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Sample records for nb mo hf

  1. A three-dimensional extended Sb network in the metallic antimonides (M',Ti)5Sb8 (M' = Zr, Hf, Nb, Mo).

    PubMed

    Kleinke, H

    2001-01-01

    (M',Ti)5Sb8 was prepared from the melt by arc-melting suitable mixtures of Ti, TiSb2, and M'Sb2, respectively. This phase exists at least with M' = Zr, Hf, Nb, and Mo. A significant phase range for Zr delta Ti5 - delta Sb8 was found to be within 1.10(8) < or = delta < or = 3.9(3). All (M',Ti)5Sb8 representatives investigated occur in the same, yet hitherto unknown structure type, as determined by single-crystal analyses. E.g., the lattice dimensions of Zr delta Ti5 - delta Sb8 range from a = 654.49(3) pm, c = 2662.4(2) pm for delta = 1.10(8) to a = 671.06(6), c = 2679.7(4) pm for delta = 3.9(3) (space group I4(1)22, No. 98, Z = 4). The three chemically inequivalent metal sites are statistically occupied by different mixtures of the M atoms M' and Ti, included in a three-dimensional network of Sb atoms on 6- to 8-fold Sb coordinated positions. Sb-Sb bonds of intermediate lengths occur in addition to the predominating heteronuclear M-Sb bonds. Physical property measurements of (Zr,Ti)5Sb8 reveal these phases being metallic exhibiting specific resistances of several m omega.cm and a small Seebeck coefficient at room temperature, in agreement with the results of the electronic structure calculations on the LMTO and extended Hückel levels. The calculations indicate a possible change to semiconducting properties by heavy doping.

  2. 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.

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

    PubMed

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

    2013-12-01

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

  4. Effect of Li/Nb Ratio on Growth and Spectrometric Characterization of Hf:Fe:LiNbO3 Crystals

    NASA Astrophysics Data System (ADS)

    Dai, Li; Wu, Shi-Ping; Guo, Jing-Jie; Xu, Chao; Su, Yan-Qing; Xu, Yu-Heng

    Hf:Fe:LiNbO3 crystals were grown by the Czochralski technique with various ratios of Li/Nb = 0.946, 1.05, 1.20 and 1.38 in the melt. The crystal composition and defect structure were analyzed by XRD, UV-Vis and IR spectroscopy. The results show that the threshold concentration of Hf in LiNbO3 crystals decrease with the increasing of the Li/Nb ratio; when the Li/Nb ratio is 1.05, the threshold concentration of Hf is less than 2 mol%, largely under the threshold concentration of Hf ions in congruent Hf:Fe:LiNbO3 crystal (4 mol).1-3 With the increase of Li/Nb, Hf ions first replace the Nb4+ Li; when the concentration of Hf ions is higher than the threshold value, Hf ions occurs on normal Nb and Li sites.

  5. 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.

    PubMed

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

    2015-03-18

    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 Co(43.5)Ta(6.1)B(50.4) 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.

  6. In vitro cytotoxicity and hemocompatibility studies of Ti-Nb, Ti-Nb-Zr and Ti-Nb-Hf biomedical shape memory alloys.

    PubMed

    Wang, B L; Li, L; Zheng, Y F

    2010-08-01

    The in vitro cytotoxicity and hemocompatibility of the Ti-Nb, Ti-Nb-Zr and Ti-Nb-Hf biomedical shape memory alloys (SMAs) were investigated by cell culture (L-929 fibroblast cell), hemolytic test and platelet adhesion test, with CP Ti as a reference material. The cytotoxicity test indicates that all the Ti-Nb, Ti-Nb-Zr and Ti-Nb-Hf SMAs show over 94% cell viability for different incubation times (2, 4 and 7 days) in comparison with a negative control and CP Ti. The cell morphology observation shows good polygon-like adherent growth and proliferation of L-929 in the extracts of all the test samples and CP Ti. These results suggest excellent cytocompatibility for the Ti-Nb, Ti-Nb-Zr and Ti-Nb-Hf SMAs. The hemolytic test reveals that the hemolysis ratios of the Ti-Nb, Ti-Nb-Zr and Ti-Nb-Hf alloys are far less than 5%, so they cannot give rise to acute hemolysis. The platelet morphology observation shows almost the same adhered platelet morphology and activation ratio for the test samples in comparison with CP Ti, except the Ti-22Nb-6Hf alloy, which shows a lower activation ratio of platelets, indicating excellent blood compatibility. Therefore, it is proposed that the Ti-Nb, Ti-Nb-Zr and Ti-Nb-Hf SMAs will be candidates to replace Ti-Ni for biomedical applications.

  7. Synthesis of amorphous alloys and amorphous-crystalline composites in the Cu-Nb-Hf system by ion beam mixing

    SciTech Connect

    Luo, S. Y.; Cui, Y. Y.; Wang, T. L.; Ding, N.; Li, J. H.; Liu, B. X.

    2011-06-15

    Seven sets of Cu-Nb-Hf multilayered films were designed and prepared with the overall compositions of Cu{sub 21}Nb{sub 65}Hf{sub 14}, Cu{sub 33}Nb{sub 49}Hf{sub 18}, Cu{sub 34}Nb{sub 34}Hf{sub 32}, Cu{sub 34}Nb{sub 10}Hf{sub 56}, Cu{sub 50}Nb{sub 23}Hf{sub 27}, Cu{sub 58}Nb{sub 10}Hf{sub 32}, and Cu{sub 70}Nb{sub 8}Hf{sub 22}, and an ion beam mixing experiment was then conducted using 200 keV xenon ions. It is found that the Cu-Nb-Hf system is a metallic glass forming one, and the single amorphous alloys could be synthesized in the Cu-Nb-based alloys with less than 18 at.% of Hf as a third addition. Also, when the Hf concentration is greater than 18 at.%, i.e., at the compositions of Cu{sub 34}Nb{sub 34}Hf{sub 32}, Cu{sub 34}Nb{sub 10}Hf{sub 56}, Cu{sub 50}Nb{sub 23}Hf{sub 27}, Cu{sub 58}Nb{sub 10}Hf{sub 32}, and Cu{sub 70}Nb{sub 8}Hf{sub 22}, ion beam mixing resulted in the formation of amorphous-crystalline composites, which might have better mechanical properties than single-phase glassy alloys. In addition, a detailed discussion was presented for the formation mechanism of the amorphous alloys and amorphous-crystalline composites.

  8. Low modulus Ti-Nb-Hf alloy for biomedical applications.

    PubMed

    González, M; Peña, J; Gil, F J; Manero, J M

    2014-09-01

    β-Type titanium alloys with a low elastic modulus are a potential strategy to reduce stress shielding effect and to enhance bone remodeling in implants used to substitute failed hard tissue. For biomaterial application, investigation on the mechanical behavior, the corrosion resistance and the cell response is required. The new Ti25Nb16Hf alloy was studied before and after 95% cold rolling (95% C.R.). The mechanical properties were determined by tensile testing and its corrosion behavior was analyzed by potentiostatic equipment in Hank's solution at 37°C. The cell response was studied by means of cytotoxicity evaluation, cell adhesion and proliferation measurements. The stress-strain curves showed the lowest elastic modulus (42GPa) in the cold worked alloy and high tensile strength, similar to that of Ti6Al4V. The new alloy exhibited better corrosion resistance in terms of open circuit potential (EOCP), but was similar in terms of corrosion current density (iCORR) compared to Ti grade II. Cytotoxicity studies revealed that the chemical composition of the alloy does not induce cytotoxic activity. Cell studies in the new alloy showed a lower adhesion and a higher proliferation compared to Ti grade II presenting, therefore, mechanical features similar to those of human cortical bone and, simultaneously, a good cell response.

  9. 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.

  10. Air sensitivity of MoS2, MoSe2, MoTe2, HfS2, and HfSe2

    NASA Astrophysics Data System (ADS)

    Mirabelli, Gioele; McGeough, Conor; Schmidt, Michael; McCarthy, Eoin K.; Monaghan, Scott; Povey, Ian M.; McCarthy, Melissa; Gity, Farzan; Nagle, Roger; Hughes, Greg; Cafolla, Attilio; Hurley, Paul K.; Duffy, Ray

    2016-09-01

    A surface sensitivity study was performed on different transition-metal dichalcogenides (TMDs) under ambient conditions in order to understand which material is the most suitable for future device applications. Initially, Atomic Force Microscopy and Scanning Electron Microscopy studies were carried out over a period of 27 days on mechanically exfoliated flakes of 5 different TMDs, namely, MoS2, MoSe2, MoTe2, HfS2, and HfSe2. The most reactive were MoTe2 and HfSe2. HfSe2, in particular, showed surface protrusions after ambient exposure, reaching a height and width of approximately 60 nm after a single day. This study was later supplemented by Transmission Electron Microscopy (TEM) cross-sectional analysis, which showed hemispherical-shaped surface blisters that are amorphous in nature, approximately 180-240 nm tall and 420-540 nm wide, after 5 months of air exposure, as well as surface deformation in regions between these structures, related to surface oxidation. An X-ray photoelectron spectroscopy study of atmosphere exposed HfSe2 was conducted over various time scales, which indicated that the Hf undergoes a preferential reaction with oxygen as compared to the Se. Energy-Dispersive X-Ray Spectroscopy showed that the blisters are Se-rich; thus, it is theorised that HfO2 forms when the HfSe2 reacts in ambient, which in turn causes the Se atoms to be aggregated at the surface in the form of blisters. Overall, it is evident that air contact drastically affects the structural properties of TMD materials. This issue poses one of the biggest challenges for future TMD-based devices and technologies.

  11. Enhanced mechanical hardness in epitaxial nonisostructural Mo/NbN and W/NbN superlattices

    SciTech Connect

    Madan, A.; Wang, Y.; Barnett, S.A.; Engstroem, C.; Ljungcrantz, H.; Hultman, L.; Grimsditch, M.

    1998-07-01

    Epitaxial Mo/NbN and W/NbN superlattices with modulation wavelengths {Lambda} ranging from 1.3 to 120 nm were grown on MgO (001) substrates by dc reactive magnetron sputtering in Ar/N{sub 2} mixtures. The superlattices were shown to be epitaxial with nearly planar layers using high- and low-angle x-ray diffraction and transmission electron microscopy. Computer simulation fits of the x-ray data indicated that interface widths were {le}0.3thinspnm. The epitaxial relationship between the layers was (001){sub metal}{parallel}(001){sub NbN} and [110]{sub metal}{parallel}[100]{sub NbN}. The nanoindenter microhardness values from W/NbN and Mo/NbN superlattices with 50 volthinsp{percent} metal were nearly identical. The largest hardnesses were 30 GPa, observed at superlattice periods {Lambda}=2{endash}3thinspnm, compared to rule-of-mixtures values of 10 GPa. The hardness decreased with increasing {Lambda} above {approx}3thinspnm, following the dependences H=10.3+26.70{Lambda}{sup {minus}0.38}thinspGPa for Mo/NbN and H=12.88+22.1{Lambda}{sup {minus}0.3}thinspGPa for W/NbN. Hardness versus metal volume fraction with {Lambda}{approx}5thinspnm showed a flat-topped dependence. Brillouin scattering results for Mo/NbN superlattices showed a minor elastic anamoly at small {Lambda}. The hardness results are compared with theories for strengthening of multilayers. {copyright} {ital 1998 American Institute of Physics.}

  12. 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.

  13. 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

  14. 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.

  15. Entropy and Diffuse Scattering: Comparison of NbTiVZr and CrMoNbV

    NASA Astrophysics Data System (ADS)

    Widom, Michael

    2016-07-01

    The chemical disorder intrinsic to high-entropy alloys inevitably creates diffuse scattering in their X-ray or neutron diffraction patterns. Through first principles hybrid Monte Carlo/molecular dynamics simulations of two BCC high-entropy alloy forming compounds, CrMoNbV and NbTiVZr, we identify the contributions of chemical disorder, atomic size, and thermal fluctuations to the diffuse scattering. As a side benefit, we evaluate the reduction in entropy due to pair correlations within the framework of the cluster variation method. Finally, we note that the preference of Ti and Zr for hexagonal structures at low temperature leads to a mechanical instability reducing the local BCC character of NbTiVZr, while preserving global BCC symmetry.

  16. 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.

  17. 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.

  18. 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.

  19. 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

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

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

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

  1. Amorphous phase formation, spinodal decomposition, and fractal growth of nanocrystals in an immiscible Hf-Nb system studied by ion beam mixing and atomistic modeling

    SciTech Connect

    Tai, K. P.; He, X.; Liu, B. X.

    2008-04-15

    In the equilibrium immiscible Hf-Nb system characterized by a positive heat of formation, five Hf-Nb metallic glasses with overall compositions of Hf{sub 84}Nb{sub 16}, Hf{sub 65}Nb{sub 35}, Hf{sub 45}Nb{sub 55}, Hf{sub 38}Nb{sub 62}, and Hf{sub 20}Nb{sub 80} are obtained by ion beam mixing with properly designed Hf-Nb multilayered films, suggesting a glass-forming composition range of 16-80 at. % of Nb. For the special case of Hf{sub 45}Nb{sub 55} located at the ridge point on the convex free energy curve, dual-glass phases are formed at a dose of 2x10{sup 15} Xe{sup +}/cm{sup 2}, which results from a spinodal decomposition of the expected Hf{sub 45}Nb{sub 55} amorphous phase. With increasing irradiation dose, fractal growth of nanocrystals (around 20 nm) appears in the major glass phase and the dimension is determined to be from 1.70 to 1.84 within a dose range of (4-7)x10{sup 15} Xe{sup +}/cm{sup 2}. In atomistic modeling, a n-body Hf-Nb potential is first constructed with the aid of ab initio calculations. Applying the constructed potential, molecular dynamics simulations using the hcp and bcc solid solution models, reveals an intrinsic glass-forming range to be within 15-83 at. % of Nb, which is compatible with the ion beam mixing experiments. Moreover, the formation of the metallic glasses and the fractal growth in association with the amorphous spinodal decomposition are also discussed in terms of the atomic collision theory and cluster-diffusion-limited-aggregation model.

  2. Two-dimensional semiconductor HfSe{sub 2} and MoSe{sub 2}/HfSe{sub 2} van der Waals heterostructures by molecular beam epitaxy

    SciTech Connect

    Aretouli, K. E.; Tsipas, P.; Tsoutsou, D.; Marquez-Velasco, J.; Xenogiannopoulou, E.; Giamini, S. A.; Vassalou, E.; Kelaidis, N.; Dimoulas, A.

    2015-04-06

    Using molecular beam epitaxy, atomically thin 2D semiconductor HfSe{sub 2} and MoSe{sub 2}/HfSe{sub 2} van der Waals heterostructures are grown on AlN(0001)/Si(111) substrates. Details of the electronic band structure of HfSe{sub 2} are imaged by in-situ angle resolved photoelectron spectroscopy indicating a high quality epitaxial layer. High-resolution surface tunneling microscopy supported by first principles calculations provides evidence of an ordered Se adlayer, which may be responsible for a reduction of the measured workfunction of HfSe{sub 2} compared to theoretical predictions. The latter reduction minimizes the workfunction difference between the HfSe{sub 2} and MoSe{sub 2} layers resulting in a small valence band offset of only 0.13 eV at the MoSe{sub 2}/HfSe{sub 2} heterointerface and a weak type II band alignment.

  3. Influence of Hf4+ ions concentration on the defect structure and exposure energy in Hf:Ho:LiNbO3

    NASA Astrophysics Data System (ADS)

    Dai, Li; Li, Dayong; Xu, Chao; Guo, Jingjie; Xu, Yuheng

    2013-02-01

    A series of Hf:Ho:LiNbO3 crystals with various levels of HfO2 doping were grown by the conventional Czochraski technique. The measurement of the Hf and Ho concentrations in the crystals was carried out with an inductively coupled plasma atomic emission spectrometer (ICP-OE/MS). The infrared (IR) spectrum was measured in order to analyze the defect structure of the crystals. The light-induced scattering was characterized quantitatively via the incident exposure energy. The results showed that the ability to resist the light-induced scattering was improved considerably with the increase in concentration of Hf4+, however, light-induced scattering resistance ability weakened as the concentration of Hf4+ surpasses the concentration to 8 mol%. The relationship between the defect structures and the light-induced scattering was discussed.

  4. 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.

  5. MoS{sub 2} on an amorphous HfO{sub 2} surface: An ab initio investigation

    SciTech Connect

    Scopel, W. L.; Miwa, R. H. Schmidt, T. M.; Venezuela, P.

    2015-05-21

    The energetic stability, electronic and structural properties of MoS{sub 2} adsorbed on an amorphous a-HfO{sub 2} surface (MoS{sub 2}/HfO{sub 2}) are examined through ab initio theoretical investigations. Our total energy results indicate that the formation of MoS{sub 2}/HfO{sub 2} is an exothermic process with an adsorption energy of 34 meV/Å{sup 2}, which means that it is more stable than similar systems like graphene/HfO{sub 2} and MoS{sub 2}/SiO{sub 2}. There are no chemical bonds at the MoS{sub 2}-HfO{sub 2} interface. Upon formation of MoS{sub 2}/HfO{sub 2}, the electronic charge distribution is mostly localized at the interface region with no net charge transfer between the adsorbed MoS{sub 2} sheet and –HfO{sub 2} surface. However, the MoS{sub 2} sheet becomes n-type doped when there are oxygen vacancies in the HfO{sub 2} surface. Further investigation of the electronic distribution reveals that there are no electron- and hole-rich regions (electron-hole puddles) on the MoS{sub 2} sheet, which makes this system promising for use in high-speed nanoelectronic devices.

  6. Electronic properties and transistors of the NbS2-MoS2-NbS2 nanoribbon heterostructure.

    PubMed

    Liu, Qi; OuYang, Fangping; Yang, Zhixiong; Peng, Shenglin; Zhou, Wenzhe; Zou, Hui; Long, Mengqiu; Pan, Jiangling

    2016-12-13

    Based on density function theory(DFT) and nonequilibrium Green's functions(NEGF), we construct a NbS2-MoS2-NbS2 nanoribbon inplane heterostructure. The effects of the channel length, width, chirality and vacancy of the heterostructure on the transport properties are systematically investigated. The electron transport of the armchair-edge heterostructure device shows ballistic transport properties, while the zigzag-edge heterostructure device exhibits resonance tunneling transport properties. Further study indicates the NbS2-MoS2-NbS2 field effect transistors(FETs) to be excellent ambipolar transistors. The FETs have high performances with current on/off ratio 4.7×10(5) and subthreshold swing 90mV/decade with the channel length m=16 and width n=6. The increase of the channel length will sharply reduce the off-state current and enhance the performances of the devices significantly.

  7. Electronic properties and transistors of the NbS2-MoS2-NbS2 NR heterostructure

    NASA Astrophysics Data System (ADS)

    Liu, Qi; Ouyang, Fangping; Yang, Zhixiong; Peng, Shenglin; Zhou, Wenzhe; Zou, Hui; Long, Mengqiu; Pan, Jiangling

    2017-02-01

    Based on density function theory and nonequilibrium Green’s functions, we construct a NbS2-MoS2-NbS2 NR inplane heterostructure. The effects of channel length, width, chirality and vacancy of the heterostructure on transport properties are systematically investigated. The electron transport of the armchair-edge heterostructure device shows ballistic transport properties, while the zigzag-edge heterostructure device exhibits resonance tunneling transport properties. Further study indicates NbS2-MoS2-NbS2 field effect transistors (FETs) to be excellent ambipolar transistors. The FETs have high performances with current on/off ratio 4.7 × 105 and subthreshold swing 90 mV/decade with channel length m = 16 and width n = 6. Increases in the channel length sharply reduce the off-state current and enhance the performance of the devices significantly.

  8. The crystal structure of Hf{sub 1.5+{delta}}Nb{sub 1.5-{delta}}As and structure-composition relations in the section Hf{sub 3}As-Nb{sub 3}As

    SciTech Connect

    Warczok, Piotr; Chumak, Igor

    2009-04-15

    The title compound Hf{sub 1.5+{delta}}Nb{sub 1.5-{delta}}As was characterized by means of single crystal X-ray diffraction. It represents a new structure type of intermetallic compounds (space group Pnma; lattice parameters a=7.142(2) A, b=3.583(2) A, c=11.640(2) A) and shows a small homogeneity range corresponding to (0.1Hf{sub 1.5+{delta}}Nb{sub 1.5-{delta}}As shows significant preferred site occupation of Hf and Nb at the three independent metal positions (differential fractional site occupancy). Structure-composition relations in the section Hf{sub 3}As-Nb{sub 3}As which also contains the new phase Hf{sub 2+{delta}}Nb{sub 1-{delta}}As with Ti{sub 3}P-type structure (space group P4{sub 2}/n) are discussed. Ground state energies of various ordered compounds with Hf{sub 1.5+{delta}}Nb{sub 1.5-{delta}}As-, Ti{sub 3}P- and Ta{sub 3}As-type structures were calculated from ab initio density functional theory. These energies were used for thermodynamic calculations employing the compound energy formalism (CEF) with the aim to model the experimentally observed site fraction data for both ternary compounds as well as Gibbs energies at the temperature of equilibration (1400 deg. C). - Graphical abstract: Hf{sub 1.5+{delta}}Nb{sub 1.5-{delta}}As with a new structure type (space group Pnma; lattice parameters a=7.142(2) A, b=3.583(2) A, c=11.640(2)A) was synthesized. Phase relations, energies and partial ordering in the section Hf{sub 3}As-Nb{sub 3}As were studied by first principle DFT calculations and thermodynamic modelling.

  9. Ultrasonic investigation of the superconducting properties of the Nb-Mo system

    NASA Technical Reports Server (NTRS)

    Lacy, L. L.

    1972-01-01

    The superconducting properties of single crystals of Nb and two alloys of Nb with Mo were investigated by ultrasonic techniques. The results of measurements of the ultrasonic attenuation and velocities as a function of temperature, Mo composition, crystallographic direction, and ultrasonic frequency are reported. The attenuation and small velocity changes associated with the superconductivity of the samples are shown to be dependent on the sample resistivity ratio which varied from 4.3 for Nb-9% Mo to 6500 for pure Nb. The ultrasonic attenuation data are analyzed in terms of the superconducting energy gap term of the BCS theory. A new model is proposed for the analysis of ultrasonic attenuation in pure superconductors with two partially decoupled energy bands. To analyze the attenuation in pure superconducting Nb, the existence of two energy gaps was assumed to be associated with the two partially decoupled energy bands. One of the gaps was found to have the normal BCS value of 3.4 and the other gap was found to have the anomalously large value of 10. No experimental evidence was found to suggest that the second energy gap had a different transition temperature. The interpretation of the results for the Nb-Mo alloys is shown to be complicated by the possible existence of a second superconducting phase in Nb-Mo alloys with a transition temperature of 0.35 of the transition temperature of the first phase. The elastic constants of Nb and Nb-Mo alloys are shown to be approximately independent of Mo composition to nine atomic percent Mo. These results do not agree with the current microscopic theory of transition temperature for the transition elements.

  10. In vitro performance assessment of new beta Ti-Mo-Nb alloy compositions.

    PubMed

    Neacsu, Patricia; Gordin, Doina-Margareta; Mitran, Valentina; Gloriant, Thierry; Costache, Marieta; Cimpean, Anisoara

    2015-02-01

    New β-titanium based alloys with low Young's modulus are currently required for the next generation of metallic implant materials to ensure good mechanical compatibility with bone. Several of these are representatives of the ternary Ti-Mo-Nb system. The aim of this paper is to assess the in vitro biological performance of five new low modulus alloy compositions, namely Ti12Mo, Ti4Mo32Nb, Ti6Mo24Nb, Ti8Mo16Nb and Ti10Mo8Nb. Commercially pure titanium (cpTi) was used as a reference material. Comparative studies of cell activity exhibited by MC3T3-E1 pre-osteoblasts over short- and long-term culture periods demonstrated that these newly-developed metallic substrates exhibited an increased biocompatibility in terms of osteoblast proliferation, collagen production and extracellular matrix mineralization. Furthermore, all analyzed biomaterials elicited an almost identical cell response. Considering that macrophages play a pivotal role in bone remodeling, the behavior of a monocyte-macrophage cell line, RAW 264.7, was also investigated showing a slightly lower inflammatory response to Ti-Mo-Nb biomaterials as compared with cpTi. Thus, the biological performances together with the superior mechanical properties recommend these alloys for bone implant applications.

  11. 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

  12. 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.

  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. Determination of Ti, Zr, Nb, V, W and Mo in seawater by a new online-preconcentration method and subsequent ICP-MS analysis

    NASA Astrophysics Data System (ADS)

    Poehle, Sandra; Schmidt, Katja; Koschinsky, Andrea

    2015-04-01

    We present a new method for the determination of Ti, Zr, Nb, V, W and Mo in seawater by adapting the online-preconcentration procedure with the system SeaFAST and subsequent analysis by ICP-MS to these metals. The trace elements Ti, Zr, Nb and W are present in seawater in ultratrace concentrations in the range of pmol kg-1, whereas Mo and V, which are biologically essential elements, are present in the concentration range of nmol kg-1. The online-preconcentration system we used consists of an autosampler, a sample loop, a preconcentration column and two valves controlling the sample loop and the preconcentration processes. The pre-packed preconcentration column contains a chelating resin with two functional groups, ethylenediamine triacetic acid (EDTriA) and iminodiacetic acid (IDA), immobilized on a polymer backbone. The preconcentration process was optimized for loading the sample and subsequent rinsing to remove residues of seawater matrix prior to elution with the optimized elution acid (0.5 M HNO3-0.002 M HF). We used acidified North Sea seawater (0.02 M HCl-0.002 M HF) for the method development. Samples and calibration standards were loaded onto the preconcentration column and after elution directly transferred to the quadrupole ICP-MS and measured immediately. Best results were achieved with matrix-matched calibration standards (0.6 M NaCl-0.02 M HCl-0.002 M HF) simulating acidified seawater samples. Titanium, Zr, Nb and W are measured simultaneously in one run, whereas V and Mo are determined simultaneously in a separate run. Low procedure blanks were calculated for Ti, Zr, Nb, W (635, 14.5, 1.35, 10.2 pmol kg-1) and for V and Mo, 9.79 and 5.61 nmol kg-1, respectively. Very good spike recoveries achieved with spiked North Sea water demonstrate the applicability for all six elements. Analysis of the seawater standard NASS-6 gave recoveries of 97-99% (0.9-2.2% standard deviation, SD) for Mo and V. We also provide Zr, Nb and W data for this reference standard

  15. Collective electronic behaviors of laterally heterostructured armchair MoS{sub 2}-NbS{sub 2} nanoribbons

    SciTech Connect

    Wu, Nannan; Zhou, Wenzhe; Zou, Hui; Chen, Yu; Yang, Zhixiong; Xiong, Xiang; Ouyang, Fangping

    2015-08-28

    Based on density functional theory, we have investigated the electronic properties of molybdenum disulfide-niobium disulfide hybrid nanoribbons (MoS{sub 2}-NbS{sub 2} NRs). It is found that the MoS{sub 2} edge, MoS{sub 2} center, NbS{sub 2} edge, and NbS{sub 2} center have distinct contributions to the collective electronic behaviors of MoS{sub 2}-NbS{sub 2} NRs. Its behavior, metallic or semiconductor, depends on whether the central area of NR contains NbS{sub 2} chain or not. This dependence has been also revealed in the electronic structures of NbS{sub 2}-MoS{sub 2}-NbS{sub 2} NR and MoS{sub 2}-NbS{sub 2}-MoS{sub 2} NR, of which the former is semiconductor and the latter is metal. In comparison with MoS{sub 2} NR of the same width, the hybrid has a different bandgap that was caused by the coupled effects between NbS{sub 2} edge and MoS{sub 2} edge. This fact makes MoS{sub 2}-NbS{sub 2} NRs a possible candidate for nanoelectronic devices based on heterostructured transition-metal dichalcogenide.

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

    DTIC Science & Technology

    2012-01-24

    metallic materials with higher melting points, such as refractory molybdenum (Mo) and niobium (Nb) alloys, are examined as alternatives by academic and...alloy was prepared by vacuum arc melting of the equimolar mixtures of the corresponding elements. Titanium , zirconium, and hafnium were in the form of...3.175 mm diameter slugs with purities of 99.98, 99.95, and 99.9%, respectively. Niobium and tantalum were in the form of 1.0 and 2.0 mm wires, and their

  17. Design of (Nb, Mo)40Ti30Ni30 alloy membranes for combined enhancement of hydrogen permeability and embrittlement resistance.

    PubMed

    Li, Xinzhong; Liang, Xiao; Liu, Dongmei; Chen, Ruirun; Huang, Feifei; Wang, Rui; Rettenmayr, Markus; Su, Yanqing; Guo, Jingjie; Fu, Hengzhi

    2017-03-16

    The effect of substitution of Nb by Mo in Nb40Ti30Ni30 was investigated with respect to microstructural features and hydrogen dissolution, diffusion and permeation. As-cast Nb40-xMoxTi30Ni30 (x = 0, 5, 10) alloys consist of primary bcc-Nb phase and binary eutectic (bcc-Nb + B2-TiNi). The substitution of Nb by Mo reduces the hydrogen solubility in alloys, but may increase (x = 5) or decrease (x = 10) the apparent hydrogen diffusivity and permeability. As-cast Nb35Mo5Ti30Ni30 exhibits a combined enhancement of hydrogen permeability and embrittlement resistance as compared to Nb40Ti30Ni30. This work confirms that Mo is a desirable alloying element in Nb that can contribute to a reduction in hydrogen absorption and an increase in intrinsic hydrogen diffusion, thus improving embrittlement resistance with minimal permeability penalty.

  18. Diffusion Barrier Selection from Refractory Metals (Zr, Mo and Nb) via Interdiffusion Investigation for U-Mo RERTR Fuel Alloy

    SciTech Connect

    K. Huang; C. Kammerer; D. D. Keiser, Jr.; Y. H. Sohn

    2014-04-01

    U-Mo alloys are being developed as low enrichment monolithic fuel under the Reduced Enrichment for Research and Test Reactor (RERTR) Program. Diffusional interactions between the U-Mo fuel alloy and Al-alloy cladding within the monolithic fuel plate construct necessitate incorporation of a barrier layer. Fundamentally, a diffusion barrier candidate must have good thermal conductivity, high melting point, minimal metallurgical interaction, and good irradiation performance. Refractory metals, Zr, Mo, and Nb are considered based on their physical properties, and the diffusion behavior must be carefully examined first with U-Mo fuel alloy. Solid-to-solid U-10wt.%Mo vs. Mo, Zr, or Nb diffusion couples were assembled and annealed at 600, 700, 800, 900 and 1000 degrees C for various times. The interdiffusion microstructures and chemical composition were examined via scanning electron microscopy and electron probe microanalysis, respectively. For all three systems, the growth rate of interdiffusion zone were calculated at 1000, 900 and 800 degrees C under the assumption of parabolic growth, and calculated for lower temperature of 700, 600 and 500 degrees C according to Arrhenius relationship. The growth rate was determined to be about 10 3 times slower for Zr, 10 5 times slower for Mo and 10 6 times slower for Nb, than the growth rates reported for the interaction between the U-Mo fuel alloy and pure Al or Al-Si cladding alloys. Zr, however was selected as the barrier metal due to a concern for thermo- mechanical behavior of UMo/Nb interface observed from diffusion couples, and for ductile-to-brittle transition of Mo near room temperature.

  19. Crystal structure and ion conducting properties of La5NbMo2O16

    NASA Astrophysics Data System (ADS)

    Vu, T. D.; Krichen, F.; Barre, M.; Busselez, R.; Adil, K.; Jouanneaux, A.; Suard, E.; Goutenoire, F.

    2016-05-01

    The new compound La5NbMo2O16 with high ionic conduction has been discovered during the study of the ternary phase diagram of La2O3-MoO3-Nb2O5. The material crystallizes in the cubic space group Pn 3 bar n (no 222) with the unit cell parameter a=11.2250(1) Å. La5NbMo2O16 is a new analogue of the R5Mo3O16 series (R=Pr, Nd). The structure was refined from a combined data X-ray and neutron powder diffraction. The ionic conductivity of the compound is then measured on sintered pellets, by means of complex impedance spectroscopy.

  20. Oxidation of Nb particulate-reinforced MoSi sub 2

    SciTech Connect

    Meschter, P.J. )

    1991-01-01

    This paper reports on molybdenum disilicide (MoSi{sub 2}) which is a promising high-temperature material because of its moderate density (6.31 g cm{sup {minus}3}), high melting temperature (2020 {degrees}C), ductility above 900-1000{degrees} C related to its b.c.c.-like C11b crystal structure, and excellent high-temperature oxidation resistance. MoSi{sub 2} is brittle below 900-1000{degrees} C and hence must be reinforced to obtain acceptable low-temperature toughness. Addition of a ductile reinforcement such as Nb as wire or particulate has been shown to increase the ambient-temperature toughness of MoSi{sub 2}. Additions of Nb, which oxidizes rapidly to form non-protective Nb{sub 2}O{sub 5}, may degrade the oxidation resistance of an MoSi{sub 2}-matrix composite. The purpose of this research is to determine the effect of particulate Nb additions on the oxidation resistance of MoSi{sub 2} in the high-temperature regime ({ge}550{degrees} C), where a protective SiO{sub 2} product layer is formed on monolithic MoSi{sub 2}, and in the low-temperature regime (400-500{degrees} C), where Mo and Si oxidize simultaneously.

  1. Effect of Sn addition on the microstructure and superelasticity in Ti-Nb-Mo-Sn alloys.

    PubMed

    Zhang, D C; Yang, S; Wei, M; Mao, Y F; Tan, C G; Lin, J G

    2012-09-01

    Ti-7.5Nb-4Mo-xSn (x=0-4at%) alloys were developed as the biomedical materials. The effect of the Sn content on the microstructure and superelasticity of the alloys was investigated. It is found that Sn is a strong stabilizer of the β phase, which is effective in suppressing the formation of α″ and ω phases in the alloys. Moreover, the Sn addition has a significant impact on the mechanical properties of the alloys. With the increase of Sn addition, the yield stress of the alloys increase, but their elastic modulus, the fracture strength and the ductility decrease, and the deformation mode of the alloys changes from (322) twining to α″ transformation and then to slip. The Ti-7.5Nb-4Mo-1Sn and Ti-7.5Nb-4Mo-3Sn alloys exhibit a good superelasticity with a high σ(SIM) due to the relatively high athermal ω phases containing or the solution hardening at room temperature. Under the maximum strain of 5%, Ti-7.5Nb-4Mo-3Sn (at%) alloy exhibits higher super elastic stability than that of Ti-7.5Nb-4Mo-1Sn alloy.

  2. Oxidation Behavior and Chlorination Treatment to Improve Oxidation Resistance of Nb-Mo-Si-B Alloys

    SciTech Connect

    Behrani, Vikas

    2004-01-01

    This thesis is written in an alternate format. The thesis is composed of a general introduction, two original manuscripts, and a general conclusion. References cited within each chapter are given at the end of each chapter. The general introduction starts with the driving force behind this research, and gives an overview of previous work on boron doped molybdenum silicides, Nb/Nb5Si3 composites, boron modified niobium silicides and molybdenum niobium silicides. Chapter 2 focuses on the oxidation behavior of Nb-Mo-Si-B alloys. Chapter 3 contains studies on a novel chlorination technique to improve the oxidation resistance of Nb-Mo-Si-B alloys. Chapter 4 summarizes the important results in this study.

  3. Ab initio study of AlxMoNbTiV high-entropy alloys.

    PubMed

    Cao, Peiyu; Ni, Xiaodong; Tian, Fuyang; Varga, Lajos K; Vitos, Levente

    2015-02-25

    The Al(x)MoNbTiV (x = 0-1.5) high-entropy alloys (HEAs) adopt a single solid-solution phase, having the body centered cubic (bcc) crystal structure. Here we employ the ab initio exact muffin-tin orbitals method in combination with the coherent potential approximation to investigate the equilibrium volume, elastic constants, and polycrystalline elastic moduli of Al(x)MoNbTiV HEAs. A comparison between the ab initio and experimental equilibrium volumes demonstrates the validity and accuracy of the present approach. Our results indicate that Al addition decreases the thermodynamic stability of the bcc structure with respect to face-centered cubic and hexagonal close packed lattices. For the elastically isotropic Al(0.4)MoNbTiV HEAs, the valence electron concentration (VEC) is about 4.82, which is slightly different from VEC ∼ 4.72 obtained for the isotropic Gum metals and refractory--HEAs.

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

    DTIC Science & Technology

    2011-07-01

    yielding at 807 MPa. A simple model of solid -solution strengthening is proposed to explain the behavior. 15. SUBJECT TERMS refractory alloy...Ta20Nb20Hf20Zr20Ti20, vacuum arc-melting, hot isostatic pressing 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT: SAR 18. NUMBER OF PAGES... solid -solution strengthening is proposed to explain the behavior. 1 INTRODUCTION Metallic alloys with superior mechanical and functional properties

  5. Thermal Behavior Study of the MoVTeNb Oxide Catalyst for Selective Oxidation Process

    SciTech Connect

    Idris, R.; Hamid, S. B. Abd.

    2009-06-01

    Several parameters involved in preparing the multi metal oxide (MMO) catalysts (Mo{sub 1}V{sub 0.3}Te{sub 0.23}Nb{sub 0.12}O{sub x}) for selective oxidation of propane to acrylic acid (AA) were investigated. These included the proper pre-calcined and calcinations atmosphere effect on the performance of the catalysts. It was found that each metal element plays a critical role to the performance of an effective catalyst and also the calcinations under a non-flow inert atmosphere. The characterization results from XRD, SEM, TG and DSC show the important differences depending on the activation procedures of the MoVTeNb oxide catalyst. The XRD analysis is used to identify the phase inventory of the MoVTeNb oxide catalysts. The structure of orthorhombic M1, M2, TeMo{sub 5}O{sub 16}, V{sub 0.95}Mo{sub 0.97}O{sub 5} and Mo{sub 5}O{sub 14} phase was investigated. The orthorhombic M1 phase is the most active and selective phase and is responsible for the major of the efficiently of the best catalyst for selective oxidation process. TGA and DTG allow the identification of the number and types, of reactions involving evaporation of small molecules from removal of ligands and water to condensation or drying processes. From all these analyses it was proven that the activation procedures would affect the performance of the MoVTeNb oxide catalyst.

  6. Some Metallurgical Issues Concerning Austenite Conditioning in Nb-Ti and Nb-Mo Microalloyed Steels Processed by Near-Net-Shape Casting and Direct Rolling Technologies

    NASA Astrophysics Data System (ADS)

    López, Beatriz; Rodriguez-Ibabe, Jose M.

    2016-08-01

    As thin slab direct rolling technologies are moving to the production of higher quality steel grades, chemical compositions based on Nb-Ti and Nb-Mo become a good option. However, with the use of multiple microalloying additions, the as-cast austenite conditioning becomes more complex. This paper analyzes some of the microstructural features that should be taken into account during the as-cast austenite conditioning in Nb-Ti and Nb-Mo microalloyed steel grades. In the case of Nb-Ti grades, it has been observed that the process parameters during solidification and post-solidification steps affect the austenite evolution during hot rolling. This is due to the differences in the size and volume fraction of TiN particles that can be formed. Fine TiN precipitates have been shown to be able to delay recrystallization kinetics. Moreover, the solute drag effect of Ti cannot be ignored in the case of hyperstoichiometric Ti/N ratios. It is observed that Nb-Ti grades tend to have lower non-recrystallization temperatures compared to Nb grades, which means that pancaking of the austenite is more difficult for these steels. The opposite is observed for the Nb-Mo grades, although in both cases the behavior is affected by the nominal content of Nb.

  7. Photoelectron imaging spectroscopy of MoC{sup −} and NbN{sup −} diatomic anions: A comparative study

    SciTech Connect

    Liu, Qing-Yu; Li, Zi-Yu; He, Sheng-Gui E-mail: chenh@iccas.ac.cn; Hu, Lianrui; Chen, Hui E-mail: chenh@iccas.ac.cn; Ning, Chuan-Gang; Ma, Jia-Bi

    2015-04-28

    The isoeletronic diatomic MoC{sup −} and NbN{sup −} anions have been prepared by laser ablation and studied by photoelectron imaging spectroscopy combined with quantum chemistry calculations. The photoelectron spectra of NbN{sup −} can be very well assigned on the basis of literature reported optical spectroscopy of NbN. In contrast, the photoelectron spectra of MoC{sup −} are rather complex and the assignments suffered from the presence of many electronically hot bands and limited information from the reported optical spectroscopy of MoC. The electron affinities of NbN and MoC have been determined to be 1.450 ± 0.003 eV and 1.360  ±  0.003 eV, respectively. The good resolution of the imaging spectroscopy provided a chance to resolve the Ω splittings of the X{sup 3}Σ{sup −} (Ω = 0 and 1) state of MoC and the X{sup 4}Σ{sup −} (Ω = 1/2 and 3/2) state of MoC{sup −} for the first time. The spin-orbit splittings of the X{sup 2}Δ state of NbN{sup −} and the a{sup 2}Δ state of MoC{sup −} were also determined. The similarities and differences between the electronic structures of the NbN and MoC systems were discussed.

  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. An ultra-high temperature Mo-Si-B based coating for oxidation protection of NbSS/Nb5Si3 composites

    NASA Astrophysics Data System (ADS)

    Su, Linfen; Lu-Steffes, Otto; Zhang, Hu; Perepezko, John H.

    2015-05-01

    A Mo-Si-B based coating was prepared on an NbSS/Nb5Si3 composite by a two-step process consisting of the initial deposition of Mo followed by pack cementation co-deposition of Si and B. After a conditioning treatment, an aluminoborosilica layer fully covered the sample. Following oxidation at 1300 °C for 24 h, the coated sample demonstrated a weight loss of about 0.55 mg/cm2 and the uncoated sample exhibited catastrophic oxidation with a weight gain of 87.6 mg/cm2. These results demonstrate that the Mo-Si-B based coating can enable the use of the NbSS/Nb5Si3 composites at temperature up to 1300 °C in an oxidizing environment.

  10. Nb-doped single crystalline MoS{sub 2} field effect transistor

    SciTech Connect

    Das, Saptarshi E-mail: das@anl.gov; Demarteau, Marcellinus; Roelofs, Andreas

    2015-04-27

    We report on the demonstration of a p-type, single crystalline, few layer MoS{sub 2} field effect transistor (FET) using Niobium (Nb) as the dopant. The doping concentration was extracted and determined to be ∼3 × 10{sup 19}/cm{sup 3}. We also report on bilayer Nb-doped MoS{sub 2} FETs with ambipolar conduction. We found that the current ON-OFF ratio of the Nb-doped MoS{sub 2} FETs changes significantly as a function of the flake thickness. We attribute this experimental observation to bulk-type electrostatic effect in ultra-thin MoS{sub 2} crystals. We provide detailed analytical modeling in support of our claims. Finally, we show that in the presence of heavy doping, even ultra-thin 2D-semiconductors cannot be fully depleted and may behave as a 3D material when used in transistor geometry. Our findings provide important insights into the doping constraints of 2D materials, in general.

  11. High strength Sn-Mo-Nb-Zr alloy tubes and method of making same

    DOEpatents

    Cheadle, Brian A.

    1977-01-01

    Tubes for use in nuclear reactors fabricated from a quaternary alloy comprising 2.5-4.0 wt% Sn, 0.5-1.5 wt% Mo, 0.5-1.5 wt% Nb, balance essentially Zr. The tubes are fabricated by a process of hot extrusion, heat treatment, cold working to size and age hardening, so as to produce a microstructure comprising elongated .alpha. grains with an acicular transformed .beta. grain boundary phase.

  12. Mechanical and electrochemical characterisation of new Ti-Mo-Nb-Zr alloys for biomedical applications.

    PubMed

    Nnamchi, Paul S; Obayi, C S; Todd, Iain; Rainforth, M W

    2016-07-01

    The development and characterisation of new metallic biomaterials that contain non-toxic and non-allergic elements but possess low elastic modulus and low biodegradation rates, has become a topic of serious investigation in orthopaedic implant application. The lowering of elastic modulus and improving of corrosion resistance can be achieved by specific chemical alloying and super-elasticity effects, associated with a stress-induced phase transformation from the BCC metastable beta phase to the orthorhombic α″ martensite. Using this framework, this paper focuses on the effect of Nb and/or Zr micro-additions on the elastic modulus/yield strength balance and discusses microstructure, and the mechanical and electrochemical behaviour of four new β-Ti-8Mo-xNb-xZr (x=2-5) alloys, using tensile tests, X-ray diffraction, SEM characterisation, ultrasound technique and potentiodynamic polarisation methods. The results reveal that the alloys exhibit a pronounced microstructural sensitivity response, with alloying elements and excellent agreement between β-stability and high mechanical strength, with increasing Nb additions. Although all the alloys possess excellent corrosion resistance and low Young׳s modulus, Ti-8Mo-4Nb-2Zr alloy, which consists of β+α'' phases, exhibits a low Young modulus of 35GPa, which is lower than those of the commercial alloys already used in biomedical implantation. The significant corrosion resistance, nontoxicity and better mechanical compatibility are properties pertinent to preventing stress shielding and bone resorption in orthopaedic implant applications.

  13. 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.

  14. Magnetic ground state of the two isostructual polymeric quantum magnets <mo>[mo>Cu<mo>(HF2<mo>)mo>(pyrazine)>2<mo>]>SbF6 and <mo>[mo>Co<mo>(HF2<mo>)mo>(pyrazine)>2<mo>]>SbF6 investigated with neutron powder diffraction

    SciTech Connect

    Brambleby, J.; Goddard, P. A.; Johnson, R. D.; Liu, J.; Kaminski, D.; Ardavan, A.; Steele, A. J.; Blundell, S. J.; Lancaster, T.; Manuel, P.; Baker, P. J.; Singleton, J.; Schwalbe, S. G.; Spurgeon, P. M.; Tran, H. E.; Peterson, P. K.; Corbey, J. F.; Manson, J. L.

    2015-10-07

    The magnetic ground state of two isostructural coordination polymers, (i) the quasi-two-dimensional S=1/2 square-lattice antiferromagnet [Cu(HF2)(pyrazine)2]SbF6 and (ii) a related compound [Co(HF2)(pyrazine)2]SbF6, was examined with neutron powder diffraction measurements. We find that the ordered moments of the Heisenberg S=1/2 Cu(II) ions in [Cu(HF2)(pyrazine)2]SbF6 are 0.6(1)μb, while the ordered moments for the Co(II) ions in [Co(HF2)(pyrazine)2]SbF6 are 3.02(6)μb. For Cu(II), this reduced moment indicates the presence of quantum fluctuations below the ordering temperature. We also show from heat capacity and electron spin resonance measurements that due to the crystal electric field splitting of the S=3/2 Co(II) ions in [Co(HF2)(pyrazine)2]SbF6, this isostructual polymer also behaves as an effective spin-half magnet at low temperatures. Furthermore, the Co moments in [Co(HF2)(pyrazine)2]SbF6 show strong easy-axis anisotropy, neutron diffraction data, which do not support the presence of quantum fluctuations in the ground state, and heat capacity data, which are consistent with 2D or close to 3D spatial exchange anisotropy.

  15. Microstructural Features Controlling Mechanical Properties in Nb-Mo Microalloyed Steels. Part II: Impact Toughness

    NASA Astrophysics Data System (ADS)

    Isasti, Nerea; Jorge-Badiola, Denis; Taheri, Mitra L.; Uranga, Pello

    2014-10-01

    The present paper is the final part of a two-part paper where the influence of coiling temperature on the final microstructure and mechanical properties of Nb-Mo microalloyed steels is described. More specifically, this second paper deals with the different mechanisms affecting impact toughness. A detailed microstructural characterization and the relations linking the microstructural parameters and the tensile properties have already been discussed in Part I. Using these results as a starting point, the present work takes a step forward and develops a methodology for consistently incorporating the effect of the microstructural heterogeneity into the existing relations that link the Charpy impact toughness to the microstructure. In conventional heat treatments or rolling schedules, the microstructure can be properly described by its mean attributes, and the ductile-brittle transition temperatures measured by Charpy tests can be properly predicted. However, when different microalloying elements are added and multiphase microstructures are formed, the influences of microstructural heterogeneity and secondary hard phases have to be included in a modified equation in order to accurately predict the DB transition temperature in Nb and Nb-Mo microalloyed steels.

  16. Phase Transformation Study in Nb-Mo Microalloyed Steels Using Dilatometry and EBSD Quantification

    NASA Astrophysics Data System (ADS)

    Isasti, Nerea; Jorge-Badiola, Denis; Taheri, Mitra L.; Uranga, Pello

    2013-08-01

    A complete microstructural characterization and phase transformation analysis has been performed for several Nb and Nb-Mo microalloyed low-carbon steels using electron backscattered diffraction (EBSD) and dilatometry tests. Compression thermomechanical schedules were designed resulting in the undeformed and deformed austenite structures before final transformation. The effects of microalloying additions and accumulated deformation were analyzed after CCT diagram development and microstructural quantification. The resulting microstructures ranged from polygonal ferrite and pearlite at slow cooling ranges, to a combination of quasipolygonal ferrite and granular ferrite for intermediate cooling rates, and finally, to bainitic ferrite with martensite for fast cooling rates. The addition of Mo promotes a shift in the CCT diagrams to lower transformation start temperatures. When the amount of Nb is increased, CCT diagrams show little variations for transformations from the undeformed austenite and higher initial transformation temperatures in the transformations from the deformed austenite. This different behavior is due to the effect of niobium on strain accumulation in austenite and its subsequent acceleration of transformation kinetics. This article shows the complex interactions between chemical composition, deformation, and the phases formed, as well as their effect on microstructural unit sizes and homogeneity.

  17. Microstructural Features Controlling Mechanical Properties in Nb-Mo Microalloyed Steels. Part I: Yield Strength

    NASA Astrophysics Data System (ADS)

    Isasti, Nerea; Jorge-Badiola, Denis; Taheri, Mitra L.; Uranga, Pello

    2014-10-01

    Low carbon Nb-Mo microalloyed steels show interesting synergies between the "micro"-alloying elements when high strength-high toughness properties are required. Strain accumulation in austenite is enhanced, and therefore grain sizes are refined in the final microstructures. The presence of Mo facilitates the presence of non-polygonal phases, and this constituent modification induces an increment in strength through a substructure formation as well as through an increase in the dislocation density. Regarding fine precipitation and its strengthening effect, the mean size of NbC is reduced in the presence of Mo and their fraction increased, thus enhancing their contribution to yield strength. In this paper, a detailed characterization of the microstructural features of a series of microalloyed steels is described using the electron-backscattered diffraction technique. Mean crystallographic unit sizes, a grain boundary misorientation analysis, and dislocation density measurements are performed. Transmission electron microscopy is carried out to analyze the chemical composition of the precipitates and to estimate their volume fraction. In this first part, the contribution of different strengthening mechanisms to yield strength is evaluated and the calculated value is compared to tensile test results for different coiling temperatures and compositions.

  18. Effect of Nb Doping on Chemical Sensing Performance of Two-Dimensional Layered MoSe2.

    PubMed

    Choi, Sun Young; Kim, Yonghun; Chung, Hee-Suk; Kim, Ah Ra; Kwon, Jung-Dae; Park, Jucheol; Kim, Young Lae; Kwon, Se-Hun; Hahm, Myung Gwan; Cho, Byungjin

    2017-02-01

    Here, we report that Nb doping of two-dimensional (2D) MoSe2 layered nanomaterials is a promising approach to improve their gas sensing performance. In this study, Nb atoms were incorporated into a 2D MoSe2 host matrix, and the Nb doping concentration could be precisely controlled by varying the number of Nb2O5 deposition cycles in the plasma enhanced atomic layer deposition process. At relatively low Nb dopant concentrations, MoSe2 showed enhanced device durability as well as NO2 gas response, attributed to its small grains and stabilized grain boundaries. Meanwhile, an increase in the Nb doping concentration deteriorated the NO2 gas response. This might be attributed to a considerable increase in the number of metallic NbSe2 regions, which do not respond to gas molecules. This novel method of doping 2D transition metal dichalcogenide-based nanomaterials with metal atoms is a promising approach to improve the performance such as stability and gas response of 2D gas sensors.

  19. 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.

  20. 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.

  1. 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

  2. A perovskite lead-free antiferroelectric xCaHfO3-(1-x) NaNbO3 with induced double hysteresis loops at room temperature

    NASA Astrophysics Data System (ADS)

    Gao, Lisheng; Guo, Hanzheng; Zhang, Shujun; Randall, Clive A.

    2016-11-01

    We demonstrated a new CaHfO3-NaNbO3 solid solution system that allows stable antiferroelectric (AFE) (P) phase to exist under ambient conditions. Based on crystal chemistry viewpoint of relative change of the Goldschmidt tolerance factor (t) and polarizability, two new solid solutions were fabricated using the perovskite end member CaHfO3. It was found that the CaHfO3 effectively stabilized the antiferroelectric (AFE) P phase in NaNbO3. In this article, electrical properties and transmission electron microscopy experiments were conducted to verify the stabilization and enhancement of antiferroelectric behavior over the various solid solutions, where both structural signature of ¼{010} superlattice diffraction reflections and electrical characteristic of double polarization-electric (P-E) hysteresis were observed.

  3. Surface characteristics of HA coating and micro-pore formation on the Ti-25Nb-xHf alloys for dental materials.

    PubMed

    Kim, Sung-Hwan; Jeong, Yong-Hoon; Choe, Han-Cheol

    2014-10-01

    Micro-pore formation on titanium surface can increase the adhesion strength with increment of surface area, and hydroxyapatite is effective coating materials as a main chemical constituent of bone tissue for biomedical field. The aim of this study was to investigate the surface characteristics of HA coating and micro-pore formation on the Ti-25Nb-xHf alloys for dental materials. The Ti-25Nb-xHf alloys consisted of (0 and 7) wt.% Hf contents which were manufactured by vacuum arc-melting furnace. The homogenization was performed at 1000 degrees C for 12 h and water quenched. Anodization was carried out using an electrochemical method in 1 M H3PO4 electrolyte. The HA films were deposited by plasma sputtering method. The microstructures of alloys were transformed from α" phase to β phase by addition of Hf element, and needle-like structures were translated to an equiaxed structure as Hf content increased. The peaks of anatase and rutile showed on the anodized surface of these alloys. The number of micro-pore decreased, with presence of Hf content increased, whereas size of micro-pore increased. Anodized surface was covered with HA particles at surface and in holes. Contact angle value of HA coating on anodized surface was lower than that of non-coating surface.

  4. Effect of Ti/Al ratio and Cr, Nb, and Hf additions on material factors and mechanical properties in TiAl

    NASA Astrophysics Data System (ADS)

    Kawabata, T.; Tamura, T.; Izumi, O.

    1993-01-01

    The effect of the Ti/Al ratio and Cr, Nb, and Hf additions on material factors, such as the grain size, second phase, la tice parameters and the axial ratio, and on mechanical properties in TiAl-base alloys has been studied. The grain size was decreased by the deviation from the stoichiometric composition o the Ti-rich side and the addition of the third elements. The Cr element was contained a little more in Ti3Al phase than in TiAl phase in two-phase Ti-rich alloys. The lattice parameters, a and c, and the axial ratio, c/a, of the binary alloys varied linearly with decreasing Al content even in the dual-phase region. The Cr addition decreased the a and c and also c/a. The Nb addition increased weakly the a and c and c/a. On the contrary, the Hf addition increased the a and c but decreased the c/a ratio. In the Cr added alloys, the decrease of volume of a unit cell, due to the substitution of Cr atoms for Ti and Al atoms, was larger than that expected from the difference of atom sizes. The Nb addition should decrease the volume of a unit cell, but it increased the volume. The Hf addition caused a larger increase of volume of a unit cell than that expected from the difference of atom sizes. We suggested that the Cr addition increases and the Nb and Hf additions decrease the bond strength in TiAl. The deviation from stoichiometry and the addition of third elements caused an increase of work-hardening rate. The alloys with Ti-rich composition have superior mechanical properties compared to those of alloys vith Al-rich composition. The Cr addition resulted in high solution hardening, and the Ti-47A1 3Cr (in atomic percent) alloys had the highest fracture strain of 2.7 pct in all alloys tested. The Nb addition resulted in poor ductility in both Ti- and Al-rich alloys. The Hf additions to the Ti-rich composition caused better mechanical properties than those of Al-rich alloys. Thi; trend was also similar to the Nb-added alloys. In the Hf-added alloys, the Ti-49Al-2Hf

  5. Phase evolution, microstructure and mechanical properties of equi-atomic substituted TiZrHfNiCu and TiZrHfNiCuM (M = Co, Nb) high-entropy alloys

    NASA Astrophysics Data System (ADS)

    Park, Hae Jin; Na, Young Sang; Hong, Sung Hwan; Kim, Jeong Tae; Kim, Young Seok; Lim, Ka Ram; Park, Jin Man; Kim, Ki Buem

    2016-07-01

    In this study, alloys with composition of equi-atomic substituted TiZrHfNiCu, TiZrHfNiCuCo, and TiZrHfNiCuNb high-entropy alloys (HEAs) were produced by suction casting method. The effects of addition elements on phase composition, microstructure and mechanical behaviors of the HEA were studied. The suction casted Ti20Zr20Hf20Ni20Cu20 HEA exhibits single C14 Laves phase (MgZn2-type) with fine homogeneous microstructure. When Co or Nb elements are added, morphologies are slightly modulated toward well-developed dendritic microstructure, phase constitutions are significantly changed from single Laves phase to mixed multi-phases as well as mechanical properties are also altered with increased plasticity and high strength. It is believed that modulated mechanical properties are mainly ascribed to the change of phase constitution and crystalline structure, together with the microstructural characteristics. This clearly reveals that the selection and addition of supplementary elements based on the formation rule for HEAs play an important role on the evolution of phase, microstructural morphology and mechanical properties of Ti20Zr20Hf20Ni20Cu20 HEA.

  6. Microstructural and precipitation characterization in Nb-Mo microalloyed steels: Estimation of the contributions to the strength

    NASA Astrophysics Data System (ADS)

    Isasti, N.; Jorge-Badiola, D.; Taheri, M. L.; Uranga, P.

    2014-09-01

    The influence of coiling temperature on the final microstructure and precipitation has been analyzed in several low carbon Nb and Nb-Mo microalloyed steels. A throughout characterization of the complex microstructures has been performed using electron backscattered diffraction, measuring low and high angle unit sizes, microstructural substructure, as well as quantifying the homogeneity. An important microstructural refinement is observed for all compositions as the coiling temperature decreases. Regarding precipitation, the coiling temperature strongly modifies the size and density of the fine precipitates, being 550 °C the optimal coiling temperature for the Nb-Mo steels. The addition of Mo to Nb steels provides a refinement of the precipitates and, therefore, enhances their contribution to strengthening. Considering all the microstructural and precipitation quantification data, the yield strength was estimated and the contribution of the different mechanisms calculated. The grain size contribution is proven to be the most important factor regarding strengthening, followed by dislocation density and precipitation especially at low coiling temperatures and Nb-Mo steels.

  7. Metal-metal bonding and aromaticity in [M2(NHCHNH)3]2 (μ-E)2 (E = O, S; M = Nb, Mo, Tc, Ru, Rh).

    PubMed

    Yan, Xiuli; Meng, Lingpeng; Sun, Zheng; Li, Xiaoyan

    2016-02-01

    The nature of M-M bonding and aromaticity of [M2(NHCHNH)3]2(μ-E)2 (E = O, S; M = Nb, Mo, Tc, Ru, Rh) was investigated using atoms in molecules (AIM) theory, electron localization function (ELF), natural bond orbital (NBO) and molecular orbital analysis. These analyses led to the following main conclusions: in [M2(NHCHNH)3]2(μ-E)2 (E = O, S; M = Nb, Mo, Tc, Ru, Rh), the Nb-Nb, Ru-Ru, and Rh-Rh bonds belong to "metallic" bonds, whereas Mo-Mo and Tc-Tc drifted toward the "dative" side; all these bonds are partially covalent in character. The Nb-Nb, Mo-Mo, and Tc-Tc bonds are stronger than Ru-Ru and Rh-Rh bonds. The M-M bonds in [M2(NHCHNH)3]2(μ-S)2 are stronger than those in [M2(NHCHNH)3]2(μ-O)2 for M = Nb, Mo, Tc, and Ru. The NICS(1)ZZ values show that all of the studied molecules, except [Ru2(NHCHNH)3]2(μ-O)2, are aromaticity molecules. O-bridged compounds have more aromaticity than S-bridged compounds. Graphical Abstract Left Molecular graph, and right electron localization function (ELF) isosurface of [M2(NHCHNH)3]2(μ-E)2(E = O, S; M = Nb, Mo, Tc, Ru, Rh).

  8. Hydrogen trapping by solute atoms in Nb-Mo(3 at. %) alloys as observed by the channeling method

    NASA Astrophysics Data System (ADS)

    Yagi, Eiichi; Nakamura, Shiho; Kano, Fumihisa; Kobayashi, Takane; Watanabe, Kenji; Fukai, Yuh; Matsumoto, Takehiko

    1989-01-01

    In order to elucidate the mechanism of the enhancement of the terminal solubility for hydrogen (TSH) in Nb by alloying with undersized Mo atoms, the state of hydrogen was studied by the channeling method using a nuclear reaction 1H(11B, α)αα in Nb-Mo(3 at. %) alloys. At room temperature H atoms are located at sites displaced from tetrahedral (T) sites by about 0.6 Å towards the nearest-neighbor lattice points, while at 373 K they are at T sites. These results give direct evidence for trapping of hydrogen by Mo atoms and strongly support the trapping model for the enhancement of the TSH in the low-concentration region of Mo atoms.

  9. Hydrogen trapping by solute atoms in Nb--Mo(3 at. %) alloys as observed by the channeling method

    SciTech Connect

    Yagi, E.; Nakamura, S.; Kano, F.; Kobayashi, T.; Watanabe, K.; Fukai, Y.; Matsumoto, T.

    1989-01-01

    In order to elucidate the mechanism of the enhancement of the terminal solubility for hydrogen (TSH) in Nb by alloying with undersized Mo atoms, the state of hydrogen was studied by the channeling method using a nuclear reaction /sup 1/H(/sup 11/B, ..cap alpha..)..cap alpha cap alpha.. in Nb--Mo(3 at. %) alloys. At room temperature H atoms are located at sites displaced from tetrahedral (T) sites by about 0.6 A towards the nearest-neighbor lattice points, while at 373 K they are at T sites. These results give direct evidence for trapping of hydrogen by Mo atoms and strongly support the trapping model for the enhancement of the TSH in the low-concentration region of Mo atoms.

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

    DTIC Science & Technology

    2012-03-01

    occurred during oxidation. The alloy has a better combination of mechanical properties and oxidation resistance than commercial Nb alloys and earlier...properties and oxidation resistance than commercial Nb alloys and earlier reported developmental Nb-Si-Al-Ti and Nb-Si-Mo alloys. Keywords: Refractory...made from Ni-based superalloys, as these alloys have the best combination of required properties, such as creep resistance , temperature capability

  11. Preparation and characterization of alloys of the Ti-15Mo-Nb system for biomedical applications.

    PubMed

    Martins Júnior, J R S; Matos, A A; Oliveira, R C; Buzalaf, M A R; Costa, I; Rocha, L A; Grandini, C R

    2017-03-09

    In the development of new metallic biomaterials, the Ti-15Mo alloy has great prominence because of its excellent corrosion resistance and good combination of mechanical properties. In this study, the element niobium was added to the Ti-15Mo alloy, forming the Ti-15Mo-Nb system for the purpose of improving their properties and promoting its application as a biomaterial. These alloys are very promising to use as biomedical implants, because they integrate a new class of titanium alloys without the presence of aluminum and vanadium, which may cause cytotoxic effects. The alloys were produced by arc-melting and characterized by density, X-ray diffraction, scanning electron microscopy, microhardness, elastic modulus, corrosion, and cytotoxicity assays. The developed alloys have β phase predominance (with bcc crystalline structure). The addition of niobium decreases the microhardness and elastic modulus, with values around 80 GPa, which is well below that of the metallic alloys used commercially for this type of application. Very low passive current densities were found for all alloys studied showing that the passive film on these alloys is highly protective. In vitro cytotoxicity tests revealed that the introduction of niobium did not cause cytotoxic effects in the studied alloys. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2017.

  12. 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.

  13. Oxidation characteristics of Ti-25Al-10Nb-3V-1Mo

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    Static oxidation kinetics of the super-alpha 2 titanium-aluminide alloy Ti-25Al-10Nb-3V-1Mo (at. percent) were investigated in air over the temperature range of 650 to 1000 C using thermogravimetric analysis. The oxidation kinetics were complex at all exposure temperatures and displayed up to three distinct oxidation rates. Breakaway oxidation occurred after long exposure times at high temperatures. Oxidation products were determined using X-ray diffraction techniques, electron microprobe analysis, and energy dispersive X-ray analysis. Oxide scale morphology was examined by scanning electron microscopy of the surfaces and cross sections of oxidized specimens. The oxides during the parabolic stages were compact and multilayered, consisting primarily of TiO2 doped with Nb, a top layer of Al2O3, and a thin bottom layer of TiN. The transition between the second and third parabolic stage was found to be linked to the formation of a TiAl layer at the oxide-metal interface. Porosity was formed during the third stage, causing degradation of the oxide and the beginning of breakaway oxidation.

  14. Oxidation characteristics of Ti-25Al-10Nb-3V-1Mo intermetallic alloy

    NASA Technical Reports Server (NTRS)

    Wallace, Terryl A.; Clark, Ronald K.; Sankaran, Sankara N.; Wiedemann, Karl E.

    1990-01-01

    Static oxidation kinetics of the super-alpha 2 titanium-aluminide alloy Ti-25Al-10Nb-3V-1Mo (at. percent) were investigated in air over the temperature range of 650 to 1000 C using thermogravimetric analysis. The oxidation kinetics were complex at all exposure temperatures and displayed up to three distinct oxidation rates. Breakaway oxidation occurred after long exposure times at high temperatures. Oxidation products were determined using x ray diffraction techniques, electron microprobe analysis, and energy dispersive x ray analysis. Oxide scale morphology was examined by scanning electron microscopy of the surfaces and cross sections of oxidized specimens. The oxides during the parabolic stages were compact and multilayered, consisting primarily of TiO2 doped with Nb, a top layer of Al2O3, and a thin bottom layer of TiN. The transition between the second and third parabolic stage was found to be linked to the formation of a TiAl layer at the oxide-metal interface. Porosity was formed during the third stage, causing degradation of the oxide and the beginning of breakaway oxidation.

  15. Microstructures and Stability Origins of β-(Ti,Zr)-(Mo,Sn)-Nb Alloys with Low Young's Modulus

    NASA Astrophysics Data System (ADS)

    Wang, Qing; Li, Qun; Li, Xiaona; Zhang, Ruiqian; Gao, Xiaoxia; Dong, Chuang; Liaw, Peter K.

    2015-09-01

    The present work investigates the microstructural evolution and β-phase stability of a multi-component [(Mo,Sn)-(Ti,Zr)14]-Nb alloy series developed using the cluster-plus-glue-atom model. Low Young's modulus ( E) can be reached, when both low- E elements, Sn and Zr, and β-Ti stabilizers, Mo and Nb, are properly incorporated in the so-called cluster formulas. After the X-ray diffraction and transmission electron microscopy analysis, and in combination with the β-Ti stability measured by the Mo equivalent, the Young's modulus of β-Ti alloys is found to increase with increasing β stabilities and is closely related to both the microstructures of the β matrix and the precipitated phases. More importantly, the morphologies of the β matrix change with β stabilities apparently so that high- E ( E >70 GPa) and low- E ( E ≤70 GPa) β-Ti alloys can be distinguished with the microstructures of the β matrix. The quinary alloy, formulated as [(Mo0.5Sn0.5)-(Ti13Zr1)]Nb1, owns its lowest E of 48 GPa among the present alloy series to the mixed thin-lamellar and rod-shaped morphology of the β structure with the lowest stability for the β formation.

