Nb Substitution Research Articles

Acidity and stability of Nb(V) active sites doped in SBA-15 and ZrSBA-15: A DFT study

Mesoporous silicas are of great interest in heterogeneous catalysis due to the structural characteristics of their pores and the adjustable catalytic properties that arise from incorporating heteroatoms. The substitution of Zr and Nb into SBA-15 introduces active sites into the material, rendering it a potential catalyst for acid catalysis reactions. However, discussions regarding the acid properties and metal-support interactions in amorphous silicas functionalized with metals are limited in computational chemistry. This study aims to determine the acid strength and charge transfer effects between Zr(IV) and Nb(V) species in mesoporous silica by proposing a representative SBA-15 cluster of type 5–6. Density Functional Theory (DFT) simulations were conducted using the B3LYP/6-31G(d,p)/def2TZVP levels. The model successfully replicated trends from larger clusters, demonstrating that the more grafted onto the silica structure (i.e. have more Si-O-M bonds), the greater the acid strength of the active site. Additionally, it was found that ZrSBA-15 structures are more stable than NbSBA-15 and possess higher acid strength, a trend supported by experimental observations. The results also suggest that Nb(V) species are more effectively stabilized in ZrSBA-15 than SBA-15, likely due to the presence of Zr(IV) centers in ZrSBA-15. This research contribute to a better understanding of how the support affects the stabilization of active phases, paving the way for the rational design of silica-based heterogeneous catalysts.

Substitutional Cu doping at the cation sites in Ba2YNbO6 toward improved visible-light photoactivity—A first-principles HSE06 study

Artificial photosynthesis holds immense promise for sustainable clean energy harvesting, with recent strides in material engineering with the earth abundant elements enabling efficient utilization of the visible solar spectrum for photoelectrochemical catalytic water splitting. Here, we have investigated the impact of substitutional Cu doping at all three cation sites in Ba2YNbO6 (BYN) using density functional theory calculations at the Heyd-Scuseria-Ernzerhof-06 level. One of the key findings is that the defect formation energy follows the hierarchy Nb > Ba > Y. The presence of an oxygen vacancy (OV) enhances the co-solubility of Cu substitution of Nb, particularly when placed outside the CuO6 unit, while it has a contrary effect for Y substitution. Cu replacement reduces the bandgap as Nb > Y ≫ Ba vis-à-vis pure BYN, while extending it into the visible part of the solar spectrum for Nb and Y replacement cases, albeit with OV causing a slight blue shift to them, without reducing the oxidation state of Cu due to strong charge-delocalization. Cu doping at Y and Nb sites retains the direct band transition character of BYN, a feature removed by OV. While all the bare Cu doped systems exhibit formation of a weak electron polaron, the placement of OV tends to annihilate this except for the system comprising first nearest neighbor placement of an OV relative to the Cu substitution at an Nb site. Notably, Cu doping at the Nb site significantly enhances optical activity, particularly ∼2.0–2.5 eV, resulting in promising candidates for photoelectrochemical catalysts.

Photo-responsive decellularized small intestine submucosa hydrogels.

Decellularized small intestine submucosa (dSIS) is a promising biomaterial for promoting tissue regeneration. Isolated from the submucosal layer of animal jejunum, SIS is rich in extracellular matrix (ECM) proteins, including collagen, laminin, and fibronectin. Following mild decellularization, dSIS becomes an acellular matrix that supports cell adhesion, proliferation, and differentiation. Conventional dSIS matrix is usually obtained by thermal crosslinking, which yields a soft scaffold with low stability. To address these challenges, dSIS has been modified with methacrylate groups for photocrosslinking into stable hydrogels. However, dSIS has not been modified with clickable handles for orthogonal crosslinking. Here, we report the development of norbornene-modified dSIS, named dSIS-NB, via reacting amine groups of dSIS with carbic anhydride in acidic aqueous reaction conditions. Using triethylamine (TEA) as a mild base catalyst, we obtained high degrees of NB substitution on dSIS. In addition to describing the synthesis of dSIS-NB, we explored its adaptability in orthogonal hydrogel crosslinking and used dSIS-NB hydrogels for cancer and vascular tissue engineering. Impressively, compared with physically crosslinked dSIS and collagen matrices, orthogonally crosslinked dSIS-NB hydrogels supported rapid dissemination of cancer cells and superior vasculogenic and angiogenic properties. dSIS-NB was also exploited as a versatile bioink for 3D bioprinting applications.

