Incorporation Of Nb Research Articles

Effect of Nb on hydrogen storage properties of Ti–V–Cr-based alloys

This research investigates the impact of incorporating Nb into Ti–V–Cr-based alloys, with compositions ranging from Ti30-xV35Cr35Nbx (x = 0, 5, 10, 15, and 20 at. %), with the objective of enhancing hydrogen storage properties. Employing a comprehensive approach encompassing design, synthesis, and characterization, the study aimed to develop novel hydrogen storage alloys. Utilizing the CALPHAD method, the alloys were designed to anticipate the formation of multicomponent single-phase structures. Structural and microstructural analyses of the synthesized alloys were conducted using XRD, SEM, and EDS techniques. The hydrogen storage capabilities were evaluated utilizing a Sieverts’ type apparatus. The investigated alloys displayed a singular-phase BCC solid solution, characterized by dendritic microstructures. Notably, the Nb-free alloy, Ti30V35Cr35, demonstrated the highest hydrogen storage capacity, reaching 3.62 wt% (∼1.9 H/M) under 20 bar of H2 at room temperature. Among the Nb-containing alloys, Ti25V35Cr35Nb5 exhibited a capacity of 2.91 wt% (∼1.6 H/M) under identical conditions. Furthermore, the incorporation of Nb up to 10 at. % effectively bolstered cycle durability. This study underscores the presence of an optimal Nb content crucial for achieving the highest hydrogen capacity and cycle durability in these alloys.

Influence of nitrogen and niobium incorporation in bcc-chromium coatings on microstructure and mechanical properties

Stoichiometric CrN and Cr:N with different nitrogen (N) content are of interest for hard coating applications. In the Cr-N material system, bcc-Cr rich coatings, containing a few percent of diluted N, provide tunability in microstructure and mechanical properties. Additionally, the incorporation of Nb into the CrNx coatings may further tailor the materials properties. In this work, bcc-CrNx and CrNbNx coatings were deposited by reactive magnetron sputtering, and their mechanical and microstructural characteristics were investigated as a function of N content. Depending on the N content, the phases observed by X-ray diffractometry (XRD) varied from metallic bcc-Cr, mixed bcc-Cr/h-Cr2N, to h-Cr2N/CrN. X-ray reflectivity (XRR), and scanning electron microscopy (SEM) measurements show that a dense and nearly columnar-free bcc-CrNx coatings was obtained at ~13–25 at.% of N, while CrNbNx coatings composed of dense, column-free, and featureless microstructure at a N content of ~10–20 at.%. The dense and nearly column-free microstructure composed of dispersion of Cr2N grains into the bcc-Cr matrix for both CrNx and CrNbNx coatings, as shown by high resolution transmission electron microscope analysis (HRTEM). Nanoindentation revealed a hardening of the coatings due to the grain refinement, solid solution strengthening, and variation in phase content.

The effects of Nb on the microstructure and performance of laser-cladded Fe50-xMn30Co10Cr10Nbx high entropy alloy coatings

A laser cladding technique was employed to produce a Fe50-XMn30Co10Cr10NbX (X = 2.5, 5, 7.5, 10at%) high entropy alloy coating. This study delved into the influence of Nb concentration on the coating’s phase constitution, microstructural features, hardness, and wear resistance. The high entropy alloy coating exhibited a multifaceted structural composition, encompassing FCC (Face-Centered Cubic), HCP (Hexagonal Close-Packed), and BCC (Body-Centered Cubic) structures, along with the presence of Laves phase. Notably, the incorporation of Nb led to an augmentation in the Laves phase and modifications within the microstructure. The hardness of the cladding layer is higher than that of the substrate. With the increase of Nb content, the hardness of the cladding layer increases first and then decreases; the average hardness of the Fe42.5Mn30Co10Cr10Nb7.5 cladding layer is the highest, the maximum hardness is 429.8Hv, and the average hardness is 382.3Hv. The friction coefficient and weight loss of the cladding layer decreases first and then increases with the increase of Nb content. The friction coefficient and weight loss of the Fe42.5Mn30Co10Cr10Nb7.5 cladding layer are the smallest, which are 0.0132 g and 0.5974, showing the best wear resistance. The wear types of high entropy alloy cladding layer are both adhesive wear and abrasive wear. The addition of Nb into high entropy alloy will form the Laves phase, which can improve the mechanical properties of high entropy alloy.

