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采用基于密度泛函的第一性原理平面波赝势方法计算Mg-Y-Zn合金三元金属间化合物X-Mg12YZn 相和W-Mg3Y2Zn3相的晶格常数、形成焓和电子结构. 形成焓的计算结果表明, X-Mg12YZn相和W-Mg3Y2Zn3相都具有负的形成焓, 并且W-Mg3Y2Zn3相的形成焓更低; 电子结构的计算分析表明, W-Mg3Y2Zn3相成键峰主要来自Mg的2p轨道、Zn的3p轨道和Y的4d轨道的贡献. 而X-Mg12YZn相成键峰主要来自Mg的3s和2p轨道、Zn的3p轨道和Y的4d轨道的贡献. 对W-Mg3Y2Zn3相(011)面和X-Mg12YZn相(0001)面的电荷密度分析表明, 两相中Zn-Y原子间都形成了共价键, 且W-Mg3Y2Zn3相的共价性比X-Mg12YZn相的共价性更强. 在费米能级低能级处, W-Mg3Y2Zn3相具有更多的成键电子数, 决定了W-Mg3Y2Zn3相比X-Mg12YZn相有更好的相稳定性. 相似文献
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采用基于密度泛函理论的平面波超软赝势法研究了Magnéli相亚氧化钛Ti8O15的电子结构和光学性能. 计算出的能带结构显示Ti8O15相比锐钛型TiO2禁带宽度大幅度降低. 态密度分析表明, 其原因在于Ti8O15的O原子的2p轨道以及Ti原子的3p, 3d轨道相对于TiO2的相应轨道向左产生了偏移, 同时由于O原子的缺失使得Ti原子的3d, 3p轨道多余电子在Fermi能级附近聚集形成新的电子能级. 态密度分析结果还显示, 相对于TiO2, Ti8O15 Fermi能级附近电子格局发生了如下变化: O原子的2p轨道电子贡献减少, Ti原子的3d轨道的电子对Fermi能级贡献增大. 光吸收计算图谱表明, TiO2仅在紫外光区有较高的光吸收能力, 而Ti8O15由于禁带宽度变窄引起光吸收范围红移到可见光区, 从而在紫外光区和可见光区都有较高的光吸收能力, 计算结果与实验得到的紫外-可见漫反射吸收光谱结果一致.
关键词:
第一性原理
8O15')" href="#">Magnéli相亚氧化钛Ti8O15
电子结构
光学性能 相似文献
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采用基于密度泛函理论的平面波超软赝势法研究了Magneli相亚氧化钛Ti8O15的电子结构和光学性能.计算出的能带结构显示Ti8O15相比锐钛型TiO2禁带宽度大幅度降低.态密度分析表明,其原因在于Ti8O15的O原子的2p轨道以及Ti原子的3p,3d轨道相对于TiO2的相应轨道向左产生了偏移,同时由于O原子的缺失使得Ti原子的3d,3p轨道多余电子在Fermi能级附近聚集形成新的电子能级.态密度分析结果还显示,相对于TiO2,Ti8O15Fermi能级附近电子格局发生了如下变化:O原子的2p轨道电子贡献减少,Ti原子的3d轨道的电子对Fermi能级贡献增大.光吸收计算图谱表明,TiO2仅在紫外光区有较高的光吸收能力,而Ti8O15由于禁带宽度变窄引起光吸收范围红移到可见光区,从而在紫外光区和可见光区都有较高的光吸收能力,计算结果与实验得到的紫外-可见漫反射吸收光谱结果一致. 相似文献
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用自洽LMTO方法计算了VPd3化合物(Cu3Au结构)的电子结构及XPS谱。计算所得状态密度与Williams等人的结果是一致的。然而,与他们预言VPd3是具有1.4μB磁矩的铁磁体结果不同,由电子结构算得的Stoner参量为1.04,表明它很可能是一种巡游电子弱铁磁体。这与Burmester等人在低温下未测得VPd3有任何铁磁序的结果的分歧尚待讨论。
关键词: 相似文献
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The spin polarization of field-emitted electrons from the (110)-surface of ferromagnetic Ni was observed to be P = (+ 5 ± 2)% (majority spin electrons predominant). This result can be understood qualitatively in the framework of the Stoner-Wohlfarth-Slater model, using hybridized s-d bands. Adsorption of hydrogen (saturation coverage) was found to reduce the spin polarization of electrons emitted along [110] to P (H2) = (+ 1 ± 2)%, suggesting a demagnetization of the (110)-surface of Ni by hydrogen chemisorption. 相似文献
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利用正电子湮没技术(PAT)测量了不同化学计量比二元Ni33Al合金及不同Zr含 量Ni33Al合金的正电子寿命谱,并估算了合金基体和晶界缺陷处的自由电子密度.结果表明,二元Ni7777Al2323合金的基体和缺陷态的自由电子密度都比二元 Ni7474Al2626合金的高. Ni33Al合金晶界缺陷处开空间大于Ni空位或Al空位的开空间,晶界缺 陷处的自
关键词:
3Al合金')" href="#">Ni33Al合金
微观机制
自由电子密度
韧化 相似文献
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本文研究了150 ℃, 1.0× 104 A/cm2条件下电迁移对Ni/Sn3.0Ag0.5Cu/Au/Pd/Ni-P倒装焊点界面反应的影响. 回流后在solder/Ni和solder/Ni-P的界面上均形成(Cu,Ni)6Sn5类型金属间化合物. 时效过程中两端界面化合物都随时间延长而增厚, 且化合物类型都由(Cu,Ni)6Sn5转变为(Ni,Cu)3Sn4. 电迁移过程中电子的流动方向对Ni-P层的消耗起着决定性作用. 当电子从基板端流向芯片端时, 电迁移促进了Ni-P层的消耗, 600 h后阴极端Ni-P层全部转变为Ni2SnP层. 阴极界面处由于Ni2SnP层的存在, 使界面Cu-Sn-Ni三元金属间化合物发生电迁移脱落溶解, 而且由于Ni2SnP层与Cu焊盘的结合力较差, 在Ni2SnP/Cu界面处会形成裂纹. 当电子从芯片端流向基板端时, 阳极端Ni-P层并没有发生明显的消耗. 电流拥挤效应导致了阴极芯片端Ni层和Cu焊盘均发生了局部快速溶解, 溶解到钎料中的Cu和Ni原子沿电子运动的方向往阳极运动并在钎料中形成了大量的化合物颗粒. 电迁移过程中(Au,Pd,Ni)Sn4的聚集具有方向性, 即(Au,Pd,Ni)Sn4因电流作用而在阳极界面处聚集. 相似文献