  16. 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.

  17. Chemical separation of Mo and W from terrestrial and extraterrestrial samples via anion exchange chromatography.

    PubMed

    Nagai, Yuichiro; Yokoyama, Tetsuya

    2014-05-20

    A new two-stage chemical separation method was established using an anion exchange resin, Eichrom 1 × 8, to separate Mo and W from four natural rock samples. First, the distribution coefficients of nine elements (Ti, Fe, Zn, Zr, Nb, Mo, Hf, Ta, and W) under various chemical conditions were determined using HCl, HNO3, and HF. On the basis of the obtained distribution coefficients, a new technique for the two-stage chemical separation of Mo and W, along with the group separation of Ti-Zr-Hf, was developed as follows: 0.4 M HCl-0.5 M HF (major elements), 9 M HCl-0.05 M HF (Ti-Zr-Hf), 9 M HCl-1 M HF (W), and 6 M HNO3-3 M HF (Mo). After the chemical procedure, Nb remaining in the W fraction was separated using 9 M HCl-3 M HF. On the other hand, Nb and Zn remaining in the Mo fraction were removed using 2 M HF and 6 M HCl-0.1 M HF. The performance of this technique was evaluated by separating these elements from two terrestrial and two extraterrestrial samples. The recovery yields for Mo, W, Zr, and Hf were nearly 100% for all of the examined samples. The total contents of the Zr, Hf, W, and Mo in the blanks used for the chemical separation procedure were 582, 9, 29, and 396 pg, respectively. Therefore, our new separation technique can be widely used in various fields of geochemistry, cosmochemistry, and environmental sciences and particularly for multi-isotope analysis of these elements from a single sample with significant internal isotope heterogeneities.

  18. Significant Improvement of Mechanical Properties in NiAl-Cr(Mo)/Hf Alloy by Suction Casting and Subsequent Hot Isostatic Pressing

    NASA Astrophysics Data System (ADS)

    Guo, J. T.; Huai, K. W.; Li, H. T.

    2007-01-01

    The NiAl-28Cr-5.5Mo-0.5Hf eutectic alloy was prepared by the suction casting (SC) technique and subsequent hot isostatic pressing (HIP) treatment, and tested for compressive strength and fracture behavior in the temperature range of 300 to 1373 K. The microstructure of suction-cast alloy is characterized by fine interlamellar spacing, large area fraction of eutectic cell, and fine Heusler (Ni2AlHf) phase distributed semicontinuously at the cell boundaries. After HIP treatment, Ni2AlHf phase at the cell boundaries is transformed into Hf solid solution phase and distributed homogeneously within the NiAl matrix. Compared with the conventionally cast alloy, the room-temperature compressive strain and elevated temperature strength of suction-cast alloy are enhanced markedly after HIP treatment. The reason is that the HIP treatment causes Hf solid solution phase to distribute homogeneously and then strengthens the NiAl matrix.

  19. Deformation behavior of metastable β-type Ti-25Nb-2Mo-4Sn alloy for biomedical applications.

    PubMed

    Guo, S; Meng, Q K; Cheng, X N; Zhao, X Q

    2014-10-01

    The deformation behavior of metastable β-type Ti-25Nb-2Mo-4Sn (wt%) alloy subjected to different thermo-mechanical treatments was discussed by the combining results from transmission electron microscope, tensile test and in-situ synchrotron X-ray diffraction. Visible "double yielding" behavior, which is characterized by the presence of stress-plateau, was observed in the solution treated specimen. Upon a cold rolling treatment, the Ti-25Nb-2Mo-4Sn alloy performs nonlinear deformation because of the combined effects of elastic deformation and stress-induced α″ martensitic transformation. After the subsequent annealing, the β phase is completely stabilized and no stress-induced martensitic transformation takes place on loading due to the inhibitory effect of grain boundaries and dislocations on martensitic transformation. As a result, the annealed specimen exhibits linear elastic deformation.

  20. The Phase Stability, Ductility and Hardness of MoN and NbN: First-Principles Study

    NASA Astrophysics Data System (ADS)

    Linghu, Yaoyao; Wu, Xiaozhi; Wang, Rui; Li, Weiguo; Liu, Qing

    2017-03-01

    The phase stabilities of Mo_{1-x}AlxN and Nb_{1-x}AlxN (x=0, 0.25, 0.5, 0.75, 1.0) with four possible WC, NiAs, B1 and B4 structures were investigated using first-principles methods. With the increase of Al contents, the most stable structure changes from WC (x=0 and 0.25) to NiAs (x=0.5) structure. When x=0.75 and 1.0, the most stable structure is B4. The elastic constants, Young's modulus, shear modulus, bulk modulus and elastic anisotropy were calculated. Based on the Pugh criterion and Poisson's ratio, the ductility and hardness of Mo_{1-x}AlxN and Nb_{1-x}AlxN were investigated. The ductility of Mo_{1-x}AlxN decreases with the increase of Al contents. However, the ductility of Nb_{1-x}AlxN enhances with the increase of Al contents. The density of states and charge density differences were used to analyze the mechanical properties. The results are in agreement with the predictions based on the Pugh criterion and Poisson's ratio.

  1. The Phase Stability, Ductility and Hardness of MoN and NbN: First-Principles Study

    NASA Astrophysics Data System (ADS)

    Linghu, Yaoyao; Wu, Xiaozhi; Wang, Rui; Li, Weiguo; Liu, Qing

    2017-01-01

    The phase stabilities of Mo_{1-x} Alx N and Nb_{1-x} Alx N (x=0, 0.25, 0.5, 0.75, 1.0) with four possible WC, NiAs, B1 and B4 structures were investigated using first-principles methods. With the increase of Al contents, the most stable structure changes from WC (x=0 and 0.25) to NiAs (x=0.5 ) structure. When x=0.75 and 1.0, the most stable structure is B4. The elastic constants, Young's modulus, shear modulus, bulk modulus and elastic anisotropy were calculated. Based on the Pugh criterion and Poisson's ratio, the ductility and hardness of Mo_{1-x} Alx N and Nb_{1-x} Alx N were investigated. The ductility of Mo_{1-x} Alx N decreases with the increase of Al contents. However, the ductility of Nb_{1-x} Alx N enhances with the increase of Al contents. The density of states and charge density differences were used to analyze the mechanical properties. The results are in agreement with the predictions based on the Pugh criterion and Poisson's ratio.

  2. 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.

  3. 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.

  4. Formation of superhard Ti-Hf-Si-N/NbN/Al2O3 multilayer coatings for highly effective protection of steel

    NASA Astrophysics Data System (ADS)

    Pogrebnyak, A. D.; Beresnev, V. M.; Kaverina, A. Sh.; Shypylenko, A. P.; Kolisnichenko, O. V.; Oyoshi, K.; Takeda, Y.; Murakami, H.; Kolesnikov, D. A.; Prozorova, M. S.

    2013-02-01

    Hard micro- and nanostructured Ti-Hf-Si-N/NbN/Al2O3 multilayer coatings on steel substrates have been obtained for the first time using various deposition technologies and characterized by a combination of methods. It is established that the proposed coatings possess, in addition to high hardness ( H = 47-56 GPa), high elastic modulus ( E = 435-570 GPa), and good plasticity index ( W e = 0.08-0.11), a rather low friction coefficient that varies within μ = 0.02-0.001 depending on the deposition conditions. The coatings remain stable at temperatures above 1000°C.

  5. Structural origin of the enhanced ionic conductivity upon Nb doping in Sr11Mo4O23 defective double perovskite.

    PubMed

    Miranda, C D; López, C A; Pedregosa, J C; Alonso, J A

    2017-03-21

    We report a substantial enhancement of the oxide-ion conductivity in Sr11Mo4O23 achieved by Nb doping the Mo sites. This series responds to the formula: Sr11Mo4-xNbxO23-δ (with x = 0.0, 0.5 and 1.0). The original structure can be related to the conventional double perovskite; however, it presents a broken corner sharing connectivity of the octahedral framework, hence leading to a complex and highly defective network. The samples were prepared via citrate precursor method, followed by thermal treatments at 1300 °C for 12 hours in air. The crystal structures were refined from X-ray and neutron powder diffraction (NPD) data. A phase transition from tetragonal to cubic symmetry is identified in a temperature-dependent NPD study, driven by an oxygen delocalization effect. The ionic conductivity measured by impedance spectroscopy is enhanced upon Nb-doping; the x = 1 doped phase exhibits a threefold increase compared to the pristine Sr11Mo4O23 oxide, with conductivity values of 7.6 × 10(-3) and 2.7 × 10(-2) S·cm(-1) at 650 and 800 °C, which are even greater than for YSZ in the 650-800 °C temperature range, and close to those reported for other state-of-the art solid-oxide electrolytes.

  6. Electrochemical comparison and biological performance of a new CoCrNbMoZr alloy with commercial CoCrMo alloy.

    PubMed

    Andrei, M; Galateanu, B; Hudita, A; Costache, M; Osiceanu, P; Calderon Moreno, J M; Drob, S I; Demetrescu, I

    2016-02-01

    A new CoCrNbMoZr alloy, with Nb and Zr content is characterized from the point of view of surface features, corrosion resistance and biological performance in order to be proposed as dental restorative material. Its properties are discussed in comparison with commercial Heraenium CE alloy based on Co, Cr and Mo as well. The microstructure of both alloys was revealed by scanning electron microscopy (SEM). The composition and thickness of the alloy native passive films were identified by X-ray photoelectron spectroscopy (XPS). The surface characteristics were analyzed by atomic force microscopy (AFM) and contact angle techniques. The quantity of ions released from alloys in artificial saliva was evaluated with inductively coupled plasma-mass spectroscopy (ICP-MS) measurements. The electrochemical stability was studied in artificial Carter-Brugirard saliva, performing open circuit potentials, polarization resistances and corrosion currents and rates. The biological performance of the new alloy was tested in vitro in terms of human adipose stem cells (hASCs) morphology, viability and proliferation status. The new alloy is very resistant to the attack of the aggressive ions from the artificial saliva. The surface properties, the roughness and wettabiliy sustain the cell behavior. The comparison of the new alloy behavior with that of existing commercial CoCrMo alloy showed the superior properties of the new metallic biomaterial.

  7. Microstructure-Property Relationship in the Thermomechanically Processed C-Mn-Si-Nb-Al-(Mo) TRIP Steels before and after PS/BH Treatment

    SciTech Connect

    Timokhina, I. B.; Enomoto, M; Miller, Michael K; Pereloma, E. V.

    2012-01-01

    The effect of prestraining and bake hardening (PS/BH) on the development of microstructures and mechanical properties in thermomechanically processed transformation-induced plasticity (TRIP) steels with additions of Nb, Mo, and Al was studied by atom probe tomography (APT) and transmission electron microscopy (TEM). An increase in number density and sizes of clusters and nanoscale precipitates was observed in both steels but was more significant in the Nb-Al-Mo steel than in the Nb-Al steel. This increase could be explained by the possible fast diffusion of Nb and Mo atoms at low temperatures, as was observed for surface diffusivity. The contributions of cluster strengthening and precipitation strengthening to the yield strength increment after PS/BH were estimated.

  8. Microstructure-Property Relationship in the Thermomechanically Processed C-Mn-Si-Nb-Al-(Mo) Transformation-Induced Plasticity Steels Before and After Prestraining and Bake Hardening Treatment

    NASA Astrophysics Data System (ADS)

    Timokhina, I. B.; Enomoto, M.; Miller, M. K.; Pereloma, E. V.

    2012-07-01

    The effect of prestraining and bake hardening (PS/BH) on the development of microstructures and mechanical properties in thermomechanically processed transformation-induced plasticity (TRIP) steels with additions of Nb, Mo, and Al was studied by atom probe tomography (APT) and transmission electron microscopy (TEM). An increase in number density and sizes of clusters and nanoscale precipitates was observed in both steels but was more significant in the Nb-Al-Mo steel than in the Nb-Al steel. This increase could be explained by the possible fast diffusion of Nb and Mo atoms at low temperatures, as was observed for surface diffusivity. The contributions of cluster strengthening and precipitation strengthening to the yield strength increment after PS/BH were estimated.

  9. Mechanical and physicochemical characterization along with biological interactions of a new Ti25Nb21Hf alloy for bone tissue engineering.

    PubMed

    Herranz-Diez, C; Gil, F J; Guillem-Marti, J; Manero, J M

    2015-08-01

    Nowadays, one of the main challenges in metal implants for bone substitution is the achievement of an elastic modulus close to that of human cortical bone as well as to provide an adequate interaction with the surrounding tissue avoiding in vivo foreign body reaction. From this perspective, a new Ti-based alloy has been developed with Nb and Hf as alloying elements which are known as non-toxic and with good corrosion properties. The microstructure, mechanical behaviour and the physicochemical properties of this novel titanium alloy have been studied. Relationship of surface chemistry and surface electric charge with protein adsorption and cell adhesion has been evaluated due to its role for understanding the mechanism of biological interactions with tissues. The Ti25Nb21Hf alloy presented a lower elastic modulus than commercial alloys with a superior ultimate strength and yield strength than CP-Ti and very close to Ti6Al4V. It also exhibited good corrosion resistance. Furthermore, the results revealed that it had no cytotoxic effect on rat mesenchymal stem cells and allowed protein adsorption and cell adhesion. The experimental results make this alloy a promising material for bone substitution or for biomedical devices.

  10. Impact and Origin of Interface States in MOS Capacitor with Monolayer MoS2 and HfO2 High-k Dielectric

    NASA Astrophysics Data System (ADS)

    Xia, Pengkun; Feng, Xuewei; Ng, Rui Jie; Wang, Shijie; Chi, Dongzhi; Li, Cequn; He, Zhubing; Liu, Xinke; Ang, Kah-Wee

    2017-01-01

    Two-dimensional layered semiconductors such as molybdenum disulfide (MoS2) at the quantum limit are promising material for nanoelectronics and optoelectronics applications. Understanding the interface properties between the atomically thin MoS2 channel and gate dielectric is fundamentally important for enhancing the carrier transport properties. Here, we investigate the frequency dispersion mechanism in a metal-oxide-semiconductor capacitor (MOSCAP) with a monolayer MoS2 and an ultra-thin HfO2 high-k gate dielectric. We show that the existence of sulfur vacancies at the MoS2-HfO2 interface is responsible for the generation of interface states with a density (Dit) reaching ~7.03 × 1011 cm-2 eV-1. This is evidenced by a deficit S:Mo ratio of ~1.96 using X-ray photoelectron spectroscopy (XPS) analysis, which deviates from its ideal stoichiometric value. First-principles calculations within the density-functional theory framework further confirms the presence of trap states due to sulfur deficiency, which exist within the MoS2 bandgap. This corroborates to a voltage-dependent frequency dispersion of ~11.5% at weak accumulation which decreases monotonically to ~9.0% at strong accumulation as the Fermi level moves away from the mid-gap trap states. Further reduction in Dit could be achieved by thermally diffusing S atoms to the MoS2-HfO2 interface to annihilate the vacancies. This work provides an insight into the interface properties for enabling the development of MoS2 devices with carrier transport enhancement.

  11. Impact and Origin of Interface States in MOS Capacitor with Monolayer MoS2 and HfO2 High-k Dielectric

    PubMed Central

    Xia, Pengkun; Feng, Xuewei; Ng, Rui Jie; Wang, Shijie; Chi, Dongzhi; Li, Cequn; He, Zhubing; Liu, Xinke; Ang, Kah-Wee

    2017-01-01

    Two-dimensional layered semiconductors such as molybdenum disulfide (MoS2) at the quantum limit are promising material for nanoelectronics and optoelectronics applications. Understanding the interface properties between the atomically thin MoS2 channel and gate dielectric is fundamentally important for enhancing the carrier transport properties. Here, we investigate the frequency dispersion mechanism in a metal-oxide-semiconductor capacitor (MOSCAP) with a monolayer MoS2 and an ultra-thin HfO2 high-k gate dielectric. We show that the existence of sulfur vacancies at the MoS2-HfO2 interface is responsible for the generation of interface states with a density (Dit) reaching ~7.03 × 1011 cm−2 eV−1. This is evidenced by a deficit S:Mo ratio of ~1.96 using X-ray photoelectron spectroscopy (XPS) analysis, which deviates from its ideal stoichiometric value. First-principles calculations within the density-functional theory framework further confirms the presence of trap states due to sulfur deficiency, which exist within the MoS2 bandgap. This corroborates to a voltage-dependent frequency dispersion of ~11.5% at weak accumulation which decreases monotonically to ~9.0% at strong accumulation as the Fermi level moves away from the mid-gap trap states. Further reduction in Dit could be achieved by thermally diffusing S atoms to the MoS2-HfO2 interface to annihilate the vacancies. This work provides an insight into the interface properties for enabling the development of MoS2 devices with carrier transport enhancement. PMID:28084434

  12. {beta} decay of the 21/2{sup +} isomer in {sup 93}Mo and level structure of {sup 93}Nb

    SciTech Connect

    Hori, T.; Masue, T.; Odahara, A.; Kura, K.; Tajiri, K.; Shimoda, T.; Fukuchi, T.; Suzuki, T.; Wakabayashi, Y.; Gono, Y.; Ogawa, K.

    2009-09-15

    The {gamma} rays associated with {beta} decay of the 21/2{sup +} isomer in {sup 93}Mo (E{sub x}=2.425 MeV, T{sub 1/2}=6.85 h) were measured with a selective sensitivity to long-lived isomer decays. A new 1262-keV transition was found in the {gamma}-{gamma} coincidence measurement, and it was attributed to a transition in {sup 93}Nb, which is the daughter nucleus of the {beta} decay of the {sup 93}Mo isomer, from the 2.753- to the 1.491-MeV levels. Accurate {gamma}-ray intensity balances have determined the {beta}-decay intensity from the {sup 93}Mo isomer to the 2.753-MeV level in {sup 93}Nb and placed no appreciable intensity for the previously reported {beta}-decay branching to the 2.180-MeV level, for which a recent in-beam {gamma}-ray experiment assigned to be I{sup {pi}} = 17/2{sup -}. Based on the {gamma}-ray intensities from the 2.753-MeV level, spin-parity assignment of this level was revised from 21/2{sup +} to 19/2{sup +}. The observed {beta}-decay intensity and the spin-parity assignment were explained by the jj-coupling shell model calculations.

  13. Rich structural phase diagram and thermoelectric properties of layered tellurides Mo{sub 1−x}Nb{sub x}Te{sub 2}

    SciTech Connect

    Ikeura, Koji; Sakai, Hideaki; Bahramy, Mohammad Saeed; Ishiwata, Shintaro

    2015-04-01

    MoTe{sub 2} is a rare transition-metal ditelluride having two kinds of layered polytypes, hexagonal structure with trigonal prismatic Mo coordination and monoclinic structure with octahedral Mo coordination. The monoclinic distortion in the latter is caused by anisotropic metal-metal bonding. In this work, we have examined the Nb doping effect on both polytypes of MoTe{sub 2} and clarified a structural phase diagram for Mo{sub 1−x}Nb{sub x}Te{sub 2} containing four kinds of polytypes. A rhombohedral polytype crystallizing in polar space group has been newly identified as a high-temperature metastable phase at slightly Nb-rich composition. Considering the results of thermoelectric measurements and the first-principles calculations, the Nb ion seemingly acts as a hole dopant in the rigid band scheme. On the other hand, the significant interlayer contraction upon the Nb doping, associated with the Te p-p hybridization, is confirmed especially for the monoclinic phase, which implies a shift of the p-band energy level. The origin of the metal-metal bonding in the monoclinic structure is discussed in terms of the d electron counting and the Te p-p hybridization.

  14. Glass formation and magnetic properties in the Co and Fe-based amorphous alloy with small Mo or Nb additions

    NASA Astrophysics Data System (ADS)

    Jo, Hye-In; Choi-Yim, Haein

    2012-02-01

    The ferromagnetic metallic glass alloys in the Co-Fe-B-Si-M (M = Mo or Nb) system were investigated. Ingots of [(Co1- x Fe x )0.75B0.2Si0.05]96Mo4 ( x = 0, 0.2, 0.5, 0.8, 1.0) and [(Co1- x Fe x )0.75 B0.2Si0.05]96Nb4 ( x = 0, 0.2, 0.5, 0.8, 1.0) alloys were cast into about 30 µm-thick ribbons by using a melt spinning method. As-spun ribbons were identified as being fully amorphous by using X-ray diffraction (XRD). The thermal stability parameters, such as the supercooled liquid region (Δ T x = T g - T x ) and the exothermic heat (Δ H Exo ), were measured by using differential scanning calorimetry (DSC). For Co-Fe-B-Si-Mo alloys, Δ T x and Δ H Exo were in the range of 41.4-81.7 K and 23.40-104.21 J/g, and for Co-Fe-B-Si-Nb alloys, Δ T x and Δ H Exo were in the range of 60.4-88.0 K and 18.45-62.05 J/g, respectively. These glassy ribbons also exhibited semi-hard magnetic properties, i.e., a coercive force ( H c ) of 67.26-100.68 Oe and a saturation magnetization ( M s ) of 341.288-746.176 emu·cm3.

  15. Microstructural Evolution of the Interdiffusion Zone between U-9 Wt Pct Mo Fuel Alloy and Zr-1 Wt Pct Nb Cladding Alloy Upon Annealing

    NASA Astrophysics Data System (ADS)

    Neogy, S.; Laik, A.; Saify, M. T.; Jha, S. K.; Srivastava, D.; Dey, G. K.

    2017-03-01

    Diffusion couple formed between U-9 wt pct Mo and Zr-1 wt pct Nb alloys, proposed as fuel and clad materials, respectively, in nuclear research reactors, was annealed to investigate the microstructural evolution of the interdiffusion zone (IZ) as a function of temperature. A layered-type IZ microstructure was observed, the mechanism of development of which was elucidated. Mo2Zr phase, present as dispersoids, in the U-rich part of the as-bonded IZ evolved into a continuous layer and into a "massive" morphology upon annealing. The discontinuous precipitation reaction in the matrix adjoining the Mo2Zr phase, instigated by Mo depletion, generated lamellae of α-U phase within the γ-U(Mo,Zr) matrix. Zr-rich α-Zr(U) precipitates were observed in U-rich U-Mo-Zr matrix in the IZ next to the U-9Mo base material due to the clustering tendency of the matrix phase. The IZ next to Zr-1Nb base material comprised a "basket weave" microstructure of α-Zr laths with β-Zr(Nb,U) interlath boundaries, wherein an omega like transformation of the latter to δ-UZr2 was also noticed. The growth rates of the IZ were orders of magnitude lower when compared with the ones reported between the compositionally similar U-10 wt pct Mo alloy and the presently used Al or Al-Si cladding alloys.

  16. Epitaxial 2D MoSe2 (HfSe2) Semiconductor/2D TaSe2 Metal van der Waals Heterostructures.

    PubMed

    Tsoutsou, Dimitra; Aretouli, Kleopatra E; Tsipas, Polychronis; Marquez-Velasco, Jose; Xenogiannopoulou, Evangelia; Kelaidis, Nikolaos; Aminalragia Giamini, Sigiava; Dimoulas, Athanasios

    2016-01-27

    Molecular beam epitaxy of 2D metal TaSe2/2D MoSe2 (HfSe2) semiconductor heterostructures on epi-AlN(0001)/Si(111) substrates is reported. Electron diffraction reveals an in-plane orientation indicative of van der Waals epitaxy, whereas electronic band imaging supported by first-principles calculations and X-ray photoelectron spectroscopy indicate the presence of a dominant trigonal prismatic 2H-TaSe2 phase and a minor contribution from octahedrally coordinated TaSe2, which is present in TaSe2/AlN and TaSe2/HfSe2/AlN but notably absent in the TaSe2/MoSe2/AlN, indicating superior structural quality of TaSe2 grown on MoSe2. Apart from its structural and chemical compatibility with the selenide semiconductors, TaSe2 has a workfunction of 5.5 eV as measured by ultraviolet photoelectron spectroscopy, which matches very well with the semiconductor workfunctions, implying that epi-TaSe2 can be used for low-resistivity contacts to MoSe2 and HfSe2.

  17. Nd-Hf isotopic mapping of Late Mesozoic granitoids in the East Qinling orogen, central China: Constraint on the basements of terranes and distribution of Mo mineralization

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoxia; Wang, Tao; Ke, Changhui; Yang, Yang; Li, Jinbao; Li, Yinghong; Qi, Qiuju; Lv, Xingqiu

    2015-05-01

    Voluminous Late Mesozoic granitoids and the world's largest Mo deposits occur in the East Qinling. This paper presents the results of Nd-Hf isotopic mapping for the Late Mesozoic granitoids (155-105 Ma) and demonstrates their constraint on the basements and distribution of the Mo deposits in the East Qinling. This isotopic map, made by 98 (21 new and 77 published) whole-rock Nd isotopic and 29 (7 new and 22 published) average zircon Hf isotopic data, shows large variations of whole-rock εNd(t) values from -22.1 to -1.5, and the correspondingly Nd model ages (TDM(Nd)) from 2.83 to 0.79 Ga, and zircon εHf(t) values from -26.3 to +0.1 and two-stage Hf model ages (TDM2(Hf)) from 2.86 to 0.96 Ga. Three regions of variations have been identified from north to south: (a) εNd(t) values range from -22.1 to -10.9 with TDM(Nd) of 2.82-1.47 Ga, and εHf(t) values 26.3 to -13.5 with TDM2(Hf) 2.86-2.04 Ga; (b) εNd(t) values -13.9 to -1.5 with TDM(Nd) 2.02-0.79 Ga, and εHf(t) values -16.2 to +0.1 with TDM2(Hf) 1.96-0.96 Ga; and (c) εNd(t) values -6.3 to -4.5 with TDM(Nd) 1.28-1.12 Ga, and εHf(t) values -1.0 to -0.3 with TDM2(Hf) 1.25-1.22 Ga, respectively. The three regions approximately correspond to the three different terranes, the southern margin of the North China Block (NCB), the North Qinling Belt (NQB) and the South Qinling Belt (SQB), respectively. These demonstrate that the granitoids in the different terranes have distinct sources and their sources change from old to more juvenile from the north (southern margin of the NCB) to the south (SQB). These also reveal the distinct basements for the terranes in Late Mesozoic. The southern margin of the NCB contains widespread Neoarchaean to Paleoproterozoic basement, the NQB comprises Archaean to Neoproterozic basement and the SQB Mesoproterozic to Neoproterozic basement. All these suggest that the three terranes underwent different tectonic evolution and the continental crust of the East Qinling were mainly formed

  18. 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.

  19. Improving tribological properties of Ti-5Zr-3Sn-5Mo-15Nb alloy by double glow plasma surface alloying

    NASA Astrophysics Data System (ADS)

    Guo, Lili; Qin, Lin; Kong, Fanyou; Yi, Hong; Tang, Bin

    2016-12-01

    Molybdenum, an alloying element, was deposited and diffused on Ti-5Zr-3Sn-5Mo-15Nb (TLM) substrate by double glow plasma surface alloying technology at 900, 950 and 1000 °C. The microstructure, composition distribution and micro-hardness of the Mo modified layers were analyzed. Contact angles on deionized water and wear behaviors of the samples against corundum balls in simulated human body fluids were investigated. Results show that the surface microhardness is significantly enhanced after alloying and increases with treated temperature rising, and the contact angles are lowered to some extent. More importantly, compared to as-received TLM alloy, the Mo modified samples, especially the one treated at 1000 °C, exhibit the significant improvement of tribological properties in reciprocating wear tests, with lower specific wear rate and friction coefficient. To conclude, Mo alloying treatment is an effective approach to obtain excellent comprehensive properties including optimal wear resistance and improved wettability, which ensure the lasting and safety application for titanium alloys as the biomedical implants.

  20. A Novel Mo and Nb Microalloyed Medium Mn TRIP Steel with Maximal Ultimate Strength and Moderate Ductility

    NASA Astrophysics Data System (ADS)

    Cai, Minghui; Li, Zhun; Chao, Qi; Hodgson, Peter D.

    2014-11-01

    The multi-phase, metastable, and multi-scale (M3) constitution of a novel transformation-induced plasticity (TRIP) steel (Fe-0.17C-6.5Mn-1.1Al-0.22Mo-0.05Nb, wt pct) was designed through thermodynamic calculations combined with experimental analysis. In this study, Mo and Nb microalloying was used to control the fraction of retained austenite and its mechanical stability during tensile deformation and to improve the yield strength. Thermodynamic calculations were developed to determine the critical annealing temperature, at which a large fraction of retained austenite (~38 pct) would be obtained through the effects of solute enrichment. The experimental observation was in good agreement with the predicted results. According to the critical annealing temperature, such an ultrafine (<200 nm) M3, microstructure with optimum mechanical stability was successfully achieved. The results of this work demonstrated the superior performance with improved yield strength of 1020 to 1140 MPa and excellent ductility (>30 pct), as compared with other TRIP steels. Both angle-selective backscatter and electron backscatter diffraction techniques were employed to interpret the transformation from the deformed martensitic laths to the ultrafine austenite and ferrite duplex structure.

  1. Memcapacitive characteristics in reactive-metal (Mo, Al)/HfO{sub X}/n-Si structures through migration of oxygen by applied voltage

    SciTech Connect

    Yang, Paul; Noh, Young Jun; Baek, Yoon-Jae; Zheng, Hong; Yoon, Tae-Sik; Kang, Chi Jung; Lee, Hyun Ho

    2016-02-01

    Memcapacitive characteristics were investigated in metal-oxide-semiconductor (MOS) structure of reactive electrode (Mo, Al) and hafnium oxide (HfO{sub X}) on n-type Si substrate. The capacitance-voltage curves exhibited sequentially changing capacitance with memory function as repeating voltage sweeps, featured the memcapacitive behaviors. The saturation capacitance was decreased by repeating +V sweeps, while barely changed by −V sweeps. Also, the capacitance-time curves disclosed the same tendency. However, the MOS structure with inert Pt electrode did not show the capacitance change. The memcapacitive behaviors were induced by the migration of oxygen ions from HfO{sub X} to reactive electrodes by applied voltage, which altered the permittivity of HfO{sub X}.

  2. Effects of annealing on electrical performance of multilayer MoS2 transistors with atomic layer deposited HfO2 gate dielectric

    NASA Astrophysics Data System (ADS)

    Wen, Ming; Xu, Jingping; Liu, Lu; Lai, Pui-To; Tang, Wing-Man

    2016-09-01

    Atomic layer deposited HfO2 annealed in different ambients (N2, O2, and NH3) is used to replace SiO2 as a gate dielectric for fabricating back-gated multilayer MoS2 transistors. Excellent electrical properties such as a mobility of 15.1 cm2/(V·s), an on/off ratio exceeding 107, and a hysteresis of 0.133 V are achieved for samples annealed in NH3 at 400 °C for 10 min. This is caused by the NH3 annealing passivation effects that reduce defective states in the HfO2 dielectric and the interface. The capacitance equivalent thickness is only 7.85 nm, which is quite small for a back-gated MoS2 transistor and is conducive to the scaling down of the device.

  3. Crystal and electronic structure and magnetic properties of divalent europium perovskite oxides EuMO3 (M = Ti, Zr, and Hf): experimental and first-principles approaches.

    PubMed

    Akamatsu, Hirofumi; Fujita, Koji; Hayashi, Hiroyuki; Kawamoto, Takahiro; Kumagai, Yu; Zong, Yanhua; Iwata, Koji; Oba, Fumiyasu; Tanaka, Isao; Tanaka, Katsuhisa

    2012-04-16

    A comparative study of the crystal and electronic structure and magnetism of divalent europium perovskite oxides EuMO(3) (M = Ti, Zr, and Hf) has been performed on the basis of both experimental and theoretical approaches playing complementary roles. The compounds were synthesized via solid-state reactions. EuZrO(3) and EuHfO(3) have an orthorhombic structure with a space group Pbnm at room temperature contrary to EuTiO(3), which is cubic at room temperature. The optical band gaps of EuZrO(3) and EuHfO(3) are found to be about 2.4 and 2.7 eV, respectively, much larger than that of EuTiO(3) (0.8 eV). On the other hand, the present compounds exhibit similar magnetic properties characterized by paramagnetic-antiferromagnetic transitions at around 5 K, spin flop at moderate magnetic fields lower than 1 T, and the antiferromagnetic nearest-neighbor and ferromagnetic next-nearest-neighbor exchange interactions. First-principles calculations based on a hybrid Hartree-Fock density functional approach yield lattice constants, band gaps, and magnetic interactions in good agreement with those obtained experimentally. The band gap excitations are assigned to electronic transitions from the Eu 4f to Mnd states for EuMO(3) (M = Ti, Zr, and Hf and n = 3, 4, and 5, respectively).

  4. Mechanical properties of monolayer sulphides: a comparative study between MoS2, HfS2 and TiS3.

    PubMed

    Kang, Jun; Sahin, Hasan; Peeters, François M

    2015-11-07

    The in-plane stiffness (C), Poisson's ratio (ν), Young's modulus and ultimate strength (σ) along two different crystallographic orientations are calculated for the single layer crystals: MoS2, HfS2 and TiS3 in 1H, 1T and monoclinic phases. We find that MoS2 and HfS2 have isotropic in-plane stiffnesses of 124.24 N m(-1) and 79.86 N m(-1), respectively. While for TiS3 the in-plane stiffness is highly anisotropic due to its monoclinic structure, with Cx = 83.33 N m(-1) and Cy = 133.56 N m(-1) (x and y are parallel to its longer and shorter in-plane lattice vectors.). HfS2 which is in the 1T phase has the smallest anisotropy in its ultimate strength, whereas TiS3 in the monoclinic phase has the largest. Along the armchair direction MoS2 has the largest σ of 23.48 GPa, whereas along y TiS3 has the largest σ of 18.32 GPa. We have further analyzed the band gap response of these materials under uniaxial tensile strain, and find that they exhibit different behavior. Along both armchair and zigzag directions, the band gap of MoS2 (HfS2) decreases (increases) as strain increases, and the response is almost isotropic. For TiS3, the band gap decreases when strain is along x, while if strain is along y, the band gap increases first and then decreases beyond a threshold strain value. The different characteristics observed in these sulphides with different structures shed light on the relationship between the structure and properties, which is useful for applications in nanotechnology.

  5. Nanostructured multielement (TiHfZrNbVTa)N coatings before and after implantation of N+ ions (1018 cm-2): Their structure and mechanical properties

    NASA Astrophysics Data System (ADS)

    Pogrebnjak, A. D.; Bondar, O. V.; Borba, S. O.; Abadias, G.; Konarski, P.; Plotnikov, S. V.; Beresnev, V. M.; Kassenova, L. G.; Drodziel, P.

    2016-10-01

    Multielement high entropy alloy (HEA) nitride (TiHfZrNbVTa)N coatings were deposited by vacuum arc and their structural and mechanical stability after implantation of high doses of N+ ions, 1018 cm-2, were investigated. The crystal structure and phase composition were characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy, while depth-resolved nanoindentation tests were used to determine the evolution of hardness and elastic modulus along the implantation depth. XRD patterns show that coatings exhibit a main phase with fcc structure, which preferred orientation varies from (1 1 1) to (2 0 0), depending on the deposition conditions. First-principles calculations reveal that the presence of Nb atoms could favor the formation of solid solution with fcc structure in multielement HEA nitride. TEM results showed that amorphous and nanostructured phases were formed in the implanted coating sub-surface layer (∼100 nm depth). Concentration of nitrogen reached 90 at% in the near-surface layer after implantation, and decreased at higher depth. Nanohardness of the as-deposited coatings varied from 27 to 38 GPa depending on the deposition conditions. Ion implantation led to a significant decrease of the nanohardness to 12 GPa in the implanted region, while it reaches 24 GPa at larger depths. However, the H/E ratio is ⩾0.1 in the sub-surface layer due to N+ implantation, which is expected to have beneficial effect on the wear properties.

  6. M5Si3(M=Ti, Nb, Mo) Based Transition-Metal Silicides for High Temperature Applications

    SciTech Connect

    Tang, Zhihong

    2007-01-01

    Transition metal silicides are being considered for future engine turbine components at temperatures up to 1600 C. Although significant improvement in high temperature strength, room temperature fracture toughness has been realized in the past decade, further improvement in oxidation resistance is needed. Oxidation mechanism of Ti5Si3-based alloys was investigated. Oxidation behavior of Ti5Si3-based alloy strongly depends on the atmosphere. Presence of Nitrogen alters the oxidation behavior of Ti5Si3 by nucleation and growth of nitride subscale. Ti5Si3.2and Ti5Si3C0.5 alloys exhibited an excellent oxidation resistance in nitrogen bearing atmosphere due to limited dissolution of nitrogen and increased Si/Ti activity ratio. MoSi2 coating developed by pack cementation to protect Mo-based Mo-Si-B composites was found to be effective up to 1500 C. Shifting coating composition to T1+T2+Mo3Si region showed the possibility to extend the coating lifetime above 1500 C by more than ten times via formation of slow growing Mo3Si or T2 interlayer without sacrificing the oxidation resistance of the coating. The phase equilibria in the Nb-rich portion of Nb-B system has been evaluated experimentally using metallographic analysis and differential thermal analyzer (DTA). It was shown that Nbss (solid solution) and NbB are the only two primary phases in the 0-40 at.% B composition range, and the eutectic reaction L {leftrightarrow} NbSS + NbB was determined to occur at 2104 ± 5 C by DTA.

  7. Microstructure and Properties of a Refractory NbCrMo0.5Ta0.5TiZr Alloy (Postprint)

    DTIC Science & Technology

    2014-04-01

    phases was con- ucted with the use of an EDS detector attached to the field mission gun SEM. The results are given in Table 2. It is found that he...Microstruc- ture and properties of a refractory TaNbHfZrTi alloy, Unpublished paper, 2011. 10] J.-W. Yeh, S.-K. Chen, S.-J. Lin, J.-Y. Gan, T.-S. Chin , T

  8. Effect of aging temperature on the microstructures and mechanical properties of ZG12Cr9Mo1Co1NiVNbNB ferritic heat-resistant steel

    NASA Astrophysics Data System (ADS)

    Yang, Xue; Sun, Lan; Xiong, Ji; Zhou, Ping; Fan, Hong-yuan; Liu, Jian-yong

    2016-02-01

    The effect of aging on the mechanical properties and microstructures of a new ZG12Cr9Mo1Co1NiVNbNB ferritic heat resistant steel was investigated in this work to satisfy the high steam parameters of the ultra-supercritical power plant. The results show that the main precipitates during aging are Fe(Cr, Mo)23C6, V(Nb)C, and (Fe2Mo) Laves in the steel. The amounts of the precipitated phases increase during aging, and correspondingly, the morphologies of phases are similar to be round. Fe(Cr, Mo)23C6 appears along boundaries and grows with increasing temperature. In addition, it is revealed that the martensitic laths are coarsened and eventually happen to be polygonization. The hardness and strength decrease gradually, whereas the plasticity of the steel increases. What's more, the hardness of this steel after creep is similar to that of other 9%-12%Cr ferritic steels. Thus, ZG12Cr9Mo1Co1NiVNbNB can be used in the project.

  9. NbTiSiMo-X Alloys-Composition, Microstructure Refinement and Properties (Preprint)

    DTIC Science & Technology

    2009-03-01

    500MPa at 1,200°C). Unfortunately, these alloys have an inhomogeneous size and spatial distribution of silicides , low fracture strength under tension...300MPa) at all temperatures, and low oxidation resistance. The high volume fraction and non‐uniform size distribution of silicides were considered...alloy system. 15. SUBJECT TERMS Nb-base Silicides , Chemistry Modification, Refinement, Fracture, Oxidation Resistance 16. SECURITY

  10. Petrogenesis of the Yaochong granite and Mo deposit, Western Dabie orogen, eastern-central China: Constraints from zircon U-Pb and molybdenite Re-Os ages, whole-rock geochemistry and Sr-Nd-Pb-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Chen, Wei; Xu, Zhaowen; Qiu, Wenhong; Li, Chao; Yu, Yang; Wang, Hao; Su, Yang

    2015-05-01

    The Dabie orogen is among the most famous continent-continent collisional orogenic belts in the world, and is characterized by intensive post-collisional extension, magmatism and Mo mineralization. However, the genetic links between the mineralization and the geodynamic evolution of the orogen remain unresolved. In this paper, the Yaochong Mo deposit and its associated granitic stocks were investigated to elucidate this issue. Our new zircon U-Pb ages yielded an Early Cretaceous age (133.3 ± 1.3 Ma) for the Yaochong granite, and our molybdenite Re-Os dating gave a similar age (135 ± 1 Ma) for the Mo deposit. The Yaochong stock is characterized by high silica and alkali but low Mg, Fe and Ca. It is enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs: Rb, K, Th and U), but strongly depleted in heavy REEs, and high field strength elements (HFSEs: Nb, Ta, Ti and Y). The Yaochong granite has initial 87Sr/86Sr ratios of 0.7087-0.7096, and Pb isotopic ratios of (206Pb/204Pb)i = 16.599-16.704, (207Pb/204Pb)i = 15.170-15.618 and (208Pb/204Pb)i = 36.376-38.248. The granite has εNd(t) of -18.0 to -16.3 and εHf(t) values of -26.5 to -20.0. All these data indicate that the Yaochong granite is a high-K calc-alkaline fractionated I-type granite, and may have originated from partial melting of the thickened Yangtze continental crust. The Mo ores also show low radiogenic Pb isotopes similar to the Yaochong stock. Medium Re content in molybdenite (21.8-74.8 ppm) also suggests that the ore-forming materials were derived from the thickened lower crust with possibly minor mixing with the mantle. Similar to the Eastern Dabie orogen, the thickened crust beneath the Western Dabie orogen may also have experienced tectonic collapse, which may have exerted fundamental geodynamic controls on the two-stage Mo mineralization in the region.

  11. Effect of Composition and Deformation on Coarse-Grained Austenite Transformation in Nb-Mo Microalloyed Steels

    NASA Astrophysics Data System (ADS)

    Isasti, N.; Jorge-Badiola, D.; Taheri, M. L.; López, B.; Uranga, P.

    2011-12-01

    Thermomechanical processing of microalloyed steels containing niobium can be performed to obtain deformed austenite prior to transformation. Accelerated cooling can be employed to refine the final microstructure and, consequently, to improve both strength and toughness. This general rule is fulfilled if the transformation occurs on a quite homogeneous austenite microstructure. Nevertheless, the presence of coarse austenite grains before transformation in different industrial processes is a usual source of concern, and regarding toughness, the coarsest high-angle boundary units would determine its final value. Sets of deformation dilatometry tests were carried out using three 0.06 pct Nb microalloyed steels to evaluate the effect of Mo alloying additions (0, 0.16, and 0.31 pct Mo) on final transformation from both recrystallized and unrecrystallized coarse-grained austenite. Continuous cooling transformation (CCT) diagrams were created, and detailed microstructural characterization was achieved through the use of optical microscopy (OM), field emission gun scanning electron microscopy (FEGSEM), and electron backscattered diffraction (EBSD). The resultant microstructures ranged from polygonal ferrite (PF) and pearlite (P) at slow cooling ranges to bainitic ferrite (BF) accompanied by martensite (M) for fast cooling rates. Plastic deformation of the parent austenite accelerated both ferrite and bainite transformation, moving the CCT curves to higher temperatures and shorter times. However, an increase in the final heterogeneity was observed when BF packets were formed, creating coarse high-angle grain boundary units.

  12. 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.

  13. Development of a Mo-Si-B coating for Nb-based Alloys and the Effects of Zr Additions to Mo-Si-B Coatings for Enhanced Oxidation Protection in Ultra-High Temperature Applications

    NASA Astrophysics Data System (ADS)

    Lu-Steffes, Otto John

    Higher efficiencies and reduced emissions performance of fossil fuel energy systems are achieved with increasing operation temperatures. This increase in operating temperature requires the use of materials with higher melting points such as refractory metal alloys. However, refractory metals suffer from catastrophic oxidation in this type of environment. Thus, oxidation protection for refractory metal alloys is a crucial step in developing next generation ultra-high temperature materials. To meet this challenge, an oxidation resistant coating for Nb based alloys has been designed as well as the incorporation of zirconium into the Mo-Si-B coating to provide further corrosion protection and a reduction in temperature for the underlying multi-layered structure. Niobium samples coated with a Mo-Si-B coating demonstrate enhanced oxidation protection compared to samples only coated with Si-B. Thermogravimetric analysis testing at 1300°C for 24 hours for both the Mo-Si-B coated Nb and Nb-based alloys show enhanced oxidation protection with mass changes of 0.44 mg/cm2 and 0.55 mg/cm2, respectively, compared to the uncoated alloy that had a mass change of 87.6 mg/cm2. To demonstrate the design concept for a coating with thermal barrier behavior, Zr is added to the Mo-Si-B coating through the pack cementation technique. The resulting coating shows that the Zr reacts with the aluminosilica top layer to form Zr silicides and ZrO2. Upon oxidation, the coating forms a mixed top layer composed of borosilica, ZrO2 and ZrSiO 4. Oxidation testing of the Zr modified Mo-Si-B coating exhibits low mass change indicating that the coating provides oxidation protection and that the Zr additions do not interfere with the oxidation protection of the Mo-Si-B coating. Finite element modeling using object oriented finite element analysis of the coating structures yielded an evaluation of the mechanical and thermal properties of the coatings, providing insight into the thermal performance and

  14. Band alignment of HfO{sub 2}/multilayer MoS{sub 2} interface determined by x-ray photoelectron spectroscopy: Effect of CHF{sub 3} treatment

    SciTech Connect

    Liu, Xinke; He, Jiazhu; Tang, Dan; Jia, Fang; Lu, Youming Zhu, Deliang; Liu, Wenjun; Cao, Peijiang; Han, Sun; Liu, Qiang; Wen, Jiao; Yu, Wenjie; Pan, Jisheng; He, Zhubing; Ang, Kah-Wee

    2015-09-07

    The energy band alignment between HfO{sub 2}/multilayer (ML)-MoS{sub 2} was characterized using high-resolution x-ray photoelectron spectroscopy. The HfO{sub 2} was deposited using an atomic layer deposition tool, and ML-MoS{sub 2} was grown by chemical vapor deposition. A valence band offset (VBO) of 1.98 eV and a conduction band offset (CBO) of 2.72 eV were obtained for the HfO{sub 2}/ML-MoS{sub 2} interface without any treatment. With CHF{sub 3} plasma treatment, a VBO and a CBO across the HfO{sub 2}/ML-MoS{sub 2} interface were found to be 2.47 eV and 2.23 eV, respectively. The band alignment difference is believed to be dominated by the down-shift in the core level of Hf 4d and up-shift in the core level of Mo 3d, or the interface dipoles, which caused by the interfacial layer in rich of F.

  15. Dynamic environmental embrittlement of an [alpha][sub 2] titanium aluminide. [Ti-25Al-10Nb-3V-1Mo

    SciTech Connect

    Ward, C.H. ); Williams, J.C. ); Thompson, A.W. )

    1993-05-01

    Titanium aluminide alloys based on the [alpha][sub 2] phase were originally developed to extend the application range of titanium by providing improved elevated temperature strength and environmental resistance. These improvements were to come from the much larger concentrations of aluminum added to make these alloys. It was hoped that the increased amount of aluminum would favor the formation of a continuous, environmentally protective layer of alumina, Al[sub 2]O[sub 3], at the alloy's surface. Tensile and creep testing these alloys at elevated temperatures ([ge][approximately]450 C) in an air environment results in circumferential cracking along the specimen surface. This cracking can lead to premature failure as compared to vacuum testing. Balsone has observed this behavior in Ti-24Al-11Nb tensile tested in air. He repeated the tensile testing in vacuum at 550 C and 650 C, finding that the surface cracking disappeared and that the tensile elongation was significantly increased. From this, Balsone deduced that there was a significant effect of the environment, presumably oxygen embrittlement, on tensile properties at temperatures as low as 550 C. Vacuum tensile testing of Ti-25Al-10Nb-3V-1Mo (Ti-25-10-3-1) also results in a significant improvement in tensile elongation. The intent of the present investigation was to further study the effect of an air environment at elevated temperature on the tensile elongation of Ti-25-10-3-1. In particular, environmentally assisted surface crack growth into the tensile specimen was of interest.

  16. 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.

  17. Development and Oxidation Resistance of Plasma Sprayed Mo(Si,Al)2 Coating on Nbss/Nb5Si3 in Situ Composites

    NASA Astrophysics Data System (ADS)

    Yao, Dendzun; Wei, Haixia; Zhou, Chungen

    A Mo(Si,Al)2 coating is developed to protect Nbss/Nb5Si3 in situ composite by plasma spraying. The binary layers of this coating consist of an inner interdiffusion layer surrounded by Mo(Si,Al)2 layer with C40 crystal structure. After oxidation at 1250°C for 100h, Mo(Si,Al)2 coating exhibited an excellent protection against oxidation and good adherence to substrate. The oxidation curve followed parabolic law and even after oxidation at high temperature for 100h, the weight gain per unit area of Mo(Si,Al)2 coating is 8.24mg/cm2. No evident spalling of coating to substrate was observed but a continuous and compact layer of Al2O3 was formed on coating surface to prevent oxidation below coating and substrate.

  18. 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.

  19. 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.

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

    PubMed

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

    2016-05-17

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

  1. 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...have the best combina- tion of required properties, such as creep resistance , tem- perature capability, environmental resistance , and damage tolerance

  2. Metastable β-type Ti-30Nb-1Mo-4Sn Alloy with Ultralow Young's Modulus and High Strength

    NASA Astrophysics Data System (ADS)

    Hu, Liang; Guo, Shun; Meng, Qingkun; Zhao, Xinqing

    2014-02-01

    The effect of thermo-mechanical treatment on the mechanical properties of a novel metastable β-type Ti-30Nb-1Mo-4Sn (wt pct) alloy has been investigated. The solution-treated alloy consists of β and α″ phases and exhibits a two-stage yielding with a low yield stress (around 100 MPa). After cold rolling at a reduction of 87.5 pct and subsequent annealing treat at 623 K (350 °C) for 30 minutes, a fine microstructure with nano-sized α precipitates distributed in small β grains as well as high density of dislocations was obtained to achieve a yield strength of 954 MPa and an ultimate tensile strength of 999 MPa. With low stability of β phase and small volume fraction of α precipitates, the annealed specimen exhibits a low Young's modulus of 45 GPa. Such an excellent combination of the low elastic modulus and high strength in mechanical properties indicates a great potential candidate for biomedical applications.

  3. Electronic structures and transport properties of a MoS2-NbS2 nanoribbon lateral heterostructure.

    PubMed

    Yang, Zhixiong; Pan, Jiangling; Liu, Qi; Wu, Nannan; Hu, Mengli; Ouyang, Fangping

    2017-01-04

    Lateral heterostructures built from an armchair MoS2 nanoribbon (AMoS2NR) and an armchair NbS2 nanoribbon (ANbS2NR) were studied based on first-principles calculations and a non-equilibrium Green's function method. It is found that the work function of the AMoS2NR shows substantial oscillation with increasing nanoribbon width, which is different from the work functions of other kinds of nanoribbons. The AMoS2NR-ANbS2NR lateral heterostructure exhibits an anomalous transport gap that is much larger than the bandgap of the AMoS2NR. As a result, a field effect transistor with AMoS2NR as the channel and ANbS2NRs as electrodes has high on-off ratios of 10(6)-10(7) and a tiny leakage current of the order of 10(-8) μA. These results suggest that lateral metal-semiconductor heterostructures of transition metal dichalcogenides may have potential applications in nanodevices with low energy consumption.

  4. Blister formation on 13Cr2MoNbVB ferritic-martensitic steel exposed to hydrogen plasma

    NASA Astrophysics Data System (ADS)

    Nikitin, A. V.; Tolstolutskaya, G. D.; Ruzhytskyi, V. V.; Voyevodin, V. N.; Kopanets, I. E.; Karpov, S. A.; Vasilenko, R. L.; Garner, F. A.

    2016-09-01

    The influence of pre-irradiation specimen deformation level on surface blister formation and sub-surface cracking of dual-phase 13Cr2MoNbVB ferritic-martensitic steel was studied using glow discharge hydrogen plasma with ion energy of 1 keV to fluences of 2 × 1025 H/m2. Protium was used for most studies, but deuterium was used for measuring the depth dependence of hydrogen diffusion. Formation of blisters was observed in the temperature range 230-340 K. It was found that pre-irradiation deformation caused changes in the threshold fluences of blister formation and also in blister size distribution. Subsurface cracks located on grain boundaries far beyond the implantation zone were formed concurrently with blisters, arising from hydrogen diffusion and trapping at defects. It was observed that cracks as long as 1 mm in length were formed in 95% deformed steel at depths up to 500 μm from surface.

  5. 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

  6. 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.

  7. 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

  8. Mathematical modeling of the hot strip rolling of microalloyed Nb, multiply-alloyed Cr-Mo, and plain C-Mn steels

    NASA Astrophysics Data System (ADS)

    Siciliano, Fulvio; Jonas, John J.

    2000-02-01

    Industrial mill logs from seven different hot strip mills (HSMs) were analyzed in order to calculate the mean flow stresses (MFSs) developed in each stand. The schedules were typical of the processing of microalloyed Nb, multiply-alloyed Cr-Mo, and plain C-Mn steels. The calculations, based on the Sims analysis, take into account work roll flattening, redundant strain, and the forward slip ratio. The measured stresses are then compared to the predictions of a model based on an improved Misaka MFS equation, in which solute effects, strain accumulation, and the kinetics of static recrystallization (SRX) and metadynamic recrystallization (MDRX) are fully accounted for. Good agreement between the measured and predicted MFSs is obtained over the whole range of rolling temperatures. The evolution of grain size and the fractional softening are also predicted by the model during all stages of strip rolling. Special attention was paid to the Nb steels, in which the occurrence of Nb(C, N) precipitation strongly influences the rolling behavior, preventing softening between passes. The present study leads to the conclusion that Mn addition retards the strain-induced precipitation of Nb; by contrast, Si addition has an accelerating effect. The critical strain for the onset of dynamic recrystallization (DRX) in Nb steels is derived, and it is shown that the critical strain/peak strain ratio decreases with increasing Nb content; furthermore, Mn and Si have marginal but opposite effects. It is demonstrated that DRX followed by MDRX occurs under most conditions of hot strip rolling; during the initial passes, it is due to high strains, low strain rates, and high temperatures, and, in the final passes, it is a consequence of strain accumulation.

  9. Conformational distribution of baclofen analogues by 1H and 13C NMR analysis and ab initio HF MO STO-3G or STO-3G* calculations

    NASA Astrophysics Data System (ADS)

    Vaccher, Claude; Berthelot, Pascal; Debaert, Michel; Vermeersch, Gaston; Guyon, René; Pirard, Bernard; Vercauteren, Daniel P.; Dory, Magdalena; Evrard, Guy; Durant, François

    1993-12-01

    The conformations of 3-(substituted furan-2-yl) and 3-(substituted thien-2-yl)-γ-aminobutyric acid 1-9 in solution (D 2O) are estimated from high-resolution (300 MHz) 1H NMR coupling data. Conformations and populations of conformers are calculated by means of a modified Karplus-like relationship for the vicinal coupling constants. The results are compared with X-ray crystallographic investigations (torsion angles) and ab initio HF MO ST-3G or STO-3G* calculations. 1H NMR spectral analysis shows how 1-9 in solution retain the preferred g- conformation around the C3C4 bond, as found in the solid state, while a partial rotation is set up around the C2C3 bond: the conformations about C2C3 are all highly populated in solution. The 13C spin-lattice relaxation times are also discussed.

  10. Topological insulators in the ordered double transition metals M2'M″C2 MXenes (M'=Mo , W; M″=Ti , Zr, Hf)

    NASA Astrophysics Data System (ADS)

    Khazaei, Mohammad; Ranjbar, Ahmad; Arai, Masao; Yunoki, Seiji

    2016-09-01

    The family of two-dimensional transition metal carbides, so called MXenes, has recently found new members with ordered double transition metals M2'M″C2 , where M' and M″ stand for transition metals. Here, using a set of first-principles calculations, we demonstrate that some of the newly added members, oxide M2'M″C2 (M'=Mo , W; M″=Ti , Zr, Hf) MXenes, are topological insulators. The nontrivial topological states of the predicted MXenes are revealed by the Z2 index, which is evaluated from the parities of the occupied bands below the Fermi energy at time reversal invariant momenta, and also by the presence of the edge states. The predicted M2'M″C2O2 MXenes show nontrivial gaps in the range of 0.041-0.285 eV within the generalized gradient approximation and 0.119-0.409 eV within the hybrid functional. The band gaps are induced by the spin-orbit coupling within the degenerate states with dx2-y2 and dx y characters of M' and M″, while the band inversion occurs at the Γ point among the degenerate dx2-y2/dx y orbitals and a nondegenerate d3 z2-r2 orbital, which is driven by the hybridization of the neighboring orbitals. The phonon dispersion calculations find that the predicted topological insulators are structurally stable. The predicted W-based MXenes with large band gaps might be suitable candidates for many topological applications at room temperature. In addition, we study the electronic structures of thicker ordered double transition metals M2'M2″C3O2 (M'=Mo , W; M″=Ti , Zr, Hf) and find that they are nontrivial topological semimetals. Among the predicted topological insulators and topological semimetals, Mo2TiC2 and Mo2Ti2C3 functionalized with a mixture of F, O, and OH have already been synthesized, and therefore some of the topological materials proposed here can be experimentally accessed.

  11. Geological, geochronological, geochemical, and Sr-Nd-O-Hf isotopic constraints on origins of intrusions associated with the Baishan porphyry Mo deposit in eastern Tianshan, NW China

    NASA Astrophysics Data System (ADS)

    Wang, Yinhong; Xue, Chunji; Liu, Jiajun; Zhang, Fangfang

    2016-10-01

    The Baishan porphyry Mo deposit (0.72 Mt; 0.06 % Mo) is located in the interior of the eastern Tianshan orogenic belt in Xinjiang, NW China. The deposit comprises 15 orebodies that are associated with monzogranite and granite porphyry stocks and are structurally controlled by roughly EW-trending faults. Secondary ion mass spectrometry (SIMS) zircon U-Pb dating of the monzogranite and granite porphyry yielded the Middle Triassic age (228 ± 2 to 227 ± 2 Ma), which coincide with the molybdenite Re-Os model ages ranging from 226 ± 3 to 228 ± 3 Ma. The Triassic monzogranite and granite porphyry belong to high-K calc-alkaline series and are characterized by high SiO2 and Al2O3 and low MgO, TiO2, and P2O5 concentrations, with negative Eu anomalies (δEu = 0.55-0.91). The least-altered monzogranite and granite porphyry yield uniform ɛ Nd( t) values from +1.6 to +3.6, and wide (87Sr/86Sr) i ratios ranging between 0.7035 and 0.7071, indicating that they were derived from the lower crust. In situ O-Hf isotopic analyses on zircon using SIMS and laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) indicate that the δ18O and ɛ Hf( t) values of zircon from a monzogranite sample vary from 6.1 to 7.3 ‰ and +8.0 to +11.7, respectively, whereas zircon from a granite porphyry sample vary from 6.2 to 6.9 ‰ and +7.3 to +11.2, respectively. The geochemical and isotopic data imply that the primary magmas of the Baishan granite were likely derived from partial melts from the lower crust involving some mantle components. The Baishan Mo deposit and granitic emplacement were proposed to be most likely related to post-orogenic lithospheric extension and magmatic underplating. An extensional event coupled with the rising of hot mantle-derived melts triggered partial melting of the lower crust, as well as provided metals (Mo).

  12. Effect of thermomechanical treatment on the superelasticity of Ti-7.5Nb-4Mo-2Sn biomedical alloy.

    PubMed

    Zhang, D C; Tan, C G; Tang, D M; Zhang, Y; Lin, J G; Wen, C E

    2014-11-01

    Effects of thermomechanical treatment on the microstructure and superelasticity of Ti-7.5Nb-4Mo-2Sn biomedical alloy were investigated by using XRD measurement, optical microscope (OM), transmission electron microscope (TEM) and tensile tests. The titanium alloy samples were prepared by annealing at a temperature in the range of 600 to 1000°C after severe cold rolling; and the samples that were annealed at 800°C were further aged at 600 and 700°C. The volume fraction of α phases decreased while that of ω phases increase with increasing annealing temperature. The α→β transformation temperature of the alloy was determined to be between 700 and 800°C. The alloy that was annealed at 700°C exhibited a high level of superelasticity with relatively high first yield stress (σSIM) at room temperature because it contained a fine α phase. A certain amount of ω phases also resulted in an increase in σSIM, leading to an improvement in the superelasticity of the alloys that were annealed at 900 and 1000°C. Aging treatment led to the precipitations of α and ω phases in the alloy after annealing at 800°C; and the volume fraction of α phases decreased while that of ω phases increased with increasing aging temperature. Excellent superelasticity with high recovered strain (εrecoverable) and strain recovery rate (η) were obtained in the aged alloy due to the reinforcement of α and ω phases induced by aging treatment. The alloy annealed at 700°C for 0.5h exhibited the best superelasticity in all the thermomechanically treated alloys due to the strengthening from the subgrain refining and the precipitating of fine α phases.

  13. Nano-sized Mo- and Nb-doped TiO2 as Anode Materials for High Energy and High Power Hybrid Li-Ion Capacitors.

    PubMed

    Bauer, Dustin; Roberts, Alexander; Matsumi, Noriyoshi; Darr, Jawwad A

    2017-03-29

    Nano-sized Mo-doped titania (Mo0.1Ti0.9O2) and Nb-doped titania (Nb0.25Ti0.75O2) were directly synthesized via a continuous hydrothermal flow synthesis process. Materials characterization was conducted using physical techniques such as transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller specific surface area measurements and energy dispersive X-ray spectroscopy. Hybrid Li-Ion supercapacitors were made with either a Mo-doped or Nb-doped TiO2 negative electrode material and an activated carbon (AC) positive electrode. Cells were evaluated using electrochemical testing (cyclic voltammetry, constant charge discharge cycling). The hybrid Li-ion capacitors showed good energy densities at moderate power densities. When cycled in the potential window 0.5 to 3.0 V, the Mo0.1Ti0.9O2/AC hybrid supercapacitor showed the highest energy densities of 51 Wh kg-1 at a power of 180 W kg-1 with energy densities rapidly declining with increasing applied specific current. In comparison, the Nb0.25Ti0.75O2/AC hybrid supercapacitor maintained its energy density of 45 Wh kg-1 at 180 W kg-1 better, showing 36 Wh g-1 at 3200 W kg-1, which is a very promising mix of high energy and power densities. Reducing the voltage window to the range 1.0 to 3.0 V led to an increase in power density, with the Mo0.1Ti0.9O2/AC hybrid supercapacitor giving energy densities of 12 Wh kg-1 and 2.5 Wh kg-1 at power densities of 6700 W kg-1 and 14000 W kg-1, respectively.

  14. XPS and AES analysis of passive films on Fe-25Cr-X (X = Mo, V, Si and Nb) model alloys.

    PubMed

    Hubschmid, C; Landolt, D; Mathieu, H J

    1995-10-01

    Corrosion resistance of stainless steel is due to the presence of a thin passive film of typically 1-2 nm thickness. The influence of ternary alloying elements on the composition of passive films on Fe-Cr alloys and their pitting corrosion resistance has been investigated. Iron-chromium alloys were analyzed by XPS and AES with model alloys (Fe-25Cr-X with X = at % Mo, Si, V and Nb) formed in sulphate solution in the presence and absence of chloride ions. All ternary alloying elements increase the pitting potential compared to the corresponding binary alloy. Films formed in chloride containing sulphate solution contain both electrolyte anions. Scanning Auger microscopy reveals that for a two phase system such as Fe-25Cr-11Nb, the dendritic phase is enriched with chromium, while essentially all of the niobium is located in the interdendritic eutectic.

  15. Studies on the local structures and spin Hamiltonian parameters for the rhombic Nb4+ centers in MO2 (M = Sn, Ti and Ge) crystals

    NASA Astrophysics Data System (ADS)

    Zhang, Z.-H.; Wu, S.-Y.; Xu, P.; Li, L.-L.; Zhang, S.-X.

    2011-02-01

    The local structures and the spin Hamiltonian parameters for the substitutional Nb4+ centers in MO2 (M = Sn, Ti and Ge) crystals are theoretically studied using the perturbation formulas of these parameters for a 4d1 ion in a rhombically compressed octahedron. The above Nb4+ centers are found to experience the Jahn-Teller distortions, characteristic of the relative axial compressions (~ 0.01-0.02 Å) and the non-axial (planar) angular increases (~ 3°). As a result, the ligand octahedra are transformed from original elongation on host tetravalent cation sites to compression in the impurity centers, with additional non-axial distortions smaller than those in the hosts. The influences of the Jahn-Teller distortions and the ligand orbital contributions are also analyzed.

  16. 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.

  17. Probing the valence orbitals of transition metal-silicon diatomic anions: ZrSi, NbSi, MoSi, PdSi and WSi.

    PubMed

    Gunaratne, K Don Dasitha; Berkdemir, Cuneyt; Harmon, C L; Castleman, A W

    2013-04-28

    Evolution of electronic properties and the nature of bonding of the 4d-transition metal silicides (ZrSi, NbSi, MoSi and PdSi) are discussed, revealing interesting trends in the transition metal-silicon interactions across the period. The electronic properties of select transition metal silicide diatomics have been determined by anion photoelectron imaging spectroscopy and theoretical methods. The electron binding energy spectra and photoelectron angular distributions obtained by 2.33 eV (532 nm) photons have revealed the distinct features of these diatomics. The theoretical calculations were performed at the density functional theory (DFT) level using the unrestricted B3LYP hybrid functional and at the ab initio unrestricted coupled cluster singles and doubles (triplets) (UCCSD(T)) methods to assign the ground electronic states of the neutral and anionic diatomics. The excited electronic states were calculated by the DFT (TD-DFT)/UB3LYP method. We have observed that the valence molecular orbital configuration of the ZrSi and NbSi anions are significantly different from that of the MoSi and PdSi anions. By combining our experimental and theoretical results, we report that the composition of the highest occupied molecular orbitals shift from a majority of transition metal s- and d-orbital contribution in ZrSi and NbSi, to mainly silicon p-orbital contribution for MoSi and PdSi. We expect these observed atomic scale transition metal-silicon interactions to be of increasing importance with the miniaturization of devices approaching the sub-nanometer size regime.

  18. Partitioning of Nb, Mo, Ba, Ce, Pb, Th and U between immiscible carbonate and silicate liquids: Evaluating the effects of P2O5,F, and carbonate composition

    NASA Technical Reports Server (NTRS)

    Jones, J. H.; Walker, D.

    1993-01-01

    Previously we have reported carbonate liq./silicate liq. partition coefficients (D) for a standard suite of trace elements (Nb, Mo, Ba, Ce, Pb, Th, and U) and Ra and Pa as well. In brief, we have found that immiscible liquid partitioning is a strong function of temperature. As the critical temperature of the carbonate-silicate solvus is approached, all partition coefficients approach unity. Additionally, for the overwhelming majority of the partitioning elements, InD is a linear function of 'ionic field strength,' z/r, where z is the charge of the partitioned cation and r is its ionic radius.

  19. Improved upconversion luminescence and temperature sensing in Mo6+-doped LuNbO4:Er3+ phosphor under 1550 nm excitation

    NASA Astrophysics Data System (ADS)

    Tian, Bining; Chen, Baojiu; Sun, Jiashi; Li, Xiangping; Zhang, Jinshu; Hua, Ruinian

    2016-11-01

    LuNbO4: Mo6+,Er3+ phosphors were prepared via a solid-state reaction and characterized by x-ray diffraction (XRD) and upconversion luminescence (UCL) as well as temperature-dependent UC spectra. Under 1550 nm excitation, the characteristic UCL of the Er3+ ion, which originates from a three-photon process, is observed. An obvious UC enhancement can be found when the Mo6+ ions are doped, which may be attributed to the lower symmetry around Er3+. The optical thermometry behavior was studied as well. It is found that the maximum sensitivity is improved from 0.0053 K-1 to 0.0069 K-1 and the temperature revolution increases from 1.0 K to 0.7 K. Therefore, this work will provide a path for improving UCL and sensing sensitivity in Er3+-doped systems at an excitation of 1550 nm.

