The microwave properties of Ag(Ta0.8Nb0.2)O3 thick film interdigital capacitors on alumina substrates

NASA Astrophysics Data System (ADS)

Lee, Ku-Tak; Koh, Jung-Hyuk

2012-01-01

In this paper, we will introduce the microwave properties of Ag(Ta0.8Nb0.2)O3 thick film planar type interdigital capacitors fabricated on alumina substrates. The tailored paraelectric state of Ag(Ta,Nb)O3 allows the material to be regarded as a part of the family of microwave materials. As thick films formed in our experiment, Ag(Ta,Nb)O3 exhibited extremely low dielectric loss with relatively high dielectric permittivity. This low dielectric loss is a very important issue for microwave applications. Therefore, we investigated the microwave properties of Ag(Ta0.8Nb0.2)O3 thick film planar type interdigital capacitors. Ag(Ta0.8Nb0.2)O3 thick films were prepared by a screen-printing method on alumina substrates and were sintered at 1140 °C for 2 hrs. The XRD analysis results showed that the Ag(Ta0.8Nb0.2)O3 thick film has the perovskite structure. The frequency dependent dielectric permittivity showed that these Ag(Ta0.8Nb0.2)O3 thick film planar type interdigital capacitors have very weak frequency dispersions with low loss tangents in the microwave range.

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

PubMed

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

2016-03-01

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

Effect of Zr substitution on the thermal and mechanical properties of Rh3A (A=Nb,Ta) - A theoretical study

NASA Astrophysics Data System (ADS)

Manjula, M.; Sundareswari, M.; Viswanathan, E.

2018-04-01

The present study focuses upon the thermal and mechanical properties of Rh3ZrxA1-x (A= Nb,Ta) ternary alloys using ab initio density functional theory where Nb/Ta is substituted by Zr. These ternary alloys were investigated for the first time using elastic moduli, hardness, Debye temperature, Debye average velocity and Gruneisen parameter. Further the ductile/brittle analysis was made by using Cauchy pressure, degree of brittleness and Poisson's ratio. Systematic addition of Zr with Rh3Nb/Ta shows that Rh3Zr0.75Nb0.25, Rh3Zr0.875Nb0.125 and Rh3Zr0.875Ta0.125combinations are more ductile. Further the melting temperature of Rh3Zr0.75Nb0.25(2227 K), Rh3Zr0.875Nb0.125(2200 K) and Rh3Zr0.875Ta0.125 (2134 K) alloys are nearer to those of their parent binary alloys namely Rh3Nb (2636 K) and Rh3Ta (2562 K). Their corresponding density values (10.84 gm/cm3, 10.77 gm/cm3 and 11.09 gm/cm3) are found to be much less than those of their parent materials.

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

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bayot, Daisy; Degand, Matthieu; Devillers, Michel

2005-09-15

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

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhai, Hai-Fa, E-mail: haifazhai@126.com; Li, Ai-Dong, E-mail: adli@nju.edu.cn; Kong, Ji-Zhou

2013-06-01

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

Mechanical Properties of TiTaHfNbZr High-Entropy Alloy Coatings Deposited on NiTi Shape Memory Alloy Substrates

NASA Astrophysics Data System (ADS)

Motallebzadeh, A.; Yagci, M. B.; Bedir, E.; Aksoy, C. B.; Canadinc, D.

2018-04-01

TiTaHfNbZr high-entropy alloy (HEA) thin films with thicknesses of about 750 and 1500 nm were deposited on NiTi substrates by RF magnetron sputtering using TiTaHfNbZr equimolar targets. The thorough experimental analysis on microstructure and mechanical properties of deposited films revealed that the TiTaHfNbZr films exhibited amorphous and cauliflower-like structure, where grain size and surface roughness increased concomitant with film thickness. More importantly, the current findings demonstrate that the TiTaHfNbZr HEA films with mechanical properties of the same order as those of the NiTi substrate constitute promising biomedical coatings effective in preventing Ni release.

Mechanical Properties of TiTaHfNbZr High-Entropy Alloy Coatings Deposited on NiTi Shape Memory Alloy Substrates

NASA Astrophysics Data System (ADS)

Motallebzadeh, A.; Yagci, M. B.; Bedir, E.; Aksoy, C. B.; Canadinc, D.

2018-06-01

TiTaHfNbZr high-entropy alloy (HEA) thin films with thicknesses of about 750 and 1500 nm were deposited on NiTi substrates by RF magnetron sputtering using TiTaHfNbZr equimolar targets. The thorough experimental analysis on microstructure and mechanical properties of deposited films revealed that the TiTaHfNbZr films exhibited amorphous and cauliflower-like structure, where grain size and surface roughness increased concomitant with film thickness. More importantly, the current findings demonstrate that the TiTaHfNbZr HEA films with mechanical properties of the same order as those of the NiTi substrate constitute promising biomedical coatings effective in preventing Ni release.

First-principles study of electronic, optical and thermoelectric properties in cubic perovskite materials AgMO3 (M = V, Nb, Ta)

NASA Astrophysics Data System (ADS)

Mahmood, Asif; Ramay, Shahid M.; Rafique, Hafiz Muhammad; Al-Zaghayer, Yousef; Khan, Salah Ud-Din

2014-05-01

In this paper, first-principles calculations of structural, electronic, optical and thermoelectric properties of AgMO3 (M = V, Nb and Ta) have been carried out using full potential linearized augmented plane wave plus local orbitals method (FP - LAPW + lo) and BoltzTraP code within the framework of density functional theory (DFT). The calculated structural parameters are found to agree well with the experimental data, while the electronic band structure indicates that AgNbO3 and AgTaO3 are semiconductors with indirect bandgaps of 1.60 eV and 1.64 eV, respectively, between the occupied O 2p and unoccupied d states of Nb and Ta. On the other hand, AgVO3 is found metallic due to the overlapping behavior of states across the Fermi level. Furthermore, optical properties, such as dielectric function, absorption coefficient, optical reflectivity, refractive index and extinction coefficient of AgNbO3 and AgTaO3, are calculated for incident photon energy up to 50 eV. Finally, we calculate thermo power for AgNbO3 and AgTaO3 at fixed doping 1019 cm-3. Electron doped thermo power of AgNbO3 shows significant increase over AgTaO3 with temperature.

Microstructure and Properties of a Refractory NbCrMo0.5Ta0.5ZrTi Alloy (Preprint)

DTIC Science & Technology

2011-10-01

slightly enriched with Nb , Mo and Ta and depleted with Zr and Cr, and its lattice parameter after HIP was a = 324.76 ± 0.16 pm. The BCC2 phase was...FCC phase was highly enriched with Cr and it was identified as a Laves C15 phase, ( Zr ,Ta)(Cr,Mo, Nb )2, with the lattice parameter a = 733.38 ± 0.18 pm...with Nb , Mo and Ta and depleted with Zr and Cr, and its lattice parameter after HIP was a = 324.76 ± 0.16 pm. The BCC2 phase was enriched with Zr and Ti

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

PubMed

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

2016-01-28

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

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

PubMed

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

2014-09-15

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

Hydriding and dehydriding rates of Mg, Mg-10TaF5, and Mg-10NbF5 prepared via reactive mechanical grinding

NASA Astrophysics Data System (ADS)

Song, Myoung Youp; Kwak, Young Jun; Lee, Seong Ho; Park, Hye Ryoung

2015-01-01

In this work, TaF5 and NbF5 were chosen as additives to enhance the hydriding and dehydriding rates of Mg. Mg, Mg-10TaF5, and Mg-10NbF5 samples were prepared by reactive mechanical grinding. The hydriding and dehydriding properties of the samples were then examined. Mg-10TaF5 had the largest amount of hydrogen absorbed for 30 min and the highest initial dehydriding rate after incubation period, followed in order by Mg-10NbF5, and Mg. At 593 K under 12 bar H2 at the first cycle, Mg-10TaF5 absorbed 3.63 wt% H for 5 min and 4.53 wt% H for 30 min. At 593 K under 1.0 bar H2 at the first cycle, Mg-10TaF5 desorbed 0 wt% H for 2.5 min, 0.59 wt% H for 5 min, 3.42 wt% H for 30 min, and 4.24 wt% H for 60 min. The reactive mechanical grinding of Mg with TaF5 or NbF5 is believed to have facilitated the nucleation and to have decreased the diffusion distances of hydrogen atoms. These two effects are believed to have increased the hydriding and dehydriding rates of Mg. The MgF2 and Ta2H formed in Mg-10TaF5, and the MgF2, NbH2, and NbF3 formed in Mg-10NbF5 are considered to have enhanced both of these effects.

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.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fukina, D.G., E-mail: dianafuk@yandex.ru; Suleimanov, E.V.; Yavetskiy, R.P.

2016-09-15

The crystal structure and non-linear optical properties of CsNbMoO{sub 6} and CsTaMoO{sub 6} defect pyrochlores have been studied. The single crystals of these compounds grown by the flux method possess an octahedral faceting and reach up to 50 µm in size. The crystal structures of CsB{sup V}MoO{sub 6} (B{sup V}=Nb, Ta) were investigated by X-ray diffraction method. Both compounds crystallize in the cubic symmetry with noncentrosymmetric space group F-43m. The second harmonic generation of CsNbMoO{sub 6} and CsTaMoO{sub 6}was found to be 1.6×10{sup −2} and 8.5×10{sup −4} of lithium niobate, correspondingly. It has been determined that distortions of [MO{sub 6}]more » polyhedra (M=Nb, Ta, Mo) as well as polarizability and covalency of Nb–O and Ta–O bonds have a great effect on the second harmonic generation. - Highlights: • CsNbMoO{sub 6} and CsTaMoO{sub 6} homogeneous single crystals have been grown. • The crystal structure of CsTaMoO{sub 6} has been studied. • Nonlinear optical properties of CsNbMoO{sub 6} and CsTaMoO{sub 6} have been found. • The microscopic origin of the second harmonic generation (SHG) response have been identified.« less

Prediction of A2 to B2 Phase Transition in the High Entropy Alloy Mo-Nb-Ta-W

NASA Astrophysics Data System (ADS)

Huhn, William; Widom, Michael

2014-03-01

In this talk we show that an effective Hamiltonian fit with first principles calculations predicts an order/disorder transition occurs in the high entropy alloy Mo-Nb-Ta-W. Using the Alloy Theoretic Automated Toolset, we find T=0K enthalpies of formation for all binaries containing Mo, Nb, Ta, and W, and in particular we find the stable structures for binaries at equiatomic concentrations are close in energy to the associated B2 structure, suggesting that at intermediate temperatures a B2 phase is stabilized in Mo-Nb-Ta-W. Our ``hybrid Monte Carlo/molecular dynamics'' results for the Mo-Nb-Ta-W system are analyzed to identify certain preferred chemical bonding types. A mean field free energy model incorporating nearest neighbor bonds will be presented, allowing us to predict the mechanism of the order/disorder transition. We find the temperature evolution of the system is driven by strong Mo-Ta bonding. Comparison of the free energy model and our MC/MD results suggest the existence of additional low-temperature phase transitions in the system likely ending with phase segregation into binary phases. We would like to thank DOD-DTRA for funding this research under contract number DTRA-11-1-0064.

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

NASA Astrophysics Data System (ADS)

Raanaei, Hossein; Fakhraee, Morteza

2017-09-01

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

Evaluating the cause(s) of Ti, Ta, and Nb (TITAN) enrichment in ocean island basalts using LA-ICP-MS

NASA Astrophysics Data System (ADS)

Lyakov, J.; Durkin, K.; Hirsch, L.; Peters, B.; Hattingh, R.; Day, J. M.

2017-12-01

Titanium, Ta, and Nb (TITAN) enrichments in some ocean island basalt (OIB) lavas have been attributed to mantle source, or to partial melting and fractional crystallization Iprocesses. TITAN anomalies in the mantle sources of OIB would imply these trace elements can be used to track mantle heterogeneity in a manner similar to some isotopic tracers (e.g., He, Os, W), whereas a petrogenetic process to account for TITAN anomalies would be more prosaic. To further evaluate this issue, we have performed laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of phenocryst phases and matrix on petrographically well-characterized polished-sections of OIB samples. These samples come from five ocean island archipelagos (Canary Islands, the Azores, Samoa, Tubuai'i, Réunion), and are used to assess the citing of Ti, Ta, Nb and associated trace-elements within bulk-rocks. We find poorly-defined but broadly positive correlations between olivine and clinopyroxene modal abundance and Ta/Ta*, Nb/Nb*, but no correlation with Ti/Ti* (where, for example, Ti/Ti* is the primitive mantle normalized ratio, written as: Ti/√[Sm × Tb]). Abundances of olivine and clinopyroxene with samples spanned a wide-range, from 0-70 modal %. We determined trace-element abundances by LA-ICP-MS in a sub-set of samples for major (olivine, clinopyroxene) and minor (e.g., magnetite) phenocryst phases, and for the typically vitrophyric to partly crystallized matrices of samples. Modal reconstruction relative to the bulk rock are broadly similar, although the Ta/Ta*, Nb/Nb* and, especially Ti/Ti* anomalies cannot always be reproduced, especially if Fe-Ti oxide phases were not analyzed due to their limited presence within polished sections. LA-ICP-MS analyses reveal that, while TITAN anomalies are dominantly preserved in the matrix and oxide phases, the role of fractional crystallization of olivine and clinopyroxene is a controlling factor in the magnitude of TITAN anomaly generated. Our

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

PubMed

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

2017-06-01

The necrotrophic fungus Rhizoctonia cerealis is the major pathogen causing sharp eyespot disease in wheat (Triticum aestivum). Nucleotide-binding leucine-rich repeat (NB-LRR) proteins often mediate plant disease resistance to biotrophic pathogens. Little is known about the role of NB-LRR genes involved in wheat response to R. cerealis. In this study, a wheat NB-LRR gene, named TaRCR1, was identified in response to R. cerealis infection using Artificial Neural Network analysis based on comparative transcriptomics and its defence role was characterized. The transcriptional level of TaRCR1 was enhanced after R. cerealis inoculation and associated with the resistance level of wheat. TaRCR1 was located on wheat chromosome 3BS and encoded an NB-LRR protein that was consisting of a coiled-coil domain, an NB-ARC domain and 13 imperfect leucine-rich repeats. TaRCR1 was localized in both the cytoplasm and the nucleus. Silencing of TaRCR1 impaired wheat resistance to R. cerealis, whereas TaRCR1 overexpression significantly increased the resistance in transgenic wheat. TaRCR1 regulated certain reactive oxygen species (ROS)-scavenging and production, and defence-related genes, and peroxidase activity. Furthermore, H 2 O 2 pretreatment for 12-h elevated expression levels of TaRCR1 and the above defence-related genes, whereas treatment with a peroxidase inhibitor for 12 h reduced the resistance of TaRCR1-overexpressing transgenic plants and expression levels of these defence-related genes. Taken together, TaRCR1 positively contributes to defence response to R. cerealis through maintaining ROS homoeostasis and regulating the expression of defence-related genes. © 2016 The Authors. Plant Biotechnology Journal published by Society for Experimental Biology and The Association of Applied Biologists and John Wiley & Sons Ltd.

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

PubMed

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

2016-01-01

The unprecedented increase in human life expectancy have produced profound changes in the prevailing patterns of disease, like the observed increased in degenerative disc diseases, which cause degradation of the bones. Ti-Nb-Ta alloys are promising materials to replace the damaged bone due to their excellent mechanical and corrosion resistance properties. In general metallic foams are widely used for medical application due to their lower elastic moduli compare to bulk materials. In this work we studied the synthesis of 34Nb-29Ta-xMn (x: 2, 4 and 6 wt.% Mn) alloy foams (50% v/v) using ammonium hydrogen carbonate as a space holder. Alloys were produced through mechanical alloying in a planetary mill for 50h. Green compacts were obtained by applying 430 MPa pressure. To remove the space holder from the matrix the green compacts were heated to 180 °C for 1.5h and after sintered at 1300 °C for 3h. Foams were characterized by x-ray diffraction, scanning, transmission electron microscopy and optical microscopy. The elastic modulus of the foam was measured as ~30 GPa, and the values are almost equal to the values predicted using various theoretical models. Copyright © 2015 Elsevier B.V. All rights reserved.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sønsteby, Henrik Hovde, E-mail: henrik.sonsteby@kjemi.iuio.no; Nilsen, Ola; Fjellvåg, Helmer

2016-07-15

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

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

PubMed

Pershina, V; Anton, J

2012-01-21

Fully relativistic, four-component density functional theory electronic structure calculations were performed for MBr(5), MOBr(3), MBr(6)(-), KMBr(6), and MBr(5)Cl(-) of group-5 elements Nb, Ta, and element 105, Db, with the aim to predict adsorption behaviour of the bromides in gas-phase chromatography experiments. It was shown that in the atmosphere of HBr/BBr(3), the pentabromides are rather stable, and their stability should increase in the row Nb < Db < Ta. Several mechanisms of adsorption were considered. In the case of adsorption by van der Waals forces, the sequence in volatility of the pentabromides should be Nb < Ta < Db, being in agreement with the sublimation enthalpies of the Nb and Ta pentabromides. In the case of adsorption by chemical forces (on a quartz surface modified with KBr∕KCl), formation of the MBr(5)L(-) (L = Cl, Br) complex should occur, so that the volatility should change in an opposite way, i.e., Nb > Ta > Db. This sequence is in agreement with the one observed in the "one-atom-at-a-time" chromatography experiments. Some other scenarios, such as surface oxide formation were also considered but found to be irrelevant. © 2012 American Institute of Physics

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

DOE PAGES

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

2017-02-15

We investigated properties of NbN and Ta xN thin films grown at ambient temperatures on SiO 2/Si substrates by reactive-pulsed laser deposition and reactive magnetron sputtering (MS) as a function of N 2 gas flow. Both techniques produced films with smooth surfaces, where the surface roughness did not depend on the N 2 gas flow during growth. High crystalline quality, (111) oriented NbN films with T c up to 11 K were produced by both techniques for N contents near 50%. The low temperature transport properties of the Ta xN films depended upon both the N 2 partial pressure usedmore » during growth and the film thickness. Furthermore, the root mean square surface roughness of Ta xN films grown by MS increased as the film thickness decreased down to 10 nm.« less

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

PubMed

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

2017-02-01

Microstructures, mechanical properties, apatite-forming ability and in vitro experiments were studied for Nb-25Ti-xTa (x=10, 15, 20, 25, 35at.%) alloys fabricated by powder metallurgy. It is confirmed that the alloys could achieve a relative density over 80%. Meanwhile, the increase in Ta content enhances the tensile strength, elastic modulus and hardness of the as-sintered alloys. When increasing the sintering temperatures, the microstructure became more homogeneous for β phase, resulting in a decrease in the modulus and strength. Moreover, the alloys showed a good biocompatibility due to the absence of cytotoxic elements, and were suitable for apatite formation and cell adhesion. In conclusion, Nb-25Ti-xTa alloys are potentially useful in biomedical applications with their mechanical and biological properties being evaluated in this work. Copyright © 2016 Elsevier B.V. All rights reserved.

High-rate deposition of LiNb 1- xTa xO 3 films by thermal plasma spray CVD

NASA Astrophysics Data System (ADS)

Majima, T.; Yamamoto, H.; Kulinich, S. A.; Terashima, K.

2000-12-01

LiNb 1- xTa xO 3 films were prepared by a thermal plasma spray CVD method using liquid source materials. Preferentially (0 0 1)-oriented LiNb 1- xTa xO 3 films with satisfactory in-plane and out-of-plane alignment were fabricated on sapphire (0 0 1) substrates. The full-width at half-maximum (FWHM) of the (0 0 6) rocking curve could achieve 0.12°, which was comparable with those of LiNbO 3 and LiTaO 3 films prepared by other conventional vapor-phase deposition methods. The deposition rate was up to 0.07 μm/min, which was 5-40 times faster than those for most other conventional vapor-phase deposition methods. From inductively coupled plasma atomic emission spectroscopy analysis, x values of these films were estimated to be 0.36-0.49.

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

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

NASA Astrophysics Data System (ADS)

Okazaki, Yoshimitsu; Nagata, Hiroyuki

2012-12-01

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

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.

Nb and Ta Co-Doped TiO2 Transparent Conductive Thin Films by Magnetron Sputtering: Fabrication, Structure, and Characteristics

NASA Astrophysics Data System (ADS)

Liu, Yang; Peng, Qian; Qiao, Yadong; Yang, Guang

2018-06-01

Nb and Ta co-doped anatase titanium dioxide (NTTO) nanocrystalline thin films were deposited on quartz and Si (100) substrates by RF magnetron sputtering. The influence of RF power on the growth, structure, morphology, and properties of the samples are discussed in detail. X-ray diffraction measurements show that the films are polycrystalline with anatase tetragonal structure, which is further confirmed by Raman spectroscopy analysis. Meanwhile, Raman spectroscopy results indicate that the peak width of E g(1) mode, which is directly correlated to the carrier density, changes obviously with RF power. It is found that the substitution of Nb5+ and Ta5+ at Ti site is significantly improved with the increase of RF power from 150 W to 210 W. For the sample deposited at 210 W, the optical transmittance is above 82% in the visible range and the electrical resistivity is as low as 1.3 × 10-3 Ω cm with carrier density of 1.1 × 1021 cm-3 and Hall mobility of 4.5 cm2 V-1 s-1. The optical and electrical properties of NTTO thin films can be compared to those of Nb or Ta doped anatase TiO2. However, co-doping with Nb and Ta gives a possible platform to complement the limitations of each individual dopant.

Calcium hydride synthesis of Ti-Nb-based alloy powders

NASA Astrophysics Data System (ADS)

Kasimtsev, A. V.; Shuitsev, A. V.; Yudin, S. N.; Levinskii, Yu. V.; Sviridova, T. A.; Alpatov, A. V.; Novosvetlova, E. E.

2017-09-01

The metallothermic (calcium hydride) synthesis of Ti-Nb alloy powders alloyed with tantalum and zirconium is experimentally studied under various conditions. Chemical, X-ray diffraction, and metallographic analyses of the synthesized products show that initial oxides are completely reduced and a homogeneous β-Ti-based alloy powder forms under the optimum synthesis conditions at a temperature of 1200°C. At a lower synthesis temperature, the end products have a high oxygen content. The experimental results are used to plot the thermokinetic dependences o formation of a bcc solid solution at various times of isothermal holding of Ti-22Nb-6Ta and Ti-22Nb-6Zr (at %) alloys. The physicochemical and technological properties of the Ti-22Nb-6Ta and Ti-22Nb-6Zr alloy powders synthesized by calcium hydride reduction under the optimum conditions are determined.

Ta-Nb-Mo-W refractory high-entropy alloys: Anomalous ordering behavior and its intriguing electronic origin

DOE PAGES

Singh, Prashant; Smirnov, A. V.; Johnson, Duane D.

2018-05-31

From electronic-structure-based thermodynamic linear response, we establish chemical ordering behavior in complex solid solutions versus how Gibbs' space is traversed—applying it on prototype refractory A2 Ta-Nb-Mo-W high-entropy alloys. Near ideal stoichiometry, this alloy has anomalous, intricate chemical ordering tendencies, with long-ranged chemical interactions that produce competing short-range order (SRO) with a crossover to spinodal segregation. This atypical SRO arises from canonical band behavior that, with alloying, creates features near the Fermi surface (well defined even with disorder) that change to simple commensurate SRO with (un)filling of these states. In conclusion, our results reveal how complexity and competing electronic effects controlmore » ordering in these alloys.« less

Ta-Nb-Mo-W refractory high-entropy alloys: Anomalous ordering behavior and its intriguing electronic origin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Prashant; Smirnov, A. V.; Johnson, Duane D.

From electronic-structure-based thermodynamic linear response, we establish chemical ordering behavior in complex solid solutions versus how Gibbs' space is traversed—applying it on prototype refractory A2 Ta-Nb-Mo-W high-entropy alloys. Near ideal stoichiometry, this alloy has anomalous, intricate chemical ordering tendencies, with long-ranged chemical interactions that produce competing short-range order (SRO) with a crossover to spinodal segregation. This atypical SRO arises from canonical band behavior that, with alloying, creates features near the Fermi surface (well defined even with disorder) that change to simple commensurate SRO with (un)filling of these states. In conclusion, our results reveal how complexity and competing electronic effects controlmore » ordering in these alloys.« less

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

DTIC Science & Technology

2011-07-01

research seems to emphasize alloys based Approved for public release; distribution unlimited. 2 on the late transition metals such as Cr, Mn, Fe, Co, Ni ...of the Nb25Mo25Ta25W25 alloy , with larger grains at the regions experiencing slower solidification , i.e. near the surfaces not contacting with the...20-30 µm, indicating similar solidification conditions. 3.2.3 Fractography of samples deformed at room temperature The high entropy alloy

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

NASA Astrophysics Data System (ADS)

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

2012-05-01

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

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

NASA Astrophysics Data System (ADS)

Škoda, Radek; Novák, Milan

2007-04-01

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

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

NASA Astrophysics Data System (ADS)

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

2013-11-01

The 19F isotropic chemical shifts (δiso) of two isomorphic compounds, NbF5 and TaF5, which involve six nonequivalent fluorine sites, have been experimentally determined from the reconstruction of 1D 19F MAS NMR spectra. In parallel, the corresponding 19F chemical shielding tensors have been calculated using the GIPAW method for both experimental and DFT-optimized structures. Furthermore, the [M4F20] units of NbF5 and TaF5 being held together by van der Waals interactions, the relevance of Grimme corrections to the DFT optimization processes has been evaluated. However, the semi-empirical dispersion correction term introduced by such a method does not show any significant improvement. Nonetheless, a complete and convincing assignment of the 19F NMR lines of NbF5 and TaF5 is obtained, ensured by the linearity between experimental 19F δiso values and calculated 19F isotropic chemical shielding σiso values. The effects of the geometry optimizations have been carefully analyzed, confirming among other matters, the inaccuracy of the experimental structure of NbF5. The relationships between the fluorine chemical shifts, the nature of the fluorine atoms (bridging or terminal), the position of the terminal ones (opposite or perpendicular to the bridging ones), the fluorine charges, the ionicity and the length of the M-F bonds have been established. Additionally, for three of the 19F NMR lines of NbF5, distorted multiplets, arising from 1J-coupling and residual dipolar coupling between the 19F and 93Nb nuclei, were simulated yielding to values of 93Nb-19F 1J-coupling for the corresponding fluorine sites.

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

NASA Technical Reports Server (NTRS)

Pathare, Viren M.

1988-01-01

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

Differences in chemical doping matter: Superconductivity in Ti 1-xTa xSe 2 but not in Ti 1-xNb xSe 2

DOE PAGES

Luo, Huixia; Zhu, Yimei; Xie, Weiwei; ...

2016-02-21

We report that 1T-TiSe 2, an archetypical layered transition metal dichalcogenide, becomes superconducting when Ta is substituted for Ti but not when Nb is substituted for Ti. This is unexpected because Nb and Ta should be chemically equivalent electron donors. Superconductivity emerges near x = 0.02 for Ti 1–xTa xSe 2, while, for Ti 1–xNb xSe 2, no superconducting transitions are observed above 0.4 K. The equivalent chemical nature of the dopants is confirmed by X-ray photoelectron spectroscopy. ARPES and Raman scattering studies show similarities and differences between the two systems, but the fundamental reasons why the Nb and Tamore » dopants yield such different behavior are unknown. We present a comparison of the electronic phase diagrams of many electron-doped 1T-TiSe 2 systems, showing that they behave quite differently, which may have broad implications in the search for new superconductors. Here, we propose that superconducting Ti 0.8Ta 0.2Se 2 will be suitable for devices and other studies based on exfoliated crystal flakes.« less

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

PubMed Central

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

2016-01-01

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

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.

First principles study of structural, vibrational and electronic properties of graphene-like MX 2 (M=Mo, Nb, W, Ta; X=S, Se, Te) monolayers

NASA Astrophysics Data System (ADS)

Ding, Yi; Wang, Yanli; Ni, Jun; Shi, Lin; Shi, Siqi; Tang, Weihua

2011-05-01

Using first principles calculations, we investigate the structural, vibrational and electronic structures of the monolayer graphene-like transition-metal dichalcogenide (MX 2) sheets. We find the lattice parameters and stabilities of the MX 2 sheets are mainly determined by the chalcogen atoms, while the electronic properties depend on the metal atoms. The NbS 2 and TaS 2 sheets have comparable energetic stabilities to the synthesized MoS 2 and WS 2 ones. The molybdenum and tungsten dichalcogenide (MoX 2 and WX 2) sheets have similar lattice parameters, vibrational modes, and electronic structures. These analogies also exist between the niobium and tantalum dichalcogenide (NbX 2 and TaX 2) sheets. However, the NbX 2 and TaX 2 sheets are metals, while the MoX 2 and WX 2 ones are semiconductors with direct-band gaps. When the Nb and Ta atoms are doped into the MoS 2 and WS 2 sheets, a semiconductor-to-metal transition occurs. Comparing to the bulk compounds, these monolayer sheets have similar structural parameters and properties, but their vibrational and electronic properties are varied and have special characteristics. Our results suggest that the graphene-like MX 2 sheets have potential applications in nano-electronics and nano-devices.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biswal, Mamata, E-mail: Mamata.Biswal-Susanta_Kumar_Nayak.Etu@univ-lemans.fr; Body, Monique, E-mail: monique.body@univ-lemans.fr; Legein, Christophe, E-mail: christophe.legein@univ-lemans.fr

2013-11-15

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

Spontaneous sulfur dioxide activation by Group V metal (V, Nb, Ta) atoms in excess argon at cryogenic temperatures.

PubMed

Liu, Xing; Wang, Xuefeng; Wang, Qiang; Andrews, Lester

2013-06-28

Reactions of laser-ablated V, Nb and Ta atoms with SO2 in excess argon during condensation gave new absorptions in the M=O stretching region, which were assigned to metal sulfide oxides SMO2 and anions SMO2(-) (M = V, Nb, Ta). The metal oxide complex OV(η(2)-SO) was also identified through the V=O and the characteristic side-on coordinated S-O stretching modes. The assignments of major vibrational modes were confirmed by appropriate S(18)O2 and (34)SO2 isotopic shifts, and density functional frequency calculations. DFT calculations were employed to study the behavior of reactions of Group V bare metal atoms with SO2, and a representative profile was derived which not only showed the preferred coordinating fashion of metal atoms but also tracked the path of S-O bond activation. The η(2)-O,O' bridge coordinated complexes are preferred with energy decreases of ca. 50 kcal mol(-1) for all three metals, which facilitate the activation of two S-O bonds in succession and finally direct the reaction to the most stable molecules SMO2 (M = V, Nb, Ta) along the potential energy surface (PES). Finally the SMO2 molecules capture electrons to give anions SMO2(-) with about 3.6 eV electron affinities based on DFT calculations.

Evidence from EXAFS for Different Ta/Ti Site Occupancy in High Critical Current Density Nb3Sn Superconductor Wires.

PubMed

Heald, Steve M; Tarantini, Chiara; Lee, Peter J; Brown, Michael D; Sung, ZuHawn; Ghosh, Arup K; Larbalestier, David C

2018-03-19

To meet critical current density, J c , targets for the Future Circular Collider (FCC), the planned replacement for the Large Hadron Collider (LHC), the high field performance of Nb 3 Sn must be improved, but champion J c values have remained static for the last 10 years. Making the A15 phase stoichiometric and enhancing the upper critical field H c2 by Ti or Ta dopants are the standard strategies for enhancing high field performance but detailed recent studies show that even the best modern wires have broad composition ranges. To assess whether further improvement might be possible, we employed Extended X-ray Absorption Fine Structure (EXAFS) to determine the lattice site location of dopants in modern high-performance Nb 3 Sn strands with J c values amongst the best so far achieved. Although Ti and Ta primarily occupy the Nb sites in the A15 structure, we also find significant Ta occupancy on the Sn site. These findings indicate that the best performing Ti-doped stand is strongly sub-stoichiometric in Sn and that antisite disorder likely explains its high average H c2 behavior. These new results suggest an important role for dopant and antisite disorder in minimizing superconducting property distributions and maximizing high field J c properties.

Evidence from EXAFS for Different Ta/Ti Site Occupancy in High Critical Current Density Nb 3Sn Superconductor Wires

DOE PAGES

Heald, Steve M.; Tarantini, Chiara; Lee, Peter J.; ...

2018-03-19

To meet critical current density, Jc, targets for the Future Circular Collider (FCC), the planned replacement for the Large Hadron Collider (LHC), the high field performance of Nb 3Sn must be improved, but champion J c values have remained static for the last 10 years. Making the A15 phase stoichiometric and enhancing the upper critical field H c2 by Ti or Ta dopants are the standard strategies for enhancing high field performance but detailed recent studies show that even the best modern wires have broad composition ranges. To assess whether further improvement might be possible, we employed EXAFS to determinemore » the lattice site location of dopants in modern high-performance Nb 3Sn strands with J c values amongst the best so far achieved. Although Ti and Ta primarily occupy the Nb sites in the A15 structure, we also find significant Ta occupancy on the Sn site. These findings indicate that the best performing Ti-doped stand is strongly sub-stoichiometric in Sn and that antisite disorder likely explains its high average H c2 behavior. These new results suggest an important role for dopant and antisite disorder in minimizing superconducting property distributions and maximizing high field J c properties.« less

Evidence from EXAFS for Different Ta/Ti Site Occupancy in High Critical Current Density Nb 3Sn Superconductor Wires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heald, Steve M.; Tarantini, Chiara; Lee, Peter J.

To meet critical current density, Jc, targets for the Future Circular Collider (FCC), the planned replacement for the Large Hadron Collider (LHC), the high field performance of Nb 3Sn must be improved, but champion J c values have remained static for the last 10 years. Making the A15 phase stoichiometric and enhancing the upper critical field H c2 by Ti or Ta dopants are the standard strategies for enhancing high field performance but detailed recent studies show that even the best modern wires have broad composition ranges. To assess whether further improvement might be possible, we employed EXAFS to determinemore » the lattice site location of dopants in modern high-performance Nb 3Sn strands with J c values amongst the best so far achieved. Although Ti and Ta primarily occupy the Nb sites in the A15 structure, we also find significant Ta occupancy on the Sn site. These findings indicate that the best performing Ti-doped stand is strongly sub-stoichiometric in Sn and that antisite disorder likely explains its high average H c2 behavior. These new results suggest an important role for dopant and antisite disorder in minimizing superconducting property distributions and maximizing high field J c properties.« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

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

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

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

NASA Astrophysics Data System (ADS)

Tel, E.; Yiğit, M.; Tanır, G.

2012-04-01

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

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

NASA Astrophysics Data System (ADS)

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

2015-10-01

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

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

PubMed

Kwon, Hanjung; Jung, Sun-A

2014-11-01

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

Ab initio study of structural, elastic, and vibrational properties of transition-metal disilicides NbSi2 and TaSi2 in hexagonal C40 structure

NASA Astrophysics Data System (ADS)

Ertürk, Esra; Gürel, Tanju

2018-05-01

We present an ab initio study of structural, elastic and vibrational properties of transition-metal disilicides NbSi2 and TaSi2. The calculations have been carried out within the density-functional theory and linear-response formalism using norm-conserving pseudopotentials and a plane-wave basis. The calculated lattice parameters, bulk moduli, and elastic constants agree well with previous theoretical and experimental results. The calculated phonon frequencies at the Brillouin zone center are in good agreement with the reported Raman spectra and provide reference values for the future infrared and neutron phonon measurements. Phonon dispersion relations, mode Grüneisen parameters, and total and partial phonon density of states are also discussed. Mode Grüneisen parameters of NbSi2 and TaSi2 at Brillouin zone center show similar trends and all values are found to be positive. From phonon dispersion relations and phonon density of states, we have found a gap around 200 cm-1 for TaSi2, where the frequencies below this gap mainly belong to Ta vibrations and frequencies above the gap is mainly related with Si vibrations. In the case of NbSi2, there is no such gap and both Nb and Si atoms contribute to the phonon density of states in an energy range of 150-270 cm-1.

Investigation of static properties of medical alloys Ti-(20-30)Nb-(10-13)Ta-5Zr

NASA Astrophysics Data System (ADS)

Sergienko, K. V.; Sevost’yanov, M. A.; Konushkin, S. V.; Nasakina, E. O.; Baikin, A. S.; Shatova, L. A.; Kolmakov, A. G.

2018-04-01

In the work, static properties of TiNbTaZr titanium alloy were carried out. The search for a NiTi alloy replacement is necessary for medical products to eliminate the negative effects of nickel on the body. Conclusions are drawn about the adequacy of the mechanical properties of the test alloy for use in stent implants.

Source and fractionation controls on subduction-related plutons and dike swarms in southern Patagonia (Torres del Paine area) and the low Nb/Ta of upper crustal igneous rocks

NASA Astrophysics Data System (ADS)

Müntener, Othmar; Ewing, Tanya; Baumgartner, Lukas P.; Manzini, Mélina; Roux, Thibaud; Pellaud, Pierre; Allemann, Luc

2018-05-01

The subduction system in southern Patagonia provides direct evidence for the variability of the position of an active continental arc with respect to the subducting plate through time, but the consequences on the arc magmatic record are less well studied. Here we present a geochemical and geochronological study on small plutons and dykes from the upper crust of the southern Patagonian Andes at 51°S, which formed as a result of the subduction of the Nazca and Antarctic plates beneath the South American continent. In situ U-Pb geochronology on zircons and bulk rock geochemical data of plutonic and dyke rocks are used to constrain the magmatic evolution of the retro-arc over the last 30 Ma. We demonstrate that these combined U-Pb and geochemical data for magmatic rocks track the temporal and spatial migration of the active arc, and associated retro-arc magmatism. Our dataset indicates that the rear-arc area is characterized by small volumes of alkaline basaltic magmas at 29-30 Ma that are characterized by low La/Nb and Th/Nb ratios with negligible arc signatures. Subsequent progressive eastward migration of the active arc culminated with the emplacement of calc-alkaline plutons and dikes 17-16 Ma with elevated La/Nb and Th/Nb ratios and typical subduction signatures constraining the easternmost position of the southern Patagonian batholith at that time. Geochemical data on the post-16 Ma igneous rocks including the Torres del Paine laccolith indicate an evolution to transitional K-rich calc-alkaline magmatism at 12.5 ± 0.2 Ma. We show that trace element ratios such as Nb/Ta and Dy/Yb systematically decrease with increasing SiO2, for both the 17-16 Ma calc-alkaline and the 12-13 Ma K-rich transitional magmatism. In contrast, Th/Nb and La/Nb monitor the changes in the source composition of these magmas. We suggest that the transition from the common calc-alkaline to K-rich transitional magmatism involves a change in the source component, while the trace element ratios

Phase coexistence and high electrical properties in (KxNa0.96-xLi0.04)(Nb0.85Ta0.15)O3 piezoelectric ceramics

NASA Astrophysics Data System (ADS)

Chang, Yunfei; Yang, Zupei; Ma, Difei; Liu, Zonghuai; Wang, Zenglin

2009-03-01

(KxNa0.96-xLi0.04)(Nb0.85Ta0.15)O3 lead-free piezoelectric ceramics were produced by conventional solid-state reaction method. The effects of K/Na ratio on the phase transitional behavior, Raman spectrum, microstructure, and dielectric, piezoelectric, and ferroelectric properties of the ceramics have been investigated. The phase structure of the ceramics undergoes a transition from orthorhombic to tetragonal phase with increasing x. A double-degenerate symmetric O-Nb-O stretching vibration v1 and a triply degenerate symmetric O-Nb-O bending vibration v5 are detected as relatively strong scattering in the Raman spectra. The peak shifts of v5 and v1 modes all have a discontinuity with x between 0.42 and 0.46, which may suggest the coexistence of orthorhombic and tetragonal phases in this range. Properly modifying x reduces the sintering temperature, promotes the grain growth behavior, and improves the density of the ceramics. The polymorphic phase transition (at To -t) is shifted to near room temperature by increasing x to 0.44 (K/Na ratio of about 0.85:1), and the coexistence of orthorhombic and tetragonal phases in the ceramics at x =0.44 results in the optimized electrical properties (d33=291 pC/N, kp=0.54, ɛr=1167, tan δ=0.018, To -t=35 °C, TC=351 °C, Pr=27.65 μC/cm2, and Ec=8.63 kV/cm). The results show that the equal K/Na ratio is not an essential condition in obtaining optimized electrical properties in (KxNa0.96-xLi0.04)(Nb0.85Ta0.15)O3 ceramics.

Investigation of the nanodomain structure formation by piezoelectric force microscopy and Raman confocal microscopy in LiNbO3 and LiTaO3 crystals

NASA Astrophysics Data System (ADS)

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

2011-09-01

Piezoelectric force microscopy (PFM) and Raman confocal microscopy have been used for studying the nanodomain structures in congruent LiNbO3 and LiTaO3 crystals. The high-resolution nanodomain images at the surface were observed via PFM. Raman confocal microscopy has been used for the visualization of the nanodomain structures in the bulk via layer-by-layer scanning at various depths. It has been shown experimentally that the nanodomain images obtained at different depths correspond to domain images at the polar surface obtained at different moments: the deeper the nanodomain, the earlier the moment. Such a correlation was applied for the reconstruction of the evolution of the domain structures with charged domain walls. The studied domain structures were obtained in highly non-equilibrium switching conditions realized in LiNbO3 and LiTaO3 via pulse laser irradiation and the electric field poling of LiNbO3, with the surface layer modified by ion implantation. The revealed main stages of the domain structure evolution allow the authors to demonstrate that all geometrically different nanodomain structures observed in LiNbO3 and LiTaO3 appeared as a result of discrete switching.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gong, Dewei, E-mail: deweigong@hit.edu.cn; Liang, Yonggan; Ou, Wenjing

2016-03-15

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

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

PubMed

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

2016-01-21

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

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

NASA Astrophysics Data System (ADS)

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

2013-09-01

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

Effects of shot-peening and atmospheric-pressure plasma on aesthetic improvement of Ti-Nb-Ta-Zr alloy for dental applications

NASA Astrophysics Data System (ADS)

Miura-Fujiwara, Eri; Suzuki, Yuu; Ito, Michiko; Yamada, Motoko; Matsutake, Sinpei; Takashima, Seigo; Sato, Hisashi; Watanabe, Yoshimi

2018-01-01

Ti and Ti alloys are widely used for biomedical applications such as artificial joints and dental devices because of their good mechanical properties and biochemical compatibility. However, dental devices made of Ti and Ti alloys do not have the same color as teeth, so they are inferior to ceramics and polymers in terms of aesthetic properties. In a previous study, Ti-29Nb-13Ta-4.6Zr was coated with a white Ti oxide layer by heat treatment to improve its aesthetic properties. Shot-peening is a severe plastic deformation process and can introduce a large shear strain on the peened surface. In this study, the effects of shot-peening and atmospheric-pressure plasma on Ti-29Nb-13Ta-4.6Zr were investigated to form a white layer on the surface for dental applications.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, R. R.; Qin, X. Y.; Li, L. L.

2012-12-15

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

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

PubMed

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

2011-03-01

Ti15Zr4Nb4Ta and Ti29Nb13Ta4.6Zr, which do not contain the potentially cytotoxic elements V and Al, represent a new generation of alloys with improved corrosion resistance, mechanical properties, and cytocompatibility. Recently it has become possible for the apatite forming ability of these alloys to be ascertained by treatment with alkali, CaCl2, heat, and water (ACaHW). In order to confirm the actual in vivo bioactivity of commercially pure titanium (cp-Ti) and these alloys after subjecting them to ACaHW treatment at different temperatures, the bone bonding strength of implants made from these materials was evaluated. The failure load between implant and bone was measured for treated and untreated plates at 4, 8, 16, and 26 weeks after implantation in rabbit tibia. The untreated implants showed almost no bonding, whereas all treated implants showed successful bonding by 4 weeks, and the failure load subsequently increased with time. This suggests that a simple and economical ACaHW treatment could successfully be used to impart bone bonding bioactivity to Ti metal and Ti-Zr-Nb-Ta alloys in vivo. In particular, implants heat treated at 700 °C exhibited significantly greater bone bonding strength, as well as augmented in vitro apatite formation, in comparison with those treated at 600 °C. Thus, with this improved bioactive treatment process these advantageous Ti-Zr-Nb-Ta alloys can serve as useful candidates for orthopedic devices. Copyright © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Relationship between covalence and displacive phase transition temperature in RAO{sub 4} and LiAO{sub 3} (R = rare-earth element and A = Nb and Ta)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsunekawa, S.; Fukuda, T.; Kimiyama, T.

Crystal structure analyses by TOF neutron powder diffraction are performed for R TaO{sub 4} (R = rare-earth element) and the Ta-O interatomic distances are determined. The relationship between the covalency of A-O bonds (A = Nb and Ta), which show the most shortening upon phase transition, and the transition temperature is discussed for RAO{sub 4} and LiAO{sub 3}, and the parameters of Ta-O covalence are determined.

Magnetic properties of mixed sulfides MUS/sub 3/ (M = V, Cr, Nb, Ta)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nutsubidze, P.V.; Chechernikov, V.I.; Gracheva, N.V.

1985-08-01

The authors synthesized US/sub 2/ (Beta-US/sub 2/), VS, CrS, NbS, and TaS by the vacuum-thermal method in quartz ampules heated to 1170 degrees K. They homogenized and sintered these samples and remixed and sintered appropriate amounts to form MUS/sub 2/, which crystallizes in a rhombic structure. They studied the magnetic properties of MUS/sub 2/ on a vibration magnetometer in the range 75500 degrees K. The results of their analysis of the magnetic coefficients proved consistent with thermodynamic theory. They present their data in a series of four charts and two tables.

Surface Modification of Ti-35Nb-10Ta-1.5Fe by the Double Acid-Etching Process

PubMed Central

Amigó, Angélica

2018-01-01

Surface topography and composition influence the osteoblastic proliferation and osseointegration rates, which favor the biomechanical stability of bone anchoring and implants. In recent years, beta titanium alloys have been developed, and are composed of biocompatible elements, have low elastic modulus, high corrosion resistance, and mechanical properties to improve the long performance behavior of biomaterials. In the present research, the influence of the acid-etching process was studied in Ti6Al4V ELI and Ti35Nb10Ta1.5Fe. Samples were etched in a two-step acid treatment. Surface roughness parameters were quantified under a confocal microscope, topography was studied by scanning electron microscopy, and surface composition was analyzed with energy dispersive X-ray spectroscopy. The results revealed that the two-step acid treatment changes the topography of the β alloy, increases the surface area, and changes the chemical composition of the surface. Two differentiated regions were identified in the Ti35Nb10Ta1.5Fe alloy after the acid-etching process: The α + β region with higher values of mean roughness due to the lower chemical resistance of this region; and the β region with lower values of roughness parameters. PMID:29587427

Amphibole Fractional Crystallization and Delamination in Arc Roots: Implications for the `Missing' Nb Reservoir in the Earth

NASA Astrophysics Data System (ADS)

Galster, F.; Chatterjee, R. N.; Stockli, D. F.

2017-12-01

Most geologic processes should not fractionate Nb from Ta but Earth's major silicate reservoirs have subchondritic Nb/Ta values. Nb/Ta of >10000 basalts and basaltic andesites from different tectonic settings (GEOROC) cluster around 16, indistinguishable from upper mantle values. In contrast, Nb/Ta in more evolved arc volcanics have progressively lower values, reaching continental crust estimates, and correlate negatively with SiO2 (see figure) and positively with TiO2 and MgO. This global trend suggests that differentiation processes in magmatic arcs could explain bulk crustal Nb/Ta estimates. Understanding processes that govern fractionation of Nb from Ta in arcs can provide key insights on continental crust formation and help identify Earth's `missing' Nb reservoir. Ti-rich phases (rutile, titanite and ilmenite) have DNb/DTa <1, and therefore, their fractionation from mafic to intermediate liquids cannot explain the observed trend. Instead, fractionation of biotite and amphibole could lower Nb/Ta values in the evolved liquid. Lack of correlation between Nb/Ta and K2O in global volcanic rocks implies that biotite plays a minor role in fractionating Nb from Ta during differentiation. Experimental petrology and evidence from exposed arc sections indicate that amphibole fractionation and delamination of island arc roots can explain the andesitic composition of bulk continental crust. Experimental studies have shown that amphibole Mg# correlate with DNb/DTa and amphibole could effectively fractionate Nb from Ta. Preliminary data from lower to middle crustal amphiboles from preserved arcs show sub- to super-chondritic Nb/Ta up to >60. This suggests that delamination of amphibole-rich cumulates can be a viable mechanism for the preferential removal of Nb from the continental crust. Future examination of Nb/Ta ratios in lower crustal amphiboles from various preserved arcs will provide improved constraints on the Nb-Ta paradox of the silicate Earth.

Multi-component solid solution alloys having high mixing entropy

DOEpatents

Bei, Hongbin

2015-10-06

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

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

NASA Astrophysics Data System (ADS)

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

2015-11-01

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

Bipolar ferroelectric fatigue in (K0.5Na0.5)(Nb0.7Ta0.3)O3 ceramics and improved fatigue endurance on addition of ZnO

NASA Astrophysics Data System (ADS)

Vineetha, P.; Shanmuga Priya, B.; Venkata Saravanan, K.

2018-04-01

Ferroelectric ceramics are the key components in piezoelectric devices used today, thus long term reliability is a major industrial concern. The two important things that have to be considered in the ferroelectric material based device are aging and fatigue. The first one describes degradation with time whereas the later one is characterized by the change of material property during electrical loading. In the present work ferroelectric polarization and bipolar fatigue properties of undoped and ZnO doped lead free (K0.5Na0.5)(Nb0.7Ta0.3)O3 (KNNT) ceramics prepared by solid state reaction method were investigated. X-ray diffraction analysis of the samples reveal perovskite monoclinic phase along with the secondary phase of K2Nb4O11. The ferroelectric studies indicate that ZnO addition reduce fatigue as well as a well saturated hysteresis loop is obtained. The results reveal that addition of ZnO enhances the ferroelectric properties of KNNT ceramics.

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

PubMed Central

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

2015-01-01

Legislation arising from health and environmental concerns has intensified research into finding suitable alternatives to lead-based piezoceramics. Recently, solid solutions based on sodium potassium niobate (K,Na)NbO3 (KNN) have become one of the globally-important lead-free counterparts, due to their favourable dielectric and piezoelectric properties. This data article provides information on the ferroelectric properties and core–shell grain structures for the system, (1−y)[(1−x)Na0.5K0.5NbO3 – xLiTaO3] – yBiScO3 (x=0–0.1, y=0.02, abbreviated as KNN–xLT–2BS). We show elemental analysis with aid of TEM spot-EDX to identify three-type grain-types in the KNN–LT–BS ternary system. Melting behaviour has been assessed using a tube furnace with build-in camera. Details for the ferroelectric properties and core–shell chemical segregation are illustrated. PMID:26217758

Laser damage comparisons of broad-bandwidth, high-reflection optical coatings containing TiO 2, Nb 2O 5, or Ta 2O 5 high-index layers

DOE PAGES

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

2016-09-21

Broad bandwidth coatings allow angle of incidence flexibility and accommodate spectral shifts due to aging and water absorption. Higher refractive index materials in optical coatings, such as TiO 2, Nb 2O 5, and Ta 2O 5, can be used to achieve broader bandwidths compared to coatings that contain HfO 2 high index layers. We have identified the deposition settings that lead to the highest index, lowest absorption layers of TiO 2, Nb 2O 5, and Ta 2O 5, via e-beam evaporation using ion-assisted deposition. We paired these high index materials with SiO 2 as the low index material to createmore » broad bandwidth high reflection coatings centered at 1054 nm for 45 deg angle of incidence and P polarization. Furthermore, high reflection bandwidths as large as 231 nm were realized. Laser damage tests of these coatings using the ISO 11254 and NIF-MEL protocols are presented, which revealed that the Ta 2O 5/SiO 2 coating exhibits the highest resistance to laser damage, at the expense of lower bandwidth compared to the TiO 2/SiO 2 and Nb 2O 5/SiO 2 coatings.« less

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

PubMed

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

2016-02-12

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

Bulk Fermi Surfaces of the Dirac Type-II Semimetallic Candidates M Al3 (Where M =V , Nb, and Ta)

NASA Astrophysics Data System (ADS)

Chen, K.-W.; Lian, X.; Lai, Y.; Aryal, N.; Chiu, Y.-C.; Lan, W.; Graf, D.; Manousakis, E.; Baumbach, R. E.; Balicas, L.

