Structure Of 3d Transition Metals Research Articles

Lab-Scale X-Ray Emission/Absorption Spectroscopy for Operando Measurement of Electronic Structure of Transition Metals in Battery Electrodes

Tracking the change in electronic structure of target elements is crucial to investigate the nature of redox reactions occurring in battery electrodes. X-ray emission spectroscopy (XES) and x-ray absorption fine structure (XAFS) perform this role well with high sensitivity and throughput, but the requisite of synchrotron facilities often limits those availability for material characterization.Using a lab-scale x-ray emission/absorption spectrometer, we investigated the changes in the local structure and chemistry around the 3d transition metal elements of LiMO2 cathodes for Li-ion batteries as a function of the battery state of charge (SoC). Ex situ measurement was prepared from the electrode samples with discrete difference in SoC. Coupled with ex situ measurement, operando measurement was performed using pouch cells with LiMO2 cathode, which enabled a real-time monitoring of chemical shift in an element-specific manner resulted from changing electrode potential.Through the XES mode of the bench-top spectrometer, fluorescence emissions from the LiMO2 cathode, or the cell containing it, was monochromatized by a spherically bent crystal analyzer (SBCA). The Kβ emissions of 3d transition metal elements such as cobalt display position/shape difference of spectrum with varying SoC. The trend of chemical shift and change in spectral features provided the information on the electronic structure variation, such as oxidation state change of 3d transition metals in LiMO2 during charge and discharge (i.e., delithiation and lithiation). Furthermore, valence-to-core (VtC) emission signals helped enable in-depth analysis such as spin structure characterization.In addition to the XES analysis, we could measure K-edge XAFS for the same 3d transition metals in LiMO2 as well. In the XAFS mode of the spectrometer, SBCA monochromatized bremsstrahlung x-ray generated from a high-power x-ray tube is used to make an incident source energy-dispersive. While Kβ XES probed occupied levels, K-edge XAFS examined unoccupied levels providing comprehensive understanding on the change in electronic structure of 3d transition metals in LiMO2. Figure 1

Impact of electron correlation on the light-induced demagnetization of elemental ferromagnetic metals

The local spin-density approximation (LSDA) is known to describe poorly the electronic structure of 3d transition metals, yet most density-functional-based ab-initio studies of ultra-fast demagnetization rely on it. One way to account for Coulomb correlations among the localized d electrons and go beyond LSDA is to include the effective correlation energy (or Hubbard) U. By doing so, we show here that electronic correlations lead to sizable changes of the laser-induced demagnetization of iron, cobalt, and nickel. We study how the various laser parameters, such as pulse duration or intensity, change the magnetization dynamics. It turns out that the total laser fluence is not suitable to quantify how much a laser pulse demagnetizes a material, as changes in pulse duration and shape influence significantly the outcome. The findings are traced back to the electronic structure of the material, and explained based on phase space for optical transitions.Graphic abstract

Prediction of spin-dependent electronic structures of 3d transition metals doped Hittorf's violet phosphorene towards spintronics

Modulation of spin-dependent properties in semiconductor is of importance in exploring the potential application in spintronics. Here, we theoretically investigated the structural deformation, electronic characters, and magnetic properties of the single-layered Hittorf's violet phosphorene nanosheet with 3 d transition metal atoms (ranging from Sc to Ni) doping and under external electric field. The electronic band structures and magnetic properties was found to be obviously modulated by the dopants: the existence of a large spin splitting of the dopant 3 d states tailors the semiconducting phosphorene into simple magnetic semiconductor or bipolar magnetic semiconductor, except for the case of Sc. The application of an appropriate electric field to V-doped system could induce a transition from bipolar magnetic semiconductor to half metal with the carriers fully spin-polarized in alternative spin channel. Moreover, Hittorf's violet phosphorene-based field-effect transistor was proposed with the aim of realizing gate-voltage control on the carriers' spin orientation. Our findings pointed out the possibilities for realizing spin-dependent field-effect transistor in doped Hittorf's violet phosphorene nanosheet and opened a window for the burgeoning field of multifunctional 2D nanoelectronics and spintronics devices. • Ranging from Ti to Ni dopants can behave (bipolar) magnetic semiconductors. • Sc-doped Hittorfene is a nonmagnetic semiconductor. • The application of the electric field to V-doped Hittorfene can induce half metal transition. • The reversed carriers' spin orientation would be potential for spintronic devices.