Catalytic activity of Nb-doped α-Fe2O3—Heterojunction structure, ferrimagnet-like character, and high activity

Photocatalytic activity of α-Fe2O3 under visible light had been studied intensively. Rapid electron-hole recombination is the main drawback of α-Fe2O3 and the photocatalytic activity can be enhanced by transition metal doping and heterojunction structure. In the present study, α-Fe2O3 doped with various amounts of Nb were synthesized using a simple sol–gel method, and further characterization and catalytic activity were investigated. PXRD, TEM-EDS and Mössbauer measurement showed the formation of weak-ferromagnetic Nb-doped α-Fe2O3 and FeNbO4, where heterojunction structure was suggested. UV–vis spectrum showed a broad absorption in visible-light regions with a narrow band gap between 2.27 and 2.97 eV. Photo-Fenton reaction using α-Fe2O3 to decompose methylene blue (MB) was conducted to evaluate the catalytic activity. Nb-doped sample showed a significant improvement compared with pure α-Fe2O3. PXRD and Mössbauer spectroscopy revealed the α-Fe2O3 and FeNbO4 phases, which were attached to a magnet due to the ferrimagentic character of Nb-doped α-Fe2O3. The high catalytic activity with k value 7.1 * 10−2/min was obtained for 7.4Nb600. Higher catalytic activity was also observed for 20Nb600 and 40Nb600, which were driven by higher surface area, Nb substitution and heterojunction structure. Mechanistic analysis revealed that the primary reaction of MB decomposition is the Photo-Fenton process.

Distribution and modes of occurrence of Nb in subbituminous coal: A case study from the Jungar Coalfield, Ordos Basin, China

Niobium has been considered to be enriched in high-Al-Ga in north China coal and coal-hosted Nb(Ta)-Zr(Hf)-REY-Ga polymetallic deposits in the southwestern region of China. However, modes of occurrence and influencing factors of Nb in Al-Ga-rich coal in North China are rarely reported. This study investigated the distribution characteristics of Nb in the No.6 high-Al-Ga coal of the Jungar Coalfield in North China. The in-situ Nb concentration of selected minerals, including kaolinite, Ti-oxides, boehmite, and zircon, is further quantitatively characterized based on multiscale in-situ elemental analyses, including SEM-EDS and LA-ICP-MS spot and mapping analyses. The results showed that Nb is rich in the tonstein and mudstone partings among bulk samples and is highly concentrated in Ti-oxides, followed by zircon among the minerals. A certain amount of Nb is associated with kaolinite and boehmite with different modes of occurrence: vermicular kaolinite (65.94 ppm) > clastic kaolinite (25.43 ppm) > altered K-bearing kaolinite (18.11 ppm) > cryptocrystalline kaolinite (17.03 ppm) > clastic boehmite (9.08 ppm) > cryptocrystalline boehmite (7.97 ppm). The Nb-Nb/Ta and Zr/Hf-Nb/Ta ratios suggest that the primary source of Nb in the No.6 coal is the altered felsic volcanic ash and bauxite deposit. The high-Fe concentration in Ti-bearing minerals indicates that anatase may originate from the alteration of ilmenite with a process of Fe depletion and Nb enrichment. The enrichment of Nb in coal is attributed to the substitution of Nb for Ti in isomorphism in all Ti-oxides, high-Ti, and Ti-bearing minerals.

