Electronic Structure Of Ions Research Articles

First principles study of the crystal, electronic structure, and diffusion mechanism of polaron-Na vacancy of Na3MnPO4CO3 for Na-ion battery applications

Based on first principles calculations, we investigate the geometry, electronic structure, and diffusion mechanism of Na ions in Na3MnPO4CO3 using density functional theory with a Hubbard potential correction. Our results suggest that the structure of Na3MnPO4CO3 can be deintercalated with more than one Na ion, and that the removal of a Na ion can form a bound polaron. We find that our calculations of the intercalation voltages for the redox couples Mn2+ /Mn3+ and Mn3+ /Mn4+ agree very well with the experimental data. In addition, we demonstrate that Na in Na3MnPO4CO3 can diffuse in three directions with low activation energy barriers, allowing a fast charging rate.

Covalency and vibronic couplings make a nonmagnetic j=3/2 ion magnetic

AbstractFor 4d1 and 5d1 spin–orbit-coupled electron configurations, the notion of nonmagnetic j=3/2 quartet ground state discussed in classical textbooks is at odds with the observed variety of magnetic properties. Here we throw fresh light on the electronic structure of 4d1 and 5d1 ions in molybdenum- and osmium-based double-perovskite systems and reveal different kinds of on-site many-body physics in the two families of compounds: although the sizable magnetic moments and g-factors measured experimentally are due to both metal d–ligand p hybridisation and dynamic Jahn–Teller interactions for 4d electrons, it is essentially d−p covalency for the 5d1 configuration. These results highlight the subtle interplay of spin–orbit interactions, covalency and electron–lattice couplings as the major factor in deciding the nature of the magnetic ground states of 4d and 5d quantum materials. Cation charge imbalance in the double-perovskite structure is further shown to allow a fine tuning of the gap between the t2g and eg levels, an effect of much potential in the context of orbital engineering in oxide electronics.

X-ray natural circular dichroism in copper metaborate

The local electronic structure of copper ions in a copper metaborate CuB2O4 crystal is studied on the ESRF synchrotron using X-ray absorption polarization-dependent spectroscopy. The X-ray natural circular dichroism near the K absorption edge of copper is measured in the direction that is perpendicular to crystal axis c. The data obtained indicate the presence of hybridized p–d electronic states of copper. Theoretical calculations are used to separate the contributions of the two crystallographically nonequivalent positions of copper atoms in the unit cell of CuB2O4 to the absorption and X-ray circular dichroism spectra of the crystal.

Plasma screening effects on the electronic structure of multiply charged Al ions using Debye and ion-sphere models

We analyze atomic structures of plasma embedded aluminum (Al) atom and its ions in the weakly and strongly coupling regimes. The plasma screening effects in these atomic systems are accounted for using the Debye and ion sphere (IS) potentials for the weakly coupling and strongly coupling plasmas, respectively. Within the Debye model, special attention is given to investigate the spherical and non-spherical plasma-screening effects considering in the electron-electron interaction potential. The relativistic coupled-cluster (RCC) method has been employed to describe the relativistic and electronic correlation effects in the above atomic systems. The variation in the ionization potentials (IPs) and excitation energies (EEs) of the plasma embedded Al ions are presented. It is found that the atomic systems exhibit more stability when the exact screening effects are taken into account. It is also showed that in the presence of strongly coupled plasma environment, the highly ionized Al ions show blue and red shifts in the spectral lines of the transitions between the states with same and different principal quantum numbers, respectively. Comparison among the results obtained from the Debye and IS models are also carried out considering similar plasma conditions.

Electronic structure of the NpMT 5 (M = Fe, Co, Ni; T = Ga, In) series of neptunium compounds

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.

Magnetocapacitance effect in ferromagnetic LiNbO3 nanoparticles

Magnetocapacitance and magnetization behavior as a function of reduction heat treatment at 650°C and 900°C in a 5%H2–Ar atmosphere on LiNbO3 nanocrystalline are reported. There is a change of intrinsic dielectric constant (κ) from 822 to 860 produced by spin polarization using an external magnetic field. The Raman, X-ray photoelectron spectroscopy and electron paramagnetic resonance spectroscopy, indicate vibration mode changes localized at Nb–O bonds in the octahedron NbO6, shifts in the binding energy of the electronic structure of ions of niobium (3d) and the oxygen (1s). It is due to the oxygen vacancies caused by reduction heat treatment process. Moreover there is ions redistribution of Nb+3, Nb+4and Nb+5 at the surface of the nanoparticles.