  20. Sub-barrier one- and two-neutron pickup measurements in {sup 32}S+{sup 93}Nb, {sup 98,100}Mo reactions at 180{degrees}

    SciTech Connect

    Roberts, R.B.; Gazes, S.B.; Mason, J.E.

    1993-04-01

    Excitation functions for sub-barrier one- and two-neutron pickup reactions were measured for E{sub lab}{le}106 MeV in {sup 32}S+{sup 93}Nb, {sup 98,100}Mo systems by detecting target-like recoils at 0{degrees} using a recoil mass spectrometer. Measured differential cross sections are compared to those predicted by the DWBA code PTOLEMY. The slopes of transfer probability versus distance of closest approach, are in good agreement with the slopes obtained from binding energies, indicating the absence of a {open_quotes}slope anomaly.{close_quotes} Angle-integrated transfer cross sections derived from measured 180{degrees} yields correlate with fusion enhancements in previously measured fusion yields for the {sup 32}S+{sup 98,100}Mo systems.

  1. Deposition and cyclic oxidation behavior of a protective (Mo,W)(Si,Ge) [sub 2] coating on Nb-base alloys

    SciTech Connect

    Mueller, A.; Wang, G. . Dept. of Materials Science and Engineering); Rapp, R.A. )

    1992-05-01

    A multicomponent diffusion coating has been developed to protect Nb-base alloys from high-temperature environmental attach. A solid solution of molybdenum and tungsten disilicide (Mo, W)Si[sub 2], constituted the primary coating layer which supported a slow-growing protective silica scale in service. Germanium additions were made during the coating process to improve the cyclic oxidation resistance by increasing the thermal expansion coefficient of the vitreous silica film formed and to avoid pesting by decreasing the viscosity of the protective film. In this paper, the development of the halide-activated pack cementation coating process to produce this (Mo,W)(Si,Ge)[sub 2] coating on Nb-base alloys is described. The results of cyclic oxidation for coupons coated under different conditions in air at 1370[degrees]C are presented. Many coupons have successfully passed 200 1 h cyclic oxidation tests at 1370[degrees]C with weight-gain values in the range of 1.2 to 1.6 mg/cm[sup 2].

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

    SciTech Connect

    Lin, Haisheng; Maggard, Paul A.

    2011-06-12

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

  4. Scalable fabrication of a hybrid field-effect and acousto-electric device by direct growth of monolayer MoS2/LiNbO3

    PubMed Central

    Preciado, Edwin; Schülein, Florian J.R.; Nguyen, Ariana E.; Barroso, David; Isarraraz, Miguel; von Son, Gretel; Lu, I-Hsi; Michailow, Wladislaw; Möller, Benjamin; Klee, Velveth; Mann, John; Wixforth, Achim; Bartels, Ludwig; Krenner, Hubert J.

    2015-01-01

    Lithium niobate is the archetypical ferroelectric material and the substrate of choice for numerous applications including surface acoustic wave radio frequencies devices and integrated optics. It offers a unique combination of substantial piezoelectric and birefringent properties, yet its lack of optical activity and semiconducting transport hamper application in optoelectronics. Here we fabricate and characterize a hybrid MoS2/LiNbO3 acousto-electric device via a scalable route that uses millimetre-scale direct chemical vapour deposition of MoS2 followed by lithographic definition of a field-effect transistor structure on top. The prototypical device exhibits electrical characteristics competitive with MoS2 devices on silicon. Surface acoustic waves excited on the substrate can manipulate and probe the electrical transport in the monolayer device in a contact-free manner. We realize both a sound-driven battery and an acoustic photodetector. Our findings open directions to non-invasive investigation of electrical properties of monolayer films. PMID:26493867

  5. Scalable fabrication of a hybrid field-effect and acousto-electric device by direct growth of monolayer MoS2/LiNbO3.

    PubMed

    Preciado, Edwin; Schülein, Florian J R; Nguyen, Ariana E; Barroso, David; Isarraraz, Miguel; von Son, Gretel; Lu, I-Hsi; Michailow, Wladislaw; Möller, Benjamin; Klee, Velveth; Mann, John; Wixforth, Achim; Bartels, Ludwig; Krenner, Hubert J

    2015-10-23

    Lithium niobate is the archetypical ferroelectric material and the substrate of choice for numerous applications including surface acoustic wave radio frequencies devices and integrated optics. It offers a unique combination of substantial piezoelectric and birefringent properties, yet its lack of optical activity and semiconducting transport hamper application in optoelectronics. Here we fabricate and characterize a hybrid MoS2/LiNbO3 acousto-electric device via a scalable route that uses millimetre-scale direct chemical vapour deposition of MoS2 followed by lithographic definition of a field-effect transistor structure on top. The prototypical device exhibits electrical characteristics competitive with MoS2 devices on silicon. Surface acoustic waves excited on the substrate can manipulate and probe the electrical transport in the monolayer device in a contact-free manner. We realize both a sound-driven battery and an acoustic photodetector. Our findings open directions to non-invasive investigation of electrical properties of monolayer films.

  6. Scalable fabrication of a hybrid field-effect and acousto-electric device by direct growth of monolayer MoS2/LiNbO3

    NASA Astrophysics Data System (ADS)

    Preciado, Edwin; Schülein, Florian J. R.; Nguyen, Ariana E.; Barroso, David; Isarraraz, Miguel; von Son, Gretel; Lu, I.-Hsi; Michailow, Wladislaw; Möller, Benjamin; Klee, Velveth; Mann, John; Wixforth, Achim; Bartels, Ludwig; Krenner, Hubert J.

    2015-10-01

    Lithium niobate is the archetypical ferroelectric material and the substrate of choice for numerous applications including surface acoustic wave radio frequencies devices and integrated optics. It offers a unique combination of substantial piezoelectric and birefringent properties, yet its lack of optical activity and semiconducting transport hamper application in optoelectronics. Here we fabricate and characterize a hybrid MoS2/LiNbO3 acousto-electric device via a scalable route that uses millimetre-scale direct chemical vapour deposition of MoS2 followed by lithographic definition of a field-effect transistor structure on top. The prototypical device exhibits electrical characteristics competitive with MoS2 devices on silicon. Surface acoustic waves excited on the substrate can manipulate and probe the electrical transport in the monolayer device in a contact-free manner. We realize both a sound-driven battery and an acoustic photodetector. Our findings open directions to non-invasive investigation of electrical properties of monolayer films.

  7. Formation of TiO2 layers on commercially pure Ti and Ti-Mo and Ti-Nb alloys by two-step thermal oxidation and their photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Sado, Shota; Ueda, Takatoshi; Ueda, Kyosuke; Narushima, Takayuki

    2015-12-01

    Anatase-containing TiO2 layers were formed on commercially pure (CP) Ti and Ti-25mass%Mo (Ti-25Mo) and Ti-25mass%Nb (Ti-25Nb) alloys by two-step thermal oxidation. The first-step treatment was conducted in an Ar-1%CO atmosphere at 1073 K for 3.6 ks, and the second-step treatment was conducted in air at 673-1073 K for 10.8 ks. The second-step temperature range for anatase formation was wider in the Ti alloys than in CP Ti. Photo-induced superhydrophilicity under UV irradiation was observed for the TiO2 layers with anatase fractions ≥0.6 on CP Ti and the Ti-25Mo alloy, and with anatase fractions ≥0.18 on the Ti-25Nb alloy. The TiO2 layers on the Ti-25Nb alloy exhibited excellent photocatalytic activity in the low anatase fraction region, which is considered to be caused by the incorporation of 1-3 at% Nb into the TiO2 layers. The rate constant of methylene blue degradation showed maxima at anatase fractions of 0.6-0.9.

  8. 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.

  9. 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.

  10. Study of the phase composition of silicide coatings, based on layered Nb-Mo structures, obtained by vacuum-arc deposition

    NASA Astrophysics Data System (ADS)

    Lozovan, A. A.; Betsofen, S. Ya; Lenkovets, A. S.

    2016-07-01

    A multilayer composite ∼1000 μm in thickness, formed by niobium and molybdenum layers (number of layers n = 230), is obtained by vacuum-arc deposition with subsequent siliconization of the surface layers at a temperature of 1200 °C. Layer-by-layer phase analysis is performed by X-ray diffraction and scanning electron microscopy. It is found that in the surface layers ∼130 μm in thickness, single-phase silicides (Nb x Mo1- x )Si2 are formed with the hexagonal C40 structure (Strukturbericht designations). Alternating layers of solid solutions based on niobium and molybdenum with a body-centered cubic (BCC) lattice are observed within the composite. The formation of solid solutions caused by heating of the coating leads to convergence of the values of the linear thermal expansion coefficient and Young's modulus at the interface between the layers.

  11. First-principles study of the mechanical properties of NiAl microalloyed by M (Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd)

    NASA Astrophysics Data System (ADS)

    Zhang, Caili; Han, Peide; Li, Jinmin; Chi, Mei; Yan, Lingyun; Liu, Yanping; Liu, Xuguang; Xu, Bingshe

    2008-05-01

    Structural, electronic and elastic properties for NiAl with 4d alloying elements M (Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd) have been studied using the first-principles pseudopotential density functional method within a generalized gradient approximation. From the elastic constants, C11, C12, C44, bulk modulus B0, Young's modulus E, the shear modulus G, the ratios of shear modulus to bulk modulus G/B0, negative Cauchy pressure parameter (C12 - C44) and Poisson's ratio ν calculated after structural full relaxation, M (Tc, Ru, Rh, Pd) alloying addition in NiAl has been shown to increase the stiffness of NiAl and improve its ductility. The density of states and charge density contour involving alloying additions of Ru were further investigated to clarify the electronic causes of the alloying additions.

  12. 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.

  13. 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.

  14. 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.

  15. Structure and electrical properties of Al-doped HfO₂ and ZrO₂ films grown via atomic layer deposition on Mo electrodes.

    PubMed

    Yoo, Yeon Woo; Jeon, Woojin; Lee, Woongkyu; An, Cheol Hyun; Kim, Seong Keun; Hwang, Cheol Seong

    2014-12-24

    The effects of Al doping in atomic-layer-deposited HfO2 (AHO) and ZrO2 (AZO) films on the evolutions of their crystallographic phases, grain sizes, and electric properties, such as their dielectric constants and leakage current densities, were examined for their applications in high-voltage devices. The film thickness and Al-doping concentration were varied in the ranges of 60-75 nm and 0.5-9.7%, respectively, for AHO and 55-90 nm and 1.0-10.3%, respectively, for AZO. The top and bottom electrodes were sputtered Mo films. The detailed structural and electrical property variations were examined as functions of the Al concentration and film thickness. The AHO films showed a transition from the monoclinic phase (Al concentration up to 1.4%) to the tetragonal/cubic phase (Al concentration 2.0-3.5%), and finally, to the amorphous phase (Al concentration >4.7%), whereas the AZO films remained in the tetragonal/cubic phase up to the Al concentration of 6.4%. For both the AHO and AZO films, the monoclinic and amorphous phases had dielectric constants of 20-25, and the tetragonal/cubic phases had dielectric constants of 30-35. The highest electrical performance levels for the application to the high-voltage charge storage capacitors in flat panel displays were achieved with the 4.7-9.7% Al-doped AHO films and the 2.6% Al-doped AZO films.

  16. Experimental investigation of the dynamic elastic modulus and vibration damping in molybdenum and alumina-coated Ti-25Al-10Nb-3V-1Mo aluminides cycled at elevated temperatures

    SciTech Connect

    Wolfenden, A.; Cantu, M.W.; Vaidya, R.U.

    1996-04-01

    Titanium aluminides such as Ti-25Al-10Nb-3V-1Mo have became the focus of high temperature materials research due to their ability to maintain their strength up to 1,000{degree}C. However, at temperatures in excess of 650{degree}C, Ti-25Al-10Nb-3V-1Mo undergoes severe oxidation which, in turn, can degrade its mechanical properties. To address this problem, plasma sprayed coatings were applied to the substrate to provide protection in the high temperature environment. In this study, 0.1-0.125 mm thick alumina and molybdenum coatings were plasma sprayed onto a Ti-25Al-10Nb-3V-1Mo substrate. Changes in dynamic elastic modulus and vibration damping due to thermal cycling at elevated temperatures were measured. The modulus and damping were measured using the piezoelectric ultrasonic composite oscillator technique (PUCOT). The behavior of the Al{sub 2}O{sub 3} and Mo coated specimens was compared to that of the uncoated samples. Thermal cycling of the coated samples at 600{degree}C led to an increase in the modulus and decrease in the damping. Most of the changes in properties occurred after the first thermal cycle. Thermal cycling of the samples at 750{degree}C and 850{degree}C led to complete failure of the coatings. A specimen with a 1.0 mm alumina coating exhibited cracks even when cycled at 600{degree}C. 7 refs., 12 figs., 3 tabs.

  17. Microstructure of a complex Nb-Si-based alloy and its behavior during high-temperature oxidation

    NASA Astrophysics Data System (ADS)

    Leont'ev, L. I.; Udoeva, L. Yu.; Chumarev, V. M.; Gulyaeva, R. I.; Pankratov, A. A.; Sel'menskikh, N. I.; Zhidovinova, S. V.

    2016-01-01

    A in-situ composite Nb-Si-Ti-Hf-Cr-Mo-Al composite material alloyed with yttrium and zirconium is studied. The evolution of the structure-phase state of the alloy during oxidation under dynamic and isothermal conditions is considered on samples prepared by vacuum remelting and directional solidification. The phase composition and the microstructure of the alloy are examined by the methods of physico-chemical analysis, and the distribution of alloying elements in initial samples and the products of oxidation is estimated. Thermogravimetric experiments are performed on powders and compacted samples during continuous (in the range 25-1400°C) and isothermal (at 900 and 1100°C) heating in air. The directional solidification of an Nb-Si-Ti-Al-Hf-Cr-Mo-Zr-Y is found to cause the formation of an ultradispersed eutectic consisting of α-Nb ss and γ-Nb5Si3 ss cells. The as-cast sample prepared by vacuum remelting has a dendritic structure and contains Nb3Si apart from these phases. Oxidation leads to the formation of a double oxide layer and an inner oxidation zone, which retain the two-phase microstructure and the ratio of alloying elements that are characteristic of the initial alloy. Diffusion redistribution is only detected for molybdenum. The cyclicity of heating at the initial stage of oxidation weakly influences the oxidation resistance of the alloy.

  18. Comparative Study On The Impact Of TiN And Mo Metal Gates On MOCVD-Grown HfO2 And ZrO2 High-κ Dielectrics For CMOS Technology

    NASA Astrophysics Data System (ADS)

    Abermann, S.; Sjoblom, G.; Efavi, J.; Lemme, M.; Olsson, J.; Bertagnolli, E.

    2007-04-01

    We compare metal oxide semiconductor capacitors, investigating Titanium-Nitride and Molybdenum as gate materials, as well as metal organic chemical vapor deposited ZrO2 and HfO2 as high-κ dielectrics, respectively. The impact of different annealing steps on the electrical characteristics of the various gate stacks is a further issue. The positive effect of post metallization annealing in forming gas atmosphere as well as observed mid-gap pinning of TiN and Mo metal gates is presented.

  19. Method of Estimating the Long-term Rupture Strength of 11Cr-2W-0.4Mo-1Cu-Nb-V Steel

    NASA Astrophysics Data System (ADS)

    Tamura, Manabu

    2015-05-01

    Long-term rupture data of 11Cr-2W-0.4Mo-1Cu-Nb-V steel were analyzed using an exponential equation for stress regarding time to rupture as a thermal activation process. The fitness was compared with the usually employed method assuming power-law creep. In the exponential method, rupture data are classified into several groups according to the thermal activation process; the activation energy, Q; the activation volume, V; then, the Larson-Miller constant, C, values are calculated, and a regression equation is obtained for each data group. The fitness level of the equation was satisfactorily high for each group. The values of Q, V, and C were unusually small for a data group where an unexpected drop in rupture strength was observed. The critical issue is how to comprehend signs of degradation within the short term. We can observe several signs at a creep time of approximately one-tenth of the times of the degradation events. The small values of Q and V indicate that completely softened regions form and creep locally, which is consistent with previous observations. From both metallurgical considerations and the variations of Q and V, it is suggested that the rate of the unexpected drop in strength is mitigated after further long-term creep.

  20. Promising half-metallic ferromagnetism in double perovskites Ba2VTO6 (T=Nb and Mo): Ab-initio LMTO-ASA investigations

    NASA Astrophysics Data System (ADS)

    Musa Saad H.-E., M.

    2012-07-01

    The electronic and magnetic properties of new ordered vanadium-based double perovskite oxides Ba2VTO6 (T=Nb and Mo) have been investigated using the ab-initio linear muffin-tin orbitals method with the atomic-sphere approximation (LMTO-ASA). The calculations performed by using the local spin-density approximation with on-site Coulomb interaction (LSDA+U) style. The self-consistent band structure calculations predict half-metallic ferromagnetic (HM-FM) ground states with total spin magnetic moments of 2.1021 μB and 3.0633 μB per formula unit cell for Ba2VNbO6 and Ba2VMoO6, respectively. HM-FM nature in two compounds organizes from the ddpπ-superexchange interactions 3d-t2g2-O (2p)-4d-t2gn (n=0 or 1), conformity with Zener-Goodenough-Kanamori rules.

  1. Estimates if population inversion for deep-UV transitions in Kr-like Y,Zr,Nb and Mo in a high-current reflex discharge

    SciTech Connect

    Finkenthal, M, May, M J; Fournier, K; Goldstein, W H; Shlyaptsev, V N; Soukhanovskii, V; Stutman, D

    1999-07-06

    Kr-like ions are good candidates for FUV lasing since they can be produced in plasmas quite easily. We present results from a spectroscopic investigation of Y IV emission from a high current density, cold cathode reflex discharge. The Y II to Y V emission is recorded in the 200-3000 {angstrom} range using photometrically calibrated spectrometers, while the emission of trace aluminum ions serves for plasma diagnostics. The intensities of the Y IV 4d - 5p and 5s - 5p transitions strongly increase relative to lines from Y II and Y III with increasing plasma current. The spectra studied here are obtained at a current density of 1.75 A/cm{sup 2}. Experimental Y IV intensity ratios spanning several excited configurations are compared with collisional radiative predictions of the HULLAC atomic physics package. Good agreement is found for the measured and predicted ratios of 4p{sup 5}5p to 4p{sup 5}5s level populations per statistical weight. Finally, the response of the Kr-like system to a fast, transient excitation pulse is examined using the RADEX code. Large transient gains are predicted for several 5s - 5p transitions in Y IV, Zr V, Nb VI and Mo VII.

  2. 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.

  3. Improvement of mechanical properties of the Ti-45Al-5Nb-1Mo-0.2B (at %) intermetallic alloy by means of microstructure controlling

    NASA Astrophysics Data System (ADS)

    Nazarova, T. I.; Imaev, V. M.; Imaev, R. M.; Mulyukov, R. R.

    2016-10-01

    The effect of heat and thermomechanical treatments conditions on the microstructure and main mechanical characteristics (obtained by tensile, high-temperature long-term strength, fracture toughness, and high-cycle fatigue tests) of the Ti-45Al-5Nb-1Mo-0.2B (et %) alloy was studied. Before the treatments, the sequence of phase transformations in the alloy after its solidification was determined by testquenching method. The obtained data were used to develop conditions for the heat and thermomechanical treatments. It was found that a small but stable increase in the plasticity and strength of the cast alloy is observed after three-stage annealing at temperatures that correspond to the (α + γ)- and (α2 + β( M2) + γ)-phase region. The thermomechanical treatment at temperatures corresponding to the (α(α2) + β( M2) + γ)-phase region and subsequent two-stage annealing at temperatures that correspond to the (α + β( M2) + γ)- and (α2 + β(M2) + γ)-phase region lead to the formation of fine-grained duplex structure. This determined the substantial improvement of the low-temperature plasticity and strength (δ = 3.1% and σu = 860 MPa at 20°C, respectively) and retained high creep resistance to 700°C.

  4. High temperature coefficient of resistance achieved by ion beam assisted sputtering with no heat treatment in V{sub y}M{sub 1−y}O{sub x} (M = Nb, Hf)

    SciTech Connect

    Vardi, Naor; Sharoni, Amos

    2015-11-15

    Thermal imaging based on room temperature bolometer sensors is a growing market, constantly searching for improved sensitivity. One important factor is the temperature coefficient of resistance (TCR), i.e., the sensitivity of the active material. Herein, the authors report the improved TCR properties attainable by the “ion beam assisted deposition” method for room temperature deposition. V{sub y}M{sub 1−y}O{sub x} (M = Nb, Hf) thin-film alloys were fabricated on 1 μm thermal SiO{sub 2} atop Si (100) substrates by reactive magnetron cosputtering at room temperature using a low energy ion source, aimed at the film, to insert dissociated oxygen species and increase film density. The authors studied the influence of deposition parameters such as oxygen partial pressure, V to M ratio, and power of the plasma source, on resistance and TCR. The authors show high TCR (up to −3.7% K{sup −1}) at 300 K, and excellent uniformity, but also an increase in resistance. The authors emphasize that samples were prepared at room temperature with no heat treatment, much simpler than common processes that require annealing at high temperatures. So, this is a promising fabrication route for uncooled microbolometers.

  5. Fluorite transition metal hydride induced destabilization of the MgH2 system in MgH2/TMH2 multilayers ( TM=Sc , Ti, V, Cr, Y, Zr, Nb, La, Hf)

    NASA Astrophysics Data System (ADS)

    Tao, S. X.; Notten, P. H. L.; van Santen, R. A.; Jansen, A. P. J.

    2010-09-01

    The structural changes in MgH2 induced by contact with fluorite transition metal hydrides ( TMH2 , TM=Sc , Ti, V, Cr, Y, Zr, Nb, La, Hf) have been studied using density-functional theory calculations. Models of MgH2(rutile)/TiH2(fluorite) and MgH2(fluorite)/TiH2(fluorite) multilayers with different Mg:TM ratios have been designed. With a fixed thickness of the TMH2 layer, structure transformation of MgH2 from rutile to fluorite occurs with a decrease in thickness of the MgH2 layer. The hydrogen desorption energy from the fluorite MgH2 layer in the multilayers is significantly lower than that of the bulk rutile MgH2 . The structural deformation of the MgH2 layer due to the strain induced by TMH2 is found to be responsible for the destabilization of the Mg-H bond: the more structural deformation, the more destabilization of the Mg-H. Our results provide an important insight for the development of new hydrogen-storage materials with desirable thermodynamic properties.

  6. Thermal stability of magnetic properties of nanocrystalline (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1 alloy with induced magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Dmitrieva, N. V.; Lukshina, V. A.; Filippov, B. N.; Potapov, A. P.

    2016-10-01

    The effect of nanocrystallizing annealing in the presence of an ac magnetic field (magnetic heat treatment) and tensile stresses (thermomechanical treatment), as well as in the presence of both tensile stresses and an ac magnetic field (complex thermomechanical magnetic treatment) on the magnetic properties of the nanocrystalline (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1 alloy and their thermal stability has been studied. It has been found that the nanocrystallization of the studied (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1 alloy in the course of magnetic heat treatment, thermomechanical treatment, and thermomechanical magnetic treatment at low tensile stresses (6-30 MPa) leads to about a threefold decrease in the coercive force, but does not ensure the thermal stability of magnetic properties at high temperatures. In nanocrystallization, in the course of thermomechanical treatment at 620°C for 20 min under tensile stresses σ = 250 MPa has been found to be optimum for the high-temperature application (up to 550°C) of the studied alloy.

  7. Effect of Laves Phase on High-Temperature Deformation and Microstructure Evolution in an 18Cr-2Mo-0.5Nb Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Ikeda, Ken-ichi; Yamoah, Nana Kwame Gyan; Reynolds, William T.; Hamada, Jun-ichi; Murayama, Mitsuhiro

    2015-08-01

    Niobium-containing ferritic stainless steels are finding new applications in automotive exhaust components because of their oxidation resistance, thermal fatigue resistance, and high-temperature strength. The mechanical behavior of Nb-containing ferritic steels at service temperatures of 973 K (700 °C) and higher results from the convolution of dynamic microstructural changes including precipitation, precipitate coarsening, strain hardening, recovery, and recrystallization. The relative contributions of these competing processes have yet to be clarified. In this study, the high-temperature flow strength of an 18Cr-2Mo-0.5Nb ferritic stainless steel (SUS 444) was correlated with microstructure under different strain and initial precipitate distributions to clarify the relative role of the strengthening and softening processes. High-temperature tensile tests at 1023 K (750 °C) of un-aged (initial microstructure is precipitate-free) and pre-aged (initial microstructure contains precipitates) samples were carried out and transmission electron microscopy was used to assess dislocation distributions and precipitate morphology. The difference in the stress-strain curves between un-aged and pre-aged samples was drastic; the yield strength of the un-aged sample was twice that of the pre-aged sample, and the un-aged sample exhibits a noticeable yield drop. Transmission electron microscopy revealed a Laves phase nucleated and grew during the high-temperature tensile test in the un-aged sample and the majority of the precipitates in the pre-aged sample were the same Laves phase. Furthermore, a strain effect on precipitate growth was recognized in un-aged and pre-aged conditions by comparing grip (no strain) and gage (strained) sections of tensile samples. The dominant strengthening contribution in un-aged samples is initially the precipitate shearing mechanism and it changes to Orowan strengthening beyond the ultimate tensile strength, whereas the dominant contribution in

  8. Role of grain size in the regulation of osteoblast response to Ti-25Nb-3Mo-3Zr-2Sn alloy.

    PubMed

    Huang, Run; Lu, Shemin; Han, Yong

    2013-11-01

    Nano- and ultrafine-grained β-Ti layers were fabricated on Ti-25Nb-3Mo-3Zr-2Sn alloy by surface mechanical attrition treatment (SMAT). After being ground and polished, the two layers exhibited the same chemical composition, similar surface roughness and topography features to the coarse-grained surface, however, higher hardness values were exhibited on the ultrafine- and nano-grained surfaces, especially on nano-grained surface compared to coarse-grained surface. Hydrophilicity test, evaluated by measuring water contact angles, showed that the nano-grained surface was much more hydrophilic than the ultrafine- and coarse-grained surfaces. The adsorption of total protein and anchoring proteins such as vitronectin and fibronectin on the different surfaces from DMEM medium containing 10% fetal bovine serum was also examined. Employing hFOB1.19 cells, the behaviors of osteoblasts on the three kinds of grain-scaled surfaces, including adhesion, proliferation and differentiation, were evaluated by examining the morphology, the number of adherent cells, actin cytoskeleton reorganization, vinculin signals, expressions of steogenesis-related genes, alkaline phosphatase activity, contents of intracellular specific proteins and collagen type I, extracellular collagen secretion as well as matrix mineralization. The significant enhancements of osteoblast adhesion, proliferation, maturation and mineralization are exhibited on the nano-grained surface, while little improvements are found on the ultrafine-grained surface compared to the conventional coarse-grained surface. The differences in the cellular response to the three kinds of grain-scaled surfaces are related to grain size and degree of hydrophilicity. The improved cell functions together with mechanical properties make SMAT-processed nanograined β-Ti a promising biomaterial for surgical implants.

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  11. Study on feasibility of producing an amorphous surface layer of Fe49Cr18Mo7B16C4Nb3 by pulsed Nd:YAG laser surface melting

    NASA Astrophysics Data System (ADS)

    Mojaver, Reza; Mojtahedi, Faezeh; Shahverdi, Hamid Reza; Torkamany, Mohammad Javad

    2013-01-01

    This work aims to investigate whether an amorphous surface layer can be obtained when as-cast Fe49Cr18Mo7B16C4Nb3 alloy is submitted to pulsed Nd:YAG laser surface melting. The experiments were conducted in the various laser scanning speeds. The microstructures of laser treated zones were investigated by X-ray diffraction XRD and Field Emission Scanning Electron Microscope (FESEM) and their microhardness were measured, too. The chemical composition of different points of each sample was analyzed by energy-dispersive X-ray spectroscopy EDS. Although the estimated cooling rates in surface layers were higher than the required cooling rate to achieve full amorphization, but the present experiments were unable to retain complete glassy microstructure on surface and a mixture of amorphous (low volume fraction) and ultrafine grained phases were produced in surface of samples. Based on the findings, it was understood that the overlapping of successive pulses and element redistributions occurred in pulsed laser melting could severely restrict amorphization. The influence of laser scan speed and laser power on heat input, melting ratio, compositional changes and cracking in laser treated zone were discussed separately. It is suggested that the limited range of laser variables in pulsed Nd:YAG laser melting may help to produce a sound amorphous phase of as-cast Fe49Cr18Mo7B16C4Nb3 alloy.

  12. Composition effects on mechanical properties of HfC-strengthened molybdenum alloys

    NASA Technical Reports Server (NTRS)

    Witzke, W. R.

    1976-01-01

    The mechanical properties of swaged rod thermomechanically processed from arc-melted Mo-2Re-Hf-C alloys containing as much as 0.9 mol pct HfC have been evaluated. The low temperature ductilities of these alloys were not influenced by the amount of HfC present but by the amount of Hf in excess of stoichiometry. Maximum ductility occurred at 0.2 to 0.3 at. pct excess Hf. At 0.3 to 0.5 mol pct HfC, alloy strength varied directly with the Mo content of extracted carbide particles, both decreasing as the amount of excess Hf increased. Additions of 2 at. pct Re had little effect on strength or ductility. Tensile and creep strengths of Mo-2Re-0.7Hf-0.5C alloy equaled or exceeded those of other high strength Mo alloys.

  13. Analysis of M···H-Si interactions in [{M(CpSiMe2H)Cl3}2], (M = Zr, Hf, Ti and Mo) complexes.

    PubMed

    Lein, Matthias; Harrison, John A; Nielson, Alastair J

    2011-10-28

    For the d(0) complex [{Zr(CpSiMe(2)H)Cl(3)}(2)] which contains a linear Si-H···Zr interaction across the dimer, DFT calculations are in good agreement with X-ray structures. The BP86 functional shows a slightly stronger interaction than B3LYP but for qualitative purposes either functional is sufficient. QTAIM analysis shows a bond critical point (bcp) for the interaction, a small negative value for the total energy density [H((r))] and the H atomic basin decreases in energy, E(H), and atomic volume compared to the free ligand. NBO analysis showed E(2) for Si-H σ to Zr(dz(2)) donation at 42.8 kcal mol(-1) and a 34% spatial overlap for the interaction consistent with an inverse hydrogen bond. The Wiberg bond index for the interaction is 0.1735 (0.7205 for the Si-H bond), ν((Si-H)) and (1)J((Si-H)) at 2060 cm(-1) and 145.4 Hz compared to 2183 cm(-1) and 172.1 Hz in the free ligand. Using a "synthesis by computation" approach to forming like complexes, similar features were found for [{Hf(CpSiMe(2)H)Cl(3)}(2)]. The titanium complex [{Ti(CpSiMe(2)H)Cl(3)}(2)] does not contain any Si-H···Ti interaction as rotation about the C-Si bond of the ligand occurs to place the Si-H bond hydrogen closer to a terminal chloro ligand across the dimer. An increase in electron density on the metal in the d(2) complex [{Mo(CpSiMe(2)H)Cl(3)}(2)] results in a stronger interaction with a distinct QTAIM analysis bcp [ρ((r)) 0.0448 a.u.], a small negative value for H((r)) and a much reduced H atomic volume. NBO analysis shows E(2) for Si-H σ to Mo(dz(2)) donation at 143.1 kcal mol(-1) and a 29% spatial overlap. Mo(dz(2)) to Si-H σ* donation (back donation) is minimal [E(2) 1.3 kcal mol(-1), ~1% spatial overlap]. The Wiberg bond index is 0.3114 (0.5667 for the Si-H bond), ν((Si-H)) 2015 cm(-1) and (1)J((Si-H)) 120.6 Hz.

  14. 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.

  15. 12. Hard HF transmitter antenna, view toward west. Lyon ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    12. Hard HF transmitter antenna, view toward west. Lyon - Whiteman Air Force Base, Oscar O-1 Minuteman Missile Alert Facility, Southeast corner of Twelfth & Vendenberg Avenues, Knob Noster, Johnson County, MO

  16. 11. Hard HF receiver antenna, view towards east. Lyon ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    11. Hard HF receiver antenna, view towards east. Lyon - Whiteman Air Force Base, Oscar O-1 Minuteman Missile Alert Facility, Southeast corner of Twelfth & Vendenberg Avenues, Knob Noster, Johnson County, MO

  17. Hf-W Chronology of CR Chondrites

    NASA Astrophysics Data System (ADS)

    Budde, G.; Kruijer, T. S.; Kleine, T.

    2017-02-01

    Hf-W systematics of CR chondrites define an age of 3.7 Ma after CAIs for CR chondrule formation. CR metal and silicates have complementary nucleosynthetic W and Mo isotope anomalies due to the uneven distribution of a presolar s-process carrier.

  18. Crystal structure of Ba2(La0.727Ba0.182M0.091)MO6 (M = Nb, Sb, Bi): symmetry nuance identified in photoluminescence and IR spectroscopy studies.

    PubMed

    Phatak, Rohan; Gupta, Santosh K; Maheshwari, Priya; Das, Amitabh; Sali, Sanjay K

    2017-01-31

    A one-third lanthanum deficiency was created in Ba2LaM(5+)O6 compounds (LaM compounds) to form Ba2La2/3M(5+)O5.5 compounds (La2/3M compounds) for M = Nb, Sb, and Bi. The compounds were prepared by a gel-combustion method using citric acid as a fuel. All the compounds were characterized by powder X-ray diffraction (XRD). The XRD analysis showed that the space group of the La2/3M compounds remains the same for the Bi and Sb samples when compared to the reported LaM compounds, except for the Nb sample. La2/3Nb and La2/3Sb adopt a rhombohedral structure with the space group R3[combining macron], whereas La2/3Bi adopts a monoclinic structure with the space group I2/m. As the positron annihilation spectroscopy (PALS) technique is sensitive to cation deficiency, it was used to detect the presence of cation vacancies in the samples, which are formed due to the decrease in the lanthanum concentration. The PALS analyses indicated that the absence of cation deficiency in the La2/3M compounds is similar to that observed in the LaM compound. Thus, the crystal structure of the La2/3M compound was modeled, such that the cation deficiency at the La site is filled by Ba(2+) and M(5+) ions, and the crystal structure formula is given as Ba2(La0.727Ba0.182M0.091)MO6. This model was confirmed by Rietveld refinement of the XRD data. The emission spectra of Eu(3+) showed a strong dependence on its local site symmetry in the host material, in which it is being doped and this can be used as a spectroscopic probe for detecting any differences in the symmetry. Comparison of the local symmetry around La(3+) cation was studied using photoluminescence (PL) by doping 2 atom% Eu(3+) in LaM and La2/3M compounds. Infrared spectroscopy (IRS) analyses were also carried out for LaM and La2/3M compounds. There was complete agreement between the PL and IRS results and they were also in concordance with the predicted crystal structure model. Interestingly in these La2/3M compounds, the equilibrium

  19. Effect of ion irradiation on the nanocrystallization and magnetic properties of soft magnetic Fe72.5Cu1Nb2Mo1.5Si14B9 alloy

    NASA Astrophysics Data System (ADS)

    Ovchinnikov, V. V.; Makhin'ko, F. F.; Gushchina, N. V.; Stepanov, A. V.; Medvedev, A. I.; Starodubtsev, Yu. N.; Kataev, V. A.; Tsepelev, V. S.; Belozerov, V. Ya.

    2017-02-01

    The effect of accelerated Ar+ ions on the crystallization process and magnetic properties of nanocrystalline Fe72.5Cu1Nb2Mo1.5Si14B9 alloy has been studied using X-ray diffraction analysis, transmission electron microscopy, thermomagnetic analysis, and other magnetic methods. Irradiation by Ar+ ions with an energy of 30 keV and a fluence of 3.75 × 1015 cm-2 at short-term heating to a temperature of 620 K (which is 150 K below the thermal threshold of crystallization) leads to the complete crystallization of amorphous alloy, which is accompanied by the precipitation of the α-Fe(Si) solid solution crystals (close in composition to Fe80Si20), Fe3Si stable phase, and metastable hexagonal phases. The crystallization caused by irradiation leads to an increase in the grain size and changes the morphology of grain boundaries and volume fraction of crystalline phases, which is accompanied by changes in the magnetic properties.

  20. Creep-rupture behavior of a developmental cast-iron-base alloy for use up to 800/sup 0/C. [NASAUT 4G-Al: Fe-15Mn-15Cr-2Mo-1. 5C-1Nb-1Si

    SciTech Connect

    Titran, R.H.; Scheuermann, C.M.

    1987-08-01

    As part of the DOE/NASA Stirling Engine Systems Project, an iron-base cast alloy was developed, designated NASAUT 4G-Al. Its nominal composition, in percent by weight, is Fe-15Mn-15Cr-2Mo-1.5C-1Nb-1Si. This report presents the results of a study of this alloy, 4G-Al, performed to determine its creep-rupture properties. The alloy was studied in the directionally solidified (DS) form with a 650/sup 0/C/100 h anneal recommended by UTRC to optimize properties and in the investment-cast (IC) form with either a 760/sup 0/C/20 h anneal recommended by UTRC to optimize properties, or a solution anneal of 790/sup 0/C/20 h followed by a simulated brazing cycle of 1065/sup 0/C/15 min + a heat treatment of 760/sup 0/C/16 h + 650/sup 0/C/16 h. Alloy 4G-Al exhibited typical 3-stage creep response under all conditions tested. The most creep resistant condition was the DS material. This condition compares very favorably to the prototype (HS-31) and prime candidate (XF-818) alloys for the automotive Stirling engine cylinder/regenerator housing. 14 refs., 7 figs., 6 tabs.

  1. On the occurrence of dynamic strain aging in near-alpha alloy Ti-5.8Al-4Sn-3.5Zr-0.7Nb-0.5Mo-0.35Si

    SciTech Connect

    Singh, N.; Prasad, N.; Singh, V.

    1999-09-01

    Alloy Ti-5.8Al-4Sn-3.5Zr-0.7Nb-0.5Mo-0.35Si (IMI 834) is the most recently developed near-alpha type titanium alloy for high-temperature application up to 873 K, as discs and blades in the high pressure part of compressors, in advanced jet engines. It possesses a good combination of creep and fatigue resistance at elevated temperature, in properly heat-treated condition, and has a fine bimodal microstructure, consisting of a small volume fraction of equiaxed alpha in a fine-grained matrix of transformed beta. Some investigations have already been done on the tensile behavior of this alloy, in different heat-treated conditions, over a wide range of temperature from 293 to 923 K. However, no report has been made on the occurrence of dynamic strain aging (DSA) in this alloy. The purpose of this article is to present the observation on the occurrence of DSA in the titanium alloy IMI 834, in the as-received (hot-rolled and mill-annealed) condition, over the temperature range 623 to 823 K.

  2. A redox-stable direct-methane solid oxide fuel cell (SOFC) with Sr2FeNb0.2Mo0.8O6-δ double perovskite as anode material

    NASA Astrophysics Data System (ADS)

    Ding, Hanping; Tao, Zetian; Liu, Shun; Yang, Yating

    2016-09-01

    Development of high-performing and redox-stable ceramic oxide electrode materials is a crucial technical step for direct hydrocarbon solid oxide fuel cells (SOFCs) operating at intermediate temperatures (550-700 °C). Here we report a nickel-free double perovskite, Sr2FeNb0.2Mo0.8O6-δ (SFNM20), for SOFC anode, and this anode shows outstanding performances with high resistance against carbon build-up and redox cycling in hydrocarbon fuels. At 800 °C, the SFNM20 anode shows electrical conductivity of 5.3 S cm-1 in 5% H2 and peak power densities of 520 and 380 mW cm-2 using H2 and CH4 as the fuel, respectively. The cell exhibits a very stable performance under different constant current loads in H2 and CH4 at 700 °C and high redox stability against the gas environment changes in the anode chamber. In addition, the electrode is structurally stable in various fuels, suggesting that it is a feasible material candidate for the electrode of high-performing SOFCs.

  3. Iron-rich low-cost superalloys. [Cr(15)-Mn(15)-Mo(2)-C(1. 5)-Si(1. 0)-Nb(1. 0)-Fe(bal. ) and Cr(20)-Mn(10)-C(3. 4)-Fe(bal. )

    SciTech Connect

    Wayne, S.F.

    1985-01-01

    An iron-rich low-cost superalloy has been developed in conjunction with United Technologies Research Center under the NASA program, Conservation of Strategic Aerospace Materials. The alloy, when processed by conventional chill casting, has physical and mechanical properties that compare favorably with existing nickel - and cobalt-based superalloys while containing significantly lower amounts of strategic elements. The composition of the alloy is Cr(15)-Mn(15)-Mo(2)-C(1.5)-Si(1.0)-Nb(1.0)-Fe(bal.), and it can be produced with chromite ore deposits located within the United States. Studies were also made on the properties of Cr(20)-Mn(10)-C(3.4)-Fe(bal.), a eutectic alloy processed by chill casting and directional solidification (D.S.) which produced an aligned microstructure consisting of M/sub 7/C/sub 3/ fibers in an ..gamma..-Fe matrix. This good alignment vanishes when molybdenum or aluminum is added in higher concentrations. Thermal expansion of the M/sub 7/C/sub 3/ (M = Fe, Cr, Mn) carbide lattice was measured up to 800/sup 0/C and found to be highly anisotropic, with the a-axis being the predominant mode of expansion. Repetitive impact-sliding wear experiments performed with the Fe-rich eutectic alloy showed that the directionally solidified microstructure greatly improved the alloy's wear resistance as compared to the chill-cast microstructure and conventional nickel-base superalloys.

  4. Microstructural effects on the deformation and fracture of the alloy Ti-25Al-10Nb-3B-1Mo. Final report, 1 July 1988-15 December 1992

    SciTech Connect

    Ward, C.H.

    1992-12-01

    The effects of microstructure and temperature on tensile and fracture behavior were explored for the titanium aluminide alloy Ti-25Al-lONb-3V-lMo (atomic percent). Three microstructures were selected for this study in an attempt to determine the role of the individual microstructural constituents. the three microstructures studied were an alpha-2 + beta processed microstructure with a fine Widmanstaetten microstructure, a beta processed microstructure with a fine Widmanstaetten microstructure, and a beta processed microstructure with a coarse Widmanstaetten microstructure. Tensile testing of both round and flat specimens was conducted in vacuum at elevated temperature and in air at room and elevated temperatures. Extensive fractography and specimen sectioning were used to study tensile deformation and the effects of environment on this alloy. Room temperature fracture toughness testing using compact tension specimens was conducted. Elevated temperature toughness testing was performed using J-bend bar specimens in an air environment. Again, extensive fractography and specimen sectioning were used to study the elevated temperature toughening mechanisms of this alloy.... Titanium, Titanium aluminide, Intermetallic, Fracture toughness, Tensile behavior, Fractography environmental interaction.

  5. Optimization of the Processing of Mo Disks

    SciTech Connect

    Tkac, Peter; Rotsch, David A.; Stepinski, Dominique; Makarashvili, Vakhtang; Harvey, James; Vandegrift, George F.

    2016-01-01

    The objective of this work is to decrease the processing time for irradiated disks of enriched Mo for the production of 99Mo. Results are given for the dissolution of nonirradiated Mo disks, optimization of the process for large-scale dissolution of sintered disks, optimization of the removal of the main side products (Zr and Nb) from dissolved targets, and dissolution of irradiated Mo disks.

  6. New (1 - x)K0.45Na0.55Nb0.96Sb0.04O3-xBi0.5Na0.5HfO3 lead-free ceramics: Phase boundary and their electrical properties

    NASA Astrophysics Data System (ADS)

    Tao, Hong; Wu, Jiagang; Zheng, Ting; Wang, Xiangjian; Lou, Xiaojie

    2015-07-01

    Here, we reported a high unipolar strain and large piezoelectricity in new (1 - x)K0.45Na0.55Nb0.96Sb0.04O3-xBi0.5Na0.5HfO3 ceramics. The rhombohedral-tetragonal (R-T) phase boundary was constructed in the ceramics with 0.03 < x ≤ 0.05, which shows a large d33 value of ˜419 pC/N. More importantly, a high unipolar strain of ˜0.31% was observed due to the multiphase coexistence. In addition, the piezoelectricity of the ceramics could be effectively enhanced if their compositions are located at the phase boundaries region, where a very low electric field of ˜1.2 kV/mm can readily rotate the R/T domains. We also noticed that the deviation from phase boundary induced by applying an external electric field results in the deterioration of piezoelectricity after the "second-poling" method. We believe that as a potassium-sodium-niobate based material, the ceramics developed in this work may find practical applications in lead-free piezoelectric devices such as actuators and fuel injectors in the future owing to the significant enhancement in their piezoelectricity as well as strain.

  7. Effect of heat input on microstructure and properties of hybrid fiber laser-arc weld joints of the 800 MPa hot-rolled Nb-Ti-Mo microalloyed steels

    NASA Astrophysics Data System (ADS)

    Wang, X.-N.; Zhang, S.-H.; Zhou, J.; Zhang, M.; Chen, C.-J.; Misra, R. D. K.

    2017-04-01

    Hybrid fiber laser-arc welding (HLAW) process was applied to a novel hot-rolled Nb-Ti-Mo microalloyed steels of 8 mm thickness. The steel is primarily used to manufacture automotive and construction machinery components, etc. To elucidate the effect of heat input on geometry, microstructure and mechanical properties, different heat inputs (3.90, 5.20 and 7.75 kJ/cm) were used by changing the welding speeds. With increased heat input, the depth/width of penetration was decreased, and the geometry of fusion zone (FZ) changed to "wine cup-like" shape. In regard to the microstructural constituents, the martensite content was decreased, but granular bainite (GB) content was increased. The main microstructural difference was in the FZ cross-section at 7.75 kJ/cm because of the effect of thermal source on the top and bottom. The microstructure of the top part consisted of GB, grain boundary ferrite, and acicular ferrite, while the bottom part was primarily lath martensite. The hardness distribution was similar for different heat inputs. Hardness in FZ, coarse-grained HAZ and mixed-grained HAZ was higher than the base metal (BM), but for the fine-grained HAZ was similar or marginally less than the base metal (BM). Tensile strain was concentrated in the BM such that the fracture occurred in this region. In summary, the geometry, microstructure, and mechanical properties of weld joints were superior at heat input of 5.20 kJ/cm.

  8. 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.

  9. Solution heat-treatment of Nb-modified MAR-M247 superalloy

    SciTech Connect

    Soares Azevedo e Silva, Paulo Ricardo; Baldan, Renato; Nunes, Carlos Angelo; Carvalho Coelho, Gilberto; and others

    2013-01-15

    MAR-M247 superalloy has excellent mechanical properties and good oxidation resistance at elevated temperatures. Niobium is an element known as {gamma} Prime phase hardener in nickel-based superalloys, besides promoting homogeneous distribution of MC carbides. This work is inserted in a project that aims to evaluate the total replacement of tantalum by niobium atoms in MAR-M247 superalloy (10.2 Co, 10.2 W, 8.5Cr, 5.6 Al, 1.6 Nb, 1.4 Hf, 1.1 Ti, 0.7 Mo, 0.15 C, 0.06 Zr, 0.015 B, Ni balance-wt.%). Based on microstructural characterizations (SEM and FEG-SEM, both with EDS) of the as-cast material and heat-treated materials as well as utilizing Thermocalc simulations and experiments of differential thermal analysis (DTA), heat-treatment at 1260 Degree-Sign C for 8 h was chosen as an ideal condition for the solution of Nb-modified MAR-M247 superalloy. The hardness of as-cast and ideally solution treated materials was 390 {+-} 14 HV and 415 {+-} 6 HV, respectively. - Highlights: Black-Right-Pointing-Pointer DTA and microstructure of MAR-M247(Nb) showed a good agreement with Thermocalc. Black-Right-Pointing-Pointer An ideal condition for solution heat-treatment of MAR-M247(Nb) is 1260 Degree-Sign C for 8 h. Black-Right-Pointing-Pointer It was an observed evidence of incipient melting in samples heat-treated at 1280 Degree-Sign C.

  10. 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.

  11. Heat-to-Heat Variation in Creep Life and Fundamental Creep Rupture Strength of 18Cr-8Ni, 18Cr-12Ni-Mo, 18Cr-10Ni-Ti, and 18Cr-12Ni-Nb Stainless Steels

    NASA Astrophysics Data System (ADS)

    Abe, Fujio

    2016-09-01

    Metallurgical factors causing the heat-to-heat variation in time to rupture have been investigated for 300 series stainless steels for boiler and heat exchanger seamless tubes, 18Cr-8Ni (JIS SUS 304HTB), 18Cr-12Ni-Mo (JIS SUS 316HTB), 18Cr-10Ni-Ti (JIS SUS321 HTB), and 18Cr-12Ni-Nb (JIS SUS 347HTB), at 873 K to 1023 K (600 °C to 750 °C) using creep rupture data for nine heats of the respective steels in the NIMS Creep Data Sheets. The maximum time to rupture was 222,705.3 hours. The heat-to-heat variation in time to rupture of the 304HTB and 316HTB becomes more significant with longer test durations at times above ~10,000 hours at 973 K (700 °C) and reaches to about an order of magnitude difference between the strongest and weakest heats at 100,000 hours, whereas that of the 321HTB and 347HTB is very large of about an order of magnitude difference from a short time of ~100 hours to long times exceeding 100,000 hours at 873 K to 973 K (600 °C to 700 °C). The heat-to-heat variation in time to rupture is mainly explained by the effect of impurities: Al and Ti for the 304HTB and 316HTB, which reduces the concentration of dissolved nitrogen available for the creep strength by the formation of AlN and TiN during creep, and boron for the 347HTB, which enhances fine distributions of M23C6 carbides along grain boundaries. The heat-to-heat variation in time to rupture of the 321HTB is caused by the heat-to-heat variation in grain size, which is inversely proportional to the concentration of Ti. The fundamental creep rupture strength not influenced by impurities is estimated for the steels. The 100,000 hours-fundamental creep rupture strength of the 347HTB steel is lower than that of 304HTB and 316HTB at 873 K and 923 K (600 °C and 650 °C) because the slope of stress vs time to rupture curves is steeper in the 347HTB than in the 304HTB and 316HTB. The 100,000 hours-fundamental creep rupture strength of the 321HTB exhibits large variation depending on grain size.

  12. Experimental cross-sections for proton-induced nuclear reactions on natMo

    NASA Astrophysics Data System (ADS)

    Červenák, Jaroslav; Lebeda, Ondřej

    2016-08-01

    In the framework of the Co-ordinated Research Project of the IAEA, we measured in detail cross-sections of the nuclear reactions natMo(p,x)93gTc, 93mTc, 93m+gTc, 94gTc, 94mTc, 95gTc, 95mTc, 96m+gTc, 97mTc, 99mTc, 90Mo, 93mMo, 99Mo, 88gNb, 88mNb, 89gNb, 89mNb, 90m+gNb, 90m+gNbcum, 91mNb, 92mNb, 95gNb, 95mNb, 95m+gNb, 96Nb, 97m+gNb, 88m+gZrcum and 89m+gZrcum in the energy range of 6.9-35.8 MeV. The data for formation of 97mTc, 88gNb, 88mNb and 89mNb are reported for the first time. The obtained results were compared to the prediction of the nuclear reaction model code TALYS adopted from the TENDL-2015 library and to the previously published cross-sections. The thick target yields for all the radionuclides were calculated from the measured data. We suggest recommended cross-sections and thick target yields for the 100Mo(p,2n)99mTc, 100Mo(p,x)99Mo and natMo(p,x)96m+gTc nuclear reactions deduced from the selected experimental data.

  13. 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.

  14. Materials performance in HF-alkylation units

    SciTech Connect

    Forsen, O.; Aromaa, J.; Somervuori, M.; Tavi, M.

    1995-11-01

    Materials selection in HF-alkylation units is mostly based on long time experience. The most widely used material in the Station units is standard carbon steel, because it is capable to form a thick protective FeF{sub 2} layer in concentrated or anhydrous hydrofluoric acid. The corrosion resistance decreases, when the acid is dilute (less than 64% HF) or the temperature is above 160F (70 C). The composition and metallurgical state are also suspected to affect the corrosion resistance of carbon steel. The effect of composition appears more complicated than believed, especially the A-106 specification on the total amount of Cr+Ni+Cu+Mo+V < 1% should be studied more closely from the corrosion point of view. Laboratory tests showed that the uniform corrosion rate may be 100 times higher in galvanic contact of two dissimilar steels. The effect of galvanic contacts can neither be excluded in the process equipment corrosion cases.

  15. 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).

  16. Pulsed inductive HF laser

    NASA Astrophysics Data System (ADS)

    Razhev, A. M.; Churkin, D. S.; Kargapol'tsev, E. S.; Demchuk, S. V.

    2016-03-01

    We report the results of experimentally investigated dependences of temporal, spectral and spatial characteristics of an inductive HF-laser generation on the pump conditions. Gas mixtures H2 - F2(NF3 or SF66) and He(Ne) - H2 - F2(NF3 or SF6) were used as active media. The FWHM pulse duration reached 0.42 μs. This value corresponded to a pulsed power of 45 kW. For the first time, the emission spectrum of an inductive HF laser was investigated, which consisted of seven groups of bands with centres around the wavelengths of 2732, 2736, 2739, 2835, 2837, 2893 and 2913 nm. The cross section profile of the laser beam was a ring with a diameter of about 20 mm and width of about 5 mm. Parameters of laser operation in the repetitively pulsed regime were sufficiently stable. The amplitude instability of light pulses was no greater than 5% - 6%.

  17. Modern HF Communications.

    DTIC Science & Technology

    1983-05-01

    AD-A131 163 MODERN HF COUNICATIONS(U) ADVISORY GROUP FOR AEROSPACE RESEARCH AND DEVELOPMENT NEUILLY-SUR-SEINE (FRANCE) d AARONS ET AL. MAY 83 AGARD...NORTH ATLANTIC TREATY ORGANIZATION ADVISORY GROUP FOR AEROSPACE RESEARCH AND DEVELOPMENT (ORGANISATION DU TRAITE DE L’ATLANTIQUE NORD) AGARD Lecture...other NATO bodies and to member nation-, in connection with research aind development problems in the aerospace field: Plros iding assistance to

  18. Serpentinization Changes Nd, but not Hf Isotopes of Abyssal Peridotites

    NASA Astrophysics Data System (ADS)

    Bizimis, M.; Frisby, C. P.; Mallick, S.

    2015-12-01

    Serpentinization of the oceanic lithosphere is a known sink for fluid mobile elements (B, Cl, Li, Sr, etc.), while high field strength elements (HFSE: e.g., Hf, Zr, Ti, Nb) are thought to be unaffected by it. In contrast, the fate of REE during serpentinization is equivocal. Correlations between REE and HFSE concentrations in abyssal peridotites suggest control by magmatic processes (Niu, 2004, J. Pet), while some LREE enrichments in serpentinized peridotites compared to their clinopyroxene (cpx) and Nd, Sr isotope data (Delacour et al., 2008, Chem. Geol.) imply seawater-derived REE addition to the mantle protolith (Paulick et al., 2006, Chem. Geol). To further constrain peridotite-seawater interaction during serpentinization we compare bulk rock and cpx Hf and Nd isotope data in partially (up to ~70%) serpentinized abyssal peridotites (9-16°E South West Indian Ridge). We also present a new method that improves yields in Hf, Nd and Pb separations from depleted (<0.03 ppm Hf) ultramafic rocks, which includes coprecipitation of metals with Al-Fe hydroxides and ether-HCl liquid-liquid exchange for Fe removal. Nd isotopes in the bulk peridotite are up to 7ɛNd units less radiogenic than their cpx (i.e., the magmatic value) while Hf isotopes remain equal to cpx within 1 ɛHf. Melt-rock reaction by the local lavas cannot generate this decoupling. The largest Nd isotopic difference between cpx and bulk is seen in the most LREE-depleted samples, while refertilized samples show little change. Leaching experiments show that 30-60% of REE are mobilized from the rock, but >90% of Hf, Zr, Ti are retained in the residue. LA-ICPMS data shows that serpentine after olivine typically has higher LREE/HREE ratios than cpx, pronounced negative Ce anomalies, high U, Sr concentrations and low HFSE, unlike the coexisting cpx. These data are consistent with some seawater-derived LREE addition to peridotite during serpentinization, localized in the serpentine and other secondary phases

  19. Discovery of a Novel Sn(II)‐Based Oxide β‐SnMoO4 for Daylight‐Driven Photocatalysis

    PubMed Central

    Katayama, Shota; Komura, Takahiro; Hinuma, Yoyo; Yokoyama, Tomoyasu; Mibu, Ko; Oba, Fumiyasu

    2016-01-01

    Daylight‐driven photocatalysts have attracted much attention in the context of “green” technology. Although various active materials have been reported and their applications are rapidly increasing, many are discovered after enormous experimental efforts. Herein the discovery of a novel oxide photocatalyst, β‐SnMoO4, is demonstrated via a rational search of 3483 known and hypothetical compounds with various compositions and structures over the whole range of SnO‐MOq /2 (M: Ti, Zr, and Hf (q = 4); V, Nb, and Ta (q = 5); Cr, Mo, and W (q = 6)) pseudobinary systems. Screening using thermodynamic stability, band gap, and band‐edge positions by density functional theory calculations identifies β‐SnMoO4 as a potential target. Then a low temperature route is used to successfully synthesize the novel crystal, which is confirmed by X‐ray powder diffraction and Mössbauer spectroscopy. β‐SnMoO4 is active for the photocatalytic decomposition of a methylene blue solution under daylight and its activity is comparable to a known photocatalyst, β‐SnWO4. PMID:28105400

  20. Pulsed inductive HF laser

    SciTech Connect

    Razhev, A M; Kargapol'tsev, E S; Churkin, D S; Demchuk, S V

    2016-03-31

    We report the results of experimentally investigated dependences of temporal, spectral and spatial characteristics of an inductive HF-laser generation on the pump conditions. Gas mixtures H{sub 2} – F{sub 2}(NF{sub 3} or SF6{sub 6}) and He(Ne) – H{sub 2} – F{sub 2}(NF{sub 3} or SF{sub 6}) were used as active media. The FWHM pulse duration reached 0.42 μs. This value corresponded to a pulsed power of 45 kW. For the first time, the emission spectrum of an inductive HF laser was investigated, which consisted of seven groups of bands with centres around the wavelengths of 2732, 2736, 2739, 2835, 2837, 2893 and 2913 nm. The cross section profile of the laser beam was a ring with a diameter of about 20 mm and width of about 5 mm. Parameters of laser operation in the repetitively pulsed regime were sufficiently stable. The amplitude instability of light pulses was no greater than 5% – 6%. (lasers)

  1. Oxidation and interdiffusion behavior of Niobium substrate coated MoSi2 coating prepared by spark plasma sintering

    NASA Astrophysics Data System (ADS)

    Yan, JianHui; Wang, Yi; Liu, LongFei; Wang, Yueming

    2014-11-01

    In order to protect Niobium material from oxidation, MoSi2 coating was prepared on the Niobium substrate by spark plasma sintering. Oxidation behavior of MoSi2 coating was investigated in air over the temperature range of 1200-1500 °C. The interfacial diffusion between MoSi2 coating and Niobium substrate was also examined. Dense MoSi2 coating was successfully prepared using spark plasma sintering. The porosities of top and side coatings are about 5.5% and 6.4%, respectively. No cracks were present in the MoSi2 coating. Cracking and spallation of the SiO2 scale did not occur at test temperatures. Two intermediate phases-(Nb,Mo)5Si3 and Nb5Si3 phases, were detected in the boundary of MoSi2 coating and Nb substrate. The growth of the reaction layer was dominated by the diffusion of Si toward the Nb substrate and obeyed a parabolic rate law. A multi-layered structural coating formed on Nb substrate, which consisted of MoSi2, (Mo,Nb)5Si3 and Nb5Si3 in turn.

  2. Oxidation of several corrosion-resistant metals in HF-DMF

    SciTech Connect

    Chulkevich, A.K.; Smolina, E.V.; Lavrent'ev, I.P.; Khidekel', M.L.

    1987-02-20

    The oxidative dissolution of transition metals in organic and aqueous organic media yields a broad range of complexes. In work, data are given on the dissolution of Ti, Zr, Nb, Ta, Cr, and Mn in HF-DMF and HF-DMF-H/sub 2/O/sub 2/ systems. The dimethylammonium oxyfluoride complexes were isolated and characterized. Metals of groups IV-VI may be oxidized in HF-DMF and HF-DMF-H/sub 2/O/sub 2/ systems. The dimethylammonium oxyfluoride complexes of titanium(IV), zirconium(IV), niobium(V), tantalum(V), and the oxyfluorides of chromium(III) and manganese(II) were isolated and characterized.

  3. Characteristics of a multicomponent Nb-Ti-Al alloy via industrial-scale practice

    SciTech Connect

    Sikka, V.K.; Loria, E.A.

    1997-05-01

    Within the spectrum of advanced intermetallic materials, an alloy containing 44Nb-35Ti-6Al-5Cr-8V-1W-0.5Mo-0.3Hf (at. %) was investigated in the industrial-scale produced condition. The alloy was tensile tested in air from room temperature to 1,000 C and in vacuum at 750 and 850 C. Results of this study have shown that the alloy can be commercially produced and has adequate ductility for its secondary processing even at an oxygen level of 1,160 wppm. The alloy has room temperature ductility of 16% and superplastic elongation of 244% at 1,000 C. This alloy shows low intermediate temperature (600--850 C) ductility when tested in air. The vacuum testing revealed that the low ductility is associated within oxygen embrittlement phenomenon. It is expected that such an embrittlement can be taken care of by an oxidation resistant coating. The alloy also possesses superior strength to similar alloys in this class. Results of this investigation suggest a strong potential for consideration of this alloy to exceed the useful temperature range of nickel-base superalloys.

  4. Hierarchical MoS2@MoP core-shell heterojunction electrocatalysts for efficient hydrogen evolution reaction over a broad pH range

    NASA Astrophysics Data System (ADS)

    Wu, Aiping; Tian, Chungui; Yan, Haijing; Jiao, Yanqing; Yan, Qing; Yang, Guoyu; Fu, Honggang

    2016-05-01

    A low-cost catalyst for the hydrogen evolution reaction (HER) over a broad pH range is highly desired to meet the practical needs in different areas. In this study, hierarchical flower-like MoS2@MoP core-shell heterojunctions (HF-MoSP) are designed as a promising catalyst for HER over a broad pH range. The materials are obtained by the controllable phosphidation of the hierarchical MoS2 flower (HF-MoS2) composed of thin silk belt-like sheets. The phosphidation degree, P/S ratio and work function (WF) of HF-MoSP can be tuned easily over broad range by changing the phosphidation temperature. Under optimized condition, HF-MoSP exhibits excellent electrocatalytic activity for HER with a low onset overpotential of 29 mV and η of 108 mV at 10 mA cm-2 in 0.5 M H2SO4 and retains its good activity for 30 h. In addition, the catalyst shows excellent activity in 1 M KOH with an onset overpotential of 42 mV and η of 119 mV at 10 mA cm-2. The catalysts also exhibit obvious activity in neutral, weak acid and weak alkaline conditions. The good performance is relative to the synergy of the MoP shell and MoS2 core and the high WF of HF-MoSP close to Pt, and the large SBET of HF-MoSP benefited from the hierarchical structure. This study represents the construction of the core-shell heterojunction and provides a new way to provide the low-cost and high-performance catalyst for HER.A low-cost catalyst for the hydrogen evolution reaction (HER) over a broad pH range is highly desired to meet the practical needs in different areas. In this study, hierarchical flower-like MoS2@MoP core-shell heterojunctions (HF-MoSP) are designed as a promising catalyst for HER over a broad pH range. The materials are obtained by the controllable phosphidation of the hierarchical MoS2 flower (HF-MoS2) composed of thin silk belt-like sheets. The phosphidation degree, P/S ratio and work function (WF) of HF-MoSP can be tuned easily over broad range by changing the phosphidation temperature. Under optimized

  5. Electronic Structure Differences in ZrO2 vs. HfO2

    SciTech Connect

    Zheng, Weijun; Bowen Jr., K.H.; Li, Jun; Dabkowska, Iwona; Gutowski, Maciej S.

    2005-12-22

    While ZrO2 and HfO2 are, for the most part, quite similar chemically, subtle differences in their electronic structures appear to be responsible for differing MO2/Si (M = Zr, Hf) interface stabilities. In order to shed light on the electronic structure differences between ZrO2 and HfO2, we have conducted joint experimental/theoretical studies. Since electron affinities are a sensitive probe of electronic structure, we have measured them by conducting photoelectron spectroscopic experiments on ZrO2- and HfO2-. The electron affinity of HfO2 was determined to be 2.14? 0.03 eV, while that of ZrO2 was determined to be 1.64 ? 0.03 eV. Concurrently, electronic structure calculations were conducted to determine electron affinities, vibrational frequencies, and geometries of these systems. The calculated electron affinities of HfO2 and ZrO2 were found to be 2.05 and 1.62 eV, respectively. The molecular results confirm earlier predictions from solid phases that HfO2 is more ionic than ZrO2. The excess electron in MO2- occupies an sd-type hybrid orbital localized on the M atom (M=Zr, Hf). The structural parameters of ZrO2 and HfO2 were found to be very similar. The difference in geometries between the neutral and the anion is along the symmetrical stretching and bending modes. Together, these studies unveil significant differences in the electronic structures of ZrO2 and HfO2.

  6. HF mitigation via the Texaco-UOP HF additive technology

    SciTech Connect

    Sheckler, J.C.; Hammershaimb, H.U. ); Ross, L.J. ); Comey, K.R. III . Research and Development)

    1994-01-01

    Alkylation is one of the key processes used by refiners to produce high-octane gasoline. In the alkylation process, light olefins and isobutane are converted to alkylate, a high-octane, low-vapor-pressure, paraffinic gasoline-blending component. Because of its clean burning characteristics and ability to contribute to lower emissions, alkylate is a highly valued component in premium and reformulated gasolines. Alkylation process technology using hydrogen fluoride (HF) as a catalyst has been widely used for many years. Since the mid-1980s, a primary concern has been the tendency of HF to form an aerosol when HF is released to the atmosphere. Much effort has gone into the development of measures to ensure the safe handling of HF in the refinery environment. Texaco and UOP have under development an HF additive technology. The key to this technology is the discovery of a class of additives that form a complex with HF to significantly reduce the aerosol-forming tendency of the catalyst system and still maintain acceptable catalytic performance and product quality. The purpose of this paper is to provide an update on the development status of the Texaco-UOP HF additive technology. Aerosol reduction has been demonstrated in small-scale laboratory release tests as well as in larger scale wind tunnel release tests. The catalytic performance of the HF additive has been demonstrated in laboratory alkylation facilities and in a short-term experimental trial in a full-scale refinery unit. On the basis of the positive results obtained in the test program, a project is under way to implement the HF additive technology on a continuous basis in an existing Texaco alkylation unit by the third quarter of 1994.