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Zhaohui Zhou 《Journal of Physics and Chemistry of Solids》2010,71(12):1707-1712
The band structures and optical absorption spectra of O vacancy and Ni ion doped anatase TiO2 were successfully calculated and simulated by a plane wave pseudopotential method based on density functional theory (DFT). From the calculated results, a phenomenon of “impurity compensation” was found: the lower formation energy for O vacancy than Ni impurity indicated that introducing the intrinsic defect of O vacancy into Ni ion doped TiO2 sample was very possible; the positive binding energy for the combination of O vacancy and Ni impurity indicated that two defects were apt to bind to each other; While Ni impurity produced the donor levels in the forbidden band of TiO2, Ni impurity with O vacancy produced the acceptor levels upon which the excitation led to the photogenerated electrons with high energy and transferability. The combination of absorption spectra for O vacancy and Ni impurity with O vacancy models could reproduce the experimental measurement very well. 相似文献
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采用密度泛函理论和slab模型,研究NH3在Ni单原子层覆盖的Pt(111)和WC(001)表面上的物理与化学行为,计算了Ni单原子覆盖表面的电子结构以及NH3的吸附与分解.表面覆盖的单原子层中,Ni原子的性质与Ni(111)面上的Ni原子明显不同.与Ni(111)相比,Ni/Pt(111)和Ni/WC(001)表面上Ni原子dz2轨道上的电子更多地转移到了其它位置,该轨道上电荷密度降低有利于NH3吸附.在Ni/Pt(111)和Ni/WC(001)面上NH3吸附能均大于Ni(111),NH3分子第一个N-H键断裂的活化能则明显比Ni(111)面上低,有利于NH3的分解,吸附能增大使NH3在Ni/Pt(111)和Ni/WC(001)面上更倾向于分解,而不是脱附.N2分子的生成是NH3分解的速控步骤,该反应能垒较高,说明N2分子只有在较高温度下才能生成.WC与Pt性质相似,但Ni/Pt(111)和Ni/WC(001)的电子结构还是有差异的,与Ni(111)表面相比,NH3在Ni/Pt(111)表面上分解速控步骤的能垒降低,而在Ni/WC(001)上却升高.要获得活性好且便宜的催化剂,需要对Ni/WC(001)表面做进一步改进,降低N2分子生成步骤的活化能. 相似文献
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Electron energy loss spectra of clean and oxygen-covered Ni(100) surfaces were observed with concomitant measurements of LEED, work function change, and Auger peak height ratio O(KL2, 3L2, 3)/Ni(L2, 3VV). The observed electronic transitions are interpreted on the basis of primary election energy dependence, and of comparison with the loss spectrum for a UHV-cleaved NiO(100) surface and optical data of Ni. The observed loss peaks at 9.1, 14, and 19 eV in the clean surface spectrum are ascribed to the bulk plasmon of the 4s electrons, the surface plasmon, and the bulk plasmon of the coupled 3d + 4s electrons, respectively, and the weak but sharp peak at 33 eV is tentatively attributed to the localized many-body effect in the final state. Three oxygen-derived peaks at 6.0, 8.0, and 10.3 eV in the low oxygen exposure region (?4 L) are ascribed to the O 2p(e) → Ni 3d, O 2p(a1) → Ni 3d, and O 2p → Ni 4s transitions, respectively. In the high oxygen exposure region (?50 L), the spectra become quite similar to that of the UHV-cleaved NiO(100) surface. The oxidation process consistent with LEED, Auger peak height ratio and work function change measurements is discussed. 相似文献