Electronic structure of transition metal ions in GaN and AlN: Comparing GGA+U with experiment

Electronic structure of Cr, Mn, Fe, and Co transition metal (TM) ions in GaN and AlN is studied within the Generalized Gradient Approximation augmented by the +U corrections, which are treated as free parameters. The main impact of U(N) is the opening of the band gap by shifting both valence and conduction band energies. The intracenter transitions between the gap states of TM impurities are weakly affected by U(N), but they are sensitive to U(TM) which directly act on d(TM) orbitals. The impact of U(TM) depends on both the level symmetry and its occupancy (i.e., on the charge state of the TM ions). Degeneracies of partially occupied multiplet levels are lifted, the effect being mainly driven by the +U correction and not by the Jahn-Teller mechanism. The role of the U-induced hybridization between TM and host states is elucidated.A comparison with experimental intracenter optical transition energies demonstrate that the best agreement is obtained for U ≈ 0 for Fe, and even negative U ≈ −1 eV for Mn. The linear response calculations give U(TM)≈3.5–4.0 eV, which leads to severe discrepancies of about 1 eV with experiment. Importantly, the results obtained with U(Fe) = U(Mn) = U(N) = 5 eV are very close to those obtained with hybrid functionals, but the discrepancies with experiment are even larger. Comparison of the results for GaN and AlN shows that relative energies of gap levels of a given TM ion in the two hosts, as well as their dependencies on U(TM), are the same to within ∼0.2 eV. The estimated valence band offset between GaN and AlN is about 0.5 eV, in agreement with experiment.

Bent and twisted: the electronic structure of 2-azapropenylium ions obtained by guanidine oxidation

New bis-2-azapropenylium ions are obtained by oxidation of guanidino-substituted aromatic compounds.

Prospects for laser spectroscopy, ion chemistry and mobility measurements of superheavy elements in buffer-gas traps

Laser spectroscopic methods are reviewed which are of potential interest for the investigation of atomic and ionic level structures of superheavy elements. The latter are defined here as the trans-fermium elements with Z>100 for which no experimental atomic or ionic level structure information is known so far, and which cannot be bred in high flux nuclear power reactors via successive neutron capture. The principles of suitable laser spectroscopic methods are described, and illustrated by examples of real experiments. The addressed methods include single-ion spectroscopy in Paul traps, laser-induced fluorescence spectroscopy (LIF), radiation-detected optical pumping (RADOP), radioactive decay-detected resonance ionization spectroscopy (RADRIS), and ion-guide-detected resonance ionization spectroscopy (IGRIS). With the exception of the first all take advantage of a storage of the ions or atoms in so-called buffer-gas traps.The developed experimental methods can, in principle, also be employed for studying ion-chemical reactions with gas admixtures like O2 as well as for performing ion mobility measurements. Both provide complementary information on the electronic structure of superheavy ions. First attempts on this road of research are reviewed as well.

Water-Soluble Fe(II)–H2O Complex with a Weak O–H Bond Transfers a Hydrogen Atom via an Observable Monomeric Fe(III)–OH

Understanding the metal ion properties that favor O-H bond formation versus cleavage should facilitate the development of catalysts tailored to promote a specific reaction, e.g., C-H activation or H2O oxidation. The first step in H2O oxidation involves the endothermic cleavage of a strong O-H bond (BDFE = 122.7 kcal/mol), promoted by binding the H2O to a metal ion, and by coupling electron transfer to proton transfer (PCET). This study focuses on details regarding how a metal ion's electronic structure and ligand environment can tune the energetics of M(HO-H) bond cleavage. The synthesis and characterization of an Fe(II)-H2O complex, 1, that undergoes PCET in H2O to afford a rare example of a monomeric Fe(III)-OH, 7, is described. High-spin 7 is also reproducibly generated via the addition of H2O to {[Fe(III)(O(Me2)N4(tren))]2-(μ-O)}(2+) (8). The O-H bond BDFE of Fe(II)-H2O (1) (68.6 kcal/mol) is calculated using linear fits to its Pourbaix diagram and shown to be 54.1 kcal/mol less than that of H2O and 10.9 kcal/mol less than that of [Fe(II)(H2O)6](2+). The O-H bond of 1 is noticeably weaker than the majority of reported M(n+)(HxO-H) (M = Mn, Fe; n+ = 2+, 3+; x = 0, 1) complexes. Consistent with their relative BDFEs, Fe(II)-H2O (1) is found to donate a H atom to TEMPO(•), whereas the majority of previously reported M(n+)-O(H) complexes, including [Mn(III)(S(Me2)N4(tren))(OH)](+) (2), have been shown to abstract H atoms from TEMPOH. Factors responsible for the weaker O-H bond of 1, such as differences in the electron-donating properties of the ligand, metal ion Lewis acidity, and electronic structure, are discussed.

