Transition Metals Nb Research Articles

Tuning the magnetism of a ZrS2monolayer by substitutional doping

In view of the important role of developing efficient approaches to induce and manipulate the magnetism in semiconducting transition metal dichalcogenide monolayers for their application in low-dimensional spintronic devices, the influence of a series of transition metal (TM) (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Y, Nb and Mo), alkali metals (Li and Na) and alkaline-earth (Ca) dopants on the electronic structure and magnetic properties of a ZrS2 monolayer are investigated using first-principles calculations. It is shown that Ca, Sc, Ti, Ni and Y dopants cannot induce the magnetism in the doped ZrS2 monolayer and the stability of the magnetic state of the Na doped system is very small, while the ground state of Li, V, Cr, Mn, Fe, Co, Nb and Mo-doped systems are magnetic and the magnetic moment induced by 3d TM, 4d TM and Li dopants are mainly contributed by the 3d states of the 3d TM atom, the 4d states of the 4d TM atom and its nearing Mo atoms, and the 3p states of the S atoms and the interstitial region around Li, respectively. The evolutions of the magnetic moments with the different TM dopants, such as Ti, V, Cr, Mn, Fe, Co, Ni, Nb and Mo, can be interpreted in terms of a simple analysis based on the molecular orbitals and electron filling. Furthermore, the magnetic coupling between the moments induced by two Li, V, Cr, Fe, Co, Nb and Mo is long-range ferromagnetic and the coupling can be attributed to the hybridization interaction involving polarized electrons or holes, whereas the coupling between the moments induced by two Mn is anti-ferromagnetic. The calculated results suggest that substitutional doping of Li, V, Cr, Fe, Co and Mo atoms can induce the room temperature ferromagnetism in the ZrS2 monolayer.

Surface energy and work function of fcc and bcc crystals: Density functional study

The surface energies and work functions for six close-packed surfaces of 19 common fcc and bcc metals in the periodic table have been systematically calculated by means of the density functional theory (DFT) method. The accuracy of the results is established in comparison with the experimental and other theoretical values. The variations of work functions with the surface crystallographic orientation display a good regularity. For alkali metals, the work functions follow the sequence Φ(110)>Φ(133)>Φ(311)>Φ(120)>Φ(100)>Φ(111). But for the same crystal structure of bcc transition metals (Nb, Mo, Ta, W), the order is Φ(110)>Φ(133)>Φ(120)>Φ(111)>Φ(311)>Φ(100). The work functions for 3d, 4d and 5d transition fcc metals also display an obvious regularity and ordered as Φ(111)>Φ(100)>Φ(211)>Φ(123)>Φ(310)>Φ(110). Particular attention is paid to the surface energies anisotropy with the same crystal structure metals and the variations present a good regularity, too. Especially, a roughly inverse proportional relationship between the surface energy and work function is found.

Influence of transition metals Fe, Ni, and Nb on dehydrogenation characteristics of Mg(BH4)2: Electronic structure mechanisms

First principles calculations on Fe, Ni, and Nb doped Mg(BH4)2 were carried out to study the influence of dopants on dehydrogenation properties of Mg(BH4)2. It was shown that all dopants considered prefer to substitute for Mg with relatively smaller occupation energies comparing to the B substitution and the interstitial occupation. However, the B substitution shows smaller hydrogen dissociation energy than the Mg substitution. Mechanisms that dopants used to improve dehydrogenation properties of Mg(BH4)2 are different. For Mg substitution, Fe strongly interacts with one H atoms of the [BH4] group, distorts its structural stability and therefore lowers the hydrogen dissociation energy, Ni may attract one particular H atom of the [BH4] group and weakens the interactions between the B and other H atoms reducing the hydrogen dissociation energy, and the Nb however may drive the formation of NbB2 and improves the dehydrogenation properties as well. In the B substitution, Fe interacts with the one of H atoms and decreases its structure stability, the Ni will attract its neighbor atoms to form a regular group which is almost identical in structure to that of the NiH4 group in Mg2NiH4, and the NbH2 and MgH2 are likely to be generated by Nb doping.

