Nb Ions Research Articles

High Coercivity and Magnetization in WSe2 by Codoping Co and Nb.

Introducing ferromagnetism in transition metal dichalcogenides has attracted lots of attention due to the possible applications in spintronics devices. Generally, single magnetic element doping is used to introduce magnetism. However, mostly, weak ferromagnetism is observed. In this work, codoping of two kinds of transition metals (Nb and Co) into WSe2 is used to study its magnetic properties. In detail, single crystal WSe2 is codoped with 4 at% Co and various concentrations of Nb by employing the physical ion implantation method. Raman, X-ray diffraction and X-ray photoelectron spectroscopy results reveal the effective substitutional doping of implanted elements (Co and Nb). Magnetic measurements illustrate that both un-doped and 4 at% Co doped WSe2 show weak ferromagnetism whereas magnetization is strongly enhanced when Co and Nb are codoped into WSe2 . The magnetization is comparable with a ferromagnet, which may be attributed to Co, Nb doping and defects. In addition, a large coercivity of ≈1.2 kOe is observed in the 1 at% Nb-4 at% Co codoped WSe2 sample, which may be ascribed to the combined effect of doping-induced stress, defect-dictated pinning and anisotropy of NbSe bond owing to the charge transfer between Nb and Se ions.

Tribological characterization of Nb ion implanted WC-5wt%Ni cold sprayed coatings in dry sliding contact

Niobium ions were implanted into WC-5wt%Ni cold sprayed coatings at an acceleration voltage of 60 keV. The ion dosages were varied as 2 × 1016, 5 × 1016, and 8 × 1016 ions cm−2, and the resulting influence on surface, friction, wear, and stress properties of the Nb-implanted layers, in comparison to the non-ion implanted coating, was investigated. Dry sliding wear behaviour was assessed using a ball-on-disk tribometer, with 100Cr6 stainless steel balls as the counterface, at a sliding velocity of 0.05 ms−1 and an applied load of 1 N. The Nb ion dosage of 8 × 1016 ions cm−2 produced the best coating surface properties, achieving a high hardness (14.58 GPa), low plasticity index (53.83), low wear rate (35.7 × 10−12 m2 N−1), low wear coefficient (0.52), high shear strength (891 MPa) and a high local maximum von Mises yield strength (1546 MPa). This coating also produced a low Rq roughness value (10.22 nm), great mean radius of asperities (35.88 × 10−2 nm), and a high reciprocal value of the comprehensive roughness fraction (4.77 × 10−3). The wear mechanisms of all the coatings were found to be similar, showing oxidation, scratching, ploughing, smearing, material transfer, and tribo-layer formation.

Understanding of electrochemical behaviors of niobium in molten LiCl–KCl eutectic for pyrochemical decontamination process

In this study, the electrochemical behaviors of niobium were examined with 1.0 wt% of NbCl5 in the molten LiCl–KCl at 450 °C via different electrochemical techniques. A chronoamperometry was performed to prepare solutions containing the selected oxidation state of the Nb ion, and the color of the solution was compared to the literature data. Cyclic voltammetries were performed with a combination of different scan ranges and scan rates using an electrochemical cell prepared by LiCl–KCl–NbCl5 salt mixture and an inert tungsten electrode. Five oxidation and four reduction peaks were found, and possible redox reactions attributing to each peak were identified based on the rate of change of the current density as a function of the scan rate. It was found that Nb(V) can be deposited as a metallic Nb via Nb(IV), Nb(III), and Nb(II), and the deposition of the metallic Nb is perturbed by the formation of insoluble nonstoichiometric Nb chloride compounds on the electrode surface. Three irreversible oxidation peaks were caused by the oxidation of metallic Nb and insoluble Nb chlorides, which competed with each other, but the dissolution of metallic Nb became dominant as the scan rate increased. X-ray diffraction analysis was performed to examine the possibility of a chemical reduction of Nb(V) to Nb(IV), but no evidence was found, which indicated the initial concentration of Nb(V) was preserved in all the experiments. It was also found that the different pyrochemical processes would desirable to separate Nb for the purpose of salt purification as well as volume reduction of radioactive waste, depending on the electrochemical behaviors for other elements that can be simultaneously dissolved with Nb.