Synergistic homovalent and heterovalent substitution effects on piezoelectric and relaxor behavior in lead-free BaTiO3 ceramics

This study investigates lead-free BaTiO3 (BT) perovskite ceramics, unraveling the synergistic effects arising from simultaneous homovalent (Zr) and heterovalent (Nb) substitution. Focusing on piezoelectric, ferroelectric, and relaxor behaviors, this research employs a comprehensive suite of analyses, including temperature-dependent dielectric measurements, polarization-electric field hysteresis loops, and bipolar strain measurements. Significantly, our study unveils that the simultaneous substitution of Zr and Nb in the BT lattice induces room-temperature relaxor behavior at relatively low concentrations (5 % Zr and 3 % Nb), yielding higher permittivity and larger maximum polarization compared to single element (Zr or Nb) substituted BT relaxors. Bipolar strain measurements showcase substantial large-signal d33* values (∼250 pm/V) across a broad temperature range (–50 °C to 30 °C) for BT ceramics with simultaneous 5 % Zr and 2 % Nb substitution. This research advances understanding of homovalent and heterovalent substitution in BT ceramics and opens avenues for tailoring properties to suit specific applications.

Experimental and Theoretical Investigation on the Enhanced Hydrogen Storage Performance of Ti–Cr–Mn–Fe-Based Alloys Modified by Nb Substitution

Experimental and Theoretical Investigation on the Enhanced Hydrogen Storage Performance of Ti–Cr–Mn–Fe-Based Alloys Modified by Nb Substitution

Achieving excellent strength-ductility-superelasticity combination in high-porosity NiTiNb scaffolds via high-temperature annealing

Metallic scaffolds with lightweight, low elastic modulus, and high energy-absorbing capacity are widely utilized in industrial applications but usually require post-heat treatment to enhance their comprehensive mechanical properties. However, it is unclear how to utilize the impact of β-Nb on the surrounding matrix for NiTiNb ternary alloys to achieve strength-ductility-superelasticity enhancement. Here, we prepared rhomboidal dodecahedral NiTiNb porous scaffolds with a porosity of 85.9% by additive manufacturing. Subsequently, annealing treatment was employed to drastically reduce the phase transformation temperatures and expand the thermal hysteresis. Interestingly, the 850 °C annealed scaffold exhibited exceeding double compressive strength of the as-built sample, with a remarkable improvement in ductility and superelasticity. From the microstructure perspective, high-temperature annealing caused a further eutectic reaction of the unmelted Nb particles with the NiTi matrix and the transformation of mesh-like β-Nb into dispersedly distributed spherical β-Nb particles. The microstructure evolution after deformation indicated that stress-induced martensitic transformation occurred in the matrix away from the NiTi-Nb eutectic region whereas almost no martensite formed nearby β-Nb particles. Atom probe tomography characterization revealed an element diffusion zone in several nanometers surrounding the β-Nb particle, where the substitution of Nb with Ti led to a higher Ni: Ti atomic ratio, lowering transformation temperatures. Molecular dynamics simulations illustrated that β-Nb particles can not only entangle dislocations internally, acting as reinforcements but also hinder the twin growth, contributing to strain hardening. This work elucidates the influence of β-Nb particles on the deformation mechanism of the NiTi-Nb eutectic region through in-depth atomic-scale investigation, which can provide inspiration for the improvement of comprehensive mechanical properties of NiTiNb alloys.

Enhancing mechanical properties of MgB2 superconductors through Nb substitution: A first-principles study

MgB2 has a wide range of applications as a crucial superconducting material in fields such as electronics and communications, but its weak mechanical properties limit its use in extreme environments such as high pressure. Therefore, this article explores the enhancement mechanism of the mechanical properties for MgB2 by substituting Mg sites with Nb element based on first principles. After substitution, NbB2 has better thermodynamic stability, and the introduction of Nb-d state enhances light absorption. In terms of mechanics, due to the higher electron accumulation density in the Nb–B bond and a shorter bond length (2.451 Å), the atomic interactions become tighter and stronger. As a result, both elastic constants and modulus are enhanced, exhibiting high stiffness, high compression resistance, etc. The spatial distribution of 3D elastic anisotropy is closer to a spherical shape and the universal anisotropy index (AU) tends to approach 0, which indicates the mechanical properties in all directions are more consistent, making it easier to predict and control. Meanwhile, the elastic modulus rises smoothly with increasing hydrostatic pressure and is not affected by lattice compression at low hydrostatic pressure. The change rate of B–B bond length is 6.8 % at 100 GPa, which becomes the main reason for the enhancement of mechanical properties. The article provides a theoretical foundation for the preparation of superconductors with excellent mechanical properties under extreme conditions.

