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Sample records for nb ta solid

  1. First principles calculation of phase diagrams of V-Nb, V-Ta and Nb-Ta alloys

    SciTech Connect

    Ravi, C.; Panigrahi, B. K.; Valsakumar, M. C.; Walle, A. Van de

    2012-06-05

    We report the solid state phase diagram of V-Nb, V-Ta and Nb-Ta alloys computed by combining the density functional theory total energies with the cluster expansion and Monte Carlo techniques. From the computed phase diagrams, we find that V-Nb and Nb-Ta alloys form continuous series of solid solutions and the solid solution phase is stable down to ambient temperatures, consistent with experiments. The calculated bcc V-Ta phase diagram exhibits complete miscibility. Since the current cluster expansion ignore V{sub 2}Ta phase, the chemical interaction due to relatively large electronegativity difference, which cause the ordering of V{sub 2}Ta phase from the bcc solid solution, appears to manifest by making the solid solution phase remain stable for the complete concentration range, down to ambient temperatures, perhaps with some short-range-order. This work further demonstrates the dominant role of constituent strains in the accurate calculation of phase diagram of alloys of constituents with significant size mismatches.

  2. Study of solid state phase stability and diffusion by x-ray microanalytical techniques. [Ta/W; U/Nb

    SciTech Connect

    Romig, A.D. Jr.

    1986-01-01

    Diffusion behavior in Ta-W has been examined in the temperature range 1300 to 2100/sup 0/C with single phase diffusion couples prepared by chemical vapor deposition. The diffusion induced concentration gradients were measured by EPMA and/or AEM and the chemical diffusivities determined with the method of Darken. Multiphase diffusion behavior and phase stability in the U-Nb system has been studied at 500 to 1200/sup 0/C by using diffusion couples and isothermally annealed multiphase bulk alloys. The concentration profiles and interface phase compositions were measured by EPMA and/or AEM.

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

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

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

    SciTech Connect

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

    2007-07-15

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

  5. Influence of ultrafast quenching on the structure of Li0.12Na0.88Ta y Nb1 - y O3 ceramics obtained by solid-phase synthesis

    NASA Astrophysics Data System (ADS)

    Aleshina, L. A.; Palatnikov, M. N.; Shcherbanich, Ya. I.; Feklistova, E. P.; Shcherbina, O. B.

    2017-03-01

    A technology of perovskite-type Li0.12Na0.88Ta y Nb1 - y O3 ceramic solid solutions based on sodium and lithium niobates and tantalates and a method of their ultrafast quenching have been presented. The influence of quenching on the structure of ceramic samples and the variations in crystallographic and fine structure parameters have been studied. It has been found that ultrafast quenching results in a preferred orientation of crystallites, severe local microstrains, and changes in the atomic structure of Li0.12Na0.88Ta y Nb1 - y O3 ceramics.

  6. Phase diagram, chemical stability and physical properties of the solid-solution Ba{sub 4}Nb{sub 2-x}Ta{sub x}O{sub 9}

    SciTech Connect

    Dunstan, Matthew T.; Southon, Peter D.; Kepert, Cameron J.; Hester, James; Kimpton, Justin A.; Ling, Chris D.

    2011-10-15

    Through the construction of the Ba{sub 4}Nb{sub 2-x}Ta{sub x}O{sub 9} phase diagram, it was discovered that the unique high-temperature {gamma} phase is a thermodynamic intermediate between the low-temperature {alpha} phase (Sr{sub 4}Ru{sub 2}O{sub 9}-type) and a 6H-perovskite. Refined site occupancies for the {gamma} phase across the Ba{sub 4}Nb{sub 2-x}Ta{sub x}O{sub 9} solid-solution indicate that Nb preferentially occupies the tetrahedral sites over the octahedral sites in the structure. When annealed in a CO{sub 2}-rich atmosphere, all of the phases studied absorb large amounts of CO{sub 2} at high temperatures between {approx}700 and 1300 K. In situ controlled-atmosphere diffraction studies show that this behaviour is linked to the formation of BaCO{sub 3} on the surface of the material, accompanied by a Ba{sub 5}(Nb,Ta){sub 4}O{sub 15} impurity phase. In situ diffraction in humid atmospheres also confirms that these materials hydrate below {approx}1273K, and that this plays a critical role in the various reconstructive phase transitions as well as giving rise to proton conduction. - Graphical abstract: Thermodynamic phase diagram of Ba{sub 4}Nb{sub 2-x}Ta{sub x}O{sub 9}. Highlights: > {gamma}-Ba{sub 4}Nb{sub 2}O{sub 9} phase is a structural intermediate between the {alpha} and 6H-perovskite phases. > Ba{sub 4}Nb{sub 2}O{sub 9} and Ba{sub 4}Ta{sub 2}O{sub 9} decompose at high temperatures in the presence of CO{sub 2}. > These materials all absorb between 5% and 6% of CO{sub 2} by mass between {approx}800 and 1200 K.

  7. 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.

  8. (Ln = Pr, Nd, M = Nb, Ta)

    NASA Astrophysics Data System (ADS)

    Noked, O.; Melchior, A.; Shuker, R.; Steininger, R.; Kennedy, B. J.; Sterer, E.

    2014-06-01

    High-pressure X-ray diffraction measurements have demonstrated that the cation-deficient perovskites Pr1/3NbO3, Pr1/3TaO3, Nd1/3NbO3, and Nd1/3TaO3 undergo irreversible pressure-induced amorphization (PIA). This occurs near 14.5 GPa for the niobates and 18.5 GPa for the tantalates. The unit cell volumes of the four oxides show an almost linear decrease as the pressure is increased. It is concluded that the PIA transition occurs at higher pressures in the tantalates due to the lower MO6 initial tilting at ambient conditions, which is associated with the larger atomic mass of the tantalum. The behavior of these oxides is compared to that of CaTiO3, and the role of both the weakening of the M-O-M π-bonding and the cation vacancies on the observed structural changes is discussed.

  9. 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. Copyright © 2015 Elsevier Ltd. All rights reserved.

  10. 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.

  11. 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.

  12. "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.

  13. Excitation of Nb, Ta, and W atoms in sputtering processes

    SciTech Connect

    Vasil`eva, E.K.; Morozov, S.N.

    1995-12-01

    Optical emission spectra of sputtered atoms that arise under the bombardment of Nb, Ta, and W surfaces by xenon ions with an energy of 40 keV are studied in the wavelength range of 380 - 600 nm. The properties and mechanisms of the formation of excited atomic states in sputtering processes are discussed. 12 refs., 3 figs.

  14. Interaction of interstitial atoms and configurational contribution to their thermodynamic activity in V, Nb, and Ta

    NASA Astrophysics Data System (ADS)

    Blanter, M. S.; Dmitriev, V. V.; Mogutnov, B. M.; Ruban, A. V.

    2017-02-01

    The pairwise interaction energies of O-O and N-N in bcc metals of group VB, which were calculated earlier using first-principles methods, have been employed to analyze the effect of the interatomic interactions on the configurational contribution to the thermodynamic activity. The strong effect of interstitial- interstitial interaction has been shown. The configurational contribution grows in the row (Nb-N) → (V-N) → (Ta-N) → (Nb-O) → (V-O) → (Ta-O), which is caused by a weakening of the mutual attraction of interstitial atoms in these solid solutions. The strong repulsion that characterizes the majority of coordination shells only weakly affects the thermodynamic activity. The character of the temperature dependence of the configurational contribution is defined by the strength of the mutual attraction of the interstitial atoms, i.e., upon strong attraction, the contribution increases with increasing temperature (Nb-N, V-N, Ta-N, and Nb-O) and, upon weak attraction, it decreases (V-O and Ta-O).

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

    PubMed

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

    2012-06-01

    Multi-principal-element (TiZrNbHfTa)N and (TiZrNbHfTa)C coatings were deposited on Ti6Al4V alloy by co-sputtering of Ti, Zr, Nb, Hf and Ta metallic targets in reactive atmosphere. The coatings were analyzed for elemental and phase compositions, crystalline structure, morphology, residual stress, hardness, friction performance, wear-corrosion resistance and cell viability. For all the films, only simple fcc solid solutions with (111) preferred orientations were found, with crystallite sizes in the range 7.2-13.5 nm. The coatings were subjected to compressive stress, with values ranging from 0.8 to 1.6 GPa. The carbide coating with the highest carbon content (carbon/metal ≈1.3) exhibited the highest hardness of about 31 GPa, the best friction behavior (μ = 0.12) and the highest wear resistance (wear rate K=0.2×10(-6)mm(3)N(-1)m(-1)), when testing in simulated body fluids (SBFs). Cell viability tests proved that the osteoblast cells were adherent to the coated substrates, and a very high percentage of live cells were observed on sample surfaces, after 72 h incubation time. Copyright © 2012 Elsevier Ltd. All rights reserved.

  16. Superelastic and shape memory properties of TixNb3Zr2Ta alloys.

    PubMed

    Zhu, Yongfeng; Wang, Liqiang; Wang, Minmin; Liu, Zhongtang; Qin, Jining; Zhang, Di; Lu, Weijie

    2012-08-01

    The microstructure and phase constitutions of TixNb3Zr2Ta alloys (x=35, 31, 27, 23) (wt%) were studied. With a lower niobium content the grain size of β phase in TixNb3Zr2Ta alloys increased significantly, and the TixNb3Zr2Ta system was more likely to form α″ phase and even α phase. Tensile tests showed that UTS of TixNb3Zr2Ta alloys improved as the Nb content was decreased. Cyclic loading-unloading tensile tests were carried on TixNb3Zr2Ta alloys. Ti23Nb3Zr2Ta and Ti27Nb3Zr2Ta alloys featured the best superelasticity among the alloys studied. The pseudoelastic strain ratio of Ti35Nb3Zr2Ta alloy decreased a lot as the cycle number increased. Ti31Nb3Zr2Ta alloy showed only minimum superelasticity. This is because Ti23Nb3Zr2Ta and Ti27Nb3Zr2Ta alloys had higher yield strength than Ti31Nb3Zr2Ta did, which allowed martensite phase to be induced. On the contrary, Ti31Nb3Zr2Ta alloy exhibited better shape memory property than Ti27Nb3Zr2Ta, Ti23Nb3Zr2Ta and Ti35Nb3Zr2Ta titanium alloys. β phase, α phase and α″ phase were found in Ti23Nb3Zr2Ta alloy by TEM observation. The dislocation density of α phase was much lower than that of β phase due to their crystal structure difference. This may explained why Ti23Nb3Zr2Ta with α phase possessed higher tensile strength. The incomplete shape recovery of Ti23Nb3Zr2Ta alloy after unloading resulted from two sources. Plastic deformation occurred in β phase, α phase and even α″ phase under dislocation slip mechanism, and incomplete decomposition of α″ martensitic phase resulted in unrecovered strain as well.

  17. Synthesis, crystal structures and magnetic properties of fluorite-related compounds Ce3MO7 (M = Nb, Ta)

    NASA Astrophysics Data System (ADS)

    Inabayashi, Masaki; Doi, Yoshihiro; Wakeshima, Makoto; Hinatsu, Yukio

    2017-10-01

    Ternary oxides Ce3NbO7 and Ce3TaO7 were successfully synthesized by the solid state reaction under flowing hydrogen atmosphere. The structures were determined by the powder X-ray diffraction. Both the compounds were crystallized in the orthorhombic space groups Pnma (for Ce3NbO7) and Cmcm (for Ce3TaO7). Both the structures have similar features: two kinds of infinite chains formed by corner-sharing NbO6 (TaO6) octahedra and edge-sharing Ce(1)O8 cubes, the slabs consisting of alternate chains, and 7-coordinated Ce(2) ions existing between the slabs. In the structure of Ce3NbO7, the NbO6 octahedra running along the a-axis are titled towards the 0 0 1 direction, while in the Ce3TaO7 structure, the TaO6 octahedra running along the c-axis are titled towards the 0 1 0 direction. Magnetic susceptibility measurements for Ce3NbO7 and Ce3TaO7 show that both compounds are paramagnetic down to 1.8 K, and confirm that the Ce ion is in the trivalent state. From specific heat (Cp) measurements, a rapid increase of Cp/T has been observed below 3 K for both the compounds, indicating the onset of magnetic ordering between Ce3+ ions at further lower temperatures.

  18. 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.

  19. NbOsSi and TaOsSi - Two new superconducting ternary osmium silicides

    NASA Astrophysics Data System (ADS)

    Benndorf, Christopher; Heletta, Lukas; Heymann, Gunter; Huppertz, Hubert; Eckert, Hellmut; Pöttgen, Rainer

    2017-06-01

    The new equiatomic silicides NbOsSi and TaOsSi as well as ZrOsSi, TIrSi (T = Zr, Hf, Nb, Ta) and TPtSi (T = Nb, Ta) were prepared from the elements by arc-melting. These silicides crystallize with the orthorhombic TiNiSi type structure, space group Pnma. Irregularly shaped crystals of ZrOsSi, NbOsSi, TaOsSi, ZrIrSi and HfIrSi were separated from the annealed samples and investigated by single-crystal X-ray diffraction (a = 640.46(7), b = 404.07(5), c = 743.66(8) pm, wR2 = 0.0285, 390 F2 values, 20 variables for ZrOsSi; a = 629.78(6), b = 388.72(4), c = 727.48(7) pm, wR2 = 0.0350, 397 F2 values, 20 variables for NbOsSi, a = 626.80(6), b = 389.36(4), c = 726.22(7) pm, wR2 = 0.0501, 385 F2 values, 20 variables for TaOsSi, a = 653.48(8), b = 395.35(4), c = 739.19(8) pm, wR2 = 0.0427, 413 F2 values, 20 variables for ZrIrSi and a = 646.34(12), b = 393.57(7), c = 736.8(14) pm, wR2 = 0.0582, 371 F2 values, 20 variables for HfIrSi). The striking structural motifs in the new osmium compounds are three-dimensional [OsSi] networks (Os-Si: 240-251 pm) in which the osmium atoms have strongly distorted tetrahedral silicon coordination. High-pressure/high-temperature experiments (9.5 GPa/1520 K) on TaOsSi gave no hint for a structural phase transition. Temperature dependent measurements of the magnetic susceptibility and the electrical conductivity of NbOsSi and TaOsSi showed superconductivity below TC = 3.5 and 5.5 K, respectively. 29Si solid state MAS NMR investigations of the prepared silicides approved the structural models and showed a correlation between the observed 29Si resonance shifts and the electronegativity of the involved refractory metal.

  20. Electronic structure of the bcc transition metals: Thermoreflectance studies of bulk V, Nb, Ta, and. cap alpha. TaH/sub x/

    SciTech Connect

    Rosei, R.; Colavita, E.; Franciosi, A.; Weaver, J.H.; Peterson, D.T.

    1980-04-15

    Thermoreflectance studies of bulk samples of V, Nb, Ta, and ..cap alpha..-phase TaH/sub x/ are reported and the results interpreted in terms of recent band calculations. The first interband transition is identified as a transition involving the ..sigma.. band at E/sub F/. An M/sub 3/ critical-point transition is attributed to states at N. Significant changes induced by interstitial hydrogen in solid solution ..cap alpha..-TaH/sub x/ are observed and interpreted as due to hybridization and lowering of the N/sup prime//sub 1/ eigenenergy.

  1. Supporting data for senary refractory high-entropy alloy Cr x MoNbTaVW.

    PubMed

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

    2015-12-01

    This data article is related to the research paper entitled "senary refractory high-entropy alloy Cr x MoNbTaVW [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 Cr x MoNbTaVW samples; and the raw EDS scan data of the arc-melted Cr x MoNbTaVW samples are also provided.

  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. 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

  4. Assessment of relative Ti, Ta, and Nb (TITAN) enrichments in ocean island basalts

    NASA Astrophysics Data System (ADS)

    Peters, Bradley J.; Day, James M. D.

    2014-11-01

    The sensitivity of trace element concentrations to processes governing solid-melt interactions has made them valuable tools for tracing the effects of partial melting, fractional crystallization, metasomatism, and similar processes on the composition of a parental melt. Recent studies of ocean island basalts (OIB) have sought to correlate Ti, Ta, and Nb (TITAN) anomalies to isotopic tracers, such as 3He/4He and 187Os/188Os ratios, which may trace primordial deep mantle sources. A new compilation of global OIB trace element abundance data indicates that positive TITAN anomalies, though statistically pervasive features of OIB, may not be compositional features of their mantle sources. OIB show a range of Ti (Ti/Ti* = 0.28-2.35), Ta (Ta/Ta* = 0.11-93.4), and Nb (Nb/Nb* = 0.13-17.8) anomalies that show negligible correlations with 3He/4He ratios, indicating that TITAN anomalies are not derived from the less-degassed mantle source traced by high-3He/4He. Positive TITAN anomalies can be modeled using variable degrees (0.1-10%) of nonmodal batch partial melting of garnet-spinel lherzolite at temperatures and pressures considered typical for OIB petrogenesis, and subjecting this partial melt to fractional crystallization and assimilation of mid-ocean ridge basalt-like crust (AFC). Correlations of TITAN anomalies with modal abundances of olivine and clinopyroxene in porphyritic Canary Islands lavas provide empirical support for this process and indicate that high abundances of these phases in OIB may create misleading trace element anomalies on primitive mantle-normalized spider diagrams. Because partial melting and AFC are common to all mantle-derived magmas, caution should be used when attributing TITAN anomalies to direct sampling of recycled or deep mantle sources by hotspots.

  5. MRI compatible Nb-Ta-Zr alloys used for vascular stents: optimization for mechanical properties.

    PubMed

    Li, Hui-Zhe; Xu, Jian

    2014-04-01

    With the increased usage of magnetic resonance imaging (MRI) as a diagnostic tool in clinic, the currently-used metals for vascular stents, such as 316L stainless steel (SS), Co-Cr alloys and Ni-Ti alloys, are challenged by their unsatisfactory MRI compatibility, due to their constituents containing ferromagnetic elements. To provide more MRI compatible vascular stents, the Nb-xTa-2Zr (30≤x≤70) series alloys were selected in the current work. Several key properties of these alloys were optimized in terms of stent requirements, including magnetic susceptibility, elastic modulus and tensile properties. In the as-cast state, a single-phase solid solution with bcc structure was formed in the alloys. The volume magnetic susceptibility (χv) and Young's modulus (E) of the alloys scaled linearly with the Ta content. Increasing the Ta content gave rise to the decreased χv and the increased E, together with the elevated yield strength but less-changed elongation. From multiple requirements for the stents, the Nb-60Ta-2Zr alloy exhibits an optimal properties, including the χv of about 3% of the 316L SS, the E of 142GPa superior to pure niobium, high mass density of 12.03g/cm(3) favored to the X-ray visibility, yield strength of ~330MPa comparable to the 316L SS and a elongation of ~24%. These remarkable advantages make it quite promising as a new candidate of stent metals.

  6. 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. Copyright © 2015 Elsevier B.V. All rights reserved.

  7. 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.

  8. Extreme Nb/Ta fractionation in metamorphic titanite from ultrahigh-pressure metagranite

    NASA Astrophysics Data System (ADS)

    Chen, Yi-Xiang; Zheng, Yong-Fei

    2015-02-01

    Extremely high Nb/Ta ratios (up to 239) occur in metamorphic titanite from ultrahigh-pressure metagranite in the Sulu orogen. This indicates significant Nb/Ta fractionation in subduction-zone fluids. By means of U-Pb dating and trace element analysis of titanite, we distinguish the metamorphic domains from the anatectic domains. Titanite U-Pb dating yields lower intercept ages of 215 ± 12 Ma to 222 ± 27 Ma for the metagranite samples, with regardless of the compositional differences between the two types of titanite domains. This indicates the two generations of titanite growth during exhumation of deeply subducted continental crust. The metamorphic titanite shows significantly elevated Nb but decreased Ta and thus higher Nb/Ta ratios than the anatectic titanite. The increase of Nb/Ta ratios for the metamorphic titanite is associated more with a decrease of Ta than an increase of Nb, suggesting the control of fluid composition on the titanite Nb/Ta ratios. Because the metamorphic titanite grew during the exhumation of deeply subducted continental crust, its unusually high Nb/Ta ratios are ascribed to the breakdown of hydrous minerals such as phengite and biotite that host much more Nb than Ta. This implies that the composition of subduction-zone fluids is primarily dictated by the geochemical property of hydrous minerals that break down during dehydration reaction at high-pressure to ultrahigh-pressure conditions. Therefore, significant Nb/Ta fractionation in Ti-rich accessory minerals such as titanite and rutile, at least on the mineral scale, during subduction-zone processes is possibly much more common than previously thought.

  9. Evolution of planetary cores and the Earth-Moon system from Nb/Ta systematics.

    PubMed

    Münker, Carsten; Pfänder, Jörg A; Weyer, Stefan; Büchl, Anette; Kleine, Thorsten; Mezger, Klaus

    2003-07-04

    It has been assumed that Nb and Ta are not fractionated during differentiation processes on terrestrial planets and that both elements are lithophile. High-precision measurements of Nb/Ta and Zr/Hf reveal that Nb is moderately siderophile at high pressures. Nb/Ta values in the bulk silicate Earth (14.0 +/- 0.3) and the Moon (17.0 +/- 0.8) are below the chondritic ratio of 19.9 +/- 0.6, in contrast to Mars and asteroids. The lunar Nb/Ta constrains the mass fraction of impactor material in the Moon to less than 65%. Moreover, the Moon-forming impact can be linked in time with the final core-mantle equilibration on Earth 4.533 billion years ago.

  10. (Nb,Ta,Ti) 3Sn multifilamentary wires using Osprey bronze with high tin content and NbTa/NbTi composite filaments

    NASA Astrophysics Data System (ADS)

    Abächerli, V.; Uglietti, D.; Seeber, B.; Flükiger, R.

    2002-08-01

    Several (Nb,Ta,Ti) 3Sn multifilamentary wires with different Ti contents (up to 0.6 wt.%), but identical configuration have been processed using the bronze route and NbTa/NbTi composite filaments. The wires were manufactured by a sequence of three extrusion steps using a Cu 15.4 Sn Osprey bronze as matrix. The wires of 1.06 mm diameter with 14641 filaments of 4.4 μm size were reacted by various heat treatments, ranging from 600 to 730 °C. Critical current density ( Jc) measurements on samples in a coil geometry have been performed up to 17 T at 4.2 K, yielding to 195 A mm -2 at 17 T. Upper critical magnetic fields ( Bc2) up to 28.2 T were estimated by Kramer extrapolation. The variation of the critical temperature ( Tc) as well as of the n factor were determined. The effect of various Ti contents was analyzed with respect to the various superconducting parameters, especially in view of applications at fields >20 T.

  11. 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.

  12. 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.

  13. Mechanical Properties of Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20 Refractory High Entropy Alloys (Postprint)

    DTIC Science & Technology

    2011-05-01

    temper ature from 548 MPa at 1000 C to 405 MPa at 1600 C (Table 2).ublic release; distribution unlimited. Table 4 Composition (in wt.%) of Inconel 718 ...values of the refractory HEAs are much higher than those of Haynes 230 at all studied temperatures and higher than those of Inconel 718 at...than twice (for the Nb25Mo25 Ta25W25 alloy) or four times (for the V20Nb20Mo20Ta20W20 alloy) higher than for Inconel 718 or Haynes 230 at 1000 C. The

  14. Laser-deposited Ti-Nb-Zr-Ta orthopedic alloys.

    PubMed

    Banerjee, R; Nag, S; Samuel, S; Fraser, H L

    2006-08-01

    The complex quaternary Ti-35Nb-7Zr-5Ta orthopedic alloy has been successfully deposited from a powder feedstock consisting of a blend of elemental titanium, niobium, zirconium, and tantalum powders, using the laser engineered net-shaping (LENStrade mark) process. In the as laser-deposited form, these alloys exhibit a substantially higher tensile strength as compared with more conventionally processed counterparts of similar composition, while maintaining excellent ductility and a low modulus. Furthermore, the as-deposited alloys appear to exhibit a <001> texture, with a substantially large number of grains of the beta phase aligning one of their <001> axes nearly normal to the substrate or parallel to the growth direction. The microstructure of the as-deposited as well as tensile-tested alloys have been characterized in detail using scanning electron microscopy (SEM), orientation microscopy (OM), and transmission electron microscopy (TEM). Formation of a high density of shear bands, possibly arising from slip localization due to precipitates of the omega phase in the beta matrix, is clearly evident in the tensile-tested sample. The enhanced tensile strength and low modulus in these laser-deposited alloys coupled with the ability to form near-net shape components makes LENS an attractive processing technology for orthopedic implants.

  15. 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.

  16. [The electrochemical behavior of TiTa30 and TiNb30 alloys for implantology].

    PubMed

    Hildebrand, H F; Ralison, A; Traisnel, M; Breme, J

    1997-11-01

    The electrochemical behavior in artificial saliva of TiNb30 and TiTa30 alloys were compared with that of commercial pure titanium. The anodic potential, the current density, the passivation potential and the galvanic corrosion vs. Au were determined. Both alloys have a similar behavior to that of pure titanium. Crevace corrosion, which is very weak in pure Ti, is completely inhibited by the addition of Nb or Ta.

  17. Homo- and heterobimetallic niobium(v) and tantalum(v) peroxo-tartrate complexes and their use as molecular precursors for Nb-Ta mixed oxides.

    PubMed

    Bayot, Daisy; Tinant, Bernard; Devillers, Michel

    2005-03-07

    New water-soluble bimetallic peroxo-tartrato complexes of niobium(V) and/or tantalum(V) have been prepared, characterized from the structural and spectroscopic point of view, and used as molecular precursors for Nb-Ta mixed oxides. Two new homometallic complexes, (gu)5[Nb2(O2)4(tart)(Htart)] x 4H2O (1a) and (gu)6[Ta2(O2)4(tart)2] x 4H2O (2a), and the corresponding heterometallic complex, (gu)5[NbTa(O2)4(tart)(Htart)] x 4H2O (3), have been obtained. The crystal structures of the homometallic compounds, (gu)5[Nb2(O2)4(tart)(Htart)] x 6H2O x 1H2O2 (1b) and (gu)6[Ta2(O2)4(tart)2] x 6H2O (2b), have been determined, showing, for both cases, two 8-fold-coordinated metal atoms, each surrounded by oxygen atoms belonging to two bidentate peroxides, two monodentate carboxylato, and two alkoxo groups from both bridging tartrato ligands. The coordination polyhedron around each metal atom is a dodecahedron. The thermal treatment of complexes 1a, 2a, and 3 in air at 700 or 800 degrees C, depending of the Ta content, provided Nb2O5, Ta2O5, and the solid solution TaNbO5, respectively. The thermal treatment of a 1:1 Nb/Ta molar ratio mixture of 1a and 2a has also been studied. BET and SEM measurements have been carried out and reveal these oxides possess relatively high specific surface areas and display a porous character. Comparison between the use of homo- and heterometallic precursors is discussed.

  18. Low Nb/Ta in the Archean Mantle: Ancient Missing Niobium in the Silicate Earth

    NASA Astrophysics Data System (ADS)

    Jochum, K. P.; Polat, A.; Stoll, B.; Hofmann, A. W.

    2001-12-01

    Recent investigations of oceanic basalts (MORB, OIB) and samples of the continental crust show that the continental crust and the sources of MORB and OIB all have Nb/Ta ratios that are significantly lower than the CI-chondritic value of 17.4. The missing, complementary high-Nb/Ta reservoir has been suggested to exist in the form of Nb-rich, high-Nb/Ta refractory eclogites deep in the mantle (McDonough, 1991; Rudnick et al., 2000). Alternatively, Wade and Wood (2001) recently showed that at high pressure Nb may fractionate into the core, and thus no hidden reservoir would be required within the silicate portion of the Earth. To get further insight of the missing Nb in the silicate portion of the Earth and to test the two hypotheses, we used spark source and ICP mass spectrometry to investigate the geochemically very similar element pairs Nb-Ta and Zr-Hf in komatiitic basalts from 6 Archean greenstone belts. Samples include 3.8 Ga old rocks from Isua (Greenland), 3.4 Ga old rocks from the Onverwacht Group (South Africa) and the Pilbara Craton (Australia), and 2.7 Ga old rocks from the Abitibi (Canada) and the Norseman-Wiluna belts (Australia). Our results show that the mean Zr/Hf ratio of 37 for the Archean samples is identical within error limits with the values found in modern oceanic basalts and in chondritic meteorites. This means that Zr and Hf have not been fractionated in the Earth's mantle since at least 3.8 Ga and that the primitive mantle has a chondritic Zr/Hf ratio. In contrast, Nb and Ta behave differently. The mean Nb/Ta ratios are about 13 for the 3.8 Ga old samples from Isua, and 14 for the 3.4 Ga and 2.7 Ga old samples. These ratios are similar to those of MORB (15), OIB (about 15) (Jochum et al., 1997), and upper crustal material (13; Barth et al., 2000), but are significantly lower than the CI chondritic Nb/Ta of 17.4. This implies that there was no significant fractionation of Nb and Ta in the major reservoirs since 3.8 Ga, not even during

  19. 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.

  20. Synthesis and characterization of nanocrystalline Co-Fe-Nb-Ta-B alloy

    NASA Astrophysics Data System (ADS)

    Raanaei, Hossein; Fakhraee, Morteza

    2017-09-01

    In this research work, structural and magnetic evolution of Co57Fe13Nb8Ta4B18 alloy, during mechanical alloying process, have been investigated by using, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, electron dispersive X-ray spectroscopy, differential thermal analysis and also vibrating sample magnetometer. It is observed that at 120 milling time, the crystallite size reaches to about 7.8 nm. Structural analyses show that, the solid solution of the initial powder mixture occurs at160 h milling time. The coercivity behavior demonstrates a rise, up to 70 h followed by decreasing tendency up to final stage of milling process. Thermal analysis of 160 h milling time sample reveals two endothermic peaks. The characterization of annealed milled sample for 160 h milling time at 427 °C shows crystallite size growth accompanied by increasing in saturation magnetization.

  1. 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.

  2. 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

  3. 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.

  4. Corrosion behavior of niobium and Nb-25 wt% Ta alloy in sulfuric acid solutions

    SciTech Connect

    Robin, A.; Nunes, C.A. ); de Almeida, M.E. )

    1991-06-01

    In this paper the corrosion behavior of niobium and Nb-25 wt% Ta alloy in H{sub 2} SO{sub 4} solutions has been studied. Using mass-loss techniques, the influences of H{sub 2}SO{sub 4} concentration, temperature, and exposure time have been examined. The Nb-Ta alloy is more corrosion resistant than pure niobium. The obtained corrosion data allowed the construction of iso-corrosion curves of both materials in sulfuric acid below and above the boiling point.

  5. Topological surface states and Fermi arcs of the noncentrosymmetric Weyl semimetals TaAs, TaP, NbAs, and NbP

    NASA Astrophysics Data System (ADS)

    Sun, Yan; Wu, Shu-Chun; Yan, Binghai

    2015-09-01

    Very recently the topological Weyl semimetal (WSM) state was predicted in the noncentrosymmetric compounds NbP, NbAs, TaP, and TaAs and soon led to photoemission and transport experiments to verify the presumed topological properties such as Fermi arcs (unclosed Fermi surfaces) and the chiral anomaly. In this work we have performed fully ab initio calculations of the surface band structures of these four WSM materials and revealed the Fermi arcs with spin-momentum-locked spin texture. On the (001) polar surface, the shape of the Fermi surface depends sensitively on the surface terminations (cations or anions), although they exhibit the same topology with arcs. The anion (P or As) terminated surfaces are found to fit recent photoemission measurements well. Such surface potential dependence indicates that the shape of the Fermi surface can be sensitively manipulated by depositing guest species (such as K atoms), as we demonstrate. On the polar surface of a WSM without inversion symmetry, Rashba-type spin polarization naturally exists in the surface states and leads to strong spin texture. By tracing the spin polarization of the Fermi surface, one can distinguish Fermi arcs from trivial Fermi circles. The four compounds NbP, NbAs, TaP, and TaAs present an increasing amplitude of spin-orbit coupling (SOC) in band structures. By comparing their surface states, we reveal the evolution of topological Fermi arcs from the spin-degenerate Fermi circle to spin-split arcs when the SOC increases from zero to a finite value. Our work presents a comprehensive understanding of the topological surface states of WSMs, which will especially be helpful for future spin-revolved photoemission and transport experiments.

  6. Synthesis of the new layered oxides NaRbLnMO{sub 5} (Ln = La, Nd, Sm, Eu, Gd; M = Nb, Ta)

    SciTech Connect

    Cavazos, Ronaldo J.; Schak, Raymond E

    2004-07-02

    The new layered transition metal oxides NaRbLnMO{sub 5} (Ln = Nd, Sm, Eu, Gd; M = Nb, Ta) were synthesized by direct solid-state reaction. NaRbLaNbO{sub 5} crystallizes with a tetragonal unit cell [a=5.839(6) A, c=8.313(1) A] analogous to that of the related compound NaKLaNbO{sub 5}, while NaRbLaTaO{sub 5} indexes to a larger monoclinic unit cell [a=9.577(2) A, b=5.834(1) A, c=8.323(2) A, {beta}=93.00(2)]. NaRbLnNbO{sub 5} can be prepared for Ln = Nd, Sm, Eu, Gd, and NaRbLnTaO{sub 5} can be prepared for Ln = Nd, Sm. Both series of compounds show the expected decrease in unit cell volume as the size of the lanthanide decreases. NaRbLaNbO{sub 5} is also amenable to ion exchange, forming Li{sub 2-x}Rb{sub x}LaNbO{sub 5} upon reaction with molten lithium nitrate.

  7. 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.

  8. Strengthening mechanisms in Ti-Nb-Zr-Ta and Ti-Mo-Zr-Fe orthopaedic alloys.

    PubMed

    Banerjee, Rajarshi; Nag, Soumya; Stechschulte, John; Fraser, Hamish L

    2004-08-01

    The microstructural evolution and attendant strengthening mechanisms in two novel orthopaedic alloy systems, Ti-Nb-Zr-Ta and Ti-Mo-Zr-Fe, have been compared and contrasted in this paper. Specifically, the alloy compositions considered are Ti-34Nb-9Zr-8Ta and Ti-13Mo-7Zr-3Fe. In the homogenized condition, both alloys exhibited a microstructure consisting primarily of a beta matrix with grain boundary alpha precipitates and a low-volume fraction of intra-granular alpha precipitates. On ageing the homogenized alloys at 600 degrees C for 4 hr, both alloys exhibited the precipitation of refined scale secondary alpha precipitates homogeneously in the beta matrix. However, while the hardness of the Ti-Mo-Zr-Fe alloy marginally increased, that of the Ti-Nb-Zr-Ta alloy decreased substantially as a result of the ageing treatment. In order to understand this difference in the mechanical properties after ageing, TEM studies have been carried out on both alloys prior to and post the ageing treatment. The results indicate the existence of a metastable B2 ordering in the Ti-Nb-Zr-Ta alloy in the homogenized condition which is destroyed by the ageing treatment, consequently leading to a decrease in the hardness.

  9. Microstructure, mechanical behavior and biocompatibility of powder metallurgy Nb-Ti-Ta alloys as biomedical material.

    PubMed

    Liu, Jue; Chang, Lin; Liu, Hairong; Li, Yongsheng; Yang, Hailin; Ruan, Jianming

    2017-02-01

    Microstructures, mechanical properties, apatite-forming ability and in vitro experiments were studied for Nb-25Ti-xTa (x=10, 15, 20, 25, 35at.%) alloys fabricated by powder metallurgy. It is confirmed that the alloys could achieve a relative density over 80%. Meanwhile, the increase in Ta content enhances the tensile strength, elastic modulus and hardness of the as-sintered alloys. When increasing the sintering temperatures, the microstructure became more homogeneous for β phase, resulting in a decrease in the modulus and strength. Moreover, the alloys showed a good biocompatibility due to the absence of cytotoxic elements, and were suitable for apatite formation and cell adhesion. In conclusion, Nb-25Ti-xTa alloys are potentially useful in biomedical applications with their mechanical and biological properties being evaluated in this work.

  10. 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. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  11. MRI-compatible Nb-60Ta-2Zr alloy used for vascular stents: haemocompatibility and its correlation with protein adsorption.

    PubMed

    Li, Xiu-Mei; Li, Hui-Zhe; Wang, Shao-Ping; Huang, Hsun-Miao; Huang, Her-Hsiung; Ai, Hong-Jun; Xu, Jian

    2014-09-01

    Nb-60Ta-2Zr is a newly developed MRI-compatible alloy used for vascular stents. In this work, its haemocompatibility was investigated, including platelet adhesion (lactate dehydrogenase activity), platelet activation (P-selectin expression), coagulation and haemolysis. For comparison, parallel assessments for these factors were performed for the niobium, tantalum, 316L stainless steel (316L SS) and L605 Co-Cr alloy (L605). In addition, albumin and fibrinogen were selected to examine the correlation of protein adsorption with platelet adhesion and metal surface properties. The propensity for platelet adhesion and activation on the Nb-60Ta-2Zr alloy was at nearly the same level as that for Nb and Ta but was slightly less than those of 316L SS and L605. The mitigated platelet adhesion and activation of the Nb-60Ta-2Zr alloy is associated with its decreased adsorption of fibrinogen. The Nb-60Ta-2Zr alloy has a longer clotting time and exhibits significantly superior thromboresistance than 316L SS and L605. Moreover, the haemolysis rate of the Nb-60Ta-2Zr alloy satisfies the bio-safety requirement of the ISO 10993-4 standard. The favourable haemocompatiblity of the Nb-60Ta-2Zr alloy provides evidence of its good biocompatibility and of its suitability as a candidate stent material.

  12. 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.

  13. The BM5Se9 phases (B = Al, Ga, Ge, Sb, Sn; M = V, Nb, Ta): superconductors or ferromagnets?

    NASA Astrophysics Data System (ADS)

    Leblanc-Soreau, A.; Molinié, P.; Jumas, J. C.

    2004-05-01

    The dissolution of some intermetallic A15 compounds in lamellar metallic diselenides (2H-NbSe2, 2H-TaSe2 and 1T-VSe2) results in original phases. Syntheses performed in the Nb3Sn/NbSe2, Nb3Ge/NbSe2, Nb3Sn/TaSe2, V3Ga/NbSe2, Nb3Sb/NbSe2 V3Ga/VSe2 systems lead to the formation of the BM5Se9 phases ( superconductors or ferromagnets). The Tc values vary from 17.5(2) K for SnNb5Se9 to 4.5(2) K for GeNb5Se9. For the ferromagnet GaV5Se9, the ESR study shows two vanadium sites with axial symmetries. Previous results in Mössbauer and Raman studies showing the existence of B-M entities, are in agreement with the Mössbauer ones obtained on SnNb5Se9 which could be obtained without any superconducting behaviour. The comparison could be done between the 3 superconductors GaNb5Se9, SnNb5Se9, SnNb0.5Ta4.5Se9 and the 3 ferromagnets GaV5Se9, Sn0.94Ga0.05Nb4.70V0.30Se9, GaV0.15Ta4.85Se9, the presence of V probably modifies the superconducting exchanges and allows ferromagnetic couplings.

  14. Phase stability and electrical conductivity of Ca-doped LaNb 1- xTa xO 4- δ high temperature proton conductors

    NASA Astrophysics Data System (ADS)

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

    The electrical conductivity, crystal structure and phase stability of La 0.99Ca 0.01Nb 1- xTa xO 4- δ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5, δ = 0.005), a potential candidate for proton conductor for solid oxide fuel cells (SOFCs), have been investigated using AC impedance technique and in situ X-ray powder diffraction. Partially substituting Nb with Ta elevates the phase transition temperature (from a monoclinic to a tetragonal structure) from ∼520 °C for x = 0 to above 800 °C for x = 0.4. AC conductivity of the La 0.99Ca 0.01Nb 1- xTa xO 4- δ both in dry and wet air decreased slightly with increasing Ta content above 750 °C, while below 500 °C, it decreased by nearly one order of magnitude for x = 0.4. It was also determined that the activation energy for the total conductivity increases with increasing Ta content from 0.50 eV (x = 0) to 0.58 eV (x = 0.3) for the tetragonal phase, while it decreases with increasing Ta content from 1.18 eV (x = 0) to 1.08 eV (x = 0.4) for the monoclinic phase. By removing the detrimental structural phase transition from the intermediate-temperature range, consequently avoiding the severe thermal expansion problem up to 800 °C, partial substitution of Nb with Ta brings this class of material closer to its application in electrode-supported thin-film intermediate-temperature SOFCs.

  15. Microstructure and Room Temperature Properties of a High-Entropy TaNbHfZrTi Alloy (Preprint)

    DTIC Science & Technology

    2011-07-01

    AFRL-RX-WP-TP-2011-4292 MICROSTRUCTURE AND ROOM TEMPERATURE PROPERTIES OF A HIGH-ENTROPY TaNbHfZrTi ALLOY (PREPRINT) O.N. Senkov, J.M...TEMPERATURE PROPERTIES OF A HIGH- ENTROPY TaNbHfZrTi ALLOY (PREPRINT) 5a. CONTRACT NUMBER In-house 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER...article submitted to the Journal of Alloys and Compounds. 14. ABSTRACT A refractory alloy , Ta20Nb20Hf20Zr20Ti20, was produced by vacuum arc-melting

  16. Purification of (NB/sub 1-x/TA/sub x/)/sub 2/O/sub 5/

    SciTech Connect

    Pastor, R.C.; Gorre, L.E.

    1988-07-12

    A process for purifying compounds of the form (Nb/sub 1-x/Ta/sub x/)/sub 2/O/sub 5/, where x ranges from 0 to 1 is described, comprising the steps of: furnishing the (Nb/sub 1-x/Ta/sub x/)/sub 2/O/sub 5/ in a finely divided form; contacting a liquid extraction phase containing a source of halide ions, and separating the liquid extraction phase and the reacted impurities contained therein from the finely divided (Nb/sub 1-x/Ta/sub x/)/sub 2/O/sub 5/.

  17. Thermal Stability and Humidity Resistance of ScTaO4 Modified (K0.5Na0.5)NbO3 Ceramics

    NASA Astrophysics Data System (ADS)

    Zheng, Li-Mei; Wang, Jin-Feng; Wang, Chun-Ming; Wu, Qing-Zao; Zang, Guo-Zhong

    2009-12-01

    Lead-free (Na0.5K0.5)NbO3-xmol% ScTaO4 (x = 0-1.5) ceramics are prepared using the conventional solid-state reaction method and their properties are investigated in detail. The results indicate that the piezoelectric properties and density are improved by the introduction of ScTaO4. Due to the high orthorhombic-tetragonal phase transition temperature TO-T (around 200° C), stable piezoelectric properties against temperature are obtained. In a wide temperature range of 15-160° C, kp of the (Na0.5K0.5)NbO3-0.5 mol% ScTaO4 ceramic remains almost unchanged and d31 increases slightly from 59 pC/N to 71 pC/N. The deliquescent problem is effectively solved by the addition of ScTaO4. The piezoelectric properties of ScTaO4 modified (Na0.5K0.5)NbO3 ceramics show no obvious reduction and dielectric loss increases slightly after 120 h of immersion. From the analysis, it is suggested that the density is an important factor that improves the humidity resistance of the specimens.

  18. Fabrication, characterization and in vitro biocompatibility evaluation of porous Ta-Nb alloy for bone tissue engineering.

    PubMed

    Wang, Huifeng; Li, Jing; Yang, Hailin; Liu, Chao; Ruan, Jianming

    2014-07-01

    Porous Ta-Nb alloys were fabricated using the sponge impregnation technique and the powder metallurgy technique (P/M) in combination. All porous Ta-Nb alloys displayed interconnected open cell structures with porosities around 64% and pore sizes in the range of 300-500 μm. No carbide, oxide, or intermetallic-related phases were detected by the X-ray diffraction (XRD). Porous Ta-Nb alloys displayed sintering neck growth, smoother surface of the particles and more shrinkage of the micropores, with Nb contents increasing from 5% to 15%. The compressive strength and Young's modulus of the Ta-Nb alloys agreed well with the requirements of trabecular bone. The normalized compressive plateau stress and Young's modulus increased from 52.27 MPa to 85.43 MPa and from 1.850 GPa to 2.540 GPa, respectively, with Nb contents increasing from 5% to 15%. Porous Ta-Nb alloys had no cytotoxicity and possessed the excellent biocompatibility similar to porous Ta scaffolds. Copyright © 2014 Elsevier B.V. All rights reserved.

  19. Senary refractory high-entropy alloy HfNbTaTiVZr

    SciTech Connect

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

    2015-09-03

    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. Here, 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.

  20. Senary refractory high-entropy alloy HfNbTaTiVZr

    DOE PAGES

    Gao, Michael C.; Zhang, B.; Yang, S.; ...

    2015-09-03

    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. Here, 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 bymore » both simulation and experimental results, the HEA formation rules are discussed.« less

  1. Raman scattering efficiency in LiTaO3 and LiNbO3 crystals

    NASA Astrophysics Data System (ADS)

    Sanna, S.; Neufeld, S.; Rüsing, M.; Berth, G.; Zrenner, A.; Schmidt, W. G.

    2015-06-01

    LiTaO3 and LiNbO3 crystals are investigated here in a combined experimental and theoretical study that uses Raman spectroscopy in a complete set of scattering geometries and corresponding density-functional theory calculations to provide microscopic information on their vibrational properties. The Raman scattering efficiency is computed from first principles in order to univocally assign the measured Raman peaks to the calculated eigenvectors. Measured and calculated Raman spectra are shown to be in qualitative agreement and confirm the mode assignment by Margueron et al. [J. Appl. Phys. 111, 104105 (2012), 10.1063/1.4716001], thus finally settling a long debate. While the two crystals show rather similar vibrational properties overall, the E-TO9 mode is markedly different in the two oxides. The deviations are explained by a different anion-cation bond type in LiTaO3 and LiNbO3 crystals.

  2. 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.

  3. Atomic layer deposition of (K,Na)(Nb,Ta)O{sub 3} thin films

    SciTech Connect

    Sønsteby, Henrik Hovde Nilsen, Ola; Fjellvåg, Helmer

    2016-07-15

    Thin films of complex alkali oxides are frequently investigated due to the large range of electric effects that are found in this class of materials. Their piezo- and ferroelectric properties also place them as sustainable lead free alternatives in optoelectronic devices. Fully gas-based routes for deposition of such compounds are required for integration into microelectronic devices that need conformal thin films with high control of thickness- and composition. The authors here present a route for deposition of materials in the (K,Na)(Nb,Ta)O{sub 3}-system, including the four end members NaNbO{sub 3}, KNbO{sub 3}, NaTaO{sub 3}, and KTaO{sub 3}, using atomic layer deposition with emphasis on control of stoichiometry in such mixed quaternary and quinary compunds.

  4. Synthesis and characterisation of the uranium pyrochlore betafite [(Ca,U)₂(Ti,Nb,Ta)₂O₇].

    PubMed

    McMaster, Scott A; Ram, Rahul; Charalambous, Fiona; Pownceby, Mark I; Tardio, James; Bhargava, Suresh K

    2014-09-15

    Betafite of composition [(Ca,U)2(Ti,Nb,Ta)2O7] was prepared via a solid state synthesis route. The synthesis was shown to be sensitive to initial reactant ratios, the atmosphere used (oxidising, neutral, reducing) and time. The optimum conditions for the synthesis of betafite were found to be heating the reactants required at 1150°C for 48 h under an inert gas atmosphere. XRD characterisation revealed that the synthesised betafite contained minor impurities. EPMA analysis of a sectioned surface showed very small regions of Ca-free betafite on grain boundaries as well as minor rutile impurities. Some heterogeneity between the Nb:Ta ratio was observed by quantitative EPMA but was generally within the nomenclature requirements stated for betafite. SEM analysis revealed the synthesised betafite was comprised mostly of hexaoctohedral crystals of ∼ 3 μm in diameter. XPS analysis of the sample showed that the uranium in the synthesised betafite was predominately present in the U(5+) oxidation state. A minor amount of U(6+) was also detected which was possibly due to surface oxidation. Copyright © 2014 Elsevier B.V. All rights reserved.

  5. 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.

  6. Direct Metal Deposition of Refractory High Entropy Alloy MoNbTaW

    NASA Astrophysics Data System (ADS)

    Dobbelstein, Henrik; Thiele, Magnus; Gurevich, Evgeny L.; George, Easo P.; Ostendorf, Andreas

    Alloying of refractory high entropy alloys (HEAs) such as MoNbTaW is usually done by vacuum arc melting (VAM) or powder metallurgy (PM) due to the high melting points of the elements. Machining to produce the final shape of parts is often needed after the PM process. Casting processes, which are often used for aerospace components (turbine blades, vanes), are not possible. Direct metal deposition (DMD) is an additive manufacturing technique used for the refurbishment of superalloy components, but generating these components from the bottom up is also of current research interest. MoNbTaW possesses high yield strength at high temperatures and could be an alternative to state-of-the-art materials. In this study, DMD of an equimolar mixture of elemental powders was performed with a pulsed Nd:YAG laser. Single wall structures were built, deposition strategies developed and the microstructure of MoNbTaW was analyzed by back scattered electrons (BSE) and energy dispersive X-ray (EDX) spectroscopy in a scanning electron microscope. DMD enables the generation of composition gradients by using dynamic powder mixing instead of pre-alloyed powders. However, the simultaneous handling of several elemental or pre-alloyed powders brings new challenges to the deposition process. The influence of thermal properties, melting point and vapor pressure on the deposition process and chemical composition will be discussed.

  7. Upper critical fields of periodic and quasiperiodic Nb-Ta superlattices

    SciTech Connect

    Cohn, J.L.; Lin, J.J.; Lamelas, F.J.; He, H.; Clarke, R.; Uher, C.

    1988-08-01

    Upper critical fields have been studied for two series of Nb-Ta superlattices grown by molecular-beam epitaxy with both periodic and quasiperiodic (Fibonacci sequence) layering. X-ray results are presented to characterize the nature and quality of the layering. Positive curvature in the perpendicular upper critical field (H/sub c//sub 2//sub perpendicular/), pronounced negative curvature near T/sub c/ in the parallel upper critical field (H/sub c//sub 2//sub X/), and dimensional crossover are observed in both types of samples. For quasiperiodic samples two upturns are observed in H/sub c//sub 2//sub X/ with decreasing temperature. These are shown to be associated with dimensional crossover occurring twice as the superconducting coherence length in the growth direction, xi/sub perpendicular/, samples the two length scales, 2d/sub Nb/ and d/sub Nb/, that are present in these structures.

  8. Upper critical fields of periodic and quasiperiodic Nb-Ta superlattices

    NASA Astrophysics Data System (ADS)

    Cohn, J. L.; Lin, J. J.; Lamelas, F. J.; He, H.; Clarke, R.; Uher, C.

    1988-08-01

    Upper critical fields have been studied for two series of Nb-Ta superlattices grown by molecular-beam epitaxy with both periodic and quasiperiodic (Fibonacci sequence) layering. X-ray results are presented to characterize the nature and quality of the layering. Positive curvature in the perpendicular upper critical field (Hc2⊥), pronounced negative curvature near Tc in the parallel upper critical field (Hc2), and dimensional crossover are observed in both types of samples. For quasiperiodic samples two upturns are observed in Hc2 with decreasing temperature. These are shown to be associated with dimensional crossover occurring twice as the superconducting coherence length in the growth direction, ξ⊥, samples the two length scales, 2dNb and dNb, that are present in these structures.

  9. 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. Copyright © 2015 Elsevier B.V. All rights reserved.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  11. 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.

  12. 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.

  13. 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

  14. Electric-field-controlled optical switch using Kerr effect and gradient of the composition ratio Nb/(Ta + Nb)

    SciTech Connect

    Gong, Dewei; Liang, Yonggan; Ou, Wenjing; Wang, Jianjun; Wu, You; Liu, Bing; Zhou, Zhongxiang

    2016-03-15

    Highlights: • An abnormal laser deflection phenomenon in KTN crystals is demonstrated. • The origin of the deflection phenomenon was discussed in detail. • By exploiting the deflection, we have designed an optical switch. • The g{sub 11}/g{sub 12} ratio (>10), wavelength range(491–1064 nm), and I–V characteristics (0–800 V) were studied. • The extinction ratio (0–1) and influence of the photorefractive effect were studied. - Abstract: By exploiting the Kerr effect and the gradient of the composition ratio m, Nb/(Ta + Nb) in mol%, in KTa{sub 1−x}Nb{sub x}O{sub 3} (KTN) crystals, we have designed an electric-field-controlled optical switch. The operating principle of the switch is described. During the switching process, the incident linearly polarized beam is orthogonally deflected as it propagates through the crystals. The g{sub 11}/g{sub 12} ratio (>10), wavelength range (491–1064 nm), I–V characteristics (0–800 V), extinction ratio (0–1), gradient of Curie temperature (21–22.9 °C), response time that may be in ns order, and influence of the photorefractive effect were studied. The results show that our design provides a new kind of optical switch with macro scale (mm order), adjustable extinction ratio (0–1), wide wavelength range (491–1064 nm).

  15. Displacement of Ta-O bonds near polymorphic phase transition in Li-, Ta-, and Sb-modified (K, Na)NbO3 ceramics

    NASA Astrophysics Data System (ADS)

    Huan, Yu; Wang, Xiaohui; Li, Longtu

    2014-06-01

    Excellent piezoelectric properties can be obtained near the polymorphic phase transition (PPT) region in (K, Na)NbO3 based piezoceramics. The enhanced piezoelectric properties resulted from the 18-fold spontaneous polarization directions caused by the coexistence of orthorhombic and tetragonal phases. In this study, the various polarization directions derived from frequently changing Ta-O bonds in Li-, Ta-, and Sb-modified (K, Na)NbO3 ceramic were directly observed by extended X-ray absorption fine structure. More than three peaks were observed and represented the nearest neighbor Ta-O bonds because of the coexistence of tetragonal and orthorhombic phases as well as Ta displacements along the [001]c and [110]c directions. Hence, the domains rotated easily and responded actively to an external electric or force field. Large Pr and optimized piezoelectric properties were obtained near the PPT region.