Enhancing Fracture Toughness of Dental Zirconia through Incorporation of Nb into the Surface.

Our previous study found that the addition of pentavalent cations like niobium (Nb) to yttria-stabilized zirconia increased fracture toughness but also raised the coefficient of thermal expansion (CTE), and opacity also increased undesirably. A new surface treatment is required to boost fracture toughness without altering CTE or translucency. The surfaces of pre-sintered 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) and 4.2 mol% yttria-stabilized partially stabilized zirconia (4.2Y-PSZ) were treated with a Nb sol solution containing Nb2O5 nanoparticles. After drying and sintering, a high-Nb-content surface layer formed with a depth of approximately 1 mm. The Nb content in this surface layer matched that of a bulk material with 1 mol% Nb2O5. The tetragonality of the surface zirconia increased, enhancing the surface fracture toughness without changing the CTE or translucency. Adding Nb near the surface improved the fracture toughness without affecting the CTE or translucency. This method could strengthen zirconia prostheses, allowing more reliable dental restorations.

Laser clad CoCrFeNiTixNby hypoeutectic high-entropy alloy coating: Effects of Ti and Nb content on mechanical, wear and corrosion properties

High-entropy alloys (HEAs) exhibit significant potential for advanced wear and corrosion-resistant applications. This study investigates the influence of Ti and Nb doping on the microstructure, phase composition, and properties of CoCrFeNiTixNby HEAs synthesized using high-speed laser cladding (HLC). The results demonstrate that increasing Ti and Nb content transforms the coating structure from a face-centered cubic (FCC) phase to a hybrid structure comprising FCC, body-centered cubic (BCC), and Laves phases, leading to a linear enhancement in surface hardness. The incorporation of Ti and Nb not only promotes the preferred orientation of the FCC phase (111) crystal plane but also significantly enhances tensile strength, though this comes at the expense of reduced plasticity. Specifically, the CoCrFeNiTi0.6Nb0.15 coating attains an ideal balance between strength and ductility, with a tensile strength of 1641.8 MPa and a tensile strain of 15.9 %, achieved through the formation of a eutectic structure. This coating also exhibits superior wear resistance and outstanding corrosion resistance, which are attributed to the stability of the passivation film, reinforced by the (111) crystal plane and high-density dislocations. These findings provide both theoretical and empirical foundations for the design of high-performance HEAs, underscoring their potential in industrial applications requiring robust wear and corrosion resistance.

Anion and Cation Co-Doping of NiO for Transparent Photovoltaics and Smart Window Applications

