The development of a high-performance ferroelectric piezo-photocatalyst is an efficient strategy for advancing sustainability within the environmental and energy sectors.Yet,a major challenge lies in the creation of a...The development of a high-performance ferroelectric piezo-photocatalyst is an efficient strategy for advancing sustainability within the environmental and energy sectors.Yet,a major challenge lies in the creation of a strong polarized electric field that can effectively hinder charge recombination,both within the bulk and on the surface of catalysts.Herein,we synthesize a series of Nb-doped Bi_(4)Ti_(3)O_(12)nanosheets via a facile one-pot hydrothermal method to achieve synergistically enhanced piezo-photocatalytic performance in CO_(2)reduction and pollutant degradation.The optimized doped Bi_(4)Ti_(3)O_(12)demonstrates remarkable efficiency in the conversion of CO_(2)into CO,with a high production rate of 72.7μmol∙g−1∙h−1 without using co-catalysts or any sacrificial agent,surpassing the performance of unmodified Bi_(4)Ti_(3)O_(12)by up to 4.69 folds.Additionally,our catalyst demonstrates ultra-fast piezo-photocatalytic degradation of organic pollutant Rhodamine B(RhB)at low concentrations and exceptional piezo-photocatalytic activity at high concentrations,outperforming most previously reported state-of-the-art catalysts.The systematic corroboration of catalyst characterization and experimental analysis reveals that the synergistic effect arises from the amplified macroscopic polarization induced by lattice distortion caused by the larger Nb ions,thereby improving piezo-photocatalytic efficiency.This research thus offers valuable insights into the direct design and fabrication of versatile catalytic systems,with applications spanning CO_(2)valorization and beyond.展开更多
This paper investigates the effect of Nb doping on the electronic structure and optical properties of Sr2TiO4 by the first-principles calculation of plane wave ultra-soft pseudo-potential based on density functional t...This paper investigates the effect of Nb doping on the electronic structure and optical properties of Sr2TiO4 by the first-principles calculation of plane wave ultra-soft pseudo-potential based on density functional theory （DFT）.The calculated results reveal that due to the electron doping,the Fermi level shifts into conduction bands（CBs） for Sr2NbxTi1-xO4 with x=0.125 and the system shows n-type degenerate semiconductor features. Sr2TiO4 exhibits optical anisotropy in its main crystal axes,and the c-axis shows the most suitable crystal growth direction for obtaining a wide transparent region.The optical transmittance is higher than 90% in the visible range for Sr2Nb0.125Ti0.875O4.展开更多
Photocatalytic CO_(2)reduction driven by green solar energy could be a promising approach for the carbon neutral practice.In this work,a novel defect engineering approach was developed to form the Sn_(x)Nb_(1-x)O_(2)s...Photocatalytic CO_(2)reduction driven by green solar energy could be a promising approach for the carbon neutral practice.In this work,a novel defect engineering approach was developed to form the Sn_(x)Nb_(1-x)O_(2)solid solution by the heavy substitutional Nb-doping of SnO_(2)through a robust hydrothermal process.The detailed analysis demonstrated that the heavy substitution of Sn^(4+)by a higher valence Nb^(5+)created a more suitable band structure,a better photogenerated charge carrier separation and transfer,and stronger CO_(2)adsorption due to the presence of abundant acid centers and excess electrons on its surface.Thus,the Sn_(x)Nb_(1-x)O_(2)solid solution sample demonstrated a much better photocatalytic CO_(2)reduction performance compared to the pristine SnO_(2)sample without the need for sacrificial agent.Its photocatalytic CO_(2)reduction efficiency reached~292.47μmol/(g·h),which was 19 times that of the pristine SnO_(2)sample.Furthermore,its main photocatalytic CO_(2)reduction product was a more preferred multi-carbon(C_(2+))compound of C_(2)H_(5)OH,while that of the pristine SnO_(2)sample was a one-carbon(C1)compound of CH_(3)OH.This work demonstrated that,the heavy doping of high valence cations in metal oxides to form solid solution may enhance the photocatalytic CO_(2)reduction and modulate its reduction process,to produce more C_(2+)products.This material design strategy could be readily applied to various material systems for the exploration of high-performance photocatalysts for the solar-driven CO_(2)reduction.展开更多
IrO2 and IrRuOx(Ir:Ru 60:40 at%),supported by 50 wt%onto titania nanotubes(TNTs)and(3 at%Nb)Nb-doped titania nanotubes(Nb-TNTs),as electrocatalysts for the oxygen evolution reaction(OER),were synthesized and character...IrO2 and IrRuOx(Ir:Ru 60:40 at%),supported by 50 wt%onto titania nanotubes(TNTs)and(3 at%Nb)Nb-doped titania nanotubes(Nb-TNTs),as electrocatalysts for the oxygen evolution reaction(OER),were synthesized and characterized by means of structural,surface analytical and electrochemical techniques.Nb doping of titania significantly increased the surface area of the support from 145(TNTs)to 260 m2g-1(Nb-TNTs),which was significantly higher than those of the Nb-doped titania supports previously reported in the literature.The surface analytical techniques showed good dispersion of the catalysts onto the supports.The X-ray photoelectron spectroscopy analyses showed that Nb was mainly in the form of Nb(IV)species,the suitable form to behave as a donor introducing free electrons to the conduction band of titania.The redox transitions of the cyclic voltammograms,in agreement with the XPS results,were found to be reversible.Despite the supported materials presented bigger crystallite sizes than the unsupported ones,the total number of active sites of the former was also higher due to their better catalyst dispersion.Considering the outer and the total charges of the cyclic voltammograms in the range 0.1–1.4 V,stability and electrode potentials at given current densities,the preferred catalyst was Ir O2 supported on the Nb-TNTs.The electrode potentials corresponding to given current densities were between the smallest ones given in the literature despite the small oxide loading used in this work and its Nb doping,thus making the Nb-TNTs-supported IrO2 catalyst a promising candidate for the OER.The good dispersion of IrO2,high specific surface area of the Nb-doped supports,accessibility of the electroactive centers,increased stability due to Nb doping and electron donor properties of the Nb(IV)oxide species were considered the main reasons for its good performance.展开更多
