Effect of copper and cobalt impurities on the electronic structure and optical spectra of the intermetallic compound PrNi5

The electronic structure and optical properties of the intermetallic compound PrNi₅ and their evolution during the substitution of copper or cobalt atoms for nickel atoms have been investigated. The band spectra of the studied compounds have been calculated in the local spin density approximation corrected to account for strong electron-electron interactions in the 4f shell of the rare-earth ion (LSDA + U method). The dispersion relations of the optical conductivity in the interband light absorption region have been interpreted using the results of calculations of the electron density of states.     

Magnetism and electronic structure of the intermetallic compound Ce5CuBi3

We have studied the electronic structure as well as magnetic, electronic transport and thermodynamic properties of the intermetallic compound Ce₅CuBi₃. It was found that Ce₅CuBi₃ undergoes three successive phase transitions at 25?K, 13.7?K and 3.5?K. We attribute the multiple magnetic phase transition to be associated with the two non-equivalent magnetic sublattices of the magnetic Ce ions. The investigated compound is characterized by an enhanced ratio C_p /T at 2?K, which may be interpreted as being due to the nearness of the 4f-level to the Fermi level and some contribution of magnon excitation. The core-level photoemission spectra indicate that Ce ions in Ce₅CuBi₃ are very close to trivalent which is consistent with the magnetic susceptibility data. The calculated band structures using the scalar-relativistic linear muffin-tin orbital method in the atomic sphere approximation and the all-electron full potential linear augmented plane wave plus local orbitals method have been performed for the non-magnetic ground state and as well as for collinear ferromagnetic and ferrimagnetic spin alignments. The largest stabilization energy is found in the case of a ferromagnetic structure. The calculated moments on the two sites of the Ce atoms are in agreement with the experimental value (0.93?μ _B /Ce). The calculations predict that the studied compound has a pseudogap in the DOS curve. Analysis of the partial DOS suggests some differences in hybridization strengths between the Ce-Bi and Ce-Cu orbitals.     

Role of Fe and Co in optical conductivity and electronic structure of TbNi4Fe and TbNi4Co

Optical properties of two intermetallic compounds TbNi₄Fe and TbNi₄Co have been studied employing ellipsometry in a spectral range 0.22–15 μm to reveal their characteristic features in comparison with the parent compound TbNi₅. The electronic structure of TbNi₄Fe and TbNi₄Co was calculated within the LSDA + U method (local spin density approximation with Hubbard U-correction). Based on the calculated electronic structure results, the theoretical optical conductivity was calculated and used to interpret experimental conductivity in the range of interband optical absorption.     

Influence of copper impurity and structure defects on the properties of compound CdSnAs2

A study was made of the mechanisms of formation and interaction of impurities and intrinsic defects in CdSnAs₂ crystals during diffusion doping of this compound with copper and during subsequent low-temperature (300°C) annealing. This was done by diffusing copper into samples with different initial defect structure under conditions of controlled arsenic vapor pressure and applying the method of quasichemical reactions to analyze the experimental data. It was found that the special features of the physical properties of n-type CdSnAs₂:Cu crystals — the low density and high mobility of electrons-were due to the high reactivity of copper resulting in binding of the original crystal defects to form neutral complexes. It was found that the anomalous annealing of CdSnAs₂: Cu samples, resulting in n-p conversion of the type of conduction, was associated with precipitation of a solid solution of an accidental donor impurity (most probably oxygen). The diffusion doping with copper was found to be one of the most effective methods for controlling the properties of CdSnAs₂, particularly in the preparation of high-resistivity crystals.Translated from Izvestiya Uchebnykh Zavedenii, Fizika, No. 5, pp, 102–108, May, 1980.     

Optical absorption and electronic structure of intermetallic compound RuIn3

The optical properties of intermetallide RuIn₃ are investigated by ellipsometry in the spectral range of 0.22–10 μm. The experimental data point to the existence of an energy gap of about 0.5 eV in the electronic spectrum of the compound. The density of the electron states and interband optical conductivity are calculated in terms of the density functional theory. The experimental and theoretical spectra of the optical conductivity are compared. It is found that the formation of basic absorption bands is caused by interband transitions of electrons of the d-band of Ru and p-band of In.     

