Number Of 3d Electrons Research Articles

Structural, electronic and magnetic properties of 8-hydroxyquinoline-based small molecules TMQx (TM=Cr, Mn, Fe, Co, Ni, Cu, Zn, and x=2 or 3)

The structural, electronic and magnetic properties of 8-hydroxyquinoline-based small molecules TMQx (TM=Cr, Mn, Fe, Co, Ni, Cu and Zn, and x=2 or 3) are systemically studied from first principles. These small molecules are spin-polarized semiconductors except for NiQ2, ZnQ2, and CoQ3. For TMQ2, the magnetic moments can be expressed as 8-nµB (n is the number of 3d electrons of TM ions. For Mn, Fe, Co, and Ni, n=5, 6, 7, and 8 respectively) and 10-nµB (n=9 and 10 for Cu and Zn, respectively). For TMQ3, the magnetic moments can be expressed as 6-nµB (n=3, 4, 5, 6 for Cr, Mn, Fe, and Co, respectively). The magnetism can be explained by the spin-polarized filling of splitting d orbitals on the basis of the crystal field theory. This provides theoretical insight for better understanding of 8-hydorquinoline-based complexes (TMQx).

Charge disproportionation in tetragonal La2MoO5, a small band gap semiconductor influenced by direct Mo-Mo bonding.

The structure of the novel compound La2MoO5 has been solved from powder X-ray and neutron diffraction data and belongs to the tetragonal space group P4/m (no. 83) with a = 12.6847(3) Å and c = 6.0568(2) Å and with Z = 8. It consists of equal proportions of bioctahedral (Mo2O10) and square prismatic (Mo2O8) dimers, both of which contain direct Mo-Mo bonds and are arranged in 1D chains. The Mo-Mo bond length in the Mo2O10 dimers is 2.684(8) Å, while there are two types of Mo2O8 dimers with Mo-Mo bonds lengths of 2.22(2) and 2.28(2) Å. Although the average Mo oxidation state in La2MoO5 is 4+, the very different Mo-Mo distances reflect the fact that the Mo2O10 dimers contain only Mo(5+) (d(1)), while the prismatic Mo2O8 dimers only contain Mo(3+) (d(3)), a result directly confirmed by density function theory calculations. This is due to the complete disproportionation of Mo(4+), a phenomenon which has not previously been observed in solid-state compounds. La2MoO5 is diamagnetic, behavior which is not expected for a nonmetallic transition-metal oxide whose cation sites have an odd number of d-electrons. The resistivity displays the Arrhenius-type activated behavior expected for a semiconductor with a band gap of 0.5 eV, exhibiting an unusually small transport gap relative to other diamagnetic oxides. Diffuse reflectance studies indicate that La2MoO5 is a rare example of a stable oxide semiconductor with strong infrared absorbance. It is shown that the d-orbital splitting associated with the Mo2O8 and Mo2O10 dimeric units can be rationalized using simple molecular orbital bonding concepts.

Magnetic and Quantum Transport Properties of Small-Sized Transition-Metal-Pentalene Sandwich Cluster

The chemical bonds and magnetic and quantum transport properties of small-sized transition-metal-pentalene sandwich clusters TM2nPnn+1 (TM = V, Cr, Mn, Co, and Ni; n = 1, 2) were investigated by using density functional theory and nonequilibrium Green’s function method. Theoretical results show that TM2nPnn+1 sandwiches have high stabilities. The TM–TM bond order gradually decreases with the increase of 3d electron number of TM atoms and TM2nPnn+1 could exhibit different spin states. With Au as two electrodes, significant spin-filter capability was observed in TM2nPnn+1, and such a filter can be switched on/off by changing the spin state. In addition, giant magnetoresistance was also found in the systems. These interesting quantum transport properties indicate that TM2nPnn+1 sandwiches are promising materials for designing molecular junction with different functions.

Metalloporphyrins with all the pyrrole nitrogens replaced with phosphorus atoms, MP(P)4 (M = Sc, Ti, Fe, Ni, Cu, Zn)

We performed first systematic DFT study of the structures and electronic features (frontier orbitals energies, HOMO/LUMO and optical gaps, IPs and EAs) of the MP(P)4 compounds, with increasing number of d-electrons: 3d14s2 (Sc)→3d24s2 (Ti)→3d64s2 (Fe)→3d84s2 (Ni)→3d104s1 (Cu)→3d104s2 (Zn). We performed systematic comparison with the tetrapyrrole MP counterparts. Complete substitution of the pyrrole nitrogens by P-atoms does not change the calculated ground spin state of the compound. All the MP(P)4 species adopt a bowl-like shape, compared to generally planar or slightly distorted shapes of their MP counterparts. Significant positive charge accumulates on P-atoms in MP(P)4. Positive charges on the metals in MP(P)4 are noticeably lower than in the MP counterparts. The calculated MP(P)4 HOMO/LUMO gaps and optical gaps are noticeably smaller than the corresponding gaps in their MP counterparts, which is explained by stabilization of the MP(P)4 LUMOs.