All-inorganic CsPbBr_(3)-based perovskite solar cells(PSCs)have attracted great attention because of their high chemical and thermal stabilities in ambient air.However,the short-circuit current density(J_(sc))of CsPbB...All-inorganic CsPbBr_(3)-based perovskite solar cells(PSCs)have attracted great attention because of their high chemical and thermal stabilities in ambient air.However,the short-circuit current density(J_(sc))of CsPbBr_(3)-based PSCs is inadequate under solar illumination because of the wide bandgap,inefficient charge extraction and recombination loss,leading to lower power-conversion efficiencies(PCEs).It is envisaged that in addition to narrowing the bandgap by alloying,J_(sc)of the PSCs could be enhanced by effective improvement of electron transportation,suppression of charge recombination at the interface between the perovskite and electron transporting layer(ETL),and tuning of the space charge field in the device.In this work,Nb-doped SnO_(2)films as ETLs in the CsPbBr_(3)-based PSCs have been deposited at room temperature by high target utilization sputtering(Hi TUS).Through optimizing the Nb doping level alone,the J_(sc)was increased by nearly 19%,from 7.51 to 8.92 mA·cm^(-2)and the PCE was enhanced by 27%from 6.73%to 8.54%.The overall benefit by replacing the spin-coated SnO_(2)with sputtered SnO_(2)with Nb doping was up to 39%increase in J_(sc)and 62%increase in PCE.Moreover,the PCE of the optimized device showed negligible degradation over exposure to ambient environment(T~25°C,RH~45%),with 95.4%of the original PCE being maintained after storing the device for 1200 h.展开更多
Nb-doped TiO2 nanoparticles were prepared by hydrothermal treatment of titanate nanotubes in niobium oxalate aqueous solution.The effect of Nb doping and rutile content on the photoelectrochemical performance based on...Nb-doped TiO2 nanoparticles were prepared by hydrothermal treatment of titanate nanotubes in niobium oxalate aqueous solution.The effect of Nb doping and rutile content on the photoelectrochemical performance based on TiO2 powder electrodes was investigated.The results show that Nb-doped TiO2 with a small amount of rutile exhibits the enhanced photoelectric conversion efficiency for dye-sensitized solar cell.The highest photoelectric conversion efficiency of 8.53%is obtained for 1%Nb—TiO2 containing a small amount of rutile.When a small amount of rutile contained in 2%Nb—TiO2,a higher photoelectric conversion efficiency of8.77%is achieved.展开更多
Spinel （O01）-orientated Mn304 thin films on Nb-doped SrTi03 （001） substrates are fabricated via the pulsed laser deposition method. X-ray diffraction and high-resolution transmission electron microscopy indicate t...Spinel （O01）-orientated Mn304 thin films on Nb-doped SrTi03 （001） substrates are fabricated via the pulsed laser deposition method. X-ray diffraction and high-resolution transmission electron microscopy indicate that the as-prepared epitaxial fihn is well crystaiHzed. In the film plane the orientation relationship between the film and the substrate is [lOOjMn3 04 ｜｜[110] Nb-doped SrTiO3. After an electroforming process, the film shows bipolar nonvolatile resistance switching behavior. The positive voltage bias drives the sample into a low resistance state, while the negative voltage switches it back to a high resistance state. The switching polarity is different from the previous studies. The complex impedance measurement suggests that the resistance switching behavior is of filament type. Due to the performance reproducibility and state stability, Mn3O4 might be a promising candidate for the resistive random access memory devices.展开更多
Nb-doped SrTiO3 (STNO) films were grown on (001)-oriented LaAlO3 substrates by a reactive ion beam sputter deposition at various mixing ratios (OMRs) with a substrate temperature of 800oC. The STNO films exhibited goo...Nb-doped SrTiO3 (STNO) films were grown on (001)-oriented LaAlO3 substrates by a reactive ion beam sputter deposition at various mixing ratios (OMRs) with a substrate temperature of 800oC. The STNO films exhibited good crystallinity with an epitaxial orientation as characterized by high-resolution X-ray diffraction, grazing-incidence X-ray diffraction, and in-plane pole figure analysis. A decrease of out-of-plane and in-plane lattice constants was observed with an increase of OMR. The surface morphology of the STNO films showed a very dense fine-grain structure. The root-mean-square roughness was found to be increased as the OMR increased. Moreover, the elemental compositions of the STNO films were examined by X-ray photoelectron spectroscopy.展开更多
To restrict grain growth in coarse grain regions caused by the diffusion of Nd-Cu eutectic alloys,the Nb element was introduced into the precursor alloy to regulate the microstructure of melt-spun powder and die-upset...To restrict grain growth in coarse grain regions caused by the diffusion of Nd-Cu eutectic alloys,the Nb element was introduced into the precursor alloy to regulate the microstructure of melt-spun powder and die-upset magnets.The magnetic properties and thermal stability of die-upset magnets were appreciably improved through the addition of Nb.For the Nb-doped diffusion die-upset magnet,the grains inside the ribbons were refined and the coarse non-oriented surface crystallite got suppressed on the interface of ribbons during the hot-deformation process to form the anisotropic magnet.Moreover,Nd gathers at the intergranular phases,which is considered to enforce domain wall pinning force.The Nb-modified microstructure is advantageous to thermal stability and coercivity enhancement.High-resolution transmission electron microscopy images revealed that the Nb element gathered on the grain boundary and triple grain boundary to form c-Nb and h-Nb Fe B to hinder the grain growth during the hot-deformation process,which led to direct enhancement in the coercivity.Furthermore,the c-Nb and h-Nb Fe B are nonmagnetic phases that strengthened the magnetic isolation.However,the h-Nb Fe B precipitated from the hard magnetic phase and formed crystal defects which led to remanence deterioration.展开更多