Correlation between valence electronic structure and magnetic properties in RCo_5(R=rare earth) intermetallic compound

The magnetisms of RCo_5(R = rare earth) intermetallics are systematically studied with the empirical electron theory of solids and molecules(EET).The theoretical moments and Curie temperatures agree well with experimental ones.The calculated results show strong correlations between the valence electronic structure and the magnetic properties in RCo_5 intermetallic compounds.The moments of RCo_5 intermetallics originate mainly from the 3d electrons of Co atoms and 4f electrons of rare earth,and the s electrons also affect the magnetic moments by the hybridization of d and s electrons.It is found that moment of Co atom at 2c site is higher than that at 3g site due to the fact that the bonding effect between R and Co is associated with an electron transformation from 3d electrons into covalence electrons.In the heavy rare-earth-based RCo_5 intermetallics,the contribution to magnetic moment originates from the 3d and 4f electrons.The covalence electrons and lattice electrons also affect the Curie temperature,which is proportional to the average moment along the various bonds.     

Magnetic properties and structure of the nanocrystalline Gd-Ti-Ge intermetallic compound

This paper reports an experimental study of the magnetization processes and structure of the Gd-Ti-Ge compound in the initial coarse-grained state and a nanostructured state obtained under torsion at a high quasihydrostatic pressure. It is established that in a nanocrystalline sample, the magnetic ordering temperature is 30 K lower, the coercive force is eight times higher, and the magnetization is 3.7 times lower than their respective values in a coarse-grained sample. The observed changes in the magnetic properties are shown to be related primarily with the conversion of a part of the initial phase with the CeScSi-type lattice to a CeFeSi-type weakly magnetic phase. The effect of structural defects and of partial disorder on the magnetic characteristics of the compound are also discussed.     

Ab initio study of structural,electronic,thermo-elastic and optical properties of Pt_3Zr intermetallic compound

Structural,elastic,electronic and optical properties of the Pt3Zr intermetallic compound are investigated using first principles calculations based on the density functional theory(DFT)within the generalized gradient approximation(GGA)and the local density approximation(LDA).The Pt3Zr compound is predicted to be of cubic L12 and hexagonal D024 structures.The calculated equilibrium ground-state properties(lattice parameters a and c,bulk modulus B and its pressure derivative B',formation enthalpy ΔH)of the Pt3Zr compound,for both cubic and hexagonal phases,show good agreement with the experimental results and other theoretical data.Elastic constants(C11,C12,C13,C33,C44,and C55)are calculated.The predicted elastic properties such as Young's modulus E and shear modulus GH,Poisson ratioν,anisotropic ratio A,Kleinman parameter ξ,Cauchy pressure(C12-C44),ratios B/C44 and B/G,and Vickers hardness Hv indicate the stiffness,hardness and ductility of the compound.Thermal characteristic parameters such as Debye temperature θD and melting temperature Tm are computed.Electronic properties such as density of states(DOS)and electronic specific heat γ are also reported.The calculated results reveal that the Fermi level is on the psedogap for the D024 structure and on the antibonding side for the L12 structure.The optical property functions(real partε1(ω)and imaginary part ε2(ω)of dielectric function),optical conductivity σ(ω),refraction index n(ω),reflectivity R(ω),absorption α(ω)and extinction coefficients k(ω)and loss function L(ω)are also investigated for the first time for Pt3Zr in a large gamme of energy from 0 to 70 eV.     

天然杂质对黄铁矿的电子结构及催化活性的影响

采用密度泛函理论和平面波赝势方法对含天然杂质黄铁矿的电子结构和光学性质进行了计算,并讨论了二十种天然杂质:钴、镍、砷、硒、碲、铜、金、银、钼、锌、铊、锡、钌、钯、铂、汞、镉、铋、铅和锑,对黄铁矿催化活性的影响.结果表明在过渡金属杂质中,杂质能级主要由它们的d轨道产生,而在主族金属及非金属杂质中,杂质能级主要由它们的s或p轨道产生.含铜、钼、砷、金、银或镍的黄铁矿对氧的还原的电催化能力增强.除锌、钼、钌、砷、锑、硒和碲外,其余杂质能增强黄铁矿表面俘获电子的能力,使光生电子和空穴复合的概率减小.光学性质计算表 关键词： 天然黄铁矿 杂质 电子结构 光学性质     

Nb掺杂影响NiTi金属间化合物电子结构的第一性原理计算

采用基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法,计算了Nb元素掺杂对B2构型NiTi金属间化合物电子结构的影响.点缺陷生成能的计算结果表明,Nb原子掺杂后,NiTi中产生Ni原子和Ti原子空位和反位点缺陷所需要的能量均明显升高;态密度计算结果表明,Nb原子掺杂后与临近原子发生了明显的s-s, p-p和d-d电子相互作用,增加了与临近原子之间的电荷密度,有利于Nb与合金原子的成键.这些由Nb掺杂所导致的NiTi电子结构和键合特征的变化均有利于促进Nb与合金原子的相互作用,在一定程 关键词： NiTi金属间化合物 点缺陷 电子结构 第一性原理计算     

Electron structure and optical properties of the compound CaS

The zone structure of the compound CaS is calculated by the self-consistent linear combined plane-wave method. The calculation is performed for 89 points of the irreducible portion of the Brillouin zone. The tetrahedron method with quadratic interpolation is used to obtain optical spectra of CaS. Experimental optical spectra are interpreted. The calculations predict a significant degree of covalence in the chemical bond in CaS.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 82–86, July, 1988.     