Core and Valence Structures in Kβ X-ray Emission Spectra of Chromium Materials

We analyze the core and valence transitions in chromium in a series of materials with a number of different ligands and including the oxidation states: CrII, CrIII, CrIV, and CrVI. To study the core-to-core transitions we employ the CTM4XAS program and investigate the shapes, widths, intensities, and energy positions of the Kβ1,3 and Kβ′ lines in each oxidation state. The theoretical spectra are compared with experimental data obtained with synchrotron radiation. We found that the Kβ1,3 peak shifts to higher energy with increasing spin state. In addition, the widths of the Kβ1,3 peak increases as the oxidation state decreases, which we explain from the increased spread of the multiplet structures. In the Kβ′ structure the presence of two peaks in CrII, CrIII, and CrIV is due to the large 3p3d exchange interaction. For the analysis of the valence transitions we utilize the DV-Xα method. We study the dependence of the relative intensities of the Kβ″ and Kβ2,5 structures on symmetry, bond length, and the effective number of 3d and 4p electrons in different chemical environments.

Estimating Hybridization of Transition Metal and Oxygen States in Perovskites from O K-edge X-ray Absorption Spectroscopy

The interaction between the transition metal 3d and the oxygen 2p states via hybridization underpins many of the phenomena in transition metal oxide materials. We report the empirical trend of this interaction using the pre-edge feature of the O K-edge X-ray absorption spectrum. Our assessment method is built on the dipole approximation and the configuration interaction between the transition metal 3d and the oxygen 2p states. We found that hybridization increases with the number of 3d electrons, consistent with the expected electronegativity trend. We support this analysis with density functional calculations, which reveal a systematic increase in the transition metal 3d and the oxygen 2p state mixing with increasing 3d-electron number. Oxidation of the transition metal was also found to increase hybridization, which we believe reflects the reduced transition metal 3d and oxygen 2p energy difference, causing increased covalency. We compare the analysis from the surface-sensitive electron-yield and the bu...

Formation Processes of Zinc Excimer Thin Films Due to Ion-Recombination Processes

In materials science, the number of d-electrons of transition metals is an essentially important factor controlling characteristics of alloys and compounds. In this paper, we show an example to control the number of d-electrons (holes) by using inner-core electron excitation of zinc atoms. An important feature of our research is that we can make a long lifetime excited electronic state of zinc (3d8), and the life-time of excited zinc is more than 307 days. At first, the experimental apparatus and boundary conditions of the ion-recombination processes were explained. From results of XPS, excited zinc films showed satellites peaks what caused by the final state of 3d8 and the charge transfer final state of 3d10L2. Excited states of zinc were formatted at the surface of substrate caused by ion-recombination process between Zn+ and Zn-. The excited zinc diffused from substrate surface to the surface of the excited zinc thin film. Intensity of excited zinc is proportional to the intensity of electron on the substrate.

Magnetic silicon carbide nanotubes by 3d transition metal atom functionalization

Abstract Interaction of 3d transition metal atoms with ( 3 , 3 ) , ( 5 , 5 ) , ( 7 , 7 ) , and ( 9 , 9 ) SiC nanotubes has been studied using hybrid density functional PBE0 and an all electron basis set 6 - 31 G ⁎ ⁎ . The interaction energy between transition metal and silicon carbide nanotubes depends both on the number of d-electrons and on the curvature of the nanotubes, with this energy, in general, increasing with increase in curvature. Except for the nanotubes functionalized by Ni and Zn, all 3d transition metal-functionalized nanotubes indicate magnetic ground states. The silicon carbide nanotubes doped with transition metals have significantly lower band gaps, in general, than those of bare nanotubes.

Non-collinear ferrimagnetic phases in the Fe2−xMnxAs system

The stabilization mechanisms of non-collinear magnetically ordered phases observed in the Fe2−xMnxAs system with 1.19 ≤ x ≤ 1.365 are considered within the framework of a model approach that uses the number of d-electrons and the form of density of their electron states, obtained from ab initio calculations. It is found that the energy stability of non-collinear structures and the kind of order-order phase transitions are determined by electron filling of the d-band and by the form of density of d-electron states, which depend on the manganese content. It is demonstrated that the pressure features of spontaneous and magnetic field-induced order-order transitions are related to a character of renormalization of the electronic structure under pressure.

Predicting adsorption on metals: simple yet effective descriptors for surface catalysis

We present a simple and efficient model for predicting the adsorption of molecules on metal surfaces. This heuristic model uses six descriptors for each metal (number of d-electrons, surface energy, first ionization potential and atomic radius, volume and mass) and three for each adsorptive (HOMO-LUMO energy gap, molecular volume and mass). Strikingly, despite its simplicity and low computational cost, this model predicts well the chemisorption of a range of adsorptives (H2, HO˙, N2, CO, NO, O2, H2O, CO2, NH3 and CH4) on a range of metals (Fe, Co, Ni, Cu, Mo, Ru, Rh, Pd, Ag, W, Ir, Pt and Au) as calculated with DFT and taken from the literature. Using only a third of the data for fitting, the rest of the data were predicted with Q(2) = 0.91-0.95 and RMSEP = 0.94-1.16 eV. Furthermore, we measured experimental adsorption data for CO, CO2, CH4, H2, N2 and O2 on Ni, Pt and Rh supported on TiO2. Using the same descriptors, we then constructed a model for this experimental data set. Once again, the model explained the data well, with R(2) = 0.95 and Q(2) = 0.86, respectively.

