8. Integration of amorphous tantalum silicon nitride (TaSiN) films as diffusion barriers in a Cu/SiLK(TM) metallization scheme

    NASA Astrophysics Data System (ADS)

    Padiyar, Sumant Devdas

    2003-09-01

    Current and future performance requirements for high- speed integrated circuit (IC) devices have placed great emphasis on the introduction of novel materials, deposition techniques and improved metrology techniques. The introduction of copper interconnects and more currently low-k dielectric materials in IC fabrication are two such examples. This introduction necessitates research on the compatibility of these materials and process techniques with adjacent diffusion barrier materials. One candidate, which has attracted significant attention is tantalum-silicon-nitride (TaSiN) on account of its superior diffusion barrier performance and high recrystallization temperature1. The subject of this dissertation is an investigation of the integration compatibility and performance of TaSiN barrier layers with a low-k dielectric polymer (SiLK ®2). A plasma- enhanced chemical vapor deposition (PECVD) approach is taken for growth of TaSiN films in this work due to potential advantages in conformal film coverage compared to more conventional physical vapor deposition methods. A Design of Experiment (DOE) methodology was introduced for PECVD of TaSiN on SiLK to optimize film properties such as film composition, resistivity, growth rate and film roughness with respect to the predictors viz. substrate temperature, precursor gas flow and plasma power. The first pass study determined the response window for optimized TaSiN film composition, growth rate and low halide contamination and the compatibility of the process with an organic polymer substrate, i.e. SiLK. Second-pass studies were carried out to deposit ultra- thin (10nm) films on: (a)blanket SiLK to investigate the performance of TaSiN films against copper diffusion, and (b)patterned SiLK to evaluate step coverage and conformality. All TaSiN depositions were carried out on SiO2 substrates for baseline comparisons. A second purpose of the diffusion barrier in IC processing is to improve interfacial adhesion between the

  9. 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.

  10. 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

  11. 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.

  12. Soft magnetic properties of nanocrystalline Fe73B7Si16Nb3Cu1 alloy after rapid heating under tensile stress.

    PubMed

    Nosenko, Anton; Mika, Taras; Rudenko, Olexandr; Yarmoshchuk, Yevhenii; Nosenko, Viktor

    2015-01-01

    Amorphous Fe73B7Si16Nb3Cu1 ribbon was crystallized rapidly by electric current heating under simultaneously applied tensile stress along the ribbon axis. As a result, strong transverse magnetic anisotropy was induced in the ribbon. Dynamic magnetic properties of the ribbons rapidly heated either under the tensile stress or without tensile stress were measured using toroidal cores. Optimal electric current heating regime that provides maximum improvement of the initial magnetic permeability and core loss was determined. Tensile stress increase from 0 to 180 MPa was shown to result in the decrease of the initial magnetic permeability down to 400 and core loss at frequencies from 0.4 to 200 kHz. Comparative analysis of magnetic properties of the cut core (with non-magnetic gap) and the cores heated under tensile stress was carried out. The magnetic properties of the latter cores are advantageous for manufacturing the reactors and linear chokes of switch-mode power supplies. PMID:25852427

  13. Soft magnetic properties of nanocrystalline Fe73B7Si16Nb3Cu1 alloy after rapid heating under tensile stress

    NASA Astrophysics Data System (ADS)

    Nosenko, Anton; Mika, Taras; Rudenko, Olexandr; Yarmoshchuk, Yevhenii; Nosenko, Viktor

    2015-03-01

    Amorphous Fe73B7Si16Nb3Cu1 ribbon was crystallized rapidly by electric current heating under simultaneously applied tensile stress along the ribbon axis. As a result, strong transverse magnetic anisotropy was induced in the ribbon. Dynamic magnetic properties of the ribbons rapidly heated either under the tensile stress or without tensile stress were measured using toroidal cores. Optimal electric current heating regime that provides maximum improvement of the initial magnetic permeability and core loss was determined. Tensile stress increase from 0 to 180 MPa was shown to result in the decrease of the initial magnetic permeability down to 400 and core loss at frequencies from 0.4 to 200 kHz. Comparative analysis of magnetic properties of the cut core (with non-magnetic gap) and the cores heated under tensile stress was carried out. The magnetic properties of the latter cores are advantageous for manufacturing the reactors and linear chokes of switch-mode power supplies.

  14. In situ surface magneto-optical Kerr effect (s-MOKE) study of ultrathin soft magnetic FeCuNbSiB alloy films

    NASA Astrophysics Data System (ADS)

    Kumar, D.; Gupta, P.; Gupta, A.

    2014-12-01

    Herein we report on an in situ surface magneto-optical Kerr effect (s-MOKE) study of ion-beam-sputtered ultra-thin films of an amorphous Fe73.9Cu0.9Nb3.1Si13.2B8.9 (FINEMET) alloy with film growth that ranges from a fraction of a nm to a few tens of nms. Extrapolating the linear variation of the Kerr signal with film thickness suggests the absence of a magnetic dead layer at the substrate/FINEMET film interface, and hence the absence of any intermixing. The presence of a thin SiO2 film at the surface of the Si substrate may be responsible for preventing possible intermixing of Fe with Si to form nonmagnetic silicide. Close to the onset of ferromagnetic ordering, a steep increase in the coercive field with film thickness can be explained in terms of the Volmer-Weber growth of the film. Furthermore, the temperature dependence of the hysteresis loops of a 41 nm-thick FINEMET film has been studied. The Curie temperature of the amorphous film is found to be lower than that of a ribbon of the same composition. The origin of a uniaxial magnetic anisotropy in the as-prepared stage is attributed to the generation of some long-range stresses in the film, which are relieved close to the onset temperature for nanocrystallization.

  15. Effect of thermo-mechanical processing on the material properties at low temperature of a large size Al-Ni stabilized Nb-Ti/Cu superconducting cable

    NASA Astrophysics Data System (ADS)

    Langeslag, S. A. E.; Curé, B.; Sgobba, S.; Dudarev, A.; ten Kate, H. H. J.; Neuenschwander, J.; Jerjen, I.

    2014-01-01

    For future high-resolution particle experiments, a prototype for a 60 kA at 5 T, 4.2 K class conductor is realized by co-extrusion of a large, 40-strand Nb-Ti/Cu superconducting cable with a precipitation type Al-0.1wt.%Ni stabilizer. Microalloying with nickel contributes to the strength of the stabilizer, and avoids significant degradation in residual resistivity ratio, owing to its low solid solubility in aluminum. Sections of the conductor are work hardened to increase the mechanical properties of the as-extruded temper. Mechanical and resistivity characteristics are assessed as function of the amount of work hardening, at room temperature as well as at 4.2 K. Thermal treatments, like resin curing after coil winding, can cause partial annealing of the cold-worked material and reverse the strengthening effect. However, targeted thermal treatments, applied at relatively low temperature can result in precipitation hardening. The depletion of nickel in the aluminum-rich matrix around the precipitates results in an increased strength and a decreased effect of nickel on the thermal and electrical resistivity of the material. The present work aims at identifying an optimal work hardening sequence, and an optimal thermal treatment, possibly coinciding with a suitable coil resin curing cycle, for the Al-Ni stabilized superconductor.

