稀土金属间化合物CeSn3和CeIn3的能带理论

本文报道了CeSn₃和CeIn₃的能带计算结果。对其f电子的行为,以及f电子与非f原子的s,p,d电子之间的杂化进行了讨论。分析了费密能级附近的态密度分布及能带结构。 关键词：     

稀土金属间化合物CeSn_3和CeIn_3的能带理论

本文报道了CeSn, 和Celn_3 的能带计算结果. 对其f 电子的行为, 以及f 电子与非f 原子的s, p , d 电子之间的杂化进行了讨论. 分析了费密能级附近的态密度分布及能带结构. 关键词：     

FeSiB非晶合金的XPS研究

用X射线光电子能谱仪对淬态和退火态的非晶Fe_(80.3)Si_(3.9)B_(15.8)合金进行了电子结构的研究。测定了合金的价带谱和芯能级谱,并与α-Fe的价带谱作了比较。实验结果表明,合金在二种状态下其d带的最大值位置和谱形是相似的,但在结合能为1.0—4.5eV范围内价态密度有轻微的差别。二种状态的芯能级间没有明显位移,这表明与相应的晶态物相比,非晶合金中并不发生从类金属原子向过渡金属原子的电子迁移。经过退火的试样,在电子分布曲线的低部出现的细结构是与B的S、P轨道与Fe的d轨道间的杂化和Fe—B键合态的形成相关的。在退火试样的表面发现B有相当大的富集。     

电致发光加速层二氧化硅的电子高场迁移率

根据非晶态半导体的能带理论，讨论了分层优化薄膜电致发光方案中非晶二氧化硅加速层中的电子在高电场中的输运行为.研究结果表明：在高电场下，由于电场的存在降低了陷阱之间的平均势垒高度.在费密能级附近处的杂质及缺陷定域态和导带尾定域态中，电子的输运主要表现为电场增强的热辅助式跳跃传导；而在导带扩展态中，电子的输运仍像晶态半导体那样表现为共有化运动.此外，以实验数据为基础，计算出了非晶二氧化硅中电子的迁移率、最小金属电导率、导带迁移率边界状态密度及费密能级处的状态密度. 关键词：     

非晶碳结构建模和电子结构的第一性原理研究

基于密度泛函理论,采用了一种更为精确的交换相关泛函OLYP(OPTX+LYP),对密度范围从2.0到3.2 g/cm³的非晶碳进行结构建模. 模拟得到的5个碳网络结构无论从径向分布函数还是sp³含量都与实验符合得很好. 对非晶碳电子结构的研究表明费米能级附近的电子态密度主要是sp²碳原子的贡献. 随着密度的增加,sp³碳原子增加,费米能级附近的态密度越来越小. 小环结构增加了费米能级附近的电子态密度,缺陷态在费米能级形 关键词： 非晶碳 密度泛函理论 电子结构     

LixFePO4(x=0.0, 0.75, 1.0)电子结构与弹性性质的第一性原理研究

采用基于密度泛函理论的第一性原理研究方法,计算了不同嵌锂态Li_xFePO₄(x=0,0.75,1.0)的电子结构. 对于橄榄石型Li_xFePO₄正极材料,虽然Fe3d电子在费米能级附近相互交错,但由于受晶体场作用的限制,并不能真正成为自由电子,Fe3d电子对体系的导电性没有很大贡献,而Fe—O键在低能成键区形成p-d杂化的局域态共价键对稳定合金骨架具有重要作用. 随着锂离子的脱 关键词： 锂离子电池 4')" href="#">LiFePO₄ 电子结构 弹性性质     

XPO4(X=Lu, Y)电子结构的第一性原理研究

基于密度泛函理论(DFT)第一性原理对LuPO₄和YPO₄两种磷酸盐晶体的电子结构进行计算模拟.结果表明:LuPO₄的带隙为5.639 eV,YPO₄的带隙为4.884 eV.通过对态密度的分析得知LuPO₄的导带主要贡献来自Lu的5d态电子,费米能级附近价带主要由Lu的4f态和O的2p态电子贡献. YPO₄的导带主要贡献来自Y的4d态电子,价带顶的主要贡献来自于O的2p态电子.通过电荷密度和布局分析得知了材料内部原子间的电荷转移情况,进而对原子间成键情况进行了分析与讨论.     