The Li1.02NbxMn2-xO4 （x=0, 0.005, 0.01, 0.0：2, 0.04 and 0.1） materials were prepared by solid-state reaction method in which Li2CO3, electrolytic MnO2 and Nb2O5 were used as reactants. The influences of the Nb5＋ d...The Li1.02NbxMn2-xO4 （x=0, 0.005, 0.01, 0.0：2, 0.04 and 0.1） materials were prepared by solid-state reaction method in which Li2CO3, electrolytic MnO2 and Nb2O5 were used as reactants. The influences of the Nb5＋ doping on structure, morphology and electrochemical performance were systemically investigated by means of X-ray diffraction （XRD）, scanning electron microscopy （SEM）, cyclic voltammetry （CV） and AC impedance. XRD test showed that the prepared samples had single spinel structure although there was impurity phase of LiNbO3 existing in Li1.02NbxMn2-xO4 phase after Nb5＋ doping. The doped materials with Nb5＋ had smaller lattice parameters and crystal volume compared with pristine Li1.02Mn2O4. The endurance of overcharge was largely improved. In addition, the small amount of Nb5＋ doping could increase the material conductivity.展开更多
In the present study, niobium-doped indium oxide thin films were prepared by sol-gel spin coating technique. The effects of different Nb-doping contents on structural, morphological, optical, and electrical properties...In the present study, niobium-doped indium oxide thin films were prepared by sol-gel spin coating technique. The effects of different Nb-doping contents on structural, morphological, optical, and electrical properties of the films were characterized by means of X-ray diffraction （XRD）, field emission scanning electron microscopy （FESEM）, atomic force microscopy （AFM）, UV-Vis spectroscopy, and four point probe methods. XRD analysis confirmed the formation of cubic bixbyite structure of In203 with a small shift in major peak position toward lower angles with addition of Nb. FESEM micrographs show that grain size decreased with increasing the Nb-doping content. Optical and electrical studies revealed that optimum opto-electronic properties, including minimum electrical resistivity of 119.4 × 10^-3 Ω cm and an average optical transmittance of 85% in the visible region with a band gap of 3.37 eV were achieved for the films doped with Nb-doping content of 3 at.%. AFM studies show that addition of Nb at optimum content leads to the formation of compact films with smooth surface and less average roughness compared with the prepared ln2O3 films.展开更多
Nb-doped SrTiO3 thermoelectric ceramics with different niobium concentrations,sintering temperatures and Sr-site vacancies are successfully prepared by high energy ball milling combined with carbon burial sintering.Fo...Nb-doped SrTiO3 thermoelectric ceramics with different niobium concentrations,sintering temperatures and Sr-site vacancies are successfully prepared by high energy ball milling combined with carbon burial sintering.For fully understanding the effect of niobium doping on SrTiO3,thermoelectric transport properties are systematically investigated in a temperature range from 300 K to 1100 K.The carrier mobility can be significantly enhanced,and the electrical conductivity is quadrupled,when the sintering temperature rises from 1673 K to 1773 K（beyond the eutectic temperature（1713 K） of SrTiO3–TiO2）.The lattice vibration can be suppressed by the lattice distortion introduced by the doped niobium atoms.However,Sr-site vacancies compensate for the lattice distortion and increase the lattice thermal conductivity more or less.Finally,we achieve a maximum value of figure-of-merit z T of 0.21 at 1100 K for Sr Ti（0.9）Nb（0.1）O3 ceramic sintered at1773 K.展开更多
Manganese dissolution and the Jahn-Teller distortion represent the primary factors limiting the cycle life of spinel LiMn_(2)O_(4).In this study,Nb^(5+)-doped Li_(1.05)Mn_(2-x)Nb_(x)O_(4)(0≤x≤0.03)with truncated oct...Manganese dissolution and the Jahn-Teller distortion represent the primary factors limiting the cycle life of spinel LiMn_(2)O_(4).In this study,Nb^(5+)-doped Li_(1.05)Mn_(2-x)Nb_(x)O_(4)(0≤x≤0.03)with truncated octahedral morphology was successfully synthesized via a simple high-temperature solid-state method.Nb^(5+)doping not only enhanced the structural stability of LiMn_(2)O_(4) but also increased the Li^(+)diffusion rate.SEM analysis revealed that Nb^(5+)doping effectively suppressed(110)plane growth,thereby mitigating Mn dissolution.Simultaneously,TEM results indicated that a thinner cathode electrolyte interphase film was formed upon doping,which contributed to enhanced cycling stability.Further DFT calculations confirmed that Nb^(5+)doping improved the structural stability of LiMn_(2)O_(4) through a dual mechanism:reducing the occupancy of the Mn eg orbitals and strengthening the Mn-O bonding energy.On the other hand,Nb^(5+)doping expands the lattice,with CV and EIS tests showing increased Li+diffusion rates.PDOS calculations revealed a narrowed band gap,which improved the electronic conductivity,thereby endowing LiMn_(2)O_(4) with high-rate performance.Hence,Li_(1.05)Mn_(2-x)Nb_(x)O_(4) exhibits superior rate capability and extended cycle life.Specifically,Li_(1.05)Mn_(1.99)Nb_(0.01)O_(4) delivered an initial discharge capacity of 124.61 mAh/g with 88.43%capacity retention after 500 cycles at 1 C,and maintained 74.61 mAh/g even at 10 C.展开更多
Perovskite solar cells are one of the most promising alternatives to conventional photovoltaic devices, and extensive studies are focused on device optimization to further improve their performance. A compact layer of...Perovskite solar cells are one of the most promising alternatives to conventional photovoltaic devices, and extensive studies are focused on device optimization to further improve their performance. A compact layer of TiO2 is generally used in perovskite solar cells to block holes from reaching the fluorine-doped tin oxide electrode. In this contribution, we engineered a TiO2 compact layer using Nb doping, which resulted in solar cells with a power conversion efficiency （PCE） of 10.26%, which was higher than that of devices with the same configuration but containing a pristine TiO2 compact layer （PCE = 9.22%）. The device performance enhancement was attributed to the decreased selective contact resistance and increased charge recombination resistance resulting from Nb doping, which was revealed by the impedance spectroscopy measurements. The developed strategy highlights the importance of interface optimization for perovskite solar cells.展开更多