Reprint of “Spin-resolved electronic structure of 3d transition metals during ultrafast demagnetization”

In this work we follow up on the pioneering work of Jean-Yves Bigot and Eric Beaurepaire about disentangling microscopic properties in femtosecond magnetization dynamics such as spin and orbital momenta (Boeglin et al., 2010). To this end, we utilize spin-resolved photoemission to distinguish spin polarization and exchange splitting as essential magnetic properties in the ultrafast demagnetization of thin Fe films on W(110). In laser photoemission (hνProbe=6.2 eV) we find an ultrafast breakdown of the spin polarization after exciting the system with 70-fs pump laser-pulses at hνPump=1.6 eV. Measuring a minority-spin surface resonance close to the Fermi level at 0.12 Å−1 in Γ‾-H‾ direction, we establish a band mirroring effect similar to the ones observed in Eich et al. (2017) and Gort et al. (2018).

Spin-resolved electronic structure of 3d transition metals during ultrafast demagnetization

In this work we follow up on the pioneering work of Jean-Yves Bigot and Eric Beaurepaire about disentangling microscopic properties in femtosecond magnetization dynamics such as spin and orbital momenta (Boeglin et al., 2010). To this end, we utilize spin-resolved photoemission to distinguish spin polarization and exchange splitting as essential magnetic properties in the ultrafast demagnetization of thin Fe films on W(110). In laser photoemission (hνProbe=6.2 eV) we find an ultrafast breakdown of the spin polarization after exciting the system with 70-fs pump laser-pulses at hνPump=1.6 eV. Measuring a minority-spin surface resonance close to the Fermi level at 0.12 Å−1 in Γ‾-H‾ direction, we establish a band mirroring effect similar to the ones observed in Eich et al. (2017) and Gort et al. (2018).

Analysis of the electronic structures of 3d transition metals doped CuGaS2 based on DFT calculations

3d transition metals doped CuGaS2 are considered as possible absorbing material candidates for intermediated band thin film solar cells. The electronic structure and optical properties of 3d transition metals doped CuGaS2 are investigated by using density functional theory calculations with the GGA + U method in the present work. The doping with 3d transition metals does not obviously change the crystal structure, band gap, and optical absorption edge of the CuGaS2 host. However, in the case of CuGa1−xTMxS2 (TM = Ti, V, Cr, Fe, and Ni), there is at least one distinct isolated impurity energy level in the band gap, and the optical absorption is enhanced in the ultraviolet-light region. Therefore, these materials are ideal absorber material candidates for intermediated band thin film solar cells. The calculated results are very well consistent with experimental observations, and could better explain them.

First Principle Calculations of the Magnetic Structures of 3d Transition Metals Doped GaN

First principle calculations were performed on the electronic and magnetic structures of the transition metals doped GaN. Seven elements in 3d transition metals from V to Cu were used as a dopant. Magnetic phase was stable compared to non-magnetic phase for all transition metals doped GaN. Total magnetic moments followed Hund’s rule to maximize the magnetic moment. Transition element projected magnetic moments showed that most of magnetic moments were concentrated on transition metals in the cases of V, Cr, and Mn doped GaN, which could not be used for DMS. Since Fe and Ni doped GaNs are intrinsic insulators, Fe and Ni doped GaNs could not be used for DMS materials unless additional dopants are introduced. The most probable candidates for DMS applications were predicted to be Co or Cu doped GaNs, respectively.

Electronic Structure of Transition Metals Fe, Ni and Cu in theGWApproximation

The quasiparticle band structures of 3d transition metals, ferromagnetic Fe, Ni and paramagnetic Cu, are calculated by the GW approximation. The width of occupied 3d valence band, which is overestimated in the LSDA, is in good agreement with experimental observation. However the exchange splitting and satellite in spectra are not reproduced and it is required to go beyond the GW approximation. The effects of static screening and dynamical correlation are discussed in detail in comparison with the results of the static COHSEX approximation. The dynamical screening effects are important for band width narrowing.

Self-interaction correction for band structure calculation based on local density approximation of iron nitrides

The band theory based on the conventional local density approximation (LDA) has not given a quantitative explanation of the mechanism of the giant magnetization of α″-Fe 16N 2 thin film. In this paper, the self-interaction correction (SIC) is applied to the LDA band calculation of α″-Fe 16N 2. The electronic structure is calculated by the self-consistent linearized augmented plane wave (LAPW) method. It can be concluded that the influence of the SIC for α″-Fe 16N 2 is large, although the calculated electronic structures of 3d transition metals and γ′-Fe 4N are little affected by the SIC. The charge density distribution of α″-Fe 16N 2 is uniformly broadened. It appears that the distribution for some sites of Fe atoms in α″-Fe 16N 2 is different from that of bcc Fe atoms. However, the SIC has little effect on the total magnetic moment. The SIC is unable to explain the giant magnetic moment. It seems that the orbits of iron nitride are probably metallic bond-like, whose orbit is Bloch function-like, although the localization of some sites of Fe atoms of α″-Fe 16N 2 results in more influence than that of γ′-Fe 4N.