2018-05-01

We report a de Haas-van Alphen (dHvA) effect study on the Dirac type-II semimetallic candidates M Al3 (where, M =V , Nb and Ta). The angular dependence of their Fermi surface (FS) cross-sectional areas reveals a remarkably good agreement with our first-principles calculations. Therefore, dHvA supports the existence of tilted Dirac cones with Dirac type-II nodes located at 100, 230 and 250 meV above the Fermi level ɛF for VAl3 , NbAl3 and TaAl3 respectively, in agreement with the prediction of broken Lorentz invariance in these compounds. However, for all three compounds we find that the cyclotron orbits on their FSs, including an orbit nearly enclosing the Dirac type-II node, yield trivial Berry phases. We explain this via an analysis of the Berry phase where the position of this orbit, relative to the Dirac node, is adjusted within the error implied by the small disagreement between our calculations and the experiments. We suggest that a very small amount of doping could displace ɛF to produce topologically nontrivial orbits encircling their Dirac node(s).

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

USGS Publications Warehouse

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

1997-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2017-07-01

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

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

DOE PAGES

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

2015-10-15

Two new two-dimensional Nb 4C 3-based solid solutions (MXenes), (Nb 0.8,Ti 0.2) 4C 3T x and (Nb 0.8,Zr 0.2) 4C 3T x (where T is a surface termination) were synthesizedas confirmed by X-ray diffractionfrom their corresponding MAX phase precursors (Nb 0.8,Ti 0.2) 4AlC 3 and (Nb 0.8,Zr 0.2) 4AlC 3. In our report we discuss Zr-containing MXene. We also studied intercalation of Li ions into these two compositions, and Nb 4C 3T x in order to determine the potential of those materials for energy storage applications. Lithiation and delithiation peaks at 2.26 and 2.35 V, respectively, appeared in the casemore » of Nb 4C 3T x, but were not present in Nb 2CT x. After 20 cycles at a rate of C/4, the specific capacities of (Nb 0.8,Ti 0.2) 4C 3T xand (Nb 0.8,Ti 0.2) 4C 3T x were 158 and 132 mAh/g, respectively, both slightly lower than the capacity of Nb 4C 3T x.« less

Research in LPE of Doped LiNbO3 and LiTaO3 Thin Films.

DTIC Science & Technology

1981-06-01

garnet films grown on single crystal garnet substrates by the LPE technique for magnetic bubble applica- tions. The choice of substrate and film are...AD-Al07 686 ROCKWELL INTERNATIONAL THOUSAND OAKS CA ELECTRONICS -EUTC F/G 2RESEARCH IN LPE OF DOPED LINBO3 AND LITA03 THIN FILMS .(U JUN Al R R NEUR...Research in LPE of Doped LiNbO3 and LiTa03 Final Report Thin Films 04/01/77 through 03/31/81 6. PERFORMING ORG. REPORT NUM9ER ERC41004.11FR 7. AUTNOR

Characterization of a High Strength, Refractory High Entropy Alloy, AlMo0.5NbTa0.5TiZr

NASA Astrophysics Data System (ADS)

Jensen, Jacob

High entropy alloys (HEAs) are a relatively new class of materials that have garnered significant interest over the last decade due to their intriguing balance of properties including high strength, toughness, and corrosion resistance. In contrast to conventional alloy systems, HEAs are based on four or more principal elements with near equimolar concentrations and tend to have simple microstructures due to the preferential formation of solid solution phases. HEAs appear to offer new pathways to lightweighting in structural applications, new alloys for elevated temperature components, and new magnetic materials, but more thorough characterization studies are needed to assess the viability of the recently developed multicomponent materials. One such HEA, AlMo0.5NbTa0.5TiZr, was selected to be the basis for this characterization study in part due to its strength at elevated temperatures (sigma0.2 = 1600 MPa at T = 800 °C) and low density compared with commercially available Ni-based superalloys. The refractory element containing HEA composition was developed in order to balance the high temperature strength of the refractory elements with the desirable properties achieved by the high entropy alloying design approach for potential use in aerospace thermal protection and structural applications. Ingots of AlMo0.5NbTa0.5TiZr were cast by vacuum arc melting followed by hot isostatic pressing (HIP) and homogenization at 1400 °C for 24 hrs with a furnace cool of 10 °C/min. The resulting microstructure was characterized at multiple length scales using x-ray diffraction (XRD), scanning transmission electron microscopy (SEM), conventional and scanning transmission electron microscopy (TEM and STEM), and x-ray energy dispersive spectroscopy (XEDS). The microstructure was found to consist of a periodic, coherent two phase mixture, where a disordered bcc phase is aligned orthogonally in an ordered B2 phase. Through microstructural evolution heat treatment studies, the

Quantum linear magnetoresistance in NbTe2

NASA Astrophysics Data System (ADS)

Chen, Hongxiang; Li, Zhilin; Fan, Xiao; Guo, Liwei; Chen, Xiaolong

2018-07-01

NbTe2 is a quasi-2D layered semimetal with charge density wave ground state showing a distorted-1T structure at room temperature. Here we report the anisotropic magneto-transport properties of NbTe2. An anomalous linear magnetoresistance up to 30% at 3 K in 9 T was observed, which can be well explained by a quantum linear magnetoresistance model. Our results reveal that a large quasi-2D Fermi surface and small Fermi pockets with linearly dispersive bands coexist in NbTe2. The comparison with the isostructural TaTe2 provides more information about the band structure evolution with charge density wave transitions in NbTe2 and TaTe2.

Porous Nb-Ti-Ta alloy scaffolds for bone tissue engineering: Fabrication, mechanical properties and in vitro/vivo biocompatibility.

PubMed

Liu, Jue; Ruan, Jianming; Chang, Lin; Yang, Hailin; Ruan, Wei

2017-09-01

Porous Nb-Ti-Ta (at.%) alloys with the pore size of 100-600μm and the porosity of 50%-80% were fabricated by the combination of the sponge impregnation technique and sintering method. The results revealed that the pores were well connected with three-dimensional (3D) network structure, which showed morphological similarity to the anisotropic porous structure of human bones. The results also showed that the alloys could provide the compressive Young's modulus of 0.11±0.01GPa to 2.08±0.09GPa and the strength of 17.45±2.76MPa to 121.67±1.76MPa at different level of porosity, indicating that the mechanical properties of the alloys are similar to those of human bones. Pore structure on the compressive properties was also discussed on the basis of the deformation mode. The relationship between compressive properties and porosity was well consistent with the Gibson-Ashby model. The mechanical properties could be tailored to match different requirements of the human bones. Moreover, the alloys had good biocompatibility due to the porous structure with higher surface, which were suitable for apatite formation and cell adhesion. In conclusion, the porous Nb-Ti-Ta alloy is potentially useful in the hard tissue implants for the appropriate mechanical properties as well as the good biocompatible properties. Copyright © 2017. Published by Elsevier B.V.

Effect of Cold Deformation and Annealing on the Microstructure and Tensile Properties of a HfNbTaTiZr Refractory High Entropy Alloy

NASA Astrophysics Data System (ADS)

Senkov, O. N.; Pilchak, A. L.; Semiatin, S. L.

2018-07-01

The microstructure and tensile properties of HfNbTaTiZr after cold working and annealing were investigated. Cold work was introduced by axial compression followed by rolling resulting in a total thickness reduction of 89 pct without any evidence of cracking. The cold-worked material retained a single-phase microstructure and had a room temperature tensile yield stress σ 0.2 = 1438 MPa, peak true stress σ p = 1495 MPa, and true fracture strain ɛ f = 5 pct. Annealing at 800 °C for up to 256 hours resulted in the precipitation of Nb and Ta rich particles with a BCC crystal structure inside a Hf-and-Zr-enriched BCC matrix. The second phase particles nucleated heterogeneously inside deformation bands and slip lines and coarsened during annealing. Analysis of the coarsening behavior suggested that kinetics were controlled by the diffusion of Nb and Ta. In the two-phase material, σ 0.2 and σ p decreased from 1159 to 1071 MPa and from 1174 to 1074 MPa, respectively, with an increase in particle diameter from 0.18 to 0.72 μm, while ɛ f remained between 5 and 8 pct. Full recrystallization and normal grain growth, with the activation energy of 238 kJ/mol and activation volume of 5.3 to 9.6 m3/mol, occurred during annealing above 1000 °C. After heat treatment at this temperature, the alloy was characterized by a single-phase BCC structure with σ 0.2 = 1110 to 1115 MPa, σ p = 1160 to 1195 MPa, and ɛ f = 12 to 19 pct with the maximum values attained after annealing for 1 hour.

Effect of Cold Deformation and Annealing on the Microstructure and Tensile Properties of a HfNbTaTiZr Refractory High Entropy Alloy

NASA Astrophysics Data System (ADS)

Senkov, O. N.; Pilchak, A. L.; Semiatin, S. L.

2018-05-01

The microstructure and tensile properties of HfNbTaTiZr after cold working and annealing were investigated. Cold work was introduced by axial compression followed by rolling resulting in a total thickness reduction of 89 pct without any evidence of cracking. The cold-worked material retained a single-phase microstructure and had a room temperature tensile yield stress σ 0.2 = 1438 MPa, peak true stress σ p = 1495 MPa, and true fracture strain ɛ f = 5 pct. Annealing at 800 °C for up to 256 hours resulted in the precipitation of Nb and Ta rich particles with a BCC crystal structure inside a Hf-and-Zr-enriched BCC matrix. The second phase particles nucleated heterogeneously inside deformation bands and slip lines and coarsened during annealing. Analysis of the coarsening behavior suggested that kinetics were controlled by the diffusion of Nb and Ta. In the two-phase material, σ 0.2 and σ p decreased from 1159 to 1071 MPa and from 1174 to 1074 MPa, respectively, with an increase in particle diameter from 0.18 to 0.72 μm, while ɛ f remained between 5 and 8 pct. Full recrystallization and normal grain growth, with the activation energy of 238 kJ/mol and activation volume of 5.3 to 9.6 m3/mol, occurred during annealing above 1000 °C. After heat treatment at this temperature, the alloy was characterized by a single-phase BCC structure with σ 0.2 = 1110 to 1115 MPa, σ p = 1160 to 1195 MPa, and ɛ f = 12 to 19 pct with the maximum values attained after annealing for 1 hour.

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

PubMed

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

2014-02-01

The materials used for internal fracture fixations and joint replacements are mainly made of metals which still face problems ranging from higher rigidity than that of natural bone to leaching cytotoxic metallic ions. Beta (β)-type titanium alloys with low elastic modulus made from non-toxic and non-allergenic elements are desirable to reduce stress shielding effect and enhance bone remodeling. In this work, a new β-type Ti-23Nb-0.7Ta-2Zr-0.5N alloy with a Young's modulus of approximately 50 GPa was designed and characterized. The behavior of MC3T3-E1 pre-osteoblasts on the new alloy, including adhesion, proliferation and differentiation, was evaluated by examining the cytoskeleton, focal adhesion formation, metabolic activity and extracellular matrix mineralization. Results indicated that the pre-osteoblast cells exhibited a similar degree of attachment and growth on Ti-23Nb-0.7Ta-2Zr-0.5N and Ti-6Al-4V. However, the novel alloy proved to be significantly more efficient in sustaining mineralized matrix deposition upon osteogenic induction of the cells than Ti-6Al-4V control. Further, the analysis of RAW 264.7 macrophages cytokine gene and protein expression indicated no significant inflammatory response. Collectively, these findings suggest that the Ti-23Nb-0.7Ta-2Zr-0.5N alloy, which has an increased mechanical biocompatibility with bone, allows a better osteogenic differentiation of osteoblast precursor cells than Ti-6Al-4V and holds great potential for future clinical prosthetic applications. Copyright © 2013 Elsevier B.V. All rights reserved.

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

NASA Astrophysics Data System (ADS)

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

2017-04-01

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

Adsorption and diffusion of Au atoms on the (001) surface of Ti, Zr, Hf, V, Nb, Ta, and Mo carbides.

PubMed

Florez, Elizabeth; Viñes, Francesc; Rodriguez, Jose A; Illas, Francesc

2009-06-28

The adsorption of atomic Au on the (001) surface of TiC, ZrC, HfC, VC, NbC, TaC, and delta-MoC and the mechanism of diffusion of this adatom through the surface have been studied in terms of a periodic density functional theory based approach. In all the cases, the Au adsorption energies are in the range of 1.90-2.35 eV. The moderately large adsorption energies allow the Au diffusion before desorption could take place. For TiC(001), ZrC(001), and HfC(001), atomic Au is adsorbed directly on top of C atoms and diffusion takes place along the diagonal of the squares formed by M-C-M-C atoms with the transition state located above the hollow sites. For the rest of transition metal carbides the situation is less simple with the appearance of more than one stable adsorption site, as for NbC and TaC, of a small energy barrier for diffusion around the most stable adsorption site and of a more complex diffusion pathway. The small energy barrier for diffusion around the most stable site will result in a highly mobile Au species which could be observed in scanning tunnel microscope experiments. After depositing Au on metal-carbide surfaces, there is a noticeable charge transfer from the substrate to the adsorbed Au atom. The electronic perturbations on Au increase when going from TiC to ZrC or TaC. Our results indicate that metal carbides should be better supports for the chemical activation of Au than metal oxides.

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

NASA Technical Reports Server (NTRS)

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

1987-01-01

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

Cation deficient layered Ruddlesden-Popper-related oxysulfides La2LnMS2O5 (Ln=La, Y; M=Nb, Ta).

PubMed

Cario, Laurent; Popa, Aurelian Florin; Lafond, Alain; Guillot-Deudon, Catherine; Kabbour, Houria; Meerschaut, A; Clarke, Simon J; Adamson, Paul

2007-11-12

The structures of the new oxysulfide Ruddlesden-Popper phases La2LnMS2O5 (Ln=La, Y; M=Nb, Ta) are reported together with an iodide-containing variant: La3-xNb1+xS2O5I2x (0Nb1+xO5I2x]. In the oxide slabs, the trivalent and pentavalent cations are disordered on the long-length scale probed by diffraction methods, but bond length considerations suggest that they must be ordered at least on the length scale of the unit cell. The [LnMO5] block of the iodide-free compounds derive from the ideal [Ti2O5] blocks found in Ln2Ti2S2O5 (Ln=Nd-Er; Y) by the formal substitution of two Ti4+ ions with one Ln3+ and one M5+ion. The unusual partial insertion of iodide in the perovskite voids of the [LaNbO5] block in La3NbS2O5 was found to be coupled to a La/Nb substitution, maintaining the charge balance within the [La1-xNb1+xO5I2x]2- block. The Nb5+ ions were found to be too resistant to reduction to undergo the intercalation of alkali metals observed in the Ln2Ti2S2O5 series.

Significant enhancement of compositional and superconducting homogeneity in Ti rather than Ta-doped Nb 3Sn

DOE PAGES

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

2016-01-25

Nb 3Sn wires are now very close to their final optimization but despite its classical nature, detailed understanding of the role of Ta and Ti doping in the A15 is not fully understood. Long thought to be essentially equivalent in their influence on H c2, they were interchangeably applied. Here we show that Ti produces significantly more homogeneous chemical and superconducting properties. Despite Ta-doped samples having a slightly higher T c onset in zero-field, they always have a wider Tc-distribution. In particular, whereas the Ta-doped A15 has a T c-distribution extending from 18 down to 5-6 K (the lowest expectedmore » Tc for the binary A15 phase), the Ti-doped samples have no A15 phase with T c below ~12 K. The much narrower T c distribution in the Ti-doped samples has a positive effect on their in-field T c-distribution too, leading to an extrapolated μ0H c2(0) 2 Tesla larger than the Ta-doped one. Ti-doping also appears to be very homogeneous even when the Sn content is reduced in order to inhibit breakdown of the diffusion barriers in very high Jc conductors. As a result, the enhanced homogeneity of the Ti-doped samples appears to result from its assistance of rapid diffusion of Sn into the filaments and by its incorporation into the A15 phase interchangeably with Sn on the Sn sites of the A15 phase.« less

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

PubMed

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

2011-03-01

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

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

NASA Astrophysics Data System (ADS)

Giannouri, M.; Papastaikoudis, C.

1999-05-01

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

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Acharya, Nikita, E-mail: acharyaniks30@gmail.com; Fatima, Bushra; Sanyal, Sankar P.

2016-05-06

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

Traces of charge density waves in NbS 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leroux, Maxime; Cario, Laurent; Bosak, Alexei

Among transition metal dichalcogenides (TMD), NbS 2 is often considered as the archetypal compound that does not have a charge density wave (CDW) in any of its polytypes. By comparison, close isoelectronic compounds such as NbSe 2, TaS 2, and TaSe 2 all have CDW in at least one polytype. Here we report traces of CDW in the 2H polytype of NbS 2, using diffuse x-ray scattering measurements at 77 K and room temperature. We observe 12 extremely weak satellite peaks located at ±13.9° from →a* and →b* around each Bragg peak in the (h,k,0) plane. These satellite peaks aremore » commensurate with the lattice via 3 →q– →q'= →a*, where →q' is the 120° rotation of →q, and define two √13a × √13a superlattices in real space. These commensurate wave vectors and tilt angle are identical to those of the CDW observed in the 1T polytype of TaS 2 and TaSe 2. In conclusion, to understand this similarity and the faintness of the peaks, we discuss possible sources of local 1T polytype environment in bulk 2H-NbS 2 crystals.« less

Traces of charge density waves in NbS2

NASA Astrophysics Data System (ADS)

Leroux, Maxime; Cario, Laurent; Bosak, Alexei; Rodière, Pierre

2018-05-01

Among transition metal dichalcogenides (TMD), NbS2 is often considered as the archetypal compound that does not have a charge density wave (CDW) in any of its polytypes. By comparison, close isoelectronic compounds such as NbSe2, TaS2, and TaSe2 all have CDW in at least one polytype. Here we report traces of CDW in the 2H polytype of NbS2, using diffuse x-ray scattering measurements at 77 K and room temperature. We observe 12 extremely weak satellite peaks located at ±13.9° from a⃗* and b⃗* around each Bragg peak in the (h ,k ,0 ) plane. These satellite peaks are commensurate with the lattice via 3 q ⃗-q ⃗'=a⃗*,where q ⃗' is the 120° rotation of q ⃗, and define two √{13 }a ×√{13 }a superlattices in real space. These commensurate wave vectors and tilt angle are identical to those of the CDW observed in the 1T polytype of TaS2 and TaSe2. To understand this similarity and the faintness of the peaks, we discuss possible sources of local 1T polytype environment in bulk 2H-NbS2 crystals.

Traces of charge density waves in NbS 2

DOE PAGES

Leroux, Maxime; Cario, Laurent; Bosak, Alexei; ...

2018-05-15

Among transition metal dichalcogenides (TMD), NbS 2 is often considered as the archetypal compound that does not have a charge density wave (CDW) in any of its polytypes. By comparison, close isoelectronic compounds such as NbSe 2, TaS 2, and TaSe 2 all have CDW in at least one polytype. Here we report traces of CDW in the 2H polytype of NbS 2, using diffuse x-ray scattering measurements at 77 K and room temperature. We observe 12 extremely weak satellite peaks located at ±13.9° from →a* and →b* around each Bragg peak in the (h,k,0) plane. These satellite peaks aremore » commensurate with the lattice via 3 →q– →q'= →a*, where →q' is the 120° rotation of →q, and define two √13a × √13a superlattices in real space. These commensurate wave vectors and tilt angle are identical to those of the CDW observed in the 1T polytype of TaS 2 and TaSe 2. In conclusion, to understand this similarity and the faintness of the peaks, we discuss possible sources of local 1T polytype environment in bulk 2H-NbS 2 crystals.« less

Possibility of Flat-Band Ferromagnetism in Hole-Doped Pyrochlore Oxides Sn2 Nb2 O7 and Sn2 Ta2 O7

NASA Astrophysics Data System (ADS)

Hase, I.; Yanagisawa, T.; Aiura, Y.; Kawashima, K.

2018-05-01

Quantum mechanics tells us that the hopping integral between local orbitals makes the energy band dispersive. In a lattice with geometric frustration, however, dispersionless flat bands may appear due to quantum interference. Several models possessing flat bands have been proposed theoretically, and many attracting magnetic and electronic properties are predicted. However, despite many attempts to realize these models experimentally, compounds that are appropriately described by this model have not been found so far. Here we show that pyrochlore oxides Sn2 Nb2 O7 and Sn2Ta2O7 are such examples, by performing first-principles band calculation and several tight-binding analyses. Moreover, spin-polarized band calculation shows that the hole-doped systems Sn2 Nb2 O6 N and Sn2 Ta2 O6 N have complete spin polarization, and their magnetic moments are mostly carried by Sn-s and N-p orbitals, which are usually nonmagnetic. These compounds are not only candidates for ferromagnets without a magnetic element, but also will provide an experimental platform for a flat-band model which shows a wide range of physical properties.

New ternary tantalum borides containing boron dumbbells: Experimental and theoretical studies of Ta2OsB2 and TaRuB

NASA Astrophysics Data System (ADS)

Mbarki, Mohammed; Touzani, Rachid St.; Rehorn, Christian W. G.; Gladisch, Fabian C.; Fokwa, Boniface P. T.

2016-10-01

The new ternary transition metal-rich borides Ta2OsB2 and TaRuB have been successfully synthesized by arc-melting the elements in a water-cooled crucible under an argon atmosphere. The crystal structures of both compounds were solved by single-crystal X-ray diffraction and their metal compositions were confirmed by EDX analysis. It was found that Ta2OsB2 and TaRuB crystallize in the tetragonal Nb2OsB2 (space group P4/mnc, no. 128) and the orthorhombic NbRuB (space group Pmma, no. 51) structure types with lattice parameters a=5.878(2) Å, c=6.857(2) Å and a=10.806(2) Å, b=3.196(1) Å, c=6.312(2) Å, respectively. Furthermore, crystallographic, electronic and bonding characteristics have been studied by density functional theory (DFT). Electronic structure relaxation has confirmed the crystallographic parameters while COHP bonding analysis indicates that B2-dummbells are the strongest bonds in both compounds. Moreover, the formation of osmium dumbbells in Ta2OsB2 through a Peierls distortion along the c-axis, is found to be the origin of superstructure formation. Magnetic susceptibility measurements reveal that the two phases are Pauli paramagnets, thus confirming the theoretical DOS prediction of metallic character. Also hints of superconductivity are found in the two phases, however lack of single phase samples has prevented confirmation. Furthermore, the thermodynamic stability of the two modifications of AMB (A=Nb, Ta; M =Ru, Os) are studied using DFT, as new possible phases containing either B4- or B2-units are predicted, the former being the most thermodynamically stable modification.

Pressure-induced phase transition of KTa1/2Nb1/2O3 solid solutions: A first-principles study

NASA Astrophysics Data System (ADS)

Zhang, Huadi; Liu, Bing; Zhang, Cong; Qiu, Chengcheng; Wang, Xuping; Zhang, Yuanyuan; Lv, Xianshun; Wei, Lei; Li, Qinggang

2018-05-01

The structures and electronic properties of KTa1/2Nb1/2O3 under high pressures have been investigated using the first-principles calculations. Three candidates with B site cation ordered along the [1 0 0], [1 1 0] and [1 1 1] directions are found stable under different pressures by thermodynamics, mechanics and dynamics stability criteria. Further electronic analysis indicates that three structures are semiconductors with different band-gap characteristics. The peculiar chemical bonds of Nb-O and Ta-O are expected to be related to the different electronegativity of the corresponding cations.

Observations on the long-lived Mossbauer effects of 93mNb

PubMed Central

Cheng, Yao; Yang, Shi-Hui; Lan, Michael; Lee, Chih-Hao

2016-01-01

Several observations of the Nb long-lived Mossbauer phenomena are presented, in consequence of an irradiation increased by an order of magnitude compared with previous work. These are 1) two β decays of 182Ta and 92mNb are enhanced, i.e., 182Ta is now 200 times faster than in previous results while 92mNb is twice as fast as normal; 2) γs emitted from two β decays compete to eject electrons in a winner-takes-all rule, rather than by superposition; 3) abrupt spectral changes reveal three decay phases of 182Ta; 4) the biphoton γγ of 93mNb is released from the sample for the first time; 5) the γγ distribution is narrow, in contrast to the broad γγ spectrum obtained from independent nuclei; 6) Nb K-lines super-radiate along the long sample axis; 7) collective scattering of multipolar MeV γs. The manipulation of nuclear decay speeds demonstrated here highlights a potential application of this work in cleaning up the nuclear wastes. PMID:27824073

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

NASA Astrophysics Data System (ADS)

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

2017-09-01

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

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bijumon, Pazhoor Varghese; Sebastian, Mailadil Thomas; Dias, Anderson

2005-05-15

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

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

NASA Astrophysics Data System (ADS)

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

2016-11-01

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

Novel elastic, lattice dynamics and thermodynamic properties of metallic single-layer transition metal phosphides: 2H-M 2P (Mo2P, W2P, Nb2P and Ta2P)

NASA Astrophysics Data System (ADS)

Yin, Jiuren; Wu, Bozhao; Wang, Yanggang; Li, Zhimi; Yao, Yuanpeng; Jiang, Yong; Ding, Yanhuai; Xu, Fu; Zhang, Ping

2018-04-01

Recently, there has been a surge of interest in the research of two-dimensional (2D) phosphides due to their unique physical properties and wide applications. Transition metal phosphides 2H-M 2Ps (Mo2P, W2P, Nb2P and Ta2P) show considerable catalytic activity and energy storage potential. However, the electronic structure and mechanical properties of 2D 2H-M 2Ps are still unrevealed. Here, first-principles calculations are employed to investigate the lattice dynamics, elasticity and thermodynamic properties of 2H-M 2Ps. Results show that M 2Ps with lower stiffness exhibit remarkable lateral deformation under unidirectional loads. Due to the largest average Grüneisen parameter, single-layer Nb2P has the strongest anharmonic vibrations, resulting in the highest thermal expansion coefficient. The lattice thermal conductivities of Ta2P, W2P and Nb2P contradict classical theory, which would predict a smaller thermal conductivity due to the much heavier atom mass. Moreover, the calculations also demonstrate that the thermal conductivity of Ta2P is the highest as well as the lowest thermal expansion, owing to its weak anharmonic phonon scattering and the lowest average Grüneisen parameter. The insight provided by this study may be useful for future experimental and theoretical studies concerning 2D transition metal phosphide materials.

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

PubMed

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

2015-07-21

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

Effect of Substitution (Ta, Al, Ga) on the Conductivity of Li7La3Zr2O12

DTIC Science & Technology

2012-01-30

xTax012). Conductivity data was not included in their report. Similarly to Ta, Nb substitution for Zr should also lower the Li content of the LLZO and a...high Li ion conductivity (0.8 mS cm−1 at 298 K) cubic garnet sample has been reported with Nb substitution for Zr by Ohta et al. [15]. However, Ta is...substitution for Zr follows this approach and it is desirable for a couple rea- sons. First, Ta is stable relative to Li [13]. Second, Ta substitution

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

PubMed Central

Osiceanu, Petre; Gloriant, Thierry

2015-01-01

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

TaEDS1 genes positively regulate resistance to powdery mildew in wheat.

PubMed

Chen, Guiping; Wei, Bo; Li, Guoliang; Gong, Caiyan; Fan, Renchun; Zhang, Xiangqi

2018-04-01

Three EDS1 genes were cloned from common wheat and were demonstrated to positively regulate resistance to powdery mildew in wheat. The EDS1 proteins play important roles in plant basal resistance and TIR-NB-LRR protein-triggered resistance in dicots. Until now, there have been very few studies on EDS1 in monocots, and none in wheat. Here, we report on three common wheat orthologous genes of EDS1 family (TaEDS1-5A, 5B and 5D) and their function in powdery mildew resistance. Comparisons of these genes with their orthologs in diploid ancestors revealed that EDS1 is a conserved gene family in Triticeae. The cDNA sequence similarity among the three TaEDS1 genes was greater than 96.5%, and they shared sequence similarities of more than 99.6% with the respective orthologs from diploid ancestors. The phylogenetic analysis revealed that the EDS1 family originated prior to the differentiation of monocots and dicots, and EDS1 members have since undergone clear structural differentiation. The transcriptional levels of TaEDS1 genes in the leaves were obviously higher than those of the other organs, and they were induced by Blumeria graminis f. sp. tritici (Bgt) infection and salicylic acid (SA) treatment. The BSMV-VIGS experiments indicated that knock-down the transcriptional levels of the TaEDS1 genes in a powdery mildew-resistant variety of common wheat compromised resistance. Contrarily, transient overexpression of TaEDS1 genes in a susceptible common wheat variety significantly reduced the haustorium index and attenuated the growth of Bgt. Furthermore, the expression of TaEDS1 genes in the Arabidopsis mutant eds1-1 complemented its susceptible phenotype to powdery mildew. The above evidences strongly suggest that TaEDS1 acts as a positive regulator and confers resistance against powdery mildew in common wheat.

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

NASA Astrophysics Data System (ADS)

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

2016-03-01

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

Search for solid conductors of Na(+) and K(+) ions: Five new conductors

NASA Technical Reports Server (NTRS)

Singer, J.; Kautz, H.; Fielder, W. L.; Fordyce, J.

1975-01-01

Five conductors of three structure types were discovered which, as solids, can transport Na(+) or K(+) ions with conductivities of approximately .00001/(omega cm) at 300 K. These compounds are: (1) the pyrochlores NaTaWO6 and NaTa2O5F, both with an activation energy for conduction delta E of 21 kJ/mole; (2) the bodycentered cubic form of NaSbO3, with delta E = 42 kJ/mole; and (3) the niobates 2Na2O with 3Nb2O5 and 2K2O with 3Nb2O5, with the alkali ions probably in open layers of the incompletely determined structure; delta E = 17 kJ/mole. On the basis of approximately 40 structure types, some generalizations were made regarding the relation between structure and ionic transport.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

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

The oxidation of TaBe sub 12 and NbBe sub 12 coatings on niobium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Courtright, E.L.

1990-01-01

The oxidation behavior of tantalum and niobium beryllide coatings on niobium were evaluated. Intermetallic bond layers consisting of Ir{sub 3}Ta and Ir{sub 3}Nb were used to butter the large thermal expansion mismatch between the beryllide coatings and underlying niobium substrate. All coatings were applied by Triode Sputtering except for a final environmental protection layer of stabilized zirconia deposited by RF Diode using a ceramic target. Severe delamination and spalling occurred during cyclic oxidation exposure, even at temperatures as low as 925{degrees}C, indicating that the bond layer did not prevent the differential expansion stresses from reaching the delamination failure threshold, particularlymore » at the edges and corners. Hot pressed samples of the two beryllide compounds were also exposed to a similar cyclic oxidation history, but, in contrast to the coatings, exhibited excellent oxidation resistance to temperatures as high as 1370{degrees}C. 9 refs., 8 figs., 1 tab.« less

Symmetry and geometry considerations of atom transfer: deoxygenation of (silox)3WNO and R3PO (R = Me, Ph, (t)Bu) by (silox)3M (M = V, NbL (L = PMe3, 4-picoline), Ta; silox = (t)Bu3SiO).

PubMed

Veige, Adam S; Slaughter, LeGrande M; Lobkovsky, Emil B; Wolczanski, Peter T; Matsunaga, Nikita; Decker, Stephen A; Cundari, Thomas R

2003-10-06

Deoxygenations of (silox)(3)WNO (12) and R(3)PO (R = Me, Ph, (t)Bu) by M(silox)(3) (1-M; M = V, NbL (L = PMe(3), 4-picoline), Ta; silox = (t)Bu(3)SiO) reflect the consequences of electronic effects enforced by a limiting steric environment. 1-Ta rapidly deoxygenated R(3)PO (23 degrees C; R = Me (DeltaG degrees (rxn)(calcd) = -47 kcal/mol), Ph) but not (t)Bu(3)PO (85 degrees, >2 days), and cyclometalation competed with deoxygenation of 12 to (silox)(3)WN (11) and (silox)(3)TaO (3-Ta; DeltaG degrees (rxn)(calcd) = -100 kcal/mol). 1-V deoxygenated 12 slowly and formed stable adducts (silox)(3)V-OPR(3) (3-OPR(3)) with OPR(3). 1-Nb(4-picoline) (S = 0) and 1-NbPMe(3) (S = 1) deoxygenated R(3)PO (23 degrees C; R = Me (DeltaG degrees (rxn)(calcd from 1-Nb) = -47 kcal/mol), Ph) rapidly and 12 slowly (DeltaG degrees (rxn)(calcd) = -100 kcal/mol), and failed to deoxygenate (t)Bu(3)PO. Access to a triplet state is critical for substrate (EO) binding, and the S --> T barrier of approximately 17 kcal/mol (calcd) hinders deoxygenations by 1-Ta, while 1-V (S = 1) and 1-Nb (S --> T barrier approximately 2 kcal/mol) are competent. Once binding occurs, significant mixing with an (1)A(1) excited state derived from population of a sigma-orbital is needed to ensure a low-energy intersystem crossing of the (3)A(2) (reactant) and (1)A(1) (product) states. Correlation of a reactant sigma-orbital with a product sigma-orbital is required, and the greater the degree of bending in the (silox)(3)M-O-E angle, the more mixing energetically lowers the intersystem crossing point. The inability of substrates EO = 12 and (t)Bu(3)PO to attain a bent 90 degree angle M-O-E due to sterics explains their slow or negligible deoxygenations. Syntheses of relevant compounds and ramifications of the results are discussed. X-ray structural details are provided for 3-OPMe(3) (90 degree angle V-O-P = 157.61(9) degrees), 3-OP(t)Bu(3) ( 90 degree angle V-O-P = 180 degrees ), 1-NbPMe(3), and (silox)(3)ClWO (9).

Multiple deformation mechanisms of Ti-22.4Nb-0.73Ta-2.0Zr-1.34O alloy

NASA Astrophysics Data System (ADS)

Yang, Y.; Li, G. P.; Cheng, G. M.; Li, Y. L.; Yang, K.

2009-02-01

Ti-22.4Nb-0.73Ta-2.0Zr-1.34O (at. %) alloy after cold compression to ˜5.2% strain was investigated. The alloy exhibited multiple plastic deformation mechanisms, including the stress-induced α″ martensitic (SIM α″) and ω phase transformations, 1/2⟨111⟩ dislocations slipping on the {112}β planes as well as {332}⟨113⟩β and {112}⟨111⟩β twinning, which have not previously been reported to coexist in a titanium alloy. It was also found that β phase with the {200} planes vertical to the compression direction was almost completely consumed away by a β →SIM α″ transformation, and a (100) texture of SIM α″ formed.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borza, F., E-mail: fborza@phys-iasi.ro; Lupu, N.; Dobrea, V.

2015-05-07

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

Structural phase transitions in the Ag{sub 2}Nb{sub 4}O{sub 11}-Na{sub 2}Nb{sub 4}O{sub 11} solid solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Woodward, David I., E-mail: d.i.woodward@warwick.ac.uk; Lees, Martin R.; Thomas, Pam A.

2012-08-15

The phase transitions between various structural modifications of the natrotantite-structured system xAg{sub 2}Nb{sub 4}O{sub 11}-(1-x)Na{sub 2}Nb{sub 4}O{sub 11} have been investigated and a phase diagram constructed as a function of temperature and composition. This shows three separate phase transition types: (1) paraelectric-ferroelectric, (2) rhombohedral-monoclinic and (3) a phase transition within the ferroelectric rhombohedral zone between space groups R3c and R3. The parent structure for the entire series has space group R3{sup Macron }c. Compositions with x>0.75 are rhombohedral at all temperatures whereas compositions with x<0.75 are all monoclinic at room temperature and below. At x=0.75, rhombohedral and monoclinic phases coexistmore » with the phase boundary below room temperature being virtually temperature-independent. The ferroelectric phase boundary extends into the monoclinic phase field. No evidence was found for the R3-R3c phase boundary extending into the monoclinic phase field and it is concluded that a triple point is formed. - Graphical abstract: Phase diagram for xAg{sub 2}Nb{sub 4}O{sub 11}-(1-x)Na{sub 2}Nb{sub 4}O{sub 11} solid solution showing changes in crystal symmetry as a function of temperature and composition. The crystal structure is depicted. Highlights: Black-Right-Pointing-Triangle Ferroelectric, rhombohedral Ag{sub 2}Nb{sub 4}O{sub 11} in solid solution with monoclinic Na{sub 2}Nb{sub 4}O{sub 11}. Black-Right-Pointing-Triangle Three phase boundaries were studied as a function of composition and temperature. Black-Right-Pointing-Triangle Both rhombohedral and monoclinic variants exhibit ferroelectricity. The parent phase of the series has space group R3{sup Macron }c.« less

Nonvolatile memories using deep traps formed in HfO2 by Nb ion implantation

NASA Astrophysics Data System (ADS)

Choul Kim, Min; Oh Kim, Chang; Taek Oh, Houng; Choi, Suk-Ho; Belay, K.; Elliman, R. G.; Russo, S. P.

2011-03-01

We report nonvolatile memories (NVMs) based on deep-energy trap levels formed in HfO2 by metal ion implantation. A comparison of Nb- and Ta-implanted samples shows that suitable charge-trapping centers are formed in Nb-implanted samples, but not in Ta-implanted samples. This is consistent with density-functional theory calculations which predict that only Nb will form deep-energy levels in the bandgap of HfO2. Photocurrent spectroscopy exhibits characteristics consistent with one of the trap levels predicted in these calculations. Nb-implanted samples showing memory windows in capacitance-voltage (V) curves always exhibit current (I) peaks in I-V curves, indicating that NVM effects result from deep traps in HfO2. In contrast, Ta-implanted samples show dielectric breakdowns during the I-V sweeps between 5 and 11 V, consistent with the fact that no trap levels are present. For a sample implanted with a fluence of 1013 Nb cm-2, the charge losses after 104 s are ˜9.8 and ˜25.5% at room temperature (RT) and 85°C, respectively, and the expected charge loss after 10 years is ˜34% at RT, very promising for commercial NVMs.

Preconcentration of Zr, Hf, Nb, Ta and W in seawater using solid-phase extraction on TSK-8-hydroxyquinoline resin and determination by inductively coupled plasma-mass spectrometry.

PubMed

Firdaus, M Lutfi; Norisuye, Kazuhiro; Sato, Taishi; Urushihara, Shouhei; Nakagawa, Yusuke; Umetani, Shigeo; Sohrin, Yoshiki

2007-02-05

Here, we present the first simultaneous preconcentration and determination of ultratrace (pmol kg(-1) level) Zr, Hf, Nb, Ta and W in seawater, both in the form of dissolved and acid-dissolvable species. 8-Hydroxyquinoline (8HQ) bonded covalently to a vinyl polymer resin, TSK-8HQ, was used in a chelating adsorbent column to concentrate the metals. The greatest advantage of this resin is its endurance to 5M HF, since this is an effective eluent for all five metals. The analytes were successfully concentrated from 250 mL seawater with a 50-fold concentration factor through the column extraction and evaporation. The detection limit was 0.009-0.15 pmol kg(-1). The procedure blank determined using ultra pure water as a sample was 0.005-0.37 pmol kg(-1). The five metals were quantitatively recovered from seawater with good precision (2-4%). The effect of sample pH, sample flow rate, eluent composition and sample pretreatment were carefully studied. This method was applied to seawater.

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

NASA Astrophysics Data System (ADS)

Niu, Yaoling; O'Hara, Michael J.

2009-09-01

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

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

PubMed

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

2017-04-01

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

Superconductivity in Cage Compounds LaTr2Al20 with Tr = Ti, V, Nb, and Ta

NASA Astrophysics Data System (ADS)

Yamada, Akira; Higashinaka, Ryuji; Matsuda, Tatsuma D.; Aoki, Yuji

2018-03-01

Electrical resistivity, magnetic susceptibility, and specific heat measurements on single crystals of LaTr2Al20 (Tr = Ti, V, Nb, and Ta) revealed that these four compounds exhibit weak-coupling superconductivity with transition temperatures Tc = 0.46, 0.15, 1.05, and 1.03 K, respectively. LaTi2Al20 is most probably a type-I superconductor, which is quite rare among intermetallic compounds. Single-crystal X-ray diffraction suggests "rattling" anharmonic large-amplitude oscillations of Al ions (16c site) on the Al16 cage, while no such feature is suggested for the cage-center La ion. Using a parameter dGFS quantifying the "guest free space" of the cage-center ion, we demonstrate that nonmagnetic RTr2Al20 superconductors are classified into two groups, i.e., (A) dGFS ≠ 0 and Tc correlates with dGFS, and (B) dGFS ≃ 0 and Tc seems to be governed by other factors.

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

PubMed Central

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

2016-01-01

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

Elucidating the Impact of Chalcogen Content on the Photovoltaic Properties of Oxychalcogenide Perovkskites: NaMO3-x Qx (M=Nb, Ta; Q=S, Se, Te).

PubMed

Park, Heesoo; Alharbi, Fahhad H; Sanvito, Stefano; Tabet, Nouar; El-Mellouhi, Fedwa

2018-03-19

In the quest for nontoxic and stable perovskites for solar cells, we have conducted a systematic study of the effect of chalcogen content in oxychalcogenide perovskite by using DFT and quasi-particle perturbation theory. We explored the changes in the electronic structure due to the substitution of O atoms in NaNbO 3 and NaTaO 3 perovskite structures with various chalcogens (S, Se, Te) at different concentrations. Interestingly, the introduction of the chalcogen atoms resulted in a drastic reduction in the electronic band gap, which made some of the compounds fall within the visible range of the solar spectrum. In addition, our analysis of the electronic structure shows that the optical transition becomes direct as a result of the strong hybridization between the orbitals of the transition metal and those of the chalcogen ion, in contrast to the indirect band feature of NaNbO 3 and NaTaO 3 . We identified candidates with a high theoretical solar conversion efficiency that approached the Shockley-Queisser limit, which makes them suitable for thin-film solar cell applications. The present work serves as a guideline for experimental efforts by identifying the chalcogen content that should be targeted during the synthetic route of thermodynamically stable and strongly photoactive absorbers for oxychalcogenide perovskites in thin-film solar cells. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

NASA Astrophysics Data System (ADS)

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

2016-06-01

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

Core-Shell Structure of Intermediate Precipitates in a Nb-Based Z-Phase Strengthened 12% Cr Steel.

PubMed

Rashidi, Masoud; Andrén, Hans-Olof; Liu, Fang

2017-04-01

In creep resistant Z-phase strengthened 12% Cr steels, MX (M=Nb, Ta, or V, and X=C and/or N) to Z-phase (CrMN, M=Ta, Nb, or V) transformation plays an important role in achieving a fine distribution of Z-phase precipitates for creep strengthening. Atom probe tomography was employed to investigate the phase transformation in a Nb-based Z-phase strengthened trial steel. Using iso-concentration surfaces with different concentration values, and subtracting the matrix contribution enabled us to reveal the core-shell structure of the transient precipitates between MX and Z-phase. It was shown that Z-phase forms by diffusion of Cr into NbN upon ageing, and Z-phase has a composition corresponding to Cr1+x Nb1-x N with x=0.08.

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

New insights into the initial stages of Ta oxide nanotube formation on polycrystalline Ta electrodes.

PubMed

El-Sayed, Hany A; Horwood, Corie A; Abhayawardhana, Anusha D; Birss, Viola I

2013-02-21

Ta oxide nanotubes (NTs) were formed by the anodization of Ta at 15 V in a solution of concentrated sulfuric acid containing 0.8-1.0 M hydrofluoric acid. To study the initial stages of NT formation, FESEM images of samples anodized for very short times were obtained. The results contradict the existing explanation of the current-time data collected during anodization, which has persisted in the literature for more than two decades. In addition to providing a first-time morphological study of Ta oxide NT formation at very early stages of anodization, we also propose a new interpretation of the i-t response, showing that pores are already present in the first few milliseconds of anodization and that NTs are formed well before present models predict. This behaviour may also extend to the anodization of other valve metals, such as Al, Ti, Zr, W, and Nb.

Structure and mechanical properties of a two-layered material produced by the E-beam surfacing of Ta and Nb on the titanium base after multiple rolling

NASA Astrophysics Data System (ADS)

Bataev, V. A.; Golkovski, M. G.; Samoylenko, V. V.; Ruktuev, A. A.; Polyakov, I. A.; Kuksanov, N. K.

2018-04-01

The study has been conducted in line with the current approach to investigation of materials obtained by considerably deep surface alloying of the titanium substrate with Ta, Nb, and Zr. The thickness of the resulting alloyed layer was equal to 2 mm. The coating was formed through weld deposition of a powder with the use of a high-voltage electron beam in the air. It has been lately demonstrated that manufactured such a way alloyed layers possess corrosion resistance which is significantly higher than the resistance of titanium substrates. It has already been shown that such two-layered materials are weldable. The study objective is to investigate the feasibility of rolling for necking the sheets with the Ti-Ta-Nb anticorrosion coating with further fourfold decrease in their thickness. The research is also aimed at investigation of the material properties after rolling. Anticorrosion layers were formed both on CP-titanium and on VT14 (Ti-4Al-3Mo-1 V) durable titanium alloy. The results of chemical composition determination, structure examination, X-ray phase analysis and mechanical properties observations (including bending properties of the alloyed layers) are presented in the paper. The combination of welding, rolling, and bending enables the manufacture of corrosion-resistant vessels and process pipes which are made from the developed material and find technological application.

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

PubMed

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

2013-05-15

Density functional theory (DFT) and coupled cluster theory (CCSD(T)) calculations are carried out to investigate the electronic and structural properties of a series of bimetallic oxide clusters MW2O9(-/0) (M=V, Nb, Ta). Generalized Koopmans' theorem is applied to predict the vertical detachment energies (VDEs) and simulate the photoelectron spectra (PES). Theoretical calculations at the B3LYP level yield singlet and doublet ground states for the bimetallic anionic and neutral clusters, respectively. All the clusters present the six-membered ring structures with different symmetries, except that the TaW2O9(-) cluster shows a chained style with a penta-coordinated tantalum atom. Spin density analyses reveal oxygen radical species in all neutral clusters, consistent with their structural characteristics. Moreover, additional calculations are performed to study the oxidation reaction of CO molecule with the W3O9(+) cation and the isoelectronic VW2O9 cluster, and results indicate that the introduction of vanadium at tungsten site can efficiently improve the oxidation reactivity. Copyright © 2013 Elsevier B.V. All rights reserved.

The solid-solution region for the langasite-type Ca3TaGa3Si2O14 crystal as determined by a lever rule

NASA Astrophysics Data System (ADS)

Zhao, Hengyu; Uda, Satoshi; Maeda, Kensaku; Nozawa, Jun; Koizumi, Haruhiko; Fujiwara, Kozo

2015-04-01

A lever rule was applied to data concerning the compositions and proportions of secondary phases coexisting with a Ca3TaGa3Si2O14 (CTGS) matrix to determine the boundary compositions of the solid-solution region for CTGS at 1320 °C, as a means of ascertaining the solid-solution for the langasite-type phase in the quaternary CaO-Ta2O5-Ga2O3-SiO2 system. The compositions and proportions of secondary phases were assessed by electron probe micro-analysis as well as through back-scattered electron images. The experimental results showed that the narrow solid-solution region for CTGS is located in a Ta-poor, Ga-poor and Si-rich region relative to its stoichiometric composition.

Fully Depleted Ti-Nb-Ta-Zr-O Nanotubes: Interfacial Charge Dynamics and Solar Hydrogen Production.

PubMed

Chiu, Yi-Hsuan; Lai, Ting-Hsuan; Chen, Chun-Yi; Hsieh, Ping-Yen; Ozasa, Kazunari; Niinomi, Mitsuo; Okada, Kiyoshi; Chang, Tso-Fu Mark; Matsushita, Nobuhiro; Sone, Masato; Hsu, Yung-Jung

2018-05-01

Poor kinetics of hole transportation at the electrode/electrolyte interface is regarded as a primary cause for the mediocre performance of n-type TiO 2 photoelectrodes. By adopting nanotubes as the electrode backbone, light absorption and carrier collection can be spatially decoupled, allowing n-type TiO 2 , with its short hole diffusion length, to maximize the use of the available photoexcited charge carriers during operation in photoelectrochemical (PEC) water splitting. Here, we presented a delicate electrochemical anodization process for the preparation of quaternary Ti-Nb-Ta-Zr-O mixed-oxide (denoted as TNTZO) nanotube arrays and demonstrated their utility in PEC water splitting. The charge-transfer dynamics for the electrodes was investigated using time-resolved photoluminescence, electrochemical impedance spectroscopy, and the decay of open-circuit voltage analysis. Data reveal that the superior photoactivity of TNTZO over pristine TiO 2 originated from the introduction of Nd, Ta, and Zr elements, which enhanced the amount of accessible charge carriers, modified the electronic structure, and improved the hole injection kinetics for expediting water splitting. By modulating the water content of the electrolyte employed in the anodization process, the wall thickness of the grown TNTZO nanotubes can be reduced to a size smaller than that of the depletion layer thickness, realizing a fully depleted state for charge carriers to further advance the PEC performance. Hydrogen evolution tests demonstrate the practical efficacy of TNTZO for realizing solar hydrogen production. Furthermore, with the composition complexity and fully depleted band structure, the present TNTZO nanotube arrays may offer a feasible and universal platform for the loading of other semiconductors to construct a sophisticated heterostructure photoelectrode paradigm, in which the photoexcited charge carriers can be entirely utilized for efficient solar-to-fuel conversion.

High-quality single crystal growth and magnetic property of Mn4Ta2O9

NASA Astrophysics Data System (ADS)

Cao, Yiming; Xu, Kun; Yang, Ya; Yang, Wangfan; Zhang, Yuanlei; Kang, Yanru; He, Xijia; Zheng, Anmin; Liu, Mian; Wei, Shengxian; Li, Zhe; Cao, Shixun

2018-06-01

A large-size single crystal of Mn4Ta2O9 with ∼3.5 mm in diameter and ∼65 mm in length was successfully grown for the first time by a newly designed one-step method based on the optical floating zone technique. Both the clear Laue spots and sharp XRD Bragg reflections suggest the high quality of the single crystal. In Mn4Ta2O9 single crystal, an antiferromagnetic phase transition was observed below Néel temperature 102 K along c axis, which is similar to the isostructural compound Mn4Nb2O9, but differs from the isostructural Co4Nb2O9. Relative dielectric constant at 30 kOe suggests that no magnetoelectric coupling exists in Mn4Ta2O9.