  7. Processing and Oxidation Behavior of Nb-Si-B Intermetallics

    SciTech Connect

    Y.LIU; A.J. Thom; M.J. Kramer; M. Akinc

    2004-09-30

    Single phase materials of {alpha}-Nb{sub 5}Si{sub 3}, Nb{sub 5}(Si,B){sub 3} (T2) and Nb{sub 5}Si{sub 3}B{sub x} (D8{sub 8}) in the Nb-Si-B system were prepared by powder metallurgy processing. T2 was almost fully dense, while {alpha}-Nb{sub 5}Si{sub 3} and D8{sub 8} were porous after sintering at 1900 C for 2 hours. The lattice parameters of T2 decreased linearly with the substitution of B for Si. Isothermal oxidation testing at 1000 C in flowing air indicated that the oxidation resistances of T2 and D8{sub 8} are much better than {alpha}-Nb{sub 5}Si{sub 3}, but still extremely poor compared to the boron-modified Mo{sub 5}Si{sub 3}. Extensive cracking in the oxide scale and matrix were observed and arose from the volume expansion associated with the formation of Nb{sub 2}O{sub 5} and boron-containing silica glass.

  8. 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.

  9. 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

  10. Marburg Hemorrhagic Fever (Marburg HF)

    MedlinePlus

    ... The CDC Cancel Submit Search The CDC Marburg hemorrhagic fever (Marburg HF) Note: Javascript is disabled or is ... was first recognized in 1967, when outbreaks of hemorrhagic fever occurred simultaneously in laboratories in Marburg and Frankfurt, ...

  11. 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

  12. Effect of Nb Addition to Ti-Bearing Super Martensitic Stainless Steel on Control of Austenite Grain Size and Strengthening

    NASA Astrophysics Data System (ADS)

    Ma, Xiaoping; Langelier, Brian; Gault, Baptiste; Subramanian, Sundaresa

    2017-03-01

    The role of Nb in normalized and tempered Ti-bearing 13Cr5Ni2Mo super martensitic stainless steel is investigated through in-depth characterization of the bimodal chemistry and size of Nb-rich precipitates/atomic clusters and Nb in solid solution. Transmission electron microscopy and atom probe tomography are used to analyze the samples and clarify precipitates/atom cluster interactions with dislocations and austenite grain boundaries. The effect of 0.1 wt pct Nb addition on the promotion of (Ti, Nb)N-Nb(C,N) composite precipitates, as well as the retention of Nb in solution after cooling to room temperature, are analyzed quantitatively. (Ti, Nb)N-Nb(C,N) composite precipitates with average diameters of approximately 24 ± 8 nm resulting from epitaxial growth of Nb(C,N) on pre-existing (Ti,Nb)N particles, with inter-particle spacing on the order of 205 ± 68 nm, are found to be associated with mean austenite grain size of 28 ± 10 µm in the sample normalized at 1323 K (1050 °C). The calculated Zener limiting austenite grain size of 38 ± 13 µm is in agreement with the experimentally observed austenite grain size distribution. 0.08 wt pct Nb is retained in the as-normalized condition, which is able to promote Nb(C, N) atomic clusters at dislocations during tempering at 873 K (600 °C) for 2 hours, and increases the yield strength by 160 MPa, which is predicted to be close to maximum increase in strengthening effect. Retention of solute Nb before tempering also leads to it preferentially combing with C and N to form Nb(C, N) atom clusters, which suppresses the occurrence of Cr- and Mo-rich carbides during tempering.

  13. Effects of Microalloying on the Microstructures and Mechanical Properties of Directionally Solidified Ni-33(at.%)Al-31Cr-3Mo Eutectic Alloys Investigated

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel; Raj, Sai V.; Locci, Ivan E.; Salem, Jonathan A.

    2002-01-01

    Despite nickel aluminide (NiAl) alloys' attractive combination of oxidation and thermophysical properties, their development as replacements for superalloy airfoils in gas turbine engines has been largely limited by difficulties in developing alloys with an optimum combination of elevated-temperature creep resistance and room-temperature fracture toughness. Alternatively, research has focused on developing directionally solidified NiAl-based in situ eutectic composites composed of NiAl and (Cr,Mo) phases in order to obtain a desirable combination of properties a systematic investigation was undertaken at the NASA Glenn Research Center to examine the effects of small additions of 11 alloying elements (Co, Cu, Fe, Hf, Mn, Nb, Re, Si, Ta, Ti, and Zr) in amounts varying from 0.25 to 1.0 at.% on the elevated-temperature strength and room-temperature fracture toughness of directionally solidified Ni-33Al-31Cr-3Mo eutectic alloy. The alloys were grown at 12.7 mm/hr, where the unalloyed eutectic base alloy exhibited a planar eutectic microstructure. The different microstructures that formed because of these fifth-element additions are included in the table. The additions of these elements even in small amounts resulted in the formation of cellular microstructures, and in some cases, dendrites and third phases were observed. Most of these elemental additions did not improve either the elevated-temperature strength or the room-temperature fracture toughness over that of the base alloy. However, small improvements in the compression strength were observed between 1200 and 1400 K when 0.5 at.% Hf and 0.25 at.% Ti were added to the base alloy. The results of this study suggest that the microalloying of Ni-33Al-31Cr-3Mo will not significantly improve either its elevatedtemperature strength or its room-temperature fracture toughness. Thus, any improvements in these properties must be acquired by changing the processing conditions.

  14. Surface Passivation of MoO₃ Nanorods by Atomic Layer Deposition toward High Rate Durable Li Ion Battery Anodes.

    PubMed

    Ahmed, B; Shahid, Muhammad; Nagaraju, D H; Anjum, D H; Hedhili, Mohamed N; Alshareef, H N

    2015-06-24

    We demonstrate an effective strategy to overcome the degradation of MoO3 nanorod anodes in lithium (Li) ion batteries at high-rate cycling. This is achieved by conformal nanoscale surface passivation of the MoO3 nanorods by HfO2 using atomic layer deposition (ALD). At high current density such as 1500 mA/g, the specific capacity of HfO2-coated MoO3 electrodes is 68% higher than that of bare MoO3 electrodes after 50 charge/discharge cycles. After 50 charge/discharge cycles, HfO2-coated MoO3 electrodes exhibited specific capacity of 657 mAh/g; on the other hand, bare MoO3 showed only 460 mAh/g. Furthermore, we observed that HfO2-coated MoO3 electrodes tend to stabilize faster than bare MoO3 electrodes because nanoscale HfO2 layer prevents structural degradation of MoO3 nanorods. Additionally, the growth temperature of MoO3 nanorods and the effect of HfO2 layer thickness was studied and found to be important parameters for optimum battery performance. The growth temperature defines the microstructural features and HfO2 layer thickness defines the diffusion coefficient of Li-ions through the passivation layer to the active material. Furthermore, ex situ high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction were carried out to explain the capacity retention mechanism after HfO2 coating.

  15. Optimization of the thermoelectric properties of FeNbSb-based half-Heusler materials

    NASA Astrophysics Data System (ADS)

    Li, Wenfeng; Yang, Gui; Zhang, Jianwei

    2016-05-01

    FeNbSb-based half-Heusler compounds have recently been reported as promising materials for good high-temperature thermoelectric materials with a ZT  >  1. Their electronic structure and thermoelectric properties are investigated based on a first-principles simulation and the semi-classical Boltzmann transport theory. The band structures show not only light and heavy bands but also high band degeneracy near the valence band maximum, which is beneficial for thermoelectric performance. The calculated Seebeck coefficients of p-type FeNbSb at high carrier concentrations exhibit the expected high values, which is consistent with experimental data. The evolution of the electrical conductivity and power factor with carrier concentration at different temperatures is investigated. Our results show that the thermoelectric performance of p-type FeNbSb can be improved by appropriate substitution; for example, by doping Hf on the Nb site, the maximum ZT of the p-type FeNb1-x Hf x Sb can reach ~1.5 at 1200 K. This study can provide some theoretical guidance for experimental research to improve the thermoelectric performance of FeNbSb-based half-Heusler compounds.

  16. Catalytic efficiency of Nb and Nb oxides for hydrogen dissociation

    SciTech Connect

    Isobe, Shigehito; Kudoh, Katsuhiro; Hino, Satoshi; Hashimoto, Naoyuki; Ohnuki, Somei; Hara, Kenji

    2015-08-24

    In this letter, catalytic efficiency of Nb, NbO, Nb{sub 2}O{sub 3}, NbO{sub 2}, and Nb{sub 2}O{sub 5} for dissociation and recombination of hydrogen were experimentally investigated. On the surface of Nb and Nb oxides in a gas mixture of H{sub 2} and D{sub 2}, H{sub 2} and D{sub 2} molecules can be dissociated to H and D atoms; then, H{sub 2}, D{sub 2}, and HD molecules can be produced according to the law of probability. With increase of frequency of the dissociation and recombination, HD ratio increases. The ratio of H{sub 2} and HD gas was analyzed by quadrupole mass spectrometry. As a result, NbO showed the highest catalytic activity towards hydrogen dissociation and recombination.

  17. Syntheses and structures of Sc2Nb(4–x)Sn5, YNb6Sn6, and ErNb6Sn5: exploratory studies in ternary rare-earth niobium stannides.

    PubMed

    Yue, Cheng-Yang; Lei, Xiao-Wu

    2012-02-20

    Three new rare-earth (RE) niobium stannides, namely, Sc(2)Nb(4-x)Sn(5) (x = 0.37, 0.52), YNb(6)Sn(6), and ErNb(6)Sn(5), have been obtained by reacting the mixture of corresponding pure elements at high temperature and structurally characterized by single-crystal X-ray diffraction studies. Sc(2)Nb(4-x)Sn(5) crystallizes in the orthorhombic space group Ibam (No. 72) and belongs to the V(6)Si(5) type. Its structure features a three-dimensional (3D) network composed of two-dimensionally (2D) corrugated [Nb(2)Sn(2)] and [Nb(2)Sn(3)] layers interconnected via Nb-Sn bonds, forming one type of one-dimensional (1D) narrow tunnels along the c axis occupied by Sc atoms. YNb(6)Sn(6) crystallizes in the hexagonal space group P6/mmm (No. 191) and adopts the HfFe(6)Ge(6) type, and ErNb(6)Sn(5) crystallizes in the trigonal space group R3m (No. 166) and belongs to the LiFe(6)Ge(5) type. Their structures both feature 3D networks based on 2D [Nb(3)Sn], [Sn(2)], and [RESn(2)] layers (RE = Y, Er). In YNb(6)Sn(6), one type of [Nb(3)Sn] layer is interconnected by [Sn(2)] and [YSn(2)] layers via Nb-Sn bonds to form a 3D network. However, in ErNb(6)Sn(5), two types of [Nb(3)Sn] layers are interlinked by [Sn(2)] and [ErSn(2)] layers via Nb-Sn bonds into a 3D framework. Electronic structure calculations and magnetic property measurements for "Sc(2)Nb(4)Sn(5)" and YNb(6)Sn(6) indicate that both compounds show semimetallic and temperature-independent diamagnetic behavior.

  18. Thermodynamics of Ternary Nitride Formation by Ammonolysis: Application to LiMoN2, Na3WN3 and Na3WO3N

    DTIC Science & Technology

    1992-01-01

    TiN -309.2 ZrO2 -1042 ZrN -336.8 V205 -1423 VN -191.2 Nb205 -1766 NbN -213.4 Ta205 -1920 Ta3N5 -1151b Cr03 -506.3 CrN -92.0 MoO3 -669.4 Mo2N -50.2 W03...reports that Nb2O5, Ta2O5, MoO3 and WCO can be reacted in flowing ammonia gas at 973 - 1123 K to produce NbN, Ta3N5, Mo 2N and W2N, respectively. 28...mol, respectively) Li20 (base) + MoO3 (acid) -4 Li2MO04 (3) Na2O (base) + W03 (acid) -+ Na2WO4 (4) when compared to their standard free energies of

  19. Formation of the giant Chalukou porphyry Mo deposit in northern Great Xing'an Range, NE China: Partial melting of the juvenile lower crust in intra-plate extensional environment

    NASA Astrophysics Data System (ADS)

    Li, Zhen-Zhen; Qin, Ke-Zhang; Li, Guang-Ming; Ishihara, Shunso; Jin, Lu-Ying; Song, Guo-Xue; Meng, Zhao-Jun

    2014-08-01

    The Chalukou porphyry Mo deposit (2.46 Mt @ 0.087% Mo), located in the northern Great Xing'an Range, NE China, is the largest Mo deposit discovered in China so far. The host rocks consist of aplite porphyry, granite porphyry and quartz porphyry, and are intruded into Lower Ordovician intermediate-felsic volcanic-sedimentary rocks and pre-ore monzogranite and are cut by post-ore feldspar porphyry, diorite porphyry and quartz monzonite porphyry. Here, we present the zircon U-Pb ages, whole-rock geochemistry, Sr-Nd isotopic and zircon Hf isotopic data for the pre-ore, syn-ore and post-ore intrusive rocks. The Chalukou ore-forming porphyries intruded during 147-148 Ma and have high-silica, alkali-rich, metaluminous to slightly peraluminous compositions and are oxidized. They are enriched in large ion lithophile elements (e.g. K, Rb, U and Th), light REE and depleted in high-field strength elements (e.g. Nb, P and Ti). Depletions in Eu, Ba, Sr, Nb, Ta, P and Ti suggest that they have experienced strong fractional crystallization of plagioclase, biotite, hornblende and accessory minerals. The pre-ore monzogranite (~ 172 Ma) also belongs to the high-K calc-alkaline series. Highly fractionated REE patterns ((La/Yb) N = 19.6-21.7), high values of Sr/Y (54-69) and La/Yb (29-32), are adakite-like geochemical features. The post-ore rocks (~ 141-128 Ma) have similar geochemical characteristics with ore-forming porphyries except that quartz monzonite porphyry shows no Ba-Sr negative anomaly. All intrusive rocks have relative low initial 87Sr/86Sr (0.705413-0.707889) and εNd (t) values (- 1.28 to + 0.92), positive εHf (t) values (+ 2.4 to + 10.1) and young two-stage Nd and Hf model ages (TDM2 (Nd) = 863-977 Ma, TDM2 (Hf) = 552-976 Ma). These geochemical and isotopic data are interpreted to demonstrate that the ore-forming porphyries formed by partial melting of the juvenile lower crust caused by underplating of mafic magmas in an intra-plate extensional setting. The pre

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

    SciTech Connect

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

    2012-06-20

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

  1. Thermodynamic Stability of High-K Dielectric Metal Oxides ZrO2 and HfO2 in Contact with Si and SiO2

    SciTech Connect

    Gutowski, Maciej S. ); Jaffe, John E. ); Lui, Chun-Li; Stoker, Matt; Hegde, Rama I.; Rai, Raghaw S.; Tobin, Philip J.

    2002-03-18

    We present theoretical and experimental results regarding the thermodynamic stability of the high-k dielectrics MO2 (M= Zr and Hf) in contact with Si and SiO2. The HfO2/Si interface is found to be stable with respect to formation of silicides whereas the ZrO2/Si interface is not. The MO2/SiO2 interface is marginally unstable with respect to formation of silicates. Cross-sectional transmission electron micrographs expose formation of nodules, identified as silicides, across the polysilicon/ZrO2/Si interfaces but not for the interfaces with HfO2. For both ZrO2 and HfO2, the X-ray photoemission spectra illustrate formation of silicate-like compounds in the MO2/SiO2 interface.

  2. Evaluation of Nb-base alloys for the divertor structure in fusion reactors

    SciTech Connect

    Purdy, I.M.

    1996-04-01

    Niobium-base alloys are candidate materials for the divertor structure in fusion reactors. For this application, an alloy should resist aqueous corrosion, hydrogen embrittlement, and radiation damage and should have high thermal conductivity and low thermal expansion. Results of corrosion and embrittlement screening tests of several binary and ternary Nb alloys in high-temperature water indicated the Mb-1Zr, Nb-5MO-1Zr, and Nb-5V-1Z4 (wt %) showed sufficient promise for further investigation. These alloys, together with pure Nb and Zircaloy-4 have been exposed to high purity water containing a low concentration of dissolved oxygen (<12 ppb) at 170, 230, and 300{degrees}C for up to {approx}3200 h. Weight-change data, microstructural observations, and qualitative mechanical-property evaluation reveal that Nb-5V-1Zr is the most promising alloy at higher temperatures. Below {approx}200{degrees}C, the alloys exhibit similiar corrosion behavior.

  3. Na2MoO2As2O7

    PubMed Central

    Jouini, Raja; Zid, Mohamed Faouzi; Driss, Ahmed

    2012-01-01

    Disodium molybdenum dioxide diarsenate, Na2MoO2As2O7, has been synthesized by a solid-state reaction. The structure is built up from MoAs2O12 linear units sharing corners to form a three-dimensional framework containing tunnels running along the a-axis direction in which the Na+ cations are located. In this framework, the AsV atoms are tetra­hedrally coordinated and form an As2O7 group. The MoVI atom is displaced from the center of an octa­hedron of O atoms. Two Na+ cations are disordered about inversion centres. Structural relationships between different compounds: A 2MoO2As2O7 (A = K, Rb), AMOP2O7 (A = Na, K, Rb; M = Mo, Nb) and MoP2O7 are discussed. PMID:23468669

  4. Subduction Contributions in the Trans-Mexican Volcanic Belt: Implications from Lava Chemistry and Hf-Nd-Pb Isotopes

    NASA Astrophysics Data System (ADS)

    Cai, Y.; Goldstein, S. L.; Langmuir, C. H.; Gómez-Tuena, A.; Lagatta, A.; Straub, S. M.; Martín Del Pozzo, A.

    2007-05-01

    Despite thick continental crust, near primitive lavas erupt throughout the Trans-Mexican Volcanic Belt (TMVB). In order to distinguish and better constrain subduction contributions and effects of crustal contamination, we analyzed samples representing subducting sediments from DSDP Site 487, and Quaternary lavas from stratovolcanoes and cinder cones, including alkaline "high-Nb" lavas from the Sierra Chichinautzin Volcanic Field (SCVF) showing negligible subduction signature in its trace element chemistry and representing melts of the mantle wedge. Our primary observations and implications are: (1) The high-Nb SCVF `intraplate' lavas define a linear trend along the "Nd-Hf mantle-crust array", defining the composition of the mantle wedge. (2) Popocatepetl and Nevado de Toluca stratovolcanoes show the highest Nd and Hf isotope ratios, higher than the `intraplate' lavas, indicating their sources are more "depleted mantle-like" than the regional mantle wedge. (3) The Popo and Toluca chemical and isotopic trends sharply contrast with Pico de Orizaba, which shows classic indications of crustal contamination (e.g. high 207Pb/204Pb, low Nd-Hf isotope ratios), consistent with contamination by local Precambrian crust. (4) Higher Nd-Hf isotopes in Popo and Toluca lavas also correlate with lower Pb isotope ratios, and lower Lu/Hf and Zr/Hf. Together, these data indicate contributions from subducted Pacific oceanic crust and hydrothermal sediment. (5) Popo and Toluca are also enriched in Th/LREE compared with `intraplate' lavas, reflecting subducted sediment contributions. (6) Nd-Hf isotope ratios of hydrothermal sediment from DSDP Site 487 lie on the "seawater array", with high Hf isotope ratios compared to the "mantle-crust array". Popo and Toluca Nd-Hf isotopes display a shallower slope than the "intraplate lava Nd-Hf array", reflecting contributions from hydrothermal sediment. Popocatepetl and Toluca lavas therefore avoid substantial crustal contamination of mantle wedge

  5. Radio HF precursors of Earthquakes

    NASA Astrophysics Data System (ADS)

    Ruzhin, Yu.; Nomicos, C.; Vallianatos, F.; Shpakovsky, V.

    The high frequency (HF) earthquake electromagnetic precursors (40-55MHz band) were recorded by the four electromagnetic stations a few days (hours) prior the event associated with earthquakes with magnitude more than 5.0 at Crete Island. These experiments were performed continuously during 1998-2002 and specific peculiarities are found. This is underhorizon epicenter position for main part of events under question. Another unusual result is that such HF preseismic radio noise-like signals are responsible for seaquakes too. We made conclusion about developing of some thunderstorm-like charged clouds activity in atmosphere before the seismic event. As result of our analysis and interpretation of the available data of continuous observations on a network of Crete island we should state here, that in an atmosphere above the sea on the eve of earthquake at heights of 0.1-10 km the spatially distributed spots of sporadic charged clouds are occurred and the conditions for the electrical discharges in an atmosphere are created which can serve a source of HF radio-emission registered by Crete network. The atmosphere theory relations are used to model a corresponding to an anomalous event emissions generation observed on the Crete. The supposed mechanism of preseismic electricity generation is the model of convection carrier started in an atmosphere. It is governed by the horizontal gradient of air temperature. The occurrence of electrical charges in a surface of the sea and transportation them further on heights up to 10 km in our model occurs due to sporadic energy injections that allocated within bottom of the sea as gases and heat. The dimensions of width and height govern the size of atmosphere convection cells in the earthquake preparation area. These dimensions of the sporadic spots are close to 3 km each as it is derived from shadow geometry and spectral fluctuations of HF signal. Based on experience of Crete HF precursors observation the method for satellite mapping

  6. HfS, Hyperfine Structure Fitting Tool

    NASA Astrophysics Data System (ADS)

    Estalella, Robert

    2017-02-01

    Hyperfine Structure Fitting (HfS) is a tool to fit the hyperfine structure of spectral lines with multiple velocity components. The HfS_nh3 procedures included in HfS simultaneously fit the hyperfine structure of the NH3 (J, K) = (1, 1) and (2, 2) transitions, and perform a standard analysis to derive {T}{ex}, NH3 column density, {T}{rot}, and {T}{{k}}. HfS uses a Monte Carlo approach for fitting the line parameters. Special attention is paid to the derivation of the parameter uncertainties. HfS includes procedures that make use of parallel computing for fitting spectra from a data cube.

  7. The dipolar endofullerene HF@C60

    NASA Astrophysics Data System (ADS)

    Krachmalnicoff, Andrea; Bounds, Richard; Mamone, Salvatore; Alom, Shamim; Concistrè, Maria; Meier, Benno; Kouřil, Karel; Light, Mark E.; Johnson, Mark R.; Rols, Stéphane; Horsewill, Anthony J.; Shugai, Anna; Nagel, Urmas; Rõõm, Toomas; Carravetta, Marina; Levitt, Malcolm H.; Whitby, Richard J.

    2016-10-01

    The cavity inside fullerenes provides a unique environment for the study of isolated atoms and molecules. We report the encapsulation of hydrogen fluoride inside C60 using molecular surgery to give the endohedral fullerene HF@C60. The key synthetic step is the closure of the open fullerene cage with the escape of HF minimized. The encapsulated HF molecule moves freely inside the cage and exhibits quantization of its translational and rotational degrees of freedom, as revealed by inelastic neutron scattering and infrared spectroscopy. The rotational and vibrational constants of the encapsulated HF molecules were found to be redshifted relative to free HF. The NMR spectra display a large 1H-19F J coupling typical of an isolated species. The dipole moment of HF@C60 was estimated from the temperature dependence of the dielectric constant at cryogenic temperatures and showed that the cage shields around 75% of the HF dipole.

  8. The dipolar endofullerene HF@C60.

    PubMed

    Krachmalnicoff, Andrea; Bounds, Richard; Mamone, Salvatore; Alom, Shamim; Concistrè, Maria; Meier, Benno; Kouřil, Karel; Light, Mark E; Johnson, Mark R; Rols, Stéphane; Horsewill, Anthony J; Shugai, Anna; Nagel, Urmas; Rõõm, Toomas; Carravetta, Marina; Levitt, Malcolm H; Whitby, Richard J

    2016-10-01

    The cavity inside fullerenes provides a unique environment for the study of isolated atoms and molecules. We report the encapsulation of hydrogen fluoride inside C60 using molecular surgery to give the endohedral fullerene HF@C60. The key synthetic step is the closure of the open fullerene cage with the escape of HF minimized. The encapsulated HF molecule moves freely inside the cage and exhibits quantization of its translational and rotational degrees of freedom, as revealed by inelastic neutron scattering and infrared spectroscopy. The rotational and vibrational constants of the encapsulated HF molecules were found to be redshifted relative to free HF. The NMR spectra display a large (1)H-(19)F J coupling typical of an isolated species. The dipole moment of HF@C60 was estimated from the temperature dependence of the dielectric constant at cryogenic temperatures and showed that the cage shields around 75% of the HF dipole.

  9. Environmentally friendly HF (DF) lasers

    NASA Astrophysics Data System (ADS)

    Apollonov, V. V.

    2016-08-01

    Dedicated to the 100th anniversary of the birth of Academician A M Prokhorov, this paper reviews the physics of self-sustained volume discharge without preionization—self-initiated volume discharge (SIVD)—in the working mixtures of non-chain hydrofluoride HF (deuterofluoride (DF)) lasers. The dynamics of SIVD in discharge gaps with different geometries is thoroughly described. The mechanisms for the restriction of current density in a diffuse channel in electric discharges in SF6 and SF6 based mixtures (which determines whether SIVD is possible) are proposed and analyzed using simple models. The most probable mechanisms are the electron impact dissociation of SF6 and other mixture components, electron-ion recombination and electron attachment to vibrationally excited SF6 molecules. Starting from a comparative analysis of the rate coefficients of these processes, it is shown that electron-ion recombination is capable of compensating for electron detachment from negative ions via electron impact. It is also established that SIVD is not only observed in SF6, but also in other strongly electronegative gases. The factors that determine the uniformity of the active medium in non-chain HF (DF) lasers are analyzed. Some special features of non-chain HF (DF) lasers with different apertures operating are carefully examined. Consideration is given to the problem of increasing the aperture and discharge volume of non-chain HF (DF) lasers. Based on our experimental results, the possibility of increasing the energy of such lasers to ~1 kJ and above is shown.

  10. Formation of amorphous alloys on 4H-SiC with NbNi film using pulsed-laser annealing

    NASA Astrophysics Data System (ADS)

    De Silva, Milantha; Ishikawa, Seiji; Miyazaki, Takamichi; Kikkawa, Takamaro; Kuroki, Shin-Ichiro

    2016-07-01

    Amorphous alloys containing Ni-Si-Nb-C were formed on 4H-SiC creating a low resistance Ohmic contact electrode. In a conventional nickel silicide (NiSi) electrode on SiC, a carbon agglomeration at the silicide/SiC interface occurs, and contact resistance between NiSi and SiC substrate becomes larger. For carbon agglomeration suppression, nanosecond non-equilibrium laser annealing was introduced, and to form metal carbides, carbon-interstitial type metals Nb and Mo were introduced. Ni, Nb, Mo, Nb/Ni, Mo/Ni multilayer contacts, and NbNi mixed contact were formed on the C-face side of n-type 4H-SiC wafers. The electrical contact properties were investigated after a 45 ns pulse laser annealing in N2 ambient. As a result, with NbNi film, an amorphous alloy with Ni-Si-Nb-C was formed, and a low specific contact resistance of 5.3 × 10-4 Ω cm2 was realized.

  11. Thermoelectric properties of monolayer MSe2 (M = Zr, Hf): low lattice thermal conductivity and a promising figure of merit

    NASA Astrophysics Data System (ADS)

    Ding, Guangqian; Gao, G. Y.; Huang, Zhishuo; Zhang, Wenxu; Yao, Kailun

    2016-09-01

    Monolayer transition-metal dichalcogenides (TMDCs) MX2 (M = Mo, W, Zr, Hf, etc; X = S, Se, Te) have become well-known in recent times for their promising applications in thermoelectrics and field effect transistors. In this work, we perform a systematic study on the thermoelectric properties of monolayer ZrSe2 and HfSe2 using first-principles calculations combined with Boltzmann transport equations. Our results point to a competitive thermoelectric figure of merit (close to 1 at optimal doping) in both monolayer ZrSe2 and HfSe2, which is markedly higher than previous explored monolayer TMDCs such as MoS2 and MoSe2. We also reveal that the higher figure of merits arise mainly from their low lattice thermal conductivity, and this is partly due to the strong coupling of acoustic modes with low frequency optical modes. It is found that the figure of merits can be better optimized in n-type than in p-type. In particular, the performance of HfSe2 is superior to ZrSe2 at a higher temperature. Our results suggest that monolayer ZrSe2 and HfSe2 with lower lattice thermal conductivity than usual monolayer TMDCs are promising candidates for thermoelectric applications.

  12. The initial abundance and distribution of 92Nb in the Solar System

    NASA Astrophysics Data System (ADS)

    Iizuka, Tsuyoshi; Lai, Yi-Jen; Akram, Waheed; Amelin, Yuri; Schönbächler, Maria

    2016-04-01

    Niobium-92 is an extinct proton-rich nuclide, which decays to 92Zr with a half-life of 37 Ma. This radionuclide potentially offers a unique opportunity to determine the timescales of early Solar System processes and the site(s) of nucleosynthesis for p-nuclei, once its initial abundance and distribution in the Solar System are well established. Here we present internal Nb-Zr isochrons for three basaltic achondrites with known U-Pb ages: the angrite NWA 4590, the eucrite Agoult, and the ungrouped achondrite Ibitira. Our results show that the relative Nb-Zr isochron ages of the three meteorites are consistent with the time intervals obtained from the Pb-Pb chronometer for pyroxene and plagioclase, indicating that 92Nb was homogeneously distributed among their source regions. The Nb-Zr and Pb-Pb data for NWA 4590 yield the most reliable and precise reference point for anchoring the Nb-Zr chronometer to the absolute timescale: an initial 92Nb/93Nb ratio of (1.4 ± 0.5) ×10-5 at 4557.93 ± 0.36 Ma, which corresponds to a 92Nb/93Nb ratio of (1.7 ± 0.6) ×10-5 at the time of the Solar System formation. On the basis of this new initial ratio, we demonstrate the capability of the Nb-Zr chronometer to date early Solar System objects including troilite and rutile, such as iron and stony-iron meteorites. Furthermore, we estimate a nucleosynthetic production ratio of 92Nb to the p-nucleus 92Mo between 0.0015 and 0.035. This production ratio, together with the solar abundances of other p-nuclei with similar masses, can be best explained if these light p-nuclei were primarily synthesized by photodisintegration reactions in Type Ia supernovae.

  13. Dopant penetration studies through Hf silicate

    NASA Astrophysics Data System (ADS)

    Quevedo-Lopez, M. A.; Visokay, M. R.; Chambers, J. J.; Bevan, M. J.; LiFatou, A.; Colombo, L.; Kim, M. J.; Gnade, B. E.; Wallace, R. M.

    2005-02-01

    We present a study of the penetration of B, P, and As through Hf silicate (HfSixOy) and the effect of N incorporation in Hf silicate (HfSixOyNz) on dopant penetration from doped polycrystalline silicon capping layers. The extent of penetration through Hf silicate was found to be dependent upon the thermal annealing budget for each dopant investigated as follows: B(T⩾950°C/60s), P(T⩾1000°C/20s), and As (T⩾1050°C/60s). We propose that the enhanced diffusion observed for these dopants in HfSixOy, compared with that of SiO2 films, is related to grain boundary formation resulting from HfSixOy film crystallization. We also find that, as in the case of SiO2, N incorporation inhibits dopant (B, P, and As) diffusion through the Hf silicate and thus penetration into the underlying Si substrate. Only B penetration is clearly observed through HfSiON films for anneals at 1050 °C for durations of 10 s or longer. The calculated B diffusivity through the HfSixOyNz layer is D0=5.2×10-15cm2/s.

  14. Origin of high thermoelectric performance of FeNb1‑xZr/HfxSb1‑ySny alloys: A first-principles study

    NASA Astrophysics Data System (ADS)

    Zhang, Xiwen; Wang, Yuanxu; Yan, Yuli; Wang, Chao; Zhang, Guangbiao; Cheng, Zhenxiang; Ren, Fengzhu; Deng, Hao; Zhang, Jihua

    2016-09-01

    The previous experimental work showed that Hf- or Zr-doping has remarkably improved the thermoelectric performance of FeNbSb. Here, the first-principles method was used to explore the possible reason for such phenomenon. The substitution of X (Zr/Hf) atoms at Nb sites increases effective hole-pockets, total density of states near the Fermi level (EF), and hole mobility to largely enhance electrical conductivity. It is mainly due to the shifting the EF to lower energy and the nearest Fe atoms around X atoms supplying more d-states to hybrid with X d-states at the vicinity of the EF. Moreover, we find that the X atoms indirectly affect the charge distribution around Nb atoms via their nearest Fe atoms, resulting in the reduced energy difference in the valence band edge, contributing to enhanced Seebeck coefficients. In addition, the further Bader charge analysis shows that the reason of more holes by Hf-doping than Zr in the experiment is most likely derived from Hf atoms losing less electrons and the stronger hybridization between Hf atoms and their nearest Fe atoms. Furthermore, we predict that Hf/Sn co-doping may be an effective strategy to further optimize the thermoelectric performance of half-Heusler (HH) compounds.

  15. Origin of high thermoelectric performance of FeNb1-xZr/HfxSb1-ySny alloys: A first-principles study.

    PubMed

    Zhang, Xiwen; Wang, Yuanxu; Yan, Yuli; Wang, Chao; Zhang, Guangbiao; Cheng, Zhenxiang; Ren, Fengzhu; Deng, Hao; Zhang, Jihua

    2016-09-08

    The previous experimental work showed that Hf- or Zr-doping has remarkably improved the thermoelectric performance of FeNbSb. Here, the first-principles method was used to explore the possible reason for such phenomenon. The substitution of X (Zr/Hf) atoms at Nb sites increases effective hole-pockets, total density of states near the Fermi level (EF), and hole mobility to largely enhance electrical conductivity. It is mainly due to the shifting the EF to lower energy and the nearest Fe atoms around X atoms supplying more d-states to hybrid with X d-states at the vicinity of the EF. Moreover, we find that the X atoms indirectly affect the charge distribution around Nb atoms via their nearest Fe atoms, resulting in the reduced energy difference in the valence band edge, contributing to enhanced Seebeck coefficients. In addition, the further Bader charge analysis shows that the reason of more holes by Hf-doping than Zr in the experiment is most likely derived from Hf atoms losing less electrons and the stronger hybridization between Hf atoms and their nearest Fe atoms. Furthermore, we predict that Hf/Sn co-doping may be an effective strategy to further optimize the thermoelectric performance of half-Heusler (HH) compounds.

  16. Origin of high thermoelectric performance of FeNb1−xZr/HfxSb1−ySny alloys: A first-principles study

    PubMed Central

    Zhang, Xiwen; Wang, Yuanxu; Yan, Yuli; Wang, Chao; Zhang, Guangbiao; Cheng, Zhenxiang; Ren, Fengzhu; Deng, Hao; Zhang, Jihua

    2016-01-01

    The previous experimental work showed that Hf- or Zr-doping has remarkably improved the thermoelectric performance of FeNbSb. Here, the first-principles method was used to explore the possible reason for such phenomenon. The substitution of X (Zr/Hf) atoms at Nb sites increases effective hole-pockets, total density of states near the Fermi level (EF), and hole mobility to largely enhance electrical conductivity. It is mainly due to the shifting the EF to lower energy and the nearest Fe atoms around X atoms supplying more d-states to hybrid with X d-states at the vicinity of the EF. Moreover, we find that the X atoms indirectly affect the charge distribution around Nb atoms via their nearest Fe atoms, resulting in the reduced energy difference in the valence band edge, contributing to enhanced Seebeck coefficients. In addition, the further Bader charge analysis shows that the reason of more holes by Hf-doping than Zr in the experiment is most likely derived from Hf atoms losing less electrons and the stronger hybridization between Hf atoms and their nearest Fe atoms. Furthermore, we predict that Hf/Sn co-doping may be an effective strategy to further optimize the thermoelectric performance of half-Heusler (HH) compounds. PMID:27604826

  17. Validity of Rigid-Band Approximation in the Study of Thermoelectric Properties of p-Type FeNbSb-Based Half-Heusler Compounds

    NASA Astrophysics Data System (ADS)

    Fang, Teng; Zheng, Shuqi; Zhou, Tian; Chen, Hong; Zhang, Peng

    2016-11-01

    Recently, we calculated the thermoelectric properties of p-type FeNbSb half-Heusler compounds by employing the rigid-band approximation (RBA) (Fang et al., RSC Adv 6:10507-10512, 2016). Traditionally, the RBA is used to understand and guide doping in semiconductors. It is therefore important to verify its reliability. To this end, we have investigated the validity of the RBA in heavily doped p-type FeNbSb by calculating the electronic structure and Seebeck coefficient of pure and Ti-, Zr-, Hf-, and Ce-doped FeNbSb using ab initio calculations. The results confirm that Ti, Zr, and Hf doping at Nb site shows rigid-band-like behavior, unlike Ce doping, which changes the density of states. We also calculated the electrical transport properties of the doped systems, indicating that the power factor of Ce-doped FeNbSb is lower than those of Ti-, Zr-, and Hf-doped FeNbSb.

  18. HfSe2 thin films: 2D transition metal dichalcogenides grown by molecular beam epitaxy.

    PubMed

    Yue, Ruoyu; Barton, Adam T; Zhu, Hui; Azcatl, Angelica; Pena, Luis F; Wang, Jian; Peng, Xin; Lu, Ning; Cheng, Lanxia; Addou, Rafik; McDonnell, Stephen; Colombo, Luigi; Hsu, Julia W P; Kim, Jiyoung; Kim, Moon J; Wallace, Robert M; Hinkle, Christopher L

    2015-01-27

    In this work, we demonstrate the growth of HfSe2 thin films using molecular beam epitaxy. The relaxed growth criteria have allowed us to demonstrate layered, crystalline growth without misfit dislocations on other 2D substrates such as highly ordered pyrolytic graphite and MoS2. The HfSe2 thin films exhibit an atomically sharp interface with the substrates used, followed by flat, 2D layers with octahedral (1T) coordination. The resulting HfSe2 is slightly n-type with an indirect band gap of ∼ 1.1 eV and a measured energy band alignment significantly different from recent DFT calculations. These results demonstrate the feasibility and significant potential of fabricating 2D material based heterostructures with tunable band alignments for a variety of nanoelectronic and optoelectronic applications.

  19. Theoretical study of the electronic states of Nb4, Nb5 clusters and their anions (Nb4?, Nb5?)

    SciTech Connect

    Balasubramanian, K; Majumdar, D

    2004-05-06

    Geometries and energy separations of the various low-lying electronic states of Nb{sub n} and Nb{sub n}{sup -} (n = 4, 5) clusters with various structural arrangements have been investigated. The complete active space multi-configuration self-consistent field (CASMCSCF) method followed by multi-reference singles and doubles configuration interaction (MRSDCI) calculations that included up to 52 million configuration spin functions have been used to compute several electronic states of these clusters. The ground states of both Nb{sub 4} ({sup 1}A', pyramidal) and Nb{sub 4}{sup -} ({sup 2}B{sub 3g}, rhombus) are low-spin states at the MRSDCI level. The ground state of Nb{sub 5} cluster is a doublet with a distorted trigonal bipyramid (DTB) structure. The anionic cluster of Nb{sub 5} has two competitive ground states with singlet and triplet multiplicities (DTB). The low-lying electronic states of these clusters have been found to be distorted due to Jahn-Teller effect. On the basis of the energy separations of our computed electronic states of Nb{sub 4} and Nb{sub 5}, we have assigned the observed photoelectron spectrum of Nb{sub n}{sup -}(n = 4, 5) clusters. We have also compared our MRSDCI results with density functional calculations. The electron affinity, ionization potential, dissociation and atomization energies of Nb{sub 4} and Nb{sub 5} have been calculated and the results have been found to be in excellent agreement with the experiment.

  20. Theoretical study of the electronic states of Nb4, Nb5 clusters and their anions (Nb4-,Nb5-)

    NASA Astrophysics Data System (ADS)

    Majumdar, D.; Balasubramanian, K.

    2004-09-01

    Geometries and energy separations of the various low-lying electronic states of Nbn and Nbn- (n=4,5) clusters with various structural arrangements have been investigated. The complete active space multiconfiguration self-consistent field method followed by multireference singles and doubles configuration interaction (MRSDCI) calculations that included up to 52×106 configuration spin functions have been used to compute several electronic states of these clusters. The ground states of both Nb4 (1A', pyramidal) and Nb4- (2B3g, rhombus) are low-spin states at the MRSDCI level. The ground state of Nb5 cluster is a doublet with a distorted trigonal bipyramid (DTB) structure. The anionic cluster of Nb5 has two competitive ground states with singlet and triplet multiplicities (DTB). The low-lying electronic states of these clusters have been found to be distorted due to Jahn-Teller effect. On the basis of the energy separations of our computed electronic states of Nb4 and Nb5, we have assigned the observed photoelectron spectrum of Nbn- (n=4,5) clusters. We have also compared our MRSDCI results with density functional calculations. The electron affinity, ionization potential, dissociation and atomization energies of Nb4 and Nb5 have been calculated and the results have been found to be in excellent agreement with the experiment.

  1. Growth and optical properties of Nb-doped WS2 monolayers

    NASA Astrophysics Data System (ADS)

    Sasaki, Shogo; Kobayashi, Yu; Liu, Zheng; Suenaga, Kazutomo; Maniwa, Yutaka; Miyauchi, Yuhei; Miyata, Yasumitsu

    2016-07-01

    We report the chemical vapor deposition growth of Nb-doped WS2 monolayers and their characterization. Electron microscopy observations reveal that the Nb atom was substituted at the W site at a rate of approximately 0.5%. Unlike Mo doping, Nb-doped samples have photoluminescence (PL) peaks at 1.4-1.6 eV at room temperature. The peak energies are lower than the optical bandgap of 1.8 eV, and a saturation behavior of PL intensity is observed with the increase in excitation power. These results indicate that the observed PL peaks are assignable to the emission from impurity states generated by the substitution of Nb.

  2. Infrared light gated MoS₂ field effect transistor.

    PubMed

    Fang, Huajing; Lin, Ziyuan; Wang, Xinsheng; Tang, Chun-Yin; Chen, Yan; Zhang, Fan; Chai, Yang; Li, Qiang; Yan, Qingfeng; Chan, H L W; Dai, Ji-Yan

    2015-12-14

    Molybdenum disulfide (MoS₂) as a promising 2D material has attracted extensive attentions due to its unique physical, optical and electrical properties. In this work, we demonstrate an infrared (IR) light gated MoS₂ transistor through a device composed of MoS₂ monolayer and a ferroelectric single crystal Pb(Mg(1/3)Nb(2/3))O₃-PbTiO₃ (PMN-PT). With a monolayer MoS₂ onto the top surface of (111) PMN-PT crystal, the drain current of MoS₂ channel can be modulated with infrared illumination and this modulation process is reversible. Thus, the transistor can work as a new kind of IR photodetector with a high IR responsivity of 114%/Wcm⁻². The IR response of MoS₂ transistor is attributed to the polarization change of PMN-PT single crystal induced by the pyroelectric effect which results in a field effect. Our result promises the application of MoS₂ 2D material in infrared optoelectronic devices. Combining with the intrinsic photocurrent feature of MoS₂ in the visible range, the MoS₂ on ferroelectric single crystal may be sensitive to a broadband wavelength of light.

  3. The study of multilayers Fe/Hf and Ni/Hf by slow positron beam technique

    NASA Astrophysics Data System (ADS)

    Tashiro, Mutsumi; Nakajyo, Terunobu; Murashige, Yusuke; Koizumi, Tomoya; Kanazawa, Ikuzo; Komori, Fumio; Soe, We-Hyo; Yamamoto, Ryoichi; Ito, Yasuo

    1997-05-01

    The S-parameters versus the incident positron energy are measured in the Ni/Hf multilayer, thin Hf film, thin Fe film and the bilayer Fe/Hf. We have analyzed the change in vacancy-type defects in these multilayers and thin films with the deposition temperature in the MBE system.

  4. Early to late Yanshanian I-type granites in Fujian Province, SE China: Implications for the tectonic setting and Mo mineralization

    NASA Astrophysics Data System (ADS)

    Yang, Yu-Long; Ni, Pei; Yan, Jun; Wu, Chang-Zhi; Dai, Bao-Zhang; Xu, Ying-Feng

    2017-04-01

    The Cathaysia Block is the southeastern part of the South China Block in Southeast (SE) China, and it hosts voluminous late Mesozoic I-, S-, and A-type granitoids, as well as minor highly fractionated granites. We present here zircon U-Pb age data and Nd-Hf isotopic data for the Dayang and Juzhou granites, together with new petrological and geochemical analyses. The Dayang pluton consists of fine-grained two-mica monzonitic granites in which the plagioclases exhibit zoning and poikilitic textures. In contrast, the Juzhou pluton consists of medium- to coarse-grained biotite K-feldspar granites that lack zoning and poikilitic textures. The emplacement ages are 143 ± 2.3 Ma for the Dayang pluton and 133 ± 2.1 Ma for the Juzhou pluton according to zircon U-Pb isotope analyses. The Dayang and Juzhou granites are both metaluminous and belong to the shoshonitic series. The Dayang granite exhibits very flat REE patterns, showing the tetrad effect, and the spidergrams show striking negative Ba, Sr, Nb, and Ti anomalies and a positive Ta anomaly. In contrast, the Juzhou granite has sloping REE patterns, but like the Dayang granite it also has striking negative Ba, Sr, Nb, Ta, and Ti anomalies. Petrographic and geochemical evidence indicates that the Dayang granite is a highly fractionated I-type granite and that the Juzhou granite is a typical I-type granite. The tetrad effect in the Dayang granite can be interpreted in terms of melt-rock interactions at a late stage of magma evolution, whereas the main mechanism during the evolution of the Juzhou magma was fractionation of plagioclase, biotite, hornblende, apatite, zircon, and allanite. Nd-Hf isotope data suggest that the Dayang and Juzhou granites were both formed partial melting of Paleoproterozoic basement rock and juvenile material (underplating basalts or Mayuan Group amphibolites), with the Juzhou granite having a greater contribution from juvenile material than the Dayang granite. Our new data, together with

  5. The thermal and electrical properties of the promising semiconductor MXene Hf2CO2

    PubMed Central

    Zha, Xian-Hu; Huang, Qing; He, Jian; He, Heming; Zhai, Junyi; Francisco, Joseph S.; Du, Shiyu

    2016-01-01

    With the growing interest in low dimensional materials, MXenes have also attracted considerable attention recently. In this work, the thermal and electrical properties of oxygen-functionalized M2CO2 (M = Ti, Zr, Hf) MXenes are investigated using first-principles calculations. Hf2CO2 is determined to exhibit a thermal conductivity better than MoS2 and phosphorene. The room-temperature thermal conductivity along the armchair direction is determined to be 86.25~131.2 Wm−1 K−1 with a flake length of 5~100 μm. The room temperature thermal expansion coefficient of Hf2CO2 is 6.094 × 10−6 K−1, which is lower than that of most metals. Moreover, Hf2CO2 is determined to be a semiconductor with a band gap of 1.657 eV and to have high and anisotropic carrier mobility. At room temperature, the Hf2CO2 hole mobility in the armchair direction (in the zigzag direction) is determined to be as high as 13.5 × 103 cm2V−1s−1 (17.6 × 103 cm2V−1s−1). Thus, broader utilization of Hf2CO2, such as the material for nanoelectronics, is likely. The corresponding thermal and electrical properties of Ti2CO2 and Zr2CO2 are also provided. Notably, Ti2CO2 presents relatively lower thermal conductivity but much higher carrier mobility than Hf2CO2. According to the present results, the design and application of MXene based devices are expected to be promising. PMID:27302597

  6. More reduced Nb/sub 6/I/sub 8/ cluster. Synthesis and structure of CsNb/sub 6/I/sub 11/ and its hydride CsNb/sub 6/I/sub 11/H

    SciTech Connect

    Imoto, H.; Corbett, J.D.

    1980-05-01

    The title compound is formed by direct reaction of Nb/sub 3/I/sub 8/ or Nb/sub 6/I/sub 11/ with Nb and CsI in a sealed Nb tube at 910/sup 0/C. The structure and composition were established by X-ray crystallography: space group P6/sub 3/22, Z = 2, a = 11.007 (2) A, c = 11.894 (2) A, R = 0.047, and R/sub w/ = 0.060 for 777 independent reflections after correction for absorption and secondary extinction. The structure of Cs/sup +/((Nb/sub 6/I/sup i//sub 8/)I/sup a//sub 6/2/)/sup -/ consists of distorted metal octahedra face-capped by I/sup i/ to give Nb/sub 6/I/sub 8/ clusters (D/sub 3d/ symmetry) which are interconnected to other octahedra in a hexagonal close-packed arrangement through bridging I/sup a/. The Nb-Nb distances range from 2.771 (2) to 2.940 (2) A, the average of 2.825 A being 0.025 (4) A less than that in the known and closely related Nb/sub 6/I/sub 11/(Nb/sub 6/I/sub 8/I/sub 6/2/). The observed distortion of the octahedra in both phases can be understood in terms of packing and strain at the bridging iodine atoms. The title phase is converted to the isostructural CsNb/sub 6/I/sub 11/H by H/sub 2/ at 400/sup 0/C, whereas Mo/sub 6/CL/sub 12/, Na/sub 4/M/sub 6/Cl/sub 18/ (M = Nb, Ta), and Ta/sub 6/Cl/sub 15/ do not react with hydrogen at 300 to 400 /sup 0/C. Hydrogen absorption by halides of transition groups 5 and 6 and zirconium appears to require an oxidation state below 2.0. The upper limits of composition (oxidation state) found for group 3 to 6 halohydrides correspond closely to the upper limits found with the binary hydrides of the same metals.

  7. Comparison of high-intensity ultraviolet and NB-UVB on the maturation of melanocytes derived from hair follicle neural crest stem cells.

    PubMed

    Dong, Dake; Chen, Shujun; Zhang, Xiaoli; Jin, Cheng; Zheng, Yuan; Yang, Lijia

    2014-09-01

    Both high-intensity ultraviolet and narrowband ultraviolet B (NB-UVB) are important therapeutic options for vitiligo management, but high-intensity ultraviolet is more effective than NB-UVB. However, the underlying mechanisms have not been well investigated. Herein, we compare the effects of high-intensity ultraviolet and NB-UVB on the pigmentation of melanocytes derived from hair follicle-derived neural crest stem cells (HF-NCSCs) in vitro and study the underlying mechanisms. The HF-NCSCs were isolated from mouse whisker follicles. After radiation with high-intensity ultraviolet and NB-UVB, respectively, the cell viability by the CCK-8 assay showed gradual inhibitory effects in a dose-dependent manner, which has no apparent difference between the two modalities. The mRNA for melanogenesis factors such as tyrosinase and tyrp1 of the differentiated melanocytes increased significantly with high-intensity ultraviolet compared to the same dose of NB-UVB exposure. Furthermore, the expression of Mc1r was significantly increased by high-intensity ultraviolet in contrast to NB-UVB at the dosage of 0.5 J. By and large, these data suggest that high-intensity ultraviolet exhibited greater efficiency on the maturation of the melanocyte lineage differentiated from HF-NCSCs compared to NB-UVB with the same dose, which was probably due to the stronger stimulatory action of Mc1r. This may provide new insights into the different efficacies of high-intensity ultraviolet and NB-UVB in the treatment of vitiligo repigmentation.

  8. A Van Der Waals Homojunction: Ideal p-n Diode Behavior in MoSe2.

    PubMed

    Jin, Youngjo; Keum, Dong Hoon; An, Sung-Jin; Kim, Joonggyu; Lee, Hyun Seok; Lee, Young Hee

    2015-10-07

    A MoSe2 p-n diode with a van der Waals homojunction is demonstrated by stacking undoped (n-type) and Nb-doped (p-type) semiconducting MoSe2 synthesized by chemical vapor transport for Nb substitutional doping. The p-n diode reveals an ideality factor of ≈1.0 and a high external quantum efficiency (≈52%), which increases in response to light intensity due to the negligible recombination rate at the clean homojunction interface.

  9. Origin of the Wunugetushan porphyry Cu-Mo deposit, Inner Mongolia, NE China: Constraints from geology, geochronology, geochemistry, and isotopic compositions

    NASA Astrophysics Data System (ADS)

    Zhang, Fang-Fang; Wang, Yin-Hong; Liu, Jia-Jun; Wang, Jian-Ping; Zhao, Chun-Bo; Song, Zhi-Wei

    2016-03-01

    The Wunugetushan porphyry Cu-Mo deposit is located in the southeastern margin of the Mongol-Okhotsk Orogenic Belt and in the northwestern segment of the Great Xing'an Range, NE China. The orebodies of this deposit are mainly hosted in the monzogranitic porphyry stock and in contact with the granitic porphyry dyke and biotite granite batholith. The SHRIMP zircon U-Pb dating of the granitic porphyry dyke yielded ages of 201.4 ± 3.1 Ma (2σ, MSWD = 1.5). These results indicate that the magmatism in the Wunugetushan area might have occurred at ca. 201 Ma in the early Jurassic, and that the mineralization age (ca. 181 Ma) of this deposit is later than the age of intrusive granitic porphyry in the area. Geochemically, the Wunugetushan granitoids belong to high-K calc-alkaline and shoshonitic series, enriched in K, Rb, Nd, and Pb, and depleted in Sr, Nb, Ti and P, with negative Eu anomalies. In situ Hf isotopic analyses of zircons using LA-MC-ICP-MS indicate that the εHf(t) values for zircons from a granitic porphyry sample vary from +2.4 to +11.8 and that the corresponding crustal model ages (TDMC) vary from 483 to 1088 Ma. The least-altered monzogranitic porphyry, granitic porphyry and biotite granite yielded relatively uniform εNd(t) values from -1.0 to +0.6 and low (87Sr/86Sr)i ratios ranging from 0.704387 to 0.708385. The geochemical and Sr-Nd-Hf isotopic data for the granitoids indicate that the source magma for these rocks could be derived from a juvenile lower crust. The δ34S values of sulfides show a narrow range (+0.76‰ to +3.20‰) similar to those of magmatic sulfur, further implying a lower crust origin. Based on the results of this study and the regional geodynamic evolution, it is proposed that the formation of the Wunugetushan deposit and associated granitoids should be linked to the southeastward subduction of the Mongol-Okhotsk oceanic plate beneath the Erguna Massif during the early Jurassic, and that the monzogranitic porphyry intrusions in

  10. Synthesis of superconducting Nb3Sn coatings on Nb substrates

    DOE PAGES

    Barzi, E.; Franz, S.; Reginato, F.; ...

    2015-12-01

    In the present work the electrochemical and thermal syntheses of superconductive Nb3Sn films are investigated. The Nb3Sn phase is obtained by electrodeposition of Sn layers and Cu intermediate layers onto Nb substrates followed by high temperature diffusion in inert atmosphere. Electrodeposition was performed from aqueous solutions at current densities in the 20 to 50 mA/cm2 range and at temperatures between 40 and 50°C. Subsequent thermal treatments were realized to obtain the Nb3Sn superconductive phase. Glow discharge optical emission spectrometry (GDOES) demonstrated that after thermal treatment interdiffusion of Nb and Sn occurred across a thickness of about 13 μm. Scanning Electronmore » Microscopy (SEM) allowed accurately measuring the thickness of the Nb3Sn phase, whose average for the various types of film samples was between 5.7 and 8.0 μm. X-ray diffraction (XRD) patterns confirmed the presence of a cubic Nb3Sn phase (A15 structure) having (210) preferred orientation. The maximum obtained Tc was 17.68 K and the Bc20 ranged between 22.5 T and 23.8 T. With the procedure described in the present paper, coating complex shapes cost-effectively becomes possible, which is typical of electrochemical techniques. Furthermore, this approach can be implemented in classical wire processes such as "Jelly Roll" or "Rod in Tube", or directly used for producing superconducting surfaces. In conclusion, the potential of this method for Superconducting Radiofrequency (SRF) structures is also outlined.« less

  11. Synthesis of superconducting Nb3Sn coatings on Nb substrates

    NASA Astrophysics Data System (ADS)

    Barzi, E.; Bestetti, M.; Reginato, F.; Turrioni, D.; Franz, S.

    2016-01-01

    In the present work the electrochemical and thermal syntheses of superconducting Nb3Sn films are investigated. The Nb3Sn phase is obtained by electrodeposition of Sn layers and Cu intermediate layers onto Nb substrates followed by high temperature diffusion in inert atmosphere. Electrodeposition was performed from aqueous solutions at current densities in the 20-50 mA cm-2 range and at temperatures between 40 °C and 50 °C. Subsequent thermal treatments were realized to obtain the Nb3Sn superconductive phase. Glow discharge optical emission spectrometry demonstrated that after thermal treatment interdiffusion of Nb and Sn occurred across a thickness of about 13 μm. Scanning electron microscopy allowed accurately measuring the thickness of the Nb3Sn phase, whose average for the various types of film samples was between 5.7 and 8.0 μm. X-ray diffraction patterns confirmed the presence of a cubic Nb3Sn phase (A15 structure) having (210) preferred orientation. The maximum obtained T c was 17.68 K and the B c20 ranged between 22.5 and 23.8 T. With the procedure described in the present paper, coating complex shapes cost-effectively becomes possible, which is typical of electrochemical techniques. Furthermore, this approach can be implemented in classical wire processes such as ‘jelly roll’ or ‘rod in tube’, or directly used for producing superconducting surfaces. The potential of this method for superconducting radiofrequency structures is also outlined.

  12. EXAFS determination of Hf localization in HDDR Nd Fe B Hf alloys

    NASA Astrophysics Data System (ADS)

    Torres, C. E. Rodríguez; Fernández van Raap, M. B.; Sánchez, F. H.; Pasquevich, A. F.

    2005-05-01

    The local structure around Hf in Nd 15.78Fe 76.3-xHf xB 7.8 ( x=0.1 and 0.2) submitted to conventional and solid hydrogenation-disproportionation-desorption-recombination (HDDR) sequence was studied by extended X-ray absorption fine structure (EXAFS) in order to understand the relation between the presence of Hf and magnetic anisotropy found only in solid-HDDR samples. EXAFS results show that Hf is not in the Nd 2Fe 14B structure but incorporated into a local atomic arrangement (HfB ClNa-type) which is the same for as-cast, solid and conventional HDDR samples. It is concluded that the magnetic anisotropy induced by Hf addition to NdFeB alloys must be related to microstructural features.

  13. On the road to HF mitigation

    SciTech Connect

    Van Zele, R.L.; Diener, R. )

    1990-07-01

    Two components were investigated as a part of tests run by Industry Cooperative HF Mitigation/Assessment Program (ICHMAP). This paper discusses how the test program included a vapor barrier component and an ambient impact assessment component.

  14. Enhanced thermoelectric properties of n-type NbCoSn half-Heusler by improving phase purity

    NASA Astrophysics Data System (ADS)

    He, Ran; Huang, Lihong; Wang, Yumei; Samsonidze, Georgy; Kozinsky, Boris; Zhang, Qinyong; Ren, Zhifeng

    2016-10-01

    Here we report the thermoelectric properties of NbCoSn-based n-type half-Heuslers (HHs) that were obtained through arc melting, ball milling, and hot pressing process. With 10% Sb substitution at the Sn site, we obtained enhanced n-type properties with a maximum power factor reaching ˜35 μW cm-1 K-2 and figure of merit (ZT) value ˜0.6 in NbCoSn0.9Sb0.1. The ZT is doubled compared to the previous report. In addition, the specific power cost ( W-1) is decreased by ˜68% comparing to HfNiSn-based n-type HH because of the elimination of Hf.

  15. Refiners discuss HF alkylation process and issues

    SciTech Connect

    Not Available

    1992-04-06

    Safety and oxygenate operations made HF alkylation a hot topic of discussion at the most recent National Petroleum Refiners Association annual question and answer session on refining and petrochemical technology. This paper provides answers to a variety of questions regarding the mechanical, process, and safety aspects of the HF alkylation process. Among the issues discussed were mitigation techniques, removal of oxygenates from alkylation unit feed, and amylene alkylation.

  16. Josephson Coupling in Nb/SmB6/Nb Junctions

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaohang; Lee, Seunghun; Drisko, Jasper; Cumings, John; Greene, Richard; Takeuchi, Ichiro

    Josephson coupling of superconductors through a topological surface has attracted considerable attention because it may provide device applications of topological insulators with implications for Majorana fermions. However, the results of previous Josephson junction studies on topological insulators have not been fully understood due to complications arising from the conducting bulk and the non-pristine nature of the surfaces/interfaces of the topological insulator materials used. In this work, SmB6 thin films with a highly insulating bulk were adopted to minimize the influence of the bulk carriers while in-situ deposition of Nb film on SmB6 surface was used to ensure the interface quality. The bilayer structure was then patterned into Nb/SmB6/Nb lateral junctions by e-beam lithography and ion milling. The Nb electrodes in our junctions had a typical width of ~1 μm and the gap between the two Nb electrodes was varied from 50 nm to 200 nm. A critical current up to 40 μA has been observed in junctions with a gap around 50 nm at 2.0 K. In this talk, I will discuss the implication of our results to the desired Josephson coupling through topological surface states. This work was supported by NSF under Grant No. DMR-1410665 and conducted at CNAM and at the Maryland NanoCenter.

  17. NbFeSb based p-type half-Heusler for power generation applications

    NASA Astrophysics Data System (ADS)

    Joshi, Giri; He, Ran; Engber, Michael; Samsonidze, Georgy; Pantha, Tej; Dahal, Ekraj; Dahal, Keshab; Yang, Jian; Lan, Yucheng; Kozinsky, Boris; Ren, Zhifeng

    2015-03-01

    We report a peak dimensionless figure-of-merit (ZT) of ~1 at 700 oC in nanostructured p-type Nb0.6Ti0.4FeSb0.95Sn0.05composition. Even though the power factor of the Nb0.6Ti0.4FeSb0.95Sn0.05 composition is improved by 25% in comparison to the previously reported p-type Hf0.44Zr0.44Ti0.12CoSb0.8Sn0.2, the ZT value is not increased due to a higher thermal conductivity. However, the higher power factor of the Nb0.6Ti0.4FeSb0.95Sn0.05 composition led to a 15% increase in power output of a thermoelectric device in comparison to a device made from the previous best material Hf0.44Zr0.44Ti0.12CoSb0.8Sn0.2. The n-type material used to make the unicouple device is the best reported nanostructured Hf0.25Zr0.75NiSn0.99Sb0.01 composition with the lowest hafnium (Hf) content. Both the p- and n-type nanostructured samples are prepared by ball milling the arc melted ingot and hot pressing the finely ground powders. Moreover, the raw material cost of the Nb0.6Ti0.4FeSb0.95Sn0.05 composition is more than six times lower compared to the cost of the previous best p-type Hf0.44Zr0.44Ti0.12CoSb0.8Sn0.2. This cost reduction is crucial for these materials to be used in large-scale quantities for vehicle and industrial waste heat recovery applications. DOE:DE-EE0004840.

  18. On the road to HF mitigation

    SciTech Connect

    VanZele, R.L.; Diener, R. )

    1990-06-01

    The hazards of hydrogen fluoride (HF) have long been recognized and industry performance reflects sound operating practices. However, full-scale industry-sponsored HF release test conducted at the U.S. Department of Energy (DOE) test site in 1986 caused concern in view of HF's toxicity. Ambient impacts were greater than anticipated. And diking, a primary mitigation technique, proved ineffective for releases of pressurized superheated HF. In partial response to these new technical data, an ad-hoc three-component Industry Cooperative Hydrogen Fluoride Mitigation Assessment Program (ICHMAP) was begun in late 1987 to study and test techniques for mitigating accidental releases of HF and alkylation unit acid (AUA) and to enhance capabilities to estimate ambient impacts from such releases. AUA is a mixture of HF and hydrocarbons. The program's mitigation components have recently been completed while work on the impact assessment component is nearing completion. This article describes the program and summarizes the objective, scope of work, structure, and conclusions from the program's two mitigation components. In addition, the objectives and scope of work of the impact assessment components are described.

  19. Late Neoproterozoic magmatism in South Qinling, Central China: Geochemistry, zircon U-Pb-Lu-Hf isotopes and tectonic implications

    NASA Astrophysics Data System (ADS)

    Wang, Ruirui; Xu, Zhiqin; Santosh, M.; Yao, Yuan; Gao, Li'e.; Liu, Chunhua

    2016-06-01

    The Neoproterozoic tectonic evolution of the northern margin of the Yangtze Block in South China remains debated. In this study, we present results from LA-ICP-MS zircon U-Pb geochronology on a suite of intermediate-felsic rocks in South Qinling, Central China which show a mean age of ca. 630 Ma. The zircon εHf(t) values of these rocks mostly range from + 0.44 to + 14.78. Geochemically, the granites and syenite show high total alkali contents, with enrichment in LREE, LILE (Rb, Ba, and K), and HFSE (Th, U, Nb, Ta, Zr, and Hf), and depletion in Sr, P, and Ti, similar to the features of A-type granites. The meta-diorite shows high Na2O, with depletion in Eu, Ti, and LILE (Sr, Rb, Ba, and K), and enrichment in HFSE (Th, U, Nb, Ta, Zr, and Hf). The geochemical features are consistent with formation of the intermediate-felsic suite through fractionation from underplated basaltic magma that originated from sub-continental lithospheric mantle metasomatized by asthenosphere-derived oceanic-island-basalt-like (OIB-like) melts, coupled with minor crustal contamination. We correlate the ca. 630 Ma magmatism with a back-arc rift setting that probably developed in relation to slab tearing during continued slab rollback.

  20. Impact of titanium addition on film characteristics of HfO2 gate dielectrics deposited by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Triyoso, D. H.; Hegde, R. I.; Zollner, S.; Ramon, M. E.; Kalpat, S.; Gregory, R.; Wang, X.-D.; Jiang, J.; Raymond, M.; Rai, R.; Werho, D.; Roan, D.; White, B. E.; Tobin, P. J.

    2005-09-01

    The impact of 8-to 45-at. % Ti on physical and electrical characteristics of atomic-layer-deposited and annealed hafnium dioxide was studied using vacuum-ultraviolet spectroscopic ellipsometry, secondary ion mass spectroscopy, transmission electron microscopy, atomic force microscopy, x-ray diffraction, Rutherford backscattering spectroscopy, x-ray photoelectron spectroscopy, and x-ray reflectometry. The role of Ti addition on the electrical performance is investigated using molybdenum (Mo)-gated capacitors. The film density decreases with increasing Ti addition. Ti addition stabilizes the amorphous phase of HfO2, resulting in amorphous films as deposited. After a high-temperature annealing, the films transition from an amorphous to a polycrystalline phase. Orthorhombic Hf-Ti-O peaks are detected in polycrystalline films containing 33-at. % or higher Ti content. As Ti content is decreased, monoclinic HfO2 becomes the predominant microstructure. No TiSi is formed at the dielectric/Si interface, indicating films with good thermal stability. The band gap of Hf-Ti-O was found to be lower than that of HfO2. Well-behaved capacitance-voltage and leakage current density-voltage characteristics were obtained for Hf-Ti-O. However, an increased leakage current density was observed with Ti addition. The data from capacitance-voltage stressing indicate a smaller flatband voltage (Vfb) shift in the HfO2 films with low Ti content when compared with the HfO2 films. This indicates less charge trapping with a small amount of Ti addition.

  1. Environmentally Assisted Cracking of Commercial Ni-Cr-Mo Alloys - A Review

    SciTech Connect

    Rebak, R B

    2004-11-09

    Nickel-Chromium-Molybdenum alloys (Ni-Cr-Mo) are highly resistant to general corrosion, localized corrosion and environmentally assisted cracking (EAC). Cr acts as a beneficial element under oxidizing acidic conditions and Mo under reducing conditions. All three elements (Ni, Cr and Mo) act synergistically to provide resistance to EAC in environments such as hot concentrated chloride solutions. Ni-Cr-Mo alloys may suffer EAC in environments such as hot caustic solutions, hot wet hydrofluoric acid (HF) solutions and in super critical water oxidation (SCWO) applications. Not all the Ni-Cr-Mo alloys have the same susceptibility to cracking in the mentioned environments. Most of the available data regarding EAC is for the oldest Ni-Cr-Mo alloys such as N10276 and N06625.