Materials engineering based on metal oxides for manipulating the solar spectrum and producing solar energy have been under intense investigation over the last years. In this work, we present NiO thin films double doped with niobium (Nb) and nitrogen (N) as cation and anion dopants (NiO:(Nb,N)) to be used as p-type layers in all oxide transparent solar cells. The films were grown by sputtering a composite Ni-Nb target on room-temperature substrates in plasma containing 50% Ar, 25% O2, and 25% N2gases. The existence of Nb and N dopants in the NiO structure was confirmed by the Energy Dispersive X-Ray and X-Ray Photoelectron Spectroscopy techniques. The nominally undoped NiO film, which was deposited by sputtering a Ni target and used as the reference film, was oxygen-rich, single-phase cubic NiO, having a visible transmittance of less than 20%. Upon double doping with Nb and N the visible transmittance of NiO:(Nb,N) film increased to 60%, which was further improved after thermal treatment to around 85%. The respective values of the direct band gap in the undoped and double-doped films were 3.28 eV and 3.73 eV just after deposition, and 3.67 eV and 3.76 eV after thermal treatment. The changes in the properties of the films such as structural disorder, direct and indirect energy band gaps, Urbach tail states, and resistivity were correlated with the incorporation of Nb and N in their structure. The thermally treated NiO:(Nb,N) film was used to form a diode with a spin-coated two-layer, mesoporous on top of a compact, TiO2 film. The NiO:(Nb,N)/TiO2heterojunction exhibited visible transparency of around 80%, showed rectifying characteristics and the diode’s parameters were deduced using the I-V method. The diode revealed photovoltaic behavior upon illumination with UV light exhibiting a short circuit current density of 0.2 mA/cm2 and open-circuit voltage of 500 mV. Improvements of the output characteristics of the NiO:(Nb,N)/TiO2 UV-photovoltaic by proper engineering of the individual layers and device processing procedures are addressed. Transparent NiO:(Nb,N) films can be potential candidates in all-oxide ultraviolet photovoltaics for tandem solar cells, smart windows, and other optoelectronic devices.

Insights into the Acidic Site in Manganese Oxide in Terms of the Sulfur and Water Tolerance of Low-Temperature NH3 Selective Catalytic Reduction.

A critical constraint impeding the utilization of Mn-based oxide catalysts in NH3 selective catalytic reduction (NH3-SCR) is their inadequate resistance to water and sulfur. This vulnerability primarily arises from the propensity of SO2 to bind to the acidic site in manganese oxide, resulting in the formation of metal sulfate and leading to the irreversible deactivation of the catalyst. Therefore, gaining a comprehensive understanding of the detrimental impact of SO2 on the acidic sites and elucidating the underlying mechanism of this toxicity are of paramount importance for the effective application of Mn-based catalysts in NH3-SCR. Herein, we strategically modulate the acidity of the manganese oxide catalyst surface through the incorporation of Ce and Nb. Comprehensive analyses, including thermogravimetry, NH3 temperature-programmed desorption, in situ diffused reflectance infrared Fourier transform spectroscopy, and density functional theory calculations, reveal that SO2 exhibits a propensity for adsorption at strongly acidic sites. This mechanistic understanding underscores the pivotal role of surface acidity in governing the sulfur resistance of manganese oxide.

Discovering Untapped Potential in Finance Markets Using NLP-Driven Sentiment Analysis

Objectives: The main objective in Sentiment Analysis, and financial data is to decode sentiments through the use of Natural Language Processing (NLP) and Machine Learning (ML). This provides insights into market trends that are essential for risk management and well-informed financial decisions. By removing emotion from financial writing, gives stakeholders practical advice for wise investments in dynamic markets. The main objective is to increase the accuracy of Multinomial Naïve Bayes (Multinomial NB). In this work, we used purely ML models to get the accuracy more than the previous works, which got 74%, and in this work, we can see the accuracy increased to approximately 82%. Methods: This specific Research Work employs Machine Learning approaches to extract sentiment polarity (positive, negative, and neutral) from financial text data. The used ML models are- Multinomial Naïve Bayes (Multinomial NB), Logistic Regression (LR), KNeighbors, Decision Tree, and Random Forest algorithms are used for Sentiment Analysis. Findings: Studies conducted in the financial sector have shown that sentiment and informational substance in stock news have a big impact on market factors such as trading volume, volatility, stock prices, and corporate earnings. This study involves approximately 6000 newspaper articles to extract the polarity from financial text data. The incorporation of Multinomial NB of Natural Language Processing techniques results in a marginal improvement in the sentiment classification model performance among all the models used, where the previous works got the lowest accuracy of 74%. Novelty: This research introduces advanced ML models for extracting financial sentiment from text, including Random Forest, LR, KNeighbors, Decision Tree, and Multinomial NB previously unexplored in similar studies. Notably, the Multinomial NB model accuracy rose significantly from 65% to 82%. The study also presents sentiment segregation (positive, negative, neutral) visualized in a donut chart. Keywords: Sentiment Analysis, Machine Learning, Natural Language Processing, Financial data, Stock market prediction