α″ Martensite and Amorphous Phase Transformation Mechanism in TiNbTaZr Alloy Incorporated with TiO2 Particles During Friction Stir Processing

NASA Astrophysics Data System (ADS)

Ran, Ruoshi; Liu, Yiwei; Wang, Liqiang; Lu, Eryi; Xie, Lechun; Lu, Weijie; Wang, Kuaishe; Zhang, Lai-Chang

2018-03-01

This work studied the formation of the α″ martensite and amorphous phases of TiNbTaZr alloy incorporated with TiO2 particles during friction stir processing. Formation of the amorphous phase in the top surface mainly results from the dissolution of oxygen, rearrangement of the lattice structure, and dislocations. High-stress stemming caused by dislocations and high-stress concentrations at crystal-amorphous interfaces promote the formation of α″ martensite. Meanwhile, an α″ martensitic transformation is hindered by oxygen diffusion from TiO2 to the matrix, thereby increasing resistance to shear.

α″ Martensite and Amorphous Phase Transformation Mechanism in TiNbTaZr Alloy Incorporated with TiO2 Particles During Friction Stir Processing

NASA Astrophysics Data System (ADS)

Ran, Ruoshi; Liu, Yiwei; Wang, Liqiang; Lu, Eryi; Xie, Lechun; Lu, Weijie; Wang, Kuaishe; Zhang, Lai-Chang

2018-06-01

This work studied the formation of the α″ martensite and amorphous phases of TiNbTaZr alloy incorporated with TiO2 particles during friction stir processing. Formation of the amorphous phase in the top surface mainly results from the dissolution of oxygen, rearrangement of the lattice structure, and dislocations. High-stress stemming caused by dislocations and high-stress concentrations at crystal-amorphous interfaces promote the formation of α″ martensite. Meanwhile, an α″ martensitic transformation is hindered by oxygen diffusion from TiO2 to the matrix, thereby increasing resistance to shear.

Determination of Activities of Niobium in Cu-Nb Melts Containing Dilute Nb

NASA Astrophysics Data System (ADS)

Wang, Daya; Yan, Baijun; Sichen, Du

2015-04-01

The activity coefficients of niobium in Cu-Nb melts were measured by equilibrating solid NbO2 with liquid copper under controlled oxygen potentials in the temperature range of 1773 K to 1898 K (1500 °C to 1625 °C). Either CO-CO2 gas mixture or H2-CO2 gas mixture was employed to obtain the desired oxygen partial pressures. Cu-Nb system was found to follow Henry's law in the composition range studied. The temperature dependence of Henry's constant in the Cu-Nb melts could be expressed as follows: The partial molar excess Gibbs energy change of niobium in Cu-Nb melts can be expressed as follows:

Hydrogen absorption properties of amorphous (Ni 0.6Nb 0.4-yTa y ) 100-x Zr x membranes

DOE PAGES

Palumbo, O.; Trequattrini, F.; Pal, N.; ...

2017-02-01

Ni based amorphous materials have great potential as hydrogen purification membranes. In the present work the melt spun (Ni 0.6Nb 0.4-yTa y) 100-xZr x with y=0, 0.1 and x=20, 30 was studied. Our result of X-ray diffraction spectra of the ribbons showed an amorphous nature of the alloys. Heating these ribbons below T < 400 °C, even in a hydrogen atmosphere (1-10 bar), the amorphous structure was retained. Furthermore, the crystallization process was characterized by differential thermal analysis and the activation energy of such process was obtained. The hydrogen absorption properties of the samples in their amorphous state were studiedmore » by the volumetric method, and the results showed that the addition of Ta did not significantly influence the absorption properties, a clear change of the hydrogen solubility was observed with the variation of the Zr content. The values of the hydrogenation enthalpy changed from ~37 kJ/mol for x=30 to ~9 kJ/mol for x=20. Our analysis of the volumetric data provides the indications about the hydrogen occupation sites during hydrogenation, suggesting that at the beginning of the absorption process the deepest energy levels are occupied, while only shallower energy levels are available at higher hydrogen content, with the available interstitial sites forming a continuum of energy levels.« less

Hydrogen absorption properties of amorphous (Ni 0.6Nb 0.4-yTa y ) 100-x Zr x membranes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palumbo, O.; Trequattrini, F.; Pal, N.

Ni based amorphous materials have great potential as hydrogen purification membranes. In the present work the melt spun (Ni 0.6Nb 0.4-yTa y) 100-xZr x with y=0, 0.1 and x=20, 30 was studied. Our result of X-ray diffraction spectra of the ribbons showed an amorphous nature of the alloys. Heating these ribbons below T < 400 °C, even in a hydrogen atmosphere (1-10 bar), the amorphous structure was retained. Furthermore, the crystallization process was characterized by differential thermal analysis and the activation energy of such process was obtained. The hydrogen absorption properties of the samples in their amorphous state were studiedmore » by the volumetric method, and the results showed that the addition of Ta did not significantly influence the absorption properties, a clear change of the hydrogen solubility was observed with the variation of the Zr content. The values of the hydrogenation enthalpy changed from ~37 kJ/mol for x=30 to ~9 kJ/mol for x=20. Our analysis of the volumetric data provides the indications about the hydrogen occupation sites during hydrogenation, suggesting that at the beginning of the absorption process the deepest energy levels are occupied, while only shallower energy levels are available at higher hydrogen content, with the available interstitial sites forming a continuum of energy levels.« less

PROCESSING OF HIGH-PERFORMANCE Nb{sub 3}Sn WIRES THROUGH A NEW DIFFUSION REACTION USING Sn BASED ALLOYS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tachikawa, K.; Sasaki, H.; Yamaguchi, M.

Tightly consolidated Sn-Ta and Sn-B based alloys have been prepared by the reaction among constituent metal powders at 750-775 deg. C. Sn-Ta and Sn-B based alloys exhibit quite similar microstructures. A small amount of Ti addition seems to improve the bonding between Ta or B particles and Sn matrix. Nb{sub 3}Sn wires have been fabricated by the Jelly Roll (JR) and Multi-rod (MR) process using Sn based alloy sheet and rod, respectively. Thick Nb{sub 3}Sn layers with nearly stoichiometric A15 composition are synthesized through a new diffusion mechanism between Nb and Sn based alloy. B{sub c2}(4.2 K)'s of 26.9 Tmore » (mid) and 26.5 T (mid) have been obtained in the JR and MR processed wires, respectively, using Sn-Ta based alloy. These wires exhibit enough non-Cu J{sub c} to be used above 20 T and 4.2 K. T{sub c} of JR wires using Sn-B based sheet is 18.14 K (offset) which is slightly higher than that of wires using Sn-Ta based sheet.« less

Orbital selectivity causing anisotropy and particle-hole asymmetry in the charge density wave gap of 2 H - TaS 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, J.; Wijayaratne, K.; Butler, A.

We report an in-depth angle-resolved photoemission spectroscopy study on 2H-TaS2, a canonical incommensurate charge density wave (CDW) system. This study demonstrates that just as in related incommensurate CDW systems, 2H-TaSe2 and 2H-NbSe2, the energy gap (triangle(CDW)) of 2H-TaS2 is localized along the K-centered Fermi surface barrels and is particle-hole asymmetric. The persistence of triangle(CDW) even at temperatures higher than the CDW transition temperature T-CDW in 2H-TaS2, reflects the similar pseudogap behavior observed previously in 2H-TaSe2 and 2H-NbSe2. However, in sharp contrast to 2H-NbSe2, where triangle(CDW) is nonzero only in the vicinity of a few "hot spots" on the innerK-centered Fermimore » surface barrels, triangle(CDW) in 2H-TaS2 is nonzero along the entirety of both K-centered Fermi surface barrels. Based on a tight-binding model, we attribute this dichotomy in the momentum dependence and the Fermi surface specificity of triangle(CDW) between otherwise similar CDW compounds to the different orbital orientations of their electronic states that participate in the CDW pairing. Our results suggest that the orbital selectivity plays a critical role in the description of incommensurate CDW materials.« less

Orbital selectivity causing anisotropy and particle-hole asymmetry in the charge density wave gap of 2 H -TaS2

NASA Astrophysics Data System (ADS)

Zhao, J.; Wijayaratne, K.; Butler, A.; Yang, J.; Malliakas, C. D.; Chung, D. Y.; Louca, D.; Kanatzidis, M. G.; van Wezel, J.; Chatterjee, U.

2017-09-01

We report an in-depth angle-resolved photoemission spectroscopy study on 2 H -TaS2 , a canonical incommensurate charge density wave (CDW) system. This study demonstrates that just as in related incommensurate CDW systems, 2 H -TaSe2 and 2 H -NbSe2 , the energy gap (ΔCDW) of 2 H -TaS2 is localized along the K -centered Fermi surface barrels and is particle-hole asymmetric. The persistence of ΔCDW even at temperatures higher than the CDW transition temperature TCDW in 2 H -TaS2 , reflects the similar pseudogap behavior observed previously in 2 H -TaSe2 and 2 H -NbSe2 . However, in sharp contrast to 2 H -NbSe2 , where ΔCDW is nonzero only in the vicinity of a few "hot spots" on the inner K -centered Fermi surface barrels, ΔCDW in 2 H -TaS2 is nonzero along the entirety of both K -centered Fermi surface barrels. Based on a tight-binding model, we attribute this dichotomy in the momentum dependence and the Fermi surface specificity of ΔCDW between otherwise similar CDW compounds to the different orbital orientations of their electronic states that participate in the CDW pairing. Our results suggest that the orbital selectivity plays a critical role in the description of incommensurate CDW materials.

A concise guide for the determination of less-studied technology-critical elements (Nb, Ta, Ga, In, Ge, Te) by inductively coupled plasma mass spectrometry in environmental samples

NASA Astrophysics Data System (ADS)

Filella, Montserrat; Rodushkin, Ilia

2018-03-01

There is an increasing demand for analytical techniques able to measure so-called 'technology-critical elements', a set of chemical elements increasingly used in technological applications, in environmental matrices. Nowadays, inductively coupled plasma-mass spectrometry (ICP-MS) has become the technique of choice for measuring trace element concentrations. However, its application is often less straightforward than often assumed. The hints and drawbacks of ICP-MS application to the measurement of a set of less-studied technology-critical elements (Nb, Ta, Ga, In, Ge and Te) is discussed here and concise guidelines given.

Solid Oxide Membrane (SOM) Process for Facile Electrosynthesis of Metal Carbides and Composites

NASA Astrophysics Data System (ADS)

Zou, Xingli; Chen, Chaoyi; Lu, Xionggang; Li, Shangshu; Xu, Qian; Zhou, Zhongfu; Ding, Weizhong

2017-02-01

Metal carbides (MCs) and composites including TiC, SiC, TaC, ZrC, NbC, Ti5Si3/TiC, and Nb/Nb5Si3 have been directly electrosynthesized from their stoichiometric metal oxides/carbon (MOs/C) mixture precursors by an innovative solid oxide membrane (SOM)-assisted electrochemical process. MOs/C mixture powders including TiO2/C, SiO2/C, Ta2O5/C, ZrO2/C, Nb2O5/C, TiO2/SiO2/C, Nb2O5/SiO2 were pressed to form porous pellets and then served as cathode precursors. A SOM-based anode, made from yttria-stabilized zirconia (YSZ)-based membrane, was used to control the electroreduction process. The SOM electrochemical process was performed at 1273 K (1000 °C) and 3.5 to 4.0 V in molten CaCl2. The oxygen component contained in the MOs/C precursors was gradually removed during electroreduction process, and thus, MOs/C can be directly converted into MCs and composites at the cathode. The reaction mechanism of the electroreduction process and the characteristics of the obtained MCs and composites products were systematically investigated. The results show that the electrosynthesis process typically involves compounding, electroreduction, dissolution-electrodeposition, and in situ carbonization processes. The products can be predesigned and controlled to form micro/nanostructured MCs and composites. Multicomponent multilayer composites (MMCs) have also been tried to electrosynthesize in this work. It is suggested that the SOM-assisted electroreduction process has great potential to be used for the facile and green synthesis of various MCs and composites.

Magnetic Studies on Eu3MO7 (M = Nb, Ta, Ir) with Fluorite-related Structure by 151Eu Mössbauer Spectroscopy and Magnetic Susceptibility Measurements

NASA Astrophysics Data System (ADS)

Hinatsu, Yukio; Doi, Yoshihiro; Wakeshima, Makoto

2018-06-01

Magnetic properties of europium-containing compounds Eu3MO7 (M = Nb, Ta, Ir) with fluorite-related structure have been investigated. Magnetic susceptibility measurements show that all these compounds are paramagnetic and have no magnetic ordering down to 1.8 K. At very low temperatures (T<50 K), the susceptibilities of each compound attain constant values, which is characteristic of the ground state for Eu3+ ions. The results of 151Eu Mössbauer spectroscopic measurements show that the asymmetric parameter for Eu(2) in seven-coordination is much larger than that for Eu(1) in cubic environment, which in accordance with the crystallographic result.

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

PubMed

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

2011-10-01

In this work, a multi-elementary Ti-10Zr-5Nb-5Ta alloy, with non-toxic alloying elements, was used to develop an accumulative roll bonding, ARB-type procedure in order to improve its structural and mechanical properties. The alloy was obtained by cold crucible semi-levitation melting technique and then was ARB deformed following a special route. After three ARB cycles, the total deformation degree per layer is about 86%; the calculated medium layer thickness is about 13 μm. The ARB processed alloy has a low Young's modulus of 46 GPa, a value very close to the value of the natural cortical bone (about 20 GPa). Data concerning ultimate tensile strength obtained for ARB processed alloy is rather high, suitable to be used as a material for bone substitute. Hardness of the ARB processed alloy is higher than that of the as-cast alloy, ensuring a better behaviour as a implant material. The tensile curve for the as-cast alloy shows an elastoplastic behaviour with a quite linear elastic behaviour and the tensile curve for the ARB processed alloy is quite similar with a strain-hardening elastoplastic body. Corrosion behaviour of the studied alloy revealed the improvement of the main electrochemical parameters, as a result of the positive influence of ARB processing. Lower corrosion and ion release rates for the ARB processed alloy than for the as-cast alloy, due to the favourable effect of ARB thermo-mechanical processing were obtained. Copyright © 2011 Elsevier Ltd. All rights reserved.

Phase Evolution in and Creep Properties of Nb-Rich Nb-Si-Cr Eutectics

NASA Astrophysics Data System (ADS)

Gang, Florian; Kauffmann, Alexander; Heilmaier, Martin

2018-03-01

In this work, the Nb-rich ternary eutectic in the Nb-Si-Cr system has been experimentally determined to be Nb-10.9Si-28.4Cr (in at. pct). The eutectic is composed of three main phases: Nb solid solution (Nbss), β-Cr2Nb, and Nb9(Si,Cr)5. The ternary eutectic microstructure remains stable for several hundred hours at a temperature up to 1473 K (1200 °C). At 1573 K (1300 °C) and above, the silicide phase Nb9(Si,Cr)5 decomposes into α-Nb5Si3, Nbss, and β-Cr2Nb. Under creep conditions at 1473 K (1200 °C), the alloy deforms by dislocation creep while the major creep resistance is provided by the silicide matrix. If the silicide phase is fragmented and, thus, its matrix character is destroyed by prior heat treatment [ e.g., at 1773 K (1500 °C) for 100 hours], creep is mainly controlled by the Laves phase β-Cr2Nb, resulting in increased minimum strain rates. Compared to state of the art Ni-based superalloys, the creep resistance of this three-phase eutectic alloy is significantly higher.

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.

Fabrication of (K0.5Na0.5)(Nb0.7Ta0.3)O3 thick films by electrophoretic deposition

NASA Astrophysics Data System (ADS)

Vineetha, P.; Saravanan, K. Venkata

2018-05-01

(K0.5Na0.5)(Nb0.7Ta0.3)O3 (KNNT) thick films were prepared by electrophoretic deposition method on copper plates (substrates). Prior to the deposition, stable suspensions of KNNT powder were prepared in isopropyl alcohol medium with and without adding triethanolamine (TEA) as dispersant. The optical transmittance spectra with time for both the suspensions were recorded and compared. Suspensions with dispersant has shown low transmittance, which indicate that the particles were dispersed very well in isopropyl alcohol. Fourier Transform Infrared (FTIR) spectroscopy was used to analyze the adsorption of TEA on KNNT particles. Suspension with dispersant was used for electrophoretic deposition. The depositions were carried out at various d.c voltages, keeping the deposition duration and inter electrode distance constant. X-Ray diffraction was used for the phase analysis of the films.

Development of Novel Garnet-Type Solid Electrolytes for Potential Application in Lithium Ion Batteries

NASA Astrophysics Data System (ADS)

Narayanan, Sumaletha

The development of promising solid electrolytes having a garnet-like structure has been successfully achieved through solid state (ceramic) method. Various approaches to improve the Li ion conductivity were employed. The first approach involved creating oxide ion vacancies into the crystal structure of parent garnet-like oxide, Li5La3Nb2O 12 to create a novel family of compounds with nominal composition, Li 5La3Nb2-xYxO12-δ (0 ≤ x ≤ 1). The second approach was Li stuffing into the garnet-like oxides to develop a series of Li stuffed novel Li5+2xLa3Nb 2-xYxO12 (0.05 ≤ x ≤ 0.75) and Li6.5 La2.5Ba0.5ZrTaO12. Powder X-ray diffraction (PXRD), thermo gravimetric analysis (TGA), scanning electron microscopy (SEM), electron probe microanalysis (EPMA) coupled with a wavelength-dispersive spectrometer (WDS), 7Li nuclear magnetic resonance (Li-NMR), and AC impedance spectroscopy were employed to characterize the structure, morphology, elemental composition, Li ion sites, and Li ion conductivity. Studies have shown that Li5+2xLa 3Nb2-xYxO12 have turned out to be promising solid electrolytes with high Li ion conductivity (10-4 Scm -1 at ambient temperatures). In addition, all families of garnets are found to be chemically stable with Li cathode materials (Li2MMn 3O8, where M = Fe, Co) up to 400 °C in air. The developed electrolyte materials have the potential to be used in all-solid-state Li ion batteries.

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

PubMed

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

2014-04-16

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

Intercalation of the layered solid acid HCa/sub 2/Nb/sub 3/O/sub 10/ by organic amines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jacobson, A.J.; Johnson, J.W.; Lewandowski, J.T.

1987-01-01

Layered compounds of formula C/sub n/H/sub 2n+1/NH/sub 3/Ca/sub 2/Nb/sub 3/O/sub 10/ are formed by reaction of n-alkylamines with the solid acid HCa/sub 2/Nb/sub 3/O/sub 10/. Other organic bases such as pyridine can also be intercalated. The lattice constants of the new compounds have been determined by powder X-ray diffraction. The unit cells are tetragonal with a axes that are unchanged with variation of the intercalated amine. The c axes lengths (layer spacings) vary systematically with the hydrocarbon chain length of the alkylamine.

Dy3TaO7, A stoichiometric spin glass and the effect of disorder via chemical substitution in the Dy3-xYxTaO7 (0 ≤ x ≤ 3) solid solution

NASA Astrophysics Data System (ADS)

Gómez-García, J. Francisco; Bucio, Lauro; Tavizon, Gustavo

2018-01-01

In this work, we present both structural and magnetic (DC magnetization and AC susceptibility) studies of the Dy3-xYxTaO7 solid solution. The structural characterization of samples was performed by Rietveld refinements of the X-ray diffraction data. All compounds crystallized in a weberite-related structure in the orthorhombic C2221 space group (No. 20); the variations of the lattice parameters obey the Vegard´s law in the whole range of composition. DC magnetic measurements of the Dy3-xYxTaO7 system showed a Curie-Weiss paramagnetic behaviour, with antiferromagnetic interactions at T>150 K. Below 3 K a spin glass behaviour in the 0 ≤ x ≤ 1 range of the solid solution was observed. The stoichiometric Dy3TaO7 compound showed spin glass behaviour although there is no evidence of structural disorder. For some Y3+ doped compounds (x = 0.33, 0.66 and 1.0), chemical disorder reduced the freezing temperature (Tg) values with a ×1/3 dependence. Cole-Cole analysis of the AC magnetic field response showed similar phenomenological parameters for the stoichiometric (x = 0) and the Y3+ doped compounds with spin glassiness, suggesting an analogous mechanism for these compounds. For the Dy3-xYxTaO7 system, in which the spin glass behaviour seems to exhibit a critical concentration, a magnetic phase diagram is proposed.

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.

Leakage current behavior in lead-free ferroelectric (K,Na)NbO3-LiTaO3-LiSbO3 thin films

NASA Astrophysics Data System (ADS)

Abazari, M.; Safari, A.

2010-12-01

Conduction mechanisms in epitaxial (001)-oriented pure and 1 mol % Mn-doped (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.1,Sb0.06)O3 (KNN-LT-LS) thin films on SrTiO3 substrate were investigated. Temperature dependence of leakage current density was measured as a function of applied electric field in the range of 200-380 K. It was shown that the different transport mechanisms dominate in pure and Mn-doped thin films. In pure (KNN-LT-LS) thin films, Poole-Frenkel emission was found to be responsible for the leakage, while Schottky emission was the dominant mechanism in Mn-doped thin films at higher electric fields. This is a remarkable yet clear indication of effect of 1 mol % Mn on the resistive behavior of such thin films.

Corrosion resistance of new beta type titanium alloy, Ti-29Nb-13Ta-4.6Zr in artificial saliva solution

NASA Astrophysics Data System (ADS)

Gunawarman; Giatmana, D. D.; Ilhamdi; Affi, J.; Fonna, S.; Niinomi, M.; Nakai, M.

2018-05-01

The corrosion resistance of Ti-29Nb-13Ta-4.6Zr (TNTZ) and Ti-6Al-4V alloys in oral cavity environment were studied by investigating its corrosion rate in artificial saliva solution. Corrosion measurement was conducted in 600 ml solution of Fusayama-Meyer artificial saliva containing 0.4g NaCl, 0.4g KCl, 0.795g CaCl2.2H2O, 0.69g NaH2PO4, and 1 g urea using a potentiostat controlled by a personal computer. The solution was maintained at pH 5.2 and controlled the temperature of 37°C to imitate oral cavity condition. After corrosion test, specimen surfaces were examined by SEM and EDX. The results show that the average corrosion rate of TNTZ and Ti-6Al-4V is 4,5×10-9 mmy-1 and 6,4×10-8 mmy-1, respectively, indicating that the corrosion resistance of TNTZ is slightly better than Ti-6Al-4V. This is suggested mainly due to the formation of multiple layers of Ti, Nb and Zr oxides in the surface of TNTZ. However, the formation of micro-pitting corrosion is more severe in TNTZ as compared to that of Ti-6Al-4V. The intense pitting corrosion in TNTZ is found strongly corresponded to its high impurities content and wide elemental segregation. It is recommended, therefore, a longer homogenizing process is required in TNTZ for reducing pitting corrosion attack. However, the details of corrosion mechanism are needed to be explored further.

Microstructure, Tensile and Creep Properties of Ta20Nb20Hf20Zr20Ti20 High Entropy Alloy

PubMed Central

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

2017-01-01

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

Fe4Nb2O9 : A magnetoelectric antiferromagnet

NASA Astrophysics Data System (ADS)

Maignan, Antoine; Martin, Christine

2018-04-01

The structural, magnetic, and electrical properties of a Fe4Nb2O9 polycrystalline sample have been characterized. It is found that this compound crystallizes in the P 3 ¯c 1 space group of the α -A l2O3 structure and is thus isostructural to Co4Nb2O9 and Mn4Nb2O9 , two linear magnetoelectric oxides. But in marked contrast, its ɛ'(T ) curve reveals two broad transitions at TN 1≅90 K and TN 2≅77 K , the former corresponding to the antiferromagnetic ordering temperature. Below TN 1, the M(H ) magnetization curves reveal the existence of spin flop at about 6 T. In this temperature region, a H-induced electric polarization for μ0H >6 T is evidenced by both sets of Ip(T) H and P (H) T curves. All these results point towards Fe4Nb2O9 being a magnetoelectric member of the A4B2O9 family (A =Mn , Fe, Co and B =Nb , Ta).

Impact of Nb vacancies and p-type doping of the NbCoSn-NbCoSb half-Heusler thermoelectrics.

PubMed

Ferluccio, Daniella A; Smith, Ronald I; Buckman, Jim; Bos, Jan-Willem G

2018-02-07

The half-Heuslers NbCoSn and NbCoSb have promising thermoelectric properties. Here, an investigation of the NbCo 1+y Sn 1-z Sb z (y = 0, 0.05; 0 ≤ z ≤ 1) solid-solution is presented. In addition, the p-type doping of NbCoSn using Ti and Zr substitution is investigated. Rietveld analysis reveals the gradual creation of Nb vacancies to compensate for the n-type doping caused by the substitution of Sb in NbCoSn. This leads to a similar valence electron count (∼18.25) for the NbCo 1+y Sn 1-z Sb z samples (z > 0). Mass fluctuation disorder due to the Nb vacancies strongly decreases the lattice thermal conductivity from 10 W m -1 K -1 (z = 0) to 4.5 W m -1 K -1 (z = 0.5, 1). This is accompanied by a transition to degenerate semiconducting behaviour leading to large power factors, S 2 /ρ = 2.5-3 mW m -1 K -2 and figures of merit, ZT = 0.25-0.33 at 773 K. Ti and Zr can be used to achieve positive Seebeck values, e.g. S = +150 μV K -1 for 20% Zr at 773 K. However, the electrical resistivity, ρ 323K = 27-35 mΩ cm, remains too large for these materials to be considered useful p-type materials.

Mechanisms of Texture Development in Lead-Free Piezoelectric Ceramics with Perovskite Structure Made by the Templated Grain Growth Process

PubMed Central

Kimura, Toshio; Yi, Yuan; Sakurai, Fumito

2010-01-01

The mechanisms of texture development were examined for BaTiO3 and a (K,Na,Li)(Nb,Ta)O3 solid solution made by the templated grain growth method, and compared with the mechanism in Bi0.5(Na,K)0.5TiO3. The dominant mechanism was different in each material; grain boundary migration in BaTiO3, solid state spreading in Bi0.5(Na,K)0.5TiO3, and abnormal grain growth in the (K,Na,Li)(Nb,Ta)O3 solid solution. The factor determining the dominant mechanism is the degree of smoothness of surface structure at an atomic level. PMID:28883364

Pressure-induced Lifshitz transition in NbP: Raman, x-ray diffraction, electrical transport, and density functional theory

NASA Astrophysics Data System (ADS)

Gupta, Satyendra Nath; Singh, Anjali; Pal, Koushik; Muthu, D. V. S.; Shekhar, C.; Qi, Yanpeng; Naumov, Pavel G.; Medvedev, Sergey A.; Felser, C.; Waghmare, U. V.; Sood, A. K.

2018-02-01

We report high-pressure Raman, synchrotron x-ray diffraction, and electrical transport studies on Weyl semimetals NbP and TaP along with first-principles density functional theoretical (DFT) analysis. The frequencies of first-order Raman modes of NbP harden with increasing pressure and exhibit a slope change at Pc˜9 GPa. The pressure-dependent resistivity exhibits a minimum at Pc. The temperature coefficient of resistivity below Pc is positive as expected for semimetals but changes significantly in the high-pressure phase. Using DFT calculations, we show that these anomalies are associated with a pressure-induced Lifshitz transition, which involves the appearance of electron and hole pockets in its electronic structure. In contrast, the results of Raman and synchrotron x-ray diffraction experiments on TaP and DFT calculations show that TaP is quite robust under pressure and does not undergo any phase transition.

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

NASA Astrophysics Data System (ADS)

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

2012-12-01

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

On the Alloying and Properties of Tetragonal Nb5Si3 in Nb-Silicide Based Alloys

PubMed Central

Tsakiropoulos, Panos

2018-01-01

The alloying of Nb5Si3 modifies its properties. Actual compositions of (Nb,TM)5X3 silicides in developmental alloys, where X = Al + B + Ge + Si + Sn and TM is a transition and/or refractory metal, were used to calculate the composition weighted differences in electronegativity (Δχ) and an average valence electron concentration (VEC) and the solubility range of X to study the alloying and properties of the silicide. The calculations gave 4.11 < VEC < 4.45, 0.103 < Δχ < 0.415 and 33.6 < X < 41.6 at.%. In the silicide in Nb-24Ti-18Si-5Al-5Cr alloys with single addition of 5 at.% B, Ge, Hf, Mo, Sn and Ta, the solubility range of X decreased compared with the unalloyed Nb5Si3 or exceeded 40.5 at.% when B was with Hf or Mo or Sn and the Δχ decreased with increasing X. The Ge concentration increased with increasing Ti and the Hf concentration increased and decreased with increasing Ti or Nb respectively. The B and Sn concentrations respectively decreased and increased with increasing Ti and also depended on other additions in the silicide. The concentration of Sn was related to VEC and the concentrations of B and Ge were related to Δχ. The alloying of Nb5Si3 was demonstrated in Δχ versus VEC maps. Effects of alloying on the coefficient of thermal expansion (CTE) anisotropy, Young’s modulus, hardness and creep data were discussed. Compared with the hardness of binary Nb5Si3 (1360 HV), the hardness increased in silicides with Ge and dropped below 1360 HV when Al, B and Sn were present without Ge. The Al effect on hardness depended on other elements substituting Si. Sn reduced the hardness. Ti or Hf reduced the hardness more than Cr in Nb5Si3 without Ge. The (Nb,Hf)5(Si,Al)3 had the lowest hardness. VEC differentiated the effects of additions on the hardness of Nb5Si3 alloyed with Ge. Deterioration of the creep of alloyed Nb5Si3 was accompanied by decrease of VEC and increase or decrease of Δχ depending on alloying addition(s). PMID:29300327

Superconductivity in the Nb-Ru-Ge σ phase

DOE PAGES

Carnicom, Elizabeth M.; Xie, Weiwei; Sobczak, Zuzanna; ...

2017-12-07

Here, we show that the previously unreported ternary σ-phase material Nb 20.4Ru 5.7Ge 3.9 (Nb 0.68Ru 0.19Ge 0.13) is a superconductor with a critical temperature of 2.2 K. Temperature-dependent magnetic susceptibility, resistance, and specific heat measurements were used to characterize the superconducting transition. The Sommerfeld constant γ for Nb 20.4Ru 5.7Ge 3.9 is 91 mJ mol-f.u. -1K -2 (~3 mJ mol-atom -1K -2) and the specific heat anomaly at the superconducting transition, ΔC/γT c, is approximately 1.38. The zero-temperature upper critical field (µ 0Hc 2(0)) was estimated to be 2 T by resistance data. Field-dependent magnetization data analysis estimated µmore » 0Hc 1(0) to be 5.5 mT. Thus, the characterization shows Nb 20.4Ru 5.7Ge 3.9 to be a type II BCS superconductor. This material appears to be the first reported ternary phase in the Nb-Ru-Ge system, and the fact that there are no previously reported binary Nb-Ru, Nb-Ge, or Ru-Ge σ-phases shows that all three elements are necessary to stabilize the material. An analogous σ-phase in the Ta-Ru-Ge system did not display superconductivity above 1.7 K, which suggests that electron count cannot govern the superconductivity observed. Preliminary characterization of a possible superconducting σ-phase in the Nb-Ru-Ga system is also reported.« less

Thermophysical Properties of Solid and Liquid Ti-6Al-4V (TA6V) Alloy

NASA Astrophysics Data System (ADS)

Boivineau, M.; Cagran, C.; Doytier, D.; Eyraud, V.; Nadal, M.-H.; Wilthan, B.; Pottlacher, G.

2006-03-01

Ti-6Al-4V (TA6V) titanium alloy is widely used in industrial applications such as aeronautic and aerospace due to its good mechanical properties at high temperatures. Experiments on two different resistive pulse heating devices (CEA Valduc and TU-Graz) have been carried out in order to study thermophysical properties (such as electrical resistivity, volume expansion, heat of fusion, heat capacity, normal spectral emissivity, thermal diffusivity, and thermal conductivity) of both solid and liquid Ti-6Al-4V. Fast time-resolved measurements of current, voltage, and surface radiation and shadowgraphs of the volume have been undertaken. At TU-Graz, a fast laser polarimeter has been used for determining the emissivity of liquid Ti-6Al-4V at 684.5 nm and a differential scanning calorimeter (DSC) for measuring the heat capacity of solid Ti-6Al-4V. This study deals with the specific behavior of the different solid phase transitions (effect of heating rate) and the melting region, and emphasizes the liquid state ( T > 2000 K).

Solid-state synthesis in the system Na 0.8Nb yW 1-yO 3 with 0⩽ y⩽0.4: A new phase, Na 0.5NbO 2.75, with perovskite-type structure

NASA Astrophysics Data System (ADS)

Debnath, Tapas; Rüscher, Claus H.; Gesing, Thorsten M.; Koepke, Jürgen; Hussain, Altaf

2008-04-01

Series of compounds in the system Na xNb yW 1-yO 3 were prepared according to the appropriate molar ratio of Na 2WO 4, WO 3, WO 2 and Nb 2O 5 with x=0.80 and 0.0⩽ y⩽0.4 at 600 °C in evacuated silica glass tubes. These compounds were investigated by X-ray powder diffraction, optical microscopy, microprobe analysis, Raman and optical microspectroscopy. A y-dependent separation into three distinct coloured crystallites with cubic perovskite-type structures is observed: (i) red-orange crystallites with composition Na xWO 3 with slightly decreasing x (i.e. 0.8-0.72) with increasing nominal y, (ii) bluish solid solution of composition Na xNb yW 1-yO 3 and (iii) white crystallites of a new phase having defect perovskite-type structure with composition Na 0.5NbO 2.75.

Phase relationships in the BaO-Ga2O3-Ta2O5 system and the structure of Ba6Ga21TaO40.

PubMed

Cao, Jiang; Yu, Xiaodi; Kuang, Xiaojun; Su, Qiang

2012-07-16

Phase relationships in the BaO-Ga(2)O(3)-Ta(2)O(5) ternary system at 1200 °C were determined. The A(6)B(10)O(30) tetragonal tungsten bronze (TTB) related solution in the BaO-Ta(2)O(5) subsystem dissolved up to ~11 mol % Ga(2)O(3), forming a ternary trapezoid-shaped TTB-related solid solution region defined by the BaTa(2)O(6), Ba(1.1)Ta(5)O(13.6), Ba(1.58)Ga(0.92)Ta(4.08)O(13.16), and Ba(6)GaTa(9)O(30) compositions in the BaO-Ga(2)O(3)-Ta(2)O(5) system. Two ternary phases Ba(6)Ga(21)TaO(40) and eight-layer twinned hexagonal perovskite solid solution Ba(8)Ga(4-x)Ta(4+0.6x)O(24) were confirmed in the BaO-Ga(2)O(3)-Ta(2)O(5) system. Ba(6)Ga(21)TaO(40) crystallized in a monoclinic cell of a = 15.9130(2) Å, b = 11.7309(1) Å, c = 5.13593(6) Å, β = 107.7893(9)°, and Z = 1 in space group C2/m. The structure of Ba(6)Ga(21)TaO(40) was solved by the charge flipping method, and it represents a three-dimensional (3D) mixed GaO(4) tetrahedral and GaO(6)/TaO(6) octahedral framework, forming mixed 1D 5/6-fold tunnels that accommodate the Ba cations along the c axis. The electrical property of Ba(6)Ga(21)TaO(40) was characterized by using ac impedance spectroscopy.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dirras, G., E-mail: dirras@univ-paris13.fr; Gubicza, J.; Heczel, A.

2015-10-15

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

Thermal stability and specular reflection behaviour of CoNbZr-based bottom spin valves with nano-oxide layer

NASA Astrophysics Data System (ADS)

Kim, Jong Soo; Lee, Seong-Rae

2004-06-01

The thermal stability and specularity aspects of a CoNbZr-based bottom spin valve (SV) employing a nano-oxide layer (NOL) were investigated. The magnetoresistance (MR) ratio of the as-deposited CoNbZr-based bottom SV increased by 62% (from 6.3 to 10.2%) with incorporation of the NOL. The enhancement of the MR ratio was considered to be due to the specular effect ( increased from 0.722 to 1.363 cm) of the NOL. The MR ratio of a Ta-based bottom SV decreased by about 45% (from 6.9 to 3.8%) when the samples were annealed at 300 °C for 240 min. By contrast, the MR ratio of the CoNbZr-based bottom SV with NOL increase d by 14 % (from 10.2 to 11.7%). The root mean square roughness value of the CoNbZr layer (0.07 nm) was superior to that of the Ta layer (0.43 nm). Although Mn in IrMn diffused out to the surface through the active layers resulting in the formation of Mn oxide at the surface in the CoNbZr-based bottom SV, no trace of Mn was found in the active layers and no significant degradation occurred.

Correlation between the structure and the piezoelectric properties of lead-free (K,Na,Li)(Nb,Ta,Sb)O3 ceramics studied by XRD and Raman spectroscopy.

PubMed

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

2011-09-01

This article reviews on the use of Raman spectroscopy for the study of (K,Na,Li)(Nb,Ta,Sb)O(3) lead-free piezoceramics. Currently, this material appears to be one of the most interesting and promising alternatives to the well-known PZT piezoelectric materials. In this work, we prepare piezoceramics with different stoichiometries and study their structural, ferroelectric, and piezoelectric properties. By using both Raman spectroscopy and X-ray diffraction, we establish a direct correlation between the structure and the properties. The results demonstrate that the wavenumber of the A(1g) vibration is proportional to the tetragonality, the remnant polarization, and the piezoelectric coefficients of these materials. Thus, Raman spectroscopy appears as a very useful technique for a fast evaluation of the crystalline structure and the ferroelectric/ piezoelectric properties.

Comparative study of the magnetic properties of La3Ni2B‧O9 for B‧ = Nb, Taor Sb

NASA Astrophysics Data System (ADS)

Chin, Chun-Mann; Battle, Peter D.; Blundell, Stephen J.; Hunter, Emily; Lang, Franz; Hendrickx, Mylène; Paria Sena, Robert; Hadermann, Joke

2018-02-01

Polycrystalline samples of La3Ni2NbO9 and La3Ni2TaO9 have been characterised by X-ray and neutron diffraction, electron microscopy, magnetometry and muon spin relaxation (μSR); the latter technique was also applied to La3Ni2SbO9. On the length scale of a neutron diffraction experiment, the six-coordinate sites of the monoclinic perovskite structure are occupied in a 1:1 ordered manner by Ni and a random ⅓Ni/⅔B‧ mixture. Electron microscopy demonstrated that this 1:1 ordering is maintained over microscopic distances, although diffuse scattering indicative of short-range ordering on the mixed site was observed. No magnetic Bragg scattering was observed in neutron diffraction patterns collected from La3Ni2B‧O9 (B‧ = Nb or Ta) at 5 K although in each case μSR identified the presence of static spins below 30 K. Magnetometry showed that La3Ni2NbO9 behaves as a spin glass below 29 K but significant short-range interactions are present in La3Ni2TaO9 below 85 K. The contrasting properties of these compounds are discussed in terms of their microstructure.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chezhina, N.V., E-mail: chezhina@nc2490.spb.edu; Zhuk, N.A.; Korolev, D.A.

2016-01-15

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

High-Temperature Thermoelectric Properties of (1 - x) SrTiO3 - ( x) La1/3NbO3 Ceramic Solid Solution

NASA Astrophysics Data System (ADS)

Srivastava, Deepanshu; Azough, F.; Molinari, M.; Parker, S. C.; Freer, R.

2015-06-01

Ceramics based on SrTiO3 are of growing interest as thermoelectric materials because of their high-temperature stability and non-toxicity. Substitution of La and Nb into the perovskite structure provides opportunities to control both the microstructure and properties. Ceramic solid solutions of (1 - x) SrTiO3 - ( x) La1/3NbO3 were prepared by the mixed oxide route, using compositional steps of x = 0.1. Pressed pellets were sintered at temperatures of 1573 K to 1723 K in air. Addition of aliovalent ions (La3+, Nb5+) on the A/B sites (Sr2+, Ti4+) led to A-Site cation deficiency in the stoichiometric compositions and other defect structures which increased carrier concentration. A maximum ZT of 0.004 was obtained for the x = 0.2 stoichiometric sample, although much higher ZT values are possible by sample reduction.

Fabrication of fine-grain tantalum diffusion barrier tube for Nb3Sn conductors

NASA Astrophysics Data System (ADS)

Hartwig, K. T.; Balachandran, S.; Mezyenski, R.; Seymour, N.; Robinson, J.; Barber, R. E.

2014-01-01

Diffusion barriers used in Nb3Sn wire are often fabricated by wrapping Ta sheet into a tube with an overlap seam. A common result of such practice is non-uniform deformation in the Ta sheet as it thins by wire drawing because of non-uniform grain size and texture in the original Ta sheet. Seamless Ta tube with a fine-grain and uniform microstructure would be much better for the diffusion barrier application, but such material is expensive and difficult to manufacture. This report presents results on a new fabrication strategy for Ta tube that shows promise for manufacture of less costly tube with an improved microstructure. The fabrication method begins with seam-welded tube but gives a fine-grain uniform microstructure with little difference between the longitudinal seam weld region and the parent metal after post-weld processing. Severe plastic deformation processing (SPD) applied by area reduction extrusion and tube equal channel angular extrusion (tECAE) are used to refine and homogenize the microstructure. Microstructure and mechanical property results are presented for Ta tubes fabricated by this new processing strategy.

High-throughput exploration of thermoelectric and mechanical properties of amorphous NbO2 with transition metal additions

NASA Astrophysics Data System (ADS)

Music, Denis; Geyer, Richard W.; Hans, Marcus

2016-07-01

To increase the thermoelectric efficiency and reduce the thermal fatigue upon cyclic heat loading, alloying of amorphous NbO2 with all 3d and 5d transition metals has systematically been investigated using density functional theory. It was found that Ta fulfills the key design criteria, namely, enhancement of the Seebeck coefficient and positive Cauchy pressure (ductility gauge). These quantum mechanical predictions were validated by assessing the thermoelectric and elastic properties on combinatorial thin films, which is a high-throughput approach. The maximum power factor is 2813 μW m-1 K-2 for the Ta/Nb ratio of 0.25, which is a hundredfold increment compared to pure NbO2 and exceeds many oxide thermoelectrics. Based on the elasticity measurements, the consistency between theory and experiment for the Cauchy pressure was attained within 2%. On the basis of the electronic structure analysis, these configurations can be perceived as metallic, which is consistent with low electrical resistivity and ductile behavior. Furthermore, a pronounced quantum confinement effect occurs, which is identified as the physical origin for the Seebeck coefficient enhancement.

Nb5+-Doped SrCoO3-δ Perovskites as Potential Cathodes for Solid-Oxide Fuel Cells.

PubMed

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

2016-07-15

SrCoO 3- δ outperforms as cathode material in solid-oxide fuel cells (SOFC) when the three-dimensional (3C-type) perovskite structure is stabilized by the inclusion of highly-charged transition-metal ions at the octahedral positions. In a previous work we studied the Nb incorporation at the Co positions in the SrCo 1- x Nb x O 3- δ system, in which the stabilization of a tetragonal P4 / mmm perovskite superstructure was described for the x = 0.05 composition. In the present study we extend this investigation to the x = 0.10-0.15 range, also observing the formation of the tetragonal P4 / mmm structure instead of the unwanted hexagonal phase corresponding to the 2H polytype. We also investigated the effect of Nb 5+ doping on the thermal, electrical, and electrochemical properties of SrCo 1- x Nb x O 3- δ ( x = 0.1 and 0.15) perovskite oxides performing as cathodes in SOFC. In comparison with the undoped hexagonal SrCoO 3- δ phase, the resulting compounds present high thermal stability and an increase of the electrical conductivity. The single-cell tests for these compositions ( x = 0.10 and 0.15) with La 0.8 Sr 0.2 Ga 0.83 Mg 0.17 O 3- δ (LSGM) as electrolyte and SrMo 0.8 Fe 0.2 CoO 3- δ as anode gave maximum power densities of 693 and 550 mW∙cm -2 at 850 °C respectively, using pure H₂ as fuel and air as oxidant.

Studies of high temperature ternary phases in mixed-metal-rich early transition metal sulfide and phosphide systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marking, Gregory Allen

1994-01-04

Investigations of ternary mixed early transition metal-rich sulfide and phosphide systems resulted in the discovery of new structures and new phases. A new series of Zr and Hf - group V transition metal - sulfur K-phases was synthesized and crystallographically characterized. When the group V transition metal was Nb or Ta, the unit cell volume was larger than any previously reported K-phase. The presence of adventitious oxygen was determined in two K-phases through a combination of neutron scattering and X-ray diffraction experiments. A compound Hf 10Ta 3S 3 was found to crystallize in a new-structure type similar to the knownmore » gamma brasses. This structure is unique in that it is the only reported "stuffed" gamma-brass type structure. The metal components, Hf and Ta, are larger in size and more electropositive than the metals found in normal gamma brasses (e.g. Cu and Zn) and because of the larger metallic radii, sulfur can be incorporated into the structure where it plays an integral role in stabilizing this phase relative to others. X-ray single-crystal, X-ray powder and neutron powder refinements were performed on this structure. A new structure was found in the ternary Nb-Zr-P system which has characteristics in common with many known early transition metal-rich sulfides, selenides, and phosphides. This structure has the simplest known interconnection of the basic building blocks known for this structural class. Anomalous scattering was a powerful tool for differentiating between Zr and Nb when using Mo Kα X-radiation. The compounds ZrNbP and HfNbP formed in the space group Prima with the simple Co 2Si structure which is among the most common structures found for crystalline solid materials. Solid solution compounds in the Ta-Nb-P, Ta-Zr-P, Nb-Zr-P, Hf-Nb-P, and Hf-Zr-S systems were crystallographically characterized. The structural information corroborated ideas about bonding in metal-rich compounds.« less

One-step internal-tin Nb/sub 3/Sn superconductor fabrication. Final report, June 1983-August 1984

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marancik, W.

1985-03-01

The object of this research is to demonstrate the feasibility of producing a Nb/sub 3/Sn superconductor in a single extrusion process with a large number of filaments with internal tin. The technique chosen uses .010'-diameter Nb and tin-plated Cu wires formed into a solenoid. The solenoid is covered with tin-plated copper foil and isostatically compacted to a pressure of 17,000 psi. The solenoid is slit along its length. This results in a ribbon about 40 inches long by about 5-inches wide, with the Nb wires running across the 5-inch-width. The ribbon is then rolled up (Jelly Roll) around a 0.5more » inch diameter Ta covered copper rod to produce a composite of about 1.5 inches in diameter by 5 inches long. The composite geometry is now a cylindrical bundle of 0.010-inch-diameter Nb wire separated from each other by tin-plated copper. Each Nb wire is aligned with the axis of cylinder. The cylinder is slid into a Ta-lined copper extrusion can which is evacuated and sealed. The can is extruded at a low temperature and drawn to final wire size without intermediate annealing. The advantage of the process is that it is an internal tin process with the tin uniformly distributed through the matrix. The Nb is in a relatively soft state having been fully annealed at 0.020-inch diameter. Only one extrusion is required since the bundling technique allows a large number of wires to be precisely aligned and spaced in the matrix.« less

Electrical and thermal properties of Cu-Ta films prepared by magnetron sputtering

NASA Astrophysics Data System (ADS)

Qin, Wen; Fu, Licai; Zhu, Jiajun; Yang, Wulin; Sang, Jianquan; Li, Deyi; Zhou, Lingping

2018-06-01

The microstructure, electrical resistivity and thermal conductivity of the sputtering deposited Cu-Ta films were investigated as a function of Ta content. The results showed that the amorphous phase formed between 20 at.% and 60 at.% Ta, and out of this range α-Cu(Ta) and β-Ta(Cu) solid solutions formed. Because the lattice distortion and β-Ta structure could significantly increase the probability of electron scattering, the electrical resistivity of the Cu-Ta films shows a 'N' type change with the increase of Ta content, and the inflection point appears at 50 at.% Ta and 60 at.% Ta respectively. As the thermal conductance is also dominated by electrons in metals films, an opposite variation tendency is found in the thermal conductivity of the Cu-Ta films. According to our knowledge, this is the first time to measure the thermal conductivity of Cu-Ta thin films.

{Nb288O768(OH)48(CO3)12}: A Macromolecular Polyoxometalate with Niobium Atoms Close to 300.

PubMed

Wu, Yan-Lan; Li, Xin-Xiong; Qi, Yan-Jie; Yu, Hao; Jin, Lu; Zheng, Shou-Tian

2018-05-29

A protein-sized (ca. 4.2 ᵡ 4.2 ᵡ 3.6 nm3) non-biologically derived molecule {Nb288O768(OH)48(CO3)12} (Nb288) containing up to 288 niobium atoms has been obtained, which is by far the largest and the highest nuclearity polyoxoniobate (PONb). Particularly, in terms of metal nuclearity number, Nb288 is the second largest cluster so far reported in classic polyoxometalate chemistry (V, Mo, W, Nb, and Ta). Nb288 can be described as a giant windmill-like cluster aggregate of six brand-new, nanoscale high-nuclearity PONb units {Nb47O128(OH)6(CO3)2} (Nb47) joined together by six additional Nb ions. Interestingly, the in situ generated 47-nuclearity Nb47 units can be isolated and bridged by copper complexes to form an inorganic-organic hybrid three-dimensional PONb framework, which exhibits effective catalytic activity for hydrolyzing nerve agent simulant of dimethyl methylphosphonate. The unique Nb47 cluster also provides a new type of topology to very limited family of Nb-O clusters. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Atomistic modeling of crystal-to-amorphous transition and associated kinetics in the Ni-Nb system by molecular dynamics simulations.

PubMed

Dai, X D; Li, J H; Liu, B X

2005-03-17

With the aid of ab initio calculations, an n-body potential of the Ni-Nb system is constructed under the Finnis-Sinclair formalism and the constructed potential is capable of not only reproducing some static physical properties but also revealing the atomistic mechanism of crystal-to-amorphous transition and associated kinetics. With application of the constructed potential, molecular dynamics simulations using the solid solution models reveal that the physical origin of crystal-to-amorphous transition is the crystalline lattice collapsing while the solute atoms are exceeding the critical solid solubilities, which are determined to be 19 atom % Ni and 13 atom % Nb for the Nb- and Ni-based solid solutions, respectively. It follows that an intrinsic glass-forming ability of the Ni-Nb system is within 19-87 atom % Ni, which matches well with that observed in ion beam mixing/solid-state reaction experiments. Simulations using the Nb/Ni/Nb (Ni/Nb/Ni) sandwich models indicate that the amorphous layer at the interfaces grows in a layer-by-layer mode and that, upon dissolving solute atoms, the Ni lattice approaches and exceeds its critical solid solubility faster than the Nb lattice, revealing an asymmetric behavior in growth kinetics. Moreover, an energy diagram is obtained by computing the energetic sequence of the Ni(x)Nb(100)(-)(x) alloy in fcc, bcc, and amorphous structures, respectively, over the entire composition range, and the diagram could serve as a guide for predicting the metastable alloy formation in the Ni-Nb system.