Structural investigation of the “tripled-tetragonal-tungsten-bronze” phases Sr2M10−xO27−y (M = Nb, Ta)

Sr2Nb10O27 and Sr2Ta10−xO27−y exhibit the tripled tetragonal-tungsten-bronze (TTTB)-related superstructures. In contrast to Sr2Ta10−xO27−y, where an extended solid solution was found, Sr2Nb10O27 only forms a narrow range of solid solution, Sr1−xNb10O27−z (0 ≤ x ≤ 0.04). Serial X-ray and neutron diffraction studies show that both compounds can be modelled in the orthorhombic Pba2 space group. Lattice parameters obtained from powder X-ray refinements are a = 12.3887(14) Å, b = 37.103(4) Å, c = 3.866(2) Å, for Sr2Ta10−xO27−y, and a = 12.3888(2) Å, b = 36.9839(5) Å, and c = 3.94027(3) Å for Sr2Nb10O27. Neutron Rietveld refinements of both structures revealed the possible reason for the differing solid solution behavior. For Sr2Nb10O27, all Nb sites are fully occupied, whereas in Sr2Ta10−xO27−y, three out of the nine crystallographically unique Ta sites were shown to be partially occupied. Charge adjustment is therefore possible by increasing the Sr concentration, leading to a solid solution series and smaller Ta/Sr ratio as compared to Sr2Nb10O27. In the TTTB-related structures, Nb and Ta ions both occupy octahedral and pentagonal bipyramidal coordination sites. Layers of interconnected corner-shared octahedra were found parallel to the ab plane, with 3-, 4- and 5-fold tunnels found in the structure running parallel to the c-axis. Sr ions partially fill the 4- and 5-fold tunnels.

Threshold switching of a NbOx device prepared by DC reactive sputtering

Threshold switching devices based on insulator-metal transition (IMT) are expected to overcome the reduction of sneak current and studies of their use for self-oscillators attract much attention. In this study, we observed threshold switching caused by IMT in a cross-point Pt/Ti/NbOx/Pt/Ti/SiO2 device after annealing at 400 °C, annealing assisted formation of stable stoichiometric NbO. The diffusion of Ti atoms of thetop electrode to the NbOx layer was observed. It is suggested that Ti oxidation caused scavenging of oxygen from NbOx, and valence number of Nb ion is reduced to form stoichiometric metallic NbO. With applying negative voltage to the upper Pt/Ti electrode, a NbO2 layer was formed by diffusion of oxygen ions from the TiOx layer. Then threshold switching has become easy to occur in the succeeding positive voltage sweeping.

The Doping of FeNb11O29 as a Way to Improve Its Electrochemical Performances

AbstractFeNb11O29, with the possibility to exchange up to 23 electrons per formula unit and a theoretical capacity value of 400 mAh/g, is nowadays a very promising anode material for Li‐ion batteries. However, the improvement of its electrochemical performances is still an open challenge, and the doping is a well‐recognized method to obtain this goal. In this paper, orthorhombic Fe0.8Mn0.2Nb11O29 and Fe0.8V0.2Nb11O29 samples were prepared by solid state synthesis. The redox processes, as determined by cyclic voltammetry, involve only Fe and Nb ions as in the undoped compound. FeNb11O29 is a well‐known mixed oxide with pseudocapacitive behavior, which is increased with the Mn doping. The doped samples show better performances during long term cycling at 2 C, with capacities of 240 and 220 mAh/g and capacity retention of 100.9 and 98.7% for Mn and V doped respectively.

Enhanced ferroelectric and energy-storage properties of Nb-doped 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 ceramics prepared by a multi-ionic sol-gel method