We have fabricated the epitaxial Nb-doped SrTiO3(NbSTO) thin films on Si substrates using a TiN film as the buffer layer.The oxygen-treatment and temperature dependence of electrical properties has been investigated.O...We have fabricated the epitaxial Nb-doped SrTiO3(NbSTO) thin films on Si substrates using a TiN film as the buffer layer.The oxygen-treatment and temperature dependence of electrical properties has been investigated.Oxygen treatment showed the surface change of NbSTO films has immense influence on the resistance switching.The resistance ratio of two resistance states decreased after oxygen treatment.With tested-temperature rising,the resistance and resistance ratio of two resistance states increased.The resistance switching of Pt/NbSTO junction as a function of oxygen-treatment and temperature can be explained by the charge trapping and detrapping process in the Pt/NbSTO interface,which will help understand the resistance switching mechanism of oxides.展开更多
We studied the effects of reductive annealing on insulating polycrystalline thin films of anatase Nb- doped TiO2 （TNO）. The insulating TNO films were intentionally fabricated by annealing conductive TNO films in oxy...We studied the effects of reductive annealing on insulating polycrystalline thin films of anatase Nb- doped TiO2 （TNO）. The insulating TNO films were intentionally fabricated by annealing conductive TNO films in oxygen ambient at 400 ℃. Reduced free carrier absorption in the insulating TNO films indicated carrier com- pensation due to excess oxygen. With H2-annealing, both carrier density and Hall mobility recovered to the level of conducting TNO, demonstrating that the excess oxygen can be efficiently removed by the annealing process without introducing additional scattering centers.展开更多
Nb-doped ZnO thin films were fabricated on glass substrates by using co-sputtering with direct-current and radio frequency magnetron sputtering.The structures,optical and electrical performances of Nb-doped ZnO thin f...Nb-doped ZnO thin films were fabricated on glass substrates by using co-sputtering with direct-current and radio frequency magnetron sputtering.The structures,optical and electrical performances of Nb-doped ZnO thin films were investigated.The results showed that all thin films have(002)c-axis preferential orientation.The minimum resistivity of 2.12×10^(-3)Ωcm and the maximum carrier concentration of 2.39×10^(19 )cm^(-3) were obtained at the direct-current sputtering power of 10W,respectively.Nb-doped ZnO thin films have also shown high average transmittance of 89.6%,and lower surface roughness of 2.74 nm.Meanwhile,a distinct absorption edge in the ultraviolet range of 300–400 nm was observed in absorbance,the optical band gap of Nb-doped ZnO thin films illustrates an increased tendency with increasing Nb concentration.展开更多
Growth temperature effects on the microstructure of Nb-doped BaTiO_(3) thin films of the composition BaTi_(0.98)Nb_(0.02)O_(3) are studied using X-ray diffraction and transmission electron microscopy(TEM).Reciprocal s...Growth temperature effects on the microstructure of Nb-doped BaTiO_(3) thin films of the composition BaTi_(0.98)Nb_(0.02)O_(3) are studied using X-ray diffraction and transmission electron microscopy(TEM).Reciprocal space maps and electron diffraction patterns show that the a-axis lattice parameter increases and the c-axis parameter decreases with increasing growth temperature,indicating a decrease of tetragonality.Bright-field TEM images show low and high densities of threading defects in films grown at low and high temperatures,respectively.The observations are discussed in terms of a hindering of the cubic-to-tetragonal phase transition by a high defect density and a high unit cell volume.展开更多
Solid-state batteries based on Li and nonflammable solid-state electrolytes(SSEs)have aroused the attention of numerous researchers because of their absolute safety and potentially high energy density.Most SSEs after ...Solid-state batteries based on Li and nonflammable solid-state electrolytes(SSEs)have aroused the attention of numerous researchers because of their absolute safety and potentially high energy density.Most SSEs after coming into contact with Li are reduced,which leads to high interfacial charge-transfer impedance and dendrites formation.In this study,an“interlayer-Li pre-reduction strategy”was proposed to solve the above problem of reduction.An intermediate layer was introduced between solid electrolyte and Li,and it reacted with Li to produce a stable and ion-conductive interphase.Cubic garnet-type Nb-doped Li_(7)La_(3)Zr_(2)O_(12)(Nb-LLZO)was selected as an example solid electrolyte since it is characterized by high ionic conductivity,feasible preparation under ambient conditions,as well as low cost.The high impedance arising from the reduction at the Nb-LLZO|Li interface has limited its application.In this paper,a nano-scale Li phosphorus oxynitride(LiPON)layer was deposited on the Nb-LLZO pellets through radio frequency(RF)magnetron sputtering,which pre-reacted with Li in-situ to produce a lithiophilic,electronically insulating,and ionic conductive interphase.The produced interphase significantly inhibited the reduction of Nb5+against Li and the formation and propagation of Li dendrites.It is noteworthy that Li|LiPON|Nb-LLZO|LiPON|Li cells stably cycled for over 2,000 h without any short circuit.This study emphasizes and demonstrates the significance of the pre-conversion of modification layer between unstable SSE and Li metal to improve interfacial stability.展开更多
基金the Natural Science Foundation of Jiangsu Province(No.BK20220596)Innovative Science and Technology Platform Project of Cooperation between Yangzhou City and Yangzhou University,China(No.YZ202026305)+3 种基金the Natural Science Foundation of China(Nos.21922202 and 21673202)the Priority Academic Program Development of Jiangsu Higher Education Institutions,Shaanxi Province High-level Talent Introduction Program(Youth Project)Doctoral Research Start-up Fund project of Xi’an Polytechnic University(No.107020589)the Biological Resources Development and the Textile Wastewater Treatment Innovation Team(No.23JP055).