  2. The Iceland plume in space and time: a Sr-Nd-Pb-Hf study of the North Atlantic rifted margin

    NASA Astrophysics Data System (ADS)

    Kempton, P. D.; Fitton, J. G.; Saunders, A. D.; Nowell, G. M.; Taylor, R. N.; Hardarson, B. S.; Pearson, G.

    2000-04-01

    mantle, consists of 'enriched' streaks or blobs dispersed in a more depleted matrix. A distinguishing feature of both the enriched and depleted components is high Nb/Y for a given Zr/Y (i.e. positive ΔNb), but the enriched component has higher Sr and Pb isotope ratios, combined with lower ɛNd and ɛHf. This heterogeneous core is surrounded by a sheath of depleted material, similar to the depleted component of the Iceland plume in its ɛNd and ɛHf, but with lower 87Sr/ 86Sr, 208Pb/ 204Pb and negative ΔNb; this material was probably entrained from near the 670 km discontinuity when the plume stalled at the boundary between the upper and lower mantle. The plume sheath displaced more normal MORB asthenosphere (distinguished by its lower ɛHf for a given ɛNd or Zr/Nb ratio), which existed in the North Atlantic prior to plume impact. Preliminary data on MORBs from near the Azores plume suggest that much of the North Atlantic may be 'polluted' not only by enriched plume material but also by depleted material similar to the Iceland plume sheath. If this hypothesis is correct, it may provide a general explanation for some of the compositional diversity and variations in inferred depth of melting [Klein and Langmuir, J. Geophys. Res. 92 (1987) 8089-8115] along the MAR in the North Atlantic.

  3. HF Accelerated Electron Fluxes, Spectra, and Ionization

    NASA Astrophysics Data System (ADS)

    Carlson, Herbert C.; Jensen, Joseph B.

    2015-10-01

    Wave particle interactions, an essential aspect of laboratory, terrestrial, and astrophysical plasmas, have been studied for decades by transmitting high power HF radio waves into Earth's weakly ionized space plasma, to use it as a laboratory without walls. Application to HF electron acceleration remains an active area of research (Gurevich in Usp Fizicheskikh Nauk 177(11):1145-1177, 2007) today. HF electron acceleration studies began when plasma line observations proved (Carlson et al. in J Atmos Terr Phys 44:1089-1100, 1982) that high power HF radio wave-excited processes accelerated electrons not to ~eV, but instead to -100 times thermal energy (10 s of eV), as a consequence of inelastic collision effects on electron transport. Gurevich et al (J Atmos Terr Phys 47:1057-1070, 1985) quantified the theory of this transport effect. Merging experiment with theory in plasma physics and aeronomy, enabled prediction (Carlson in Adv Space Res 13:1015-1024, 1993) of creating artificial ionospheres once ~GW HF effective radiated power could be achieved. Eventual confirmation of this prediction (Pedersen et al. in Geophys Res Lett 36:L18107, 2009; Pedersen et al. in Geophys Res Lett 37:L02106, 2010; Blagoveshchenskaya et al. in Ann Geophys 27:131-145, 2009) sparked renewed interest in optical inversion to estimate electron spectra in terrestrial (Hysell et al. in J Geophys Res Space Phys 119:2038-2045, 2014) and planetary (Simon et al. in Ann Geophys 29:187-195, 2011) atmospheres. Here we present our unpublished optical data, which combined with our modeling, lead to conclusions that should meaningfully improve future estimates of the spectrum of HF accelerated electron fluxes. Photometric imaging data can significantly improve detection of emissions near ionization threshold, and confirm depth of penetration of accelerated electrons many km below the excitation altitude. Comparing observed to modeled emission altitude shows future experiments need electron density profiles

  4. TbNb6Sn6: the first ternary compound from the rare earth–niobium–tin system

    PubMed Central

    Oshchapovsky, Igor; Pavlyuk, Volodymyr; Fässler, Thomas F.; Hlukhyy, Viktor

    2010-01-01

    The title compound, terbium hexa­niobium hexastannide, TbNb6Sn6, is the first ternary compound from the rare earth–niobium–tin system. It has the HfFe6Ge6 structure type, which can be analysed as an inter­growth of the Zr4Al3 and CaCu5 structures. All the atoms lie on special positions; their coordination geometries and site symmetries are: Tb (dodeca­hedron) 6/mmm; Nb (distorted icosa­hedron) 2mm; Sn (Frank–Caspar polyhedron, CN = 14–15) 6mm and m2; Sn (distorted icosa­hedron) m2. The structure contains a graphite-type Sn network, Kagome nets of Nb atoms, and Tb atoms alternating with Sn2 dumbbells in the channels. PMID:21589205

  5. Properties of Superconducting Mo, Mo2n and Trilayer Mo2n-Mo-Mo2n Thin Films

    NASA Technical Reports Server (NTRS)

    Barrentine, E. M.; Stevenson, T. R.; Brown, A. D.; Lowitz, A. E.; Noroozian, O.; U-Yen, K.; Eshan, N.; Hsieh, W. T.; Moseley, S. H.; Wollack, E. J.

    2014-01-01

    We present measurements of the properties of thin film superconducting Mo, Mo2N and Mo2N/Mo/Mo2N trilayers of interest for microwave kinetic inductance detector (MKID) applications. Using microwave resonator devices, we investigate the transition temperature, energy gaps, kinetic inductance, and internal quality factors of these materials. We present an Usadel-based interpretation of the trilayer transition temperature as a function of trilayer thicknesses, and a 2-gap interpretation to understand the change in kinetic inductance and internal resonance quality factor (Q) as a function of temperature.

  6. Improved techniques for monitoring the HF spectrum

    NASA Astrophysics Data System (ADS)

    Giesbrecht, James E.; Clarke, Russell; Abbott, Derek

    2004-03-01

    A critical review of contemporary papers on modulation recognition, signal separation, and Single Station Location (SSL) is described in the context of High-Frequency (HF) radio-communications. High-frequency communications is undergoing resurgence despite advances in long-range satellite communication systems. Defense agencies are using the HF spectrum for backup communications as well as for spectrum surveillance applications. Spectrum management organizations are monitoring the HF spectrum to control and enforce licensing. This type of activity usually requires a system that is able to determine the location of a source of transmissions, separate valid signals from interferers and noise, and characterize signals-of-interest (SOI). The immediate aim is to show that commercial-off-the-shelf (COTS) equipment can be used to locate HF transmission sources, enhance SOIs and reject interference, and recognize signal types. The described work on single-station-location (SSL), signal separation, and modulation recognition is contributing to these goals. This paper describes the overall objectives and some of the disadvantages and benefits of various schemes for single-station-location (SSL), signal separation, and modulation recognition. It also proposes new approaches that may relieve shortcomings of existing methods -- including selection of benchmarks or modulations for various transmission scenarios and propagation modes, and use of multiple digital receivers or compression techniques to improve modulation recognition, signal separation, and location of HF emitters.

  7. Adaptive tracking of narrowband HF channel response

    NASA Astrophysics Data System (ADS)

    Arikan, F.; Arikan, O.

    2003-12-01

    Estimation of channel impulse response constitutes a first step in computation of scattering function, channel equalization, elimination of multipath, and optimum detection and identification of transmitted signals through the HF channel. Due to spatial and temporal variations, HF channel impulse response has to be estimated adaptively. Based on developed state-space and measurement models, an adaptive Kalman filter is proposed to track the HF channel variation in time. Robust methods of initialization and adaptively adjusting the noise covariance in the system dynamics are proposed. In simulated examples under good, moderate and poor ionospheric conditions, it is observed that the adaptive Kalman filter based channel estimator provides reliable channel estimates and can track the variation of the channel in time with high accuracy.

  8. The ADMX-HF (High Frequency) Experiment

    NASA Astrophysics Data System (ADS)

    Lehnert, K. W.

    2013-04-01

    For many years, the Axion Dark Matter eXperiment (ADMX) has searched for dark-matter axions by their resonant conversion to photons in a high-Q microwave cavity embedded in a strong magnetic field; to date focusing on the ˜1 GHz range, or ma˜ few micro-eV. A second platform, ADMX-HF is now being constructed at Yale University which will focus on technology development and a first look at data in the ˜10 GHz range. Consisting of a 9T superconducting magnet (40 cm long x 14 cm diameter), a dilution refrigerator and a quantum-limited receiver based on Josephson Parametric Amplifiers (JPA) ADMX-HF is projected to achieve sensitivity within the axion model band, despite its smaller volume than ADMX. ADMX-HF is a collaboration of Yale, JILA/Colorado, UC Berkeley and LLNL, and by agreement will create a unified data set with ADMX.

  9. HF Radio Wave Production of Artificial Ionospheres

    NASA Astrophysics Data System (ADS)

    Carlson, Herbert

    In 1993 it was predicted that artificial ionospheres would be produced by high power HF radio waves, once HF transmitters approached a GWatt ERP. When that threshold was very recently achieved, such production was indeed detected and published at two high latitude high power HF facilities. Here we review: the first-principles logic behind that prediction, which aspects of such production are critically dependent on magnetic latitude, and which aspects of such production depend only on physical parameters independent of latitude. These distinctions follow directly from decomposition of the problem of ionization production into its components of: radio-wave propagation, wave-particle interactions, electron transport, and quantitative elastic/inelastic cross-sections. We outline this analysis to show that, within the context of early observations, the production of ionization is inevitable, and only a question of competing instability thresholds, and scale of ionization production. This illustrates complimentary aeronomy and plasma physics to advance understanding of both.

  10. Removal of uranium from aqueous HF solutions

    DOEpatents

    Pulley, Howard; Seltzer, Steven F.

    1980-01-01

    This invention is a simple and effective method for removing uranium from aqueous HF solutions containing trace quantities of the same. The method comprises contacting the solution with particulate calcium fluoride to form uranium-bearing particulates, permitting the particulates to settle, and separting the solution from the settled particulates. The CaF.sub.2 is selected to have a nitrogen surface area in a selected range and is employed in an amount providing a calcium fluoride/uranium weight ratio in a selected range. As applied to dilute HF solutions containing 120 ppm uranium, the method removes at least 92% of the uranium, without introducing contaminants to the product solution.

  11. General concepts of modern HF communications

    NASA Astrophysics Data System (ADS)

    Aarons, Jules

    Both conceptual and hardware advancements have led to substantial systems developments in military HF communications; the former encompass coding and error correction techniques for security, in order to minimize propagation and interference, while the latter prominently include digital equipment permitting the selection of a frequency for a particular path and propagation mode, as well as modulation selection. Propagation-related advancements involve better statistical models as well as advancements in short-term forecasting methods responsive to changes in solar-geophysical parameters. Adaptive HF systems have been developed for meteor-scatter radio communications.

  12. Effect of time-dependent 3-D electron density gradients on high angle of incidence HF radiowave propagation

    NASA Astrophysics Data System (ADS)

    Zawdie, K. A.; Drob, D. P.; Huba, J. D.; Coker, C.

    2016-07-01

    One of the challenges for the utilization of HF radiowaves in practical applications is to understand how the signals propagate in time- and range-dependent multipath environments. For typical quiescent ionospheric conditions it is often reasonably straightforward to interpret received HF signals. For disturbed ionospheric conditions, however, such as in the presence of large tilts, irregularities, and medium-scale traveling ionospheric disturbances (MSTIDs), data interpretation and utilization often becomes challenging. This paper presents a theoretical HF propagation modeling study that exploits the capabilities of a first principles, mesoscale resolution ionosphere code, SAMI3 (Sami3 is Another Model of the Ionosphere) and a new implementation of the 3-D ray trace equations, MoJo-15 (Modernized Jones Code) in order to examine the relationship between various HF propagation observables and MSTID characteristics. This paper demonstrates the implications of MSTIDS on high angle of incidence HF propagation during typical low-latitude, postsunset ionospheric conditions and examines the spatiotemporal evolution of multiple propagation paths that may connect a given source and receiver.

  13. Low Temperature Silicon Surface Cleaning by HF Etching/Ultraviolet Ozone Cleaning (HF/UVOC) Method (I)—Optimization of the HF Treatment—

    NASA Astrophysics Data System (ADS)

    Suemitsu, Maki; Kaneko, Tetsuya; Miyamoto, Nobuo

    1989-12-01

    Several variations of fluoric acid (HF) treatments of silicon substrates were examined for their adaptability as a pretreatment method for a silicon epitaxy process. Treatments with and without distilled, deionized (DI) water rinse, of different HF concentrations, and of different methods of HF supply were tested and their residual carbonic impurity contents were measured using RHEED. As a result, HF treatments by themselves were found to be insufficient in passivating the surface dangling bonds irrespective of the method of HF supply: dipping into the solution or exposure to the vapor. The optimum procedure of HF treatment thus proposed is a succession of (a) HF dipping, (b) DI-water rinsing, (c) nitrogen-gas blowing, and (d) UV-ozone cleaning.

  14. Nanometer-scale crystallization of thin HfO2 films studied by HF-chemical etching

    NASA Astrophysics Data System (ADS)

    Fujii, Shinji; Miyata, Noriyuki; Migita, Shinji; Horikawa, Tsuyoshi; Toriumi, Akira

    2005-05-01

    We used a HF-chemical etching process to examine crystalline structures in thin HfO2 films grown by metal organic chemical vapor deposition at 350-550°C. Nanometer-scale crystalline HfO2 nuclei were identified from all the HfO2 films. The nucleus density exponentially increased with increasing deposition temperature, but the diameter of the nuclei did not depend on the deposition temperature. We propose that the crystallization of thin HfO2 film during growth proceeds in a patchwork process with the increase of the crystalline HfO2 nuclei.

  15. Materials Analysis of CED Nb Films Being Coated on Bulk Nb Single Cell SRF Cavities

    SciTech Connect

    Zhao, Xin; Reece, Charles; Palczewski, Ari; Ciovati, Gianluigi; Krishnan, Mahadevan; James, Colt; Irfan, Irfan

    2013-09-01

    This study is an on-going research on depositing a Nb film on the internal wall of bulk Nb single cell SRF cavities, via a cathodic arc Nb plasma ions source, an coaxial energetic condensation (CED) facility at AASC company. The motivation is to firstly create a homoepitaxy-like Nb/Nb film in a scale of a ~1.5GHz RF single cell cavity. Next, through SRF measurement and materials analysis, it might reveal the baseline properties of the CED-type homoepitaxy Nb films. Literally, a top-surface layer of Nb films which sustains SRF function, always grows up in homo-epitaxy mode, on top of a Nb nucleation layer. Homo-epitaxy growth of Nb must be the final stage (a crystal thickening process) of any coatings of Nb film on alternative cavity structure materials. Such knowledge of Nb-Nb homo-epitaxy is useful to create future realistic SRF cavity film coatings, such as hetero-epitaxy Nb/Cu Films, or template-layer-mitigated Nb films. One large-grain, and three fine grain bulk Nb cavities were coated. They went through cryogenic RF measurement. Preliminary results show that the Q0 of a Nb film could be as same as the pre-coated bulk Nb surface (which received a chemically-buffered polishing plus a light electro-polishing); but quality factor of two tested cavities dropped quickly. We are investigating if the severe Q-slope is caused by hydrogen incorporation before deposition, or is determined by some structural defects during Nb film growth.

  16. SEMICONDUCTOR TECHNOLOGY: Wet etching characteristics of a HfSiON high-k dielectric in HF-based solutions

    NASA Astrophysics Data System (ADS)

    Yongliang, Li; Qiuxia, Xu

    2010-03-01

    The wet etching properties of a HfSiON high-k dielectric in HF-based solutions are investigated. HF-based solutions are the most promising wet chemistries for the removal of HfSiON, and etch selectivity of HF-based solutions can be improved by the addition of an acid and/or an alcohol to the HF solution. Due to densification during annealing, the etch rate of HfSiON annealed at 900 °C for 30 s is significantly reduced compared with as-deposited HfSiON in HF-based solutions. After the HfSiON film has been completely removed by HF-based solutions, it is not possible to etch the interfacial layer and the etched surface does not have a hydrophobic nature, since N diffuses to the interface layer or Si substrate formation of Si-N bonds that dissolves very slowly in HF-based solutions. Existing Si-N bonds at the interface between the new high-k dielectric deposit and the Si substrate may degrade the carrier mobility due to Coulomb scattering. In addition, we show that N2 plasma treatment before wet etching is not very effective in increasing the wet etch rate for a thin HfSiON film in our case.

  17. Antitumor activities of a new indolocarbazole substance, NB-506, and establishment of NB-506-resistant cell lines, SBC-3/NB.

    PubMed

    Kanzawa, F; Nishio, K; Kubota, N; Saijo, N

    1995-07-01

    The novel anticancer glucosyl derivative of indolo-carbazole (NB-506), an inhibitor of DNA topoisomerase I, exhibited strong in vitro cytotoxicity against various human cancer cell lines. In order to elucidate its cytotoxic mechanisms, we established nine NB-506-resistant sublines with different resistance ratios from human small cell lung cancer cells (SBC-3/P) by stepwise and brief exposure (24 h) to NB-506. Among them, SBC-3/NB#9 was 454 times more resistant to NB-506 than the parent cell line. The SBC-3/NB#9 cells showed cross-resistance only to topoisomerase I inhibitors, such as 11,7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecia and 7-ethyl-10-hydroxy-camptothecin, and not to other anticancer drugs, such as vincristine, vinblastine, Adriamycin, etoposide, and teniposide. These results indicate that the difference on the effect of topoisomerase I was considered to be related to a resistance mechanism. The topoisomerase I activities of nuclear extracts eluted from SBC-3/NB#9 cells was only one-tenth of the parent cell activity. A Western blotting study indicated that this lower activity was due to a lower amount of DNA topoisomerase I. Furthermore, we found correlations between topoisomerase I activity and sensitivity to NB-506 in sublines with different degrees of resistance. Accumulation of 3H-labeled NB-506 by SBC-3/NB#9 cells was only one-fifth of that by the parent cells, whereas intracellular accumulation of 3H-labeled camptothecin by both cell lines did not differ. The reduction of accumulation was specific to NB-506, and this result may explain why the resistance ratio for NB-506 was higher than those for 11,7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecin and 7-ethyl-10-hydroxy-camptothecin.

  18. Oxidation and interdiffusion behavior of a germanium-modified silicide coating on an Nb-Si-based alloy

    NASA Astrophysics Data System (ADS)

    Li, Jin-long; Wang, Wan; Zhou, Chun-gen

    2017-03-01

    To investigate the interdiffusion behavior of Ge-modified silicide coatings on an Nb-Si-based alloy substrate, the coating was oxidized at 1250°C for 5, 10, 20, 50, or 100 h. The interfacial diffusion between the (Nb,X)(Si,Ge)2 (X = Ti, Cr, Hf) coating and the Nb-Si based alloy was also examined. The transitional layer is composed of (Ti,Nb)5(Si,Ge)4 and a small amount of (Nb,X)5(Si,Ge)3. With increasing oxidation time, the thickness of the transitional layer increases because of the diffusion of Si from the outer layer to the substrate, which obeys a parabolic rate law. The parabolic growth rate constant of the transitional layer under oxidation conditions is 2.018 μm·h-1/2. Moreover, the interdiffusion coefficients of Si in the transitional layer were determined from the interdiffusion fluxes calculated directly from experimental concentration profiles.

  19. Al-La-Nb (068)

    NASA Astrophysics Data System (ADS)

    Carow-Watamura, U.; Louzguine, D. V.; Takeuchi, A.

    This document is part of Part 1 http://dx.doi.org/10.1007/97.etType="URL"/> 'Systems from Ag-Al-Ca to Au-Pd-Si' of Subvolume B 'Physical Properties of Ternary Amorphous Alloys' of Volume 37 'Phase Diagrams and Physical Properties of Nonequilibrium Alloys' of Landolt-Börnstein - Group III 'Condensed Matter'. It contains the Chapter 'Al-La-Nb (068)' with the content:

  20. HF Channel Availability under Ionospheric Disturbances: Model, Method and Measurements as Contributions

    NASA Astrophysics Data System (ADS)

    Tulunay, E.; Senalp, E. T.; Tulunay, Y.; Warrington, E. M.; Sari, M. O.

    2009-04-01

    variation of group range and line-of-sight Doppler velocity of the HF Radar echo signal were investigated. HF radar system under ionospheric disturbances has been identified globally and some operational suggestions have been presented. It is possible for the HF radar operator to estimate the possible skip distance and possible single hop group ranges for the given frequencies of 11 MHz and 14 MHz [Buyukpabuscu, 2007]. (iii) The measurements over the HF band during the 29 March 2006 total solar eclipse in Antalya (36° N; 30° E) Turkey was conducted from the channel occupancy and atmospheric noise points of view. The whole HF band ranging from 1 to 30 MHz has been swept using 10 kHz peak and 200 Hz average detectors of a certified EMI receiver equipped with a calibrated active monopole antenna. The changes in the atmospheric noise during the eclipse were reported [Tulunay, 2006]. The model based, theoretical and experimental works mentioned are promising and have potential for future research and developments. References Buyukpabuscu S.O. (2007), System Identification with Particular Interest On The High Frequency Radar Under Ionospheric Disturbances, MS Thesis, Electrical and Electronics Eng., Middle East Technical Univ., Ankara, Turkey, February 2007. Sari M.O. (2006), A New Approach For The Assessment Of Hf Channel Availability Under Ionospheric Disturbances, MS Thesis, Electrical and Electronics Eng., Middle East Technical Univ., Ankara, Turkey, September 2006. Tulunay E., E. M. Warrington, Y. Tulunay, Y. Bahadırlar, A.S. Türk, R. Çaputçu, T. Yapıcı , E.T. Şenalp (2006), Propagation Related Measurements during Three Solar Eclipses in Turkey, IET 10th International Conference on Ionospheric Radio Systems & Techniques, IRST 2006, 18-21 July 2006, London, UK.

  1. Phosphine Chemistry on Mo(110) and Oxidized Mo(110)

    DTIC Science & Technology

    1993-01-01

    temperature the O(KLL) peak of MoOx (0(520 eV)/Mo(187 eV) ratioy = shoulder (85 K) developed; it originates from multilayer phys- 0.3). It was found...400 TEMPERATURE (K) MOOx (o/Mo-4.0J Figure 6. Comparison of PH3 TPD spectra from PH3/Mo(I 10) and from PH3/D2/Mo(l 10). so 150 250 350 450 550

  2. Heterogeneous chemistry of HBr and HF

    SciTech Connect

    Hanson, D.R.; Ravishankara, A.R.

    1992-11-12

    The authors present information on heterogeneous chemistry of HF and HBr on glass and ice surfaces at a temperature of 200K. Their objective is to study whether heterogeneous reactions of these species could be important in the atmospheric chemistry occuring on NAT particles or cloud condensation nuclei, and be a contributor to ozone depletion. HF showed no significant uptake or reactions with ClONO{sub 2} or HOCl. HBr was found to adsorb on these surfaces, and did not exhibit saturation for even relative high concentrations. In addition it showed reactivity with ClONO{sub 2}, Cl{sub 2} and N{sub 2}O{sub 5} on ice surfaces.

  3. Soft X-ray photoemission studies of Hf oxidation

    SciTech Connect

    Suzer, S.; Sayan, S.; Banaszak Holl, M.M.; Garfunkel, E.; Hussain, Z.; Hamdan, N.M.

    2002-02-01

    Soft X-Ray Photoemission Spectroscopy using surface sensitive Synchrotron Radiation has been applied to accurately determine the binding energy shifts and the valence band offset of the HfO2 grown on Hf metal. Charging of oxide films under x-rays (or other irradiation) is circumvented by controlled and sequential in-situ oxidation. Photoemission results show the presence of metallic Hf (from the substrate) with the 4f7/2 binding energy of 14.22 eV, fully oxidized Hf (from HfO2) with the 4f7/2 binding energy of 18.16 eV, and at least one clear suboxide peak. The position of the valence band of HfO2 with respect to the Hf(m) Fermi level is determined as 4.05 eV.

  4. Compact Reconfigurable HF-UHF Antennas

    DTIC Science & Technology

    2007-11-02

    7] P. J. Rainville, F. J. Harackewiez, Magnetic Tuning of a Microstrip Patch Antenna Fabricated on a Ferrite Film, IEEE Microwave and Guided Wave...Letters, 1992, Vol. 2 pp. 483-5. [8] R. K. Misra, S. S. Pattnaik, N. Das, Tuning of Microstrip Antenna on Ferrite Substrate, IEEE Transactions on...DATES COVERED Final , 01 June 1999 to 31 Dec., 2003 4. TITLE AND SUBTITLE Compact Reconfigurable HF-UHF antennas 5. FUNDING

  5. Improved HF Data Network Simulator. Volume 1

    DTIC Science & Technology

    1993-07-01

    flares - may cause HF blackouts, as can large terrestrial events such as volcanic eruptions and atomic explosions. The ionosphere exhibits a remarkable...of the earth interacts with the solar wind, causing rapid changes in the ionosphere that are made visible in part by the aurora borealis. The effects...backscatter - unpredictable changes in refraction from sporadic-E and F layers - excess path delays caused by non-great-circle modes propagating via

  6. Digitally Driven Antenna for HF Transmission

    DTIC Science & Technology

    2010-09-01

    ferrite -loaded loop as the receive antenna . The 1-MHz signal is clearly evident in the time-domain received signal on an oscilloscope, and also in the... MICROWAVE THEORY AND TECHNIQUES, VOL. 58, NO. 9, SEPTEMBER 2010 Digitally Driven Antenna for HF Transmission Steven D. Keller, Member, IEEE, W...MHz reference signal on the pulsewidth modulator as the transmitter and a highly inductive 470- H ferrite -loaded loop as the receive antenna . The 1-MHz

  7. Surface characteristics of TiN/ZrN coated nanotubular structure on the Ti-35Ta-xHf alloy for bio-implant applications

    NASA Astrophysics Data System (ADS)

    Moon, Byung-Hak; Choe, Han-Cheol; Brantley, William A.

    2012-01-01

    In this study, we investigated the surface characteristics of the TiN/ZrN-coated nanotubular structure on Ti-35Ta-xHf ternary alloys for bio-implant applications. These ternary alloys contained from 3 wt.% to 15 wt.% Hf contents and were manufactured in an arc-melting furnace. The Ti-35Ta-xHf alloys were heat treated in Ar atmosphere at 1000 °C for 24 h, followed by water quenching. Formation of the nanotubular structure was achieved by an electrochemical method in 1 M H3PO4 electrolytes containing 0.8 wt.% NaF. The TiN coating and ZrN coating were subsequently prepared by DC-sputtering on the nanotubular surface. Microstructures and nanotubular morphology of the alloys were examined by FE-SEM, EDX and XRD. The microstructure showed a duplex (α‧‧ + β) phase structure. Traces of martensite disappeared with increasing Hf content, and the Ti-35Nb-15Hf alloy had an entirely equiaxed structure of β phase. This research has shown that highly ordered, high aspect ratio, and nanotubular morphology surface oxide layers can be formed on the ternary titanium alloys by anodization. The TiN and ZrN coatings formed on the nanotubular surfaces were uniform and stable. The top of the nanotube layers was uniformly covered with the ZrN film compared to the TiN film when the Ti-35Ta-xHf alloys had high Hf content.

  8. The Influence of Composition upon Surface Degradation and Stress Corrosion Cracking of the Ni-Cr-Mo Alloys in Wet Hydrofluoric Acid

    SciTech Connect

    Crook, P; Meck, N S; Rebak, R B

    2006-12-04

    At concentrations below 60%, wet hydrofluoric acid (HF) is extremely corrosive to steels, stainless steels and reactive metals, such as titanium, zirconium, and tantalum. In fact, only a few metallic materials will withstand wet HF at temperatures above ambient. Among these are the nickel-copper (Ni-Cu) and nickel-chromium-molybdenum (Ni-Cr-Mo) alloys. Previous work has shown that, even with these materials, there are complicating factors. For example, under certain conditions, internal attack and stress corrosion cracking (SCC) are possible with the Ni-Cr-Mo alloys, and the Ni-Cu materials can suffer intergranular attack when exposed to wet HF vapors. The purpose of this work was to study further the response of the Ni-Cr-Mo alloys to HF, in particular their external corrosion rates, susceptibility to internal attack and susceptibility to HF-induced SCC, as a function of alloy composition. As a side experiment, one of the alloys was tested in two microstructural conditions, i.e. solution annealed (the usual condition for materials of this type) and long-range ordered (this being a means of strengthening the alloy in question). The study of external corrosion rates over wide ranges of concentration and temperature revealed a strong beneficial influence of molybdenum content. However, tungsten, which is used as a partial replacement for molybdenum in some Ni-Cr-Mo alloys, appears to render the alloys more prone to internal attack. With regard to HF-induced SCC of the Ni-Cr-Mo alloys, this study suggests that only certain alloys (i.e., those containing tungsten) exhibit classical SCC. It was also discovered that high external corrosion rates inhibit HF-induced SCC, presumably due to rapid progression of the external attack front. With regard to the effects of long-range ordering, these were only evident at the highest test temperatures, where the ordered structure exhibited much higher external corrosion rates than the annealed structure.

  9. Room temperature formation of Hf-silicate layer by pulsed laser deposition with Hf-Si-O ternary reaction control

    NASA Astrophysics Data System (ADS)

    Hotta, Yasushi; Ueoka, Satoshi; Yoshida, Haruhiko; Arafune, Koji; Ogura, Atsushi; Satoh, Shin-ichi

    2016-10-01

    We investigated the room temperature growth of HfO2 layers on Si substrates by pulsed laser deposition under ultra-high vacuum conditions. The laser fluence (LF) during HfO2 layer growth was varied as a growth parameter in the experiments. X-ray photoemission spectroscopy (XPS) was used to observe the interface chemical states of the HfO2/Si samples produced by various LFs. The XPS results indicated that an interface Hf-silicate layer formed, even at room temperature, and that the thickness of this layer increased with increasing pulsed LF. Additionally, Hf-Si bonds were increasingly formed at the interface when the LF was more than 2 J/cm2. This bond formation process was related to decomposition of HfO2 to its atomic states of Hf and O by multiphoton photochemical processes for bandgap excitation of the HfO2 polycrystalline target. However, the Hf-Si bond content of the interface Hf-silicate layer is controllable under high LF conditions. The results presented here represent a practical contribution to the development of room temperature processing of Hf-compound based devices.

  10. Oxygen Atom Adsorption on and Diffusion into Nb(110) and Nb(100) from First Principles

    SciTech Connect

    Tafen, De Nyago; Gao, Michael C

    2013-11-01

    In order to understand the dynamics of oxidation of Nb, we examine the adsorption, absorption, and diffusion of an oxygen atom on, in, and into Nb(110) and Nb(100) surfaces, respectively, using density functional theory. Our calculations predict that the oxygen atom adsorbs on the threefold site on Nb(110) and the fourfold hollow site on Nb(100), and the adsorption energy is -5.08 and -5.18 eV respectively. We find the long and short bridge sites to be transition states for O diffusion on Nb(110), while the on top site is a rank-2 saddle point. In the subsurface region, the oxygen atom prefers the octahedral site, as in bulk niobium. Our results also show that the O atom is more stable on Nb(110) subsurface than on Nb(100) subsurface. The diffusion of oxygen atoms into niobium surfaces passes through transition states where the oxygen atom is coordinated to four niobium atoms. The diffusion barriers of the oxygen atom into Nb(110) and Nb(100) are 1.81 and 2.05 eV, respectively. Analysis of the electronic density of states reveals the emergence of well localized electronic states below the lowest states of clean Nb surfaces due to d-p orbital hybridization.

  11. Magnetic properties of Hf177 and Hf180 in the strong-coupling deformed model

    NASA Astrophysics Data System (ADS)

    Muto, S.; Stone, N. J.; Bingham, C. R.; Stone, J. R.; Walker, P. M.; Audi, G.; Gaulard, C.; Köster, U.; Nikolov, J.; Nishimura, K.; Ohtsubo, T.; Podolyak, Z.; Risegari, L.; Simpson, G. S.; Veskovic, M.; Walters, W. B.

    2014-04-01

    This paper reports NMR measurements of the magnetic dipole moments of two high-K isomers, the 37/2-, 51.4 m, 2740 keV state in Hf177 and the 8-, 5.5 h, 1142 keV state in Hf180 by the method of on-line nuclear orientation. Also included are results on the angular distributions of γ transitions in the decay of the Hf177 isotope. These yield high precision E2/M1 multipole mixing ratios for transitions in bands built on the 23/2+, 1.1 s, isomer at 1315 keV and on the 9/2+, 0.663 ns, isomer at 321 keV. The new results are discussed in the light of the recently reported finding of systematic dependence of the behavior of the gR parameter upon the quasiproton and quasineutron make up of high-K isomeric states in this region.

  12. LU-HF Age and Isotope Systematics of ALH84001

    NASA Technical Reports Server (NTRS)

    Righter, M.; Lapen, T. J.; Brandon, A. D.; Beard, B. L.; Shafer, J. T.; Peslier, A. H.

    2009-01-01

    Allan Hills (ALH) 84001 is an orthopyroxenite that is unique among the Martian meteorites in having the oldest inferred crystallization age (approx..4.5 to 4.0 Gyr) [e.g., 1-6 and references therein 7]. Its ancient origin makes this stone a critical constraint on early history of Mars, in particular the evolution of different planetary crust and mantle reservoirs. However, because there is significant variability in reported crystallization ages, determination of initial isotope compositions is imprecise making assessment of planetary reservoirs difficult. Here we report a new Lu-Hf mineral isochron age, initial Hf-176/Hf-177 isotope composition, and inferred Martian mantle source compositions for ALH84001 that place constraints on longlived source reservoirs for the enriched shergottite suite of Martian meteorites including Shergotty, Zagami, NWA4468, NWA856, RBT04262, LAR06319, and Los Angeles. Sm-Nd isotope analyses are under way for the same mineral aliquots analyzed for Lu-Hf. The Lu-Hf system was utilized because Lu and Hf are both lithophile and refractory and are not easily redistributed during short-lived thermal pulses associated with shock metamorphism. Moreover, chromite has relatively modest Hf concentrations with very low Lu/Hf ratios [9] yielding tight constraints on initial Hf-176/Hf-177 isotope compositions

  13. TeleEducation NB. Report 1994.

    ERIC Educational Resources Information Center

    TeleEducation NB, Fredericton (New Brunswick).

    This is the first report of TeleEducation NB, the bilingual education network of New Brunswick, Canada. The mission of TeleEducation NB is to provide residents of New Brunswick and other regions cost-effective, equitable access to a range of training, information, and educational services in both official languages, English and French. The network…

  14. Investigation of activation cross-sections of proton induced nuclear reactions on natMo up to 40 MeV: New data and evaluation

    NASA Astrophysics Data System (ADS)

    Tárkányi, F.; Ditrói, F.; Hermanne, A.; Takács, S.; Ignatyuk, A. V.

    2012-06-01

    Cross-sections of proton induced nuclear reactions on natural molybdenum have been studied in the frame of a systematic investigation of charged particle induced nuclear reactions on metals for different applications. The excitation functions of 93mTc, 93gTc(m+), 94mTc, 94gTc, 95mTc, 95gTc, 96gTc(m+), 99mTc, 90Mo(cum), 93mMo, 99Mo(cum), 90Nb(cum), 92mNb, 95mNb, 95gNb, 96Nb and 88Zr(cum), 89Zr(cum) were measured up to 40 MeV proton energy by a using stacked foil technique and activation method. The main goals of this work were to study the production possibility of the medically important 99mTc and its 99Mo parent nucleus, to get experimental data for accelerator technology, for monitoring of proton beam, for thin layer activation technique and for testing nuclear reaction theories. The experimental data were compared with critically analysed published data and with the results of model calculations, obtained by using the ALICE-IPPE, EMPIRE-II and TALYS codes.

  15. Evidence for Slab Melt Contributions to the Mexican Volcanic Belt and Other Young Hot Slab Arcs from Lu-Hf Isotopes

    NASA Astrophysics Data System (ADS)

    Goldstein, S. L.; Cai, Y. M.; Langmuir, C. H.; Lagatta, A.; Straub, S. M.; Gomez-Tuena, A.; Martin Del Pozzo, A.

    2007-12-01

    Despite major advances in delineating the processes that govern magma generation at convergent margins, the problem persists of distinguishing slab, mantle wedge, and crustal contributions. A corrollary question is whether there is significant melting of subducted ocean crust. Especially in thick crust regions, the importance of crustal versus mantle contributions to lavas represents a long-standing fundamental issue in arc magma geochemistry. We show that frontal arc magmas from the Central Mexican Volcanic Belt (CMVB), including the large andesitic stratovolcanoes Popocatepetl and Nevado de Toluca, display negligible crustal contamination, and contain substantial contributions from melting of subducted Pacific ocean crust. Despite ca. 50 km thick continental crust, the CMVB erupts near primitive lavas including "high-Nb" alkaline basalts that show negligible "subduction signatures" in their trace element patterns. These "high-Nb" basalts define the regional mantle wedge composition in isotope-trace element space. The "normal" calcalkaline lavas form a negative correlation between Hf isotopes and Lu/Hf. One endmember is like the high Nb basalts representing the regional mantle wedge. The other endmember has higher Hf isotopes (approaching values of Pacific MORB) and very low Lu/Hf of less than 0.04 (e.g. compared to typical values of ca. 0.2 in Pacific MORB). The low Lu/Hf values require low degree partial melting of a source rich in garnet. The high Hf isotopes require a depleted mantle source with isotopes like Pacific MORB. Together the Lu-Hf data indicate a substantial component derived from melting of eclogitic Pacific ocean crust. A key feature of the data is that the stratovolcano lavas showing the largest slab melt signature also show the highest Hf isotope ratios and thus are more "depleted mantle-like" than the regional mantle wedge. Thus, the integrated data allow us to clearly distinguish between mantle and crustal sources in the CMVB and point to

  16. Atomically Thin-Layered Molybdenum Disulfide (MoS2) for Bulk-Heterojunction Solar Cells.

    PubMed

    Singh, Eric; Kim, Ki Seok; Yeom, Geun Young; Nalwa, Hari Singh

    2017-02-01

    Transition metal dichalcogenides (TMDs) are becoming significant because of their interesting semiconducting and photonic properties. In particular, TMDs such as molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2), tungsten disulfide (WS2), tungsten diselenide (WSe2), titanium disulfide (TiS2), tantalum sulfide (TaS2), and niobium selenide (NbSe2) are increasingly attracting attention for their applications in solar cell devices. In this review, we give a brief introduction to TMDs with a focus on MoS2; and thereafter, emphasize the role of atomically thin MoS2 layers in fabricating solar cell devices, including bulk-heterojunction, organic, and perovskites-based solar cells. Layered MoS2 has been used as the hole-transport layer (HTL), electron-transport layer (ETL), interfacial layer, and protective layer in fabricating heterojunction solar cells. The trilayer graphene/MoS2/n-Si solar cell devices exhibit a power-conversion efficiency of 11.1%. The effects of plasma and chemical doping on the photovoltaic performance of MoS2 solar cells have been analyzed. After doping and electrical gating, a power-conversion efficiency (PCE) of 9.03% has been observed for the MoS2/h-BN/GaAs heterostructure solar cells. The MoS2-containing perovskites-based solar cells show a PCE as high as 13.3%. The PCE of MoS2-based organic solar cells exceeds 8.40%. The stability of MoS2 solar cells measured under ambient conditions and light illumination has been discussed. The MoS2-based materials show a great potential for solar cell devices along with high PCE; however, in this connection, their long-term environmental stability is also of equal importance for commercial applications.

  17. Level structure of {sup 95}Nb

    SciTech Connect

    Rahman, M.A.; Chowdhury, M.S.

    2005-11-01

    The level structure of the {sup 95}Nb nucleus has been studied with the (t,p) reaction in {sup 93}Nb using a tandem Van de Graaff accelerator and a multichannel magnetic spectrograph at an incident beam energy of 12 MeV. Proton spectra are obtained at 12 different angles from 5 deg. to 87.5 deg. at an interval of 7.5 deg. Measurements of the proton distributions from the {sup 93}Nb(t,p){sup 95}Nb reaction were made for the ground and 54 excited states up to the excitation energy of 3.669 MeV. Absolute differential cross sections for the levels have been measured. The experimental angular distributions are compared with the theoretical distorted-wave Born approximation calculations to determine L values and J{sup {pi}} values. The level structure of {sup 95}Nb is compared with previous results.

  18. Electronic and magnetic properties of NbSe2 monolayer doped vacancy and transition metal atoms

    NASA Astrophysics Data System (ADS)

    Manchanda, Priyanka; Sellmyer, David; Skomski, Ralph

    2015-03-01

    Two-dimensional transition-metal dichalcogenides (2D TMDs) have attracted much attention recently due to potential applications including optoelectronic devices. Atomically thin layers of materials such as MoS2, WS2, NbS2, NbSe2, TaTe2 can easily be synthesized by exfoliation techniques and exhibit variety electronic phases such as metal, semiconductor, superconductor depending on the choice of metal. Most of the TMDs are nonmagnetic and various techniques have been proposed to induce or modulate magnetic properties that are essential for nanoelectronic device applications. We use DFT calculations to analyze the effect of strain, hydrogen adsorption, and doping. Emphasis is on the magnetic properties of NbSe2 monolayers containing vacancies and 3 d transition metal atoms. We find that magnetism can be induced by vacancy creation and transition metal-substitution in NbSe2, with effects similar to strain and hydrogen adsorption. The moment mainly arises from the localized nonbonding 3d electrons of the transition-metal atoms. Our findings contribute to the ongoing search ``for-better-than-graphene'' thin-film materials for novel electronic devices. This research is partially supported by DOE BES (DE-FG02-04ER46152).

  19. Syntheses and Properties of Homoleptic Carbonyl and Trifluorophosphane Niobates: [Nb(CO)(6)](-), [Nb(PF(3))(6)](-) and [Nb(CO)(5)](3)(-) (,)(1).

    PubMed

    Barybin, Mikhail V.; Ellis, John E.; Pomije, Marie K.; Tinkham, Mary L.; Warnock, Garry F.

    1998-12-14

    Reductive carbonylations of NbCl(4)(THF)(2), THF = tetrahydrofuran, mediated by sodium naphthalene in 1,2-dimethoxyethane, DME, or sodium anthracene in THF, provide [Nb(CO)(6)](-) as the tetraethylammonium salt in 60% or 70% isolated yields, respectively, the highest known for atmospheric pressure syntheses of this metal carbonyl. Corresponding reductions involving PF(3) give about 40% yields of [Et(4)N][Nb(PF(3))(6)], which in the past was only accessible by a photochemical route. Electrochemical data for [Nb(CO)(6)](-) and [Nb(PF(3))(6)](-) are compared and show that the PF(3) complex is almost 1 V more difficult to oxidize than the CO analogue. Protonation of [Nb(PF(3))(6)](-) by concentrated sulfuric acid yields a volatile, thermally unstable species, which has been shown by (1)H NMR and mass spectral studies to be the new niobium hydride, Nb(PF(3))(6)H. Previously unpublished (93)Nb and (13)C NMR studies corroborate prior claims that the sodium metal reduction of [Nb(CO)(6)](-) in liquid ammonia affords [Nb(CO)(5)](3)(-), the only known Nb(III-) species. The first details of this synthesis and those of [Nb(CO)(5)H](2)(-), [Nb(CO)(5)SnPh(3)](2)(-), [Nb(CO)(5)NH(3)](-), and [Nb(CO)(5)(CNtBu)](-) are presented.

  20. The Nicotiana benthamiana mitogen-activated protein kinase cascade and WRKY transcription factor participate in Nep1(Mo)-triggered plant responses.

    PubMed

    Zhang, Huajian; Li, Deqing; Wang, Meifang; Liu, Jiewen; Teng, Wenjun; Cheng, Baoping; Huang, Qian; Wang, Min; Song, Wenwen; Dong, Suomeng; Zheng, Xiaobo; Zhang, Zhengguang

    2012-12-01

    Many bacterial, fungal, and oomycete species secrete necrosis and ethylene-inducing peptide 1 (Nep1)-like proteins (NLP) that trigger programmed cell death (PCD) and innate immune responses in dicotyledonous plants. However, how NLP induce such immune responses is not understood. Here, we show that silencing of the MAPKKKα-MEK2-WIPK mitogen-activated protein kinase (MAPK) cascade through virus-induced gene silencing compromises hydrogen peroxide accumulation and PCD induced by Nep1(Mo) from Magnaporthe oryzae. WIPK interacts with NbWRKY2, a transcription factor in Nicotiana benthamiana, in vitro and in vivo, suggesting an effector pathway that mediates Nep1(Mo)-induced cell death. Unexpectedly, salicylic acid-induced protein kinase (SIPK)- and NbWRKY2-silenced plants showed impaired Nep1(Mo)-induced stomatal closure, decreased Nep1(Mo)-promoted nitric oxide (NO) production in guard cells, and a reduction in Nep1(Mo)-induced resistance against Phytophthora nicotianae. Expression studies by real-time polymerase chain reaction suggested that the MEK2-WIPK-NbWRKY2 pathway regulated Nep1(Mo)triggered NO accumulation could be partly dependent on nitrate reductase, which was implicated in NO synthesis. Taken together, these studies demonstrate that the MAPK cascade is involved in Nep1(Mo)-triggered plant responses and MAPK signaling associated with PCD exhibits shared and distinct components with that for stomatal closure.

  1. Completing the nuclear reaction puzzle of the nucleosynthesis of 92Mo

    NASA Astrophysics Data System (ADS)

    Tveten, G. M.; Spyrou, A.; Schwengner, R.; Naqvi, F.; Larsen, A. C.; Eriksen, T. K.; Bello Garrote, F. L.; Bernstein, L. A.; Bleuel, D. L.; Crespo Campo, L.; Guttormsen, M.; Giacoppo, F.; Görgen, A.; Hagen, T. W.; Hadynska-Klek, K.; Klintefjord, M.; Meyer, B. S.; Nyhus, H. T.; Renstrøm, T.; Rose, S. J.; Sahin, E.; Siem, S.; Tornyi, T. G.

    2016-08-01

    One of the greatest questions for modern physics to address is how elements heavier than iron are created in extreme astrophysical environments. A particularly challenging part of that question is the creation of the so-called p -nuclei, which are believed to be mainly produced in some types of supernovae. The lack of needed nuclear data presents an obstacle in nailing down the precise site and astrophysical conditions. In this work, we present for the first time measurements on the nuclear level density and average γ strength function of 92Mo. State-of-the-art p -process calculations systematically underestimate the observed solar abundance of this isotope. Our data provide stringent constraints on the 91Nb(p ,γ )92Mo reaction rate, which is the last unmeasured reaction in the nucleosynthesis puzzle of 92Mo. Based on our results, we conclude that the 92Mo abundance anomaly is not due to the nuclear physics input to astrophysical model calculations.

  2. Plastic deformation of directionally solidified ingots of binary and some ternary MoSi2/Mo5Si3 eutectic composites

    PubMed Central

    Matsunoshita, Hirotaka; Sasai, Yuta; Fujiwara, Kosuke; Kishida, Kyosuke; Inui, Haruyuki

    2016-01-01

    Abstract The high-temperature mechanical properties of directionally solidified (DS) ingots of binary and some ternary MoSi2/Mo5Si3 eutectic composites with a script lamellar structure have been investigated as a function of loading axis orientation and growth rate in a temperature range from 900 to 1500°C. These DS ingots are plastically deformed above 1000 and 1100 °C when the compression axis orientations are parallel to [11¯0]MoSi2 (nearly parallel to the growth direction) and [001]MoSi2, respectively. [11¯0]MoSi2-oriented DS eutectic composites are strengthened so much by forming a script lamellar microstructure and they exhibit yield stress values several times higher than those of MoSi2 single crystals of the corresponding orientation. The yield stress values increase with the decrease in the average thickness of MoSi2 phase in the script lamellar structure, indicating that microstructure refinement is effective in obtaining better high-temperature strength of these DS eutectic composites. Among the four ternary alloying elements tested (V, Nb, Ta and W), Ta is found to be the most effective in obtaining higher yield strength at 1400 °C. PMID:27877900

  3. High-aspect-ratio HfC nanobelts accompanied by HfC nanowires: Synthesis, characterization and field emission properties

    NASA Astrophysics Data System (ADS)

    Tian, Song; Zhang, Yulei; Ren, Jincui; Qiang, Xinfa; Zhang, Shouyang; Li, Hejun

    2017-04-01

    As a key refractory carbide, hafnium carbide (HfC) is commonly used as structural materials while the field emission (FE) application of HfC in the field of vacuum microelectronics is almost the only one for functional material purposes. Based on its outstanding physical and chemical characteristics, HfC is identified as a potential candidate with satisfactory mechanical properties and long-term and/or high-temperature FE stability for future applications in high-performance field emitters. However, the development of HfC in various FE applications is hindered because it is not facile to fabricate large-scale low-dimensional HfC field nanoemitters. Herein, High-aspect-ratio HfC nanobelts accompanied by HfC nanowires were synthesized on a large scale by a traditional and simple catalytic chemical vapor deposition (CVD) method. Classical vapor-liquid-solid (VLS) theory was employed to explain the growth of the HfC nanowires and nanobelts along axial direction. The thin HfO2 shell and thin C layer surrounding the nanostructures might give rise to the diameter fluctuation of HfC nanowires and the width increase of HfC nanobelts in lateral direction. Field emission results show that the high-aspect-ratio HfC nanobelts accompanied by the nanowires are promising field nanoemitters, which exhibit excellent field emission properties with a fairly low turn-on field of ∼1.5 V μm-1 and a low current fluctuation less than ∼10%. This suggests that HfC ceramics with high-aspect-ratio nanostructures are ideal cathode material for various field emission applications.

  4. Materials Data on Hf(MoO4)2 (SG:163) by Materials Project

    SciTech Connect

    Kristin Persson

    2014-07-09

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  5. Materials Data on HfMoP (SG:189) by Materials Project

    SciTech Connect

    Kristin Persson

    2016-07-14

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  6. Physics of the Geospace Response to Powerful HF Radio Waves

    DTIC Science & Technology

    2012-10-31

    Final 3. DATES COVERED (From - To) 10.01.2009-09.30.2012 4. TITLE AND SUBTITLE Physics of the Geospace Response to Powerful HF Radio Waves...facility in Alaska under the 2010-2012 AFOSR task `Physics of the Geospace Response to Powerful HF Radio Waves’. A first-principle model of a HF-created...Boulder, CO. 3. Mishin, E., Effects of high-power high frequency radio waves on geospace , Boston University Center for Space Physics, 18 March

  7. Test results of a Nb3Al/Nb3Sn subscale magnet for accelerator application

    DOE PAGES

    Iio, Masami; Xu, Qingjin; Nakamoto, Tatsushi; ...

    2015-01-28

    The High Energy Accelerator Research Organization (KEK) has been developing a Nb3Al and Nb3Sn subscale magnet to establish the technology for a high-field accelerator magnet. The development goals are a feasibility demonstration for a Nb3Al cable and the technology acquisition of magnet fabrication with Nb3Al superconductors. KEK developed two double-pancake racetrack coils with Rutherford-type cables composed of 28 Nb3Al wires processed by rapid heating, quenching, and transformation in collaboration with the National Institute for Materials Science and the Fermi National Accelerator Laboratory. The magnet was fabricated to efficiently generate a high magnetic field in a minimum-gap common-coil configuration with twomore » Nb3Al coils sandwiched between two Nb3Sn coils produced by the Lawrence Berkeley National Laboratory. A shell-based structure and a “bladder and key” technique have been used for adjusting coil prestress during both the magnet assembly and the cool down. In the first excitation test of the magnet at 4.5 K performed in June 2014, the highest quench current of the Nb3Sn coil, i.e., 9667 A, was reached at 40 A/s corresponding to 9.0 T in the Nb3Sn coil and 8.2 T in the Nb3Al coil. The quench characteristics of the magnet were studied.« less

  8. Identification of Mo-Rich M23C6 Carbides in Alloy 718

    NASA Astrophysics Data System (ADS)

    Aghajani, Ali; Tewes, Jürgen; Parsa, Alireza Basir; Hoffmann, Thorsten; Kostka, Alexander; Kloewer, Jutta

    2016-09-01

    In the present study, we systematically identify and characterize a (Nb, Mo)-rich M23C6 type of M23C6 carbide with a lattice parameter of 1.094 nm in alloy 718 for the first time using a combination of selected area electron diffraction pattern and powder X-ray diffraction analysis. The time-temperature-precipitation diagrams of the precipitates in both annealed and strained conditions are obtained by particle analysis using an automated scanning electron microscopy method. (Nb, Mo)-rich M23C6 carbides first precipitate after 24 hours at 1223 K (950 °C) annealing, while they form after 10 minutes at 1273 K (1000 °C) in the strained condition. This correlates with the excess dislocations produce during deformation.

  9. Epitaxial Thin Films of Y doped HfO2

    NASA Astrophysics Data System (ADS)

    Serrao, Claudy; Khan, Asif; Ramamoorthy, Ramesh; Salahuddin, Sayeef

    Hafnium oxide (HfO2) is one of a few metal oxides that is thermodynamically stable on silicon and silicon oxide. There has been renewed interest in HfO2 due to the recent discovery of ferroelectricity and antiferroelectricity in doped HfO2. Typical ferroelectrics - such as strontium bismuth tantalate (SBT) and lead zirconium titanate (PZT) - contain elements that easily react with silicon and silicon oxide at elevated temperatures; therefore, such ferroelectrics are not suited for device applications. Meanwhile, ferroelectric HfO2 offers promise regarding integration with silicon. The stable phase of HfO2 at room temperature is monoclinic, but HfO2 can be stabilized in the tetragonal, orthorhombic or even cubic phase by suitable doping. We stabilized Y-doped HfO2 thin films using pulsed laser deposition. The strain state can be controlled using various perovskite substrates and controlled growth conditions. We report on Y-doped HfO2 domain structures from piezo-response force microscopy (PFM) and structural parameters via X-ray reciprocal space maps (RSM). We hope this work spurs further interest in strain-tuned ferroelectricity in doped HfO2.

  10. Mitigating Doppler shift effect in HF multitone data modem

    NASA Astrophysics Data System (ADS)

    Sonlu, Yasar

    1989-09-01

    Digital communications over High Frequency (HF) radio channels are getting important in recent years. Current HF requirements are for data transmission at rates 2.4 kbps or more to accommodate computer data links and digital secure voice. HF modems which were produced to meet these speeds are, serial modems and parallel modems. On the other hand, the HF sky-wave communication medium, the ionosphere, has some propagation problems such as multipath and Doppler shift. The effect of Doppler shift in a parallel modem which employs Differential Quadrature Phase Shift Keying (DQPSK) modulation is considered and a correction method to mitigate the Doppler Shift effect is introduced.

  11. HF-stabilization of plasma with sharp boundary

    NASA Astrophysics Data System (ADS)

    Kotelnikov, I. A.; Yakovchenko, S. G.

    The effect of HF natural oscillations of a plasma filament in a conducting cylindrical housing on the flute disturbance stability is investigated. Flute development leads to HF oscillation frequency (omega) variation connected with the energy W variation by the condition of constancy of the adiabatic invariant W/(omega) = const. The last is conserved owing to relative slow variations of flute disturbances. The adiabatic approximation used permits one to obtain simple criteria for flute instability stabilization by a HF field. HF oscillations of a plasma with a sharp boundary are considered.

  12. 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

  13. Evidence for a π-junction in Nb/F/Nb' trilayers from superfluid density measurements

    NASA Astrophysics Data System (ADS)

    Lemberger, Thomas; Hinton, Michael; Steers, Stanley; Peters, Bryan; Yang, Fengyuan

    Two-coil measurements of the sheet superfluid density of Nb/NiV/Nb' trilayers reveal the transition temperatures and volume superfluid densities of both Nb layers, as functions of the thickness, dF, of the intervening ferromagnetic (F) Ni0.96V0.04 layer. The upper transition occurs when the thicker Nb layer goes superconducting and superfluid first appears. Fitting the high-temperature superfluid density to an appropriate functional form reveals the presence of a lower ``transition'' where additional superfluid appears. This event is really a crossover, but the difference is irrelevant here. There is a surprising minimum in superfluid densities of both Nb layers at dF ~ 30 Å, followed by a slow rise. This behavior suggests that a π phase difference between the Nb layers develops at dF ~ 30 Å and continues to larger F thickness. Supported in part by NSF Grant DMR-0805227.

  14. "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.

  15. Ferroelectricity of nondoped thin HfO2 films in TiN/HfO2/TiN stacks

    NASA Astrophysics Data System (ADS)

    Nishimura, Tomonori; Xu, Lun; Shibayama, Shigehisa; Yajima, Takeaki; Migita, Shinji; Toriumi, Akira

    2016-08-01

    We report on the impact of TiN interfaces on the ferroelectricity of nondoped HfO2. Ferroelectric properties of nondoped HfO2 in TiN/HfO2/TiN stacks are shown in capacitance-voltage and polarization-voltage characteristics. The Curie temperature is also estimated to be around 500 °C. The ferroelectricity of nondoped HfO2 clearly appears by thinning HfO2 film down to ˜35 nm. We directly revealed in thermal treatments that the ferroelectric HfO2 film on TiN was maintained by covering the top surface of HfO2 with TiN, while it was followed by a phase transition to the paraelectric phase in the case of the open surface of HfO2. Thus, it is concluded that the ferroelectricity in nondoped HfO2 in this study was mainly driven by both of top and bottom TiN interfaces.

  16. Properties of Porous TiNbZr Shape Memory Alloy Fabricated by Mechanical Alloying and Hot Isostatic Pressing

    NASA Astrophysics Data System (ADS)

    Ma, L. W.; Chung, C. Y.; Tong, Y. X.; Zheng, Y. F.

    2011-07-01

    In the past decades, systematic researches have been focused on studying Ti-Nb-based SMAs by adding ternary elements, such as Mo, Sn, Zr, etc. However, only arc melting or induction melting methods, with subsequent hot or cold rolling, were used to fabricate these Ni-free SMAs. There is no work related to powder metallurgy and porous structures. This study focuses on the fabrication and characterization of porous Ti-22Nb-6Zr (at.%) shape memory alloys produced using elemental powders by means of mechanical alloying and hot isostatic pressing. It is found that the porous Ti-22Nb-6Zr alloys prepared by the HIP process exhibit a homogenous pore distribution with spherical pores, while the pores have irregular shape in the specimen prepared by conventional sintering. X-ray diffraction analysis showed that the solid solution-treated Ti-22Nb-6Zr alloy consists of both β phase and α″ martensite phase. Morphologies of martensite were observed. Finally, the porous Ti-22Nb-6Zr SMAs produced by both MA and HIP exhibit good mechanical properties, such as superior superelasticity, with maximum recoverable strain of ~3% and high compressive strength.

  17. Processing of U-2.5Zr-7.5Nb and U-3Zr-9Nb alloys by sintering process

    SciTech Connect

    Dos Santos, A. M. M.; Ferraz, W. B.; Lameiras, F. S.; Mazzeu, T. D. O.

    2012-07-01

    To minimize the risk of nuclear proliferation, there is worldwide interest in reducing fuel enrichment of research and test reactors. To achieve this objective while still guaranteeing criticality and cycle length requirements, there is need of developing high density uranium metallic fuels. Alloying elements such as Zr, Nb and Mo are added to uranium to improve fuel performance in reactors. In this context, the Centro de Desenvolvimento da Tecnologia Nuclear (CDTN) is developing the U-2.5Zr-7.5Nb and U-3Zr-9Nb (weight %) alloys by the innovative process of sintering that utilizes raw materials in the form of powders. The powders were pressed at 400 MPa and then sintered under a vacuum of about 1x10{sup -4} Torr at temperatures ranging from 1050 deg. to 1500 deg.C. The densities of the alloys were measured geometrically and by hydrostatic method and the phases identified by X ray diffraction (XRD). The microstructures of the pellets were observed by scanning electron microscopy (SEM) and the alloying elements were analyzed by energy dispersive X-ray spectroscopy (EDS). The results obtained showed the fuel density to slightly increase with the sintering temperature. The highest density achieved was approximately 80% of theoretical density. It was observed in the pellets a superficial oxide layer formed during the sintering process. (authors)

  18. Hf isotope and concentration systematics of the Mariana arc

    NASA Astrophysics Data System (ADS)

    Tollstrup, D. L.; Gill, J. B.

    2004-12-01

    Negative Hf concentration anomalies are common but little-discussed geochemical features of island arcs. Because both light rare earth elements (LREE) and Hf may be mobile even in `fluid-dominated' island arcs, it is important to relate their isotopic and elemental ratios to models of slab-mantle mixing. We report new Hf isotope and trace element data for K-rich submarine basalts from the Kasuga seamounts located 10-20 km behind the volcanic front of the southern Northern Seamount Province (NSP) of the Mariana arc. These data, when combined with published data for other Mariana samples, span the full range from low-K tholeiites to high-K shoshonites. Rear-arc Kasuga seamounts seamounts of the NSP have lower 143Nd/144Nd and 176Hf/177Hf ratios than arc-front volcanoes of the Mariana Central Island Province (CIP). Within the CIP, Hf concentration anomalies correlate positively with 176Hf/177Hf ratios. Radiogenic Hf and little or no concentration anomalies characterize samples from fluid-dominated volcanoes (Guguan and Maug), whereas samples from sediment-melt dominated volcanoes (Anatahan and Sarigan) have less radiogenic Hf and larger concentration anomalies. Samples from the Kasuga and Hiyoshi seamounts have even larger negative concentration anomalies and less radiogenic Hf, although the two are not always correlated. These data are consistent with mixing between a depleted mantle and a partial melt of subducted sediment that is saturated with trace accessory phases including zircon, rutile, and monazite. A more volcaniclastic source is needed for the NSP than the CIP. Implications of these findings are three-fold. Partial melts of subducting sediment affect the HFSE and REE budgets of even fluid-dominated island arcs. Slab temperatures must be high enough for a peraluminous melt to be present, even where old, cold slabs are subducting. Refractory accessory phases have the potential to become exotic "nuggets" in the convecting mantle, potentially controlling the

  19. Large enhanced perpendicular magnetic anisotropy in CoFeB/MgO system with the typical Ta buffer replaced by an Hf layer

    NASA Astrophysics Data System (ADS)

    Liu, T.; Cai, J. W.; Sun, Li

    2012-09-01

    By systematically comparing the magnetic properties of the Ta/CoFeB/Ta and MgO/CoFeB/MgO structures with and without a submonolayer of MgO, Ta, V, Nb, Hf and W inserted in the middle of the CoFeB layer, we have proved that the observed perpendicular magnetic anisotropy (PMA) in Ta/CoFeB/MgO sandwiches is solely originated from the CoFeB/MgO interface with the Ta buffer acting to enhance the CoFeB/MgO interface anisotropy significantly. Moreover, replacing Ta with Hf causes the CoFeB/MgO interfacial PMA further enhanced by 35%, and the CoFeB layer with perpendicular magnetization has a much larger critical thickness accordingly, leaving a wider thickness margin for the CoFeB/MgO-based perpendicular magnetic tunnel junction optimization. Also the sputter deposited thin Hf films are amorphous with low surface roughness. These results will ensure the Hf/CoFeB/MgO more promising material system for PMA device development.

  20. Mechanical Properties of Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20 Refractory High-Entropy Alloys (Preprint)

    DTIC Science & Technology

    2011-07-01

    stability, oxidation resistance and other properties, rather than forming the conventionally expected complex and brittle intermetallic phases. Using...W. Yeh, Annales de Chimie: Science des Materiaux , 31 (2006) 633-648. 6 J.-W. Yeh, Y.-L. Chen, S.-J. Lin, S.-K. Chen, Mater. Sci. Forum, 560 (2007

  1. Use of Mo/ller-Plesset perturbation theory in molecular calculations: Spectroscopic constants of first row diatomic molecules

    SciTech Connect

    Dunning, T.H. , Jr.; Peterson, K.A.

    1998-03-01

    The convergence of Mo/ller{endash}Plesset perturbation expansions (MP2{endash}MP4/MP5) for the spectroscopic constants of a selected set of diatomic molecules (BH, CH, HF, N{sub 2}, CO, and F{sub 2}) has been investigated. It was found that the second-order perturbation contributions to the spectroscopic constants are strongly dependent on basis set, more so for HF and CO than for BH. The MP5 contributions for HF were essentially zero for the cc-pVDZ basis set, but increased significantly with basis set illustrating the difficulty of using small basis sets as benchmarks for correlated calculations. The convergence behavior of the {ital exact} Mo/ller{endash}Plesset perturbation expansions were investigated using estimates of the {ital complete basis set limits} obtained using large correlation consistent basis sets. For BH and CH, the perturbation expansions of the spectroscopic constants converge monotonically toward the experimental values, while for HF, N{sub 2}, CO, and F{sub 2}, the expansions oscillate about the experimental values. The perturbation expansions are, in general, only slowly converging and, for HF, N{sub 2}, CO, and F{sub 2}, appear to be far from convergence at MP4. In fact, for HF, N{sub 2}, and CO, the errors in the calculated spectroscopic constants for the MP4 method are {ital larger} than those for the MP2 method (the only exception is D{sub e}). The current study, combined with other recent studies, raises serious doubts about the use of Mo/ller{endash}Plesset perturbation theory to describe electron correlation effects in atomic and molecular calculations. {copyright} {ital 1998 American Institute of Physics.}

  2. Surface Treatments of Nb by Buffered Electropolishing

    SciTech Connect

    Wu, Andy T.; Rimmer, Robert A.; Ciovati, Gianluigi; Manus, Robert L.; Reece, Charles E.; Williams, J. S.; Eozénou, F.; Jin, S.; Wang, E.

    2009-11-01

    Buffered electropolishing (BEP) is a Nb surface treatment technique developed at Jefferson Lab1. Experimental results obtained from flat Nb samples show2-4 that BEP can produce a surface finish much smoother than that produced by the conventional electropolishing (EP), while Nb removal rate can be as high as 4.67 μm/min. This new technique has been applied to the treatments of Nb SRF single cell cavity employing a vertical polishing system5 constructed at JLab as well as a horizontal polishing system at CEA Saclay. Preliminary results show that the accelerating gradient can reach 32 MV/m for a large grain cavity and 26.7 MV/m for a regular grain cavity. In this presentation, the latest progresses from the international collaboration between Peking University, CEA Saclay, and JLab on BEP will be summarized.

  3. Nb3Sn Artificial Pinning Microstructures

    SciTech Connect

    Dietderich, D.R.; Scanlan, R.M.

    1996-12-12

    Extension of the APC approach to Nb{sub 3}Sn requires that a second phae be incorporated into the Nb{sub 3}Sn layer. The second phase would increase pinning strength by either reducing the grain size or by the second phase pinning the flux itwelf. The following criteria for elements to be candidates for the APC approach are: (1) they must form intermetallic compounds with Cu or Sn and (2) they must have negligible solubility in Cu and Nb or they must be strong oxide formers. many of the rare earth elements satisfy these criteria. To circumvent the large strains required to produce wires with a fine distribution of the second phase, film deposition techniques have been used. Critical current densities for Nb films doped with Ti and Y are about 4,000 A/mm{sup 2} at 6T and 4.2 K.

  4. Nb3Sn for Radio Frequency Cavities

    SciTech Connect

    Godeke, A.

    2006-12-18

    In this article, the suitability of Nb3Sn to improve theperformance of superconducting Radio-Frequency (RF)cavities is discussed.The use of Nb3Sn in RF cavitiesis recognized as an enabling technology toretain a veryhigh cavity quality factor (Q0) at 4.2 K and tosignificantly improve the cavity accelerating efficiency per unitlength(Eacc). This potential arises through the fundamental properties ofNb3Sn. The properties that are extensively characterized in theliterature are, however, mainly related to improvements in currentcarrying capacity (Jc) in the vortex state. Much less is available forthe Meissner state, which is of key importance to cavities. Relevantdata, available for the Meissner state is summarized, and it is shown howthis already validates the use of Nb3Sn. In addition, missing knowledgeis highlighted and suggestions are given for further Meissner statespecific research.

  5. 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.