Tuning phase structure for enhanced electrostrain in Nb5+-doped Bi0.5(Na0.81K0.19)0.5TiO3 lead-free piezoelectric ceramics

The synthesis of Bi0.5(Na0.81K0.19)0.5Ti1−xNbxO3 (BNKT-xNb) lead-free piezoelectric ceramics via the traditional solid-state method, with varying x from 0.5 % to 4.0 %, is reported. Investigating the influence of Nb5+ ions on dielectric, ferroelectric, and electrostrain properties, alongside assessing the temperature stability of electrical properties, unveiled a notable electrostrain of 0.46 % at room temperature under 80 kV/cm for the 2.0 mol.% Nb5+ doped composition. The incorporation of Nb5+ prompted a transition from the ferroelectric to the relaxor phase, facilitating reversible induction into the ferroelectric phase under an external electric field, leading to the observed large electrostrain. Leveraging the first-order reversal curve (FORC) approach, a detailed analysis of the dynamic response process of different phase structures under the influence of the external electric field was conducted. This analysis elucidated that the continuous polarization response near the boundary of ferroelectric and relaxor phases, induced by the external electric field, primarily drives strain enhancement. These findings underscore the effective modulation of phase structure through Nb5+ doping, offering significant advancements in strain properties. This study opens avenues for the utilization of the material in micro actuators and provides valuable insights for the development of high-performance lead-free piezoelectric ceramics.

Laser Powder Bed Fusion Processing of Low Cost CoCrFeNiMoxNby High Entropy Alloys with Promising High-Temperature Properties via In Situ Alloying Commercial Powders

A blend of only commercial powders, including Ni625, CoCrF75, and 316L, were used as the raw material for fabricating non-equiatomic CoCrFeNiMoxNby high entropy alloys (HEAs) through laser powder bed fusion (PBF-LB/M) via in situ alloying, instead of using pure elemental powders, thus reducing the raw materials cost. The rapid cooling inherent in the PBF-LB/M process facilitated the dissolution of Mo and Nb, resulting in a single FCC phase characterized by high relative densities. High-temperature tensile tests were conducted at room temperature, 700 °C, 800 °C, and 900 °C, revealing mechanical properties that surpassed those reported in existing HEA literature. The remarkable strength of the HEAs developed in this study primarily stemmed from the incorporation of Mo and Nb, leading to the precipitation of Mo and Nb-rich lave phases at elevated temperatures. While constraining elongation when confined to grain boundaries, these precipitates enhanced strength without compromising elongation when distributed throughout the matrix. This work is a feasibility study to explore the usage of commodity compositions from the market to develop HEAs using PBF-LB/M, which opens the possibility of using scraps to further the development of new materials. Consequently, this study presents a rapid and cost-effective approach for HEA development, improving efficiency and sidestepping the direct utilization of critical raw metals for sustainable manufacturing. Moreover, this work also underscores the outstanding mechanical performance of these HEAs at high temperatures, paving the way for the design of innovative alloys for future high-temperature applications.

Experimental Investigation of the Impact of Niobium Additions on the Structural Characteristics and Properties of Ti-5Cr-xNb Alloys for Biomedical Applications.

In this study, a series of Ti-5Cr-xNb alloys with varying Nb content (ranging from 1 to 40 wt.%) were investigated to assess their suitability as implant materials. Comprehensive analyses were conducted, including phase analysis, microscopy examination, mechanical testing, and corrosion resistance evaluation. The results revealed significant structural alterations attributed to Nb addition, notably suppressing the formation of the ω phase and transitioning from α' + β + ω to single β phase structures. Moreover, the incorporation of Nb markedly improved the alloys' plastic deformation ability and reduced their elastic modulus. In particular, the Ti-5Cr-25Nb alloy demonstrated high values in corrosion potential and polarization resistance, signifying exceptional corrosion resistance. This alloy also displayed high bending strength (approximately 1500 MPa), a low elastic modulus (approximately 80 GPa), and outstanding elastic recovery and plastic deformation capabilities. These aggregate outcomes indicate the promising potential of the β-phase Ti-5Cr-25Nb alloy for applications in orthopedic and dental implants.