Fabrication of Polyaniline/Graphene/Tb3+ Conductive Composite Material

Polyaniline/graphene/Tb3+(PANI/GN/Tb3+) composite material was successfully prepared by the method of in-situ polymerization. The morphology of this as-formed composite material has been confirmed by scanning electron microscope (SEM) analysis. SEM images illustrated that the PANI were uniformly deposited on GN nanosheets. PANI/GN/Tb3+ composite material exhibited high electrical conductivity than the pristine PANI. What's more, results also demonstrated that the synthesized composite material has found wide promising applications in capacitors. Finally, the conductive mechanism of PANI/GN/rare earth composite is discussed in this paper, the conductivity of nanocomposites offered upgrade first than descending latter tendency with different content of Tb3+ ions. The results should be attributed to the special electronic structure and excellent magnetic of rare earth ions, which can influence the polymer chains.

Operando X-ray diffraction and X-ray absorption studies of the structural transformation upon cycling excess Li layered oxide Li[Li1/18Co1/6Ni1/3Mn4/9]O2 in Li ion batteries

Co helps maintain the lithium ions stably in the transition metal inter slabs and the surface electronic structure of oxygen ions is reversible during cycling between 4.6 V and 2.5 V.

Ion mobility spectrometry coupled to laser-induced fluorescence for probing the electronic structure and conformation of gas-phase ions

We report on an improved design of a differential ion mobility analyzer (DMA) coupled to laser-induced fluorescence (LIF) for the simultaneous retrieval of two-dimensional information on the electric mobility and fluorescence spectroscopy of gas-phase ions. This enhanced design includes an ion funnel inter-face at the input orifice of the DMA and a nozzle beam stage at the output of the DMA. These improvements allow the detection of fluorescence not only from pure dyes and their clusters, as was demonstrated recently, but also from fluorophore-tagged biomolecules. Complex mixtures of fluorescent compounds can be separated by the DMA and studied by LIF. This unique combination of instruments also provides a powerful platform for probing fluorescent proteins in the gas phase. The green fluorescent protein (GFP) was tested on a new setup. In contrast to high vacuum, where no GFP fluorescence was detected, the presence of a LIF signal at the output of the DMA could explain some specific fluorescent properties of GFP in the gas phase. Given that both conformation and fluorescence are key properties of biological molecules in the gas phase, we expect that our enhanced design will answer the question whether gas-phase proteins retain their liquid-phase native structure or not.

Structure Dependence of Magnetic Properties for Annealed GaMnN Films Grown by MOCVD

GaMnN/GaN multilayers and conventional GaMnN single layers are grown by metal-organic chemical vapor deposition. Both kinds of samples show room-temperature ferromagnetism. After thermal annealing, the sample with GaMnN/GaN multilayer structure displays a larger coercivity and better thermal stability compared to the GaMnN single layer. The annealing effects on VGa related defects are observed from photoluminescence measurements. Moreover, a different magnetic behavior is also found in the annealed GaMnN films grown on different (n-type GaN and p-type GaN) templates. These kinds of structure-dependent magnetic behaviors indicate that defects or carriers transformation introduced during annealing may have important effects on the electronic structure of Mn ions and on the ferromagnetism. Our work may be helpful for further understanding the origin of ferromagnetism in GaN-based diluted magnetic semiconductors.

Solute-Solvent Charge-Transfer Excitations and Optical Absorption of Hydrated Hydroxide from Time-Dependent Density-Functional Theory.

The electronic structure of simple hydrated ions represents one of the most challenging problems in electronic-structure theory. Spectroscopic experiments identified the lowest excited state of the solvated hydroxide as a charge-transfer-to-solvent (CTTS) state. In the present work we report computations of the absorption spectrum of the solvated hydroxide ion, treating both solvent and solute strictly at the same level of theory. The average absorption spectrum up to 25 eV has been computed for samples taken from periodic ab initio molecular dynamics simulations. The experimentally observed CTTS state near the onset of the absorption threshold has been analyzed at the generalized-gradient approximation (GGA) and with a hybrid density-functional. Based on results for the lowest excitation energies computed with the HSE hybrid functional and a Davidson diagonalization scheme, the CTTS transition has been found 0.6 eV below the first absorption band of liquid water. The transfer of an electron to the solvent can be assigned to an excitation from the solute 2pπ orbitals, which are subject to a small energetic splitting due to the asymmetric solvent environment, to the significantly delocalized lowest unoccupied orbital of the solvent. The distribution of the centers of the excited state shows that CTTS along the OH(-) axis of the hydroxide ion is avoided. Furthermore, our simulations indicate that the systematic error arising in the calculated spectrum at the GGA originates from a poor description of the valence band energies in the solution.