  16. Effect of electron count and chemical complexity in the Ta-Nb-Hf-Zr-Ti high-entropy alloy superconductor

    PubMed Central

    von Rohr, Fabian; Winiarski, Michał J.; Tao, Jing; Klimczuk, Tomasz; Cava, Robert Joseph

    2016-01-01

    High-entropy alloys are made from random mixtures of principal elements on simple lattices, stabilized by a high mixing entropy. The recently discovered body-centered cubic (BCC) Ta-Nb-Hf-Zr-Ti high-entropy alloy superconductor appears to display properties of both simple crystalline intermetallics and amorphous materials; e.g., it has a well-defined superconducting transition along with an exceptional robustness against disorder. Here we show that the valence electron count dependence of the superconducting transition temperature in the high-entropy alloy falls between those of analogous simple solid solutions and amorphous materials and test the effect of alloy complexity on the superconductivity. We propose high-entropy alloys as excellent intermediate systems for studying superconductivity as it evolves between crystalline and amorphous materials. PMID:27803330

  17. Effect of electron count and chemical complexity in the Ta-Nb-Hf-Zr-Ti high-entropy alloy superconductor

    NASA Astrophysics Data System (ADS)

    von Rohr, Fabian; Winiarski, Michał J.; Tao, Jing; Klimczuk, Tomasz; Cava, Robert Joseph

    2016-11-01

    High-entropy alloys are made from random mixtures of principal elements on simple lattices, stabilized by a high mixing entropy. The recently discovered body-centered cubic (BCC) Ta-Nb-Hf-Zr-Ti high-entropy alloy superconductor appears to display properties of both simple crystalline intermetallics and amorphous materials; e.g., it has a well-defined superconducting transition along with an exceptional robustness against disorder. Here we show that the valence electron count dependence of the superconducting transition temperature in the high-entropy alloy falls between those of analogous simple solid solutions and amorphous materials and test the effect of alloy complexity on the superconductivity. We propose high-entropy alloys as excellent intermediate systems for studying superconductivity as it evolves between crystalline and amorphous materials.

  18. Effect of electron count and chemical complexity in the Ta-Nb-Hf-Zr-Ti high-entropy alloy superconductor.

    PubMed

    von Rohr, Fabian; Winiarski, Michał J; Tao, Jing; Klimczuk, Tomasz; Cava, Robert Joseph

    2016-11-15

    High-entropy alloys are made from random mixtures of principal elements on simple lattices, stabilized by a high mixing entropy. The recently discovered body-centered cubic (BCC) Ta-Nb-Hf-Zr-Ti high-entropy alloy superconductor appears to display properties of both simple crystalline intermetallics and amorphous materials; e.g., it has a well-defined superconducting transition along with an exceptional robustness against disorder. Here we show that the valence electron count dependence of the superconducting transition temperature in the high-entropy alloy falls between those of analogous simple solid solutions and amorphous materials and test the effect of alloy complexity on the superconductivity. We propose high-entropy alloys as excellent intermediate systems for studying superconductivity as it evolves between crystalline and amorphous materials.

  19. Effect of electron count and chemical complexity in the Ta-Nb-Hf-Zr-Ti high-entropy alloy superconductor

    DOE PAGES

    von Rohr, Fabian; Winiarski, Michał J.; Tao, Jing; ...

    2016-11-01

    High-entropy alloys are made from random mixtures of principal elements on simple lattices, stabilized by a high mixing entropy. The recently discovered body-centered cubic (BCC) Ta-Nb-Hf-Zr-Ti high-entropy alloy superconductor appears to display properties of both simple crystalline intermetallics and amorphous materials; e.g., it has a well-defined superconducting transition along with an exceptional robustness against disorder. Here we show that the valence electron count dependence of the superconducting transition temperature in the high-entropy alloy falls between those of analogous simple solid solutions and amorphous materials and test the effect of alloy complexity on the superconductivity. We propose high-entropy alloys as excellentmore » intermediate systems for studying superconductivity as it evolves between crystalline and amorphous materials.« less

  20. The electrical properties and relaxation behavior of AgNb1/2Ta1/2O3 ceramic

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

    Polycrystalline AgNb1/2Ta1/2O3 powder was prepared by solid state reaction method. Preliminary x-ray diffractogram analysis of some aspects of crystal structure showed that a single phase compound formed exhibiting a monoclinic system. Impedance spectroscopy showed the presence of both bulk and grain boundary effects in the material. The relaxation behavior was studied by fitting electric modulus with Bergman function confirms us the existence of non-Debye type of relaxation the material. The ac conductivity spectrum obeyed Funke's double power law and fitting in results, the hopping parameters n1,n2 were indicating the existence of small and large range polaron hopping in the material. The band gap of the material 3.02 eV measured by using UV visible spectroscopy.

  1. 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

  2. Investigations into Ti-(Nb,Ta)-Fe alloys for biomedical applications.

    PubMed

    Biesiekierski, Arne; Lin, Jixing; Li, Yuncang; Ping, Dehai; Yamabe-Mitarai, Yoko; Wen, Cuie

    2016-03-01

    In this study, a Ti-(Ta,Nb)-Fe system was investigated with aims toward the development of high strength, biocompatible titanium alloy suitable for the development of porous orthopedic biomaterials with minimal processing. Notable findings include yield strengths of 740, 1250 and 1360 MPa for the Ti-12Nb-5Fe, Ti-7Ta-5Fe and Ti-10Ta-4Fe alloys, respectively, with elastic moduli comparable to existing Ti-alloys, yielding admissible strains of 0.9 ± 0.3, 1.2 ± 0.2 and 1.13 ± 0.02% for the Ti-12Nb-5Fe, Ti-7Ta-5Fe and Ti-10Ta-4Fe alloys, respectively; more than twice that of human bone. Observed microstructure varied significantly depending on alloy; near pure β-phase was seen in Ti-12Nb-5Fe, β with some ω precipitation in Ti-10Ta-4Fe, and a duplex α+β structure was observed throughout the Ti-7Ta-5Fe. In addition to suitable mechanical parameters, all investigated alloys exhibited promising corrosion potentials on the order of -0.24 V SCE, equalling that seen for a C.P.-Ti control at -0.25V SCE, and substantially more noble than that seen for Ti-6Al-4V. Electrochemical corrosion rates of 0.5-3 μm/year were likewise seen to agree well with that measured for C.P.-Ti. Further, no statistically significant difference could be seen between any of the alloys relative to a C.P.-Ti control regards to cell proliferation, as investigated via MTS assay and confocal microscopy. As such, the combination of high admissible strain and low corrosion indicate all investigated alloys show significant promise as potential porous biomaterials while in the as-cast state, with the Ti-10Ta-4Fe alloy identified as the most promising composition investigated. The findings of this paper are of significance to the field of metallic biomaterials as they detail the development of alloys of satisfactory biocompatibility and electrochemical behaviour, that furthermore display exceptional mechanical properties. Notably, both extremely high compressive yield strengths and admissible strains

  3. Existence of topological nontrivial surface states in strained transition metals: W, Ta, Mo, and Nb

    NASA Astrophysics Data System (ADS)

    Thonig, Danny; Rauch, Tomáš; Mirhosseini, Hossein; Henk, Jürgen; Mertig, Ingrid; Wortelen, Henry; Engelkamp, Bernd; Schmidt, Anke B.; Donath, Markus

    2016-10-01

    We show that a series of transition metals with strained body-centered cubic lattice—W, Ta, Nb, and Mo—hosts surface states that are topologically protected by mirror symmetry and, thus, exhibits nonzero topological invariants. These findings extend the class of topologically nontrivial systems by topological crystalline transition metals. The investigation is based on calculations of the electronic structures and of topological invariants. The signatures of a Dirac-type surface state in W(110), e.g., the linear dispersion and the spin texture, are verified. To further support our prediction, we investigate Ta(110) both theoretically and experimentally by spin-resolved inverse photoemission: unoccupied topologically nontrivial surface states are observed.

  4. Microstructure and Elevated Temperature Properties of a Refractory TaNbHfZrTi Alloy

    DTIC Science & Technology

    2012-01-24

    Compression properties of a refractory multicomponent alloy, Ta20Nb20Hf20Zr20Ti20, were determined in the temperature range of 296-1473 K and strain rate range of 10(-1)-10(-5)s(-1). The properties were correlated with the microstructure developed during compression testing. The alloy was produced by vacuum arc melting, and it was hot isostatically pressed (HIPd) and homogenized at 1473 K for 24 h prior to testing. It had a single-phase body-centered cubic structure with the

  5. Long Periodic Helimagnetic Ordering in CrM 3S6 (M = Nb and Ta)

    NASA Astrophysics Data System (ADS)

    Kousaka, Y.; Ogura, T.; Zhang, J.; Miao, P.; Lee, S.; Torii, S.; Kamiyama, T.; Campo, J.; Inoue, K.; Akimitsu, J.

    2016-09-01

    We report long periodic chiral helimagnetic orderings in ferromagnetic inorganic compounds CrM 3S6 (M = Nb and Ta) with a chiral space group of P6322. Magnetization in polycrystalline samples and high resolution powder neutron diffraction were measured. Our powder neutron diffraction measurements in CrM 3S6 successfully separated nuclear and magnetic satellite peaks, having the period of hundreds of angstroms along the c— axis. Therefore, we propose that the magnetic ordering in ferromagnetic CrM3S6 is not ferromagnetic, but long periodic chiral helimagnetic ordering.

  6. Competing interactions in metallic superlattices. [Cu/Nb; Mo/Ta

    SciTech Connect

    Falco, C.M.; Makous, J.L.; Bell, J.A.; Bennett, W.R.; Zanoni, R.; Stegeman, G.I.; Seaton, C.T.

    1987-01-01

    Metallic superlattices provide an excellent system to study in a controlled manner a variety of physical phenomena, including superconductivity, magnetism, and electrical transport properties. As will be discussed in this paper, changes in certain of these properties as a function of superlattice modulation wavelength ..lambda.. are found to be correlated with structural changes and elastic property anomalies. The propeties of two particular metallic superlattices, Cu/Nb and Mo/Ta, are discussed in this paper, as examples of how competing interactions manifest themselves in the physical properties of these superlattices. 15 refs., 3 figs.

  7. Surface phonons of the superconducting materials NbC(100) and TaC(100)

    SciTech Connect

    Oshima, C.; Souda, R.; Aono, M.; Otani, S.; Ishizawa, Y.

    1986-01-20

    The dispersion curves of both the optical and acoustical surface phonons in the superconducting compounds NbC(100) and TaC(100) have been determined over the entire Brillouin zone of the Gamma-bar-M-bar symmetry axis by use of angle-resolved high-resolution electron-energy-loss spectroscopy. In contrast to the bulk phonon, no anomalies (dip) due to the electron-phonon coupling in the dispersion curves of the longitudinal phonon have been found at these surfaces. Conversely, the in-plane force constant between carbon and metal atoms is strongly enhanced there.

  8. The bone tissue compatibility of a new Ti35Nb2Ta3Zr alloy with a low Young's modulus.

    PubMed

    Guo, Yongyuan; Chen, Desheng; Cheng, Mengqi; Lu, Weijie; Wang, Liqiang; Zhang, Xianlong

    2013-03-01

    Titanium (Ti) alloys of the β-type are highly attractive metallic materials for biomedical applications due to their low elastic modulus, high corrosion resistance and notable biocompatibility. A new β-type Ti35Nb2Ta3Zr alloy with a low Young's modulus of approximately 48 GPa was previously fabricated. In the present study, the biocompatibility of this alloy was evaluated. In an in vitro assay, the Ti35Nb2Ta3Zr alloy did not markedly affect the adhesion of MG63 osteoblast cells, but it increased their proliferation, alkaline phosphatase (ALP) activity, calcium deposition and mRNA expression of osteogenic genes (i.e., ALP, osteocalcin, osteopontin). In an in vivo study, no marked histological differences were observed between the new bone formed on the surface of Ti35Nb2Ta3Zr and that formed on the surface of control Ti6Al4V rods placed in the medullary canal of rabbit femurs. Additionally, no significant differences were observed in the failure load of Ti35Nb2Ta3Zr and Ti6Al4V in pull-out tests. In conclusion, the Ti35Nb2Ta3Zr alloy with a lower elastic modulus closer to that of human bone has significant bone tissue compatibility equal to that of Ti6Al4V, which has been widely used in orthopedic applications.

  9. 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.

  10. 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.

  11. CO2 reduction over NaNbO3 and NaTaO3 perovskite photocatalysts.

    PubMed

    Fresno, F; Jana, P; Reñones, P; Coronado, J M; Serrano, D P; de la Peña O'Shea, V A

    2017-01-18

    The activity of NaNbO3 and NaTaO3 perovskites for the photocatalytic reduction of CO2 is studied in this work. For this purpose, sodium niobate and tantalate have been prepared using solid-state reactions, extensively characterised by means of powder X-ray diffraction, UV-vis, photoluminescence and Raman spectroscopies and N2 adsorption isotherms, and tested in the gas-phase reduction of CO2 under UV light in a continuous flow photoreactor. NaNbO3 is constituted of an orthorhombically distorted perovskite structure, while a ca. 4.5 : 1 combination of the orthorhombic and monoclinic modifications is found in the tantalate. Both catalysts exhibit interesting intrinsic activities, with the tantalate material giving rise to a slightly higher performance. This is attributed to a compromise situation between electron-hole recombination and the reducing potential of conduction band electrons. In addition, a decrease in the competition of water protons for photogenerated electrons is observed with both catalysts with respect to TiO2.

  12. Columbite solubility in granitic melts: consequences for the enrichment and fractionation of Nb and Ta in the Earth's crust

    NASA Astrophysics Data System (ADS)

    Linnen, Robert L.; Keppler, Hans

    The behaviour of niobium and tantalum in magmatic processes has been investigated by conducting MnNb2O6 and MnTa2O6 solubility experiments in nominally dry to water-saturated peralkaline (aluminium saturation index, A.S.I. 0.64) to peraluminous (A.S.I. 1.22) granitic melts at 800 to 1035°C and 800 to 5000 bars. The attainment of equilibrium is demonstrated by the concurrence of the solubility products from dissolution, crystallization, Mn-doped and Nb- or Ta-doped experiments at the same pressure and temperature. The solubility products of MnNb2O6 (KspNb) and MnTa2O6 (KspTa) at 800°C and 2 kbar both increase dramatically with alkali contents in water-saturated peralkaline melts. They range from 1.2×10-4 and 2.6×10-4 mol2/kg2, respectively, in subaluminous melt (A.S.I. 1.02) to 202×10-4 and 255×10-4 mol2/kg2, respectively, in peralkaline melt (A.S.I. 0.64). This increase from the subaluminous composition can be explained by five non-bridging oxygens being required for each excess atom of Nb5+ or Ta5+ that is dissolved into the melt. The KspNb and KspTa also increase weakly with Al content in peraluminous melts, ranging up to 1.7×10-4 and 4.6×10-4 mol2/kg2, respectively, in the A.S.I. 1.22 composition. Columbite-tantalite solubilities in subaluminous and peraluminous melts (A.S.I. 1.02 and 1.22) are strongly temperature dependent, increasing by a factor of 10 to 20 from 800 to 1035°C. By contrast columbite-tantalite solubility in the peralkaline composition (A.S.I. 0.64) is only weakly temperature dependent, increasing by a factor of less than 3 over the same temperature range. Similarly, KspNb and KspTa increase by more than two orders of magnitude with the first 3 wt% H2O added to the A.S.I. 1.02 and 1.22 compositions, whereas there is no detectable change in solubility for the A.S.I. 0.64 composition over the same range of water contents. Solubilities are only slightly dependent on pressure over the range 800 to 5000 bars. The data for water-saturated sub

  13. The structural and electronic properties of cubic AgMO{sub 3} (M=Nb, Ta) by first principles calculations

    SciTech Connect

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

    2016-05-06

    We report the electronic structure of the AgMO{sub 3}(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)O{sub 3} 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.

  14. 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.

  15. 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.

  16. 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.

  17. Laser deposition and deformation behavior of Ti-Nb-Zr-Ta alloys for orthopedic implants.

    PubMed

    Nag, S; Banerjee, R

    2012-12-01

    Microstructure and mechanical properties of laser deposited complex quaternary Ti-34Nb-7Zr-7Ta (all wt%), an orthopedic load-bearing implant alloy, has been investigated in detail in both as-deposited as well as heat-treated (β-solutionized and quenched) conditions. The difference in stress-strain behavior of this alloy in the above conditions has been characterized using scanning electron microscopy (SEM), orientation imaging microscopy (OIM™) and transmission electron microscopy (TEM). Compared to the sample in heat-treated condition, the as-deposited sample showed evidence of strong growth related texture. Again in the as-deposited post tensile-tested condition formation of a high density of shear bands, possibly arising from slip localization due to shearing of ω precipitates in the β matrix is observed. TEM investigations also show the presence of lenticular shaped deformation induced ω phase within the shear bands. In contrast, in case of the β-solutionized sample, twinning and the formation of stress-induced plates appears to be the primary mode of deformation. The change in deformation mechanism and thus the tensile property of this alloy could be attributed to the crystallographic texture along the growth direction as well as diffusion mediated isothermal ω precipitates, that cause an enrichment of Nb and Ta in the β matrix, during the laser-deposition process. This is no longer present after the solutionizing treatment. Copyright © 2012 Elsevier Ltd. All rights reserved.

  18. Texture Evolution in a Ti-Ta-Nb Alloy Processed by Severe Plastic Deformation

    NASA Astrophysics Data System (ADS)

    Cojocaru, Vasile-Danut; Raducanu, Doina; Gloriant, Thierry; Cinca, Ion

    2012-05-01

    Titanium alloys are extensively used in a variety of applications because of their good mechanical properties, high biocompatibility, and corrosion resistance. Recently, β-type Ti alloys containing Ta and Nb have received much attention because they feature not only high specific strength but also biocorrosion resistance, no allergic problems, and biocompatibility. A Ti-25Ta-25Nb β-type titanium alloy was subjected to severe plastic deformation (SPD) processing by accumulative roll bonding and investigated with the aim to observe the texture developed during SPD processing. Texture data expressed by pole figures, inverse pole figures, and orientation distribution functions for the (110), (200), and (211) β-Ti peaks were obtained by XRD investigations. The results showed that it is possible to obtain high-intensity share texture modes ({001}<110>) and well-developed α and γ-fibers; the most important fiber is the α-fiber ({001} < {1bar{1}0} > to {114} < {1bar{1}0} > to {112} < {1bar{1}0} > ). High-intensity texture along certain crystallographic directions represents a way to obtain materials with high anisotropic properties.

  19. 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.

  20. 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.

  1. 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.

  2. Temperature independent Seebeck coefficient through quantum confinement modulation in amorphous Nb-O/Ni-Ta-O multilayers

    NASA Astrophysics Data System (ADS)

    Music, Denis; Hunold, Oliver; Coultas, Sarah; Roberts, Adam

    2017-05-01

    Employing a correlative experimental and theoretical methodology, we have investigated amorphous monoxide Nb-O/Ni-Ta-O multilayers. It is feasible to obtain a temperature independent Seebeck coefficient up to 500 °C for these metallic-like conductors, attaining -25 μV K-1. While Nb and Ta strongly interact with O, Ni experiences the metallic and monoxide-like bonding. We observe a 3 eV wide region below the Fermi level convoluted through several first nearest neighbor Ni - Ni and second nearest neighbor Nb - Nb interactions resulting in many confined states. It can be proposed that by increasing temperature these modulated quantum states gradually become thermally accessible eradicating the temperature dependence of the Seebeck coefficient.

  3. Microstructure and Room Temperature Properties of a High-Entropy TaNbHfZrTi Alloy (Postprint)

    DTIC Science & Technology

    2014-04-01

    AND ROOM TEMPERATURE PROPERTIES OF A HIGH - ENTROPY TaNbHfZrTi ALLOY (POSTPRINT) 5a. CONTRACT NUMBER In-house 5b. GRANT NUMBER 5c. PROGRAM...is worth noting that, among all other high entropy alloys with the BCC structure produced so far, the Ta20Nb20Hf20Zr20Ti20 alloy has the highest RT...concentration of the matrix element (solvent) exceeds 60–70%, and these mechanisms may not be applicable to high - entropy alloys , where all elements are at

  4. 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

  5. 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.

  6. 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. Copyright © 2012 Elsevier Ltd. All rights reserved.

  7. 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

  8. 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.

  9. Microwave Dielectric Characteristics of ZnTa1.7Nb0.3O6 Ceramics

    NASA Astrophysics Data System (ADS)

    Cheng, Chien-Min; Chen, Ying-Chung; Yang, Cheng-Fu; Meen, Teen-Hang

    2003-11-01

    ZnTa2O6 ceramic sintered at 1300°C exhibits the microwave dielectric characteristics of dielectric constant \\varepsilonr{=}36.1, quality value Q× f{=}60180 GHz, temperature coefficient of resonant frequency τf{=}9.31 ppm/°C, and density d{=}8.184 g/cm3, and 1200°C-sintered ZnNb2O6 ceramic shows the microwave dielectric characteristics of \\varepsilonr{=}23.9, Q× f{=}77270 GHz, τf{=}-58.2 ppm/°C, and d{=}5.436 g/cm3. An empirical model is used to predict that τf{=}0 ppm/°C in ZnTa1.72Nb0.28O6. Therefore, ZnTa1.7Nb0.3O6 is adopted as the main composition for developing dielectric resonators with τf values close to 0 ppm/°C, and its sintering and microwave dielectric characteristics are investigated in this study. As the sintering temperature increases, the \\varepsilonr, Q× f, and τf values of ZnTa1.7Nb0.3O6 ceramics increase and they saturate in 1300°C-sintered ceramics.

  10. 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)

  11. Diffusion of oxygen in amorphous Al2O3, Ta2O5, and Nb2O5

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    The self-diffusivity of oxygen in amorphous Al2O3 (a-Al2O3), a-Ta2O5, and a-Nb2O5 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-Ta2O5 and a-Nb2O5 with lower bond energy was two orders of magnitude larger than that for a-Al2O3 with higher bond energy. PDF analyses revealed that the short-range configuration in a-Ta2O5 and a-Nb2O5 was more broadly distributed than that in a-Al2O3. Due to the larger variety of atomic configurations of a-Ta2O5 and a-Nb2O5, these oxides have a higher activation entropy for diffusion than a-Al2O3. The entropy term for diffusion associated with short-range structures was shown to be a dominant factor for diffusion in amorphous oxides.

  12. 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)

  13. 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.

  14. The origin of hyperferroelectricity in LiBO3 (B = V, Nb, Ta, Os)

    PubMed Central

    Li, Pengfei; Ren, Xinguo; Guo, Guang-Can; He, Lixin

    2016-01-01

    The electronic and structural properties of LiBO3 (B = V, Nb, Ta, Os) are investigated via first-principles methods. We show that LiBO3 belong to the recently proposed hyperferroelectrics (hyperFEs), i.e., they all have unstable longitudinal optic phonon modes. Especially, the ferroelectric-like instability in the metal LiOsO3, whose optical dielectric constant goes to infinity, is a limiting case of hyperFEs. Via an effective Hamiltonian, we further show that, in contrast to normal proper ferroelectricity, in which the ferroelectric instability usually comes from long-range coulomb interactions, the hyperFE instability is due to the structure instability driven by short-range interactions. This could happen in systems with large ion size mismatches, which therefore provides a useful guidance in searching for novel hyperFEs. PMID:27694996

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

  16. Analytic bond-order potentials for the bcc refractory metals Nb, Ta, Mo and W.

    PubMed

    Čák, M; Hammerschmidt, T; Rogal, J; Vitek, V; Drautz, R

    2014-05-14

    Bond-order potentials (BOPs) are based on the tight-binding approximation for determining the energy of a system of interacting atoms. The bond energy and forces are computed analytically within the formalism of the analytic BOPs. Here we present parametrizations of the analytic BOPs for the bcc refractory metals Nb, Ta, Mo and W. The parametrizations are optimized for the equilibrium bcc structure and tested for atomic environments far from equilibrium that had not been included in the fitting procedure. These tests include structural energy differences for competing crystal structures; tetragonal, trigonal, hexagonal and orthorhombic deformation paths; formation energies of point defects as well as phonon dispersion relations. Our tests show good agreement with available experimental and theoretical data. In practice, we obtain the energetic ordering of vacancy, [1 1 1], [1 1 0], and [1 0 0] self-interstitial atom in agreement with density functional theory calculations.

  17. Oxidation characteristics of Ti-33Al-6Nb-1.4Ta

    NASA Technical Reports Server (NTRS)

    Wallace, T. A.; Clark, R. K.; Sankaran, S. N.; Wiedemann, K. E.

    1991-01-01

    Static oxidation kinetics of the gamma titanium-aluminide alloy Ti-33Al-6Nb-1.4Ta (wt pct) have been investigated in air from 700 to 1000 C and in oxygen from 800 to 1000 C using thermogravimetric analysis. The oxidation kinetics were controlled by the presence of alumina for all oxygen exposures and in air below 800 C, while the kinetics in air above 800 C were more complex. Oxidation products were identified using X-ray diffraction techniques. Oxide scale morphology was examined by SEM and TEM of the surfaces and across sections of oxidized specimens. The oxidation products formed depended on the exposure: Al2O3 and TiO2 were identified on all specimens exposed in and air and oxygen; the nitride phases TiN and Ti2AlN were also found on specimens exposed in air.

  18. Oxidation characteristics of Ti-33Al-6Nb-1.4Ta

    NASA Technical Reports Server (NTRS)

    Wallace, T. A.; Clark, R. K.; Sankaran, S. N.; Wiedemann, K. E.

    1991-01-01

    Static oxidation kinetics of the gamma titanium-aluminide alloy Ti-33Al-6Nb-1.4Ta (wt pct) have been investigated in air from 700 to 1000 C and in oxygen from 800 to 1000 C using thermogravimetric analysis. The oxidation kinetics were controlled by the presence of alumina for all oxygen exposures and in air below 800 C, while the kinetics in air above 800 C were more complex. Oxidation products were identified using X-ray diffraction techniques. Oxide scale morphology was examined by SEM and TEM of the surfaces and across sections of oxidized specimens. The oxidation products formed depended on the exposure: Al2O3 and TiO2 were identified on all specimens exposed in and air and oxygen; the nitride phases TiN and Ti2AlN were also found on specimens exposed in air.

  19. Characterization of novel borides in Ti-Nb-Zr-Ta + 2B metal-matrix composites

    SciTech Connect

    Nag, Soumya; Samuel, Sonia; Puthucode, Anantha; Banerjee, Rajarshi

    2009-02-15

    Metal-matrix composites consisting of a complex quaternary Ti-35Nb-7Zr-5Ta alloy reinforced by borides have been successfully deposited from a powder feedstock consisting of a blend of elemental titanium, niobium, zirconium, tantalum, and, titanium diboride (TiB{sub 2}) powders, using the laser engineered net-shaping (LENS{sup TM}) process. The microstructures of the as-deposited composites have been characterized using scanning electron microscopy, orientation microscopy, and, transmission electron microscopy. Both primary and eutectic boride precipitates, exhibiting the orthorhombic B27 structure, are observed in these as-deposited composites. The complex primary borides exhibit an unusual compositional variation within the same precipitate, which has been investigated in detail using site-specific characterization with a transmission electron microscope. The ability to form near-net shape components using the Laser Engineered Net Shaping process makes these laser-deposited composites promising candidates for wear-resistant applications in biomedical implants.

  20. The origin of hyperferroelectricity in LiBO3 (B = V, Nb, Ta, Os)

    NASA Astrophysics Data System (ADS)

    Li, Pengfei; Ren, Xinguo; Guo, Guang-Can; He, Lixin

    2016-10-01

    The electronic and structural properties of LiBO3 (B = V, Nb, Ta, Os) are investigated via first-principles methods. We show that LiBO3 belong to the recently proposed hyperferroelectrics (hyperFEs), i.e., they all have unstable longitudinal optic phonon modes. Especially, the ferroelectric-like instability in the metal LiOsO3, whose optical dielectric constant goes to infinity, is a limiting case of hyperFEs. Via an effective Hamiltonian, we further show that, in contrast to normal proper ferroelectricity, in which the ferroelectric instability usually comes from long-range coulomb interactions, the hyperFE instability is due to the structure instability driven by short-range interactions. This could happen in systems with large ion size mismatches, which therefore provides a useful guidance in searching for novel hyperFEs.

  1. Synthesis and physical properties of Ca- and Ta-modified (K,Na)NbO3 lead-free piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Coondoo, Indrani; Panwar, Neeraj; Rai, Radheshyam; Amorín, Harvey; Kholkin, Andrei L.

    2013-11-01

    Polycrystalline samples of lead-free Ca and Ta co-substituted potassium sodium niobate (K0.5Na0.5NbO3, KNN) ceramics have been prepared by solid state reaction technique. X-ray diffraction showed formation of a single-phase perovskite structure with orthorhombic symmetry. Substitution inhibits the grain growth, improves densification and decreases the ferro-paraelectric phase transition temperature. Temperature dependent dielectric permittivity studies demonstrate significant decrease in peak-permittivity values in the substituted samples. Bulk longitudinal piezoelectric coefficient is significantly enhanced, up to ∼155 pC/N for (K0.48Na0.48Ca0.02)(Nb0.85Ta0.15O3) as compared to 95 pC/N for pristine KNN ceramic. Local piezoelectric properties have been observed by piezoresponse force microscopy (PFM) technique. Distinct piezocontrast was studied in both vertical and in-plane modes of PFM for all samples. The samples exhibit self-polarization effect in the unpoled state and effective local vertical piezoelectric coefficient was the largest in Ca and Ta co-substituted sample whereas the in-plane piezoelectric coefficient was maximum for Ca-substituted KNN sample. These studies are important for using substituted lead free KNN materials in various piezoelectric applications.

  2. 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.

  3. Influence of Ta and Ti Doping on the High Field Performance of (Nb, Ta, Ti)3Sn Multifilamentary Wires based on Osprey Bronze with High Tin Content

    NASA Astrophysics Data System (ADS)

    Abächerli, V.; Uglietti, D.; Lezza, P.; Seeber, B.; Flükiger, R.; Cantoni, M.; Buffat, P.-A.

    2006-06-01

    Ta and Ti are the most widely used additions for technical Nb3Sn multifilamentary superconductors. These elements are known to influence grain growth, grain morphology and chemical composition in the A15 layer, hence the current carrying properties of the wires over a wide magnetic field range. So far only few studies tried to compare systematically Ta and Ti doped and undoped Nb3Sn wires in the frame of the same work, down to a nanometric scale. We present an investigation on several multifilamentary (Nb, Ta, Ti)3Sn bronze route wires, fabricated at a laboratory scale, with various amounts of additives. The wires consist of fine filaments embedded in a Cu-Sn or Cu-Sn-Ti Osprey bronze with > 15 wt.% Sn and an external Cu stabilization. Microstructural observations are compared with the results of Jc and n values measured up to 21 T at 4.2 and 2.2 K, and for longitudinal strains up to 0.5%. Non-Cu Jc values up to 300 Amm-2 and n values up to 50 at 17 T and 4.2 K show clearly that wires with Ti addition to the bronze have a better performance with respect to wires with Ti additions to the filaments.

  4. Experimental Evidence for Linear Metal-Azide Coordination: The Binary Group 5 Azides [Nb(N3)5], [Ta(N3)5], [Nb(N3)6], and [Ta(N3)6], and 1:1 Acetonitrile Adducts [Nb(N3)5(CH3CN)] and (Ta(N3)5(CH3CN))

    DTIC Science & Technology

    2006-03-20

    significantly longer than the equatorial ones, as expected from VSEPR argu- ments.[29] In contrast, the axial M-N-N arrangements in [Nb(N3)5] and [Ta(N3)5...Int. Ed. 2000, 39, 2108. [29] a) R. J. Gillespie, I. Hargittai, The VSEPR Model of Molecular Geometry, Allyn and Bacon, Needham Heights, MA, 1991; b

  5. Synthesis and Characterization of Cu 3NbSe 4 and KCu 2TaSe 4

    NASA Astrophysics Data System (ADS)

    Lu, Ying-Jie; Ibers, James A.

    1993-11-01

    Cu 3NbSe 4 has been synthesized from a stoichiometric reaction of the elements at 950°C. The material, which has the sulvanite (Cu 3VS 4) structure, crystallizes in space group T 1d- P4¯3 m of the cubic system with one formula unit in a cell with a = 5.638(1) Å at - 165°C. Cu 3NbSe 4 has a three-dimensional structure with edge-sharing of CuSe 4 and NbSe 4 tetrahedra and corner-sharing among CuSe 4 tetrahedra extending equally in all directions. KCu 2TaSe 4 was prepared from a reaction of K 2Se 5, Cu, Ta, and Se in the ratio 1:4:2:3 at 850°C. KCu 2TaSe 4 crystallizes in space group C43 - Cc of the monoclinic system with four formula units in a cell of dimensions a = 5.660(1), b = 18.829(4), c = 7.662(2) Å, β = 90.04(3)° at - 165°C. In this structure the Ta and two independent Cu atoms are in tetrahedral sites. The CuSe 4 and TaSe 4 tetrahedra share edges and corners to make up two-dimensional layers. These layers are separated from one another by K + ions. KCu 2TaSe 4 is not isostructural with KCu 2NbSe 4, although the structures are similar.

  6. (23)Na multiple-quantum MAS NMR of the perovskites NaNbO(3) and NaTaO(3).

    PubMed

    Ashbrook, Sharon E; Le Pollès, Laurent; Gautier, Régis; Pickard, Chris J; Walton, Richard I

    2006-08-07

    The distorted perovskites NaTaO(3) and NaNbO(3) have been studied using (23)Na multiple-quantum (MQ) MAS NMR. NaTaO(3) was prepared by high temperature solid state synthesis and the NMR spectra are consistent with the expected room temperature structure of the material (space group Pbnm), with a single crystallographic sodium site. Two samples of NaNbO(3) were studied. The first, a commercially available sample which was annealed at 900 degrees C, showed two crystallographic sodium sites, as expected for the room temperature structure of the material (space group Pbcm). The second sample, prepared by a low temperature hydrothermal method, showed the presence of four sodium sites, two of which match the expected room temperature structure and the second pair, another polymorph of the material (space group P21ma). This is consistent with powder X-ray diffraction data which showed weak extra peaks which can be accounted for by the presence of this second polymorph. Density functional theory (DFT) calculations support our conclusions, and aid assignment of the NMR spectra. Finally, we discuss the measured NMR parameters in relation to other studies of sodium in high coordination sites in the solid state.

  7. Nano-Particle Formation of Mn/HA on the Ti-35Ta-xNb Alloy by Electrochemical Methods.

    PubMed

    Jo, Chae-Ik; Choe, Han-Cheol

    2015-08-01

    In this study, nano-particle formation of Mn/HA on the Ti-35Ta-xNb alloy by electrochemical methods has researched using various experiments. These alloys were performed by arc-melting furnace and then heat treated for 1000 °C at 12 h in Ar gas atmosphere and quenched at 0 °C water. Hydroxyapatite precipitation has been synthesized from 5 mM Ca(NO3)2 · 4 H2O+3 mM NH4H2PO4 at 80±1 °C. Manganese doped Hydroxyapatite precipitation has been synthesized from 4.95 mM Ca(NO3)2 · 4 H2O+3 mM NH4H2PO4+0.05 mM MnCl2 · 4 H2O at 80±1 °C. Morphology and structure were examined by FE-SEM, EDS and XRD. The microstructure of Ti-35Ta-xNb alloys was transformed from a phase to α phase as Nb content increased. The nano-scale HA shapes were plate-like precipitates and Mn doped HA shapes were net-like precipitates on Ti-35Ta-xNb alloys, and Ca, P and Mn peaks were detected on the Mn/HA deposited surface.

  8. Study of the in vitro corrosion behavior and biocompatibility of Zr-2.5Nb and Zr-1.5Nb-1Ta (at%) crystalline alloys.

    PubMed

    Rosalbino, F; Macciò, D; Giannoni, P; Quarto, R; Saccone, A

    2011-05-01

    The in vitro corrosion behavior and biocompatibility of two Zr alloys, Zr-2.5Nb, employed for the manufacture of CANDU reactor pressure tubes, and Zr-1.5Nb-1Ta (at%), for use as implant materials have been assessed and compared with those of Grade 2 Ti, which is known to be a highly compatible metallic biomaterial. The in vitro corrosion resistance was investigated by open circuit potential and electrochemical impedance spectroscopy (EIS) measurements, as a function of exposure time to an artificial physiological environment (Ringer's solution). Open circuit potential values indicated that both the Zr alloys and Grade 2 Ti undergo spontaneous passivation due to spontaneously formed oxide film passivating the metallic surface, in the aggressive environment. It also indicated that the tendency for the formation of a spontaneous oxide is greater for the Zr-1.5Nb-1Ta alloy and that this oxide has better corrosion protection characteristics than the ones formed on Grade 2 Ti or on the Zr-2.5Nb alloy. EIS study showed high impedance values for all samples, increasing with exposure time, indicating an improvement in corrosion resistance of the spontaneous oxide film. The fit obtained suggests a single passive film presents on the metals surface, improving their resistance with exposure time, presenting the highest values to the Zr-1.5Nb-1Ta alloy. For the biocompatibility analysis human osteosarcoma cell line (Saos-2) and human primary bone marrow stromal cells (BMSC) were used. Biocompatibility tests showed that Saos-2 cells grow rapidly, independently of the surface, due to reduced dependency from matrix deposition and microenvironment recognition. BMSC instead display a reduced proliferation, possibly caused by a reduced crosstalk with the metal surface microenvironment. However, once the substrate has been colonized, BMSC seem to respond properly to osteoinduction stimuli, thus supporting a substantial equivalence in the biocompatibility among the Zr alloys and Grade

  9. Quantifying protein adsorption on combinatorially sputtered Al-, Nb-, Ta- and Ti-containing films with electron microprobe and spectroscopic ellipsometry

    NASA Astrophysics Data System (ADS)

    Byrne, T. M.; Lohstreter, L.; Filiaggi, M. J.; Bai, Zhijun; Dahn, J. R.

    2009-04-01

    Although metallic biomaterials are widely used, systematic studies of protein adsorption onto such materials are generally lacking. Combinatorial binary libraries of Al 1-xNb x, Al 1-xTa x, Al 1-xTi x, Nb 1-xTa x, Nb 1-xTi x, and Ta 1-xTi x (0 ⩽ x ⩽ 1) and a ternary library of Al 1-xTi xTa y (0 ⩽ x ⩽ 1 and 0 ⩽ y ⩽ 0.7), along with their corresponding pure element films were sputtered onto glass substrates using a unique magnetron sputtering technique. Films were characterized with wavelength-dispersive spectroscopy (WDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Fibrinogen and albumin adsorption amounts were measured by wavelength-dispersive spectroscopy (WDS) and spectroscopic ellipsometry (SE) equipment, both high throughput techniques with automated motion stage capabilities. Protein adsorption onto these films was found to be closely correlated to the alumina surface fraction, with high alumina content at the surface leading to low amounts of adsorbed fibrinogen and albumin. Protein adsorption amounts obtained with WDS and SE were in good agreement for all films.

  10. Characterization of cryogenic materials by x-ray absorption methods. [Ta, Zr additions in Nb/sub 3/Sn

    SciTech Connect

    Heald, S.M.; Tranquada, J.M.

    1985-01-01

    X-ray absorption techniques have in recent years been developed into powerful probes of the electronic and structural properties of materials difficult to study by other techniques. In particular, the extended x-ray absorption fine structure (EXAFS) technique can be applied to a variety of cryogenic materials. Three examples are used to demonstrate the power of the technique. The first is the determination of the lattice location of dilute alloying additions such as Ta and Zr in Nb/sub 3/Sn. The Ta additions are shown to reside predominately in Nb lattice sites, while Zr is not uniquely located at either Nb or Sn sites. In addition to structural information, temperature dependent EXAFS studies can be used to determine the rms deviations of atomic bond lengths, providing information about the temperature dependence of interatomic force constants. For Nb/sub 3/Sn deviations are found from simple harmonic behavior at low temperatures which indicate a softening of the Nb-Sn bond strength. The final example is the study of interfacial properties in thin film systems. This is accomplished by making x-ray absorption measurements under conditions of total external reflection of the incident x-rays. As some examples show, this technique has great potential for studying interfacial reactions, a process used in the fabrication of many superconducting materials.

  11. 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.

  12. 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.

  13. The formation of the Yichun Ta-Nb deposit, South China, through fractional crystallization of magma indicated by fluid and silicate melt inclusions

    NASA Astrophysics Data System (ADS)

    Li, Shenghu; Li, Jiankang; Chou, I.-Ming; Jiang, Lei; Ding, Xin

    2017-04-01

    The Yichun Ta-Nb deposit, which is located in Jiangxi Province, South China, can be divided into four lithological zones (from bottom upward): two-mica granite, muscovite granite, albite granite, and lepidolite-albite granite zones. It remains controversial whether these distinct vertical zones were formed through late magmatic-hydrothermal metasomatic alteration or fractional crystallization of magma. To investigate the evolution mechanism of rock- and ore-forming fluid in this deposit, we studied fluid and melt inclusions in quartz and lepidolite in these four granite zones. These fluid inclusions are mainly composed of H2O-NaCl, and have homogenization temperatures ranging from 160 °C to 240 °C, with densities between 0.86 and 0.94 g/cm3 and salinities between 0.5 and 6.5 wt% NaCl equivalent. Raman spectroscopic analyses showed that the daughter minerals contained in silicate melt inclusions are mainly quartz, lepidolite, albite, muscovite, microcline, topaz, and sassolite. From the lower to upper granite zones, the albite contents in silicate melt inclusions increase, while the muscovite contents decrease gradually until muscovite is substituted by lepidolite in the lepidolite-albite granite zone. Additionally, the calculated densities of the silicate melt inclusions exhibit decreasing trends from bottom upward. The total homogenization temperatures of silicate melt inclusions, which were observed under external pressures created in the sample chamber of a hydrothermal diamond-anvil cell, decreased from 860 °C in the lower lithological zone to 776 °C in the upper lithological zone, and the initial melting temperatures of solid phases were 570-710 °C. The calculated initial H2O contents of granitic magma showed an increasing trend from the lower (∼2 wt% in the two-mica granite zone) to the upper granitic zones (∼3 wt% in the albite granite zone). All of these features illustrate that the vertical granite zones in the Yichun Ta-Nb deposit formed through

  14. Are lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) ferroelectrics bioactive?

    PubMed

    Vilarinho, Paula Maria; Barroca, Nathalie; Zlotnik, Sebastian; Félix, Pedro; Fernandes, Maria Helena

    2014-06-01

    The use of functional materials, such as ferroelectrics, as platforms for tissue growth in situ or ex situ, is new and holds great promise. But the usage of materials in any bioapplication requires information on biocompatibility and desirably on bioactive behavior when bone tissue engineering is envisaged. Both requirements are currently unknown for many ferroelectrics. Herein the bioactivity of LiNbO3 and LiTaO3 is reported. The formation of apatite-like structures on the surface of LiNbO3 and LiTaO3 powders after immersion in simulated body fluid (SBF) for different soaking periods indicates their bioactive potential. The mechanism of apatite formation is suggested. In addition, the significant release of lithium ions from the ferroelectric powders in the very first minutes of soaking in SBF is examined and ways to overcome this likely hurdle addressed.

  15. Adsorption ability of samples with nanoscale anatase to extract Nb(V) and Ta(V) ions from aqueous media

    NASA Astrophysics Data System (ADS)

    Demina, P. A.; Zybinskii, A. M.; Kuz'micheva, G. M.; Obolenskaya, L. N.; Savinkina, E. V.; Prokudina, N. A.

    2014-05-01

    The adsorption ability of titanium dioxide samples with nanoscale anatase prepared by the sulfate method and Degussa (Evonik) P25, Hombfine N, and Hombikate UV-100 commercial agents with different compositions and characteristics to extract Nb(V) and Ta(V) ions from a model aqueous system has been investigated for the first time. It is established that the degree of sorption R (%) depends on the sorption conditions and the nature of analyte. It is demonstrated that the degree of sorption of Nb(V) ions in the presence of all samples is the highest ( R max = 99.9%) for Degussa P25, except for the peroxide-modified samples on which the maximum sorption of Ta(V) ions with R max = 99.9% has been attained.

  16. Growth and study of SrBi 2 (Ta, Nb) 2 O 9 thin films by pulsed excimer laser ablation

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, S.; Bharadwaja, S. S. N.; Krupanidhi, S. B.

    2000-05-01

    Thin films of SrBi 2(Ta,Nb) 2O 9 (SBTN) were grown using pulsed-laser ablation and were ex situ crystallized. Ferroelectric properties were achieved by low temperature deposition. A polycrystalline structure was achieved, with a Ta- to Nb-ratio nearly 1:1. The smaller thickness of the film allowed the switching voltage to be low enough (1.5 V), without affecting the insulating nature of the films. The hysteresis results showed an excellent square shaped loop with a remnant polarization ( Pr) of 7.6 μC/cm 2 and a coercive field ( Ec) of 75 kV/cm. This ferroelectric material composition is having a very high Curie temperature with higher stability and can be used in non-volatile random access memory (NVRAM) devices.

  17. In Vitro Cytotoxicity of a Ti-35Nb-7Zr-5Ta Alloy Doped with Different Oxygen Contents

    PubMed Central

    Donato, Tatiani Ayako Goto; de Almeida, Luciano Henrique; Arana-Chavez, Victor Elias; Grandini, Carlos Roberto

    2014-01-01

    Cp-Ti is the most common material used for dental implants, but its elastic modulus is around five times higher than that of bone. Recently, promising alloys that add Nb, Ta, Zr and Mo to Ti have been developed. The mechanical properties of these alloys are directly related to its microstructure and the presence of interstitial elements, such as oxygen, carbon, nitrogen and hydrogen. In this study, the in vitro cytotoxicity of Ti-35Nb-7Zr-5Ta (TNZT) alloys was analyzed in the as-received condition and after being doped with several small quantities of oxygen on a cultured osteogenic cell. The cell’s morphology was also examined by scanning electron microscopy (SEM). The TNZT alloy presented no cytotoxic effects on osteoblastic cells in the studied conditions. PMID:28788562

  18. 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.

  19. 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

  20. (dme)MCl3(NNPh2) (dme = dimethoxyethane; M = Nb, Ta): a versatile synthon for [Ta=NNPh2] hydrazido(2-) complexes.

    PubMed

    Tonks, Ian A; Bercaw, John E

    2010-05-17

    Complexes (dme)TaCl(3)(NNPh(2)) (1) and (dme)NbCl(3)(NNPh(2)) (2) (dme =1,2-dimethoxyethane) were synthesized from MCl(5) and diphenylhydrazine via a Lewis-acid assisted dehydrohalogenation reaction. Monomeric 1 has been characterized by X-ray, IR, UV-vis, (1)H NMR, and (13)C NMR spectroscopy and contains a kappa(1)-bound hydrazido(2-) moiety. Unlike the corresponding imido derivatives, 1 is dark blue because of an LMCT that has been lowered in energy as a result of an N(alpha)-N(beta) antibonding interaction that raises the highest occupied molecular orbital (HOMO). Reaction of 1 with a variety of neutral, mono- and dianionic ligands generates the corresponding ligated complexes retaining the kappa(1)-bound [Ta-NNPh(2)] moiety.

  1. Mechanical and corrosion resistance of a new nanostructured Ti-Zr-Ta-Nb alloy.

    PubMed

    Raducanu, D; Vasilescu, E; Cojocaru, V D; Cinca, I; Drob, P; Vasilescu, C; Drob, S I

    2011-10-01

    In this work, a multi-elementary Ti-10Zr-5Nb-5Ta alloy, with non-toxic alloying elements, was used to develop an accumulative roll bonding, ARB-type procedure in order to improve its structural and mechanical properties. The alloy was obtained by cold crucible semi-levitation melting technique and then was ARB deformed following a special route. After three ARB cycles, the total deformation degree per layer is about 86%; the calculated medium layer thickness is about 13 μm. The ARB processed alloy has a low Young's modulus of 46 GPa, a value very close to the value of the natural cortical bone (about 20 GPa). Data concerning ultimate tensile strength obtained for ARB processed alloy is rather high, suitable to be used as a material for bone substitute. Hardness of the ARB processed alloy is higher than that of the as-cast alloy, ensuring a better behaviour as a implant material. The tensile curve for the as-cast alloy shows an elastoplastic behaviour with a quite linear elastic behaviour and the tensile curve for the ARB processed alloy is quite similar with a strain-hardening elastoplastic body. Corrosion behaviour of the studied alloy revealed the improvement of the main electrochemical parameters, as a result of the positive influence of ARB processing. Lower corrosion and ion release rates for the ARB processed alloy than for the as-cast alloy, due to the favourable effect of ARB thermo-mechanical processing were obtained.

  2. Petrogenesis of the Yangzhuang Nb- and Ta-rich A-type granite porphyry in West Junggar, Xinjiang, China

    NASA Astrophysics Data System (ADS)

    Mao, Wei; Li, Xiaofeng; Wang, Guo; Xiao, Rong; Wang, Mou; Li, Yanlong; Ren, Manchuan; Bai, Yanping; Yang, Feng

    2014-06-01

    West Junggar is featured with a wide spread of Late Carboniferous-Early Permian A-type granites. Systematic comparison of the Yangzhuang granite porphyry and the regional coeval A-type granites (RCAG) shows that: (1) all the Late Carboniferous-Early Permian A-type granites are of the A2 group except the Yangzhuang granite porphyry; (2) the Nb and Ta contents of the Yangzhuang granite porphyry are nearly 10 times that of the RCAG while Ti content is more depleted; (3) εNd (t) of the Yangzhuang granite porphyry is slightly lower and the Sr isotope has a wider range relative to the RCAG. Previous research revealed that highly incompatible elements including Nb and Ta can be transferred into the mantle wedge by precipitation of amphibole from the ascending fluids generated by dehydration of subducted slab. It is inferred that enhanced heat flux brought by the Late Carboniferous ridge subduction decomposed amphibole in the mantle wedge to generate Nb and Ta-rich melt and finally produced the Yangzhuang granite porphyry.

  3. A first-principles study of the tetragonal and hexagonal R 2Al (R = Cr, Zr, Nb, Hf, Ta) phases

    NASA Astrophysics Data System (ADS)

    Shang, Xiu; Shen, Jiang; Tian, Fuyang

    2016-10-01

    The crystal structures, elastic moduli, electronic structure, and phonon dispersion of the tetragonal R 2Al (R = Cr, Zr, Nb, Hf, Ta) intermetallic compounds are investigated by using the first-principles method. The space group number is 139 for tetragonal Cr2Al, 136 for tetragonal Nb2Al and Ta2Al, and the space group numbers are 140 and 194 for tetragonal and hexagonal Zr2Al and Hf2Al, respectively. The results of elastic constants and phonon dispersion indicate that the present intermetallic compounds are thermodynamically stable. The stability of hexagonal Zr2Al and Hf2Al is analyzed via the electronic density of state, compared to the tetragonal Zr2Al and Hf2Al compounds. For the R2Al intermetallic compounds, the less ductility and strong anisotropy are predicted. The more negative formation enthalpy and thermodynamic stability of R2Al (R = Nb, Zr, Hf) shed light on the Nb2Al, Zr2Al, Hf2Al phases found experimentally in refractory high entropy alloys.

  4. TiZrNbTaMo high-entropy alloy designed for orthopedic implants: As-cast microstructure and mechanical properties.

    PubMed

    Wang, Shao-Ping; Xu, Jian

    2017-04-01

    Combining the high-entropy alloy (HEA) concept with property requirement for orthopedic implants, we designed a Ti20Zr20Nb20Ta20Mo20 equiatomic HEA. The arc-melted microstructures, compressive properties and potentiodynamic polarization behavior in phosphate buffer solution (PBS) were studied in detail. It was revealed that the as-cast TiZrNbTaMo HEA consisted of dual phases with bcc structure, major bcc1 and minor bcc2 phases with the lattice parameters of 0.3310nm and 0.3379nm, respectively. As confirmed by nanoindentation tests, the bcc1 phase is somewhat harder and stiffer than the bcc2 phase. The TiZrNbTaMo HEA exhibited Young's modulus of 153GPa, Vickers microhardness of 4.9GPa, compressive yield strength of σy=1390MPa and apparent plastic strain of εp≈6% prior to failure. Moreover, the TiZrNbTaMo HEA manifested excellent corrosion resistance in PBS, comparable to the Ti6Al4V alloy, and pitting resistance remarkably superior to the 316L SS and CoCrMo alloys. These preliminary advantages of the TiZrNbTaMo HEA over the current orthopedic implant metals in mechanical properties and corrosion resistance offer an opportunity to explore new orthopedic-implant alloys based on the TiZrNbTaMo concentrated composition.

  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. Experimental Evidence for Linear Metal-Azide Bonds. The Binary Group 5 Azides Nb(N3)5, Ta(N3)5, [Nb(N3)6]- and [Ta(N3)6]-, and 1:1 Adducts of Nb(N3)5 and Ta(N3)5 with CH3CN

    DTIC Science & Technology

    2005-04-27

    bonds are significantly longer than the equatorial ones, as expected from VSEPR arguments.[29] In contrast, the axial M-N-N bonds in Nb(N3)5 and Ta...Klapötke, H. Nöth, T. Schütt, M. Warchhold, Angew. Chem. Int. Ed. 2000, 39, 2108. [29] (a) R. J. Gillespie, I. Hargittai, The VSEPR Model of

  7. Synthesis and structure of new framework phosphates Li{sub 1/4M7/4}(PO{sub 4}){sub 3}(M = Nb, Ta)

    SciTech Connect

    Sukhanov, M. V.; Gobechiya, E. R.; Kabalov, Yu. K.; Pet'kov, V. I.