Stabilization of γ-Fe2O3 nanoparticles to heat by doping Nb and its property studied by Mössbauer spectroscopy

Nb5+-doped γ-Fe2O3 was synthesized by sol–gel method followed by calcination at various temperatures from 200 to 700 °C, analyzed using Powder X-ray Diffraction (PXRD), Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectroscopy (EDS) and Mössbauer Spectroscopy. PXRD results show the formation of γ-Fe2O3 at 300 °C and it begins to transform to α-Fe2O3 at 350 °C for pure and 2 at.% Nb-doped samples. As the Nb doping increases (≥3.8 at.%), the transformation was suppressed up to 600 °C. TEM EDS confirms the incorporation of Nb to γ-Fe2O3 lattice in 9.1 at.% Nb sample calcined at 500 °C. At elevated temperature of 700 °C, γ-Fe2O3 went through full transformation to α-Fe2O3 by expelling large amount of Nb to the surface forming FeNbO4. TEM EDS confirms the compositional change during this process with reduced Nb content in α-Fe2O3 and Nb-rich nanoparticle on the surface of α-Fe2O3. Superparamagnetic properties were observed for Mössbauer spectra when the Nb doping increased, which is caused by decreased particle size. The slight increase in internal magnetic field also indicated the transformation from γ-Fe2O3 to α-Fe2O3. High Nb doping with 20 and 40 at.% shows the formation of FeNbO4 at lower temperature where limited or almost no Nb substitution in α-Fe2O3 was detected by EDS.

Influence of Nb substitution and sintering atmosphere on thermoelectric properties of CaTiO3-based ceramics

Co-substitution of Eu and Nb into insulating CaTiO3 can make it a good n-type potential thermoelectric (TE) material. In the present work, solid solution compounds with the nominal composition Ca0.8Eu0.2Ti1–xNbxO3–δ (x = 0.05, 0.08, 0.1, 0.12) were synthesized and sintered in different atmospheres, including argon (Ar) and forming gas (5 vol% H2 in Ar). Notably, the different reduction effects of these atmospheres resulted in significant differences in phase formation, grain size, oxygen deficiency, and TE properties of the synthesized samples. Introducing additional electrons to the system by donor substitution of Ti with Nb leads to significant changes in the electrical conductivity and Seebeck coefficient. The most favorable TE performance of the prepared samples was found in the sample with x = 0.05, primarily attributed to its proper charge carrier concentration. This work highlights the crucial role of the sintering atmosphere in manipulating the TE performance of n-type CaTiO3-based ceramics, an effect similar to donor doping.

Atomic-scale environment of niobium in ore minerals as revealed by XANES and EXAFS at the Nb K-edge

Abstract. The mineralogy of niobium (Nb) is characterized by multicomponent oxides such as AB2O6, A2B2O7, ABO4, and ABO3 in which Nb is incorporated in the B site. Such complex crystal-chemistry prevents their unambiguous identification in ore deposits such as hydrothermal rocks and laterites which exhibit complex and fine-grained textures. The understanding of the processes controlling Nb ore deposit formation in various geological settings is therefore limited, although Nb is a critical element. In this study, we use X-ray absorption spectroscopy (XAS) at the Nb K-edge to investigate the local atomic-scale structure around Nb in a large set of natural and synthetic minerals of geological and technological importance. Our X-ray absorption near-edge structure (XANES) data at the Nb K-edge show three major features of variable position and intensity and then can be related to the local distortion and coordination number of the Nb site. Shell-by-shell fits of the extended X-ray absorption fine structure (EXAFS) data reveal that the NbO6 octahedra are distorted in a variety of pyrochlore species. At least two distinct first shells of O atoms are present while reported crystallographic data yield regular octahedra in the same minerals. Next-nearest Nb–Nb distances in pyrochlore and Nb-bearing perovskite mirror a corner-sharing NbO6 network, whereas the two Nb–Nb distances in columbite are typical of edge- and corner-sharing NbO6 octahedra. Such a resolution on the Nb site geometry and the intersite relationships between the next-nearest NbO6 octahedra is made possible by collecting EXAFS data under optimal conditions at 20 K and up to 16 Å−1. The local structure around substituted Nb5+ in Fe3+, Ti4+, and Ce4+ oxides suffers major changes relative to the unsubstituted structures. The substitution of Nb5+ for Ti4+ in anatase leads to the increase in the interatomic distances between Nb and its first and second Ti4+ neighbors. The substitution of Nb5+ for Ce4+ in cerianite reduces the coordination number of the cation from eight to four, and the Nb–O bonds are shortened compared to Ce–O ones. In hematite, Nb5+ occupies a regular site, whereas the Fe3+ site is strongly distorted suggesting major site relaxation due to charge mismatch. The sensitivity of XANES and EXAFS spectroscopies at the Nb K-edge to the local site geometry and next-nearest neighbors demonstrated in this study would help decipher Nb speciation and investigate mineralogical reactions of Nb minerals in deposit-related contexts such as hydrothermal and lateritic deposits.