  16. Novel tri-modal defect structure in Nb-doped MOCVD YBa2Cu3O7: A paradigm for pinning landscape control

    SciTech Connect

    Aytug, Tolga; Maroni, Victor A.; Chen, Z; Miller, Dean; Kropft, Jeremy; Zaluzec, Nestor J; Zuev, Yuri L; Specht, Eliot D; Paranthaman, Mariappan Parans

    2012-01-01

    Immobilization of vortices, or flux pinning, is both an enduring scientific issue and one of the most important problems in optimizing high temperature superconductors (HTS) for commercial use. Here, we demonstrate a practical approach to the creation of a multi-modal flux pinning landscape in YBa2Cu3O7 (YBCO) films employing an industrially scalable metal organic chemical vapor deposition technique. Through controlled additions of Nb, we have achieved a novel distribution of crystallographic defects that immobilize (pin) vortices in the YBCO matrix. That is, with only the addition of a single dopant element, a tri-modal defect structure that threads through the YBCO matrix laterally (parallel to the ab planes of YBCO), vertically (parallel to the YBCO c-axis), and isotropically in the form of random spherical defects is induced. For optimally doped samples, the influence of these multi-modal nanocrystalline defect structures on the flux pinning properties manifests itself as a superior improvement in the critical current density (Jc) for all magnetic field orientations. The results demonstrate the possibility of achieving an ideal flux pinning landscape (from an orientation and strength viewpoint), which permits the design of HTS wires with fully-tuneable properties by processes suitable for large-scale manufacturing.

  17. Determination of structural, mechanical and corrosion properties of Nb2O5 and (NbyCu 1-y)Ox thin films deposited on Ti6Al4V alloy substrates for dental implant applications.

    PubMed

    Mazur, M; Kalisz, M; Wojcieszak, D; Grobelny, M; Mazur, P; Kaczmarek, D; Domaradzki, J

    2015-02-01

    In this paper comparative studies on the structural, mechanical and corrosion properties of Nb2O5/Ti and (NbyCu1-y)Ox/Ti alloy systems have been investigated. Pure layers of niobia and niobia with a copper addition were deposited on a Ti6Al4V titanium alloy surface using the magnetron sputtering method. The physicochemical properties of the prepared thin films were examined with the aid of XRD, XPS SEM and AFM measurements. The mechanical properties (i.e., nanohardness, Young's modulus and abrasion resistance) were performed using nanoindentation and a steel wool test. The corrosion properties of the coatings were determined by analysis of the voltammetric curves. The deposited coatings were crack free, exhibited good adherence to the substrate, no discontinuity of the thin film was observed and the surface morphology was homogeneous. The hardness of pure niobium pentoxide was ca. 8.64GPa. The obtained results showed that the addition of copper into pure niobia resulted in the preparation of a layer with a lower hardness of ca. 7.79 GPa (for niobia with 17 at.% Cu) and 7.75 GPa (for niobia with 25 at.% Cu). The corrosion properties of the tested thin films deposited on the surface of titanium alloy depended on the composition of the thin layer. The addition of copper (i.e. a noble metal) to Nb2O5 film increased the corrosion resistance followed by a significant decrease in the value of corrosion currents and, in case of the highest Cu content, the shift of corrosion potential towards the noble direction. The best corrosion properties were obtained from a sample of Ti6Al4V coated with (Nb0.75Cu0.25)Ox thin film. It seems that the tested materials could be used in the future as protection coatings for Ti alloys in biomedical applications such as implants. PMID:25492191

  18. 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.

  19. Synthesis and characterisation of the novel double perovskites La{sub 2}CrB{sub 2/3}Nb{sub 1/3}O{sub 6}, B = Mg, Ni, Cu

    SciTech Connect

    Svensson, G.; Grins, J.; Shafeie, S.; Masson, D.; Norberg, S.T.; Eriksson, S.; Hull, S.; Zakharov, K.V.; Volkova, O.S.; Vasil’ev, A.N.; Istomin, S.Ya.

    2012-09-15

    Highlights: ► La{sub 2}CrB{sub 2/3}Nb{sub 1/3}O{sub 6}, B = Mg, Ni, Cu perovskites adopt the GdFeO{sub 3} type structure. ► HREM and ED study indicating week ordering of B-cations for B = Mg. ► Antiferromagnetics with T{sub N} 90 (Mg), 125 (Ni) and 140 K (Ni). -- Abstract: The novel perovskites La{sub 2}CrB{sub 2/3}Nb{sub 1/3}O{sub 6}, B = Mg, Ni, and Cu have been synthesised at 1350 °C in air via the citrate route. Rietveld refinements using neutron powder diffraction (NPD) data showed that the compounds adopt the GdFeO{sub 3} type structure with space group Pbnm, and unit cell parameters a≈b≈√(2)×a{sub p} and c ≈ 2 × a{sub p}, where a{sub p} ≈ 3.8 Å. Selected area electron diffraction (SAED) of B = Ni and Cu samples confirmed space group Pbnm. However, distinct reflections forbidden in Pbnm symmetry, but allowed in the monoclinic sub-group P2{sub 1}/n and unit cell parameters a≈b≈√(2)×a{sub p} and c ≈ 2 × a{sub p}, β ≈ 90° were present in SAED patterns of B = Mg sample. This indicates an ordering of the B-cations within the crystal structure of La{sub 2}CrMg{sub 2/3}Nb{sub 1/3}O{sub 6}. High-resolution electron microscopy (HREM) study indicating uniform, without formation of clusters, ordering of B-cations in the crystallites of La{sub 2}CrMg{sub 2/3}Nb{sub 1/3}O{sub 6}. Magnetic susceptibility measurements show that the compounds are antiferromagnetic (with some glass or spin clustering effects due to additional ferromagnetic interactions between the B-cations) with T{sub N} for La{sub 2}CrB{sub 2/3}Nb{sub 1/3}O{sub 6}, B = Mg, Ni, Cu being 90, 125 and 140 K, respectively.

  20. Cu/Nb nano-composite wires processed by severe plastic deformation for applications in high pulsed magnets: effects of the multi-scale microstructure on the mechanical properties

    SciTech Connect

    Dubois, J. B.; Thilly, L.; Renault, P.O.; Lecouturier, F.; Olier, P.

    2012-06-15

    Copper-based high strength and high electrical conductivity nano-composite wires reinforced by Nb nano-tubes are prepared by severe plastic deformation, applied with an Accumulative Drawing and Bundling process (ADB), for the windings of high pulsed magnets. The ADB process leads to a multi-scale Cu matrix containing up to N = 85{sub 4} (52.2.10{sup 6}) continuous parallel Nb tubes with diameter down to few tens nano-meters. After heavy strain, the Nb nano-tubes exhibit a homogeneous microstructure with grain size below 100 nm. The Cu matrix presents a multi-scale microstructure with multi-modal grain size distribution from the micrometer to the nano-meter range. The use of complementary characterization techniques at the microscopic and macroscopic level (in-situ tensile tests in the TEM, nano-indentation, in-situ tensile tests under high energy synchrotron beam) shed light on the interest of the multi-scale nature of the microstructure to achieve extreme mechanical properties, therefore allowing for design guidelines to further improve these properties. (authors)

  1. Mössbauer spectroscopic studies of the moment distribution in Fe73.5Cu1Nb3Si13.5B9

    NASA Astrophysics Data System (ADS)

    Aghamohammadzadeh, H.; Williams, J. M.; Gibbs, M. R. J.; Parmar, B. S.; Davies, H. A.

    2000-05-01

    57Fe Mössbauer spectroscopy can be used to determine the distribution of moment directions in magnetic materials. Here, we have applied this technique to a study of Fe73.5Cu1Nb3Si13.5B9 (isocompositional with FINEMET). We are particularly interested in establishing the distribution of moment directions in the nanophase material, obtained by devitrification from an amorphous precursor. The nanophase material consists of Fe-Si grains embedded in an amorphous matrix. Current understanding of the resulting magnetic properties, which involves application of the random anisotropy model to these materials, assumes that the magnetization in the grains is exchange coupled to neighbors, giving a long exchange length compared with the nanometer grain size. We present data for the amorphous precursor, the standard nanophase material, and nanophase material devitrified in an external magnetic field. If σu and σv represent the Gaussian widths of the out-of-plane and in-plane moment direction distributions respectively, we have found that σu=14° and σv=68° for the amorphous precursor, σu=14° and σv=92° for the standard nanophase material, and σu=22° and σv=79° for a magnetic field aligned specimen. We interpret these data as demonstrating that standard devitrification does result in grains with a wide spread of moment direct ions over the volume sampled by this technique, even allowing for exchange coupling. These results and the implications for macroscopic magnetic properties such as anisotropy will be discussed.