Lead-free ferroelectric Na0.5Bi0.5TiO3 (NBT), 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (NBT-6BT) and (Na0.5Bi0.5)0.94Ba0.06(Nb0.05Ti0.95)O3 (Nb-NBBT6) ceramics were synthesized via a multi-ionic sol-gel method process. The effects of Nb on the structural, dielectric and ferroelectric properties were studied. Doped Nb ions distributed uniformly in the Nb-NBBT6 ceramics and shrank the grain sizes of Nb-NBBT6. All NBT, NBT-6BT and Nb-NBBT6 ceramics consisted of the rhombohedral phase and the tetragonal phase according to XRD Rietveld refinements. The dielectric constants of the Nb-NBBT6 ceramics were improved compared to NBT and NBT-6BT below 200 °C. The introduction of Nb ions enhanced the dielectric stability, and the temperature difference between two dielectric peaks increased from 153 °C for NBT to 197 °C for Nb-NBBT6. The remnant polarization (Pr) of Nb-NBBT6 ceramics decreased, but the reduced Ec of 7.01 kV/cm and the maximum polarization of 40.79 μC/cm2 (90 kV/cm) revealed the enhanced ferroelectric property. The temperature-dependent ferroelectric hysteresis loops of Nb-NBBT6 ceramics (65–150 °C) exhibited the largest energy-storage density (W) of 0.399 J/cm3 at 90 °C.

Fabrication and optical property improvement of gasochromic switchable mirror based on Pd/Mg[sbnd]Nb2O5 thin film

Recently, the application of magnesium-based gasochromic switchable mirror has been baffled by the low optical dynamic range due to the insufficient conversion between Mg and MgH2. Based on the excellent catalytic property of Nb2O5 for the magnesium-hydrogen reaction, we fabricated fluorocarbon (FC)/Pd/MgNb2O5 switchable films via magnetron sputtering and low-temperature inductively coupled plasma chemical vapor deposition technologies in this study, and the optical performance and microstructure of the films were investigated. The results show that the FC/Pd/Mg-3 mol% Nb2O5 film exhibits the higher dynamic ranges of the luminous (49.4%) and solar transmittance (54.7%), compared with most of reported Mg-based alloys and MgTiO2 systems. The addition of Nb2O5 and covering a FC layer on the Pd/Mg film could effectively accelerate the switching response and improve such optical properties as transmittance at transparent state and dynamic range. The microstructural analysis reveals that the Nb2O5 and appropriate amount of ternary MgNbO phase in the Mg-based layer are supposed to facilitate rapid and sufficient hydrogen absorption and desorption. Furthermore, the high-valence Nb ions scattering around Mg atoms may act as a transfer station for catalyzing the reversible reaction between Mg and H. The excellent optical modulation performance and enhanced hydrophobicity of the FC/Pd/MgNb2O5 films signify an application prospect for gasochromic switchable mirror.

Effect of Gd and Nb on dielectric and magnetic transition temperature of BaTiO3- Li0.5Fe2.5O4 composites

The Gd and Nb doped 90 BaTiO3- 10 Li0.5Fe2.5O4 composites are prepared using solid state technique. The structural, functional, dielectric, magnetic and magneto-electric properties of Gd and Nb doped 90 BaTiO3- 10 Li0.5Fe2.5O4 have been studied using X-ray diffraction, FTIR, dielectric spectrometer, vibrating sample magnetometer and DSP lock-in amplifier respectively. The XRD peaks indicate the absence of impurities in the undoped and doped BLF composite which confirms the high crystalline nature of all the composites. The FTIR spectrum reveals a strong absorption bands at 468 cm−1 and 853 cm−1. The transition temperature of BLF decreases slightly and the dielectric constant of all composites is maximum for different temperatures at fixed frequency due to mechanical strain in the grains and inhomogeneous distribution of Gd and Nb ions in place of Ti. The dielectric dissipation (tan δ) of BLF decreases with increase in the concentration of Gd and Nb in BLF which indicates the less number of defects like oxygen vacancies in BLF. The magnetic transition increases with increase in the concentration of Gd and Nb in BLF composites and this increase of the magnetic transition may due to the presence of exchange interaction between Fe3+ and Gd 3+, Nb5+ ions through neighboring octahedrons. The M-E coefficient of BLF decreases after doping Gd, Nb in BLF which may be due to the resistivity of ferroelectric phase greater than ferrite phase.