Effects of alkyl chain length and anion size on thermal and structural properties for 1-alkyl-3-methylimidazolium hexafluorocomplex salts (C(x)MImAF6, x = 14, 16 and 18; A = P, As, Sb, Nb and Ta).

PubMed

Xu, Fei; Matsumoto, Kazuhiko; Hagiwara, Rika

2012-03-28

A series of 1-alkyl-3-methylimidazolium hexafluorocomplex salts (C(x)MImAF(6), x = 14, 16 and 18, A = P, As, Sb, Nb and Ta) have been characterized by thermal analysis, X-ray diffraction and polarized optical microscopy. A liquid crystalline mesophase is observed for all the C(16)MIm and C(18)MIm salts. The C(14)MIm(+) cation gives a liquid crystalline mesophase only with PF(6)(-). The temperature range of the liquid crystalline mesophase increases with an increase in alkyl chain length or with decrease in anion size. Single-crystal X-ray diffraction revealed that all the C(18)MImAF(6) salts (A = P, As, Sb, Nb and Ta) are isostructural with each other in the crystalline phase and have a layered structure. The interdigitated alkyl chain of the cation has a bent shape like a spoon near the imidazolium ring in the crystalline phase at -100 °C and is tilted with respect to the sheets of the imidazolium headgroups and anions. An increase of temperature increases the ratio of an all-trans conformation to the bent conformation in the crystalline phase. X-ray diffraction and polarized optical microscopy suggested that the liquid crystalline mesophase has a smectic A(2) structure. The interlayer distance increases with a decrease in the anion size since the smaller anion has a stronger coulombic interaction with the imidazolium headgroup, resulting in the decrease of the interdigitated part to give a larger layer spacing.

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.

A new insight into high-strength Ti62Nb12.2Fe13.6Co6.4Al5.8 alloys with bimodal microstructure fabricated by semi-solid sintering

PubMed Central

Liu, L. H.; Yang, C.; Kang, L. M.; Qu, S. G.; Li, X. Q.; Zhang, W. W.; Chen, W. P.; Li, Y. Y.; Li, P. J.; Zhang, L. C.

2016-01-01

It is well known that semi-solid forming could only obtain coarse-grained microstructure in a few alloy systems with a low melting point, such as aluminum and magnesium alloys. This work presents that semi-solid forming could also produce novel bimodal microstructure composed of nanostructured matrix and micro-sized (CoFe)Ti2 twins in a titanium alloy, Ti62Nb12.2Fe13.6Co6.4Al5.8. The semi-solid sintering induced by eutectic transformation to form a bimodal microstructure in Ti62Nb12.2Fe13.6Co6.4Al5.8 alloy is a fundamentally different approach from other known methods. The fabricated alloy exhibits high yield strength of 1790 MPa and plastic strain of 15.5%. The novel idea provides a new insight into obtaining nano-grain or bimodal microstructure in alloy systems with high melting point by semi-solid forming and into fabricating high-performance metallic alloys in structural applications. PMID:27029858

Nb sbnd Th sbnd Zr mineralization in microgranite—microsyenite at Jabal Tawlah, Midyan region, Kingdom of Saudi Arabia

NASA Astrophysics Data System (ADS)

Drysdall, Alan R.; Douch, Colin J.

A composite sill of mineralized and highly radioactive microgranite—microsyenite caps Jabal Tawlah, a low ridge in the extreme NW of the Arabian Shield. The leucocratic composition, distribution of quartz and low K 2O:Na 2O ratios indicate that deuteric processes, including separation of a silica-rich phase and albitization, played a major role. Mineralization is in the form of a disseminated enrichment in Nb, Ta, Sn, Th, Y, heavy REE and Zr. Four Y- and heavy REE-bearing minerals, gagarinite [NaCaY(F,Cl) 6], fergusonite [(Y,Er,Ce,Fe)(Nb,Ta,Ti)O 4], xenotime and yttrian fluorite, as well as zircon, columbite, thorite, sphalerite, galena, pyrite, ilmenite, hematite, limonite, magnetite, goethite, siderite, possible chrysocolla and an MnO-bearing mineral have been identified. The geochemical signature of the mineralization is similar to that which distinguishes alkali granites from other granitic rocks. Jabal az Zuhd, a major plutonic complex consisting largely of alkali granite, crops out only 5 km NW of Jabal Tawlah. However, there is no other evidence of possible derivation from a parental alkali granite magma. Reserves indicated by outcrop dimensions and three drill-hole intersections are 6.4 million tonnes to an average depth of 65 m below wadi level, grading 0.34% Nb, 0.52% Y, 0.47% Zn and approximately 4% zircon (plus 175 ppm Ta, 380 ppm Sn, 700 ppm Th and heavy REE).

Preparation of core-shell Ti-Nb oxide nanocrystals

NASA Astrophysics Data System (ADS)

Simakov, David S. A.; Tsur, Yoed

2008-01-01

Nanosized powders of Ti-Nb oxide core-shell nanocrystals with atomic ratios of Nb/Ti = 0.11, 0.25, and 0.38 have been prepared by two preparation routes. The first route was co-precipitation, followed by␣annealing, using NbCl5 as a source of Nb. The second route was coating of pure TiO2 nanocrystals by Nb-isopropoxide in liquid medium, followed by impregnation of the Nb into the nanoparticles by annealing. Both methods yielded anatase nanocrystals with a Nb-rich shell and a core, which had much lower Nb loadings. The anatase structure solid solution (with Nb incorporated) was stable under annealing up to 760°C. The particle size remained within the nanometric scale ( <50 nm) under heat-treatment up to 760°C. It has been shown that the fabricated powders can be redispersed in aqueous media by simple ultrasound treatment, resulting in nanosized dispersions. Using a variety of analytical techniques, including depth profiling of single nanocrystallites by AES combined with sputtering by Ar ions, the mechanism of the core-shell structure creation was studied. It is proposed that the formation of the core-shell structure is governed by solubility limitations in the co-precipitation route and by solubility and diffusion limitations in the coating-incorporation route.

Nb(x)Ti(1-x)N Superconducting-Nanowire Single-Photon Detectors

NASA Technical Reports Server (NTRS)

Stern, Jeffrey A.; Farr, William H.; Leduc, Henry G.; Bumble, Bruce

2008-01-01

Superconducting-nanowire single-photon detectors (SNSPDs) in which Nb(x)Ti(1-x)N (where x<1) films serve as the superconducting materials have shown promise as superior alternatives to previously developed SNSPDs in which NbN films serve as the superconducting materials. SNSPDs have potential utility in optical communications and quantum cryptography. Nb(x)Ti(1-x)N is a solid solution of NbN and TiN, and has many properties similar to those of NbN. It has been found to be generally easier to stabilize Nb(x)Ti(1-x)N in the high-superconducting-transition temperature phase than it is to so stabilize NbN. In addition, the resistivity and penetration depth of polycrystalline films of Nb(x)Ti(1-x)N have been found to be much smaller than those of films of NbN. These differences have been hypothesized to be attributable to better coupling at grain boundaries within Nb(x)Ti(1-x)N films.

High-throughput exploration of thermoelectric and mechanical properties of amorphous NbO{sub 2} with transition metal additions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Music, Denis, E-mail: music@mch.rwth-aachen.de; Geyer, Richard W.; Hans, Marcus

2016-07-28

To increase the thermoelectric efficiency and reduce the thermal fatigue upon cyclic heat loading, alloying of amorphous NbO{sub 2} with all 3d and 5d transition metals has systematically been investigated using density functional theory. It was found that Ta fulfills the key design criteria, namely, enhancement of the Seebeck coefficient and positive Cauchy pressure (ductility gauge). These quantum mechanical predictions were validated by assessing the thermoelectric and elastic properties on combinatorial thin films, which is a high-throughput approach. The maximum power factor is 2813 μW m{sup −1} K{sup −2} for the Ta/Nb ratio of 0.25, which is a hundredfold increment compared to puremore » NbO{sub 2} and exceeds many oxide thermoelectrics. Based on the elasticity measurements, the consistency between theory and experiment for the Cauchy pressure was attained within 2%. On the basis of the electronic structure analysis, these configurations can be perceived as metallic, which is consistent with low electrical resistivity and ductile behavior. Furthermore, a pronounced quantum confinement effect occurs, which is identified as the physical origin for the Seebeck coefficient enhancement.« less

Preparation of Ferroelectric Thin Films of Bismuth Layer Structured Compounds

NASA Astrophysics Data System (ADS)

Watanabe, Hitoshi; Mihara, Takashi; Yoshimori, Hiroyuki; Araujo, Carlos

1995-09-01

Ferroelectric thin films of bismuth layer structured compounds, SrBi2Ta2O9, SrBi2Nb2O9, SrBi4Ti4O15 and their solid solutions, were formed onto a sputtered platinum layer on a silicon substrate using spin-on technique and metal-organic decomposition (MOD) method. X-ray diffraction (XRD) analysis and some electrical measurements were performed on the prepared thin films. XRD results of SrBi2(Ta1- x, Nb x)2O9 films (0≤x≤1) showed that niobium ions substitute for tantalum ions in an arbitrary ratio without any change of the layer structure and lattice constants. Furthermore, XRD results of SrBi2 xTa2O9 films (0≤x≤1.5) indicated that the formation of the bismuth layer structure does not always require an accurate bismuth content. The layer structure was formed above 50% of the stoichiometric bismuth content in the general formula. SrBi2(Ta1- x, Nb x)2O9 films with various Ta/Nb ratios have large enough remanent polarization for nonvolatile memory application and have shown high fatigue resistance against 1011 cycles of full switching of the remanent polarization. Mixture films of the three compounds were also investigated.

Nb(x)Ti(1-x)N Superconducting-Nanowire Single-Photon Detectors

NASA Technical Reports Server (NTRS)

Stem, Jeffrey A.; Farr, William H.; Leduc, Henry G.; Bumble, Bruce

2008-01-01

Superconducting-nanowire singlephoton detectors (SNSPDs) in which Nb(x)Ti(1-x)N (where x<1) films serve as the superconducting materials have shown promise as superior alternatives to previously developed SNSPDs in which NbN films serve as the superconducting materials. SNSPDs have potential utility in optical communications and quantum cryptography. Nb(x)Ti(1-x)N is a solid solution of NbN and TiN, and has many properties similar to those of NbN. It has been found to be generally easier to stabilize NbxTi1 xN in the high-superconducting-transitiontemperature phase than it is to so stabilize NbN. In addition, the resistivity and penetration depth of polycrystalline films of Nb(x)Ti(1-x)N have been found to be much smaller than those of films of NbN. These differences have been hypothesized to be attributable to better coupling at grain boundaries within Nb(x)Ti(1-x)N films.

The effect of microstructure on the deformation modes and mechanical properties of Ti-6Al-2Nb-1Ta-0.8Mo: Part II. Equiaxed structures

NASA Astrophysics Data System (ADS)

Lin, Fu-Shiong; Starke, E. A.; Gysler, A.

1984-10-01

The Ti-6Al-2Nb-lTa-0.8Mo alloy was processed to develop both near-basal and transverse textures. Samples were annealed at different temperatures to vary the equiaxed alpha grain size and the thick-ness of the grain boundary beta, and subsequently quenched in order to transform the beta phase to either martensite, tempered martensite, or Widmanstätten alpha + beta. The effect of microstructure and texture on tensile properties and on fracture toughness was investigated. In addition, yield locus diagrams were constructed in order to study the texture strengthening effect. The yield strength was found to be strongly dependent on the thickness and Burgers relationship of the transformed beta phase surrounding the alpha grains. A texture hardening effect as large as 60 pct was found for the basal-texture material but only 15 pct for the transverse texture material. These variations are asso-ciated with differences in deformation behavior.

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

PubMed Central

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

2016-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2016-02-01

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

Photoelectron Spectroscopy Study of [Ta2B6]-: a Hexagonal Bipyramdial Cluster

NASA Astrophysics Data System (ADS)

Jian, Tian; Li, Weili; Romanescu, Constantin; Wang, Lai-Sheng

2014-06-01

It has been a long-sought goal in cluster science to discover stable atomic clusters as building blocks for cluster-assembled nanomaterials, as exemplified by the fullerenes and their subsequent bulk syntheses.[1,2] Clusters have also been considered as models to understand bulk properties, providing a bridge between molecular and solid-state chemistry.[3] Herein we report a joint photoelectron spectroscopy and theoretical study on the [Ta2B6]- and [Ta2B6] clusters.[4] The photoelectron spectrum of [Ta2B6]- displays a simple spectral pattern and a large HOMO-LUMO gap, suggesting its high symmetry. Theoretical calculations show that both the neutral and anion are D6h pyramidal. The chemical bonding analyses for [Ta2B6] revealed the nature of the B6 and Ta interactions and uncovered strong covalent bonding between B6 and Ta. The D6h-[TaB6Ta] gaseous cluster is reminiscent of the structural pattern in the ReB6X6Re core in the [(Cp*Re)2B6H4Cl2] and the TiB6Ti motif in the newly synthesized Ti7Rh4Ir2B8 solid-state compound.[5,6] The current work provides an intrinsic link between a gaseous cluster and motifs for solid materials. Continued investigations of the transition-metal boron clusters may lead to the discovery of new structural motifs involving pure boron clusters for the design of novel boride materials. Reference [1] H.W. Kroto, J. R. Heath, S. C. OBrien, R. F. Curl, R. E. Smalley, Nature 1985, 318, 162 - 163. [2] W. Krtschmer, L. D. Lamb, K. Fostiropoulos, D. R. Huffman, Nature 1990, 347, 354 - 358. [3] T. P. Fehlner, J.-F. Halet, J.-Y. Saillard, Molecular Clusters: A Bridge to Solid-State Chemitry, Cambridge University Press, UK, 2007. [4] W. L. Li, L. Xie, T. Jian, C. Romanescu, X. Huang, L.-S. Wang, Angew. Chem. Int. Ed. 2014, 126, 1312 - 1316. [5] B. Le Guennic, H. Jiao, S. Kahlal, J.-Y. Saillard, J.-F. Halet, S. Ghosh, M. Shang, A. M. Beatty, A. L. Rheingold, T. P. Fehlner, J. Am. Chem. Soc. 2004, 126, 3203 - 3217. [6] B. P. T. Fokwa, M. Hermus, Angew

Synthesis, crystal structure and ionic conductivity of the Ba3Mo1-xWxNbO8.5 solid solution

NASA Astrophysics Data System (ADS)

Bernasconi, Andrea; Tealdi, Cristina; Mühlbauer, Martin; Malavasi, Lorenzo

2018-02-01

Ba3MoNbO8.5 compound has been recently discovered as novel oxide ionic conductor with a structure that is a hybrid between 9R hexagonal perovskite and palmierite. In this work, the full substitution of Mo with W has been demonstrated as possible, without altering significantly the conductivity of the material. The crystal structure of the Ba3Mo1-xWxNbO8.5 solid solution (with x equals 0, 0.25, 0.5, 0.75 and 1) has been investigated by X-ray powder diffraction, showing a reduction of the unit cell by increasing the molybdenum content, despite the larger size of tungsten compared to molybdenum. Neutron powder diffraction measurements have been performed, indicating different levels of contribution of 9R polytype and of palmierite to the hybrid structure of the material as a function of the W-content.

Structure and physical properties of EuTa{sub 2}O{sub 6} tungsten bronze polymorph

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kolodiazhnyi, T., E-mail: kolodiazhnyi.taras@nims.go.jp; Sakurai, H.; Vasylkiv, O.

A tetragonal tungsten bronze (TTB) polymorph of EuTa{sub 2}O{sub 6} was prepared and analyzed. EuTa{sub 2}O{sub 6} crystallizes in the centrosymmetric Pnam space group (with unit cell: a = 12.3693, b = 12.4254, and c = 7.7228 Å) isomorphous with orthorhombic β-SrTa{sub 2}O{sub 6}. In contrast to early reports, we see no evidence of deviation from paramagnetic Curie-Weiss behavior among the Eu{sup 2+} 4f{sup 7}spins in EuTa{sub 2}O{sub 6} down to 2 K. Dielectric constant shows a broad peak at ca. 50 K with dielectric dispersion resembling diffuse phase transition. The relaxation time, however, follows a simple (non-freezing) thermally activated process with an activation energy of 92 meV and anmore » attempt frequency of f{sub 0} = 5.79 × 10{sup 12 }Hz. A thermal conductivity of EuTa{sub 2}O{sub 6} shows a low-temperature (T ≈ 30 K) “plateau” region reminiscent of a glass-like behaviour in Nb-based TTB compounds. This behaviour can be attributed to the loosely bound Eu{sup 2+} ions occupying large tricapped trigonal prismatic sites in the EuTa{sub 2}O{sub 6} structure.« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Risskov Sørensen, Daniel; Nielsen, Ulla Gro; Skou, Eivind M., E-mail: ems@kbm.sdu.dk

2014-11-15

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

Direct Ink Writing of Three-Dimensional (K, Na)NbO3-Based Piezoelectric Ceramics

PubMed Central

Li, Yayun; Li, Longtu; Li, Bo

2015-01-01

A kind of piezoelectric ink was prepared with Li, Ta, Sb co-doped (K, Na)NbO3 (KNN) powders. Piezoelectric scaffolds with diameters at micrometer scale were constructed from this ink by using direct ink writing method. According to the micro-morphology and density test, the samples sintered at 1100 °C for 2 h have formed ceramics completely with a high relative density of 98%. X-ray diffraction (XRD) test shows that the main phase of sintered samples is orthogonal (Na0.52K0.4425Li0.0375)(Nb0.87Sb0.07Ta0.06)O3. The piezoelectric constant d33 of 280 pC/N, dielectric constant ε of 1775, remanent polarization Pr of 18.8 μC/cm2 and coercive field Ec of 8.5 kV/cm prove that the sintered samples exhibit good electrical properties. The direct ink writing method allows one to design and rapidly fabricate piezoelectric structures in complex three-dimensional (3D) shapes without the need for any dies or lithographic masks, which will simplify the process of material preparation and offer new ideas for the design and application of piezoelectric devices. PMID:28788028

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

PubMed

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

2005-08-11

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

Effect of Nb2O5 doping on improving the thermo-mechanical stability of sealing interfaces for solid oxide fuel cells.

PubMed

Zhang, Qi; Du, Xinhang; Tan, Shengwei; Tang, Dian; Chen, Kongfa; Zhang, Teng

2017-07-13

Nb 2 O 5 is added to a borosilicate sealing system to improve the thermo-mechanical stability of the sealing interface between the glass and Fe-Cr metallic interconnect (Crofer 22APU) in solid oxide fuel cells (SOFCs). The thermo-mechanical stability of the glass/metal interface is evaluated experimentally as well as by using a finite element analysis (FEA) method. The sealing glass doped with 4 mol.% Nb 2 O 5 shows the best thermo-mechanical stability, and the sealing couple of Crofer 22APU/glass/GDC (Gd 0.2 Ce 0.8 O 1.9 ) remains intact after 50 thermal cycles. In addition, all sealing couples show good joining after being held at 750 °C for 1000 h. Moreover, the possible mechanism on the thermo-mechanical stability of sealing interface is investigated in terms of stress-based and energy-based perspectives.

Structural transformation in antiferroelectric PbZrO3-relaxor ferroelectric Pb(Ni1/3Nb2/3)O3 solid solution system

NASA Astrophysics Data System (ADS)

Wirunchit, S.; Vittayakorn, N.

2008-07-01

The solid solution between the antiferroelectric (AFE) PbZrO3 (PZ) and the relaxor ferroelectric (FE) Pb(Ni1/3Nb2/3)O3 (PNN) was synthesized by the columbite precursor method. The crystal structure, phase transformations, and dielectric and thermal properties of (1-x )PZ-xPNN where x =0.00-0.30 were investigated. With these data, the FE phase diagram between PZ and PNN has been established. The crystal structure data obtained from X-ray diffraction indicate that the solid solution PZ-PNN, where x =0.00-0.30, successively transforms from orthorhombic to rhombohedral symmetry with an increase in the PNN concentration. The AFE phase→FE phase transition occurs in compositions of 0.00⩽x⩽0.08. The AFE →FE phase transition shifts to lower temperatures with higher compositions of x. The FE phase temperature range width increases with increased PNN. Apparently the replacement of the Zr4+ ion by Ni2+/Nb5+ ions decreases the driving force for an antiparallel shift of Pb2+ ions because they interrupt the translational symmetry and facilitates the appearance of a rhombohedral FE phase when the amount of PNN is higher than 8mol%.

Ferroelectric, piezoelectric, and leakage current properties of (K0.48Na0.48Li0.04)(Nb0.775Ta0.225)O3 thin films grown by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Wang, D. Y.; Lin, D. M.; Kwok, K. W.; Chan, N. Y.; Dai, J. Y.; Li, S.; Chan, H. L. W.

2011-01-01

Lead-free (K0.48Na0.48Li0.04)(Nb0.775Ta0.225)O3 (KNLNT) thin films were deposited on Pt(111)/Ti/SiO2/Si(001) substrates using pulsed laser deposition. The film exhibited a well-defined ferroelectric hysteresis loop with a remnant polarization 2Pr of 22.6 μC/cm2 and a coercive field Ec of 10.3 kV/mm. The effective piezoelectric coefficient d33,f of the KNLNT thin films was found to be about 49 pm/V by piezoelectric force microscope. The dominant conduction mechanisms of Au/KNLNT/Pt thin film capacitor were determined to be bulk-limited space-charge-limited-current and Poole-Frenkle emission at low and high electric field strengths, respectively, within a measured temperature range of 130-370 K.

K(3)TaF(8) from laboratory X-ray powder data.

PubMed

Smrcok, Lubomír; Cerný, Radovan; Boca, Miroslav; Macková, Iveta; Kubíková, Blanka

2010-02-01

The crystal structure of tripotassium octafluoridotantalate, K(3)TaF(8), determined from laboratory powder diffraction data by the simulated annealing method and refined by total energy minimization in the solid state, is built from discrete potassium cations, fluoride anions and monocapped trigonal-prismatic [TaF(7)](2-) ions. All six atoms in the asymmetric unit are in special positions of the P6(3)mc space group: the Ta and one F atom in the 2b (3m) sites, the K and two F atoms in the 6c (m) sites, and one F atom in the 2a (3m) site. The structure consists of face-sharing K(6) octahedra with a fluoride anion at the center of each octahedron, forming chains of composition [FK(3)](2+) running along [001] with isolated [TaF(7)](2-) trigonal prisms in between. The structure of the title compound is different from the reported structure of Na(3)TaF(8) and represents a new structure type.

Containerless processing of Nb-Ge alloys in a long drop tube

NASA Technical Reports Server (NTRS)

Bayuzick, R. J.

1982-01-01

The thirty-two meter drop tube at the Marshall Space Flight Center was used to study the effect of zero gravity containerless processing on the structure and properties of materials. The concept involves the suppression of heterogeneous nucleation of solid in liquid and, therefore, solidification accompanied by large degrees of undercooling. Under these conditions metastable phases can be formed or, at the very least, unique nonequilibrium microstructures (containing equilibrium phases) with unique properties can be produced. The drop tube solidification was applied to niobium base alloys with emphasis on the Nb-Ge binary system in an effort to produce metastable phases with high superconducting transition temperatures in bulk specimens. In the past, only lower Ge alloys (Nb-13 a/o, Nb-18 a/o, and Nb-22 a/o) could be undercooled. Higher Ge alloys (e.g., Nb-25 a/o Ge and Nb-27 a/o Ge) can now be undercooled on a routine basis.

A model for phase evolution and volume expansion in tube type Nb3Sn conductors

NASA Astrophysics Data System (ADS)

Xu, X.; Sumption, M. D.; Collings, E. W.

2013-12-01

In this work, an analytic model for phase formation and volume expansion during heat treatment in tube type Nb3Sn strands is presented. Tube type Nb3Sn conductors consist of Nb or Nb-Ta alloy tube with a simple Cu/Sn binary metal insert to form the basic subelement (filament). A number of these elements, each with an outer Cu jacket, are restacked to form a multifilamentary strand. The present tube type conductors, with 4.2 K, 12 T non-Cu critical current density (Jc) in the 2000-2500 A mm-2 range and effective subelement diameters (deff) in the 12-36 μm range, are of interest for a number of applications. During the reaction of typical tube type strands, the Sn-Cu becomes molten and reacts with the Nb tube first to form NbSn2, then Nb6Sn5. At later times in the reaction sequence, all of the NbSn2 and Nb6Sn5 is converted to Nb3Sn. Some of the Nb3Sn is formed by a Nb-Sn reaction and has a fine grain (FG) structure, while some is converted from Nb6Sn5, which results in a coarse grain (CG) region. The fractions of FG and CG A15 are important in determining the final conductor properties. In this work we develop an analytic model to predict the radial extents of the various phases, and in particular the final FG and CG fractions based on the starting Nb, Cu, and Sn amounts in the subelements. The model is then compared to experimental results and seen to give reasonable agreement. By virtue of this model we outline an approach to minimize the CG regions in tube type and PIT strands and maximize the final FG area fractions. Furthermore, the volume change during the various reaction stages was also studied. It is proposed that the Sn content in the Cu-Sn alloy has a crucial influence on the radial expansion.

Evidence for anisotropic polar nanoregions in relaxor Pb(Mg1/3Nb2/3)O3: A neutron study of the elastic constants and anomalous TA phonon damping in PMN

NASA Astrophysics Data System (ADS)

Stock, C.; Gehring, P. M.; Hiraka, H.; Swainson, I.; Xu, Guangyong; Ye, Z.-G.; Luo, H.; Li, J.-F.; Viehland, D.

2012-09-01

We use neutron inelastic scattering to characterize the acoustic phonons in the relaxor Pb(Mg1/3Nb2/3)O3 (PMN) and demonstrate the presence of a highly anisotropic damping mechanism that is directly related to short-range polar correlations. For a large range of temperatures above Tc˜210 K, where dynamic, short-range polar correlations are present, acoustic phonons propagating along [11¯0] and polarized along [110] (TA2 phonons) are overdamped and softened across most of the Brillouin zone. By contrast, acoustic phonons propagating along [100] and polarized along [001] (TA1 phonons) are overdamped and softened for a more limited range of wave vectors q. The anisotropy and temperature dependence of the acoustic phonon energy linewidth Γ are directly correlated with neutron diffuse scattering cross section, indicating that polar nanoregions are the cause of the anomalous behavior. The damping and softening vanish for q→0, i.e., for long-wavelength acoustic phonons near the zone center, which supports the notion that the anomalous damping is a result of the coupling between the relaxational component of the diffuse scattering and the harmonic TA phonons. Therefore, these effects are not due to large changes in the elastic constants with temperature because the elastic constants correspond to the long-wavelength limit. We compare the elastic constants we measure to those from Brillouin scattering experiments and to values reported for pure PbTiO3. We show that while the values of C44 are quite similar, those for C11 and C12 are significantly less in PMN and result in a softening of (C11-C12) over PbTiO3. The elastic constants also show an increased elastic anisotropy [2C44/(C11-C12)] in PMN versus that in PbTiO3. These results are suggestive of an instability to TA2 acoustic fluctuations in PMN and other relaxor ferroelectrics. We discuss our results in the context of the current debate over the “waterfall” effect and show that they are inconsistent with

Influence of defect distribution on the thermoelectric properties of FeNbSb based materials.

PubMed

Guo, Shuping; Yang, Kaishuai; Zeng, Zhi; Zhang, Yongsheng

2018-05-21

Doping and alloying are important methodologies to improve the thermoelectric performance of FeNbSb based materials. To fully understand the influence of point defects on the thermoelectric properties, we have used density functional calculations in combination with the cluster expansion and Monte Carlo methods to examine the defect distribution behaviors in the mesoscopic FeNb1-xVxSb and FeNb1-xTixSb systems. We find that V and Ti exhibit different distribution behaviors in FeNbSb at low temperature: forming the FeNbSb-FeVSb phase separations in the FeNb1-xVxSb system but two thermodynamically stable phases in FeNb1-xTixSb. Based on the calculated effective mass and band degeneracy, it seems the doping concentration of V or Ti in FeNbSb has little effect on the electrical properties, except for one of the theoretically predicted stable Ti phases (Fe6Nb5Ti1Sb6). Thus, an essential methodology to improve the thermoelectric performance of FeNbSb should rely on phonon scattering to decrease the thermal conductivity. According to the theoretically determined phase diagrams of Fe(Nb,V)Sb and Fe(Nb,Ti)Sb, we propose the (composition, temperature) conditions for the experimental synthesis to improve the thermoelectric performance of FeNbSb based materials: lowering the experimental preparation temperature to around the phase boundary to form a mixture of the solid solution and phase separation. The point defects in the solid solution effectively scatter the short-wavelength phonons and the (coherent or incoherent) interfaces introduced by the phase separation can additionally scatter the middle-wavelength phonons to further decrease the thermal conductivity. Moreover, the induced interfaces could enhance the Seebeck coefficient as well, through the energy filtering effect. Our results give insight into the understanding of the impact of the defect distribution on the thermoelectric performance of materials and strengthen the connection between theoretical predictions and

Sr- and Nb-co-doped Li7La3Zr2O12 solid electrolyte with Al2O3 addition towards high ionic conductivity

NASA Astrophysics Data System (ADS)

Lin, Changwei; Tang, Yu; Song, Jun; Han, Lei; Yu, Jingbo; Lu, Anxian

2018-06-01

In the present study, series of garnet-type Li6.75+ x La3- x Sr x Zr1.75Nb0.25O12 solid electrolytes [LLSZN with various Sr contents ( x = 0.05-0.25)] have been prepared via conventional solid-state method. The effects of Sr contents on their phase structure and ionic conductivity have been systematically investigated on the combined measurements of X-ray diffraction and scanning electron microscopy and alter current impedance spectroscopy. Our results reveal that a phase transition from tetragonal to cubic structure occurs when both Sr and Nb elements is introduced, and such a cubic structure can be stable over the whole Sr contents variation, which is suggested to provide a beneficial impact on the performance of LLSZN. Accordingly, both relative density and total ionic conductivity exhibit a favorable tendency of increasing first and then decreasing with increased Sr contents, wherein a peak value at 93.46% and 5.09 × 10-4 S cm-1, respectively, can be well achieved. Particularly, the maximum ionic conductivity is almost twice that of the compared sample (2.93 × 10-4 S cm-1), and possess the minimum activation energy 0.30 eV. Such a modification method, featured with higher efficiency and lower cost, is expected to be helpful for the development of solid electrolyte.

Electrochemical Characterization of a Low Modulus Ti-35.5Nb-7.3Zr-5.7Ta Alloy in a Simulated Body Fluid Using Eis for Biomedical Applications

NASA Astrophysics Data System (ADS)

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

2011-06-01

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

Structural and electronic investigations of PbTa4O11 and BiTa7O19 constructed from α-U3O8 types of layers

NASA Astrophysics Data System (ADS)

Boltersdorf, Jonathan; Maggard, Paul A.

2015-09-01

The PbTa4O11 and BiTa7O19 phases were prepared by ion-exchange and solid-state methods, respectively, and their structures were characterized by neutron time-of-flight diffraction and Rietveld refinement methods (PbTa4O11, R 3 (No. 146), a=6.23700(2) Å, c=36.8613(1) Å; BiTa7O19, P 6 bar c 2 (No. 188), a=6.2197(2) Å, c=20.02981(9) Å). Their structures are comprised of layers of TaO6 octahedra surrounded by three 7-coordinate Pb(II) cations or two 8-coordinate Bi(III) cations. These layers alternate down the c-axis with α-U3O8 types of single and double TaO7 pentagonal bipyramid layers. In contrast to earlier studies, both phases are found to crystallize in noncentrosymmetric structures. Symmetry-lowering structural distortions within PbTa4O11, i.e. R 3 bar c →R3, are found to be a result of the displacement of the Ta atoms within the TaO7 and TaO6 polyhedra, towards the apical and facial oxygen atoms, respectively. In BiTa7O19, relatively lower reaction temperatures leads to an ordering of the Bi/Ta cations within a lower-symmetry structure, i.e., P63/mcm→ P 6 bar c 2 . In the absence of Bi/Ta site disorder, the Ta-O-Ta bond angles decrease and the Ta-O bond distances increase within the TaO7 double layers. Scanning electron microscopy images reveal two particle morphologies for PbTa4O11, hexagonal rods and finer irregularly-shaped particles, while BiTa7O19 forms as aggregates of irregularly-shaped particles. Electronic-structure calculations confirm the highest-energy valence band states are comprised of O 2p-orbitals and the respective Pb 6s-orbital and Bi 6s-orbital contributions. The lowest-energy conduction band states are composed of Ta 5d-orbital contributions that are delocalized over the TaO6 octahedra and layers of TaO7 pentagonal bipyramids. The symmetry-lowering distortions in the PbTa4O11 structure, and the resulting effects on its electronic structure, lead to its relatively higher photocatalytic activity compared to similar structures without

Polar catastrophe and the structure of KTa 1-xNb xO₃ surfaces: Results from elastic and inelastic helium atom scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flaherty, F. A.; Trelenberg, T. W.; Li, J. A.

2015-07-13

The structure and dynamics of cleaved (001) surfaces of potassium tantalates doped with niobium, KTa 1-xNb xO₃ (KTN), with x ranging from 0% to 30%, were measured by helium atom scattering (HAS). Through HAS time-of-flight (TOF) experiments, a dispersionless branch (Einstein phonon branch) with energy of 13-14 meV was observed across the surface Brillouin zone in all samples. When this observation is combined with the results from earlier experimental and theoretical studies on these materials, a consistent picture of the stable surface structure emerges: After cleaving the single-crystal sample, the surface should be composed of equal areas of KO andmore » TaO₂/NbO₂ terraces. The data, however, suggest that K⁺ and O²⁻ ions migrate from the bulk to the surface, forming a charged KO lattice that is neutralized primarily by additional K⁺ ions bridging pairs of surface oxygens. This structural and dynamic modification at the (001) surface of KTN appears due to its formally charged KO(-1) and TaO₂/NbO₂(+1) layers and avoids a “polar catastrophe.” This behavior is contrasted with the (001) surface behavior of the fluoride perovskite KMnF₃ with its electrically neutral KF and MnF₂ layers.« less

New NbCd2 Phase in Niobium-Cadmium Coating Films

NASA Astrophysics Data System (ADS)

Volodin, V. N.; Tuleushev, Yu. Zh.; Zhakanbaev, E. A.; Tsai, K. V.; Rofman, O. V.

2018-02-01

Solid solutions in the form of alloy coatings have been obtained for the first time in the Cd concentration range of 64.5% using ion-plasma sputtering and the codeposition of Nb and Cd ultrafine particles. This supports thermal fluctuation melting and the coalescence of fine particles. A coating of niobium and cadmium layers less than 2 nm thick at 68 at % Cd results in the formation of a new phase identified as NbCd2. The tetragonal fcc phase with lattice parameters a = 0.84357 nm and c = 0.54514 nm forms directly during film coating. XRD data for the identification of the intermetallic compound have been determined. The thermal stability of the NbCd 2 intermetallic compound is limited by 200°C. The properties of the synthesized NbCd 2 phase are typical of semiconductors.

Structural characterization of niobium oxide thin films grown on SrTiO3 (111) and (La,Sr)(Al,Ta)O3 (111) substrates

NASA Astrophysics Data System (ADS)

Dhamdhere, Ajit R.; Hadamek, Tobias; Posadas, Agham B.; Demkov, Alexander A.; Smith, David J.

2016-12-01

Niobium oxide thin films have been grown by molecular beam epitaxy on SrTiO3 (STO) (111) and (La0.18Sr0.82)(Al0.59Ta0.41)O3 (LSAT) (111) substrates. Transmission electron microscopy (TEM) confirmed the formation of high quality films with coherent interfaces. Films grown with higher oxygen pressure on STO (111) resulted in a (110)-oriented NbO2 phase with a distorted rutile structure, which can be described as body-centered tetragonal. The a lattice parameter of NbO2 was determined to be ˜13.8 Å in good agreement with neutron diffraction results published in the literature. Films grown on LSAT (111) at lower oxygen pressure produced the NbO phase with a defective rock salt cubic structure. The NbO lattice parameter was determined to be a ≈ 4.26 Å. The film phase/structure identification from TEM was in good agreement with in situ x-ray photoelectron spectroscopy measurements that confirmed the dioxide and monoxide phases, respectively. The atomic structure of the NbO2/STO and NbO/LSAT interfaces was determined based on comparisons between high-resolution electron micrographs and image simulations.

Separation of Niobium and Tantalum Pentafluoride by Selective Precipitation Using p-Phenylenediamine

NASA Astrophysics Data System (ADS)

Nete, M.; Purcell, W.; Nel, J. T.

2016-11-01

The similarity between Ta and Nb chemistry makes it difficult to find the appropriate reagents and chemical reactions for the separation of the two elements. This study investigated the precipitation behavior of TaF5 and NbF5 with p-phenylenediamine (PPDA). PPDA preferentially precipitated Nb from a 1:1 ratio of NbF5 and TaF5. Niobium recoveries of >80%, and only 4% Ta, were found in the precipitate of the reaction between (Nb/Ta)F5 and PPDA in ethanol. A separation factor of 100(9) indicated the potential for successful separation of Nb and Ta in a fluoride environment. A spectrophotometric study of the formation ratio of the newly formed Nb compound indicated a 1:1 metal:ligand ratio.

Investigation of compatible anode systems for LaNbO 4-based electrolyte in novel proton conducting solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Magrasó, Anna; Fontaine, Marie-Laure

In the current manufacturing process of novel LaNbO 4-based proton conducting fuel cells a thin layer of the electrolyte is deposited by wet ceramic coating on NiO-LaNbO 4 based anode and co-sintered at 1200-1300 °C. The chemical compatibility of NiO with acceptor doped LaNbO 4 material is crucial to ensure viability of the cell, so potential effects of other phases resulting from off-stoichiometry in acceptor doped LaNbO 4 should also be explored. Compatibility of NiO with Ca-doped LaNbO 4 and its typical off-set compositions (La 3NbO 7 and LaNb 3O 9) are investigated in this work. It is shown that while NiO does not react with Ca-doped LaNbO 4, fast reaction occurs with La 3NbO 7 or LaNb 3O 9. La 3NbO 7 and NiO form a mixed conducting perovskite phase LaNi 2/3Nb 1/3O 3, while LaNb 3O 9 and NiO form either NiNb 2O 6 or Ni 4Nb 2O 9 depending on the annealing temperature. This implies that manufacturing LaNbO 4-based proton conducting fuel cells requires a strict control of the stoichiometry of the electrolyte.

Effect of alloying elements and heat treatment on the fracture toughness of Ti-Al-Nb alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kamat, S.V.; Gogia, A.K.; Banerjee, D.

The fracture toughness and toughening mechanisms of Ti{sub 3}Al based alloy compositions covering a large range of Nb, small variations in Al and quaternary substitutions of Nb have been studied in a variety of heat treated conditions designed to vary the volume fractions of the constituents phases. It was found that the B2 phase of these alloys failed by cleavage in a coarse grained condition but in a ductile manner when fine grained. A higher Nb and a lower Al content improved the cleavage fracture stress of the B2 phase while replacement of a part of Nb and a lowermore » Al content improved the cleavage fracture stress of the B2 phase while replacement of a part of Nb with Mo or Ta had no significant effect. Heat treatments which result in a two phase microstructure ({alpha}{sub 2} + {beta}/B2) exhibited a trend of increasing fracture toughness with increasing volume fraction of {beta}/B2 up to about 60--80 volume fraction of {beta}/B2. This behavior was largely explained by quantifying the role of crack tip blunting. The effect of alloying elements on fracture toughness in two phase microstructures was similar to that observed in the coarse grained B2 condition.« less

Garnet-type solid-state fast Li ion conductors for Li batteries: critical review.

PubMed

Thangadurai, Venkataraman; Narayanan, Sumaletha; Pinzaru, Dana

2014-07-07

Batteries are electrochemical devices that store electrical energy in the form of chemical energy. Among known batteries, Li ion batteries (LiBs) provide the highest gravimetric and volumetric energy densities, making them ideal candidates for use in portable electronics and plug-in hybrid and electric vehicles. Conventional LiBs use an organic polymer electrolyte, which exhibits several safety issues including leakage, poor chemical stability and flammability. The use of a solid-state (ceramic) electrolyte to produce all-solid-state LiBs can overcome all of the above issues. Also, solid-state Li batteries can operate at high voltage, thus, producing high power density. Various types of solid Li-ion electrolytes have been reported; this review is focused on the most promising solid Li-ion electrolytes based on garnet-type metal oxides. The first studied Li-stuffed garnet-type compounds are Li5La3M2O12 (M = Nb, Ta), which show a Li-ion conductivity of ∼10(-6) at 25 °C. La and M sites can be substituted by various metal ions leading to Li-rich garnet-type electrolytes, such as Li6ALa2M2O12, (A = Mg, Ca, Sr, Ba, Sr0.5Ba0.5) and Li7La3C2O12 (C = Zr, Sn). Among the known Li-stuffed garnets, Li6.4La3Zr1.4Ta0.6O12 exhibits the highest bulk Li-ion conductivity of 10(-3) S cm(-1) at 25 °C with an activation energy of 0.35 eV, which is an order of magnitude lower than that of the currently used polymer, but is chemically stable at higher temperatures and voltages compared to polymer electrolytes. Here, we discuss the chemical composition-structure-ionic conductivity relationship of the Li-stuffed garnet-type oxides, as well as the Li ion conduction mechanism.

The Crystallization Clinic-A TA Orientation Exercise

NASA Astrophysics Data System (ADS)

Kandel, Marjorie

1999-01-01

Our orientation exercise for TAs in the organic laboratories is a Crystallization Clinic, and the main feature is a contest. Each TA has a different unknown solid to recrystallize. The products are judged by the students in the organic lab courses. Beauty of the crystals is the single criterion. The contest serves to refresh the TAs' technique and to give them empathy with the beginning students.

Geology, market and supply chain of niobium and tantalum—a review

NASA Astrophysics Data System (ADS)

Mackay, Duncan A. R.; Simandl, George J.

2014-12-01

Tantalum (Ta) and niobium (Nb) are essential metals in modern society. Their use in corrosion prevention, micro-electronics, specialty alloys and high-strength low-alloy (HSLA) steel earns them a strategic designation in most industrialised countries. The Ta market is unstable due in part to historic influx of `conflict' columbite-tantalite concentrate, or "Coltan," that caused Ta mines in Australia and Canada to be placed on care and maintenance. More recently, the growing appetite of modern society for consumer goods made of `conflict-free' minerals or metals has put pressure on suppliers. Pegmatites, rare-element-enriched granites, related placer deposits and weathered crusts overlying carbonatite and peralkaline complexes account for the majority of Ta production. Several carbonatite-related deposits (e.g. Upper Fir and Crevier, Canada) are being considered for potential co-production of Ta and Nb. Pyrochlore (Nb-Ta), columbite-tantalite (Nb-Ta), wodginite (Ta, Nb and Sn) and microlite (Ta and Nb) are the main ore minerals. Approximately 40 % of Ta used in 2012 came from Ta mines, 30 % from recycling, 20 % from tin slag refining and 10 % from secondary mine concentrates. Due to rapid industrialisation and increased use of Nb in steel making in countries such as China and India, demand for Nb is rising. Weathered crusts overlying carbonatite complexes in Brazil and one hard rock carbonatite deposit in Canada account for about 92 and 7 % of Nb world mine production, respectively. Since the bulk of the production is geographically and politically restricted to a single country, security of supply is considered at risk. Other prospective resources of Nb, beside carbonatites and associated weathered crusts, are peralkaline complexes (e.g. Nechalacho; where Nb is considered as a potential co-product of REE and zirconium). Economically, significant deposits of Ta and Nb contain pyrochlore, columbite-tantalite, fersmite, loparite and strüverite. Assuming continued

STUDY ON SYNTHESIS AND EVOLUTION OF NANOCRYSTALLINE Mg4Ta2O9 BY AQUEOUS SOL-GEL PROCESS

NASA Astrophysics Data System (ADS)

Wu, H. T.; Yang, C. H.; Wu, W. B.; Yue, Y. L.

2012-06-01

Nanosized and highly reactive Mg4Ta2O9 were successfully synthesized by aqueous sol-gel method compared with conventional solid-state method. Ta-Mg-citric acid solution was first formed and then evaporated resulting in a dry gel for calcination in the temperature ranging from 600°C to 800°C for crystallization in oxygen atmosphere. The crystallization process from the gel to crystalline Mg4Ta2O9 was identified by thermal analysis and phase evolution of powders was studied using X-ray diffraction (XRD) technique during calcinations. Particle size and morphology were examined by transmission electron microscopy (TEM) and high resolution scanning electron microscopy (HR-SEM). The results revealed that sol-gel process showed great advantages over conventional solid-state method and Mg4Ta2O9 nanopowders with the size of 20-30 nm were obtained at 800°C.

A model for Nb-Zr-REE-Ga enrichment in Lopingian altered alkaline volcanic ashes: Key evidence of H-O isotopes

NASA Astrophysics Data System (ADS)

Dai, Shifeng; Nechaev, Victor P.; Chekryzhov, Igor Yu.; Zhao, Lixin; Vysotskiy, Sergei V.; Graham, Ian; Ward, Colin R.; Ignatiev, Alexander V.; Velivetskaya, Tatyana A.; Zhao, Lei; French, David; Hower, James C.

2018-03-01

Clay-altered volcanic ash with highly-elevated concentrations of Nb(Ta), Zr(Hf), rare earth elements (REE), and Ga, is a new type of critical metal deposit with high commercial prospects that has been discovered in Yunnan Province, southwest China. Previous studies showed that the volcanic ashes had been subjected to hydrothermal fluids, the nature of which, however, is not clear. Here we show that the volcanic ashes were originated from alkaline magmatism, followed by a continuous hydrothermal-weathering process. Heated meteoric waters, which were sourced from acidic rains and mixed with CO2 from degassing of the Emeishan plume, have caused partial, but widespread, acidic leaching of Nb, Ta, Zr, Hf, REE, and Ga into ground water and residual enrichment of these elements, along with Al and Ti, in the deeply altered rocks. Subsequent alteration occurring under cooler, neutral or alkaline conditions, caused by water-rock interaction, resulted in precipitation of the leached critical metals in the deposit. Polymetallic mineralization of similar origin may be found in other continental regions subjected to explosive alkaline volcanism associated with deep weathering in humid conditions.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao, Yong; Duan, Nanqi; Yan, Dong, E-mail: yand@hust.edu.cn

Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} (x=0, 0.1, 0.2, 0.4, 0.6, 0.8, 0.99) is prepared by using a solid reaction route, and single phase is achieved. Structural and phase transformation of Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} have been characterized by high temperature X-ray diffraction. The lattice parameters a, b, c decrease and γ increases with increasing x, at both room and high temperature. The phase transformation temperature increases linearly with increasing x for Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ}. The electrical conductivity of Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} is measured in wet air. A clear relationship between the structural, phase transformation andmore » electrical conductivity of Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} is built, which will provide a guideline to tailor the electrical conductivity. - Graphical abstract: Structural and phase transformation of Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} have been characterized by high temperature X-ray diffraction, as well as the conductivity of Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} in wet air. A clear relationship between the structural, phase transformation and electrical conductivity of Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} is built. - Highlights: • Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} with various Sm contents was prepared. • Structure, phase transformation and electrical conductivity of Ca{sub 0.01}La{sub 0.99−x}Sm{sub x}NbO{sub 4−δ} were characterized. • A relationship between the structure, phase transformation and electrical conductivity was well established.« less

Directionally solidified iron-base eutectic alloys

NASA Technical Reports Server (NTRS)

Tewari, S. N.

1976-01-01

Pseudobinary eutectic alloys with nominal compositions of Fe-25Ta-22Ni-10Cr and Fe-15.5Nb-14.5Ni-6.0Cr were directionally solidified at 0.5 centimeter per hour. Their microstructure consisted of the fcc, iron solid-solution, matrix phase reinforced by about 41-volume-percent, hcp, faceted Fe2Ta fibers and 41-volume-percent, hcp, Fe2Nb lamellae for the tantalum- and niobium-containing alloys, respectively. The microstructural stability under thermal cycling and the temperature dependence of tensile properties were investigated. These alloys showed low elevated-temperature strength and were not considered suitable for application in aircraft-gas-turbine blades although they may have applicability as vane materials.

High-Entropy Metal Diborides: A New Class of High-Entropy Materials and a New Type of Ultrahigh Temperature Ceramics

NASA Astrophysics Data System (ADS)

Gild, Joshua; Zhang, Yuanyao; Harrington, Tyler; Jiang, Sicong; Hu, Tao; Quinn, Matthew C.; Mellor, William M.; Zhou, Naixie; Vecchio, Kenneth; Luo, Jian

2016-11-01

Seven equimolar, five-component, metal diborides were fabricated via high-energy ball milling and spark plasma sintering. Six of them, including (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)B2, (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2, (Hf0.2Zr0.2Mo0.2Nb0.2Ti0.2)B2, (Hf0.2Mo0.2Ta0.2Nb0.2Ti0.2)B2, (Mo0.2Zr0.2Ta0.2Nb0.2Ti0.2)B2, and (Hf0.2Zr0.2Ta0.2Cr0.2Ti0.2)B2, possess virtually one solid-solution boride phase of the hexagonal AlB2 structure. Revised Hume-Rothery size-difference factors are used to rationalize the formation of high-entropy solid solutions in these metal diborides. Greater than 92% of the theoretical densities have been generally achieved with largely uniform compositions from nanoscale to microscale. Aberration-corrected scanning transmission electron microscopy (AC STEM), with high-angle annular dark-field and annular bright-field (HAADF and ABF) imaging and nanoscale compositional mapping, has been conducted to confirm the formation of 2-D high-entropy metal layers, separated by rigid 2-D boron nets, without any detectable layered segregation along the c-axis. These materials represent a new type of ultra-high temperature ceramics (UHTCs) as well as a new class of high-entropy materials, which not only exemplify the first high-entropy non-oxide ceramics (borides) fabricated but also possess a unique non-cubic (hexagonal) and layered (quasi-2D) high-entropy crystal structure that markedly differs from all those reported in prior studies. Initial property assessments show that both the hardness and the oxidation resistance of these high-entropy metal diborides are generally higher/better than the average performances of five individual metal diborides made by identical fabrication processing.