  6. Nanoscale decomposition of Nb-Ru-O

    NASA Astrophysics Data System (ADS)

    Music, Denis; Geyer, Richard W.; Chen, Yen-Ting

    2016-11-01

    A correlative theoretical and experimental methodology has been employed to explore the decomposition of amorphous Nb-Ru-O at elevated temperatures. Density functional theory based molecular dynamics simulations reveal that amorphous Nb-Ru-O is structurally modified within 10 ps at 800 K giving rise to an increase in the planar metal - oxygen and metal - metal population and hence formation of large clusters, which signifies atomic segregation. The driving force for this atomic segregation process is 0.5 eV/atom. This is validated by diffraction experiments and transmission electron microscopy of sputter-synthesized Nb-Ru-O thin films. Room temperature samples are amorphous, while at 800 K nanoscale rutile RuO2 grains, self-organized in an amorphous Nb-O matrix, are observed, which is consistent with our theoretical predictions. This amorphous/crystalline interplay may be of importance for next generation of thermoelectric devices.

  7. Fractionation of Zr and Hf in surface processes

    SciTech Connect

    Chyi, L.L.; Garg, A.N.

    1985-01-01

    Zircons from a pegmatite near Tuxedo, North Carolina were crushed and treated with different reagents under different conditions. The treated and untreated samples were determined for Zr and Hf with radiochemical neutron activation analysis. Zircons treated with 50% sulfuric acid were having lowered Zr content and Zr/Hf ratio. The conclusions are that a portion of Zr and Hf in zircons is sensitive to leaching, and Zr appears to be selectively leached over Hf. The conclusions of this work support the observations of small dissolutions of Zr in both acidic podzolic soils and in alkaline laterites, of lower Zr content in soils on glacial drift, and of lower Zr/Hf ratios in loess deposits from various parts of the world. The fractionation of Zr and Hf in surface processes appears to be due to selective leaching. Weakening of Zr-O over Hf-O bonds in zircon by fission projectiles is postulated to be the viable process. The observed fractionation from leaching experiments suggest that areas receiving leachates such as swamps, lakes, and oceans should have high to very high Zr/Hf ratios preserved in rocks. High ratios are found in the Springfield (No. 9) Coal, the Green River Shale, and various limestones. High ratio is also found in orchard leaves, which grow by absorbing leachate from soil.

  8. Thermal stability of the nickel-base superalloy B-1900 + Hf with tantalum variations

    NASA Technical Reports Server (NTRS)

    Harmon, B. S.; Pletka, B. J.; Janowski, G. M.

    1987-01-01

    The microstructure of the solutionized and aged nickel-base superalloy B-1900 + Hf was examined after additional aging at 982 C for 72, 250, and 1000 hours. Alloy compositions that were examined contained the normal 1.34 at. pct (4.3 wt pct) Ta as well as 0.67 at. pct and zero Ta levels. The gamma-prime phase agglomerated, became platelike in morphology, and decreased in volume fraction for all three alloys throughout the aging treatments. Changes which occurred in the gamma and gamma-prime phase compositions were nearly complete after 72 hours of aging while changes in the MC carbide composition continued throughout the aging. Blocky M6C carbides precipitated along the grain boundaries of all three alloys in the first 72 hours of aging. In addition, an acicular form of this Mo/Cr/Ni-rich carbide developed in the intragranular regions of the Ta-containing alloys.

  9. LiNbO3 Cylinder Fiber

    NASA Technical Reports Server (NTRS)

    2004-01-01

    We have successfully fabricate optical fiber with a thin layer of LiNbO3 at the boundary of the glass core and dear glass cladding. The construction of this fiber is based on our successful Semiconductor Cylinder Fibers (SCF). A schematic representation of a LiNbO3 Cylinder Fiber is shown. These fibers can be used as light modulators, sonar detectors and in other applications. The core diameter of the fiber is sufficiently small compared to the light wavelength and the indices of refraction of the core and cladding glasses are sufficiently close in value so that there is sufficient light at the core cladding boundary to interact with the LiNbO3 layer. This fiber functions best when just a single light mode propagates through the fiber. The idea for a LiNbO3 Cylinder Fiber came from Dr. Tracee Jamison of NASA. The optical properties of LiNbO3 can be changed with strain or the application of an electric field. Thus these fibers can be used as acoustic sensors as for example in a sonar. They can also be used as electric field operated light modulators. However, for this application the fibers would be made with a cross section in the form of a 'D'. The core with its surrounding LiNbO, layer would be close to the flat portion of the 'D' shaped fiber. Two metal contacts would be deposited on the flat portion of the fiber on either side of the core. A voltage applied across these contacts will result in an electric field in the core region that can be used for modulating the optical properties of the LiNbO, layer. To our knowledge this is the first ever LiNbO, Cylinder Fiber made.

  10. Crystal structure of Si-doped HfO2

    NASA Astrophysics Data System (ADS)

    Zhao, Lili; Nelson, Matthew; Aldridge, Henry; Iamsasri, Thanakorn; Fancher, Chris M.; Forrester, Jennifer S.; Nishida, Toshikazu; Moghaddam, Saeed; Jones, Jacob L.

    2014-01-01

    Si-doped HfO2 was prepared by solid state synthesis of the starting oxides. Using Rietveld refinement of high resolution X-ray diffraction patterns, a substitutional limit of Si in HfO2 was determined as less than 9 at. %. A second phase was identified as Cristobalite (SiO2) rather than HfSiO4, the latter of which would be expected from existing SiO2-HfO2 phase diagrams. Crystallographic refinement with increased Si-dopant concentration in monoclinic HfO2 shows that c/b increases, while β decreases. The spontaneous strain, which characterizes the ferroelastic distortion of the unit cell, was calculated and shown to decrease with increasing Si substitution.

  11. Calculation of Electron Affinity and Partial Cross Sections of Hf^-

    NASA Astrophysics Data System (ADS)

    Pan, Lin; Beck, Donald

    2008-05-01

    We have calculated for the first time the electron affinity (EA) of Hf^-, using the relativistic configuration interaction method. Our calculations show Hf^- has only one bound state 5d^26s^26p J=5/2, which is a 6p attachment to the ground state of Hf I. By combining our valence stage result with the separate estimate for the modest core-valence contribution, the EA of Hf^- is about 0.114 eV. So far there have been only two experimental results [1,2] for the EA of Hf^-, but both gave only the limits. Our result falls within both of the limits. We also calculate the partial cross sections for photodetachment to the lower lying neutral thresholds. [1] M-J. Nadeau et al, Nucl. Instr. and Meth. B 123, 521 (1997) [2] Vernon T. Davis et al, Nucl. Instr. and Meth. B 241, 118 (2005)

  12. Hf propagation through actively modified ionospheres

    SciTech Connect

    Argo, P.E.; Fitzgerald, T.J.; Wolcott, J.H.; Simons, D.J. ); Warshaw, S.; Carlson, R. )

    1990-01-01

    We have developed a computer modeling capability to predict the effect of localized electron density perturbations created by chemical releases or high-power radio frequency heating upon oblique, one-hop hf propagation paths. We have included 3-d deterministic descriptions of the depleted or enhanced ionization, including formation, evolution, and drift. We have developed a homing ray trace code to calculate the path of energy propagation through the modified ionosphere in order to predict multipath effects. We also consider the effect of random index of refraction variations using a formalism to calculate the mutual coherence functions for spatial and frequency separations based upon a path integral solution of the parabolic wave equation for a single refracted path through an ionosphere which contains random electron density fluctuations. 5 refs., 8 figs.

  13. Time synchronisation of an HF radio modem

    NASA Astrophysics Data System (ADS)

    Clark, A. P.; McVerry, F.

    1982-12-01

    The present investigation is concerned with a technique for time synchronization which is of potential value in any application of time synchronization where an estimate of the sampled impulse response of a time-varying linear baseband channel is required but the particular phase of the sampling instants is hot important. The technique appears to be both simple and effective and to be capable of development into a useful practical system. Attention is given to the results of computer simulation tests which show the performance of the technique in a 9600 bit/s quadrature-amplitude-modulated (QAM) data-transmission system operating over a model of an HF radio link. The data-transmission system is considered along with the control of the sampling instants, and details concerning the computer simulation tests.

  14. {ital Ab initio} characterization of the structure and energetics of the ArHF complex

    SciTech Connect

    van Mourik, T.; Dunning, T.H. Jr.

    1997-08-01

    The ArHF complex has been investigated using correlation consistent basis sets at several levels of theory, including Mo/ller{endash}Plesset perturbation theory (MP2, MP3, MP4) and coupled cluster techniques [CCSD, CCSD(T)]. The three stationary points (the primary linear Ar{endash}HF minimum, the secondary linear Ar{endash}FH minimum, and the interposed transition state TS) on the counterpoise-corrected potential energy surface have been characterized. Calculations with the aug-cc-pV5Z basis set predict D{sub e} for the Ar{endash}HF minimum to be (with estimated complete basis set limits in parentheses) {minus}215 ({minus}218)cm{sup {minus}1} for MP4 and {minus}206 ({minus}211)cm{sup {minus}1} for CCSD(T). For the Ar{endash}FH minimum and the TS, calculations with the d-aug-cc-pVQZ sets predict D{sub e}{close_quote}s (and CBS limits) of {minus}97 ({minus}99) and {minus}76 ({minus}78)cm{sup {minus}1} (MP4) and {minus}93 ({minus}94) and {minus}75 ({minus}76)cm{sup {minus}1} [CCSD(T)], respectively. The corresponding values for the H6(4,3,2) potential of Hutson [J. Chem. Phys. {bold 96}, 6752 (1992)] are {minus}211.1{plus_minus}4cm{sup {minus}1}, {minus}108.8{plus_minus}10cm{sup {minus}1}, and {minus}82.6{plus_minus}10cm{sup {minus}1}. While the agreement of our CCSD(T) estimate with Hutson{close_quote}s value is excellent for the global minimum, it is less so for the other two stationary points, suggesting that the H6(4,3,2) potential may be too attractive around the secondary minimum and the transition state. {copyright} {ital 1997 American Institute of Physics.}

  15. Doping against the native propensity of MoS₂: Degenerate hole doping by cation substitution

    SciTech Connect

    Suh, Joonki; Park, Tae-Eon; Lin, Der-Yuh; Fu, Deyi; Park, Joonsuk; Jung, Hee Joon; Chen, Yabin; Ko, Changhyun; Jang, Chaun; Sun, Yinghui; Sinclair, Robert; Chang, Joonyeon; Tongay, Sefaattin; Wu, Junqiao

    2014-12-10

    Layered transition metal dichalcogenides (TMDs) draw much attention as the key semiconducting material for two-dimensional electrical, optoelectronic, and spintronic devices. For most of these applications, both n- and p-type materials are needed to form junctions and support bipolar carrier conduction. However, typically only one type of doping is stable for a particular TMD. For example, molybdenum disulfide (MoS₂) is natively an n-type presumably due to omnipresent electron-donating sulfur vacancies, and stable/controllable p-type doping has not been achieved. The lack of p-type doping hampers the development of charge-splitting p–n junctions of MoS₂, as well as limits carrier conduction to spin-degenerate conduction bands instead of the more interesting, spin-polarized valence bands. Traditionally, extrinsic p-type doping in TMDs has been approached with surface adsorption or intercalation of electron-accepting molecules. However, practically stable doping requires substitution of host atoms with dopants where the doping is secured by covalent bonding. In this work, we demonstrate stable p-type conduction in MoS₂ by substitutional niobium (Nb) doping, leading to a degenerate hole density of ~3 × 10¹⁹ cm⁻³. Structural and X-ray techniques reveal that the Nb atoms are indeed substitutionally incorporated into MoS₂ by replacing the Mo cations in the host lattice. van der Waals p–n homojunctions based on vertically stacked MoS₂ layers are fabricated, which enable gate-tunable current rectification. A wide range of microelectronic, optoelectronic, and spintronic devices can be envisioned from the demonstrated substitutional bipolar doping of MoS₂. From the miscibility of dopants with the host, it is also expected that the synthesis technique demonstrated here can be generally extended to other TMDs for doping against their native unipolar propensity.

  16. Neutron yields from 435 MeV/nucleon Nb stopping in Nb and 272 MeV/nucleon Nb stopping in Nb and Al

    NASA Technical Reports Server (NTRS)

    Heilbronn, L.; Madey, R.; Elaasar, M.; Htun, M.; Frankel, K.; Gong, W. G.; Anderson, B. D.; Baldwin, A. R.; Jiang, J.; Keane, D.; McMahan, M. A.; Rathbun, W. H.; Scott, A.; Shao, Y.; Watson, J. W.; Westfall, G. D.; Yennello, S.; Zhang, W. M.; Miller, J. (Principal Investigator)

    1998-01-01

    Neutron fluences were measured from 435 MeV/nucleon Nb ions stopping in a Nb target and 272 MeV/nucleon Nb ions stopping in targets of Nb and Al for neutrons above 20 MeV and at laboratory angles between 3 degrees and 80 degrees. The resultant spectra were integrated over angles to produce neutron energy distributions and over energy to produce neutron angular distributions. The total neutron yields for each system were obtained by integrating over the angular distributions. The angular distributions from all three systems are peaked forward, and the energy distributions from all three systems show an appreciable yield of neutrons with velocities greater than the beam velocity. Comparison of the total neutron yields from the two Nb + Nb systems suggests that the average neutron multiplicity decreases with decreasing projectile energy. Comparison of the total yields from the two 272 MeV/nucleon systems suggests that the total yields show the same dependence on projectile and target mass number as do total inclusive neutron cross sections. The data are compared with Boltzmann-Uehling-Uhlenbeck model calculations.

  17. 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.

  18. Microstructure and mechanical properties of as-cast Ti-Mo-xCr alloy for biomedical application

    NASA Astrophysics Data System (ADS)

    Senopati, Galih; Sutowo, Cahya; P. A., I. Nyoman Gede; Utomo, Edy Priyanto; Amal, M. Ikhlasul

    2016-02-01

    Beta Ti alloys is one of the most attractive biomaterials due to their better corrosion resistance, biocompatibility, greater specific strength and lower elastic modulus than stainless steels and Co-Cr based alloys. Cr is the strong beta Ti stabilizer and has lower density than Nb, Sn and Ta. In this study As cast Ti-12Mo and Ti-12-xCr with Cr content range 1, 3, 5, and 10 wt.% prepared by using arc melting vacuum-pressure casting were investigated. The as cast Ti-Mo and Ti-Mo-xCr examined using X-ray diffraction (XRD), optical microscope (OM) and Vickers hardness tester. Experimental result indicate Ti-12Mo-xNb match for β phase peaks but TiO2 phase occurred in all alloys. The vickers hardness values of all the Ti-12Mo-xCr alloys are higher than HV 1000. The optical microscope investigation indicate Cr content influence Ti-Mo-xCr microstructure.

  19. Constitution and thermodynamics of the Mo-Ru, Mo-Pd, Ru-Pd and Mo-Ru-Pd systems

    NASA Astrophysics Data System (ADS)

    Kleykamp, H.

    1989-09-01

    The constitution of the Mo-Ru, Mo-Pd and Ru-Pd systems was reinvestigated between 800 and 2000°C. The Mo-Ru system is of the eutectic type, a σ-phase Mo 5Ru 3 exists between 1915 and 1143°C. The Mo-Pd system is characterized by an hcp phase Mo 9Pd 11 and by two peritectic reactions, β- Mo( Pd) + L = Mo9Pd11andMo9Pd11 + L = α- Pd( Mo). Mo 9Pd 11 decomposes eutectoidally at 1370°C. The Ru-Pd system is simple peritectic. The continuous series of the hcp solid solutions between Mo 9Pd 11 and ɛ-Ru(Mo, Pd) in the ternary Mo-Ru-Pd system observed at 1700°C are suppressed below 1370°C near the Mo-Pd boundary system by the formation of a narrow α + β + ɛ three-phase field. Relative partial molar Gibbs energies of Mo, Mo and Ru in the respective binary systems and of Mo in the ternary system were measured by the EMF method with a Zr(Ca)O 2 electrolyte. xsΔ ḠMo∞ quantities were evaluated at 1200 K which give -43 kJ/mol Mo in Ru and -94 kJ/mol Mo in Pd at infinite dilution. Gibbs energies of formation of the Mo-Ru and Mo-Pd systems were calculated.

  20. Metastable phase formation in Be-Nb intermetallic compounds

    SciTech Connect

    Brimhall, J.L.; Charlot, L.A.; Bruemmer, S.M.

    1990-11-01

    Amorphous structures or metastable crystalline phases are produced in sputter-deposited Beryllium-Niobium (Be-Nb) alloys (5-15 at. % Nb) depending on the substrate temperature. The metastable phases transform to the stable Be{sub 12}Nb, Be{sub 17}Nb{sub 2}Nb phases on annealing at temperatures >800{degree}C. No Be{sub 5}Nb phase was found and the Be{sub 17}Nb{sub 2} phase is stable to low temperature. The Be{sub 12}Nb phase appeared to have a stoichiometric range of about 5.5 to 7.7 at. % Nb. The formation of the metastable phases is consistent with current models and theories. 17 refs., 1 fig., 2 tabs.

  1. Ferroelectricity-modulated resistive switching in Pt/Si:HfO2/HfO2-x /Pt memory

    NASA Astrophysics Data System (ADS)

    Ran, Jiang; Xianghao, Du; Zuyin, Han

    2016-08-01

    It is investigated for the effect of a ferroelectric Si:HfO2 thin film on the resistive switching in a stacked Pt/Si:HfO2/highly-oxygen-deficient HfO2-x /Pt structure. Improved resistance performance was observed. It was concluded that the observed resistive switching behavior was related to the modulation of the width and height of a depletion barrier in the HfO2-x layer, which was caused by the Si:HfO2 ferroelectric polarization field effect. Reliable switching reproducibility and long data retention were observed in these memory cells, suggesting their great potential in non-volatile memories applications with full compatibility and simplicity. Project supported by the National Natural Science Foundation of China (No. 11374182), the Natural Science Foundation of Shandong Province (No. ZR2012FQ012), and the Jinan Independent Innovation Projects of Universities (No. 201303019).

  2. Anti-P2 structured Na0.5NbO2 and its negative strain effect

    SciTech Connect

    Wang, Xuefeng; Gao, Yurui; Shen, Xi; Li, Yejing; Kong, Qingyu; Lee, Sungsik; Wang, Zhaoxiang; Yu, Richeng; Hu, Yong-Sheng; Chen, Liquan

    2015-01-01

    Layer-structured oxides are studied for their essential roles in various applications (e.g. high-energy batteries and superconductors) due to their distinctive physical structures and chemical properties. Most of the layered AxMO2 (A = alkali ions, M = transition metals) are composed of MO6 octahedra and various A coordination polyhedra such as octahedra (O), tetrahedra (T) or trigonal prisms (P). Herein, we report a new layered oxide material, anti-P2 Na0.5NbO2, which is composed of NbO6 trigonal prisms and NaO6 octahedra. Its lattice shrinks as sodium (Na) ions are intercalated in it and expands when the ions are deintercalated (a negative volume or strain effect). Analysis by X-ray absorption spectroscopy and density functional theory (DFT) calculations indicates that the negative volume effect is mainly a result of the enhanced interlayer (Na–O) interaction and the weakened Nb– Nb and Nb–O bonding in the O–Nb–O slab upon Na intercalation. Moreover, Na0.5NbO2 exhibits high structural stability, a long cycle life and prominent rate performance for Na-ion batteries. These distinctive features make Na0.5NbO2 an ideal ‘‘volume buffer’’ to compensate for positive-strain electrode materials. These findings will arouse great interest in anti-P2 layered oxides for materials science and applications, and enrich the understanding of novel negative-strain materials for energy storage either as excellent independent active electrode materials or as volume buffers for constructing long-life composite electrodes made of positive-strain materials.

  3. Hydrolysis of ZrCl4 and HfCl4: The Initial Steps in the High-Temperature Oxidation of Metal Chlorides to Produce ZrO2 and HfO2

    SciTech Connect

    Fang, Zongtang; Dixon, David A.

    2013-03-08

    The gas-phase hydrolysis of MCl4 (M = Zr, Hf) to produce the initial particles on the way to zirconia and hafnia nanoparticles has been studied with electronic structure theory. The potential energy surfaces, the themochemistry of the reaction species, and the reaction paths for the initial steps of MCl4 reacting with H2O have been calculated. The hydrolysis of MCl4 at higher temperatures begins with the formation of oxychlorohydroxides followed by the elimination of HCl instead of the direct production of MOCl2 and HCl or MO2 and HCl due to the substantial endothermicities associated with the formation of gas-phase MO2. The structural properties and heats of formation of the reactants and products are consistent with the available experimental results. A number of metal oxychlorides (oxychlorohydroxides) intermediate clusters have been studied to assess their role in the production of MO2 nanoparticles. The calculated clustering reaction energies of those intermediates are highly exothermic, so they could be readily formed in the hydrolysis process. These intermediate clusters can be formed exothermically from metal oxychlorohydroxides by the elimination of one HCl or H2O molecule. Our calculations show that the mechanisms leading to the formation of MO2 nanoparticles are complicated and are accompanied by the potential production of a wide range of intermediates, as found for the production of TiO2 particles from the high-temperature oxidation of TiCl4.

  4. Hf-Nd isotope and trace element constraints on subduction inputs at island arcs: limitations of Hf anomalies as sediment input indicators

    NASA Astrophysics Data System (ADS)

    Handley, H. K.; Turner, S.; MacPherson, C.; Davidson, J. P.; Gertisser, R.

    2010-12-01

    New Nd-Hf isotope and trace element data for Javanese volcanoes are combined with recently published data to place constraints on subduction inputs at the Sunda arc in Indonesia and assess the value of Hf anomalies (expressed as Hf/Hf* and Sm/Hf ratios) as tracers of such inputs. Hf anomaly does not correlate with Hf isotope ratio in Javanese lavas however, Hf/Hf* and Sm/Hf ratios do correlate with SiO2. Contrary to previous work, we show that Hf anomaly variation may be controlled by fractionation of clinopyroxene and/or amphibole during magmatic differentiation and does not represent the magnitude or type of subduction input in some arcs. Correlation of Sm/Hf with indices of differentiation for other arcs (e.g. Vanuatu, New Britain, Mariana) suggests that differentiation control on Sm/Hf ratios of volcanic rocks may be a relatively common phenomenon. This study corroborates the use of Nd-Hf isotope co-variations in arc volcanic rocks to ascertain subduction input characteristics. The trajectories of regional volcano groups (East, Central and West Java) in Nd-Hf isotope space reveal heterogeneity in the subducted sediment input along Java, which reflects present-day spatial variations in sediment compositions on the down-going plate in the Java Trench.

  5. A convergent continent marginal volcanism source of ash beds near the Permian-Triassic boundary, South China: Constraints from trace elements and Hf-isotopes

    NASA Astrophysics Data System (ADS)

    Wang, X.; Zhao, L.; Chen, Z. Q.; Ma, D.; Yan, P.; Guo, F.; Wang, F.; Wan, Q.; Han, X.

    2015-12-01

    Growing evidence shows that volcanism near the Permian-Triassic boundary (PTB) may have been crucial in triggering the PTB biocrisis. However, whether this trigger is the Siberian traps or arc island volcanisms has long been debating. Meanwhile, multiple claystone beds are prominent near the PTB, South China. The nature and origin of the volcanic ashes therefore provide clue to find out the trigger of the PTB mass extinction. Following previous studies (Gao et al., 2013), 21 PTB ash beds from three additional PTB sections, namely the Shangsi, Jianshi and Meishan, all from South China have been systematically sampled. The U-Pb ages, trace elements, and Hf-isotope compositions of zircon grains from these ash beds were analyzed using LA-ICPMS and LA-MC-ICPMS. Volcanic ash geochemistry shows presence of Rhyolite or Dacite and reveal a collision-tectonic setting. Zircons from these ash layers yield comparatively low Nb/Hf and high Th/Nb ratios, dropping into the range of arc/orogenic-related settings. Zircon Hf-isotope compositions show that ɛHf(t) values vary from -11.7 to 1.8, indicating that at least two kinds of crustal component have been involved: juvenile lower crust and ancient middle-upper crust. The ash beds (Ss27a, Js129, Js130, Ms25, Ms26) near biotic extinction horizon have significant larger variation range of ɛHf(t) and relatively positive averages, implying that more juvenile lower crustal material had contributed to the volcanisms. This means that these volcanisms may have originated deeper depth or the volcanisms erupted so rapidly that there was no enough time for the mixing of different components. The volcanisms associated with biotic extinction should be the most intense and have greatest heat put. Spatial and temporal distributions of ash beds from thirty PTB sections worldwide reveal that the PTB volcanic ashes occurred only in the Paleo-Tethys region, suggesting that the volcanisms may be likely limited to the Paleo-Tethys continental

  6. Submicron area NbN/MgO/NbN tunnel junctions for SIS mixer applications

    NASA Technical Reports Server (NTRS)

    Leduc, H. G.; Judas, A.; Cypher, S. R.; Bumble, B.; Hunt, B. D.

    1991-01-01

    The development of submicron area mixer elements for operation in the submillimeter wave range is discussed. High-current-density NbN/MgO/NbN tunnel junctions with areas down to 0.1 sq microns have been fabricated in both planar and edge geometries. The planar junctions were fabricated from in situ deposited trilayers using electron-beam lithography to pattern submicron area mesas. Modifications of fabrication techniques used in larger-area NbN tunnel junctions are required and are discussed. The NbN/MgO/NbN edge junction process using sapphire substrates has been transferred to technologically important quartz substrates using MgO buffer layers to minimize substrate interactions. The two junction geometries are compared and contrasted in the context of submillimeter wave mixer applications.

  7. NbN/MgO/NbN SIS tunnel junctions for submm wave mixers

    NASA Technical Reports Server (NTRS)

    Stern, J. A.; Hunt, B. D.; Leduc, H. G.; Judas, A.; Mcgrath, W. R.; Cypher, S. R.; Khanna, S. K.

    1989-01-01

    The authors report on the fabrication and testing of all-refractory NbN/MgO/NbN SIS (superconductor-insulator-superconductor) tunnel junctions for use as high-frequency mixers. Progress in the development of techniques for the fabrication of submicron-area tunnel junctions is described. Junction structures which have been investigated include mesa, crossline, and edge geometries. Using reactive sputtering techniques, NbN tunnel junctions with critical currents in excess of 104 A/sq cm have been fabricated with Vm values as high as 65 mV and areas down to 0.1 sq micron. Specific capacitance measurements on NbN/MgO/NbN mesa-type tunnel junctions give values in the range 60-90 fF/sq micron. These SIS tunnel junctions have been integrated with antennas and coupling structures for mixer tests in a waveguide receiver at 207 GHz. Preliminary mixer results are reported.

  8. Large Nd-Hf isotopic decoupling in Himalayan River Sediments

    NASA Astrophysics Data System (ADS)

    Garcon, M.; Chauvel, C.; France-Lanord, C.

    2011-12-01

    Nd isotopic compositions of river sediments are widely used to trace sediment provenance in the Himalayan mountain range. In contrast, Hf isotopic compositions are not used even though they are excellent proxies to record the history of continental areas (Hawkesworth and Kemp, Chem. Geol. 226, 2006). Here, we focus on the Hf isotopic message carried by Himalayan river sediments and combine it to the more classical Nd isotopes to better understand the behavior of the two systems during erosion. We report Nd-Hf isotopic compositions of bedloads and suspended loads sampled at different depths in the Narayani River in Nepal (upstream of the Ganga floodplain), in the Ganga River in Bangladesh (downstream of the Ganga floodplain) and in the Yamuna River, a major tributary of the Ganga in India. Nd-Hf isotopic compositions of bedloads span a small range of values (-18< ɛNd <-16 and -30< ɛHf <-23) and lie next to the terrestrial array in a ɛHf vs. ɛNd diagram. Nd isotopic compositions are similar to those of the main Himalayan sources. By contrast, suspended loads have much more variable ratios (-19< ɛNd <-10 and -25< ɛHf <-7) and plot well above the terrestrial array in a ɛHf vs. ɛNd diagram. Like oceanic sediments, they are characterized by high ɛHf compared to their ɛNd. We explain this Nd-Hf decoupling by mineralogical sorting, a process that enriches bottom sediments in coarse and dense minerals, such as unradiogenic zircons, while the surface sediments are enriched in fine material with radiogenic Hf signatures. Bedloads and suspended loads, collected at the same sampling site at different depths in the Narayani and Ganga Rivers, share similar ɛNd. However, differences of about 5 ɛNd and 15 ɛHf units are observed between bedload and surface samples in the Yamuna River. In this river, both Nd and Hf isotopic ratios decrease from surface to bottom. We believe that part of the Hf isotopic variability is due to mineralogical sorting but the rest of it

  9. LiNbO3 Cylinder Fiber

    NASA Technical Reports Server (NTRS)

    Kornreich, Philip

    2004-01-01

    We have successfully fabricate optical fiber with a thin layer of LiNbO3 at the boundary of the glass core and clear glass cladding. The construction of this fiber is based on our successful Semiconductor Cylinder Fibers (SCF). A schematic representation of a LiN bo, Cylinder Fiber. These fibers can be used as light modulators, sonar detectors and in other applications. The core diameter of the fiber is sufficiently small compared to the light wavelength and the indices of refraction of the core and cladding glasses are sufficiently close in value so that there is sufficient light at the core cladding boundary to interact with the LiNbO3 layer. This fiber functions best when just a single light mode propagates through the fiber. The idea for a LiNbO3 Cylinder Fiber came from Dr. Tracee Jamison of NASA. The optical properties of LiNbO3 can be changed with strain or the application of an electric field. Thus these fibers can be used as acoustic sensors as for example in a sonar. They can also be used as electric field operated light modulators. However, for this application the fibers would be made with a cross section in the form of a "D". The core with its surrounding LiNbO, layer would be close to the flat portion of the "D" shaped fiber. Two metal contacts would be deposited on the flat portion of the fiber on either side of the core. A voltage applied across these contacts will result in an electric field in the core region that can be used for modulating the optical properties of the LiNbO3 layer. To our knowledge this is the first ever LiNbO3 Cylinder Fiber made.

  10. Power-Stepped HF Cross Modulation Experiments at HAARP

    NASA Astrophysics Data System (ADS)

    Greene, S.; Moore, R. C.; Langston, J. S.

    2013-12-01

    High frequency (HF) cross modulation experiments are a well established means for probing the HF-modified characteristics of the D-region ionosphere. In this paper, we apply experimental observations of HF cross-modulation to the related problem of ELF/VLF wave generation. HF cross-modulation measurements are used to evaluate the efficiency of ionospheric conductivity modulation during power-stepped modulated HF heating experiments. The results are compared to previously published dependencies of ELF/VLF wave amplitude on HF peak power. The experiments were performed during the March 2013 campaign at the High Frequency Active Auroral Research Program (HAARP) Observatory. HAARP was operated in a dual-beam transmission format: the first beam heated the ionosphere using sinusoidal amplitude modulation while the second beam broadcast a series of low-power probe pulses. The peak power of the modulating beam was incremented in 1-dB steps. We compare the minimum and maximum cross-modulation effect and the amplitude of the resulting cross-modulation waveform to the expected power-law dependence of ELF/VLF wave amplitude on HF power.

  11. Critical Questions about PARADIGM-HF and the Future.

    PubMed

    Chen, Chen-Huan

    2016-07-01

    Cardiovascular (CV) diseases in general and heart failure (HF) in particular are major contributors to death and morbidity and are also recognized as important drivers of health care expenditure. The PARADIGM-HF trial was a pivotal trial designed to compare the long-term effects of LCZ696 with enalapril in patients with symptomatic HF with reduced ejection fraction (HFrEF). This review article presents an in-depth view of the PARADIGM-HF trial and the implications of the results in the management of patients with HF and is based on peer reviewed manuscripts, editorials, perspectives and opinions written about the PARADIGM-HF trial. The article presents the key safety and efficacy results of the trial with specific emphasis on the clinical implications of these findings. The review highlights the highly statistically significant, 20% reduction in the primary composite endpoint of cardiovascular death or HF hospitalization, and a 16% reduction in the risk of death from any cause. It also provides an overview of the design, clinical findings, limitations and special areas of clinical interest. The review discusses the future of LCZ696 and additional trials that seek to answer questions in other sub-populations of patients with HF. The article reiterates what has been concluded by many experts in the field of HF- the introduction of LCZ696 into routine clinical care, while dependent on the regulatory approvals in various countries as well as acceptance by physicians, payers and patients, will change the treatment landscape for patients with HFrEF.

  12. Critical Questions about PARADIGM-HF and the Future

    PubMed Central

    Chen, Chen-Huan

    2016-01-01

    Cardiovascular (CV) diseases in general and heart failure (HF) in particular are major contributors to death and morbidity and are also recognized as important drivers of health care expenditure. The PARADIGM-HF trial was a pivotal trial designed to compare the long-term effects of LCZ696 with enalapril in patients with symptomatic HF with reduced ejection fraction (HFrEF). This review article presents an in-depth view of the PARADIGM-HF trial and the implications of the results in the management of patients with HF and is based on peer reviewed manuscripts, editorials, perspectives and opinions written about the PARADIGM-HF trial. The article presents the key safety and efficacy results of the trial with specific emphasis on the clinical implications of these findings. The review highlights the highly statistically significant, 20% reduction in the primary composite endpoint of cardiovascular death or HF hospitalization, and a 16% reduction in the risk of death from any cause. It also provides an overview of the design, clinical findings, limitations and special areas of clinical interest. The review discusses the future of LCZ696 and additional trials that seek to answer questions in other sub-populations of patients with HF. The article reiterates what has been concluded by many experts in the field of HF- the introduction of LCZ696 into routine clinical care, while dependent on the regulatory approvals in various countries as well as acceptance by physicians, payers and patients, will change the treatment landscape for patients with HFrEF. PMID:27471351

  13. A hybrid origin for two Cretaceous monzonitic plutons in eastern Zhejiang Province, Southeast China: Geochronological, geochemical, and Sr-Nd-Hf isotopic evidence

    NASA Astrophysics Data System (ADS)

    Liu, Liang; Qiu, Jian-Sheng; Zhao, Jiao-Long

    2016-01-01

    Monzonites can provide important information about the nature of the mantle sources and the mechanism of crust-mantle interactions. However, details on the origin of Late Mesozoic monzonites in the Southeastern China remain poorly constrained. This paper presents whole-rock geochemical, Sr-Nd isotopic and zircon U-Pb and Hf isotopic data for two monzonitic plutons (Huangtanyang and Kanggu) in eastern Zhejiang Province, with the aim of elucidating their petrogenesis, and providing important insights into the process of crust-mantle interaction. LA-ICP-MS zircon U-Pb dating results imply that the Huangtanyang and Kanggu quartz monzonites were emplaced in Cretaceous (104-109 Ma). All quartz monzonites are intermediate to acidic, metaluminous to weakly peraluminous, subalkaline, and K-rich in composition. They are enriched in large ion lithophile (e.g., Rb, Ba and Pb) and light rare earth elements, depleted in high-field strength elements (e.g., Nb, Ta, and Ti), and show weakly negative or no Eu anomalies (δEu = 0.78-1.02). All quartz monzonites have homogeneous initial ISr values (0.7084-0.7090) and εNd(t) values (-7.50 to -6.84). They are characterised by highly variable zircon Hf isotopic compositions, with εHf(t) values ranging from -13.3 to -5.7. The combined geochemical evidences (such as high Mg# values, low Nb/U and Ta/U ratios, and variable zircon Hf isotopic compositions) suggests that both depleted asthenospheric and metasomatically enriched mantle components were involved in the formation of the monzonites. The existence of some zircons with unusually low εHf(t) values (low to -13.3) and Palaeoproterozoic two-stage Hf model ages from the Huangtanyang and Kanggu quartz monzonites also argues strongly for Palaeoproterozoic crustal involvement. Magma mixing played a dominated role in the genesis of these monzonites, as indicated by their wide range in zircon Hf isotopic compositions and the occurrence of mafic microgranular enclaves (MMEs). The MMEs show

  14. Coupling with a narrow-band-gap semiconductor for the enhancement of visible-light photocatalytic activity: preparation of Bi2OxS3-x/Nb6O17 and application to the degradation of methyl orange.

    PubMed

    Yan, Gang; Shi, Hongfei; Tan, Huaqiao; Zhu, Wanbin; Wang, Yonghui; Zang, Hongying; Li, Yangguang

    2016-09-21

    A series of 2D sheet Bi2OxS3-x/Nb6O17 (Bi/Nb) heterostructure photocatalysts were synthesized through a facile hydrothermal vulcanization method between Bi(3+) exchanged K4Nb6O17 and thiourea (NH2CSNH2). XRD results confirm that the heterostructures were composed of Bi2OxS3-x and Nb6O17. HRTEM indicates that Bi2OxS3-x was successfully intercalated into layers of K4Nb6O17. Such large interfacial contacts can be beneficial to the transfer and separation of photogenerated charge carriers. Thus the composites exhibit good photocatalytic performance for the degradation of methyl orange (MO) under visible light irradiation (λ > 400 nm), which is superior to that of both precursors, pure Bi2S3 and K4Nb6O17. Radical capture tests reveal that photogenerated holes h(+) and ˙O2(-) play important roles in the photodegradation of MO. And based on the UV-visible diffuse reflectance spectra (DRS) and the band gap of the semiconductors, the mechanism of the enhanced visible light photocatalytic activity of these composites has been proposed.

  15. Transionospheric HF Propagation Experiments at Auroral Latitudes

    NASA Astrophysics Data System (ADS)

    James, H. G.; Benson, R. F.

    2004-05-01

    High-frequency (HF) propagation experiments are planned as part of the Enhanced Polar Outflow Probe (ePOP) satellite mission to be launched for the Canadian Space Agency in 2007. Ground transmitters such as the CADI ionosondes and the SuperDARN radars will be operated collaboratively to emit waves for detection by the Radio Receiver Instrument of ePOP during passes in the vicinity. The scientific goals include improved understanding of F-region morphology and dynamics, wave scattering and microphysical plasma processes. Partly as preparation for ePOP, transionospheric HF propagation data recorded by the receivers of the ISIS-I and ISIS-II spacecraft are being analyzed. The measurements were made in spring-summer 1978. A ground transmitter was built in Ottawa especially for the project. Some of the ISIS data were obtained in digital form from http://nssdc.gsfc.nasa.gov/space/isis/isis-status.html. These digital data are being surveyed in an attempt to establish repeatable propagation characteristics. From these characteristics, the goal is to understand the processes experienced by waves passing through the ionosphere. Several tens of ISIS-II passes recorded at a fixed frequency of 9.303 MHz have been examined. Swept-frequency ionograms interleaved with these fixed-frequency measurements allow two-dimensional electron density distributions to be modeled in altitude and latitude. Computer code has been developed for three-dimensional ray tracing. The computed latitudinal extent of the zone irradiated at the ISIS-II altitude is approximately as observed. Within this "iris" of accessibility, the peak intensity of waves recorded at the spacecraft is within about 10 dB of what is computed with a link calculation. This calculation is based on a model for the 1-kW transmitter, a radiant-transfer calculation that follows the focusing/defocusing of rays using a three-ray pencil between ground and the satellite, and the orientation of the sounder receiving dipole. Poleward

  16. Beta Decay Half-Life of 84Mo

    NASA Astrophysics Data System (ADS)

    Stoker, J. B.; Mantica, P. F.; Bazin, D.; Bickley, A.; Becerril, A.; Crawford, H.; Cruse, K.; Estrade, A.; Mosby, M.; Guess, C. J.; Hitt, G. W.; Lorusso, G.; Matos, M.; Meharchand, R.; Minamisono, K.; Montes, F.; Pereira, J.; Perdikakis, G.; Pinter, J. S.; Schatz, H.; Vredevoogd, J.; Zegers, R. G. T.

    2008-10-01

    The β-decay half-life ^84Mo governs leakage out of the Zr-Nb cycle, a high temperature rp-process endpoint in x-ray binaries [1]. Treatment of the background and the poor statistics accumulated during the previous half-life measurement leave questions about statistical and systematic errors. We have remeasured the half-life of ^84Mo using a concerted setup of the NSCL β-Counting System [3] and 16 detectors from the Segmented Germanium Array [4]. We will report the half-life for ^84Mo, deduced using 40 times the previous sample size. The application of the NSCL RF Fragment Separator to remove unwanted isotopes, and hence reduce background for the half-life measurement, will also be discussed. [1] H. Schatz et al., Phys. Rep. 294, 167 1998 [2] P. Kienle et al., Prog. Part. Nuc. Phys. 46, 73 2001 [3] J. Prisciandaro et al., NIM A 505, 140 2003 [4] W. Mueller et al., NIM A 466, 492 2001 [5] D. Gorelov et al. PAC 2005, Knoxville, TN, May 16-20

  17. Superconductivity with extremely large upper critical fields in Nb2Pd0.81S5

    NASA Astrophysics Data System (ADS)

    Zhang, Qiu; Li, Gang; Rhodes, Daniel; Kiswandhi, Andhika; Basara, Tiglet; Sung, J.; Siegrist, Theo; Johannes, Michelle; Balicas, Luis

    2013-03-01

    Here, we report the discovery of superconductivity in a new transition metal-chalcogenide compound, i.e. Nb2Pd0.81S5, with a transition temperature Tc ≅ 6.6 K. Despite its relatively low Tc, it displays remarkably high and anisotropic superconducting upper critical fields, e.g. μ0Hc 2 (T --> 0 K) > 37 T for fields applied along the crystallographic b-axis. This value is considerably larger than the value reported for the technologically relevant Nb3Sn compound (μ0Hc 2 ~ 30 T, with Tc = 18 K)1,2. Its ratio of μ0Hc 2 (T --> 0 K) to Tc, is also larger than those of the new Fe based superconductors, e.g. β-FeSe (20 T/8.7 K)3, Ba1-xKxFe2As2 (~ 70 T/28 K)4, and even higher than the reported ratio for the Chevrel-phase PbMo6S8(60T/13.3 K)5 compound. For a field applied perpendicularly to the b-axis, μ0Hc 2 shows a linear dependence in temperature which coupled to a temperature-dependent anisotropy of the upper critical fields, suggests that Nb2Pd0.81S5 is a multi-band superconductor. This is confirmed by band structure calculations which reveal nearly cylindrical and quasi-one-dimensional Fermi surface sheets having hole and electron character, respectively.

  18. Control of the static and high-frequency magnetic properties of perpendicular anisotropic Co–HfN granular films through insertion of HfN interlayers

    NASA Astrophysics Data System (ADS)

    Cao, Yang; Zhang, Yiwen; Ohnuma, Shigehiro; Kobayashi, Nobukiyo; Masumoto, Hiroshi

    2017-04-01

    We propose a multilayer granular structure wherein Hf–nitride (HfN) interlayers are inserted into Co–HfN granular films with perpendicular magnetic anisotropy (PMA) to control their static and high-frequency magnetic properties. The transition between soft ferromagnetic properties and PMA was achieved by varying the thickness of Co–HfN layers (2–30 nm) and HfN interlayers (1–4 nm). The resonance frequency of the Co–HfN (24 nm)/HfN films decreased from 2 to 0.9 GHz with increasing HfN interlayer thickness, owning to the separation of the columnar granules and reduced interlayer interaction between Co–HfN granular layers via a HfN interlayer.

  19. High-RRR thin-films of NB produced using energetic condensation from a coaxial, rotating vacuum ARC plasma (CEDTM)

    SciTech Connect

    Enrique Francisco Valderrama, Colt James, Mahadevan Krishnan, Xin Zhao, Larry Phillips, Charles Reece, Kang Seo

    2012-07-01

    We have recently demonstrated unprecedentedly high values of RRR (up to 542) in thin-films of pure Nb deposited on a-plane sapphire and MgO crystal substrates. The Nb films were grown using a vacuum arc discharge struck between a reactor grade Nb cathode rod (RRR {approx} 30) and a coaxial, semi-transparent Mo mesh anode, with a heated substrate placed just outside it. The substrates were pre-heated for several hours prior to deposition at different temperatures. Low pre-heat temperatures (<300 C) and deposition temperatures (<300 C) give low RRR (<50) films, whereas higher pre-heat (700 C) and coating temperatures (500 C) give RRR=214 on a-sapphire and RRR=542 on MgO. XRD (Bragg-Brentano scans and Pole Figures), EBSD and SIMS data reveal several features: (1) on asapphire, higher temperatures show better 3D registry for epitaxial growth of Nb; the crystal structure evolves from textured, polycrystalline (with twins) to single-crystal; (2) on MgO, there is a transition from {l_brace}110{r_brace} planes to {l_brace}100{r_brace} as the temperature is increased beyond 500 C. The dramatic increase in RRR (from {approx}10 at <300 C to {approx}500 at >600 C) is correlated with better epitaxial crystal structure in both a-sapphire and MgO substrate grown films. However, the SIMS data reveal that the most important requirement for high-RRR Nb films on either substrate is the reduction of impurities in the film, especially hydrogen. The hydrogen content in the MgO grown films is 1000 times lower than in bulk Nb tested as a reference from SRF cavity grade Nb. This result has potential implications for SRF accelerators. Coating bulk Nb cavities with an MgO layer followed by our CEDTM deposited Nb films, might create superior SRF cavities that would avoid Q-slope and operate at higher peak fields.

  20. Genesis and open-system evolution of Quaternary magmas beneath southeastern margin of Tibet: Constraints from Sr-Nd-Pb-Hf isotope systematics

    NASA Astrophysics Data System (ADS)

    Zou, Haibo; Ma, Mingjia; Fan, Qicheng; Xu, Bei; Li, Shuang-Qing; Zhao, Yongwei; King, David T.

    2017-02-01

    Post-collisional volcanic rocks on the Tibetan Plateau and its margins contain valuable information about the geodynamic processes associated with this Cenozoic continent-continent collision. The Quaternary Tengchong volcanic field at the southeastern margin of the Tibetan Plateau formed high-potassium calc-alkaline volcanic rocks. Herein, we present comprehensive Nd-Sr-Pb-Hf isotopic and elemental data for trachybasalts, basaltic trachyandesites, and trachyandesites from four Quaternary Tengchong volcanoes (Maanshan, Dayingshan, Heikongshan, and Laoguipo) in order to understand their magma genesis and evolution as well as tectonic significance. Good correlations between SiO2 content and the ratios 87Sr/86Sr, 143Nd/144Nd, 206Pb/204Pb, and 177Hf/176Hf for these Quaternary volcanics strongly suggest that the combined assimilation and fractional crystallization (AFC) was an important process in the origin of basaltic trachyandesites and trachyandesites. High Y and Yb contents and low Sr/Y ratios of these basaltic trachyandesites and trachyandesites are uncharacteristic of adakites that formed by partial melting of eclogitic lower crust or partial melting of basaltic oceanic crust with eclogite as a restite. A combined assimilation-fractional crystallization model is proposed for these basaltic trachyandesites and trachyandesites. Nd-Sr-Pb-Hf isotopes for the uncontaminated Tengchong magma (trachybasalts with SiO2 < 52.5 wt.% and MgO > 5.5% wt.%) reflect a heterogeneous enriched mantle source. High Th/U, Th/Ta, and Rb/Nb ratios and Nd-Sr-Pb-Hf isotope characteristics of the uncontaminated magmas suggest that the enriched mantle beneath Tengchong formed as a result of subduction of clay-rich sediments, which probably came from the Indian continental plate. Partial melting of the enriched mantle was generated by deep continental subduction coupled with recent regional extension in the Tengchong area.

  1. Design of refractory high-entropy alloys

    SciTech Connect

    Gao, M. C.; Carney, C. S.; Dogan, O. N.; Jablonksi, P. D.; Hawk, J. A.; Alman, D. E.

    2015-09-15

    Here, this report presents a design methodology for refractory high-entropy alloys with a body-centered cubic (bcc) structure using select empirical parameters (i.e., enthalpy of mixing, atomic size difference, Ω-parameter, and electronegativity difference) and CALPHAD approach. Sixteen alloys in equimolar compositions ranging from quinary to ennead systems were designed with experimental verification studies performed on two alloys using x-ray diffraction, energy-dispersive spectroscopy, and scanning electron microscopy. Two bcc phases were identified in the as-cast HfMoNbTaTiVZr, whereas multiple phases formed in the as-cast HfMoNbTaTiVWZr. Observed elemental segregation in the alloys qualitatively agrees with CALPHAD prediction. Comparisons of the thermodynamic mixing properties for liquid and bcc phases using the Miedema model and CALPHAD are presented. This study demonstrates that CALPHAD is more effective in predicting HEA formation than empirical parameters, and new single bcc HEAs are suggested: HfMoNbTiZr, HfMoTaTiZr, NbTaTiVZr, HfMoNbTaTiZr, HfMoTaTiVZr, and MoNbTaTiVZr.

  2. Design of Refractory High-Entropy Alloys

    NASA Astrophysics Data System (ADS)

    Gao, M. C.; Carney, C. S.; Doğan, Ö. N.; Jablonksi, P. D.; Hawk, J. A.; Alman, D. E.

    2015-11-01

    This report presents a design methodology for refractory high-entropy alloys with a body-centered cubic (bcc) structure using select empirical parameters (i.e., enthalpy of mixing, atomic size difference, Ω-parameter, and electronegativity difference) and CALPHAD approach. Sixteen alloys in equimolar compositions ranging from quinary to ennead systems were designed with experimental verification studies performed on two alloys using x-ray diffraction, energy-dispersive spectroscopy, and scanning electron microscopy. Two bcc phases were identified in the as-cast HfMoNbTaTiVZr, whereas multiple phases formed in the as-cast HfMoNbTaTiVWZr. Observed elemental segregation in the alloys qualitatively agrees with CALPHAD prediction. Comparisons of the thermodynamic mixing properties for liquid and bcc phases using the Miedema model and CALPHAD are presented. This study demonstrates that CALPHAD is more effective in predicting HEA formation than empirical parameters, and new single bcc HEAs are suggested: HfMoNbTiZr, HfMoTaTiZr, NbTaTiVZr, HfMoNbTaTiZr, HfMoTaTiVZr, and MoNbTaTiVZr.

  3. Design of refractory high-entropy alloys

    DOE PAGES

    Gao, M. C.; Carney, C. S.; Dogan, O. N.; ...

    2015-09-15

    Here, this report presents a design methodology for refractory high-entropy alloys with a body-centered cubic (bcc) structure using select empirical parameters (i.e., enthalpy of mixing, atomic size difference, Ω-parameter, and electronegativity difference) and CALPHAD approach. Sixteen alloys in equimolar compositions ranging from quinary to ennead systems were designed with experimental verification studies performed on two alloys using x-ray diffraction, energy-dispersive spectroscopy, and scanning electron microscopy. Two bcc phases were identified in the as-cast HfMoNbTaTiVZr, whereas multiple phases formed in the as-cast HfMoNbTaTiVWZr. Observed elemental segregation in the alloys qualitatively agrees with CALPHAD prediction. Comparisons of the thermodynamic mixing properties formore » liquid and bcc phases using the Miedema model and CALPHAD are presented. This study demonstrates that CALPHAD is more effective in predicting HEA formation than empirical parameters, and new single bcc HEAs are suggested: HfMoNbTiZr, HfMoTaTiZr, NbTaTiVZr, HfMoNbTaTiZr, HfMoTaTiVZr, and MoNbTaTiVZr.« less

  4. Grindability of cast Ti-Hf alloys.

    PubMed

    Kikuchi, Masafumi; Takahashi, Masatoshi; Sato, Hideki; Okuno, Osamu; Nunn, Martha E; Okabe, Toru

    2006-04-01

    As part of our systematic studies characterizing the properties of titanium alloys, we investigated the grindability of a series of cast Ti-Hf alloys. Alloy buttons with hafnium concentrations up to 40 mass% were made using an argon-arc melting furnace. Each button was cast into a magnesia-based mold using a dental titanium casting machine; three specimens were made for each metal. Prior to testing, the hardened surface layer was removed. The specimens were ground at five different speeds for 1 min at 0.98 N using a carborundum wheel on an electric dental handpiece. Grindability was evaluated as the volume of metal removed per minute (grinding rate) and the volume ratio of metal removed compared to the wheel material lost (grinding ratio). The data were analyzed using ANOVA. A trend of increasing grindability was found with increasing amounts of hafnium, although there was no statistical difference in the grindability with increasing hafnium contents. We also found that hafnium may be used to harden or strengthen titanium without deteriorating the grindability.

  5. Ionospheric heating with oblique HF waves

    NASA Astrophysics Data System (ADS)

    Field, Edward C., Jr.; Bloom, Ron M.

    1990-10-01

    Calculations of ionospheric electron density perturbations and ground-level signal changes produce by intense oblique high frequency (HF) transmitters are presented. This analysis considers radio field focusing at caustics, the consequent joule-heating of the surrounding plasma, heat conduction, diffusion, and recombination processes: these being the effects of a powerful oblique 'modifying' wave. It neglects whatever plasma instabilities might occur. Then effects on a secondary 'test' wave that is propagated along the same path as the first are investigated. Calculations predict ground-level field-strength reductions of several dB in the test wave for modifying waves having ERP in the 85 to 90 dBW range. These field-strength changes are similar in sign, magnitude, and location to ones measured in Soviet experiments. The results are sensitive to the model ionosphere assumed, so future experiments should employ the widest possible range of frequencies and propagation conditions. An effective power of 90 dBW seems to be a sort of threshold that, if exceeded, results in substantial rather than small signal changes. The conclusions are based solely on joule-heating and subsequent defocusing of waves passing through caustic regions.

  6. Pulsed HF laser ablation of dentin

    NASA Astrophysics Data System (ADS)

    Papagiakoumou, Eirini I.; Papadopoulos, Dimitris N.; Makropoulou, Mersini I.; Khabbaz, Maruan G.; Serafetinides, Alexander A.

    2005-03-01

    The interaction of a TEA (Transversally Excited Atmospheric pressure) corona preionized oscillator double amplifier HF (hydrogen fluoride) laser beam with dentin tissue is reported. Pulses of 39 ns in the wavelength range of 2.65-3.35 μm and output energies in the range of 10-45 mJ, in a predominantly TEM00 beam were used to interact with dentin tissue. Ablation experiments were conducted with the laser beam directly focused on the tissue. Several samples of freshly extracted human teeth were used, cut longitudinally in facets of about 1mm thick and stored in phosphate buffered saline after being cleaned from the soft tissue remains. The experimental data (ablation thresholds, ablation rates) are discussed with respect to the ablation mechanism(s). Adequate tissue removal was observed and the ablation behavior was, in the greates part of the available fluences, almost linear. From the microscopic examination of teh samples, in a scanning electron microscope (SEM), the irradiated surfaces displayed oval craters (reflecting the laser beam shape) with absence of any melting or carbonization zone. It is suggested that the specific laser removes hard tissue by a combined photothermal and plasma mediated ablation mechanism, leaving a surface free from thermal damage and with a well-shaped crater.

  7. High temperature coarsening of Cr2Nb precipitates in Cu-8 Cr-4 Nb alloy

    NASA Technical Reports Server (NTRS)

    Anderson, Kenneth Reed

    1996-01-01

    A new high-temperature-strength, high-conductivity Cu-Cr-Nb alloy with a CrNb ratio of 2:1 was developed to achieve improved performance and durability. The Cu-8 Cr4 Nb alloy studied has demonstrated remarkable thermal and microstructural stability after long exposures at temperatures up to 0.98 T(sub m). This stability was mainly attributed to the slow coarsening kinetics of the Cr2Nb precipitates present in the alloy. At all temperatures, the microstructure consists of a bimodal and sometimes trimodal distribution of strengthening Cr2Nb precipitates, depending on precipitation condition, i.e. from liquid or solid solution, and cooling rates. These precipitates remain in the same size range, i.e. large precipitates of approximately I pm, and small precipitates less dm 300 nm, and effectively pin the grain boundaries thus retaining a fine grain size of 2.7 micro-m after 100 h at 1323 K. (A relatively small number of Cr-rich and Nb-rich particles were also present.) This grain boundary pinning and sluggish coarsening of Cr2Nb particles explain the retention of good mechanical properties after prolonged holding at very high temperatures, e.g., 75% of the original hardness after aging for 100 h at 1273 K. Application of LSW-based coarsening models indicated that the coarsening kinetics of the large precipitates are most likely governed by grain boundary diffsion and, to a lesser extent, volume diffusion mechanisms.

  8. Na1.67Mn2.17(MoO4)3

    PubMed Central

    Bouzidi, Chahira; Zid, Mohamed Faouzi; Driss, Ahmed; Frigui, Wafa

    2014-01-01

    The title compound, disodium dimanganese(II) tris­[ortho­molybdate(VI)], was prepared by solid-state reactions. The structure can be described as being composed of Mn2Mo2O14 double-chains that are inter­connected by corner-sharing with MoO4 tetra­hedra, leading to a three-dimensional framework with channels propagating in [100] and [001] in which the Na+ counter-cations are located. One of these Na sites is located on an inversion centre, one is partially occupied [occupancy 0.341 (9)], and one is statistically occupied by Na and Mn in a ratio of 0.829 (5):0.171 (5). Na1.67Mn2.17(MoO4)3 is isotypic with structures of the Ag2 M 2(MoO4)3 (M = Zn, Mg, Co, Mn) family. A comparative structural description is provided between the structure of the title compound and those of related phases containing (MXO8)n chains (M = Mo, Mn and X = As) or M 2O10 (M = Mo, Mn, Nb, V) dimers. PMID:24826084

  9. Low-Frequency Waves in HF Heating of the Ionosphere

    NASA Astrophysics Data System (ADS)

    Sharma, A. S.; Eliasson, B.; Milikh, G. M.; Najmi, A.; Papadopoulos, K.; Shao, X.; Vartanyan, A.

    2016-02-01

    Ionospheric heating experiments have enabled an exploration of the ionosphere as a large-scale natural laboratory for the study of many plasma processes. These experiments inject high-frequency (HF) radio waves using high-power transmitters and an array of ground- and space-based diagnostics. This chapter discusses the excitation and propagation of low-frequency waves in HF heating of the ionosphere. The theoretical aspects and the associated models and simulations, and the results from experiments, mostly from the HAARP facility, are presented together to provide a comprehensive interpretation of the relevant plasma processes. The chapter presents the plasma model of the ionosphere for describing the physical processes during HF heating, the numerical code, and the simulations of the excitation of low-frequency waves by HF heating. It then gives the simulations of the high-latitude ionosphere and mid-latitude ionosphere. The chapter also briefly discusses the role of kinetic processes associated with wave generation.

  10. Sequential sputtered Co-HfO2 granular films

    NASA Astrophysics Data System (ADS)

    Chadha, M.; Ng, V.

    2017-03-01

    A systematic study of magnetic, magneto-transport and micro-structural properties of Co-HfO2 granular films fabricated by sequential sputtering is presented. We demonstrate reduction in ferromagnetic-oxide formation by using HfO2 as the insulting matrix. Microstructure evaluation of the films showed that the film structure consisted of discrete hcp-Co grains embedded in HfO2 matrix. Films with varying compositions were prepared and their macroscopic properties were studied. We correlate the variation in these properties to the variation in film microstructure. Our study shows that Co-HfO2 films with reduced cobalt oxide and varying properties can be prepared using sequential sputtering technique.

  11. EPA study on HF acid could spell trouble for refiners

    SciTech Connect

    Lobsenz, G.

    1993-06-30

    Hydrofluoric acid, a highly toxic substance used at petroleum refineries, uranium fuel fabrication plants and many other industrial plants, could cause {open_quotes}severe impacts{close_quotes} more than six miles downwind of a worst-case accident, according to preliminary findings of an Environmental Protection Agency study. The study, also found that local governments and communities near some HF facilities were largely unaware of the serious risks posed by an HF release and the protective measures that were needed. HF is present at hundreds of industrial facilities nationwide, including petroleum refineries, where it is used to produce clean-burning gasoline, uranium fuel fabrication facilities and manufacturers of refrigerants, electronics, detergents and drugs. Among other issues, petroleum refiners are strongly concerned about suggestions from environmentalists that EPA consider requiring the industry to phase out HF alkylation units and replace them with an alternative process using sulfuric acid.

  12. Lu-Hf constraints on the evolution of lunar basalts

    NASA Technical Reports Server (NTRS)

    Fujimaki, H.; Tatsumoto, M.

    1984-01-01

    It is shown that a cumulate-remelting model best explains the recently acquired data on the Lu-Hf systematics of lunar mare basalts. The model is constructed using Lu and Hf concentration data and is strengthened by Hf isotopic evidence of Unruh et al. (1984). It is shown that the similarity in MgO/FeO ratios and Cr2O3 content in high-Ti and low-Ti basalts are not important constraints on lunar basalt petrogenesis. The model demonstrates that even the very low Ti or green glass samples are remelting products of a cumulate formed after at least 80-90 percent of the lunar magma ocean had solidified. In the model, all the mare basalts and green glasses were derived from 100-150 km depth in the lunar mantle. The Lu-Hf systematics of KREEP basalts clearly indicate that they would be the final residual liquid of the lunar magma ocean.

  13. Superconducting properties of the noncentrosymmetric superconductor Re6Hf

    NASA Astrophysics Data System (ADS)

    Singh, D.; Hillier, A. D.; Thamizhavel, A.; Singh, R. P.

    2016-08-01

    We report synthesis and detailed characterization of the noncentrosymmetric superconductor Re6Hf using powder x-ray diffraction (XRD), magnetization, transport, and thermodynamic measurements. XRD confirmed the noncentrosymmetric, α -Mn cubic structure in Re6Hf with the cubic cell parameter a =9.6850 (3 ) Å. Resistivity, DC, and AC magnetization measurements confirmed the type-II superconductivity in Re6Hf with the transition temperature Tconset˜5.96 K, having the lower critical field Hc 1(0 ) 5.6 mT and upper critical field Hc 2(0 ) 12.2 T. The electronic specific heat data fits well with the single-gap BCS model. The Sommerfeld coefficient (γ ) also shows linear relation with the magnetic field. All above results suggest s -wave superconductivity in Re6Hf .

  14. Theoretical Assessment of 178m2Hf De-Excitation

    SciTech Connect

    Hartouni, E P; Chen, M; Descalle, M A; Escher, J E; Loshak, A; Navratil, P; Ormand, W E; Pruet, J; Thompson, I J; Wang, T F

    2008-10-06

    This document contains a comprehensive literature review in support of the theoretical assessment of the {sup 178m2}Hf de-excitation, as well as a rigorous description of controlled energy release from an isomeric nuclear state.

  15. Spectroscopic constants and potential energy curves of HfH

    NASA Astrophysics Data System (ADS)

    Balasubramanian, K.; Das, Kalyan K.

    1991-01-01

    Complete active space multiconfiguration self-consistent field (CAS-MCSFC) followed by full second-roder CI (SOCI) and relativistic configuration interaction (RCI) including spin-orbit coupling calculations are carried out on 14 λ- s and 10 ω-ω states of HfH. The spectroscopic constants ( re, Te, ωe, μe, De) of these states are computed. The potential energy curves of these states are also reported. We find several electronic transitions in the IR-UV regions for HfH which are yet to be observed. The ground state of HfH is found to be a {3}/{2} state (82% 2Δ, 8% 2Π) with r e = 1.854 Å, ωe = 1704 cm -1 and μe = 0.66 D. The spin-orbit effects are found to be very significant for HfH.

  16. Single-layer MoS2 electronics.

    PubMed

    Lembke, Dominik; Bertolazzi, Simone; Kis, Andras

    2015-01-20

    CONSPECTUS: Atomic crystals of two-dimensional materials consisting of single sheets extracted from layered materials are gaining increasing attention. The most well-known material from this group is graphene, a single layer of graphite that can be extracted from the bulk material or grown on a suitable substrate. Its discovery has given rise to intense research effort culminating in the 2010 Nobel Prize in physics awarded to Andre Geim and Konstantin Novoselov. Graphene however represents only the proverbial tip of the iceberg, and increasing attention of researchers is now turning towards the veritable zoo of so-called "other 2D materials". They have properties complementary to graphene, which in its pristine form lacks a bandgap: MoS2, for example, is a semiconductor, while NbSe2 is a superconductor. They could hold the key to important practical applications and new scientific discoveries in the two-dimensional limit. This family of materials has been studied since the 1960s, but most of the research focused on their tribological applications: MoS2 is best known today as a high-performance dry lubricant for ultrahigh-vacuum applications and in car engines. The realization that single layers of MoS2 and related materials could also be used in functional electronic devices where they could offer advantages compared with silicon or graphene created a renewed interest in these materials. MoS2 is currently gaining the most attention because the material is easily available in the form of a mineral, molybdenite, but other 2D transition metal dichalcogenide (TMD) semiconductors are expected to have qualitatively similar properties. In this Account, we describe recent progress in the area of single-layer MoS2-based devices for electronic circuits. We will start with MoS2 transistors, which showed for the first time that devices based on MoS2 and related TMDs could have electrical properties on the same level as other, more established semiconducting materials. This

  17. Application of HF radar currents to oil spill modelling.

    PubMed

    Abascal, Ana J; Castanedo, Sonia; Medina, Raul; Losada, Inigo J; Alvarez-Fanjul, Enrique

    2009-02-01

    In this work, the benefits of high-frequency (HF) radar currents for oil spill modeling and trajectory analysis of floating objects are analyzed. The HF radar performance is evaluated by means of comparison between a drifter buoy trajectory and the one simulated using a Lagrangian trajectory model. A methodology to optimize the transport model performance and to calculate the search area of the predicted positions is proposed. This method is applied to data collected during the Galicia HF Radar Experience. This experiment was carried out to explore the capabilities of this technology for operational monitoring along the Spanish coast. Two long-range HF radar stations were installed and operated between November 2005 and February 2006 on the Galician coast. In addition, a drifter buoy was released inside the coverage area of the radar. The HF radar currents, as well as numerical wind data were used to simulate the buoy trajectory using the TESEO oil spill transport model. In order to evaluate the contribution of HF radar currents to trajectory analysis, two simulation alternatives were carried out. In the first one, wind data were used to simulate the motion of the buoy. In the second alternative, surface currents from the HF radar were also taken into account. For each alternative, the model was calibrated by means of the global optimization algorithm SCEM-UA (Shuffled Complex Evolution Metropolis) in order to obtain the probability density function of the model parameters. The buoy trajectory was computed for 24h intervals using a Monte Carlo approach based on the results provided in the calibration process. A bivariate kernel estimator was applied to determine the 95% confidence areas. The analysis performed showed that simulated trajectories integrating HF radar currents are more accurate than those obtained considering only wind numerical data. After a 24h period, the error in the final simulated position improves using HF radar currents. Averaging the

  18. Characterization of an HF-Pumped CO2 Laser.

    DTIC Science & Technology

    1981-10-01

    the 101 and 100 energy levels and lasing action is achieved at 4.3 microns. The results of a theoretical analysis and an experimental study are used...14 3 Predicted HF Power Pulse Shape .................. 30 4 Optical Pumping Schemes ......................... 31 5 CO2 Energy Level Diaqram...32 6 12C1802 Energy Level Diagram .................... 34 7 HF and CO2 Line Broadeninq ....................... 36 8 CO Absorption

  19. Propagation Impact on Modern HF (High Frequency) Communications System Design

    DTIC Science & Technology

    1986-03-01

    to 2.4 kbits/s and above - in the same way as with line circuits or other less dispersive media . However, as will be shown in Section 2, the capacity...time interval. (c) An assumption that HF communication can replace, or back-up, other types of less dispersive communication media and still...reliable. The following media may be considered for interconnection purposes: (a) HF skywave and surface-wave point-to-point links; (b) meteor

  20. Monitoring the HF spectrum in the presence of noise

    NASA Astrophysics Data System (ADS)

    Giesbrecht, James E.; Clarke, Russell; Abbott, Derek

    2004-05-01

    This paper reviews modulation recognition in the context of HF radio-communications. We investigate entropic distance measures and coherence measures for recognizing HF modulations. Preliminary results shown that it may be possible to identify a modulation and its transmit power level based on the entropic distance between it and another modulation. Coherence estimates may provide characteristic signatures that can be used to identify modulation types.