A first-principles calculation on electronic structure and optical performance of chromium and nitrogen codoped anatase titanium dioxide

In this article, the supercells of pure anatase titanium dioxide, nitrogen and/or chromium doping anatase titanium dioxide were computed using first-principles with the plane-wave ultrasoft pseudopotentials method, and the electronic structure and optical properties of different ions doping models were also studied. The results indicated that the band gap and charge carriers recombination rate of nitrogen and chromium codoped system are all decreased effectively, and the separation of electron–hole pairs becomes more favorable due to impurity energy levels formation in the band gap of anatase titanium dioxide, which could play an important role in enhancing the catalytic activity and visible light absorption of anatase titanium dioxide. Furthermore, the optical absorption curves of nitrogen and chromium codoped anatase titanium dioxide indicate the highest photoresponse for visible-light, which is consistent with the previous experimental results. The above results would be quite helpful for research guiding and further developing of titanium dioxide photocatalyst.

Insight into Enhanced Cycling Performance of Li-O2 Batteries Based on Binary CoSe2/CoO Nanocomposite Electrodes.

In this study, binary core-shell CoSe2/CoO nanocomposites are synthesized as cathodic electrodes for the Li-O2 cell, which exhibits enhanced cycle performance. From theoretical calculations, aberration-corrected scanning transmission electron microscopy observation, and gas chromatography mass spectrum verification, we propose that an enhanced cycle performance can be attributed to the improvement of the compatibility of the cathode/Li2O2 interface, which results from preferable interaction between Li2O2 intermediates and the CoO "shell" and then reduction of interfacial Li2CO3 formation on the carbon surface. Furthermore, our findings demonstrate that the CoSe2 "core" may impact the electronic structure of surface metal ions, generating a superior cycling performance than that of pristine CoO materials. These results will offer some critical insights into the mechanistic process of Li-O2 batteries.

Theoretical Study on Electronic Structure and Optical Performance of Nickel and Nitrogen Codoped Rutile Titanium Dioxide

The nickel doped, nitrogen doped and nickel + nitrogen codoped rutile titanium dioxide have been investigated by ab initio calculations based on density functional theory. The electronic structure and optical performance of different ions doping models are researched through the obtained results, which reflects that the band gap of nickel and nitrogen codoped system declines apparently; the decrease of electron-hole pairs separation and charge carriers recombination rate becomes more desirable. Moreover, the optical absorption curves of nitrogen and nickel codoped rutile titanium dioxide demonstrate the higher photoresponse for visible-light than that of nickel or nitrogen single doped. The above results could provide theoretical basis for further developing of titanium dioxide photocatalyst and related experimental studies.

X-ray Magnetic Circular Dichroism Investigation of the Electron Transfer Phenomena Responsible for Magnetic Switching in a Cyanide-Bridged [CoFe] Chain

The cyanide-bridged [CoFe] one-dimensional chain, [Co(II)((R)-pabn)][Fe(III)(Tp)(CN)3](BF4)·MeOH·2H2O, where (R)-pabn = (R)-N2,N(2')-bis(pyridin-2-ylmethyl)-1,1'-binaphthyl-2,2'-diamine and Tp = hydrotris(pyrazolyl)borate, exhibits magnetic and electric bistabilities originating from an electron transfer coupled spin transition between Fe-CN-Co pairs. The use of L-edge X-ray absorption spectroscopy (XAS) in combination with L-edge X-ray magnetic circular dichroism (XMCD) is explored for the investigation of the electronic structure and magnetization of Co and Fe ions separately, in both diamagnetic and paramagnetic states. It has been established from susceptibility results that the switching between diamagnetic and paramagnetic phases emanates from electron transfer between low spin Fe(II) and Co(III), resulting in low spin Fe(III) (S = 1/2) and high spin Co(II) (S = 3/2). The XAS and XMCD results are consistent with the bulk susceptibility measurements, where greater detail regarding the charge transfer process is determined. The Fe-CN-Co electron transfer pathway is highlighted by a strongly XMCD dependent transition to a cyanide back bonding orbital, giving evidence for strong hybridization with Fe(III) t2g orbitals. In addition to thermally induced and photoinduced switching, [CoFe] is found to exhibit a switching by grinding induced dehydration. Analysis of XAS shows that on grinding diamagnetic [CoFe], 75% of metal ions lock into the magnetic Co(II)Fe(III) phase. Density functional theory calculations based on the [CoFe] crystal structure in the magnetic and nonmagnetic phases aid the spectroscopic results and provide a complementary insight into the electronic configuration of the [CoFe] 3d shells, quantifying the change in ligand field around Co and Fe centers on charge transfer.

ChemInform Abstract: Electronic Structure of Ions and Molecules in Solution: A View from Modern Soft X‐Ray Spectroscopies

AbstractReview: 130 refs.