共查询到20条相似文献,搜索用时 31 毫秒
1.
The evolution of the electronic structure of CeNi4M (M = Fe, Co, Ni, Cu) intermetallics depending on the type of nickel substitutional impurity is explored. We have calculated band structures of these compounds and considered options of substituting one atom in nickel 3d sublattice in both types of crystallographic positions: 2c and 3g. The analysis of total energy self-consistent calculations has shown that positions of 2c type are more energetically advantageous for single iron and cobalt impurities, whereas a position of 3g type is better for a copper impurity. The Cu substitutional impurity does not change either the nonmagnetic state of ions or the total density at the Fermi level states. Fe and Co impurities, on the contrary, due to their considerable magnetic moments, induce magnetization of 3d states of nickel and cause significant changes in the electronic state density at the Fermi level. 相似文献
2.
Lingping Xiao Xiaobin Li Xue Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》2018,91(5):85
We report first-principles studies the structural, electronic, and optical properties of the Fe2SiO4 fayalite in orthorhombic structure, including pressure dependence of structural parameters, band structures, density of states, and optical constants up to 30 GPa. The calculated results indicate that the linear compressibility along b axis is significantly higher than a and c axes, which is in agreement with earlier work. Meanwhile, the pressure dependence of the electronic band structure, density of states and partial density of states of Fe2SiO4 fayalite up to 30 GPa were presented. Moreover, the evolution of the dielectric function, absorption coefficient (α(ω)), reflectivity (R(ω)), and the real part of the refractive index (n(ω)) at high pressure are also presented. 相似文献
3.
Evolution of the electronic structure of the NpMGa5 (M = Fe, Co, Ni) series of neptunium compounds, whose crystal structure is similar to that of the known family of Pu115 superconductors, was studied by the LDA + U + SO method. The calculations took into account both the strong electron correlations and the spin?orbit coupling in the 5f shell of neptunium. For the first time, the electronic structure was calculated for a hypothetical series of compounds in which gallium is replaced with indium. Parameters of the crystal structure of the given series were obtained using the relationship between the parameters of the crystal structure of the earlier-studied compounds PuCoGa5 and PuCoIn5. The analysis of the electronic structure and characteristics of neptunium ions calculated in the framework of the LDA + U + SO method showed that the neptunium ions in NpMIn5 with M = Fe, Co, and Ni should have an electron configuration closer to f4, but a spin and magnetic characteristics close to those in NpMGa5. 相似文献
4.
The electronic structure and the exchange interactions in EuNi4Co and YbNi4Co compounds have been calculated in terms of a theoretical approach with the inclusion of electronic correlations (LSDA + U method); the variants of substitution of cobalt ion for nickel in the 3d lattice in both types of crystallographic positions 2c and 3g are considered. The total energies obtained in self-consistent calculations show that individual cobalt impurities are more preferably arranged in position of the 3g type. A Co ion in RNi4Co (R = Eu, Yb) is characterized by a significant magnetic moment, which leads to significant increase in the exchange interaction of Co and Ni ions in the 3d metal sublattice. 相似文献
5.
A. D. Molchanova 《Physics of the Solid State》2018,60(10):1957-1965
The results of studies of the absorption spectra of nickel orthoborate Ni3(BO3)2 in the range of electronic d–d-transitions are reported. The obtained data are analyzed in the framework of the crystal field theory. The Ni2+ ions are located in two crystallographically nonequivalent positions 2a and 4f with point symmetry groups C2h and C2, respectively, surrounded by six oxygen ions forming deformed octahedra. The absorption spectra exhibit three intense bands corresponding to spin-resolved transitions from the ground state of nickel ion 3A2g (3F) to the sublevels of the 3T2g (3F), 3T1g (3F) and 3T1g (3P) triplets split by the spinorbit interaction and the rhombic component of the crystal field. At temperatures below 100 K, the spectra exhibit a thin structure, in which phonon-free lines can be distinguished. Comparison of the calculated frequencies of the zero-phonon transitions with the experimental data allows estimating parameters of the crystal field acting on the nickel ions in the 2a- and 4f-positions, as well as the parameters of electrostatic interaction between the 3d electrons and spin-orbit interaction constants. 相似文献
6.
High-frequency broad-band (65–240 GHz) EPR is used to study impurity centers of bivalent chromium in a CdGa2S4 crystal. It is found that the EPR spectra correspond to tetragonal symmetry. The spin Hamiltonian H = βB · g · S + B 2 0 O 2 0 + B 4 0 O 4 0 + B 4 4 O 4 4 with the parameters B 2 0 =23659±2 MHz, B 4 0 =1.9±1 MHz, |B 4 4 |=54.2±2 MHz, g‖=1.93±0.02, and g⊥=1.99±0.02 is used to describe the observed spectra. It is concluded that chromium ions occupy one of the tetrahedrally coordinated cation positions. 相似文献
7.