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

    SciTech Connect

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

    2013-06-17

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

  2. Mechanical Properties of Ingot Nb Cavities

    SciTech Connect

    Ciovati, Gianluigi; Dhakal, Pashupati; Kneisel, Peter; Mammosser, John; Matalevich, Joseph; Rao Myneni, Ganapati

    2014-07-01

    This contribution presents the results of measurements of the resonant frequency and of strain along the contour of a single-cell cavity made of ingot Nb subjected to increasing uniform differential pressure, up to 6 atm. The data were used to infer mechanical properties of this material after cavity fabrication, by comparison with the results from simulation calculations done with ANSYS. The objective is to provide useful information about the mechanical properties of ingot Nb cavities which can be used in the design phase of SRF cavities intended to be built with this material.

  3. Aluminum-stabilized NB3SN superconductor

    DOEpatents

    Scanlan, Ronald M.

    1988-01-01

    An aluminum-stabilized Nb.sub.3 Sn superconductor and process for producing same, utilizing ultrapure aluminum. Ductile components are co-drawn with aluminum to produce a conductor suitable for winding magnets. After winding, the conductor is heated to convert it to the brittle Nb.sub.3 Sn superconductor phase, using a temperature high enough to perform the transformation but still below the melting point of the aluminum. This results in reaction of substantially all of the niobium, while providing stabilization and react-in-place features which are beneficial in the fabrication of magnets utilizing superconducting materials.

  4. Temperature Dependence of Vibrational Relaxation from the Upper Vibrational Levels of HF and DF.

    DTIC Science & Technology

    1980-08-29

    dependent quenching rate coefficients for relaxation of HF(v) and DF(v) by HF(v = 0) and DF(v = 0). The temperature dependence is predicted to be...halide molecules. This theoretical study is the first in which the temperature dependence of the V to R rate coefficients for HF(v sub 1) + HF(v sub 2

  5. 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.

  6. What determines the interfacial configuration of Nb/Al2O3 and Nb/MgO interface

    PubMed Central

    Du, J. L.; Fang, Y.; Fu, E. G.; Ding, X.; Yu, K. Y.; Wang, Y. G.; Wang, Y. Q.; Baldwin, J. K.; Wang, P. P.; Bai, Q.

    2016-01-01

    Nb films are deposited on single crystal Al2O3 (110) and MgO(111) substrates by e-beam evaporation technique. Structure of Nb films and orientation relationships (ORs) of Nb/Al2O3 and Nb/MgO interface are studied and compared by the combination of experiments and simulations. The experiments show that the Nb films obtain strong (110) texture, and the Nb film on Al2O3(110) substrate shows a higher crystalline quality than that on MgO(111) substrate. First principle calculations show that both the lattice mismatch and the strength of interface bonding play major roles in determining the crystalline perfection of Nb films and ORs between Nb films and single crystal ceramic substrates. The fundamental mechanisms for forming the interfacial configuration in terms of the lattice mismatch and the strength of interface bonding are discussed. PMID:27698458

  7. Mass measurements of very neutron-deficient Mo and Tc isotopes and their impact on rp process nucleosynthesis.

    PubMed

    Haettner, E; Ackermann, D; Audi, G; Blaum, K; Block, M; Eliseev, S; Fleckenstein, T; Herfurth, F; Hessberger, F P; Hofmann, S; Ketelaer, J; Ketter, J; Kluge, H-J; Marx, G; Mazzocco, M; Novikov, Yu N; Plass, W R; Rahaman, S; Rauscher, T; Rodríguez, D; Schatz, H; Scheidenberger, C; Schweikhard, L; Sun, B; Thirolf, P G; Vorobjev, G; Wang, M; Weber, C

    2011-03-25

    The masses of ten proton-rich nuclides, including the N=Z+1 nuclides ⁸⁵Mo and ⁸⁷Tc, were measured with the Penning trap mass spectrometer SHIPTRAP. Compared to the Atomic Mass Evaluation 2003 a systematic shift of the mass surface by up to 1.6 MeV is observed causing significant abundance changes of the ashes of astrophysical x-ray bursts. Surprisingly low α separation energies for neutron-deficient Mo and Tc are found, making the formation of a ZrNb cycle in the rp process possible. Such a cycle would impose an upper temperature limit for the synthesis of elements beyond Nb in the rp process.

  8. Mass Measurements of Very Neutron-Deficient Mo and Tc Isotopes and Their Impact on rp Process Nucleosynthesis

    SciTech Connect

    Haettner, E.; Plass, W. R.; Scheidenberger, C.; Ackermann, D.; Block, M.; Eliseev, S.; Herfurth, F.; Hessberger, F. P.; Hofmann, S.; Kluge, H.-J.; Audi, G.; Blaum, K.; Ketter, J.; Fleckenstein, T.; Ketelaer, J.; Marx, G.; Schweikhard, L.; Mazzocco, M.; Novikov, Yu. N.; Vorobjev, G.

    2011-03-25

    The masses of ten proton-rich nuclides, including the N=Z+1 nuclides {sup 85}Mo and {sup 87}Tc, were measured with the Penning trap mass spectrometer SHIPTRAP. Compared to the Atomic Mass Evaluation 2003 a systematic shift of the mass surface by up to 1.6 MeV is observed causing significant abundance changes of the ashes of astrophysical x-ray bursts. Surprisingly low {alpha} separation energies for neutron-deficient Mo and Tc are found, making the formation of a ZrNb cycle in the rp process possible. Such a cycle would impose an upper temperature limit for the synthesis of elements beyond Nb in the rp process.

  9. The isobutylene-isobutane alkylation process in liquid HF revisited.

    PubMed

    Esteves, P M; Araújo, C L; Horta, B A C; Alvarez, L J; Zicovich-Wilson, C M; Ramírez-Solís, A

    2005-07-07

    Details on the mechanism of HF catalyzed isobutylene-isobutane alkylation were investigated. On the basis of available experimental data and high-level quantum chemical calculations, a detailed reaction mechanism is proposed taking into account solvation effects of the medium. On the basis of our computational results, we explain why the density of the liquid media and stirring rates are the most important parameters to achieve maximum yield of alkylate, in agreement with experimental findings. The ab initio Car-Parrinello molecular dynamics calculations show that isobutylene is irreversibly protonated in the liquid HF medium at higher densities, leading to the ion pair formation, which is shown to be a minimum on the potential energy surface after optimization using periodic boundary conditions. The HF medium solvates preferentially the fluoride anion, which is found as solvated [FHF](-) or solvated F(-.)(HF)(3). On the other hand, the tert-butyl cation is weakly solvated, where the closest HF molecules appear at a distance of about 2.9 Angstrom with the fluorine termination of an HF chain.

  10. Thermal stability of HfO2 nanotube arrays

    SciTech Connect

    Qiu, Xiaofeng; Howe, Jane Y; Meyer III, Harry M; Tuncer, Enis; Paranthaman, Mariappan Parans

    2010-01-01

    Thermal stability of highly ordered hafnium oxide (HfO2) nanotube arrays prepared through an electrochemical anodization method in the presence of ammonium fluoride is investigated in a temperature range of room temperature to 900 C in flowing argon atmosphere. The formation of the HfO2 nanotube arrays was monitored by current density transient characteristics during anodization of hafnium metal foil. Morphologies of the as-grown and post-annealed HfO2 nanotube arrays were analyzed by powder Xray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Although monoclinic HfO2 is thermally stable up to 2000K in bulk, the morphology of HfO2 nanotube arrays degraded at 900 C. A detailed X-ray photoelectron spectroscopy (XPS) study revealed that the thermal treatment significantly impacted the composition and the chemical environment of the core elements (Hf and O), as well as F content coming from the electrolyte. Possible reasons for the degradation of the nanotube at high temperature were discussed based on XPS study and possible future improvements have also been suggested. Moreover, dielectric measurements were carried out on both the as-grown amorphous film and 500 C post-annealed crystalline film. This study will help us to understand the temperature impact on the morphology of nanotube arrays, which is important to its further applications at elevated temperatures.

  11. A new uranyl niobate sheet in the cesium uranyl niobate Cs{sub 9}[(UO{sub 2}){sub 8}O{sub 4}(NbO{sub 5})(Nb{sub 2}O{sub 8}){sub 2}

    SciTech Connect

    Saad, S.; Obbade, S. Yagoubi, S.; Renard, C.; Abraham, F.

    2008-04-15

    A new cesium uranyl niobate, Cs{sub 9}[(UO{sub 2}){sub 8}O{sub 4}(NbO{sub 5})(Nb{sub 2}O{sub 8}){sub 2}] or Cs{sub 9}U{sub 8}Nb{sub 5}O{sub 41} has been synthesized by high-temperature solid-state reaction, using a mixture of U{sub 3}O{sub 8}, Cs{sub 2}CO{sub 3} and Nb{sub 2}O{sub 5}. Single crystals were obtained by incongruent melting of a starting mixture with metallic ratio=Cs/U/Nb=1/1/1. The crystal structure of the title compound was determined from single crystal X-ray diffraction data, and solved in the monoclinic system with the following crystallographic data: a=16.729(2) A, b=14.933(2) A, c=20.155(2) A{beta}=110.59(1){sup o}, P2{sub 1}/c space group and Z=4. The crystal structure was refined to agreement factors R{sub 1}=0.049 and wR{sub 2}=0.089, calculated for 4660 unique observed reflections with I{>=}2{sigma}(I), collected on a BRUKER AXS diffractometer with MoK{alpha} radiation and a CCD detector. In this structure the UO{sub 7} uranyl pentagonal bipyramids are connected by sharing edges and corners to form a uranyl layer {sub {infinity}}{sup 2}[U{sub 8}O{sub 36}] corresponding to a new anion-sheet topology, and creating triangular, rectangular and square vacant sites. The two last sites are occupied by Nb{sub 2}O{sub 8} entities and NbO{sub 5} square pyramids, respectively, to form infinite uranyl niobate sheets {sub {infinity}}{sup 2}[(UO{sub 2}){sub 8}O{sub 4}(NbO{sub 5})(Nb{sub 2}O{sub 8}){sub 2}]{sup 9-} stacking along the [010] direction. The Nb{sub 2}O{sub 8} entities result from two edge-shared NbO{sub 5} square pyramids. The Cs{sup +} cations are localized between layers and ensured the cohesion of the structure. The cesium cation mobility between the uranyl niobate sheets was studied by electrical measurements. The conductivity obeys the Arrhenius law in all the studied temperature domains. The observed low conductivity values with high activation energy may be explained by the strong connection of the Cs{sup +} cations to the infinite

  12. Tracking magmatic processes through Zr/Hf ratios in rocks and Hf and Ti zoning in zircons: An example from the Spirit Mountain batholith, Nevada

    USGS Publications Warehouse

    Lowery, Claiborne L.E.; Miller, C.F.; Walker, B.A.; Wooden, J.L.; Mazdab, F.K.; Bea, F.

    2006-01-01

    Zirconium and Hf are nearly identical geochemically, and therefore most of the crust maintains near-chondritic Zr/Hf ratios of ???35-40. By contrast, many high-silica rhyolites and granites have anomalously low Zr/Hf (15-30). As zircon is the primary reservoir for both Zr and Hf and preferentially incorporates Zr, crystallization of zircon controls Zr/ Hf, imprinting low Zr/Hf on coexisting melt. Thus, low Zr/Hf is a unique fingerprint of effective magmatic fractionation in the crust. Age and compositional zonation in zircons themselves provide a record of the thermal and compositional histories of magmatic systems. High Hf (low Zr/ Hf) in zircon zones demonstrates growth from fractionated melt, and Ti provides an estimate of temperature of crystallization (TTiZ) (Watson and Harrison, 2005). Whole-rock Zr/Hf and zircon zonation in the Spirit Mountain batholith, Nevada, document repeated fractionation and thermal fluctuations. Ratios of Zr/Hf are ???30-40 for cumulates and 18-30 for high-SiO2 granites. In zircons, Hf (and U) are inversely correlated with Ti, and concentrations indicate large fluctuations in melt composition and TTiZ (>100??C) for individual zircons. Such variations are consistent with field relations and ion-probe zircon geochronology that indicate a >1 million year history of repeated replenishment, fractionation, and extraction of melt from crystal mush to form the low Zr/Hf high-SiO2 zone. ?? 2006 The Mineralogical Society.

  13. Global potential energy hypersurface for dynamical studies of energy transfer in HF--HF collisions

    SciTech Connect

    Redmon, M.J.; Binkley, J.S.

    1987-07-15

    The interaction energy of two HF molecules at 1332 individual points has been calculated with Moeller--Plesset (many--body) perturbation theory at the MP4-SDTQ level using a 6-311G** basis set. 293 of the points correspond to stretching of one HF molecule from its equilibrium geometry. No attempt was made to use a sufficiently fine grid to accurately describe the well region corresponding to hydrogen bonding. However, the location and minimum energy are consistent with experiment and other accurate theoretical results. An extensive global fit (rms error of 1 kcal/mol) is reported of 1319 points (below 10 eV of potential energy) using a modified London potential with corrections obtained using polynomials through four-body interactions. A model electrostatic potential represents the long-range interaction. In addition, the use of an expansion in products of three Legendre functions is discussed. It is shown that the latter approach, although accurately fitting the ab initio data, has difficulties interpolating in regions of the surface exhibiting diverse magnitudes of potential energy, and therefore must be used with caution. This surface should be useful for studies of T--V--R processes in this system.

  14. A Study on the Oxidation Behavior of Nb Alloy (Nb-1 pct Zr-0.1 pct C) and Silicide-Coated Nb Alloys

    NASA Astrophysics Data System (ADS)

    Vishwanadh, B.; Naina, R. H.; Majumdar, S.; Tewari, R.; Dey, G. K.

    2013-05-01

    In the current work, silicide coatings were produced on the Nb alloy (Nb-1 pct Zr-0.1 pct C) using the halide activated pack cementation (HAPC) technique. Coating parameters (temperature and time) were optimized to produce a two-layer (Nb5Si3 and NbSi2) coating on the Nb alloy. Subsequently, the oxidation behavior of the Nb alloy (Nb-1 pct Zr-0.1 pct C) and silicide-coated Nb alloy was studied using thermogravimetric analysis (TGA) and isothermal weight gain oxidation experiments. Phase identification and morphological examinations were carried out using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. TGA showed that the Nb alloy started undergoing accelerated oxidation at and above 773 K (500 °C). Isothermal weight gain experiments carried out on the Nb alloy under air environment at 873 K (600 °C) up to a time period of 16 hours exhibited a linear growth rate law of oxidation. In the case of silicide-based coatings, TGA showed that oxidation resistance of silicide coatings was retained up to 1473 K (1200 °C). Isothermal weight gain experiments on the silicide coatings carried out at 1273 K (1000 °C) in air showed that initially up to 8 hours, the weight of the sample increased, and beyond 8 hours the weight of the sample remained constant. The oxide phases formed on the bare samples and on the coated samples during oxidation were found to be Nb2O5 and a mixture of SiO2 and Nb2O5 phases, respectively. SEM showed the formation of nonprotective oxide layer on the bare Nb alloy and a protective (adherent, nonporous) oxide layer on silicide-coated samples. The formation of protective SiO2 layer on the silicide-coated samples greatly improved the oxidation resistance at higher temperatures.

  15. Role of Hf on Phase Formation in Ti45Zr(38-x)Hf(x)Ni17 Liquids and Solids

    NASA Technical Reports Server (NTRS)

    Wessels, V.; Sahu, K. K.; Gangopadhyay, A. K.; Huett, V. T.; Canepari, S.; Goldman, A. I.; Hyers, R. W.; Kramer, M. J.; Rogers, J. R.; Kelton, K. F.; Robinson, D.

    2008-01-01

    Hafnium and zirconium are very similar, with almost identical sizes and chemical bonding characteristics. However, they behave differently when alloyed with Ti and Ni. A sharp phase formation boundary near 18-21 at.% Hf is observed in rapidly-quenched and as-cast Ti45Zr38-xHfxNi17 alloys. Rapidly-quenched samples that contain less than 18 at.% Hf form the icosahedral quasicrystal phase, whiles samples containing more than 21 at.% form the 3/2 rational approximant phase. In cast alloys, a C14 structure is observed for alloys with Hf lower than the boundary concentration, while a large-cell (11.93 ) FCC Ti2Ni-type structure is found in alloys with Hf concentrations above the boundary. To better understand the role of Hf on phase formation, the structural evolution with supercooling and the solidification behavior of liquid Ti45Zr38-xHfxNi17 alloys (x=0, 12, 18, 21, 38) were studied using the Beamline Electrostatic Levitation (BESL) technique using 125keV x-rays on the 6ID-D beamline at the Advanced Photon Source, Argonne National Laboratory. For all liquids primary crystallization was to a BCC solid solution phase; interestly, an increase in Hf concentration leads to a decrease in the BCC lattice parameter in spite of the chemical similarity between Zr and Hf. A Reitveld analysis confirmed that as in the cast alloys, the secondary phase that formed was the C14 below the phase formation boundary and a Ti2Ni-type structure at higher Hf concentrations. Both the liquidus temperature and the reduced undercooling change sharply on traversing the phase formation boundary concentration, suggesting a change in the liquid structure. Structural information from a Honeycutt-Anderson index analysis of reverse Monte Carlo fits to the S(q) liquid data will be presented to address this issue.

  16. Intramolecular monomer-on-monomer (MoM) Mitsunobu cyclization for the synthesis of benzofused thiadiazepine-dioxides.

    PubMed

    Maity, Pradip K; Kainz, Quirin M; Faisal, Saqib; Rolfe, Alan; Samarakoon, Thiwanka B; Basha, Fatima Z; Reiser, Oliver; Hanson, Paul R

    2011-12-14

    The utilization of a monomer-on-monomer (MoM) intramolecular Mitsunobu cyclization reaction employing norbornenyl-tagged (Nb-tagged) reagents is reported for the synthesis of benzofused thiadiazepine-dioxides. Facile purification was achieved via ring-opening metathesis (ROM) polymerization initiated by one of three metathesis catalyst methods: (i) free metathesis catalyst, (ii) surface-initiated catalyst-armed silica, or (iii) surface-initiated catalyst-armed Co/C magnetic nanoparticles.

  17. Radio Frequency Magnetic Field Limits of Nb and Nb_{3}Sn.

    PubMed

    Posen, S; Valles, N; Liepe, M

    2015-07-24

    Superconducting radio frequency (srf) cavities, essential components of many large particle accelerators, rely on the metastable flux-free state of superconducting materials. In this Letter, we present results of experiments measuring the magnetic field limits of two srf materials, Nb and Nb_{3}Sn. Resonators made using these materials were probed using both high power rf pulses and dc magnetic fields. Nb, which is the current standard material for srf cavities in applications, was found to be limited by the superheating field H_{sh} when prepared using methods to avoid excessive rf dissipation at high fields. Nb_{3}Sn, which is a promising alternative material that is still in the early stages of development for srf purposes, was found to be limited between the onset field of metastability H_{c1} and H_{sh}. Analysis of the results shows that the limitation is consistent with nucleation of flux penetration at defects in the rf layer.

  18. Radio Frequency Magnetic Field Limits of Nb and Nb3 Sn

    NASA Astrophysics Data System (ADS)

    Posen, S.; Valles, N.; Liepe, M.

    2015-07-01

    Superconducting radio frequency (srf) cavities, essential components of many large particle accelerators, rely on the metastable flux-free state of superconducting materials. In this Letter, we present results of experiments measuring the magnetic field limits of two srf materials, Nb and Nb3 Sn . Resonators made using these materials were probed using both high power rf pulses and dc magnetic fields. Nb, which is the current standard material for srf cavities in applications, was found to be limited by the superheating field Hsh when prepared using methods to avoid excessive rf dissipation at high fields. Nb3Sn , which is a promising alternative material that is still in the early stages of development for srf purposes, was found to be limited between the onset field of metastability Hc 1 and Hsh. Analysis of the results shows that the limitation is consistent with nucleation of flux penetration at defects in the rf layer.

  19. Threshold Switching Characteristics of Nb/NbO 2 /TiN Vertical Devices

    SciTech Connect

    Wang, Yuhan; Comes, Ryan B.; Wolf, Stuart A.; Lu, Jiwei

    2016-01-01

    Nb/NbO2/TiN vertical structures were synthesized in-situ and patterned to devices with different contact areas. The devices exhibited threshold resistive switching with minimal hysteresis and a small EThreshold (60~90 kV/cm). The switching behavior was unipolar, and demonstrated good repeatability. A less sharp but still sizable change in the device resistance was observed up to 150 °C. It was found that the resistive switching without Nb capping layer exhibited the hysteretic behavior and much larger EThreshold (~250 kV/cm) likely due to a 2-3 nm surface Nb2O5 layer. The stable threshold switching behavior well above room temperature shows the potential applications of this device as an electronic switch.

  20. NbN/MgO/NbN edge-geometry tunnel junctions

    NASA Technical Reports Server (NTRS)

    Hunt, B. D.; Leduc, H. G.; Cypher, S. R.; Stern, J. A.; Judas, A.

    1989-01-01

    The fabrication and low-frequency testing of the first edge-geometry NbN/MgO/NbN superconducting tunnel junctions are reported. The use of an edge geometry allows very small junction areas to be obtained, while the all-NbN electrodes permit operation at 8-10 K with a potential maximum operating frequency above 1 THz. Edge definition in the base NbN film was accomplished utilizing Ar ion milling with an Al2O3 milling mask, followed by a lower energy ion cleaning step. This process has produced all-refractory-material tunnel junctions with areas as small as 0.1 sq micron, resistance-area products less than 21 ohm sq micron, and subgap to normal state resistance ratios larger than 18.

  1. Effectiveness of Diffusion Barrier Coatings for Mo-Re Embedded in C/SiC and C/C

    NASA Technical Reports Server (NTRS)

    Glass, David E.; Shenoy, Ravi N.; Wang, Zeng-Mei; Halbig, Michael C.

    2001-01-01

    Advanced high-temperature cooling applications may often require the elevated-temperature capability of carbon/silicon carbide or carbon/carbon composites in combination with the hermetic capability of metallic tubes. In this paper, the effects of C/SiC and C/C on tubes fabricated from several different refractory metals were evaluated. Though Mo, Nb, and Re were evaluated in the present study, the primary effort was directed toward two alloys of Mo-Re, namely, arc cast Mo-41Re and powder metallurgy Mo-47.5Re. Samples of these refractory metals were subjected to either the PyC/SiC deposition or embedding in C/C. MoSi2(Ge), R512E, and TiB2 coatings were included on several of the samples as potential diffusion barriers. The effects of the processing and thermal exposure on the samples were evaluated by conducting burst tests, microhardness surveys, and scanning electron microscopic examination (using either secondary electron or back scattered electron imaging and energy dispersive spectroscopy). The results showed that a layer of brittle Mo-carbide formed on the substrates of both the uncoated Mo-41Re and the uncoated Mo-47.5Re, subsequent to the C/C or the PyC/SiC processing. Both the R512E and the MoSi2(Ge) coatings were effective in preventing not only the diffusion of C into the Mo-Re substrate, but also the formation of the Mo-carbides. However, none of the coatings were effective at preventing both C and Si diffusion without some degradation of the substrate.

  2. Effects of phase constitution on magnetic susceptibility and mechanical properties of Zr-rich Zr-Mo alloys.

    PubMed

    Suyalatu; Kondo, Ryota; Tsutsumi, Yusuke; Doi, Hisashi; Nomura, Naoyuki; Hanawa, Takao

    2011-12-01

    The effects of the microstructures and phases of Zr-rich Mo alloys on their magnetic susceptibilities and mechanical properties were investigated in order to develop a Zr alloy with low magnetic susceptibility for use in magnetic resonance imaging (MRI). The magnetic susceptibility was measured with a magnetic susceptibility balance, while mechanical properties were evaluated by a tensile test. The microstructure was evaluated with an X-ray diffractometer, an optical microscope, and a transmission electron microscope. Evaluation of the microstructures revealed that the α' phase was the dominant form at less than 2% Mo content in the as-cast alloy. The ω phase was formed in as-cast Zr-3Mo but disappeared with aging at 973 K. Magnetic susceptibility was reflected in the phase constitution: the susceptibility showed a local minimum at Zr-(0.5-1)Mo with mostly α' phase and a minimum at Zr-3Mo with mostly β and ω phases. The magnetic susceptibility of as-cast Zr-3Mo increased at 973 K due to disappearance of the ω phase. However, the susceptibility was still as low as that of as-cast Zr-1Mo. The ultimate tensile strength of α'-based Zr-Mo alloys was tailored from 674 to 970 MPa, and the corresponding elongation varied from 11.1% to 2.9%. Because Zr-Mo alloys containing ω phase were found, through tensile tests, to be brittle this phase should be avoided, irrespective of the low magnetic susceptibility, in order to maintain mechanical reliability. Elongation of the Zr-3Mo alloy was dramatically improved when the phase constitution was changed to α and β phases by aging at 973 K for 86.4 ks. The magnetic susceptibilities of the α'-based Zr-Mo alloys are one-third those of Ti-6Al-4V and Ti-6Al-7Nb, and thus these Zr alloys are useful for medical devices under MRI.

  3. Sub micron area Nb/AlO(x)/Nb tunnel junctions for submillimeter mixer applications

    NASA Technical Reports Server (NTRS)

    Leduc, Henry G.; Bumble, B.; Cypher, S. R.; Judas, A. J.; Stern, J. A.

    1992-01-01

    In this paper, we report on a fabrication process developed for submicron area tunnel junctions. We have fabricated Nb/AlO(x)/Nb tunnel junctions with areas down to 0.1 sq micron using these techniques. The devices have shown excellent performance in receiver systems up to 500 GHz and are currently in use in radio astronomy observatories at 115, 230, and 500 GHz.

  4. Traditional applications and novel approaches in Lu-Hf geochronology

    NASA Astrophysics Data System (ADS)

    Herwartz, D.; Nagel, T. J.; Sandmann, S.; Vitale Brovarone, A.; Rexroth, S.; Rojas-Agramonte, Y.; Froitzheim, N.; Kröner, A.; Skublov, S. G.; Münker, C.

    2012-04-01

    Lutetium-Hf geochronology is currently becoming a routine method for dating metamorphism of garnet bearing rocks, such as eclogites. Prograde garnet growth ages are mostly preserved because blocking temperatures exceed 630 °C [1] and prograde Lu zoning patterns have even been observed in samples that were exposed to temperatures above 800 °C [2]. Here we discuss Lu-Hf ages from various eclogite localities, such as the Northern Tianshan, Kyrgyzstan (~ 470 Ma), the Kola Peninsula, Russia (~ 1900 Ma) [3], Cuba (~70 Ma and ~124 Ma), Alpine Corsica (~ 34 Ma) and the Tauern Window (~32.7 Ma). Age precisions are in the order of 0.1 to 1 % and all ages can be safely attributed to the timing of garnet growth. Some samples, however, contain two garnet populations which complicates Lu-Hf geochronology. In the Adula Nappe (Central Alps) relict garnet has survived a second orogenic cycle, including subduction to mantle depth. By carefully separating the two garnet populations present within the same eclogite sample we obtained a minimum Variscan age of 333 Ma and a maximum Alpine age of 38 Ma [4]. A similar relationship is now evident in samples from the Tauern Window (Eastern Alps), where only one population of garnet generation is visible macroscopically. However, few relics of Variscan garnet inside Alpine garnet are observed in electron microprobe element maps and are also evident from isotopic heterogeneity in 176Lu/177Hf vs. 176Hf/177Hf space. Garnet relics stemming from previous metamorphic events are frequently observed in HP units around the world and the Lu-Hf system is a promising tool to resolve the respective growth ages. Apart from garnet, lawsonite Lu-Hf geochronology was recently identified as a new tool to investigate subduction processes [5]. Here we present a lawsonite Lu-Hf isochron 37,6 ± 1.4 Ma (MSWD = 0.30; n =5) from a lawsonite blueschist from Alpine Corsica. The lawsonite slightly predates the timing of garnet growth (~34 Ma) in three eclogite

  5. Nb2O5 nanofiber memristor

    NASA Astrophysics Data System (ADS)

    Grishin, A. M.; Velichko, A. A.; Jalalian, A.

    2013-07-01

    Non-woven bead-free 100 μm long and 80-200 nm in diameter highly crystalline orthorhombic T-Nb2O5 nanofibers were sintered by sol-gel assisted electrospinning technique. Electrical and dielectric spectroscopy tests of individual fibers clamped onto Pt coated Si substrate were performed using a spreading resistance mode of atomic force microscope. Reproducible resistive switching with ON-OFF resistance ratio as high as 2 × 104 has a bipolar character, starts with a threshold voltage of 0.8-1.7 V, and follows by continuous growth of conductivity. Resistive memory effect is associated with a voltage-driven accumulation/depletion of oxygen vacancies at Nb2O5/Pt cathode interface. Poole-Frenkel emission from the electronic states trapped at reduced NbOx complexes determines a shape of Nb2O5/Pt diode I-V characteristics. Simple thermodynamic model explains a threshold character of switching, relates experimentally observed characteristics in low and high resistive states, and gives a reasonable estimate of the concentration of oxygen vacancies.

  6. Hf-Nd isotope and trace element constraints on subduction inputs at island arcs: Limitations of Hf anomalies as sediment input indicators

    NASA Astrophysics Data System (ADS)

    Handley, Heather K.; Turner, Simon; Macpherson, Colin G.; Gertisser, Ralf; Davidson, Jon P.

    2011-04-01

    New Nd-Hf isotope and trace element data for Javanese volcanoes are combined with recently published data to place constraints on subduction inputs at the Sunda arc in Indonesia and assess the value of Hf anomalies (expressed as Hf/Hf* and Sm/Hf ratios) as tracers of such inputs. Hf anomaly does not correlate with Hf isotope ratio in Javanese lavas, however, Hf/Hf* and Sm/Hf ratios do correlate with SiO 2. Contrary to previous work, we show that Hf anomaly variation may be controlled by fractionation of clinopyroxene and/or amphibole during magmatic differentiation and does not represent the magnitude or type of subduction input in some arcs. Correlation of Sm/Hf with indices of differentiation for other arcs (e.g., Vanuatu, New Britain, and Mariana) suggests that differentiation control on Sm/Hf ratios in volcanic arc rocks may be a relatively common phenomenon. This study corroborates the use of Nd-Hf isotope co-variations in arc volcanic rocks to ascertain subduction input characteristics. The trajectories of regional volcano groups (East, Central and West Java) in Nd-Hf isotope space reveal heterogeneity in the subducted sediment input along Java, which reflects present-day spatial variations in sediment compositions on the down-going plate in the Java Trench. The high Sm/Hf ratio required in the sediment end-member for some Javanese basalts suggests that partial melting of subducted sediment occurs in the presence of residual zircon, and is inconsistent with residual monazite or allanite.

  7. Investigation and Development of Data-Driven D-Region Model for HF Systems Impacts

    NASA Technical Reports Server (NTRS)

    Eccles, J. V.; Rice, D.; Sojka, J. J.; Hunsucker, R. D.

    2002-01-01

    Space Environment Corporation (SEC) and RP Consultants (RPC) are to develop and validate a weather-capable D region model for making High Frequency (HF) absorption predictions in support of the HF communications and radar communities. The weather-capable model will assimilate solar and earth space observations from NASA satellites. The model will account for solar-induced impacts on HF absorption, including X-rays, Solar Proton Events (SPE's), and auroral precipitation. The work plan includes: I . Optimize D-region model to quickly obtain ion and electron densities for proper HF absorption calculations. 2. Develop indices-driven modules for D-region ionization sources for low, mid, & high latitudes including X-rays, cosmic rays, auroral precipitation, & solar protons. (Note: solar spectrum & auroral modules already exist). 3. Setup low-cost monitors of existing HF beacons and add one single-frequency beacon. 4. Use PENEX HF-link database with HF monitor data to validate D-region/HF absorption model using climatological ionization drivers. 5. Develop algorithms to assimilate NASA satellite data of solar, interplanetary, and auroral observations into ionization source modules. 6. Use PENEX HF-link & HF-beacon data for skill score comparison of assimilation versus climatological D-region/HF absorption model. Only some satellites are available for the PENEX time period, thus, HF-beacon data is necessary. 7. Use HF beacon monitors to develop HF-link data assimilation algorithms for regional improvement to the D-region/HF absorption model.

  8. Complexities of Lu-Hf geochronology in convergent orogens

    NASA Astrophysics Data System (ADS)

    Mulcahy, S. R.; Vervoort, J. D.

    2015-12-01

    Subduction, terrane accretion, and arc magmatism leave a complex and sometimes incomplete record of metamorphism and deformation. The range of metamorphic temperatures and assemblages produced throughout the tectonic evolution of a single orogen often requires multiple isotopic systems to date distinct events. Lu-Hf geochronology, notably, has proven successful for dating metamorphism from a variety of bulk compositions spanning temperatures <350-850 C. We review the success of applying Lu-Hf geochronology in combination with other isotopic systems to date metamorphism from range of metamorphic conditions within convergent margins. We then discuss some complexities of Lu-Hf geochronology when dating samples with complicated metamorphic histories. Garnet and lawsonite isochrons often exhibit excess scatter (high MSWD's) that can be attributed to a number of factors: secondary mineral inclusions, prolonged garnet growth durations, disequilibrium at low temperatures, and polyphase metamorphic histories. Samples with high-Hf inclusions in isotopic equilibrium host phases can lead to decreased precision, but still produce meaningful ages. At high temperatures Lu-Hf ages may date peak metamorphism, cooling from peak temperatures, or result in spurious ages because of preferential retention of 176Hf over 176Lu in garnet. Despite these complexities, and perhaps because of them, new aspects of the metamorphic history may be revealed that are not readily recorded by other isotopic systems. Minerals other than garnet and lawsonite, particularly apatite, and perhaps epidote, offer exciting new possibilities for Lu-Hf geochronology. Careful fieldwork, detailed petrology and geochemistry, and collaborative efforts using multiple isotopic systems offer the best approach to solving tectonic problems in convergent orogens.

  9. 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.

  10. Paleoproterozoic arc basalt-boninite-high magnesian andesite-Nb enriched basalt association from the Malangtoli volcanic suite, Singhbhum Craton, eastern India: Geochemical record for subduction initiation to arc maturation continuum

    NASA Astrophysics Data System (ADS)

    Rajanikanta Singh, M.; Manikyamba, C.; Ganguly, Sohini; Ray, Jyotisankar; Santosh, M.; Dhanakumar Singh, Th.; Chandan Kumar, B.

    2017-02-01

    The Singhbhum Craton of eastern India preserves distinct signatures of ultramafic-mafic-intermediate-felsic magmatism of diverse geodynamic affiliations spanning from Paleo-Mesoarchean to Proterozoic. Here we investigate the 2.25 Ga Malangtoli volcanic rocks that are predominantly clinopyroxene- and plagioclase-phyric, calc-alkaline in nature, display basalt-basaltic andesite compositions, and preserve geochemical signatures of subduction zone magmatism. Major, trace and rare earth element characteristics classify the Malangtoli volcanic rocks as arc basalts, boninites, high magnesian andesites (HMA) and Nb enriched basalts (NEB). The typical LILE enriched-HFSE depleted geochemical attributes of the arc basalts corroborate a subduction-related origin. The boninitic rocks have high Mg# (0.8), MgO (>25 wt.%), Ni and Cr contents, high Al2O3/TiO2 (>20), Zr/Hf and (La/Sm)N (>1) ratios with low (Gd/Yb)N (<1) ratio, TiO2, and Zr concentrations. The HMA samples are marked by moderate SiO2 (>54 wt.%), MgO (>6 wt.%), Mg# (0.47) with elevated Cr, Co, Ni and Th contents, depleted (Nb/Th)N, (Nb/La)N, high (Th/La)N and La/Yb (<9) ratio, moderate depletion in HREE and Y with low Sr/Y. The NEBs have higher Nb contents (6.3-24 ppm), lower magnitude of negative Nb anomalies with high (Nb/Th)pm = 0.28-0.59 and (Nb/La)pm = 0.40-0.69 and Nb/U = 2.8-34.4 compared to normal arc basalts [Nb = <2 ppm; (Nb/Th)pm = 0.10-1.19; (Nb/La)pm 0.17-0.99 and Nb/U = 2.2-44 respectively] and HMA. Arc basalts and boninites are interpreted to be the products of juvenile subduction processes involving shallow level partial melting of mantle wedge under hydrous conditions triggered by slab-dehydrated fluid flux. The HMA resulted through partial melting of mantle wedge metasomatized by slab-dehydrated fluids and sediments during the intermediate stage of subduction. Slab-melting and mantle wedge hybridization processes at matured stages of subduction account for the generation of NEB. Thus, the arc basalt

  11. Infrared spectra of UF sub 6 , WF sub 6 , MoF sub 6 , and SF sub 6 complexes with hydrogen fluoride in solid argon

    SciTech Connect

    Hunt, R.D.; Andrews, L. ); Mac Toth, L. )

    1991-02-07

    UF{sub 6}, WF{sub 6}, MoF{sub 6}, and SF{sub 6} have been codeposited with hydrogen fluoride in excess argon at 12 K. The FTIR spectra of UF{sub 6} and HF revealed a strong UF{sub 6}-HF complex absorption at 3,848 cm{sup {minus}1} along with a weak, broad band at 3,903 cm{sup {minus}1} due to the UF{sub 6}-FH complex. Only one 1:2 complex with a UF{sub 6}-H{sub a}F-H{sub b}F arrangement was detected at higher HF concentrations and sample annealings. Similarly, the HF interaction with tungsten hexafluoride formed two 1:1 complexes. However, the 3,884-cm{sup {minus}1} band due to the anti-hydrogen-bonded complex WF{sub 6}-FH was considerably stronger than the WF{sub 6}-FH{sub b}-FH{sub a} structure. The band positions and relative intensities for the MoF{sub 6} complexes with HF and DF were very comparable to their WF{sub 6} counterparts.

  12. High Frequency (HF) Radio Signal Amplitude Characteristics, HF Receiver Site Performance Criteria, and Expanding the Dynamic Range of HF Digital New Energy Receivers by Strong Signal Elimination

    DTIC Science & Technology

    1990-06-21

    COVERAGE PLAN AND ................................... 148 NOTCH FILTERING B. STRONG SIGNAL ELIMINATION SYSTEM ............................ 151 C... filters , and switching systems must process the entire HF spectrum without distortion. This means that designers must use special care to preserve...appear only at the antenna, impedance matching networks, filters , preamplifiers, and any superheterodyne initial stages. The RF Distribution System

  13. First-principles study of the Hf-based Heusler alloys: Hf2CoGa and Hf2CoIn

    NASA Astrophysics Data System (ADS)

    Hu, Yan; Zhang, Jian-Min

    2017-01-01

    The electronic structures and magnetic properties of the new Heusler alloys Hf2CoGa and Hf2CoIn have been studied by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA). Both Hf2CoGa and Hf2CoIn Heusler alloys have the half-metallic character and completely (100%) spin polarization at the Fermi level (EF) and the indirect band gaps of 0.733 eV and 0.654 eV, respectively, in the minority spin channel. The total magnetic moments μt are all 2μB per formula unit, linearly scaled with the total number of valence electrons (Zt) by μt=Zt-18 and the atomic magnetic moments have localized character due to less affected by deformations. The origin of the indirect band gaps for these two new Heusler alloys is well understood. These two new Heusler alloys are the ideal candidates for spintronic devices.

  14. Amorphous-crystalline transition in thermoelectric NbO2

    NASA Astrophysics Data System (ADS)

    Music, Denis; Chen, Yen-Ting; Bliem, Pascal; Geyer, Richard W.

    2015-06-01

    Density functional theory was employed to design enhanced amorphous NbO2 thermoelectrics. The covalent-ionic nature of Nb-O bonding is identical in amorphous NbO2 and its crystalline counterpart. However, the Anderson localisation occurs in amorphous NbO2, which may affect the transport properties. We calculate a multifold increase in the absolute Seebeck coefficient for the amorphous state. These predictions were critically appraised by measuring the Seebeck coefficient of sputtered amorphous and crystalline NbO2 thin films with the identical short-range order. The first-order phase transition occurs at approximately 550 °C, but amorphous NbO2 possesses enhanced transport properties at all temperatures. Amorphous NbO2, reaching  -173 μV K-1, exhibits up to a 29% larger absolute Seebeck coefficient value, thereby validating the predictions.

  15. Characterization of phases in the Fe-Nb system

    NASA Astrophysics Data System (ADS)

    Raposo, M. T.; Ardisson, J. D.; Persiano, A. I. C.; Mansur, R. A.

    1994-12-01

    The Fe-Nb system was investigated by means of X-ray diffraction and Mössbauer spectroscopy (at 300 and 77 K), in the range from 1 to 66.7 at%. We have found that the limit of solubility of Fe in Nb at 1100°C is between 3 and 4 at% Fe, and observed the coexistence of the Nb solid solution (Nbss) phase and Fe21Nb19 in the range from 4 to 40 at% Fe. The Mössbauer parameters of all the single phases are reported. The lattice parameters of Nbss phase present no significant variation with the Nb content. The X-ray pattern for the Fe21Nb19 phase could not be solved. The Laves phase Fe2Nb presents Mössbauer and X-ray parameters that agree with the literature.

  16. Influence of cooling rate on the precipitation behavior in Ti–Nb–Mo microalloyed steels during continuous cooling and relationship to strength

    SciTech Connect

    Bu, F.Z.; Wang, X.M.; Chen, L.; Yang, S.W.; Shang, C.J.; Misra, R.D.K.

    2015-04-15

    In this study we elucidate carbide precipitation at varied cooling rates in Ti–Nb–Mo microalloyed steels during continuous cooling. The study suggests that increasing the cooling rate prevents precipitate formation in the ferrite phase during continuous cooling after finish rolling at 850 °C. At a lower cooling rate of 0.5 °C/s, the microhardness of ferrite grains exhibited maxima because of high volume fraction of fine carbides. A high density of nanoscale carbides with similar precipitation characteristics, including interphase precipitates, was observed at cooling rates of 0.5 and 1 °C/s, but the carbides were marginally larger and the spacing between them was increased with cooling rate. Additionally, carbide precipitation at a high cooling rate was associated with strain-induced precipitation. Through the analysis of selection area electron diffraction patterns and high-resolution transmission electron microscopy, lattice imaging, the fine spherical-shaped carbides of size ~ 6–10 nm were identified as MC-type carbides of the type (Ti,Nb,Mo)C and NbC. - Highlights: • We model three cooling rates which have indicated different precipitation behaviors. • We find two types of precipitates including NbC and (Ti,Nb,Mo)C based on HRTEM study. • Increasing cooling rate will decrease volume fraction and size of the precipitates. • There is no absence of interphase precipitation when the cooling rate increases to 5 °C/s.

  17. Comparison of HfAlO, HfO2/Al2O3, and HfO2 on n-type GaAs using atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Lu, Bin; Lv, Hongliang; Zhang, Yuming; Zhang, Yimen; Liu, Chen

    2016-11-01

    Different high-permittivity (high-k) gate dielectric structures of HfO2, HfAlO, and HfO2/Al2O3 deposited on HF-etched n-GaAs using ALD have been investigated. It has been demonstrated that the stacked structure of HfO2/Al2O3 has the lowest interface state density of 8.12 × 1012eV-1 cm-2 due to the "self-cleaning" reaction process, but the sample of HfAlO shows much better frequency dispersion and much higher dielectric permittivity extracted from the C-V curves. The investigation reveals that the electrical properties of gate dielectrics are improved by introducing alumina into HfO2.

  18. ^93Nb NMR investigation of the multiferroic system Ba3NbFe3Si2O14

    NASA Astrophysics Data System (ADS)

    Lumata, Lloyd; Hoch, M. J. R.; Zhou, H. D.; Brooks, J. S.; Kuhns, P. L.; Reyes, A. P.; Wiebe, C. R.

    2009-03-01

    We present ^93Nb nuclear magnetic resonance spectroscopy and relaxation data on the new multiferroic system Ba3NbFe3Si2O14. The spin-lattice relaxation rate ^931/T1 and spin-spin relaxation rate ^931/T2 show a peak at 26 K accompanied by broadening of the NMR lineshapes, characteristic of N'eel ordering. Salient features of ^93Nb NMR lineshapes in the ordered phase and temperature-dependent ^93Nb Knight shifts will be discussed in relation to the possible bulking or tilting of the NbO6 octahedra (caused by magneto-lattice coupling) around the transition.

  19. Improved Mo-Re VPS Alloys for High-Temperature Uses

    NASA Technical Reports Server (NTRS)

    Hickman, Robert; Martin, James; McKechnie, Timothy; O'Dell, John Scott

    2011-01-01

    Dispersion-strengthened molybdenum- rhenium alloys for vacuum plasma spraying (VPS) fabrication of high-temperature-resistant components are undergoing development. In comparison with otherwise equivalent non-dispersion-strengthened Mo-Re alloys, these alloys have improved high-temperature properties. Examples of VPS-fabricated high-temperature-resistant components for which these alloys are expected to be suitable include parts of aircraft and spacecraft engines, furnaces, and nuclear power plants; wear coatings; sputtering targets; x-ray targets; heat pipes in which liquid metals are used as working fluids; and heat exchangers in general. These alloys could also be useful as coating materials in some biomedical applications. The alloys consist of 60 weight percent Mo with 40 weight percent Re made from (1) blends of elemental Mo and Re powders or (2) Re-coated Mo particles that have been subjected to a proprietary powder-alloying-and-spheroidization process. For most of the dispersion- strengthening experiments performed thus far in this development effort, 0.4 volume percent of transition-metal ceramic dispersoids were mixed into the feedstock powders. For one experiment, the proportion of dispersoid was 1 volume percent. In each case, the dispersoid consisted of either ZrN particles having sizes <45 m, ZrO2 particles having sizes of about 1 m, HfO2 particles having sizes <45 m, or HfN particles having sizes <1 m. These materials were chosen for evaluation on the basis of previously published thermodynamic stability data. For comparison, Mo-Re feedstock powders without dispersoids were also prepared.

  20. HF omnidirectional spectral CW auroral radar (HF-OSCAR) at very high latitude. Part 1: Technique

    NASA Astrophysics Data System (ADS)

    Olesen, J. K.; Jacobsen, K. E.; Stauning, P.; Henriksen, S.

    1983-12-01

    An HF system for studies of very high latitude ionospheric irregularities was described. Radio aurora from field-aligned E-region irregularities of the Slant E Condition type were discussed. The complete system combines an ionosonde, a 12 MHz pulse radar and a 12 MHz bistatic CW Doppler-range set-up. The two latter units use alternately a 360 deg rotating Yagi antenna. High precision oscillators secure the frequency stability of the Doppler system in which the received signal is mixed down to a center frequency of 500 Hz. The Doppler shift range is max + or - 500 Hz. The received signal is recorded in analog form on magnetic tape and may be monitored visually and audibly. Echo range of the CW Doppler signal is obtained by a 150 Hz amplitude modulation of the transmitted signal and phase comparison with the backscattered signal.

  1. Materials Data on Nb2MoO8 (SG:15) by Materials Project

    SciTech Connect

    Kristin Persson

    2016-02-11

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  2. Exfoliation and thermal transformations of Nb-substituted layered titanates

    SciTech Connect

    Song Haiyan; Sjastad, Anja O.; Fjellvag, Helmer; Okamoto, Hiroshi; Vistad, Ornulv B.; Arstad, Bjornar; Norby, Poul

    2011-12-15

    Single-layer Nb-substituted titanate nanosheets of ca. 1 nm thickness were obtained by exfoliating tetrabutylammonium (TBA)-intercalated Nb-substituted titanates in water. AFM images and turbidity measurements reveal that the exfoliated nanosheets crack and corrugate when sonicated. Upon heating, the thermal transformation into anatase and further to rutile is retarded. This suppression of the phase transition upon higher valent substitution may promote technological applications of anatase thin films, hereunder development of films with TCO properties. Depending on the oxygen partial pressure during the transformation, the Nb-substitution into TiO{sub 2} provokes different defect situations and also electronic properties. At reducing conditions, Nb is incorporated as Nb{sup V} and an equivalent amount of Ti{sup IV} is transformed to Ti{sup III} as evidenced by XPS. Magnetic susceptibility data show accordingly paramagnetic behavior. For samples heated in air Ti{sup IV} and Nb{sup V} cations prevail, the latter is compensated by cation vacancies. {sup 93}Nb MAS NMR data prove that Nb is finely dispersed into the transformed (Ti,Nb)O{sub 2} oxide matrices without sign of Nb{sub 2}O{sub 5} (nano)precipitates. The Nb-O-Ti bonds and defects at cation sites are considered key factors for increasing the transformation temperatures for conversion of the nanosheets to anatase and finally into rutile. It is further tempting to link the delay in crystallization to morphology limitations originating from the nanosheets. The present work shows that layered Nb-titanates are appropriate precursors for formation of highly oriented Nb-substituted anatase thin films via delamination, reconstruction and subsequent heat treatment. - Graphical abstract: Layered Nb-titanates are appropriate precursors for formation of highly oriented Nb-substituted anatase thin films via delamination, reconstruction and subsequent heat treatment. Highlights: Black-Right-Pointing-Pointer Single layer Nb

  3. Large-Area Deposition of MoS2 by Pulsed Laser Deposition with In Situ Thickness Control.

    PubMed

    Serna, Martha I; Yoo, Seong H; Moreno, Salvador; Xi, Yang; Oviedo, Juan Pablo; Choi, Hyunjoo; Alshareef, Husam N; Kim, Moon J; Minary-Jolandan, Majid; Quevedo-Lopez, Manuel A

    2016-06-28

    A scalable and catalyst-free method to deposit stoichiometric molybdenum disulfide (MoS2) films over large areas is reported, with the maximum area limited by the size of the substrate holder. The method allows deposition of MoS2 layers on a wide range of substrates without any additional surface preparation, including single-crystal (sapphire and quartz), polycrystalline (HfO2), and amorphous (SiO2) substrates. The films are deposited using carefully designed MoS2 targets fabricated with excess sulfur and variable MoS2 and sulfur particle size. Uniform and layered MoS2 films as thin as two monolayers, with an electrical resistivity of 1.54 × 10(4) Ω cm(-1), were achieved. The MoS2 stoichiometry was confirmed by high-resolution Rutherford backscattering spectrometry. With the method reported here, in situ graded MoS2 films ranging from ∼1 to 10 monolayers can be deposited.

  4. Developments in HF equipment and systems mobile and portable terminals

    NASA Astrophysics Data System (ADS)

    Wilson, Q. C.

    1986-03-01

    Before the advent of satellite platforms, sophisticated high frequency (HF) propagation and system research promised improved capability during disturbed ionospheric propagation conditions. However, satellite relays captured the imaginations and pocketbooks of the communications community in the mid-1960s. Consequently, extant HF systems aged while satellite systems were implemented. During peacetime, satellite systems transmit quality low data rate communications and navigation aids to mobile users, but there is now renewed interest in the low cost and survivability attributes of HF radio. At this time, when old HF prime systems need replacement for logistical reasons, the need for low cost communications that can survive jamming, nuclear effects, and space warfare is not satisfied. The HF renaissance is the response to this challenge. Logistical replacement procurements that provide new capabilities are redressing the attrition of vacuum-tube radio equipment over the last decade. Procuring organizations typically compile specifications comprising state-of-the-art and new capabilities offered by competing vendors. Integrated circuits, which include microprocessors, synthesizer ele ments, and other evolving components, have led to new circuit architectures. The first of the following three sections describes: Receivers; Transceivers and Antenna Couplers; Antenna Kits; and Audio Channel Peripherals.

  5. HF acid blends based on formation conditions eliminate precipitation problems

    SciTech Connect

    Gdanski, R.; Shuchart, C.

    1997-03-01

    Formulating HCl-HF acid blends based on the mineralogy and temperature of a formation can increase the success of hydrofluoric acid (HF) treatments. Sodium and potassium in the structures of formation minerals can cause precipitation and matrix plugging problems during acidizing. Slight modifications of the acid blend used in the treatment can help eliminate fluosilicate precipitation. Researchers recently conducted tests to determine how acid blends react in different formations under varying temperatures. The results of the tests indicate that the minimum HCl:HF ratio in an acid blend is 6-to-1, and the optimum ratio is 9-to-1. Regular mud acid (12% HCl-3% HF) has been used successfully for years to enhance production in sandstone formations. By the 1980s, operators began to vary the concentration of HF and HCl acids to solve excessive sanding problems in sandstone. The paper discusses treatment problems, formation characteristics, alumino-silicate scaling, research results, brine compatibility, optimum treatment, and acid volume guidelines.

  6. Geochemistry, zircon U-Pb and Lu-Hf isotopes of an Early Cretaceous intrusive suite in northeastern Jiangxi Province, South China Block: Implications for petrogenesis, crust/mantle interactions and geodynamic processes

    NASA Astrophysics Data System (ADS)

    Deng, Zhengbin; Liu, Shuwen; Zhang, Lifei; Wang, Zongqi; Wang, Wei; Yang, Pengtao; Luo, Ping; Guo, Boran

    2014-07-01

    The Early Cretaceous Tieshan intrusive suite, in northeastern Jiangxi Province along the northern margin of the Eastern Cathaysia Block, is composed of diabase porphyrites, monzodiorites, syenite porphyries, quartz monzonites, monzogranites and granite porphyries. LA-ICPMS zircon U-Pb isotopic analyses reveal that this intrusive complex was emplaced between 142 Ma and 117 Ma. The ~ 135 Ma diabase porphyrites, monzodiorites, and syenite porphyries are characterized by low to moderate SiO2 and MgO contents, with high K2O and total alkaline contents. These rocks exhibit slightly to strongly fractionated REE patterns and upper crust-like multi-element patterns with depletions of Nb, Ta and Ti, and show strongly negative εHf (t) values of - 9.0 to - 11.8. All these patterns are identical to those of the Caiyuan syenites, Huangtuling gabbros in the east, and Lengshuikeng trachyandesites and quartz syenites in the west. These geochemical and zircon Lu-Hf isotopic features indicate that their magmatic precursors were generated by 0.2%-2% partial melting of a phlogopite-bearing enriched subcontinental lithospheric mantle source that was metasomatized by sediments. The ~ 117 Ma quartz monzonite has slightly higher εHf (t) values (- 5.6 to - 8.7) like those of the Honggong syenites, indicating an interaction between the asthenosphere and the lithosphere. The ~ 142-134 Ma granite porphyries and monzogranites are characterized by high SiO2 levels but low concentrations of refractory elements, and show enrichment of LREEs and LILEs, with variable negative anomalies of Nb, Ta, Ti, Sr, P and Ba in multi-element diagrams normalized by primitive mantle. The monzogranite exhibits strongly negative εHf (t) values of - 10.5 to - 13.3 and TDM2 (Hf) values of 1849-2023 Ma, and the granite porphyries display relatively wide εHf (t) values of - 7.2 to - 13.4 and TDM2 (Hf) values of 1645-2043 Ma, indicating that these monzogranites and granite porphyries are highly fractionated granites

  7. Synthesis of superconducting Nb3Sn coatings on Nb substrates

    SciTech Connect

    Barzi, E.; Franz, S.; Reginato, F.; Turrioni, D.; Bestetti, M.

    2015-12-01

    In the present work the electrochemical and thermal syntheses of superconductive Nb3Sn films are investigated. The Nb3Sn phase is obtained by electrodeposition of Sn layers and Cu intermediate layers onto Nb substrates followed by high temperature diffusion in inert atmosphere. Electrodeposition was performed from aqueous solutions at current densities in the 20 to 50 mA/cm2 range and at temperatures between 40 and 50°C. Subsequent thermal treatments were realized to obtain the Nb3Sn superconductive phase. Glow discharge optical emission spectrometry (GDOES) demonstrated that after thermal treatment interdiffusion of Nb and Sn occurred across a thickness of about 13 μm. Scanning Electron Microscopy (SEM) allowed accurately measuring the thickness of the Nb3Sn phase, whose average for the various types of film samples was between 5.7 and 8.0 μm. X-ray diffraction (XRD) patterns confirmed the presence of a cubic Nb3Sn phase (A15 structure) having (210) preferred orientation. The maximum obtained Tc was 17.68 K and the Bc20 ranged between 22.5 T and 23.8 T. With the procedure described in the present paper, coating complex shapes cost-effectively becomes possible, which is typical of electrochemical techniques. Furthermore, this approach can be implemented in classical wire processes such as "Jelly Roll" or "Rod in Tube", or directly used for producing superconducting surfaces. In conclusion, the potential of this method for Superconducting Radiofrequency (SRF) structures is also outlined.

  8. Effect of HF leaching on 14C dates of pottery

    NASA Astrophysics Data System (ADS)

    Goslar, Tomasz; Kozłowski, Janusz; Szmyt, Marzena; Czernik, Justyna

    2013-01-01

    This paper presents the experiments with 14C dating of two potsherds, which contained carbon dispersed rather homogeneously in their clay fabric. After AAA treatment, the potsherds still appeared to be contaminated with young carbon, presumably connected with humic acids. To make removal of humic acids more effective, we treated the sherds with HF acid of different concentration. The 14C results obtained demonstrate that HF treatment indeed helps to remove humic contaminants, but it also mobilizes carbon bound to raw clay, which may make 14C dates too old. We conclude therefore, that using a simple combination of HF and AAA treatment seems insufficient in reliable 14C dating of carbon homogeneously dispersed in the volume of potsherds.

  9. Centrifugal stretching along the ground state band of Hf168

    NASA Astrophysics Data System (ADS)

    Costin, A.; Reese, M.; Ai, H.; Casten, R. F.; Dusling, K.; Fitzpatrick, C. R.; Gürdal, G.; Heinz, A.; McCutchan, E. A.; Meyer, D. A.; Möller, O.; Petkov, P.; Pietralla, N.; Qian, J.; Rainovski, G.; Werner, V.

    2009-02-01

    The lifetimes of the Jπ=4+, 6+, 8+, and 10+ levels along the ground state band in Hf168 were measured by means of the recoil distance Doppler shift (RDDS) method using the New Yale Plunger Device (NYPD) and the SPEEDY detection array at Wright Nuclear Structure Laboratory of Yale University. Excited states in Hf168 were populated using the Sn124(Ti48,4n) fusion evaporation reaction. The new lifetime values are sufficiently precise to clearly prove the increase of quadrupole deformation as a function of angular momentum in the deformed nucleus Hf168. The data agree with the predictions from the geometrical confined β-soft (CBS) rotor model that involves centrifugal stretching in a soft potential.

  10. MIMO communications within the HF band using compact antenna arrays

    NASA Astrophysics Data System (ADS)

    Gunashekar, S. D.; Warrington, E. M.; Feeney, S. M.; Salous, S.; Abbasi, N. M.

    2010-12-01

    Measurements have been made over a 255 km radio path between Durham and Leicester in the UK in order to investigate the potential applicability of multiple input multiple output (MIMO) techniques to communications within the HF band. This paper describes the results from experiments in which compact heterogeneous antenna arrays have been employed. The results of these experiments indicate that traditional spaced HF antenna arrays can be replaced by compact, active, heterogeneous arrays in order to achieve the required levels of decorrelation between the various antenna elements. An example case study is also presented which highlights the importance of the variable nature of the ionosphere in the context of HF-MIMO radio links.

  11. Feature Modeling of HfO2 Atomic Layer Deposition Using HfCl4/H2O

    NASA Astrophysics Data System (ADS)

    Stout, Phillip J.; Adams, Vance; Ventzek, Peter L. G.

    2003-03-01

    A Monte Carlo based feature scale model (Papaya) has been applied to atomic layer deposition (ALD) of HfO2 using HfCl_4/H_20. The model includes physical effects of transport to surface, specular and diffusive reflection within feature, adsorption, surface diffusion, deposition and etching. Discussed will be the 3D feature modeling of HfO2 deposition in assorted features (vias and trenches). The effect of feature aspect ratios, pulse times, cycle number, and temperature on film thickness, feature coverage, and film Cl fraction (surface/bulk) will be discussed. Differences between HfO2 ALD on blanket wafers and in features will be highlighted. For instance, the minimum pulse times sufficient for surface reaction saturation on blanket wafers needs to be increased when depositing on features. Also, HCl products created during the HfCl4 and H_20 pulses are more likely to react within a feature than at the field, reducing OH coverage within the feature (vs blanket wafer) thus limiting the maximum coverage attainable for a pulse over a feature.

  12. Importance of the Lu-Hf isotopic system in studies of planetary chronology and chemical evolution

    USGS Publications Warehouse

    Patchett, P.J.

    1983-01-01

    The 176Lu-176Hf isotope method and its applications in earth sciences are discussed. Greater fractionation of Lu/Hf than Sm/Nd in planetary magmatic processes makes 176Hf 177Hf a powerful geochemical tracer. In general, proportional variations of 176Hf 177Hf exceed those of 143Nd l44Nd by factors of 1.5-3 in terrestrial and lunar materials. Lu-Hf studies therefore have a major contribution to make in understanding of terrestrial and other planetary evolution through time, and this is the principal importance of Lu-Hf. New data on basalts from oceanic islands show unequivocally that whereas considerable divergences occur in 176Hf 177Hf- 87Sr 86Sr and 143Nd l44Nd- 87Sr 86Sr diagrams, 176Hf 177Hf and 143Nd 144Nd display a single, linear isotopic variation in the suboceanic mantle. These discordant 87Sr 86Sr relationships may allow, with the acquisition of further Hf-Nd-Sr isotopic data, a distinction between processes such as mantle metasomatism, influence of seawater-altered material in the magma source, or recycling of sediments into the mantle. In order to evaluate the Hf-Nd isotopic correlation in terms of mantle fractionation history, there is a need for measurements of Hf distribution coefficients between silicate minerals and liquids, and specifically for a knowledge of Hf behavior in relation to rareearth elements. For studying ancient terrestrial Hf isotopic variations, the best quality Hf isotope data are obtained from granitoid rocks or zircons. New data show that very U-Pb discordant zircons may have upwardly-biased 176Hf 177Hf, but that at least concordant to slightly discordant zircons appear to be reliable carriers of initial 176Hf 177Hf. Until the controls on addition of radiogenic Hf to zircon are understood, combined zircon-whole rock studies are recommended. Lu-Hf has been demonstrated as a viable tool for dating of ancient terrestrial and extraterrestrial samples, but because it offers little advantage over existing methods, is unlikely to find

  13. Hf--Co--B alloys as permanent magnet materials

    DOEpatents

    McGuire, Michael Alan; Rios, Orlando; Ghimire, Nirmal Jeevi

    2017-01-24

    An alloy composition is composed essentially of Hf.sub.2-XZr.sub.XCo.sub.11B.sub.Y, wherein 0Hf.sub.2-XZr.sub.XCo.sub.11B.sub.Y, wherein 0.ltoreq.X<2 and 0

  14. First HF radar measurements of summer mesopause echoes at SURA

    NASA Astrophysics Data System (ADS)

    Karashtin, A. N.; Shlyugaev, Y. V.; Abramov, V. I.; Belov, I. F.; Berezin, I. V.; Bychkov, V. V.; Eryshev, E. B.; Komrakov, G. P.

    1997-07-01

    HF sounding of the mesosphere was first carried out at SURA in summer 1994 at frequencies in the range 8-9 MHz using one of the sub-arrays of the SURA heating facility. The observations had a range resolution of 3 km. Almost all measurements indicated the presence of strong radar returns from altitudes between 83 and 90 km with features very similar to VHF measurements of mesopause summer echoes at mid-latitudes and polar mesopause summer echoes. In contrast to VHF observations, HF mesopause echoes are almost always present.

  15. Field operations with cesium clocks in HF navigation systems

    NASA Technical Reports Server (NTRS)

    Christy, E. H.; Clayton, D. A.

    1982-01-01

    Networks of HF phase comparison marine navigation stations employing cesium clocks are discussed. The largest permanent network is in the Gulf of Mexico where some fourteen base stations are continuously active and others are activated as needed. These HF phase comparison systems, which operate on a single transmission path, require a clock on the mobile unit as well. Inventory consists of upwards of 70 clocks from two different manufacturers. The maintenance of this network as an operating system requires a coordinated effort involving clock preparation, clock environment control, station performance monitoring and field service.

  16. Wideband model of man-made HF noise and interference

    NASA Astrophysics Data System (ADS)

    Lemmon, John J.

    1997-03-01

    A mathematical model of the waveform generated by man-made high frequency (HF) noise and interference is presented and discussed. The model is based on wideband (800 kHz) recordings of the noise and interference at various frequencies in the HF band. Representative examples of first- and higher-order statistics of the measured waveforms are described, including probability distributions of the envelope and phase of the noise and interference in the time and frequency domains, power spectra, autocorrelation functions, and level crossing distributions. The statistics of waveforms generated by the model closely resemble the statistics of the measured data.

  17. HF-Induced Airglow at Magnetic Zenith: Theoretical Considerations

    DTIC Science & Technology

    2007-11-02

    7.8 MHz. Significantly, green -to-red ratios fgr >0.3 are often ob- For a heater ERP Po= 150 MW and distance R=250 kin, served. Gustavsson et al...and 145.15’W) show that the HF-induced airglow maximizes 557.7nm ( green line) during HF modification experiments during injections toward magnetic...1989; Pedersen and injected frequency f0. Here, Oc=arcsin( fsinx), f, is Carlson, 2001; Gustavsson et al., 2001, 2002; Kosch et al., the electron

  18. New process additive reduces HF cloud-forming potential

    SciTech Connect

    Sheckler, J.C.; Hammershaimb, H.U. ); Ross, L.J. ); Comey, K.R. III )

    1994-08-22

    The Texaco-UOP HF additive technology has demonstrated significant aerosol reduction in both small-scale and large-scale releases. The pilot plant testing did not indicate any adverse impact on the alkylation reaction, as was confirmed in a short trial at Texaco Refining and Marketing Inc.'s El Dorado, Kan., refinery in 1992. Equipment to enable continuous addition of the additive was installed in the second quarter of 1994 at the refinery. The paper discusses HF alkylation, mitigation technology, additive development, aerosol reduction, and testing on pilot scale and large scale.

  19. European coordination for coastal HF radar data in EMODnet Physics

    NASA Astrophysics Data System (ADS)

    Mader, Julien; Novellino, Antonio; Gorringe, Patrick; Griffa, Annalisa; Schulz-Stellenfleth, Johannes; Montero, Pedro; Montovani, Carlo; Ayensa, Garbi; Vila, Begoña; Rubio, Anna; Sagarminaga, Yolanda

    2015-04-01

    Historically, joint effort has been put on observing open ocean, organizing, homogenizing, sharing and reinforcing the impact of the acquired information based on one technology: ARGO with profilers Argo floats, EuroSites, ESONET-NoE, FixO3 for deep water platforms, Ferrybox for stations in ships of opportunities, and GROOM for the more recent gliders. This kind of networking creates synergies and makes easier the implementation of this source of data in the European Data exchange services like EMODnet, ROOSs portals, or any applied services in the Blue economy. One main targeted improvement in the second phase of EMODnet projects is the assembling of data along coastline. In that sense, further coordination is recommended between platform operators around a specific technology in order to make easier the implementation of the data in the platforms (4th EuroGOOS DATAMEQ WG). HF radar is today recognized internationally as a cost-effective solution to provide high spatial and temporal resolution current maps (depending on the instrument operation frequency, covering from a few kilometres offshore up to 200 km) that are needed for many applications for issues related to ocean surface drift or sea state characterization. Significant heterogeneity still exists in Europe concerning technological configurations, data processing, quality standards and data availability. This makes more difficult the development of a significant network for achieving the needed accessibility to HF Radar data for a pan European use. EuroGOOS took the initiative to lead and coordinate activities within the various observation platforms by establishing a number of Ocean Observing Task Teams such as HF-Radars. The purpose is to coordinate and join the technological, scientific and operational HF radar communities at European level. The goal of the group is on the harmonization of systems requirements, systems design, data quality, improvement and proof of the readiness and standardization of

  20. Ca + HF - The anatomy of a chemical insertion reaction

    NASA Technical Reports Server (NTRS)

    Jaffe, R. L.; Pattengill, M. D.; Mascarello, F. G.; Zare, R. N.

