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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. 相似文献
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Microwave Absorbing Materials: Solutions for Real Functions under Ideal Conditions of Microwave Absorption
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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. 相似文献
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Electromagnetic Parameters Model and Microwave Absorption for Composite Coatings Containing Magnetic Particles
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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. 相似文献
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Modeling and Computing Example for Effective Electromagnetic Parameters of Multiphase Composite Media
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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. 相似文献
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热解石墨含有高定向石墨烯层,表现出各向异性电输运和热输运行为,因而在电子器件、电催化和储能领域具有广泛应用。针对铝配离子AlCl— 4嵌入/脱出热解石墨对其输运性质的影响机制问题,本文开展了脱嵌过程中不同阶结构热解石墨的电子结构、晶体结构以及输运行为演化的研究。建立了微观阶结构与宏观电化学性质及充放电平台之间的关系,揭示了铝配离子嵌入后在石墨价带中引入空穴,增加载流子浓度从而提升电子电导率的新机制;明确了AlCl— 4铝配离子直径可以加权平均系数的方式改变电导率,建立了电导率随充放电状态变化的定量模型;随着铝配离子嵌入,电子电导率可提升至原始高定向石墨的3.8倍(40858 S·cm?1),比原始石墨表现出更好的电磁屏蔽性能。 相似文献
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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 SiO 2 is explained. Such particular dielectric properties could potentially make specific attraction for extensive practical applications. 相似文献
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Shape-Controlled Synthesis and Related Growth Mechanism of Pb(OH)2 Nanorods by Solution-Phase Reaction
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We present a simple method to synthesize Pb(OH)2 nanorods by solution-phase reaction. Rod-like lead hydroxide precipitates are obtained by mixing lead nitrate with a concentration of about 0.01 M and potassium hydroxide with concentration of about O.03 M in an aqueous solution. Sodium chloride as an additive is premixed with the lead nitrate aqueous solution. The presence of chloride ions in the precursor solution results in the rod-like morphology of lead hydroxide precipitates. The growth mechanism of the lead hydroxide nanorods is discussed. 相似文献
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