Yu. V. Knyazev A. V. Lukoyanov Yu. I. Kuz’min A. G. Kuchin M. Vasundhara 《Optics and Spectroscopy》2018,124(6):784-788
Investigations of the electronic structure and optical properties of TmNi5–хСux (х = 0, 1, 2, 3) compounds were performed. Self-consistent calculations of the band spectrum have been performed in the local electron-spin-density approximation with a correction on strong electron interactions within the LSDA + U method. Total and partial densities of electron states associated with thulium, nickel, and copper atoms have been calculated. Optical conductivity, the behavior of which is interpreted for each compound taking into account the performed calculations, has been measured by the ellipsometry method in a wide wavelength range of 0.22–16 μm. Concentration dependences of plasma and relaxation frequencies of conduction electrons have been determined. 相似文献
8.
I. R. Shein R. Wilks A. Moewes E. Z. Kurmaev D. A. Zatsepin A. I. Kukharenko S. O. Cholakh 《Physics of the Solid State》2008,50(4):615-620
The electronic structure of crystalline phenakite Be2SiO4 is investigated using x-ray emission spectroscopy (XES) (Be K α XES, Si L 2, 3 XES, O K α XES) and x-ray absorption spectroscopy (XAS) (Be 1s XAS, Si 2p XAS, O 1s XAS). The energy band structure is calculated by the ab initio full-potential linearized augmented-plane-wave (FLAPW) method. The total and partial densities of states and the dispersion curves for the Be2SiO4 compound are presented. It is shown that the top of the valence band and the bottom of the conduction band of the Be2SiO4 compound are predominantly formed by the oxygen 2p states. According to the results obtained, the electron transition with the lowest energy supposedly can occur at the center of the Brillouin zone. The effective masses of electrons (0.5m e ) and holes (3.0m e ) for the Be2SiO4) compound are estimated. 相似文献
9.
N. Yu. Svechnikov V. G. Stankevich A. M. Lebedev L. P. Sukhanov K. A. Menshikov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2016,10(1):23-34
The electron and spin structure of thick smooth hydrocarbon CD x films (“flakes”) with a high relative deuterium concentration of x ~ 0.5, redeposited from deuterium plasma discharge onto the walls of the vacuum chamber of the T-10 tokamak and containing ~1 at % of 3d-metal impurities due to erosion of the chamber walls, are studied using electron paramagnetic resonance (EPR) and photoluminescence (PL). The resulting spectra are compared for the first time to the EPR and photoluminescence spectra of polymer (soft) a-C:H(D) films (H(D)/C ~ 0.5), which are considered model analogues of smooth CD x films. A certain similarity of the CD x films with a-C:H films was found in the electronic structure of the valence band. At the same time, the differences in the EPR and photoluminescence spectra were observed due to the presence of 3d-metal impurities in the CD x samples, contributing to the conversion of sp 3 → sp 2 in the formation of films in the tokamak and upon heating and thermal desorption. An impurity of, presumably, 3d metals was detected for the first time by EPR in the a-C:H films in an amount of approximately 0.2 ppm, related to the evaporation of graphite. 相似文献
10.
Z. A. Kazeĭ V. V. Snegirev M. Goaran L. P. Kozeeva M. Yu. Kameneva 《Journal of Experimental and Theoretical Physics》2008,106(3):550-561
Microwave absorption in the tetragonal singlet paramagnets HoVO4 (zircon structure) and HoBa2Cu3O
x
(x ≈ 6, layered perovskite structure) is studied and compared in pulsed magnetic fields up to 40 T at low temperatures. These
paramagnets are characterized by a singlet-doublet scheme of the low-lying levels of the Ho3+ ion in a crystal field. In a magnetic field directed along the tetragonal axis, HoVO4 exhibits resonance absorption lines at wavelengths of 871, 406, and 305 μm, which correspond to electron transitions between
the low-lying levels of the Ho3+ ion in the crystal field. The positions and intensities of these absorption lines in HoVO4 are well described in terms of the crystal-field formalism with the well-known interaction parameters. The absorption spectra
of HoBa2Cu3O
x
at a wavelength of 871 μm exhibit broad resonance absorption lines against the background of strong nonresonance absorption.
The effects of low-symmetry (orthorhombic, monoclinic) crystal-field components, the deviation of a magnetic field from a
symmetry axis, and various pair interactions on the absorption spectra of the HoVO4 and HoBa2Cu3O
x
crystals are discussed.