Comprehensive Structural Analysis Identifies the Relationships Between the Electrical Characteristics of Environmentally Friendly NBTMn-BAl-NaNb Ceramics

We give an in-depth examination of the structural and electrical features of NBTMn–BAl–NaNb ceramics in the paper. The comprehensive structural investigation indicated an important connection among the phase and polarization mechanisms of the compounds/samples by Nb substitution. The quantitative study of phase contribution shown by Raman spectroscopy is confirmed by structural refinement inquiries. The significant polarization difference in NBTMn–BAl–NaNb was found to be in excellent show with the structural presence of a dual phase contribution, which was confirmed through structural refinement. The substitution of NaNb in NBTMn–BAl led to a significant shift in average grain size (∼1 μm). It was additionally found that the dielectric constant of NBTMn–BAl–NaNb was greater than NBTMn–BAl lowering the depolarization temperature ∼30 °C. This modification resulted in reduced dielectric loss as well as shifts in coordination and structural features. The ferroelectric examines demonstrated that the synthesized compounds exhibited a strong ferroelectric character, Pr slightly increases ΔPr = 4 μC cm−2 and coercive field changes ΔEC=10kV/cm in presence of NaNb. The room temperature bipolar and unipolar strain S(%) ∼1.5, and the fact that the substitution of NaNb leads to an increase in both (bipolar and unipolar), represents structural symmetry modulation. As a result of this, these were discovered to be feasible prospects for current generation applications.

Weak electron-phonon coupling contributing to enhanced thermoelectric performance in n-type TiCoSb half-Heusler alloys

n-type TiCoSb half-Heusler (HH) alloys show lower thermoelectric performance may be notably owing to the low valley degeneracy of the conduction band. Here, we show that this drawback can be counterbalanced by a decrease in the deformation potential coefficient and hence, weak electron-phonon coupling strength driven by the substitution of Nb for Ti in the n-type alloys Ti1-xNbxCoSb0.96Bi0.04. The combined substitutions of Nb and Bi yield a reduction of ∼86% in the deformation potential of the conduction band minimum, with the lowest value of ∼5 eV at 300 K achieved in Ti0.85Nb0.15CoSb0.96Bi0.04. This effect leads to enhanced power factor from ∼0.018 mW m−1 K−2 for x = 0 to ∼1.69 mW m−1 K−2 for x = 0.15 at RT due to the resulting strong increase in electron mobility by one order of magnitude. Both the isovalent Bi and aliovalent Nb substitutions further contribute to decrease the lattice thermal conductivity owing to enhanced mass and strain field fluctuations. The beneficial combined effects of weaker electron-phonon coupling and enhanced point-defect phonon scattering results in a higher dimensionless thermoelectric figure of merit ZT, with a peak value ∼ 0.37 at 870 K in Ti0.85Nb0.15CoSb0.96Bi0.04, representing a ∼ 375% improvement with respect to pristine TiCoSb.