    2008-11-15

    New lithium-niobium and lithium-tantalum phosphates Li{sub 1/4}M{sub 7/4}(PO{sub 4}){sub 3}(M = Nb, Ta) are synthesized by the solid-phase method. The compounds prepared are characterized using electron microprobe analysis, X-ray powder diffraction, and IR spectroscopy. The crystal structure of the Li{sub 1/4}Ta{sub 7/4}(PO{sub 4}){sub 3} phosphate is determined from the X-ray powder diffraction data (the Rietveld method) and belongs to the framework type. The framework of the structure consists of TaO{sub 6} and LiO{sub 6} vertex-shared octahedra and PO{sub 4} tetrahedra. The isostructural phosphates Li{sub 1/4}M{sub 7/4}(PO{sub 4}){sub 3} crystallize in the trigonal crystal system (space group R3-barc, Z = 6) and belong to the NaZr{sub 2}(PO{sub 4}){sub 3} structure type.

  8. 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.

  9. 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

  10. Interfacial bonding stabilizes rhodium and rhodium oxide nanoparticles on layered Nb oxide and Ta oxide supports.

    PubMed

    Strayer, Megan E; Binz, Jason M; Tanase, Mihaela; Shahri, Seyed Mehdi Kamali; Sharma, Renu; Rioux, Robert M; Mallouk, Thomas E

    2014-04-16

    Metal nanoparticles are commonly supported on metal oxides, but their utility as catalysts is limited by coarsening at high temperatures. Rhodium oxide and rhodium metal nanoparticles on niobate and tantalate supports are anomalously stable. To understand this, the nanoparticle-support interaction was studied by isothermal titration calorimetry (ITC), environmental transmission electron microscopy (ETEM), and synchrotron X-ray absorption and scattering techniques. Nanosheets derived from the layered oxides KCa2Nb3O10, K4Nb6O17, and RbTaO3 were compared as supports to nanosheets of Na-TSM, a synthetic fluoromica (Na0.66Mg2.68(Si3.98Al0.02)O10.02F1.96), and α-Zr(HPO4)2·H2O. High surface area SiO2 and γ-Al2O3 supports were also used for comparison in the ITC experiments. A Born-Haber cycle analysis of ITC data revealed an exothermic interaction between Rh(OH)3 nanoparticles and the layered niobate and tantalate supports, with ΔH values in the range -32 kJ·mol(-1) Rh to -37 kJ·mol(-1) Rh. In contrast, the interaction enthalpy was positive with SiO2 and γ-Al2O3 supports. The strong interfacial bonding in the former case led to "reverse" ripening of micrometer-size Rh(OH)3, which dispersed as 0.5 to 2 nm particles on the niobate and tantalate supports. In contrast, particles grown on Na-TSM and α-Zr(HPO4)2·H2O nanosheets were larger and had a broad size distribution. ETEM, X-ray absorption spectroscopy, and pair distribution function analyses were used to study the growth of supported nanoparticles under oxidizing and reducing conditions, as well as the transformation from Rh(OH)3 to Rh nanoparticles. Interfacial covalent bonding, possibly strengthened by d-electron acid/base interactions, appear to stabilize Rh(OH)3, Rh2O3, and Rh nanoparticles on niobate and tantalate supports.

  11. The wake of H in V, Nb and Ta at elevated temperatures: Irreversibility and non-central forces revisited

    NASA Astrophysics Data System (ADS)

    Reidinger, Franz

    2011-03-01

    At elevated temperatures U and Do of the Arrhenius equation for diffusion describe the amplitude and relaxation rate, respectively, of the stern wave wake of H in V, Nb and Ta. The key evidence for this hypothesis is the close correlation between the isotope dependence of U derived from the Gorsky measurements 1 and the shear distortion of the orthorhombic phases of NbH(D) and TaH(D). The isotope dependence of U can be expressed in closed form: U= a √{ M } + b √{ m } where M and m are the atomic numbers of the host metal and H isotope and a and b are 7.4 and 37 for Nb and Ta, and 0 and 55 for V, respectively, in units of meV. I explain this correlation in two steps: a) the cubic symmetry of the nearest neighbor strain field 2 of the interstitial H is the result of a dynamic superposition, possibly caused by a JT resonance 3 , of the two orthorhombic variants of β -NbH0.75 and b) the successful characterization of the diffusion process as jump diffusion 4 eliminates the transition state from consideration. Instead it is the relaxation of the just emptied site from its residual orthorhombic distortion towards the cubic symmetry of the bcc metal which is being measured. 1)Z Qi, J Voelkl, R Laesser and H Wenzl: J. Phys. F 13, 2053 (1983) 2)G Bauer, E Seitz, W Schmatz and H Horner: Sol. State Comm. 17, 161 (1975) 3)G C Abell: J. Phys. F 12, 1143 (1982) 4) V Lottner, A Heim and T Springer: Z. Physik B 32, 157 (1979).

  12. 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.

  13. The wheat NB-LRR gene TaRCR1 is required for host defence response to the necrotrophic fungal pathogen Rhizoctonia cerealis.

    PubMed

    Zhu, Xiuliang; Lu, Chungui; Du, Lipu; Ye, Xingguo; Liu, Xin; Coules, Anne; Zhang, Zengyan

    2016-11-18

    The necrotrophic fungus Rhizoctonia cerealis is the major pathogen causing sharp eyespot disease in wheat (Triticum aestivum). Nucleotide-binding leucine-rich repeat (NB-LRR) proteins often mediate plant disease resistance to biotrophic pathogens. Little is known about the role of NB-LRR genes involved in wheat response to R. cerealis. In this study, a wheat NB-LRR gene, named TaRCR1, was identified in response to R. cerealis infection using Artificial Neural Network analysis based on comparative transcriptomics and its defence role was characterized. The transcriptional level of TaRCR1 was enhanced after R. cerealis inoculation and associated with the resistance level of wheat. TaRCR1 was located on wheat chromosome 3BS and encoded an NB-LRR protein that was consisting of a coiled-coil domain, an NB-ARC domain and 13 imperfect leucine-rich repeats. TaRCR1 was localized in both the cytoplasm and the nucleus. Silencing of TaRCR1 impaired wheat resistance to R. cerealis, whereas TaRCR1 overexpression significantly increased the resistance in transgenic wheat. TaRCR1 regulated certain reactive oxygen species (ROS)-scavenging and production, and defence-related genes, and peroxidase activity. Furthermore, H2 O2 pretreatment for 12-h elevated expression levels of TaRCR1 and the above defence-related genes, whereas treatment with a peroxidase inhibitor for 12 h reduced the resistance of TaRCR1-overexpressing transgenic plants and expression levels of these defence-related genes. Taken together, TaRCR1 positively contributes to defence response to R. cerealis through maintaining ROS homoeostasis and regulating the expression of defence-related genes.

  14. Comparative study on structural, elastic, dynamical, and thermodynamic properties of Weyl semimetals MX (M = Ta or Nb; X = As or P)

    NASA Astrophysics Data System (ADS)

    Liu, Lei; Wang, Zhao-Qi; Hu, Cui-E.; Cheng, Yan; Ji, Guang-Fu

    2017-09-01

    We present a comparative investigation on structural, elastic, dynamical and thermodynamic properties of Weyl semimetals MX (M = Ta or Nb; X = As or P) using density functional theory (DFT) within the generalized gradient approximation. The elastic properties of NbAs, TaP and NbP are obtained for the first time, then we compared them with each other and with some well-studied materials. Among four Weyl semimetals, TaP and NbAs possess the largest and smallest bulk modulus B, shear modulus G, and Young's modulus E, respectively, while NbP and TaAs own the maximum and minimum elastic Debye temperature. Through the analysis of three dimensional (3D) representations and two dimensional (2D) projections of Young's modulus, MX series exhibit distinct elastic anisotropy, especially for TaAs and NbAs. The calculated phonon dispersions of four Weyl semimetals show no imaginary frequency throughout the Brillouin zone, indicating they are dynamically stable. In addition, compared with other theoretical results, our calculated Brillouin-zone-center frequencies of MX series are more in line with experimental data. Furthermore, Phonon velocities are obtained using phonon spectra, and anisotropic phonon group velocities are responsible for their anisotropic lattice thermal conductivity. Additionally, thermodynamic properties are also predicted using the calculated phonon density of states. The results are in good agreement with available experimental values. We expect our work can provide more information for further experimental studies.

  15. Structure analysis on the Ba{sub 3}Mg(Ta{sub 1-x}Nb{sub x}){sub 2}O{sub 9} ceramics: Coexistence of order and disorder

    SciTech Connect

    Janaswamy, Srinivas Murthy, G. Sreenivasa; Dias, E.D.; Murthy, V.R.K.

    2008-03-04

    The Ba{sub 3}ZnTa{sub 2}O{sub 9} (BZT) and Ba{sub 3}MgTa{sub 2}O{sub 9} (BMT) ceramics, a family of A{sub 3}B{sup 2+}B{sup 5+}{sub 2}O{sub 9} complex perovskites, are extensively utilized in mobile based technologies due to their intrinsic high unloaded quality factor, high dielectric constant and a low (near-zero) resonant frequency temperature coefficient at microwave frequencies. The preparation conditions as well as size and nature of B cations have a profound effect on the final dielectric properties. In this article, we report the effect of Nb{sup 5+} at the Ta{sup 5+} site on the BMT structure prepared at four synthesis temperatures (1300, 1400, 1500 and 1600 deg. C). The analysis has been carried out using the Rietveld technique on the X-ray powder diffraction data. Results suggest that both the preparation temperatures and Nb{sup 5+} content have significant effect on the ordering of B cations in the Ba{sub 3}Mg(Ta{sub 1-x}Nb{sub x}){sub 2}O{sub 9} solid solution. A disordered (cubic) structure is preferred by the 1300 deg. C compounds. The weight percentage of the ordered (trigonal) phase escalates, for a given composition, with increasing calcination temperature. A fully ordered trigonal arrangement exists only for x = 0.0 and 0.2 compounds calcined at 1600 deg. C, and the rest are biphasic (cubic and trigonal). The increase in the cubic fraction upon Nb{sup 5+} augmentation suggests that the solid solution leans more toward the disordered structural arrangement of B{sup 2+} and B{sup 5+} cations.

  16. Comparisons of immersion and electrochemical properties of highly biocompatible Ti-15Zr-4Nb-4Ta alloy and other implantable metals for orthopedic implants

    NASA Astrophysics Data System (ADS)

    Okazaki, Yoshimitsu; Nagata, Hiroyuki

    2012-12-01

    Metal release from implantable metals and the properties of oxide films formed on alloy surfaces were analyzed, focusing on the highly biocompatible Ti-15Zr-4Nb-4Ta alloy. The thickness and electrical resistance (Rp) of the oxide film on such an alloy were compared with those of other implantable metals. The quantity of metal released during a 1-week immersion test was considerably smaller for the Ti-15Zr-4Nb-4Ta than the Ti-6Al-4V alloy. The potential (E10) indicating a current density of 10 μA cm-2 estimated from the anodic polarization curve was significantly higher for the Ti-15Zr-4Nb-4Ta than the Ti-6Al-4V alloy and other metals. Moreover, the oxide film (4-7 nm thickness) formed on the Ti-15Zr-4Nb-4Ta surface is electrochemically robust. The oxide film mainly consisted of TiO2 with small amounts of ZrO2, Nb2O5 and Ta2O5 that made the film electrochemically stable. The Rp of Ti-15Zr-4Nb-4Ta was higher than that of Ti-6Al-4V, i.e. 0.9 Ω cm2 in 0.9% NaCl and 1.3 Ω cm2 in Eagle's medium. This Rp was approximately five-fold higher than that of stainless steel, which has a history of more than 40 years of clinical use in the human body. Ti-15Zr-4Nb-4Ta is a potential implant material for long-term clinical use. Moreover, E10 and Rp were found to be useful parameters for assessing biological safety.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  18. Production of superconducting Nb sub 3 Sn wire using Nb or Nb(Ti) and Sn(Ga) solid solution powders

    SciTech Connect

    Thieme, C.L.H. . Francis Bitter National Magnet Lab.); Foner, S. . Dept. of Physics)

    1991-03-01

    This paper reports on superconducting Nb{sub 3}Sn wire produced by the powder metallurgy method using Nb or Nb-2.9 at% Ti powder in combination with Sn-x at% Ga powders (x = 3, 4.2, 6.2 and 9.0). Ga additions to the Sn caused considerable solid solution hardening which improved its workability. It made the Nb-Sn(Ga) powder combinations convenient for swaging and extensive wire drawing. Anneals at 950{degrees}C produced wires with an overall J{sub c} of 10{sup 4} A/cm{sup 2} at 21.9 T for wires with both Ti in the Nb and 6.2 at% Ga in the Sn. Comparison of this wire with the best Nb(Ti)-Cu-internal Sn(Ti) shows a higher J{sub c} per A15 areas, especially in fields of 22T and above.

  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. 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.

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

    USGS Publications Warehouse

    Hedrick, James B.; Sinha, Shyama P.; Kosynkin, Valery 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.

  2. Electronic structure of metal hydrides. VI. Photoemission studies and band theory of VH, NbH, and TaH

    SciTech Connect

    Peterman, D.J.; Misemer, D.K.; Weaver, J.H.; Peterson, D.T.

    1983-01-15

    The electronic structures of VH/sub x/, NbH/sub x/, and TaH/sub x/ (0.6< or =x< or =1.0) have been studied with the use of photoemission spectroscopy with synchrotron radiation (10< or =h..nu..< or =100 eV). Two hydrogen-derived features are observed at approx.5.5- and 7.5-eV binding energies, and the metal d bands are shown to be modified by the hydrogen interaction. These results show no agreement with rigid-band models based on the density of states of the pure metals and relatively poor agreement with previous band-structure calculations for monohydrides. We have calculated the energy bands of ..gamma..-phase NbH (self-consistently) and of NbH/sub 0/ and NbH/sub 2/ (non-self-consistently). Together, the calculations and experiments show how the metal-hydrogen interaction alters the electronic properties of the bcc metals.

  3. Roles of Li and Ta in Pb-free piezoelectric (Na,K)NbO3 ceramics

    NASA Astrophysics Data System (ADS)

    Sung, Y. S.

    2014-10-01

    Piezoelectric coefficient (d33) of (Na,K)NbO3 (NKN) is enhanced not only at its morphotropic phase boundary (MPB) composition but also enhanced at its polymorphic phase transition (PPT) temperature between orthorhombic and tetragonal phases (TO-T). Thus, for NKN-based ceramics, even higher d33 could be obtained if both MPB and PPT are simultaneously optimized. This temperature as well as composition dependence of piezoelectric properties of NKN-based ceramics requires a systematic approach that differentiates factors for MPB and PPT. In this paper, the roles of Li and Ta known to affect d33 and TO-T were identified in relation with lattice parameters.

  4. Quantum and superconducting fluctuations effects in disordered Nb 1- xTa x thin films above Tc

    NASA Astrophysics Data System (ADS)

    Giannouri, M.; Papastaikoudis, C.

    1999-05-01

    Disordered Nb 1- xTa x thin films are prepared with e-gun coevaporation. The influence of the β-phase of tantalum in the critical temperature Tc is observed as a function of the substrate temperature. The measurements of transverse magnetoresistance at various isothermals are interpreted in terms of weak-localization and superconducting fluctuations. From the fitting procedure, the phase breaking rate τφ-1 and the Larkin parameter βL are estimated as a function of temperature. Conclusions about the dominant inelastic scattering mechanisms at various temperature regions as well as for the dominant mechanism of superconducting fluctuations near the transition temperature are extracted.

  5. Theoretical predictions of properties and gas-phase chromatography behaviour of bromides of group-5 elements Nb, Ta, and element 105, Db

    NASA Astrophysics Data System (ADS)

    Pershina, V.; Anton, J.

    2012-01-01

    Fully relativistic, four-component density functional theory electronic structure calculations were performed for MBr5, MOBr3, MBr6-, KMBr6, and MBr5Cl- of group-5 elements Nb, Ta, and element 105, Db, with the aim to predict adsorption behaviour of the bromides in gas-phase chromatography experiments. It was shown that in the atmosphere of HBr/BBr3, the pentabromides are rather stable, and their stability should increase in the row Nb < Db < Ta. Several mechanisms of adsorption were considered. In the case of adsorption by van der Waals forces, the sequence in volatility of the pentabromides should be Nb < Ta < Db, being in agreement with the sublimation enthalpies of the Nb and Ta pentabromides. In the case of adsorption by chemical forces (on a quartz surface modified with KBr/KCl), formation of the MBr5L- (L = Cl, Br) complex should occur, so that the volatility should change in an opposite way, i.e., Nb > Ta > Db. This sequence is in agreement with the one observed in the "one-atom-at-a-time" chromatography experiments. Some other scenarios, such as surface oxide formation were also considered but found to be irrelevant.

  6. 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.

  7. Extreme High Field Strength Element Depletion and Chondritic Nb/Ta in Central Andean Adakite-like Lavas (~27° S, ~68° W)

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

    We present new high precision ICP-MS HFSE data on ~30 samples from the adakite-like Pircas Negras (SiO2 =57-62 %; La/Yb= 20-60; Sr = 600-900 ppm, Cr to 200 ppm) and Dos Hermanos (SiO2 =56-59 %; La/Yb= 57-61; Sr = 1200-1500 ppm, Cr to 60 ppm) andesites from the southernmost Andean Central Volcanic Zone (CVZ). These andesites erupted in a broadened arc as the volcanic front was displaced about 50 km to the east between 8 and 3 Ma and likely reflect melting of a garnet bearing crustal source. Our data reveal a discrete change from chondritic Nb/Ta ratios (19-21) and low Zr/Sm (25-30) in older 8-7 Ma Dos Hermanos lavas to dominantly subchondritic Nb/Ta ratios (11-18) and higher Zr/Sm (30-45) in <6 Ma Pircas Negras lavas. These ratios are uncommon since frontal arc lavas worldwide typically have subchondritic Nb/Ta ratios (<19.9 ± 2) consistent with flux melting of uniformly subchondritic sources (i.e. depleted mantle, subducted sediments, crustal assimilation). The highest Nb/Ta ratios begin to approach those of kimberlitic eclogites (mean Nb/Ta = 24) from Siberia and western Africa where residual rutile controls the budget of eclogitic Nb and Ta (Rudnick et al., 2003). Extreme depletions in HFSE in both Pircas Negras (La/Ta = 40-80) and Dos Hermanos (La/Ta= 90-100) lavas are best explained as hydrous and oxidizing conditions within the mantle wedge initially stabilized Ti-oxides (i.e. rutile) as the arc front migrated. These steeper REE patterns and high La/Ta are a transient feature measured in lavas erupting during the peak of arc migration, as mafic <2 Ma CVZ lavas to the north (~26° S) have lower La/Yb (< 20) and La/Ta (< 40). The observed temporal shift in Nb/Ta coupled with a general increase in Zr/Sm suggests a change from residual rutile to low-Mg amphibole within an eclogitic/granulitic crustal residue during the course of arc migration. A potential factor in explaining these data is that a transient period of increased subduction erosion associated with

  8. Single crystal structure and SHG of defect pyrochlores CsB{sup V}MoO{sub 6} (B{sup V}=Nb,Ta)

    SciTech Connect

    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.

    2016-09-15

    The crystal structure and non-linear optical properties of CsNbMoO{sub 6} and CsTaMoO{sub 6} 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 CsB{sup V}MoO{sub 6} (B{sup V}=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 CsNbMoO{sub 6} and CsTaMoO{sub 6}was found to be 1.6×10{sup −2} and 8.5×10{sup −4} of lithium niobate, correspondingly. It has been determined that distortions of [MO{sub 6}] 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. - Highlights: • CsNbMoO{sub 6} and CsTaMoO{sub 6} homogeneous single crystals have been grown. • The crystal structure of CsTaMoO{sub 6} has been studied. • Nonlinear optical properties of CsNbMoO{sub 6} and CsTaMoO{sub 6} have been found. • The microscopic origin of the second harmonic generation (SHG) response have been identified.

  9. Electronic transition in solid Nb at high pressure and temperature

    NASA Astrophysics Data System (ADS)

    Ezenwa, Innocent C.; Secco, Richard A.

    2017-06-01

    The electrical resistivity of high purity solid Nb has been measured at fixed pressures up to 5 GPa in a large volume press and temperatures up to ˜1900 K. The expected resistivity decrease with pressure and increase with temperature were found. A transition was observed in the temperature dependence of resistivity at high temperature. The transition is discussed in terms of the effects of pressure and temperature on the electronic band structure of Nb causing a resistivity behavior characteristic of a change from the "minus group" to the "plus group." Extrapolation of the pressure dependence of the transition temperature suggests that Nb would show plus group behavior at room T at an estimated pressure of ˜27 ± 7 GPa. The electronic thermal conductivity was calculated using the Wiedemann-Franz law and was in very good agreement with 1 atm data. We show that the temperature dependence of the calculated electronic thermal conductivity increases with a steep slope from room temperature up to the electronic transition temperature for all fixed pressures. Above the transition temperature, the T-dependence of electronic thermal conductivity remained constant at 2 GPa and exhibited an increasingly negative slope at higher pressures. The isothermal pressure-dependence of electronic thermal conductivity is positive.

  10. Design of medium band gap Ag-Bi-Nb-O and Ag-Bi-Ta-O semiconductors for driving direct water splitting with visible light.

    PubMed

    Wang, Limin; Cao, Bingfei; Kang, Wei; Hybertsen, Mark; Maeda, Kazuhiko; Domen, Kazunari; Khalifah, Peter G

    2013-08-19

    Two new metal oxide semiconductors belonging to the Ag-Bi-M-O (M = Nb, Ta) chemical systems have been synthesized as candidate compounds for driving overall water splitting with visible light on the basis of cosubstitution of Ag and Bi on the A-site position of known Ca2M2O7 pyrochlores. The low-valence band edge energies of typical oxide semiconductors prevents direct water splitting in compounds with band gaps below 3.0 eV, a limitation which these compounds are designed to overcome through the incorporation of low-lying Ag 4d(10) and Bi 6s(2) states into compounds of nominal composition "AgBiM2O7". It was found that the "AgBiTa2O7" pyrochlores are in fact a solid solution with an approximate range of Ag(x)Bi(5/6)Ta2O(6.25+x/2) with 0.5 < x < 1. The structure of Ag4/5Bi5/6Ta2O6.65 was determined from the refinement of time-of-flight neutron diffraction data and was found to be a cubic pyrochlore with a = 10.52268(2) Å and a volume of 1165.143(6) Å(3). The closely related compound, AgBiNb2O7, appears to have an integer stoichiometry and to adopt an orthorhombically distorted pyrochlore-related structure with a subcell of a = 7.50102(8) Å, b = 7.44739(7) Å, c = 10.5788(1) Å, and V = 590.93(2) Å(3). Density functional theory-based calculations predict this distortion should result from A-site cation ordering. Fits to UV-vis diffuse reflectance data suggest that AgBiNb2O7 and "AgBiTa2O7" are both visible-light-absorbing semiconductors with the onset of strong direct absorption at 2.72 and 2.96 eV, respectively. Electronic structure calculations for an ordered AgBiNb2O7 structure show that the band gap reduction and the elevation of the valence band primarily result from hybridized Ag d(10)-O 2p orbitals that lie at higher energy than the normal O 2p states in typical pyrochlore oxides. While the minimum energy gap is direct in the band structure, the lowest energy dipole allowed optical transitions start about 0.2 eV higher in energy than the minimum energy

  11. Piezoelectric properties of Li- and Ta-modified (K0.5Na0.5)NbO3 ceramics

    NASA Astrophysics Data System (ADS)

    Hollenstein, Evelyn; Davis, Matthew; Damjanovic, Dragan; Setter, Nava

    2005-10-01

    Lead-free, potassium sodium niobate piezoelectric ceramics substituted with lithium (K0.5-x/2,Na0.5-x/2,Lix)NbO3 or lithium and tantalum (K0.5-x/2,Na0.5-x/2,Lix)(Nb1-y,Tay)O3 have been synthesized by traditional solid state sintering. The compositions chosen are among those recently reported to show high piezoelectric properties [Y. Saito, H. Takao, T. Tani, T. Nonoyama, K. Takatori, T. Homma, T. Nagaya, and M. Nakamura, Nature (London) 42, 84 (2004); Y. Guo, K. Kakimoto, and H. Ohsato, Appl. Phys. Lett. 85, 4121 (2004); Mater. Lett. 59, 241 (2005)]. We show that high densities and piezoelectric properties can be obtained for all compositions by pressureless sintering in air, without cold isostatic pressing, and without any sintering aid or special powder treatment. Resonance and converse piezoelectric (strain-field) measurements show a thickness coupling coefficient kt of 53% and converse piezoelectric coefficient d33 around 200pm/V for the Li-substituted ceramics, and a kt of 52% and d33 over 300pm/V for the Li- and Ta-modified samples. The unipolar strain-field hysteresis is small and comparable to that measured under similar conditions in hard Pb(Zr ,Ti)O3. A peak of piezoelectric properties can be noted close to the morphotropic phase boundary. These ceramics look very promising as possible, practicable, lead-free replacements for lead zirconate titanate.

  12. Piezoelectric properties of Li- and Ta-modified (K{sub 0.5}Na{sub 0.5})NbO{sub 3} ceramics

    SciTech Connect

    Hollenstein, Evelyn; Davis, Matthew; Damjanovic, Dragan; Setter, Nava

    2005-10-31

    Lead-free, potassium sodium niobate piezoelectric ceramics substituted with lithium (K{sub 0.5-x/2},Na{sub 0.5-x/2},Li{sub x})NbO{sub 3} or lithium and tantalum (K{sub 0.5-x/2},Na{sub 0.5-x/2},Li{sub x})(Nb{sub 1-y},Ta{sub y})O{sub 3} have been synthesized by traditional solid state sintering. The compositions chosen are among those recently reported to show high piezoelectric properties [Y. Saito, H. Takao, T. Tani, T. Nonoyama, K. Takatori, T. Homma, T. Nagaya, and M. Nakamura, Nature (London) 42, 84 (2004); Y. Guo, K. Kakimoto, and H. Ohsato, Appl. Phys. Lett. 85, 4121 (2004); Mater. Lett. 59, 241 (2005)]. We show that high densities and piezoelectric properties can be obtained for all compositions by pressureless sintering in air, without cold isostatic pressing, and without any sintering aid or special powder treatment. Resonance and converse piezoelectric (strain-field) measurements show a thickness coupling coefficient k{sub t} of 53% and converse piezoelectric coefficient d{sub 33} around 200 pm/V for the Li-substituted ceramics, and a k{sub t} of 52% and d{sub 33} over 300 pm/V for the Li- and Ta-modified samples. The unipolar strain-field hysteresis is small and comparable to that measured under similar conditions in hard Pb(Zr,Ti)O{sub 3}. A peak of piezoelectric properties can be noted close to the morphotropic phase boundary. These ceramics look very promising as possible, practicable, lead-free replacements for lead zirconate titanate.

  13. 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

  14. 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.

  15. Effect of Crystal Structure on Microwave Dielectric Properties of (Ni1/3B2/3)1-xTixO2 (B=Nb and Ta)

    NASA Astrophysics Data System (ADS)

    Kim, Eung Soo; Kang, Dong Ho; Kim, Sung Joo

    2007-10-01

    Dependence of microwave dielectric properties on the crystal structure of (Ni1/3B2/3)1-xTixO2 (B5+=Nb, Ta, 0.3≤ x≤ 0.6) were investigated. Single phase of tetragonal rutile structure was detected through the entire range of compositions (0.3≤ x≤ 0.6). Dielectric constant (K) and the temperature coefficient of resonant frequency (\\mathit{TCF}) of (Ni1/3B2/3)1-xTixO2 (B5+=Nb, Ta) increased with an increase of TiO2 content due to the increase of bond length ratio of (dapical)/(dequatorial), and the octahedral distortion of rutile structure, respectively. The specimens with smaller Ti content and/or B5+=Ta showed larger Q f value than those with larger Ti content and/or B5+=Nb.

  16. Corrosion resistance and in vitro response of a novel Ti35Nb2Ta3Zr alloy with a low Young's modulus.

    PubMed

    Guo, Yongyuan; Chen, Desheng; Lu, Weijie; Jia, Yuhua; Wang, Liqiang; Zhang, Xianlong

    2013-10-01

    β type titanium alloys have attracted much attention in the biomedical field because they consist of non-cytotoxic elements, show high corrosion resistance, and are biologically compatible. In this study, a novel β type titanium alloy (Ti35Nb3Zr2Ta) with a Young's modulus of 48 GPa was fabricated and the alloy's corrosion resistance and in vitro response were determined. The results indicate that the novel alloy exhibits comparable corrosion resistance when compared with Ti6Al4V, but in vitro experiments show that osteoblasts attach, spread, proliferate, and differentiate better on Ti35Nb2Ta3Zr than on Ti6Al4V. The high corrosion resistance and satisfactory biocompatibility make the novel Ti35Nb3Zr2Ta alloy a promising biomaterial for surgical implants.

  17. Modelling potential photovoltaic absorbers Cu3MCh4(M = V, Nb, Ta; Ch = S, Se, Te) using density functional theory.

    PubMed

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

    2016-05-05

    The geometric and electronic properties of a series of potential photovoltaic materials, the sulvanite structured Cu3MCh4(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.

  18. XPS study of bioactive graded layer in Ti-In-Nb-Ta alloy prepared by alkali and heat treatments.

    PubMed

    Lee, Baek-Hee; Kim, Young Do; Lee, Kyu Hwan

    2003-06-01

    Ti and Ti-based alloys have been widely used for the biomedical applications due to their superiorities of biocompatibility, mechanical properties and corrosion resistance. However, there has been the limiting factor for these metals to show the low affinity to the living bone. Most of commercially used Ti alloys have harmful alloying elements such as Al, V, etc. The purposes of this study are design of new Ti alloy having the good mechanical properties and corrosion resistivity without harmful alloying elements and to improve the bone-bonding ability between Ti-based alloy and living bone through the chemically activated process (alkali treatment) and thermally activated one (heat treatment). Mechanical properties of the Ti-In-Nb-Ta alloy were observed by tensile test (Instron model 8511). Corrosion potential and corrosion rate were investigated using a Potentiostate machine (EG&G, Princeton Applied Model 273, Boston, USA) with saline solution (9% NaCl) without dissolved oxygen at 37 degrees C. After alkali and heat treatments, the effects of the pre-treatments on the bonding property were evaluated by in vitro test. In this study, the surface changing behavior, which is apatite formation, of newly designed Ti-In-Nb-Ta alloy without harmful alloying elements was investigated through analyzing its surface by using X-ray photoelectron spectroscopy after surface activation treatments (alkali and heat treatments) and after subsequent soaking in the simulated body fluid.

  19. Diffusion Bonding of TA15 and Ti2AlNb Alloys: Interfacial Microstructure and Mechanical Properties

    NASA Astrophysics Data System (ADS)

    Li, Ping; Ji, Xiaohu; Xue, Kemin

    2017-03-01

    TA15 and Ti2AlNb alloys were joined by diffusion welding. The influence of holding time on morphology and mechanical properties of the joint was studied under two conditions of different bonding pressure and temperature. The interface structure was analyzed by BSE and EDS. The mechanical properties of joints were tested. The results show that the typical interfacial microstructure consists of lath α-phase (TA15 alloy)/flake α phase + α-interfacial phase + α2 phase/B2-rich phase/Ti2AlNb alloy. When bonding at 920 °C and 15 MPa with increasing holding time, the interface microstructure evolves into flake α phase and distributes as a basket-weave and the interfacial coarse spherical α phase distributes as a line. α2 phase and O phase disappear gradually while the content of the B2 phase increases. The tensile strength of the joints is 870, 892 and 903 MPa, for 120, 150 and 210 min holding time, respectively, while the elongation rises as well. When bonding at 940 °C and 10 MPa with increasing holding time, the interfacial area includes more Widmanstatten structure and B2 phase. The tensile strength of joints decreases from 921 to 908 MPa, while the elongation increases from 12 to 15.5%, for holding 120 and 210 min, respectively. The tendency of plastic fracture also increases with holding time for both temperature-pressure combinations.

  20. Corrosion resistance and in vitro response of laser-deposited Ti-Nb-Zr-Ta alloys for orthopedic implant applications.

    PubMed

    Samuel, Sonia; Nag, Soumya; Nasrazadani, Seifollah; Ukirde, Vaishali; El Bouanani, Mohamed; Mohandas, Arunesh; Nguyen, Kytai; Banerjee, Rajarshi

    2010-09-15

    While direct metal deposition of metallic powders, via laser deposition, to form near-net shape orthopedic implants is an upcoming and highly promising technology, the corrosion resistance and biocompatibility of such novel metallic biomaterials is relatively unknown and warrants careful investigation. This article presents the results of some initial studies on the corrosion resistance and in vitro response of laser-deposited Ti-Nb-Zr-Ta alloys. These new generation beta titanium alloys are promising due to their low elastic modulus as well as due the fact that they comprise of completely biocompatible alloying elements. The results indicate that the corrosion resistance of these laser-deposited alloys is comparable and in some cases even better than the currently used commercially-pure (CP) titanium (Grade 2) and Ti-6Al-4V ELI alloys. The in vitro studies indicate that the Ti-Nb-Zr-Ta alloys exhibit comparable cell proliferation but enhanced cell differentiation properties as compared with Ti-6Al-4V ELI.

  1. 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

  2. Ba 3M IIITiM VO 9 (M III = Fe, Ga, Y, Lu; M V = Nb, Ta, Sb) perovskite oxides: Synthesis, structure and dielectric properties

    NASA Astrophysics Data System (ADS)

    Joy, Joby E.; Atamanik, Eric; Mani, Rohini; Nag, Abanti; Tiwari, R. M.; Thangadurai, V.; Gopalakrishnan, J.

    2010-12-01

    We describe the synthesis, structures and dielectric properties of new perovskite oxides of the formula, Ba 3M IIITiM VO 9, for M III = Fe, Ga, Y, Lu and M V = Nb, Ta, Sb. While M V = Nb and Ta oxides adopt disordered/partially ordered 3C perovskite structures where M III/Ti/M V metal-oxygen octahedra are corner-connected, the M V = Sb oxides show a distinct preference for the 6H structure, where Sb V/Ti IV metal-oxygen octahedra share a common face forming (Sb,Ti)O 9 dimers that are corner-connected to the M IIIO 6 octahedra. The preference of antimony oxides (Sb V:4d 10) for the 6H structure - which arises from a special Sb V-O chemical bonding that tends to avoid linear Sb-O-Sb linkages unlike Nb V/Ta V:d 0 atoms which prefer ˜180° Nb/Ta-O-Nb/Ta linkages - is consistent with the crystal chemistry of M V-O oxides in general. The dielectric properties reveal a significant difference among M III members. All the oxides with the 3C structure excepting those with M III = Fe show a normal low loss dielectric behaviour with ɛ = 20-60 in the temperature range 50-400 °C; the M III = Fe members with this structure (M V = Nb, Ta) display a relaxor-like ferroelectric behaviour with large ɛ values at frequencies ≤1 MHz (50-500 °C).

  3. 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.

  4. 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

  5. A time-resolved diffraction study of the Ta--C solid combustion system

    SciTech Connect

    Larson, E.M.; Wong, J.; Holt, J.B.; Waide, P.A.; Nutt, G.; Rupp, B.; Terminello, L.J. )

    1993-07-01

    The formation of TaC and Ta[sub 2]C by combustion synthesis from their elemental constituents has been studied by time-resolved x-ray diffraction (TRXRD) using synchrotron radiation. The reactions have been followed with a time resolution down to 50 ms. Since the adiabatic temperatures for both reactions are well below any liquidus temperature in the Ta--C phase diagram, no melting occurs and these combustion reactions occur purely in the solid state. The phase transformations associated with these reactions are followed by monitoring the disappearance of reactant and appearance of product powder diffraction peaks in real time as the reaction front propagates through the combusting specimen. In the synthesis of TaC, the results show the formation of the subcarbide (Ta[sub 2]C) phase as an intermediate. In the synthesis of Ta[sub 2]C, the reaction proceeds directly to the product with no discernable intermediate Ta--C phase within a 50 ms time frame. The chemical dynamics associated with the combustion synthesis of TaC may be described by an initial phase transformation to hexagonal Ta[sub 2]C arising from carbon diffusion into the Ta metal lattice. As more carbon is available this intermediate subcarbide phase, which has one-half of its octahedral interstices occupied by the carbon, further transforms to the cubic TaC final product, in which all octahedral sites are now occupied. The time-resolved data indicate that the rate of formation of Ta[sub 2]C is a factor of two faster than that of TaC.

  6. Reverse Transformation of Deformation-Induced Phases and Associated Changes in the Microstructure of Explosively Clad Ti-5Ta-2Nb and 304L SS

    NASA Astrophysics Data System (ADS)

    Prasanthi, T. N.; Sudha, C.; Murugesan, S.; Thomas Paul, V.; Saroja, S.

    2015-10-01

    Ti-5Ta-2Nb alloy was joined to 304L austenitic stainless steel by explosive cladding technique. Explosive cladding resulted in the formation of deformation-induced martensite in 304L SS and fcc phase of Ti in the Ti-5Ta-2Nb side of the joint. The stability of these metastable phases was systematically studied using high-temperature X-ray diffraction technique and transmission electron microscopy, which enabled the optimization of the temperature window for post-cladding heat treatments.

  7. Crystal structures and photocatalysis of the triclinic polymorphs of BiNbO{sub 4} and BiTaO{sub 4}

    SciTech Connect

    Muktha, B.; Darriet, J.; Madras, Giridhar; Guru Row, T.N. . E-mail: ssctng@sscu.iisc.ernet.in

    2006-12-15

    The high-temperature polymorphs of two photocatalytic materials, BiNbO{sub 4} and BiTaO{sub 4} were synthesized by the ceramic method. The crystal structures of these materials were determined by single-crystal X-ray diffraction. BiNbO{sub 4} and BiTaO{sub 4} crystallize into the triclinic system P1-bar (No. 2), with a=5.5376(4) A, b=7.6184(3) A, c=7.9324(36) A, {alpha}=102.565(3){sup o}, {beta}=90.143(2){sup o}, {gamma}=92.788 (4){sup o}, V=326.21 (5) A{sup 3}, Z=4 and a=5.931 (1) A, b=7.672 (2) A, c=7.786 (2) A, {alpha}=102.94 (3){sup o}, {beta}=90.04 (3){sup o}{gamma}=93.53 (3){sup o}, V=344.59 (1) A{sup 3} and Z=4, respectively. The structures along the c-axis, consist of layers of [Bi{sub 2}O{sub 2}] units separated by puckered sheets of (Nb/Ta)O{sub 6} octahedra. Photocatalytic studies on the degradation of dyes indicate selectivity of BiNbO{sub 4} towards aromatics containing quinonic and azo functional groups. - Graphical abstract: Crystal structures of Bi(Nb/Ta)O{sub 4} along b-axis: triclinic form.

  8. Influence of Ti and Ta doping on the irreversible strain limit of ternary Nb3Sn superconducting wires made by the restacked-rod process

    SciTech Connect

    Cheggour, N.; Ghosh, A.; Goodrich, L.F., Stauffer, T.C., Splett, J.D., Lu, X.F., Ambrosio, G.

    2010-06-22

    Nb{sub 3}Sn superconducting wires made by the restacked-rod process (RRP{reg_sign}) were found to have a dramatically improved resilience to axial tensile strain when alloyed with Ti as compared to Ta. Whereas Ta-alloyed Nb{sub 3}Sn in RRP wires showed permanent damage to its current-carrying capacity (I{sub c}) when tensioned beyond an intrinsic strain as small as 0.04%, Ti-doped Nb{sub 3}Sn in RRP strands exhibits a remarkable reversibility up to a tensile strain of about 0.25%, conceivably making Ti-doped RRP wires more suitable for the high field magnets used in particle accelerators and nuclear magnetic resonance applications where mechanical forces are intense. A strain cycling experiment at room temperature caused a significant drop of I{sub c} in Ta-alloyed wires, but induced an increase of I{sub c} in the case of Ti-doped strands. Whereas either Ti or Ta doping yield a similar enhancement of the upper critical field of Nb{sub 3}Sn, the much improved mechanical behavior of Ti-alloyed wires possibly makes Ti a better choice over Ta, at least for the RRP wire processing technique.

  9. 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).

  10. 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.

  11. (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.

  12. 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).

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

    DOE PAGES

    Tarantini, C.; Sung, Z. -H.; Lee, P. J.; ...

    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

  14. 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.

  15. Spark Plasma Sintering of AlN Ceramics and Surface Metallization by Refractory Metal of Ti, Nb, Mo, Ta or W at Low Temperature

    NASA Astrophysics Data System (ADS)

    Kai, Ayako; Johkoh, Naoji; Miki, Toshikatsu

    2003-06-01

    Aluminum nitride (AlN) powder with no additives was sintered successfully at 1200°C in low-pressure N2 gas using a spark plasma sintering (SPS) process. The density value of the resultant ceramic is as high as 95% of the theoretical one. No openings were left in the grain boundary. If AlN powder is sandwiched by refractory metal (Ti, Nb, Mo, Ta and W) foils during SPS, one obtains AlN ceramics metallized by the refractory metals even at 1200°C. The adhesion strength of Ti, Mo or W to AlN ceramics is sufficiently high, but that of Nb or Ta is low. The characterization of metal/AlN interfaces by X-ray diffractometory (XRD), scanning electron microscopy (SEM) and electron-probe microanalysis (EPMA) has revealed the formation of a thin reaction layer at the Ti/AlN interface, which may be the reason for the high adhesion strength of the Ti/AlN interface. The high adhesion strengths of Mo/AlN and W/AlN might also be associated with thinner metal/AlN reaction layers, which were unfortunately undetectable in our XRD data. The weak adhesion of Nb/AlN and Ta/AlN interfaces was elucidated by large differences in the thermal-expansion coefficient between metallic Nb or Ta and the AlN ceramics.

  16. 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. .

  17. 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

    2016-06-07

    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.

  18. 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

  19. Large-scale Molecular Dynamics Simulations of Shock-induced Plasticity and Twinning in bcc Nb and Ta

    NASA Astrophysics Data System (ADS)

    Germann, Timothy; Zhang, Ruifeng; Ravelo, Ramon

    2013-06-01

    Large-scale classical molecular dynamics (MD) simulations are used to investigate dislocation slip and twinning activity in bcc metals under shock compression. We will discuss both the orientation-dependent response of Nb and Ta single crystals, as well as the more complex response of nanocrystalline samples. Of particular importance as MD simulations are becoming applied to model more complex materials, we will discuss issues related to the interatomic potential description and the analysis of the deformation response. Embedded atom method (EAM) potentials for shock compression studies must properly describe the energy landscape under the pressure range of interest; and an orientation imaging map technique is described for following the plastic response of fcc and bcc metals.

  20. 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. Copyright © 2016 Elsevier B.V. All rights reserved.

  1. 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.

  2. Theoretical study of B2 type technetium AB (A=Tc, B=Ti, V, Nb and Ta) intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Acharya, Nikita; Fatima, Bushra; Sanyal, Sankar P.

    2016-12-01

    The structural, electronic, elastic and thermal properties of the cubic AB type (A=Tc, B=Ti, V, Nb and Ta) technetium intermetallic compounds have been studied using the full potential linearized augmented plane wave (FP-LAPW) method within the generalized gradient approximation (GGA) and local density approximation (LDA) used for the exchange-correlation potential. The calculated lattice parameters agree well with the experimental results. The calculated electronic properties reveal that these compounds are metallic in nature with partial ionic bonding. The elastic constants obey the stability criteria for cubic system. Ductility for these compounds has been analyzed using the Pugh's rule and Cauchy's pressure revealing ductile in nature of all the compounds. Bonding nature is discussed using Fermi surface, band structure and charge density difference plots.

  3. Growth and characterization of lead-free ferroelectric (K,Na,Li)(Nb,Ta,Sb)O3 single crystal

    NASA Astrophysics Data System (ADS)

    Wang, Junjun; Zheng, Limei; Yang, Bin; Wang, Rui; Huo, Xiaoqing; Sang, Shijing; Wu, Jie; Chang, Yunfei; Ning, Huanpo; Lv, Tianquan; Cao, Wenwu

    2015-01-01

    In this work, a large size lead-free piezoelectric single crystal, (K,Na,Li)(Nb,Ta,Sb)O3 (KNLNTS) with the dimensions of 8.5×8.5×13.5 mm3 was successfully grown by the top-seeded solution growth method. This KNLNTS single crystal with high compositional homogeneity is in the tetragonal phase at room temperature. The Curie temperature TC of the tetragonal-cubic phase transition temperature is 210 °C. The piezoelectric coefficients and electromechanical coupling factors of the [001]C oriented KNLNTS single crystal are d33=172.55 pC/N, d31=-71.90 pC/N, k31=0.327, k33=0.523, and kt=0.541. In addition, the crystal shows good thermal stability so that it can be used for making high temperature electromechanical devices.

  4. First-principles investigations of metal (V, Nb, Ta)-doped monolayer MoS2: Structural stability, electronic properties and adsorption of gas molecules

    NASA Astrophysics Data System (ADS)

    Zhu, Jia; Zhang, Hui; Tong, Yawen; Zhao, Ling; Zhang, Yongfan; Qiu, Yuzhi; Lin, Xianning

    2017-10-01

    Two-dimensional (2D) layered materials are at the forefront of research because of their unique structures and promising catalytic abilities. Here, the structural stability, electronic properties and gas adsorption of metal (V, Nb, Ta)-doped monolayer MoS2 have been investigated by density functional theory calculations. Our results show that the metal (V, Nb, Ta)-doped monolayer MoS2 is a stable catalyst under room temperature, due to the strong interaction between the doped metals (V, Nb, Ta) and S vacancy of monolayer MoS2. Compared with the gas adsorption (CO, NO2, H2O, NH3) on pristine monolayer MoS2, doped metal (V, Nb, Ta) can significantly improve the adsorption properties, chemical activity and the sensitivity of that of adsorbed gas molecules. This effect occurs due to the strong overlap between the metal nd orbitals and gas molecule orbitals, result in activation of the adsorbed gas molecules. Analysis of Bader charge shows that, more charge transfer (-0.66 e to -0.72 e) occur from metal (V, Nb, Ta)-doped monolayer MoS2 to the oxidizing gas molecules (NO2) acting as acceptors. While for the adsorption of CO molecules, the relative less electrons (about -0.24 e - -0.35 e) transfer occuring from substrate to the adsorbed gases. Whereas the direction of charge transfers is reversed for the adsorption of the reducing gas (H2O and NH3) behaving as donors, in which small electrons (0.04 e -0.09 e) transfer from adsorbed gas to metal (V, Nb, Ta)-doped monolayer MoS2. Our results suggested that metal (V, Nb, Ta)-doped monolayer MoS2 might be a good candidate for low-cost, highly active, and stable catalysts and gas sensors, providing an avenue to facilitate the design of high active MoS2-based two dimensional catalysts and gas sensors.

  5. Coexistence of 1-dimensional and 3-dimensional spectral characteristics in TaTe4 and NbTe4

    NASA Astrophysics Data System (ADS)

    Zwick, F.; Berger, H.; Forro, L.; Margaritondo, G.; Grioni, M.; Laveigne, J.; Tanner, D.; Onellion, M.

    2000-03-01

    We have measured TaTe4 and NbTe4 using resistivity, optical conductivity, and angle-resolved photoemission.[1,2] Consistent with earlier reports, the resistivity and optical conductivity in different directions in the crystal exhibit a small ( ~ 10%) anisotropy. The optical conductivity exhibits a Drude peak and conductivity that scales as (1/w)2 for low photon energies (hw), again consistent with earlier results and as expected for a three-dimensional metal. The residual resistivity is below 5 mW-cm, indicating that disorder does not play a major role in these samples. However, the angle-resolved photoemission data indicate a coexistence of three-dimensional and one-dimensional properties. The three-dimensional properties include (a) quasiparticle states in all major symmetry directions of the Brillouin zone, both parallel to and perpendicular to the Ta (Nb) chains, and (b) an energy resolution-limited Fermi-Dirac cutoff of the spectral function. The quasi-one-dimensional properties include (a) dispersing coherent states only for wavevectors along the cation chains, and (b) no coherent state dispersing through or within 0.2 eV of the chemical potential. Further, we measure the resolution-limited Fermi-Dirac cutoff of the spectral function at every point of the Brillouin zone for which we took data, including all three high symmetry directions. (*) Present address: ABB Corp., Zürich, Switzerland 1. F. Zwick et.al., Phys. Rev. B 59 , 7762 (1999). 2. F. Zwick, Ph.D. thesis, EPFL, September, 1998.

  6. 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.

  7. 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. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

  8. Low-temperature structural and dielectric phenomena in La1/3NbO3 and La1/3TaO3: Comparative study

    NASA Astrophysics Data System (ADS)

    Salak, Andrei N.; Vyshatko, Nikolai P.; Khalyavin, Dmitry D.; Prokhnenko, Oleksandr; Ferreira, Victor M.

    2008-10-01

    The crystal structures of the perovskites La1/3NbO3 and La1/3TaO3 were studied between 10 and 350 K using high-resolution neutron powder diffraction and compared with their radio-frequency dielectric response over the same temperature range. The structure of La1/3NbO3 remains orthorhombic Cmmm, while La1/3TaO3 undergoes continuous transition from the high-temperature tetragonal P4/mmm to Cmmm phase at about 220 K. This transition is tricritical in nature and accompanied by no dielectric anomaly. In La1/3NbO3, the frequency-dependent peak of the dielectric permittivity is associated with an atypical increase in the lattice parameters below about 80 K.

  9. Electrical Properties and Superconductivity of MSr2Nd2-xCexCu2O10-δ (M=Ta, Nb)

    NASA Astrophysics Data System (ADS)

    Zhu, Yingjie; Qian, Yitai; Li, Rukang; Wang, Shiwei; Chen, Zuyao; Chen, Zhaojia; Wang, Nanling; Zhou, Guien

    1992-09-01

    A new series of layered cuprate compounds MSr2Nd2-xCexCu2O10-δ (M=Ta, Nb) have been synthesized. The structure of the compounds is similar to that of T1-1222. A peak in the R-T curve for the sample of TaSr2Nd1.3Ce0.7Cu2O10-δ has been observed at about 50 K. For the sample of NbSr2Nd1.45Ce0.55Cu2O10-δ, metal-like conductivity behaviour has been observed. We have found superconductivity at about 13.2 K in the samples of NbSr2Nd2-xCexCu2O10-δ (x=0.49, 0.50, 0.51, 0.52).

  10. 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.

  11. The optical band gap of LiTaO3 and Nb2O5-doped LiTaO3 thin films based on Tauc Plot method to be applied on satellite

    NASA Astrophysics Data System (ADS)

    Estrada, R.; Djohan, N.; Pasole, D.; Dahrul, M.; Kurniawan, A.; Iskandar, J.; Hardhienata, H.; Irzaman

    2017-01-01

    This research observed the optical band gap of thin films made from LiTaO3 undoped (0%) and doped (5% and 10%) with Nb2O5 in the 1 M-solubility deposited on n-type Si (111) substrates. The thin films are manufactured with coating process of substrates by Chemical Solution Deposition (CSD) method using a spin coater device at a rotation speed of 3000 rpm for 30 seconds and annealed in furnace (Nabertherm B180) at a temperature of 850°C for 15 hours. The optical absorption data of thin films are obtained by using an Ocean Optics USB2000 device in the wavelength of visible light. The band gap curve is determined from optical absorption data processing using Tauc Plot method. The Tauc Plot with indirect transition shows that LiTaO3 doped with Nb2O5 provides increased optical band gap value in a range less than 3.5 eV. Based on the results of this research, it can be concluded that LiTaO3 and Nb2O5-doped LiTaO3 thin films on n-type Si (111) substrate are semiconductor materials and has the potential to be applied on satellite.

  12. Materials Study of NbN and Ta x N Thin Films for SNS Josephson Junctions

    DOE PAGES

    Missert, Nancy; Brunke, Lyle; Henry, Michael D.; ...

    2017-02-15

    We investigated properties of NbN and TaxN thin films grown at ambient temperatures on SiO2/Si substrates by reactive-pulsed laser deposition and reactive magnetron sputtering (MS) as a function of N2 gas flow. Both techniques produced films with smooth surfaces, where the surface roughness did not depend on the N2 gas flow during growth. High crystalline quality, (111) oriented NbN films with Tc up to 11 K were produced by both techniques for N contents near 50%. The low temperature transport properties of the TaxN films depended upon both the N2 partial pressure used during growth and the film thickness. Furthermore,more » the root mean square surface roughness of TaxN films grown by MS increased as the film thickness decreased down to 10 nm.« less

  13. NbF5 and TaF5: Assignment of 19F NMR resonances and chemical bond analysis from GIPAW calculations

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

    The 19F isotropic chemical shifts (δiso) of two isomorphic compounds, NbF5 and TaF5, which involve six nonequivalent fluorine sites, have been experimentally determined from the reconstruction of 1D 19F MAS NMR spectra. In parallel, the corresponding 19F chemical shielding tensors have been calculated using the GIPAW method for both experimental and DFT-optimized structures. Furthermore, the [M4F20] units of NbF5 and TaF5 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 19F NMR lines of NbF5 and TaF5 is obtained, ensured by the linearity between experimental 19F δiso values and calculated 19F isotropic chemical shielding σiso values. The effects of the geometry optimizations have been carefully analyzed, confirming among other matters, the inaccuracy of the experimental structure of NbF5. 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 19F NMR lines of NbF5, distorted multiplets, arising from 1J-coupling and residual dipolar coupling between the 19F and 93Nb nuclei, were simulated yielding to values of 93Nb-19F 1J-coupling for the corresponding fluorine sites.

  14. Two-Dimensional Nb-Based M 4 C 3 Solid Solutions (MXenes)

    DOE PAGES

    Yang, Jian; Naguib, Michael; Ghidiu, Michael; ...