Gibbs-Bogoliubov variational scheme calculations for the liquid structure of 3d transition metals

The results of calculations of the static structure factor S(q) for liquid 3d transition metals are presented. These have been studied using effective inter-ionic pair potentials proposed by two of the authors (JLB and MS), that combine the empty-core model used to describe the nearly-free-electron band and a d-band contribution deduced via an inverse scattering approach. They have potential wells that are shallower and shifted towards the larger values of r than the corresponding Wills-Harrison potentials used by other authors. The fluid aspects are modelled through a charged hard-sphere reference system optimised via the Gibbs-Bogoliubov variational scheme. The results for S(q) agree reasonably well with the available experimental data. The optimized values found for the hard-sphere diameters reveal that the ions never sample the hard cores, confirming earlier findings on the need to use a soft-core reference system for liquid transition metals.

Analysis of the liquid structure of 3d transition metals from the Wills-Harrison model

Calculations of the liquid structure of 3d transition metals from the effective pair interactions of Wills and Harrison are performed by using the optimized random phase approximation in order to point out the influence of thes-electron pseudopotential on the repulsive and attractive forces governing the liquid structure. Our results are compared to those obtained in the Weeks, Chandler Andersen approximation and in the thermodynamic variational method.

Extended energy loss fine structure measurement above shallow and deep core levels of 3d transition metals

The authors present a systematic investigation of surface structure of 3d transition metals through electron energy loss fine structure (EELFS) measurements, above the edges of shallow and deep core levels in the reflection mode. Fine structures above these edges, similar to those measured in X-ray absorption spectra and transmission energy loss spectra, extend for several hundred eV from the threshold. From the Fourier analysis of these features they obtained the radial distribution function around the excited atom. They discuss the EELFS analysis (Fourier transformations, backscattering amplitudes and phase shifts) above the M2,3 edges of Cu, Ni, Co, Fe and Ti metals. The experimental NiM2.3 phase shift is compared with recent theoretical calculations of shallow core levels and the discrepancy observed is ascribed to possible Fano-interference relaxation effects. They present a direct comparison between the EELFS spectrum of the TiL2.3 edge with the EXAFS spectrum obtained with synchrotron radiation. This comparison gives the most convincing evidence that the dipole (q equivalent to 0 AA-1, Delta l=+or-1) is the predominant term in the inelastic cross-section even when low primary beam energies are used and high energy loss are involved. Finally the surface sensitivity of the present technique is shown through the modification of surface-EELFS features above the FeM2,3 edge during the early stages of oxidation.

The structures of 3d-transition metals in the liquid state

Abstract The structures of 3d-transition metals (Ti, V, Cr, Mn, Fe, Co, Ni and Cu) in the liquid state have been systematically examined by X-ray diffraction at temperatures above their melting points. In terms of the usual Fourier analysis, the atomic radial distribution functions were obtained from which interatomic distance and coordination number were estimated.

The Electronic Structure of 3d Transition Metals

AbstractIn the present paper each point of the lattice is assumed to be surrounded by a neutral sphere of the radius R < rs for pure ferromagnetic metals and R > rs for non‐ferromagnetic 3d‐metals while in the Stern method the neutral sphere is the Wigner‐Seitz sphere of radius rs. The atom in the sphere is taken as characterized by the starting electronic configuration depending on the type of the crystal structure: 3dC−24s2 for f.c.c. (Ni and Sc), 3dC−14s1 for h.c.p. (Co and Ti), 3dC for b.c.c. (Fe, Cr, V. α‐Mn), C being the number of electrons out of the argon shell of the neutral atom in the ground state. Only one of all the lattice points is surrounded by the so‐called central sphere; the atom in it interacts with its nearest neighbours when R < rs as also with next‐nearest neighbours, when R > rs. Owing to this interaction the starting electronic configuration mentioned is transformed into an electronic configuration actually realized in metals. The electronic structure calculated on this basis is in agreement with that calculated by some other methods.