Silicon-based material is an important anode material for next-generation lithium-ion batteries.In order to overcome its shortcomings,carbon coating is often employed to improve the electrochemical performance.However...Silicon-based material is an important anode material for next-generation lithium-ion batteries.In order to overcome its shortcomings,carbon coating is often employed to improve the electrochemical performance.However,the carbon source,carbon content,and different contact and mixing schemes between carbon sources and silicon are all complex factors and need to be clarified.In this study,nano-silicon is coated by the chemical vapor deposition method using different carbon sources,such as acetylene,methane,propane,and propylene.Carbon content after coating is designed to stay at the same level to reduce the experimental error.Results show the sample with higher conductivity provides higher cycle performance.Propylene is the best choice of the four carbon sources studied in this work.These results indicate that the selection of the carbon source is an important factor that plays a significant role in electrochemical performance.展开更多
A method using strong fluctuation theory （SFT） to compute the effective electromagnetic parameters of multiphase composite media, and common materials used to design radar-absorbing materials, is demonstrated. The e...A method using strong fluctuation theory （SFT） to compute the effective electromagnetic parameters of multiphase composite media, and common materials used to design radar-absorbing materials, is demonstrated. The effective electromagnetic parameters of ultrafine carbonyl-iron （DT-50） and fiber fabric, which are both multiphase composite media and represent coated and structured radar absorbing materials, respectively, are investigated, and the corresponding equations of electromagnetic parameters by using the SFT are attained. Moreover, we design a program to simplify the solutions, and the results are discussed.展开更多
Dielectric properties of SiC/Ni nanocomposites prepared by a simple and facile electroless plating approach at X band are investigated. Compared to the original SiC nanopartieles （SiCp）, the real part of the permitt...Dielectric properties of SiC/Ni nanocomposites prepared by a simple and facile electroless plating approach at X band are investigated. Compared to the original SiC nanopartieles （SiCp）, the real part of the permittivity, ε＇, and the dielectric loss tangent tang δe of SiC/Ni nanocomposites are clearly enhanced by about 31% and 33%, respectively. The effective equations for complex permittivity of SiC/Ni nanoeomposites are proposed. We also calculate ε＇ and tan δe of SiC/Ni nanoeomposites and the calculated results are well consistent with the measured data.展开更多
We present general equations for metal-substrate single-layer microwave absorbing materials. The optimum electromagnetic parameters and matching thicknesses for electric-loss, magnetic-loss, and electromagnetic-loss m...We present general equations for metal-substrate single-layer microwave absorbing materials. The optimum electromagnetic parameters and matching thicknesses for electric-loss, magnetic-loss, and electromagnetic-loss materials are given, and possible solutions for the equations and the corresponding theoretic curves are discussed as well. The results may be helpful for designing high-performance microwave absorbing materials.展开更多
Considering the eddy current effect of the magnetic metal particles in a high frequency electromagnetic field, we extend the Maxwell-Garnett law by introducing the eddy-effect parameter A which is as functions of the ...Considering the eddy current effect of the magnetic metal particles in a high frequency electromagnetic field, we extend the Maxwell-Garnett law by introducing the eddy-effect parameter A which is as functions of the radius, permeability and electric conductivity of the metal particle medium. It is obvious that the computational result agrees with the experiment, which indicates that the extended Maxwell-Garnett law can be used to predict the effective electromagnetic parameters of a dilute metal-insulator composite medium in a high-frequency electromagnetic field.展开更多