Enhancement of plasticity in Co–Nb–B ternary bulk metallic glasses with ultrahigh strength

A family of ultrahigh strength Co-based bulk metallic glasses (BMGs) with critical diameters up to 2mm was fabricated in ternary Co65−xNb8B27+x (at.%, x=1–5) alloy system. The highest glass forming ability for the alloy composition with x=3 is in agreement with its largest supercooled liquid region, lowest liquidus temperature and eutectic behavior, which are closely related to the presence of backbone structure formed by transition metal (Nb) and metalloid elements (B). The present glassy alloy system also possesses excellent mechanical properties including both yield strength of 4610–5340MPa and plasticity up to 5% simultaneously, which is rarely reported for other BMGs known so far. It is found that changes in the proportion of metalloid B contents have significant influence on the atom packing fraction and therefore the enhanced yield strength. Meanwhile, the enhancement of plasticity is ascribed to the formation of nanoscale-range order clusters in the CoNbB BMGs.

First-principles prediction of metastable niobium and tantalium nitrides M 4N 5 and M 5N 6 stoichiometry

A first-principles plane-wave pseudopotential method based on the density functional theory is used to investigate the structural, elastic and electronic properties of M 4N 5 and M 5N 6 (M = a transition metal (TM) Nb, Ta). C 33 elastic constant for all compounds is found to be much larger than C 11, indicating that a-axis is more compressible than c-axis. Interestingly, we find that C 33 and C 11 are significantly larger than other elastic constants, resulting in a pronounced elastic anisotropy.

High Induction, Low Loss FeCo-Based Nanocomposite Alloys With Reduced Metalloid Content

We present a comparative study of reductions in metalloid and early transition metal content aimed at increasing inductions in FeCo-based nanocomposite alloys. Metalloid B and early transition metal Nb glass formers were replaced with magnetic late transition metals to determine the limits of amorphous and nanocrystalline formation and increase the magnetic flux density. Alloys of composition (Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">65</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">35</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">80+x+y</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13-x</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4-y</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> (x=0-3, y=0,3) were cast by melt-spinning 50g batches into 2.5 mm wide, 30 μm thick ribbons. Ribbons were nanocrystallized and screened for their magnetic flux densities. The highest magnetic flux density of 1.85 T for quality ribbon was realized for the alloy with x=1, y=3. Magnetization as a function of temperature is reported for amorphous alloys to illustrate the effects of metalloid and early transition metal content on high temperature stability of magnetic properties and crystallization temperatures. Notable alloys were also synthesized by planar flow casting into 2.54 cm wide, 20 μ m ribbons and annealed under a 2.0 T transverse magnetic field. AC magnetic property measurements include permeability, coercive field, and core loss. The x=3, y=0 alloy demonstrated low core loss of 5.1 W/kg under a 0.2 T field and 20 kHz frequency with a high flux density of 1.70 T.

Effect of Compensated Codoping on the Photoelectrochemical Properties of Anatase TiO2 Photocatalyst

An effective codoping approach is described to modify the photoelectrochemical properties of anatase TiO2 by doping with nonmetal (N or C) and transition metal (Nb or Ta) impurities. Here, compensated and noncompensated codoped TiO2 systems are constructed with different proportions and dopant species, and then their dopant formation energies and electronic properties are calculated to study the stability and visible-light photoactivity by first-principles density functional theory incorporating the LDA+U formalism, respectively. The calculated results demonstrate that the codoping with transition metals facilitates the enhancement of the concentration of p-type dopants (N and C) in the host lattice. Especially, both 1:2 compensated Nb/C/Nb and Ta/C/Ta codopings not only reduce the energy gap to enhance the optical absorption and eliminate the local trapping to improve carrier mobility and conversion efficiency but also do not lower the reduction potential of the conduction band edge. Our designated strat...