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

NASA Astrophysics Data System (ADS)

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

1992-08-01

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

Synthesis, structure and electrical properties of Cu{sub 3.21}Ti{sub 1.16}Nb{sub 2.63}O{sub 12} and the CuO{sub x}-TiO{sub 2}-Nb{sub 2}O{sub 5} pseudoternary phase diagram

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reeves-McLaren, Nik, E-mail: n.reeves@sheffield.ac.uk; Ferrarelli, Matthew C.; Tung, Yuan-Wei

2011-07-15

Subsolidus phase relations in the CuO{sub x}-TiO{sub 2}-Nb{sub 2}O{sub 5} system were determined at 935 deg. C. The phase diagram contains one new phase, Cu{sub 3.21}Ti{sub 1.16}Nb{sub 2.63}O{sub 12} (CTNO) and one rutile-structured solid solution series, Ti{sub 1-3x}Cu{sub x}Nb{sub 2x}O{sub 2}: 0Nb{sup 5+} on the octahedral sites. It is a modest semiconductor with relative permittivity {approx}63 and displays non-Arrhenius conductivity behavior that ismore » essentially temperature-independent at the lowest temperatures. - Graphical abstract: The CuO{sub x}-TiO{sub 2}-Nb{sub 2}O{sub 5} phase diagram was determined at 935 deg. C and contains one new phase, Cu{sub 3.21}Ti{sub 1.16}Nb{sub 2.63}O{sub 12}, pictured, a modest semiconductor with {epsilon}{sub r}{approx}63, and one rutile-structured solid solution series, Ti{sub 1-3x}Cu{sub x}Nb{sub 2x}O{sub 2}. Highlights: > Subsolidus phase relations in the CuO{sub x}-TiO{sub 2}-Nb{sub 2}O{sub 5} system were determined at 935 deg. C. > A new phase, Cu{sub 3.21}Ti{sub 1.16}Nb{sub 2.63}O{sub 12} (CTNO), was found with a CaCu{sub 3}Ti{sub 4}O{sub 12}-like crystal structure. > We discovered one rutile-structured solid solution series, Ti{sub 1-3x}Cu{sub x}Nb{sub 2x}O{sub 2}: 0 CTNO has square planar Cu{sup 2+}, A site vacancies and Cu{sup +}, Ti{sup 4+} and Nb{sup 5+} disordered on octahedral sites. > CTNO is a modest semiconductor with relative permittivity {approx}63.« less

Crystal structure of the new A2SnTa6X18 (A = K, Rb, Cs; X = Cl, Br) cluster compounds

NASA Astrophysics Data System (ADS)

Lemoine, P.; Wilmet, M.; Malaman, B.; Paofai, S.; Dumait, N.; Cordier, S.

2018-01-01

The crystal structure of the new cluster compounds A2SnTa6X18 (with A = K, Rb, Cs, and X = Cl, Br) was determined by using single-crystal and powder X-ray diffraction, and 119Sn Mössbauer spectroscopy. Those compounds crystallize in the Cs2EuNb6Br18-type structure of space group R 3 ̅. This type of structure is built up on discrete edge-bridged [M6Xi12Xa6]4- cluster units arranged according to a pseudo face-centered cubic stacking, where the octahedral and tetrahedral vacancies are fully occupied by divalent tin cations and monovalent alkaline cations, respectively. The tin cations influence on the halogen matrix and the electronic effects on the cluster units in the Cs2EuNb6Br18-type structure are discussed by comparison with isotype compounds. From those analyses, the ionic radius of Sn2+ in coordination number VI is estimated to be 1.14(1) Å. Finally, K2SnTa6Br18 might be considered as a new example of compound containing a quite bare stannous ion (5 s2 configuration).

Alloy Engineering of Topological Semimetal Phase Transition in MgTa2 -xNbxN3

NASA Astrophysics Data System (ADS)

Huang, Huaqing; Jin, Kyung-Hwan; Liu, Feng

2018-03-01

Dirac, triple-point, and Weyl fermions represent three topological semimetal phases, characterized with a descending degree of band degeneracy, which have been realized separately in specific crystalline materials with different lattice symmetries. Here we demonstrate an alloy engineering approach to realize all three types of fermions in one single material system of MgTa2 -xNbx N3 . Based on symmetry analysis and first-principles calculations, we map out a phase diagram of topological order in the parameter space of alloy concentration and crystalline symmetry, where the intrinsic MgTa2 N3 with the highest symmetry hosts the Dirac semimetal phase, which transforms into the triple-point and then the Weyl semimetal phases with increasing Nb concentration that lowers the crystalline symmetries. Therefore, alloy engineering affords a unique approach for the experimental investigation of topological transitions of semimetallic phases manifesting different fermionic behaviors.

Synthesis of layered perovskite oxides, ACa[sub 2-x]La[sub x]Nb[sub 3-x]Ti[sub x]O[sub 10] (A = K, Rb, Cs), and characterization of new solid acids, HCa[sub 2-x]La[sub x]Nb[sub 3-x]Ti[sub x]O[sub 10] (O < x [le] 2), exhibiting variable Bronsted acidity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gopalakrishnan, J.; Uma, S.; Bhat, V.

1993-01-01

Layered perovskite oxides of the formula ACa[sub 2-x]La[sub x]Nb[sub 3-x]Ti[sub x]O[sub 10] (A = K, Rb, Cs and 0 , x [le] 2) have been prepared. The members adopt the structures of the parent ACa[sub 2]Nb[sub 3]O[sub 10]. Interlayer alkali cations in the niobium-titanium oxide series can be ion-exchanged with Li[sup +], Na[sup +], NG[sub 4][sup +], of H[sup +] to give new derivatives. Intercalation of the protonated derivatives with organic bases reveals that the Bronsted acidity of the solid solution series, HCa[sub 2-x]La[sub x]Nb[sub 3-x]Ti[sub x]O[sub 10], depends on the titanium content. While the x = 1 member (HCaLaNb[submore » 2]TiO[sub 10]) is nearly as acidic as the parent HCa[sub 2]Nb[sub 3]O[sub 10], the x = 2 member (HLA[sub 2]NbTi[sub 2]O[sub 10]) is a weak acid hardly intercalating organic bases with pK[sub a] [approximately] 11.3. The variation of acidity is probably due to an ordering of Nb/Ti atoms in the triple octahedral perovskite slabs, [Ca[sub 2-x]La[sub x]Nb[sub 3-x]Ti[sub x]O[sub 10

Submillimeter SIS Mixers Using High Current Density Nb/AIN/Nb Tunnel Junctions and NbTiN Films

NASA Astrophysics Data System (ADS)

Kawamura, J.; Miller, D.; Chen, J.; Kooi, J.; Zmuidzinas, J.; Bumble, B.; Leduc, H.; Stern, J.

1999-03-01

We are currently exploring ways to improve the performance of SIS mixers above 700 GHz. One approach is to use NbTiN in place of Nb for all or some of the mixer circuitry. With its high gap frequency and low losses demonstrated up to 800 GHz, it should be possible to fabricate an all-NbTiN SIS mixer with near quantum-limited noise performance up to 1.2 THz. Using a quasioptical twin-slot two-junction mixer with NbTiN ground plane and wiring and hybrid Nb/A1N/NbTiN junctions, we measured an uncorrected receiver noise temperature of TRx ~ 500 K across 790-850 GHz at 4.2 K bath temperature. Our second approach is to reduce the RC product of the mixer by employing very high current density Nb/A1N/Nb junctions. By using these we will greatly relax the requirement on tuning circuits, which is where substantial losses occur in mixers operating above the Nb gap frequency. These junctions have resistance-area products of R_N*A ~ 5.6 Ohm um2, good subgap to normal resistance ratios, R_sg/R_N ~ 10, and good run-to-run reproducibility. From FTS measurements we infer that omega*R_N*C = 1 at 270 GHz in these junctions. This is a substantial improvement over that available using Nb/Al0x/Nb technology. The sensitivity of a receiver incorporating these high current density mixers is T_Rx = 110 K at 533 GHz using a design for lower J_c mixers, which is close to the best we have measured with lower J_c Nb/Al0x/Nb mixers.

Extreme magnetoresistance and SdH oscillation in compensated semimetals of NbSb2 single crystals

NASA Astrophysics Data System (ADS)

Guo, Lei; Liu, Yu-Kuai; Gao, Guan-Yin; Huang, Ye-Yu; Gao, Heng; Chen, Lei; Zhao, Weiyao; Ren, Wei; Li, Shi-Yan; Li, Xiao-Guang; Dong, Shuai; Zheng, Ren-Kui

2018-04-01

Topological semimetals represent one of the most interesting classes of materials that continue to attract worldwide interest. Here, we report magnetotransport properties of MPn2-type (M = Nb, Ta; Pn = P, As, Sb) NbSb2 single-crystal semimetals with a centrosymmetric C12/m1 space group, paramagnetic ground state, and non-saturation parabolic-like magnetoresistance. The NbSb2 crystals show metallic conductivity down to 2 K and undergo a metal-to-insulator-like transition under a magnetic field B (B ≥ 4 T) and exhibit a resistivity plateau in the low-temperature region (T ≤ 10 K), where the value of resistivity strongly depends on the magnitude and direction of the magnetic field. Upon sweeping the magnetic field from 0 to 14.5 T in the transverse configuration at T = 1.5 K, the NbSb2 crystal shows a large positive magnetoresistance (4.2 × 103% at B = 14.5 T) with Shubnikov-de Haas (SdH) oscillation. Hall measurements reveal that both the carrier compensation between electrons and holes and the high mobility and large mean free path of carriers contribute to the large magnetoresistance. Fast Fourier transform analyses of angle-resolved SdH oscillation indicate that the Fermi surface of the NbSb2 crystal is quasi-two-dimensional with three-dimensional components. These findings, together with the theoretically calculated electronic band structure obtained within the framework of density functional theory, suggest that NbSb2 is a good candidate compensated semimetal for further theoretical and experimental investigation of this family of materials.

HFSE systematics of rutile-bearing eclogites: New insights into subduction zone processes and implications for the earth’s HFSE budget

NASA Astrophysics Data System (ADS)

Schmidt, Alexander; Weyer, Stefan; John, Timm; Brey, Gerhard P.

2009-01-01

The depleted mantle and the continental crust are generally thought to balance the budget of refractory and lithophile elements of the Bulk Silicate Earth (BSE), resulting in complementary trace element patterns. However, the two high field strength elements (HFSE) niobium and tantalum appear to contradict this mass balance. All reservoirs of the silicate Earth exhibit subchondritic Nb/Ta ratios, possibly as a result of Nb depletion. In this study a series of nineteen orogenic MORB-type eclogites from different localities was analyzed to determine their HFSE concentrations and to contribute to the question of whether subducted oceanic crust could form a hidden reservoir to account for the mass imbalance of Nb/Ta between BSE and the chondritic reservoir. Concentrations of HFSE were analyzed with isotope dilution (ID) techniques. Additionally, LA-ICPMS analyses of clinopyroxene, garnet and rutile have been performed. Rutile is by far the major host for Nb and Ta in all analyzed eclogites. However, many rutiles revealed zoning in Nb/Ta ratios, with cores being higher than rims. Accordingly, in situ analyses of rutiles have to be evaluated carefully and rutile cores do not necessarily reflect a bulk rock Nb and Ta composition, although over 90% of these elements reside in rutile. The HFSE concentration data in bulk rocks show that the orogenic eclogites have subchondritic Nb/Ta ratios and near chondritic Zr/Hf ratios. The investigated eclogites show neither enrichment of Nb compared to similarly incompatible elements (e.g. La), nor fractionation of Nb/Ta ratios relative to MOR-basalts, the likely precursor of these rocks. This indicates that during the conversion of the oceanic crust to eclogites in most cases, (1) HFSE and REE have similar mobility on average, possibly because both element groups remain in the down going slab, and (2) no significant fractionation of Nb/Ta occurs in subducted oceanic crust. With an average Nb/Ta ratio of 14.2 ± 1.4 (2s.e.), the

Examining metallic glass formation in LaCe:Nb by ion implantation

DOE PAGES

Sisson, Richard; Reinhart, Cameron; Bridgman, Paul; ...

2017-01-01

In order to combine niobium (Nb) with lanthanum (La) and cerium (Ce), Nb ions were deposited within a thin film of these two elements. According to the Hume-Rothery rules, these elements cannot be combined into a traditional crystalline metallic solid. The creation of an amorphous metallic glass consisting of Nb, La, and Ce is then investigated. Amorphous metallic glasses are traditionally made using fast cooling of a solution of molten metals. In this paper, we show the results of an experiment carried out to form a metallic glass by implanting 9 MeV Nb 3+ atoms into a thin film ofmore » La and Ce. Prior to implantation, the ion volume distribution is calculated by Monte Carlo simulation using the SRIM tool suite. As a result, using multiple methods of electron microscopy and material characterization, small quantities of amorphous metallic glass are indeed identified.« less

TaRAR1 and TaSGT1 associate with TaHsp90 to function in bread wheat (Triticum aestivum L.) seedling growth and stripe rust resistance.

PubMed

Wang, Guan-Feng; Fan, Renchun; Wang, Xianping; Wang, Daowen; Zhang, Xiangqi

2015-04-01

RAR1 and SGT1 are important co-chaperones of Hsp90. We previously showed that TaHsp90.1 is required for wheat seedling growth, and that TaHsp90.2 and TaHsp90.3 are essential for resistance (R) gene mediated resistance to stripe rust fungus. Here, we report the characterization of TaRAR1 and TaSGT1 genes in bread wheat. TaRAR1 and TaSGT1 each had three homoeologs, which were located on wheat groups 2 and 3 chromosomes, respectively. Strong inhibition of seedling growth was observed after silencing TaSGT1 but not TaRAR1. In contrast, decreasing the expression of TaRAR1 or TaSGT1 could all compromise R gene mediated resistance to stripe rust fungus infection. Protein-protein interactions were found among TaRAR1, TaSGT1 and TaHsp90. The N-terminus of TaHsp90, the CHORD-I and CHORD-II domains of TaRAR1 and the CS domain of TaSGT1 may be instrumental for the interactions among the three proteins. Based on this work and our previous study on TaHsp90, we speculate that the TaSGT1-TaHsp90.1 interaction is important for maintaining bread wheat seedling growth. The TaRAR1-TaSGT1-TaHsp90.2 and TaRAR1-TaSGT1-TaHsp90.3 interactions are involved in controlling the resistance to stripe rust disease. The new information obtained here should aid further functional investigations of TaRAR1-TaSGT1-TaHsp90 complexes in regulating bread wheat growth and disease resistance.

Fabrication of Ca-Mn-Nb-O compounds and their structural, electrical, magnetic and thermoelectric properties

NASA Astrophysics Data System (ADS)

Oz, E.; Demirel, S.; Altin, S.; Altin, E.; Baglayan, O.; Bayri, A.; Avci, S.

2018-03-01

CaMn1-xNbxO3-δ (0 ≤ x ≤ 1) were synthesized by conventional solid state reaction method. The structural properties were determined by FTIR, Raman, XRD, XAS measurements. The FTIR and Raman modes change by increasing Nb content and the lattice volume increases by increasing Nb content. The solubility limit of Nb is determined as x ≤ 0.3 and impurity phases start to appear above this limit. The temperature dependence of the magnetization data shows an antiferromagnetic transition below 120 K for low Nb content. Increasing the Nb content causes a change in the magnetic phase from antiferromagnetic to paramagnetic. The oxygen deficiency in CaMnO3-δ may cause the formation of polaron effect which is destroyed by the Nb ions. The difference graph of XAS data for x = 0 and 0.5 show that the number of Mn3+ ions increases by increasing Nb content to maintain the charge neutrality.

Stabilized antiferroelectricity in xBiScO3-(1-x)NaNbO3 lead-free ceramics with established double hysteresis loops

NASA Astrophysics Data System (ADS)

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

2018-02-01

We previously reported various solid solution systems that demonstrated the stabilized antiferroelectric (P) phases in NaNbO3 through lowering the tolerance factor. However, all those reported modifications were achieved by adding A2+B4+O3 type solid solutions. A lead-free antiferroelectric (AFE) solid solution xBiScO3-(1-x)NaNbO3 was rationalized by adopting the tolerance factor design rule. Specifically, adding BiScO3 was found to effectively stabilize the AFE phase without changing the crystal symmetry of NaNbO3. Microstructure and electron zone axis diffraction patterns from transmission electron microscopy revealed the stabilized AFE (P) phase in this solid solution. Besides, the electric-field-induced polarization with a double-hysteresis loop was observed. The present results pointed out that the strategy could also be applied while adding A3+B3+O3 type solid solutions. In addition, it expanded the compositional design that can be applied to antiferroelectric materials.

Investigating the highest melting temperature materials: A laser melting study of the TaC-HfC system.

PubMed

Cedillos-Barraza, Omar; Manara, Dario; Boboridis, K; Watkins, Tyson; Grasso, Salvatore; Jayaseelan, Daniel D; Konings, Rudy J M; Reece, Michael J; Lee, William E

2016-12-01

TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (>4000 K) among other properties. The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta 1-x Hf x C, with x = 0.8, 0.5 and 0.2) have long been identified as the highest known. In the current research, they were reassessed, for the first time in the last fifty years, using a laser heating technique. They were found to melt in the range of 4041-4232 K, with HfC having the highest and TaC the lowest. Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC 0.98 , (4232 ± 84) K, is the highest recorded for any compound studied until now.

Investigating the highest melting temperature materials: A laser melting study of the TaC-HfC system

NASA Astrophysics Data System (ADS)

Cedillos-Barraza, Omar; Manara, Dario; Boboridis, K.; Watkins, Tyson; Grasso, Salvatore; Jayaseelan, Daniel D.; Konings, Rudy J. M.; Reece, Michael J.; Lee, William E.

2016-12-01

TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (>4000 K) among other properties. The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta1-xHfxC, with x = 0.8, 0.5 and 0.2) have long been identified as the highest known. In the current research, they were reassessed, for the first time in the last fifty years, using a laser heating technique. They were found to melt in the range of 4041-4232 K, with HfC having the highest and TaC the lowest. Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC0.98, (4232 ± 84) K, is the highest recorded for any compound studied until now.

Investigating the highest melting temperature materials: A laser melting study of the TaC-HfC system

PubMed Central

Cedillos-Barraza, Omar; Manara, Dario; Boboridis, K.; Watkins, Tyson; Grasso, Salvatore; Jayaseelan, Daniel D.; Konings, Rudy J. M.; Reece, Michael J.; Lee, William E.

2016-01-01

TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (>4000 K) among other properties. The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta1−xHfxC, with x = 0.8, 0.5 and 0.2) have long been identified as the highest known. In the current research, they were reassessed, for the first time in the last fifty years, using a laser heating technique. They were found to melt in the range of 4041–4232 K, with HfC having the highest and TaC the lowest. Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC0.98, (4232 ± 84) K, is the highest recorded for any compound studied until now. PMID:27905481

Glass Forming Ability in the Equilibrium Immiscible Ag-Ta System Studied by Molecular Dynamics Simulation and Ion Beam Mixing

NASA Astrophysics Data System (ADS)

Zhao, Man; Dai, Xiaodong; Shen, Yixiong; Liu, Baixin

2008-07-01

For the equilibrium immiscible Ag-Ta system characterized by a positive heat of formation of +23 kJ/mol, a proved realistic extended Finnis-Sinclair potential is applied to study the crystal-to-amorphous transition through molecular dynamics simulations and a glass-forming range (GFR) of the Ag-Ta system is determined to be from 10 to 80 at. % of Ta, within which a disordered state is energetically favored than its crystalline counterpart of solid solution. In experiment, the uniform amorphous phases are indeed obtained, by ion beam mixing of far-from-equilibrium, in the Ag38Ta62, Ag30Ta70 and Ag20Ta80 Ag-Ta multilayered films, which fall within the GFR and thus confirm the relevance of the calculated GFR of the system.

Atomistic study of ternary oxides as high-temperature solid lubricants

NASA Astrophysics Data System (ADS)

Gao, Hongyu

Friction and wear are important tribological phenomena tightly associated with the performance of tribological components/systems such as bearings and cutting machines. In the process of contact and sliding, friction and wear lead to energy loss, and high friction and wear typically result in shortened service lifetime. To reduce friction and wear, solid lubricants are generally used under conditions where traditional liquid lubricants cannot be applied. However, it is challenging to maintain the functionality of those materials when the working environment becomes severe. For instance, at elevated temperatures (i.e., above 400 °C), most traditional solid lubricants, such as MoS2 and graphite, will easily oxidize or lose lubricity due to irreversible chemical changes. For such conditions, it is necessary to identify materials that can remain thermally stable as well as lubricious over a wide range of temperatures. Among the currently available high-temperature solid lubricants, Ag-based ternary metal oxides have recently drawn attention due to their low friction and ability to resist oxidation. A recent experimental study showed that the Ag-Ta-O ternary exhibited an extremely low coefficient of friction (0.06) at 750 °C. To fully uncover the lubricious nature of this material as a high-temperature solid lubricant, a series of tribological investigations were carried out based on one promising candidate - silver tantalate (AgTaO3). The study was then extended to alternative materials, Cu-Ta-O ternaries, to accommodate a variety of application requirements. We aimed to understand, at an atomic level, the effects of physical and chemical properties on the thermal, mechanical and tribological behavior of these materials at high temperatures. Furthermore, we investigated potassium chloride films on a clean iron surface as a representative boundary lubricating system in a nonextreme environment. This investigation complemented the study of Ag/Cu-Ta-O and enhanced the

Novel Method for Making Biomedical Segregation-Free Ti-30Ta Alloy Spherical Powder for Additive Manufacturing

NASA Astrophysics Data System (ADS)

Xia, Yang; Fang, Zhigang Zak; Sun, Pei; Zhang, Ying; Zhu, Jun

2018-03-01

Ti-Ta alloys offer a good combination of high strength and low modulus among Ti-based alloys, and are ideal for biomedical applications. However, making Ti-Ta alloys has always been challenging because they tend to suffer from compositional segregation during melting due to the large difference between the melting points of Ti and Ta. This article describes a novel process for making spherical Ti-30Ta alloy powder through a unique powder metallurgy technique, namely the granulation-sintering-deoxygenation process. The results indicate that the compositional segregation problem can be overcome using this process technology. Combined with use of a deoxygenation process, the critical interstitial element, oxygen, can be controlled to < 400 ppm for powder with particle size < 75 µm. The destabilization effect of Ta on Ti-O solid solutions, and the resulting improved deoxygenation process for Ti-Ta, are discussed, as well as the phase composition and microstructure of the powders.

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

NASA Astrophysics Data System (ADS)

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

2017-01-01

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

On Nb Silicide Based Alloys: Alloy Design and Selection

PubMed Central

Tsakiropoulos, Panos.

2018-01-01

The development of Nb-silicide based alloys is frustrated by the lack of composition-process-microstructure-property data for the new alloys, and by the shortage of and/or disagreement between thermodynamic data for key binary and ternary systems that are essential for designing (selecting) alloys to meet property goals. Recent publications have discussed the importance of the parameters δ (related to atomic size), Δχ (related to electronegativity) and valence electron concentration (VEC) (number of valence electrons per atom filled into the valence band) for the alloying behavior of Nb-silicide based alloys (J Alloys Compd 748 (2018) 569), their solid solutions (J Alloys Compd 708 (2017) 961), the tetragonal Nb5Si3 (Materials 11 (2018) 69), and hexagonal C14-NbCr2 and cubic A15-Nb3X phases (Materials 11 (2018) 395) and eutectics with Nbss and Nb5Si3 (Materials 11 (2018) 592). The parameter values were calculated using actual compositions for alloys, their phases and eutectics. This paper is about the relationships that exist between the alloy parameters δ, Δχ and VEC, and creep rate and isothermal oxidation (weight gain) and the concentrations of solute elements in the alloys. Different approaches to alloy design (selection) that use property goals and these relationships for Nb-silicide based alloys are discussed and examples of selected alloy compositions and their predicted properties are given. The alloy design methodology, which has been called NICE (Niobium Intermetallic Composite Elaboration), enables one to design (select) new alloys and to predict their creep and oxidation properties and the macrosegregation of Si in cast alloys. PMID:29783707

Phase relations in Ti-Al-Nb alloys at 1200 degrees C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suryanarayana, C.; Lee, D.S.

1992-03-15

This paper reports that titanium aluminides based on both Ti{sub 3}Al ({alpha}{sub 2}) and TiAl ({gamma}) have received considerable attention during the past few years as potential candidates for high temperature structural applications in the aerospace industry. This has been due to the attractive combination of properties such as low density, high specific strength, elevated temperature strength and modulus retention, excellent creep resistance and high resistance to oxidation. A serious handicap in using these alloys has been their vary poor ductility. Refinement of grain size, addition of ternary and quaternary alloying elements (e.g., Nb, Mn and Ta) and microstructural refinementsmore » through either innovative heat treatments or by production of nanometer-sized grains through mechanical alloying or magnetron sputtering methods have been explored to increase the ductility. Amongst these approaches, addition of alloying elements, especially of niobium, has proven extremely beneficial. Thus, there have been several investigations in recent years on the constitution, microstructure and properties of ternary Ti-Al-Nb alloys.« less

Processing and characterization of Al-Al3Nb prepared by mechanical alloying and equal channel angular pressing

NASA Astrophysics Data System (ADS)

Chandran, P.; Zafari, A.; Lui, E. W.; Xia, K.

2017-05-01

Mechanically alloyed Al with immiscible elements such as Nb can lead to a uniform distribution of nanoscaled precipitates which are highly stable compared to conventional alloying and with excellent interface, resulting in significant increase in strength without problems associated with nano ceramic particles in metal matrix composites. Although immiscible, Nb can be alloyed with Al through mechanical milling, forming trialuminide (Al3Nb), either directly or upon subsequent precipitation, which possesses high strength, stiffness and stability at elevated temperatures. In the present study, Al-5 at.% Nb supersaturated solid solution was achieved after prolonged ball milling and nano Al3Nb precipitates were formed during subsequent ageing at 530°C. The Al-Al3Nb powder was consolidated by equal channel angular pressing (ECAP) at 400°C, resulting in a fully dense material with a uniform distribution of nanoscaled Al3Nb precipitates in the Al matrix.

Synthesis, structure and electrical properties of Cu 3.21Ti 1.16Nb 2.63O 12 and the CuO x-TiO 2-Nb 2O 5 pseudoternary phase diagram

NASA Astrophysics Data System (ADS)

Reeves-McLaren, Nik; Ferrarelli, Matthew C.; Tung, Yuan-Wei; Sinclair, Derek C.; West, Anthony R.

2011-07-01

Subsolidus phase relations in the CuO x-TiO 2-Nb 2O 5 system were determined at 935 °C. The phase diagram contains one new phase, Cu 3.21Ti 1.16Nb 2.63O 12 (CTNO) and one rutile-structured solid solution series, Ti 1-3 xCu xNb 2 xO 2: 0< x<0.2335 (35). The crystal structure of CTNO is similar to that of CaCu 3Ti 4O 12 (CCTO) with square planar Cu 2+ but with A site vacancies and a disordered mixture of Cu +, Ti 4+ and Nb 5+ on the octahedral sites. It is a modest semiconductor with relative permittivity ˜63 and displays non-Arrhenius conductivity behavior that is essentially temperature-independent at the lowest temperatures.

Evolutionary Optimization of a Charge Transfer Ionic Potential Model for Ta/Ta-Oxide Heterointerfaces

DOE PAGES

Sasikumar, Kiran; Narayanan, Badri; Cherukara, Mathew; ...

2017-03-19

Heterostructures of tantalum and its oxide are of tremendous technological interest for a myriad of technological applications, including electronics, thermal management, catalysis and biochemistry. In particular, local oxygen stoichiometry variation in TaO x memristors comprising of thermodynamically stable metallic (Ta) and insulating oxide (Ta 2O 5) have been shown to result in fast switching on the subnanosecond timescale over a billion cycles. This rapid switching opens up the potential for advanced functional platforms such as stateful logic operations and neuromorphic computation. Despite its broad importance, an atomistic scale understanding of oxygen stoichiometry variation across Ta/TaO x heterointerfaces, such as duringmore » early stages of oxidation and oxide growth, is not well understood. This is mainly due to the lack of a unified interatomic potential model for tantalum oxides that can accurately describe metallic (Ta), ionic (TaO x) as well as mixed (Ta/TaO x interfaces) bonding environments simultaneously. To address this challenge, we introduce a Charge Transfer Ionic Potential (CTIP) model for Ta/Ta-oxide system by training against lattice parameters, cohesive energies, equations of state (EOS), elastic properties, and surface energies of the various experimentally observed Ta 2O 5 polymorphs (hexagonal, orthorhombic and monoclinic) obtained from density functional theory (DFT) calculations. The best CTIP parameters are determined by employing a global optimization scheme driven by genetic algorithms followed by local Simplex optimization. Our newly developed CTIP potential accurately predicts structure, thermodynamics, energetic ordering of polymorphs, as well as elastic and surface properties of both Ta and Ta 2O 5, in excellent agreement with DFT calculations and experiments. We employ our newly parameterized CTIP potential to investigate the early stages of oxidation and atomic scale mechanisms associated with oxide growth on Ta surface

Thermodynamics of superconducting Nb3Al, Nb3Ge, Nb3Sn, and V3Ga

NASA Astrophysics Data System (ADS)

Mitrović, B.; Schachinger, E.; Carbotte, J. P.

1984-06-01

We have calculated the superconducting thermodynamic properties for several high-transition-temperature A15 compounds: Nb-Al, Nb-Ge, Nb-Sn, and V-Ga. In our calculations we have used the tunneling electron-phonon-coupling spectra α2F for all four systems considered, and in the case of Nb-Al and Nb-Ge we have also used α2F=CG, where G is the measured generalized phonon density of states and C is a constant. We find that all Nb-based A15 compounds display similar thermodynamic properties, which do not depend explicitly on the band density of states: 2Δ0κBTc≅4.6, ΔCγTc≅2.5-2.6,-Tc[dHc(T)dT]TcHc(0)≅2.1, γ[TcHc(0)]2≅0.134, and positive D(t)'s with the maximum value around 0.02. For Nb3Sn we find good agreement between the calculated properties and the old specific-heat experimental results (γ≅52 mJ/mol K2). The same applies to V3Ga, where the theoretical results have been compared with the experiments of Junod et al. However, we do not find good agreement between calculated ΔCγTc, - Tc[dHc(T)dT]TcHc(0), γ[TcHc(0)]2, and experimental values for Nb3Al and Nb3Ge, presumably due to broadened transitions. It is argued that the tunneling experiments underestimate the value of the gap which should be associated with the inverted α2F.

Halo Formation During Solidification of Refractory Metal Aluminide Ternary Systems

NASA Astrophysics Data System (ADS)

D'Souza, N.; Feitosa, L. M.; West, G. D.; Dong, H. B.

2018-02-01

The evolution of eutectic morphologies following primary solidification has been studied in the refractory metal aluminide (Ta-Al-Fe, Nb-Al-Co, and Nb-Al-Fe) ternary systems. The undercooling accompanying solid growth, as related to the extended solute solubility in the primary and secondary phases can be used to account for the evolution of phase morphologies during ternary eutectic solidification. For small undercooling, the conditions of interfacial equilibrium remain valid, while in the case of significant undercooling when nucleation constraints occur, there is a departure from equilibrium leading to unexpected phases. In Ta-Al-Fe, an extended solubility of Fe in σ was observed, which was consistent with the formation of a halo of μ phase on primary σ. In Nb-Al-Co, a halo of C14 is formed on primary CoAl, but very limited vice versa. However, in the absence of a solidus projection it was not possible to definitively determine the extended solute solubility in the primary phase. In Nb-Al-Fe when nucleation constraints arise, the inability to initiate coupled growth of NbAl3 + C14 leads to the occurrence of a two-phase halo of C14 + Nb2Al, indicating a large undercooling and departure from equilibrium.

The crystal structure of lueshite at 298 K resolved by high-resolution time-of-flight neutron powder diffraction

NASA Astrophysics Data System (ADS)

Mitchell, Roger H.; Kennedy, Brendan J.; Knight, Kevin S.

2018-01-01

Refinement of time-of-flight high-resolution neutron powder diffraction data for lueshite (Na, Ca)(Nb, Ta, Ti)O3, the natural analogue of synthetic NaNbO3, demonstrates that lueshite at room temperature (298 K) adopts an orthorhombic structure with a 2 a p × 2 a p × 4 a p superlattice described by space group Pmmn [#59: a = 7.8032(4) Å; b = 7.8193(4) Å; c = 15.6156(9) Å]. This structure is analogous to that of phase S of synthetic NaNbO3 observed at 753-783 K (480-510 °C). In common with synthetic NaNbO3, lueshite exhibits a series of phase transitions with decreasing temperature from a cubic (Pm\\bar{3}m) aristotype through tetragonal ( P4/ mbm) and orthorhombic ( Cmcm) structures. However, the further sequence of phase transitions differs in that for lueshite the series terminates with the room temperature S ( Pmmn) phase, and the R ( Pmmn or Pnma) and P ( Pbcm) phases of NaNbO3 are not observed. The appearance of the S phase in lueshite at a lower temperature, relative to that of NaNbO3, is attributable to the effects of solid solution of Ti, Ta and Ca in lueshite.

Direct evidence on Ta-Metal Phases Igniting Resistive Switching in TaOx Thin Film

PubMed Central

Kyu Yang, Min; Ju, Hyunsu; Hwan Kim, Gun; Lee, Jeon-Kook; Ryu, Han-Cheol

2015-01-01

A Ta/TaOx/Pt stacked capacitor-like device for resistive switching was fabricated and examined. The tested device demonstrated stable resistive switching characteristics including uniform distribution of resistive switching operational parameters, highly promising endurance, and retention properties. To reveal the resistive switching mechanism of the device, micro structure analysis using high-resolution transmission electron microscope (HR-TEM) was performed. From the observation results, two different phases of Ta-metal clusters of cubic α-Ta and tetragonal β-Ta were founded in the amorphous TaOx mother-matrix after the device was switched from high resistance state (HRS) to low resistance state (LRS) by externally applied voltage bias. The observed Ta metal clusters unveiled the origin of the electric conduction paths in the TaOx thin film at the LRS. PMID:26365532

Direct evidence on Ta-Metal Phases Igniting Resistive Switching in TaOx Thin Film

NASA Astrophysics Data System (ADS)

Kyu Yang, Min; Ju, Hyunsu; Hwan Kim, Gun; Lee, Jeon-Kook; Ryu, Han-Cheol

2015-09-01

A Ta/TaOx/Pt stacked capacitor-like device for resistive switching was fabricated and examined. The tested device demonstrated stable resistive switching characteristics including uniform distribution of resistive switching operational parameters, highly promising endurance, and retention properties. To reveal the resistive switching mechanism of the device, micro structure analysis using high-resolution transmission electron microscope (HR-TEM) was performed. From the observation results, two different phases of Ta-metal clusters of cubic α-Ta and tetragonal β-Ta were founded in the amorphous TaOx mother-matrix after the device was switched from high resistance state (HRS) to low resistance state (LRS) by externally applied voltage bias. The observed Ta metal clusters unveiled the origin of the electric conduction paths in the TaOx thin film at the LRS.

Crystal structure and superconducting properties of KSr2Nb3O10

NASA Astrophysics Data System (ADS)

Kawaguchi, T.; Horigane, K.; Itoh, Y.; Kobayashi, K.; Horie, R.; Kambe, T.; Akimitsu, J.

2018-05-01

We performed X-ray diffraction (XRD) and DC magnetic susceptibility measurements to elucidate the crystal structure and superconducting properties of KSr2Nb3O10. From the diffraction pattern indexing, it was found that KSr2Nb3O10 crystallizes with monoclinic symmetry, space group P21/m(11). We succeeded in preparing high temperature (HT) and low temperature (LT) phases of KSr2Nb3O10 powder samples synthesized by a conventional solid state reaction and an ion-exchange reaction, respectively. Superconductivity was observed at 4 K by Li intercalation and it was found that the superconducting volume fraction of the LT phase ( 1.4%) is clearly larger than that of the HT phase (0.07%).

B-site cation order/disorder and their valence states in Ba3MnNb2O9 perovskite oxide

NASA Astrophysics Data System (ADS)

Xin, Yan; Huang, Qing; Shafieizadeh, Zahra; Zhou, Haidong

2018-06-01

Polycrystalline samples Ba3MnNb2O9 synthesized by solid state reaction and single crystal samples grown by optical floating zone have been characterized using scanning transmission electron microscopy and electron energy loss spectroscopy. Three types of B-site Mn and Nb ordering phase are observed: fully ordered 1Mn:2Nb; fully disordered; nano-sized 1Mn:1Nb ordered. No electronic structure change for crystals with different ordering/disordering. The Mn valence is determined to be 2+, and Nb valence is 5+. Oxygen 2p orbitals hybridize with Mn 3d and Nb 4d orbitals. Factors that affect the electron energy loss near edge structures of transition metal white-lines in electron energy loss spectroscopy are explicitly illustrated and discussed.

The use of solid lipid nanoparticles to target a lipophilic molecule to the liver after intravenous administration to mice.

PubMed

Lu, Wen; He, Lang Chong; Wang, Chang He; Li, Yan Hua; Zhang, San Qi

2008-10-01

Taspine solid lipid nanoparticles (Ta-SLN) and taspine solid lipid nanoparticles modified by galactoside (Ta-G2SLN) were prepared by the film evaporation-extrusion method. The nanoparticles were spherical or near-spherical particles with smooth surface, small size and high encapsulation efficiency. Ta-G2SLN and Ta-SLN showed significant inhibition on 7721 cell growth. Intravenous injection of either Ta-SLN or Ta-G2SLN resulted in a higher plasma and liver concentration and a longer retention time in mice compared with the administration of Ta. These results suggested that SLN tended to be preferentially delivered to the liver and Ta-G2SLN may further enhance liver targeting.

A niobium and tantalum co-doped perovskite cathode for solid oxide fuel cells operating below 500 °C

PubMed Central

Li, Mengran; Zhao, Mingwen; Li, Feng; Zhou, Wei; Peterson, Vanessa K.; Xu, Xiaoyong; Shao, Zongping; Gentle, Ian; Zhu, Zhonghua

2017-01-01

The slow activity of cathode materials is one of the most significant barriers to realizing the operation of solid oxide fuel cells below 500 °C. Here we report a niobium and tantalum co-substituted perovskite SrCo0.8Nb0.1Ta0.1O3−δ as a cathode, which exhibits high electroactivity. This cathode has an area-specific polarization resistance as low as ∼0.16 and ∼0.68 Ω cm2 in a symmetrical cell and peak power densities of 1.2 and 0.7 W cm−2 in a Gd0.1Ce0.9O1.95-based anode-supported fuel cell at 500 and 450 °C, respectively. The high performance is attributed to an optimal balance of oxygen vacancies, ionic mobility and surface electron transfer as promoted by the synergistic effects of the niobium and tantalum. This work also points to an effective strategy in the design of cathodes for low-temperature solid oxide fuel cells. PMID:28045088

Direct solid analysis of powdered tungsten carbide hardmetal precursors by laser-induced argon spark ablation with inductively coupled plasma atomic emission spectrometry.

PubMed

Holá, Markéta; Kanický, Viktor; Mermet, Jean-Michel; Otruba, Vítezslav

2003-12-01

The potential of the laser-induced argon spark atomizer (LINA-Spark atomizer) coupled with ICP-AES as a convenient device for direct analysis of WC/Co powdered precursors of sintered hardmetals was studied. The samples were presented for the ablation as pressed pellets prepared by mixing with powdered silver binder containing GeO2 as internal standard. The pellets were ablated with the aid of a Q-switched Nd:YAG laser (1064 nm) focused 16 mm behind the target surface with a resulting estimated power density of 5 GW cm(-2). Laser ablation ICP-AES signals were studied as a function of ablation time, and the duration of time prior to measurement (pre-ablation time) which was necessary to obtain reliable results was about 40 s. Linear calibration plots were obtained up to 10% (m/m) Ti, 9% Ta and 3.5% Nb both without internal standardization and by using germanium as an added internal standard or tungsten as a contained internal standard. The relative uncertainty at the centroid of the calibration line was in the range from +/- 6% to +/- 11% for Nb, Ta and Ti both with and without internal standardisation by Ge. A higher spread of points about the regression was observed for cobalt for which the relative uncertainty at the centroid was in the range from +/- 9% to +/- 14%. Repeatability of results was improved by the use of both Ge and W internal standards. The lowest determinable quantities calculated for calibration plots were 0.060% Co, 0.010% Nb, 0.16% Ta and 0.030% Ti with internal standardization by Ge. The LA-ICP-AES analyses of real samples led to good agreement with the results obtained by solution-based ICP determination with a relative bias not exceeding 10%. The elimination of the dissolution procedure of powdered tungsten (Nb, Ta, Ti) carbide is the principal advantage of the developed LA-ICP-AES method.

Computational studies of physical properties of Nb-Si based alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ouyang, Lizhi

2015-04-16

The overall goal is to provide physical properties data supplementing experiments for thermodynamic modeling and other simulations such as phase filed simulation for microstructure and continuum simulations for mechanical properties. These predictive computational modeling and simulations may yield insights that can be used to guide materials design, processing, and manufacture. Ultimately, they may lead to usable Nb-Si based alloy which could play an important role in current plight towards greener energy. The main objectives of the proposed projects are: (1) developing a first principles method based supercell approach for calculating thermodynamic and mechanic properties of ordered crystals and disordered latticesmore » including solid solution; (2) application of the supercell approach to Nb-Si base alloy to compute physical properties data that can be used for thermodynamic modeling and other simulations to guide the optimal design of Nb-Si based alloy.« less

AlNbO oxides as new supports for hydrocarbon oxidation II. Catalytic properties of VO sub x -grafted AlNbO oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oliveira, P.G. Pries de; Eon, J.G.; Volta, J.C.

1992-09-01

Vanadium oxides were immobilized by grafting VOCl{sub 3} on AlNbO oxides calcined between 500 and 750 C. Chemical analysis, XPS, and STEM measurements suggest an incomplete but homogeneous stoichiometric reaction between superficial hydroxyl groups and vanadyl oxychloride. By FTIR studies, it is observed that the interaction involves preferentially basic hydroxyl groups bonded to aluminium cations. UV-visible spectra show that mainly V{sup 5+} is present at the solid surface. Corresponding spectra are compatible with tetrahedral symmetry, in agreement with a previous {sup 51}V NMR investigation. The acido-basic properties of the catalyst were tested by isopropanol decomposition and compared with the correspondingmore » supports. It has been observed that basicity is higher for VO{sub x} grafted on AlBnO oxide calcined at high temperature and corresponding to the AlNbO{sub 4} structure. VO{sub x} grafted on AlNbO oxides calcined at intermediate temperatures and corresponding to a AlNbO disorganized structure present a good selectivity for the oxidative dehydrogenation of propane into propene. It has been observed that, for both reactions, the turnover number increases with the temperature of calcination of the catalysts. The reactivity of the aluminium niobiate support.« less

Effect of manganese doping on remnant polarization and leakage current in (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 epitaxial thin films on SrTiO3

NASA Astrophysics Data System (ADS)

Abazari, M.; Akdoǧan, E. K.; Safari, A.

2008-05-01

Single phase, epitaxial, ⟨001⟩ oriented, undoped and 1mol% Mn-doped (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films of 400nm thickness were synthesized on SrRuO3 coated SrTiO3. Such films exhibit well saturated hysteresis loops and have a spontaneous polarization (Ps) of 10μC /cm2, which is a 150% higher over the Ps of the undoped composition. The coercive field of 1mol% Mn doped films is 13kV/cm. Mn-doping results in three orders of magnitude decrease in leakage current above 50kV/cm electric field, which we attribute to the suppression of intrinsic p-type conductivity of undoped films by Mn donors.

Synthesis, processing and properties of TaC-TaB2-C Ceramics

DTIC Science & Technology

2010-01-01

powder used. • A very important conclusion from the present study is that the grain size of nominally pure TaC ceramics is a strong function of carbon...ceramics at temperatures as low as 1500 ◦C. The grain size of nominally pure TaC ceramics was a strong function of carbon stoichiometry. Enhanced grain...evaluate the properties of ceramics in the TaC–TaB2–C system. Published by Elsevier Ltd. Keywords: A . Sintering; B. Microstructure; D. Carbides; D. Carbon

Experimental partitioning of Zr, Ti, and Nb between silicate liquid and a complex noble metal alloy and the partitioning of Ti between perovskite and platinum metal

NASA Technical Reports Server (NTRS)

Jurewicz, Stephen R.; Jones, John H.

1993-01-01

El Goresy et al.'s observation of Nb, Zr, and Ta in refractory platinum metal nuggets (RPMN's) from Ca-Al-rich inclusions (CAI's) in the Allende meteorite led them to propose that these lithophile elements alloyed in the metallic state with noble metals in the early solar nebula. However, Grossman pointed out that the thermodynamic stability of Zr in the oxide phase is vastly greater than metallic Zr at estimated solar nebula conditions. Jones and Burnett suggested this discrepancy may be explained by the very non-ideal behavior of some lithophile transition elements in noble metal solutions and/or intermetallic compounds. Subsequently, Fegley and Kornacki used thermodynamic data taken from the literature to predict the stability of several of these intermetallic compounds at estimated solar nebula conditions. Palme and Schmitt and Treiman et al. conducted experiments to quantify the partitioning behavior of certain lithophile elements between silicate liquid and Pt-metal. Although their results were somewhat variable, they did suggest that Zr partition coefficients were too small to explain the observed 'percent' levels in some RPMN's. Palme and Schmitt also observed large partition coefficients for Nb and Ta. No intermetallic phases were identified. Following the work of Treiman et al., Jurewicz and Jones performed experiments to examine Zr, Nb, and Ti partitioning near solar nebula conditions. Their results showed that Zr, Nb, and Ti all have an affinity for the platinum metal, with Nb and Ti having a very strong preference for the metal. The intermetallic phases (Zr,Fe)Pt3, (Nb,Fe)Pt3, and (Ti,Fe)Pt3 were identified. Curiously, although both experiments and calculations indicate that Ti should partition strongly into Pt-metal (possibly as TiPt3), no Ti has ever been observed in any RPMN's. Fegley and Kornacki also noticed this discrepancy and hypothesized that the Ti was stabilized in perovskite which is a common phase in Allende CAI's.

Strength design of Zr(x)Ti(x)Hf(x)Nb(x)Mo(x) alloys based on empirical electron theory of solids and molecules

NASA Astrophysics Data System (ADS)

Li, Y. K.; Chen, Y. W.; Cheng, X. W.; Wu, C.; Cheng, B.

2018-05-01

In this paper, the valence electron structure parameters of Zr(x)Ti(x)Hf(x)Nb(x)Mo(x) alloys were calculated based on the empirical electron theory of solids and molecules (EET), and their performance through these parameters were predicted. Subsequently, the alloys with special valence electron structure parameters were prepared byarc melting. The hardness and high-temperature mechanical properties were analyzed to verify the prediction. Research shows that the influence of shared electron number nA on the strongest bond determines the strength of these alloys and the experiments are consistent with the theoretical prediction.

Synthesis of Ti-Ta alloys with dual structure by incomplete diffusion between elemental powders.

PubMed

Liu, Yong; Li, Kaiyang; Wu, Hong; Song, Min; Wang, Wen; Li, Nianfeng; Tang, Huiping

2015-11-01

In this work, powder metallurgical (PM) Ti-Ta alloys were sintered using blended elemental powders. A dual structure, consisting of Ti-rich and Ta-rich zones, was formed due to the insufficient diffusion between Ti and Ta powders. The microstructure, mechanical properties and in vitro biological properties of the alloys were studied. Results indicated that the alloys have inhomogenous microstructures and compositions, but the grain structures were continuous from the Ti-rich zone to the Ta-rich zone. The Ta-rich zone exhibited a much finer grain size than the Ti-rich zone. The alloys had a high relative density in the range of 95-98%, with the porosity increasing with the content of Ta due to the increased difficulty in sintering and the formation of Kirkendall pores. The alloys had a good combination of low elastic modulus and high tensile strength. The strength of alloys was almost doubled compared to that of the ingot metallurgy alloys with the same compositions. The low elastic modulus was due to the residual pores and the alloying effect of Ta, while the high tensile strength resulted from the strengthening effects of solid solution, fine grain size and α phase. The alloys had a high biocompatibility due to the addition of Ta, and were suitable for the attachment of cells due to the surface porosity. It was also indicated that PM Ti-(20-30)Ta alloys are promising for biomedical applications after the evaluations of both the mechanical and the biological properties. Copyright © 2015 Elsevier Ltd. All rights reserved.

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Federal Register 2010, 2011, 2012, 2013, 2014

2010-07-26

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(Nbx, Zr1-x)4AlC3 MAX Phase Solid Solutions: Processing, Mechanical Properties, and Density Functional Theory Calculations.

PubMed

Lapauw, Thomas; Tytko, Darius; Vanmeensel, Kim; Huang, Shuigen; Choi, Pyuck-Pa; Raabe, Dierk; Caspi, El'ad N; Ozeri, Offir; To Baben, Moritz; Schneider, Jochen M; Lambrinou, Konstantina; Vleugels, Jozef

2016-06-06

The solubility of zirconium (Zr) in the Nb4AlC3 host lattice was investigated by combining the experimental synthesis of (Nbx, Zr1-x)4AlC3 solid solutions with density functional theory calculations. High-purity solid solutions were prepared by reactive hot pressing of NbH0.89, ZrH2, Al, and C starting powder mixtures. The crystal structure of the produced solid solutions was determined using X-ray and neutron diffraction. The limited Zr solubility (maximum of 18.5% of the Nb content in the host lattice) in Nb4AlC3 observed experimentally is consistent with the calculated minimum in the energy of mixing. The lattice parameters and microstructure were evaluated over the entire solubility range, while the chemical composition of (Nb0.85, Zr0.15)4AlC3 was mapped using atom probe tomography. The hardness, Young's modulus, and fracture toughness at room temperature as well as the high-temperature flexural strength and E-modulus of (Nb0.85, Zr0.15)4AlC3 were investigated and compared to those of pure Nb4AlC3. Quite remarkably, an appreciable increase in fracture toughness was observed from 6.6 ± 0.1 MPa/m(1/2) for pure Nb4AlC3 to 10.1 ± 0.3 MPa/m(1/2) for the (Nb0.85, Zr0.15)4AlC3 solid solution.

Limited Range Sesame EOS for Ta

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greeff, Carl William; Crockett, Scott; Rudin, Sven Peter

2017-03-30

A new Sesame EOS table for Ta has been released for testing. It is a limited range table covering T ≤ 26, 000 K and ρ ≤ 37.53 g/cc. The EOS is based on earlier analysis using DFT phonon calculations to infer the cold pressure from the Hugoniot. The cold curve has been extended into compression using new DFT calculations. The present EOS covers expansion into the gas phase. It is a multi-phase EOS with distinct liquid and solid phases. A cold shear modulus table (431) is included. This is based on an analytic interpolation of DFT calculations.

Microstructure of rapidly solidified Nb-based pre-alloyed powders for additive manufacturing

NASA Astrophysics Data System (ADS)

Guo, Yueling; Jia, Lina; Kong, Bin; Zhang, Shengnan; Zhang, Fengxiang; Zhang, Hu

2017-07-01

For powder-based additive manufacturing, sphere-shaped Nb-37Ti-13Cr-2Al-1Si pre-alloyed powders were prepared by plasma rotating electrode processing (PREP). The microstructure, surface oxidation and microhardness of the pre-alloyed powders were systematically investigated. Results showed that the main phases were Nb solid solution (Nbss) and Cr2Nb. The Cr2Nb phases were further determined using transmission electron microscopy (TEM). Fine dendrite structures were observed in the as-fabricated pre-alloyed powders, which transformed to large grains after heat treatment (HT) at 1450 °C for 3 h. With the increase of powder size, the secondary dendrite arm spacing (SDAS) increased and the microhardness (HV) decreased. A clean powder surface free of oxide particles was obtained by PREP and an oxide layer with 9.39 nm in thickness was generated on the powder surface. Compared with Cr- and Nb-oxides, more Ti-oxides were formed on outmost powder surface with a higher content of Ti (up to 47.86 at.%). The differences upon the microstructure and microhardness of the pre-alloyed powders with different sizes were discussed.