The high-temperature dielectric properties of SiO2/Si3N4 nanocomposites are investigated theoretically and experimentally. Its permittivities and loss tangents at the temperature ranging from room temperature to 1300...The high-temperature dielectric properties of SiO2/Si3N4 nanocomposites are investigated theoretically and experimentally. Its permittivities and loss tangents at the temperature ranging from room temperature to 1300℃ at 9.0 GHz are measured by the resonant cavity method. The SiO2/Si3N4 nanocomposites show complex dielectric behaviour at elevated temperature, and a multi-scale model is proposed to describe the dependence of the dielectric properties in the SiO2/Si3N4 on its compositional variations. Such a theory is needed so that the available property measurements could be extrapolated to other operating frequencies and temperatures.展开更多
The geometrical and electronic structures of nitrogen-doped β-SiC are investigated by employing the first principles of plane wave ultra-soft pseudo-potential technology based on density functional theory. The struct...The geometrical and electronic structures of nitrogen-doped β-SiC are investigated by employing the first principles of plane wave ultra-soft pseudo-potential technology based on density functional theory. The structures of SiC1-xNx （x = 0, 1/32, 1/16, 1/8, 1/4） with different doping concentrations are optimized. The results reveal that the band gap of β-SiC transforms from an indirect band gap to a direct band gap with band gap shrinkage after carbon atoms are replaced by nitrogen atoms. The Fermi level shifts from valence band top to conduction band by doping nitrogen in pure β-SiC, and the doped β-SiC becomes metallic. The degree of Fermi levels entering into the conduction band increases with the increment of doping concentration; however, the band gap becomes narrower. This is attributed to defects with negative electricity occurring in surrounding silicon atoms. With the increase of doping concentration, more residual electrons, more easily captured by the 3p orbit in the silicon atom, will be provided by nitrogen atoms to form more defects with negative electricity.展开更多
This paper reports that single-phase γ-Y2Si2O7 is prepared via a sufficient blending and cold-pressed sintering technique from Y2O3 powder and SiO2 nanopowder. It studies the dielectric properties of γ-Y2Si2O7 as a ...This paper reports that single-phase γ-Y2Si2O7 is prepared via a sufficient blending and cold-pressed sintering technique from Y2O3 powder and SiO2 nanopowder. It studies the dielectric properties of γ-Y2Si2O7 as a function of the temperature and frequency. The γ-Y2Si2O7 exhibits low dielectric loss and non-Debye relaxation behaviour from 25 to 1400℃ in the range of 7.3 18 GHz. The mechanism for polarization relaxation of the as-prepared γ-Y2Si2O7 differing from that of SiO2 is explained. Such particular dielectric properties could potentially make specific attraction for extensive practical applications.展开更多
基金Project supported by Beijing Natural Science Foundation(Grant No.2182065)the National Natural Science Foundation of China(Grant No.11922202)。
文摘Silicon-based material is an important anode material for next-generation lithium-ion batteries.In order to overcome its shortcomings,carbon coating is often employed to improve the electrochemical performance.However,the carbon source,carbon content,and different contact and mixing schemes between carbon sources and silicon are all complex factors and need to be clarified.In this study,nano-silicon is coated by the chemical vapor deposition method using different carbon sources,such as acetylene,methane,propane,and propylene.Carbon content after coating is designed to stay at the same level to reduce the experimental error.Results show the sample with higher conductivity provides higher cycle performance.Propylene is the best choice of the four carbon sources studied in this work.These results indicate that the selection of the carbon source is an important factor that plays a significant role in electrochemical performance.
基金Supported by the National Natural Science Foundation under Grant Nos 50572010 and 50872159, the National Defense Funds under Grant Nos 51420205BQ0154, 513180303 and A2220061080, and the Doctoral Fund of Ministry of Education of China under Grant No 2004007021.
文摘A method using strong fluctuation theory （SFT） to compute the effective electromagnetic parameters of multiphase composite media, and common materials used to design radar-absorbing materials, is demonstrated. The effective electromagnetic parameters of ultrafine carbonyl-iron （DT-50） and fiber fabric, which are both multiphase composite media and represent coated and structured radar absorbing materials, respectively, are investigated, and the corresponding equations of electromagnetic parameters by using the SFT are attained. Moreover, we design a program to simplify the solutions, and the results are discussed.