Novel MRI-compatible Zr–Mo–Nb alloys with superior mechanical performance, high corrosion resistance and good cytocompatibility for biomedical applications

Nowadays, MRI diagnostics have become indispensable in modern medicine, and the development of MRI-compatible materials is an urgent requirement for both modern medicine and materials science. Herein, MRI-compatible Zr–Mo–Nb alloys were developed by plasma arc melting and hot rolling process for biomedical applications. The Nb addition induces the composition segregation, β-Zr phase precipitations, and significant grain refinements in Zr–1Mo-xNb alloys, thereby contributing to an ultrafine α+β lamellar structure in hot-rolled (HRed) Zr–1Mo–3Nb alloys. Thanks to the nano-sized α+β lamellar structure, a high yield strength (YS) of 819.6 ± 20.9 MPa and an acceptable elongation of 11.8 ± 1% were realized in the HRed Zr–1Mo–3Nb alloy. Additionally, the incorporation of Nb with a high PB ratio and a relatively high equilibrium potential in the Zr–1Mo matrix enhances the stability of the passivation layer, leading to a more positive corrosion potential. Consequently, this significantly improves the corrosion resistance of HRed Zr–1Mo-xNb alloys. The Zr–1Mo–3Nb alloy exhibits lower magnetic susceptibility than the Zr–1Mo alloy, indicating improved MRI compatibility. Moreover, the HRed Zr–1Mo-xNb alloy shows excellent cytocompatibility to MC3T3-E1 cells, and good hemocompatibility of the experimental alloys were confirmed by the blood compatibility test. These findings highlight the potential of the MRI-compatible Zr–1Mo–3Nb alloy as a promising material for implants and devices in MRI environments, offering superior mechanical performance, high corrosion resistance and good biocompatibility.

Enabling 20 min fast-charging Ah-level pouch cell by tailoring the electronic structure and ion diffusion in TiNb2O7

TiNb2O7 has garnered attention as promising anode materials due to its remarkable cycling durability and rate capability, but its practical applications are currently hampered by the sluggish ion/electron kinetics. Herein, we propose a bimetallic synergistic strategy to enhance ionic and electronic transport kinetics, improving electrochemical performance. DFT calculation results further confirm the synergistic effect of Zn and Nb can increase the lattice parameters, promote Li+ diffusion, and enhance electronic conductivity. Benefiting from this, the Zn0.02Ti0.94Nb2.04O7 exhibits excellent cycling stability (a capacity loss of 0.02 % per cycle over 1000 cycles). An Ah-level pouch cell presents potential application with an impressive cycle lifespan, corresponding to an ultra-high retention ratio of 88.6 % (2.34 Ah) over 2700 cycles. Importantly, in-situ XRD and Nano-CT techniques elucidate the positive impact of the incorporation of Zn and Nb on the fundamental ion transport mechanisms, which is verified by the decreased mechanic effects, and promoted Li+-diffusion kinetics. This work offers a straightforward strategy to significantly improve the rate performance and cycling stability of TiNb2O7, establishing guidelines for fabricating fast-charging batteries with long cycling lifespans.