    2015-10-15

    Two new two-dimensional Nb4C3-based solid solutions (MXenes), (Nb0.8,Ti0.2)4C3Tx and (Nb0.8,Zr0.2)4C3Tx (where T is a surface termination) were synthesizedas confirmed by X-ray diffractionfrom their corresponding MAX phase precursors (Nb0.8,Ti0.2)4AlC3 and (Nb0.8,Zr0.2)4AlC3. In our report we discuss Zr-containing MXene. We also studied intercalation of Li ions into these two compositions, and Nb4C3Tx in order to determine the potential of those materials for energy storage applications. Lithiation and delithiation peaks at 2.26 and 2.35 V, respectively, appeared in the case of Nb4C3Tx, but were not present in Nb2CTx. After 20 cycles at a rate of C/4, the specific capacities of (Nb0.8,Ti0.2)4C3Txand (Nb0.8,Ti0.2)4C3Tx weremore » 158 and 132 mAh/g, respectively, both slightly lower than the capacity of Nb4C3Tx.« less

  15. 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.

  16. Ion-Beam Deposition of Nb and Ta Refractory Superconducting Films,

    DTIC Science & Technology

    1982-01-01

    physical separation of the deposition substrate from the plasma t5 and high energy particles. Photoresist processing is one such advantage.5 Refractory...grid current to 13 mA and the plasma discharge voltage (a lesser value for Xe) produced the highest T Nb films at c a given beam power. This...Electron Dev. ED-27, 1998 (1980). 10.) E. I. Alessandrini, R. B. Laibowitz, and J. M. Viggiano , J. Vac. Sci. Technol. 18, 318 (1981). 11.) W. E. J. Neal

  17. Transport and thermoelectric properties of Sr3(Ti0.95R0.05)2O7 (R = Ta, Nb, W) oxides

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    The Sr3(Ti0.95R0.05)2O7 (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 ρ for all the doped compounds increases monotonically with temperature, and basically can be described by a relation ρ ∝ TM at T > ˜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 ρ of Sr3(Ti0.95Ta0.05)2O7 exhibits a metallic-like behavior at the temperature as low as 5 K, a transition from metallic state (dρ/dT > 0) to semiconductor-like state (dρ/dT < 0) was observed at a critical low temperature ˜41 K and ˜79 K for R = Nb and W, respectively. At T < ˜22 K, ˜57 K, and ˜80 K, a relation of σ ∝ T1/2 (here conductivity σ = 1/ρ) holds for the doped compounds with R = Nb, Ta, and W, respectively, suggesting that at the low temperatures the main transport mechanism is electron-electron interaction due to the presence of disorder induced by the dopants. The thermoelectric figure of merit (ZT) for Ta-doped compound increases more steeply with increasing temperature among the three compounds and reaches 0.066 at 1000 K.

  18. Differing reactivities of (trimpsi)M(CO)(2)(NO) complexes [M = V, Nb, Ta; trimpsi = (t)BuSi(CH(2)PMe(2))(3)] with halogens and halogen sources.

    PubMed

    Hayton, Trevor W; Legzdins, Peter; Patrick, Brian O

    2002-10-21

    Treatment of (trimpsi)V(CO)(2)(NO) (trimpsi = (t)BuSi(CH(2)PMe(2))(3)) with 1 equiv of PhICl(2) or C(2)Cl(6) or 2 equiv of AgCl affords (trimpsi)V(NO)Cl(2) (1) in moderate yields. Likewise, (trimpsi)V(NO)Br(2) (2) and (trimpsi)V(NO)I(2) (3) are formed by the reactions of (trimpsi)V(CO)(2)(NO) with Br(2) and I(2), respectively. The complexes (trimpsi)M(NO)I(2)(PMe(3)) (M = Nb, 4; Ta, 5) can be isolated in moderate to low yields when the (trimpsi)M(CO)(2)(NO) compounds are sequentially treated with 1 equiv of I(2) and excess PMe(3). The reaction of (trimpsi)V(CO)(2)(NO) with 2 equiv of ClNO forms 1 in low yield, but the reactions of (trimpsi)M(CO)(2)(NO) (M = Nb, Ta) with 1 equiv of ClNO generate (trimpsi)M(NO)(2)Cl (M = Nb, 6; Ta, 7). Complexes 6 and 7 are thermally unstable and decompose quickly at room temperature; consequently, they have been characterized solely by IR and (31)P[(1)H] NMR spectroscopies. All other new complexes have been fully characterized by standard methods, and the solid-state molecular structures of 1.3CH(2)Cl(2), 4.(3/4)CH(2)Cl(2), and 5.THF have been established by single-crystal X-ray diffraction analyses. A convenient method of generating Cl(15)NO has also been developed during the course of these investigations.

  19. STRUCTURE AND HIGH-FIELD PERFORMANCE OF JELLY ROLL PROCESSED Nb{sub 3}Sn WIRES USING Sn-Ta AND Sn-Ti BASED ALLOY SHEET

    SciTech Connect

    Tachikawa, K.; Tsuyuki, T.; Hayashi, Y.; Nakata, K.; Takeuchi, T.

    2008-03-03

    Sn-Ta based alloy buttons of different compositions were prepared by the melt diffusion process among constituent metal powders, and then pressed into plates. Meanwhile Sn-Ti based alloy plates were sliced from the melt and cast ingot. Resulting Sn-based alloy plates were rolled into thin sheets. The Sn-based alloy sheet was laminated with a Nb sheet, and wound into a Jelly Roll (JR) composite. The composite was encased in a sheath, and fabricated into a thin wire followed by the heat treatment. The application of hydrostatic extrusion is useful at the initial stage of the fabrication. The JR wires using Sn-Ta and Sn-Ti based alloy sheets show a non-Cu J{sub c} of {approx}250 A/mm{sup 2} and {approx}150 A/mm{sup 2} at 20 T and 22 T, respectively, at 4.2 K. It has been found that the Nb impregnates into the Sn-based alloy layers during the reaction, and Nb{sub 3}Sn layers are synthesized by the mutual diffusion between the Nb sheet and the Sn-based alloy sheet without formation of voids. Sn-Ti based alloy sheets are attractive due to their easiness of mass production. Structure and high-field performance of JR processed Nb{sub 3}Sn wires prepared from Sn-based alloy sheets with different compositions are compared in this article.

  20. 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.

  1. CO oxidation on Ta-Modified SnO2 solid solution catalysts

    NASA Astrophysics Data System (ADS)

    Han, Xue; Xu, Xianglan; Liu, Wenming; Wang, Xiang; Zhang, Rongbin

    2013-06-01

    Co-precipitation method was adopted to prepare Sn-Ta mixed oxide catalysts with different Sn/Ta molar ratios and used for CO oxidation. The catalysts were investigated by N2-Brunauer-Emmett-Teller (N2-BET), X-ray diffraction patterns (XRD), H2-temperature programmed reduction (H2-TPR), Thermal Gravity Analysis - Differential Scanning Calorimetry (TGA-DSC) techniques. It is revealed that a small amount of Ta cations can be doped into SnO2 lattice to form solid solution by co-precipitation method, which resulted in samples having higher surface areas, improved thermal stability and more deficient oxygen species on the surface of SnO2. As a result, those Sn rich Sn-Ta solid solution catalysts with an Sn/Ta molar ratio higher than 4/2 showed significantly enhanced activity as well as good resistance to water deactivation. It is noted here that if tantala disperses onto SnO2 surface instead of doping into its lattice, it will then have negative effect on its activity.

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

    SciTech Connect

    Wachowski, S.; Gazda, M.

    2014-11-15

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

  3. Intergrowth of hexagonal tungsten bronze and perovskite-like structures: The oxides ACu 3M7O 21 ( A = K, Rb, Cs, TI; M = Nb, Ta)

    NASA Astrophysics Data System (ADS)

    Benmoussa, A.; Groult, D.; Studer, F.; Raveau, B.

    1982-02-01

    Seven oxides ACu 3M7O 21 have been isolated with A = K, Rb, Tl, Cs for M = Ta and A = K, Rb, Cs for M = Nb. These phases are orthorhombic: a ⋍ 28 Å, b ⋍ 7.50 Å, and c ⋍ 7.55 Å, probable space group Cmmm. Their structure has been established from an X-ray diffraction study and from high-resolution microscopy observations. The structure consists of an intergrowth of single hexagonal tungsten bronze AM3O 9 slices and double distorted perovskite Cu 3M4O 12 slabs ( M = Nb, Ta) in which copper has a square coordination. The host lattice of these compounds can be considered as the member " n = 1; n' = 2" of a series of intergrowths corresponding to the formulation | M3O 9| Hn| M2O 6| Pn' .

  4. Li6La3SnMO12 (M = Sb, Nb, Ta), a Family of Lithium Garnets with High Li-Ion Conductivity

    SciTech Connect

    Bridges, Craig A; Goodenough, J. B.; Gupta, Dr Asha; Nakanishi, Masahiro; Paranthaman, Mariappan Parans; Sokolov, Alexei P; Bi, Zhonghe; Li, Yutao; Han, Jiantao; Dong, Youzhong; Wang, Long; Xu, Maowen

    2012-01-01

    In order to investigate the influence of covalent bonding within the garnet framework on the conductivity of Li+ in the interstitial space, the Li+ conductivities in the family of Sn-based compounds Li6La3 SnMO12 (M = Sb, Nb, Ta) have been obtained and are compared with those of Li6La3ZrMO12. Refinement of the neutron diffraction pattern of Li6La3 SnNbO12shows that the interstitial tetrahedral sites (24d ) are about half-occupied and most of the Li in the interstitial bridging octahedral sites are displaced from the center position (48g ). The Sb-based compound has the largest lattice parameter while the Ta-based compound has the highest Li+-ion conductivity of 0.42 10 4 Scm 1.

  5. Shock compression of NbH0.75 and TaH0.50: Universal compression behavior of hydrogen in metallic environments

    NASA Astrophysics Data System (ADS)

    Taguchi, Hiroaki; Fukai, Yuh; Atou, Toshiyuki; Fukuoka, Kiyoto; Syono, Yasuhiko

    1994-02-01

    Shock-compression experiments were performed on NbH0.75 to 150 GPa and TaH0.50 to 210 GPa using a 25-mm propellant gun and a 20-mm two-stage light-gas gun. Linear relations were found between the shock velocity Us and the particle velocity up: Us=4.79+1.14up for NbH0.75 and Us=3.44+1.23up for TaH0.50. Compression curves of interstitial hydrogen, deduced from the Hugoniots of these hydrides and original metals, come close to the one calculated for metallic hydrogen. These data provide additional examples of a universal compression behavior of hydrogen in a metallic environment.

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

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

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

  7. Niobium-tantalum oxide minerals in the Jezuitské Lesy granitic pegmatite, Bratislava Massif, Slovakia: Ta to Nb and Fe to Mn evolutionary trends in a narrow Be,Cs-rich and Li,B-poor dike

    NASA Astrophysics Data System (ADS)

    Chudík, Peter; Uher, Pavel; Gadas, Petr; Škoda, Radek; Pršek, Jaroslav

    2011-10-01

    A complex assemblage of Nb-Ta-(Sn) oxide minerals occur in a relatively narrow (~1-2 m thick) extensively albitized, Hercynian granitic pegmatite dike intruding biotite granodiorites near Bratislava, SW Slovakia. The dike shows enrichment in beryl (locally Cs-rich) but absence of Li- and B-rich phases. Compositions and textural relationships indicate complex evolutions of Nb-Ta oxide phases with several generations presenting distinct textural and compositional features. The first generation of the Nb-Ta minerals from the quartz-microcline-muscovite zone show Ta,Fe-rich compositions with Ta# [Ta/(Ta + Nb)] = 0.52-0.70 (Ct I columbite-tantalite), 0.88-0.90 (Tap I ferrotapiolite) and 0.73-0.86 (Fw I ferrowodginite); Mn# [Mn/(Mn + Fe)] = 0.32-0.49 (Ct I), 0.06-0.10 (Tap I) and 0.33-0.41 (Fw I). The 2nd generation is represented by ferrocolumbite to ferrotantalite (Ct II) in saccharoidal albite zone, replacement zones of Ct II in Ct I, and irregular overgrowths of ferrotapiolite (Tap II) and ferrowodginite (Fw II) on Tap I grains. The minerals of the 2nd generation show decreasing of Ta# in comparison to the 1st group: 0.10-0.60 (Ct II), 0.85-0.87 (Tap II) and 0.73-0.77 (Fw II); Mn# attains 0.30-0.45 (Ct II), 0.06-0.09 (Tap II) and 0.26-0.37 (Fw II). The 3rd generation includes fissure fillings, overgrowths and replacement zones of manganocolumbite and manganotantalite (Ct III), ferrotapiolite (Tap III) and ferrowodginite (Fw III) on the older Nb-Ta phases (Ct I, Tap I, Fw I, Fw II), in the coarse-grained unit. The 3rd population displays distinct Mn# increasing (Ct III: 0.51-0.69, Tap III: 0.11-0.24, Fw III: 0.40-0.41), Ta# values reach 0.16-0.79 (Ct III), 0.88-0.92 (Tap III) and 0.80-0.81 (Fw III). The latest, 4th generation of the Nb-Ta phases represents irregular veinlets and patches of fluorcalciomicrolite, replacing Ct I, Tap I, Fw I, Ct II and Tap III. Decrease of Ta/(Ta + Nb) values in Ct II from the saccharoidal albite unit can be explained by crystallization

  8. Direct observation of {beta}-TaH phase precipitation in tantalum{endash}hydrogen solid solution

    SciTech Connect

    Chen, C.L.; Zhou, D.S.; Mitchell, T.E.; Ye, H.Q.

    1996-07-01

    An ordered {beta}-Ta{sub 2}H tantalum hydride precipitate and a disordered {alpha}-Ta{endash}H solid solution matrix have been observed directly by field ion microscopy and analyzed by atom probe analysis. The ordered and disordered field ion images have been explained by the electronic transition rate in the theory of field ionization. On the other hand, we found surprisingly that the field evaporation voltage dramatically decreased to approximately one half of its original evaporation voltage as the evaporation of the precipitate moves toward the phase boundary, which may due to the effects of the interface energy. {copyright} {ital 1996 American Vacuum Society}

  9. 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.

  10. 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.

  11. 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.

  12. Dispersion and solubility of In, Tl, Ta and Nb in the aquatic environment and intertidal sediments of the Scheldt estuary (Flanders, Belgium).

    PubMed

    Folens, Karel; Du Laing, Gijs

    2017-09-01

    Certain specialty elements are indispensable in modern technologies for their particular properties. Yet, potential risks associated to the release of these elements at any stage, remains unknown. Therefore, the dispersion of indium (In), thallium (Tl), tantalum (Ta) and niobium (Nb) in the aquatic environment of the Scheldt estuary (Flanders, Belgium) was studied. Maximum concentrations in intertidal sediments of 101 ± 15 μg kg(-1) for In, 481 ± 37 μg kg(-1) for Tl, 88 ± 19 μg kg(-1) for Ta and 1162 ± 4 μg kg(-1) for Nb appeared on the sampling location closest to the river mouth, i.e. 57.5 km upstream. Their distribution in the intertidal sediments depends on the physicochemical sediment characteristics along the flow of the river Scheldt. The same was the case for most other metals and aluminum as their occurrence also correlated (p < 0.05) with the occurrence of In, Tl and Nb. While in general, studied elements correlate to the OM content and sulfur and phosphorus herein included, a relative enrichment of In, Tl and Nb was seen at Rupelmonde (92.0 km from the river mouth). Mainly the intertidal sediment silt fraction is capable of retaining the elements by exchanging with other ions in the mineral interlayer. Increasing salinity towards the river mouth can furthermore induce the formation of insoluble chloride species. Overall, the solubility of In, Tl, Ta and Nb appeared extremely low upon extraction of pore water from intertidal sediments saturated to 100% field capacity. Copyright © 2017 Elsevier Ltd. All rights reserved.

  13. Microstructure, Tensile and Creep Properties of Ta20Nb20Hf20Zr20Ti20 High Entropy Alloy.

    PubMed

    Larianovsky, Natalya; Katz-Demyanetz, Alexander; Eshed, Eyal; Regev, Michael

    2017-07-31

    This paper examines the microstructure and mechanical properties of Ta20Nb20Hf20Zr20Ti20. Two casting processes, namely, gravity casting and suction-assisted casting, were applied, both followed by Hot Isostatic Pressing (HIP). The aim of the current study was to investigate the creep and tensile properties of the material, since the literature review revealed no data whatsoever regarding these properties. The main findings are that the HIP process is responsible for the appearance of a Hexagonal Close Packed (HCP) phase that is dispersed differently in these two castings. The HIP process also led to a considerable increase in the mechanical properties of both materials under compression, with values found to be higher than those reported in the literature. Contrary to the compression properties, both materials were found to be highly brittle under tension, either during room temperature tension tests or creep tests conducted at 282 °C. Fractography yielded brittle fracture without any evidence of plastic deformation prior to fracture.

  14. Increasing strength of a biomedical Ti-Nb-Ta-Zr alloy by alloying with Fe, Si and O.

    PubMed

    Stráský, Josef; Harcuba, Petr; Václavová, Kristína; Horváth, Klaudia; Landa, Michal; Srba, Ondřej; Janeček, Miloš

    2017-07-01

    Low-modulus biomedical beta titanium alloys often suffer from low strength which limits their use as load-bearing orthopaedic implants. In this study, twelve different Ti-Nb-Zr-Ta based alloys alloyed with Fe, Si and O additions were prepared by arc melting and hot forging. The lowest elastic modulus (65GPa) was achieved in the benchmark TNTZ alloy consisting only of pure β phase with low stability due to the 'proximity' to the β to α'' martensitic transformation. Alloying by Fe and O significantly increased elastic modulus, which correlates with the electrons per atom ratio (e/a). Sufficient amount of Fe/O leads to increased yield stress, increased elongation to fracture and also to work hardening during deformation. A 20% increase in strength and a 20% decrease in the elastic modulus when compared to the common Ti-6Al-4V alloy was achieved in TNTZ-Fe-Si-O alloys, which proved to be suitable for biomedical use due to their favorable mechanical properties. Copyright © 2017 Elsevier Ltd. All rights reserved.

  15. The Mode of Deformation in a Cold-Swaged Multifunctional Ti-Nb-Ta-Zr-O Alloy

    NASA Astrophysics Data System (ADS)

    Guo, W.; Quadir, M. Z.; Ferry, M.

    2013-05-01

    Multifunctional titanium alloys, termed Gum Metal™, are β-phase Ti alloys first developed in 2003. These alloys exhibit many interesting properties including, for example, low rate of work-hardening and superplasticity during cold deformation. The original report described a new plastic deformation mechanism not involving major dislocation activity to explain such deformation behavior. In the current study, a comparable Ti-36.8Nb-2.7Zr-2.0Ta-0.44O (wt pct) alloy to the original investigators was produced by powder sintering, hot forging, solution treatment, and cold swaging with the aim at investigating the microstructural development during swaging. XRD and TEM showed that the forged/solution-treated alloy was β-phase with a small amount of ω-phase. After cold swaging by up to 96 pct area reduction, TEM/HRTEM revealed the existence of dislocations, deformation twins, ω-phase, nanodisturbances, and lattice bending, with EBSD showing the grains to be highly elongated in the swaging direction, fragmented, and distorted. Most notably, swaging also generated a strong <110> fiber texture, even after moderate strains. The foregoing structural analysis provides substantial evidence that dislocations are present in the alloy after cold swaging. The major support of dislocation glide processes acting as the dominant plastic deformation mode in the swaged alloy is the strong <110> fiber texture that develops, which is a characteristic feature of all cold-drawn/swaged body centered cubic metals and alloys.

  16. Evolution of Microstructure and Texture during Recrystallization of the Cold-Swaged Ti-Nb-Ta-Zr-O Alloy

    NASA Astrophysics Data System (ADS)

    Guo, W. Y.; Xing, H.; Sun, J.; Li, X. L.; Wu, J. S.; Chen, R.

    2008-03-01

    The deformed microstructure and evolution of microstructure and texture during recrystallization of the cold-swaged multifunctional Ti-23Nb-0.7Ta-2Zr-1.2O (TNTZO, at. pct) alloy were investigated by optical microscope, electron backscatter diffraction, and transmission electron microscope. This alloy has been reported, by Saito et al., to possess a specific dislocation-free plastic deformation mechanism. In this study, the results show a curly grain or swirled structure and a pronounced fibrous {left< {110} rightrangle } texture along the swaging axis in the cold-swaged TNTZO alloy. The normal to the swirled grain surface is near {left< {001} rightrangle } in the cross section of the rod. This characteristic microstructure can be considered to arise from the plane strain deformation of the grains under applied stress, which is similar to that in ordinary bcc metals after heavily drawing or swaging. It is also shown that recovery involves the redistribution and partial annihilation of dislocations within the deformation bands, and recrystallization proceeds by a typical new grain nucleation-growth mechanism during annealing of the TNTZO alloy. The fibrous {left< {110} rightrangle } deformation texture is gradually replaced by random orientations with increasing annealing time. Thus, it could be concluded that the TNTZO alloy deforms by the traditional dislocation glide on {left< {111} rightrangle }{left\\{ {110} right\\}} , {112}, or {123} slip systems, rather than the dislocation-free mechanism.

  17. 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.

  18. 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. Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  19. Microstructure, Tensile and Creep Properties of Ta20Nb20Hf20Zr20Ti20 High Entropy Alloy

    PubMed Central

    Larianovsky, Natalya; Katz-Demyanetz, Alexander; Eshed, Eyal; Regev, Michael

    2017-01-01

    This paper examines the microstructure and mechanical properties of Ta20Nb20Hf20Zr20Ti20. Two casting processes, namely, gravity casting and suction-assisted casting, were applied, both followed by Hot Isostatic Pressing (HIP). The aim of the current study was to investigate the creep and tensile properties of the material, since the literature review revealed no data whatsoever regarding these properties. The main findings are that the HIP process is responsible for the appearance of a Hexagonal Close Packed (HCP) phase that is dispersed differently in these two castings. The HIP process also led to a considerable increase in the mechanical properties of both materials under compression, with values found to be higher than those reported in the literature. Contrary to the compression properties, both materials were found to be highly brittle under tension, either during room temperature tension tests or creep tests conducted at 282 °C. Fractography yielded brittle fracture without any evidence of plastic deformation prior to fracture. PMID:28773245

  20. (K, Na, Li)(Nb, Ta)O3:Mn lead-free single crystal with high piezoelectric properties

    PubMed Central

    Huo, Xiaoqing; Zhang, Rui; Zheng, Limei; Zhang, Shujun; Wang, Rui; Wang, Junjun; Sang, Shijing; Yang, Bin; Cao, Wenwu

    2016-01-01

    Lead-free single crystal, (K, Na, Li)(Nb, Ta)O3:Mn, was successfully grown using top-seeded solution growth method. Complete matrix of dielectric, piezoelectric and elastic constants for [001]C poled single crystal was determined. The piezoelectric coefficient d33 measured by the resonance method was 545 pC/N, which is almost three times that of its ceramic counterpart. The values measured by the Berlincourt meter ( d33∗=630pC/N) and strain-field curve ( d33∗∗=870pm/V) were even higher. The differences were assumed to relate with the different extrinsic contributions of domain wall vibration and domain wall translation during the measurements by different approaches, where the intrinsic contribution (on the order of 539 pm/V) was supposed to be the same. The crystal has ultrahigh electromechanical coupling factor (k33 ~ 95%) and high ultrasound velocity, which make it promising for high frequency medical transducer applications. PMID:27594704

  1. 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

  2. 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.

  3. 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

    2016-07-15

    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'.

  4. 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’.

  5. 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.

  6. 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

    2016-10-01

    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.

  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. 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.

  9. Temperature-induced solid-phase oriented rearrangement route to the fabrication of NaNbO3 nanowires.

    PubMed

    Liu, Lei; Li, Bo; Yu, Dinghua; Cui, Yuming; Zhou, Xingfu; Ding, Weiping

    2010-01-21

    We proposed here a temperature-induced solid-phase oriented rearrangement route to the fabrication of NaNbO(3) nanowires by using sandia octahedral molecular sieves (SOMS) Na(2)Nb(2)O(6) x H(2)O as a precursor. The SOMS precursor was prepared by using metal Nb powder as a raw material through the hydrothermal approach.

  10. Oxidation Behavior of a Refractory NbCrMo0.5Ta0.5TiZr Alloy

    DTIC Science & Technology

    2014-04-01

    better combination of mechanical properties and oxidation resistance than commercial Nb alloys and earlier reported developmental Nb–Si–Al–Ti and Nb...The alloy has a better combination of mechanical properties and oxidation resistance than com- mercial Nb alloys and earlier reported developmental Nb...damage, is dif- ficult to achieve [2]. Thus, new metallic systems with higher melting points and a good balance of structural properties at high

  11. Extension of the La{sub 7}Mo{sub 7}O{sub 30} structural type with La{sub 7}Nb{sub 3}W{sub 4}O{sub 30} and La{sub 7}Ta{sub 3}W{sub 4}O{sub 30} compounds

    SciTech Connect

    Goutenoire, F. . E-mail: goutenoire.francois@univ-lemans.fr; Kodjikian, S.; Suard, E.

    2005-09-15

    Two compounds of formula La{sub 7}A{sub 3}W{sub 4}O{sub 30} (with A=Nb and Ta) were prepared by solid-state reaction at 1450 and 1490{sup o}C. They crystallize in the rhombohedric space group R-3 (No. 148), with the hexagonal parameters: a=17.0640(2)A, c=6.8859(1)A and a=17.0701(2)A, c=6.8851(1)A. The structure of the materials was analyzed from X-ray, neutron and electronic diffraction. These oxides are isostructural of the reduced molybdenum compound La{sub 7}Mo{sub 7}O{sub 30}, which are formed of perovskite rod along [111]. An order between (Nb, Ta) and W is observed.

  12. Improvement of Li ion conductivity of Li5La3Ta2O12 solid electrolyte by substitution of Ge for Ta

    NASA Astrophysics Data System (ADS)

    Kotobuki, Masashi; Song, Shufeng; Takahashi, Rika; Yanagiya, Shunichi; Lu, Li

    2017-05-01

    Li5La3Ta2O12 (LLTa) is a promising solid electrolyte for all-solid-state batteries due to its high stability in contact with Li metal, however, low Li ion conductivity of LLTa has restricted its application. In this study, improvement of the Li ion conductivity of LLTa solid electrolyte by substitution of Ge4+ for Ta5+ is studied because the improvement is thought to be achieved by increase of charge carrier concentration caused by the substitution of low valence Ge4+ for high valence Ta5+. The Ge substitution shrinks a lattice of cubic LLTa due to small ion radius of Ge4+ (0.530 Å) compared with Ta5+ (0.640 Å). The Li ion conductivity of LLTa is improved by the Ge substitution. The highest bulk and total Li ion conductivities are obtained in Li5.25La3Ta1.75Ge0.25O12 prepared by spark plasma sintering at 1100 °C and the values are 1.3 × 10-4 and 8.4 × 10-5 S cm-1 at 28 °C, respectively. The lithium transference number of the Ge-substituted LLTa determined by Hebb-Wagner (HW) polarization method is ≈ 1. Also, it is verified that the new solid electrolyte is stable in a potential range of 0-10 V vs. Li/Li+, indicating that the Ge-substituted LLTa is a promising solid electrolyte for all-solid-state battery application.

  13. Structural characterization and electrical properties of NiNb{sub 2-x}Ta{sub x}O{sub 6} (0<=x<=2) and some Ti-substituted derivatives

    SciTech Connect

    Lopez-Blanco, M.; Amador, U.; Garcia-Alvarado, F.

    2009-07-15

    A structural and electrical characterization of the system NiNb{sub 2-x}Ta{sub x}O{sub 6} (0<=x<=2) is presented. For x<=0.25 materials with the columbite-type structure typical of NiNb{sub 2}O{sub 6} have been obtained whereas for x>=1 tri-rutile-like oxides were obtained. The electrical properties are similar in both cases; they are semiconducting with very low electrical conductivity and very high activation energy, though slight differences were found as a function of Ta content. Improvement of conductivity by reducing the stoichiometric materials could not be achieved due to decomposition. In this connection, partial substitution of Nb or Ta by Ti has been carried out in order to create oxygen vacancies. Tantalum was partially replaced by Ti to a significant extent in the tri-rutile structure inducing a slight increasing of conductivity. However, for the columbite case neither Nb nor Ta could be partially replaced. This behavior is quite different from that reported for other similar columbites such as MnNb{sub 2}O{sub 6-{delta}}, which exhibits high electrical conductivity upon substitution of niobium by titanium. - Graphical abstract: NiNb{sub 2-x}Ta{sub x}O{sub 6} exhibits the columbite structure for low tantalum contents whereas high contents of tantalum stabilize a trirutile-like structure. Electrical conductivity decreases as tantalum content increases in both columbite and tri-rutile.

  14. 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

  15. Instability of the Ionic Conductor Li6BaLa2B2O12 (B = Nb, Ta): Barium Exsolution from the Garnet Network Leading to CO2 Capture.

    PubMed

    Galven, Cyrille; Corbel, Gwenaël; Le Berre, Françoise; Crosnier-Lopez, Marie-Pierre

    2016-12-19

    The instability of the two garnets Li6BaLa2B2O12 (B = Nb, Ta) has been studied on samples prepared in powder form by solid-state reaction. For this study, we coupled different techniques: powder X-ray diffraction, IR spectrometry, thermal analysis, transmission electron microscopy, and complex impedance spectroscopy. We showed that in ambient air and at low temperature (<150 °C), a spontaneous Li(+)/H(+) exchange occurs. At higher temperature (500-700 °C), a progressive exsolution of the barium from the garnet framework is observed, leading to the formation of a second garnet, BaCO3, and a 3D cubic perovskite. To conclude this work, we studied the impact of barium exsolution on the ionic conductivity measured by complex impedance spectroscopy. We observed a significant decrease in the starting bulk conductivity (60%) when the pellet is heated at 500 °C for 5 h.

  16. 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.

  17. 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.

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

    NASA Astrophysics Data System (ADS)

    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.

    2010-04-01

    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 MF73- (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.

  19. Bond dissociation energies of TiSi, ZrSi, HfSi, VSi, NbSi, and TaSi

    NASA Astrophysics Data System (ADS)

    Sevy, Andrew; Sorensen, Jason J.; Persinger, Thomas D.; Franchina, Jordan A.; Johnson, Eric L.; Morse, Michael D.

    2017-08-01

    Predissociation thresholds have been observed in the resonant two-photon ionization spectra of TiSi, ZrSi, HfSi, VSi, NbSi, and TaSi. It is argued that because of the high density of electronic states at the ground separated atom limit in these molecules, the predissociation threshold in each case corresponds to the thermochemical bond dissociation energy. The resulting bond dissociation energies are D0(TiSi) = 2.201(3) eV, D0(ZrSi) = 2.950(3) eV, D0(HfSi) = 2.871(3) eV, D0(VSi) = 2.234(3) eV, D0(NbSi) = 3.080(3) eV, and D0(TaSi) = 2.999(3) eV. The enthalpies of formation were also calculated as Δf,0KH°(TiSi(g)) = 705(19) kJ mol-1, Δf,0KH°(ZrSi(g)) = 770(12) kJ mol-1, Δf,0KH°(HfSi(g)) = 787(10) kJ mol-1, Δf,0KH°(VSi(g)) = 743(11) kJ mol-1, Δf,0KH°(NbSi(g)) = 879(11) kJ mol-1, and Δf,0KH°(TaSi(g)) = 938(8) kJ mol-1. Using thermochemical cycles, ionization energies of IE(TiSi) = 6.49(17) eV and IE(VSi) = 6.61(15) eV and bond dissociation energies of the ZrSi- and NbSi- anions, D0(Zr-Si-) ≤ 3.149(15) eV, D0(Zr--Si) ≤ 4.108(20) eV, D0(Nb-Si-) ≤ 3.525(31) eV, and D0(Nb--Si) ≤ 4.017(39) eV, have also been obtained. Calculations on the possible low-lying electronic states of each species are also reported.

  20. 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

    2014-05-07

    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.

  1. Kinetics and thermal stability of the Ni62Nb38- x Ta x ( x=5, 10, 15, 20 and 25) bulk metallic glasses

    NASA Astrophysics Data System (ADS)

    He, MengKe; Zhang, Yi; Xia, Lei; Yu, Peng

    2017-07-01

    We studied thermal stability and its relationship to the glass-forming ability (GFA) of the Ni62Nb38- x Ta x ( x=5, 10, 15, 20, 25) bulk metallic glasses (BMG) from a kinetic point of view. By fitting the heating-rate dependence of glass transition temperature ( T g onset) and crystallization temperatures ( T x onset and T x peak) of the Ni62Nb38- x Ta x BMG using the Vogel-Fulcher-Tammann (VFT) equation, we obtained the ideal glass transition and crystallization temperatures ( T g 0 and T x 0) and the fragility parameter ( m), and also constructed continuous heating transition (CHT) diagrams for crystallization of the BMG. The CHT diagrams of the BMG indicate enhanced thermal stability by Ta addition; the T g 0 as well as the T x 0 also illustrates this improved stability limit. The compositional dependence of m, which agrees well with that of the reduced glass-transition temperature, indicates a strong correlation between liquid fragility and glass-forming ability in the present alloy system. These results provide new evidence for understanding thermal stability, liquid fragility, and GFA in BMG.

  2. Structures and crystal chemistry of the double perovskites Ba{sub 2}LnB'O{sub 6} (Ln=lanthanide and B'=Nb, Ta):

    SciTech Connect

    Saines, Paul J.; Spencer, Jarrah R.; Kennedy, Brendan J. Kubota, Yoshiki; Minakata, Chiharu; Hano, Hiroko; Kato, Kenichi; Takata, Masaki

    2007-11-15

    The structures of eight members of the series of double perovskites of the type Ba{sub 2}LnB'O{sub 6} (Ln=La{sup 3+}-Sm{sup 3+} and Y{sup 3+} and B'=Nb{sup 5+} and Ta{sup 5+}) were examined both above and below room temperature using synchrotron X-ray powder diffraction. The La{sup 3+} and Pr{sup 3+} containing compounds had an intermediate rhombohedral phase whereas the other tantalates and niobates studied have a tetragonal intermediate. This difference in symmetry appears to be a consequence of the larger size of the La{sup 3+} and Pr{sup 3+} cations compared to the other lanthanides. The temperature range over which the intermediate symmetry is stable is reduced in those compounds near the point where the preferred intermediate symmetry changes from tetragonal to rhombohedral. In such compounds the transition to the cubic phase involves higher order terms in the Landau expression. This suggests that in this region the stability of the two intermediate phases is similar. - Graphical abstract: Variable temperature structural studies of Ba{sub 2}LaTaO{sub 6} show the presence of a unexpected rhombohedral phase. Other Ba{sub 2}LnB'O{sub 6} (B'=Nb, Ta) have a tetragonal intermediate phase.

  3. Structure and Properties of Ti-19.7Nb-5.8Ta Shape Memory Alloy Subjected to Thermomechanical Processing Including Aging

    NASA Astrophysics Data System (ADS)

    Dubinskiy, S.; Brailovski, Vladimir; Prokoshkin, S.; Pushin, V.; Inaekyan, K.; Sheremetyev, V.; Petrzhik, M.; Filonov, M.

    2013-09-01

    In this work, the ternary Ti-19.7Nb-5.8Ta (at.%) alloy for biomedical applications was studied. The ingot was manufactured by vacuum arc melting with a consumable electrode and then subjected to hot forging. Specimens were cut from the ingot and processed by cold rolling with e = 0.37 of logarithmic thickness reduction and post-deformation annealing (PDA) between 400 and 750 °C (1 h). Selected samples were subjected to aging at 300 °C (10 min to 3 h). The influence of the thermomechanical processing on the alloy's structure, phase composition, and mechanical and functional properties was studied. It was shown that thermomechanical processing leads to the formation of a nanosubgrained structure (polygonized with subgrains below 100 nm) in the 500-600 °C PDA range, which transforms to a recrystallized structure of β-phase when PDA temperature increases. Simultaneously, the phase composition and the β → α″ transformation kinetics vary. It was found that after conventional cold rolling and PDA, Ti-Nb-Ta alloy manifests superelastic and shape memory behaviors. During aging at 300 °C (1 h), an important quantity of randomly scattered equiaxed ω-precipitates forms, which results in improved superelastic cyclic properties. On the other hand, aging at 300 °C (3 h) changes the ω-precipitates' particle morphology from equiaxed to elongated and leads to their coarsening, which negatively affects the superelastic and shape memory functional properties of Ti-Nb-Ta alloy.

  4. In vitro bio-functional performances of the novel superelastic beta-type Ti-23Nb-0.7Ta-2Zr-0.5N alloy.

    PubMed

    Ion, Raluca; Gordin, Doina-Margareta; Mitran, Valentina; Osiceanu, Petre; Dinescu, Sorina; Gloriant, Thierry; Cimpean, Anisoara

    2014-02-01

    The materials used for internal fracture fixations and joint replacements are mainly made of metals which still face problems ranging from higher rigidity than that of natural bone to leaching cytotoxic metallic ions. Beta (β)-type titanium alloys with low elastic modulus made from non-toxic and non-allergenic elements are desirable to reduce stress shielding effect and enhance bone remodeling. In this work, a new β-type Ti-23Nb-0.7Ta-2Zr-0.5N alloy with a Young's modulus of approximately 50 GPa was designed and characterized. The behavior of MC3T3-E1 pre-osteoblasts on the new alloy, including adhesion, proliferation and differentiation, was evaluated by examining the cytoskeleton, focal adhesion formation, metabolic activity and extracellular matrix mineralization. Results indicated that the pre-osteoblast cells exhibited a similar degree of attachment and growth on Ti-23Nb-0.7Ta-2Zr-0.5N and Ti-6Al-4V. However, the novel alloy proved to be significantly more efficient in sustaining mineralized matrix deposition upon osteogenic induction of the cells than Ti-6Al-4V control. Further, the analysis of RAW 264.7 macrophages cytokine gene and protein expression indicated no significant inflammatory response. Collectively, these findings suggest that the Ti-23Nb-0.7Ta-2Zr-0.5N alloy, which has an increased mechanical biocompatibility with bone, allows a better osteogenic differentiation of osteoblast precursor cells than Ti-6Al-4V and holds great potential for future clinical prosthetic applications.

  5. Characterization of passive oxide film on a Ti-5%Ta-1.8%Nb alloy on exposure to severe oxidizing conditions

    SciTech Connect

    Mythili, R.; Saroja, S. Vijayalakshmi, M.

    2010-12-15

    This paper presents the results of a study on the characteristics of the passive oxide film that forms on the surface of an {alpha} + {beta} Ti-5%Ta-1.8%Nb alloy, which possesses good corrosion resistance in severe oxidizing environment of boiling 11.5 M nitric acid. Through systematic structure-property studies, the microstructure with low corrosion rate (< 1 mpy) in liquid, vapor and condensate phases of nitric acid was identified. The characteristics of the passive film, which imparts corrosion resistance to the alloy, are influenced by its microstructure, temperature and concentration of the acid. The microstructure, thickness and composition of the oxide film were characterized using different techniques. TiO{sub 2}, Nb{sub 2}O{sub 5} and Ta{sub 2}O{sub 5} formed on exposure to vapor and condensate phases, while TiO{sub 2} was observed on exposure to the liquid phase. Detailed microstructural studies showed that the passive film consists of nano-crystalline phases of titanium and tantalum oxides, predominantly anatase in an amorphous matrix. Based on these studies, the mechanism of corrosion of the alloy is derived. - Research Highlights: {yields}Liquid phase corrosion results in a thicker and protective oxide film. {yields}Oxide film is a mixture of amorphous and nano-crystalline anatase. {yields}Higher amounts of Nb{sub 2}O{sub 5} and Ta{sub 2}O{sub 5} form on vapor and condensate phase corrosion. {yields}High corrosion rate in condensate phase is due to selective dissolution of Ti in {alpha} phase.

  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. Improved Piezoelectricity in (K0.44Na0.52Li0.04) (Nb0.91Ta0.05Sb0.04)O3- xBi0.25Na0.25NbO3 Lead-Free Piezoelectric Ceramics

    NASA Astrophysics Data System (ADS)

    Zhao, Yan; Xu, Zhijun; Li, Huaiyong; Hao, Jigong; Du, Juan; Chu, Ruiqing; Wei, Dongdong; Li, Guorong

    2017-01-01

    (1 - x)[(K0.44Na0.52Li0.04)(Nb0.91Ta0.05Sb0.04)O3]- xBi0.25Na0.25NbO3 (KNLNTS- xBNN) lead-free piezoelectric ceramics have been prepared using a conventional solid-state reaction method and the effects of BNN on their phase structure, microstructure, and electrical properties systematically studied. X-ray diffraction analysis suggested that BNN substitution into KNLNTS induced coexistence of orthorhombic-tetragonal mixed phase and thus improved the ferroelectric and piezoelectric properties. The surface morphologies indicated that different amounts of BNN had two different effects on grain growth. Good electrical properties ( d 33 = 256 pC N-1, T c = 354.27°C, k p = 43.43%, P r = 26.85 μC cm-2, E c = 24.47 kV cm-1) were simultaneously obtained at x = 0.0025, suggesting that our research could benefit development of (K,Na)NbO3-based ceramics and widen their application range.

  8. Temperature independent electrostrictive coefficients of K0.95Li0.05Ta0.73Nb0.27O3 single crystals

    NASA Astrophysics Data System (ADS)

    Kawamura, S.; Imai, T.; Sakamoto, T.

    2017-09-01

    The temperature dependence of the electrostrictive coefficients (Q11 and Q12) of K0.95Li0.05Ta0.73Nb0.27O3 single crystals, which were applied to electro-optical devices, was measured to calculate precisely the refractive index modulation. To measure the electrostrictive coefficients accurately, we prevented electron injection by employing Pt electrodes. We also determined the electric field range applied to the sample by measuring P-E curves to avoid the field induced phase transition. The experimental results showed that both Q11 and Q12 were temperature independent and had values of approximately 0.070 and -0.026 m4/C2, respectively. These results differed from a previous study of KTa0.55Nb0.45O3, which revealed an anomalous temperature dependence. The reason for the different results is discussed.

  9. Control of the Crystalline Structure and Piezoelectric Properties of (K,Na,Li)(Nb,Ta,Sb)O3 Ceramics through Transition Metal Oxide Doping

    NASA Astrophysics Data System (ADS)

    Rubio-Marcos, Fernando; José Romero, Juan; Francisco Fernández, José; Marchet, Pascal

    2011-10-01

    Divalent transition metal oxide doping of lead-free (K,Na,Li)(Nb,Ta,Sb)O3 piezoceramics is studied. Two different behaviors were observed independently of the doping metal: at low concentrations, the tetragonal structure is preserved, while at a high doping level, the material becomes orthorhombic. For any given doping level, a linear dependence was found between the pseudo-tetragonal lattice distortion and the ionic radii of doping ions. The ferroelectric and piezoelectric properties of the material are reduced by the doping, whereas the mechanical quality factor increases. Thus, the piezoelectric and ferroelectric properties of these lead-free piezoceramics can be easily controlled through metal oxide doping.

  10. 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.

  11. Ab-initio study of B{sub 2}-type technetium AB (A=Tc, B=Nb and Ta) intermetallic compounds

    SciTech Connect

    Acharya, Nikita Fatima, Bushra; Sanyal, Sankar P.

    2016-05-06

    The structural, electronic and elastic properties of AB type (A = Tc, B = Nb and Ta) technetium intermetallic compounds are studied using full potential linearized plane wave (FP-LAPW) method within generalized gradient approximation (GGA). The calculated lattice parameters agree well with the experimental results. The elastic constants obey the stability criteria for cubic system. Ductility for these compounds has been analyzed using the Pugh’s rule and Cauchy’s pressure and found that all the compounds are ductile in nature. Bonding nature is discussed in terms of Fermi surface and band structures.

  12. Shock compression of VH0.50, NbH0.75 and TaH0.50: A comparative study

    NASA Astrophysics Data System (ADS)

    Syono, Y.; Taguchi, H.; Fukai, Y.; Atou, T.; Kusaba, K.; Fukuoka, K.

    1994-07-01

    Shock compression data of VH0.50, NbH0.75 and TaH0.50 up to the pressure range of 135, 148 and 216 GPa respectively are summarized. Compressibility of these hydrides were found to be comparable to those of the corresponding metals, indicating that the hydrogen-metal bonds in these hydrides are no less incompressible than the metal-metal bonds in the corresponding Group Va bcc metals. Implication of these data for the equation-of-state of metallic hydrogen is discussed.

  13. 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.

  14. Core-shell grain structures and ferroelectric properties of Na0.5K0.5NbO3-LiTaO3-BiScO3 piezoelectric ceramics.

    PubMed

    Zhu, Fangyuan; Ward, Michael B; Li, Jing-Feng; Milne, Steven J

    2015-09-01

    Legislation arising from health and environmental concerns has intensified research into finding suitable alternatives to lead-based piezoceramics. Recently, solid solutions based on sodium potassium niobate (K,Na)NbO3 (KNN) have become one of the globally-important lead-free counterparts, due to their favourable dielectric and piezoelectric properties. This data article provides information on the ferroelectric properties and core-shell grain structures for the system, (1-y)[(1-x)Na0.5K0.5NbO3 - xLiTaO3] - yBiScO3 (x=0-0.1, y=0.02, abbreviated as KNN-xLT-2BS). We show elemental analysis with aid of TEM spot-EDX to identify three-type grain-types in the KNN-LT-BS ternary system. Melting behaviour has been assessed using a tube furnace with build-in camera. Details for the ferroelectric properties and core-shell chemical segregation are illustrated.

  15. 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.

  16. 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.

  17. 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

  18. First principle study on electronic structure, structural phase stability, optical and vibrational properties of Ba2ScMO6 (M = Nb, Ta)

    NASA Astrophysics Data System (ADS)

    Rameshe, Balasubramaniam; Murugan, Ramaswamy; Palanivel, Balan

    2016-12-01

    First principle calculations are performed to investigate the electronic structure, structural phase stability, optical and vibrational properties of double perovskite oxide semiconductors namely Ba2ScMO6 (M = Nb, Ta) in the cubic symmetry using WIEN2k. In order to study the ground state properties of these compounds, the total energies are calculated as a function of reduced volumes and fitted with Brich Murnaghan equation. The estimated ground state parameters are comparable with the available experimental data. Calculations of electronic band structure on these compounds reveal that both Ba2ScNbO6 and Ba2ScTaO6 exhibit a semiconducting behavior with a direct energy gap of 2.78 and 3.15 eV, respectively. To explore the optical transitions in these compounds, the real and imaginary parts of the dielectric function, refractive index, extinction coefficient, reflectivity, optical absorption coefficient, real part of optical conductivity and the energy-loss function are calculated at ambient pressure and analyzed. The collective Raman active modes of the atoms of these materials are also calculated in order to understand the structural stability of these compounds.

  19. Weakly Bound and Strongly Interacting: NbSe2 and 1T-TaS2 in the 2D Limit

    NASA Astrophysics Data System (ADS)

    Tsen, Adam

    The layered metallic dichalcogenides are known to exhibit rich collective electron phases such as charge density waves, spin density waves, and superconductivity. In the past, studies on graphene and various semiconducting dichalcogenides have shown that taking layered materials to their physical two-dimensional (2D) limit leads to fundamental changes in band structure, allowing for a powerful experimental knob to tune for electronic functionality. In contrast, due to their instability in the ambient environment, the effect of thickness control over such collective electron phases has been largely unexplored in metallic systems. We have recently demonstrated a new experimental platform for the isolation and assembly of environmentally sensitive 2D materials in inert atmosphere. I will discuss our recent studies of the charge density wave material 1T-TaS2 and superconducting NbSe2 in the atomically thin limit, made possible using this technique. For 1T-TaS2, we find that the lock-in transition to commensurate charge ordering becomes increasingly metastable for reduced thickness, allowing for all-electrical control over this phase transition in the 2D state. In NbSe2, a small magnetic field induces a transition to a quantum metallic phase, the resistivity of which obeys a unique field-scaling property. These methods and experiments open new doors for the study of other correlated 2D materials in the immediate future.

  20. Electrochemical characterization of pulsed layer deposited hydroxyapatite-zirconia layers on Ti-21Nb-15Ta-6Zr alloy for biomedical application

    NASA Astrophysics Data System (ADS)

    Izquierdo, Javier; Bolat, Georgiana; Cimpoesu, Nicanor; Trinca, Lucia Carmen; Mareci, Daniel; Souto, Ricardo Manuel

    2016-11-01

    A new titanium base Ti-21Nb-15Ta-6Zr alloy covered with hydroxyapatite-zirconia (HA-ZrO2) by pulsed laser deposition (PLD) technique was characterized regarding its corrosion resistance in simulated physiological Ringer's solution at 37 °C. For the sake of comparison, Ti-6Al-4V standard implant alloy, with and without hydroxyapatite-zirconia coating, was also characterized. Multiscale electrochemical analysis using both conventional averaging electrochemical techniques, namely electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization, and spatially-resolved microelectrochemical techniques (scanning electrochemical microscopy, SECM) were used to investigate the electrochemical behaviour of the materials. In addition, scanning electron microscopy evidenced that no relevant surface morphology changes occurred on the materials upon immersion in the simulated physiological solution, despite variations in their electrochemical behaviour. Although uncoated metals appear to show better performances during conventional corrosion tests, the response is still quite similar for the HA-ZrO2 coated materials while providing superior resistance towards electron transfer due to the formation of a more dense film on the surface, thus effectively behaving as a passive material. It is believed corrosion of the HA-ZrO2 coated Ti-21Nb-15Ta-6Zr alloy will have negligible effect upon biochemical and cellular events at the bone-implant interface and could facilitate osseointegration.

  1. Striking Doping Effects on Thermal Methane Activation Mediated by the Heteronuclear Metal Oxides [XAlO4 ](.+) (X=V, Nb, and Ta).

    PubMed

    Wu, Xiao-Nan; Li, Jilai; Schlangen, Maria; Zhou, Shaodong; González-Navarrete, Patricio; Schwarz, Helmut

    2017-01-18

    The thermal reactivity of the heteronuclear metal-oxide cluster cations [XAlO4 ](.+) (X=V, Nb, and Ta) towards methane has been studied by using mass spectrometry in conjunction with quantum mechanical calculations. Experimentally, a hydrogen-atom transfer (HAT) from methane is mediated by all the three oxide clusters at ambient conditions. However, [VAlO4 ](.+) is unique in that this cluster directly transforms methane into formaldehyde. The absence of this reaction for the Nb and Ta analogues demonstrates a striking doping effect on the chemoselectivity in the conversion of methane. Mechanistic aspects of the two reactions have been elucidated by quantum-chemical calculations. The HAT reactivity can be attributed to the significant spin density localized at the terminal oxygen atom (Ot(.-) ) of the cluster ions, while the ionic/covalent character of the Lewis acid-base unit [X-Ob ] plays a crucial role for the generation of formaldehyde. The mechanistic insight derived from this combined experimental/computational investigation may provide guidance for a more rational design of catalysts.

  2. Phase Composition of a CrMo0.5NbTa0.5TiZr High Entropy Alloy: Comparison of Experimental and Simulated Data (Postprint)

    DTIC Science & Technology

    2014-04-01

    COMPOSITION OF A CrMo0 5NbTa0 5TiZr HIGH ENTROPY ALLOY : COMPARISON OF EXPERIMENTAL AND SIMULATED DATA (POSTPRINT) 5a. CONTRACT NUMBER In-house 5b. GRANT...e15093796. 14. ABSTRACT Microstructure and phase composition of a CrMo0 5NbTa0 5TiZr high entropy alloy were studied in the as-solidified and heat...15. SUBJECT TERMS refractory high entropy alloy , microstructure and phase analysis, CALPHAD 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

  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.

  4. Differences in chemical doping matter: Superconductivity in Ti1-xTaxSe2 but not in Ti1-xNbxSe2

    SciTech Connect

    Luo, Huixia; Zhu, Yimei; Xie, Weiwei; Tao, Jing; Pletikosic, Ivo; Valla, Tonica; Sahasrabudhe, Girija S.; Osterhoudt, Gavin; Sutton, Eric; Burch, Kenneth S.; Seibel, Elizabeth M.; Krizan, Jason W.; Cava, Robert J.

    2016-02-21

    We report that 1T-TiSe2, an archetypical layered transition metal dichalcogenide, becomes superconducting when Ta is substituted for Ti but not when Nb is substituted for Ti. This is unexpected because Nb and Ta should be chemically equivalent electron donors. Superconductivity emerges near x = 0.02 for Ti1–xTaxSe2, while, for Ti1–xNbxSe2, no superconducting transitions are observed above 0.4 K. The equivalent chemical nature of the dopants is confirmed by X-ray photoelectron spectroscopy. ARPES and Raman scattering studies show similarities and differences between the two systems, but the fundamental reasons why the Nb and Ta dopants yield such different behavior are unknown. We present a comparison of the electronic phase diagrams of many electron-doped 1T-TiSe2 systems, showing that they behave quite differently, which may have broad implications in the search for new superconductors. Here, we propose that superconducting Ti0.8Ta0.2Se2 will be suitable for devices and other studies based on exfoliated crystal flakes.

  5. 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.

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

    PubMed

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

    2007-10-28

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

  7. Substitution features in the isomorphous replacement series for metal-organic compounds (Nb{sub x}Ta{sub 1-x}){sub 4}O{sub 2}(OMe){sub 14}(ReO{sub 4}){sub 2}, x=0.7, 0.5, 0.3-Single-source precursors of complex oxides with organized porosity

    SciTech Connect

    Nikonova, Olesya A.; Kessler, Vadim G.; Seisenbaeva, Gulaim A.