  2. Superconducting properties of YaBa2Cu3O7-delta films deposited on commercial tape substrates, decorated with Pd or Ta nano-islands

    SciTech Connect

    Polat, Ozgur; Ertugrul, Memhet; Thompson, James R; Leonard, Keith J; Sinclair IV, John W; Paranthaman, Mariappan Parans; Wee, Sung Hun; Zuev, Yuri L; Xiong, X.; Selvamanickam, V.; Christen, David K; Aytug, Tolga

    2012-01-01

    To obtain an engineered surface for deposition of high-Tc superconductors, nanoscale modulations of the surface of the underlying LaMnO3 (LMO) cap layer is a potential source for generating microstructural defects in YBa2Cu3O7- (YBCO) films. These defects may improve the flux-pinning and consequently increase the critical current density, Jc. To provide such nanoscale modulation via a practical and scalable process, tantalum (Ta) and palladium (Pd) nano-islands were deposited using dc-magnetron sputtering on the surface of the cap layer of commercial metal tape templates for second-generation wires. The size and density of these nano-islands can be controlled by changing sputtering conditions such as the power and deposition time. Compared to the reference sample grown on an untreated LMO cap layer, the YBCO films grown on the LMO cap layers with Ta or Pd nano-islands exhibited improved in-field Jc performance. Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) were used to assess the evolving size and density of the nano-islands.

  3. 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.

  4. 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

  5. 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.

  6. LA-ICP-MS mineral chemistry of titanite and the geological implications for exploration of porphyry Cu deposits in the Jinshajiang - Red River alkaline igneous belt, SW China

    NASA Astrophysics Data System (ADS)

    Xu, Leiluo; Bi, Xianwu; Hu, Ruizhong; Tang, Yongyong; Wang, Xinsong; Xu, Yue

    2015-04-01

    The Jinshajiang-Red River alkaline igneous belt in the eastern Indian-Asian collision zone, of southwestern China, hosts abundant, economically important Cu-Mo-Au mineralization of Cenozoic age. Major- and trace-element compositions of titanites from representative Cu-mineralized intrusions determined by LA-ICP-MS show higher values for Fe2O3/Al2O3, ΣREE + Y, LREE/HREE, Ce/Ce*, (Ce/Ce*)/(Eu/Eu*), U, Th, Ta, Nb and Ga, and lower values for Al2O3, CaO, Eu/Eu*, Zr/Hf, Nb/Ta and Sr than those for titanites from barren intrusions. Different ΣREE + Y, LREE/HREE, U, Th, Ta and Nb values of titanites between Cu-mineralized and barren intrusions were controlled mainly by the coexisting melt compositions. However, different Sr concentrations and negative Eu anomalies of titanites between Cu-mineralized and barren intrusions were most probably caused by different degrees of crystallization of feldspar from melts. In addition, different Ga concentrations and positive Ce anomalies of titanites between Cu-mineralized and barren intrusions were most likely caused by different magmatic fO2 conditions. Pronounced compositional differences of titanites between Cu-mineralized and barren intrusions can provide a useful tool to help discriminate between ore-bearing and barren intrusions at an early stage of exploration, and, thus, have a potential application in exploration for porphyry Cu deposits in the Jinshajiang - Red River alkaline igneous belt, and to other areas.

  7. Anomalous laser deflection phenomenon based on the interaction of electro-optic and graded refractivity effects in Cu-doped KTa{sub 1−x}Nb{sub x}O{sub 3} crystal

    SciTech Connect

    Wang, Xuping Liu, Bing; Yang, Yuguo; Zhang, Yuanyuan; Lv, Xianshun; Hong, Guanglie; Shu, Rong; Yu, Haohai; Wang, Jiyang

    2014-08-04

    An abnormal laser deflection phenomenon in a copper-doped KTa{sub 1−x}Nb{sub x}O{sub 3} (Cu:KTN) crystal is demonstrated in this Letter. A near-50 mrad beam deflection angle was observed when a voltage of 1.2 kV was applied to a Cu:KTN block with size of 2.8 mm × 1.2 mm × 7.5 mm at room temperature. The special features of this deflection phenomenon are that the laser beam deflection direction is perpendicular to the electric field direction, and the beam deflection angle remains unchanged when the electric field direction is reversed. The operating principle of the phenomenon is investigated and the origin of the deflection phenomenon is attributed to an interaction between the graded refractivity effect and the quadratic electro-optic effect of the crystal.

  8. 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.

  9. Microstructure, dielectric and piezoelectric properties of (K0.5Na0.5)NbO3-Ba(Ti0.95Zr0.05)O3 lead-free ceramics with CuO sintering aid

    NASA Astrophysics Data System (ADS)

    Lin, D.; Kwok, K. W.; Chan, H. L. W.

    2007-08-01

    Using an ordinary ceramic fabrication technique, we fabricated lead-free (1-x)(K0.5Na0.5)NbO3-xBa(Ti0.95Zr0.05)O3 ceramics with CuO sintering aid . Ba(Ti0.95Zr0.05)O3 diffuses into (K0.5Na0.5)NbO3 to form a new solid solution. The ceramics with perovskite structure possess orthorhombic phase at x≤0.04 and become tetragonal phase at x≥0.06. Both the paraelectric cubic-ferroelectric tetragonal and the ferroelectric tetragonal-ferroelectric orthorhombic phase transition temperatures decrease with increasing the concentration of Ba(Ti0.95Zr0.05)O3. The doping of CuO effectively promotes the densification of the ceramics. The coexistence of the orthorhombic and tetragonal phases at 0.04

  10. Enhanced GMI effect in Fe 73.5-xMn xSi 13.5B 9Nb 3Cu I (x=1,3,5) nanocomposites due to Mn substitution for Fe

    NASA Astrophysics Data System (ADS)

    Phan, Manh-Huong; Peng, Hua-Xin; Yu, Seong-Cho; Tho, Nguyen D.; Chau, Nguyen

    2006-03-01

    Influence of Mn partial substitution for Fe on the magnetic and magnetoimpedance properties of Fe 73.5-xMn xSi 13.5B 9Nb 3Cu I (x = 1, 3, and 5) nanocomposite ribbons were investigated. The results indicated that the Mn addition led to an improved exchange coupling between grains and hence in the magnetic softness. Consequently, the giant magnetoimpedance (GMI) effect was significantly enhanced in these nanocomposites. In the frequency range of 0.1-10 Mhz, the GMI ratio reached the highest values of 83%, 94%, and 130% at the frequency of 2 MHz for x = 1, 3, and 5 compositions, respectively. The corresponding field sensitivity of GMI reached the highest values of 6, 7, and 16 %/Oe, respectively. These indicate that Fe 73.5-xMn xSi 13.5B 9Nb 3Cu I (x = 1, 3, and 5) nanocomposites are potential candidate materials for making GMI sensors.