Tunable Photoluminescence of Atomically Thin MoS2 via Nb Doping

ABSTRACTThe emergence of 2D materials has led to increased attention on correlating the structural, optical, and optoelectronic properties of atomically thin transition metal chalcogenides like MoS2. We demonstrate the tunability of the photoluminescence (PL) properties of bulk MoS2 via implantation of Nb ions. Raman spectroscopy is used to confirm the p-type doping. The PL intensity of MoS2 is drastically enhanced by the adsorption of p-type dopants. X-ray photoelectron spectroscopy (XPS) is used to study the change of MoS2 structure post-implantation. Our results provide a new route for modulating the optical properties of two-dimensional semiconductors. The strong and stable PL from defect sites of MoS2 created by Nb ion implantation may have promising applications in optoelectronic devices.

FORMATION OF HARD AND WEAR-RESISTANT NIOBIUM CARBIDE COATINGS ON HARD-ALLOY TOOLS BY A VACUUM–ARC METHOD

The temperature fields of a hard-alloy tool surface during niobium ion impact were determined by thermography. The temperature of the surface layers reaches a maximum value of 1100–1250°C after exposure of 40 s to Nb ion, and it does not change with increase in the exposure time to 1 min. Ion exposure for 1 min leads to the formation of a carbide layer (Nb, W)C0.7, in the surface layer with a thickness of about 0.4 μm. Subsequent plasma deposition of Nb in methane atmosphere forms an NbC coating. The hardness of the formed niobium-based and tungsten carbide-based layers reaches 35–65 GPa. Adhesive resistance to cracking and destruction of NbC coatings with a sublayer of (Nb, W)C0.7 increases at least 2 times compared to an NbC coating.

Influence of Ar gas pressure on ion energy and charge state distributions in pulsed cathodic arc plasmas from Nb–Al cathodes studied with high time resolution

For cathodic arcs, the cathode material is one of the most important determinants of plasma properties. Consequently, the cathode material—plasma relationship is of special interest in related fundamental research as well as in applications like the synthesis of thin films and coatings. In the latter, the use of multi-element cathodes in inert as well as reactive gas atmospheres is common practice. To further improve the physical understanding of cathodic arcs in such settings, we analyze ions in pulsed cathodic arc plasmas from Nb, Al and two composite Nb–Al cathodes with high time-resolution using a mass-energy-analyzer. The experiments were conducted in Ar atmosphere at total pressures of 0.04, 0.20 and 0.40 Pa, and are compared to earlier results in high vacuum at 10−4. In addition to examining the influence of Ar on ion properties and their cathode material dependence, the results are used to discuss physical concepts in cathodic arcs, like the gas-dynamic expansion of the cathode spot plasma, or the influence of charge exchange collisions of ions with neutrals. While such inelastic collisions e.g. with Ar atoms cause a reduction of charge states to mainly Al+ and Nb2+ at the highest pressure, Ar atoms also seem to take part in near-cathode processes. Ar ions in different time and energy regimes up to 150 eV were observed and compared to Nb and Al ions, showing overlapping velocity distributions for Nb, Al and Ar+ ions, but also Ar2+ ions faster than other ion species.

Metal-Drug Interactions: Synthesis and Spectroscopic Characteristics, Surface Morphology, and Pharmacological Activity of Ephedrine–HCl Complexes with Mo(V), Nb(V), Ga(III), and Ge(IV)

Four new Mo(V), Nb(V), Ga(III), and Ge(IV) ephedrine complexes, [Mo(Eph)2(Cl)4].Cl, [Nb(Eph)2(Cl)3], [Ga(Eph)2(Cl)3], and [Ge(Eph)2(Cl)2] are synthesized and characterized. Composition and coordination behavior of ephedrine drug towards Mo(V), Nb(V), Ga(III), and Ge(IV) ions are deduced from microanalysis, IR spectra, molar conductance, magnetic and thermal analysis data. These support coordination of the eph ligand in its neutral state. Ephedrine has two powerful chelating sites, OH and NH, that determine its uni- or bidentate mode of action. IR spectra indicate that Mo(V) and Ga(III) coordinate to ephedrine via nitrogen atom of the NH group as a unidentate chelator with six and five coordination geometry, respectively. On the other hand, Eph ligand behaves as a monoanionic bidentate no chelating agent via the NH and deprotonated OH groups in Nb(V) and Ge(IV) complexes. Mo(V) complex demonstrates electrolytic properties, the other complexes are non-electrolytes in DMSO solutions. TG/DTG analysis makes it possible to calculate the number of solvent molecules in and outside the coordination sphere, and estimate stability of the synthesized complexes. The Eph complexes are screened in vitro for antibacterial (Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis and Staphylococcus aureus) and antifungal (Aspergillus flavus and Candida albicans) activities. Anti-cancer action of the Mo(V) and Ga(III) complexes is assessed against the human hepato cellular carcinoma (HepG-2) tumor cell line (IC50 >1000 μg/mL).