    2008-12-15

    Trimetallic oxoalkoxide complexes (Nb{sub 0.7}Ta{sub 0.3}){sub 4}O{sub 2}(OMe){sub 14}(ReO{sub 4}){sub 2} (I), (Nb{sub 0.3}Ta{sub 0.7}){sub 4}O{sub 2}(OMe){sub 14}(ReO{sub 4}){sub 2} (II) and (Nb{sub 0.5}Ta{sub 0.5}){sub 4}O{sub 2}(OMe){sub 14}(ReO{sub 4}){sub 2} (III) were obtained by the interaction of rhenium heptoxide (VII) Re{sub 2}O{sub 7} with niobium and tantalum alkoxides M{sub 2}(OMe){sub 10} (M=Nb, Ta) in toluene. The centrosymmetric molecules (I)-(III) can be considered as a product of condensation of two M{sub 2}(OMe){sub 9}(OReO{sub 3}) molecules with the formation of two oxo-bridges. The specific feature of the structure is the uneven distribution of metal atoms in the crystallographic positions, where one symmetry-independent position, connected via {mu}-O with a perrhenate ReO{sub 4}{sup -} group, is predominantly occupied by niobium atoms, while the other one connected via alkoxide groups has a higher tantalum content. The distribution of Nb and Ta in the structure is truly even only for compound III. The niobium and tantalum content is varied to a different extent for I (less) and for II (more), which is apparently due to small differences in the sizes of these two cations, resulting in preferences for packing of different molecules in the structures. Thermal decomposition of (Nb{sub 1-x}Ta{sub x}){sub 4}O{sub 2}(OMe){sub 14}(ReO{sub 4}){sub 2} (x=0.3, 0.5, 0.7) in air leads to the formation of crystalline species of solid solutions based on tantalum and niobium oxides displaying semi-ordered pores with the size of 100-250 nm. In the dry nitrogen atmosphere, the decomposition leads to the amorphous complex oxides containing rhenium, niobium and tantalum. - Graphical abstract: Thermal decomposition of (Nb{sub 1-x}Ta{sub x}){sub 4}O{sub 2}(OMe){sub 14}(ReO{sub 4}){sub 2} (x=0.3, 0.5, 0.7), single-source complex precursors, in air leads to the formation of crystalline solid solutions based on tantalum and niobium oxides, displaying semi

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

    SciTech Connect

    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 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 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.

  9. Bond dissociation energies of diatomic transition metal selenides: TiSe, ZrSe, HfSe, VSe, NbSe, and TaSe

    NASA Astrophysics Data System (ADS)

    Sorensen, Jason J.; Persinger, Thomas D.; Sevy, Andrew; Franchina, Jordan A.; Johnson, Eric L.; Morse, Michael D.

    2016-12-01

    Predissociation thresholds have been observed in the resonant two-photon ionization spectra of TiSe, ZrSe, HfSe, VSe, NbSe, and TaSe. It is argued that the sharp onset of predissociation corresponds to the bond dissociation energy in each of these molecules due to their high density of states as the ground separated atom limit is approached. The bond dissociation energies obtained are D0(TiSe) = 3.998(6) eV, D0(ZrSe) = 4.902(3) eV, D0(HfSe) = 5.154(4) eV, D0(VSe) = 3.884(3) eV, D0(NbSe) = 4.834(3) eV, and D0(TaSe) = 4.705(3) eV. Using these dissociation energies, the enthalpies of formation were found to be Δf,0 KHo(TiSe(g)) = 320.6 ± 16.8 kJ mol-1, Δf,0 KHo(ZrSe(g)) = 371.1 ± 8.5 kJ mol-1, Δf,0 KHo(HfSe(g)) = 356.1 ± 6.5 kJ mol-1, Δf,0 KHo(VSe(g)) = 372.9 ± 8.1 kJ mol-1, Δf,0 KHo(NbSe(g)) = 498.9 ± 8.1 kJ mol-1, and Δf,0 KHo(TaSe(g) ) = 562.9 ± 1.5 kJ mol-1. Comparisons are made to previous work, when available. Also reported are calculated ground state electronic configurations and terms, dipole moments, vibrational frequencies, bond lengths, and bond dissociation energies for each molecule. A strong correlation of the measured bond dissociation energy with the radial expectation value, ⟨r⟩nd, for the metal atom is found.

  10. Crystal chemistry, band engineering, and photocatalytic activity of the LiNb3O8-CuNb3O8 solid solution.

    PubMed

    Sahoo, Prangya Parimita; Maggard, Paul A

    2013-04-15

    A new solid solution has been prepared in the system LiNb3O8-CuNb3O8, and the impacts of chemical composition and crystal structure have been investigated for the resulting band gap sizes and photocatalytic activities for water reduction to hydrogen under visible light. All members of the solid solution were synthesized by solid-state methods within evacuated fused-silica vessels, and their phase purities were confirmed via powder X-ray diffraction techniques (space group P2(1)/a, a = 15.264(5)-15.367(1) Å, b = 5.031(3)-5.070(1) Å, c = 7.456(1)-7.536(8) Å, and β = 107.35(1)-107.14(8)°, for 0 ≤ x ≤ 1). Rietveld refinements were carried out for the x = 0.09, 0.50, and 0.70 members of the solid solution, which reveal the prevailing isostructurality of the continuous solid solution. The structure consists of chains of (Li/Cu)O6 and NbO6 octahedra. The optical band gap size across the solid solution exhibits a significant red-shift from ∼3.89 eV (direct) to ∼1.45 eV and ∼1.27 eV (direct and indirect) with increasing Cu(I) content, consistent with the change in sample color from white to dark brown to black. Electronic structure calculations based on density-functional theory methods reveal the rapid formation of a new Cu 3d(10)-based valence band that emerges higher in energy than the O 2p band. While the pure LiNb3O8 is a highly active UV-photocatalyst for water reduction, the Li(1-x)Cu(x)Nb3O8 solid is shown to be photocatalytically active under visible-light irradiation for water reduction to hydrogen.

  11. Solid state Rayleigh-Taylor measurements in Ta and V at high pressures and strain rates

    NASA Astrophysics Data System (ADS)

    Remington, Bruce; Park, Hye-Sook; Cavallo, Robert; Prisbrey, Shon; Rudd, Robert; Plechaty, Chris; Wehrenberg, Chris; Maddox, Brian; Kostinski, Natalie; Terry, Matthew; Huntington, C.

    2013-06-01

    We will report on Rayleigh-Taylor (RT) strength experiments in solid-state driven foils of vanadium and tantalum at high strain rates (~1.e7 1/s) and high pressures (~1 Mbar), where softening (a decrease in strength) is observed when the strains get large. When the single-mode RT bubble penetration in this plastic flow regime reaches ~20-30% of the initial foil thickness, the inferred high strength in the foils starts to drop. In the extreme, this drop in strength may be an indication of incipient failure. We will discuss the similarities and differences between the observed softening in the V-RT and Ta-RT experiments, and consider the implications for future planned experiments on the National Ignition Facility (NIF) at higher pressures (~5 Mbar), but similar strain rates. Prepared by LLNL under Contract DE-AC52-07NA27344.

  12. 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.

  13. 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.

  14. 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.

  15. Chemical Coupling SERS Properties of Pyridine on Silver-Caged Metal Clusters M@Ag12 (M = V-, Nb-, Ta-, Cr, Mo, W, Mn+, Tc+, Re+)

    NASA Astrophysics Data System (ADS)

    Chen, Lei; Wang, Zhigang; Li, Zhengqiang; Zhang, Rui-Qin

    2016-10-01

    Using density functional theory, this work presents a comprehensive analysis of nonresonant surface-enhanced Raman scattering enhancement of pyridine on M@Ag12 (M = V-, Nb-, Ta-, Cr, Mo, W, Mn+, Tc+, Re+). Computational results indicate that the chemical enhancement of pyridine on M@Ag12 is closely associated with the charge properties of silver-caged clusters. Pyridine on negative clusters exhibits the strongest chemical enhancement with a factor of about 103, while the chemical enhancement is only about 102 for pyridine on neutral clusters and 10 for pyridine on positive clusters. The polarizability analyses elucidate the nature of the chemical enhancement that delocalized electrons of negative adsorption systems occupy higher molecular orbitals than those of neutral and positive adsorption systems, which can lead to stronger nonresonant chemical enhancement.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Electronic, mechanical, phase transition, and thermo-physical properties of TMC (TM = V, Nb, and Ta): high pressure ab initio study

    NASA Astrophysics Data System (ADS)

    Chauhan, Mamta; Gupta, Dinesh C.

    2015-12-01

    The structural, electronic, mechanical, phase transition, and thermo-physical properties of refractory carbides, viz. VC, NbC, and TaC have been computed in stable B1 and high pressure B2 phases by means of two different ab initio calculations using pseudo- and full-potential schemes. These materials have mixed covalent-, metallic-, and ionic-type bonding. The calculations of elastic constants show the mechanical stability of these materials in B1 phase only. The brittle nature and anisotropy is observed in these materials in B1 phase. Non-central forces are present in both the phases. Elastic wave velocities and Debye temperature have also been calculated. The present results on structural, phase transition, elastic, and other properties are in reasonably good agreement with the available experimental and theoretical data. The calculations in high pressure phase need experimental verification.

  1. Phase transformation and its effect on mechanical characteristics in warm-deformed Ti-29Nb-13Ta-4.6Zr alloy

    NASA Astrophysics Data System (ADS)

    Lee, Taekyung; Nakai, Masaaki; Niinomi, Mitsuo; Park, Chan Hee; Lee, Chong Soo

    2015-01-01

    Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy has been extensively studied as it is promising for use in biomedical applications. Despite its potential, the effects of warm plastic deformation on the alloy have not yet been revealed. This study investigated the differences in phase constitution of two warm-deformed TNTZ alloys and revealed relevant mechanisms with particular attention to martensitic transformation. The influence of phase constituents on mechanical characteristics was discussed as well. The TNTZ alloy deformed at 823 K possessed α, β, and ω phases as well as α″ martensite, and demonstrated a low Young's modulus and double-yielding phenomenon. In contrast, the alloy deformed at 723 K had no martensite but more ω phase, leading to increased strength, hardness, and Young's modulus. The absence of α″ martensite in the alloy deformed at 723 K was interpreted in light of β-stability of the parent phase and reduced M s temperature.

  2. Thermally induced A'-A site exchange in novel layered perovskites Ag2[Ca1.5M3O10] (M = Nb, Ta).

    PubMed

    Bhuvanesh, Nattamai S P; Woodward, Patrick M

    2002-12-04

    We have synthesized and characterized new layered perovskites Ag2[A1.5M3O10] (A = Ca, M = Nb, Ta), from their lithium analogues, by soft-chemical ion exchange. These oxides show topotactic irreversible thermally induced A'-A site exchange, resulting in Ag1.1Ca0.9[Ca0.6Ag0.9M3O10], conferred from our high-temperature X-ray and ionic conductivity studies. The latter phases are the first compounds where Ag+ ions reside in both A' and A sites in layered perovskites. The absence of similar phase transition for A = Sr suggests that these transitions strongly depend on the size, charge, and the coordination preference of A' and A cations. This result provides a new synthetic tool for modifying the occupation of the 12-coordinate A site of layered perovskites using soft chemical routes.

  3. Chemical Twinning of Salt and Metal in the Subnitridometalates Ba23 Na11 (MN4 )4 with M=V, Nb, Ta.

    PubMed

    Wörsching, Matthias; Tambornino, Frank; Datz, Stefan; Hoch, Constantin

    2016-08-26

    The subnitridometalates Ba23 Na11 (MN4 )4 (M=V, Nb, Ta) crystallize in a new structure type, which shows ionic ortho-nitridometalate anions and motifs from simple (inter)metallic packings: Na-centered [Na8 ] cubes as cutouts of the bcc structure of elemental Na and Na-centered [Ba10 Na2 ] icosahedra as found in Laves phases, for example. Single-crystal and powder X-ray diffraction studies in combination with quantum-chemical calculations of the electronic structure and Raman spectroscopy support the characterization of the subnitridometalates as "chemical twins". They consist of independent building units with locally prevalent ionic or metallic bonding in an overall metallic compound.

  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. 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

    2016-02-18

    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.

  6. Atomic defects and dopants in ternary Z-phase transition-metal nitrides Cr M N with M =V , Nb, Ta investigated with density functional theory

    NASA Astrophysics Data System (ADS)

    Urban, Daniel F.; Elsässer, Christian

    2017-09-01

    A density functional theory study of atomic defects and dopants in ternary Z-phase transition-metal nitrides Cr M N with M =V , Nb, or Ta is presented. Various defect formation energies of native point defects and of substitutional atoms of other metal elements which are abundant in the steel as well are evaluated. The dependence thereof on the thermodynamic environment, i.e., the chemical conditions of a growing Z-phase precipitate, is studied, and different growth scenarios are compared. The results obtained may help to relate results of experimental atomic-scale analysis by atom probe tomography or transmission electron microscopy to the theoretical modeling of the formation process of the Z phase from binary transition-metal nitrides.

  7. Chemical Coupling SERS Properties of Pyridine on Silver-Caged Metal Clusters M@Ag12 (M = V-, Nb-, Ta-, Cr, Mo, W, Mn+, Tc+, Re+)

    NASA Astrophysics Data System (ADS)

    Chen, Lei; Wang, Zhigang; Li, Zhengqiang; Zhang, Rui-Qin

    2017-07-01

    Using density functional theory, this work presents a comprehensive analysis of nonresonant surface-enhanced Raman scattering enhancement of pyridine on M@Ag12 (M = V-, Nb-, Ta-, Cr, Mo, W, Mn+, Tc+, Re+). Computational results indicate that the chemical enhancement of pyridine on M@Ag12 is closely associated with the charge properties of silver-caged clusters. Pyridine on negative clusters exhibits the strongest chemical enhancement with a factor of about 103, while the chemical enhancement is only about 102 for pyridine on neutral clusters and 10 for pyridine on positive clusters. The polarizability analyses elucidate the nature of the chemical enhancement that delocalized electrons of negative adsorption systems occupy higher molecular orbitals than those of neutral and positive adsorption systems, which can lead to stronger nonresonant chemical enhancement.

  8. Coordination adducts of niobium(V) and tantalum(V) azide M(N₃)₅ (M=Nb, Ta) with nitrogen donor ligands and their self-ionization.

    PubMed

    Haiges, Ralf; Deokar, Piyush; Christe, Karl O

    2014-05-19

    Several new donor-acceptor adducts of niobium and tantalum pentaazide with N-donor ligands have been prepared from the pentafluorides by fluoride-azide exchange with Me3SiN3 in the presence of the corresponding donor ligand. With 2,2'-bipyridine and 1,10-phenanthroline, the self-ionization products [MF4(2,2'-bipy)2](+)[M(N3)6](-), [M(N3)4(2,2'-bipy)2](+)[M(N3)6](-) and [M(N3)4(1,10-phen)2](+)[M(N3)6](-) were obtained. With the donor ligands 3,3'-bipyridine and 4,4'-bipyridine the neutral pentaazide adducts (M(N3)5)2⋅L (M=Nb, Ta; L=3,3'-bipy, 4,4'-bipy) were formed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. 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

  10. Beneficial effect of Cu on Ti-Nb-Ta-Zr sputtered uniform/adhesive gum films accelerating bacterial inactivation under indoor visible light.

    PubMed

    Alhussein, Akram; Achache, Sofiane; Deturche, Regis; Sanchette, Frederic; Pulgarin, Cesar; Kiwi, John; Rtimi, Sami

    2017-04-01

    This article presents the evidence for the significant effect of copper accelerating the bacterial inactivation on Ti-Nb-Ta-Zr (TNTZ) sputtered films on glass up to a Cu content of 8.3 at.%. These films were deposited by dc magnetron co-sputtering of an alloy target Ti-23Nb-0.7Ta-2Zr (at.%) and a Cu target. The fastest bacterial inactivation of E. coli on this later TNTZ-Cu surface proceeded within ∼75min. The films deposited by magnetron sputtering are chemically homogenous. The film roughness evaluated by atomic force spectroscopy (AFM) on the TNTZ-Cu 8.3 at.% Cu sample presented an RMS-value of 20.1nm being the highest RMS of any Cu-sputtered TNTZ sample. The implication of the RMS value found for this sample leading to the fastest interfacial bacterial inactivation kinetics is also discussed. Values for the Young's modulus and hardness are reported for the TNTZ films in the presence of various Cu-contents. Evaluation of the bacterial inactivation kinetics of E. coli under low intensity actinic hospital light and in the dark was carried out. The stable repetitive bacterial inactivation was consistent with the extremely low Cu-ion release from the samples of 0.4 ppb. Evidence is presented by the bacterial inactivation dependence on the applied light intensity for the intervention of Cu as semiconductor CuO during the bacterial inactivation at the TNTZ-Cu interface. The mechanism of CuO-intervention under light is suggested based on the pH/and potential changes registered during bacterial disinfection. Copyright © 2017 Elsevier B.V. All rights reserved.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  12. Synthesis and characterization of K(Ta(x)Nb(1_x))O3 particles by high temperature mixing method under hydrothermal and solvothermal conditions.

    PubMed

    Gu, Honghui; Zhu, Kongjun; Qiu, Jinhao; Ji, Hongli; Cao, Yang; Jin, Jiamei

    2013-02-01

    KTa(x)Nb(1_x)O3 (KTN) particles with an orthorhombic perovskite structure were synthesized via a high temperature mixing method (HTMM) under hydrothermal and solvothermal conditions. The obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high-resolution transmission electron microcopy (HRTEM). The influences of alkaline concentration and Ta doping amounts on the phase structure and morphology of the obtained powders were investigated. The results showed that KTN powders could be solvothermally prepared when the KOH concentration is as low as 0.5 M. In comparison with the hydrothermal process, supercritical isopropanol plays an important role in synthesizing KTN particles under milder conditions. The KTa(0.4)Nb(0.6)O3 particles solvothermally synthesized in isopropanol are made of well crystallized and single crystalline particles with a size of about 100-200 nm. Room temperature PL studies excited at different wavelengths reveal five emission bands centered at about 421 nm, 446 nm, 468 nm, 488 nm, and 498 nm, respectively. The supercritical process proposed here provides a new potential route for synthesizing other perovskite-type materials.

  13. Electrical Properties of Textured (KNa)0.44Li0.06Nb0.84Sb0.06Ta0.1O3 Thick Films

    NASA Astrophysics Data System (ADS)

    Fu, Fang; Zhai, Jiwei; Xu, Zhengkui; Bai, Wangfeng; Kong, Lingbing

    2012-11-01

    Lead-free (KNa)0.44Li0.06Nb0.84Sb0.06Ta0.1O3 textured thick films with 25 μm thickness were fabricated by the reactive templated grain growth method. The influence of LiSbO3 substitution on the degree of grain orientation was investigated. The addition of LiSbO3 improved the dielectric properties of the K0.5Na0.5NbO3 potassium sodium niobate (KNN) textured thick films. Leakage current behavior of the thick film was also reduced due to the LiSbO3 doping, which is explicable based on the space-charge-limited current mechanism. It was also found that the problem of interface effect was alleviated due to the presence of LiSbO3. Piezoelectric properties of thick film were improved dramatically owing to the co-effect of texturing and LiSbO3 doping, with d {33/*} being sharply increased from 38 pm/V to 173 pm/V.

  14. 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.

  15. 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. Copyright © 2013 Elsevier B.V. All rights reserved.

  16. NbN and NaNbN2 particles: selective solid state synthesis and conduction performance.

    PubMed

    Wang, Liangbiao; Zhu, Yongchun; Shi, Liang; Si, Lulu; Li, Qianwen; Qian, Yitai

    2012-09-01

    Starting from Nb2O5, NaN3 and different metallic reductants such as magnesium or aluminum, cubic NbN and hexagonal NaNbN2 were selectively synthesized in a stainless steel autoclave at 400-700 degrees C. When magnesium was used as a metallic reductant, NbN can be synthesized at 400 degrees C for 10 h. If the metallic reductant was replaced by aluminum, NaNbN2 was obtained at 700 degrees C for 40 h. The structures and morphologies of the samples were derived from X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and field emission-scanning electron microscopy (FE-SEM). FE-SEM images showed that the NbN sample consisted of particles with an average size of about 100 nm, and the NaNbN2 sample is composed of with an average size of 500 nm. Furthermore, the electric resistivity of the obtained samples reveals the obtained NbN sample is a superconductor with transition temperature of 17 K, and the obtained NaNbN2 sample can be classified as a semiconductor.

  17. Crystallographic and dielectric properties of flux grown PbB1/2'B1/2″O (B'B″: InNb, InTa, YbNb, YbTa and MgW) single crystals

    NASA Astrophysics Data System (ADS)

    Kania, Antoni

    2008-05-01

    Single crystals of PbIn 1/2Nb 1/2O 3 (PIN), PbIn 1/2Ta 1/2O 3 (PIT), PbYb 1/2Nb 1/2O 3 (PYN), PbYb 1/2Ta 1/2O 3 (PYT) and PbMg 1/2W 1/2O 3 (PMW) have been grown by the flux method. The PbO-based solvents were used. Transparent, light yellow and arrow like shaped PIN and PIT crystals of the perovskite structure were obtained. Small amounts of red and of octahedron habit PIN and PIT crystals of the pyrochlore type were simultaneously grown. In the case of PYN, PYT and PMW only the crystals of the perovskite structure have been grown. The transparent and brown PYN and PYT crystals of octahedron habit were obtained. The transparent, light yellow and of octahedron or truncated octahedron shape PMW crystals were grown. The crystals were characterised by X-ray and dielectric studies. They showed that as-grown PIN crystals are nearly disordered, exhibit the rhombohedral distortion of the pseudo-perovskite unit cell and reveal relaxor behaviour. The partially ordered PIT crystals show monoclinic distortion and undergo antiferroelectric-paraelectric phase transition. The PYN, PYT and PMW single crystals, characterised by chemical order in the B'/B″ ion sublattice, exhibit orthorhombic symmetry and undergo the first-order antiferroelectric-paraelectric phase transitions.

  18. Investigation of the nanodomain structure formation by piezoelectric force microscopy and Raman confocal microscopy in LiNbO{sub 3} and LiTaO{sub 3} crystals

    SciTech Connect

    Shur, V. Ya.; Zelenovskiy, P. S.; Nebogatikov, M. S.; Alikin, D. O.; Sarmanova, M. F.; Ievlev, A. V.; Mingaliev, E. A.; Kuznetsov, D. K.

    2011-09-01

    Piezoelectric force microscopy (PFM) and Raman confocal microscopy have been used for studying the nanodomain structures in congruent LiNbO{sub 3} and LiTaO{sub 3} crystals. The high-resolution nanodomain images at the surface were observed via PFM. Raman confocal microscopy has been used for the visualization of the nanodomain structures in the bulk via layer-by-layer scanning at various depths. It has been shown experimentally that the nanodomain images obtained at different depths correspond to domain images at the polar surface obtained at different moments: the deeper the nanodomain, the earlier the moment. Such a correlation was applied for the reconstruction of the evolution of the domain structures with charged domain walls. The studied domain structures were obtained in highly non-equilibrium switching conditions realized in LiNbO{sub 3} and LiTaO{sub 3} via pulse laser irradiation and the electric field poling of LiNbO{sub 3}, with the surface layer modified by ion implantation. The revealed main stages of the domain structure evolution allow the authors to demonstrate that all geometrically different nanodomain structures observed in LiNbO{sub 3} and LiTaO{sub 3} appeared as a result of discrete switching.

  19. FAST TRACK COMMUNICATION: Phase structure and electrical properties of K0.5Na0.5(Nb0.94Sb0.06)O3-LiTaO3 lead-free piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Lin, Dunmin; Kwok, K. W.; Lam, K. H.; Chan, H. L. W.

    2008-03-01

    Lead-free piezoelectric ceramics (1-x)K0.5Na0.5(Nb0.94Sb0.06)O3-xLiTaO3 have been fabricated by a conventional solid-state sintering technique. The ceramics can be well sintered at 1080-1110 °C and exhibit a dense, single-phase perovskite structure at x <= 0.06. Coexistence of the tetragonal and orthorhombic phases is formed in the ceramics with 0.02 < x < 0.05, leading to a significant enhancement in piezoelectric properties. For the ceramic with x = 0.04, the piezoelectric properties become optimum: piezoelectric constant d33 = 271 pC N-1, electromechanical coupling coefficients kP = 0.53 and kt = 0.43. Moreover, the ceramics are non-deliquescent and exhibit excellent performance in transducer applications, indicating that the ceramics are ready for replacing lead-containing ceramics in practical applications.

  20. Piezoelectric properties and diffusion phase transition around PPT of La-doped (Na0.52K0.44Li0.04) Nb0.8Ta0.2O3 lead-free piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Yang, Wenlong; Wang, Li; Li, Haidong; Han, Junsheng; Xiu, Hanjiang; Zhou, Zhongxiang

    2016-10-01

    Lead-free ceramics (Na0.52K0.44Li0.04)1-3xLaxNb0.8Ta0.2O3 (KNLNT-Lax, x=0.00, 0.25, 0.5, 0.75, 1.00, 1.25 mol%) as non-polluting materials were prepared by solid state reaction method. The structure, piezoelectric proprieties and temperature stability of KNLNT ceramic with different La doping concentrations were investigated. The results show a transition from orthorhombic-tetragonal mix phase to tetragonal single phase with the variation of La3+ concentrations. The SEM micrographs of surface and fractured surface show a dense microstructure with few micropores. The La-doped KNLTN ceramic will be an alternative candidate contributes to excellent piezoelectric properties, which are found in the 0.75 mol% La-doped KNLNT ceramics, with d33=215pC/N, kp=42.8%and Qm=89. It has been remarkably improved that the temperature stability of KNLTN-Lax piezoelectric properties at room temperature, and the dielectric relaxation can be observed obviously. The mechanism of La doping was analyzed in terms of valence compensation and polymorphic phase transition (PPT) diffusion. The orthorhombic-tetragonal phase transition around room temperature and the relaxation transition were considered contributing to the excellent piezoelectric performance and improved temperature stability of La3+-doped KNLTN.

  1. 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.

  2. 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.

  3. 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.

  4. Cross sections of X-ray production induced by C and Si ions with energies up to 1 MeV/u on Ti, Fe, Zn, Nb, Ru and Ta

    NASA Astrophysics Data System (ADS)

    Prieto, José Emilio; Zucchiatti, Alessandro; Galán, Patricia; Prieto, Pilar

    2017-09-01

    X-ray production differential cross sections induced by C and Si ions with energies from 1 MeV/u down to 0.25 MeV/u, produced by the CMAM 5 MV tandem accelerator, have been measured for thin targets of Ti, Fe, Zn, Nb, Ru and Ta in a direct way. X-rays have been detected by a fully characterized silicon drift diode and beam currents have been measured by a system of two Faraday cups. Measured cross sections agree in general with previously published results. The ECPSSR theory with the united atoms correction gives absolute values close to the experimental ones for all the studied elements excited by C ions and for Ta, Nb and Ru excited by Si ions. For Ti, Fe and Zn excited by Si, the matching with theory is poor since even the ionization cross section is below the measured data.

  5. Enhanced second harmonic generation and photoluminescence in Pr-doped LiNb0.5Ta0.5O3 nanocrystals embedded in a borate based glass

    NASA Astrophysics Data System (ADS)

    Jaschin, P. W.; Varma, K. B. R.

    2017-08-01

    Non-linear optical properties and photoluminescence exhibited by Pr-doped LiNb0.5Ta0.5O3 nanocrystals embedded in a borate based glass are presented here. The glasses of composition 1.5Li2O-2B2O3-0.5Nb2O5-0.5Ta2O5:xPr6O11 (x = 0.0025, 0.005, and 0.01) were synthesized via the conventional melt-quenching technique, and the nanocrystal growth was induced by subjecting the as-quenched glasses to heat treatment between 530 and 560 °C for 3 h. Coalesced nanocrystals of sizes in the 20-38 nm range, resulting in the formation of dendritic spherulites, were obtained from the isothermal heat treatment. Effect of doping on the structural units of LiNb0.5Ta0.5O3 lattice was analysed by Raman studies, which indicated that Pr ions occupied Li+ vacancies or Nb/Ta antisites. A strong red emission at 620 nm, due to 1D2 → 3H4 electronic transition of Pr3+ ions, was observed upon excitation by a 450 nm radiation. The maximum intensity was exhibited by the composition corresponding to Pr-doping level, x = 0.005, while the crystallization had a pronounced effect on the intensity of the red output. A non-linear optical coefficient as high as 0.77 pm/V (twice that of d36 of potassium dihydrogen phosphate single crystal) was obtained from the bulk glass-nanocrystal composites of the composition in which x = 0.0025.

  6. Magnetic properties of the (CoxMn1-x)4Nb2O9 solid solution series

    NASA Astrophysics Data System (ADS)

    Schwarz, B.; Kraft, D.; Theissmann, R.; Ehrenberg, H.

    2010-03-01

    Co4Nb2O9 and Mn4Nb2O9 order collinear antiferromagnetically with the same magnetic spin structure type below 30 and 125 K, respectively. Magnetization measurements on powder samples of the solid solution series (Co,Mn)4Nb2O9 prepared by arc melting reveal a linear progression of the Néel-temperature with Co/Mn ratio. Powder neutron diffraction experiments performed for a selected composition confirm the existence of the same magnetic structure type as found for the end members. (Co,Mn)4Nb2O9 samples prepared by subsolidus reaction and comparably much lower cooling rates after tempering contain very small amounts of additional (Co,Mn)3O4 spinel phases with strongly varying transition temperatures as a function of the Co/Mn ratio.

  7. 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.

  8. 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.

  9. 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.

  10. Microstructure evolution and mechanical properties of a Ti-35Nb-3Zr-2Ta biomedical alloy processed by equal channel angular pressing (ECAP).

    PubMed

    Lin, Zhengjie; Wang, Liqiang; Xue, Xiaobing; Lu, Weijie; Qin, Jining; Zhang, Di

    2013-12-01

    In this paper, an equal channel angular pressing method is employed to refine grains and enhance mechanical properties of a new β Ti-35Nb-3Zr-2Ta biomedical alloy. After the 4th pass, the ultrafine equiaxed grains of approximately 300 nm and 600 nm are obtained at pressing temperatures of 500 and 600°C respectively. The SEM images of billets pressed at 500°C reveal the evolution of shear bands and finally at the 4th pass intersectant networks of shear bands, involving initial band propagation and new band broadening, are formed with the purpose of accommodating large plastic strain. Furthermore, a unique herringbone microstructure of twinned martensitic variants is observed in TEM images. The results of microhardness measurements and uniaxial tensile tests show a significant improvement in microhardness and tensile strength from 534 MPa to 765 MPa, while keeping a good level of ductility (~16%) and low elastic modulus (~59 GPa). The maximum superelastic strain of 1.4% and maximum recovered strain of 2.7% are obtained in the billets pressed at 500°C via the 4th pass, which exhibits an excellent superelastic behavior. Meanwhile, the effects of different accumulative deformations and pressing temperatures on superelasticity of the ECAP-processed alloys are investigated. © 2013. Published by Elsevier B.V. All rights reserved.

  11. First-principles and molecular-dynamics study of structure and bonding in perovskite-type oxynitrides ABO(2)N (A = Ca, Sr, Ba; B = Ta, Nb).

    PubMed

    Wolff, Holger; Dronskowski, Richard

    2008-10-01

    A series of perovskite-type phases of alkaline-earth-based tantalum and niobium oxynitrides has been studied using both first-principles electronic-structure calculations and molecular-dynamics simulations, in particular by investigating different structural arrangements and anion distributions in terms of total-energy calculations. The structural properties are explained on the basis of COHP chemical bonding analyses and semiempirical molecular orbital calculations. We provide theoretical proof for the surprising result that the local site symmetries of these phases are lower than cubic because density-functional calculations clearly show that all crystallographic unit cells are better described as being orthorhombic with space group Pmc2(1) to optimize metal-nitrogen bonding; nonetheless, there is no contradiction with a macroscopic cubic description of the structures of BaTaO(2)N and BaNbO(2)N adopting space group Pm3m. Additionally, we find that the anionic sublattice is ordered in all compounds studied over a wide temperature range.

  12. Electronic structures and properties of eight-coordinate metal-polyarsenic complexes MAs8n- (M = V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re).

    PubMed

    Li, J; Wu, K

    2000-04-03

    The eight-coordinate early transition metal polyarsenic complexes, MAs(8)3- (M = V, Nb, Ta), MAs(8)2- (M = Cr, Mo, W), and MAs8- (M = Mn, Tc, Re), have been studied using density functional theory (DFT). The geometry optimizations of these complexes indicate that in the most stable structures the transition metal atoms are trapped in a crownlike cavity consisting of a zigzag eight-membered ring of As8 cluster. The scalar-relativistic effects and spin-orbit coupling effects on the electronic structures and energy levels were taken into account. The stabilities of gas-phase MAs8n- ions and bonding between the As8 ring and early transition metals are discussed on the basis of population analysis, atomization energies, and decomposition reaction energies. All these complex ions are found to be diamagnetic with notable HOMO-LUMO energy gaps. The vibrational frequencies and infrared absorption intensities of the MAs8n- series are predicted theoretically. Brief theoretical calculations of the similar MoA(8)2- pnictide ions indicate that the analogous P, Sb, and even Bi complexes are likely to be stable, whereas the crownlike MoN(8)2- is not a stable complex.

  13. 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

  14. Electrical conductivity and impedance spectroscopy studies of cerium based aeschynite type semiconducting oxides: CeTiMO6 (M=Nb or Ta)

    NASA Astrophysics Data System (ADS)

    Sumi, S.; Rao, P. Prabhakar; Deepa, M.; Koshy, Peter

    2010-09-01

    Complex ceramic oxides, CeTiMO6 (M=Nb or Ta) having aeschynite type mineral structure were prepared by the conventional ceramic route. Complex impedance analysis in the frequency range 10 Hz-1 MHz over a wide temperature range (30-600 °C) indicates the presence of grain boundary effect along with the bulk contribution and also confirms the presence of non-Debye type of multiple relaxations in the material. The frequency dependent conductivity plots exhibit double power law dependence suggesting three types of conduction mechanisms: low frequency (10 Hz-1 kHz) conductivity owing to long range translational motion of electrons (frequency independent), mid-frequency conductivity (1-10 kHz) due to short-range hopping, and high frequency (10 kHz-1 MHz) conduction due to localized orientation hopping mechanism. The hopping model can explain the nature of the conduction mechanism completely. The electrical conductivity measurements with temperature suggest the negative temperature coefficient of resistance behavior. The activation energy studies allow insight into the nature of the conduction mechanisms.

  15. Micro-arc oxidation treatment to improve the hard-tissue compatibility of Ti-29Nb-13Ta-4.6Zr alloy

    NASA Astrophysics Data System (ADS)

    Tsutsumi, Yusuke; Niinomi, Mitsuo; Nakai, Masaaki; Tsutsumi, Harumi; Doi, Hisashi; Nomura, Naoyuki; Hanawa, Takao

    2012-12-01

    Micro-arc oxidation (MAO) was performed on a β-type Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) in this study to improve its bioactivity in a body fluid and its hard-tissue compatibility. The surface oxide layer formed on TNTZ by MAO treatment in a mixture of calcium glycerophosphate and magnesium acetate was characterized using various surface analyses. The oxide layer was mainly composed of two types of TiO2 (rutile and anatase), and it also contained Ca, P, and Mg, which were incorporated from the electrolyte during the treatment. The calcium phosphate formation on the surface of the specimens after immersion in Hanks' solution was evaluated to determine the bioactivity of TNTZ with and without MAO treatment. As a result, thick calcium phosphate layers formed on the TNTZ specimen that underwent MAO treatment, whereas only a small amount of precipitate was observed on TNTZ without treatment. Thus, the MAO treatment is a promising method to improve the bioactivity and hard-tissue compatibility of TNTZ.

  16. High-coupling leaky surface acoustic waves on LiNbO3 or LiTaO3 thin plate bonded to high-velocity substrate

    NASA Astrophysics Data System (ADS)

    Gomi, Masashi; Kataoka, Takuya; Hayashi, Junki; Kakio, Shoji

    2017-07-01

    The propagation properties of leaky surface acoustic waves (LSAWs) and longitudinal-type LSAWs (LLSAWs) on a LiNbO3 (LN) or LiTaO3 (LT) thin plate bonded to an AT-cut quartz or c-plane sapphire (c-Al2O3) substrate with a high phase velocity were investigated. It was theoretically revealed that when the LN or LT thin-plate thickness is less than one wavelength, the particle displacement of LLSAWs was concentrated in the thin plate and the electromechanical coupling factor (K 2) was increased to two to three times that in the single substrate. Furthermore, for 36° Y-cut X-propagating LT/c-Al2O3 with an LT thin-plate thickness of 0.35 λ and X-cut 36° Y-propagating LN/c-Al2O3 with an LN thin-plate thickness of 0.19 λ, the values of K 2 for an LSAW and an LLSAW were experimentally found to increase from 5.6 and 10.4% in the single substrate to 11.5 and 19.7% in the thin-plate bonded structure, respectively.

  17. 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.

  18. Effect of spin-orbit coupling on formation of native defects in Weyl fermion semimetals: The case of T X (T =Ta ,Nb ; X =As ,P )

    NASA Astrophysics Data System (ADS)

    Yu, Zhi Gen; Zhang, Yong-Wei

    2016-11-01

    How to control the formation of native defects is crucial to obtaining high-quality samples and realizing the balance between electrons and holes for achieving high carrier mobilities in noncentrosymmetric Weyl fermion semimetals (WSMs). Using first-principles calculations, we explore the formation mechanisms of native defects in the family of T X (T =Ta , Nb; X =As , P), and find that the spin-orbit coupling (SOC) is not only intrinsic to these semimetals but also plays a significant role in dictating the formation of native defects. The calculated defect formation energies with the SOC are lower than those without the SOC. The detailed analyses of partial density of states reveal that the valence shells of T -d and X -p hybridization states contribute to the antibonding states in T X compounds. The broadness of T -d and X -4 p hybridization states with the SOC inclusion increases by about 1 eV compared with the corresponding T X without the SOC consideration. The more delocalized T -d and X -p hybridization states increase the energy of antibonding states and further attribute to the stabilization of native defects with the reduced formation energies in T X compounds. We also estimate the defect concentrations based on our accurately calculated formation energies of native defects, and propose practical strategies to control their concentrations to grow high-quality samples. Our results provide insights to the defect behavior under the effect of the SOC in WSMs.

  19. Manipulation of electronic and magnetic properties of M2C (M = Hf, Nb, Sc, Ta, Ti, V, Zr) monolayer by applying mechanical strains

    NASA Astrophysics Data System (ADS)

    Zhao, Shijun; Kang, Wei; Xue, Jianming

    2014-03-01

    Tuning the electronic and magnetic properties of a material through strain engineering is an effective strategy to enhance the performance of electronic and spintronic devices. In this paper, first-principles calculations based on density functional theory are carried out to investigate the electronic and magnetic properties of M2C(M = Hf, Nb, Sc, Ta, Ti, V, Zr, known as MXenes) subjected to biaxial symmetric mechanical strains. At the strain-free state, all these MXenes exhibit no spontaneous magnetism except for Ti2C and Zr2C which show a magnetic moment of 1.92 and 1.25 μB/unit, respectively. As the tensile strain increases, the magnetic moments of MXenes are greatly enhanced and a transition from nonmagnetism to ferromagnetism is observed for those nonmagnetic MXenes at zero strains. The most distinct transition is found in Hf2C, in which the magnetic moment is elevated to 1.5 μB/unit at a strain of 1.80%. We further show that the magnetic properties of Hf2C are attributed to the band shift mainly composed of Hf(5d) states.

  20. 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.

  1. Spectral and fluorescent kinetics features of Nd3+ ion in Nb2O5, Ta2O5 and La2O3 mixed lithium zirconium silicate glasses.

    PubMed

    Srikumar, T; Brik, M G; Srinivasa Rao, Ch; Gandhi, Y; Rao, D Krishna; Ravi Kumar, V; Veeraiah, N

    2011-10-15

    Li(2)O-ZrO(2)-SiO(2):Nd(3+) glasses mixed with Nb(2)O(5), Ta(2)O(5) and La(2)O(3) were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature. The Judd-Ofelt theory was successfully applied to characterize Nd(3+) spectra of all the three glasses. From this theory, various radiative properties like transition probability A, branching ratio β(r), the radiative lifetime τ(r), for (4)F(3/2) emission level in the spectra of these glasses has been evaluated. The radiative life time for (4)F(3/2) level of Nd(3+) ions has also been measured and quantum efficiencies were estimated. Among the three glasses studied, the La(2)O(3) mixed glass has exhibited the highest quantum efficiency. The reasons for such higher value have been discussed based on the relationship between the structural modifications taking place around the Nd(3+) ions. Copyright © 2011 Elsevier B.V. All rights reserved.

  2. Quaternary Ti-20Nb-10Zr-5Ta alloy during immersion in simulated physiological solutions: formation of layers, dissolution and biocompatibility.

    PubMed

    Milošev, Ingrid; Hmeljak, Julija; Žerjav, Gregor; Cör, Andrej; Calderon Moreno, Jose Maria; Popa, Monica

    2014-04-01

    Samples of the quaternary Ti-20Nb-10Zr-5Ta alloy were immersed in Hanks' simulated physiological solution and in minimum essential medium (MEM) for 25 days. Samples of Ti metal served as controls. During immersion, the concentration of ions dissolved in MEM was measured by inductively coupled plasma mass spectrometry, while at the end of the experiment the composition of the surface layers was analyzed by X-ray photoelectron spectroscopy, and their morphology by scanning electron microscopy equipped for chemical analysis. The surface layer formed during immersion was comprised primarily of TiO2 but contained oxides of alloying elements as well. The degree of oxidation differed for different metal cations; while titanium achieved the highest valency, tantalum remained as the metal or is oxidized to its sub-oxides. Calcium phosphate was formed in both solutions, while formation of organic-related species was observed only in MEM. Dissolution of titanium ions was similar for metal and alloy. Among alloying elements, zirconium dissolved in the largest quantity. The long-term effects of alloy implanted in the recipient's body were investigated in MEM, using two types of human cells-an osteoblast-like cell line and immortalized pulmonary fibroblasts. The in vitro biocompatibility of the quaternary alloy was similar to that of titanium, since no detrimental effects on cell survival, induction of apoptosis, delay of growth, or change in alkaline phosphatase activity were observed on incubation in MEM.

  3. Vibrational properties of Cu3XY4 sulvanites (X = Nb, Ta, and V; and Y = S, and Se) by ab initio molecular dynamics

    NASA Astrophysics Data System (ADS)

    Peralta, Joaquín; Valencia-Balvín, Camilo

    2017-09-01

    In this work, we present a structural and dynamic characterisation of six different types of sulvanites Cu3 X Y 4 with X = Nb, V and Ta, and Y = S and Se. These materials have been the subject of intense study in recent times primarily as potential candidates for solar cell devices, as well as for their enhanced opto-electrical properties. Here, by means of first-principles calculations, we study the structural and dynamic behaviour of these materials at different temperatures, which is important for use of these materials in high-temperature conditions. In this work the dynamic and structural properties are studied using the Density Functional Theory technique. The simulations were performed at four different temperatures, ranging from room temperature to 1500 K. By using first-principles molecular dynamics in the microcanonical ensemble, we are able to determine the vibrational spectra of these sulvanites. With this information we report for the first time the partial vibrational density of states of these structures at different temperatures. With these results we determine the vibrational properties of the basic building blocks of those sulvanites and their dynamic behaviour under temperature effects. We also show that the building blocks that which make up these structures, remain stable as the temperature increases.

  4. Development of thermo-mechanical processing for fabricating highly durable β-type Ti-Nb-Ta-Zr rod for use in spinal fixation devices.

    PubMed

    Narita, Kengo; Niinomi, Mitsuo; Nakai, Masaaki; Hieda, Junko; Oribe, Kazuya

    2012-05-01

    The mechanical strength of a beta titanium alloy such as Ti-Nb-Ta-Zr alloy (TNTZ) can be improved significantly by thermo-mechanical treatment. In this study, TNTZ was subjected to solution treatment, cold caliber rolling, and cold swaging before aging treatment to form a rod for spinal fixation. The {110}(β) are aligned parallel to the cross-section with two strong peaks approximately 180° apart, facing one another, in the TNTZ rods subjected to cold caliber rolling and six strong peaks at approximately 60° intervals, facing one another, in the TNTZ rods subjected to cold swaging. Therefore, the TNTZ rods subjected to cold swaging have a more uniform structure than those subjected to cold caliber rolling. The orientation relationship between the α and β phases is different. A [110](β)//[121](α), (112)(β)//(210)(α) orientation relationship is observed in the TNTZ rods subjected to aging treatment at 723 K after solution treatment and cold caliber rolling. On the other hand, a [110](β)//[001](α), (112)(β)//(200)(α) orientation relationship is observed in TNTZ rod subjected to aging treatment at 723 K after cold swaging. A high 0.2% proof stress of about 1200 MPa, high elongation of 18%, and high fatigue strength of 950 MPa indicate that aging treatment at 723 K after cold swaging is the optimal thermo-mechanical process for a TNTZ rod. Copyright © 2012 Elsevier Ltd. All rights reserved.

  5. Frictional wear characteristics of biomedical Ti-29Nb-13Ta-4.6Zr alloy with various microstructures in air and simulated body fluid.

    PubMed

    Niinomi, Mitsuo; Nakai, Masaaki; Akahori, Toshikazu

    2007-09-01

    The frictional wear characteristics of Ti-29Nb-13Ta-4.6Zr alloy subjected to solution treatment (referred to as TNTZ(ST)) and aged at 598, 673 and 723 K after solution treatment (referred to as TNTZ(598K), TNTZ(673K) and TNTZ(723K), respectively) were investigated in air and a simulated body environment (Ringer's solution) as a function of the loading level. Ti-6Al-4V ELI alloy aged at 813 K after solution treatment (referred to as T64(STA)) was employed as a reference material. Wear weight losses of TNTZ(ST), TNTZ(598K), TNTZ(673K), TNTZ(723K) and Ti64(STA) are lower in Ringer's solution than in air under both low and high loading conditions (1.96 and 29.4 N, respectively). It is considered that the frictional factor decreases because of the lubricating effect of Ringer's solution between the contact surface of the specimen and the zirconia ball-the mating material. Moreover, the wear weight losses of TNTZ(598K), TNTZ(673K) and TNTZ(723K) are lower than that of Ti64(STA) in both air and Ringer's solution under the low loading condition, but are higher under the high loading condition. This result implies that the transition from severe wear to mild wear versus loading level depends on the type of material.

  6. Motif of misfit layer compounds (SnS) xTS 2 (T=Ti, V, Nb, Ta) in the matrix of SnS 2

    NASA Astrophysics Data System (ADS)

    Abramov, S. P.

    1999-09-01

    The possibility of T (T=Ti, V, Nb, Ta) insertion in the layer matrix of SnS 2 (when T≪Sn) presents a special case of intercalation for the specific interactions that are inherent in the misfit layer compounds (SnS) xTS 2 ( x≈1). FT Raman spectra of T xSnS 2 (T=Ti, V) with x≪1 testify to the SnS 2 matrix that is invariable with respect to a charge transfer from T to SnS 2 layers as compared with the pristine SnS 2. At the same time the T xSnS 2 structure ( x≪1) taken as a whole has substantial features in the UV-IR spectra as compared with the pristine SnS 2 but is still a semiconductor at least in the case of T=Ti. This points out in the cluster manner of TS 2 insertion in the matrix of SnS 2 with the interactions that are typical of the misfit layer compounds (SnS) xTS 2 in which metallic conductivity occurs in the TS 2 layers.

  7. Comparison of single-beam and dual-beam laser welding of Ti-22Al-25Nb/TA15 dissimilar titanium alloys

    NASA Astrophysics Data System (ADS)

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

    2017-08-01

    Laser beam welding (LBW) was used to join Ti-22Al-25Nb/TA15 dissimilar titanium alloys. The microstructure and mechanical properties of the welded joints under single and dual beam welding were analyzed and compared. In the mode of single laser beam, the fusion zone only consisted of B2 phase because of existence of β-phase stabilizer and rapid cooling rate of LBW. However, O phase was formed in the fusion zone while applying dual-beam laser welding due to decrease of the cooling rate. The microhardness distribution of the welded joint in dual-beam welding mode was consistent with that in single mode, but the hardness of the weld under dual laser beam was higher than that of single laser beam. In room-temperature tensile tests, the fractures all occurred in the weld, but the morphology exhibited a quasi-cleavage feature in single mode while the morphology was dimple fracture in the mode of dual laser beam. The tensile strength and elongation were both increased under dual-beam laser welding compared with those under single-beam laser welding.

  8. Manipulation of electronic and magnetic properties of M{sub 2}C (M = Hf, Nb, Sc, Ta, Ti, V, Zr) monolayer by applying mechanical strains

    SciTech Connect

    Zhao, Shijun; Kang, Wei; Xue, Jianming

    2014-03-31

    Tuning the electronic and magnetic properties of a material through strain engineering is an effective strategy to enhance the performance of electronic and spintronic devices. In this paper, first-principles calculations based on density functional theory are carried out to investigate the electronic and magnetic properties of M{sub 2}C(M = Hf, Nb, Sc, Ta, Ti, V, Zr, known as MXenes) subjected to biaxial symmetric mechanical strains. At the strain-free state, all these MXenes exhibit no spontaneous magnetism except for Ti{sub 2}C and Zr{sub 2}C which show a magnetic moment of 1.92 and 1.25 μ{sub B}/unit, respectively. As the tensile strain increases, the magnetic moments of MXenes are greatly enhanced and a transition from nonmagnetism to ferromagnetism is observed for those nonmagnetic MXenes at zero strains. The most distinct transition is found in Hf{sub 2}C, in which the magnetic moment is elevated to 1.5 μ{sub B}/unit at a strain of 1.80%. We further show that the magnetic properties of Hf{sub 2}C are attributed to the band shift mainly composed of Hf(5d) states.

  9. 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.

  10. Laser damage comparisons of broad-bandwidth, high-reflection optical coatings containing TiO2, Nb2O5, or Ta2O5 high-index layers

    NASA Astrophysics Data System (ADS)

    Field, Ella S.; Bellum, John C.; Kletecka, Damon E.

    2017-01-01

    Broad bandwidth coatings allow angle of incidence flexibility and accommodate spectral shifts due to aging and water absorption. Higher refractive index materials in optical coatings, such as TiO2, Nb2O5, and Ta2O5, can be used to achieve broader bandwidths compared to coatings that contain HfO2 high index layers. We have identified the deposition settings that lead to the highest index, lowest absorption layers of TiO2, Nb2O5, and Ta2O5, via e-beam evaporation using ion-assisted deposition. We paired these high index materials with SiO2 as the low index material to create broad bandwidth high reflection coatings centered at 1054 nm for 45 deg angle of incidence and P polarization. High reflection bandwidths as large as 231 nm were realized. Laser damage tests of these coatings using the ISO 11254 and NIF-MEL protocols are presented, which revealed that the Ta2O5/SiO2 coating exhibits the highest resistance to laser damage, at the expense of lower bandwidth compared to the TiO2/SiO2 and Nb2O5/SiO2 coatings.

  11. Laser damage comparisons of broad-bandwidth, high-reflection optical coatings containing TiO2, Nb2O5, or Ta2O5 high-index layers

    DOE PAGES

    Field, Ella Suzanne; Bellum, John Curtis; Kletecka, Damon E.

    2016-09-21

    Broad bandwidth coatings allow angle of incidence flexibility and accommodate spectral shifts due to aging and water absorption. Higher refractive index materials in optical coatings, such as TiO2, Nb2O5, and Ta2O5, can be used to achieve broader bandwidths compared to coatings that contain HfO2 high index layers. We have identified the deposition settings that lead to the highest index, lowest absorption layers of TiO2, Nb2O5, and Ta2O5, via e-beam evaporation using ion-assisted deposition. We paired these high index materials with SiO2 as the low index material to create broad bandwidth high reflection coatings centered at 1054 nm for 45 degmore » angle of incidence and P polarization. Furthermore, high reflection bandwidths as large as 231 nm were realized. Laser damage tests of these coatings using the ISO 11254 and NIF-MEL protocols are presented, which revealed that the Ta2O5/SiO2 coating exhibits the highest resistance to laser damage, at the expense of lower bandwidth compared to the TiO2/SiO2 and Nb2O5/SiO2 coatings.« less

  12. 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

  13. 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.

  14. Martensitic transformation between competing phases in Ti-Ta alloys: a solid-state nudged elastic band study.

    PubMed

    Chakraborty, Tanmoy; Rogal, Jutta; Drautz, Ralf

    2015-03-25

    A combined density functional theory and solid-state nudged elastic band study is presented to investigate the martensitic transformation between β → (α″, ω) phases in the Ti-Ta system. The minimum energy paths along the transformation are calculated and the transformation mechanisms as well as relative stabilities of the different phases are discussed for various compositions. The analysis of the transformation paths is complemented by calculations of phonon spectra to determine the dynamical stability of the β, α″, and ω phase. Our theoretical results confirm the experimental findings that with increasing Ta concentration there is a competition between the destabilisation of the α″ and ω phase and the stabilisation of the high-temperature β phase.