Insight into Nb-sbustitution effects on Li1.17Mn0.57Ni0.24Nb0.02O2 cathode material for lithium-ion batteries application

Lithium-rich layered oxides (LLOs) have been intensively studied due to their high energy density, but still face the drawbacks such as capacity decay and voltage decay, and poor cycling stability. In this work, the Nb substituted Li1.17Mn0.57Ni0.24Nb0.02O2 (LMN-Nb) is successfully prepared, and the effects of Nb substitution on the microstructure, voltage attenuation, cycling stability and electrochemical kinetics are characterized and investigated compared with the host material Li1.17Mn0.58Ni0.25O2 (LMN). A proper amount of Nb substitution not only extends the interlayer spacing and increases conductivity of LMN-Nb, but also inhibits the release of lattice oxygen, the migration of transition metal ions into lithium layer and the dissolution of transition metal ions in the electrolyte. As a result, LMN-Nb exhibits significantly improved initial coulombic efficiency, specific capacity and excellent cycling stability (99.1 % remaining after 150 cycles at 2C rate). In addition, the LMN-Nb also shows good electrochemical performance in pouch-type cell (full cell). This results demonstrate that the strategy of using 4d/5d transition metals substitution to design high-performance LLOs is feasible in the following work.

High-Capacity Nickel-Based Layered Oxides Containing Niobium Ions for Lithium-Ion Batteries

Lithium-ion batteries have been widely used in recent years, from portable electronic devices to electric vehicles. Although LiNiO2, is expected to be ideal electrode materials for electric vehicle applications due to its high reversible capacity, Ni ions migrate from octahedral sites of transition metal layers to tetrahedral sites of adjacent Li layers during charging. This process is partly reversible process but Ni ions are left the tetrahedral sites of the Li layer after the continuous cycle test, which prevents the re-insertion of Li ions, resulting in capacity degradation. [1]To suppress the capacity degradation LiNiO2, the effect on the phase transition behavior by Nb substitution for Ni ions in LiNiO2 is examined.The samples with different Nb contents LixNi1–xNbxO2, are synthesized and tested as electrode materials. The Nb-substituted sample shows highly improved cycle characteristics compared with non-substituted LiNiO2. SEM observation of the samples reveals that the primary particles become smaller, suggesting that the Nb-substituted influences the crystallization process for LiNiO2. By comparing the results of electrochemical and structural characterizations for the samples with or without Nb substitution, the origin of the improvement of electrode reversibility is discussed in details.Reference [1] N. Ikeda et al., and N. Yabuuchi, Journal of Materials Chemistry A, 9, 15963 (2021).

In-gap states and local structures around substitutional defects in La- or Nb-doped n-type SrTiO3

First-principles calculations with DFT+U method were conducted on the local structures and the in-gap electronic states of n-type SrTiO3, whose electron doping was realized by substitution of Sr by La or Ti by Nb. For both La-doped and Nb-doped SrTiO3, cubic structures were proved to be stable e3ven when tetragonal structures were assumed, as suggested also in a reported experimental study. In La-doped SrTiO3, O atoms neighboring the substitutional La were symmetrically attracted toward the dopants. Sharp electron band observed at the top of the bandgap, which gave n-type conductivity and resulted from the intersection of Fermi energy level at the conduction band bottom with La-doping, was composed of 3d orbitals in Ti. The La-doping transformed some of the p electrons in O into the d electrons in Ti in the sharp band, and these electrons at Fermi level were expected to act as n-type carriers. In Nb-doped SrTiO3, on the other hand, Ti atoms at the first, second and third nearest neighbors of the Nb, which were in the same Ti-O plane surrounding the dopants, were repelled away from the Nb dopants to be isotropic local expansion, while O atoms neighboring Nb were attracted toward the dopants in the expanded local structure. Sharp band of the in-gap states just below the Fermi energy of the Nb-doped SrTiO3 was not only of the 3d orbitals in the first nearest-neighbor Ti atoms, but also of those in the second and third nearest-neighbor Ti atoms of the dopants. The degree of Fermi level intrusion into conduction band and atomic rearrangements near Nb substitutions were milder than those of La substitutions. As replacement of Sr atoms by La not contained in Ti-O network does not disturb the electron transport within Ti-O conduction planes, Nb-doping in Ti site does not interrupt the n-type carrier transportation even though Nb atoms are in Ti-O network, because of the formation of conduction path which bypasses the unit cell containing the dopants.