文摘The development of a high-performance ferroelectric piezo-photocatalyst is an efficient strategy for advancing sustainability within the environmental and energy sectors.Yet,a major challenge lies in the creation of a strong polarized electric field that can effectively hinder charge recombination,both within the bulk and on the surface of catalysts.Herein,we synthesize a series of Nb-doped Bi_(4)Ti_(3)O_(12)nanosheets via a facile one-pot hydrothermal method to achieve synergistically enhanced piezo-photocatalytic performance in CO_(2)reduction and pollutant degradation.The optimized doped Bi_(4)Ti_(3)O_(12)demonstrates remarkable efficiency in the conversion of CO_(2)into CO,with a high production rate of 72.7μmol∙g−1∙h−1 without using co-catalysts or any sacrificial agent,surpassing the performance of unmodified Bi_(4)Ti_(3)O_(12)by up to 4.69 folds.Additionally,our catalyst demonstrates ultra-fast piezo-photocatalytic degradation of organic pollutant Rhodamine B(RhB)at low concentrations and exceptional piezo-photocatalytic activity at high concentrations,outperforming most previously reported state-of-the-art catalysts.The systematic corroboration of catalyst characterization and experimental analysis reveals that the synergistic effect arises from the amplified macroscopic polarization induced by lattice distortion caused by the larger Nb ions,thereby improving piezo-photocatalytic efficiency.This research thus offers valuable insights into the direct design and fabrication of versatile catalytic systems,with applications spanning CO_(2)valorization and beyond.
基金Project supported by the Natural Science Foundation of ShaanXi Province of China (Grant No 2005F06)Northwest University(NWU) Graduate Innovation and Creativity Funds (Grant No 08YZZ47)
文摘This paper investigates the effect of Nb doping on the electronic structure and optical properties of Sr2TiO4 by the first-principles calculation of plane wave ultra-soft pseudo-potential based on density functional theory （DFT）.The calculated results reveal that due to the electron doping,the Fermi level shifts into conduction bands（CBs） for Sr2NbxTi1-xO4 with x=0.125 and the system shows n-type degenerate semiconductor features. Sr2TiO4 exhibits optical anisotropy in its main crystal axes,and the c-axis shows the most suitable crystal growth direction for obtaining a wide transparent region.The optical transmittance is higher than 90% in the visible range for Sr2Nb0.125Ti0.875O4.
基金This study was supported by the National Natural Science Foundation of China(Grant No.51902271)the Fundamental Research Funds for the Central Universities(Grant Nos.2682020CX07,2682020CX08,and 2682021CX116)Sichuan Science and Technology Program(Grant Nos.2020YJ0072,2020YJ0259,and 2021YFH0163)。
文摘Photocatalytic CO_(2)reduction driven by green solar energy could be a promising approach for the carbon neutral practice.In this work,a novel defect engineering approach was developed to form the Sn_(x)Nb_(1-x)O_(2)solid solution by the heavy substitutional Nb-doping of SnO_(2)through a robust hydrothermal process.The detailed analysis demonstrated that the heavy substitution of Sn^(4+)by a higher valence Nb^(5+)created a more suitable band structure,a better photogenerated charge carrier separation and transfer,and stronger CO_(2)adsorption due to the presence of abundant acid centers and excess electrons on its surface.Thus,the Sn_(x)Nb_(1-x)O_(2)solid solution sample demonstrated a much better photocatalytic CO_(2)reduction performance compared to the pristine SnO_(2)sample without the need for sacrificial agent.Its photocatalytic CO_(2)reduction efficiency reached~292.47μmol/(g·h),which was 19 times that of the pristine SnO_(2)sample.Furthermore,its main photocatalytic CO_(2)reduction product was a more preferred multi-carbon(C_(2+))compound of C_(2)H_(5)OH,while that of the pristine SnO_(2)sample was a one-carbon(C1)compound of CH_(3)OH.This work demonstrated that,the heavy doping of high valence cations in metal oxides to form solid solution may enhance the photocatalytic CO_(2)reduction and modulate its reduction process,to produce more C_(2+)products.This material design strategy could be readily applied to various material systems for the exploration of high-performance photocatalysts for the solar-driven CO_(2)reduction.
文摘IrO2 and IrRuOx(Ir:Ru 60:40 at%),supported by 50 wt%onto titania nanotubes(TNTs)and(3 at%Nb)Nb-doped titania nanotubes(Nb-TNTs),as electrocatalysts for the oxygen evolution reaction(OER),were synthesized and characterized by means of structural,surface analytical and electrochemical techniques.Nb doping of titania significantly increased the surface area of the support from 145(TNTs)to 260 m2g-1(Nb-TNTs),which was significantly higher than those of the Nb-doped titania supports previously reported in the literature.The surface analytical techniques showed good dispersion of the catalysts onto the supports.The X-ray photoelectron spectroscopy analyses showed that Nb was mainly in the form of Nb(IV)species,the suitable form to behave as a donor introducing free electrons to the conduction band of titania.The redox transitions of the cyclic voltammograms,in agreement with the XPS results,were found to be reversible.Despite the supported materials presented bigger crystallite sizes than the unsupported ones,the total number of active sites of the former was also higher due to their better catalyst dispersion.Considering the outer and the total charges of the cyclic voltammograms in the range 0.1–1.4 V,stability and electrode potentials at given current densities,the preferred catalyst was Ir O2 supported on the Nb-TNTs.The electrode potentials corresponding to given current densities were between the smallest ones given in the literature despite the small oxide loading used in this work and its Nb doping,thus making the Nb-TNTs-supported IrO2 catalyst a promising candidate for the OER.The good dispersion of IrO2,high specific surface area of the Nb-doped supports,accessibility of the electroactive centers,increased stability due to Nb doping and electron donor properties of the Nb(IV)oxide species were considered the main reasons for its good performance.