  15. Geology and genesis of the Toongi rare metal (Zr, Hf, Nb, Ta, Y and REE) deposit, NSW, Australia, and implications for rare metal mineralization in peralkaline igneous rocks

    NASA Astrophysics Data System (ADS)

    Spandler, Carl; Morris, Caitlin

    2016-12-01

    The Toongi Deposit, located in central NSW, Australia, hosts significant resources of Zr, Hf, Nb, Ta, Y and REE within a small (ca. 0.3 km2), rapidly cooled trachyte laccolith. Toongi is part of regional Late Triassic to Jurassic alkaline magmatic field, but is distinguished from the other igneous bodies by its peralkaline composition and economically significant rare metal content that is homogenously distributed throughout the trachyte body. The primary ore minerals are evenly dispersed throughout the rock and include lueshite/natroniobite and complex Na-Fe-Zr-Nb-Y-REE silicate minerals dominated by a eudialyte group mineral (EGM). The EGM occurs in a unique textural setting in the rock, commonly forming spheroidal or irregular-shaped globules, herein called "snowballs", within the rock matrix. The snowballs are often protruded by aegirine and feldspar phenocrysts and contain swarms of fine aegirine and feldspar grains that often form spiral or swirling patterns within the snowball. Secondary ore minerals include REE carbonates, Y milarite, catapleiite and gaidonnayite that fill fractures and vesicles in the rock. Based on bulk-rock geochemical and Nd isotope data, and thermodynamic modelling of magma fractionation, the alkaline rocks of the region are interpreted to represent extrusive to hyperbyssal products of mantle-derived magma that ponded at mid-crustal levels (ca. 0.3 GPa) and underwent extensive fractionation under low-oxygen fugacity conditions. The high Na2O, peralkaline nature of the Toongi Deposit trachyte developed via extensive fractionation of an alkali olivine basalt parental magma initially in the mid-crust and subsequently at shallow levels (ca. 0.1 GPa). This extended fractionation under low fO2 and relatively low H2O-activity conditions limited volatile release and allowed build-up of rare metal contents to ore grades. We speculate that the ore minerals may have originally formed from rare metal-rich sodic-silicate melt that formed immiscible

  16. Origin of magnetoelectric effect in Co4Nb2O9 and Co4Ta2O9 : The lessons learned from the comparison of first-principles-based theoretical models and experimental data

    NASA Astrophysics Data System (ADS)

    Solovyev, I. V.; Kolodiazhnyi, T. V.

    2016-09-01

    We report results of joint experimental and theoretical studies on magnetoelectric (ME) compounds Co4Nb2O9 and Co4Ta2O9 . On the experimental side, we present results of the magnetization and dielectric permittivity measurements in the magnetic field. On the theoretical side, we construct the low-energy Hubbard-type model for the magnetically active Co 3 d bands in the Wannier basis, using the input of the first-principles electronic structure calculations, solve this model in the mean-field Hartree-Fock approximation, and evaluate the electric polarization in terms of the Berry phase theory. Both experimental and theoretical results suggest that Co4Ta2O9 is magnetically softer than Co4Nb2O9 . Therefore, it is reasonable to expect that the antiferromagnetic structure of Co4Ta2O9 can be easier deformed by the external magnetic field, yielding larger polarization. This trend is indeed reproduced by our theoretical calculations, but does not seem to be consistent with the experimental behavior of the polarization and dielectric permittivity. Thus, we suggest that there should be a hidden mechanism controlling the ME coupling in these compounds, probably related to the magnetic striction or a spontaneous change of the magnetic structure, which breaks the inversion symmetry. Furthermore, we argue that unlike in other ME systems (e.g., Cr2O3 ), in Co4Nb2O9 and Co4Ta2O9 there are two crystallographic sublattices, which contribute to the ME effect. These contributions are found to be of the opposite sign and tend to compensate each other. The latter mechanism can be also used to control and reverse the electric polarization in these compounds.

  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.

  18. Synthesis, crystal structure and characterization of new 12H hexagonal perovskite-related oxides Ba 6M2Na 2X2O 17 ( M=Ru, Nb, Ta, Sb; X=V, Cr, Mn, P, As)

    NASA Astrophysics Data System (ADS)

    Quarez, Eric; Abraham, Francis; Mentré, Olivier

    2003-11-01

    The new Ba 6Ru 2Na 2X2O 17 ( X=V, Mn) compounds have been prepared by electrosynthesis in molten NaOH and their crystal structures have been refined from single crystals X-ray diffraction, space group P6 3/ mmc, Z=2, for X=V: a =5.8506(1) Å, c =29.6241(4) Å, R1=4.76%, for X=Mn : a =5.8323(1) Å, c =29.5299(3) Å, R1=3.48%. The crystal structure is a 12H-type perovskite with a ( c' cchcc) 2 stacking sequence of [BaO 3] c, [BaO 3] h and [BaO 2] c' layers. The tridimensional edifice is formed by blocks of Ru 2O 9 dimers that share corners with NaO 6 octahedra. These blocks sandwich double sheets of X5+O 4 tetrahedra. Several isotypic Ba 6M5+2Na 2X5+2O 17 materials ( X=V, Cr, Mn, P, As) and ( M=Ru, Nb, Ta, Sb) have been prepared by solid state reaction and characterized by Rietveld analysis. The magnetic and electric properties have been investigated and show besides the Ru 5+2O 9 typical intradimer antiferromagnetic couplings, discrepancies of both χ and ρ versus T at 50 and 100 K for Ba 6Ru 2Na 2X2O 17 ( X=V, As). In this work, a review of the identified Ru-hexagonal perovskite materials is also reported in order to overview the wide variety of possibilities in the field of new compounds synthesis.

  19. Two-Dimensional Nb-Based M 4 C 3 Solid Solutions (MXenes)

    SciTech Connect

    Yang, Jian; Naguib, Michael; Ghidiu, Michael; Pan, Li-Mei; Gu, Jian; Nanda, Jagjit; Halim, Joseph; Gogotsi, Yury; Barsoum, Michel W.; Zhou, Y.

    2015-10-15

    Two new two-dimensional Nb4C3-based solid solutions (MXenes), (Nb0.8,Ti0.2)4C3Tx and (Nb0.8,Zr0.2)4C3Tx (where T is a surface termination) were synthesizedas confirmed by X-ray diffractionfrom their corresponding MAX phase precursors (Nb0.8,Ti0.2)4AlC3 and (Nb0.8,Zr0.2)4AlC3. In our report we discuss Zr-containing MXene. We also studied intercalation of Li ions into these two compositions, and Nb4C3Tx in order to determine the potential of those materials for energy storage applications. Lithiation and delithiation peaks at 2.26 and 2.35 V, respectively, appeared in the case of Nb4C3Tx, but were not present in Nb2CTx. After 20 cycles at a rate of C/4, the specific capacities of (Nb0.8,Ti0.2)4C3Txand (Nb0.8,Ti0.2)4C3Tx were 158 and 132 mAh/g, respectively, both slightly lower than the capacity of Nb4C3Tx.

  20. Abnormal Deformation Behavior of Oxygen-Modified β-Type Ti-29Nb-13Ta-4.6Zr Alloys for Biomedical Applications

    NASA Astrophysics Data System (ADS)

    Liu, Huihong; Niinomi, Mitsuo; Nakai, Masaaki; Cong, Xin; Cho, Ken; Boehlert, Carl J.; Khademi, Vahid

    2017-01-01

    Oxygen was added to the biomedical β-type Ti-29Nb-13Ta-4.6Zr alloy (TNTZ, mass pct) in order to improve its strength, while keeping its Young's modulus low. Conventionally, with an increase in the oxygen content, an alloy's tensile strength increases, while its tensile elongation-to-failure decreases. However, an abnormal deformation behavior has been reported in the case of oxygen-modified TNTZ alloys in that their strength increases monotonically while their elongation-to-failure initially decreases and then increases with the increase in the oxygen content. In this study, this abnormal tensile deformation behavior of oxygen-modified TNTZ alloys was investigated systematically. A series of TNTZ-(0.1, 0.3, and 0.7 mass pct)O alloy samples was prepared, treated thermomechanically, and finally solution treated; these samples are denoted as 0.1ST, 0.3ST, and 0.7ST, respectively. The main tensile deformation mechanisms in 0.1ST are a deformation-induced α″-martensitic transformation and {332}<113> mechanical twinning. The large elongation-to-failure of 0.1ST is attributable to multiple deformation mechanisms, including the deformation-induced martensitic transformation and mechanical twinning as well as dislocation glide. In both 0.3ST and 0.7ST, dislocation glide is the predominant deformation mode. 0.7ST shows more homogeneous and extensive dislocation glide along with multiple slip systems and a higher frequency of cross slip. As a result, it exhibits a higher work-hardening rate and greater resistance to local stress concentration, both of which contribute to its elongation-to-failure being greater than that of 0.3ST.

  1. Fractionation of Li, Be, Ga, Nb, Ta, In, Sn, Sb, W and Bi in the peraluminous Early Permian Variscan granites of the Cornubian Batholith: Precursor processes to magmatic-hydrothermal mineralisation

    NASA Astrophysics Data System (ADS)

    Simons, Beth; Andersen, Jens C. Ø.; Shail, Robin K.; Jenner, Frances E.

    2017-05-01

    The Early Permian Variscan Cornubian Batholith is a peraluminous, composite pluton intruded into Devonian and Carboniferous metamorphosed sedimentary and volcanic rocks. Within the batholith there are: G1 (two-mica), G2 (muscovite), G3 (biotite), G4 (tourmaline) and G5 (topaz) granites. G1-G2 and G3-G4 are derived from greywacke sources and linked through fractionation of assemblages dominated by feldspars and biotite, with minor mantle involvement in G3. G5 formed though flux-induced biotite-dominate melting in the lower crust during granulite facies metamorphism. Fractionation enriched G2 granites in Li (average 315 ppm), Be (12 ppm), Ta (4.4 ppm), In (74 ppb), Sn (18 ppm) and W (12 ppm) relative to crustal abundances and G1 granites. Gallium (24 ppm), Nb (16 ppm) and Bi (0.46 ppm) are not significantly enriched during fractionation, implying they are more compatible in the fractionating assemblage. Sb (0.16 ppm) is depleted in G1-G2 relative to the average upper and lower continental crust. Muscovite, a late-stage magmatic/subsolidus mineral, is the major host of Li, Nb, In, Sn and W in G2 granites. G2 granites are spatially associated with W-Sn greisen mineralisation. Fractionation within the younger G3-G4 granite system enriched Li (average 364 ppm), Ga (28 ppm), In (80 ppb), Sn (14 ppm), Nb (27 ppm), Ta (4.6 ppm), W (6.3 ppm) and Bi (0.61 ppm) in the G4 granites with retention of Be in G3 granites due to partitioning of Be into cordierite during fractionation. The distribution of Nb and Ta is controlled by accessory phases such as rutile within the G4 granites, facilitated by high F and lowering the melt temperature, leading to disseminated Nb and Ta mineralisation. Lithium, In, Sn and W are hosted in biotite micas which may prove favourable for breakdown on ingress of hydrothermal fluids. Higher degrees of scattering on trace element plots may be attributable to fluid-rock interactions or variability within the magma chamber. The G3-G4 system is more boron

  2. Effects of Li content on the phase structure and electrical properties of lead-free (K0.46-x/2Na0.54-x/2Lix)(Nb0.76Ta0.20Sb0.04)O3 ceramics

    NASA Astrophysics Data System (ADS)

    Chang, Yunfei; Yang, Zupei; Hou, Yuting; Liu, Zonghuai; Wang, Zenglin

    2007-06-01

    Lead-free (K0.46-x/2Na0.54-x/2Lix)(Nb0.76Ta0.20Sb0.04)O3 piezoelectric ceramics were prepared by the conventional solid state sintering method without cold-isostatic pressing process. The x-ray diffraction and Raman scattering results show that the phase structure of the ceramics undergoes a transition from pseudocubic to tetragonal phase with increasing x from 0 to 0.10. Significantly enhanced electrical properties (d33=259pC/N, kp=0.42, ɛr=1653, and tan δ =0.027) were obtained in the ceramics with x =0.04 near the morphotropic phase boundary, and only the tetragonal-cubic phase transition was observed above the room temperature in the ɛr-T curve. The temperature stability of the ceramics with x =0.04 was also investigated.

  3. Structural and mechanical properties of lanthanide doped La1/3Nb0.8Ta0.2O3 thin films prepared by sol-gel method

    NASA Astrophysics Data System (ADS)

    Brunckova, Helena; Medvecky, Lubomir; Kovalcikova, Alexandra; Fides, Martin; Mudra, Erika; Durisin, Juraj; Skvarla, Jiri; Kanuchova, Maria

    2017-04-01

    Transparent Eu and Nd doped lanthanum niobate tantalate La1/3Nb0.8Ta0.2O3 (LNT) thin films (˜150 nm) were prepared by sol-gel/spin-coating process on Pt/SiO2/Si substrates and annealing at 1100 °C. The x-ray diffraction analysis of films confirmed formation of the perovskite La1/3NbO3 and La1/3TaO3 phases with traces of pyrochlore LaNbO4. Eu and Nd doped LNT films were smoother with roughness 17.1 and 25.4 nm in comparison with LNT (43.3 nm). In all films was observed heterogeneous microstructure with the perovskite spherical and pyrochlore needle-like particles. The mechanical properties of films were characterized for the first time by conventional and continuous stiffness (CSM) nanoindentation. The Eu and Nd doped LNT film modulus (E) and hardness (H) were higher than LNT (˜99.8 and 4.4 GPa) determined by conventional nanoindentation. It was measured the significant effect of substrate on properties of Eu or Nd films (H ˜ 5.9 or 4.9 GPa and E ˜ 107.3 or 104.1 GPa) by CSM nanoindentation.

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  6. A new, lead free, family of perovskites with a diffuse phase transition: NaNbO3-based solid solutions

    NASA Astrophysics Data System (ADS)

    Raevski, I. P.; Prosandeev, S. A.

    2002-10-01

    (1-x)NaNbO3-(x)ABO3 perovskite solid solutions belonging to group II according to the Krainik classification [Izv. Akad. Nauk SSSR, Ser. Phys. 28 (1964) 643] exhibit a dramatic diffusion of the dielectric permittivity ε‧ maximum and relaxor-type behavior when the second component concentration exceeds a threshold value x0. The concentration phase transition to this relaxor-like phase is abrupt (of the first order kind) that is seen from the step in the dependence of the ε‧(T) maximum temperature, Tm, on x. Some relaxor-like properties appear even at xNbO3-ABO3 relaxor-type compositions are well below the room temperature and the dielectric permittivity maximal values, ε‧m, are much lower than in the case of Pb-containing relaxors. However both Tm and ε‧m values can be increased substantially by Li or K-doping leading to the formation of NaNbO3-ABO3-LiNbO3 (KNbO3) solid solutions.

  7. Design and development of hot corrosion-resistant nickel-base single-crystal superalloys by the d-electrons alloy design theory: Part II--Effect of refractory metals Ti, Ta, and Nb on microstructures and properties

    SciTech Connect

    Zhang, J.S. . Inst. of Metal Research Beijing Univ. of Science and Technology, ); Hu, Z.Q. . Inst. of Metal Research); Murata, Y.; Morinaga, M.; Yukawa, N. . Dept. of Production Systems Engineering)

    1993-11-01

    A systematic study of the effects of refractory metals Ti, Ta, and Nb on the microstructures and properties was conducted with a hot corrosion-resistant alloy system Ni-16Cr-9Al-4Co-2W-1Mo-(0 [approximately] 4)Ti-(0 [approximately] 4)Ta-(0 [approximately] 4)Nb (in atomic percent) which was selected based on the d-electrons alloy design theory and some basic considerations in alloying features of single-crystal nickel-base superalloys. The contour lines of solidification reaction temperatures and eutectic ([gamma] + [gamma][prime]) volume fraction in the Ti-Ta-Nb compositional triangle were determined by differential thermal analysis (DTA) and imaging analyzer. Compared with the reference alloy IN738LC, in most of the compositional ranges studied, the designed alloys show very low amounts of eutectic ([gamma] + [gamma][prime]) ([le]0.4 vol pct), narrow solidification ranges ([le]65 C), and wide heat-treatment windows'' (> 100 C). This indicates that the alloys should have the promising microstructural stability, single-crystal castability, and be easier for complete solution treatment. In a wide compositional range, the designed alloys showed good hot corrosion resistance (weight loss less than 20 mg/cm[sup 2] after 24 hours kept in molten salt at 900 C). By summarizing the results, the promising alloy compositional ranges of the alloys with balanced properties were determined for the final step of the alloy design, i.e., to grow single crystal and characterize mechanical properties of the alloys selected from the previously mentioned regions.

  8. 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.

  9. β-Nb9VO25

    PubMed Central

    Nasri, Rawia; Chérif, Saïda Fatma; Zid, Mohamed Faouzi; Driss, Ahmed

    2014-01-01

    The title compound, nona­niobium vanadium penta­cosa­oxide, was prepared by a solid-state reaction at 1198 K. It is isotypic with Nb9AsO25, Nb9PO25 and Ta9VO25. The structure consists of NbO6 octa­hedra (one with 4/m.. and two with m.. symmetry) and VO4 tetra­hedra (-4.. symmetry) sharing corners and edges to form a three-dimensional framework. This framework can be considered as a junction between ribbons made up from NbO6 octa­hedra and chains of NbO6 octa­hedra and chains of VO4 tetra­hedra. The V site shows half-occupancy, hence one half of the VO4 tetra­hedra is unoccupied. The structural differences with α-Nb9VO25, VOSO4, SbOPO4 and NbOPO4 oxides are discussed. PMID:24860297

  10. 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.

  11. 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.

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

    PubMed

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

    2015-07-21

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

  13. 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

  14. Magnetic properties: M{umlt o}ssbauer, x-ray absorption spectroscopy, and specific-heat studies of Pr{sub 1.5}Ce{sub 0.5}{ital M}Sr{sub 2}Cu{sub 2}O{sub {ital z}} ({ital M}=Ta, In, Nb, Nb+Ga) compounds

    SciTech Connect

    Asaf, U.; Felner, I.; Schmitt, D.; Barbara, B.; Godart, C.; Alleno, E. |

    1996-12-01

    We have investigated Pr{sub 1.5}Ce{sub 0.5}{ital M}Sr{sub 2}Cu{sub 2}O{sub {ital z}} ({ital z}=9 or 10) materials ({ital M}=Ta, In, and Nb+Ga) by complementary experimental techniques. All materials studied are not superconducting. Magnetic susceptibility studies for {ital M}=Ta reveal one magnetic anomaly at 23 K and irreversibility phenomena at higher temperatures. The presence of 0.5{percent} {sup 57}Fe dramatically affects the positions of the anomalies, and M{umlt o}ssbauer spectroscopy studies (MS) reveal that the Cu(2) sites are magnetically ordered below {ital T}{sub {ital N}}(Cu)=130 K. This low {ital T}{sub {ital N}}(Cu) obtained is discussed. No specific heat anomaly was observed at 23 K, suggesting that the Pr sublattice does not order magnetically, and the anomalies in the susceptibility originate from the Cu moments. No anomalies in the susceptibility curves are found for {ital M}=In and Nb+Ga compounds. However, MS indicate that for the mixed compound, the Cu sites are magnetically ordered at low temperatures. The magnetic behavior of {ital M}=Ta is compared to similar systems with two anomalies for {ital M}=Nb at 11 and 52 K, and three anomalies for {ital M}=Ga at 12, 52, and 94 K. X-ray absorption spectroscopy (XAS) indicates that in all materials studied, the Pr has a mixed valence close to 3. The Pr valence does not change with temperature. {copyright} {ital 1996 The American Physical Society.}

  15. MORB mantle hosts the missing Eu (Sr, Nb, Ta and Ti) in the continental crust: New perspectives on crustal growth, crust-mantle differentiation and chemical structure of oceanic upper mantle

    NASA Astrophysics Data System (ADS)

    Niu, Yaoling; O'Hara, Michael J.

    2009-09-01

    We have examined the high quality data of 306 mid-ocean ridge basalt (MORB) glass samples from the East Pacific Rise (EPR), near-EPR seamounts, Pacific Antarctic Ridge (PAR), near-PAR seamounts, Mid-Atlantic Ridge (MAR), and near-MAR seamounts. The data show a correlated variation between Eu/Eu* and Sr/Sr*, and both decrease with decreasing MgO, pointing to the effect of plagioclase crystallization. The observation that samples with MgO > 9.5 wt.% (before plagioclase on the liquidus) show Eu/Eu* > 1 and Sr/Sr* > 1 and that none of the major phases (i.e., olivine, orthopyroxene, clinopyroxene, spinel and garnet) in the sub-ridge mantle melting region can effectively fractionate Eu and Sr from otherwise similarly incompatible elements indicates that the depleted MORB mantle (DMM) possesses excess Sr and Eu, i.e., [Sr/Sr*]DMM > 1 and [Eu/Eu*]DMM > 1. Furthermore, the well-established observation that DNb ≈ DTh, DTa ≈ DU and DTi ≈ DSm during MORB mantle melting, yet primitive MORB melts all have [Nb/Th]PMMORB > 1, [Ta/U]PMMORB > 1 and [Ti/Sm]PMMORB > 1 (where PM indicates primitive mantle normalized), also points to the presence of excess Nb, Ta and Ti in the DMM, i.e., [Nb/Th]PMDMM > 1, [Ta/U]PMDMM > 1 and [Ti/Sm]PMDMM > 1. The excesses of Eu, Sr, Nb, Ta and Ti in the DMM complement the well-known deficiencies of these elements in the bulk continental crust (BCC). These new observations, which support the notion that the DMM and BCC are complementary in terms of the overall abundances of incompatible elements, offer new insights into the crust-mantle differentiation. These observations are best explained by partial melting of amphibolite of MORB protolith during continental collision, which produces andesitic melts with a remarkable compositional (major and trace element abundances as well as key elemental ratios) similarity to the BCC, as revealed by andesites in southern Tibet produced during the India-Asia continental collision. An average amphibolite of MORB

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  17. 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.

  18. 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.

  19. Theoretical study of interface structure and energetics in semicoherent Fe(001)/MX(001) systems ( M=Sc , Ti, V, Cr, Zr, Nb, Hf, Ta; X=C or N)

    NASA Astrophysics Data System (ADS)

    Fors, Dan H. R.; Wahnström, Göran

    2010-11-01

    We perform a systematic ab initio study of the electronic and atomic structure of semicoherent interfaces between bcc Fe and NaCl MX ( M=Sc , Ti, V, Cr, Zr, Nb, Hf, Ta; X=C or N). The interface energetics is accessed by using a Peierls-Nabarro framework, in which ab initio data for the chemical interactions across the interface are combined with a continuum description to account for the elastic distortions. The key factors to the trends in the interface energy are identified and discussed with respect to the size of the misfit and the electronic structure of the MX phase. Our approach shows that the inclusion of lattice misfit can have a significant contribution to the interface energy (up to 1.5J/m2 ) and must therefore be thoroughly accounted for in the interface description. The results will have important bearings on our ability to understand and describe precipitate stability in steels.

  20. 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.

  1. Synthesis of new visible light active photocatalysts of Ba(In(1/3)Pb(1/3)M'(1/3))O3 (M' = Nb, Ta): a band gap engineering strategy based on electronegativity of a metal component.

    PubMed

    Hur, Su Gil; Kim, Tae Woo; Hwang, Seong-Ju; Park, Hyunwoong; Choi, Wonyong; Kim, Sung Jin; Kim, Sun Jin; Choy, Jin-Ho

    2005-08-11

    We have synthesized new, efficient, visible light active photocatalysts through the incorporation of highly electronegative non-transition metal Pb or Sn ions into the perovskite lattice of Ba(In(1/3)Pb(1/3)M'(1/3))O3 (M = Sn, Pb; M' = Nb, Ta). X-ray diffraction, X-ray absorption spectroscopic, and energy dispersive spectroscopic microprobe analyses reveal that tetravalent Pb or Sn ions exist in the B-site of the perovskite lattice, along with In and Nb/Ta ions. According to diffuse UV-vis spectroscopic analysis, the Pb-containing quaternary metal oxides Ba(In(1/3)Pb(1/3)M'(1/3))O3 possess a much narrower band gap (E(g) approximately 1.48-1.50 eV) when compared to the ternary oxides Ba(In(1/2)M'(1/2))O3 (E(g) approximately 2.97-3.30 eV) and the Sn-containing Ba(In(1/3)Sn(1/3)M'(1/3))O3 derivatives (E(g) approximately 2.85-3.00 eV). Such a variation of band gap energy upon the substitution is attributable to the broadening of the conduction band caused by the dissimilar electronegativities of the B-site cations. In contrast to the ternary or the Sn-substituted quaternary compounds showing photocatalytic activity under UV-vis irradiation, the Ba(In(1/3)Pb(1/3)M'(1/3))O3 compounds induce an efficient photodegradation of 4-chlorophenol under visible light irradiation (lambda > 420 nm). The present results highlight that the substitution of electronegative non-transition metal cations can provide a very powerful way of developing efficient visible light harvesting photocatalysts through tuning of the band structure of a semiconductive metal oxide.

  2. Microstructural investigation of plastically deformed Ti{sub 20}Zr{sub 20}Hf{sub 20}Nb{sub 20}Ta{sub 20} high entropy alloy by X-ray diffraction and transmission electron microscopy

    SciTech Connect

    Dirras, G.; Gubicza, J.; Heczel, A.; Lilensten, L.; Couzinié, J.-P.; Perrière, L.; Guillot, I.; Hocini, A.

    2015-10-15

    The microstructure evolution in body-centered cubic (bcc) Ti{sub 20}Zr{sub 20}Hf{sub 20}Nb{sub 20}Ta{sub 20} high entropy alloy during quasi-static compression test was studied by X-ray line profile analysis (XLPA) and transmission electron microscopy (TEM). The average lattice constant and other important parameters of the microstructure such as the mean crystallite size, the dislocation density and the edge/screw character of dislocations were determined by XLPA. The elastic anisotropy factor required for XLPA procedure was determined by nanoindentation. XLPA shows that the crystallite size decreased while the dislocation density increased with strain during compression, and their values reached about 39 nm and 15 × 10{sup 14} m{sup −2}, respectively, at a plastic strain of ~ 20%. It was revealed that with increasing strain the dislocation character became more screw. This can be explained by the reduced mobility of screw dislocations compared to edge dislocations in bcc structures. These observations are in line with TEM investigations. The development of dislocation density during compression was related to the yield strength evolution. - Highlights: • Ti{sub 20}Zr{sub 20}Hf{sub 20}Nb{sub 20}Ta{sub 20} high entropy alloy was processed by arc-melting. • The mechanical was evaluated by RT compression test. • The microstructure evolution was studied by XLPA and TEM. • With increasing strain the dislocation character became more screw. • The yield strength was related to the development of the dislocation density.

  3. Mechanical behavior and microstructure of Ti{sub 20}Hf{sub 20}Zr{sub 20}Ta{sub 20}Nb{sub 20} high-entropy alloy loaded under quasi-static and dynamic compression conditions

    SciTech Connect

    Dirras, G.; Couque, H.; Lilensten, L.; Heczel, A.; Tingaud, D.; Couzinié, J.-P.; Perrière, L.; Gubicza, J.; Guillot, I.

    2016-01-15

    The microstructure and the mechanical behavior of equimolar Ti{sub 20}Hf{sub 20}Zr{sub 20}Ta{sub 20}Nb{sub 20} high-entropy alloy in a wide range of initial strain rates between ~ 10{sup −3} s{sup −1} and ~ 3.4 × 10{sup 3} s{sup −1} were studied. A significant increment in the yield strength with increasing strain rate was observed. The yield strength at ~ 3.4 × 10{sup 3} s{sup −1} was about 40% higher than that measured at ~ 10{sup −3} s{sup −1}. Analysis by electron backscatter diffraction shows that in the low strain rate regime (up to ~ 10 s{sup −1}) the deformation occurs mainly in evenly distributed bands, while in the dynamic regime the deformation is strongly localized in macroscopic shear bands accompanied by softening even after the onset of yielding. The Kernel Average Misorientation technique reveals a high level of lattice rotation within these bands that also carries intense shear. In addition, X-ray diffraction line profile analysis indicates that the sharp increase in the flow stress is mostly related to an increase of the dislocation density. - Highlights: • Strain rate effect on the plastic behavior of Ti{sub 20}Hf{sub 20}Zr{sub 20}Ta{sub 20}Nb{sub 20} HEA was studied. • Low strain rate regime was characterized by a continuous hardening. • At high strain rates softening occurred shortly after the onset of yielding. • Intense strain localization in shear bands occurred in the high strain rate regime. • High dislocation density explained the upturn of flow stress at high strain rates.

  4. Pressure-induced phase transitions of piezoelectric single crystals from the langasite family: La3Nb0.5Ga5.5O14 and La3Ta0.5Ga5.5O14.

    PubMed

    Pavlovska, A; Werner, S; Maximov, B; Mill, B

    2002-12-01

    The hydrostatic compression of piezoelectric single crystals of La(3)Nb(0.5)Ga(5.5)O(14) (LNG) and La(3)Ta(0.5)Ga(5.5)O(14) (LTG) was studied at pressures of up to 23 GPa in diamond-anvil high-pressure cells using single-crystal X-ray diffraction techniques. The reflection-intensity data for LNG and LTG were collected at pressures of up to 22.8 GPa and 16.7 GPa, respectively. Both compounds show anisotropic behaviour under pressure, which is caused by differences in bonding parallel to the a and c directions. The compression of strongly rigid structures leads to increasing internal strains and results, at pressures of 12.4 (3) GPa for LNG and 11.7 (3) GPa for LTG, in a transition to lower symmetry. The compressibilities along the c axis are almost the same for LNG and LTG through the whole investigated pressure range. In contrast, the pressure dependencies of the a axis of these materials are similar only for the initial phase, and the axial compressibilities for the high-pressure polymorphs of LNG and LTG are significantly different to each other. The volume compressibilities of trigonal LNG and LTG (space group P321) are about 0.007 GPa(-1); respective bulk moduli are 145 (3) GPa and 144 (2) GPa. The monoclinic high-pressure phases (space group A2) of LNG and LTG show differing compressions, which can be explained by the substitution of Ta(5+) for Nb(5+). Thus, the bulk moduli for the high-pressure polymorphs of LNG and LTG are B(0) = 93 (2) GPa and B(0) = 128 (12) GPa, respectively. The volume compressibilities of the high-pressure phases at 0.011 GPa(-1) for LNG and 0.008 GPa(-1) for LTG are higher than the initial phases, this effect being more pronounced in the case of LNG.

  5. S = 1/2 Square-Lattice Antiferromagnets: (CuX)LaB_2O_7 and (CuCl)A_2B_3O10 (X = Cl, Br; A = Ca, Sr; B = Nb, Ta)

    NASA Astrophysics Data System (ADS)

    Kageyama, H.; Kitano, T.; Nakanishi, R.; Yasuda, J.; Oba, N.; Baba, Y.; Nishi, M.; Ueda, Y.; Ajiro, Y.; Yoshimura, K.

    A series of magnetic compounds with the formula (CuX)LaB_2O_7 and (CuCl)A_2B_3O10 (X = Cl, Br; A = Ca, Sr; B = Nb, Ta) have been prepared through a low-temperature topochemical route starting from nonmagnetic double- (n = 2) and triple- (n = 3) layered perovskites, respectively. The magnetic susceptibility of these compounds typically exhibits a broad maximum at low temperatures, characteristic of low-dimensional antiferromagnetic compounds. However, depending on the choice of the parameters, X, A, B and n, physical quantities such as the Weiss temperature and the temperature at a maximum susceptibility vary to a great extent, which enables us to study the phase diagram of the S = 1/2 frustrated square-lattice antiferromagnets (the so-called J_1-J_2 model). In particular, (CuCl)LaNb_2O_7, possibly having a ferromagnetic J_1 and an antiferromagnetic J_2, shows a spin-liquid behavior with the spin gap of 27 K.

  6. Direct ICP-MS determination of trace and ultratrace elements in geological materials after decomposition in a microwave oven. Part II. Quantitation of Ba, Cs, Ga, Hf, In, Mo, Nb, Pb, Rb, Sn, Sr, Ta and Tl.

    PubMed

    Gupta, J G; Bertrand, N B

    1995-12-01

    A new method has been developed for the rapid determination of traces of Ba, Cs, Ga, Hf, In, Mo, Nb, Pb, Rb, Sn, Sr, Ta and Tl in silicate rocks and lake, stream and river sediments. The method involved dissolution of samples in a microwave oven by heating in a pressure decomposition Teflon vessel with a mixture of HF + HNO(3) + HCl + H(3)BO(3) + EDTA followed by direct multielement determination using inductively coupled plasma-mass spectrometry (ICP MS ). The method is faster than conventional dissolution of samples by open vessel acid digestion and fusion and determination by instrumental methods. The accuracy and precision of the developed method were tested by replicate analyses of a number of international geochemical reference samples of established trace element contents. Satisfactory correlation with the "recommended" or "consensus" values was found and recoveries were in most cases 95-100%. New values for Ga, In, Nb and Tl in several international geochemical reference materials are first reported in this paper.

  7. 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.

  8. 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.

  9. Anisotropy of ionic conduction in single-crystal Li x La(1- x )/3NbO3 solid electrolyte grown by directional solidification

    NASA Astrophysics Data System (ADS)

    Fujiwara, Yasuyuki; Taishi, Toshinori; Hoshikawa, Keigo; Kohama, Keiichi; Iba, Hideki

    2016-09-01

    The anisotropy of ionic conduction in a solid electrolyte (Li x La(1- x )/3NbO3) was experimentally confirmed for the first time. Ionic conduction measurements were carried out on the (100), (010), (001), (110), (111), and (112) planes of single-crystal ingots of Li x La(1- x )/3NbO3 grown by directional solidification. We found that the ionic conductivity in Li x La(1- x )/3NbO3 with x = 0.08 was 3.6 × 10-4 S cm-1 in the [100] and [010] directions, approximately 10 times higher than that in the [001] direction. Such anisotropy of the ionic conduction is discussed with respect to the characteristic layered structure of Li x La(1- x )/3NbO3.

  10. Oxidation Behavior of a Refractory NbCrMo0.5Ta0.5TiZr Alloy (Preprint)

    DTIC Science & Technology

    2012-03-01

    contact with gaseous oxygen, and diffusion through the oxide layer becomes the rate-controlling process for the oxidation reaction. In this case, the...public release ; distribution unlimited 12 close to n = 0.5 indicating diffusion controlling formation of a protective oxide layer. Indeed, naked eye... diffusivity in the Nb matrix and protective Approved for public release ; distribution unlimited 14 coatings are absolutely necessary for these alloys

  11. Disilicide solid solutions, phase diagram, and resistivities. II. TaSi/sub 2/-WSi/sub 2/

    SciTech Connect

    Gas, P.; Tardy, J.; LeGoues, F.K.; d'Heurle, F.M.

    1987-03-15

    The preparation of TaSi/sub 2/-WSi/sub 2/ alloys from the reaction of Si with Ta-W films allows one to explore the constitution diagram of the TaSi/sub 2/-WSi/sub 2/ pseudobinary system. The structure of the alloys has been investigated by means of Rutherford backscattering, x-ray diffraction, and transmission electron microscopy. The ''equilibrium'' phase diagrams for the system TaSi/sub 2/-WSi/sub 2/ and for TiSi/sub 2/-WSi/sub 2/ are compared in light of simple ideas of alloy theory based on the consideration of the electron to atom ratios. The resistivity of the alloys is analyzed in terms of what has been established about the transport properties of the disilicides and of possible contributions of structural defects, mostly stacking faults, to scattering processes.

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

    SciTech Connect

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

    2014-05-01

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

  13. The exchange interactions and the state of manganese atoms in the solid solutions in Bi{sub 3}NbO{sub 7} of cubic and tetragonal modifications

    SciTech Connect

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

    2016-01-15

    The comparative analysis of magnetic behavior of manganese-containing solid solutions Bi{sub 3}Nb{sub 1−x}Mn{sub x}O{sub 7−δ} (x=0.01−0.10) of cubic and tetragonal modifications was performed. Based on the results of magnetic susceptibility studies paramagnetic manganese atoms in solid solutions of cubic and tetragonal modifications were found to be in the form of Mn(III), Mn(IV) monomers and exchange-coupled dimers of Mn(III)–O–Mn(III), Mn(IV)–O–Mn(IV), Mn(III)–O–Mn(IV). The exchange parameters and the distribution of monomers and dimers in solid solutions as a function of the content of paramagnetic atoms were calculated. - Graphical abstract: Structural transition of cubic to tetragonal Bi{sub 3}NbO{sub 7−δ}.

  14. Raman scattering and far infrared reflectivity of Ba{sub 5}Ta{sub 4}O{sub 15} and Ba{sub 5}Nb{sub 4}O{sub 15{minus}x} (0.0{le}x{le}0.56)

    SciTech Connect

    Massa, N.E.; Pagola, S.; Carbonio, R.E.; Alonso, J.A.; Rasines, I.; Polla, G.; Leyva, G.

    1996-12-31

    Quite often the literature cites superconductors with high critical temperature as having an anharmonic lattice close to a structural phase transition. It is of interest then to find materials, with distorted perovskite structure, that reveal bare phonon behavior expected for such environment. Here the authors discuss layered Ba{sub 5}Nb{sub 4}O{sub 15} and Ba{sub 5}Ta{sub 4}O{sub 15{minus}x} (0.0{le}x{le}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)O{sub 6} sublattice. As consequence, one expect strong anharmonicities that translate into several subtle anomalous shapes and wide phonon band profiles in the low temperature Raman and infrared spectra. They will see that while a centrosymmetric D{sub 3d}{sup 3}-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 Ba{sub 5}Nb{sub 4}O{sub 15}. Weaker structure on the band lower frequency side suggest 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 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 Ba{sub 5}Nb{sub 4}O{sub 15}, are understood as local modes due to unrelaxed portions of the lattice that may be related to changes the phonon damping in infrared reflectivity spectra. It is also noteworthy to point that the replacement Nb by Ta induces a hardening of most phonons. This is reflected in an increase of frequencies in spite of a heavier Ta ion.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  16. Nb(5+)-Doped SrCoO3-δ Perovskites as Potential Cathodes for Solid-Oxide Fuel Cells.

    PubMed

    Cascos, Vanessa; Alonso, José Antonio; Fernández-Díaz, María Teresa

    2016-07-15

    SrCoO3-δ outperforms as cathode material in solid-oxide fuel cells (SOFC) when the three-dimensional (3C-type) perovskite structure is stabilized by the inclusion of highly-charged transition-metal ions at the octahedral positions. In a previous work we studied the Nb incorporation at the Co positions in the SrCo1-xNbxO3-δ system, in which the stabilization of a tetragonal P4/mmm perovskite superstructure was described for the x = 0.05 composition. In the present study we extend this investigation to the x = 0.10-0.15 range, also observing the formation of the tetragonal P4/mmm structure instead of the unwanted hexagonal phase corresponding to the 2H polytype. We also investigated the effect of Nb(5+) doping on the thermal, electrical, and electrochemical properties of SrCo1-xNbxO3-δ (x = 0.1 and 0.15) perovskite oxides performing as cathodes in SOFC. In comparison with the undoped hexagonal SrCoO3-δ phase, the resulting compounds present high thermal stability and an increase of the electrical conductivity. The single-cell tests for these compositions (x = 0.10 and 0.15) with La0.8Sr0.2Ga0.83Mg0.17O3-δ (LSGM) as electrolyte and SrMo0.8Fe0.2CoO3-δ as anode gave maximum power densities of 693 and 550 mW∙cm(-2) at 850 °C respectively, using pure H₂ as fuel and air as oxidant.

  17. Co-doped Sr 2FeNbO 6 as cathode materials for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Xia, Tian; Lin, Nan; Zhao, Hui; Huo, Lihua; Wang, Jingping; Grenier, Jean-Claude

    Sr 2Fe 1- xCo xNbO 6 (0.1 ≤ x ≤ 0.9) (SFCN) oxides with perovskite structure have been developed as the cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). These materials are synthesized via solid-state reaction and characterized by XRD, SEM, electrical conductivity, AC impedance spectroscopy and DC polarization measurements. The reactivity tests show that the Sr 2Fe 1- xCo xNbO 6 electrodes are chemically compatible with the Zr 0.85Y 0.15O 1.925 (YSZ) and Ce 1.9Gd 0.1O 1.95 (CGO) electrolytes at 1200 °C, and the electrode forms a good contact with the electrolyte after sintering at 1200 °C for 12 h. The total electrical conductivity that has a considerable effect on the electrode properties is determined in a temperature range from 200 °C to 800 °C. The highest conductivity of 5.7 S cm -1 is found for Sr 2Fe 0.1Co 0.9NbO 6 at 800 °C in air. The electrochemical performances of these cathode materials are studied using impedance spectroscopy at various temperatures and oxygen partial pressures. Two different kinds of reaction rate-limiting steps exist on the Sr 2Fe 0.1Co 0.9NbO 6 electrode, depending on the temperature. The Sr 2Fe 0.1Co 0.9NbO 6 electrode on CGO electrolyte exhibits a polarization resistance of 0.74 Ω cm 2 at 750 °C in air, which indicates that the Sr 2Fe 0.1Co 0.9NbO 6 electrode is a promising cathode material for IT-SOFCs.

  18. 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.

  19. Structural instabilities and sequence of phase transitions in SrBi2Nb2O9 and SrBi2Ta2O9 from first principles and Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Petralanda, Urko; Etxebarria, I.

    2015-05-01

    Despite their structural similarities, SrBi2Ta2O9 (SBT) and SrBi2Nb2O9 (SBN) undergo a different sequence of phase transitions. The phase diagram of SBT as a function of the temperature includes an intermediate phase between the high-temperature phase and the ferroelectric ground state, while in the niobium compound the intermediate phase is suppressed and a direct transition between the high- and low-temperature structures is observed. We present ab initio calculations that reveal the relevance of a trilinear coupling between three symmetry-adapted modes to stabilize the ground state in both compounds. This coupling is much stronger in SBN than in SBT. Within the framework of the phenomenological Landau theory, it is shown that, by solely increasing the strength of the trilinear coupling, the topology of the phase diagram of SBT can change enough to suppress the intermediate phase. Monte Carlo simulations on an idealized ϕ4 Hamiltonian confirm that the trilinear coupling is the key parameter that determines the sequence of phase transitions, and that for higher dimensionality of the order parameters the stability region of the intermediate phase is narrower.

  20. 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. Copyright © 2014 Elsevier Ltd. All rights reserved.

  1. Investigation into the evolution of the structure of K{sub 1-x}Li{sub x}Ta{sub 1-y}Nb{sub y}O{sub 3} single crystals under variations in temperature

    SciTech Connect

    Borisov, S. A.; Vakhrushev, S. B.; Koroleva, E. Yu.; Naberezhnov, A. A. Syrnikov, P. P.; Simkin, V. G.; Kutnjak, Z.; Egami, T.; Dmowski, W.; Piekarz, P.

    2007-05-15

    The evolution of the structure of K{sub 1-x}Li{sub x}Ta{sub 1-y}Nb{sub y}O{sub 3} single crystals with x = 0.001, y = 0.026, and 1900 ppm Cu (KLTN277) and with x = 0.0014 and y = 0.024 (KLTN123), which exhibit an extremely high permittivity (up to 4 x 10{sup 5} in the quasi-static regime for the KLTN277 crystal), is investigated in the range from room temperature to 20 K. It is demonstrated that, upon cooling to the lowest temperatures, both crystals retain their cubic structure, but the lattice parameters pass through a minimum at the temperature of the observed anomalies of the dielectric response ({approx}50 K). In the neutron diffraction pattern of the KLTN123 sample, satellites appear in the vicinity of the (hhh) reflections at temperatures below {approx}50 K. These satellites can be associated with the nucleation of the rhombohedral phase.

  2. Combined effects of Li content and sintering temperature on polymorphic phase boundary and electrical properties of Li/Ta co-doped (Na, K)NbO3 lead-free piezoceramics

    NASA Astrophysics Data System (ADS)

    Shen, Zong-Yang; Wang, Ke; Li, Jing-Feng

    2009-12-01

    Crystallographic structure, phase transition and electrical properties of lead-free (Na0.535K0.485)1- x Li x (Nb0.942Ta0.058)O3 ( x=0.042-0.098) (NKL x NT) piezoelectric ceramics were investigated. The experimental results show that both Li content and sintering temperature strongly affect the orthorhombic-tetragonal polymorphic phase boundary (PPB), which results in remarkable differences of the piezoelectric property and its temperature stability in the NKL x NT ceramics. Chemical analysis indicates that sodium volatilizes more seriously than potassium and lithium with increasing sintering temperature. Due to the comprehensively optimized effects of Li content and sintering temperature, an enhanced piezoelectric constant d 33 (276 pC/N) was obtained at room temperature in the ceramics with x=0.074 sintered at 1000°C. In the same composition, a further high d 33 up to 354 pC/N was obtained at 43°C, which is close to its T o-t temperature. Furthermore, better temperature stability can be obtained when x=0.082 sintered at 1000°C, whose piezoelectric constant d 33 (236 pC/N) keeps almost constant from room temperature to 100°C. Such a temperature-independent piezoelectric property is available in the NKL x NT ceramics with high Li content because its T o-t was moved below room temperature.

  3. Solid-State Reaction Mechanism and Deliquescence Phenomenon of K0.5Na0.5Nb0.7Al0.3O3 Ceramic

    NASA Astrophysics Data System (ADS)

    Gao, Lu; Zhou, Wancheng; Luo, Fa; Zhu, Dongmei

    2017-10-01

    Development of (K,Na)NbO3-based ceramics has attracted much attention in recent decades. In this work, K0.5Na0.5Nb0.7Al0.3O3 ceramic was prepared using conventional solid-state processing. A deliquescence phenomenon was observed when the specimen was exposed to moist atmosphere. The reaction mechanism and cause of deliquescence were investigated using x-ray diffraction analysis, scanning electron microscopy, energy-dispersive spectrometry, electron microprobe analysis, inductively coupled plasma mass spectrometry, and thermogravimetric/differential scanning calorimetric analysis. The results revealed interactions mainly amongst the raw materials K2CO3, Na2CO3, and Nb2O5 as well as K2CO3, Na2CO3, and Al2O3, which can influence the sintering behavior of the mixture. (K,Na)NbO3 and (K,Na)AlO2 were present in the sintered K0.5Na0.5Nb0.7Al0.3O3 ceramic, with the latter leading to deliquescence. During the sintering process, Al2O3 reacts with alkali oxides (Na2O and K2O), which are the decomposition products of carbonates, to form (K,Na)AlO2. In addition, Al2O3 is more likely to react with K2O compared with Na2O.

  4. Fabrication of lead-free piezoelectric (Na(0.5)K(0.5))NbO(3) ceramics by a modified solid-state reaction method.

    PubMed

    Fukada, M; Saito, T; Kume, H; Wada, T

    2008-05-01

    Sodium potassium niobate, (Na(0.5)K(0.5))NbO(3), fine powder has been successfully synthesized at the low temperature of 550 degrees C through a modified solid-state reaction method, in which urea [CO(NH(2))(2)] plays an important role. High-density (Na(0.5)K(0.5))NbO(3) ceramics could be obtained by conventional sintering of the synthesized (Na(0.5)K(0.5))NbO(3) fine powder with the addition of 0.03 mol% Co(3)O(4) as a sintering additive. The crystal structure, microstructure, and dielectric and piezoelectric properties were characterized. The (Na(0.5)K(0.5))NbO(3) ceramic showed a comparatively saturated P-E hysteresis loop. The (Na(0.5)K(0.5))NbO(3) ceramic also displayed piezoelectricity with a piezoelectric constant d(33) of 126 pC/N and a planar electromechanical coupling factor k(p) of 33%.

  5. Synthesis of anatase nanoparticles with extremely wide solid solution range and ScTiNbO{sub 6} with alpha-PbO{sub 2} structure

    SciTech Connect

    Hirano, Masanori; Ito, Takaharu

    2009-06-15

    Anatase-type nanoparticles Sc{sub X}Ti{sub 1-2X}Nb{sub X}O{sub 2} with wide solid solution range (X=0-0.35) were hydrothermally formed at 180 deg. C for 5 h. The lattice parameters a{sub 0} and c{sub 0}, and the optical band gap of anatase gradually and linearly increased with the increase of the content of niobium and scandium from X=0 to 0.35. Their photocatalytic activity and adsorptivity by the measurement of the concentration of methylene blue (MB) that remained in the solution in the dark or under UV-light irradiation were evaluated. The anatase phase existed stably up to 900 deg. C for the samples with X=0.25-0.30 and 750 deg. C for that with X=0.35 during heat treatment in air. The phase with alpha-PbO{sub 2} structure and the rutile phases coexisted in the samples with X=0.25-0.30 after heated at temperatures above 900-950 deg. C. The alpha-PbO{sub 2} structure having composition ScTiNbO{sub 6} with possibly some cation order similar to that seen in wolframite existed as almost completely single phase after heat treatment at temperatures 900-1500 deg. C through phase transformation from anatase-type ScTiNbO{sub 6}. - Graphical abstract: Anatase-type Sc{sub X}Ti{sub 1-2X}Nb{sub X}O{sub 2} solid solutions with wide solid solution range (X=0-0.35) were hydrothermally formed as nanoparticles from the precursor solutions of Sc(NO{sub 3}){sub 3}, TiOSO{sub 4}, NbCl{sub 5} at 180 deg. C for 5 h using the hydrolysis of urea. Anatase-type ScTiNbO{sub 6} was synthesized under hydrothermal condition. ScTiNbO{sub 6} having alpha-PbO{sub 2} structure with possibly some cation order similar to that seen in wolframite was formed through phase transformation above 900 deg. C.

  6. Evidence of the chemical stability of the garnet-type solid electrolyte Li5La3Ta2O12 towards lithium by a surface science approach

    NASA Astrophysics Data System (ADS)

    Fingerle, Mathias; Loho, Christoph; Ferber, Thimo; Hahn, Horst; Hausbrand, René

    2017-10-01

    The chemical stability between Li metal and garnet-type solid electrolytes is currently under debate, mainly catalyzed by theoretical studies. Here, we investigate the stability of Li5La3Ta2O12 (LLTaO) towards lithium experimentally. Using a surface science approach, lithium is stepwise evaporated on an LLTaO thin film grown by CO2-laser assisted chemical vapor deposition. By annealing of the LLTaO thin film, the Li2CO3 surface layer can be removed, leaving only small traces of Li2CO3, Li2O2 and Li2O behind. The interface formation of LLTaO towards lithium is then monitored by means of X-ray and ultraviolet photoelectron spectroscopy. Neither reaction products related to decomposition nor structural changes in the matrix of the Ta-based garnet-type solid-electrolyte can be detected, indicating that LLTaO exhibits chemical stability under equilibrium conditions. Furthermore, a model for the energy level alignment at the LLTaO/Li interface is discussed.

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

    SciTech Connect

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

    2014-11-15

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

  8. Enhancing the high rate capability and cycling stability of LiMn₂O₄ by coating of solid-state electrolyte LiNbO₃.

    PubMed

    Zhang, Zhi-Jia; Chou, Shu-Lei; Gu, Qin-Fen; Liu, Hua-Kun; Li, Hui-Jun; Ozawa, Kiyoshi; Wang, Jia-Zhao

    2014-12-24

    To study the influence of solid-state electrolyte coating layers on the performance of cathode materials for lithium-ion batteries in combination with organic liquid electrolyte, LiNbO3-coated Li1.08Mn1.92O4 cathode materials were synthesized by using a facile solid-state reaction method. The 0.06LiNbO3-0.97Li1.08Mn1.92O4 cathode exhibited an initial discharge capacity of 125 mAh g(-1), retaining a capacity of 119 mAh g(-1) at 25 °C, while at 55 °C, it exhibited an initial discharge capacity of 130 mAh g(-1), retaining a capacity of 111 mAh g(-1), both at a current density of 0.5 C (where 1 C is 148 mAh g(-1)). Very good rate capability was demonstrated, with the 0.06LiNbO3-0.97Li1.08Mn1.92O4 cathode showing more than 85% capacity at the rate of 50 C compared with the capacity at 0.5 C. The 0.06LiNbO3-0.97Li1.08Mn1.92O4 cathode showed a high lithium diffusion coefficient (1.6 × 10(-10) cm(2) s(-1) at 55 °C), and low apparent activation energy (36.9 kJ mol(-1)). The solid-state electrolyte coating layer is effective for preventing Mn dissolution and maintaining the high ionic conductivity between the electrode and the organic liquid electrolyte, which may improve the design and construction of next-generation large-scale lithium-ion batteries with high power and safety.

  9. Structural state of relaxor ferroelectrics PbSc0.5Ta0.5O3 and PbSc0.5Nb0.5O3 at high pressures up to 30 GPa

    NASA Astrophysics Data System (ADS)

    Maier, B. J.; Waeselmann, N.; Mihailova, B.; Angel, R. J.; Ederer, C.; Paulmann, C.; Gospodinov, M.; Friedrich, A.; Bismayer, U.

    2011-11-01

    The pressure-induced structural changes in perovskite-type (ABO3) Pb-based relaxor ferroelectrics are studied on the basis of in situ single-crystal synchrotron x-ray diffraction and Raman scattering experiments on PbSc0.5Ta0.5O3 and PbSc0.5Nb0.5O3 conducted under hydrostatic conditions up to 30 GPa. Complementary density functional theory calculations have been performed to compare the stability of various atomic configurations for both compounds at high pressures. By combining the experimental and theoretical results, the following sequence of structural transformations is proposed. At a characteristic pressure p1 the mesoscopic polar order is violated and a local antipolar order of Pb atoms as well as quasidynamical long-range order of antiphase octahedral tilts is developed. These structural changes facilitate the occurrence of a continuous phase transition at pc1>p1 from cubic to a nonpolar rhombohedral structure comprising antiphase octahedral tilts of equal magnitude (a-a-a-). At a characteristic pressure p2>pc1 the octahedral tilts around the cubic [100], [010], and [001] directions become different from each other on the mesoscopic scale. The latter precedes a second phase transition at pc2, which involves long-range order of Pb antipolar displacements along cubic [uv0] directions and a compatible mixed tilt system (a+b-b-) or long-range ordered antiphase tilts with unequal magnitudes (a0b-b-) without Pb displacement ordering. The phase-transition pattern at pc2 depends on the fine-scale degree of chemical B-site order in the structure.

  10. 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.