Crystal structure and optical property of complex perovskite oxynitrides ALi0.2Nb0.8O2.8N0.2, ANa0.2Nb0.8O2.8N0.2, and AMg0.2Nb0.8O2.6N0.4 (A = Sr, Ba)

NASA Astrophysics Data System (ADS)

Moon, Keon Ho; Avdeev, Maxim; Kim, Young-Il

2017-10-01

Oxynitride type complex perovskites AM0.2Nb0.8O3-xNx (A = Sr, Ba; M = Li, Na, Mg) were newly synthesized by the solid state diffusion of Li+, Na+, or Mg2+ into the layered oxide, A5Nb4O15, with concurrent O/N substitution. Neutron and synchrotron X-ray Rietveld refinement showed that SrLi0.2Nb0.8O2.8N0.2, SrNa0.2Nb0.8O2.8N0.2, and SrMg0.2Nb0.8O2.6N0.4 had body-centered tetragonal symmetry (I4/mcm), while those with A = Ba had simple cubic symmetry (Pm 3 ̅ m). In the tetragonal Sr-compounds, the nitrogen atoms were localized on the c-axial 4a site. However, the octahedral cations, M/Nb (M = Li, Na, Mg) were distributed randomly in all six compounds. The lattice volume of AM0.2Nb0.8O3-xNx was dependent on various factors including the type of A and the electronegativity of M. Compared to the simple perovskites, ANbO2N (A = Sr, Ba), AM0.2Nb0.8O3-xNx had wider band gaps (1.76-2.15 eV for A = Sr and 1.65-2.10 eV for A = Ba), but significantly lower sub-gap absorption.

Alkali oxide-tantalum oxide and alkali oxide-niobium oxide ionic conductors

NASA Technical Reports Server (NTRS)

Roth, R. S.; Parker, H. S.; Brower, W. S.; Minor, D.

1974-01-01

A search was made for new cationic conducting phases in alkali-tantalate and niobate systems. The phase equilibrium diagrams were constructed for the six binary systems Nb2O5-LiNbO3, Nb2O5-NaNbO3, Nb2O5-KNbO3, Ta2O5-NaTaO3, Ta2O5-LiTaO3, and Ta2O5-KTaO3. Various other binary and ternary systems were also examined. Pellets of nineteen phases were evaluated (by the sponsoring agency) by dielectric loss measurements. Attempts were made to grow large crystals of eight different phases. The system Ta2O5-KTaO3 contains at least three phases which showed peaks in dielectric loss vs. temperature. All three contain structures related to the tungsten bronzes with alkali ions in non-stoichiometric crystallographic positions.

Strategy for stabilization of the antiferroelectric phase (Pbma) over the metastable ferroelectric phase (P2{sub 1}ma) to establish double loop hysteresis in lead-free (1−x)NaNbO{sub 3}-xSrZrO{sub 3} solid solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Hanzheng, E-mail: hug17@psu.edu; Randall, Clive A.; Shimizu, Hiroyuki

A new lead-free antiferroelectric solid solution system, (1−x)NaNbO{sub 3}-xSrZrO{sub 3}, was rationalized through noting the crystal chemistry trend, of decreasing the tolerance factor and an increase in the average electronegativity of the system. The SrZrO{sub 3} doping was found to effectively stabilize the antiferroelectric (P) phase in NaNbO{sub 3} without changing its crystal symmetry. Preliminary electron diffraction and polarization measurements were presented which verified the enhanced antiferroelectricity. In view of our recent report of another lead-free antiferroelectric system (1−x)NaNbO{sub 3}-xCaZrO{sub 3} [H. Shimizu et al. “Lead-free antiferroelectric: xCaZrO{sub 3} - (1−x)NaNbO{sub 3} system (0 ≤ x ≤ 0.10),” Dalton Trans.more » (published online)], the present results point to a general strategy of utilizing tolerance factor to develop a broad family of new lead-free antiferroelectrics with double polarization hysteresis loops. We also speculate on a broad family of possible solid solutions that could be identified and tested for this important type of dielectric.« less

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

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

PubMed

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

2008-04-07

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

Green synthesis of Ni-Nb oxide catalysts for low-temperature oxidative dehydrogenation of ethane.

PubMed

Zhu, Haibo; Rosenfeld, Devon C; Anjum, Dalaver H; Caps, Valérie; Basset, Jean-Marie

2015-04-13

The straightforward solid-state grinding of a mixture of Ni nitrate and Nb oxalate crystals led to, after mild calcination (T<400 °C), nanostructured Ni-Nb oxide composites. These new materials efficiently catalyzed the oxidative dehydrogenation (ODH) of ethane to ethylene at a relatively low temperature (T<300 °C). These catalysts appear to be much more stable than the corresponding composites prepared by other chemical methods; more than 90 % of their original intrinsic activity was retained after 50 h with time on-stream. Furthermore, the stability was much less affected by the Nb content than in composites prepared by classical "wet" syntheses. These materials, obtained in a solvent-free way, are thus promising green and sustainable alternatives to the current Ni-Nb candidates for the low-temperature ODH of ethane. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis and visible light photocatalytic property of polyhedron-shaped AgNbO3.

PubMed

Li, Guoqiang; Yan, Shicheng; Wang, Zhiqiang; Wang, Xiangyan; Li, Zhaosheng; Ye, Jinhua; Zou, Zhigang

2009-10-28

Polyhedron-shaped AgNbO3 photocatalysts were synthesized by solvothermal and liquid-solid methods. Their photocatalytic properties were evaluated from the photocatalytic O2 evolution under visible light irradiation. The polyhedron-shaped AgNbO3 was induced to grow by shaped silver particles followed by the free-growth model. The photocatalytic results indicate that the polyhedron-shaped morphology is favourable for the photocatalytic O2 evolution under visible light irradiation in comparison with the spherical one. Furthermore, the Cu doping on the surface would enhance the visible light photocatalytic activity significantly.

Effects of background oxygen pressure on dielectric and ferroelectric properties of epitaxial (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films on SrTiO3

NASA Astrophysics Data System (ADS)

Abazari, M.; Akdoǧan, E. K.; Safari, A.

2008-11-01

Oxygen partial pressure (PO_2) in pulsed laser deposition significantly influences the composition, microstructure, and electrical properties of epitaxial misfit strain-relieved 450nm ⟨001⟩ oriented epitaxial (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films on SrRuO3 coated SrTiO3. Films deposited at 400mTorr exhibit high remnant and saturated polarization of 7.5 and 16.5μC /cm2, respectively, which is ˜100% increase over the ones grown at 100mTorr. The dielectric constant linearly increases from 220 to 450 with increasing PO2. The observed changes in surface morphology of the films and their properties are shown to be due to the suppression of volatile A-site cation loss.

A 93Nb solid-state NMR and density functional theory study of four- and six-coordinate niobate systems.

PubMed

Hanna, John V; Pike, Kevin J; Charpentier, Thibault; Kemp, Thomas F; Smith, Mark E; Lucier, Bryan E G; Schurko, Robert W; Cahill, Lindsay S

2010-03-08

A variable B(0) field static (broadline) NMR study of a large suite of niobate materials has enabled the elucidation of high-precision measurement of (93)Nb NMR interaction parameters such as the isotropic chemical shift (delta(iso)), quadrupole coupling constant and asymmetry parameter (C(Q) and eta(Q)), chemical shift span/anisotropy and skew/asymmetry (Omega/Deltadelta and kappa/eta(delta)) and Euler angles (alpha, beta, gamma) describing the relative orientation of the quadrupolar and chemical shift tensorial frames. These measurements have been augmented with ab initio DFT calculations by using WIEN2k and NMR-CASTEP codes, which corroborate these reported values. Unlike previous assertions made about the inability to detect CSA (chemical shift anisotropy) contributions from Nb(V) in most oxo environments, this study emphasises that a thorough variable B(0) approach coupled with the VOCS (variable offset cumulative spectroscopy) technique for the acquisition of undistorted broad (-1/2<-->+1/2) central transition resonances facilitates the unambiguous observation of both quadrupolar and CSA contributions within these (93)Nb broadline data. These measurements reveal that the (93)Nb electric field gradient tensor is a particularly sensitive measure of the immediate and extended environments of the Nb(V) positions, with C(Q) values in the 0 to >80 MHz range being measured; similarly, the delta(iso) (covering an approximately 250 ppm range) and Omega values (covering a 0 to approximately 800 ppm range) characteristic of these niobate systems are also sensitive to structural disposition. However, their systematic rationalisation in terms of the Nb-O bond angles and distances defining the immediate Nb(V) oxo environment is complicated by longer-range influences that usually involve other heavy elements comprising the structure. It has also been established in this study that the best computational method(s) of analysis for the (93)Nb NMR interaction parameters

A study of nitrogen behavior in the formation of Ta/TaN and Ti/TaN alloyed metal electrodes on SiO2 and HfO2 dielectrics

NASA Astrophysics Data System (ADS)

Gassilloud, R.; Maunoury, C.; Leroux, C.; Piallat, F.; Saidi, B.; Martin, F.; Maitrejean, S.

2014-04-01

We studied Ta, TaN, and sub-stoichiometric TaNx electrodes (obtained by nitrogen redistribution in Ta/TaN or Ti/TaN bilayers) deposited on thermal SiO2 and HfO2/IL (0.8 nm SiO2 IL, i.e., interlayer) stacks. Effective work-functions (WF) were extracted on MOS capacitor structures on SiO2 bevelled insulator of 4.2 eV for pure Ta, 4.6 eV for TaN, and 4.3 eV for sub-stoichiometric TaNx. This intermediate WF value is explained by TaN nitrogen redistribution with reactive Ta or Ti elements shifting the gate work-function toward the Si conduction band. The same electrodes deposited on an HfO2/IL dielectric showed different behavior: First, the Ta/HfO2/IL stack shows a +200 meV WF increase (towards the Si valence band) compared to the SiO2 dielectric stack. This increase is explained by the well-known HfO2/IL dipole formation. Second, in contrast to electrodes deposited on SiO2, sub-stoichiometric TaNx/HfO2 is found to have a lower WF (4.3 eV), than pure Ta on HfO2 (4.4 eV). This inversion in work-function behavior measured on SiO2 vs. HfO2 is explained by the nitrogen redistribution in Ta/TaN bilayer together with diffusion of nitrogen through the HfO2 layer, leading to Si-N formation which prevents dipole formation at the HfO2/IL interface.

Effects of oxygen deficiency on the transport and dielectric properties of NdSrNbO

NASA Astrophysics Data System (ADS)

Hzez, W.; Benali, A.; Rahmouni, H.; Dhahri, E.; Khirouni, K.; Costa, B. F. O.

2018-06-01

In the present study, Nd0.7Sr0.3NbO3-y (y = 0.1, 0.15, 0.2) compounds were prepared via a solid-solid reaction route. The prepared samples were characterized by electrochemical impedance spectroscopy in order to establish the effects of temperature, frequency, and oxygen vacancies on both the transport and dielectric properties of NdSrNbO. We found that both the electrical and dielectric properties were highly sensitive to the concentration of oxygen vacancies. The conduction mechanism data were explained well according to the Mott model and adiabatic small polaronic hopping model. Electrochemical impedance spectroscopy analysis showed that one relaxation process was present in the Nd0.7Sr0.3NbO2.9 system whereas two relaxation processes were observed in the Nd0.7Sr0.3NbO2.85 and Nd0.7Sr0.3NbO2.8 systems, where the latter behavior indicated the presence of many active regions (due to the contributions of different microstructures). The temperature and frequency dependences of the dielectric constant confirmed the contributions of different polarization mechanisms. In particular, the high dielectric constant values at low frequencies and high temperatures were mainly related to the presence of different Schottky barriers, whereas the low dielectric constant values at high frequencies were essentially related to the intrinsic effect. The constant dielectric values obtained for the samples are greater than those in the NdSrFeO system, which makes them interesting materials for use in applications that require high dielectric constants.

On Nb Silicide Based Alloys: Alloy Design and Selection.

PubMed

Tsakiropoulos, Panos

2018-05-18

The development of Nb-silicide based alloys is frustrated by the lack of composition-process-microstructure-property data for the new alloys, and by the shortage of and/or disagreement between thermodynamic data for key binary and ternary systems that are essential for designing (selecting) alloys to meet property goals. Recent publications have discussed the importance of the parameters δ (related to atomic size), Δχ (related to electronegativity) and valence electron concentration (VEC) (number of valence electrons per atom filled into the valence band) for the alloying behavior of Nb-silicide based alloys (J Alloys Compd 748 (2018) 569), their solid solutions (J Alloys Compd 708 (2017) 961), the tetragonal Nb₅Si₃ (Materials 11 (2018) 69), and hexagonal C14-NbCr₂ and cubic A15-Nb₃X phases (Materials 11 (2018) 395) and eutectics with Nb ss and Nb₅Si₃ (Materials 11 (2018) 592). The parameter values were calculated using actual compositions for alloys, their phases and eutectics. This paper is about the relationships that exist between the alloy parameters δ, Δχ and VEC, and creep rate and isothermal oxidation (weight gain) and the concentrations of solute elements in the alloys. Different approaches to alloy design (selection) that use property goals and these relationships for Nb-silicide based alloys are discussed and examples of selected alloy compositions and their predicted properties are given. The alloy design methodology, which has been called NICE (Niobium Intermetallic Composite Elaboration), enables one to design (select) new alloys and to predict their creep and oxidation properties and the macrosegregation of Si in cast alloys.

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

NASA Technical Reports Server (NTRS)

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

2004-01-01

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

78 FR 28627 - TA-W-80,340; TA-W-80,340A; TA-W-80,340B

Federal Register 2010, 2011, 2012, 2013, 2014

2013-05-15

...] Bush Industries, Inc., Mason Drive Facility, Including On-Site Leased Workers From Morris Security...., Mason Drive Facility, Jamestown, New York (TA-W-80,340) and Bush Industries, Inc., Allen Street Facility... applicable to TA-W-80,340 is hereby issued as follows: All workers of Bush Industries, Inc., Mason Drive...

Protective interlayer for high temperature solid electrolyte electrochemical cells

DOEpatents

Singh, P.; Vasilow, T.R.; Richards, V.L.

1996-05-14

The invention is comprised of an electrically conducting doped or admixed cerium oxide composition with niobium oxide and/or tantalum oxide for electrochemical devices, characterized by the general formula: Nb{sub x}Ta{sub y}Ce{sub 1{minus}x{minus}y}O{sub 2} where x is about 0.0 to 0.05, y is about 0.0 to 0.05, and x+y is about 0.02 to 0.05, and where x is preferably about 0.02 to 0.05 and y is 0, and a method of making the same is also described. This novel composition is particularly applicable in forming a protective interlayer of a high temperature, solid electrolyte electrochemical cell, characterized by a first electrode; an electrically conductive interlayer of niobium and/or tantalum doped cerium oxide deposited over at least a first portion of the first electrode; an interconnect deposited over the interlayer; a solid electrolyte deposited over a second portion of the first electrode, the first portion being discontinuous from the second portion; and, a second electrode deposited over the solid electrolyte. The interlayer is characterized as being porous and selected from the group consisting of niobium doped cerium oxide, tantalum doped cerium oxide, and niobium and tantalum doped cerium oxide or admixtures of the same. The first electrode, an air electrode, is a porous layer of doped lanthanum manganite, the solid electrolyte layer is a dense yttria stabilized zirconium oxide, the interconnect layer is a dense, doped lanthanum chromite, and the second electrode, a fuel electrode, is a porous layer of nickel-zirconium oxide cermet. The electrochemical cell can take on a plurality of shapes such as annular, planar, etc. and can be connected to a plurality of electrochemical cells in series and/or in parallel to generate electrical energy. 5 figs.

Protective interlayer for high temperature solid electrolyte electrochemical cells

DOEpatents

Singh, Prabhakar; Vasilow, Theodore R.; Richards, Von L.

1996-01-01

The invention comprises of an electrically conducting doped or admixed cerium oxide composition with niobium oxide and/or tantalum oxide for electrochemical devices, characterized by the general formula: Nb.sub.x Ta.sub.y Ce.sub.1-x-y O.sub.2 where x is about 0.0 to 0.05, y is about 0.0 to 0.05, and x+y is about 0.02 to 0.05, and where x is preferably about 0.02 to 0.05 and y is 0, and a method of making the same. This novel composition is particularly applicable in forming a protective interlayer of a high temperature, solid electrolyte electrochemical cell (10), characterized by a first electrode (12); an electrically conductive interlayer (14) of niobium and/or tantalum doped cerium oxide deposited over at least a first portion (R) of the first electrode; an interconnect (16) deposited over the interlayer; a solid electrolyte (18) deposited over a second portion of the first electrode, the first portion being discontinuous from the second portion; and, a second electrode (20) deposited over the solid electrolyte. The interlayer (14) is characterized as being porous and selected from the group consisting of niobium doped cerium oxide, tantalum doped cerium oxide, and niobium and tantalum doped cerium oxide or admixtures of the same. The first electrode (12), an air electrode, is a porous layer of doped lanthanum manganite, the solid electrolyte layer (18) is a dense yttria stabilized zirconium oxide, the interconnect layer (16) is a dense, doped lanthanum chromite, and the second electrode (20), a fuel electrode, is a porous layer of nickel-zirconium oxide cermet. The electrochemical cell (10) can take on a plurality of shapes such as annular, planar, etc. and can be connected to a plurality of electrochemical cells in series and/or in parallel to generate electrical energy.

Drought-Up-Regulated TaNAC69-1 is a Transcriptional Repressor of TaSHY2 and TaIAA7, and Enhances Root Length and Biomass in Wheat.

PubMed

Chen, Dandan; Richardson, Terese; Chai, Shoucheng; Lynne McIntyre, C; Rae, Anne L; Xue, Gang-Ping

2016-10-01

A well-known physiological adaptation process of plants encountering drying soil is to achieve water balance by reducing shoot growth and maintaining or promoting root elongation, but little is known about the molecular basis of this process. This study investigated the role of a drought-up-regulated Triticum aestivum NAC69-1 (TaNAC69-1) in the modulation of root growth in wheat. TaNAC69-1 was predominantly expressed in wheat roots at the early vegetative stage. Overexpression of TaNAC69-1 in wheat roots using OsRSP3 (essentially root-specific) and OsPIP2;3 (root-predominant) promoters resulted in enhanced primary seminal root length and a marked increase in maturity root biomass. Competitive growth analysis under water-limited conditions showed that OsRSP3 promoter-driven TaNAC69-1 transgenic lines produced 32% and 35% more above-ground biomass and grains than wild-type plants, respectively. TaNAC69-1 overexpression in the roots down-regulated the expression of TaSHY2 and TaIAA7, which are from the auxin/IAA (Aux/IAA) transcriptional repressor gene family and are the homologs of negative root growth regulators SHY2/IAA3 and IAA7 in Arabidopsis. The expression of TaSHY2 and TaIAA7 in roots was down-regulated by drought stress and up-regulated by cytokinin treatment, which inhibited root growth. DNA binding and transient expression analyses revealed that TaNAC69-1 bound to the promoters of TaSHY2 and TaIAA7, acted as a transcriptional repressor and repressed the expression of reporter genes driven by the TaSHY2 or TaIAA7 promoter. These data suggest that TaNAC69-1 is a transcriptional repressor of TaSHY2 and TaIAA7 homologous to Arabidopsis negative root growth regulators and is likely to be involved in promoting root elongation in drying soil. © The Author 2016. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.

Nb-Based Nb-Al-Fe Alloys: Solidification Behavior and High-Temperature Phase Equilibria

NASA Astrophysics Data System (ADS)

Stein, Frank; Philips, Noah

2018-03-01

High-melting Nb-based alloys hold significant promise for the development of novel high-temperature materials for structural applications. In order to understand the effect of alloying elements Al and Fe, the Nb-rich part of the ternary Nb-Al-Fe system was investigated. A series of Nb-rich ternary alloys were synthesized from high-purity Nb, Al, and Fe metals by arc melting. Solidification paths were identified and the liquidus surface of the Nb corner of the ternary system was established by analysis of the as-melted microstructures and thermal analysis. Complementary analysis of heat-treated samples yielded isothermal sections at 1723 K and 1873 K (1450 °C and 1600 °C).

Photoluminescent properties of Eu-doped ZnLiNbO4

NASA Astrophysics Data System (ADS)

Huang, Meng-Hsi; Lin, Ming-Hong; Fang, Te-Hua; Chang, Chia-Wei

2018-04-01

In this study, fluorescent Eu3+-doped ZnLiNbO4 materials were prepared via a vibrating milled solid-state reaction method. The objective was to develop new fluorescent oxide materials and study their fluorescent properties. The ZnLiNbO4 tetragonal spinel structure was formed with a single phase at a sintering temperature of 800 °C and with a regular shape at 1000 °C. The main exciton band was at 466 nm (7F0 → 5D2), and the main emission band was at 615 nm (5D0 → 7F2), which was an orange–red light band. The emission intensity was approximately 5% when the doping concentration reached 7%. The decay time was 2.96 ms.

Pressure-induced ferroelectric to paraelectric transition in LiTaO 3 and (Li,Mg)TaO 3

DOE PAGES

Yamanaka, Takamitsu; Nakamoto, Yuki; Takei, Fumihiko; ...

2016-02-16

X-ray powder diffraction and Raman scattering of LiTaO 3 (LT) and (Li,Mg)TaO 3 (LMT) have been measured under pressure up to 46 GPa. Above 30 GPa, the ferroelectric rhombohedral phase (R3c, Z – 6) of LiTaO 3 transforms to a paraelectric orthorhombic phase (Pnma with Z – 4) with a large hysteresis. Rietveld profile fitting analysis shows that the Li-O bond is compressed and approaches that of Ta-O with pressure. The cation distribution analysis of the orthorhombic perovskite structure shows that Li and Ta are located in the octahedral 8-fold coordination sites. Difference Fourier |F obs(hkl)| - |F cal(hkl)| mapsmore » of LiTaO 3 and (Li,Mg)TaO 3 indicate polarization in the c axis direction and a more distinct electron density distribution around the Ta position for (Li,Mg)TaO 3 compared to LiTaO 3. The observed effective charges indicate that for (Li,Mg)TaO 3 without vacancies Ta 5+ becomes less ionized as a function of Mg substitution. Considering both site occupancy and effective charge analysis, Ta 5+ is reduced to Ta 4.13+. Mg 2+ and O 2- change to Mg 1.643+ and O 1.732 -, respectively. The space- and time-averaged structures of the dynamical vibration of atoms can be elucidated from the electron density analysis by difference Fourier and temperature factors T(hkl) in the structure refinement. The refinement of the temperature factor is consistent with the cation distribution assuming full stoichiometry. The residual electron density induced from the excess electron in (Li,Mg)TaO 3 indicates more electrons around the Ta site, as confirmed by the effective charge analysis. Raman spectra of LiTaO 3 and (Li,Mg)TaO 3 show notable changes over the measured pressure range. Raman peaks centered at 250 cm –1 and 350 cm –1 at ambient pressure merge above 8 GPa, which we associate with the diminishing of difference in distances between Li-O and Ta-O bonds with pressure in both materials. Finally, Raman spectra show significant changes at 28 GPa and 33 GPa for

Investigation of the thermoelectric properties of Nb and oxygen vacancy co-doped SrTiO3 ceramics

NASA Astrophysics Data System (ADS)

Gong, Jing; Yuan, Zhanhui; Xu, Shikui; Li, Zhuangzhi; Xu, Jingzhou; Tang, Guide

2017-05-01

High quality Nb doped SrTi1-x Nb x O3 polycrystalline ceramics were fabricated using a conventional solid state reaction method. By annealing in a reducing atmosphere at an elevated temperature, a series of Nb and oxygen vacancy co-doped SrTi1-x Nb x O3-δ (0  ⩽  x  ⩽  0.2) samples was obtained. The thermoelectric properties of the samples were measured in the temperature range from 15 K to 380 K. These measurements showed that the transport behavior of these samples is consistent with the small polaron conduction mechanism for the temperature range from room temperature to 380 K. Furthermore, after annealing, samples with a lower Nb doping were found to give a relative higher ZT value, while excess Nb led to a reduced ZT value. The x  =  0.02 sample gave the optimal thermoelectric properties, with a ZT value of 0.023 at 300 K, and 0.028 at 380 K.

Synthesis of superconducting Nb 3Sn coatings on Nb substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

In the present work the electrochemical and thermal syntheses of superconductive Nb 3Sn films are investigated. The Nb 3Sn 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/cm 2 range and at temperatures between 40 and 50°C. Subsequent thermal treatments were realized to obtain the Nb 3Sn superconductive phase. Glow discharge optical emission spectrometry (GDOES) demonstrated that after thermal treatment interdiffusion of Nb and Sn occurred across a thickness of aboutmore » 13 μm. Scanning Electron Microscopy (SEM) allowed accurately measuring the thickness of the Nb 3Sn 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 Nb 3Sn phase (A15 structure) having (210) preferred orientation. The maximum obtained T c was 17.68 K and the B c20 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

Synthesis of superconducting Nb 3Sn 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 Nb 3Sn films are investigated. The Nb 3Sn 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/cm 2 range and at temperatures between 40 and 50°C. Subsequent thermal treatments were realized to obtain the Nb 3Sn superconductive phase. Glow discharge optical emission spectrometry (GDOES) demonstrated that after thermal treatment interdiffusion of Nb and Sn occurred across a thickness of aboutmore » 13 μm. Scanning Electron Microscopy (SEM) allowed accurately measuring the thickness of the Nb 3Sn 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 Nb 3Sn phase (A15 structure) having (210) preferred orientation. The maximum obtained T c was 17.68 K and the B c20 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

Electric Properties of Pb(Sb1/2Nb1/2)O3 PbTiO3 PbZrO3 Ceramics

NASA Astrophysics Data System (ADS)

Kawamura, Yasushi; Ohuchi, Hiromu

1994-09-01

Solid-solution ceramics of ternary system xPb(Sb1/2Nb1/2)O3 yPbTiO3 zPbZrO3 were prepared by the solid-state reaction of powder materials. Ceramic, electric, dielectric and piezoelectric properties and crystal structures of the system were studied. Sintering of the system xPb(Sb1/2Nb1/2)O3 yPbTiO3 zPbZrO3 is much easier than that of each end composition, and well-sintered high-density ceramics were obtained for the compositions near the morphotropic transformation. Piezoelectric ceramics with high relative dielectric constants, high radial coupling coefficient and low resonant resistance were obtained for the composition near the morphotropic transformation. The composition Pb(Sb1/2Nb1/2)0.075Ti0.45Zr0.475O3 showed the highest dielectric constant (ɛr=1690), and the composition Pb(Sb1/2Nb1/2)0.05Ti0.45Zr0.5O3 showed the highest radial coupling coefficient (kp=64%).

Design and Development of Mixed-Metal Oxide Photocatalysts: the Band Engineering Approach

NASA Astrophysics Data System (ADS)

Boltersdorf, Jonathan Andrew

The design and development of mixed-metal oxides incorporating Ag(I), Pb(II), Sn(II), and Bi(III), i.e., with filled d10 or d10s2 electron configurations, have yielded new approaches to tune optical and photocatalytic properties for solar energy conversion. My research efforts in the area of solid-state photochemistry have focused on utilizing flux-mediated ion-exchange methods in conjunction with the band engineering approach to synthesize new materials for solar energy driven total water splitting. Layered perovskite phases and the polysomatic family of tantalate/niobate structures, with the general formula Am+ ( n+1)/mB(3 n+1)O(8n +3) (A = Na, Ag; B = Ta, Nb), have received increasing attention owing to their synthetic flexibility, tunable optical band gaps, and photocatalytic activities for total water splitting. Structures in the family of A m+ (n+1)/ mB(3n +1)O(8n+3) structures are based on the stacking of pentagonal bipyramidal layers, where n defines the average thickness (1 ≤ n ≤ 2) of the BO7 layers that alternate with isolated BO6 octahedra surrounded by A-site cations. Synthetic limitations in the discovery of new phases within the layered perovskites and the Am + (n+1)/mB(3 n+1)O(8n +3) structural families can be addressed with the aid of a metal-salt solvent, known as the molten-salt flux method. The flux synthetic route requires the use of an inorganic salt heated above its melting temperature in order to serve as a solvent system for crystallization. Molten fluxes allow for synthetic modification of particle characteristics and can enable the low temperature stabilization of new compositions and phases with limited stability using ion-exchange reactions (e.g., PbTa4O11, AgLaNb 2O7). Solid-state and flux-mediated exchange methods were utilized in order to synthetically explore and investigate the layered perovskites ALaNb2O7, AA2Nb3O 10, A'2La2Ti3O10 (A' = Rb, Ag; A = Ca, Sr), the Am+ (n+1)/mB 3n+1O(8 n+3) structural family (Am + = Na(I), Ag

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.

Orientation dependences of atomic structures in chemically heterogeneous Cu{sub 50}Ta{sub 50}/Ta glass-crystal interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Guiqin; Gao, Xiaoze; Li, Jinfu

2015-01-07

Molecular dynamics simulations based on an angular-dependent potential were performed to examine the structural properties of chemically heterogeneous interfaces between amorphous Cu{sub 50}Ta{sub 50} and crystalline Ta. Several phenomena, namely, layering, crystallization, intermixing, and composition segregation, were observed in the Cu{sub 50}Ta{sub 50} region adjacent to the Ta layers. These interfacial behaviors are found to depend on the orientation of the underlying Ta substrate: Layering induced by Ta(110) extends the farthest into Cu{sub 50}Ta{sub 50}, crystallization in the Cu{sub 50}Ta{sub 50} region is most significant for interface against Ta(100), while inter-diffusion is most pronounced for Ta(111). It turns out thatmore » the induced layering behavior is dominated by the interlayer distances of the underlying Ta layers, while the degree of inter-diffusion is governed by the openness of the Ta crystalline layers. In addition, composition segregations are observed in all interface models, corresponding to the immiscible nature of the Cu-Ta system. Furthermore, Voronoi polyhedra 〈0,5,2,6〉 and 〈0,4,4,6〉 are found to be abundant in the vicinity of the interfaces for all models, whose presence is believed to facilitate the structural transition between amorphous and body centered cubic.« less

Investigation of Thermal Conductivities and Expansion Coefficients of (Yb1 - x La x )2AlTaO7 Ceramics

NASA Astrophysics Data System (ADS)

Xiaoge, Chen; Hongsong, Zhang; Sai, Su; Yongde, Zhao; An, Tang; Haoming, Zhang

2017-12-01

The (Yb1 - x La x )2AlTaO7 ( x = 0, 0.1, 0.3, 0.5) ceramics were prepared by solid-state reaction method. The phase composition, microstructure, thermophysical properties of (Yb1 - x La x )2AlTaO7 ceramics were investigated. Results reveal that (Yb1 - x La x )2AlTaO7 ( x = 0, 0.1, 0.3) ceramics exhibit a single pyrochlore-type structure, and the (Yb0.5La0.5)2AlTaO7 has an orthorhombic weberite structure. The thermal conductivities of (Yb1 - x La x )2AlTaO7 ( x = 0, 0.1, 0.3) ceramics decrease with increasing Yb2O3 contents. (Yb0.5La0.5)2AlTaO7 has the highest thermal conductivity among all the ceramics studied, within the range of 1.48-1.75 W/m K (20-1200 °C). The thermal expansion coefficients of (Yb1 - x La x )2AlTaO7 ceramics decrease gradually with increasing La2O3 fractions, and the thermal expansion coefficients are close to those of YSZ.

Planar Metal-Insulator-Metal Diodes Based on the Nb/Nb2O5/X Material System

DTIC Science & Technology

2013-10-01

high -quality Nb2O5 insulator can be grown reproducibly as a pinhole-free, uniform layer on top of the Nb using an anodic oxidation process under atmos...harvesting applications. Six cathode materials (M2): Nb, Ag, Cu, Ni, Au, and Pt are studied in conjunction with Nb as the anode (M1) and Nb2O5 (I) as the...are studied in conjunction with Nb as the anode (M1) and Nb2O5 (I) as the dielectric. The cathode materials selections were based on results from a

Hydrometallurgical Separation of Niobium and Tantalum: A Fundamental Approach

NASA Astrophysics Data System (ADS)

Nete, Motlalepula; Purcell, Walter; Nel, Johann T.

2016-02-01

A mixture of pure Ta2O5 and Nb2O5 was dissolved using two different fluxes, namely NH4F·HF and Na2HPO4/NaH2PO4·H2O. Selective precipitation and ion exchange were used as separation techniques. Selective precipitation using p-phenylediamine in a fluoride matrix resulted in the isolation of 73(3)% tantalum accompanied by 23(5)% niobium. A separation factor of 11(4) was obtained. A single solvent extraction step using methyl-isobutyl ketone at a 4 M H2SO4 yielded excellent Ta and Nb separation in the fluoride solution with 80% of the Ta and only 2% Nb recovered in the organic layer. A two-step extraction recovered 100% Ta at 0.5-4 M H2SO4 with a separation factor of ~2000. A study of the extraction mechanism indicated that the stability of the protonated compounds such as H2TaF7/H2NbOF5 is in the extraction and separation determining steps in this process. A K' (double de-protonated constant) of approximately 0.2 was calculated for H2TaF7. Only 91.7% Nb and 73.4% Ta were recovered from anion separation using strong Amberlite resin and 96.1% Nb and 52.3% using the weak Dowex Marathon resin from fluoride dissolution.

Electrodeposition of Al-Ta alloys in NaCl-KCl-AlCl3 molten salt containing TaCl5

NASA Astrophysics Data System (ADS)

Sato, Kazuki; Matsushima, Hisayoshi; Ueda, Mikito

2016-12-01

To form Al-Ta alloys for high temperature oxidation resistance components, molten salt electrolysis was carried out in an AlCl3-NaCl-KCl melt containing TaCl5 at 423 K. The voltammogram showed two cathodic waves at 0.45 V and 0.7 V vs. Al/Al(III), which may correspond to reduction from Ta(V) to Ta(III) and from Ta(III) to tantalum metal, respectively. Electrodeposits of Al and Ta were obtained in the range from -0.05 to 0.3 V and the highest concentration of Ta in the electrodeposit was 72 at% at 0.3 V. With increasing Ta content in the alloy, the morphology of the electrodeposits became powdery and the particle size smaller.

Amorphous tantala and its relationship with the molten state

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alderman, Oliver L.G.; Benmore, C. J.; Neuefeind, Joerg C.

The structure factors of molten Ta 2O 5 and Nb 2O 5 have been measured by high-energy x-ray and pulsed neutron diffraction. These are compared to transmission-mode x-ray diffraction through a self-supported 15-μm ion-beam sputtered amorphous tantala film. Atomistic models derived from the diffraction data by means of empirical potential structure refinement reveal that tantala and niobia liquids are very close to isomorphous, as confirmed by measurement of a molten mixture, Ta 0.8Nb 1.2O 5. Nonetheless, peak Nb-O bond lengths are about 1% shorter than those for Ta-O, at temperatures, T*=T/T melt, scaled to the melting points. Mean coordination numbersmore » are n MO≃5.6(1),n OM≃2.23(4) in the liquid state, and n TaO≃6.6(2),n OTa≃2.63(8) in the solid. The liquids are built from five- and six-fold M-O polyhedra which connect principally by corner sharing, with a minority of edge sharing; a-Ta 2O 5 on the other hand has a local structure more akin to the crystalline polymorphs, built primarily from six- and seven-fold polyhedra, with a larger degree of edge sharing. The structural differences between liquid and amorphous Ta 2O 5, coupled with observations of increasing peak bond lengths upon cooling, are consistent with the interpretation that the amorphous film reaches a supercooled liquidlike metastable equilibrium during deposition. In other words, the amorphous film shares a common progenitor state with a hypothetical glass quenched from a fragile melt. In addition, we show that recent classical interatomic potentials do not fully reproduce the diffraction data, and infer that inclusion of attractive (non-Coulombic) Ta-Ta interactions is important, particularly for obtaining the correct degree of edge sharing, coordination numbers, and densities. In conclusion, nanoscale inhomogeneity of the amorphous film is confirmed by the observation of small-angle x-ray scattering.« less

Amorphous tantala and its relationship with the molten state

DOE PAGES

Alderman, Oliver L.G.; Benmore, C. J.; Neuefeind, Joerg C.; ...

2018-04-01

The structure factors of molten Ta 2O 5 and Nb 2O 5 have been measured by high-energy x-ray and pulsed neutron diffraction. These are compared to transmission-mode x-ray diffraction through a self-supported 15-μm ion-beam sputtered amorphous tantala film. Atomistic models derived from the diffraction data by means of empirical potential structure refinement reveal that tantala and niobia liquids are very close to isomorphous, as confirmed by measurement of a molten mixture, Ta 0.8Nb 1.2O 5. Nonetheless, peak Nb-O bond lengths are about 1% shorter than those for Ta-O, at temperatures, T*=T/T melt, scaled to the melting points. Mean coordination numbersmore » are n MO≃5.6(1),n OM≃2.23(4) in the liquid state, and n TaO≃6.6(2),n OTa≃2.63(8) in the solid. The liquids are built from five- and six-fold M-O polyhedra which connect principally by corner sharing, with a minority of edge sharing; a-Ta 2O 5 on the other hand has a local structure more akin to the crystalline polymorphs, built primarily from six- and seven-fold polyhedra, with a larger degree of edge sharing. The structural differences between liquid and amorphous Ta 2O 5, coupled with observations of increasing peak bond lengths upon cooling, are consistent with the interpretation that the amorphous film reaches a supercooled liquidlike metastable equilibrium during deposition. In other words, the amorphous film shares a common progenitor state with a hypothetical glass quenched from a fragile melt. In addition, we show that recent classical interatomic potentials do not fully reproduce the diffraction data, and infer that inclusion of attractive (non-Coulombic) Ta-Ta interactions is important, particularly for obtaining the correct degree of edge sharing, coordination numbers, and densities. In conclusion, nanoscale inhomogeneity of the amorphous film is confirmed by the observation of small-angle x-ray scattering.« less

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

NASA Astrophysics Data System (ADS)

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

2014-03-01

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

Reactive Fabrication and Effect of NbC on Microstructure and Tribological Properties of CrS Co-Based Self-Lubricating Coatings by Laser Cladding

PubMed Central

Fang, Liuyang; Yan, Hua; Yao, Yansong; Zhang, Peilei; Gao, Qiushi; Qin, Yang

2017-01-01

The CrS/NbC Co-based self-lubricating composite coatings were successfully fabricated on Cr12MoV steel surface by laser clad Stellite 6, WS2, and NbC mixed powders. The phase composition, microstructure, and tribological properties of the coatings ware investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS), as well as dry sliding wear testing. Based on the experimental results, it was found reactions between WS2 and Co-based alloy powder had occurred, which generated solid-lubricant phase CrS, and NbC play a key role in improving CrS nuclear and refining microstructure of Co-based composite coating during laser cladding processing. The coatings were mainly composed of γ-Co, CrS, NbC, Cr23C6, and CoCx. Due to the distribution of the relatively hard phase of NbC and the solid lubricating phase CrS, the coatings had better wear resistance. Moreover, the suitable balance of CrS and NbC was favorable for further decreasing the friction and improving the stability of the contact surfaces between the WC ball and the coatings. The microhardness, friction coefficient, and wear rate of the coating 4 (Clad powders composed of 60 wt % Stellite 6, 30 wt % NbC and 10 wt % WS2) were 587.3 HV0.5, 0.426, and 5.61 × 10−5 mm3/N·m, respectively. PMID:29283411

Reactive Fabrication and Effect of NbC on Microstructure and Tribological Properties of CrS Co-Based Self-Lubricating Coatings by Laser Cladding.

PubMed

Fang, Liuyang; Yan, Hua; Yao, Yansong; Zhang, Peilei; Gao, Qiushi; Qin, Yang

2017-12-28

The CrS/NbC Co-based self-lubricating composite coatings were successfully fabricated on Cr12MoV steel surface by laser clad Stellite 6, WS₂, and NbC mixed powders. The phase composition, microstructure, and tribological properties of the coatings ware investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS), as well as dry sliding wear testing. Based on the experimental results, it was found reactions between WS₂ and Co-based alloy powder had occurred, which generated solid-lubricant phase CrS, and NbC play a key role in improving CrS nuclear and refining microstructure of Co-based composite coating during laser cladding processing. The coatings were mainly composed of γ-Co, CrS, NbC, Cr 23 C₆, and CoC x . Due to the distribution of the relatively hard phase of NbC and the solid lubricating phase CrS, the coatings had better wear resistance. Moreover, the suitable balance of CrS and NbC was favorable for further decreasing the friction and improving the stability of the contact surfaces between the WC ball and the coatings. The microhardness, friction coefficient, and wear rate of the coating 4 (Clad powders composed of 60 wt % Stellite 6, 30 wt % NbC and 10 wt % WS₂) were 587.3 HV 0.5 , 0.426, and 5.61 × 10 -5 mm³/N·m, respectively.

EUSO-TA prototype telescope

NASA Astrophysics Data System (ADS)

Bisconti, Francesca; JEM-EUSO Collaboration

2016-07-01

EUSO-TA is one of the prototypes developed for the JEM-EUSO project, a space-based large field-of-view telescope to observe the fluorescence light emitted by cosmic ray air showers in the atmosphere. EUSO-TA is a ground-based prototype located at the Telescope Array (TA) site in Utah, USA, where an Electron Light Source and a Central Laser Facility are installed. The purpose of the EUSO-TA project is to calibrate the prototype with the TA fluorescence detector in presence of well-known light sources and cosmic ray air showers. In 2015, the detector started the first measurements and tests using the mentioned light sources have been performed successfully. A first cosmic ray candidate has been observed, as well as stars of different magnitude and color index. Since Silicon Photo-Multipliers (SiPMs) are very promising for fluorescence telescopes of next generation, they are under consideration for the realization of a new prototype of EUSO Photo Detector Module (PDM). The response of this sensor type is under investigation through simulations and laboratory experimentation.

Undercooling studies on Nb-Pt and Nb-Si alloys using the 105 meter drop tube

NASA Technical Reports Server (NTRS)

Robinson, M. B.; Bayuzick, R. J.; Hofmeister, W. H.

1988-01-01

Niobium-platinum samples of compositions ranging from 16 to 32 at. pct have been undercooled to as much as 540 K in the low gravity, containerless environment of a 105 meter drop tube. Undercooling was terminated in the Nb-Pt samples by the nucleation and growth of the Nb3Pt phase. In the 16-18 at. pct Pt samples, this resulted in samples which are completely Nb3Pt, in contrast to both the equilibrium phase diagram and the nonundercooled samples which formed with Nb dendrites and interdendritic Nb3Pt. Undercoolings for the Nb-Si samples were up to 670 K, which corresponds to 27 percent of the liquidus temperature or 80 percent of the estimated hypercooling limit. In the Nb-Si system, a coupled zone was identified as well as a metastable extension of the solubility limit of Si in Nb due to deep undercooling.

Microstructures evolution and physical properties of laser induced NbC modified nanocrystalline composites

NASA Astrophysics Data System (ADS)

Li, Jianing; Liu, Kegao; Yuan, Xingdong; Shan, Feihu; Zhang, Bolun; Wang, Zhe; Xu, Wenzhuo; Zhang, Zheng; An, Xiangchen

2017-10-01

The nanoscale quasicrystals (NQs), amorphous and ultrafine nanocrystals (UNs) modified hard composites are produced by laser cladding (LC) of the Ni60A-TiC-NbC-Sb mixed powders on the additive manufacturing (AM) TA1 titanium alloy. The LC technique is favorable to formations of icosahedral quasicrystals (I-phase) with five-fold symmetry due to its rapid cooling and solidification characteristics. The formation mechanism of this I-phase is explained here. Under the actions of NQs, amorphous and UNs, such LC composites exhibited an extremely high micro-hardness. UNs may also intertwin with amorphous, forming yarn-shape materials. This research provides essential theoretical basis to improve the quality of laser-treated composites.

Dielectric relaxation and electrical conductivity in Bi 5NbO 10 oxygen ion conductors prepared by a modified sol-gel process

NASA Astrophysics Data System (ADS)

Hou, Jungang; Vaish, Rahul; Qu, Yuanfang; Krsmanovic, Dalibor; Varma, K. B. R.; Kumar, R. V.

Crystalline Bi 5NbO 10 nanoparticles have been achieved through a modified sol-gel process using a mixture of ethylenediamine and ethanolamine as a solvent. The Bi 5NbO 10 nanoparticles were characterized by X-ray diffraction (XRD), differential scanning calorimetry/thermogravimetry (DSC/TG), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and Raman spectroscopy. The results showed that well-dispersed 5-60 nm Bi 5NbO 10 nanoparticles were prepared through heat-treating the precursor at 650 °C and the high density pellets were obtained at temperatures lower than those commonly employed. The frequency and temperature dependence of the dielectric constant and the electrical conductivity of the Bi 5NbO 10 solid solutions were investigated in the 0.1 Hz to 1 MHz frequency range. Two distinct relaxation mechanisms were observed in the plots of dielectric loss and the imaginary part of impedance (Z″) versus frequency in the temperature range of 200-350 °C. The dielectric constant and the loss in the low frequency regime were electrode dependent. The ionic conductivity of Bi 5NbO 10 solid solutions at 700 °C is 2.86 Ω -1 m -1 which is in same order of magnitude for Y 2O 3-stabilized ZrO 2 ceramics at same temperature. These results suggest that Bi 5NbO 10 is a promising material for an oxygen ion conductor.

SOLID SOLUTION CARBIDES ARE THE KEY FUELS FOR FUTURE NUCLEAR THERMAL PROPULSION

NASA Technical Reports Server (NTRS)

Panda, Binayak; Hickman, Robert R.; Shah, Sandeep

2005-01-01

Nuclear thermal propulsion uses nuclear energy to directly heat a propellant (such as liquid hydrogen) to generate thrust for space transportation. In the 1960 s, the early Rover/Nuclear Engine for Rocket Propulsion Application (NERVA) program showed very encouraging test results for space nuclear propulsion but, in recent years, fuel research has been dismal. With NASA s renewed interest in long-term space exploration, fuel researchers are now revisiting the RoverMERVA findings, which indicated several problems with such fuels (such as erosion, chemical reaction of the fuel with propellant, fuel cracking, and cladding issues) that must be addressed. It is also well known that the higher the temperature reached by a propellant, the larger the thrust generated from the same weight of propellant. Better use of fuel and propellant requires development of fuels capable of reaching very high temperatures. Carbides have the highest melting points of any known material. Efforts are underway to develop carbide mixtures and solid solutions that contain uranium carbide, in order to achieve very high fuel temperatures. Binary solid solution carbides (U, Zr)C have proven to be very effective in this regard. Ternary carbides such as (U, Zr, X) carbides (where X represents Nb, Ta, W, and Hf) also hold great promise as fuel material, since the carbide mixtures in solid solution generate a very hard and tough compact material. This paper highlights past experience with early fuel materials and bi-carbides, technical problems associated with consolidation of the ingredients, and current techniques being developed to consolidate ternary carbides as fuel materials.

Formation and characterization of Ta2O5/TaOx films formed by O ion implantation

NASA Astrophysics Data System (ADS)

Ruffell, S.; Kurunczi, P.; England, J.; Erokhin, Y.; Hautala, J.; Elliman, R. G.

2013-07-01

Ta2O5/TaOx (oxide/suboxide) heterostructures are fabricated by high fluence O ion-implantation into deposited Ta films. The resultant films are characterized by depth profiling X-ray photoelectron spectroscopy (XPS), cross-sectional transmission electron microscopy (XTEM), four-point probe, and current-voltage and capacitance-voltage measurements. The measurements show that Ta2O5/TaOx oxide/suboxide heterostructures can be fabricated with the relative thicknesses of the layers controlled by implantation energy and fluence. Electrical measurements show that this approach has promise for high volume manufacturing of resistive switching memory devices based on oxide/suboxide heterostructures.

Geochronology, geochemical and Sr-Nd-Hf-Pb isotopic compositions of the granitoids in the Yemaquan orefield, East Kunlun orogenic belt, northern Qinghai-Tibet Plateau: Implications for magmatic fractional crystallization and sub-solidus hydrothermal alteration

NASA Astrophysics Data System (ADS)

Yin, Shuo; Ma, Changqian; Xu, Jiannan

2017-12-01

A general consensus has emerged that high field strength elements (HFSE) can mobile to some extent in a hydrothermal fluid. However, there are hot debates on whether sub-solidus hydrothermal alteration can lower the Nb/Ta ratio in evolved melts. In this study, we present petrography, geochronology and geochemistry of the barren and mineralized rocks in the Yemaquan skarn iron deposit, northern Qinghai-Tibet Plateau, to probe magmatic-hydrothermal transition. The barren rocks consist of diorites, granodiorites, granites and syenogranites, whereas the porphyritic granodiorites are associated with mineralization for an excellent consistency between the magmatic zircon U-Pb age (225 ± 2 Ma) and the hydrothermal phlogopite 40Ar-39Ar age (225 ± 1.5 Ma). The Sr-Nd-Hf-Pb isotopic data demonstrate that the Yemaquan granitoids are originated from a relatively homogenous enriched mantle with different degrees of crust contamination (assimilation fractional crystallization, AFC). Trace elements signatures indicate that the porphyritic granodiorites related to mineralization display amphibole crystallization for high water contents, whereas the barren granites have gone through biotite crystallization due to potassium enrichment by continuous upper crust contamination, both of which are responsible for their Nb/Ta ratios, respectively. Modeling results suggest that a basaltic melt with Nb/Ta ratio of 15.3 can reach a minimum Nb/Ta ratio of 12 in the producing granodioritic melt by amphibole fractional crystallization based on partition coefficients of Nb and Ta between amphibole and melts from previous experiments. This may explain the average Nb/Ta ratio (13.7) of the barren granodiorites, while it cannot account for the average Nb/Ta ratio (8.4) of the mineralized porphyritic granodiorites, and it is even lower than that of the granites (10.3) with biotite fractional crystallization. Exsolution of a magmatic-hydrothermal fluid is inevitable when a water saturated magma

High-field specific heats of A15 V3Si and Nb3Sn

NASA Astrophysics Data System (ADS)

Stewart, G. R.; Brandt, B. L.

1984-04-01

In order to further understand the anomalous behavior of the specific heat of Nb3Sn in an 18-T magnetic field discovered by Stewart, Cort, and Webb

Electron backscatter diffraction analysis of Nb3Al multifilamentary strands prepared by rapid heating, quenching and transformation annealing

NASA Astrophysics Data System (ADS)

Takeuchi, T.; Tsuchiya, K.; Saeda, M.; Banno, N.; Kikuchi, A.; Iijima, Y.