Strong-Field Ionization and Dissociation Studies on Small Early Transition Metal Carbide Clusters via Time-of-Flight Mass Spectrometry

In this work, we report experimental results from the strong-field ionization and subsequent Coulomb explosion of narrow distributions of small (<40 atoms) heteronuclear clusters composed of transition metal (Ti, V, Cr, Nb, or Ta) and carbon atoms. Analysis of the resulting multiply charged ions was performed through time-of-flight mass spectrometry, and evidence regarding ionization dynamics was obtained. The data reveal the presence of enhanced ionization during exposure to the ultrashort (∼100 fs) pulse resulting in the formation of ions possessing significantly higher charge states than those predicted from atomic species. Regardless of the transition metal species, we observe the absorption of similar amounts of energy from the external field, as indicated by the maximum observed charge states in each experiment. These results are compared to our previously reported study on the strong-field ionization of transition metal oxide clusters. We observe identical maximum observable charge states for each of the transition metal species resulting from both metal oxide and metal carbide clusters.

A DFT study of substrate effect on the magnetism of V(001) surface

The effect of isoelectric transition metals (TM) Nb and Ta on the magnetism of the V(001) surface is investigated from first principles using Density functional theory (DFT), with the generalized gradient approximation (GGA). Ferromagnetic (FM) moments of 2.5 μ B and 2.2 μ B are obtained for the relaxed surface V monolayer (ML) in the V/Nb(001) and the V/Ta(001) systems respectively, at T = 0 K. The values are almost twice of those obtained with Mo and W of group VIB and can be attributed to the comparatively smaller bandwidths of the substrates Nb and Ta. Small induced magnetic moments are present on the Nb and Ta interfacial layers, which are coupled anti-ferromagnetically with the V ML.

Atomic parameter model for the solid solubilities in binary transition metal based alloys

Based on the same method by us which describes the solid solubilities of the binary nontransition metal based alloys, the solid solubilities at room temperature in 1380 binary alloys which are based on the 23 transition metals (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Y, Zr, Nb, Mo, Ru, Rh, Pd, La, Hf, Ta, W, Re, Os, Ir and Pt) of the fourth, fifth and sixth long periods have been studied in this paper. It has been found that the soluble elements can be separated from the insoluble elements by an ellipse equation (x−m)2/c2+(y−n)2/d2 = 1, by using a criterion of 0.5at% solubility at room temperature for every host element. The results show that the overall reliability for the ellipse equation is up to 90% for the 1380 alloys, which indicates the theoretical results are very good in agreement with the experimental data. The parameters m, n, c and d in the ellipse equation can be explained by the appropriate parameters for every host metal.

ChemInform Abstract: Metal Hydrides: A Review of Group V Transition Metals - Niobium, Vanadium and Tantalum

Abstract The group V transition metal (Nb, V, Ta)-hydrogen systems are reviewed. Consideration is given to the different types of hydrides formed, their crystallography, thermodynamic data and hysteresis effects on hydriding/dehydriding. The group V transition metals do not themselves react with hydrogen at room temperature, but quite readily react with hydrogen when alloyed with other bcc metals of smaller atomic radii. There are uncertainties regarding the structures of hydrides formed by this group of metals. These uncertainties mainly arise because of the limited number of neutron diffraction studies of the hydrides. Monohydrides have been reported for Nb, V and Ta, while dihydrides have been reported only for Nb and V. Thermodynamic data show that the niobium-hydrogen solid solution is more stable than the vanadium- or tantalum-hydrogen solid solutions. Hysteresis have been seen in metal-H systems in this group and, as yet there is no complete explanation for its occurrence.

Correlation between transition temperature and crystal structure of niobium, vanadium, tantalum and mercury superconductors

The bond length ( x) of transition metals Nb, V, Ta and Hg represents the shortest atomic separation in a crystal unit cell. It is suggested that there exists a strong correlation between ( x) and the inverse of the critical superconducting transition temperature T c in the form (2 x) 2 N eff = m 2 1/ T c . Here N eff is the number of electrons in the outermost s-shell. The slope of the fitted straight line has a value of m 2≈3.0×10 −18 m 2 K.

ChemInform Abstract: Thermoelectric Properties of Ternary Transition Metal Antimonides

Novel compounds T6MBi2, where T=Zr, Hf; M=Fe, Co, Ni, were synthesised by arc melting elemental combinations. Isotypism of these compounds with the ordered Fe2P-type was established from Rietveld X-ray powder data. Physical properties (electrical resistivity and thermoelectric power) were investigated for a series of ternary transition metal compounds with stoichiometries such as TM1−xX and T6MX2, where T is an electropositive transition metal (Zr, Hf and Nb), M is a metal from the iron group (Fe, Co, Ni) and X is Sb or Bi. Resistivities reveal a general metallic behaviour except for ZrCoSb and NbFeSb which are characterized by variable range hopping conductivity in a substantial temperature region. Thermoelectric power of these materials does not exceed 100 μV K−1.