Original Russian Text ? Z.A. Kazeĭ, V.V. Snegirev, M. Goaran, L.P. Kozeeva, M.Yu. Kameneva, 2008, published in Zhurnal éksperimental’noĭ
i Teoreticheskoĭ Fiziki, 2008, Vol. 133, No. 3, pp. 632–645. 相似文献
11.
The structural, mechanical, electronic and thermoelectric properties of the low temperature orthorhombic perovskite phase of CH3NH3PbI3 have been investigated using density functional theory (DFT). Elastic parameters bulk modulus B, Young’s modulus E, shear modulus G, Poisson’s ratio ν and anisotropy value A have been calculated by the Voigt–Reuss–Hill averaging scheme. Phonon dispersions of the structure were investigated using a finite displacement method. The relaxed system is dynamically stable, and the equilibrium elastic constants satisfy all the mechanical stability criteria for orthorhombic crystals, showing stability against the influence of external forces. The lattice thermal conductivity was calculated within the single-mode relaxation-time approximation of the Boltzmann equation from first-principles anharmonic lattice dynamics calculations. Our results show that lattice thermal conductivity is anisotropic, and the corresponding lattice thermal conductivity at 150 K was found to be 0.189, 0.138, and 0.530 Wm?1K?1 in the a, b, and c directions. Electronic structure calculations demonstrate that this compound has a DFT direct band gap at the gamma point of about 1.57 eV. The electronic transport properties have been calculated by solving the semiclassical Boltzmann transport equation on top of DFT calculations, within the constant relaxation time approximation. The Seebeck coefficient S is almost constant from 50 to 150 K. At temperatures 100 and 150 K, the maximal figure of merit is found to be 0.06 and 0.122 in the direction of the c-axis, respectively. 相似文献
12.
Cubic paramagnetic centers formed by Yb3+ impurity ions in fluorite-type crystals MeF2 (Me = Cd, Ca, Pb) have been investigated using electron paramagnetic resonance, magnetic circular dichroism, magnetic circular polarization of luminescence, Zeeman splitting of optical absorption and luminescence lines, and optical detection of electron paramagnetic resonance. The g factors of the 2Γ7 state in the excited multiplet 2 F 5/2 of Yb3+ ions in Me F2 crystals, the hyperfine interaction constant 171 A (171Yb) for the excited multiplet 2 F 5/2 in the CaF2 crystal, and the energies and symmetry properties of all energy levels of Yb3+ ions in MeF2 crystals are determined. The crystal-field parameters for the crystals under investigation are calculated. 相似文献
13.
A. V. Lukoyanov I. A. Nekrasov V. I. Sokolov V. I. Anisimov 《Physics of the Solid State》2005,47(8):1560-1562
The results of calculating the electronic structure of semiconductor compounds AIIBVI: 3d(A = Zn; B = S, Se, Te; 3d = Sc-Cu) at a low content of 3d impurities are discussed. The excess charge of an impurity ion with respect to the charge of the zinc ion is determined for the whole series of 3d impurities. It is found that the excess charge gradually varies from +0.6|e| for the scandium impurity to ?0.2|e| for the copper impurity. Photoionization of an impurity ion is simulated by adding a hole or an electron to the impurity center. The added charge is redistributed between the impurity ion and its nearest neighbors, thus decreasing or increasing the total excess charge of the impurity center by a magnitude of ~ 0.2|e|. 相似文献
14.
P. A. Shchepanskyi V. Yo. Stadnyk M. Ya. Rudysh R. S. Brezvin B. V. Andrievskii 《Optics and Spectroscopy》2018,125(3):353-357
The energy band structure of a LiNaSO4 has been calculated within the framework of density functional theory for space group P31c. It has been established that bandgap width Eg in the GGA approximation is 5.49 eV. The valence band top is generally formed of oxygen p-electrons, while the conduction band bottom is composed of lithium and sodium s-states. The effect of the cationic substitution Na → K → Rb → NH4 on the electron structure of LiBSO4 group crystals is considered. Based on the calculated dielectric functions, the spectral dependences of the refractive indices and extinction coefficient of a crystal were calculated and compared with experimental data. 相似文献
15.
16.