2010-12-01

To enhance the non-Cu critical current density Jc at 15 T and 4.2 K (1000 A mm - 2 at present) we have endeavoured to refine the grain size of rapid heating, quenching and transformation (RHQT)-processed Nb3Al. In the present study, the grain boundary structures of RHQT-processed Nb3Al were examined by electron backscatter diffraction (EBSD) because transgranular fracture prevents the observation of fractured cross sections of Nb3Al to statistically determine the grain size. The grain size distributions of body-centred-cubic supersaturated-solid-solution Nb(Al)ss and A15 Nb3Al filaments were measured for grains misoriented by more than 2°, 5° and 15°. A mixed grain structure, which consists of a few large grains (>25 µm) and many small grains (<1 µm), was observed for an Nb3Al filament that had been transformed from non-deformed Nb(Al)ss. Plastic deformation that had been made between the rapid heating and quenching steps and the transformation step apparently homogenized the grain size distribution and then reduced the average grain size. The misorientation angle distributions of Nb(Al)ss and Nb3Al were also measured and compared with each other. A clear relationship between the Jc and the inverse grain size was not confirmed for the RHQT Nb3Al conductors examined in the present study, which indicates the importance of making a filament compositionally homogeneous to obtain a high Jc.

Test results of a Nb 3Al/Nb 3Sn 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 Nb 3Al and Nb 3Sn subscale magnet to establish the technology for a high-field accelerator magnet. The development goals are a feasibility demonstration for a Nb 3Al cable and the technology acquisition of magnet fabrication with Nb 3Al superconductors. KEK developed two double-pancake racetrack coils with Rutherford-type cables composed of 28 Nb 3Al 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 amore » minimum-gap common-coil configuration with two Nb 3Al coils sandwiched between two Nb 3Sn 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 Nb 3Sn coil, i.e., 9667 A, was reached at 40 A/s corresponding to 9.0 T in the Nb 3Sn coil and 8.2 T in the Nb 3Al coil. The quench characteristics of the magnet were studied.« less

A-site- and/or B-site-modified PbZrTiO3 materials and (Pb, Sr, Ca, Ba, Mg) (Zr, Ti, Nb, Ta)O3 films having utility in ferroelectric random access memories and high performance thin film microactuators

NASA Technical Reports Server (NTRS)

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

2001-01-01

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

Exploring hardness enhancement in superhard tungsten tetraboride-based solid solutions using radial X-ray diffraction

DOE PAGES

Xie, Miao; Mohammadi, Reza; Turner, Christopher L.; ...

2015-07-29

In this paper, we explore the hardening mechanisms in WB4-based solid solutions upon addition of Ta, Mn, and Cr using in situ radial X-ray diffraction techniques under nonhydrostatic pressure. By examining the lattice-supported differential strain, we provide insights into the mechanism for hardness increase in binary solid solutions at low dopant concentrations. Speculations on the combined effects of electronic structure and atomic size in ternary WB 4 solid solutions containing Ta with Mn or Cr are also included to understand the extremely high hardness of these materials.

Solid-state lithium battery

DOEpatents

Ihlefeld, Jon; Clem, Paul G; Edney, Cynthia; Ingersoll, David; Nagasubramanian, Ganesan; Fenton, Kyle Ross

2014-11-04

The present invention is directed to a higher power, thin film lithium-ion electrolyte on a metallic substrate, enabling mass-produced solid-state lithium batteries. High-temperature thermodynamic equilibrium processing enables co-firing of oxides and base metals, providing a means to integrate the crystalline, lithium-stable, fast lithium-ion conductor lanthanum lithium tantalate (La.sub.1/3-xLi.sub.3xTaO.sub.3) directly with a thin metal foil current collector appropriate for a lithium-free solid-state battery.

Nanostructured TaON/Ta3N5 as a highly efficient type-II heterojunction photoanode for photoelectrochemical water splitting.

PubMed

Pei, Lang; Wang, Hongxu; Wang, Xiaohui; Xu, Zhe; Yan, Shicheng; Zou, Zhigang

2018-06-20

Enhancing the charge separation by a semiconductor heterojunction is greatly promising and challenging for photoelectrochemical (PEC) water splitting. Here, we report for the first time the design and fabrication of a TaON/Ta3N5 heterojunction photoanode, in which the electrode Ta3N5 is the primary light absorber and TaON acts as an electron conductor. By combining the merits of the substantial light harvesting of Ta3N5 with the excellent charge transport capability of TaON, the TaON/Ta3N5 heterojunction photoanode, without any co-catalysts, shows a 350 mV negative shift of photocurrent onset potential to 0.65 V versus the reversible hydrogen electrode (RHE) compared to that of the Ta3N5 photoanode. The design and fabrication scheme can be readily extended to other (oxy)nitride semiconductors for heterojunction construction.

A Ta/W mixed addenda heteropolyacid with excellent acid catalytic activity and proton-conducting property

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Shujun; Peng, Qingpo; Chen, Xuenian, E-mail: xnchen@htu.edu.cn

A new HPAs H{sub 20}[P{sub 8}W{sub 60}Ta{sub 12}(H{sub 2}O){sub 4}(OH){sub 8}O{sub 236}]·125H{sub 2}O (H-1) which comprises a Ta/W mixed addenda heteropolyanion, 20 protons, and 125 crystalline water molecules has been prepared through ion-exchange method. The structure and properties of H-1 have been explored in detail. AC impedance measurements indicate that H-1 is a good solid state proton conducting material at room temperature with a conductivity value of 7.2×10{sup −3} S cm{sup −1} (25 °C, 30% RH). Cyclic voltammograms of H-1 indicate the electrocatalytic activity towards the reduction of nitrite. Hammett acidity constant H{sub 0} of H-1 in CH{sub 3}CN ismore » −2.91, which is the strongest among the present known HPAs. Relatively, H-1 exhibits excellent catalytic activities toward acetal reaction. - Highlights: • A Ta/W mixed addenda Heteropolyacid (H-1) was isolated. • Hammett acidity constant H{sub 0} of H-1 is the strongest among the present known HPAs. • H-1 exhibits excellent catalytic activities toward acetal reaction. • H-1 is a good solid state proton conducting material at room temperature.« less

On the Effects of Hot Forging and Hot Rolling on the Microstructural Development and Mechanical Response of a Biocompatible Ti Alloy

PubMed Central

Okazaki, Yoshimitsu

2012-01-01

Zr, Nb, and Ta as alloying elements for Ti alloys are important for attaining superior corrosion resistance and biocompatibility in the long term. However, note that the addition of excess Nb and Ta to Ti alloys leads to higher manufacturing cost. To develop low-cost manufacturing processes, the effects of hot-forging and continuous-hot-rolling conditions on the microstructure, mechanical properties, hot forgeability, and fatigue strength of Ti-15Zr-4Nb-4Ta alloy were investigated. The temperature dependences with a temperature difference (ΔT) from β-transus temperature (Tβ) for the volume fraction of the α- and β-phases were almost the same for both Ti-15Zr-4Nb-4Ta and Ti-6Al-4V alloys. In the α-β-forged Ti-15Zr-4Nb-4Ta alloy, a fine granular α-phase structure containing a fine granular β-phase at grain boundaries of an equiaxed α-phase was observed. The Ti-15Zr-4Nb-4Ta alloy billet forged at Tβ-(30 to 50) °C exhibited high strength and excellent ductility. The effects of forging ratio on mechanical strength and ductility were small at a forging ratio of more than 3. The maximum strength (σmax) markedly increased with decreasing testing temperature below Tβ. The reduction in area (R.A.) value slowly decreased with decreasing testing temperature below Tβ. The temperature dependences of σmax for the Ti-15Zr-4Nb-4Ta and Ti-6Al-4V alloys show the same tendency and might be caused by the temperature difference (ΔT) from Tβ. It was clarified that Ti-15Zr-4Nb-4Ta alloy could be manufactured using the same manufacturing process as for previously approved Ti-6Al-4V alloy, taking into account the difference (ΔT) between Tβ and heat treatment temperature. Also, the manufacturing equivalency of Ti-15Zr-4Nb-4Ta alloy to obtain marketing approval of implants was established. Thus, it was concluded that continuous hot rolling is useful for manufacturing α-β-type Ti alloy.

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

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

2017-05-01

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.

Computational modeling of high-entropy alloys: Structures, thermodynamics and elasticity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Michael C.; Gao, Pan; Hawk, Jeffrey A.

This study provides a short review on computational modeling on the formation, thermodynamics, and elasticity of single-phase high-entropy alloys (HEAs). Hundreds of predicted single-phase HEAs were re-examined using various empirical thermo-physical parameters. Potential BCC HEAs (CrMoNbTaTiVW, CrMoNbReTaTiVW, and CrFeMoNbReRuTaVW) were suggested based on CALPHAD modeling. The calculated vibrational entropies of mixing are positive for FCC CoCrFeNi, negative for BCC MoNbTaW, and near-zero for HCP CoOsReRu. The total entropies of mixing were observed to trend in descending order: CoCrFeNi > CoOsReRu > MoNbTaW. Calculated lattice parameters agree extremely well with averaged values estimated from the rule of mixtures (ROM) if themore » same crystal structure is used for the elements and the alloy. The deviation in the calculated elastic properties from ROM for select alloys is small but is susceptible to the choice used for the structures of pure components.« less

Computational modeling of high-entropy alloys: Structures, thermodynamics and elasticity

DOE PAGES

Gao, Michael C.; Gao, Pan; Hawk, Jeffrey A.; ...

2017-10-12

This study provides a short review on computational modeling on the formation, thermodynamics, and elasticity of single-phase high-entropy alloys (HEAs). Hundreds of predicted single-phase HEAs were re-examined using various empirical thermo-physical parameters. Potential BCC HEAs (CrMoNbTaTiVW, CrMoNbReTaTiVW, and CrFeMoNbReRuTaVW) were suggested based on CALPHAD modeling. The calculated vibrational entropies of mixing are positive for FCC CoCrFeNi, negative for BCC MoNbTaW, and near-zero for HCP CoOsReRu. The total entropies of mixing were observed to trend in descending order: CoCrFeNi > CoOsReRu > MoNbTaW. Calculated lattice parameters agree extremely well with averaged values estimated from the rule of mixtures (ROM) if themore » same crystal structure is used for the elements and the alloy. The deviation in the calculated elastic properties from ROM for select alloys is small but is susceptible to the choice used for the structures of pure components.« less

Releasing metal catalysts via phase transition: (NiO)0.05-(SrTi0.8Nb0.2O3)0.95 as a redox stable anode material for solid oxide fuel cells.

PubMed

Xiao, Guoliang; Wang, Siwei; Lin, Ye; Zhang, Yanxiang; An, Ke; Chen, Fanglin

2014-11-26

Donor-doped perovskite-type SrTiO3 experiences stoichiometric changes at high temperatures in different Po2 involving the formation of Sr or Ti-rich impurities. NiO is incorporated into the stoichiometric strontium titanate, SrTi0.8Nb0.2O3-δ (STN), to form an A-site deficient perovskite material, (NiO)0.05-(SrTi0.8Nb0.2O3)0.95 (Ni-STN), for balancing the phase transition. Metallic Ni nanoparticles can be released upon reduction instead of forming undesired secondary phases. This material design introduces a simple catalytic modification method with good compositional control of the ceramic backbones, by which transport property and durability of solid oxide fuel cell anodes are largely determined. Using Ni-STN as anodes for solid oxide fuel cells, enhanced catalytic activity and remarkable stability in redox cycling have been achieved. Electrolyte-supported cells with the cell configuration of Ni-STN-SDC anode, La0.8Sr0.2Ga0.87Mg0.13O3 (LSGM) electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode produce peak power densities of 612, 794, and 922 mW cm(-2) at 800, 850, and 900 °C, respectively, using H2 as the fuel and air as the oxidant. Minor degradation in fuel cell performance resulted from redox cycling can be recovered upon operating the fuel cells in H2. Such property makes Ni-STN a promising regenerative anode candidate for solid oxide fuel cells.

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.

Growth and photo-response of NbSe2 and NbS2 crystals

NASA Astrophysics Data System (ADS)

Patel, Kunjal; Solanki, G. K.; Pataniya, Pratik; Patel, K. D.

2018-05-01

Transition metal dichalcogenides(TMDCs) have attracted intense research efforts due to their drastic properties change as we move towards ultra-thin crystalline layers from their bulk counterparts. Many well studied members of this family such as MoS2, WS2, WSe2, WS2 etc. have shown potential for flexible electronic devices including photovoltaic applications. The TMDCs like NbSe2 and NbS2 are relatively less studied layered compounds consisting of staked sandwiches of Se-Nb-Se/S-Nb-Se tri-layers with strong covalent/ionic intra layer bonds and weak Van der Waals interlayer interactions. In the present work, author have grown the crystals of NbSe2 and NbS2 by Direct Vapour Transport (DVT) technique and the material composition is confirmed using EDAX data. Photoelectrochemical (PEC) solar cell measurements are performed under monochromatic light illumination at different intensities and various solar cell parameters are calculated. These crystalline semiconductor electrodes were also analysed by photocurrent-voltage characteristics in a PEC solar cell structure (Cu/NbSe2/(0.1M K4Fe(CN)6 + 0.1M K3Fe(CN)6) and Cu/NbS2/(0.1M K4Fe(CN)6 +0.1M K3Fe(CN)6)). Blue coloured light gave the maximum efficiency. For further analysis of photodetection properties of the grown crystals, Ag painted broad low contact resistance electrical contacts were drawn from the crystals and its transient photoresponse was studied to evaluate different detector parameters.

Silicide formation process of Er films with Ta and TaN capping layers.

PubMed

Choi, Juyun; Choi, Seongheum; Kim, Jungwoo; Na, Sekwon; Lee, Hoo-Jeong; Lee, Seok-Hee; Kim, Hyoungsub

2013-12-11

The phase development and defect formation during the silicidation reaction of sputter-deposited Er films on Si with ∼20-nm-thick Ta and TaN capping layers were examined. TaN capping effectively prevented the oxygen incorporation from the annealing atmosphere, which resulted in complete conversion to the ErSi2-x phase. However, significant oxygen penetration through the Ta capping layer inhibited the ErSi2-x formation, and incurred the growth of several Er-Si-O phases, even consuming the ErSi2-x layer formed earlier. Both samples produced a number of small recessed defects at an early silicidation stage. However, large rectangular or square-shaped surface defects, which were either pitlike or pyramidal depending on the capping layer identity, were developed as the annealing temperature increased. The origin of different defect generation mechanisms was suggested based on the capping layer-dependent silicidation kinetics.

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.

A Ta-rich low-P peraluminous granite: the Rechla cupola (Hoggar, Algeria) and associated pegmatites, the result of extreme fractionation of a A2-type magma.

NASA Astrophysics Data System (ADS)

Kesraoui, M.; Marignac, C.; Hamis, A.; Cuney, M.

2012-04-01

In the c. 525 Ma RMG province of the Laouni terrane of the Pan-African Tuareg Shield (Hoggar), the small N20°E elliptic Rechla cupola (200x100 m) is particularized by a rim of Qtz-Kfs-Znw pegmatite. It is a medium-grained Na-Li-F granite, with quartz, albite (An01), rare microcline, topaz, Mn-lepidolite (≤ 8% MnO) and Hf-zircon, and: 71.4 % SiO2, 0.93% FeO+MgO+MnO (Mg # 0.19, Mg/Mg+Fe+Mn 0.09), 9.22% Na2O+K2O (Na # 0.7), Al-Na-K-2Ca from 55 to 85, and low P2O5 (0.05%) and ∑ REE (23 ppm) contents, with a pronounced tetrad effect and <0 Eu anomaly in the REE pattern. Such a composition is typical of a low-P peraluminous RMG deriving from highly potassic calcalkaline suites (A2 type) (Linnen & Cuney 2005), enriched in F (1.6%), Li (1,600 ppm), Zn (300 ppm), Be (7 ppm), Sn (740 ppm), W (40 ppm) and specially Ta (165 ppm, Ta/Nb between 2.4 and 2.6), the latter as columbo-tantalite and Mn-wodginite (Ta # 0.8). The pegmatite rim comprises, towards the intrusion (i) thick Kfs lenses (palissadic crystals ≥ 50 cm), (ii) a laminated quartz-zinnwaldite-(beryl) sequence , and (iii) a discontinuous band of fine-grained granite, with quartz, albite, topaz, Mn-lepidolite and beryl, equally fractionated: 69.4% SiO2, 0.85% FeO+MgO+MnO (Mg# 0.06, Mg/Mg+Fe+Mn 0.02), Al-Na-K-2Ca = 32, F 0.4%, Li 610 ppm, Ta 240 ppm (Ta/Nb = 2.4), Be 500 ppm. The laminated sequence overprints the Kfs lenses. It comprises thick (≤ 20 m) quartz lenses cross-cut by 10 cm-sized alternating bands of euhedral quartz and Mn-zinnwaldite (≤ 6.5% MnO). REE-patterns of the Mn-Znw display a clear inverse tetrad effect, symmetrical of the granite pattern. At the boundary with the fine-grained internal band, euhedral quartz crystals are projecting toward the inner wall. The Rechla body and its surrounding pegmatites are intrusive into a porphyritic biotite-granite representative of the evolved magmas of the A2-type Taourirt suite (Azzouni-Sekkal & Boissonnas 1993), with a classical "seagull" pattern and a

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

PubMed

Su, Shih-Hao; Su, Ming-Der

2016-06-28

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

Effects of poling over the orthorhombic-tetragonal phase transition temperature in compositionally homogeneous (K,Na)NbO3-based ceramics

NASA Astrophysics Data System (ADS)

Morozov, M. I.; Kungl, H.; Hoffmann, M. J.

2011-03-01

Li-, Ta-, and Mn-modified (K,Na)NbO3 ceramics with various compositional homogeneity have been prepared by conventional and precursor methods. The homogeneous ceramic has demonstrated a sharper peak in temperature dependent piezoelectric response. The dielectric and piezoelectric properties of the homogeneous ceramics have been characterized at the experimental subcoercive electric fields near the temperature of the orthorhombic-tetragonal phase transition with respect to poling in both phases. Poling in the tetragonal phase is shown to enhance the low-signal dielectric and piezoelectric properties in the orthorhombic phase.

Pd/NbOPO₄ multifunctional catalyst for the direct production of liquid alkanes from aldol adducts of furans.

PubMed

Xia, Qi-Neng; Cuan, Qian; Liu, Xiao-Hui; Gong, Xue-Qing; Lu, Guan-Zhong; Wang, Yan-Qin

2014-09-08

Great efforts have been made to convert renewable biomass into transportation fuels. Herein, we report the novel properties of NbO(x)-based catalysts in the hydrodeoxygenation of furan-derived adducts to liquid alkanes. Excellent activity and stability were observed with almost no decrease in octane yield (>90% throughout) in a 256 h time-on-stream test. Experimental and theoretical studies showed that NbO(x) species play the key role in C-O bond cleavage. As a multifunctional catalyst, Pd/NbOPO4 plays three roles in the conversion of aldol adducts into alkanes: 1) The noble metal (in this case Pd) is the active center for hydrogenation; 2) NbO(x) species help to cleave the C-O bond, especially of the tetrahydrofuran ring; and 3) a niobium-based solid acid catalyzes the dehydration, thus enabling the quantitative conversion of furan-derived adducts into alkanes under mild conditions. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

LiNbO3 coating on concrete surface: a new and environmentally friendly route for artificial photosynthesis.

PubMed

Nath, Ranjit K; Zain, M F M; Kadhum, Abdul Amir H

2013-01-01

The addition of a photocatalyst to ordinary building materials such as concrete creates environmentally friendly materials by which air pollution or pollution of the surface can be diminished. The use of LiNbO3 photocatalyst in concrete material would be more beneficial since it can produce artificial photosynthesis in concrete. In these research photoassisted solid-gas phases reduction of carbon dioxide (artificial photosynthesis) was performed using a photocatalyst, LiNbO3, coated on concrete surface under illumination of UV-visible or sunlight and showed that LiNbO3 achieved high conversion of CO2 into products despite the low levels of band-gap light available. The high reaction efficiency of LiNbO3 is explained by its strong remnant polarization (70 µC/cm(2)), allowing a longer lifetime of photoinduced carriers as well as an alternative reaction pathway. Due to the ease of usage and good photocatalytic efficiency, the research work done showed its potential application in pollution prevention.

Threshold Switching Characteristics of Nb/NbO 2 /TiN Vertical Devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Yuhan; Comes, Ryan B.; Wolf, Stuart A.

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 thismore » device as an electronic switch.« less

Tribological properties of self-lubricating Ta-Cu films

NASA Astrophysics Data System (ADS)

Qin, Wen; Fu, Licai; Zhu, Jiajun; Yang, Wulin; Li, Deyi; Zhou, Lingping

2018-03-01

In this paper, Ta and TaCu films were deposited by using magnetron sputtering, and the tribological properties of the films against Si3N4 balls were investigated under the loads of 2 N and 5 N. The average grain sizes of both films are below 25 nm. Ta and TaCu films have approximate hardness. While the wear rate of TaCu film is much smaller than that of Ta film. Post-wear testing XRD, Raman and XPS revealed the formation of tantalum oxide on the worn surface of both Ta and TaCu films. Tantalum oxidation is effectively lubricating to reduce friction coefficient. So the friction coefficient of both Ta and TaCu film is about 0.45 under different applied loads. Meanwhile, the addition of Cu could increase the toughness of the film, and avoid the generation of wear debris, resulting in a significant increase in wear resistance.

Mechanism of action of NB2001 and NB2030, novel antibacterial agents activated by beta-lactamases.

PubMed

Stone, Geoffrey W; Zhang, Qin; Castillo, Rosario; Doppalapudi, V Ramana; Bueno, Analia R; Lee, Jean Y; Li, Qing; Sergeeva, Maria; Khambatta, Gody; Georgopapadakou, Nafsika H

2004-02-01

Two potent antibacterial agents designed to undergo enzyme-catalyzed therapeutic activation were evaluated for their mechanisms of action. The compounds, NB2001 and NB2030, contain a cephalosporin with a thienyl (NB2001) or a tetrazole (NB2030) ring at the C-7 position and are linked to the antibacterial triclosan at the C-3 position. The compounds exploit beta-lactamases to release triclosan through hydrolysis of the beta-lactam ring. Like cephalothin, NB2001 and NB2030 were hydrolyzed by class A beta-lactamases (Escherichia coli TEM-1 and, to a lesser degree, Staphylococcus aureus PC1) and class C beta-lactamases (Enterobacter cloacae P99 and E. coli AmpC) with comparable catalytic efficiencies (k(cat)/K(m)). They also bound to the penicillin-binding proteins of S. aureus and E. coli, but with reduced affinities relative to that of cephalothin. Accordingly, they produced a cell morphology in E. coli consistent with the toxophore rather than the beta-lactam being responsible for antibacterial activity. In biochemical assays, they inhibited the triclosan target enoyl reductase (FabI), with 50% inhibitory concentrations being markedly reduced relative to that of free triclosan. The transport of NB2001, NB2030, and triclosan was rapid, with significant accumulation of triclosan in both S. aureus and E. coli. Taken together, the results suggest that NB2001 and NB2030 act primarily as triclosan prodrugs in S. aureus and E. coli.

Mechanism of generation of large (Ti,Nb,V)(C,N)-type precipitates in H13 + Nb tool steel

NASA Astrophysics Data System (ADS)

Xie, You; Cheng, Guo-guang; Chen, Lie; Zhang, Yan-dong; Yan, Qing-zhong

2016-11-01

The characteristics and generation mechanism of (Ti,Nb,V)(C,N) precipitates larger than 2 μm in Nb-containing H13 bar steel were studied. The results show that two types of (Ti,Nb,V)(C,N) phases exist—a Ti-V-rich one and an Nb-rich one—in the form of single or complex precipitates. The sizes of the single Ti-V-rich (Ti,Nb,V)(C,N) precipitates are mostly within 5 to 10 μm, whereas the sizes of the single Nb-rich precipitates are mostly 2-5 μm. The complex precipitates are larger and contain an inner Ti-V-rich layer and an outer Nb-rich layer. The compositional distribution of (Ti,Nb,V)(C,N) is concentrated. The average composition of the single Ti-V-rich phase is (Ti0.511V0.356Nb0.133)(C x N y ), whereas that for the single Nb-rich phase is (Ti0.061V0.263Nb0.676)(C x N y ). The calculation results based on the Scheil-Gulliver model in the Thermo-Calc software combining with the thermal stability experiments show that the large phases precipitate during the solidification process. With the development of solidification, the Ti-V-rich phase precipitates first and becomes homogeneous during the subsequent temperature reduction and heat treatment processes. The Nb-rich phase appears later.

Hierarchical Ti-Nb oxide microspheres with synergic multiphase structure as ultra-long-life anode materials for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Wang, Guanqin; Wen, Zhongsheng; Du, Lulu; Yang, Yan-E.; Li, Song; Sun, Juncai; Ji, Shijun

2017-11-01

Titanium/niobium oxides have drawn wide attention due to their attractive high lithium-intercalation voltage avoiding the formation of solid electrochemical interface. However, their poor electronic conductivity hinders the commercial applications because of the low electrochemical kinetics in lithiating and de-lithiating process. In the study, new approach to improving the low conductivity of the conventional oxides in micrometers are tactically proposed via the synergic effect of highly mixed multiphase oxide nanocrystals. Ti-Nb oxide composite microspheres with hierarchical microstructure are fabricated successfully via a very facile method combined solvothermal process and calcination. Interconnected crystalline nanoparticles of TiO2, Nb2O5 and TiNb2O7 nanocrystals are involved in the obtained Ti-Nb oxides, demonstrating high structure stability during electrochemical reaction. Meanwhile, the ionic/electronic conductivity is remarkably enhanced by the defects of O2- vacancies and Ti3+/Nb4+ ions. The remained specific capacity of the multiphase Ti-Nb oxides is up to 185.3 mAh g-1 at 5 C with very weak capacity fade of 5.3% after 1800 cycles, showing a very long cycling stability.

Fabrication and characterization of microstructure of stainless steel matrix composites containing up to 25 vol% NbC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kan, Wen Hao, E-mail: wkan6795@uni.sydney.edu.au

AISI 440 stainless steels reinforced with various volume fractions of niobium carbide (NbC) particles of up to 25 vol% were fabricated in-situ using an argon arc furnace and then heat-treated to produce a martensitic matrix. Optical and scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and electron back-scatter diffraction (EBSD) techniques were used to analyze the microstructure, phases and composition of these composites. Interestingly, it was found that Chinese-script NbC could nucleate on existing primary NbC particles creating NbC clusters with complex microstructures. Additionally, hardness tests were used to evaluate viability in mining and mineral processing applications. The increasemore » in NbC content resulted in an overall increase in the hardness of the composites while causing a marginal decrease in the amount of Cr in solid solution with the matrix, which could be a concern for corrosion resistance. The latter was due to the fact that the NbC lattice could dissolve a minor amount of Cr. Thermodynamic simulations also attributed this to a slight increase in M{sub 7}C{sub 3} precipitation. Nonetheless, these novel composites show great promise for applications in wear and corrosive environments. - Highlights: •Stainless steels reinforced with NbC particles of up to 25 vol% were fabricated. •NbC was formed in-situ in the steels using an arc melter. •Martensitic transformation of the matrix of each sample was achieved. •NbC reinforcements increased the bulk hardness values of the steels. •Dissolved Cr in the matrix of each sample was sufficient for passivity in theory.« less

Nanoarchitectured Nb2O5 hollow, Nb2O5@carbon and NbO2@carbon Core-Shell Microspheres for Ultrahigh-Rate Intercalation Pseudocapacitors

NASA Astrophysics Data System (ADS)

Kong, Lingping; Zhang, Chuanfang; Wang, Jitong; Qiao, Wenming; Ling, Licheng; Long, Donghui

2016-02-01

Li-ion intercalation materials with extremely high rate capability will blur the distinction between batteries and supercapacitors. We construct a series of nanoarchitectured intercalation materials including orthorhombic (o-) Nb2O5 hollow microspheres, o-Nb2O5@carbon core-shell microspheres and tetragonal (t-) NbO2@carbon core-shell microspheres, through a one-pot hydrothermal method with different post-treatments. These nanoarchitectured materials consist of small nanocrystals with highly exposed active surface, and all of them demonstrate good Li+ intercalation pseudocapacitive properties. In particular, o-Nb2O5 hollow microspheres can deliver the specific capacitance of 488.3 F g-1, and good rate performance of 126.7 F g-1 at 50 A g-1. The o-Nb2O5@carbon core-shell microspheres show enhanced specific capacitance of 502.2 F g-1 and much improved rate performance (213.4 F g-1 at 50 A g-1). Furthermore, we demonstrate for the first time, t-NbO2 exhibits much higher rate capability than o-Nb2O5. For discharging time as fast as 5.9 s (50 A g-1), it still exhibits a very high specific capacitance of 245.8 F g-1, which is 65.2% retention of the initial capacitance (377.0 F g-1 at 1 A g-1). The unprecedented rate capability is an intrinsic feature of t-NbO2, which may be due to the conductive lithiated compounds.

Nanoarchitectured Nb2O5 hollow, Nb2O5@carbon and NbO2@carbon Core-Shell Microspheres for Ultrahigh-Rate Intercalation Pseudocapacitors

PubMed Central

Kong, Lingping; Zhang, Chuanfang; Wang, Jitong; Qiao, Wenming; Ling, Licheng; Long, Donghui

2016-01-01

Li-ion intercalation materials with extremely high rate capability will blur the distinction between batteries and supercapacitors. We construct a series of nanoarchitectured intercalation materials including orthorhombic (o-) Nb2O5 hollow microspheres, o-Nb2O5@carbon core-shell microspheres and tetragonal (t-) NbO2@carbon core-shell microspheres, through a one-pot hydrothermal method with different post-treatments. These nanoarchitectured materials consist of small nanocrystals with highly exposed active surface, and all of them demonstrate good Li+ intercalation pseudocapacitive properties. In particular, o-Nb2O5 hollow microspheres can deliver the specific capacitance of 488.3 F g−1, and good rate performance of 126.7 F g−1 at 50 A g−1. The o-Nb2O5@carbon core-shell microspheres show enhanced specific capacitance of 502.2 F g−1 and much improved rate performance (213.4 F g−1 at 50 A g−1). Furthermore, we demonstrate for the first time, t-NbO2 exhibits much higher rate capability than o-Nb2O5. For discharging time as fast as 5.9 s (50 A g−1), it still exhibits a very high specific capacitance of 245.8 F g−1, which is 65.2% retention of the initial capacitance (377.0 F g−1 at 1 A g−1). The unprecedented rate capability is an intrinsic feature of t-NbO2, which may be due to the conductive lithiated compounds. PMID:26880276

Radio frequency magnetic field limits of Nb and Nb 3Sn

DOE PAGES

Posen, S.; Valles, N.; Liepe, M.

2015-07-21

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 3Sn. 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 3Sn, which is a promisingmore » 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. Furthermore, analysis of the results shows that the limitation is consistent with nucleation of flux penetration at defects in the rf layer.« less

76 FR 77015 - Solid Urea From Russia and Ukraine

Federal Register 2010, 2011, 2012, 2013, 2014

2011-12-09

... Urea From Russia and Ukraine Determination On the basis of the record \\1\\ developed in the subject five... orders on solid urea from Russia and Ukraine would be likely to lead to continuation or recurrence of... 2011), entitled Solid Urea from Russia and Ukraine: Investigation Nos. 731-TA- 340-E and 340-H (Third...

Degradation of superconducting Nb/NbN films by atmospheric oxidation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henry, M. David; Wolfley, Steve; Young, Travis

2017-03-01

Niobium and niobium nitride thin films are transitioning from fundamental research toward wafer scale manufacturing with technology drivers that include superconducting circuits and electronics, optical single photon detectors, logic, and memory. Successful microfabrication requires precise control over the properties of sputtered superconducting films, including oxidation. Previous work has demonstrated the mechanism in oxidation of Nb and how film structure could have deleterious effects upon the superconducting properties. This study provides an examination of atmospheric oxidation of NbN films. By examination of the room temperature sheet resistance of NbN bulk oxidation was identified and confirmed by secondary ion mass spectrometry. Asmore » a result, Meissner magnetic measurements confirmed the bulk oxidation not observed with simple cryogenic resistivity measurements.« less

Flexible Nb2O5 nanowires/graphene film electrode for high-performance hybrid Li-ion supercapacitors

NASA Astrophysics Data System (ADS)

Song, Hao; Fu, Jijiang; Ding, Kang; Huang, Chao; Wu, Kai; Zhang, Xuming; Gao, Biao; Huo, Kaifu; Peng, Xiang; Chu, Paul K.

2016-10-01

The hybrid Li-ion electrochemical supercapacitor (Li-HSC) combining the battery-like anode with capacitive cathode is a promising energy storage device boasting large energy and power densities. Orthorhombic Nb2O5 is a good anode material in Li-HSCs because of its large pseudocapacitive Li-ion intercalation capacity. Herein, we report a high-performance, binder-free and flexible anode consisting of long Nb2O5 nanowires and graphene (L-Nb2O5 NWs/rGO). The paper-like L-Nb2O5 NWs/rGO film electrode has a large mass loading of Nb2O5 of 93.5 wt% as well as short solid-state ion diffusion length, and enhanced conductivity (5.1 S cm-1). The hybrid L-Nb2O5 NWs/rGO paper electrode shows a high reversible specific capacity of 160 mA h g-1 at a current density of 0.2 A g-1, superior rate capability with capacitance retention of 60% when the current density increases from 0.2 to 5 A g-1, as well as excellent cycle stability. The Li-HSC device based on the L-Nb2O5/rGO anode and the cathode of biomass-derived carbon nanosheets delivers an energy density of 106 Wh kg-1 at 580 W kg-1 and 32 Wh kg-1 at a large power density of 14 kW kg-1. Moreover, the Li-HSC device exhibits excellent cycling performance without obvious capacitance decay after 1000 cycles.

Calculations of stopping powers of 100 eV-30 keV electrons in 31 elemental solids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanuma, S.; Powell, C. J.; Penn, D. R.

We present calculated electron stopping powers (SPs) for 31 elemental solids (Li, Be, glassy C, graphite, diamond, Na, Mg, K, Sc, Ti, V, Fe, Y, Zr, Nb, Mo, Ru, Rh, In, Sn, Cs, Gd, Tb, Dy, Hf, Ta, W, Re, Os, Ir, and Bi). These SPs were determined with an algorithm previously used for the calculation of electron inelastic mean free paths and from energy-loss functions (ELFs) derived from experimental optical data. The SP calculations were made for electron energies between 100 eV and 30 keV and supplement our earlier SP calculations for ten additional solids (Al, Si, Cr, Ni,more » Cu, Ge, Pd, Ag, Pt, and Au). Plots of SP versus atomic number for the group of 41 solids show clear trends. Multiple peaks and shoulders are seen that result from the contributions of valence-electron and various inner-shell excitations. Satisfactory agreement was found between the calculated SPs and values from the relativistic Bethe SP equation with recommended values of the mean excitation energy (MEE) for energies above 10 keV. We determined effective MEEs versus maximum excitation energy from the ELFs for each solid. Plots of effective MEE versus atomic number showed the relative contributions of valence-electron and different core-electron excitations to the MEE. For a maximum excitation energy of 30 keV, our effective MEEs agreed well for Be, graphite, Na, Al, and Si with recommended MEEs; a difference for Li was attributed to sample oxidation in the SP measurements for the recommended MEE. Substantially different effective MEEs were found for the three carbon allotropes (graphite, diamond, and glassy C)« less

Crystal Structure, Piezoelectric and Dielectric Properties of (Li, Ce)4+, Nb5+ and Mn2+ Co-doped CaBi4Ti4O15 High-Temperature Ceramics

NASA Astrophysics Data System (ADS)

Xin, Deqiong; Chen, Qiang; Wu, Jiagang; Bao, Shaoming; Zhang, Wen; Xiao, Dingquan; Zhu, Jianguo

2016-07-01

Bismuth-layered structured ceramics Ca0.85(Li,Ce)0.075Bi4Ti4- x Nb x O15-0.01MnCO3 were prepared by the conventional solid-state reaction method. The evolution of microstructure and corresponding electrical properties were studied. All the samples presented a single bismuth layered-structural phase with m = 4, indicating that (Li, Ce)4+, Nb5+ and Mn2+ adequately enter into the pseudo-perovskite structure and form solid solutions. It was found that Ca0.85(Li,Ce)0.075Bi4Ti3.98Nb0.02O15-0.01MnCO3 (CBTLCM-0.02Nb) ceramics possess the optimum electrical properties. The piezoelectric coefficient d 33, dielectric constant ɛ r, loss tan δ, planar electromechanical coupling factor k p and Curie-temperature T C of CBTLCM-0.02Nb ceramics were found to be ˜19.6 pC/N, 160, 0.16%, 8.1% and 767°C, respectively. Furthermore, the thermal depoling behavior demonstrates that the d 33 value of x = 0.02 content remains at 16.8 pC/N after annealing at 500°C. These results suggest that the (Li, Ce)4+-, Nb5+- and Mn2+-doped CBT-based ceramics are promising candidates for high-temperature piezoelectric applications.

Solidification processing of intermetallic Nb-Al alloys

NASA Technical Reports Server (NTRS)

Smith, Preston P.; Oliver, Ben F.; Noebe, Ronald D.

1992-01-01

Several Nb-Al alloys, including single-phase NbAl3 and the eutectic of Nb2Al and NbAl3, were prepared either by nonconsumable arc melting in Ar or by zone processing in He following initial induction melting and rod casting, and the effect of the solidification route on the microstructure and room-temperature mechanical properties of these alloys was investigated. Automated control procedures and melt conditions for directional solidification of NbAl3 and the Nb2Al/Nb3Al eutectic were developed; high purity and stoichiometry were obtained. The effects of ternary additions of Ti and Ni are described.

Tuning the effective parameters in (Ta/Cu/[Ni/Co]x/Ta) multilayers with perpendicular magnetic anisotropy

NASA Astrophysics Data System (ADS)

Ayareh, Zohreh; Moradi, Mehrdad; Mahmoodi, Saman

2018-06-01

In this paper, we report perpendicular magnetic anisotropy (PMA) in a (Ta/Cu/[Ni/Co]x/Ta) multilayers structure. These typical structures usually include a multilayer of ferromagnetic and transition metal thin films. Usually, magnetic anisotropy is characterized by magnetization loops determined by magnetometer or magneto-optical Kerr effect (MOKE). The interface between ferromagnetic and metallic layers plays an important role in magnetic anisotropy evolution from out-of-plane to in-plane in (Ta/Cu/[Ni/Co]/Ta) structure. Obtained results from MOKE and magnetometry of these samples show that they have different easy axes due to change in thickness of Cu as spacer layer and difference in number of repetition of [Ni/Co] stacks.

Fabrication of a Tantalum-Based Josephson Junction for an X-Ray Detector

NASA Astrophysics Data System (ADS)

Morohashi, Shin'ichi; Gotoh, Kohtaroh; Yokoyama, Naoki

2000-06-01

We have fabricated a tantalum-based Josephson junction for an X-ray detector. The tantalum layer was selected for the junction electrode because of its long quasiparticle lifetime, large X-ray absorption efficiency and stability against thermal cycling. We have developed a buffer layer to fabricate the tantalum layer with a body-centered cubic structure. Based on careful consideration of their superconductivity, we have selected a niobium thin layer as the buffer layer for fabricating the tantalum base electrode, and a tungsten thin layer for the tantalum counter electrode. Fabricated Nb/AlOx-Al/Ta/Nb and Nb/Ta/W/AlOx-Al/Ta/Nb Josephson junctions exhibited current-voltage characteristics with a low subgap leakage current.

Phase Composition of Samarium Niobate and Tantalate Thin Films Prepared by Sol-Gel Method

NASA Astrophysics Data System (ADS)

Bruncková, H.; Medvecký, Ľ.; Múdra, E.; Kovalčiková, A.; Ďurišin, J.; Šebek, M.; Girman, V.

2017-12-01

Samarium niobate SmNbO4 (SNO) and tantalate SmTaO4 (STO) thin films ( 100 nm) were prepared by sol-gel/spin-coating process on alumina substrates with PZT interlayer and annealing at 1000°C. The precursors of films were synthesized using Nb or Ta tartrate complexes. The improvement of the crystallinity of monoclinic M'-SmTaO4 phase via heating was observed through the coexistence of small amounts of tetragonal T-SmTa7O19 phase in STO precursor at 1000°C. The XRD results of SNO and STO films confirmed monoclinic M-SmNbO4 and M'-SmTaO4 phases, respectively, with traces of orthorhombic O-SmNbO4 (in SNO). In STO film, the single monoclinic M'-SmTaO4 phase was revealed. The surface morphology and topography of thin films were investigated by SEM and AFM analysis. STO film was smoother with roughness 3.2 nm in comparison with SNO (6.3 nm). In the microstructure of SNO film, small spherical ( 50 nm) and larger cuboidal particles ( 100 nm) of the SmNbO4 phase were observed. In STO, compact clusters composed of fine spherical SmTaO4 particles ( 20-50 nm) were found. Effect of samarium can contribute to the formation different polymorphs of these films for the application to environmental electrolytic thin film devices.

(Na{sub x}k{sub 1−x}){sub 2}Ta{sub 4}O{sub 11}(x≈0.93) piezoelectric phase from the transformation of Ta{sub 2}O{sub 5} thin films of monoclinic structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Le Gallic, M., E-mail: Marie.Le-Gallic@grenoble-inp.fr; Roussel, H.

2013-04-15

A phase of trigonal structure has been reported in previous articles to be piezoelectric with a very high longitudinal d{sub 33} coefficient of several thousand pm/V (J. Solid State Chem. 184 (2011) 2023, 2033). It was observed in Ta{sub 2}O{sub 5} thin films and assumed to be the result of a reversible monoclinic–trigonal phase transition. However, new investigations are reported because the cell parameters of this phase are actually very close to those of the natrotantite mineral Na{sub 2}Ta{sub 4}O{sub 11}. From analyses by X-ray energy dispersive spectroscopy (XEDS), the chemical composition of this trigonal phase corresponds to (Na{sub x}K{submore » 1−x}){sub 2}Ta{sub 4}O{sub 11} with x≈0.93. The origin of sodium, potassium, iron and oxygen atoms is found to be due to a pollution coming from alumina crucibles used for thermal treatments. Knowing both atomic structures Ta{sub 2}O{sub 5} and Na{sub 2}Ta{sub 4}O{sub 11} and their structural relationships, observed by high resolution transmission electron microscopy (HRTEM), the mechanism of the reaction of transformation is re-examined and discussed. This mechanism implies that Ta{sup 5+} vacancies likely exist in monoclinic structures of tantalum oxide and that electrical neutrality could be due to incorporated proton H{sup +} instead of O{sup 2−} vacancies or Ta{sup 5+} interstitials. - Graphical abstract: (a, b) TEM images of interfaces between Ta{sub 2}O{sub 5} monoclinic and (Na{sub 0.93}K{sub 0.07}){sub 2}Ta{sub 4}O{sub 11} trigonal phases where it appears that the ratio of periods for the transformation monoclinic-to-trigonal is 3/2 (c, d) corresponding schema of the reaction of transformation, (a, c) viewed along the zone axes [010]{sub o}∥[1{sup ¯}21{sup ¯}]{sub R} and (b, d) along the zone axes [100]{sub o}∥[101{sup ¯}]{sub R}. Highlights: ► The formation of a piezoelectric phase in Ta{sub 2}O{sub 5} thin films, reported in previous articles, is re-examined. ► Its composition is

Electronic structure and optical properties of Ta-doped and (Ta, N)-codoped SrTiO3 from hybrid functional calculations

NASA Astrophysics Data System (ADS)

Liu, Yanyu; Zhou, Wei; Wu, Ping

2017-02-01

A systematic study has been carried out to research the effect of Ta monodoping and (Ta, N)-codoping on the electronic structure and optical properties of SrTiO3. The results indicate that the incorporation of N into the SrTiO3 lattice is in favor of the substitution of Ta at a Ti site, which is the most favorable structure with respect to both the energetic stability and high photocatalytic activity. Furthermore, the carrier recombination centers induced by Ta monodoping are passivated in the (Ta, N)-codoped SrTiO3 system with Ta at a Ti site. Simultaneous incorporation of N and Ta results in a band gap decreasing about 0.7 eV due to the appearance of the new states hybridized by N-p states with the O-p states above the valence band. The band alignment verifies that the (Ta, N)-codoped SrTiO3 simultaneously meets the criteria of band-edge energetic positions and band gap for the overall water splitting under visible light.

Directional growth and characterization of Fe?Al?Nb eutectic alloys

NASA Astrophysics Data System (ADS)

Mota, M. A.; Coelho, A. A.; Bejarano, J. M. Z.; Gama, S.; Caram, R.

1999-03-01

The manufacturing of components for operation at high temperatures requires the use of metallic materials which can keep satisfactory mechanical and chemical properties, even at temperatures beyond 1000°C. An interesting alternative to solve such a problem is the use of directionally solidified eutectic alloys. A potentially promising system for the manufacture of structural materials, and so far not totally studied, is the eutectic based on the Fe-Al-Nb system, which involves the (FeAl) 2Nb phase and the FeAl solid solution. Eutectic samples from this system were directionally solidified in a vertical Bridgman crystal growth unit. The objective of the experiments was to determine the influence of the growth rate on the eutectic microstructure. The ingots obtained were investigated by using optical and electron scanning microscopy. At low growth rate, the eutectic microstructure remained regular, even though it showed several types of microstructure defects. As the growth rate was increased, a transition from lamellar to fibrous morphology was observed.

Anion photoelectron spectroscopy of germanium and tin clusters containing a transition- or lanthanide-metal atom; MGe(n)- (n = 8-20) and MSn(n)- (n = 15-17) (M = Sc-V, Y-Nb, and Lu-Ta).

PubMed

Atobe, Junko; Koyasu, Kiichirou; Furuse, Shunsuke; Nakajima, Atsushi

2012-07-14

The electronic properties of germanium and tin clusters containing a transition- or lanthanide-metal atom from group 3, 4, or 5, MGe(n) (M = Sc, Ti, V, Y, Zr, Nb, Lu, Hf, and Ta) and MSn(n) (M = Sc, Ti, Y. Zr, and Hf), were investigated by anion photoelectron spectroscopy at 213 nm. In the case of the group 3 elements Sc, Y, and Lu, the threshold energy of electron detachment of MGe(n)(-) exhibits local maxima at n = 10 and 16, while in the case of the group 4 elements Ti, Zr, and Hf, it exhibits a local minimum only at n = 16, associated with the presence of a small bump in the spectrum. A similar behavior is observed for MSn(n)(-) around n = 16, and these electronic characteristics of MGe(n) and MSn(n) are closely related to those of MSi(n). Compared to MSi(n), however, the larger cavity size of a Ge(n) cage allows metal atom encapsulation at a smaller size n. A cooperative effect between the electronic and geometric structures of clusters with a large cavity of Ge(16) or Sn(16) is discussed together with the results of experiments that probe their geometric stability via their reactivity to H(2)O adsorption.

Direct evidence of an incommensurate phase in NaNbO{sub 3} and its implication in NaNbO{sub 3}-based lead-free antiferroelectrics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Hanzheng; Randall, Clive A., E-mail: car4@psu.edu; Shimizu, Hiroyuki

2015-09-14

Hot-stage in situ transmission electron microscopy was employed to investigate the temperature-induced complex sequence of phase transitions in NaNbO{sub 3} polycrystalline. In addition to the commonly recognized P (Pbma) → R (Pmnm) → S (Pnmm) phase transitions, incommensurate phases were observed to exist in P and R phase regions. The former (in the P → R transition region) is coincident with a diffused dielectric peak appearing at ∼170 °C, and the latter (in the R → S transition region) serves as an intermediate structure to bridge the two sub-phases in the R phase region. The incommensurate phase in the P phasemore » region can be inferred from the polarization current density and differential dielectric permittivity anomalies, and it provides the bridge structure during the electric field-induced polarization reversal and antiferroelectric-to-ferroelectric transition in NaNbO{sub 3} solid solutions.« less

Low-Temperature Sintering Li3Mg1.8Ca0.2NbO6 Microwave Dielectric Ceramics with LMZBS Glass

NASA Astrophysics Data System (ADS)

Wang, Gang; Zhang, Huaiwu; Liu, Cheng; Su, Hua; Jia, Lijun; Li, Jie; Huang, Xin; Gan, Gongwen

2018-05-01

Li3Mg1.8Ca0.2NbO6 ceramics doped with Li2O-MgO-ZnO-B2O3-SiO2 glass (LMZBS) were prepared via a solid-state route. The LMZBS glass effectively reduced the sintering temperature of Li3Mg1.8Ca0.2NbO6 ceramics to 950°C. The effects of the LMZBS glass on the sintering behavior, microstructures and microwave dielectric properties of Li3Mg1.8Ca0.2NbO6 ceramics are discussed in detail. Among all the LMZBS doped Li3Mg1.8Ca0.2NbO6 ceramics, the sample with 1 wt.% of LMZBS glass sintered at 950°C for 4 h exhibited good dielectric properties: ɛ r = 16.7, Q × f = 31,000 GHz (9.92 GHz), τ f = - 1.3 ppm/°C. The Li3Mg1.8Ca0.2NbO6 ceramics possessed excellent chemical compatibility with Ag electrodes, and could be applied in low temperature co-fired ceramics (LTCC) applications.

Structural and dielectric properties of Sr3(MgTa2)O9 and Sr3(ZnTa2)O9

NASA Astrophysics Data System (ADS)

Hoque, Md. M.; Dutta, Alo; Kumar, S.; Sinha, T. P.