文摘Dielectric properties of SiC/Ni nanocomposites prepared by a simple and facile electroless plating approach at X band are investigated. Compared to the original SiC nanopartieles （SiCp）, the real part of the permittivity, ε＇, and the dielectric loss tangent tang δe of SiC/Ni nanocomposites are clearly enhanced by about 31% and 33%, respectively. The effective equations for complex permittivity of SiC/Ni nanoeomposites are proposed. We also calculate ε＇ and tan δe of SiC/Ni nanoeomposites and the calculated results are well consistent with the measured data.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50872159 and 50972014, the National Defense Funds of China under Grant No A2220061080, and the Shanghai Education Committee under Grant No 06 0Z 018. To whom correspondence should be addressed.
文摘We present general equations for metal-substrate single-layer microwave absorbing materials. The optimum electromagnetic parameters and matching thicknesses for electric-loss, magnetic-loss, and electromagnetic-loss materials are given, and possible solutions for the equations and the corresponding theoretic curves are discussed as well. The results may be helpful for designing high-performance microwave absorbing materials.
基金Supported by the National Defense Funds under Grant Nos A2220061080, 51420205BQ0154 and 513180303, the National Natural Science Foundation under Grant Nos 50572010 and 50872159, and the Doctoral Fund of Ministry of Education of China under Grant No 2004007021.
文摘Considering the eddy current effect of the magnetic metal particles in a high frequency electromagnetic field, we extend the Maxwell-Garnett law by introducing the eddy-effect parameter A which is as functions of the radius, permeability and electric conductivity of the metal particle medium. It is obvious that the computational result agrees with the experiment, which indicates that the extended Maxwell-Garnett law can be used to predict the effective electromagnetic parameters of a dilute metal-insulator composite medium in a high-frequency electromagnetic field.
文摘The high-temperature dielectric properties of SiO2/Si3N4 nanocomposites are investigated theoretically and experimentally. Its permittivities and loss tangents at the temperature ranging from room temperature to 1300℃ at 9.0 GHz are measured by the resonant cavity method. The SiO2/Si3N4 nanocomposites show complex dielectric behaviour at elevated temperature, and a multi-scale model is proposed to describe the dependence of the dielectric properties in the SiO2/Si3N4 on its compositional variations. Such a theory is needed so that the available property measurements could be extrapolated to other operating frequencies and temperatures.
文摘The geometrical and electronic structures of nitrogen-doped β-SiC are investigated by employing the first principles of plane wave ultra-soft pseudo-potential technology based on density functional theory. The structures of SiC1-xNx （x = 0, 1/32, 1/16, 1/8, 1/4） with different doping concentrations are optimized. The results reveal that the band gap of β-SiC transforms from an indirect band gap to a direct band gap with band gap shrinkage after carbon atoms are replaced by nitrogen atoms. The Fermi level shifts from valence band top to conduction band by doping nitrogen in pure β-SiC, and the doped β-SiC becomes metallic. The degree of Fermi levels entering into the conduction band increases with the increment of doping concentration; however, the band gap becomes narrower. This is attributed to defects with negative electricity occurring in surrounding silicon atoms. With the increase of doping concentration, more residual electrons, more easily captured by the 3p orbit in the silicon atom, will be provided by nitrogen atoms to form more defects with negative electricity.
基金Project supported by the National Natural Science Foundation of China (Grant No. 50872159)the National Defense Pre-research Foundation of China (Grant Nos. 513180303 and A2220061080)
文摘This paper reports that single-phase γ-Y2Si2O7 is prepared via a sufficient blending and cold-pressed sintering technique from Y2O3 powder and SiO2 nanopowder. It studies the dielectric properties of γ-Y2Si2O7 as a function of the temperature and frequency. The γ-Y2Si2O7 exhibits low dielectric loss and non-Debye relaxation behaviour from 25 to 1400℃ in the range of 7.3 18 GHz. The mechanism for polarization relaxation of the as-prepared γ-Y2Si2O7 differing from that of SiO2 is explained. Such particular dielectric properties could potentially make specific attraction for extensive practical applications.