  11. Structural dependence of piezoelectric, dielectric and ferroelectric properties of K{sub 0.5}Na{sub 0.5}(Nb{sub 1−2x/5}Cu{sub x})O{sub 3} lead-free ceramics with high Q{sub m}

    SciTech Connect

    Tan, Xiaohui; Fan, Huiqing; Ke, Shanming; Zhou, Limin; Mai, Yiu-Wing; Huang, Haitao

    2012-12-15

    Graphical abstract: Display Omitted Highlights: ► Double hysteresis loops were observed in K{sub 0.5}Na{sub 0.5}(Nb{sub 1−2x/5}Cu{sub x})O{sub 3}. ► Cu substitution caused structural discontinuity in KNNC. ► Dimeric defect complex (Cu{sup ‴}{sub Nb}–V{sub O}··){sup ′} with a dipole moment was formed in KNNC. -- Abstract: (K{sub 0.5}Na{sub 0.5})(Nb{sub 1−2x/5}Cu{sub x})O{sub 3} (abbreviated as KNNC, x = 0–2%) lead-free ceramics were synthetized by the solid state solution method. Pure perovskite phase with orthorhombic symmetry was observed. The evolution of the structure of KNNC was examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman scattering spectra techniques. Our results revealed that, defect dipoles (Cu{sup ‴}{sub Nb}–V{sub O}··){sup ′} were formed and provided a restoring force to reverse the switched polarization, which resulted in double P–E hysteresis loops in KNNC with Cu doping at x = 0.75% and 1%. However, non-polar defect complex (V{sub O}··–Cu{sup ‴}{sub Nb}–V{sub O}··)· caused a lattice shrinkage and the observed square shaped P–E loops in KNNC ceramics under high doping levels (x > 1%).

  12. Erratum to "Mirroring the dynamic magnetic behavior of magnetostrictive Co/(Ag,Cu,Ta) multilayers grown onto rigid and flexible substrates" [J. Magn. Magn. Mater. 393 (2015) 593-599

    NASA Astrophysics Data System (ADS)

    Agra, K.; Gomes, R. R.; Della Pace, R. D.; Dorneles, L. S.; Bohn, F.; Corrêa, M. A.

    2016-01-01

    The correct version of Fig. 3 in J. Magn. Magn. Mater. 393 (2015) 593-599 is presented below. The quasi-static magnetic behavior of the Co/Ta multilayer grown onto flexible substrate (F//(Co/Ta), Fig. 1(f)) is updated, since the experimental results presented for the Co/Ta multilayer grown onto rigid substrate (named R//(Co/Ta)) have been shown in duplicity in the previous published paper.

  13. Crystal structure and antiferromagnetic ordering of quasi-2D [Cu(HF{sub 2})(pyz){sub 2}]TaF{sub 6} (pyz = pyrazine).

    SciTech Connect

    Manson, J. L.; Schlueter, J. A.; McDonald, R. D.; Singleton, J.; Materials Science Division; Eastern Washington Univ.; LANL

    2010-04-01

    The crystal structure of the title compound was determined by X-ray diffraction at 90 and 295 K. Copper(II) ions are coordinated to four bridging pyz ligands to form square layers in the ab-plane. Bridging HF{sub 2}{sup -} ligands join the layers together along the c-axis to afford a tetragonal, three-dimensional (3D) framework that contains Taf{sub 6}{sup -} anions in every cavity. At 295 K, the pyz rings lie exactly perpendicular to the layers and cooling to 90 K induces a canting of those rings. Magnetically, the compound exhibits 2D antiferromagnetic correlations within the 2D layers with an exchange interaction of -13.1(1) K. Weak interlayer interactions, as mediated by Cu-F-H-F-Cu, leads to long-range magnetic order below 4.2 K. Pulsed-field magnetization data at 0.5 K show a concave curvature with increasing B and reveal a saturation magnetization at 35.4 T.

  14. CuO/V2O5-Codoped Bi3/2ZnNb3/2O7 (BZN) Ceramic for Embedded Capacitor Layer in Integrated LTCC Modules

    NASA Astrophysics Data System (ADS)

    Lee, Kyoungho; Kang, Seungjin

    2016-06-01

    Sintering additives for Bi3/2ZnNb3/2O7 (BZN) ceramic have been studied to facilitate use of BZN as a material for embedded decoupling capacitors in high-density multilayered low-temperature cofired ceramic (LTCC) modules for mobile communication systems and three-dimensional printing modules. Among the additives studied, a CuO/V2O5 mixture was the most promising for cofiring BZN ceramic with a commercial low-permittivity ( ɛ r) LTCC sheet (MLS-22; NEG Co., Japan) and Ag electrode. BZN codoped with 0.5 wt.% CuO/V2O5 was successfully densified at 860°C by reactive liquid-phase sintering, and the resulting dielectric properties were acceptable for use of the CuO/V2O5-codoped BZN for embedded capacitors in LTCC modules. The room-temperature permittivity ( ɛ r) of the CuO/V2O5-codoped BZN was 148 at 1 MHz, and the capacitance thermal stability was ±1.3% within the temperature range of -55°C to 125°C. The physical and chemical compatibilities of the CuO/V2O5-codoped BZN with heterogeneous layers (low- ɛ r LTCC layer and Ag electrode layer) in LTCC modules were also examined. A cofiring test of the doped BZN ceramic with MLS-22 LTCC sheet revealed that thickness control of the two heterogeneous layers was a key factor to avoid crack formation during cofiring. The optimum thickness ratio of doped BZN to MLS-22 layers was less than 0.25:1. A chemical compatibility test revealed no severe reaction between the doped BZN/MLS-22 and doped BZN/Ag layers.

  15. Field-induced recoverable strain behavior of CuO-added K0.5Na0.5NbO3 ceramics and 1-3 fiber/epoxy piezocomposites

    NASA Astrophysics Data System (ADS)

    Mensur Alkoy, Ebru

    2010-11-01

    Lead-free, dense, 1 mol % CuO-added potassium sodium niobate K0.5Na0.5NbO3 (KNN) fibers were successfully drawn using a novel alginate gelation technique. Piezocomposites with 1-3 connectivity were prepared with an epoxy matrix with various fiber volume fractions (Vf). Electrical properties of the piezocomposites were investigated and compared with bulk KNN ceramics of the same composition. The dielectric constant of the piezocomposites were found to increase from 67 to 191 with the addition of CuO into KNN and increasing Vf in the piezocomposite. A constricted, antiferroelectriclike double hysteresis polarization versus electric field (P-E) loop was observed in bulk KNN. A large and fully recoverable electrostrain of 0.07% was measured for bulk KNN and 0.03% for the piezocomposites under an electric field of 50 kV/cm, respectively. The double hysteresis P-E loop and the recoverable nature of the electrostrain was due to the CuNb‴-VO•• defect dipoles creating an internal field that restores the original domain pattern when the field is removed. A very high electrostrictive Q33 coefficient of 35.6×10-3 m4/C2 and an even higher Q33 of 162×10-3 m4/C2 was obtained for bulk KNN and piezocomposites, respectively.

  16. 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.

  17. Partial substitution of calcium in Bi-Sr-Ca-Cu-O superconductor

    NASA Astrophysics Data System (ADS)

    Sýkorová, D.; Smrková, O.; Michna, E.

    2006-09-01

    Chemical substitutions may change structural and physical parameters in HTS. Substituents influence formation of Bi-2223 phase, pinning centers, intergrain connection and change hole carrier concentration. Bulk samples with partial substitution of calcium in Bi3.2Pb0.8Sr4Ca5-yMxCu7Oy by 5 B elements (M = V, Nb, Ta), x = 0-0.8 were prepared by solid state reaction in air. Resistivity and magnetic susceptibility measurements evaluated superconducting properties. Phase composition was checked by X-ray diffraction

  18. Preparation of in situ and ex situ reinforced Fe-10Cr-1Cu-1Ni-1Mo-2C containing NbC particles by milling and hot pressing

    NASA Astrophysics Data System (ADS)

    Li, Xiao-qiang; Li, Zi-yang; Ye, Yong-quan; Hu, Ke

    2015-02-01

    An in situ and ex situ reinforced powder metallurgy (PM) steel was prepared by the combination of high-energy ball milling and subsequent hot pressing of elemental mixed powders of Fe-10Cr-1Cu-1Ni-1Mo-2C by mass with the addition of NbC particles. A 40-h milling pretreatment makes the powder particles nearly equiaxed with an average diameter of ˜8 μm, and the ferrite grain size is refined to ˜6 nm. The sintered density reaches 99.0%-99.7% of the theoretical value when the sintering is conducted at temperatures greater than 1000°C for 30 min. In the sintered bulk specimens, the formation of an in situ M7C3 (M = Cr, Fe, Mo) phase is confirmed. M7C3 carbides with several hundred nanometers in size are uniformly distributed in the matrix. Some ultra-fine second phases of 50-200 nm form around the ex situ NbC and in situ M7C3 particles. The sintered steel exhibits an excellent combination of hardness (> Hv 500) and compressive strength (2100-2420 MPa).

