X.Sun
,
Z.J.Ding
,
H.M.Li
,
K.Salma
,
Z.M.Zhang
,
W.S.Tan
金属学报(英文版)
A Monte Carlo model considering the electron spin direction and spin asymmetry has been developed. The energy distribution of the secondary electron polarization and the primary energy dependence of the polarization from Fe are studied. The simulation results show that: (1) the intensity of the spin-up secondary electrons is larger thanvthat of thevspin-down secondary electrons, suggesting the secondary electrons are spin polarized; (2) the spin polarization of secondary electrons with nearly zero kinetic energy is higher than the average valance spin polarization, Pb=27 0.000000or Fe. With increasing kinetic energy, the spin polarization of the secondary electrons decreases to the value of Pu remaining constant at higher kinetic energies; (3) the spin polarization increases with an increase in the primary energy and reaches a saturation value at higher primary energy in both the Monte Carlo simulation and experimental results.
关键词:
spin polarization
,
null
,
null
K.Salma
,
Z.J.Ding
,
H.M.Li
,
Z.M.Zhang
金属学报(英文版)
The investigation of influence of surface effects on the energy spectra of electrons is essential for comprehensive understanding of electron-solid interactions as well as quantitative analysis. The accuracy of the analysis depends on the models for elastic and inelastic interactions. Electrons impinging on a solid or escaping from it suffer losses in the surface layer. The energy loss spectra therefore have contributions from surface excitations. The role of surface excitations is characterized by surface excitation parameter (SEP), which indicates the number of surface plasmons created by an electron crossing the surface. The imaginary part of complex self-energy of an electron is related to the energy.' loss cross section. SEP is numerically computed using self-energy formalism and compared with the results as described and calculated by different workers.
关键词:
surface plasmons
,
null
,
null
Journal of Materials Research
The effect of Li(3)N additive on the Li-Mg-N-H system was examined with respect to the reversible dehydrogenation performance. Screening Study with varying Li(3)N additions (5, 10, 20, and 30 mol%) demonstrates that all are effective for improving the hydrogen desorption capacity. Optimally, incorporation of 10 mol% Li(3)N improves the practical capacity from 3.9 wt% to approximately 4.7 wt% hydrogen at 200 degrees C, which drives the dehydrogenation reaction toward completion. Moreover, the capacity enhancement persists well over 10 de-/rehydrogenation cycles. Systematic x-ray diffraction examinations indicate that Li(3)N additive transforms into LiNH(2) and LiH phases and remains during hydrogen cycling. Combined structure/property investigations suggest that the LiNH(2) "seeding" should be responsible for the capacity enhancement, which reduces the kinetic barrier associated with the nucleation of intermediate LiNH(2). In addition, the concurrent incorporation of LiH is effective for mitigating the ammonia release.
关键词:
complex hydrides;improvement;mixtures;imides;amide;h-2
胡标
,
尹明
,
王庆平
,
闵凡飞
,
杜勇
兵器材料科学与工程
基于文献报道的实验数据,采用相图计算(CALPHAD:CALculation of PHAse Diagrams)方法对V-M(M=Li,Na,K,Sc,Ag)5个二元系进行相图热力学研究.通过热力学优化计算获得了一套描述液相、(V)、(Li)、(Na)、(K)、(αSc)、(βSc)和(Ag)相的热力学参数.V-Li、V-Na和V-K体系中的气相视为由组元V、Li、Li2、Na、Na2、K和K2混合的理想气体.与实验相图数据对比表明,获得的热力学参数能够准确地描述实验相平衡数据.
关键词:
V-M(M=Li,Na,K,Sc,Ag)
,
CALPHAD方法
,
相图
,
热力学模型
曹笃盟
,
李志友
,
周科朝
稀有金属材料与工程
采用固相反应法制备了Li1+xV3-yMyO8(M=Mo,P;0≤y≤0.4),研究了不同Mo和P含量对Li1+xV3O8相的影响,并首次对其进行了高温阴极放电性能的研究.结果表明:Mo和P掺杂量分别为y≤0.2和y＜0.2时可获得纯Li1+xV3O8相;Mo掺杂使Li1+xV3O8峰值电压提高0.3 V,比容量提高25%,嵌入的Li+量最高可达x=3.8;P掺杂(y≤0.20)对Li1+xV3O8的峰值电压和比容量影响较小.化学嵌锂实验也证实掺杂后的材料具有更快的Li+嵌入速度.