  11. The incommensurately modulated(1 - x)Ta 2O 5· xWO 3, 0 ≤ x ≤ 0.267 solid solution

    NASA Astrophysics Data System (ADS)

    Schmid, Siegbert; Withers, Ray L.; Thompson, John G.

    1992-08-01

    The phase(1 - x)Ta 2O 5 · WO 3, 0 ≤ x ≤ 0.267 has been studied by X-ray powder diffraction and transmission electron microscopy. It was previously described as an infinite series of anion-deficient, α-UO 3-type "line phases," with compositions resulting from intergrowths of different blocks made up by small numbers of α-UO 3-type cells. More correctly(1 - x)Ta 2O 5· xWO 3, 0 ≤ x ≤ 0.267 is described as an incommensurately modulated structure with a linearly composition-dependent primary modulation wave-vector qprim. = qb*. The underlying orthorhombically distorted α-UO 3-type parent structure has space group symmetry Cmmm ( a ≈ 6.20-6.14, b ≈ 3.66, c ≈ 3.89-3.85Å). Characteristic extinction conditions imply a superspace group symmetry of P : Cmmmm : s, -1,1. The four previously reported crystal structures in the solid solution field are examined by means of apparent valence calculations. Crystal chemical reasons are proposed for the width of the composition range,0 ≤ x ≤ 0.267, observed for the title phase.

  12. Laser damage comparisons of broad-bandwidth, high-reflection optical coatings containing TiO2, Nb2O5, or Ta2O5 high-index layers

    SciTech Connect

    Field, Ella Suzanne; Bellum, John Curtis; Kletecka, Damon E.

    2016-09-21

    Broad bandwidth coatings allow angle of incidence flexibility and accommodate spectral shifts due to aging and water absorption. Higher refractive index materials in optical coatings, such as TiO2, Nb2O5, and Ta2O5, can be used to achieve broader bandwidths compared to coatings that contain HfO2 high index layers. We have identified the deposition settings that lead to the highest index, lowest absorption layers of TiO2, Nb2O5, and Ta2O5, via e-beam evaporation using ion-assisted deposition. We paired these high index materials with SiO2 as the low index material to create broad bandwidth high reflection coatings centered at 1054 nm for 45 deg angle of incidence and P polarization. Furthermore, high reflection bandwidths as large as 231 nm were realized. Laser damage tests of these coatings using the ISO 11254 and NIF-MEL protocols are presented, which revealed that the Ta2O5/SiO2 coating exhibits the highest resistance to laser damage, at the expense of lower bandwidth compared to the TiO2/SiO2 and Nb2O5/SiO2 coatings.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

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

    SciTech Connect

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

    2007-02-15

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

  15. Structural control on the emplacement of contemporaneous Sn-Ta-Nb mineralized LCT pegmatites and Sn bearing quartz veins: Insights from the Musha and Ntunga deposits of the Karagwe-Ankole Belt, Rwanda

    NASA Astrophysics Data System (ADS)

    Hulsbosch, Niels; Van Daele, Johanna; Reinders, Nathan; Dewaele, Stijn; Jacques, Dominique; Muchez, Philippe

    2017-10-01

    The Nb-Ta-Sn pegmatites and Sn quartz veins of the Rwamagana-Musha-Ntunga area in eastern Rwanda are part of the Mesoproterozoic Karagwe-Ankole Belt. These commodities are on a regional scale spatiotemporally associated to the early Neoproterozoic fertile G4-granite generation. Although a transition from the lithium-cesium-tantalum pegmatites to cassiterite-microcline-quartz veins has been observed in the Rwamagana-Musha-Ntunga area, the structural control and the paragenetic relationship between the mineralized pegmatites and the Sn bearing quartz veins is largely unknown. Consequently, this study investigates the occurrence of pegmatites and quartz veins and the structural and lithological controls on their emplacement. The metasediments in the area are affected by a regional compressional regime with a shortening direction oriented N70E, which resulted in a N20W-oriented fold sequence. The Lake Muhazi granite is present in center of the Karehe anticline. The structural orientations of pegmatites and quartz veins show that two important factors control their emplacement. The first control is the reactivation of pre-existing discontinuities such as the bedding, bedding-parallel joints or strike-slip fault planes. In view of the regional structural grain in the Rwamagana-Musha-Ntunga area, this corresponds with abundant N20W-oriented pegmatites and quartz veins. The reactivation is strongly related to the lithology of the host rocks. The Musha Formation, which mainly consists of decimeter- to meter-scale lithological alternations of metapelite, metasiltstone and metasandstone, represents the most suitable environment for bedding reactivation. This is reflected in the predominance of bedding-parallel pegmatites and quartz veins hosted by the Musha Formation. Strike-parallel joints were mainly observed in the competent lithologies. The second controlling factor is related to the regional post-compressional stress regime. New joints initiated upon emplacement of the

  16. Flexible relaxor materials: Ba(2)Pr(x)Nd(1-x)FeNb(4)O(15) tetragonal tungsten bronze solid solution.

    PubMed

    Castel, Elias; Josse, Michaël; Michau, Dominique; Maglione, Mario

    2009-11-11

    Relaxors are very interesting materials but most of the time they are restricted to perovskite materials and thus their flexibility is limited. We have previously shown that tetragonal tungsten bronze (TTB) niobate Ba(2)PrFeNb(4)O(15) was a relaxor below 170 K and that Ba(2)NdFeNb(4)O(15) displays a ferroelectric behavior with a T(C) = 323 K. On scanning the whole solid solution Ba(2)Pr(x)Nd(1-x)FeNb(4)O(15) (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1), we demonstrate here a continuous crossover between these end member behaviors with a coexistence of ferroelectricity and relaxor in the intermediate range. This tunability is ascribed to the peculiar structure of the TTB networks which is more open than the classical perovskites. This allows for the coexistence of long range and short range orders and thus opens up the range of relaxor materials.

  17. 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…

  18. Novel SrCo 1- yNb yO 3- δ cathodes for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Wang, Fang; Zhou, Qingjun; He, Tianmin; Li, Guodong; Ding, Hong

    Perovskite oxides SrCo 1- yNb yO 3- δ (SCN y, y = 0.00-0.20) are investigated as potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) on La 0.9Sr 0.1Ga 0.8Mg 0.2O 3- δ (LSGM) electrolyte. Compared to the undoped SrCoO 3- δ, the Nb doping significantly improves the thermal stability and enhances the electrical conductivity of the SCN y oxides. The cubic phase of the SCN y oxides with high thermal stability can be totally obtained when the Nb doping content y ≥ 0.10. Among the investigated compositions, the SrCo 0.9Nb 0.1O 3- δ oxide exhibits the highest electrical conductivity of 461-145 S cm -1 over the temperature range of 300-800 °C in air. The SCN y cathode has a good chemical compatibility with the LSGM electrolyte for temperatures up to 1050 °C for 5 h. The area specific resistances of SCN y with y = 0.10, 0.15 and 0.20 cathodes on LSGM electrolyte are 0.083, 0.099 and 0.110 Ω cm 2 at 700 °C, respectively. At y = 0.10, 0.15 and 0.20, the maximum power densities of a single-cell with SCN y cathodes on 300-μm thick LSGM electrolyte achieve 675, 642 and 625 mW cm -2 at 800 °C, respectively. These results indicate that SCN y perovskite oxides with cubic phase are potential cathode materials for application in IT-SOFCs.

  19. Breakdown of the Hume-Rothery Rules in Sub-Nanometer-Sized Ta-Containing Bimetallic Small Clusters

    NASA Astrophysics Data System (ADS)

    Miyajima, Ken; Fukushima, Naoya; Himeno, Hidenori; Yamada, Akira; Mafuné, Fumitaka

    2009-11-01

    The Hume-Rothery rules are empirical rules to predict the solid solubility of metals. We examined whether the rules hold for sub-nanometer-sized small particles. We prepared bimetallic cluster ions in the gas phase by a double laser ablation technique. Taking advantage of the magic compositions of the bimetallic cluster ions relating to the distinguished stabilities, the coalescence or the segregation of Ta and another element in the sub-nanometer-sized clusters was discussed. It was found that W, Nb, and Mo readily coalesce with Ta, while Ag, Al, Au, Co, Cu, Fe, Hf, Ni, Pt, Ti, and V are segregated from Ta. On the basis of these results, we concluded that the Hume-Rothery rules do not hold for sub-nanometer-sized particles.

  20. Computer-aided control of electrolysis of solid Nb2O5 in molten CaCl2.

    PubMed

    Wu, Tian; Xiao, Wei; Jin, Xianbo; Liu, Chao; Wang, Dihua; Chen, George Z

    2008-04-07

    Low energy production of Nb powders via computer-aided control (CAC) of two-electrode electrolysis of porous Nb2O5 pellets (ca. 1.0 g) has been successfully demonstrated in molten CaCl2 at 1123 K. It was observed that potentiostatic electrolysis of the oxide in a three-electrode cell led to a cell voltage, i.e. the potential difference between the working (cathode) and counter (anode) electrodes, that decreased to a low and stable value within 1-2 h of the potential application until the end of the electrolysis (up to 12 h in this work). The cell voltage varied closely according to the current change. The stabilised cell voltage was below 2.5 V when the cathode potential was more positive than that for the reduction of Ca2+, leading to much lower energy consumption than that of constant voltage (>3.0 V) two-electrode electrolysis, as previously reported. Using a computer to program the variation of the cell voltage of two-electrode electrolysis according to that observed in the potentiostatic three-electrode electrolysis (0.05 V vs. Ca/Ca2+), a Nb powder with ca. 3900 ppm oxygen was produced in 12 h, with the energy consumption being 37.4% less than that of constant voltage two-electrode electrolysis at 3.0 V. Transmission electron microscopy revealed thin oxide layers (4-6 nm) on individual nodular particles (1-5 microm) of the obtained Nb powder. The oxide layer was likely formed in post-electrolysis processing operations, including washing in water, and contributed largely to the oxygen content in the obtained Nb powder.

  1. Ab initio calculations of SrTiO3, BaTiO3, PbTiO3, CaTiO3, SrZrO3, PbZrO3 and BaZrO3 (001), (011) and (111) surfaces as well as F centers, polarons, KTN solid solutions and Nb impurities therein

    NASA Astrophysics Data System (ADS)

    Eglitis, R. I.

    2014-03-01

    In this paper, the review of recent results of calculations of surface relaxations, energetics, and bonding properties for ABO3 perovskite (001), (011) and (111) surfaces using mostly a hybrid description of exchange and correlation is presented. Both AO and BO2-terminations of the nonpolar (001) surface and A, BO, and O terminations of the polar (011) surface, as well as B and AO3-terminations of the polar (111) surface were considered. On the AO-terminated (001) surface, all upper-layer A atoms relax inwards, while all second layer atoms relax outwards. For the BO2-terminated (001) surface, in most cases, the largest relaxations are on the second-layer metal atoms. For almost all ABO3 perovskites, the surface rumpling is much larger for the AO-terminated than for the BO2-terminated (001) surface, but their surface energies are always quite similar. In contrast, different terminations of the (011) ABO3 surface lead to very different surface energies for the O-terminated, A-terminated, and BO-terminated (011) surface, respectively. A considerable increase in the Ti-O or Zr-O, respectively, chemical bond covalency near the (011) surface as compared both to the bulk and to the (001) surface in ABO3 perovskites were predicted. According to the results of ab initio calculations for Nb doped SrTiO3, Nb is a shallow donor; six nearest O ions are slightly displaced outwards from the Nb ion. The F center in ABO3 perovskites resembles electron defects in the partially-covalent SiO2 crystal rather than usual F centers in ionic crystals like MgO and alkali halides. The results of calculations for several perovskite KNbxTa1-xO3 (KTN) solid solutions, as well as hole and electron polarons in ABO3 perovskites are analyzed.

  2. Multi-component solid solution alloys having high mixing entropy

    DOEpatents

    Bei, Hongbin

    2015-10-06

    A multi-component high-entropy alloy includes a composition selected from the following group: VNbTaTiMoWRe, VNbTaTiMoW, VNbTaTiMoRe, VNbTaTiWRe, VNbTaMoWRe, VNbTiMoWRe, VTaTiMoWRe, NbTaTiMoWRe, VNbTaTiMo, VNbTaTiW, VNbTaMoW, VNbTiMoW, VTaTiMoW, NbTaTiMoW, VNbTaTiRe, VNbTaMoRe, VNbTiMoRe, VTaTiMoRe, NbTaTiMoRe, VNbTaWRe, VNbTiWRe, VTaTiWRe, NbTaTiWRe, VNbMoWRe, VTaMoWRe, NbTaMoWRe, VTiMoWRe, NbTiMoWRe, TaTiMoWRe, wherein relative amounts of each element vary by no more than .+-.15 atomic %.

  3. Evaluation of sample recovery of malodorous livestock gases from air sampling bags, solid-phase microextraction fibers, Tenax TA sorbent tubes, and sampling canisters.

    PubMed

    Koziel, Jacek A; Spinhirne, Jarett P; Lloyd, Jenny D; Parker, David B; Wright, Donald W; Kuhrt, Fred W

    2005-08-01

    Odorous gases associated with livestock operations are complex mixtures of hundreds if not thousands of compounds. Research is needed to know how best to sample and analyze these compounds. The main objective of this research was to compare recoveries of a standard gas mixture of 11 odorous compounds from the Carboxen/PDMS 75-microm solid-phase microextraction fibers, polyvinyl fluoride (PVF; Tedlar), fluorinated ethylene propylene copolymer (FEP; Teflon), foil, and polyethylene terephthalate (PET; Melinex) air sampling bags, sorbent 2,b-diphenylene-oxide polymer resin (Tenax TA) tubes, and standard 6-L Stabilizer sampling canisters after sample storage for 0.5, 24, and 120 (for sorbent tubes only) hrs at room temperature. The standard gas mixture consisted of 7 volatile fatty acids (VFAs) from acetic to hexanoic, and 4 semivolatile organic compounds including p-cresol, indole, 4-ethylphenol, and 2'-aminoacetophenone with concentrations ranging from 5.1 ppb for indole to 1270 ppb for acetic acid. On average, SPME had the highest mean recovery for all 11 gases of 106.2%, and 98.3% for 0.5- and 24-hr sample storage time, respectively. This was followed by the Tenax TA sorbent tubes (94.8% and 88.3%) for 24 and 120 hr, respectively; PET bags (71.7% and 47.2%), FEP bags (75.4% and 39.4%), commercial Tedlar bags (67.6% and 22.7%), in-house-made Tedlar bags (47.3% and 37.4%), foil bags (16.4% and 4.3%), and canisters (4.2% and 0.5%), for 0.5 and 24 hr, respectively. VFAs had higher recoveries than semivolatile organic compounds for all of the bags and canisters. New FEP bags and new foil bags had the lowest and the highest amounts of chemical impurities, respectively. New commercial Tedlar bags had measurable concentrations of N,N-dimethyl acetamide and phenol. Foil bags had measurable concentrations of acetic, propionic, butyric, valeric, and hexanoic acids.

  4. The contribution of amphibole from deep arc crust to the silicate Earth's Nb budget

    NASA Astrophysics Data System (ADS)

    Tiepolo, Massimo; Vannucci, Riccardo

    2014-11-01

    The continental crust (CC) and the depleted mantle (DM) are generally assumed to be complementary reservoirs within the Earth. However, the mixture between CC and upper mantle does not generate the Nb/Ta and Nb/La ratios of chondrites. A reservoir with superchondritic ratios for Nb/Ta and Nb/La is thus required in the Earth's system. The occurrence of a hidden amphibole reservoir in the lower arc crust has been recently proposed. This, coupled with the capability of calcic amphibole to give rise to a superchondritic Nb/Ta and Nb/La reservoir, led us to determine to what extent amphibole-rich ultramafic rocks can account for the Nb (and Nb/Ta, Nb/La as well) imbalance on Earth. We have considered lower crust mafic and ultramafic amphibole-rich intrusive rocks from collisional settings worldwide. Because CC is considered to have primarily formed in collisional setting these rocks are important for its genetic model. We modeled Nb, Ta and La contents of the hidden Nb reservoir by mass balance calculations between continental crust, depleted mantle and primitive mantle. Modeling shows that amphibole-rich mafic lower crust can solve the so-called Nb paradox if large volumes of materials are supposed to be returned into the mantle during the Earth's history. A possible mechanism is recycling, particularly in Precambrian times, of eclogites that underwent pre-eclogitic melting in the amphibolite facies field and then recrystallized under eclogite-facies conditions.

  5. Direct formation of new, phase-stable, and photoactive anatase-type Ti{sub 1-2X}Nb{sub X}Sc{sub X}O{sub 2} solid solution nanoparticles by hydrothermal method

    SciTech Connect

    Hirano, Masanori Ito, Takaharu

    2008-08-04

    A new anatase phase of photoactive Ti{sub 1-2X}Nb{sub X}Sc{sub X}O{sub 2} (X = 0-0.2) solid solutions was directly formed as nanoparticles from precursor solutions of TiOSO{sub 4}, NbCl{sub 5}, and Sc(NO{sub 3}){sub 3} under mild hydrothermal conditions at 180 deg. C for 5 h using the hydrolysis of urea. With the increase of the content of niobium and scandium from X = 0 to 0.2, the lattice parameters a{sub 0} and c{sub 0}, the crystallite size, and the optical band gap of anatase gradually increased. Their photocatalytic activity and adsorptivity were evaluated separately by the measurement of the concentration of methylene blue (MB) remained in the solution in the dark or under UV-light irradiation. The anatase-type Ti{sub 1-2X}Nb{sub X}Sc{sub X}O{sub 2} (X = 0.05) showed approximately two times and three times as high photocatalytic activity as those of the hydrothermal anatase-type pure TiO{sub 2} and commercially available reference pure TiO{sub 2} (ST-01), respectively. The anatase phase of Ti{sub 1-2X}Nb{sub X}Sc{sub X}O{sub 2} (X = 0-0.2) existed stably up to 900 deg. C during heat treatment in air. New rutile-type Ti{sub 1-2X}Nb{sub X}Sc{sub X}O{sub 2} solid solutions are formed through the phase transformation. The starting temperature of anatase-to-rutile phase transformation for Ti{sub 1-2X}Nb{sub X}Sc{sub X}O{sub 2} (X = 0-0.2) solid solutions was delayed but its completing temperature was accelerated.

  6. 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.

  7. Lithium ion diffusion measurements on a garnet-type solid conductor Li6.6La3Zr1.6Ta0.4O12 by using a pulsed-gradient spin-echo NMR method.

    PubMed

    Hayamizu, Kikuko; Matsuda, Yasuaki; Matsui, Masaki; Imanishi, Nobuyuki

    2015-09-01

    The garnet-type solid conductor Li7-xLa3Zr2-xTaxO12 is known to have high ionic conductivity. We synthesized a series of compositions of this conductor and found that cubic Li6.6La3Zr1.6Ta0.4O12 (LLZO-Ta) has a high ionic conductivity of 3.7×10(-4)Scm(-1) at room temperature. The (7)Li NMR spectrum of LLZO-Ta was composed of narrow and broad components, and the linewidth of the narrow component varied from 0.69kHz (300K) to 0.32kHz (400K). We carried out lithium ion diffusion measurements using pulsed-field spin-echo (PGSE) NMR spectroscopy and found that echo signals were observed at T≥313K with reasonable sensitivity. The lithium diffusion behavior was measured by varying the observation time and pulsed-field gradient (PFG) strength between 313 and 384K. We found that lithium diffusion depended significantly on the observation time and strength of the PFG, which is quite different from lithium ion diffusion in liquids. It was shown that lithium ion migration in the solid conductor was distributed widely in both time and space. Copyright © 2015 Elsevier Inc. All rights reserved.

  8. Solid-state synthesis in the system Na{sub 0.8}Nb{sub y}W{sub 1-y}O{sub 3} with 0{<=}y{<=}0.4: A new phase, Na{sub 0.5}NbO{sub 2.75}, with perovskite-type structure

    SciTech Connect

    Debnath, Tapas Ruescher, Claus H.; Gesing, Thorsten M.; Koepke, Juergen; Hussain, Altaf

    2008-04-15

    Series of compounds in the system Na{sub x}Nb{sub y}W{sub 1-y}O{sub 3} were prepared according to the appropriate molar ratio of Na{sub 2}WO{sub 4}, WO{sub 3}, WO{sub 2} and Nb{sub 2}O{sub 5} with x=0.80 and 0.0{<=}y{<=}0.4 at 600 deg. C in evacuated silica glass tubes. These compounds were investigated by X-ray powder diffraction, optical microscopy, microprobe analysis, Raman and optical microspectroscopy. A y-dependent separation into three distinct coloured crystallites with cubic perovskite-type structures is observed: (i) red-orange crystallites with composition Na{sub x}WO{sub 3} with slightly decreasing x (i.e. 0.8-0.72) with increasing nominal y, (ii) bluish solid solution of composition Na{sub x}Nb{sub y}W{sub 1-y}O{sub 3} and (iii) white crystallites of a new phase having defect perovskite-type structure with composition Na{sub 0.5}NbO{sub 2.75}. - Graphical abstract: Optical micrograph of a polished sample of nominal composition Na{sub 0.8}Nb{sub 0.4}W{sub 0.6}O{sub 3} showing a mixture of three different coloured crystals: red, light blue and white. The scale bar is 30 {mu}m.

  9. Role of site-disorder in energy materials: case of LixNb2O5 pseudocapacitor and β-Li3PS4 solid electrolyte

    NASA Astrophysics Data System (ADS)

    Ganesh, P.; Lubimtsev, Andrew A.; Dathar, Gopi K. P.; Anchell, Jonathan; Kent, Paul R. C.; Rondinone, Adam J.; Sumpter, Bobby G.

    2015-03-01

    In this study, we will present computational studies to elucidate the importance of site-disorder in energy materials. We will specifically focus on two recently discovered materials: a Li-ion intercalation pseudocapacitor LixNb2O5 (Nature Materials, 12 518 (2013)) and a Li-ion solid-electrolyte.(JACS, 135 975 (2013)). A combination of theoretical methods, such as density functional theory (DFT) based cluster-expansion, basin hopping, ab initio molecular dynamics, and nudged-elastic-bands calculations were employed to understand the origin of intercalation pseudocapacitance in the niobate-system.(J. Materials Chem. 114951 (2013)). It was found that having multiple sites with similar energies for ion-adsorption, lead to a site-occupancy disorder that eventually lead to a capacitative slope in the voltage profile over the entire range of ion intercalation, as seen in experiments. A similar site-occupancy induced sublattice melting in the β-Li3PS4 solid-electrolyte, which when ``frozen'' to RT, lead to high Li-ion conductivity.(G.K.P.Dathar et al, submitted (2014)). Further, we will elucidate how to take advantage of this control over site-disorder to better engineer improved energy materials for batteries and fuel-cells. (PG, GKPD, PRCK, AJR, BGS) were supported by the CNMS at ORNL, (AAL and JA) were supported by the DOE-HERE program. Computations were performed at NERSC.

  10. Structural characterization and electrical conductivity of the Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} solid series

    SciTech Connect

    Cao, Yong; Duan, Nanqi; Yan, Dong

    2016-05-15

    Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} (x=0, 0.1, 0.2, 0.4, 0.6, 0.8, 0.99) is prepared by using a solid reaction route, and single phase is achieved. Structural and phase transformation of Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} have been characterized by high temperature X-ray diffraction. The lattice parameters a, b, c decrease and γ increases with increasing x, at both room and high temperature. The phase transformation temperature increases linearly with increasing x for Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ}. The electrical conductivity of Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} is measured in wet air. A clear relationship between the structural, phase transformation and electrical conductivity of Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} is built, which will provide a guideline to tailor the electrical conductivity. - Graphical abstract: Structural and phase transformation of Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} have been characterized by high temperature X-ray diffraction, as well as the conductivity of Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} in wet air. A clear relationship between the structural, phase transformation and electrical conductivity of Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} is built. - Highlights: • Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} with various Sm contents was prepared. • Structure, phase transformation and electrical conductivity of Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} were characterized. • A relationship between the structure, phase transformation and electrical conductivity was well established.

  11. Conditions for Ta(IV)-Ta(IV) bonding in trirutile Li(x)MTa2O6.

    PubMed

    Gupta, Asha; Singh, Preetam; Celio, Hugo; Mullins, C Buddie; Goodenough, John B

    2015-02-16

    Stabilization of Ta-Ta bonding in an oxide across a shared octahedral-site edge of a Ta2 dimer is not known. Investigation of Li insertion into the trirutile structure of MTa2O6 with M = Mg, Cr, Fe, Co, and Ni indicates that Ta-Ta bonding across the shared octahedral-site edge of the dimer can be stabilized by a reversible electrochemical reduction of Ta(V) to Ta(IV) for M = Cr, Fe, Co, and Ni but not for M = Mg. Chemical reduction of MTa2O6 by n-butyl lithium only reduced NiTa2O6 to any significant extent. With M = Fe, Co, or Ni, electrochemical formation of the Ta-Ta bonds is accompanied by a partial reduction of the Fe(II), Co(II), or Ni(II) to Fe(0), Co(0), or Ni(0). For M = Cr, two Li per formula unit can be inserted reversibly with no displacement of Cr(0). For M = Mg, no Mg(II) are displaced by Li insertion, but a solid-electrolyte interphase (SEI) layer is formed on the oxide with no evidence of Ta-Ta bonding. Stabilization of Ta-Ta bonding across a shared octahedral-site edge in a dimer appears to require significant hybridization of the Ta(V) 5d(0) and M 4s(0) states.

  12. Charge-discharge characteristics of all-solid-state thin-filmed lithium-ion batteries using amorphous Nb 2O 5 negative electrodes

    NASA Astrophysics Data System (ADS)

    Nakazawa, Hiromi; Sano, Kimihiro; Abe, Takashi; Baba, Mamoru; Kumagai, Naoaki

    All-solid-state thin-filmed lithium-ion rechargeable batteries composed of amorphous Nb 2O 5 negative electrode with the thickness of 50-300 nm and amorphous Li 2Mn 2O 4 positive electrode with a constant thickness of 200 nm, and amorphous Li 3PO 4- xN x electrolyte (100 nm thickness), have been fabricated on glass substrates with a 50 mm × 50 mm size by a sputtering method, and their electrochemical characteristics were investigated. The charge-discharge capacity based on the volume of positive electrode increased with increasing thickness of negative electrode, reaching about 600 mAh cm -3 for the battery with the negative electrode thickness of 200 nm. But the capacity based on the volume of both the positive and negative electrodes was the maximum value of about 310 mAh cm -3 for the battery with the negative electrode thickness of 100 nm. The shape of charge-discharge curve consisted of a two-step for the batteries with the negative electrode thickness more than 200 nm, but that with the thickness of 100 nm was a smooth S-shape curve during 500 cycles.

  13. X-Ray diffraction characteristics of Ti /SUB 1-x/ Nb /SUB x/ C /SUB o. 5/ N /SUB 0. 5/ solid solutions

    SciTech Connect

    Ordan'yan, S.S.; Maskhuliya, L.G.; Panteleev, I.B.; Pavlyuk, E.G.; Persinin, S.A.

    1986-05-01

    A study of the influence of production factors (temperature and length of synthesis, method of addition of the components, repeated refinement and homogenization) on the parameters of the structure of phases of variable composition was made. The solid solutions were synthesized from titanium and niobium carbide and nitride powders, and the carbonitride of the composition Ti /SUB 0.77/ Nb /SUB 0.23/ C /SUB 0.5/ N /SUB 0.5/ , by the carbothermal method. X-ray diffraction was taken by a DRON-3 diffractometer controlled by an SM-1 computer. The lattice parameter, the characteristics of the fine crystal structure and the residual macrostresses were determined. It was concluded that the nature of the original components does not influence the character of the concentration relationship of the microstructural parameters, a change in which occurs only under the influence of synethesis temperature and is accompanied by effects of diffusion perfection of the structure of the phases of variable composition.

  14. Development of Ta-based Superconducting Tunnel Junction X-ray Detectors for Fluorescence XAS

    SciTech Connect

    Friedrich, S; Drury, O; Hall, J; Cantor, R

    2009-09-23

    We are developing superconducting tunnel junction (STJ) soft X-ray detectors for chemical analysis of dilute samples by fluorescence-detected X-ray absorption spectroscopy (XAS). Our 36-pixel Nb-based STJ spectrometer covers a solid angle {Omega}/4{pi} {approx} 10{sup -3}, offers an energy resolution of {approx}10-20 eV FWHM for energies up to {approx}1 keV, and can be operated at total count rates of {approx}10{sup 6} counts/s. For increased quantum efficiency and cleaner response function, we have now started the development of Ta-based STJ detector arrays. Initial devices modeled after our Nb-based STJs have an energy resolution below 10 eV FWHM for X-ray energies below 1 keV, and pulse rise time discrimination can be used to improve their response function for energies up to several keV. We discuss the performance of the Ta-STJs and outline steps towards the next-generation of large STJ detector arrays with higher sensitivity.

  15. Low temperature pulsed laser deposition of garnet Li6.4La3Zr1.4Ta0.6O12 films as all solid-state lithium battery electrolytes

    NASA Astrophysics Data System (ADS)

    Saccoccio, Mattia; Yu, Jing; Lu, Ziheng; Kwok, Stephen C. T.; Wang, Jian; Yeung, Kan Kan; Yuen, Matthew M. F.; Ciucci, Francesco

    2017-10-01

    With its stability against Li and good ionic conductivity, Li7La3Zr2O12 (LLZO) has emerged as a promising electrolyte material for lithium-based solid-state batteries (SSBs). Thin layers of solid electrolyte are needed to enable the practical use of SSBs. We report the first deposition of Li-conductive crystalline Ta-doped LLZO thin films on MgO (100) substrates via pulsed laser deposition. Further, we investigate the impact of laser fluence, deposition temperature (in the 50 °C-700 °C range), and post-deposition annealing on the structural, compositional, and transport properties of the film. We analyze the structure of the deposited films via grazing incident X-ray diffraction, their morphology via scanning electron microscopy, and the composition via depth profiling X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. The Li ionic conductivity is investigated via electrochemical impedance spectroscopy. Contrary to previous reports for LLZO films, the crystalline Ta-doped films presents a pure cubic LLZO structure for deposition temperatures as low as 50 °C, with resulting conductivities not significantly influenced by the temperature deposition. Instead, the laser fluence has a major effect on the growth rate of the thin films.

  16. Structures and crystal chemistry of the double perovskites Ba{sub 2}LnB'O{sub 6} (Ln=lanthanide B'=Nb{sup 5+} and Ta{sup 5+}): Part I. Investigation of Ba{sub 2}LnTaO{sub 6} using synchrotron X-ray and neutron powder diffraction

    SciTech Connect

    Saines, Paul J.; Spencer, Jarrah R.; Kennedy, Brendan J. Avdeev, Maxim

    2007-11-15

    The structure of 14 compounds in the series Ba{sub 2}LnTaO{sub 6} have been examined using synchrotron X-ray diffraction and found to undergo a sequence of phase transitions from I2/m monoclinic to I4/m tetragonal to Fm3-bar m cubic symmetry with decreasing ionic radii of the lanthanides. Ba{sub 2}LaTaO{sub 6} is an exception to this with variable temperature neutron diffraction being used to establish that the full series of phases adopted over the range of 15-500 K is P2{sub 1}/n monoclinic to I2/m monoclinic to R3-bar rhombohedral. The chemical environments of these compounds have also been investigated and the overbonding to the lanthanide cations is due to the unusually large size for the B-site in these perovskites. - Graphical abstract: The evolution of the structure across the series of double perovskites Ba{sub 2}LnTaO{sub 6} is established using a combination of synchrotron X-ray and neutron diffraction. The symmetry increases from monoclinic to tetragonal and then cubic as the size of the lanthanide decreases.

  17. Solid State Physics. Nitrogen Adsorption by Thermoexfoliated Graphite / Slāpekļa Adsorbcija Uz Termoeksfoliētā Grafīta

    NASA Astrophysics Data System (ADS)

    Grehov, V.; Kalnacs, J.; Matzui, L.; Knite, M.; Murashov, A.; Vilken, A.

    2013-02-01

    Adsorption by thermochemically exfoliated graphite (TEG) is studied and compared with that by other carbon structures under the same conditions. In BET determination of the specific surface area (SBET) for the TEG samples it was found that good approximation could be observed in two different pressure ranges. Such ranges of BET approximation are also visible in the isotherms of aquadag and milled graphite. The experimental results are discussed and their interpretation proposed Ar sorbcijas iekārtu Autosorb-1 (Quantochrome Instruments Co, Florida, USA) pētīta termiski eksfoliēta grafīta slāpekļa sorbcijas spēja salīdzinājumā ar citu oglekļa struktūru sorbciju tādos pašos apstākļos. Atrasti divi izotermu rajoni, kas raksturojas ar mazu (SBET1) un palielinātu (SBET2) īpatnējo virsmu.. Šāda veida izotermas raksturīgas slikti adsorbējošiem materiāliem, pie kādiem pieder arī akvadags. Labi adsorbējošās oglekļa struktūrām, tādām kā aktīvā ogle un oglekļa nanocaurules, raksturīgas cita veida izotermas. Apspriesta eksperimentālā rezultāta interpretācija

  18. 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.

  19. Domain structures and dielectric properties resulting from tweed precursors of relaxor ferroelectric solid-solution single-crystal 24Pb(In1/2Nb1/2)O3-46Pb (Mg1/3Nb2/3)O3-30PbTio3.

    PubMed

    Yasuda, Naohiko; Nur Hidayah, Z A; Ohwa, Hidehiro; Tachi, Yoshihito; Yamashita, Yohachi

    2012-09-01

    The domain structures of poled and depoled lead-based relaxor ferroelectric solid-solution single-crystal 24Pb(In(1/2)Nb(1/2))O(3)-46Pb (Mg(1/3)Nb(2/3))O(3)-30PbTio(3) are studied by polarized light microscopy, piezoresponse force microscopy (PFM), scanning electron microscopy (SEM), and dielectric spectroscopy. The domain structures in the nonergodic relaxor state are found by PFM to consist of tweed structures resulting from random fields from the competition between ferroelectric and antiferroelectric distortion, and planar defects found by SEM are treated as dislocations associated with strain accommodation, resulting in superior piezoelectric properties. This domain structure is found to be connected with hierarchical domain structures.

  20. Multinuclear Solid-State NMR Investigation of Hexaniobate and Hexatantalate Compounds.

    PubMed

    Deblonde, Gauthier J-P; Coelho-Diogo, Cristina; Chagnes, Alexandre; Cote, Gérard; Smith, Mark E; Hanna, John V; Iuga, Dinu; Bonhomme, Christian

    2016-06-20

    This work determines the potential of solid-state NMR techniques to probe proton, alkali, and niobium environments in Lindqvist salts. Na7HNb6O19·15H2O (1), K8Nb6O19·16H2O (2), and Na8Ta6O19·24.5H2O (3) have been studied by solid-state static and magic angle spinning (MAS) NMR at high and ultrahigh magnetic field (16.4 and 19.9 T). (1)H MAS NMR was found to be a convenient and straightforward tool to discriminate between protonated and nonprotonated clusters AxH8-xM6O19·nH2O (A = alkali ion; M = Nb, Ta). (93)Nb MAS NMR studies at different fields and MAS rotation frequencies have been performed on 1. For the first time, the contributions of NbO5Oμ2H sites were clearly distinguished from those assigned to NbO6 sites in the hexaniobate cluster. The strong broadening of the resonances obtained under MAS was interpreted by combining chemical shift anisotropy (CSA) with quadrupolar effects and by using extensive fitting of the line shapes. In order to obtain the highest accuracy for all NMR parameters (CSA and quadrupolar), (93)Nb WURST QCPMG spectra in the static mode were recorded at 16.4 T for sample 1. The (93)Nb NMR spectra were interpreted in connection with the XRD data available in the literature (i.e., fractional occupancies of the NbO5Oμ2H sites). 1D (23)Na MAS and 2D (23)Na 3QMAS NMR studies of 1 revealed several distinct sodium sites. The multiplicity of the sites was again compared to structural details previously obtained by single-crystal X-ray diffraction (XRD) studies. The (23)Na MAS NMR study of 3 confirmed the presence of a much larger distribution of sodium sites in accordance with the 10 sodium sites predicted by XRD. Finally, the effect of Nb/Ta substitutions in 1 was also probed by multinuclear MAS NMR ((1)H, (23)Na, and (93)Nb).

  1. 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.

  2. The reactivity of 1,1-dialkoxyalkanes with niobium and tantalum pentahalides. Formation of coordination compounds, C-H and C-C bond activation and the X-ray structure of the stable carboxonium species [Me(2)C=CHC(=OMe)Me][NbCl(5)(OMe)].

    PubMed

    Marchetti, Fabio; Pampaloni, Guido; Zacchini, Stefano

    2009-10-14

    The reactions of the pentahalides NbX5 (X = Cl, Br) with the 1,1-dialkoxyalkanes CHR'(OEt)2 or 1,3-dioxolane yield the coordination adducts NbX5[kappa1-(OEt)CHR'(OEt)] (X = Cl, R' = H, 2a; X = Br, R' = H, 2b; X = Cl, R' = Me, 2c; X = Br, R' = Me, 2d) or NbCl5(kappa1-right angle OCH2OCH2C right angle H2), 3, respectively. Compounds 2a-c and 3 are stable at room temperature, while 2d slowly converts into the alkoxide NbBr4[OCH(Me)OEt], 4. Room-temperature fragmentations are observed upon reacting CH2(OMe)2, CHMe(OMe)2 and CMe2(OMe)2 with MX5 (M = Nb, Ta; X = Cl, Br). The complexes MX5[O(Me)(CH2X)], 5, and [MX3(OMe)2]2, 6, form selectively from MX5/CH2(OMe)2 (M = Nb, Ta; X = Cl, Br), while mixtures of [NbX4(OMe)]2 (X = Cl, 8a; X = Br, 8b) and organic halides are obtained from NbX5/CHMe(OMe)2. Instead, the reaction of NbCl5 with CMe2(OMe)2 affords the stable carboxonium species [Me2C=CHC(=OMe)Me][NbCl5(OMe)], 7, as prevalent product. Furthermore, 1,1-dialkoxyalkanes are generally activated by MF5 (M = Nb, Ta) at room temperature: according to the cases, alcohols, ethers, esters and ketones have been detected in the reaction mixtures after hydrolysis. In agreement with NMR data, the carboxonium ion [Me2C=CHC(=OMe)Me]+ is produced from NbF5/CMe2(OMe)2. The complexes NbF5[OEt(Me)], 9a, and NbF5[O=CH(OEt)], 9b, obtained by addition of CH2(OEt)2 to NbF5, have been characterised by NMR spectroscopy. Trimethyl formate, CH(OMe)3, reacts with NbX5 (X = Cl, Br) with formation of the alkoxides 6 and 8, in admixture with NbX5[O=CH(OMe)] and MeX; otherwise, MF5[O=CH(OMe)] and MF5(OMe2) have been synthesised from MF5/CH(OMe)3 (M = Nb, Ta). Complete screening of the organic fragments produced in the distinct reactions has been carried out by both GC-MS and NMR analyses on the reaction mixtures, after treatment with water. The solid state structures of the mixed halo-alkoxy complexes [TaX3(OMe)(mu-OMe)]2 (X = Cl, 6c; X = Br, 6d) and of the stable alkylated ketone containing species 7

  3. Phase transition and electrical properties of (K0.5Na0.5)(Nb1-xTax)O3 lead-free piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

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

    2008-04-01

    (K0.5Na0.5)(Nb1-xTax)O3 lead-free piezoelectric ceramics have been prepared by an ordinary sintering technique. The results of X-ray diffraction reveal that Ta5+ diffuses into the K0.5Na0.5NbO3 lattices to form a solid solution with an orthorhombic perovskite structure. Because of the high melting temperature of KTaO3, the (K0.5Na0.5)(Nb1-xTax)O3 ceramics can be sintered at higher temperatures. The partial substitution of Ta5+ for the B-site ion Nb5+ decreases both paraelectric/cubic ferroelectric/tetragonal and ferroelectric/tetragonal ferroelectric/orthorhombic phase transition temperatures, TC and TO-T. It also induces a relaxor phase transition and weakens the ferroelectricity of the ceramics. The ceramics become ‘softened’, leading to improvements in d33, kp, kt and ɛr and a decease in Ec, Qm and Np. The ceramics with x=0.075 0.15 become optimum, having d33=127 151 pC/N, kp=0.43 0.44, kt=0.43 0.44, ɛr=541 712, tanδ=1.75 2.48% and TC=378 329 °C.

  4. A new insight into high-strength Ti62Nb12.2Fe13.6Co6.4Al5.8 alloys with bimodal microstructure fabricated by semi-solid sintering

    PubMed Central

    Liu, L. H.; Yang, C.; Kang, L. M.; Qu, S. G.; Li, X. Q.; Zhang, W. W.; Chen, W. P.; Li, Y. Y.; Li, P. J.; Zhang, L. C.

    2016-01-01

    It is well known that semi-solid forming could only obtain coarse-grained microstructure in a few alloy systems with a low melting point, such as aluminum and magnesium alloys. This work presents that semi-solid forming could also produce novel bimodal microstructure composed of nanostructured matrix and micro-sized (CoFe)Ti2 twins in a titanium alloy, Ti62Nb12.2Fe13.6Co6.4Al5.8. The semi-solid sintering induced by eutectic transformation to form a bimodal microstructure in Ti62Nb12.2Fe13.6Co6.4Al5.8 alloy is a fundamentally different approach from other known methods. The fabricated alloy exhibits high yield strength of 1790 MPa and plastic strain of 15.5%. The novel idea provides a new insight into obtaining nano-grain or bimodal microstructure in alloy systems with high melting point by semi-solid forming and into fabricating high-performance metallic alloys in structural applications. PMID:27029858

  5. A new insight into high-strength Ti62Nb12.2Fe13.6Co6.4Al5.8 alloys with bimodal microstructure fabricated by semi-solid sintering

    NASA Astrophysics Data System (ADS)

    Liu, L. H.; Yang, C.; Kang, L. M.; Qu, S. G.; Li, X. Q.; Zhang, W. W.; Chen, W. P.; Li, Y. Y.; Li, P. J.; Zhang, L. C.

    2016-03-01

    It is well known that semi-solid forming could only obtain coarse-grained microstructure in a few alloy systems with a low melting point, such as aluminum and magnesium alloys. This work presents that semi-solid forming could also produce novel bimodal microstructure composed of nanostructured matrix and micro-sized (CoFe)Ti2 twins in a titanium alloy, Ti62Nb12.2Fe13.6Co6.4Al5.8. The semi-solid sintering induced by eutectic transformation to form a bimodal microstructure in Ti62Nb12.2Fe13.6Co6.4Al5.8 alloy is a fundamentally different approach from other known methods. The fabricated alloy exhibits high yield strength of 1790 MPa and plastic strain of 15.5%. The novel idea provides a new insight into obtaining nano-grain or bimodal microstructure in alloy systems with high melting point by semi-solid forming and into fabricating high-performance metallic alloys in structural applications.

  6. Effects of BaO on the structure and electrical properties of 0.95K0.5Na0.5(Nb0.94Sb0.06)O3 0.05LiTaO3 lead-free ceramics

    NASA Astrophysics Data System (ADS)

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

    2007-11-01

    Lead-free ceramics 0.95K0.5Na0.5(Nb0.94Sb0.06)O3-0.05 LiTaO3 + xmol%BaO (0 <= x <= 3.00) have been fabricated by an ordinary sintering technique. The results of x-ray diffraction show that the ceramic with a perovskite structure changes from tetragonal phase to pseudocubic phase by increasing the doping level of Ba, and the ceramics with 1.00 < x < 1.50 contain both the tetragonal and the pseudocubic phases at room temperature. After the doping with Ba, the grain growth is inhibited, the ferroelectric-paraelectric phase transition temperature (Tc) is decreased, and a diffuse phase transition is induced. The ferroelectric properties (Pr and Ec) show a slight decrease with increasing x up to 1.25, and then become weakened significantly. Because of the coexistence of the tetragonal and pseudocubic phases, the piezoelectric and dielectric properties of the ceramics with 1.00 < x < 1.50 are enhanced significantly. The ceramic with x = 1.25 exhibits the optimum properties: d33 = 261 pC N-1, kP = 0.52, kt = 0.46, ɛr = 1503, tan δ = 2.5% and Tc = 314 °C. Our results have also demonstrated that the ceramics are non-deliquescent.

  7. Dielectric and piezoelectric properties of the KNN ceramic compound doped with Li, La and Ta

    NASA Astrophysics Data System (ADS)

    Fuentes, J.; Portelles, J.; Durruthy-Rodríguez, M. D.; H'Mok, H.; Raymond, O.; Heiras, J.; Cruz, M. P.; Siqueiros, J. M.

    2015-02-01

    With the purpose of improving the dielectric and piezoelectric properties of (K0.5Na0.5)NbO3 (KNN), a multiple doping strategy was tested in this research. Piezoceramics with composition [(K0.5Na0.5)0.94Li0.06]0.97La0.01(Nb0.9Ta0.1)O3 were prepared by the traditional ceramic method. The calcined powders were sintered in their own atmosphere at 1,100 °C for 1.0, 1.5 and 2.5 h. X-ray diffraction analysis showed that the Li+, La3+ and Ta5+ cations diffuse into the KNN structure to form a perovskite-structured solid solution. For 1 h sintering time, a dominant orthorhombic phase is obtained, whereas for the longer times, the dominant phase was tetragonal. The presence of a tetragonal tungsten-bronze minority second phase is confirmed. Scanning electron micrographs show rectangular-shaped grains with a mean size of 1.1 ± 0.2 μm. The existence of pores and traces of a liquid phase favoring grain growth and homogeneity is also observed. Experimental results show an enhancement of the permittivity associated with the enlargement of the c parameter of the cell that increases with sintering time. Li+ incorporation into the structure is made evident by its transition temperature at 400 °C different from those of KNNLaTi (81-110 °C) and KNNLaTa (340 °C). An analysis of the phase transition of the samples indicates a normal rather than a diffuse transition. The electromechanical parameters k p, Q m, σ p, s 11, d 31 and g 31 are determined and compared to those of commercial PZT ceramics.

  8. Dielectric and piezoelectric properties of the KNN ceramic compound doped with Li, La and Ta

    NASA Astrophysics Data System (ADS)

    Fuentes, J.; Portelles, J.; Durruthy-Rodríguez, M. D.; H'Mok, H.; Raymond, O.; Heiras, J.; Cruz, M. P.; Siqueiros, J. M.

    2014-09-01

    With the purpose of improving the dielectric and piezoelectric properties of (K0.5Na0.5)NbO3 (KNN), a multiple doping strategy was tested in this research. Piezoceramics with composition [(K0.5Na0.5)0.94Li0.06]0.97La0.01(Nb0.9Ta0.1)O3 were prepared by the traditional ceramic method. The calcined powders were sintered in their own atmosphere at 1,100 °C for 1.0, 1.5 and 2.5 h. X-ray diffraction analysis showed that the Li+, La3+ and Ta5+ cations diffuse into the KNN structure to form a perovskite-structured solid solution. For 1 h sintering time, a dominant orthorhombic phase is obtained, whereas for the longer times, the dominant phase was tetragonal. The presence of a tetragonal tungsten-bronze minority second phase is confirmed. Scanning electron micrographs show rectangular-shaped grains with a mean size of 1.1 ± 0.2 μm. The existence of pores and traces of a liquid phase favoring grain growth and homogeneity is also observed. Experimental results show an enhancement of the permittivity associated with the enlargement of the c parameter of the cell that increases with sintering time. Li+ incorporation into the structure is made evident by its transition temperature at 400 °C different from those of KNNLaTi (81-110 °C) and KNNLaTa (340 °C). An analysis of the phase transition of the samples indicates a normal rather than a diffuse transition. The electromechanical parameters k p, Q m, σ p, s 11, d 31 and g 31 are determined and compared to those of commercial PZT ceramics.

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

    SciTech Connect

    Nyman, May D.; Anderson, Travis Mark; Alam, Todd Michael; Rodriguez, Mark A; Joel N. Bixler; Francois Bonhomme

    2007-10-01

    Tantalate materials play a vital role in our high technology society: tantalum capacitors are found in virtually every cell phone. Furthermore, electronic characteristics and the incredibly inert nature of tantalates renders them ideal for applications such as biomedical implants, nuclear waste forms, ferroelectrics, piezoelectrics, photocatalysts and optical coatings. The inert and insoluble nature of tantalates is not fundamentally understood; and furthermore poor solubility renders fabrication of novel or optimized tantalates very difficult. We have developed a soft chemical route to water-soluble tantalum oxide clusters that can serve as both precursors for novel tantalate materials and ideal models for experimental and computational approaches to understanding the unusually inert behavior of tantalates. The water soluble cluster, [Ta6O19]8- is small, highly symmetric, and contains the representative oxygen types of a metal oxide surface, and thus ideally mimics a complex tantalate surface in a simplistic form that can be studied unambiguously. Furthermore; in aqueous solution, these highly charged and super-basic clusters orchestrate surprising acid-base behavior that most likely plays an important role in the inertness of related oxide surfaces. Our unique synthetic approach to the [Ta6O19]8- cluster allowed for unprecedented enrichment with isotopic labels (17O), enabling detailed kinetic and mechanistic studies of the behavior of cluster oxygens, as well as their acid-base behavior. This SAND report is a collection of two publications that resulted from these efforts.

  10. TiTaN Reconsidered

    NASA Astrophysics Data System (ADS)

    Natland, J. H.

    2008-12-01

    Strongly positive TiO2, Ta, and Nb (TiTaN) anomalies (1) in a Samoan ankaramite from Ofu Island have been attributed to the presence of refractory yet titanian eclogite in the mantle source. From chemical compositions, however, the anomalies could instead result from concentration of phenocrysts in magmas produced by mixing between a highly differentiated alkalic basalt and a crystal sludge carrying abundant olivine, clinopyroxene and especially titanomagnetite phenocrysts, the latter producing much of the TiTaN anomalies, and behaving much like rutile in eclogite. This is consistent with petrography. The distinctive effects of addition of each mineral are well illustrated on major-oxide variation diagrams. Separation of these minerals from liquids (to concentrate in ankaramites and dunite-wehrlite-pyroxenite cumulates) beginning at about 0.15 GPa in the mantle produces residual felsic differentiates (hawaiites, mugearites) with low TiTan anomalies (<1), exemplified by samples dredged elsewhere in Samoa from Savai'i (2). The Ofu samples have a low EMII signature (high 3He/4He), whereas the Savai'i samples have a high EMII signature (low 3He/4He), the extremes at Samoa. This gives a coincidental positive correlation at Samoa overall between TiTan anomalies and 3He/4He, TiTan anomalies being accentuated at the two places by the contrasting effects of phenocryst addition and subtraction during differentiation. High 3He/4He beneath several eastern Samoan volcanoes appears to be an attribute of near-FOZO mantle sources with minimal EM2 signature. (1) Jackson, M., et al., 2008. G-Cubed 9: doi:1029/2007GC001876 (2) Jackson, M., et al., 2007, Nature 448: 684-687, doi:10.1038/nature060488

  11. Phase transformations during the interaction of Nb2O5 and FeNb2O6 with aluminum

    NASA Astrophysics Data System (ADS)

    Mansurova, A. N.; Chumarev, V. M.; Leont'ev, L. I.; Gulyaeva, R. I.; Sel'menskikh, N. I.

    2012-11-01

    The phase transformations that occur during the interaction of niobium pentoxide and iron niobate with aluminum are studied by differential scanning calorimetry, X-ray diffraction analysis and electronprobe microanalysis. The sequence of the formation of intermediate phases based on an NbO2 solid solution is revealed. It is shown that the reduction of niobium from Nb2O5 is hindered by the formation of hard-to-reduce oxides Al2O3 · 25Nb2O5, Al2O3 · 9Nb2O5 and AlNbO4. The interaction of FeNb2O6 with aluminum is accompanied by the formation of [(Fe,Nb)O2]s.s and NbO2 solid solutions.

  12. 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.

  13. Search for solid conductors of Na(+) and K(+) ions: Five new conductors

    NASA Technical Reports Server (NTRS)

    Singer, J.; Kautz, H.; Fielder, W. L.; Fordyce, J.

    1975-01-01

    Five conductors of three structure types were discovered which, as solids, can transport Na(+) or K(+) ions with conductivities of approximately .00001/(omega cm) at 300 K. These compounds are: (1) the pyrochlores NaTaWO6 and NaTa2O5F, both with an activation energy for conduction delta E of 21 kJ/mole; (2) the bodycentered cubic form of NaSbO3, with delta E = 42 kJ/mole; and (3) the niobates 2Na2O with 3Nb2O5 and 2K2O with 3Nb2O5, with the alkali ions probably in open layers of the incompletely determined structure; delta E = 17 kJ/mole. On the basis of approximately 40 structure types, some generalizations were made regarding the relation between structure and ionic transport.

  14. Highly CO2-Tolerant Cathode for Intermediate-Temperature Solid Oxide Fuel Cells: Samarium-Doped Ceria-Protected SrCo0.85Ta0.15O3-δ Hybrid.

    PubMed

    Li, Mengran; Zhou, Wei; Zhu, Zhonghua

    2017-01-25

    Susceptibility to CO2 is one of the major challenges for the long-term stability of the alkaline-earth-containing cathodes for intermediate-temperature solid oxide fuel cells. To alleviate the adverse effects from CO2, we incorporated samarium-stabilized ceria (SDC) into a SrCo0.85Ta0.15O3-δ (SCT15) cathode by either mechanical mixing or a wet impregnation method and evaluated their cathode performance stability in the presence of a gas mixture of 10% CO2, 21% O2, and 69% N2. We observed that the CO2 tolerance of the hybrid cathode outperforms the pure SCT15 cathode by over 5 times at 550 °C. This significant enhancement is likely attributable to the low CO2 adsorption and reactivity of the SDC protective layer, which are demonstrated through thermogravimetric analysis, energy-dispersive spectroscopy, and electrical conductivity study.