  19. Screening on binary Zr-1X (X = Ti, Nb, Mo, Cu, Au, Pd, Ag, Ru, Hf and Bi) alloys with good in vitro cytocompatibility and magnetic resonance imaging compatibility.

    PubMed

    Zhou, F Y; Qiu, K J; Li, H F; Huang, T; Wang, B L; Li, L; Zheng, Y F

    2013-12-01

    In this study, the microstructures, mechanical properties, corrosion behaviors, in vitro cytocompatibility and magnetic susceptibility of Zr-1X alloys with various alloying elements, including Ti, Nb, Mo, Cu, Au, Pd, Ag, Ru, Hf and Bi, were systematically investigated to explore their potential use in biomedical applications. The experimental results indicated that annealed Zr-1X alloys consisted entirely or primarily of α phase. The alloying elements significantly increased the strength and hardness of pure Zr and had a relatively slight influence on elastic modulus. Ru was the most effective enhancing element and Zr-1Ru alloy had the largest elongation. The results of electrochemical corrosion indicated that adding various elements to Zr improved its corrosion resistance, as indicated by the reduced corrosion current density. The extracts of the studied Zr-1X alloys produced no significant deleterious effects on osteoblast-like cells (MG 63), indicating good in vitro cytocompatibility. All except for Zr-1Ag alloy showed decreased magnetic susceptibility compared to pure Zr, and Zr-1Ru alloy had the lowest magnetic susceptibility value, being comparable to that of α' phase Zr-Mo alloy and Zr-Nb alloy and far lower than that of Co-Cr alloy and Ti-6Al-4V alloy. Among the experimental Zr-1X alloys, Zr-1Ru alloy possessing high strength coupled with good ductility, good in vitro cytocompatibility and low magnetic susceptibility may be a good candidate alloy for medical devices within a magnetic resonance imaging environment. PMID:23928334

  20. Synthesis, magnetic properties and magnetostriction of Pr(Fe0.75Co0.15Cu0.01Nb0.04B0.05)1.93 bulk nanocrystalline synthesized under high pressure

    NASA Astrophysics Data System (ADS)

    Hu, Cheng-Chao; Shi, Yang-Guang; Shi, Da-Ning; Chen, Long-Qing

    2016-05-01

    Bulk nanocrystalline Pr(Fe0.75Co0.15Cu0.01Nb0.04B0.05)1.93 alloys were synthesized by annealing its melt-spinning ribbons under different pressures and temperatures. It was demonstrated that the average grain size decreases with increasing pressure from 3 GPa to 6 GPa under the same annealing temperature of 853 K but increases with increasing temperature from 823 K to 923 K under the same annealing pressure of 6 GPa. A negative correlation between the coercivity and average grain size was found in the present investigated system. Grain refinement without losing the advantage of volume fraction of magnetostrictive phase offers the sample annealed under 6 GPa and 853 K the optimized magnetostrictive property, which might make it potential material for magnetostrictive application.

  1. High hard magnetic properties and cellular structure of nanocomposite magnet Nd 4.5Fe 73.8B 18.5Cr 0.5Co 1.5Nb 1Cu 0.2

    NASA Astrophysics Data System (ADS)

    The, N. D.; Chau, N.; Vuong, N. V.; Quyen, N. H.

    2006-08-01

    The formation of special nanostructure, cellular structure, in Nd 4.5Fe 73.8B 18.5Cr 0.5Co 1.5Nb 1Cu 0.2 nanocomposite magnet has been observed by means of SEM for the first time. Ultrafine structure of cellules with thickness of 20-25 nm and length in range of 200-300 nm leads to high shape anisotropy of the materials. Therefore, high hard magnetic properties were obtained with ( BH) max up to 17.3 MG Oe in ribbons with very high remanence of 13.5 kG. The role of Cr and Co in the formation and refinement of cellular structure is proposed. Effect of heat treatment on hard magnetic properties is discussed in detail.

  2. 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.

  3. 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

  4. 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.

  5. 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

  6. Ta2O5-based redox memory formed by neutral beam oxidation

    NASA Astrophysics Data System (ADS)

    Ohno, Takeo; Samukawa, Seiji

    2016-06-01

    A room temperature neutral beam oxidation process using a tantalum (Ta) metal film was used to obtain a high quality Ta oxide (Ta2O5) film. After irradiation of a Ta metal film with a neutral oxygen beam, a nanometer-thick Ta2O5 film with a film density of 7.5 g/cm3 was obtained. We also confirmed that the fabricated Cu/Ta2O5/Pt redox memory structure shows a bipolar resistive switching characteristic. This result demonstrates the great potential of neutral beam metal oxidation for the development of redox-based memory devices.

  7. Advances in Nb3Sn Performance

    SciTech Connect

    Godeke, Arno

    2008-05-19

    Nb{sub 3}Sn wires with non-Cu critical current densities (J{sub c}) that surpass 3 kAmm{sup -2} at 12 T and 4.2 K are commercially available in piece lengths longer than 10 km. Accelerator-type magnets that utilize these conductors have achieved record magnetic fields. This article summarizes key developments in the last decade that have led to these significant improvements in the performance of Nb{sub 3}Sn wires.

  8. 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

  9. 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.

  10. Binary Ni-Nb bulk metallic glasses

    SciTech Connect

    Xia, L.; Li, W.H.; Fang, S.S.; Wei, B.C.; Dong, Y.D.

    2006-01-15

    We studied the glass forming ability of Ni-Nb binary alloys and found that some of the alloys can be prepared into bulk metallic glasses by a conventional Cu-mold casting. The best glass former within the compositional range studied is off-eutectic Ni{sub 62}Nb{sub 38} alloy, which is markedly different from those predicted by the multicomponent and deep eutectic rules. The glass formation mechanism for binary Ni-Nb alloys was studied from the thermodynamic point of view and a parameter {gamma}* was proposed to approach the ability of glass formation against crystallization.

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. The existence of giant magnetocaloric effect and laminar structure in Fe 73.5-xCr xSi 13.5B 9Nb 3Cu 1

    NASA Astrophysics Data System (ADS)

    Chau, N.; Thanh, P. Q.; Hoa, N. Q.; The, N. D.

    2006-09-01

    Amorphous soft magnetic ribbons Fe 73.5-xCr xSi 13.5B 9Nb 3Cu 1 ( x=1-5) have been fabricated by rapid quenching on a single copper wheel. The differential scanning calorimetry (DSC) patterns showed that the crystallization temperature of α-Fe(Si) phase is ranging from 542 to 569 °C, a little higher than that of pure Finemet ( x=0). With the same annealing regime, the crystallization volume fraction as well as the particle size of α-Fe(Si) crystallites decreased with increasing Cr amount substituted for Fe in studied samples. Especially, the interesting fact is that the laminar structure of heat-treated ribbons on the surface contacted to copper wheel in the fabricating process has been firstly discovered and explained to be related to the existence of Cr in studied samples. The hysteresis loop measurement indicated that there is the pinning of displacement of domain walls. The giant magnetocaloric effect (GMCE) has been found in amorphous state of the samples. After annealing, the soft magnetic properties of investigated nanocomposite materials are desirably improved.