Effect of Nb as dopant of hydrotalcite catalysts during the ethanol condensation to optimize n-Butanol production

The present study optimizes Cu-supported catalysts on hydrotalcite for the synthesis of n-butanol whose interest is in its use as biofuel, due to its superior performance in comparison with other short-chain alcohols. The catalytic performance was improved by adding Nb to the catalytic formulation. In this way, several Cu-Nb catalysts supported on hydrotalcites (Mg/Al) with different Nb loadings were synthesized by incipient wetness impregnation and characterized by H2−temperature-programmed reduction, X-ray diffraction, N2 physisorption, CO2− and NH3−thermo-programmed desorption and X-ray photoelectron spectroscopy. It was shown that the incorporation of Nb promoted a suitable balance between the acid-basic and redox sites, modulating the Cu0/Cu+ dehydrogenation/hydrogenation properties for the n-BuOH production. The synthesis of multiple value-added products (n-BuOH, acetaldehyde, ethyl acetate, and 1-hexanol) was achieved in both the liquid− (at 180 ºC) and gas−phase (150−350 ºC), where it was demonstrated that both the n-BuOH selectivity and ethanol conversion improved with the Nb addition. The performance of the catalysts under time on stream and their recycling is also described.

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.

Processing and enhancement of thermoelectric performance of Nb doped ZnO (NZO) ceramics

In this investigation, we extensively studied the effect of various parameters on the processing, microstructure, sintering and thermoelectric characteristics of ZnO ceramics. Different Nb-doped ZnO-based ceramics, ranging from 0 to 0.25 wt %, were fabricated and sintered at the temperature of 1450 °C for 2 h in an inert atmosphere of argon (Ar). Various characterizations were employed to discern the performance attributes of these ceramics, encompassing phase analysis, densification, and microstructure evaluations. Thermal conductivity properties were studied from room temperature up to the temperature of 800 °C. Thermoelectric properties and efficiency of the sintered ceramics were evaluated across the temperature range of 100–800 °C. Results indicated that the incorporation of Nb into ZnO ceramics resulted in a harmonious structure due to the attained homogeneous and complete solid solution diffusion reaction. It was found that the optimal values for thermal conductivity, electrical resistivity, and thermoelectric properties were achieved at 0.15 wt % Nb doping. ZnO doped ceramics exhibited typical behavior of n-type semiconductors, showcasing exceptional thermoelectric properties at elevated temperatures. Our findings indicate that native defects, such as oxygen vacancies (OV), contribute to decreased band gap energy values and increased carrier concentration, thereby enhancing electrical conductivity and power factor. Hence, this study underscores the viability and practicality of Nb-doping ZnO sintered in an argon atmosphere as an effective approach to enhance its thermoelectric performance.

Enhancing Thermoelectric Performance in P-Type Sb2Te3-Based Compounds Through Nb─Ag Co-Doping with Donor-Like Effect.

P-type Sb2Te3 has been recognized as a potential thermoelectric material for applications in low-medium temperature ranges. However, its inherent high carrier concentration and lattice thermal conductivity led to a relatively low ZT value, particularly around room temperature. This study addresses these limitations by leveraging high-energy ball milling and rapid hot-pressing techniques to substantially enhance the Seebeck coefficient and power factor of Sb2Te3, yielding a remarkable ZT value of 0.55 at 323K due to the donor-like effect. Furthermore, the incorporation of Nb─Ag co-doping increases hole concentration, effectively suppressing intrinsic excitations ≈548K while maintaining the favorable power factor. Simultaneously, the lattice thermal conductivity can be significantly reduced upon doping. As a result, the ZT values of Sb2Te3-based materials attain an impressive range of 0.5-0.6 at 323K, representing an almost 100% improvement compared to previous research endeavors. Finally, the ZT value of Sb1.97Nb0.03Ag0.005Te3 escalates to 0.92 at 548K with a record average ZT value (ZTavg) of 0.75 within the temperature range of 323-573K. These achievements hold promising implications for advancing the viability of V-VI commercialized materials for low-medium temperature application.