2015-07-01

Herein, we report the crystal structures and morphological properties of Sr3(MgTa2)O9 (SMT) and Sr3(ZnTa2)O9 (SZT) synthesized by solid state ceramic method along with the results of alternating current impedance spectroscopic (ACIS) study in a frequency range from 50 Hz to 1 MHz at selective temperatures between 393 and 573 K. The crystal structures of SMT and SZT have been determined by Rietveld refinement of powder X-ray diffraction pattern using an initial structural model developed on the basis of literature survey. The results indicate that both the samples possess hexagonal structure of trigonal P 3 bar m 1 space group. The lattice parameters of SMT are a=b=5.65162 Å, c=6.94440 Å, α=β=90° and γ=120° and those of SZT are a=b=5.65832 Å, c=6.95911 Å and α=β=90° and γ=120°. SMT and SZT are isostructural and they exhibit 2:1 B site ordering with the staking sequence of {-Ta-Ta-Mg (Zn)-} (Mg for SMT and Zn for SZT) layer repeat on (111) plane of the pseudocells. The characteristic vibrational bands due to Ta-O, Mg-O and Zn-O bonds have been observed in the FTIR spectra of the samples. The FESEM micrographs of the samples show that the grains size ranges between 0.40 and 3.65 μm and 0.9 to 4.2 μm for SMT and SZT, respectively. To account for the polydispersive nature of the dielectric relaxation mechanism along with the effects of dc conductivity and localized space charges the variation of real (ε‧) and imaginary (ε″) parts of dielectric constant with frequency has been analytically interpreted in the framework of modified Cole-Cole model. SMT and SZT having the activation energies of 0.35 eV and 0.33 eV, respectively (obtained from the Arrhenius plot of dc conductivity), are semiconducting in nature. The electrical current conduction in the samples occurs by polaron hopping process. Further, we have shown that chemical property of A site cations has significant role in determining the dielectric properties of A3B‧B″2O9 type perovskites

O-GlcNAc-mediated interaction between VER2 and TaGRP2 elicits TaVRN1 mRNA accumulation during vernalization in winter wheat

PubMed Central

Xiao, Jun; Xu, Shujuan; Li, Chunhua; Xu, Yunyuan; Xing, Lijing; Niu, Yuda; Huan, Qing; Tang, Yimiao; Zhao, Changping; Wagner, Doris; Gao, Caixia; Chong, Kang

2014-01-01

Vernalization, sensing of prolonged cold, is important for seasonal flowering in eudicots and monocots. While vernalization silences a repressor (FLC, MADS-box transcription factor) in eudicots, it induces an activator (TaVRN1, an AP1 clade MADS-box transcription factor) in monocots. The mechanism for TaVRN1 induction during vernalization is not well understood. Here we reveal a novel mechanism for controlling TaVRN1 mRNA accumulation in response to prolonged cold sensing in wheat. The carbohydrate-binding protein VER2, a jacalin lectin, promotes TaVRN1 upregulation by physically interacting with the RNA-binding protein TaGRP2. TaGRP2 binds to TaVRN1 pre-mRNA and inhibits TaVRN1 mRNA accumulation. The physical interaction between VER2 and TaGRP2 is controlled by TaGRP2 O-GlcNAc modification, which gradually increases during vernalization. The interaction between VER2 and O-GlcNAc-TaGRP2 reduces TaGRP2 protein accumulation in the nucleus and/or promotes TaGRP2 dissociation from TaVRN1, leading to TaVRN1 mRNA accumulation. Our data reveal a new mechanism for sensing prolonged cold in temperate cereals. PMID:25091017

The impact of Ti and temperature on the stability of Nb5Si3 phases: a first-principles study

PubMed Central

Papadimitriou, Ioannis; Utton, Claire; Tsakiropoulos, Panos

2017-01-01

Abstract Nb-silicide based alloys could be used at T > 1423 K in future aero-engines. Titanium is an important additive to these new alloys where it improves oxidation, fracture toughness and reduces density. The microstructures of the new alloys consist of an Nb solid solution, and silicides and other intermetallics can be present. Three Nb5Si3 polymorphs are known, namely αNb5Si3 (tI32 Cr5B3-type, D8l), βNb5Si3 (tI32 W5Si3-type, D8m) and γNb5Si3 (hP16 Mn5Si3-type, D88). In these 5–3 silicides Nb atoms can be substituted by Ti atoms. The type of stable Nb5Si3 depends on temperature and concentration of Ti addition and is important for the stability and properties of the alloys. The effect of increasing concentration of Ti on the transition temperature between the polymorphs has not been studied. In this work first-principles calculations were used to predict the stability and physical properties of the various Nb5Si3 silicides alloyed with Ti. Temperature-dependent enthalpies of formation were computed, and the transition temperature between the low (α) and high (β) temperature polymorphs of Nb5Si3 was found to decrease significantly with increasing Ti content. The γNb5Si3 was found to be stable only at high Ti concentrations, above approximately 50 at. % Ti. Calculation of physical properties and the Cauchy pressures, Pugh’s index of ductility and Poisson ratio showed that as the Ti content increased, the bulk moduli of all silicides decreased, while the shear and elastic moduli and the Debye temperature increased for the αNb5Si3 and γNb5Si3 and decreased for βNb5Si3. With the addition of Ti the αNb5Si3 and γNb5Si3 became less ductile, whereas the βNb5Si3 became more ductile. When Ti was added in the αNb5Si3 and βNb5Si3 the linear thermal expansion coefficients of the silicides decreased, but the anisotropy of coefficient of thermal expansion did not change significantly. PMID:28740563

Porous TiNb24O62 microspheres as high-performance anode materials for lithium-ion batteries of electric vehicles.

PubMed

Yang, Chao; Deng, Shengjue; Lin, Chunfu; Lin, Shiwei; Chen, Yongjun; Li, Jianbao; Wu, Hui

2016-11-10

TiNb 24 O 62 is explored as a new anode material for lithium-ion batteries. Microsized TiNb 24 O 62 particles (M-TiNb 24 O 62 ) are fabricated through a simple solid-state reaction method and porous TiNb 24 O 62 microspheres (P-TiNb 24 O 62 ) are synthesized through a facile solvothermal method for the first time. TiNb 24 O 62 exhibits a Wadsley-Roth shear structure with a structural unit composed of a 3 × 4 octahedron-block and a 0.5 tetrahedron at the block-corner. P-TiNb 24 O 62 with an average sphere size of ∼2 μm is constructed by nanoparticles with an average size of ∼100 nm, forming inter-particle pores with a size of ∼8 nm and inter-sphere pores with a size of ∼55 nm. Such desirable porous microspheres are an ideal architecture for enhancing the electrochemical performances by shortening the transport distance of electrons/Li + -ions and increasing the reaction area. Consequently, P-TiNb 24 O 62 presents outstanding electrochemical performances in terms of specific capacity, rate capability and cyclic stability. The reversible capacities of P-TiNb 24 O 62 are, respectively, as large as 296, 277, 261, 245, 222, 202 and 181 mA h g -1 at 0.1, 0.5, 1, 2, 5, 10 and 20 C, which are obviously larger than those of M-TiNb 24 O 62 (258, 226, 210, 191, 166, 147 and 121 mA h g -1 ). At 10 C, the capacity of P-TiNb 24 O 62 still remains at 183 mA h g -1 over 500 cycles with a decay of only 0.02% per cycle, whereas the corresponding values of M-TiNb 24 O 62 are 119 mA h g -1 and 0.04%. These impressive results indicate that P-TiNb 24 O 62 can be a promising anode material for lithium-ion batteries of electric vehicles.

The characterisation of second phases in the Zr-Nb and Zr-Nb-Sn-Fe alloys: A critical review

NASA Astrophysics Data System (ADS)

Harte, Allan; Griffiths, Malcolm; Preuss, Michael

2018-07-01

The nature and evolution of the Fe environment in Zr-Nb and Zr-Nb-Sn-Fe systems is essential to alloy performance during corrosion, hardening and irradiation-induced growth. Unfortunately, there is ambiguity in the literature regarding the characterisation of secondary phases in these systems. The presence, or not, of Fe in β-Nb phase has been a source of disagreement. In ternary ZrNbFe intermetallics, identical compositions have been designated as Zr(Nb,Fe)2 or (Zr,Nb)3Fe. We show that while Zr(Nb,Fe)2 is commonly reported, it is not always justified. The cubic phase (Zr,Nb)2Fe is easily identified, but its composition is more variable after low temperature heat treatments. We demonstrate the need for correlative approaches in the assessment of phase composition, crystallography and local Fe environment under different heat treatment regimes. Irradiation effects allow us to draw clues regarding phase designation, but there is diverse behaviour under irradiation due to initial phase composition, irradiation dose rate and temperature.

Effect of [Li]/[Nb] ratio on composition and defect structure of Zr:Yb:Tm:LiNbO3 crystals

NASA Astrophysics Data System (ADS)

Liu, Chunrui; Dai, Li; Wang, Luping; Shao, Yu; Yan, Zhehua; Xu, Yuheng

2018-04-01

Zr:Yb:Tm:LiNbO3 crystals with various [Li]/[Nb] ratios (0.946, 1.05, 1.20 and 1.38) were grown by the Czochralski technique. Distribution coefficients of Zr4+, Yb3+ and Tm3+ ions were analyzed by the inductively coupled plasma-atomic emission spectrometer (ICP-AES). The influence of [Li]/[Nb] ratio on the composition and defect structure of Zr:Yb:Tm:LiNbO3 crystals was investigated by X-ray diffraction and IR transmission spectrum. The results show that as the [Li]/[Nb] ratio increases in the melt, the distribution coefficients of Yb3+ and Tm3+ ions both increase while that of Zr4+ ion deceases. When the [Li]/[Nb] ratio increases to 1.20 in the melt, Zr:Yb:Tm:LiNbO3 crystal is nearly stoichiometric. In addition, when the [Li]/[Nb] ratio reaches up to 1.38, NbLi4+ are completely replaced and Li+ starts to impel the Zr4+, Yb3+ and Tm3+ into the normal Li sites.

Electrical and structural properties of Nb-doped TiO2 at different Nb concentrations deposited by spin coating technique

NASA Astrophysics Data System (ADS)

Saurdi, I.; Shafura, A. K.; Mamat, M. H.; Ishak, A.; Rusop, M.

2018-05-01

In this paper, the Nb-doped TiO2 films were deposited on glass substrate and their electrical and structural properties were investigated. The results revealed that the resistivity of Nb-doped TiO2 films of 0 at.%, 1 at.%, 3 at.%, 5 at.% and 7 at.% were 2.78 × 105, 1.35 × 105 Ω.cm, 5.89 × 104 Ω.cm, 9.20 × 102 Ω.cm and 9.56 × 103 Ω.cm, respectively. Where, the lowest resistivity of 9.20 × 102 Ω.cm was obtained at 5at.% Nb-doped TiO2 films. The resistivity of Nb-doped TiO2 films decreases as the Nb concentration increased from 0 at.% to 5 at.%. However, the resistivity decrease at 7 at.% Nb-doped TiO2 films. Meanwhile, from the FESEM images the Nb-doped TiO2 films with 0 at.%, 1 at.%, 3 at.% and 5 at.% Nb had a rough and porous structures were observed. However, the Nb-doped TiO2 at 7 at.% has a agglomerated and denser structures.

Superstructure Ta2O5 mesocrystals derived from (NH4)2Ta2O3F6 mesocrystals with efficient photocatalytic activity.

PubMed

Yu, Xin; Li, Wei; Huang, Jian; Li, Zhonghua; Liu, Jiawen; Hu, PingAn

2018-02-06

Superstructured mesocrystalline Ta 2 O 5 nanosheets were successfully prepared from mesocrystalline (NH 4 ) 2 Ta 2 O 3 F 6 nanorods by the annealing method for the first time. The as-prepared mesocrystalline Ta 2 O 5 nanosheets in this work showed remarkable visible light absorption, mainly due to the formation of oxygen vacancy defects in the mesocrystalline Ta 2 O 5 nanosheets, which was also confirmed by XPS spectra, Raman spectra and EPR spectra. Besides, the mesocrystalline Ta 2 O 5 nanosheets showed a highly enhanced photocatalytic activity of 11 268.24 μmol g -1 h -1 , about 3.95 times that of commercial Ta 2 O 5 . Moreover, the specific surface area of the mesocrystalline Ta 2 O 5 -800 nanosheets was 16.34 m 2 g -1 , about 5.32 times that of the commercial Ta 2 O 5 (3.072 m 2 g -1 ). The valence band XPS spectra indicated a strong oxidizing ability of the mesocrystalline Ta 2 O 5 nanosheets in comparison to that of commercial Ta 2 O 5 . The formation of superstructured Ta 2 O 5 mesocrystals generated long lifetime carriers and effective conduction pathways, which greatly enhanced the photocatalytic activity for hydrogen production.

Experimental and first principle study of the structure, electronic, optical and luminescence properties of M-type GdNbO4 phosphor

NASA Astrophysics Data System (ADS)

Ding, Shoujun; Zhang, Haotian; Zhang, Qingli; Chen, Yuanzhi; Dou, Renqin; Peng, Fang; Liu, Wenpeng; Sun, Dunlu

2018-06-01

In this work, GdNbO4 polycrystalline with monoclinic phase was prepared by traditional high-temperature solid-state reaction. Its structure was determined by X-ray diffraction and its unit cell parameters were obtained with Rietveld refinement method. Its luminescence properties (including absorbance, emission and luminescence lifetime) were investigated with experiment method and the CIE chromaticity coordinate was presented. Furthermore, a systematic theoretical calculation (including band gap, density of states and optical properties) based on the density function theory methods was performed on GdNbO4. Lastly, a comparison between experiment and calculated results was conducted. The calculated and experiment results obtained in this work can provide an essential understanding of GdNbO4 material.

Phase formation of V{sub 2}O{sub 5}.xNb{sub 2}O{sub 5} compounds via gels and freeze-dried precursors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Langbein, Hubert; Mayer-Uhma, Tobias

2009-03-05

An X-ray powder diffraction study of the phase formation in the system V{sub 2}O{sub 5}/Nb{sub 2}O{sub 5} is performed. Freeze-dried ammonium vanadate and ammonium oxalato niobate, alkoxide-derived xerogels and a mixture of active oxides are used as precursors to compare the resulting phase composition. Thermal decomposition of the freeze-dried precursor is monitored with DTA/TG and mass spectrometry. In the quasi-binary system V{sub 2}O{sub 5}-Nb{sub 2}O{sub 5} metastable VNbO{sub 5}, V{sub 4}Nb{sub 18}O{sub 55}, VNb{sub 9}O{sub 25} and solid solutions of V{sub 2}O{sub 5} in TT-Nb{sub 2}O{sub 5} as also thermodynamically stable VNb{sub 9}O{sub 25} exist. The thermal decomposition of freeze-driedmore » vanadate-oxalatoniobate solution allows the synthesis of all these phases in a relative simple manner. Structural relationships between an intermediate phase and the product, or, in the case of solid-state reactions, between one of the starting oxide and the product, favour the desired reaction. Therefore, the structure of a former phase influences or directs the structure of the product similar to a topotactic reaction.« less

Structure-property relationship of cast Ti-Nb alloys.

PubMed

Lee, C M; Ju, C P; Chern Lin, J H

2002-04-01

The present work is a study of the microstructure, mechanical properties and corrosion behaviour of a series of binary Ti-Nb alloys with Nb contents up to 35 wt%, with emphasis placed on the structure-property relationship of the alloys. The results indicate that crystal structure and morphology of the Ti-Nb alloys are sensitive to the Nb content. The cast c.p. Ti has a hexagonal alpha phase with a lath type morphology. The alloys containing 15 wt% or less Nb are dominated by a hexagonal alpha' phase with an acicular, martensitic structure. When containing 17.5-25 wt% Nb, the alloys are primarily comprised of an orthorhombic alpha" phase. With 27.5 wt% Nb, metastable beta phase starts to be retained. With Nb contents higher than 30 wt%, the equi-axed beta phase is almost entirely retained. Small amounts of omega phase are detected in alloys containing 27.5 and 30 wt% Nb. Among all present alloys, Ti-10Nb and Ti-27.5Nb exhibit the highest strengths, while the alpha"-dominated (17.5 and 20Nb) and beta-dominated (> 30Nb) alloys have the lowest moduli. All Ti-Nb alloys show excellent corrosion resistance in Hank's solution at 37 degrees C. From the present data, the microhardness, bending strength and modulus of the various phases in Ti-Nb alloys are compared and tentatively summarized as follows: Microhardness: omega > alpha' > alpha" > beta > alpha (c.p. Ti) Bending strength: omega > alpha' > alpha" > beta > alpha (c.p. Ti) Bending modulus: omega > alpha (c.p. Ti) > alpha' > alpha" > beta

Retention Model of TaO/HfO x and TaO/AlO x RRAM with Self-Rectifying Switch Characteristics.

PubMed

Lin, Yu-De; Chen, Pang-Shiu; Lee, Heng-Yuan; Chen, Yu-Sheng; Rahaman, Sk Ziaur; Tsai, Kan-Hsueh; Hsu, Chien-Hua; Chen, Wei-Su; Wang, Pei-Hua; King, Ya-Chin; Lin, Chrong Jung

2017-12-01

A retention behavior model for self-rectifying TaO/HfO x - and TaO/AlO x -based resistive random-access memory (RRAM) is proposed. Trapping-type RRAM can have a high resistance state (HRS) and a low resistance state (LRS); the degradation in a LRS is usually more severe than that in a HRS, because the LRS during the SET process is limited by the internal resistor layer. However, if TaO/AlO x elements are stacked in layers, the LRS retention can be improved. The LRS retention time estimated by extrapolation method is more than 5 years at room temperature. Both TaO/HfO x - and TaO/AlO x -based RRAM structures have the same capping layer of TaO, and the activation energy levels of both types of structures are 0.38 eV. Moreover, the additional AlO x switching layer of a TaO/AlO x structure creates a higher O diffusion barrier that can substantially enhance retention, and the TaO/AlO x structure also shows a quite stable LRS under biased conditions.

Epitaxial NbN/AlN/NbN tunnel junctions on Si substrates with TiN buffer layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Rui; University of Chinese Academy of Sciences, Beijing 100049; Makise, Kazumasa

We have developed epitaxial NbN/AlN/NbN tunnel junctions on Si (100) substrates with a TiN buffer layer. A 50-nm-thick (200)-oriented TiN thin film was introduced as the buffer layer for epitaxial growth of NbN/AlN/NbN trilayers on Si substrates. The fabricated NbN/AlN/NbN junctions demonstrated excellent tunneling properties with a high gap voltage of 5.5 mV, a large I{sub c}R{sub N} product of 3.8 mV, a sharp quasiparticle current rise with a ΔV{sub g} of 0.4 mV, and a small subgap leakage current. The junction quality factor R{sub sg}/R{sub N} was about 23 for the junction with a J{sub c} of 47 A/cm{supmore » 2} and was about 6 for the junction with a J{sub c} of 3.0 kA/cm{sup 2}. X-ray diffraction and transmission electron microscopy observations showed that the NbN/AlN/NbN trilayers were grown epitaxially on the (200)-orientated TiN buffer layer and had a highly crystalline structure with the (200) orientation.« less

Synthesis and photoluminescence properties of Dy{sup 3+} doped white light emitting CdTa{sub 2}O{sub 6} phosphors

DOE Office of Scientific and Technical Information (OSTI.GOV)

İlhan, Mustafa, E-mail: mustafa.ilhan@marmara.edu.tr; Ekmekçi, Mete Kaan

2015-03-15

The undoped and CdTa{sub 2}O{sub 6}:Dy{sup 3+} (0.2≤x≤2.0 mol%) phosphors were synthesized at 1100 °C for 12 h by the conventional solid state reaction method. The synthesized CdTa{sub 2}O{sub 6}:Dy{sup 3+} phosphors were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and Photoluminescence (PL) analyses. The PL spectra showed the presence of excitation peaks between 310 and 440 nm due to the 4f–4f transitions of Dy{sup 3+}. The emission of Dy{sup 3+} ions at 353.0 nm excitation was observed at 487.1 nm (blue) and 577.8 nm (yellow) due to the {sup 4}F{sub 9/2}→{sup 6}H{sub 15/2}more » transitions and {sup 4}F{sub 9/2}→{sup 6}H{sub 13/2} transitions, respectively. The PL analysis results also showed that the emissions increase with the increasing Dy{sup 3+} ion content. The emissions increased with the doping concentration of up to 1 mol%, and above this level decreased due to concentration quenching effect. The CIE chromaticity color coordinates (x,y) of the CdTa{sub 2}O{sub 6}:Dy{sup 3+} phosphors were found to be in the white light region of the chromaticity diagram. - Graphical abstract: Emission spectra at λ{sub ex}=353.0 nm and CIE chromaticity coordinate diagram of CdTa{sub 2}O{sub 6}:Dy{sup 3+} phosphors. - Highlights: • Pure and CdTa{sub 2}O{sub 6}:Dy{sup 3+} was produced by solid state reaction method. • CdTa{sub 2}O{sub 6}:Dy{sup 3+} phosphor exhibited blue and yellow emissions due to the {sup 4}F{sub 9/2}→{sup 6}H{sub 15/2} and {sup 4}F{sub 9/2}→{sup 6}H{sub 13/2} transitions. • The CCT value for 1.0 mol% CdTa{sub 2}O{sub 6}:Dy{sup 3+} was 5133 K which was located in the cool white daylight region. • Dy{sup 3+} doped CdTa{sub 2}O{sub 6} phosphor has potential in the production of white LEDs.« less

Resonances in odd-odd 182Ta

NASA Astrophysics Data System (ADS)

Brits, C. P.; Wiedeking, M.; Bello Garrote, F. L.; Bleuel, D. L.; Giacoppo, F.; Görgen, A.; Guttormsen, M.; Hadynska-Klek, K.; Hagen, T. W.; Ingeberg, V. W.; Kheswa, B. V.; Klintefjord, M.; Larsen, A. C.; Malatji, K. L.; Nyhus, H. T.; Papka, P.; Renstrøm, T.; Rose, S.; Sahin, E.; Siem, S.; Tveten, G. M.; Zeiser, F.

2017-09-01

Enhanced γ-decay on the tail of the giant electric dipole resonance, such as the scissors or pygmy resonances, can have significant impact on (n,γ) reaction rates. These rates are important input for modeling processes that take place in astrophysical environments and nuclear reactors. Recent results from the University of Oslo indicate the existence of a significant enhancement in the photon strength function for nuclei in the actinide region due to the scissors resonance. Further, the M1 strength distribution of the scissors resonances in rare earth nuclei has been studied extensively over the years. To investigate the evolution and persistence of the scissor resonance in other mass regions, an experiment was performed utilizing the NaI(Tl) γ-ray detector array (CACTUS) and silicon particle telescopes (SiRi) at the University of Oslo Cyclotron laboratory. Particle-γ coincidences from the 181Ta(d,p)182Ta and 181Ta(d,d')181Ta reactions were used to measure the nuclear level density and photon strength function of the well-deformed 181Ta and 182Ta systems, to investigate the existence of resonances below the neutron separation energy. Note to the reader: the title of this article has been corrected on September 19, 2017.

Critical Assessment 14: High Entropy Alloys and Their Development as Structural Materials (Postprint)

DTIC Science & Technology

2015-01-01

Mn and Cu or on refractory metals such as V, Cr, Ti, Mo, Nb , Ta, W, Zr and Hf.5,6 The compound forming elements Al and Ti are often added to both...additional properties include environmental resistance , processibil- ity, appearance (for architectural uses) and low cost. Workhardening and solid...be successful, and some work already reports on the corrosion resistance , oxidation behaviour and wear properties of structural HEAs.5 High entropy

Dopant occupancy and exposure energy in Hf:Nd:LiNbO3 crystal as a function of [Li]/[Nb] ratios

NASA Astrophysics Data System (ADS)

Dai, Li; Liu, Chunrui; Han, Xianbo; Yan, Zhehua; Tan, Chao; Wang, Luping; Xu, Yuheng

2017-09-01

A series of Hf: Nd: LiNbO3 crystals with various [Li]/[Nb] ratios ([Li]/[Nb] = 0.94, 1.05, 1.20, 1.38) in the melt were grown by conventional Czochralski technique. The distribution coefficients of Hf4+ and Nd3+ ions were recorded by an inductively coupled plasma-atomic emission spectrometer (ICP-AES). The effective distribution coefficient of Hf4+ is reduced and that of Nd3+ is increased with the increase of [Li]/[Nb] ratio in the melts. In all cases, the effective distribution coefficients is less than 1. The IR transmission spectroscopy of the Hf: Nd: LiNbO3 crystals were measured, getting the results that Hf: Yb: Ho: LiNbO3 crystals with 1.05 [Li]/[Nb] ratios was the stoichiometric. The optical damage resistance ability of Hf:Nd:LiNbO3 crystals were studied by light-induced scattering exposure energy flux threshold method and it increases with the increasing of [Li]/[Nb] ratios. When the [Li]/[Nb] ratio is 1.38 in the melt (the sample 4#), the exposure energy achieves 687.35 J/cm2, approximately 441 folds than that of the sample 1# ([Li]/[Nb] = 0.94) in magnitude.

Bridging the opposite chemistries of tantalum and tungsten polyoxometalates.

PubMed

Molina, P I; Sures, D J; Miró, P; Zakharov, L N; Nyman, M

2015-09-28

The disparate solubility, redox activity, and pH stability of the group V and group VI polyoxometalates (POMs) confer very different functionality on these species, and tailoring cluster properties by varying the ratio of group V to group VI metals poses both an opportunity and a synthetic challenge. A classic series of studies reported over 40 years ago provided some insight into W/Nb POMs, from which researchers have built on to date. However, the analogous W/Ta series has never been addressed in a systematic manner. Three members of this W/Ta series are presented here, synthesized from simple oxo- and peroxocoltanate precursors. [Ta3W3O19](5-) displays the Lindqvist-type structure, while [TaW9O32](5-) and [Ta2W8O32](6-) are isostructural with decatungstate ([W10O32](4-)). Additionally, the use of peroxoniobate instead of hexaniobate as the starting material drives the formation of the decatungstate-type structure [NbW9O32](5-) instead of the Lindqvist ion that was established to be the foundational cluster geometry in prior work. The electronic structure of the Nb/Ta substituted decatungstates is directly related to the degree of substitution inasmuch as the HOMO-LUMO energy gap (Egap) slightly increases as more Nb/Ta atoms are incorporated into the structure. The poor mixing of the d-orbitals of Nb/Ta and W is responsible for the observed trends in the UV spectra and cyclic voltammetry. Moreover, the stability of the molecular frameworks in the gas phase is also related to the extent of substitution as revealed by electrospray mass-spectrometry (ESI-MS).

The glass-like thermal conductivity in ZrO2-Dy3TaO7 ceramic for promising thermal barrier coating application

NASA Astrophysics Data System (ADS)

Wu, Peng; Hu, Ming Yu; Chong, Xiao Yu; Feng, Jing

2018-03-01

Using the solid-state reaction method, the (ZrO2)x-(Dy3TaO7)1-x (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1) ceramics are synthesized in this work. The identification of the crystal structures indicates that the (ZrO2)x-(Dy3TaO7)1-x ceramics belong to the orthorhombic system, and the space group is C2221 in spite of the value of x increasing to 0.1. The thermal conductivities of the (ZrO2)x-(Dy3TaO7)1-x ceramics range from 1.3 W/(m K) to 1.8 W/(m K), and this value is much lower than that of 7-8 YSZ (yttria-stabilized zirconia). Besides, the (ZrO2)x-(Dy3TaO7)1-x ceramics possess the glass-like thermal conductivity caused by intrinsic oxygen vacancies existing in the lattice of Dy3TaO7. Moreover, the results of thermal expansion rates demonstrate that the (ZrO2)x-(Dy3TaO7)1-x ceramics possess excellent high temperature phase stability, and the thermal expansion coefficients [(9.7-11) × 10-6 K-1] are comparable to that of 7-8 YSZ.

Highly conducting divalent Mg{sup 2+} cation solid electrolytes with well-ordered three-dimensional network structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tamura, Shinji; Yamane, Megumi; Hoshino, Yasunori

2016-03-15

A three-dimensionally well-ordered NASICON-type Mg{sup 2+} cation conductor, (Mg{sub x}Hf{sub 1−x}){sub 4/(4−2x)}Nb(PO{sub 4}){sub 3}, was firstly developed by partial substitution of lower valent Mg{sup 2+} cation onto the Hf{sup 4+} sites in a HfNb(PO{sub 4}){sub 3} solid to realize high Mg{sup 2+} cation conductivity even at moderate temperatures. Due to the formation of well-ordered NASICON-type structure, both the high Mg{sup 2+} cation conductivity below 450 °C and the low activation energy for Mg{sup 2+} cation migration was successfully realized for the (Mg{sub 0.1}Hf{sub 0.9}){sub 4/3.8}Nb(PO{sub 4}){sub 3} solid. Pure Mg{sup 2+} cation conduction in the NASICON-type (Mg{sub 0.1}Hf{sub 0.9}){sub 4/3.8}Nb(PO{submore » 4}){sub 3} solid was directly and quantitatively demonstrated by means of two kinds of dc electrolysis. - Graphical abstract: Image of the Mg{sup 2+} cation conduction in NASICON-type (Mg{sub 0.1}Hf{sub 0.9}){sub 4/3.8}Nb(PO{sub 4}){sub 3} and its Mg{sup 2+} conductivity. - Highlights: • We develop a three-dimensionally well-ordered NASICON-type Mg{sup 2+} cation conductor. • A high magnesium cation conductivity is realized even at moderate temperatures. • Divalent magnesium cation conduction is demonstrated directly and quantitatively.« less

Diode-pumped passively Q-switched Nd:GdTaO4 laser based on tungsten disulfide nanosheets saturable absorber at 1066 nm

NASA Astrophysics Data System (ADS)

Li, M. X.; Jin, G. Y.; Li, Y.

2018-05-01

In this paper, we investigated the passively Q-switched Nd:GdTaO4 laser based on tungsten disulfide (WS2) saturable absorber (SA). The preparation method of WS2 SA was to attach the WS2-alcohol dispersion onto the quartz substrates. The diode-pumped passively Q-switched Nd:GdTaO4 laser operated at a central wavelength of 1066 nm. The stable pulse output could be obtained at the single pulse width of 560 ns. In a word, WS2 seems to be a suitable saturable absorber for solid state lasers.

Local Variability of the Peierls Barrier of Screw Dislocations in Ta-10W.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Foiles, Stephen M.

2017-10-01

It is well know that the addition of substitutional elements changes the mechanical behavior of metals, a effect referred to solid solution hardening. For body-centered-cubic (BCC) metals, screw dislocation play a key role in the mechanical properties. Here the detailed modification of the Peierls barrier for screw dislocation motion in Ta with W substitutional atoms is computing using density functional theory (DFT). A reduced order model (ROM) of the influence of W substitution on the Peierls barrier is developed. The mean field change in the Peierls barrier for a Ta10W alloy is determined and shown to be larger than anticipatedmore » based on simple elasticity considerations. The ROM could be used in future calculations to determine the local variability of the Peierls barrier and the resultant influence on the motion of screw dislocation in this alloy.« less

75 FR 43564 - TA-W-71,483, Continental Airlines, Inc., Reservations Division, Houston, TX; TA-W-71,483A...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-07-26

... DEPARTMENT OF LABOR Employment and Training Administration TA-W-71,483, Continental Airlines, Inc., Reservations Division, Houston, TX; TA-W-71,483A, Continental Airlines, Inc., Reservations Division, Tampa, FL; TA-W-71,483B, Continental Airlines, Inc., Reservations Division, Salt Lake City, UT; Notice of Negative Determination Regarding...

The Triticum aestivum non-specific lipid transfer protein (TaLtp) gene family: comparative promoter activity of six TaLtp genes in transgenic rice.

PubMed

Boutrot, Freddy; Meynard, Donaldo; Guiderdoni, Emmanuel; Joudrier, Philippe; Gautier, Marie-Françoise

2007-03-01

Plant non-specific lipid transfer proteins (nsLTPs) are encoded by a multigene family and support physiological functions, which remain unclear. We adapted an efficient ligation-mediated polymerase chain reaction (LM-PCR) procedure that enabled isolation of 22 novel Triticum aestivum nsLtp (TaLtp) genes encoding types 1 and 2 nsLTPs. A phylogenetic tree clustered the wheat nsLTPs into ten subfamilies comprising 1-7 members. We also studied the activity of four type 1 and two type 2 TaLtp gene promoters in transgenic rice using the 1-Glucuronidase reporter gene. The activities of the six promoters displayed both overlapping and distinct features in rice. In vegetative organs, these promoters were active in leaves and root vascular tissues while no beta-Glucuronidase (GUS) activity was detected in stems. In flowers, the GUS activity driven by the TaLtp7.2a, TaLtp9.1a, TaLtp9.2d, and TaLtp9.3e gene promoters was associated with vascular tissues in glumes and in the extremities of anther filaments whereas only the TaLtp9.4a gene promoter was active in anther epidermal cells. In developing grains, GUS activity and GUS immunolocalization data evidenced complex patterns of activity of the TaLtp7.1a, TaLtp9.2d, and TaLtp9.4a gene promoters in embryo scutellum and in the grain epicarp cell layer. In contrast, GUS activity driven by TaLtp7.2a, TaLtp9.1a, and TaLtp9.3e promoters was restricted to the vascular bundle of the embryo scutellum. This diversity of TaLtp gene promoter activity supports the hypothesis that the encoded TaLTPs possess distinct functions in planta.

Strengthening Mechanisms in Thermomechanically Processed NbTi-Microalloyed Steel

NASA Astrophysics Data System (ADS)

Kostryzhev, Andrii G.; Marenych, Olexandra O.; Killmore, Chris R.; Pereloma, Elena V.

2015-08-01

The effect of deformation temperature on microstructure and mechanical properties was investigated for thermomechanically processed NbTi-microalloyed steel with ferrite-pearlite microstructure. With a decrease in the finish deformation temperature at 1348 K to 1098 K (1075 °C to 825 °C) temperature range, the ambient temperature yield stress did not vary significantly, work hardening rate decreased, ultimate tensile strength decreased, and elongation to failure increased. These variations in mechanical properties were correlated to the variations in microstructural parameters (such as ferrite grain size, solid solution concentrations, precipitate number density and dislocation density). Calculations based on the measured microstructural parameters suggested the grain refinement, solid solution strengthening, precipitation strengthening, and work hardening contributed up to 32 pct, up to 48 pct, up to 25 pct, and less than 3 pct to the yield stress, respectively. With a decrease in the finish deformation temperature, both the grain size strengthening and solid solution strengthening increased, the precipitation strengthening decreased, and the work hardening contribution did not vary significantly.

Investigation on relaxation and conduction mechanism in Pb0.75K0.5Nb2O6 new ferroelectric ceramic

NASA Astrophysics Data System (ADS)

Belboukhari, A.; Choukri, E.; Gagou, Y.; Elmoznine, R.; Abdelmoula, N.; Neqali, A.; El Marssi, M.; Khemakhem, H.; Mezzane, D.

2014-07-01

Using conventional solid state synthesis under air, the sample Pb0.75K0.5Nb2O6 was prepared in a single-phase TTB structure as indicated from X-ray analysis. Impedance spectroscopy analysis of the dielectric properties of Pb0.75K0.5Nb2O6 ceramic were investigated in the frequency range, 1 Hz-1 MHz and in the temperature duration from room temperature to 550 °C. Impedance and modulus plots were used as tools to analyze the sample behavior as a function of frequency. Cole-Cole plots showed non-Debye relaxation. The nature of variation of the electrical conductivity, and value of activation energy of different temperature regions, suggest that the conduction process is of mixed-type (i.e., ionic polaronic and space charge generated from the oxygen ion vacancies). The structural and dielectric results are compared with three others TTB compounds derived from Pb0.75K0.5Nb2O6 (PKN) family: Pb1.85K1.15Li0.15Nb5O15 (PKLN), K3Li2Nb5O15 (KLN) and Pb1.8Gd0.1K1.1Nb5O15 (PGKN).

Nb and Pd co-doped La0.57Sr0.38Co0.19Fe0.665Nb0.095Pd0.05O3-δ as a stable, high performance electrode for barrier-layer-free Y2O3-ZrO2 electrolyte of solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Chen, Kongfa; He, Shuai; Li, Na; Cheng, Yi; Ai, Na; Chen, Minle; Rickard, William D. A.; Zhang, Teng; Jiang, San Ping

2018-02-01

La0.6Sr0.2Co0.2Fe0.8O3-δ (LSCF) is the most intensively investigated high performance cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs), but strontium segregation and migration at the electrode/electrolyte interface is a critical issue limiting the electrocatalytic activity and stability of LSCF based cathodes. Herein, we report a Nb and Pd co-doped LSCF (La0.57Sr0.38Co0.19Fe0.665Nb0.095Pd0.05O3-δ, LSCFNPd) perovskite as stable and active cathode on a barrier-layer-free anode-supported yttria-stabilized zirconia (YSZ) electrolyte cell using direct assembly method without pre-sintering at high temperatures. The cell exhibits a peak power density of 1.3 W cm-2 at 750 °C and excellent stability with no degradation during polarization at 500 mA cm-2 and 750 °C for 175 h. Microscopic and spectroscopic analysis show that the electrochemical polarization promotes the formation of electrode/electrolyte interface in operando and exsolution of Pd/PdO nanoparticles. The Nb doping in the B-site of LSCF significantly reduces the Sr surface segregation, enhancing the stability of the cathode, while the exsoluted Pd/PdO nanoparticles increases the electrocatalytic activity for the oxygen reduction reaction. The present study opens up a new route for the development of cobaltite-based perovskite cathodes with high activity and stability for barrier-layer-free YSZ electrolyte based IT-SOFCs.

Pre-Test Analysis Predictions for the Shell Buckling Knockdown Factor Checkout Tests - TA01 and TA02

NASA Technical Reports Server (NTRS)

Thornburgh, Robert P.; Hilburger, Mark W.

2011-01-01

This report summarizes the pre-test analysis predictions for the SBKF-P2-CYL-TA01 and SBKF-P2-CYL-TA02 shell buckling tests conducted at the Marshall Space Flight Center (MSFC) in support of the Shell Buckling Knockdown Factor (SBKF) Project, NASA Engineering and Safety Center (NESC) Assessment. The test article (TA) is an 8-foot-diameter aluminum-lithium (Al-Li) orthogrid cylindrical shell with similar design features as that of the proposed Ares-I and Ares-V barrel structures. In support of the testing effort, detailed structural analyses were conducted and the results were used to monitor the behavior of the TA during the testing. A summary of predicted results for each of the five load sequences is presented herein.

Superconducting wire manufactured

NASA Astrophysics Data System (ADS)

Fu, Yuexian; Sun, Yue; Xu, Shiming; Peng, Ying

1985-10-01

The MF Nb/Cu Extrusion Tube Method was used to manufacture 3 kg of stable practical MF Nb2Sn composite superconducting wire containing pure Cu(RRR approx. 200)/Ta. The draw state composite wire diameter was 0.56 mm, it contained 11,448 x 2.6 micron Nb core, and the twist distance was 1.5 cm. The composite wire cross-section was pure Cu/Ta/11,448 Nb core/Cu/ 91Sn-Cu; containing 22.8 v. % pure Cu, 13.3 v. % Ta; within the Ta layer to prevent Sn diffusion. The wire was sheathed in nonalkaline glass fiber as an insulating layer. A section of wire weighing 160 g was cut off and coiled it into a small solenoid. After reaction diffusion processing at 675 C/30 and curing by vacuum dipping in paraffin, it was measured in a Nb-Ti backfield of 7.2 T intensity, a current of 129 A was passed through the Nb3Sn solenoid and produced a strength of 2.5 T, the overall magnetic field intensity of the composite magnet reached 9.7 T. At this time, the wire full current density J sub c.w. = 5.2 x 10 to the 4th power A/sq cm; the effective current density J sub c (Nb + Sn - Cu) = 8.2 x 10 to the 4th power A/sq cm.

Evidence for a π junction in Nb/Ni 0.96V0.04/Nb trilayers revealed by superfluid density measurements

NASA Astrophysics Data System (ADS)

Hinton, M. J.; Steers, Stanley; Peters, Bryan; Yang, F. Y.; Lemberger, T. R.

2016-07-01

We report measurements of the superfluid density, λ-2(T ) , in ferromagnet-on-superconductor (F/S) bilayers and S/F/S' trilayers comprising Nb with Ni, Py, CoFe, and NiV ferromagnets. Bilayers provide information about F/S interface transparency and the T dependence of λ-2 that inform interpretation of trilayer data. The Houzet-Meyer theory accounts well for the measured dependence of λ-2(0 ) and Tc of F/S bilayers on thickness of F layer, dF, except that λ-2(0 ) is slightly under expectations for CoFe/Nb bilayers. For Nb/F/Nb' trilayers, we are able to extract Tc and and λ-2 for both Nb layers when F is thick enough to weaken interlayer coupling. The lower "Tc" is actually a crossover identified by onset of superfluid in the lower-Tc Nb layer. For Nb/NiV/Nb' trilayers, λ-2(0 ) versus dF for both Nb layers has a minimum followed by a recovery, suggestive of a π junction.

Bubble template synthesis of Sn2Nb2O7 hollow spheres for enhanced visible-light-driven photocatalytic hydrogen production.

PubMed

Zhou, Chao; Zhao, Yufei; Bian, Tong; Shang, Lu; Yu, Huijun; Wu, Li-Zhu; Tung, Chen-Ho; Zhang, Tierui

2013-10-28

Hierarchical Sn2Nb2O7 hollow spheres were prepared for the first time via a facile hydrothermal route using bubbles generated in situ from the decomposition of urea as soft templates. The as-obtained hollow spheres with a large specific surface area of 58.3 m(2) g(-1) show improved visible-light-driven photocatalytic H2 production activity in lactic acid aqueous solutions, about 4 times higher than that of the bulk Sn2Nb2O7 sample prepared by a conventional high temperature solid state reaction method.

TA-55 change control manual

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blum, T.W.; Selvage, R.D.; Courtney, K.H.

This manual is the guide for initiating change at the Plutonium Facility, which handles the processing of plutonium as well as research on plutonium metallurgy. It describes the change and work control processes employed at TA-55 to ensure that all proposed changes are properly identified, reviewed, approved, implemented, tested, and documented so that operations are maintained within the approved safety envelope. All Laboratory groups, their contractors, and subcontractors doing work at TA-55 follow requirements set forth herein. This manual applies to all new and modified processes and experiments inside the TA-55 Plutonium Facility; general plant project (GPP) and line itemmore » funded construction projects at TA-55; temporary and permanent changes that directly or indirectly affect structures, systems, or components (SSCs) as described in the safety analysis, including Facility Control System (FCS) software; and major modifications to procedures. This manual does not apply to maintenance performed on process equipment or facility SSCs or the replacement of SSCs or equipment with documented approved equivalents.« less

Structural and low temperature dielectric studies on Pb0.8Bi0.2Fe0.6Nb0.4O3 multiferroic solid solution

NASA Astrophysics Data System (ADS)

Dadami, Sunanda T.; Matteppanvar, Shidaling; Shivaraja, I.; Rayaprol, Sudhindra; Deshapande, S. K.; Angadi, Basavaraj

2018-05-01

In this paper the structural and low temperature dielectric properties of Pb0.8Bi0.2Fe0.6Nb0.4O3 (PBFNO) multiferroic solid solution were reported. PBFNO multiferroic was synthesized by single step solid state reaction method. Calcination was carried out at 700 °/2hr with different sintering temperature (800 °C, 850 °C, 900 °C, 950 °C, 1000 °C and 1050 °C for 1 hr) and time duration (800 °C for 1 to 5 hr). Single phase was confirmed through room temperature (RT) X-ray Diffraction (XRD). It was found that sintering carried out at 800°C/3 hr gives single phase. Rietveld refined lattice parameters using monoclinic structure are: a = 5.6663(1) Å, b = 5.6694(1) Å, c = 4.0112(1) Å and β = 90.038(1)° with the average grain size as 2.987 µm. The dielectric properties studied over a wide range of frequency (100 Hz - 5 MHz) and temperature (133 K - 293 K). Dielectric constant and loss tangent exhibits frequency dispersion nature at low frequency region. AC conductivity increases with increase in temperature corresponds to negative temperature coefficient of resistance (NTCR) behaviour.

Comparison of Fatigue Properties and Fatigue Crack Growth Rates of Various Implantable Metals

PubMed Central

Okazaki, Yoshimitsu

2012-01-01

The fatigue strength, effects of a notch on the fatigue strength, and fatigue crack growth rate of Ti-15Zr-4Nb-4Ta alloy were compared with those of other implantable metals. Zr, Nb, and Ta are important alloying elements for Ti alloys for attaining superior long-term corrosion resistance and biocompatibility. The highly biocompatible Ti-15Zr-4Nb-4Ta alloy exhibited an excellent balance between strength and ductility. Its notched tensile strength was much higher than that of a smooth specimen. The strength of 20% cold-worked commercially pure (C.P.) grade 4 Ti was close to that of Ti alloy. The tension-to-tension fatigue strength of an annealed Ti-15Zr-4Nb-4Ta rod at 107 cycles was approximately 740 MPa. The fatigue strength of this alloy was much improved by aging treatment after solution treatment. The fatigue strengths of C.P. grade 4 Ti and stainless steel were markedly improved by 20% cold working. The fatigue strength of Co-Cr-Mo alloy was markedly increased by hot forging. The notch fatigue strengths of 20% cold-worked C.P. grade 4 Ti, and annealed and aged Ti-15Zr-4Nb-4Ta, and annealed Ti-6Al-4V alloys were less than those of the smooth specimens. The fatigue crack growth rate of Ti-15Zr-4Nb-4Ta was the same as that of Ti-6Al-4V. The fatigue crack growth rate in 0.9% NaCl was the same as that in air. Stainless steel and Co-Cr-Mo-Ni-Fe alloy had a larger stress-intensity factor range (ΔK) than Ti alloy.

Drought-responsive WRKY transcription factor genes TaWRKY1 and TaWRKY33 from wheat confer drought and/or heat resistance in Arabidopsis.

PubMed

He, Guan-Hua; Xu, Ji-Yuan; Wang, Yan-Xia; Liu, Jia-Ming; Li, Pan-Song; Chen, Ming; Ma, You-Zhi; Xu, Zhao-Shi

2016-05-23

Drought stress is one of the major causes of crop loss. WRKY transcription factors, as one of the largest transcription factor families, play important roles in regulation of many plant processes, including drought stress response. However, far less information is available on drought-responsive WRKY genes in wheat (Triticum aestivum L.), one of the three staple food crops. Forty eight putative drought-induced WRKY genes were identified from a comparison between de novo transcriptome sequencing data of wheat without or with drought treatment. TaWRKY1 and TaWRKY33 from WRKY Groups III and II, respectively, were selected for further investigation. Subcellular localization assays revealed that TaWRKY1 and TaWRKY33 were localized in the nuclei in wheat mesophyll protoplasts. Various abiotic stress-related cis-acting elements were observed in the promoters of TaWRKY1 and TaWRKY33. Quantitative real-time PCR (qRT-PCR) analysis showed that TaWRKY1 was slightly up-regulated by high-temperature and abscisic acid (ABA), and down-regulated by low-temperature. TaWRKY33 was involved in high responses to high-temperature, low-temperature, ABA and jasmonic acid methylester (MeJA). Overexpression of TaWRKY1 and TaWRKY33 activated several stress-related downstream genes, increased germination rates, and promoted root growth in Arabidopsis under various stresses. TaWRKY33 transgenic Arabidopsis lines showed lower rates of water loss than TaWRKY1 transgenic Arabidopsis lines and wild type plants during dehydration. Most importantly, TaWRKY33 transgenic lines exhibited enhanced tolerance to heat stress. The functional roles highlight the importance of WRKYs in stress response.

Room temperature structural and dielectric studies of Pb(Fe0.585Nb0.25W0.165)O3 solid solution

NASA Astrophysics Data System (ADS)

Nagaraja, T.; Dadami, Sunanda T.; Angadi, Basavaraj

2018-05-01

The perovskite A(B'B''B''')O3 structure Pb(Fe0.585Nb0.25W0.165)O3 (PFNW) multiferroic material was synthesized by single step solid state reaction method. The single phase was achieved at low temperature with optimized synthesis parameters as calcination (700°C/2hr) and sintering (800 °C /3hr). Single phase was confirmed by room temperature (RT) X-ray diffraction (XRD). The scanning electron microscopy (SEM) shows the uniform distribution of grains throughout the surface of PFNW and the energy dispersive X-ray spectroscopy (EDX) confirms the exact elemental composition as that of the experimental. Fourier transform infrared spectroscopy (FTIR) exhibits two absorption bands at 602 cm-1 and 1385 cm-1 corresponds to the bending and stretching vibrations of metal oxides. RT dielectric studies (dielectric constant, tanδ, AC conductivity) exhibits maximum values at lower frequency region and decreases as the frequency increases. Thesingle semicircular arc in RT impedance spectra (Nyquist plot)indicatesthe contribution to the conductivity is from grains only. Hence PFNW is a potential candidate for near room temperature applications.

Scaling of anomalous Hall effect in Ta/CoFeB/MgAl2O4/Ta multilayers

NASA Astrophysics Data System (ADS)

Wu, Yong; Zhang, Qimeng; Meng, Kangkang; Chen, Jikun; Xu, Xiaoguang; Miao, Jun; Jiang, Yong

2017-06-01

The anomalous Hall effect (AHE) is studied in Ta/CoFeB/MgAl2O4/Ta multilayers with different thicknesses of MgAl2O4 (t), which causes in-plane magnetic anisotropy (IMA) for t = 1.0 nm and perpendicular magnetic anisotropy (PMA) for t ≥ 1.2 nm. Conventional scaling was demonstrated to be not inadequate in our case. The origin of the AHE in Ta/CoFeB/MgAl2O4/Ta multilayers is mainly an extrinsic mechanism. The contribution of skew scattering (SS) is unneglectable, and both the SS and side jump are enhanced when the magnetic anisotropy changes from IMA to PMA, indicating that the oxidation at the interface of CoFeB/MgAl2O4 has a dominant influence on the AHE.

Reactive magnetron cosputtering of hard and conductive ternary nitride thin films: Ti-Zr-N and Ti-Ta-N

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abadias, G.; Koutsokeras, L. E.; Dub, S. N.

2010-07-15

Ternary transition metal nitride thin films, with thickness up to 300 nm, were deposited by dc reactive magnetron cosputtering in Ar-N{sub 2} plasma discharges at 300 deg. C on Si substrates. Two systems were comparatively studied, Ti-Zr-N and Ti-Ta-N, as representative of isostructural and nonisostructural prototypes, with the aim of characterizing their structural, mechanical, and electrical properties. While phase-separated TiN-ZrN and TiN-TaN are the bulk equilibrium states, Ti{sub 1-x}Zr{sub x}N and Ti{sub 1-y}Ta{sub y}N solid solutions with the Na-Cl (B1-type) structure could be stabilized in a large compositional range (up to x=1 and y=0.75, respectively). Substituting Ti atoms by eithermore » Zr or Ta atoms led to significant changes in film texture, microstructure, grain size, and surface morphology, as evidenced by x-ray diffraction, x-ray reflectivity, and scanning electron and atomic force microscopies. The ternary Ti{sub 1-y}Ta{sub y}N films exhibited superior mechanical properties to Ti{sub 1-x}Zr{sub x}N films as well as binary compounds, with hardness as high as 42 GPa for y=0.69. All films were metallic, the lowest electrical resistivity {rho}{approx}65 {mu}{Omega} cm being obtained for pure ZrN, while for Ti{sub 1-y}Ta{sub y}N films a minimum was observed at y{approx}0.3. The evolution of the different film properties is discussed based on microstructrural investigations.« less

First-principles study on elastic and superconducting properties of Nb3Sn and Nb3Al under hydrostatic pressure

NASA Astrophysics Data System (ADS)

Zhang, Rui; Gao, Peifeng; Wang, Xingzhe; Zhou, Youhe

2015-10-01

The low temperature superconducting materials, such as Nb3Sn and Nb3Al, have similar crystal structures and elastic properties. However, their critical-temperature degradations always show the distinct way under mechanical stresses. In this study, first-principles calculations for the low temperature superconductors based on plane-wave pseudo-potential density functional theory within the generalized gradient approximation are implemented, and the elastic moduli of Nb3Sn and Nb3Al and those superconductivities in the presence of hydrostatic pressure are evaluated. The Debye temperatures are obtained by the bulk moduli and shear moduli of superconducting materials. The MacMillan equation is further used to acquire the critical temperatures of Nb3Sn and Nb3Al under different hydrostatic pressures. It is found that the elastic constants and bulk moduli of the low temperature superconductors are enhanced by the applied hydrostatic pressure, while the critical temperatures usually are decreased with the pressure. Additionally, the decrease of critical-temperature for Nb3Sn is more sensitive to the hydrostatic pressure than the one for Nb3Al. The prediction results show good agreement with the experimental results in the literatures qualitatively.

Ternary metal-rich sulfide with a layered structure

DOEpatents