A. P. Skvortsov V. A. Trepakov S. Kapphan A. Dejneka L. Jastrabik 《Physics of the Solid State》2009,51(7):1470-1472
The first results of the study of optical absorption spectra of KTaO3: Er3+ crystals are presented. In the 350–660-nm region, lines are observed deriving from intraconfigurational electronic transitions from the 4 I 15/2 ground state to levels of the 4 F 9/2, 4 S 3/2, 2 H 11/2, 4 F 7/2, 4 F 5/2(4 F 3/2), 2 G 9/2, and 4 G 11/2 excited states of the Er3+ ions. A comprehensive study of transitions to the 4 F 9/2, 4 S 3/2, 2 H 11/2, and 4 F 7/2 levels at 77 K is carried out. The number of lines observed for the above transitions fits the theoretically possible number for ?-? electronic transitions in Er3+ ions in the cubic crystal field. In the case of a differently charged substituted ion, this situation occurs only under nonlocal impurity charge compensation. The energies of the excited state levels for the transitions under study are determined. 相似文献
17.
Zafer Kandemir Selma Mayda Nejat Bulut 《The European Physical Journal B - Condensed Matter and Complex Systems》2016,89(5):113
We study the electronic structure and correlations of vitamin B12 (cyanocobalamine) by using theframework of the multi-orbital single-impurity Haldane-Anderson model of atransition-metal impurity in a semiconductor host. The parameters of the effectiveHaldane-Anderson model are obtained within the Hartree-Fock (HF) approximation. Thequantum Monte Carlo (QMC) technique is then used to calculate the one-electron andmagnetic correlation functions of this effective model. We observe that new states forminside the semiconductor gap found by HF due to the intra-orbital Coulomb interaction atthe impurity 3d orbitals. In particular, the lowest unoccupiedstates correspond to an impurity bound state, which consists of states from mainly the CNaxial ligand and the corrin ring as well as the Co eg-like orbitals. We alsoobserve that the Co?(3d) orbitals can develop antiferromagneticcorrelations with the surrounding atoms depending on the filling of the impurity boundstates. In addition, we make comparisons of the HF+QMC data with the density functionaltheory calculations. We also discuss the photoabsorption spectrum of cyanocobalamine. 相似文献
18.
A. A. Gippius E. N. Morozova K. S. Okhotnikov E. A. Alkaev 《Journal of Experimental and Theoretical Physics》2007,105(1):27-29
The magnetic structure of the Sr2Cu3O4Cl2 two-subsystem antiferromagnet is studied by the nuclear quadrupole resonance (NQR) method on the 63, 65Cu and 35Cl nuclei. The resonance spectrum above T N2 = 40 K is determined by the Zeeman splitting of the levels of the 63, 65Cu nuclei of the copper atoms at the Cu1 site with the first-order quadrupole perturbation. The magnetic field on the copper nuclei is equal to 93 kOe. The spectrum below n is significantly different: it includes a low-frequency part, which is associated with the ordering of the second magnetic subsystem Cu2. The splitting of the NQR lines of 35Cl is observed above and below T N2. This fact indicates the ferromagnetic ordering of the moments of the Cu1 subsystem, which are located along the c axis of the crystal, and makes it possible to determine the direction of the magnetic field on Cu1 copper as (110). 相似文献
19.
Spin polarized ab initio calculations have been carried out to study the structural, electronic, elastic and thermal properties of RHg (R = Ce, Pr, Eu and Gd) intermetallic compounds in B2 structure. The calculations have been performed by using both generalized gradient approximation (GGA) and local spin density approximation (LSDA). The calculated value of lattice constant (a 0) for these compounds with GGA is in better agreement with the experimental data than those with LSDA. Bulk modulus (B), first-order pressure derivative of bulk modulus and magnetic moment (μ B ) are also presented. The energy band structure and electron density of states show the occupancy of 4f states for light as well as heavy rare earth atom. The elastic constants are predicted from which all the related mechanical properties like Poisson’s ratio (σ), Young’s modulus (E), shear modulus (G H ) and anisotropy factor (A) are calculated. The ductility or brittleness of these compounds is predicted from Pugh’s rule (B/G H ) and Cauchy pressure (C 12 ? C 44). The Debye temperature (θ D ) is estimated from the average sound velocity, which have not been calculated and measured yet. 相似文献
20.
The influence of variable valence on NSR spectra of 53Cr nuclei in ferromagnetic CuCr2?xSbxS4 (x = 0, 0.02, 0.07) at T = 77 K is considered. For quadrupole nuclei in locally anisotropic positions, the effects of variable valence result in averaging of not only the resonance frequency but also of the quadrupole and magnetic anisotropy constants. The significant difference between the experimental and calculated values of these constants indicates the important role of the intrinsic electronic contribution to the anisotropy of hyperfine fields of compounds containing Cr4+ ions. Additional lines caused by intrinsic and induced defects in the structure are observed in the spectra of doped and undoped compounds. 相似文献