Green extraction of Niobium and Tantalum from Kenticha Tantalite ore using 1-Ethyl-3-Methyl Imidazolium Chloride ionic liquid

The decomposition of the Ethiopian Kenticha tantalite ore was studied using the KOH fusion and H2O leaching system at 400 0C for a 1 h reaction time. The experimental results obtained showed that 27 wt% of Ta2O5 was mainly transformed into insoluble KTaO3, not to be KNbO3, and as well, into the dissolved liquor containing 94.73 vol% of Nb2O5 and 75.80 vol% of Ta2O5. The observations, supported by the EDXRF, XRD, and ICP-OES techniques, showed that the ratio of the dissolved mixture of Nb and Ta metal ions was beneficial to the solvent extraction from both Ta2O5 and Nb2O5. Niobium and tantalum were extracted from their neutralized alkaline dissolved and hydrolyzed solution by a new process using the EMIC/AlCl3 ionic liquid as the extractant using selective stripping, precipitation, and calcination of a highly crystalline pure 99.84 wt% of Nb2O5 and amophours 90.81 wt% of Ta2O5. The compositions of the dissolved metal ions and solids were analyzed by the ICP-OES, EDXRF, XRD, and FT-IR techniques.

High-temperature electrical resistivity and loss tangent of langasite-family Ca3Nb(Ga,Al)3Si2O14 single crystals

Langasite-family Ca3Nb(Ga1−xAlx)3Si2O14 (CNGAS) (x = 0–0.6) single crystals were grown by a Czochralski technique along the x-axis. When the Al substituent was 0.5, electrical resistivity was greatly improved to 1010 Ω cm at 500 °C, which was more than two orders of magnitude higher than that of Ca3NbGa3Si2O14 (CNGS). This value is the highest resistivity among members of the langasite family at present. However, the dielectric features associated with loss tangent jump at about 400 °C were not improved by the Al substituent. The bandgap Eg was measured by spectroscopic ellipsometry, and Eg was changed by both temperature and amount of Al substituent. Real and imaginary dielectric constants at a frequency from 0.1 to 20,000 Hz were measured from 150 to 600 °C. There was no marked difference between Cole–Cole plots of specimens with x = 0.1 and 0.5. Oxygen vacancies associated with Nb ions were discussed for DC conductivity and AC loss tangent.

AFM, RBS and tribological properties of WC/WS2 nanostructures after 1.5 MeV Nb+ implantation

The purpose of this study was to evaluate the impact of Nb+ ion implantation in WC/WS2 nanostructures and their tribological properties. The films were deposited on silicon and stainless-steel substrates by DC and RF magnetron sputtering at 400 °C. Different concentrations for sputtering of the WC targets were used while the concentration for WS2 was maintained constant for all the deposition processes. Nb ion implantation with an energy of 1.5 MeV and a dose of 6 × 1014 ions/cm2 at room temperature was done at the 3 MV Tandetron™ accelerator from “Horia Hulubei” National Institute for Physics and Nuclear Engineering – IFIN-HH. The topography of the samples was analyzed by atomic force microscopy (AFM). Rutherford backscattering spectrometry (RBS) investigations gave information regarding stoichiometry and thicknesses of the coatings while tribological properties were studied using a pin–on–ball tribometer before and after Nb ion implantation. We have found that after the Nb implantation the values measured for the coefficient of friction were lower as compared to the unimplanted samples thought to be due to the discrete amorphization sites which could be produced at this lower fluence by energy deposition through elastic and inelastic collisions.