非晶碳结构建模和电子结构的第一性原理研究

基于密度泛函理论，采用了一种更为精确的交换相关泛函OLYP(OPTX+LYP)，对密度范围从2.0到3.2 g/cm³的非晶碳进行结构建模. 模拟得到的5个碳网络结构无论从径向分布函数还是sp³含量都与实验符合得很好. 对非晶碳电子结构的研究表明费米能级附近的电子态密度主要是sp²碳原子的贡献. 随着密度的增加，sp³碳原子增加，费米能级附近的态密度越来越小. 小环结构增加了费米能级附近的电子态密度，缺陷态在费米能级形     

La65X35(X=Ni,Al)非晶合金原子结构的第一性原理研究

运用基于密度泛函理论的第一性原理分子动力学和静态电子结构计算,研究了La₆₅X₃₅（X=Ni,Al）非晶合金体系原子结构随温度演化的规律及其相关电子结构特性.使用径向分布函数、Voronoi团簇以及键对分析等给出了从高温液体快速冷却到玻璃态过程中原子结构的演化规律.研究发现,该类合金体系的原子排布符合局域密堆模型,两体系中占比最大的特征多面体类型由溶质与溶剂原子半径比调控;两体系中高五次对称性局域结构随温度的下降而增加验证了其在抑制晶化方面的重要作用;利用投影态密度分析两体系电子结构之间的差异,指出La-5d与Ni-3d电子间强烈的杂化是La–Ni 间键长缩短的电子结构起源,为理解成分相关的结构和物性提供了重要线索.     

Half-Heusler合金NiFeSb和NiMnSb的磁性及电子结构的第一性原理研究

用基于密度泛函理论的第一性原理方法,计算了half-Heusler合金NiFeSb和NiMnSb的晶体结构、磁性及电子结构。计算结果表明,磁性原子Fe和Mn在两种合金的总磁矩中贡献最大,在NiFeSb总磁矩中,Ni原子贡献比例接近在NiMnSb中的2倍,而Sb原子的贡献比例是在NiMnSb中的1/5;两种合金的自旋向上能带都具有明显的金属特征,而自旋向下能带有明显的差别;两种合金费米能级以下的总态密度(DOS)主要由Ni-3d 和Fe-3d（Mn-3d）态决定,费米能级以上主要由Fe-3d（Mn-3d）自旋向下部分决定。     

Electronic structure of amorphous Zr based alloys with V,Cr and Mn studied by photoelectron spectroscopy and bandstructure calculations

The electronic structure of the amorphous alloys V₃₆Zr₆₄, Cr₃₀Zr₇₀ and Mn₃₀Zr₇₀ has been studied by photoelectron spectroscopy (UPS, XPS) and bandstructure calculations for the ordered analogs. The valence band photoelectron spectra and the calculated density of states reveal a large contribution to the state density at the Fermi level from the 3d metal. This behavior is characteristic of Zr based alloys with early 3d transition metals and differs from alloys with higher 3d electron numbers in which the 3d band is located at higher energies. The implications of the high density of states at E_F of the amorphous Zr-(V, Cr, Mn) alloys for magnetism and the occurrence of superconductivity is discussed.     

掺杂MgCNi3超导电性和磁性的第一性原理研究

从第一性原理出发，计算了MgCNi₃的电子能带结构.MgCNi₃中C 2p与Ni 3d轨道杂化使穿梭费米面上的Ni 3d能带表现出平面性，费米面落在态密度范霍夫奇异(vHs)峰的右坡上.vHs峰上大的电子态密度和铁磁相变点附近的自旋涨落是决定MgCNi₃超导电性的重要因素.研究了三种替代式掺杂对其超导电性和磁性的影响，发现电子掺杂使费米能级下滑到态密度较低的位置，导致体系转变为无超导电性的顺磁相；同构等价电子数的金属间化合物的轨道杂化，引起费米面上态密度的减少，降低了超导电性；而空穴掺杂使费米面向vHs峰值方向移动，虽然费米面上电子态密度增大可能提高超导电性，但增强了的Ni原子磁交换作用产生铁磁序，破坏了超导电性. 关键词： 电子结构 超导电性 磁性 掺杂     

Electronic structures of the LaBO3 (B = Co, Fe, Al) perovskite oxides related to their catalysis

The discrete-variational (DV) X α molecular orbital method has been applied to investigate the bulk and surface electronic structures of perovskite oxides such as LaCoO₃, LaFeO₃ and LaAlO₃. The calculated XPS spectra for these oxides are in good agreement with the experimental ones and only the LaCoO₂ exhibited a rather high electron density of states near the Fermi level (E_F). The catalytic behavior of these oxides is discussed on the basis of their electronic structures; the marked catalysis by LaCoO₃ is associated with electron occupation of crystal field d states near E_F and with the buildup of surface charge so as to enhance the electron transfer between a surface cation and an interacting molecule.     

Photoemission (XPS,UPS) studies of Pd-Si metallic glasses

The valence bands of glassy $\text{Pd}{}_{\mathrm{100?x}}\text{Si}{}_{\mathrm{x}}\text{(15?x?21)}$ and pure Pd were studied by XPS and UPS. The valence band spectra of the alloys show a strongly reduced density of states at the Fermi energy E_F compared to Pd. From the measured relative photoelectric cross sections for the different excitation energies we conclude that the electron states near E_F of the glassy alloys have mainly d-character. This is in good agreement with recent measurements of the low-temperature specific heat, the magnetic susceptibility and the optical reflectivity.     