  17. Cu/Nb-Ti MRI wires with improved stability by incorporating filaments of large heat capacity substance PrB6

    NASA Astrophysics Data System (ADS)

    Keilin, V. E.; Kovalev, I. A.; Kruglov, S. L.; Sсherbakov, V. I.; Shutova, D. I.; Vorobjeva, A. E.; Salunin, N. I.; Potanina, L. V.

    2015-03-01

    In this paper we report our recent research on thermal stabilization of low-temperature superconducting magnets by means of large heat capacity substances (LHCS). Two samples (lengths ˜100 m) of NbTi composite wires with additional internal filaments made from intermetallic compound PrB6 (5.9-7.3 vol.%) were produced and tested. The design of the wires was similar to that of the conventional MRI sc wires, except for their smaller diameter (0.835 mm instead of 1.345 mm). Our final goal was the investigation of the possibility to minimize (or even eliminate completely) the necessity of MRI magnets training before their commissioning. The comparative stability measurements showed a twofold increase of the minimum quench energies (MQEs) of the doped wires against short heat disturbances. The magnetic field corresponding to the first flux jump increased by 50%. In MQE tests, the PrB6 heat capacity was fully utilized over the course of a 1 ms heat pulse. In the thermomagnetic stability measurements, the efficiency of LHCS doping was about 75% due to the fast evolution of the flux jumps.

  18. 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.

  19. Numerical Simulation of Critical Current Performance in Nb3Sn Strand Subjected to Periodic Bending Deformation

    NASA Astrophysics Data System (ADS)

    Murakami, Haruyuki; Ueda, Hiroshi; Ishiyama, Atsushi; Koizumi, Norikiyo; Okuno, Kiyoshi

    In the ITER Engineering Design Activity (EDA), four Nb3Sn model coils were developed and successfully tested. However, it was revealed that the critical current of the conductor degraded with the increase of electromagnetic force. One of the explanations of this phenomenon is a strand bending caused by enormous electromagnetic force. The authors therefore developed a simulation code using the distributed circuit model to investigate dependency of the critical current performance on the periodic bending deformation. The simulation results were in good agreement with the experiments. The dependence of the critical current on the periodic transverse load, temperature, periodic load pitch, thickness of Ta barrier which prevents Cu stabilizer to be contaminated by Sn, twist pitch of the strand and RRR of the bronze matrix was investigated using the developed code. The results showed that the critical current degraded less with decreasing the pitch of the transverse load and increasing the Ta barrier thickness. It suggests that the shorter cabling pitch and the larger bending stiffness prevent the critical current degradation.

  20. Evaluation of critical current density and residual resistance ratio limits in powder in tube Nb3Sn conductors

    NASA Astrophysics Data System (ADS)

    Segal, Christopher; Tarantini, Chiara; Hawn Sung, Zu; Lee, Peter J.; Sailer, Bernd; Thoener, Manfred; Schlenga, Klaus; Ballarino, Amalia; Bottura, Luca; Bordini, Bernardo; Scheuerlein, Christian; Larbalestier, David C.

    2016-08-01

    High critical current density (J c) Nb3Sn A15 multifilamentary wires require a large volume fraction of small grain (SG), superconducting A15 phase, as well as Cu stabilizer with high Residual Resistance Ratio (RRR) to provide electromagnetic stabilization and protection. In powder-in-tube (PIT) wires the unreacted Nb7.5 wt%Ta outer layer of the tubular filaments acts as a diffusion barrier and protects the interfilamentary Cu stabilizer from Sn contamination. A high RRR requirement generally imposes a restricted A15 reaction heat treatment to prevent localized full reaction of the filament that could allow Sn to reach the Cu. In this study we investigate recent high quality PIT wires that achieve a J c (12 T, 4.2 K) up to ∼2500 A mm‑2 and find that the minimum diffusion barrier thickness decreases as the filament aspect ratio increases from ∼1 in the inner rings of filaments to 1.3 in the outer filament rings. We found that just 2–3 diffusion barrier breaches can degrade RRR from 300 to 150 or less. Using progressive etching of the Cu we also found that the RRR degradation is localized near the external filaments where deformation is highest. Consequently minimizing filament distortion during strand fabrication is important for reducing RRR degradation. The additional challenge of developing the highest possible J c must be addressed by forming the maximum fraction of high J c SG A15 and minimizing low J c large-grain (LG) A15 morphologies. In one wire we found that 15% of the filaments had a significantly enhanced SG/LG A15 ratio and no residual A15 in the core, a feature that opens a path to substantial J c improvement.

  1. Ultra-soft magnetic properties and correlated phase analysis by 57Fe Mössbauer spectroscopy of Fe74Cu0.8Nb2.7Si15.5B7 alloy

    NASA Astrophysics Data System (ADS)

    Manjura Hoque, S.; Liba, S. I.; Anirban, A.; Choudhury, Shamima; Akhter, Shireen

    2016-02-01

    A detailed study of magnetic softness has been performed on FINEMENT type of ribbons by investigating the BH loop with maximum applied field of 960 A/m. The ribbon with the composition of Fe74Cu0.8Nb2.7Si15.5B7 was synthesized by rapid solidification technique and the compositions volume fraction was controlled by changing the annealing condition. Detail phase analysis was performed through X-ray diffraction (XRD), Differential scanning calorimetry (DSC), Vibrating sample magnetometer (VSM) and Mössbauer spectroscopy in order to correlate the ultrasoft magnetic properties with the volume fraction of amorphous and α-Fe(Si) soft nano composites. Bright (BF) and dark field (DF) image with selective area diffraction (SAD) patterns by the transmission electron microscopy (TEM) of the sample annealed for the optimized annealed condition at 853 K for 3 min reveals nanocrystals with an average size between 10-15 nm possessing the bcc structure which matches with the grain size revealed by the X-ray diffraction. Kinetics of crystallization of α-Fe(Si) phases has been determined by DSC curves. Extremely small coercivity of 30.9 A/m and core loss of 2.5 W/Kg for the sample annealed at 853 K for 3 min was found. Similar values for other crystalline conditions were determined by using BH loop tracer with a maximum applied field of around 960 A/m. Mössbauer spectroscopy was used to determine chemical shift, hyperfine field distribution (HFD), and peak width of different phases. The volume fractions of the relative amount of amorphous and crystalline phases are also determined by Mössbauer spectroscopy. High saturation magnetization along with ultrasoft magnetic properties exhibits very high potentials technological applications.

  2. Study of the nanocrystalline Fe{sub 73.5}Nb{sub 4.5}Cr{sub 5}Cu{sub 1}B{sub 16} alloy by the radio-frequency-M{umlt o}ssbauer technique

    SciTech Connect

    Kopcewicz, M.; Grabias, A.; Skorvanek, I.

    1998-01-01

    The influence of Cr on the structural and magnetic properties of iron based amorphous and nanocrystalline alloys is studied for the Fe{sub 73.5}Nb{sub 4.5}Cr{sub 5}Cu{sub 1}B{sub 16} alloy by an unconventional technique which combines the M{umlt o}ssbauer spectroscopy with the effects induced by the radio-frequency (rf) magnetic fields (rf collapse and rf sideband effects). The nanocrystalline bcc-Fe phase, formed by annealing the amorphous precursor for 1 h at temperatures 490{degree}C{endash}550{degree}C, was embedded in the retained amorphous matrix. The conventional M{umlt o}ssbauer measurements allowed the identification of three types of phases in the nanocrystalline alloy: (i) the retained amorphous matrix, (ii) the nanocrystalline bcc-Fe phase, whose abundance increased with increasing annealing temperature, and (iii) the interfacial phase formed at the bcc-Fe grain boundaries. The rf collapse effect observed in the M{umlt o}ssbauer spectra of the samples exposed to the rf field of 60.9 MHz permits the study of the magnetic anisotropy in all phases present. The rf collapse effect occurs only in the amorphous phase, thus revealing that the magnetic anisotropy of the amorphous matrix is significantly smaller than that encountered in the nanocrystalline phase. The rf-M{umlt o}ssbauer experiments performed as a function of the rf field intensity allowed the determination of the distributions of the anisotropy fields in the nanocrystalline-amorphous composite alloy. The rf sidebands effect reveals a strong reduction of magnetostriction related to the formation of the nanocrystalline phase. {copyright} {ital 1998 American Institute of Physics.}

  3. Theoretical electron scattering amplitudes and spin polarizations. Electron energies 100 to 1500 eV Part II. Be, N, O, Al, Cl, V, Co, Cu, As, Nb, Ag, Sn, Sb, I, and Ta targets

    NASA Astrophysics Data System (ADS)

    Wildhaber, M. L.; Wikle, C. K.; Anderson, C. J.; Franz, K. J.; Moran, E. H.; Dey, R.