基金supported by the National Natural Science Foundation of China(Nos.51602290,91233101,11174256)the Fundamental Research Program from the Ministry of Science and Technology of China(No.2014CB31704)+4 种基金Project funded by China Postdoctoral Science Foundation(No.2016M592310)the financial support from EPSRC New Investigator Award(2018EP/R043272/1)H2020-EU grant(2018CORNET 760949)
文摘All-inorganic CsPbBr_(3)-based perovskite solar cells(PSCs)have attracted great attention because of their high chemical and thermal stabilities in ambient air.However,the short-circuit current density(J_(sc))of CsPbBr_(3)-based PSCs is inadequate under solar illumination because of the wide bandgap,inefficient charge extraction and recombination loss,leading to lower power-conversion efficiencies(PCEs).It is envisaged that in addition to narrowing the bandgap by alloying,J_(sc)of the PSCs could be enhanced by effective improvement of electron transportation,suppression of charge recombination at the interface between the perovskite and electron transporting layer(ETL),and tuning of the space charge field in the device.In this work,Nb-doped SnO_(2)films as ETLs in the CsPbBr_(3)-based PSCs have been deposited at room temperature by high target utilization sputtering(Hi TUS).Through optimizing the Nb doping level alone,the J_(sc)was increased by nearly 19%,from 7.51 to 8.92 mA·cm^(-2)and the PCE was enhanced by 27%from 6.73%to 8.54%.The overall benefit by replacing the spin-coated SnO_(2)with sputtered SnO_(2)with Nb doping was up to 39%increase in J_(sc)and 62%increase in PCE.Moreover,the PCE of the optimized device showed negligible degradation over exposure to ambient environment(T~25°C,RH~45%),with 95.4%of the original PCE being maintained after storing the device for 1200 h.
基金supported by the National Natural Science Foundation of China(No.51172233)the Major State Basic Research Development Program of China("973 Program",No. 2009CB220002)the Key Laboratory of Water and Air Pollution Control of Guandong Province,China(GD2012A05)
文摘Nb-doped TiO2 nanoparticles were prepared by hydrothermal treatment of titanate nanotubes in niobium oxalate aqueous solution.The effect of Nb doping and rutile content on the photoelectrochemical performance based on TiO2 powder electrodes was investigated.The results show that Nb-doped TiO2 with a small amount of rutile exhibits the enhanced photoelectric conversion efficiency for dye-sensitized solar cell.The highest photoelectric conversion efficiency of 8.53%is obtained for 1%Nb—TiO2 containing a small amount of rutile.When a small amount of rutile contained in 2%Nb—TiO2,a higher photoelectric conversion efficiency of8.77%is achieved.
基金Supported by the National Basic Research Program of China under Grant Nos 2011CB921904 and 2012CB927402the National Natural Science Foundation of China under Grant Nos 11074142 and 11021464the Key Project of the Ministry of Education of China under Grant No 309003
文摘Spinel （O01）-orientated Mn304 thin films on Nb-doped SrTi03 （001） substrates are fabricated via the pulsed laser deposition method. X-ray diffraction and high-resolution transmission electron microscopy indicate that the as-prepared epitaxial fihn is well crystaiHzed. In the film plane the orientation relationship between the film and the substrate is [lOOjMn3 04 ｜｜[110] Nb-doped SrTiO3. After an electroforming process, the film shows bipolar nonvolatile resistance switching behavior. The positive voltage bias drives the sample into a low resistance state, while the negative voltage switches it back to a high resistance state. The switching polarity is different from the previous studies. The complex impedance measurement suggests that the resistance switching behavior is of filament type. Due to the performance reproducibility and state stability, Mn3O4 might be a promising candidate for the resistive random access memory devices.
文摘Nb-doped SrTiO3 (STNO) films were grown on (001)-oriented LaAlO3 substrates by a reactive ion beam sputter deposition at various mixing ratios (OMRs) with a substrate temperature of 800oC. The STNO films exhibited good crystallinity with an epitaxial orientation as characterized by high-resolution X-ray diffraction, grazing-incidence X-ray diffraction, and in-plane pole figure analysis. A decrease of out-of-plane and in-plane lattice constants was observed with an increase of OMR. The surface morphology of the STNO films showed a very dense fine-grain structure. The root-mean-square roughness was found to be increased as the OMR increased. Moreover, the elemental compositions of the STNO films were examined by X-ray photoelectron spectroscopy.
基金supported by the Major Project of“Science and Technology Innovation 2025 in Ningbo City(Nos.2020Z064,2019B10093)the Basic research expenses for provincial universities of Zhejiang Ocean University(No.2019J00036)the Talent introduction research fund of Zhejiang Ocean University(Nos.xjrcyj201801,11045091021)。
文摘To restrict grain growth in coarse grain regions caused by the diffusion of Nd-Cu eutectic alloys,the Nb element was introduced into the precursor alloy to regulate the microstructure of melt-spun powder and die-upset magnets.The magnetic properties and thermal stability of die-upset magnets were appreciably improved through the addition of Nb.For the Nb-doped diffusion die-upset magnet,the grains inside the ribbons were refined and the coarse non-oriented surface crystallite got suppressed on the interface of ribbons during the hot-deformation process to form the anisotropic magnet.Moreover,Nd gathers at the intergranular phases,which is considered to enforce domain wall pinning force.The Nb-modified microstructure is advantageous to thermal stability and coercivity enhancement.High-resolution transmission electron microscopy images revealed that the Nb element gathered on the grain boundary and triple grain boundary to form c-Nb and h-Nb Fe B to hinder the grain growth during the hot-deformation process,which led to direct enhancement in the coercivity.Furthermore,the c-Nb and h-Nb Fe B are nonmagnetic phases that strengthened the magnetic isolation.However,the h-Nb Fe B precipitated from the hard magnetic phase and formed crystal defects which led to remanence deterioration.