A high rate and stability cathode material for half/full sodium-ion batteries: Nb-substituted NaNi1/3Mn1/3−xFe1/3NbxO2 layered oxides

O3 layered oxide cathode materials have infinite development potential in sodium ion batteries (SIBs), but complex phase transitions usually result in poor rate capacity. In this study, NaNi1/3Mn1/3−xFe1/3NbxO2 (NFM-Nb x, x = 0, 0.01, 0.02) precursor were synthesized through ball-milling spray drying method. The structure morphology characterization confirmed that Nb was successfully doped into the material and replaced part of Mn in the transition metal. The chemical valence analysis shows that Nb doping promoted the reduction of Mn4+ to Mn3+, and the increase of Mn3+ improved the ionic conductivity. NFM-Nb 0.01 significantly improved long cycle stability and rate capacity, the capacity of NFM-Nb 0.01 at 1 C and 5 C were 125.4 and 115.5 mAh g−1, respectively, and the corresponding cycle retention rate maintained 83. 81% and 83.12%. NFM-Nb 0.01 has a 25.06% higher capacity retention rate than NFM after 100 cycles at 1 C in the voltage range 2–4.3 V. For full-cell, NFM-Nb 0.01//HC delivered the capacity of 79.4 mAh g−1 at 10 C after 200 cycles and kept 71.16% cycle retention. The results of ex-situ XRD further investigated Nb-substitution enhanced the structure recoverability of cathode materials. The failure analysis result showed that Nb substitution is beneficial to stabilize the layered structure of materials, improve the cycling performance under high voltage.

Influence of Nb and Mo Substitution on the Structure and Magnetic Properties of a Rapidly Quenched Fe79.4Co5Cu0.6B15 Alloy.

The importance of amorphous and nanocrystalline Fe-based soft magnetic materials is increasing annually. Thus, characterisation of the chemical compositions, alloying additives, and crystal structures is significant for obtaining the appropriate functional properties. The purpose of this work is to present comparative studies on the influence of Nb (1, 2, 3 at.%) and Mo (1, 2, 3 at.%) in Fe substitution on the thermal stability, crystal structure, and magnetic properties of a rapidly quenched Fe79.4Co5Cu0.6B15 alloy. Additional heat treatments in a vacuum (260-640 °C) were performed for all samples based on the crystallisation kinetics. Substantial improvement in thermal stability was achieved with increasing Nb substitution, while this effect was less noticeable for Mo-containing alloys. The heat treatment optimisation process showed that the least lossy states (with a minimum value of coercivity below 10 A/m and high saturation induction up to 1.7 T) were the intermediate state of the relaxed amorphous state and the nanocomposite state of nanocrystals immersed in the amorphous matrix obtained by annealing in the temperature range of 340-360 °C for 20 min. Only for the alloy with the highest thermal stability (Nb = 3%), the α-Fe(Co) nanograin grows, without the co-participation of the hard magnetic Fe3B, in a relatively wide range of annealing temperatures up to 460 °C, where the second local minimum in coercivity and core power losses exists. For the remaining annealed alloys, due to lower thermal stability than the Nb = 3% alloy, the Fe3B phase starts to crystallise at lower annealing temperatures, making an essential contribution to magneto-crystalline anisotropy, thus the substantial increase in coercivity and induction saturation. The air-annealing process tested on the studied alloys for optimal annealing conditions has potential use for this type of material. Additionally, optimally annealed Mo-containing alloys are less lossy materials than Nb-containing alloys in a frequency range up to 400 kHz and magnetic induction up to 0.8 T.

Al/Nb Co-Doped La2Ti2O7 As an Efficient Photocatalyst for H2 Production from Water

Al/Nb co-doped La2Ti2O7 has been prepared by a facile sol-gel method and investigated as the photocatalyst for H2 evolution. Optimal photocatalytic H2 production is achieved at the sample of La2Ti1.6Al0.2Nb0.2O7 with a production rate of ~37 µmolg-1h-1, which is ~ 2.5 fold higher than that of pristine sample. Further analysis the substitution of Al and Nb in B-site inhibits the growth of grain size, which helps increase the number of active sites. In addition, the introduction of Al and Nb decrease the Ti3+ species, which plays a negative role in photocatalysis as they could provide recombination spot for the photogenerated charges and thus shorten the electron lifetime.