    1987-01-01

    A comprehensive first-principles theoretical investigation of the gas phase reaction Ca + HF - CaF + H is reported. Ab initio potential energy calculations are first discussed, along with characteristics of the computed potential energy surface. Next, the fitting of the computed potential energy points to a suitable analytical functional form is described, and maps of the fitted potential surface are displayed. The methodology and results of a classical trajectory calculation utilizing the fitted potential surface are presented. Finally, the significance of the trajectory study results is discussed, and generalizations concerning dynamical aspects of Ca + HF scattering are drawn.

  1. Precipitates in Nb and Nb-V microalloyed X80 pipeline steel.

    PubMed

    Li, Zhongyi; Liu, Delu; Zhang, Jianping; Tian, Wenhuai

    2013-08-01

    Precipitates in two X80 pipeline steels were studied by transmission electron microscopy equipped with an energy filtering system. The steels are microalloyed with niobium and niobium-vanadium (Nb-V), respectively, and produced by continuous hot rolling. Besides the precipitates TiN and (Ti, Nb) (C, N), which were 10-100 nm in size, a large number of precipitates smaller than 10 nm distributed in the two steels have been observed. In the Nb-V microalloyed steel, only a few titanium nitrides covered by vanadium compounds on the surface have been observed. It is inferred that the vanadium exists mainly in the matrix as a solid solution element. The fact has been accepted that there was no contribution to the precipitation strengthening of the X80 steel by adding 0.04-0.06% vanadium under the present production process. By contrast, the toughness of the Nb-V steel is deteriorated. Therefore, a better toughness property of the Nb microalloyed X80 results from the optimum microalloying composition design and the suitable accelerating cooling after hot rolling.

  2. Magnetotransport of single crystalline NbAs

    DOE PAGES

    Ghimire, N. J.; Luo, Yongkang; Neupane, M.; ...

    2015-03-27

    We report transport measurement in zero and applied magnetic field on a single crystal of NbAs. Transverse and longitudinal magnetoresistance in the plane of this tetragonal structure does not saturate up to 9 T. In the transverse configuration (H ∥ c, I ⊥ c) it is 230,000% at 2 K. The Hall coefficient changes sign from hole-like at room temperature to electron-like below ~150 K. The electron carrier density and mobility calculated at 2 K based on a single band approximation are 1.8 × 1019 cm-3 and 3.5 × 105 cm2/Vs, respectively. These values are similar to reported values formore » TaAs and NbP, and further emphasize that this class of noncentrosymmetric, transition-metal monopnictides is a promising family to explore the properties of Weyl semimetals and the consequences of their novel electronic structure.« less

  3. LARP Long Nb3Sn Quadrupole Design

    SciTech Connect

    Ambrosio, G.; Andreev, N.; Anerella, M.; Barzi, E.; Bossert, R.; Caspi, S.; Chlachidize, G.; Dietderich, D.; Feher, S.; Ferracin, P.; Ghosh, A.; Hafalia, R.; Hannaford, R.; Kashikhin, V.V.; Kerby, J.; Lamm, M.; Lietzke, A.; McInturff, A.; Muratore, J.; Nobrega, F.; Novitsky, I.; Sabbi, G.L.; Schmalzle, J.; Tartaglia, M.; Turrioni, D.; Wanderer, P.; Whitson, G.; Zlobin, A.V.

    2008-06-01

    A major milestone for the LHC Accelerator Research Program (LARP) is the test, by the end of 2009, of two 4m-long quadrupole magnets (LQ) wound with Nb{sub 3}Sn conductor. The goal of these magnets is to be a proof of principle that Nb{sub 3}Sn is a viable technology for a possible LHC luminosity upgrade. The design of the LQ is based on the design of the LARP Technological Quadrupoles, presently under development at FNAL and LBNL, with 90-mm aperture and gradient higher than 200 T/m. The design of the first LQ model will be completed by the end of 2007 with the selection of a mechanical design. In this paper we present the coil design addressing some fabrication technology issues, the quench protection study, and three designs of the support structure.

  4. AlNb-Based Titanium Aluminide

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    The microstructure of laser-tungsten inert gas hybrid welded Ti2AlNb-based joints and their tensile properties at room temperature were investigated in this paper. The results showed that good-quality joints could be obtained by hybrid welding process. The microstructure evolution was identified by means of optical microscopy, scanning electron microscopy, x-ray diffraction, and transmission electron microscopy. The fusion zone mainly consisted of B2 phase due to the rapid cooling rate, as well as high Nb content. The phase compositions of the heat-affected zone were varied with different thermal cycles during the welding process. Tensile tests at room temperature showed that fracture tended to occur in the fusion zone, and the tensile strength and elongation were 950 MPa and 4.3%, respectively. The fracture mode was quasi-cleavage based on the observation of the fracture morphology.

  5. LARP Long Nb3Sn Quadrupole Design.

    SciTech Connect

    Ambrosio,G.; Andreev, N.; Anerella, M.; Barzi, E.; Bossert, R.; Caspi, S.; Chlachidize, G.; Dietderich, D.; Feher, S.; Felice, H.; Ferracin, P.; Ghosh, A.; Hafalia, A.R.; Hannaford, C.R.; Kashikhin, V.V.; Kerby, J.; Lamm, M.; Lietzke, A.; McInturff, A.; Muratore, J.; Nobrega, F.; Novitsky, I.; Sabbi, G.L.; Schmalzle, J.; Tartaglia, M.; Turrioni, D.; Wanderer, P.; Whitson, G.; Zlobin, A.V.

    2007-08-27

    A major milestone for the LHC Accelerator Research Program (LARP) is the test, by the end of 2009, of two 4m-long quadrupole magnets (LQ) wound with Nb{sub 3}Sn conductor. The goal of these magnets is to be a proof of principle that Nb{sub 3}Sn is a viable technology for a possible LHC luminosity upgrade. The design of the LQ is based on the design of the LARP Technological Quadrupoles, presently under development at FNAL and LBNL, with 90-mm aperture and gradient higher than 200 T/m. The design of the first LQ model will be completed by the end of 2007 with the selection of a mechanical design. In this paper we present the coil design addressing some fabrication technology issues, the quench protection study, and three designs of the support structure.

  6. LARP Long Nb3Sn Quadrupole Design

    SciTech Connect

    Ambrosio, G.; Andreev, N.; Anerella, M.; Barzi, E.; Bossert, R.; Caspi, S.; Chlachidze, G.; Dietderich, D.; Feher, S.; Felice, H.; Ferracin, P.; /Fermilab /Brookhaven /LBL, Berkeley /Texas A-M

    2007-08-01

    A major milestone for the LHC Accelerator Research Program (LARP) is the test, by the end of 2009, of two 4m-long quadrupole magnets (LQ) wound with Nb3Sn conductor. The goal of these magnets is to be a proof of principle that Nb3Sn is a viable technology for a possible LHC luminosity upgrade. The design of the LQ is based on the design of the LARP Technological Quadrupoles, presently under development at FNAL and LBNL, with 90-mm aperture and gradient higher than 200 T/m. The design of the first LQ model will be completed by the end of 2007 with the selection of a mechanical design. In this paper we present the coil design addressing some fabrication technology issues, the quench protection study, and three designs of the support structure.

  7. Effects of substrate temperature on properties of NbNx films grown on Nb by pulsed laser deposition

    SciTech Connect

    Ashraf Hassan Farha, Ali Oguz Er, Yüksel Ufuktepe, Ganapati Myneni, Hani E. Elsayed-Ali

    2011-12-01

    NbN{sub x} films were deposited on Nb substrate using pulsed laser deposition. The effects of substrate deposition temperature, from room temperature to 950 C, on the preferred orientation, phase, and surface properties of NbN{sub x} films were studied by X-ray diffraction, atomic force microscopy, and electron probe micro analyzer. We find that the substrate temperature is a critical factor in determining the phase of the NbN{sub x} films. For a substrate temperature up to 450 C the film showed poor crystalline quality. With temperature increase the film became textured and for a substrate temperature of 650-850 C, mix of cubic {delta}-NbN and hexagonal phases ({beta}-Nb{sub 2}N + {delta}'-NbN) were formed. Films with a mainly {beta}-Nb{sub 2}N hexagonal phase were obtained at deposition temperature above 850 C. The c/a ratio of {beta}-Nb{sub 2}N hexagonal shows an increase with increased nitrogen content. The surface roughness of the NbN{sub x} films increased as the temperature was raised from 450 to 850 C.

  8. Nonequilibrium synthesis of NbAl3 and Nb-Al-V alloys by laser cladding. II - Oxidation behavior

    NASA Technical Reports Server (NTRS)

    Haasch, R. T.; Tewari, S. K.; Sircar, S.; Loxton, C. M.; Mazumder, J.

    1992-01-01

    Isothermal oxidation behaviors of NbAl3 alloy synthesized by laser cladding were investigated at temperatures between 800 and 1400 C, and the effect of vanadium microalloying on the oxidation of the laser-clad alloy was examined. The oxidation kinetics of the two alloys were monitored using thermal gravimetric weight gain data, and the bulk and surface chemistries were analyzed using XRD and XPS, respectively. It was found that NbAl3 did not form an exclusive layer of protective Al2O3. The oxidation products at 800 C were found to be a mixture of Nb2O5 and Al2O3. At 1200 C, a mixture of NbAlO4, Nb2O5, and Al2O3 formed; and at 1400 C, a mixture of NbAlO4, Al2O3, NbO2, NbO(2.432), and Nb2O5 formed. The addition of V led to a dramatic increase of the oxidation rate, which may be related to the formation of (Nb, V)2O5 and VO2, which grows in preference to protective Al2O3.

  9. Zircon U-Pb age, Hf isotope and geochemistry of Carboniferous intrusions from the Langshan area, Inner Mongolia: Petrogenesis and tectonic implications

    NASA Astrophysics Data System (ADS)

    Liu, Min; Zhang, Da; Xiong, Guangqiang; Zhao, Hongtao; Di, Yongjun; Wang, Zhong; Zhou, Zhiguang

    2016-04-01

    Late Paleozoic was a critical period for the tectonic evolution of the northern margin of the Alxa-North China craton, but the evolutionary history is not well constrained. The Carboniferous intrusions in the Langshan area in the western part of the northern margin of the Alxa-North China craton are mainly composed of tonalite, quartz diorite, olivine gabbro and pyroxene peridotite. Zircon LA-ICP-MS U-Pb dating indicates that the Langshan Carboniferous intrusions were emplaced at ca. 338-324 Ma. The quartz diorites are characterized by high amounts of compatible trace elements (Cr, Ni and V) and high Mg# values, which may suggest a significant mantle source. The positive Pb and negative Nb-Ta-Ti anomalies, the variable εHf(t) (-6.9 to 2.0) values and the old Hf model ages (1218-1783 Ma) imply some involvement of ancient continental materials in its petrogenesis. The tonalite has relatively high Sr/Y ratios, low Mg#, Yb and Y contents, features of adakite-like rocks, negative εHf(t) values (-9.8 to -0.1) and older Hf model ages (1344-1953 Ma), which suggest significant involvement of ancient crust materials and mantle-derived basaltic component in its petrogenesis. The high Mg# values, high Cr and Ni contents, and low Zr and Hf contents of the mafic-ultramafic rocks show evidence of a mantle source, and the relatively low zircon εHf(t) values (-5.9 to 3.2) might point to an enriched mantle. The trace element characteristics indicate the influence of subducted sediments and slab-derived fluids. In the tectonic discrimination diagrams, all the rocks plot in subduction-related environment, such as volcanic arc and continental arc. Considering the regional geology, we suggest that the Carboniferous intrusions in the Langshan area were likely emplaced during the late stage of the southward subduction of the Paleo-Asian Ocean plate, which formed a continental arc along the northern margin of the Alxa-North China craton.

  10. "Fine grain Nb tube for SRF cavities"

    SciTech Connect

    Robert E. Barber

    2012-07-08

    Superconducting radio frequency (SRF) cavities used in charged particle linear accelerators, are currently fabricated by deep drawing niobium sheets and welding the drawn dishes together. The Nb sheet has a non-uniform microstructure, which leads to unpredictable cavity shape and surface roughness, and inconsistent "spring-back" during forming. In addition, weld zones cause hot spots during cavity operation. These factors limit linear accelerator performance and increase cavity manufacturing cost. Equal channel angular extrusion (ECAE) can be used to refine and homogenize the microstructure of Nb tube for subsequent hydroforming into SRF cavities. Careful selection of deformation and heat treatment conditions during the processing steps can give a uniform and consistent microstructure in the tube, leading to improved deformability and lower manufacturing costs. Favorable microstructures were achieved in short test samples of RRR Nb tube, which may be particularly suitable for hydroforming into SRF cavity strings. The approach demonstrated could be applicable to microstructure engineering of other tube materials including tantalum, titanium, and zirconium.

  11. Review of oxidation of Nb-1Zr

    SciTech Connect

    DiStefano, J.R.

    1989-04-01

    A major objective of the SP-100 Program Nuclear Assembly Test is to demonstrate the performance of a full-scale nuclear subsystem of a 100-kWe space nuclear power supply. The test will be run in a large vacuum chamber to protect the Nb-1Zr components from oxidation during operation. Much information about the oxidation of niobium and Nb-1Zr alloy already exists, and previous work in this area is reviewed. Oxidation of Nb-1Zr can proceed by solution, internal oxidation, and/or film formation. At temperatures up to about 650 K (377/degree/C), oxidation generally follows a parabolic rate law because of the formation of protective oxide(s). At higher temperatures, oxidation becomes linear, but results are extremely sensitive to pressure and other system variables. Results obtained by several investigators could not be predicted using empirical equations developed by one investigator relating the increase in oxygen concentration to pressure, temperature, time, and specimen thickness. Additional data are required to provide more reliable guidelines for system operation that will protect against catastrophic effects. 20 refs., 12 figs., 7 tabs.

  12. A routine high-precision method for Lu-Hf isotope geochemistry and chronology

    USGS Publications Warehouse

    Patchett, P.J.; Tatsumoto, M.

    1981-01-01

    A method for chemical separation of Lu and Hf from rock, meteorite and mineral samples is described, together with a much improved mass spectrometric running technique for Hf. This allows (i) geo- and cosmochronology using the176Lu???176Hf+??- decay scheme, and (ii) geochemical studies of planetary processes in the earth and moon. Chemical yields for the three-stage ion-exchange column procedure average 90% for Hf. Chemical blanks are <0.2 ng for Lu and Hf. From 1 ??g of Hf, a total ion current of 0.5??10-11 Ampere can be maintained for 3-5 h, yielding 0.01-0.03% precision on the ratio176Hf/177Hf. Normalisation to179Hf/177Hf=0.7325 is used. Extensive results for the Johnson Matthey Hf standard JMC 475 are presented, and this sample is urged as an international mass spectrometric standard; suitable aliquots, prepared from a single batch of JMC 475, are available from Denver. Lu-Hf analyses of the standard rocks BCR-1 and JB-1 are given. The potential of the Lu-Hf method in isotope geochemistry is assessed. ?? 1980 Springer-Verlag.

  13. 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.

  14. Investigation of etching techniques for superconductive Nb/Al-Al2O3/Nb fabrication processes

    NASA Technical Reports Server (NTRS)

    Lichtenberger, A. W.; Lea, D. M.; Lloyd, F. L.

    1993-01-01

    Wet etching, CF4 and SF6 reactive ion etching (RIE), RIE/wet hybrid etching, Cl-based RIE, ion milling, and liftoff techniques have been investigated for use in superconductive Nb/Al-Al2O3/Nb fabrication processes. High-quality superconductor-insulator-superconductor (SIS) junctions have been fabricated using a variety of these etching methods; however, each technique offers distinct tradeoffs for a given process an wafer design. In particular, it was shown that SF6 provides an excellent RIE chemistry for low-voltage anisotropic etching of Nb with high selectivity to Al. The SF6 tool has greatly improved the trilevel resist junction insulation process. Excellent repeatability, selectivity with respect to quartz, and submicron resolution make Cl2 + BCl3 + CHCl3 RIE a very attractive process for trilayer patterning.

  15. Comparative study of atomic-layer-deposited HfO2/Al2O3, Hf0.8Al0.2Ox and Hf0.5Al0.5Ox on N-GaAs

    NASA Astrophysics Data System (ADS)

    Yu, Xinjiang; Lv, Hongliang; Zhang, Yuming; Zhang, Yimen; Qin, Zaiyang

    2016-11-01

    Interfacial properties of n-GaAs metal-oxide-semiconductor (MOSCAPs) with the gate dielectrics of HfO2/Al2O3, Hf0.8Al0.2Ox and Hf0.5Al0.5Ox are investigated. The results reveal that Hf0.5Al0.5Ox has larger permittivity and lower interface trap density than that of HfO2/Al2O3. In order to explain the result from the physical perspective, the XPS tests of all three samples are performed. It is found that the main reason to form interface trap of three samples treated with 500 °C post-deposition annealing, is attributed to the interfacial component of Ga2O3 and The Hf0.5Al0.5Ox dielectric is beneficial to reducing the formation of Ga2O3.

  16. Draft Genome Sequence of Uropathogenic Escherichia coli Strain NB8

    PubMed Central

    Mi, Zu-huang; Wang, Chun-xin; Zhu, Jian-ming

    2016-01-01

    Escherichia coli NB8 is a clinical pyelonephritis isolate. Here, we report the draft genome sequence of uropathogenic E. coli NB8, which contains drug resistance genes encoding resistance to beta-lactams, aminoglycosides, quinolones, macrolides, colistin, sulfonamide-trimethoprim, and tetracycline. NB8 infects the kidney and bladder, making it an important tool for studying E. coli pathogenesis. PMID:27609920

  17. The Status of Rotational Nonequilibrium in HF Chemical Lasers

    DTIC Science & Technology

    1986-05-01

    8217 -" II. EVIDENCE FOR ROTATIONAL NONEQUILIBRIU IN HF LASERS Since 1967 there has been a mounting body of evidence that the rotational populations within a...Physique C9 41, 17 (1980). 100. L. H. Sentman and W. Rushmore , ATAA 81-4272 19j 1323 (1981). 101. L. H. Sentman, W. 0. Mosebach, and P. Renzoni, A

  18. First 100 ms of HF modification at Tromso, Norway

    NASA Astrophysics Data System (ADS)

    Djuth, F. T.; Isham, B.; Rietveld, M. T.; Hagfors, T.; La Hoz, C.

    Experiments were performed with the high-power high-frequency HF facility at Troms o Norway to test theoretical predictions for the excitation of ion and Langmuir oscillations in the ionosphere The principal diagnostic of wave-plasma interactions was the VHF radar at the European Incoherent Scatter EISCAT facility High resolution radar techniques were used to monitor the temporal development of the ion and Langmuir oscillations HF pulses 100 ms in duration were periodically transmitted into a smooth background F region plasma Measurements of the radar backscatter spectra show that all key spectral features predicted by strong Langmuir turbulence SLT theory modified Zakharov model are simultaneously present in the plasma and that their evolution is in agreement with theoretical expectations However several new features have been observed that cannot be anticipated by current theory because of limitations in the electric field strength within the simulations The experimental results reinforce the notion that new theoretical developments are needed to accommodate the large HF electric fields produced at Troms o and HAARP Gakona Alaska and to treat the electron acceleration process in a self-consistent fashion The F region response to two HF effective radiated power levels sim 58 MW and sim 125 MW was investigated at Troms o These ERP values include absorptive losses resulting from the sunlit D region In general the results at 58 MW ERP and 125 MW ERP are consistent with many of the SLT

  19. ORIGIN OF EXCESS {sup 176}Hf IN METEORITES

    SciTech Connect

    Thrane, Kristine; Connelly, James N.; Bizzarro, Martin; Meyer, Bradley S.; The, Lih-Sin

    2010-07-10

    After considerable controversy regarding the {sup 176}Lu decay constant ({lambda}{sup 176}Lu), there is now widespread agreement that (1.867 {+-} 0.008) x 10{sup -11} yr{sup -1} as confirmed by various terrestrial objects and a 4557 Myr meteorite is correct. This leaves the {sup 176}Hf excesses that are correlated with Lu/Hf elemental ratios in meteorites older than {approx}4.56 Ga meteorites unresolved. We attribute {sup 176}Hf excess in older meteorites to an accelerated decay of {sup 176}Lu caused by excitation of the long-lived {sup 176}Lu ground state to a short-lived {sup 176m}Lu isomer. The energy needed to cause this transition is ascribed to a post-crystallization spray of cosmic rays accelerated by nearby supernova(e) that occurred after 4564.5 Ma. The majority of these cosmic rays are estimated to penetrate accreted material down to 10-20 m, whereas a small fraction penetrate as deep as 100-200 m, predicting decreased excesses of {sup 176}Hf with depth of burial at the time of the irradiation event.

  20. Noble gas encapsulation: clathrate hydrates and their HF doped analogues.

    PubMed

    Mondal, Sukanta; Chattaraj, Pratim Kumar

    2014-09-07

    The significance of clathrate hydrates lies in their ability to encapsulate a vast range of inert gases. Although the natural abundance of a few noble gases (Kr and Xe) is poor their hydrates are generally abundant. It has already been reported that HF doping enhances the stability of hydrogen hydrates and methane hydrates, which prompted us to perform a model study on helium, neon and argon hydrates with their HF doped analogues. For this purpose 5(12), 5(12)6(8) and their HF doped analogues are taken as the model clathrate hydrates, which are among the building blocks of sI, sII and sH types of clathrate hydrate crystals. We use the dispersion corrected and gradient corrected hybrid density functional theory for the calculation of thermodynamic parameters as well as conceptual density functional theory based reactivity descriptors. The method of the ab initio molecular dynamics (AIMD) simulation is used through atom centered density matrix propagation (ADMP) techniques to envisage the structural behaviour of different noble gas hydrates on a 500 fs timescale. Electron density analysis is carried out to understand the nature of Ng-OH2, Ng-FH and Ng-Ng interactions. The current results noticeably demonstrate that the noble gas (He, Ne, and Ar) encapsulation ability of 5(12), 5(12)6(8) and their HF doped analogues is thermodynamically favourable.

  1. The multilayer Fe/Hf studied with slow positron beam

    NASA Astrophysics Data System (ADS)

    Murashige, Y.; Tashiro, M.; Nakajyo, T.; Koizumi, T.; Kanazawa, I.; Komori, F.; Ito, Y.

    1997-04-01

    The positron annihilation parameter versus the incident positron energy is measured in the thin Fe films and the Fe/Hf bilayer on silica substrate, by means of the variable energetic slow-positron beam technique. We have analyzed the change in open-volume spaces and vacancy-type defects among the Fe microcrystals in these thin films with the deposition temperature.

  2. Spectral output from a premixed chain reaction cw HF laser

    SciTech Connect

    Stanton, A.C.; Bien, F.

    1980-07-01

    Spectral measurements of the output from a purely chemical chain reaction cw HF laser are reported. The laser is a subsonic H/sub 2/-F/sub 2/ flame, with supersonic premixing and spatially uniform initiation by a stationary normal shock. Initial chemical production of fluorine atoms is by the bimolecular reaction of F/sub 2/ with NO. Spectral measurements of the laser output near the initiating shock indicate lasing transitions in the P branches of the v=3 ..-->.. v=2, v=2 ..-->.. v=1, and v=1 ..-->.. v=0 HF bands. Further downstream, the upper vibrational levels are strongly deactivated, and lasing occurs only in the v=1 ..-->.. v=0 band. Laser emission in the v=2 ..-->.. v=1 band reappears at reduced NO flow rates, suggesting efficient deactivation of HF (v) by NO, possibly through multiquantum V-V exchange. An approximate rate of 5 x 10/sup -13plus-or-minus0.5/ cm/sup 3//sec for deactivation of HF (v=2) by NO is inferred.

  3. Regioselective toluene nitration catalyzed with layered HNbMoO6

    NASA Astrophysics Data System (ADS)

    Hu, Li-Fang; Tang, Yuan; He, Jie; Chen, Kai; Lv, Wei

    2017-03-01

    HNbMoO6 layered oxide was obtained by the ion-exchange from LiNbMoO6 prepared by solid state reaction (SSR). The micro-structure, textural characteristics and acidity of the as-prepared catalyst were characterized by powder X-ray diffraction (XRD), laser Raman spectroscopy (LRS) and ammonia temperature- programmed desorption (NH3-TPD). Catalytic performance was evaluated in the regioselective nitration of toluene with a novel nitration system containing acetic anhydride and CCl4. The optimal nitration conditions comprise the application of 95 wt % HNO3, HNO3-to-toluene molar ratio of 2.5, catalyst pretreatment temperature of 503 K, reaction temperature of 313 K, and reaction time of 2.5 h. The toluene conversion rate and para-selectivity were also attributable to the strong acidity and the appropriate interlayer distance of the studied catalyst.

  4. Structure change, layer sliding, and metallization in high-pressure MoS2

    NASA Astrophysics Data System (ADS)

    Tosatti, Erio; Hromadova, Liliana; Martonak, Roman

    2013-03-01

    Based on ab initio calculations and metadynamics simulations, we predict that 2H-MoS2, a layered insulator, will metallize under pressures in excess of 20-30 GPa. In the same pressure range, simulations and enthalpy optimization predict a structural transition. Reminiscent of this material's frictional properties, free mutual sliding of layers takes place at this transition, where the original 2Hc stacking changes to a 2Ha stacking typical of 2H-NbSe2, a transformation which explains for the first time previously mysterious X-ray diffraction data. Phonon and electron phonon calculations suggest that metallic pristine MoS2 will require ultrahigh pressures in order to develop superconductivity. Supported by EU-Japan Project LEMSUPER, by a SNF Sinergia Project, and by the Slovak Research and Development Agency

  5. Freestanding HfO2 grating fabricated by fast atom beam etching

    NASA Astrophysics Data System (ADS)

    Wang, Yongjin; Wu, Tong; Kanamori, Yoshiaki; Hane, Kazuhiro

    2011-04-01

    We report here the fabrication of freestanding HfO2 grating by combining fast atom beam etching (FAB) of HfO2 film with dry etching of silicon substrate. HfO2 film is deposited onto silicon substrate by electron beam evaporator. The grating patterns are then defined by electron beam lithography and transferred to HfO2 film by FAB etching. The silicon substrate beneath the HfO2 grating region is removed to make the HfO2 grating suspend in space. Period- and polarization-dependent optical responses of fabricated HfO2 gratings are experimentally characterized in the reflectance measurements. The simple process is feasible for fabricating freestanding HfO2 grating that is a potential candidate for single layer dielectric reflector. PACS: 73.40.Ty; 42.70.Qs; 81.65.Cf.

  6. Nb-H system at high pressures and temperatures

    NASA Astrophysics Data System (ADS)

    Liu, Guangtao; Besedin, Stanislav; Irodova, Alla; Liu, Hanyu; Gao, Guoying; Eremets, Mikhail; Wang, Xin; Ma, Yanming

    2017-03-01

    We studied the Nb-H system over extended pressure and temperature ranges to establish the highest level of hydrogen abundance we could achieve from the resulting alloy. We probed the Nb-H system with laser heating and x-ray diffraction complemented by numerical density functional theory-based simulations. New quenched double hexagonal close-packed (hcp) Nb H2.5 appears under 46 GPa, and above 56 GPa cubic Nb H3 is formed as theoretically predicted. Nb atoms are arranged in close-packed lattices which are martensitically transformed in the sequence: face-centered cubic (fcc) → hcp → double hcp (dhcp) → distorted body-centered cubic (bcc) as pressure increases. The appearance of fcc Nb H2.5 -3 and dhcp Nb H2.5 cannot be understood in terms of enthalpic stability, but can be rationalized when finite temperatures are taken into account. The structural and compressional behavior of Nb Hx >2 is similar to that of NbH. Nevertheless, a direct H-H interaction emerges with hydrogen concentration increases, which manifests itself via a reduction in the lattice expansion induced by hydrogen dissolution.

  7. In-reactor deformation of cold-worked Zr 2.5Nb pressure tubes

    NASA Astrophysics Data System (ADS)

    Holt, R. A.

    2008-01-01

    Over forty years of in-reactor testing and over thirty years of operating experience in power reactors have provided a broad understanding of the in-reactor deformation of cold-worked Zr-2.5Nb pressure tubes, and an extensive data-base upon which to base models for managing the life of existing reactors and for designing new ones. The effects of the major operating variables and many of the metallurgical variables are broadly understood. The deformation is often considered to comprise three components: thermal creep, irradiation growth and irradiation creep. Of the three, irradiation growth is best understood - it is thought to be driven by the diffusional anisotropy difference (DAD). It is still not clear whether the enhancement of creep by irradiation is due to climb-plus-glide (CPG), stress-induced preferred absorption (SIPA) or elasto-diffusion (ED). The least understood area is the transition between thermal creep and irradiation where the fast neutron flux may either suppress or enhance the creep rate. The three components are generally treated as additive in the models, although it is recognized that this is only a crude approximation of reality. There are still significant gaps in our knowledge besides the thermal- to irradiation-creep transition, for example, the effect of Mo which is produced from Nb by transmutation in the thermal neutron flux is not known, and on-going work is required in a number of areas. This paper reviews the current state of knowledge of the in-reactor deformation of cold-worked Zr-2.5Nb pressure tubes, and highlights areas for further research.

  8. Effects of Zr impurity on microscopic behavior of Hf metal

    NASA Astrophysics Data System (ADS)

    Dey, S. K.; Dey, C. C.; Saha, S.

    2016-08-01

    Hf metal with ∼ 3 wt% Zr impurity has been reinvestigated by perturbed angular correlation (PAC) spectroscopy using a LaBr3(Ce)-BaF2 detector set up to understand the microscopic behavior of this metal with temperature. From present measurements, five quadrupole interaction frequencies have been found at room temperature where both pure hcp fraction (∼33%) with 12 nearest neighbor Hf surrounding the probe 181Hf atom and the probe-impurity fraction (∼33%) corresponding to 11 nearest neighbor Hf plus one dissimilar Zr atom are clearly distinguished. At room temperature, the results for quadrupole frequency and asymmetry parameter are found to be ωQ=51.6(4) Mrad/s, η=0.20(4) for the impurity fraction and ωQ=46.8(2) Mrad/s, η=0 for the pure fraction with values of frequency distribution width δ=0 for both components. At 77 K, only 1 NN Zr impurity (∼93%) and pure hcp (∼7%) components have been found with a value of δ ∼ 10% for the impurity fraction. A drastic change in microstructural configuration of Hf metal is observed at 473 K where the impurity fraction increases to ∼ 50% and the pure hcp fraction reduces to ∼ 15% with abrupt changes in quadrupole frequencies for both components. The pure fraction then increases with temperature and enhances to ∼50% at 973 K. In the temperature range 473-973 K, quadrupole frequencies for both components are found to decrease slowly with temperature. Using the Arrhenius relation, binding energy (B) for the probe-impurity pair and the entropy of formation are measured from temperature dependent fractions of probe-impurity and pure hcp in the temperature range 473-773 K. The three other minor components found at different temperatures are attributed to crystalline defects.

  9. Mo-Si alloy development

    SciTech Connect

    Liu, C.T.; Heatherly, L.; Wright, J.L.

    1996-06-01

    The objective of this task is to develop new-generation corrosion-resistant Mo-Si intermetallic alloys as hot components in advanced fossil energy conversion and combustion systems. The initial effort is devoted to Mo{sub 5}-Si{sub 3}-base (MSB) alloys containing boron additions. Three MSB alloys based on Mo-10.5Si-1.1B (wt %), weighing 1500 g were prepared by hot pressing of elemental and alloy powders at temperatures to 1600{degrees}C in vacuum. Microporosities and glassy-phase (probably silicate phases) formations are identified as the major concerns for preparation of MSB alloys by powder metallurgy. Suggestions are made to alleviate the problems of material processing.

  10. Mo-Si-B Alloy Development

    SciTech Connect

    Schneibel, J.H.; Kruzie, J.J.; Ritchie, R.O.

    2003-04-24

    Mo-Si-B silicides consisting of the phases {alpha}-Mo (Mo solid solution), Mo{sub 3}Si, and Mo{sub 5}SiB{sub 2} have melting points on the order of 2000 C and have potential as ultra-high temperature structural materials. Mo-Si-B alloys can be processed such that the {alpha}-Mo is present in the form of isolated particles in a silicide matrix, or as a continuous matrix ''cementing'' individual silicide particles together. The latter microstructure is similar to that of WC-Co hard metals. This paper focuses on the relationship between the topology as well as scale of the microstructure of Mo-Mo{sub 3}Si-Mo{sub 5}SiB{sub 2} alloys, and their creep strength and fracture toughness. For example, the creep strength of Mo-Si-B alloys is improved by reducing the {alpha}-Mo volume fraction and by making the {alpha}-Mo phase discontinuous. The fracture toughness is improved by increasing the {alpha}-Mo volume fraction and by making the {alpha}-Mo phase continuous. Room temperature stress intensity factors as high as 21 MPa m{sup 1/2} were obtained. The room temperature fracture toughness of Mo-Si-B alloys can also be improved by microalloying with Zr. The room temperature ductility of Mo itself can be improved by adding MgAl{sub 2}O{sub 4} spinel particles suggesting yet another way to improve the ductile phase toughening of Mo-Si-B alloys.

  11. A first principles thermodynamic study of Si-HfO2 and Pt-HfO2 interfaces

    NASA Astrophysics Data System (ADS)

    Zhu, Hong; Ramprasad, Rampi

    2012-02-01

    Atomic-level control of dielectric-semiconductor and dielectric-metal interfaces has become critical in determining the properties of the emerging high-k oxide-based MOSFETs. Using Si-HfO2 and Pt-HfO2 as an example, we investigate the evolution of these interface structures and electronic properties as a function of processing conditions by combining density functional theory results and statistical thermodynamics. Firstly, using first principles thermodynamics (FPTs), we determine the phase diagrams of Si-HfO2 and Pt-HfO2 interfaces. The vibrational and configurational entropic contributions to the free energies of the condensed phases are explicitly included. We demonstrate that the predictions of the FPT approach are in quantitative agreement with experiments for the interfaces considered. Secondly, a parameter-free methodology to determine the work function shift (or effective work function, EWF) of metal when interfaced with oxide is developed. This strategy is combined with statistical thermodynamics to predict the most probable EWF at given processing condition. The favorable agreement between the computed and experimental EWFs under generally adopted conditions is indicative of the usefulness of such full first-principles property-processing relationship studies.

  12. Observation of Reliability of HfZrOX Gate Dielectric Devices with Different Zr/Hf Ratios

    NASA Astrophysics Data System (ADS)

    Liao, Jing-Chyi; Fang, Yean-Kuen; Tian Hou, Yong; Hsiung Tseng, Wei; Yang, Chih I.; Hsu, Peng Fu; Chao, Yuen Shun; Lin, Kang Cheng; Huang, Kuo Tai; Lee, Tzu Liang; Liang, Meng Sung

    2008-04-01

    The impact of the Zr/Hf ratio on the reliability of a HfZrOX gate dielectric has been investigated in detail. By a frequency-varied charge-pumping method, we found that the density of bulk traps is reduced with increasing Zr content. Also, a comparable Dit value observed by the rising/falling time-varied charge-pumping method suggests that Zr incorporation does not degrade the interface quality. Consequently, mobility increases with increasing Zr content in the HfZrOX dielectric and ˜25% mobility enhancement compared with that of HfO2 can be observed. However, the bulk trap density reduction reaches saturation at a higher Zr content. The improvement in positive-bias temperature instability (PBTI) was also demonstrated by both DC and pulse techniques. The smaller Vth shift in PBTI is attributed to the reduction of fast trapping and the generation of slow traps. Finally, a reduced gate-induced drain leakage current (GIDL) was also observed with increasing Zr content because of the reduction of trap-assisted tunneling in a high-k film.

  13. 40 CFR 180.1273 - Beauveria bassiana HF23; exemption from the requirement of a tolerance.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 23 2010-07-01 2010-07-01 false Beauveria bassiana HF23; exemption... FOOD Exemptions From Tolerances § 180.1273 Beauveria bassiana HF23; exemption from the requirement of a tolerance. Residues of Beauveria bassiana HF23 are exempt from the requirement of a tolerance on all...

  14. 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.

  15. Level structure of 89Mo

    NASA Astrophysics Data System (ADS)

    García-Bermúdez, G.; Cardona, M. A.; Ribas, R. V.; Filevich, A.; Achterberg, E.; Szybisz, L.

    1993-10-01

    The level structure of 89Mo has been studied with the 60Ni(32S,2pn) reaction at 110 MeV beam energy. Mainly two bands of γ rays depopulating states of probable spin-parity values ranging up to (27/2)+ were determined from the excitation function, neutron and γ-γ coincidences, and γ-ray angular distributions. The high-spin states of 89Mo show a scheme very similar to that of the 87Zr isotone. The interpretation of these states in terms of the three neutron-hole configuration (νg9/2)-3 and core-excited states is discussed.

  16. Petrogenesis of the Cretaceous Zhangzhou batholith in southeastern China: Zircon U-Pb age and Sr-Nd-Hf-O isotopic evidence

    NASA Astrophysics Data System (ADS)

    Chen, Jing-Yuan; Yang, Jin-Hui; Zhang, Ji-Heng; Sun, Jin-Feng; Wilde, Simon A.

    2013-03-01

    Whole-rock geochemical and Sr-Nd-Hf isotopic data and in situ zircon U-Pb and Hf-O isotopes have been determined for mafic (gabbro and diorite) and felsic (I- and A-type granites) rocks from the Zhangzhou batholith in southeastern (SE) China, in order to constrain their source and petrogenesis. The batholith consists of gabbro, diorite, granodiorite, monzogranite and alkali feldspar granite, with mafic microgranular enclaves in the monzogranite. Zircon SIMS and LA-ICP-MS U-Pb dating gives consistent emplacement ages of 107-97 Ma for these rocks, establishing that the mafic and felsic magmas were coeval. The gabbros and diorites have relatively high MgO contents (up to 5.2 wt.%) at low silica concentrations (up to 49.9 wt.%), with relatively homogeneous whole-rock initial 87Sr/86Sr ratios (~ 0.706), negative ɛNd(t) values of - 3.4 to - 2.7, chondrite-like ɛHf(t) values of - 0.3 to + 0.5, zircon ɛHf(t) values of - 0.8 to + 3.2 and δ18O values of + 5.0 to + 6.1‰, indicating that they were derived by partial melting of an enriched subcontinental lithospheric mantle, coupled with olivine and pyroxene fractionation. The calc-alkaline granodiorites and monzogranites are metaluminous and have relatively high SiO2 and low MgO contents. They have whole-rock initial 87Sr/86Sr ratios of 0.706, ɛNd(t) ratio of - 3.0 to - 4.0, ɛHf(t) values of - 2.0 to + 0.3 and zircon ɛHf(t) values of - 4.4 to + 0.3, with Nd and Hf model ages of about 1.3 Ga, indicating that they were mainly derived by partial melting of old continental crustal materials. The alkali feldspar granites have geochemical features similar to A-type granite, with relatively high K2O + Na2O and Nb contents and FeO/MgO and Ga/Al ratios. They have distinct isotopic compositions from the associated mafic rocks, with ɛNd(t) values of - 4.9, ɛHf(t) values of - 3.2 to - 3.5, zircon ɛHf(t) values of - 5.1 to + 1.0 and δ18O values of + 5.1‰ to + 6.3‰. They are depleted in Sr, Ba and Eu, indicating that they

  17. Molybdenum(VI) oxosulfato complexes in MoO3-K2S2O7-K2SO4 molten mixtures: stoichiometry, vibrational properties, and molecular structures.

    PubMed

    Kalampounias, Angelos G; Tsilomelekis, George; Berg, Rolf W; Boghosian, Soghomon

    2012-09-06

    ) stretching modes: (1) at 957 (polarized) and 918 (depolarized) cm(–1) for the ν(s) and ν(as) Mo(═O)(2) modes of MoO(2)(SO(4))(2)(2–) and [MoO(2)(SO(4))(2)](m)(2m–) and (2) at 935 (polarized) and 895 (depolarized) cm(–1) for the respective modes of MoO(2)(SO(4))(3)(4–) and [MoO(2)(SO(4))(3)](m)(4m–). The results were tested and found to be in accordance with ab initio quantum chemical calculations carried out on [MoO(2)(SO(4))(3)](4–) and [{MoO(2)}(2)(SO(4))(4)(μ-SO(4))(2)](8–) ions, in assumed isolated gaseous free states, at the DFT/B3LYP (HF) level and with the 3-21G basis set. The calculations included determination of vibrational infrared and Raman spectra, by use of force constants in the Gaussian 03W program.

  18. Structural stability of characteristic interface for NiTi/Nb Nanowire: First-Principle study

    NASA Astrophysics Data System (ADS)

    Li, G. F.; Zheng, H. Z.; Shu, X. Y.; Peng, P.

    2016-01-01

    Compared with some other conventional interface models, the interface of NiTi(211)/Nb(220) in NiTiNb metal nanocomposite had been simulated and analyzed carefully. Results show that only several interface models, i.e., NiTi(100)/Nb(100)(Ni⃡Nb), NiTi(110)/Nb(110) and NiTi(211)/Nb(220), can be formed accordingly with their negative formation enthalpy. Therein the cohesive energy Δ E and Griffith rupture work W of NiTi(211)/Nb(220) interface model are the lowest among them. Density of states shows that there exists only one electronic bonding peak for NiTi(211)/Nb(220) interface model at -2.5 eV. Electron density difference of NiTi(211)/ Nb(220) shows that the Nb-Nb, Nb-Ti and Nb-Ni bonding characters seem like so peaceful as a fabric twisting every atom, which is different from conventional metallic bonding performance. Such appearance can be deduced that the metallic bonding between Nb-Nb, Nb-Ti and Nb-Ni in NiTi(211)/Nb(220) may be affected by its nanostructure called nanometer size effect. Thus, our findings open an avenue for detailed and comprehensive studies of nanocomposite.

  19. Low temperature properties of spin filter NbN/GdN/NbN Josephson junctions

    NASA Astrophysics Data System (ADS)

    Massarotti, D.; Caruso, R.; Pal, A.; Rotoli, G.; Longobardi, L.; Pepe, G. P.; Blamire, M. G.; Tafuri, F.

    2017-02-01

    A ferromagnetic Josephson junction (JJ) represents a special class of hybrid system where different ordered phases meet and generate novel physics. In this work we report on the transport measurements of underdamped ferromagnetic NbN/GdN/NbN JJs at low temperatures. In these junctions the ferromagnetic insulator gadolinium nitride barrier generates spin-filtering properties and a dominant second harmonic component in the current-phase relation. These features make spin filter junctions quite interesting also in terms of fundamental studies on phase dynamics and dissipation. We discuss the fingerprints of spin filter JJs, through complementary transport measurements, and their implications on the phase dynamics, through standard measurements of switching current distributions. NbN/GdN/NbN JJs, where spin filter properties can be controllably tuned along with the critical current density (Jc), turn to be a very relevant term of reference to understand phase dynamics and dissipation in an enlarged class of JJs, not necessarily falling in the standard tunnel limit characterized by low Jc values.

  20. Edge-Geometry NbN/MgO/NbN Tunnel Junctions

    NASA Technical Reports Server (NTRS)

    Hunt, Brian D.; Leduc, Henry G.

    1991-01-01

    Superconductor/insulator/superconductor (SIS) tunnel junctions fabricated with base and counter electrodes of NbN separated by thin layers of MgO. Useful as submillimeter-wave mixers and fast switches. Use of edge geometry to define small junction makes possible to fabricate junction by process including conventional photolithography.

  1. Observed and simulated time evolution of HCl, ClONO2, and HF total columns

    NASA Astrophysics Data System (ADS)

    Ruhnke, Roland; Geomon, Ndacc Infrared, Modelling Working Group

    2010-05-01

    GEOmon, NDACC Infrared, and Modelling Working Group: M.P. Chipperfield (2), M. De Mazière (3), J. Notholt (4), S. Barthlott (1), R.L. Batchelor (5,17), R.D. Blatherwick (16), Th. Blumenstock (1), M.T. Coffey (17), P. Duchatelet (6), H. Fast (7), W. Feng (2), A. Goldman (16), D.W.T. Griffith (8), K. Hamann (1), J.W. Hannigan (17), F. Hase (1), N.B. Jones (8), A. Kagawa (9,10), Y. Kasai (9), O. Kirner (19), R. Kohlhepp (1), W. Kouker (1), I. Kramer (1), R. Lindenmaier (5), E. Mahieu (6), R.L. Mittermeier (7), B. Monge-Sanz (2), I. Murata (12), H. Nakajima (13), I. Morino (11), M. Palm (4), C. Paton-Walsh (8), Th. Reddmann (1), M. Rettinger (15), C.P. Rinsland (18), M. Schneider (1), C. Senten (3), B.-M. Sinnhuber (4), D. Smale (14), K. Strong (5), R. Sussmann (15), J.R. Taylor (5), G. Vanhaelewyn (3), T. Warneke (4), C. Whaley (5), M. Wiehle (1), and S.W. Wood (14) (1) Karlsruhe Institute of Technology (KIT), IMK-ASF, Karlsruhe, Germany, (2) University of Leeds, Leeds, United Kingdom, (3) Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium, (4) University of Bremen, Institute of Environmental Physics, Bremen, Germany, (5) Department of Physics, University of Toronto, Toronto, Ontario, Canada, (6) University of Liège, Institute of Astrophysics and Geophysics, Liège, Belgium, (7) Environment Canada, Toronto, Ontario, Canada, (8) Centre for Atmospheric Chemistry, University of Wollongong, Wollongong, Australia, (9) National Institute of Information and Communications Technology, Tokyo, Japan, (10) Fujitsu FIP Corporation, Tokyo, Japan, (11) Center for Global Environmental Research, National Institute for Environmental Studies (NIES), Japan, (12) Department of Environmental Studies, Graduate School of Environmental Studies, Tohoku University, Japan, (13) Atmospheric Environment Division, National Institute for Environmental Studies, Japan, (14) National Institute of Water and Atmospheric Research Ltd (NIWA), Lauder, New Zealand, (15) Karlsruhe

  2. The production of W-0.35HfC (Mol %) wirebar by arc melting and high energy rate extrusion of small diameter ingots

    NASA Astrophysics Data System (ADS)

    Buckman, R. William; Begg, Lester L.

    1991-01-01

    Tungsten alloy fiber reinforced tungsten is a candidate emitter material for space nuclear thermionic multi-kilowatt power systems. Fuel swelling which results in emitter deformation has been a primary concern for being able to achieve long lived (7 years or greater) thermionic fuel elements (TFE) operating at temperatures at or above 1900 K. The tungsten alloy (W-0.35 mo/%HfC) has extremely attractive mechanical properties above 1900 K and is a candidate reinforcement of tungsten for emitters. Because of its high strength, processing of the W-035HfC alloy to small diameter (0.38mm) wire has been difficult and the yield of useable product has been low. The purpose of this work was to demonstrate that by vacuum arc melting 38mm diameter ingots and high energy rate extrusions, small diameter (18mm) rod could be produced which is more compatible with swaging equipment used in tungsten wire production. Six 38 mm diameter ingots of W-0.35 HfC were produced by consumable electrode vacuum arc melting. The ingots were clad in 46 mm diameter molybdenum heated to 2270K and successfully extruded through a zirconia coated die at a reduction ratio of 7:1. The microstructure of the as-extruded bars is highly worked and should be amenable to processing to small diameter wire.

  3. The production of W-0. 35HfC (Mol %) wirebar by arc melting and high energy rate extrusion of small diameter ingots

    SciTech Connect

    Buckman, R.W. Jr. ); Begg, L.L. )

    1991-01-01

    Tungsten alloy fiber reinforced tungsten is a candidate emitter material for space nuclear thermionic multi-kilowatt power systems. Fuel swelling which results in emitter deformation has been a primary concern for being able to achieve long lived (7 years or greater) thermionic fuel elements (TFE) operating at temperatures at or above 1900 K. The tungsten alloy (W-0.35 mo/%HfC) has extremely attractive mechanical properties above 1900 K and is a candidate reinforcement of tungsten for emitters. Because of its high strength, processing of the W-035HfC alloy to small diameter (0.38mm) wire has been difficult and the yield of useable product has been low. The purpose of this work was to demonstrate that by vacuum arc melting 38mm diameter ingots and high energy rate extrusions, small diameter (18mm) rod could be produced which is more compatible with swaging equipment used in tungsten wire production. Six 38 mm diameter ingots of W-0.35 HfC were produced by consumable electrode vacuum arc melting. The ingots were clad in 46 mm diameter molybdenum heated to 2270K and successfully extruded through a zirconia coated die at a reduction ratio of 7:1. The microstructure of the as-extruded bars is highly worked and should be amenable to processing to small diameter wire.

  4. GalevNB: from simulations to observations

    NASA Astrophysics Data System (ADS)

    Pang, Xiaoying; Olczak, Christoph; Spurzem, Rainer

    2017-03-01

    We present GalevNB (Galev for N-body simulations), an utility that converts fundamental stellar properties of N-body simulations into observational properties using the GALEV (GAlaxy EVolutionary synthesis models) package, and thus allowing direct comparisons between observations and N-body simulations. It converts the fundamental stellar properties of N-body simulations, i.e., stellar mass, temperature, stellar luminosity and metallicity, into observational magnitudes for a variety of filters of widely used instruments/telescopes (HST, ESO, SDSS, 2MASS), and into spectra that span from far-UV (90 Å) to near-IR (160 μm).

  5. Surface studies of plasma processed Nb samples

    SciTech Connect

    Tyagi, Puneet V.; Doleans, Marc; Hannah, Brian S.; Afanador, Ralph; Stewart, Stephen; Mammosser, John; Howell, Matthew P; Saunders, Jeffrey W; Degraff, Brian D; Kim, Sang-Ho

    2015-01-01

    Contaminants present at top surface of superconducting radio frequency (SRF) cavities can act as field emitters and restrict the cavity accelerating gradient. A room temperature in-situ plasma processing technology for SRF cavities aiming to clean hydrocarbons from inner surface of cavities has been recently developed at the Spallation Neutron Source (SNS). Surface studies of the plasma-processed Nb samples by Secondary ion mass spectrometry (SIMS) and Scanning Kelvin Probe (SKP) showed that the NeO2 plasma processing is very effective to remove carbonaceous contaminants from top surface and improves the surface work function by 0.5 to 1.0 eV.

  6. First-principles study of electronic properties of La2Hf2O7 and Gd2Hf2O7

    SciTech Connect

    Li, Ni; Xiao, H. Y.; Zu, Xiaotao T.; Wang, Lumin M.; Ewing, R. C.; Lian, Jie; Gao, Fei

    2007-09-15

    The structural and electronic properties of A2Hf2O7 (A=La and Gd) pyrochlore compounds are investigated by means of first-principles total energy calculations. Also, the formation energies of defects are calculated, and the results can be used to explain the stability of pyrochlores. Hybridizations between A 5p and O 2s and between A 5d and O 2p states are observed, but the interaction between A 5p and O 2s orbitals is much stronger in Gd2Hf2O7 than that in La2Hf2O7. Gd2Hf2O7 compound shows much different density of state distribution from that of La2Hf2O7. Mulliken overlap population analysis shows that the A-O48f and A-O8b bonds in Gd2Hf2O7 are more ionic than the corresponding bonds in La2Hf2O7, while the Hf-O48f bond in Gd2Hf2O7 is more covalent. These calculations suggest that A-O48f and A-O8b bonds may play important roles in their responses to irradiation-induced amorphization observed experimentally.

  7. Action mechanism of hydrogen gas on deposition of HfC coating using HfCl4-CH4-H2-Ar system

    NASA Astrophysics Data System (ADS)

    Wang, Yalei; Li, Zehao; Xiong, Xiang; Li, Xiaobin; Chen, Zhaoke; Sun, Wei

    2016-12-01

    Hafnium carbide coatings were deposited on carbon/carbon composites by low pressure chemical vapor deposition using HfCl4-CH4-H2-Ar system. The microstructure, mechanical and ablation resistance performance of HfC coatings deposited with various H2 concentrations were investigated. The effect of hydrogen gas on the deposition of HfC coating was also discussed. Results show that all of the deposited coatings are composed of single cubic HfC phase, the hydrogen gas acted as a crucial role in determining the preferred orientation, microstructure and growth behavior of HfC coatings. During the deposition process, the gas phase supersaturation of the reaction species can be controlled by adjusting the hydrogen gas concentration. When deposited with low hydrogen gas concentration, the coating growth was dominated by the nucleation of HfC, which results in the particle-stacked structure of HfC coating. Otherwise, the coating growth was dominated by the crystal growth at high hydrogen gas concentration, which leads to the column-arranged structure of HfC coating. Under the ablation environment, the coating C2 exhibits better configurational stability and ablation resistance. The coating structure has a significant influence on the mechanical and ablation resistance properties of HfC coating.

  8. Discovery of Superconductivity in Hard Hexagonal ε-NbN.

    PubMed

    Zou, Yongtao; Qi, Xintong; Zhang, Cheng; Ma, Shuailing; Zhang, Wei; Li, Ying; Chen, Ting; Wang, Xuebing; Chen, Zhiqiang; Welch, David; Zhu, Pinwen; Liu, Bingbing; Li, Qiang; Cui, Tian; Li, Baosheng

    2016-02-29

    Since the discovery of superconductivity in boron-doped diamond with a critical temperature (TC) near 4 K, great interest has been attracted in hard superconductors such as transition-metal nitrides and carbides. Here we report the new discovery of superconductivity in polycrystalline hexagonal ε-NbN synthesized at high pressure and high temperature. Direct magnetization and electrical resistivity measurements demonstrate that the superconductivity in bulk polycrystalline hexagonal ε-NbN is below ∼11.6 K, which is significantly higher than that for boron-doped diamond. The nature of superconductivity in hexagonal ε-NbN and the physical mechanism for the relatively lower TC have been addressed by the weaker bonding in the Nb-N network, the co-planarity of Nb-N layer as well as its relatively weaker electron-phonon coupling, as compared with the cubic δ-NbN counterpart. Moreover, the newly discovered ε-NbN superconductor remains stable at pressures up to ∼20 GPa and is significantly harder than cubic δ-NbN; it is as hard as sapphire, ultra-incompressible and has a high shear rigidity of 201 GPa to rival hard/superhard material γ-B (∼227 GPa). This exploration opens a new class of highly desirable materials combining the outstanding mechanical/elastic properties with superconductivity, which may be particularly attractive for its technological and engineering applications in extreme environments.

  9. Discovery of superconductivity in hard hexagonal ε-NbN

    DOE PAGES

    Zou, Yongtao; Li, Qiang; Qi, Xintong; ...

    2016-02-29

    Since the discovery of superconductivity in boron-doped diamond with a critical temperature (TC) near 4 K, great interest has been attracted in hard superconductors such as transition-metal nitrides and carbides. Here we report the new discovery of superconductivity in polycrystalline hexagonal ε-NbN synthesized at high pressure and high temperature. Direct magnetization and electrical resistivity measurements demonstrate that the superconductivity in bulk polycrystalline hexagonal ε-NbN is below ~11.6 K, which is significantly higher than that for boron-doped diamond. The nature of superconductivity in hexagonal ε-NbN and the physical mechanism for the relatively lower TC have been addressed by the weaker bondingmore » in the Nb-N network, the co-planarity of Nb-N layer as well as its relatively weaker electron-phonon coupling, as compared with the cubic δ-NbN counterpart. Moreover, the newly discovered ε-NbN superconductor remains stable at pressures up to ~20 GPa and is significantly harder than cubic δ-NbN; it is as hard as sapphire, ultra-incompressible and has a high shear rigidity of 201 GPa to rival hard/superhard material γ-B (~227 GPa). Furthermore, this exploration opens a new class of highly desirable materials combining the outstanding mechanical/elastic properties with superconductivity, which may be particularly attractive for its technological and engineering applications in extreme environments.« less

  10. Discovery of superconductivity in hard hexagonal ε-NbN

    SciTech Connect

    Zou, Yongtao; Li, Qiang; Qi, Xintong; Zhang, Cheng; Ma, Shuailing; Zhang, Wei; Li, Ying; Chen, Ting; Wang, Xuebing; Chen, Zhiqiang; Welch, David; Pinwen Zhu; Cui, Tian; Li, Bingbing; Li, Baosheng

    2016-02-29

    Since the discovery of superconductivity in boron-doped diamond with a critical temperature (TC) near 4 K, great interest has been attracted in hard superconductors such as transition-metal nitrides and carbides. Here we report the new discovery of superconductivity in polycrystalline hexagonal ε-NbN synthesized at high pressure and high temperature. Direct magnetization and electrical resistivity measurements demonstrate that the superconductivity in bulk polycrystalline hexagonal ε-NbN is below ~11.6 K, which is significantly higher than that for boron-doped diamond. The nature of superconductivity in hexagonal ε-NbN and the physical mechanism for the relatively lower TC have been addressed by the weaker bonding in the Nb-N network, the co-planarity of Nb-N layer as well as its relatively weaker electron-phonon coupling, as compared with the cubic δ-NbN counterpart. Moreover, the newly discovered ε-NbN superconductor remains stable at pressures up to ~20 GPa and is significantly harder than cubic δ-NbN; it is as hard as sapphire, ultra-incompressible and has a high shear rigidity of 201 GPa to rival hard/superhard material γ-B (~227 GPa). Furthermore, this exploration opens a new class of highly desirable materials combining the outstanding mechanical/elastic properties with superconductivity, which may be particularly attractive for its technological and engineering applications in extreme environments.

  11. Field quality study in Nb(3)Sn accelerator magnets

    SciTech Connect

    Kashikhin, V.V.; Ambrosio, G.; Andreev, N.; Barzi, E.; Bossert, R.; DiMarco, J.; Kashikhin, V.S.; Lamm, M.; Novitski, I.; Schlabach, P.; Velev, G.; Yamada, R.; Zlobin, A.V.; /Fermilab

    2005-05-01

    Four nearly identical Nb{sub 3}Sn dipole models of the same design were built and tested at Fermilab. It provided a unique opportunity of systematic study the field quality effects in Nb{sub 3}Sn accelerator magnets. The results of these studies are reported in the paper.

  12. Quantitative Auger analysis of Nb-Ge superconducting alloys

    SciTech Connect

    Buitrago, R.H.

    1980-01-01

    The feasibility of using Auger electron analysis for quantitative analysis was investigated by studying Nb/sub 3/Ge thin-film Auger data with different approaches. A method base on elemental standards gave consistent quantitative values with reported Nb-Ge data. Alloy sputter yields were also calculated and results were consistent with those for pure elements.

  13. Discovery of Superconductivity in Hard Hexagonal ε-NbN

    PubMed Central

    Zou, Yongtao; Qi, Xintong; Zhang, Cheng; Ma, Shuailing; Zhang, Wei; Li, Ying; Chen, Ting; Wang, Xuebing; Chen, Zhiqiang; Welch, David; Zhu, Pinwen; Liu, Bingbing; Li, Qiang; Cui, Tian; Li, Baosheng

    2016-01-01

    Since the discovery of superconductivity in boron-doped diamond with a critical temperature (TC) near 4 K, great interest has been attracted in hard superconductors such as transition-metal nitrides and carbides. Here we report the new discovery of superconductivity in polycrystalline hexagonal ε-NbN synthesized at high pressure and high temperature. Direct magnetization and electrical resistivity measurements demonstrate that the superconductivity in bulk polycrystalline hexagonal ε-NbN is below ∼11.6 K, which is significantly higher than that for boron-doped diamond. The nature of superconductivity in hexagonal ε-NbN and the physical mechanism for the relatively lower TC have been addressed by the weaker bonding in the Nb-N network, the co-planarity of Nb-N layer as well as its relatively weaker electron-phonon coupling, as compared with the cubic δ-NbN counterpart. Moreover, the newly discovered ε-NbN superconductor remains stable at pressures up to ∼20 GPa and is significantly harder than cubic δ-NbN; it is as hard as sapphire, ultra-incompressible and has a high shear rigidity of 201 GPa to rival hard/superhard material γ-B (∼227 GPa). This exploration opens a new class of highly desirable materials combining the outstanding mechanical/elastic properties with superconductivity, which may be particularly attractive for its technological and engineering applications in extreme environments. PMID:26923318

  14. Discovery of Superconductivity in Hard Hexagonal ε-NbN

    NASA Astrophysics Data System (ADS)

    Zou, Yongtao; Qi, Xintong; Zhang, Cheng; Ma, Shuailing; Zhang, Wei; Li, Ying; Chen, Ting; Wang, Xuebing; Chen, Zhiqiang; Welch, David; Zhu, Pinwen; Liu, Bingbing; Li, Qiang; Cui, Tian; Li, Baosheng

    2016-02-01

    Since the discovery of superconductivity in boron-doped diamond with a critical temperature (TC) near 4 K, great interest has been attracted in hard superconductors such as transition-metal nitrides and carbides. Here we report the new discovery of superconductivity in polycrystalline hexagonal ε-NbN synthesized at high pressure and high temperature. Direct magnetization and electrical resistivity measurements demonstrate that the superconductivity in bulk polycrystalline hexagonal ε-NbN is below ∼11.6 K, which is significantly higher than that for boron-doped diamond. The nature of superconductivity in hexagonal ε-NbN and the physical mechanism for the relatively lower TC have been addressed by the weaker bonding in the Nb-N network, the co-planarity of Nb-N layer as well as its relatively weaker electron-phonon coupling, as compared with the cubic δ-NbN counterpart. Moreover, the newly discovered ε-NbN superconductor remains stable at pressures up to ∼20 GPa and is significantly harder than cubic δ-NbN it is as hard as sapphire, ultra-incompressible and has a high shear rigidity of 201 GPa to rival hard/superhard material γ-B (∼227 GPa). This exploration opens a new class of highly desirable materials combining the outstanding mechanical/elastic properties with superconductivity, which may be particularly attractive for its technological and engineering applications in extreme environments.

  15. Chemically-mediated quantum criticality in NbFe2

    SciTech Connect

    Alam, Aftab; Johnson, Duane

    2011-11-09

    Laves-phase Nb{sub 1+c}Fe{sub 2-c} is a rare itinerant intermetallic compound exhibiting magnetic quantum criticality at c{sub cr} {approx} 1.5% Nb excess; its origin, and how alloying mediates it, remains an enigma. For NbFe{sub 2}, we show that an unconventional band critical point above the Fermi level E{sub F} explains most observations and that chemical alloying mediates access to this unconventional band critical point by an increase in E{sub F} with decreasing electrons (increasing %Nb), counter to rigid-band concepts. We calculate that E{sub F} enters the unconventional band critical point region for c{sub cr} > 1.5% Nb and by 1.74% Nb there is no Nb site-occupation preference between symmetry-distinct Fe sites, i.e., no electron-hopping disorder, making resistivity near constant as observed. At larger Nb (Fe) excess, the ferromagnetic Stoner criterion is satisfied.

  16. Computer Series, 114: MO Theory Made Visible.

    ERIC Educational Resources Information Center

    Mealli, Carlo; Proserpio, Davide M.

    1990-01-01

    A collection of Molecular Orbital (MO) programs that have been integrated into routines and programs to illustrate MO theory are presented. Included are discussions of Computer Aided Composition of Atomic Orbitals (CACAO) and Walsh diagrams. (CW)

  17. A Simple MO Treatment of Metal Clusters.

    ERIC Educational Resources Information Center

    Sahyun, M. R. V.

    1980-01-01

    Illustrates how a qualitative description of the geometry and electronic characteristics of homogeneous metal clusters can be obtained using semiempirical MO (molecular orbital theory) methods. Computer applications of MO methods to inorganic systems are also described. (CS)

  18. Characterization of nanostructured HfO 2 films using RBS and PAC

    NASA Astrophysics Data System (ADS)

    Cavalcante, F. H. M.; Gomes, M. R.; Carbonari, A. W.; Pereira, L. F. D.; Rossetto, D. A.; Costa, M. S.; Alves, E.; Barradas, N. P.; Franco, N.; Redondo, L. M.; Lopes, A. M. L.; Soares, J. C.

    2012-02-01

    The hyperfine field at 181Ta lattice sites in a nanostructured HfO 2 thin film doped with Fe was studied using Rutherford Backscattering Spectrometry and Perturbed Angular Correlation techniques. The 409 nm Hf film was deposited by Electron Beam Evaporation on a silicon substrate. The radioactive 181Hf ions were produced by neutron activation of the nanofilm in the Brazilian Research Reactor (IPEN IEA-R1) by the reaction 180Hf(n,γ) 181Hf. These studies provided an excellent opportunity to obtain unique information regarding local arrangement of the grains, structure, phase transformations of nanoparticles and interfaces of nanostructured materials and the thin film.

  19. 3D surface topography study of the biofunctionalized nanocrystalline Ti-6Zr-4Nb/Ca-P

    SciTech Connect

    Jakubowicz, J.; Adamek, G.; Jurczyk, M.U.; Jurczyk, M.

    2012-08-15

    In this work surface of the sintered Ti-6Zr-4Nb nanocrystalline alloy was electrochemically biofunctionalized. The porous surface was produced by anodic oxidation in 1 M H{sub 3}PO{sub 4} + 2%HF electrolyte at 10 V for 30 min. Next the calcium-phosphate (Ca-P) layer was deposited, onto the formed porous surface, using cathodic potential - 5 V kept for 60 min in 0.042 M Ca(NO{sub 3}){sub 2} + 0.025 M (NH{sub 4}){sub 2}HPO{sub 4} + 0.1 M HCl electrolyte. The deposited Ca-P layer anchored in the pores. The biofunctionalized surface was studied by XRD, SEM and EDS. In vitro tests culture of normal human osteoblast (NHOst) cells showed very good cells proliferation, colonization and multilayering. Using optical profiler, roughness and hybrid 3D surface topography parameters were estimated. Correlation between surface composition, morphology, roughness and biocompatibility results was done. It has been shown by us that surface with appropriate chemical composition and topography, after combined electrochemical anodic and cathodic surface treatment, supports osteoblast adhesion and proliferation. 3D topography measurements using optical profiler play a key role in the biomaterials surface analysis. - Highlights: Black-Right-Pointing-Pointer Nanocrystalline Ti-6Zr-4Nb/Ca-P material was produced for hard tissue implant applications. Black-Right-Pointing-Pointer Calcium-phosphate results in surface biofunctionalization. Black-Right-Pointing-Pointer The biofunctionalized surface shows good in-vitro behavior.

  20. In-situ formation of alumina coatings in niobium toughened Mo(Si,Al)[sub 2

    SciTech Connect

    Costa e Silva, A.; Kaufman, M.J. . Dept. of Materials Science and Engineering)

    1994-10-01

    One approach that has been explored for the toughening and strengthening of MoSi[sub 2] based materials is the introduction of ductile refractory metal reinforcements. Due to the considerable stability of the transition metal silicides and the relatively high mobility of silicon in systems consisting of silicides and refractory metals, it has been found that this approach leads to materials that have poor long term stability at high temperature, unless a coating is interposed between the silicide matrix and the refractory metal reinforcement. Both Xiao and Abbaschian and Lu and coworkers have applied coatings to these reinforcements using conventional techniques. The most promising coatings were oxides, namely alumina and yttria. Besides the difficulties associated with preserving these conventional coatings during processing, it has also been observed that silica inclusions possibly degrade the coating during high temperature exposure. While in-situ coatings have been applied to refractory metal reinforcements in NbAl[sub 3] and NiAl matrices, the authors known of no successful scheme developed for in-situ coating of these metals in silicide matrices. In this work, an attempt was made to produce in-situ alumina coatings on preoxidized Nb fibers by using an aluminum-rich Mo(Si, Al)[sub 2]-(C40) matrix. Furthermore, the effectiveness of this layer for (a) protecting the fiber from interaction with the matrix and (b) promoting debonding was investigated.