基金supported by the National Natural Science Foundation of China (No. 51004028)the Special Fund for Basic Scientific Research of Central Colleges, China (No.N100402002)
文摘The Li1.02NbxMn2-xO4 （x=0, 0.005, 0.01, 0.0：2, 0.04 and 0.1） materials were prepared by solid-state reaction method in which Li2CO3, electrolytic MnO2 and Nb2O5 were used as reactants. The influences of the Nb5＋ doping on structure, morphology and electrochemical performance were systemically investigated by means of X-ray diffraction （XRD）, scanning electron microscopy （SEM）, cyclic voltammetry （CV） and AC impedance. XRD test showed that the prepared samples had single spinel structure although there was impurity phase of LiNbO3 existing in Li1.02NbxMn2-xO4 phase after Nb5＋ doping. The doped materials with Nb5＋ had smaller lattice parameters and crystal volume compared with pristine Li1.02Mn2O4. The endurance of overcharge was largely improved. In addition, the small amount of Nb5＋ doping could increase the material conductivity.
基金Iran Initiative Nanotechnology Council for partially supporting this workMahar Fan Abzar Co.for AFM spectroscopy results
文摘In the present study, niobium-doped indium oxide thin films were prepared by sol-gel spin coating technique. The effects of different Nb-doping contents on structural, morphological, optical, and electrical properties of the films were characterized by means of X-ray diffraction （XRD）, field emission scanning electron microscopy （FESEM）, atomic force microscopy （AFM）, UV-Vis spectroscopy, and four point probe methods. XRD analysis confirmed the formation of cubic bixbyite structure of In203 with a small shift in major peak position toward lower angles with addition of Nb. FESEM micrographs show that grain size decreased with increasing the Nb-doping content. Optical and electrical studies revealed that optimum opto-electronic properties, including minimum electrical resistivity of 119.4 × 10^-3 Ω cm and an average optical transmittance of 85% in the visible region with a band gap of 3.37 eV were achieved for the films doped with Nb-doping content of 3 at.%. AFM studies show that addition of Nb at optimum content leads to the formation of compact films with smooth surface and less average roughness compared with the prepared ln2O3 films.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFA0403803)the National Natural Science Foundation of China(Grant Nos.51774065,51525401,51690163,and 51601028)the Dalian Support Plan for Innovation of High-level Talents(Top and Leading Talents)(Grant No.2015R013)
文摘Nb-doped SrTiO3 thermoelectric ceramics with different niobium concentrations,sintering temperatures and Sr-site vacancies are successfully prepared by high energy ball milling combined with carbon burial sintering.For fully understanding the effect of niobium doping on SrTiO3,thermoelectric transport properties are systematically investigated in a temperature range from 300 K to 1100 K.The carrier mobility can be significantly enhanced,and the electrical conductivity is quadrupled,when the sintering temperature rises from 1673 K to 1773 K（beyond the eutectic temperature（1713 K） of SrTiO3–TiO2）.The lattice vibration can be suppressed by the lattice distortion introduced by the doped niobium atoms.However,Sr-site vacancies compensate for the lattice distortion and increase the lattice thermal conductivity more or less.Finally,we achieve a maximum value of figure-of-merit z T of 0.21 at 1100 K for Sr Ti（0.9）Nb（0.1）O3 ceramic sintered at1773 K.
基金This work was carried out in part using computing resources at the High Performance Computing Center of Central South University.
文摘Manganese dissolution and the Jahn-Teller distortion represent the primary factors limiting the cycle life of spinel LiMn_(2)O_(4).In this study,Nb^(5+)-doped Li_(1.05)Mn_(2-x)Nb_(x)O_(4)(0≤x≤0.03)with truncated octahedral morphology was successfully synthesized via a simple high-temperature solid-state method.Nb^(5+)doping not only enhanced the structural stability of LiMn_(2)O_(4) but also increased the Li^(+)diffusion rate.SEM analysis revealed that Nb^(5+)doping effectively suppressed(110)plane growth,thereby mitigating Mn dissolution.Simultaneously,TEM results indicated that a thinner cathode electrolyte interphase film was formed upon doping,which contributed to enhanced cycling stability.Further DFT calculations confirmed that Nb^(5+)doping improved the structural stability of LiMn_(2)O_(4) through a dual mechanism:reducing the occupancy of the Mn eg orbitals and strengthening the Mn-O bonding energy.On the other hand,Nb^(5+)doping expands the lattice,with CV and EIS tests showing increased Li+diffusion rates.PDOS calculations revealed a narrowed band gap,which improved the electronic conductivity,thereby endowing LiMn_(2)O_(4) with high-rate performance.Hence,Li_(1.05)Mn_(2-x)Nb_(x)O_(4) exhibits superior rate capability and extended cycle life.Specifically,Li_(1.05)Mn_(1.99)Nb_(0.01)O_(4) delivered an initial discharge capacity of 124.61 mAh/g with 88.43%capacity retention after 500 cycles at 1 C,and maintained 74.61 mAh/g even at 10 C.
基金This work was financially supported by the National Natural Science Foundation of China （Grant Nos. 21103032 and 51272049）, the National Basic Research Program of China （973 Program） （No. 2011CB932702）, and SInberise R279-000-393-592. Dr. X. Yin thanks Mr. Jin Fang for help on IPCE measurements and Au evaporation.