Room temperature nanoindentation creep behavior of CoNiCrMo-based high entropy amorphous alloy coatings prepared by HVAF

The present study aimed to explore the creep behavior of CoNiCrMo-based high entropy amorphous alloy coatings at room temperature using nanoindentation creep experiments. The coatings were subjected to different loading rates to assess their performance. The findings indicate that the high entropy effect of the (Co0.33Ni0.33Cr0.23Mo0.1)80-xNbx(B0.7Si0.3)20 (x = 0, 2 and 4 at. %) high entropy amorphous alloy coatings has a notable impact on the creep resistance and facilitates a uniform plastic deformation during creep. The shear transition zone (STZ) size and the free volume content during creep deformation exhibit an increase in response to the concentration of Nb. This phenomenon can be attributed to the elevated atomic packing density and the hindered movement of atoms resulting from the incorporation of Nb. Nb content has a favorable impact on the creep stress index, increasing creep stress. Also, the high concentration of Nb is found to mitigate the propensity of the stress exponent to drop with increasing loading rates. The high entropy effect of the as-sprayed coatings promotes high creep resistance and homogenous creep deformation.

Improved electrochemical performance of Nb5+ doped NCM cathode upon 4.5 V application beneficial from the suppressed H2-H3 phase transition and promoted Li+ migration kinetics

As a commercial cathode material, Li(Ni,Co,Mn)O2 cathode (NCM) suffers from rapid performance degradation due to structural instability. In this paper, Nb5+ is introduced to NCM layered structure upon the application with a cut-off voltage up to 4.5 V. After the doping of Nb5+, XRD investigation suggests that the average bond length of LiO increases while that of TM-O reduces, due to the changes in charge density around the transition metal cations as confirmed from DFT calculation. The shortened TM-O bond length enhances stability of the lattice that suppresses H2-H3 phase conversion so the capacity retention is promoted. On the other hand, GITT investigation indicates that the increased LiO bond length offers enhanced diffusion coefficient which accelerates the migration of the Li cations and therefore improves the rate behavior. As a whole, the incorporation of Nb5+ leads to reversible cycling of NCM cathode upon 4.5 V, with specific capacity of 205 mA h g−1 at 0.1C, capacity retention of 89.12 % after 100 cycles and rate capacity of 158 mA h g−1 at 5C. Such performance exceeds those of other NCM cathode materials and suggests high potential of Nb5+ doped NCM cathode for application in high energy batteries.

Improving low-temperature NH3-SCR denitration activity and resistance to H2O and SO2 over Nb-modified NbaSn0.3CeOx catalysts by enhancing acidity to compensate for its weak oxidation ability

In this paper, a series of Nb-modified NbaSn0.3CeOx (a = 0.2, 0.4, 0.5) catalysts for denitrification were prepared using a facile co-precipitation method. In order to explore the various individual properties of the samples, the catalysts were characterized by XRD, Raman, N2 adsorption and desorption, TEM, NH3-TPD, H2-TPR, XPS and in-situ DRIFTS tests to understand the influences of the Nb introduction on the NH3-SCR reaction. Among these catalysts, the Nb0.4Sn0.3CeOx catalyst exhibit excellent NH3-SCR performance in the temperature range of 155–450 °C with more than 90 % NO conversion, 100 % N2 selectivity, and possess good resistance to H2O and SO2. Compared with the Sn0.3CeOx catalyst, we believe that the improvement of the low-temperature NH3-SCR performance of the Nb0.4Sn0.3CeOx catalysts is mainly due to the change in the amount of acid, special for the increase in B acid content, which compensates for the effect of the weaken oxidizing ability on the low-temperature activity. Beyond that, the good H2O and SO2 resistance at low temperature after the introduction of Nb into Nb0.4Sn0.3CeOx catalysts was analyzed by using in-situ DRIFTS characterization in detail, and the results indicate that the incorporation of Nb can inhibit the oxidation of SO2 to form sulfate on the catalysts, and prevent the competing adsorption of H2O and NOx, but the adsorption of NH3 is not affected. This work proves that the acidity regulation can improve low-temperature SCR activity by the synergistic effect between oxidation capacity and acidity.