    2012-12-01

    Recent decades have brought substantive changes in land use and climate across the earth, prompting a need to think of population and community ecology not as a static entity, but as a dynamic process. Increasingly there is evidence of ecological changes due to climate change. Although much of this evidence comes from ground-truth observations of biogeographic data, there is increasing reliance on models that relate climate variables to biological systems. Such models can then be used to explore potential changes to population and community level ecological systems in response to climate scenarios as obtained from global climate models (GCMs). A key issue associated with modeling ecosystem response to climate is GCM downscaling to regional and local ecological/biological response models that can be used in vulnerability and risk assessments of the potential effects of climate change. The need is for an explicit means for scaling results up or down multiple hierarchical levels and an effective assessment of the level of uncertainty surrounding current knowledge, data, and data collection methods with these goals identified as in need of acceleration in the U.S. Climate Change Science Program FY2009 Implementation Priorities. In the end, such work should provide the information needed to develop adaptation and mitigation methodologies to minimize the effects of directional and nonlinear climate change on the Nation's land, water, ecosystems, and biological populations. We are working to develop an approach that includes multi-scale and hierarchical Bayesian modeling of Missouri River sturgeon population dynamics. Statistical linkages are defined to quantify implications of climate on fish populations of the Missouri River ecosystem. This approach is a hybrid between physical (deterministic) downscaling and statistical downscaling, recognizing that there is uncertainty in both. The model must include linkages between climate and habitat, and between habitat and population. A key advantage of the hierarchical approach used in this study is that it incorporates various sources of observations and includes established scientific knowledge, and associated uncertainties. The goal is to evaluate the potential distributional changes in an ecological system, given distributional changes implied by a series of linked climate and system models under various emissions/use scenarios. The predictive modeling system being developed will be a powerful tool for evaluating management options for coping with global change consequences and assessing uncertainty of those evaluations. Specifically for the endangered pallid sturgeon (Scaphirhynchus albus), we are already able to assess potential effects of any climate scenario on growth and population size distribution. Future models will incorporate survival and reproduction. Ultimately, these models provide guidance for successful recovery and conservation of the pallid sturgeon. Here we present a basic outline of the approach we are developing and a simple pallid sturgeon example to demonstrate how multiple scales and parameter uncertainty are incorporated.

  4. Effect of Alloying Elements on Nb-Rich Portion of Nb-Si-X Ternary Systems and In Situ Crack Observation of Nb-Si-Based Alloys

    NASA Astrophysics Data System (ADS)

    Miura, Seiji; Hatabata, Toru; Okawa, Takuya; Mohri, Tetsuo

    2014-01-01

    To find a new route for microstructure control and to find additive elements beneficial for improving high-temperature strength, a systematic investigation is performed on hypoeutectic Nb-15 at. pct Si-X ternary alloys containing a transition element, Fe, Co, Ni, Cu, Ru, Rh, Pd, Re, Os, Ir, Pt, or Au. Information on phase equilibrium is classified in terms of phase stability of silicide phases, α Nb5Si3, Nb4SiX, and Nb3Si, and the relationship between microstructure and mechanical properties both at room temperature and high temperature is investigated. All the additive elements are found to stabilize either α Nb5Si3 or Nb4SiX but destabilize Nb3Si. A microstructure of Nbss/α Nb5Si3 alloy composed of spheroidized α Nb5Si3 phase embedded in the Nbss matrix is effective for toughening, regardless of the initial as-cast microstructure. Also the plastic deformation of Nbss dendrites may effectively suppress the propagation of longer cracks. High-temperature strength of alloys is governed by the deformation of Nbss phase and increases with higher melting point additives.

  5. Magnetization anomaly of Nb3Al strands and instability of Nb3Al Rutherford cables

    SciTech Connect

    Yamada, Ryuji; Kikuchi, Akihiro; Wake, Masayoshi; /KEK, Tsukuba

    2006-08-01

    Using a Cu stabilized Nb{sub 3}Al strand with Nb matrix, a 30 meter long Nb{sub 3}Al Rutherford cable was made by a collaboration of Fermilab and NIMS. Recently the strand and cable were tested. In both cases instability was observed at around 1.5 Tesla. The magnetization of this Nb{sub 3}Al strand was measured first using a balanced coil magnetometer at 4.2 K. Strands showed an anomalously large magnetization behavior around at 1.6 T, which is much higher than the usual B{sub c2} {approx} 0.5 Tesla (4.2 K) of Nb matrix. This result is compared with the magnetization data of short strand samples using a SQUID magnetometer, in which a flux-jump signal was observed at 0.5 Tesla, but not at higher field. As a possible explanation for this magnetization anomaly, the interfilament coupling through the thin Nb films in the strands is suggested. The instability problem observed in low field tests of the Nb{sub 3}Al Rutherford cables is attributed to this effect.

  6. 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.

  7. Nb3Sn multifilamentary superconductors fabricated through a diffusion reaction between Nb and Ag-Sn alloys

    NASA Astrophysics Data System (ADS)

    Matsumoto, G.; Inoue, K.; Kikuchi, A.; Takeuchi, T.; Kiyoshi, T.

    2006-06-01

    Ag-Sn alloy is very attractive for fabricating Nb3Sn wires through diffusion reaction, because Ag-based alloy including a large amount of Sn is ductile. Therefore we investigated the Nb3Sn formation through the diffusion reaction between Nb and Ag-Sn alloys. With using Ag-9 at% Sn fcc phase, Ag-12 at% Sn ζ phase, and Ag-24at% Sn epsilon phase alloys, we fabricated single-core, 200-core, and 40000-core composite wires with Nb matrix and Ag-Sn alloy cores. With increase of Sn content in Ag-Sn alloys, the obtained superconducting properties of heat treated composite wires were improved. Tc and Bc2(4.2 K) for the Nb/Ag-Sn are similar to those for the Nb/Cu-Sn. However, the Ic values are relatively small, due to the formed very thin Nb3Sn layers. Ag is apparently not so effective to increase the formation rate of Nb3Sn layer as Cu. We obtained very interesting results by making the 200-core and 40000-core wires, which show the improved Tc and Bc2(4.2 K) by 0.5-1 K and 2-5 T, respectively. From 10 to 500 times larger Ic(4.2 K) were also obtained for the multifilamentary wires.

  8. 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.

  9. 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

  10. Constant permeability of (Fe{sub 0.75}B{sub 0.20}Si{sub 0.05}){sub 96}Nb{sub 4} bulk metallic glass prepared by B{sub 2}O{sub 3} flux melting and Cu-mold casting

    SciTech Connect

    Bitoh, T.; Shibata, D.