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Relative cross sections, differential in energy and angle, for electrons ejected from CH4 and C3H8 molecules under 16.0 keV electron impact have been measured. Electrons were analyzed by a 45° parallel plate electrostatic
analyzer at emission angles varying from 60° to 135° with energies from 50 eV to 1000 eV. The angular distributions of electrons
exhibit structures which are found to arise from Coulomb and non-Coulomb interactions. Furthermore, the double differential
cross sections of electrons ejected from C3H8 molecule are found to be higher in magnitude than those from CH4. This result supports the fact that the number of ejected electrons participating in collisions with C3H8 molecules is more than that in CH4. Also, the angular distributions of C-K-shell Auger electrons emitted from the target molecules have been studied and shown
to be isotropic within the experimental uncertainty 相似文献
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Scattering of H
3
+
ions from a clean Ni(111) surface is observed at energies below 1 keV and grazing incidence in a time-of-flight system. The interaction with the surface leads to neutral particles mainly which are identified from the energy distributions as H and H2. The neutralisation/dissociation mechanism is probably a resonant charge transfer of Ni electrons into the non-binding ground state of H3. 相似文献
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J. G. Du X. Y. Sun G. Jiang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,55(1):111-120
The equilibrium structures, electronic properties of bimetallic Ti1-4M
(M=V, Fe, Ni) clusters are investigated by using the density functional
method within generalized gradient approximation in conjunction with the
valence basis set. Considering the spin multiplicity effect, the geometries
with different spins are optimized to find the ground states. For the ground
states, the natural bonding orbital analysis (NBO) is performed and shows
that the 4s electrons always transfer to the 3d orbital in the bonding atoms
so that 4s and 3d orbitals hybridize with each other. The electron transfers
from Ti atoms to the ‘impurity’ atoms (V, Fe, and Ni) are also found. The
two kinds of electron transfer mechanisms are considered to be the
contributor for the stabilities of the studied clusters. The Wiberg bond order and
AIM (atoms in molecules) analyses indicate that the relative stabilities of
chemical bonds are: $\text{Ti-V/Ti-Fe} > \text{Ti-Ti} > \text{Ti-Ni}$\text{Ti-V/Ti-Fe} > \text{Ti-Ti} > \text{Ti-Ni}. The spin magnetic
moments are found to be mostly located at Ti atoms. Several clusters like
Ti2V, Ti3V, Ti3Ni and Ti4Ni present the high moments. 相似文献
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采用基于密度泛函理论的第一性原理方法对未掺杂以及不同浓度过渡金属Fe,Co,Ni,Zn掺杂金红石TiO2的超晶胞体系进行了几何优化,并讨论了其晶格常数,电子能带结构和光学性质.研究结果表明:掺杂前后的晶格参数与实验值偏差在3.6%以下;适量的过渡金属掺杂不但影响体系能带结构,拓宽光吸收范围,而且扮演着俘获电子的重要角色,有利于光生电子-空穴对的有效分离以及增强光吸收能力;Fe,Co,Ni,Zn最佳理论掺杂体系分别为Ti0.75Fe0.25O2,Ti0.75Co0.25O2,Ti0.75Ni0.25O2,Ti0.83Zn0.17O2;Fe,Co,Ni3d态分裂为t2g和eg态,分别贡献于价带高能级和导带低能级部分,促进了电子-空穴对的生成,从而可提高TiO2的光催化性能;Zn3d态电子成对填满轨道,不易被激发,故光催化活性无明显提高. 相似文献