  15. Synergistic Coupling between Li6.75La3Zr1.75Ta0.25O12 and Poly(vinylidene fluoride) Induces High Ionic Conductivity, Mechanical Strength, and Thermal Stability of Solid Composite Electrolytes.

    PubMed

    Zhang, Xue; Liu, Ting; Zhang, Shuofeng; Huang, Xin; Xu, Bingqing; Lin, Yuanhua; Xu, Ben; Li, Liangliang; Nan, Ce-Wen; Shen, Yang

    2017-10-04

    Easy processing and flexibility of polymer electrolytes make them very promising in developing all-solid-state lithium batteries. However, their low room-temperature conductivity and poor mechanical and thermal properties still hinder their applications. Here, we use Li6.75La3Zr1.75Ta0.25O12 (LLZTO) ceramics to trigger structural modification of poly(vinylidene fluoride) (PVDF) polymer electrolyte. By combining experiments and first-principle calculations, we find that La atom of LLZTO could complex with the N atom and C═O group of solvent molecules such as N,N-dimethylformamide along with electrons enriching at the N atom, which behaves like a Lewis base and induces the chemical dehydrofluorination of the PVDF skeleton. Partially modified PVDF chains activate the interactions between the PVDF matrix, lithium salt, and LLZTO fillers, hence leading to significantly improved performance of the flexible electrolyte membrane (e.g., a high ionic conductivity of about 5 × 10(-4) S cm(-1) at 25 °C, high mechanical strength, and good thermal stability). For further illustration, a solid-state lithium battery of LiCoO2|PVDF-based membrane|Li is fabricated and delivers satisfactory rate capability and cycling stability at room temperature. Our study indicates that the LLZTO modifying PVDF membrane is a promising electrolyte used for all-solid-state lithium batteries.

  16. 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.

  17. Molten salt synthesis of NaNbxTa1-xO3 perovskites with enhanced photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Wang, Meng; Fang, Minghao; Min, Xin; Huang, Zhaohui; Tang, Chao; Liu, Yan'gai; Wu, Xiaowen

    2017-10-01

    NaNbxTa1-xO3 perovskite photocatalysts with cubic microstructures were synthesized by the molten salt method. Furthermore, the photocatalysts were characterized in detail by XRD, SEM, TEM, XPS, PL. SEM results indicated that the added Nb significantly affects the microstructure. XPS results confirmed the presence of the Nb5+ dopant in NaNbxTa1-xO3. Compared to NaTaO3, the catalyst doped with Nb significantly affected the photocatalytic production of hydrogen in an aqueous solution and the photocatalytic degradation of RhB under UV light irradiation. NaNb0.5Ta0.5O3 exhibited the best activity for the photocatalytic degradation of RhB as well as excellent performance for the photocatalytic production of hydrogen.

  18. Far infrared linear response and radio frequency nonlinear response of charge density wave conductors and high T/sub c/ superconductors. [(TaSe/sub 4/)/sub 2/I; La/sub 1. 85/Sr/sub 0. 15/CuO/sub 4/; La/sub 1. 85/Ca/sub 0. 15/CuO/sub 4/; ac-dc mode lock of NbSe/sub 3/

    SciTech Connect

    Sherwin, M.S.

    1988-06-01

    The far-ir (FIR) linear response of the charge-density-wave (CDW) conductor (TaSe/sub 4/)/sub 2/I and polycrystalline La/sub 1.85/Sr/sub 0.15/CuO/sub 4/ and La/sub 1.85/Ca/sub 0.15/CuO/sub 4/ was measured at 8--350 cm/sup /minus/1/ and 5 to 300K. At low T in (TaSe/sub 4/)/sub 2/I, a mode with giant oscillator strength was found at 38 cm/sup -1/. This giant FIR mode lies between the pinned mode and the Peierls gap. It is suggested that a giant FIR mode distinct from the pinned mode is a common feature of CDW conductors. At low T in the high-T/sub c/ superconductors, a reflectance edge was observed near 2.5k/sub B/T/sub c/. The BCS-like temperature-dependence of the reflectance edge is suggestive of an energy gap. However, a simple model shows that a BCS-like temperature dependence is also consistent with an interpretation of the reflectance edge as a low-frequency plasmon. It is not yet possible to deduce the energy gap from the FIR spectra. The rf nonlinear response of the CDW conductor NbSe/sub 3/ was also measured. In combined rf- and dc-electric fields, mode-locking occurs in NbSe/sub 3/. Complete mode-locking in conventional samples dramatically suppresses sliding CDW conduction fluctuations. Combined rf and dc electric fields on switching NbSe/sub 3/ induced a large amplitude /open quotes/ac switching noise/close quotes/ for rf frequencies <1 MHz, and a period-doubling route to chaos for rf-frequencies >1 MHz. The mode-locking behavior of switching and nonswitching NbSe/sub 3/ is analyzed. A model of CDW elasticity qualitatively reproduces all of the experimental anomalies for dc-, ac- and combined ac- and dc-electric fields. It is suggested that, during mode-locking, the number of degrees of freedom active in CDW transport is reduced.

  19. First-principles study of the charge transfer and evolution of Si doping 2N2Ta islands adsorption on TaN (001) surfaces

    NASA Astrophysics Data System (ADS)

    Ren, Yuan; Zhang, Honglv; Zhang, Chao; Zeng, Haiqing; Liu, Xuejie

    2017-01-01

    The separation and aggregation of Si atoms around TaN grains during deposition of Ta-Si-N nanocomposite films were studied, and the adsorption energies, charge transfer and atomic partial density of state of Si-2N2Ta islands on the TaN (001) surface and diffusion energy of the islands during their evolution were evaluated using the first-principles method based on density functional theory (DFT). In the lowest total energy stable configuration, N and Ta atoms tended to combine to form 2N2Ta islands, whereas Si atoms tended to stay at a position diagonal to the Ta atom outside of the island. Si atoms entered the position of the missing N atom of the TaN island and formed a substitute solid solution during Ta-Si-N growth. The Si atoms of the solid solution in the island could be easily extruded by Ta- or N-rich island during the deposition process. The process of Si atom extrusion by a N atom which was the configuration of N-by-2Ta1N1Si island evolved into Si-by-2N2Ta island in rich N-atom. The process of Si atom was extruded by the Ta atom which was the configuration of Ta-by-2N1Ta1Si island evolved into Si-of-2Ta2N island, that reduced the total energy of island. The diffusion energies of these evolutions were 0.974 and 1.712 eV, respectively. The Si atoms and TaN grain phase tended to separate during the deposition process. Si atoms could give way to Ta and N atoms during the Ta-Si-N nanocomposite film deposition process.

  20. 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.

  1. Crystal-structure and magnetic phase transformations in solid solutions of BiFeO{sub 3}-AFe{sub 0.5}Nb{sub 0.5}O{sub 3} (A = Ca, Sr, Ba, Pb)

    SciTech Connect

    Troyanchuk, I. O.; Bushinsky, M. V. Chobot, A. N.; Mantytskaya, O. S.; Pushkarev, N. V.; Szymczak, R.

    2008-08-15

    Solid solutions of Bi{sub 1-x}A{sub x}(Fe{sub 1-x/2}Nb{sub x/2})O{sub 3}, where A = Ca, Ba, and Pb, are obtained and their crystal structure and magnetic properties are investigated. It is shown that for A = Ca and x {approx} 0.15, the symmetry of the unit cell changes from rhombohedral (space group R3c) to orthorhombic (Pbnm). The transformation leads to the emergence of spontaneous magnetization due to the Dzyaloshinskii-Moriya interaction. Solid solutions with A = Pb remain rhombohedral up to a concentration of x = 0.3. Spontaneous magnetization sharply increases in the compound with x {approx} 1 at low temperatures and is due to the formation of the spin-glass component.

  2. Phase diagram of (Na0.5K0.5)NbO3-(Bi0.5Na0.5)ZrO3 solid solution

    NASA Astrophysics Data System (ADS)

    Wang, Ruiping; Itoh, Mitsuru

    2016-06-01

    Phase diagram of (1-x)Na0.5K0.5NbO3-x(Bi0.5Na0.5)ZrO3 solid solution has been established from dielectric constant measurements and structure analyses. It is found that with increasing x, the C-T phase transition temperature TC-T and the T-O phase transition temperature TT-O decrease, while the O-R phase transition temperature TO-R increases. TT-O of NKN-xBNZ is much different from that of NKN-xBZ solid solution. The result could be mainly elucidated by the hybridization between the A-site ion and oxygen.

  3. Structure and Charge Density Properties of (1 - x)(Na1-y K y NbO3)-xBaTiO3 Lead-Free Ceramic Solid Solution

    NASA Astrophysics Data System (ADS)

    Sasikumar, S.; Saravanan, R.

    2017-02-01

    (1 - x)(Na1-y K y )NbO3-xBaTiO3 (abbreviated as NKN-BT, x = 0.1, 0.2; y = 0.01, 0.05) ceramics were synthesized by the solid-state reaction method. Powder x-ray diffraction analysis in combination with the profile refinement method was employed for quantitative phase analysis and structural refinement. The x-ray diffraction study shows that phase transition occurs from tetragonal to distorted cubic with the compositions between x = 0.1 and x = 0.2. The spatial arrangements of the electron distribution and bonding nature of the samples have been analyzed through the maximum entropy method. The optical band gap energy of the prepared solid solutions has been determined using UV-visible spectrophotometry. The optical band gap energy of the solid solutions decreases with the increase in BaTiO3 content. The elemental composition of these ceramics has been studied using energy dispersive x-ray analysis and the microstructure has been examined by scanning electron microscopy. The piezoelectric coefficient (d 33 ) measurement of the ceramics shows the enhancement of piezoelectric properties in the tetragonal phase. The maximum value of the piezoelectric coefficient (d 33 ) obtained for the solid solution is 120 pC/N. With increasing BaTiO3 content in the solid solutions, the ferroelectric behavior weakens.

  4. Structure and Charge Density Properties of (1 - x)(Na1- y K y NbO3)- xBaTiO3 Lead-Free Ceramic Solid Solution

    NASA Astrophysics Data System (ADS)

    Sasikumar, S.; Saravanan, R.

    2017-07-01

    (1 - x)(Na1- y K y )NbO3- xBaTiO3 (abbreviated as NKN-BT, x = 0.1, 0.2; y = 0.01, 0.05) ceramics were synthesized by the solid-state reaction method. Powder x-ray diffraction analysis in combination with the profile refinement method was employed for quantitative phase analysis and structural refinement. The x-ray diffraction study shows that phase transition occurs from tetragonal to distorted cubic with the compositions between x = 0.1 and x = 0.2. The spatial arrangements of the electron distribution and bonding nature of the samples have been analyzed through the maximum entropy method. The optical band gap energy of the prepared solid solutions has been determined using UV-visible spectrophotometry. The optical band gap energy of the solid solutions decreases with the increase in BaTiO3 content. The elemental composition of these ceramics has been studied using energy dispersive x-ray analysis and the microstructure has been examined by scanning electron microscopy. The piezoelectric coefficient ( d 33 ) measurement of the ceramics shows the enhancement of piezoelectric properties in the tetragonal phase. The maximum value of the piezoelectric coefficient ( d 33 ) obtained for the solid solution is 120 pC/N. With increasing BaTiO3 content in the solid solutions, the ferroelectric behavior weakens.

  5. A Study of NbCr and NbCr^{-} by Anion Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Baudhuin, Melissa A.; Boopalachandran, Praveenkumar; Rajan, Srijay S.; Leopold, Doreen G.

    2013-06-01

    We report the 488 nm photoelectron spectrum of the NbCr^{-} anion. For the ^{2}Δ ground state of neutral NbCr, the short bond length (1.894 Å) and high bond energy (D_0 3.0263(6) eV) measured by R2PI spectroscopy indicate high order multiple bonding. We find that the NbCr^{-} anion has a ^{1}Σ^{+} ground state, in which the "extra" electron occupies the (4d)δ bonding orbital, giving a 1σ^{2}1π^{4}1δ^{4}2σ^{2} valence electron configuration and a formal bond order of 6. Low-lying excited states of NbCr (assigned as two ^{2}Σ^{+} states) and NbCr^{-} (^{3}Δ) are also observed. The spectra provide the electron affinity of NbCr, energies of the ^{2}Σ^{+} and the ^{3}Δ excited states, vibrational frequencies for the NbCr and NbCr^{-} ground states and for the ^{2}Σ^{+} excited states, and (from Franck-Condon analyses) differences among the bond lengths of the observed states. These results are compared with our previous data for the Group 5/6 congeners NbMo, VCr, and VMo, and with DFT predictions. We also report results for ongoing experiments on the flow tube reactions of the Group V metals Nb and Ta with butadiene, and the vibrationally-resolved photoelectron spectra of some of the organometallic reaction product anions. S. M. Sickafoose, J. D. Langenberg, and M. D. Morse, J. Phys. Chem. A. 104, 3521-3527 (2000).

  6. Assessment of refining effectiveness of self-prepared nano-(TiNb)C/(NbTi)/Al complex powder inoculation on A356 alloy

    NASA Astrophysics Data System (ADS)

    Qiao, Gui-ying; Wu, Da-yong; Wei, Teng-fei; Liao, Bo; Xiao, Fu-ren

    2017-07-01

    Inoculation plays an effective role to refine the microstructure of as-cast aluminium alloys, which strongly depend on the effectiveness of the inoculants. In this work, a new concept of nano-(TiNb)C/(NbTi)/Al complex powder as an inoculant for refining the as-cast aluminium alloys was proposed, and the nano-(TiNb)C/(NbTi)/Al complex powder was prepared by mechanical alloying (MA) method, furthermore, the refining effectiveness of inoculation on A356 alloy was investigated. Results show that the nano-(TiNb)C/(NbTi)/Al complex powder consists of three phases of α-Al, nano-(TiNb)C and (NbTi) solid solution. The nano-(TiNb)C/(NbTi)/Al complex powder as an inoculant have higher refining effectiveness as well as good recyclability on the microstructure of cast A356 alloy, and improve the mechanical properties, especially the ductility.

  7. Thermopower of doped and damaged NbSe 3

    NASA Astrophysics Data System (ADS)

    Chaikin, P. M.; Fuller, W. W.; Lacoe, R.; Kwak, J. F.; Greene, R. L.; Eckert, J. C.; Ong, N. P.

    1981-07-01

    We have measured the thermoelectric power of pure NbSe 3 as well as samples which have been substitutionally doped with isoelectronic Ta and the charged impurity Ti and separate samples which have been radiation damaged by 2.5 MeV protons. We find that 5% Ta doping supresses the lower temperature charge density wave transition. In contrast, the radiation damaged samples and 0.1% Ti samples with larger residual resistivities then the Ta doped samples retain the CDW transitions. A discussion is given of the difference between doping and radiation damage.

  8. Preparation and properties of all-solid-state inorganic thin film glass/ITO/WO3/LiNbO3/NiOx/ITO electrochromic device

    NASA Astrophysics Data System (ADS)

    Wu, Zhonghou; Diao, Xungang; Dong, Guobo

    2016-01-01

    The all-thin-film inorganic electrochromic device (ECD) with LiNbO3 as the ion conductor layer was prepared. The ECD was fabricated monolithically in a same vacuum chamber layer by layer using DC reactive sputtering for WO3, NiOx and ITO, and radio frequency (RF) sputtering for LiNbO3. The properties and performance of WO3 thin film and the ECD were studied through X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet-visible spectrometry. WO3 thin film has more than 60% optical modulation with porous amorphous structure. The visible transmittance modulation of the ECD is more than 65%, and the response time of coloring and bleaching are 45 s and 25 s, respectively.

  9. Hyperfine characterization of Bi 1.9Te 0.1SrNb 1.9Hf 0.1O 9

    NASA Astrophysics Data System (ADS)

    Alonso, R. E.; López-García, A.; Martínez, J. A.; Castro, A.; Paschoal, A. R.; Silva, E. N.; Ayala, A. P.; Guedes, I.

    2006-07-01

    The Aurivillius type oxide Bi 1.9Te 0.1SrNb 1.9Hf 0.1O 9 has been studied by Perturbed Angular Correlations spectroscopy using 181Ta probes. The spin precession curves were measured from room temperature up to 873 K. Two sites are occupied by probes and the temperature dependence of both indicates a continuous phase transition at about 625 K. One site is ordered while the other is disordered. This situation is analyzed in terms of simple models already applied to perovskites. The transition temperature of the solid solution Bi 2- xTe xSrNb 2- xHf xO 9 (with 0≤x≤0.5) shows a strong dependence on composition.

  10. Releasing metal catalysts via phase transition: (NiO)0.05-(SrTi0.8Nb0.2O3)0.95 as a redox stable anode material for solid oxide fuel cells.

    PubMed

    Xiao, Guoliang; Wang, Siwei; Lin, Ye; Zhang, Yanxiang; An, Ke; Chen, Fanglin

    2014-11-26

    Donor-doped perovskite-type SrTiO3 experiences stoichiometric changes at high temperatures in different Po2 involving the formation of Sr or Ti-rich impurities. NiO is incorporated into the stoichiometric strontium titanate, SrTi0.8Nb0.2O3-δ (STN), to form an A-site deficient perovskite material, (NiO)0.05-(SrTi0.8Nb0.2O3)0.95 (Ni-STN), for balancing the phase transition. Metallic Ni nanoparticles can be released upon reduction instead of forming undesired secondary phases. This material design introduces a simple catalytic modification method with good compositional control of the ceramic backbones, by which transport property and durability of solid oxide fuel cell anodes are largely determined. Using Ni-STN as anodes for solid oxide fuel cells, enhanced catalytic activity and remarkable stability in redox cycling have been achieved. Electrolyte-supported cells with the cell configuration of Ni-STN-SDC anode, La0.8Sr0.2Ga0.87Mg0.13O3 (LSGM) electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode produce peak power densities of 612, 794, and 922 mW cm(-2) at 800, 850, and 900 °C, respectively, using H2 as the fuel and air as the oxidant. Minor degradation in fuel cell performance resulted from redox cycling can be recovered upon operating the fuel cells in H2. Such property makes Ni-STN a promising regenerative anode candidate for solid oxide fuel cells.

  11. Preparation and electrical properties of bismuth layer-structured ceramic Bi{sub 3}NbTiO{sub 9} solid solution

    SciTech Connect

    Zhang Zhen; Yan Haixue; Dong Xianlin; Wang Yongling

    2003-01-25

    Bi{sub 3}NbTiO{sub 9} (BNT) ceramic materials with the density ratios of 95-97% to the theoretical density were prepared by the conventional mixed-oxide method. The Curie temperature (T{sub c}), 914 deg. C was found to be almost the highest one among those of all the ceramics known to date. The crystal structure of the ceramic was investigated by X-ray diffraction method. Anisometric plate-like crystalline grains were observed, which revealed the layered structure of the material. The temperature dependence of the electrical resistivity was measured. For the first time the dielectric properties of Bi{sub 3}NbTiO{sub 9} in the vicinity of its transition temperature were measured. Finally, the hysteresis (P-E) loop measurement showed a good ferroelectricity in the Bi{sub 3}NbTiO{sub 9} ceramics, and the piezoelectric constant (d{sub 33}) was found to be 7 pC/N.

  12. Characterization of SrCo0.7Fe0.2Nb0.1O3-δ cathode materials for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Lü, Shiquan; Yu, Bo; Meng, Xiangwei; Zhao, Xiaoyu; Ji, Yuan; Fu, Chengwei; Zhang, Yongjun; Yang, Lili; Fan, Hougang; Yang, Jinghai

    2015-01-01

    A new cubic perovskite oxide, SrCo0.7Fe0.2Nb0.1O3-δ (SCFN), is investigated as a cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). XRD results show that there are no serious reactions between SCFN and Sm0.2Ce0.8O1.9 (SDC) except a slight peak shift. XPS analysis shows that the transition-metal cations in the SCFN exist in two different valence states, i.e., [Sr2+][Co3+/Co4+]0.7[Fe3+/Fe4+]0.2[Nb4+/Nb5+]0.1O3-δ. The electrical conductivity of the SCFN sample reaches a maximum 304 S cm-1 at 350 °C in air. In order to optimize thermal expansion coefficients (TECs) and electrochemical performance of the SCFN cathode, we fabricate SCFN-xSDC (x = 0, 20, 30, 40, 50, 60, wt%) composite cathodes. The thermal expansion behavior shows that the TECs value of SCFN cathode decreases greatly with SDC addition. The SDC addition reduces the polarization resistance, and the lowest polarization resistance 0.0255 Ω cm2 is achieved at 800 °C for SCFN-50SDC composite cathode. For SCFN-xSDC (x = 0, 40, 50, 60) composites, the maximum power densities of single-cells with SCFN-xSDC cathodes on 300 μm thick SDC electrolyte achieve 417, 557, 630 and 517 mW cm-2 at 800 °C, respectively. These results indicate that SCFN-50SDC composite is a potential cathode material for application in IT-SOFCs.

  13. A robust high performance cobalt-free oxygen electrode La0.5Sr0.5Fe0.8Cu0.15Nb0.05O3-δ for reversible solid oxide electrochemical cell

    NASA Astrophysics Data System (ADS)

    Zhou, Ning; Yin, Yi-Mei; Li, Jingcheng; Xu, Lei; Ma, Zi-Feng

    2017-02-01

    A novel cobalt-free perovskite oxide La0.5Sr0.5Fe0.8Cu0.15Nb0.05O3-δ (LSFCN) has been synthesized and evaluated as oxygen electrode for reversible solid oxide electrochemical cells (RSOCs). The performance and stability of the LSFCN based RSOCs have been characterized in fuel cell and electrolysis modes, and the reversibility of the cells has been proven. In FC mode, the cell exhibits the maximum power density of 1.10 Wcm-2 at 800 °C, and a stable output under 0.7 V at 700 °C during 108 h. The performance and stability of the cell in electrolysis mode are also remarkable. An electrolysis current of 0.85 A cm-2 is achieved at 750 °C with an applied voltage of 1.3 V, and no degradation as well as delamination are observed for the cell after 50 h electrolysis under voltage of 1.60 V (∼1.27 A cm-2) at 800 °C. The high performance of the LSFCN at both cathodic and anodic conditions may be attributed to the inherent high electrochemical activity of copper-iron based perovskites; and the incorporation of Nb5+ cations into perovskite lattice is responsible for the stability of LSFCN, which leads to the more stable crystal structure, lower thermal expansion coefficient and the reduced Sr segregation at surface.

  14. Solid-state NMR characterization of the structure and thermal stability of hybrid organic-inorganic compounds based on a HLaNb2O7 Dion-Jacobson layered perovskite.

    PubMed

    Cattaneo, Alice S; Ferrara, Chiara; Marculescu, Adriana Mossuto; Giannici, Francesco; Martorana, Antonino; Mustarelli, Piercarlo; Tealdi, Cristina

    2016-08-03

    Dion-Jacobson phases, like MLaNb2O7, are an interesting class of ion-exchangeable layered perovskites possessing electronic and photocatalytic properties. Their protonated and organo-modified homologues, in particular, have already been indicated as promising catalysts. However, the structural analysis of these highly tailorable materials is still incomplete, and both the intercalation process and thermal stability of the included organic moieties are far from being completely understood. In this study, we present a thorough solid-state NMR characterization of HLaNb2O7·xH2O intercalated with different amounts of octylamine, or with decylamine. Samples were analyzed as prepared, and after thermal treatment at different temperatures up to 220 °C. The substitution of pristine proton ions was followed via(1)H MAS NMR spectroscopy, whereas the alkyl chains were monitored through (13)C((1)H) CP MAS experiments. The interactions in the interlayer space were explored using (13)C((1)H) 2D heteronuclear correlation experiments. We demonstrate that some of the protons are involved in the functionalization reaction, and some of them are in close proximity to the alkyl ammonium chains. Heating of the hybrid materials leads first to a rearrangement of the alkyl chains and then to their degradation. The spatial arrangement of the chains, their interactions and the thermal behavior of the materials depend on the extent of the functionalization, and on the nature of the intercalated alkyl ammonium ions.

  15. Characterization of solid-phase welds between Ti-6Al-2Sn-4Zr-2Mo-0. 01Si and Ti-13. 5A1-21. 5Nb titanium aluminide

    SciTech Connect

    Baeslack, W.A. III; Juhas, M.; Fraser, H.L. ); Broderick, T.F. . Materials Directorate)

    1994-12-01

    Dissimilar-alloy welds have been produced between Ti-6Al-2Sn-4Zr-2Mo-0.1Si (wt.%) and Ti-13.5Al-21.5Nb (wt.%) titanium aluminide using three different solid-phase welding processes that create significantly different thermo-mechanical conditions at the weld interface. Exposure to supertransus temperatures, appreciable deformation and rapid cooling of the weld interface region during linear-friction welding promote dynamic recrystallization of beta grains and beta decomposition to fine martensitic products. In contrast, diffusion welding at temperatures below the base metal beta transus temperatures and at relatively low pressures minimizes deformation and microstructural variations in the weld interface region relative to the unaffected base metal. During capacitor-discharge resistance spot welding, extremely rapid heating of the weld interface region to near-solidus temperatures, and subsequent rapid cooling, result in the formation of a metastable, ordered-beta microstructure in the Ti-13.5ASl-21.5Nb and fine alpha-prime martensite in the Ti-6Al-2Sn-4Zr-2Mo-0.1Si.

  16. Structural and kinetic investigation of the hydride composite Ca(BH4)2 + MgH2 system doped with NbF5 for solid-state hydrogen storage.

    PubMed

    Karimi, Fahim; Pranzas, P Klaus; Pistidda, Claudio; Puszkiel, Julián A; Milanese, Chiara; Vainio, Ulla; Paskevicius, Mark; Emmler, Thomas; Santoru, Antonio; Utke, Rapee; Tolkiehn, Martin; Minella, Christian B; Chaudhary, Anna-Lisa; Boerries, Stefan; Buckley, Craig E; Enzo, Stefano; Schreyer, Andreas; Klassen, Thomas; Dornheim, Martin

    2015-11-07

    Designing safe, compact and high capacity hydrogen storage systems is the key step towards introducing a pollutant free hydrogen technology into a broad field of applications. Due to the chemical bonds of hydrogen-metal atoms, metal hydrides provide high energy density in safe hydrogen storage media. Reactive hydride composites (RHCs) are a promising class of high capacity solid state hydrogen storage systems. Ca(BH4)2 + MgH2 with a hydrogen content of 8.4 wt% is one of the most promising members of the RHCs. However, its relatively high desorption temperature of ∼350 °C is a major drawback to meeting the requirements for practical application. In this work, by using NbF5 as an additive, the dehydrogenation temperature of this RHC was significantly decreased. To elucidate the role of NbF5 in enhancing the desorption properties of the Ca(BH4)2 + MgH2 (Ca-RHC), a comprehensive investigation was carried out via manometric measurements, mass spectrometry, Differential Scanning Calorimetry (DSC), in situ Synchrotron Radiation-Powder X-ray Diffraction (SR-PXD), X-ray Absorption Spectroscopy (XAS), Anomalous Small-Angle X-ray Scattering (ASAXS), Scanning and Transmission Electron Microscopy (SEM, TEM) and Nuclear Magnetic Resonance (NMR) techniques.

  17. Fast ultradense GdTa1-xNbxO4 scintillator crystals

    NASA Astrophysics Data System (ADS)

    Voloshyna, Olesia; Gerasymov, Iaroslav; Sidletskiy, Oleg; Kurtsev, Daniil; Gorbacheva, Tatyana; Hubenko, Kateryna; Boiaryntseva, Ianina; Ivanov, Alexey; Spassky, Dmitry; Omelkov, Sergey; Belsky, Andrei

    2017-04-01

    Single crystals of GdTaO4 and GdTa0.8Nb0.2O4 were grown by the Czochralski technique, and their luminescent and scintillation properties were studied. Both crystals demonstrate fast emission with decay time around 10-8 s. Meanwhile, in GdTaO4 the fast decay is accompanied by a huge build-up with the decay time around 1 μs, while in the mixed crystal the contribution of slow components is negligible. UV- and X-ray excited luminescence, curves of thermostimulated luminescence and absolute light yields of crystals are presented as well. GdTa0.8Nb0.2O4 crystal is shown to be an ultradense (8.37 g/cm3) and fast (shortest component decay time 17 ns) scintillator with a high stopping power.

  18. Electronic interactions in metal-hydrogen solid solutions: ScH/sub x/, YH/sub x/, and V/sub 0. 75/Nb/sub 0. 25/H/sub x/

    SciTech Connect

    Weaver, J.H.; Peterson, D.T.; Butera, R.A.; Fujimori, A.

    1985-09-15

    The electronic interactions of hydrogen in a host metal lattice have been studied with synchrotron-radiation photoemission for low-x solid solution phases of ScH/sub x/, YH/sub x/, and V/sub 0.75/Nb/sub 0.25/H/sub x/ for 0.15< or =x< or =0.25. For each system, a single well-defined hydrogen-induced feature is observed 5 eV below the Fermi level due to the local interaction of H with bonding metal-derived states, in agreement with linear combination of atomic orbitals save no evidence for hydride formation induced by cleaving the ..cap alpha..-phase hydride samples.

  19. Fabrication and characterization of binary piezoelectric (Bi1/2Na1/2)TiO3-Ba(Mn1/3Nb2/3)O3 solid solutions

    NASA Astrophysics Data System (ADS)

    Matsumato, Hirokazu; Kobune, Masafumi; Kikuchi, Takeyuki

    2014-12-01

    High-density solid solutions with compositions of (1- x)(Bi1/2Na1/2)TiO3- xBa(Mn1/3Nb2/3)O3 (BNT-BMN), with x = 0 - 0.06, were prepared by using the conventional ceramic fabrication process. The optimal composition that yielded the best piezoelectric properties for high-power piezoelectric applications was investigated. X-ray diffraction (XRD) analyses of BNT-BMN with x = 0 - 0.06 suggested that the rhombohedral-pseudocubic morphotropic phase boundary (MPB) for this material system is in the compositional region 0.035 ≤ x ≤ 0.04 at room temperature. A hard-mode BNT-BMN with x = 0.03, which lay on the rhombohedral side near the MPB region, exhibited excellent piezo- and ferroelectric properties.

  20. Relaxor Behavior and Dielectric Relaxation in Lead-Free Solid Solutions of (1 - x)(Bi0.5Na0.5TiO3)- x(SrNb2O6)

    NASA Astrophysics Data System (ADS)

    Bajpai, P. K.; Singh, K. N.; Tamrakar, Preeti

    2016-02-01

    Lead-free compositions (1 - x) (Bi0.5Na0.5TiO3)- x(SrNb2O6) (BNT-SN) are synthesized by a simple solid state reaction route. SN diffuse in distorted perovskite BNT for low concentrations of SN ( x ≤ 0.03) and are stabilized in rhombohedral perovskite phase with experimentally observed relative density of the ceramics >92%. A temperature-dependent dielectric response exhibits a broad dielectric peak that shows frequency-dependent shifts towards higher temperatures reflecting typical relaxor behavior. Modified Curie-Weiss law and Lorentz-type empirical relationships are used to fit the dielectric data that exhibit almost complete diffuse phase transition characteristics. In addition, significant dielectric dispersion is observed in a low-frequency regime in both components of the dielectric response and a small dielectric relaxation peak is observed. Cole-Cole plots indicate the poly-dispersive nature of the dielectric relaxation.

  1. New solid conductors of Na/+/ and K/+/ ions

    NASA Technical Reports Server (NTRS)

    Singer, J.; Fielder, W. L.; Kautz, H. E.; Fordyce, J. S.

    1976-01-01

    About 40 structure types for solid conductors of Na(+) and K(+) ions are surveyed. Five compounds in three structure types are discovered to be good solid conductors of alkali metal ions, capable of ion transport with conductivities in the vicinity of 0.00001/ohm-cm at 25 C. These compounds are a bcc form of NaSbO3, an orthorhombic layer structure of the composition 2M2O.3Nb2O5 with M equal to Na or K, and the Na pyrochlores NaTa2O5F and NaTaWO6. Ion exchange is required to produce each of these Na compounds. Only the 2K2O.3Nb2O5 can so far be synthesized directly from the oxides and thus is the only one which can be sintered readily. The niobate is about as good a conductor of K(+) ion as is K-beta alumina. The NaSbO3 compares well with Na beta at 280 C. A number of phase diagrams are developed.

  2. New solid conductors of Na/+/ and K/+/ ions

    NASA Technical Reports Server (NTRS)

    Singer, J.; Fielder, W. L.; Kautz, H. E.; Fordyce, J. S.

    1976-01-01

    About 40 structure types for solid conductors of Na(+) and K(+) ions are surveyed. Five compounds in three structure types are discovered to be good solid conductors of alkali metal ions, capable of ion transport with conductivities in the vicinity of 0.00001/ohm-cm at 25 C. These compounds are a bcc form of NaSbO3, an orthorhombic layer structure of the composition 2M2O.3Nb2O5 with M equal to Na or K, and the Na pyrochlores NaTa2O5F and NaTaWO6. Ion exchange is required to produce each of these Na compounds. Only the 2K2O.3Nb2O5 can so far be synthesized directly from the oxides and thus is the only one which can be sintered readily. The niobate is about as good a conductor of K(+) ion as is K-beta alumina. The NaSbO3 compares well with Na beta at 280 C. A number of phase diagrams are developed.

  3. Rapid solidification of Nb-base alloys

    NASA Technical Reports Server (NTRS)

    Gokhale, A. B.; Javed, K. R.; Abbaschian, G. J.; Lewis, R. E.

    1988-01-01

    New Nb-base alloys are of interest for aerospace structural applications at high temperatures, viz, 800 to 1650 C. Fundamental information regarding the effects of rapid solidification in achieving greatly refined microstructures, extended solid solubility, suppression of embrittling equilibrium phases, and formation of new phases is desired in a number of Nb-X alloys. The microstructures and selected properties of Nb-Si and other Nb-base alloys are presented for materials both rapidly quenched from the equilibrium liquidus and rapidly solidified following deep supercooling. Electromagnetic levitation was used to achieve melting and supercooling in a containerless inert gas environment. A variety of solidification conditions were employed including splatting or drop casting of supercooled samples. The morphology and composition of phases formed are discussed in terms of both solidification history and bulk composition.

  4. Investigation on structural, Mössbauer and ferroelectric properties of (1-x)PbFe0.5Nb0.5O3-(x)BiFeO3 solid solution

    NASA Astrophysics Data System (ADS)

    Dadami, Sunanda T.; Matteppanavar, Shidaling; Shivaraja, I.; Rayaprol, Sudhindra; Angadi, Basavaraj; Sahoo, Balaram

    2016-11-01

    In this study, (1-x)PbFe0.5Nb0.5O3(PFN)-(x)BiFeO3(BFO) multiferroic solid solutions with x=0.0, 0.1, 0.2, 0.3 and 0.4 were synthesized through single step solid state reaction method and characterized thoroughly through X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infra-Red (FTIR), Raman, Mössbauer spectroscopy and ferroelectric studies. The room temperature (RT) XRD studies confirmed the formation of single phase with negligible amount of secondary phases (x=0.2 and 0.4). The zoomed XRD patterns of (1-x)PFN-(x)BFO solid solutions showed the clear structural phase transition from monoclinic (Cm) to rhombohedral (R3c) at x=0.4. The Raman spectra of the (1-x)PFN-(x)BFO solid solutions showed the composition dependent phase transition from monoclinic (Cm) to rhombohedral (R3c). With increasing x in PFN, the modes related monoclinic symmetry changes to those of rhombohedral symmetry. The RT Mössbauer spectroscopy results evidenced the existence of composition dependent phase transition from paramagnetic to weak antiferromagnetic ordering and weak antiferromagnetic to antiferromagnetic ordering. The Mössbauer spectroscopy showed paramagnetic behavior with a doublet for x=0.0, 0.1 and 0.2 are shows the weak antiferromagnetic with paramagnetic ordering. For x=0.3 and 0.4 shows the sextet pattern and it is a clear evidence of antiferromagnetism. The ferroelectric (P-E) loops at RT indicate the presence of small polarization, as the x concentration increases in PFN, the remnant polarization and coercive field were decreased, which may due to the increase in the conductivity and leaky behavior of the samples.

  5. Piezoelectric and ferroelectric properties of lead-free (1-x)(Na1-yKy)(Nb1-zSbz)O3-xBaTiO3 solid solution

    NASA Astrophysics Data System (ADS)

    Sasikumar, S.; Saravanan, R.; Aravinth, K.

    2017-05-01

    The solid solutions of lead-free (1-x)(Na1-yKy)(Nb1-zSbz)O3-xBaTiO3 (with x=0.1, 0.2; y=0.03, 0.05; z=0.05, 0.1) (abbreviated as (1-x)NKNS-xBT) ceramics have been synthesized using conventional solid-state reaction method. The results of X-ray diffraction analysis show that all the grown specimens of NKNS display typical perovskite structure. With BaTiO3 (BT) addition, a structural phase transition from tetragonal to cubic structure has been observed. The structural parameters of (1-x)NKNS-xBT powders were determined by profile refinements based on the analysis of X-ray powder diffraction. The charge density distributions of the prepared samples have been investigated by observed structure factors to understand the chemical bonding nature of (1-x)NKNS-xBT powders. The optical absorption of the ceramics has been investigated using UV-visible spectrophotometer. Scanning electron microscopic (SEM) measurements were performed to study the surface morphology of the prepared solid solutions. The elemental compositions of the (1-x)NKNS-xBT samples were analyzed by energy-dispersive X-ray (EDS) spectrometer. The dielectric constant versus temperature plots of the solid solutions exhibit ferroelectric to paraelectric phase transition, which is dependent on the BaTiO3 content. The ferroelectric nature of the samples has been determined through polarization and electric field hysteresis measurements.

  6. Ionic Conductivity in Lithium Hexaoxometallate Solid Solutions.

    DTIC Science & Technology

    1983-07-26

    Bi2O3 and ZrO 2. Mixtures of appropriate composition were throughly mixed using agate mortar in a He dry box. For example, Li7Tal-xNbxO6 and Li7Tal...xBixO6 were prepared from Li20, Ta205 and Nb2O5 , and Li20, Ta205 and Bi2O3 , respectively, according to the following equation 7Li2O + (l-x)Ta2O5

  7. Pressure dependence of the monoclinic phase in (1–x)Pb(Mg1/3Nb2/3)O3-xPbTiO₃ solid solutions

    SciTech Connect

    Ahart, Muhtar; Sinogeikin, Stanislav; Shebanova, Olga; Ikuta, Daijo; Ye, Zuo-Guang; Mao, Ho-kwang; Cohen, R. E.; Hemley, Russell J.

    2012-12-26

    We combine high-pressure x-ray diffraction, high-pressure Raman scattering, and optical microscopy to investigate a series of (1–x)Pb(Mg1/3Nb2/3)O3-xPbTiO₃ (PMN-xPT) solid solutions (x=0.2, 0.3, 0.33, 0.35, 0.37, 0.4) in diamond anvil cells up to 20 GPa at 300 K. The Raman spectra show a peak centered at 380 cm⁻¹ starting above 6 GPa for all samples, in agreement with previous observations. X-ray diffraction measurements are consistent with this spectral change indicating a structural phase transition; we find that the triplet at the pseudocubic (220) Bragg peak merges into a doublet above 6 GPa. Our results indicate that the morphotropic phase boundary region (x=0.33–0.37) with the presence of monoclinic symmetry persists up to 7 GPa. The pressure dependence of ferroelectric domains in PMN-0.32PT single crystals was observed using a polarizing optical microscope. The domain wall density decreases with pressure and the domains disappear at a modest pressure of 3 GPa. We propose a pressure-composition phase diagram for PMN-xPT solid solutions.

  8. Pressure dependence of the monoclinic phase in (1–x)Pb(Mg1/3Nb2/3)O3-xPbTiO₃ solid solutions

    DOE PAGES

    Ahart, Muhtar; Sinogeikin, Stanislav; Shebanova, Olga; ...

    2012-12-26

    We combine high-pressure x-ray diffraction, high-pressure Raman scattering, and optical microscopy to investigate a series of (1–x)Pb(Mg1/3Nb2/3)O3-xPbTiO₃ (PMN-xPT) solid solutions (x=0.2, 0.3, 0.33, 0.35, 0.37, 0.4) in diamond anvil cells up to 20 GPa at 300 K. The Raman spectra show a peak centered at 380 cm⁻¹ starting above 6 GPa for all samples, in agreement with previous observations. X-ray diffraction measurements are consistent with this spectral change indicating a structural phase transition; we find that the triplet at the pseudocubic (220) Bragg peak merges into a doublet above 6 GPa. Our results indicate that the morphotropic phase boundary regionmore » (x=0.33–0.37) with the presence of monoclinic symmetry persists up to 7 GPa. The pressure dependence of ferroelectric domains in PMN-0.32PT single crystals was observed using a polarizing optical microscope. The domain wall density decreases with pressure and the domains disappear at a modest pressure of 3 GPa. We propose a pressure-composition phase diagram for PMN-xPT solid solutions.« less

  9. Pressure dependence of the monoclinic phase in (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 solid solutions

    NASA Astrophysics Data System (ADS)

    Ahart, Muhtar; Sinogeikin, Stanislav; Shebanova, Olga; Ikuta, Daijo; Ye, Zuo-Guang; Mao, Ho-kwang; Cohen, R. E.; Hemley, Russell J.

    2012-12-01

    We combine high-pressure x-ray diffraction, high-pressure Raman scattering, and optical microscopy to investigate a series of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) solid solutions (x=0.2, 0.3, 0.33, 0.35, 0.37, 0.4) in diamond anvil cells up to 20 GPa at 300 K. The Raman spectra show a peak centered at 380 cm-1 starting above 6 GPa for all samples, in agreement with previous observations. X-ray diffraction measurements are consistent with this spectral change indicating a structural phase transition; we find that the triplet at the pseudocubic (220) Bragg peak merges into a doublet above 6 GPa. Our results indicate that the morphotropic phase boundary region (x=0.33-0.37) with the presence of monoclinic symmetry persists up to 7 GPa. The pressure dependence of ferroelectric domains in PMN-0.32PT single crystals was observed using a polarizing optical microscope. The domain wall density decreases with pressure and the domains disappear at a modest pressure of 3 GPa. We propose a pressure-composition phase diagram for PMN-xPT solid solutions.

  10. Room temperature neutron diffraction and magnetic studies of multiferroic Pb{sub 0.9}Bi{sub 0.1}Fe{sub 0.55}Nb{sub 0.45}O{sub 3} solid solution

    SciTech Connect

    Dadami, S. T.; Matteppanavar, S.; Shivaraja, I.; Angadi, B.; Rayaprol, S.; Deshpande, S. K.

    2016-05-23

    The Pb{sub 0.9}Bi{sub 0.1}Fe{sub 0.55}Nb{sub 0.45}O{sub 3} (PBFNO) solid solution was synthesized by single step solid state reaction method and the optimized parameters are 700°C for 2hr (calcination) and 800°C for 3hr (sintering). The formation of desired material was confirmed using X-Ray Diffraction (XRD) and Neutron Diffraction (ND) studies. The structural and magnetic properties of the sintered pellets were investigated at room temperature (RT) through XRD, ND and Magnetic (M-H) studies. The structural analysis was carried out by Rietveld refinement through the Full Prof program. Rietveld refined XRD and ND patterns confirms the monoclinic structure with Cm space group and obtained cell parameters from the ND data are a = 5.651(2) Å, b = 5.658(2) Å, c = 4.005(1) Å and α = 90°, β = 89.98(1)°, γ = 90°. RT M-H curve studies have been carried out. It shows the clear opening of hysteresis (M–H) loop, is evidenced as the existence of weak ferromagnetism at RT. The M-H data shows existence weak ferromagnetism embedded in an antiferromagnetic matrix structure. The dielectric constant with frequency shows the formation of barrier layers at the grain and grain boundary interfaces gives rise to interfacial space charge polarization.

  11. Morphotropic phase boundary of heterovalent perovskite solid solutions: Experimental and theoretical investigation of Pb Sc1/2 Nb1/2 O3 -PbTi O3

    NASA Astrophysics Data System (ADS)

    Haumont, R.; Al-Barakaty, A.; Dkhil, B.; Kiat, J. M.; Bellaiche, L.

    2005-03-01

    X-ray and neutron diffraction techniques are combined with first-principles-based simulations to derive and understand the structural properties of Pb(Sc,Nb,Ti)O3 (PSN-PT) near its morphotropic phase boundary (MPB). An analysis of our measurements yields, at room and low temperatures, an overall tetragonal T —monoclinic MC —monoclinic MB —rhombohedral R path (when adopting the notations of Vanderbilt and Cohen, Phys. Rev. B 63, 94108 (2001) for the monoclinic phases) as the Ti composition decreases across the MPB. A composition- and temperature-dependent significant mixing between some of these phases is also measured and reported here. The overall T-MC-MB-R path, which has also been proposed for Pb(Mg,Nb,Ti)O3 [A. K. Singh and D. Pandey, Phys. Rev. B 67, 64102 (2003)] is rather complex since it involves a change in the polarization path: this polarization first rotates in a (100) plane for the T-MC part of the path and then in a (1-10) plane for the MB-R part of the path. Moreover, a comparison between these measurements and first-principles-based calculations raises the possibility that this complex path, and the associated MC and MB phases, can only occur if the samples exhibit a deviation from a perfectly homogeneous and disordered situation, e.g. possess nanoscale chemically-ordered regions. If not, homogeneously disordered PSN-PT is predicted to exhibit at low temperature the same polarization path as Pb(Zr,Ti)O3 , that is T -monoclinic MA-R which involves a “single” polarization rotation in a (1-10) plane. Nanoscale inhomogeneity may thus play a key role on the macroscopic properties of PSN-PT, in particular, and of other heterovalent complex solid solutions, in general, near their MPB.

  12. Synthesis of a 12R-type hexagonal perovskite solid solution Sr3NdNb(3-x)Ti(x)O(12-δ) and the influence of acceptor doping on electrical properties.

    PubMed

    Chinelatto, Adilson L; Boulahya, Khalid; Pérez-Coll, Domingo; Amador, Ulises; Tabacaru, Corina; Nicholls, Simon; Hoelzel, Markus; Sinclair, Derek C; Mather, Glenn C

    2015-04-28

    A solid solution forms for Sr3NdNb(3-x)Ti(x)O(12-δ) with approximate limits 0 ≤ x ≤ 0.06. The system crystallizes with a 12R-type hexagonal perovskite structure in the space group R3, as determined by neutron diffraction and selected area electron diffraction. The electrical properties of the end members have been investigated by impedance spectroscopy in the temperature range 550-800 °C under various gas atmospheres and as a function of oxygen and water-vapour partial pressure. Proton transport dominates under wet oxidising conditions in the temperature range 550-700 °C, as confirmed by the H(+)/D(+) isotope effect. Acceptor doping considerably enhances proton conductivity with a value of 3.3 × 10(-6) S cm(-1) for the bulk response of x = 0.06 at 700 °C in moistened air. The presence of a -¼ slope for both doped and undoped samples in the range 10(-19) ≤ pO2 ≤ 10(-8) atm at 900 °C indicates n-type transport under reducing conditions following the extrinsic model attributable to acceptor centres. The conductivity is essentially independent of pO2 at 600 °C under dry oxidising conditions, consistent with oxide-ion transport; a positive power-law dependence at higher temperature indicates extrinsic behaviour and a significant electron-hole contribution. The dielectric constant at RT of nominally stoichiometric Sr3NdNb3O12 is εr ∼ 37, with a moderately high quality factor of Q × f ∼ 16,400 GHz at fr ∼ 6.4 GHz. The temperature coefficient of resonant frequency of x = 0 is τf ∼ 12 ppm °C(-1), which lowers to -3 ppm °C(-1) for the Ti-doped phase x = 0.06.

  13. Sodium niobate adsorbents doped with tantalum (TaV) for the removal of bivalent radioactive ions in waste waters.

    PubMed

    Paul, Blain; Yang, Dongjiang; Martens, Wayde N; Frost, Ray L

    2011-04-01

    Sodium niobates doped with different amounts of tantalum (Ta(V)) were prepared via a thermal reaction process. It was found that pure nanofibrils and bar like solids can be obtained when tantalum is introduced into the reaction system. For the well crystallized fibril solids, the Na(+) ions are difficult to exchange, and the radioactive ions such as Sr(2+) and Ra(2+) just deposit on the surface of the fibers during the sorption process, resulting in lower sorption capacity and distribution coefficients (K(d)). However, the bar like solids are poorly crystallized and have many exchangeable Na(+) ions. They are able to remove highly hazardous bivalent radioactive isotopes such as Sr(2+) and Ra(2+) ions. Even in the presence of many Na(+) ions, they also have higher K(d). More importantly, such sorption finally intelligently triggers considerable collapse of the structure, resulting in permanent entrapment of the toxic bivalent cations in the solids, so that they can be safely disposed of. This study highlights new opportunities for the preparation of Nb-based adsorbents to efficiently remove toxic radioactive ions from contaminated water. Copyright © 2010 Elsevier Inc. All rights reserved.

  14. Atomic and electronic structure of Ni-Nb metallic glasses

    SciTech Connect

    Yuan, C. C.; Yang, Y.-F. Xi, X. K.

    2013-12-07

    Solid state {sup 93}Nb nuclear magnetic resonance spectroscopy has been employed to investigate the atomic and electronic structures in Ni-Nb based metallic glass (MG) model system. {sup 93}Nb nuclear magnetic resonance (NMR) isotropic metallic shift of Ni{sub 60}Nb{sub 35}Sn{sub 5} has been found to be ∼100 ppm lower than that of Ni{sub 60}Nb{sub 35}Zr{sub 5} MG, which is correlated with their intrinsic fracture toughness. The evolution of {sup 93}Nb NMR isotropic metallic shifts upon alloying is clearly an electronic origin, as revealed by both local hyperfine fields analysis and first-principle computations. This preliminary result indicates that, in addition to geometrical considerations, atomic form factors should be taken into a description of atomic structures for better understanding the mechanical behaviors of MGs.

  15. Interface Roughness in Copper-Tantalum Wire and NB3SN Superconductor Composites

    NASA Astrophysics Data System (ADS)

    Hartwig, K. T.; Balachandran, S.; Mathaudhu, S. N.; Barber, R. E.; Pyon, T.; Griffin, R. B.

    2008-03-01

    Poor deformation behavior of tantalum (Ta) sheet used for tin diffusion barriers in Nb3Sn composite superconductors can lead to Ta layer rupture and even strand fracture during wire drawing. These problems arise because the Ta layer deforms nonuniformly as it is reduced in thickness. The origin of the problem resides in the microstructure of the Ta and the co-deformation mechanics of relatively strong body centered cubic Ta with surrounding weaker and more ductile face centered cubic Cu. In an attempt to remedy this problem, 25 mm square bars of Ta were processed by multi-axis severe plastic deformation (SPD) via equal channel angular extrusion (ECAE), then rolled to sheet and recrystallized. The SPD processing was done to refine the microstructure and reduce nonuniformities in grain size and texture. Measurements of the Cu-Ta interface roughness in experimental Cu-Ta composite wires were made and compared with the interface roughness seen in commercial Ta diffusion barrier layers. Results show that Ta sheet made from SPD processed bulk Ta co-deforms well with Cu and leads to less interface roughening than is developed in commercial Ta sheet material fabricated into superconductor wire.

  16. A new synthesis route of perovskite-related Sr2TaO3N oxynitride via Sr2Ta6O10.188

    NASA Astrophysics Data System (ADS)

    Sarda, Narendra G.; Hayashi, Takanori; Takeuchi, Yuta; Harada, Kyosuke; Murai, Kei-Ichiro; Moriga, Toshihiro

    2016-12-01

    Formation process of the new layered perovskite Sr2TaO3N oxynitride having a K2NiF4-type structure from oxide precursor of Sr6Ta2O10.188 was examined under an ammonia flow. Using the oxide precursor, it is possible to make a Sr2TaO3N phase within a shorter period of the nitridation than the previous paper reported by Marchant et al. (J. Solid State Chem., 146: 390-393(1999)). Excess amount of strontium deviated from the stoichiometric composition of Sr/Ta=2 also seemed to promote the formation of Sr2TaO3N under the ammonia flow. The synthesized Sr2TaO3N after two cycles of 24h-nitridation of the oxide precursors showed brighter reddish-orange color than SrTaO2N.

  17. Solid-state chemistry on a surface and in a beaker: Unconventional routes to transition metal chalcogenide nanomaterials

    SciTech Connect

    Stender, Christopher L.; Sekar, Perumal; Odom, Teri W.

    2008-07-15

    This article focuses on two different approaches to create nanoscale transition metal chalcogenide materials. First, we used chemical nanofabrication, a combination of top-down patterning and bottom-up solid-state synthesis, to achieve control over the shape, size, and ordering of the patterned nanomaterials. We demonstrated orientational control over nanocrystals within sub-300 nm patterns of MoS{sub 2} and formed free-standing nanostructures of crystalline NiS{sub 2}. In addition, crossed line arrays of mixed metal chalcogenide nanostructures were achieved, and TaS{sub 2} nanopatterns were made by the chemical transformation of tantalum oxide templates. Second, we developed a one-pot procedure using molecular precursors to synthesize two-dimensional NbSe{sub 2}, TaS{sub 2} and TaSe{sub 2} nanoplates and one-dimensional NbSe{sub 2} wires depending on the relative amount of surfactants in the reaction mixture. Prospects for these transition metal chalcogenide nanomaterials with controlled shapes and morphologies will be discussed. - Graphical abstract: This paper describes how transition metal chalcogenide nanomaterials can be produced by two approaches. First, chemical nanofabrication-a combination of top-down patterning and bottom-up solid-state synthesis-was used to achieve control over the shape, size, and ordering of patterned nanomaterials. Second, a one-pot procedure using molecular precursors was developed to synthesize two-dimensional nanoplates and one-dimensional nanowires of conducting transition metal dichalcogenides.