    2009-04-01

    The effect of B{sub 2}O{sub 3} flux melting on the soft magnetic properties of (Fe{sub 0.75}B{sub 0.20}Si{sub 0.05}){sub 96}Nb{sub 4} bulk metallic glass prepared by casting has been investigated. Ring-shaped bulk specimens that were prepared by B{sub 2}O{sub 3} flux melting and Cu-mold casting (fluxed specimens) show a flat hysteresis curve, indicating a good linear relationship between the magnetic induction and the applied magnetic field. Although the permeability of the fluxed specimens is lower than that of the specimens prepared by conventional Cu-mold casting by one order of magnitude, their coercivities are almost same. These results show that it is possible to develop a new soft magnetic material that exhibits constant permeability with low core loss.

  11. Enhanced Photocatalytic Property of Cu Doped Sodium Niobate

    SciTech Connect

    Xu, Jianbin; Zhang, Feng; Sun, Bingyang; Du, Yingge; Li, Guoqiang; Zhang, Weifeng

    2015-09-29

    We investigate the photocatalytic activity of Cu doped NaNbO3 powder sample prepared by the modified polymer complex method. The photocatalytic activity of hydrogen evolution from methanol aqueous solution was improved by Cu 2.6 at% doping. The photocatalytic degradation of rhodamine B under visible light irradiation was enhanced in comparison with pure NaNbO3. Cu inctroduction improved the adsorption property of NaNbO3, judging from the Fourier transform infrared spectra. Moreover, the ultraviolet light excitation in Cu doped sample was found to accelerate the mineralized process.

  12. Vitrification and determination of the crystallization time scales of the bulk-metallic-glass-forming liquid Zr{sub 58.5}Nb{sub 2.8}Cu{sub 15.6}Ni{sub 12.8}Al{sub 10.3}

    SciTech Connect

    Hays, C. C.; Schroers, J.; Johnson, W. L.; Rathz, T. J.; Hyers, R. W.; Rogers, J. R.; Robinson, M. B.

    2001-09-10

    The crystallization kinetics of Zr{sub 58.5}Nb{sub 2.8}Cu{sub 15.6}Ni{sub 12.8}Al{sub 10.3} were studied in an electrostatic levitation (ESL) apparatus. The measured critical cooling rate is 1.75 K/s. Zr{sub 58.5}Nb{sub 2.8}Cu{sub 15.6}Ni{sub 12.8}Al{sub 10.3} is the first bulk-metallic-glass-forming liquid that does not contain beryllium to be vitrified by purely radiative cooling in the ESL. Furthermore, the sluggish crystallization kinetics enable the determination of the time-temperature-transformation (TTT) diagram between the liquidus and the glass transition temperatures. The shortest time to reach crystallization in an isothermal experiment; i.e., the nose of the TTT diagram is 32 s. The nose of the TTT diagram is at 900 K and positioned about 200 K below the liquidus temperature.

  13. Structural and magnetic characterization of FeNbBCu alloys as a function of Nb content

    NASA Astrophysics Data System (ADS)

    Torrens-Serra, J.; Bruna, P.; Roth, S.; Rodriguez-Viejo, J.; Clavaguera-Mora, M. T.

    2009-05-01

    In this work we describe the changes in the crystallization behaviour and the magnetic properties with variation of the Nb content in Fe79-xNb5+xB15Cu1 (x = 0,2,4) alloys. The microstructure of the samples, as-quenched and after several heat treatments, is analysed by transmission Mössbauer spectroscopy (TMS), x-ray diffraction, differential scanning calorimetry and vibrating sample magnetometry. The saturation polarization, Curie temperature, magnetic entropy change and the maximum value of the hyperfine field distribution of the amorphous phase are composition dependent and are enhanced with a reduction in Nb content. Devitrification is produced by the nanocrystallization of bcc-Fe followed by the precipitation of iron borides. The calorimetric analysis indicates that Nb stabilizes the alloy against nanocrystallization. Both the amount of bcc-Fe precipitates and their mean grain size decrease significantly with increasing Nb content, suggesting a higher level of disorder at the interface between the amorphous matrix and the nanocrystal that reduces grain growth. The variation in the Fe environments after crystallization events deduced from TMS measurements are analysed in terms of the amount of Nb in the alloy. Both amorphous and nanocrystallized alloys show a soft magnetic behaviour with coercivity values in the range 4-10 A m-1.

  14. 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.

  15. 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

  16. Pulsed laser deposition growth of heteroepitaxial YBa2Cu3O7/La0.67Ca0.33MnO3 superlattices on NdGaO3 and Sr0.7La0.3Al0.65Ta0.35O3 substrates

    SciTech Connect

    Malik, V. K.; Marozau, I.; Das, S.; Doggett, B.; Satapathy, D. K.; Uribe-Laverde, M. A.; Biskup, Nevenko; Varela del Arco, Maria; Schneider, C. W.; Marcelot, C.; Stahn, J.; Bernhard, C.

    2012-01-01

    Heteroepitaxial superlattices of [YBa{sub 2}Cu{sub 3}O{sub 7}(n)/La{sub 0.67}Ca{sub 0.33}MnO{sub 3}(m)]{sub x} (YBCO/LCMO), where n and m are the number of YBCO and LCMO monolayers and x the number of bilayer repetitions, have been grown with pulsed laser deposition on NdGaO{sub 3} (110) and Sr{sub 0.7}La{sub 0.3}Al{sub 0.65}Ta{sub 0.35}O{sub 3} (001). These substrates are well lattice matched with YBCO and LCMO and, unlike the commonly used SrTiO{sub 3}, they do not give rise to complex and uncontrolled strain effects at low temperature. The growth dynamics and the structure have been studied in situ with reflection high-energy electron diffraction and ex situ with scanning transmission electron microscopy, x-ray diffraction, and neutron reflectometry. The individual layers are found to be flat and continuous over long lateral distances with sharp and coherent interfaces and with a well-defined thickness of the individual layer. The only visible defects are antiphase boundaries in the YBCO layers that originate from perovskite unit-cell height steps at the interfaces with the LCMO layers. We also find that the first YBCO monolayer at the interface with LCMO has an unusual growth dynamics and is lacking the CuO chain layer, while the subsequent YBCO layers have the regular Y-123 structure. Accordingly, the CuO{sub 2} bilayers at both the LCMO/YBCO and the YBCO/LCMO interfaces are lacking one of their neighboring CuO chain layers and, thus, half of their hole-doping reservoir. Nevertheless, from electric transport measurements on a superlattice with n = 2 we obtain evidence that the interfacial CuO{sub 2} bilayers remain conducting and even exhibit the onset of a superconducting transition at very low temperature. Finally, we show from dc magnetization and neutron reflectometry measurements that the LCMO layers are strongly ferromagnetic.

  17. 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.

  18. Cu and CuO/titanate nanobelt based network assemblies for enhanced visible light photocatalysis.

    PubMed

    Logar, Manca; Bračko, Ines; Potočnik, Anton; Jančar, Boštjan

    2014-04-29

    3D network configurations of copper(II) oxide/titanate nanobelt (CuO/TiNBs) and copper/titanate nanobelt (Cu/TiNBs) were formed using a two-step polyelectrolyte-assisted synthesis and assembly approach. The photoactivity of the TiNB/CuO and Cu/TiNB composite networks is significantly enhanced as compared to the activity of 3D structures formed of pristine TiNB. An efficient, UV-vis-light-induced electron transfer at the two-component interface achieved by the intimate coupling of TiNB with p-type semiconducting CuO and plasmonic Cu nanoparticles in composite heterostructures facilitates control over the system's exciton dynamics, which results in highly efficient UV-vis photocatalytic performance of heterostructures. The superior photocatalytic activity of the metal and semiconductor/semiconductor nanocomposite structures in the visible region is discussed, highlighting the role of interfacial electron-charge transfer (IFCT) in semiconductor-semiconductor (CuO/TiNB) and surface plasmon resonance (SPR) of Cu nanoparticles in metal-semiconductor heterostructures. PMID:24697758

  19. 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.

  20. 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.