文摘Perovskite solar cells are one of the most promising alternatives to conventional photovoltaic devices, and extensive studies are focused on device optimization to further improve their performance. A compact layer of TiO2 is generally used in perovskite solar cells to block holes from reaching the fluorine-doped tin oxide electrode. In this contribution, we engineered a TiO2 compact layer using Nb doping, which resulted in solar cells with a power conversion efficiency （PCE） of 10.26%, which was higher than that of devices with the same configuration but containing a pristine TiO2 compact layer （PCE = 9.22%）. The device performance enhancement was attributed to the decreased selective contact resistance and increased charge recombination resistance resulting from Nb doping, which was revealed by the impedance spectroscopy measurements. The developed strategy highlights the importance of interface optimization for perovskite solar cells.
基金supported by the National Natural Science Foundation of China(Grant No 11004251)the Basic Foundation of China University of Petroleum(Beijing)(Grant No.01JB0007)the Development Foundation of China University of Petroleum(Beijing)(Grant No.01JB0021)
文摘We have fabricated the epitaxial Nb-doped SrTiO3(NbSTO) thin films on Si substrates using a TiN film as the buffer layer.The oxygen-treatment and temperature dependence of electrical properties has been investigated.Oxygen treatment showed the surface change of NbSTO films has immense influence on the resistance switching.The resistance ratio of two resistance states decreased after oxygen treatment.With tested-temperature rising,the resistance and resistance ratio of two resistance states increased.The resistance switching of Pt/NbSTO junction as a function of oxygen-treatment and temperature can be explained by the charge trapping and detrapping process in the Pt/NbSTO interface,which will help understand the resistance switching mechanism of oxides.
基金partially supported by JSPS KAKENHI Grant Number 15K04687
文摘We studied the effects of reductive annealing on insulating polycrystalline thin films of anatase Nb- doped TiO2 （TNO）. The insulating TNO films were intentionally fabricated by annealing conductive TNO films in oxygen ambient at 400 ℃. Reduced free carrier absorption in the insulating TNO films indicated carrier com- pensation due to excess oxygen. With H2-annealing, both carrier density and Hall mobility recovered to the level of conducting TNO, demonstrating that the excess oxygen can be efficiently removed by the annealing process without introducing additional scattering centers.
文摘Nb-doped ZnO thin films were fabricated on glass substrates by using co-sputtering with direct-current and radio frequency magnetron sputtering.The structures,optical and electrical performances of Nb-doped ZnO thin films were investigated.The results showed that all thin films have(002)c-axis preferential orientation.The minimum resistivity of 2.12×10^(-3)Ωcm and the maximum carrier concentration of 2.39×10^(19 )cm^(-3) were obtained at the direct-current sputtering power of 10W,respectively.Nb-doped ZnO thin films have also shown high average transmittance of 89.6%,and lower surface roughness of 2.74 nm.Meanwhile,a distinct absorption edge in the ultraviolet range of 300–400 nm was observed in absorbance,the optical band gap of Nb-doped ZnO thin films illustrates an increased tendency with increasing Nb concentration.
基金supported by the Korea Research Council of Fundamental Science and Technology(KRCF)through a Basic Research Project managed by the Korea Research Institute of Standards and Science(KRISS)Support was also given by the Natural Science Foundation of China(Grant No.61271127).
文摘Growth temperature effects on the microstructure of Nb-doped BaTiO_(3) thin films of the composition BaTi_(0.98)Nb_(0.02)O_(3) are studied using X-ray diffraction and transmission electron microscopy(TEM).Reciprocal space maps and electron diffraction patterns show that the a-axis lattice parameter increases and the c-axis parameter decreases with increasing growth temperature,indicating a decrease of tetragonality.Bright-field TEM images show low and high densities of threading defects in films grown at low and high temperatures,respectively.The observations are discussed in terms of a hindering of the cubic-to-tetragonal phase transition by a high defect density and a high unit cell volume.
基金the National Key Research and Development Program of China(No.2018YFE0181300)the National Natural Science Foundation of China(No.21805055)+3 种基金the Guangdong Natural Science Funds(No.2019A1515010675)the Guangxi Natural Science Funds(No.2019JJA120043)the Department of Science and Technology of Guangxi Province(No.2021AB17045)the Science and Technology Project of Shenzhen(Nos.JCYJ20210324094206019 and JCYJ20190808142209376).
文摘Solid-state batteries based on Li and nonflammable solid-state electrolytes(SSEs)have aroused the attention of numerous researchers because of their absolute safety and potentially high energy density.Most SSEs after coming into contact with Li are reduced,which leads to high interfacial charge-transfer impedance and dendrites formation.In this study,an“interlayer-Li pre-reduction strategy”was proposed to solve the above problem of reduction.An intermediate layer was introduced between solid electrolyte and Li,and it reacted with Li to produce a stable and ion-conductive interphase.Cubic garnet-type Nb-doped Li_(7)La_(3)Zr_(2)O_(12)(Nb-LLZO)was selected as an example solid electrolyte since it is characterized by high ionic conductivity,feasible preparation under ambient conditions,as well as low cost.The high impedance arising from the reduction at the Nb-LLZO|Li interface has limited its application.In this paper,a nano-scale Li phosphorus oxynitride(LiPON)layer was deposited on the Nb-LLZO pellets through radio frequency(RF)magnetron sputtering,which pre-reacted with Li in-situ to produce a lithiophilic,electronically insulating,and ionic conductive interphase.The produced interphase significantly inhibited the reduction of Nb5+against Li and the formation and propagation of Li dendrites.It is noteworthy that Li|LiPON|Nb-LLZO|LiPON|Li cells stably cycled for over 2,000 h without any short circuit.This study emphasizes and demonstrates the significance of the pre-conversion of modification layer between unstable SSE and Li metal to improve interfacial stability.