Improving the electrochemical performance of Lithium–Sulfur batteries using an Nb-Doped TiO2 additive layer for the chemisorption of lithium polysulfides

This study presents a method to suppress the migration of lithium polysulfides in lithium–sulfur batteries by introducing a dual-layer electrode structure. Herein, unlike conventional methods of mixing the polar additives with sulfur/carbon composites, melted sulfur mixed with mesocarbon microbeads are used as the electrode and covered with an additive layer of Nb-doped TiO2/graphite composite via two-step blade coating. By doping TiO2 with Nb, electrical and lithium ion conductivity of TiO2 can be increased, thereby enhancing the redox reaction kinetics. Most importantly, chemisorption of lithium polysulfides to Nb–TiO2 can effectively mitigate the shuttle effect, resulting in higher capacity and longer cycle life. The electrode with the Nb–TiO2 additive layer results in a 1st and 100th cycle specific capacity of 1883 mAh g−1 and 894 mAh g−1, respectively, at 0.1 C (1 C = 1675 mAh), indicating enhanced electrochemical performance as compared with that of bare lithium-sulfur batteries. X-ray photoelectron spectroscopy (XPS) study was conducted to investigate the interaction between polysulfides and Nb–TiO2. The results indicate that the Nb–TiO2–layered electrode efficiently traps polysulfides on the cathode and improves the rate capability, cycle performance, and specific capacity.

Intercombination Transitions in the n = 4 Shell of Zn-, Ga-, and Ge-Like Ions of Elements Kr through Xe

Earlier beam-foil measurements have targeted 4s-4p intercombination transitions in the Zn-, Ga- and Ge-like ions of Nb (Z=41), Mo (Z=42), Rh (Z=44), Ag (Z=47) and I (Z=53). At the time, the spectra were calibrated with literature data on prominent lines in the Cu- and Zn-like ions. Corresponding literature data on the intercombination transitions in Ga- and Ge-like ions were largely lacking, which caused some ambiguity in the line identifications. We review the (mostly computational) progress made since. We find that a consistent set of state-of-the-art computations of Ga- and Ge-like ions would be highly desirable for revisiting the beam-foil data and the former line identifications for the elements from Kr (Z=36) to Xe (Z=54). We demonstrate that the literature data for these two isoelectronic sequences are insufficient, and we contribute reference computations in the process. We discuss the option of electron beam ion trap measurements as an alternative to the earlier use of classical light sources, beam-foil interaction and laser-produced plasmas, with the example of Xe (Z=54).

Enhanced performance of Sb2S3 mesoscopic sensitized solar cells employing TiO2:Nb compact layer

This paper reports on the enhancement of charge transport and recombination by niobium doped compact layers of TiO2 in a solar cell with Sb2S3 absorber layer by characterizing both thin films of TiO2:Nb and working solar cell devices with the layer stack FTO/cp-TiO2:Nb/mp-TiO2/Sb2S3/P3HT/MoOx/Ag. The electron transport layers of TiO2 doped with 0.14 and 0.27 at.% Nb were prepared by spin coating and have no structural change as determined from the analysis of GIXRD spectra. SEM images show thin pin hole free layers of the cp-TiO2:Nb on FTO crystals that are agglomerates of particles. Analysis of the current–voltage curves of the solar cells with Sb2S3 as the absorber material showed increased short-circuit current, fill factor and power conversion efficiency from 1.3 to 1.7%. The enhancement of the device performance is attributed to substitution of Ti ions with Nb ions in the TiO2 resulting in a change in the band alignment of the solar cells with Nb content. This results in increase in charge recombination resistance in the Sb2S3 layer as determined from the analysis of the impedance spectroscopy measurements.

The Role of Nb Addition in TiO2 Nanoparticles: Phase Transition and Photocatalytic Properties

This paper reports an experimental investigation on the effects of Nb addition on the phase transformation and photocatalytic properties of TiO2 nanoparticles. Differential thermal analysis, Raman spectroscopy, X‐ray diffraction measurements reveal that Nb addition retarded the anatase‐to‐rutile phase transition. Photocatalysis experiments indicate an enhancement of the degradation of methylene blue and rhodamine B dyes with the addition of Nb to TiO2 lattice. This behavior was attributed to the presence of Nb ions acting as active sites formers as well as the removal of organic species, since the presence of hydroxyls groups remained unchanged, as revealed by X‐ray photoelectron spectroscopy.