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
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
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
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
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.