Superconducting and normal state properties of dilute alloys of LaSn3 containing Ce impurities

The dependence of the superconducting transition temperature T_c on Ce impurity concentration and the specific heat jump at T_c as a function of T_c are reported for the system ($\text{La}$Ce)Sn₃. The experimental results are analyzed using a theory due to Kaiser concerning the effect on superconductivity of nonmagnetic localized resonant impurity states This analysis yields values for the intraatomic Coulomb repulsion parameter U_eff and the Ce local density of states at the Fermi level N_? (E_F). The results of low temperature normal state heat capacity and magnetic susceptibility measurements which give independent estimates of N_? (E_F) are also reported. A large pressure dependence of the T_c of ($\text{La}$Ce)Sn₃ alloys was observed for pressures up to 20 kbar. This behavior is similar to that previously observed in several other superconducting matrix-Ce impurity systems in which the Ce solute 4f electron shell undergoes a continuous-pressure induced demagnetization.     

First-principles study of ferromagnetism in N doped TiO2 and TiO

N doped TiO is nonmagnetic, in which spin-split impurity states are not induced near the Fermi energy (E_F) by N dopant. N doped TiO₂ along with transition-metal (TM) doped TiO is magnetic, in which spin-split impurity states are induced across E_F. The magnetic moment is determined by the 3d4s electron configurations and the valence states of TM-dopant ions when they substitute Ti. Hence, the origin of ferromagnetism of N doped TiO₂ and TiO is not closely related to the width of the band gaps of host oxides, but would be crucially related to that if the dopant can induce spin-split impurity states near E_F.     

Electronic structure of uranium monochalcogenides and uranium monopnictides

Single crystals of the uranium chalcogenides US, USe, UTe and the pnictides UAs and USb have been cleaved under high and ultrahigh vacuum conditions and the near normal incidence reflectivity has been measured in situ from 0.03 to 12 eV. In the case of US the spectral range of the measurement was further extended down to 0.0017 eV. The various optical functions (?₁, ?₂, σ, E_loss, n_eff) have been deduced by a Kramers-Kronig analysis. Typical features of all spectra are weak intraband contributions and the extension of strong interband transitions to very low photon energies. Highly damped plasmons are found at 4.25 eV for US, 3.5 eV for USe nad 2.2 eV for UTe. For the pnictides UAs and USb the corresponding values are 2 eV and 1.6 eV, respectively.The apparent contradiction between the presence of a large number of conduction electrons and only very weak intraband contributions is resolved within the spectral exclusion model of Keller. In this self-consistent cellular multiple scattering calculation the coupling of the narrow 5f states and the much wider 6d states produces a dip in the density of d states near E_F where the f electrons form a resonance state. Quantitative agreement is obtained between theory and experiment for US. For all investigated compounds empirical energy level schemes are derived.The reflectivity measurements down to 1.7 meV for US reveal the existence of a further excitation at 39 meV which is assigned to a transverse optical phonon mode. This unique observation of an optical phonon in a direct reflectivity measurement of a metal supports the picture of a small density of conduction electrons at E_F. Further arguments in favor of the spectral exclusion model are presented and the question of the localization of thr 5f electrons in various uranium compounds is discussed.     

Hybridization and bonding in transition metal compound superconductors: X-ray photoemission from crystalline and amorphous Nb3Ge.

An XPS (or ESCA) study of the high T_c crystalline and the low T_c amorphous phases of Nb₃Ge indicates a change of the Nb-Ge bonding from covalent to metallic upon the amorphous to crystalline transition. The high T_c superconductivity of Nb₃Ge does not appear to stem only from an unusually high electronic density of states at the Fermi level but rather from another property such as a resonant enhancement of the electron-phonon coupling resulting from cation-anion hybridization at E_F.     

Optical conductivity of CePd3, YPd3 and PrPd3

The optical conductivity of intermediate valence CePd₃ at 300 K exhibits a maximum near 16 meV, which is absent in the reference materials YPd₃ and PrPd₃. Using a modified Drude model with a memory function ansatz this anomaly has been identified as a resonant electron-electron scattering process of conduction electrons at the localized 4f states near the Fermi level E_F. The model fit gives estimates of the width of the 4f states, of their separation from E_F and of the f-d hybridization energy. Intra-4f transitions of CePd₃ are stronger compared to those of PrPd₃ due to the stronger f-d hybirdization. 4d→4f transition energies of CePd₃ are reduced due to an electron-hole Coulomb binding energy.     

Magnetic susceptibility of titanium diselenide intercalated with copper

The temperature dependence of the magnetic susceptibility of Cu _x TiSe₂ polycrystalline samples has been measured. The electron density of states near the Fermi level N(E _F) in the Pauli model of paramagnetism has been calculated and discussed. The concentration dependences of the density of states N(E _F) and the unit cell parameter in the direction perpendicular to the layers in Cu _x TiSe₂ correlate with the concentration of centers V-Ti-Cu and Cu-Ti-V (V is the vacancy).