Electronic structure of the intermetallic compound TiNi

We present the results of self-consistent band structure calculations for the intermetallic compound TiNi in the CsCl structure. The calculated Fermi surface shows nesting features that appear to be consistent with the suggestion of an incommensurate charge density wave.     

Magnetic structure of the intermetallic compound DyAg

Neutron diffraction measurements were performed for an antiferromagnetic compound DyAg with T_N=56.7 K. Magnetic structures were found to be the (π π 0)-type at 12 K and rthe sinusoidally modulated transverse static spin wave propagating along the 110 direction and polarized in the 001 direction at 50.7 K.     

Magnetic properties of the intermetallic compound PrAg

The field and temperature dependences of the magnetization of PrAg are found to be those of an antiferromagnet whose Néel point is ～11°K and which undergoes a spin-flop transition at a critical field of ～5 kOe, as confirmed by high-field neutron diffraction measurements. Preliminary comparisons are made with properties calculated from crystal-field theory.     

Nb掺杂γ-TiAl金属间化合物的电子结构与力学性能

运用基于密度泛函理论的第一性原理方法计算了Nb掺杂γ-TiAl金属间化合物的结构参数、能带结构、电子态密度及弹性常数.结果表明:Nb替代Ti掺杂相比Nb替代Al掺杂的形成能低,Nb在替位掺杂时更倾向于取代Ti原子形成稳定的结构,Nb替代Ti掺杂能够提高γ-TiAl金属间化合物的抵御塑性变形能力、断裂强度和延展性;与Nb替代Ti掺杂相比,Nb替代Al掺杂同样增强γ-TiAl金属间化合物的断裂强度且其增强延展性的效果更好,但抵御塑性变形的能力有所削弱.     

Crystal field and magnetic properties of the tetragonal TbNi2Si2 compound

The magnetic properties of a TbNi₂Si₂ single crystal have been investigated experimentally by specific heat, anisotropy of the susceptibility and magnetization, and inelastic neutron scattering, leading to the determination of its fundamental coupling parameters. The lowest crystalline electric field states are two singlets close to each other, that explains the different magnetic structures evidenced in TbNi₂Si₂: an amplitude modulated structure, close to T _N , a simple antiferromagnetic one at low temperature and an antiphase one when an external magnetic field is applied along the c direction.     

CaB6电子结构及光学性质的第一性原理计算

采用基于密度泛函理论的第一性原理的分子动力学方法系统地计算了温度为300K时CaB6基态的电子结构、态密度和光学性质.能带结构分析表明CaB6属于一种直接带隙半导体;其导带主要由Ca的3d态电子构成,价带主要由B的2p态电子构成,静态介电常数ε1(0)=7.8,折射率n(0)=2.8,吸收系数最大峰值为4.37×105...     

OsSi2电子结构和光学性质的研究

采用基于第一性原理的密度泛函理论赝势平面波方法,对正交相OsSi₂的电子结构、态密度和光学性质进行了理论计算,能带结构计算表明它是一种间接带隙半导体,禁带宽度为0813 eV;其价带主要由Os的5d和Si的3p态电子构成;导带主要由Si的3s,3p以及Os的5d态电子构成;静态介电常数ε₁（0）=1543; 折射率n＝393并利用计算的能带结构和态密度分析了OsSi₂的介电函数、吸收系数、折射率、反射率、 关键词： 2')" href="#">OsSi₂ 第一性原理 电子结构 光学性质     

C掺杂AlN的电子结构和光学性质的第一性原理研究

采用基于密度泛函理论(DFT)的平面波超软赝势法,研究了C掺杂铅锌矿AlN的电子结构、磁性和光学性质.结果表明,C掺杂AlN产生了自旋极化,在带隙中引入杂质带形成受主能级,实现p型掺杂,同时表现出较强的半金属铁磁性,半金属能隙为0.315eV,理论上可实现100%的自旋载流子注入.掺杂后体系的介电函数虚部和光吸收系数在低能区出现新的峰值,吸收边向低能方向延展,能量损失明显减少.