Perovskite catalyst (La, Ba)(Fe, Nb, Pd)O3 applicable to NO storage and reduction system

Abstract We have developed a perovskite catalyst, (La0.7Ba0.3)(Fe0.776Nb0.194Pd0.03)O3, applicable to the NOx storage-reduction system. The perovskite catalyst exhibits 47% of NOx conversion rate at 523 K under the 54–6 s alternation of the lean–rich-burning where the lean and rich gases contain 512 ppm NO + 5 vol.% O2 and 512 ppm NO + 4 vol.% CO, respectively. The base perovskite, LaFe0.97Pd0.03O3, was endowed with a NOx adsorbing capability by partially substituting Ba for La in the A-site of ABO3 structure. Partially replacing Fe in the B-site with pentavalent transition metals (Nb, V and Ta) was also required to develop the NOx-reducing ability.

CHARACTERIZATION OF FLUX-GROWN TRACE-ELEMENT-DOPED TITANITE USING THE HIGH-MASS-RESOLUTION ION MICROPROBE (SHRIMP-RG)

Crystals of titanite can be readily grown under ambient pressure from a mixture of CaO, TiO 2 and SiO 2 in the presence of molten sodium tetraborate. The crystals produced are euhedral and prismatic, lustrous and transparent, and up to 5 mm in length. Titanite obtained by this method contains approximately 4300 ppm Na and 220 ppm B contributed from the flux. In addition to dopant-free material, titanite containing trace alkali and alkaline earth metals (K, Sr, Ba), transition metals (Sc, Cr, Ni, Y, Zr, Nb, Hf and Ta), rare-earth elements (REE), actinides (Th, U) and p-block elements (F, S, Cl, Ge, Sn and Pb) have been prepared using the same procedure. Back-scattered electron (BSE) imaging accompanied by ion-microprobe (SHRIMP–RG) analysis confirms significant incorporation of selected trace-elements at structural sites. Regardless of some zonation, the large size of the crystals and broad regions of chemical homogeneity make these crystals useful as experimental starting material, and as matrix-matched trace-element standards for a variety of microbeam analytical techniques where amorphous titanite glass, heterogeneous natural titanite or a non-titanite standard may be less than satisfactory. Trace-element-doped synthetic crystals can also provide a convenient proxy for a better understanding of trace-element incorporation in natural titanite. Comparisons with igneous, authigenic and high-temperature metasomatic titanite are examined. The use of high-mass-resolution SIMS also demonstrates the analytical challenges inherent to any in situ mass-spectrometry-based analysis of titanite, owing to the production of difficult-to-resolve molecular interferences. These interferences are dominated by Ca–Ca, Ca–Ti and Ti–Ti dimers that are significant in the mass range of 80–100, affecting all isotopes of Sr and Zr, as well as 89 Y and 93 Nb. Methods do exist for the evaluation of interferences by these dimers and of polyatomic interferences on the LREE.

Investigation of the catalytic activities of sulfated mesoporous Ti, Nb, and Ta oxides in 1-hexene isomerization

In the present work, a series of porous transition metal (Ti, Nb, and Ta) oxides with different pore sizes (12–30 Å) were synthesized using a ligand-assisted amine templating approach. The as-synthesized samples were further treated with 1M sulfuric acid and were characterized by nitrogen adsorption/desorption, powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and elemental analysis (EA). The experimental results in the isomerization of 1-hexene were compared with the commercially available zeolites (HY-zeolite and H-ZSM5) and the ion exchange resin Amberlyst 15. The best results were achieved when using C 12H 2SO 4 mesoporous Ta oxide, which possesses a Ho of −8.2 and 19.8 mmol g −1 acid sites. The conversion of 1-hexene to trans/cis 2-isomers reaches 95.89% in 4 h and the ratio of trans/cis isomers reaches up to 3.7 after 6 h, which is very close to their theoretical ratio in thermodynamic equilibrium (3.37) under the same conditions. This conspicuously high selectivity and short reaction time were not detected with the Ta materials synthesized with C 18 or C 6 templates, nor with Ti and Nb materials of any pore size under the same reaction conditions. Temperature-programed desorption (TPD) of ammonia was used to investigate the much higher activity of the Ta materials. The results showed that the Ta materials had a much greater concentration of Brønsted sites in the active Ho range for this reaction than the Nb materials. The unique performance of the C 12H 2SO 4 Ta material was thus attributed to its high BET surface area, increased concentration of effective Brønsted acid sites and optimal pore size for this particular reaction.