关键词:
Li1+xV3O8
,
热电池
,
掺杂
,
比容量
Journal of Physical Chemistry C
The Li-Mg-N-H system was prepared by reacting magnesium amide [Mg(NH(2))(2)] with lithium nitride (Li(3)N) and investigated with regard to the hydrogen storage properties. Our study shows that the present method is superior to the conventional route in enhancing the reversible dehydrogenation properties. Through optimizing the Li(3)N:Mg(NH(2))(2) ratio in the starting materials, the reversible capacity of U-Mg-N-H system increases to 4.9 wt %, 18% higher than that typically obtained from the Mg(NH(2))(2) + 2LiH mixture at 200 degrees C. Furthermore, increasing the Li(3)N:Mg(NH(2))(2) ratio is effective for mitigating the ammonia release from thus-prepared samples. Combined property/structure investigations indicate that the obtained enhancements should be ascribed to the effects of LiNH(2) and LiH that were in situ generated from the excess Li(3)N. LiNH(2) may promote the dehydrogenation reaction via seeding the reaction intermediate. The concurrently generated LiH acts as an effective ammonia trapping agent. These findings highlight the potential of "intermediate seeding" as a strategy to enhance the reversible hydrogen storage properties of metal-N-H systems.
关键词:
complex hydrides;ultrafast reaction;amide;improvement;desorption;linh2;destabilization;mechanism;mixtures;imides
裴增文
,
刘晓鹏
,
黄倬
,
李志念
,
王树茂
,
蒋利军
稀有金属
doi:10.3969/j.issn.0258-7076.2010.04.013
采用等容法研究了机械球磨工艺制备的Li-Mg-N-H材料储氧性能,结果发现,在室温下采用氦气对样品室体积进行标定时,由于Li-Mg-N-H材料对氦气有一定量的物理吸附,造成准确Li-Mg-N-H材料样品体积标定误差,进而造成Li-Mg-N-H储氢材料在503 K下放氢容量随压力的降低而增加异常变化.为准确标定样品体积,通过对Li-Mg-N-H材料室温氮气吸附容量测定,并采用迭代计算方法获得准确的储氢材料样品体积,进而测定Li-Mg-N-H储氢材料503 K下放氢PCT曲线,其表现为放氢容量随压力降低而减小的正常变化规律.Li-Mg-N-H储氢材料503 K,9.6 MPa氢压下的最大储氢容量为4.81%(质量分数),放氢过程表现为单一放氢平台特性.
关键词:
轻质储氢材料
,
Li-Mg-N-H
,
储氢性能
,
等容测试方法
Acta Physica Sinica
A first-principles plane-wave pseudopotential method based on the density functional theory is used to investigate the dehydrogenation properties and the influence mechanism of Li(4)BN(3)H(10) hydrogen storage materials. The binding energy, the density of states and the Mulliken overlap population are calculated. The results show that the binding energy of crystal has no direct correlation with the dehydrogenation ability of (LiM)(4)BN(3)H(10)(M = Ni, Ti, Al, Mg). The width of band gap and the energy level of impurity are key factors to affect the dehydrogenation properties of (LiM)(4)BN(3)H(10) hydrogen storage materials: the wider the energy gap is, the more strongly the electron is bound to the bond, the more difficulty the bond breaks, and the higher wile the dehydrogenation temperature be. Alloying introduces the impurity energy level in band gap, which leads the Fermi level to enter into the conduction band and the bond to be weakened, thereby resulting in the improvement of the dehydrogenation properties of Li(4)BN(3)H(10). It is found from the charge population analysis that the bond strengths of N-H and B-H are weakened by alloying, which improves the dehydrogenation properties of Li(4)BN(3)H(10).
关键词:
hydrogen storage materials;first-principles calculation;element;substitution;dehydrogenation;linh2
Journal of Alloys and Compounds
Motivated by the ion migration mechanism proposed by David et al. [J. Am. Chem. Soc. 129 (2007) 1594-1601], we mechanically mill the Li3N/Co powder mixture to obtain defective Li3N-type structure with enhanced Li+ mobility. Compared with Li3N the hydrogen storage property of such defective phase is markedly improved, presumably due to the ion-migration-enhancing effect from the incorporation of Co and Fe (from milling utensils). During subsequent cycling, however, this effect cannot persist due to the precipitation of Co-Fe alloy upon hydrogenation. The close correlation between Co-Fe incorporation/precipitation and property variation of Li3N hydrogen storage material provides a preliminary evidence to support the ion migration mechanism. (C) 2007 Elsevier B.V. All rights reserved.
关键词:
Hydrogen absorbing materials;Nitride materials;hydrogen-storage;lithium amide;mechanism;nitride;batteries;mixtures;hydride;imides;linh2;anode