X-ray Absorption Spectroscopic Study on Valence State and Local Atomic Structure of Transition Metal Oxides Doped in MgH2

A valence state and a local structure of transition metals (Nb, V, and Ti) in MgH2 doped with metal oxides (Nb2O5, V2O5, and TiO2nano) by ball milling were examined by X-ray absorption spectroscopy (XAS). The main edge regions of the Nb, V, and Ti K-edges in the X-ray absorption near edge structure (XANES) profiles are located between 0 and +5 in the oxidation states. Since these spectra coincide with those of NbO, VO, and Ti2O3, respectively, the additives are reduced by MgH2 to the metal oxides, which have lower oxidation states than those of the starting materials. Furthermore, in order to examine the local structures around the transition metal atoms, the extended X-ray absorption fine structure (EXAFS) spectra were analyzed. In the Fourier transformation curves of the EXAFS spectra, all samples doped with the metal oxides show two peaks corresponding to metal−oxygen and metal−metal bonds, being the same as the references of NbO, VO, and Ti2O3. The local structure formed after ball milling or dehydrog...

Chemical interaction of fluoropolymers with transition metals

Chemical interaction of transition metals (Mo, W, Ta, Nb, and Ti) with a tetrafluoroethylene-vinylidene fluoride (TFE-VDF) copolymer (21 mol % TFE + 79 mol % VDF) has been studied by differential scanning calorimetry (DSC) and mass spectrometry. The DSC curves of mixtures of the fluoropolymer with Ta, Nb, and Ti showed exothermic peaks, and those of composites with W and Mo showed endothermic peaks. Mass spectrometric analysis indicated that the fluoropolymer reacted with the transition metals to form the higher fluorides TaF5, NbF5, TiF4, WF6, and MoF6. In addition, WOF4 and MoOF4 molecules were detected in the case of tungsten and molybdenum. At temperatures above 700 K, the mass spectra of all the systems showed ions corresponding to low-molecular hydrocarbon molecules.

Evolution of the plasma composition of a high power impulse magnetron sputtering system studied with a time-of-flight spectrometer

The plasma of a high power impulse magnetron sputtering system has been investigated using a time-of-flight spectrometer. The target materials included high sputter yield materials (Cu, Ag), transition metals (Nb, Cr, Ti), and carbon (graphite); the sputtering gases were argon, krypton, and nitrogen, and two different target thicknesses were selected to consider the role of the magnetic field strength. Measurements for selected combinations of those parameters give quantitative information on the transition from gas-dominated to metal-dominated (self-sputtering) plasma, on the fractions of ion charge states, and in the case of molecular gases, on the fraction of atomic and molecular ions.

In situ x-ray diffraction study of metal induced crystallization of amorphous germanium

Metal induced crystallization (MIC) is a technique that lowers the crystallization temperature of amorphous semiconductors. The process has mainly been used to influence the crystallization of amorphous silicon (a-Si) and multiple studies on this subject have already been performed. The research of the MIC of amorphous Ge (a-Ge) has been mostly limited to the use of a Ni or Al film. This paper focuses on the characterization of the crystallization behavior of a-Ge films in the presence of 20 transition metals (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, and Al). The kinetics of the crystallization process are also systematically studied for the seven metals that lower the initial crystallization temperature the most. In addition, the influence of the thickness of the metal film was determined for the case of a Au and Al film. A comparison of the influence of the various metals on a-Ge and a-Si is made and the similarities and differences are discussed using existing models for the MIC process.