Noncollinear magnetic ordering in a magnetic dimer supported on a metallic substrate

Self-consistent electronic structure calculations for a magnetic dimer supported on a metal surface are performed on the basis of the microscopic Hamiltonian for itinerant electrons. The possibility of a noncollinear ground state in the absence of spin-orbit interaction and magnetic frustration is shown. The effective exchange interaction of moments is determined by the number of quasi-localized d-electrons per atom and, in general, is not described by the Heisenberg model.

Covalency, double-counting, and the metal-insulator phase diagram in transition metal oxides

Dynamical mean field theory calculations are used to show that for late transition-metal-oxides a critical variable for the Mott/charge-transfer transition is the number of d-electrons, which is determined by charge transfer from oxygen ions. Insulating behavior is found only for a narrow range of d-occupancy, irrespective of the size of the intra-d Coulomb repulsion. The result is useful in interpreting 'density functional +U' and 'density functional plus dynamical mean field' methods in which additional correlations are applied to a specific set of orbitals and an important role is played by the 'double counting correction' which dictates the occupancy of these correlated orbitals. General considerations are presented and are illustrated by calculations for two representative transition metal oxide systems: layered perovskite Cu-based "high-Tc" materials, an orbitally non-degenerate electronically quasi-two dimensional systems, and pseudocubic rare earch nickelates, an orbitally degenerate electronically three dimensional system. Density functional calculations yield d-occupancies very far from the Mott metal-insulator phase boundary in the nickelate materials, but closer to it in the cuprates, indicating the sensitivity of theoretical models of the cuprates to the choice of double counting correction and corroborating the critical role of lattice distortions in attaining the experimentally observed insulating phase in the nickelates.

Discotic liquid crystals of transition metal complexes 45: parity effect of the number of d-electrons on stacking distances in the columnar mesophases of octakis-(m-alkoxyphenoxy)phthalocyaninato metal(II) complexes

We have synthesized 34 novel homologous discotic liquid crystals, octakis(m-alkoxyphenoxy)phthalocyaninato metal(II) {abbreviated as (m- CnOPhO)8PcM (M = Co(1), Ni(2), Cu(3), Zn(4) and H2 (5); n = 8(a), 10(b), 12(c), 14(d), 16(e), 18(f) and 20(g))}, and investigated parity effect of the number of d-electrons on the stacking distances in their columnar mesophases. It was revealed from temperature-dependent wide angle X-ray diffraction studies that each of the cobalt(II) (d7) complexes (1a–1g) and the copper(II) (d9) complexes (3b–3g) showed a single hexagonal ordered columnar (Colho) mesophase with a very short stacking distance at 3.3 Å, and that the nickel(II) (d8) complexes (2a–2g) and the metal-free (d0) derivatives (5a–5g) showed a single pseudo-hexagonal ordered columnar (Colrho) mesophase with a little bit longer stacking distances at 3.4 Å. Very interestingly, the nickel complex (2a) and metal-free derivatives (5a–5c) gave an extremely big (001) reflection peak with the second (002) reflection peak. Furthermore, the zinc(II) (d10) complexes (4a–4g) showed two different rectangular ordered columnar mesophases, Colro(P2/m) and Colro(P21/a), with a little bit longer stacking distance at 3.4 Å. Thus, the shorter stacking distance, 3.3 Å, appeared for the odd number of d-electrons, whereas the longer stacking distance, 3.4 Å, appeared for the even number of d-electrons. Hence, the stacking distances depend on parity of the number of d-electrons in the central metal(II). To our best knowledge, it is the first example of parity effect on the stacking distances in columnar mesophases.

Magnetic field induced order–order phase transition in magnetocaloric systems Mn2−xFexAs0.5P0.5 and MnFeAsyP1−y

An analysis is presented of experimental and theoretical results of the MnFeAsyP1−y (0.15≤y≤0.66) and Mn2−xFexAs0.5P0.5 (0.5≤x≤1.0) systems to identify main traits that underlie the mechanism of formation of different antiferromagnetic (AF) phases in the two systems. The discrepancy between the calculated from first principles and experimental values of the magnetic moment in the ferromagnetic phase with cation substitution in the system Mn2−xFexAs0.5P0.5 is due to the appearance of a canted magnetic structure. In this case, the emergence of an AF phase with decreasing iron concentration precedes a significant change in the electronic d-band filling. In the model of the spiral structure in the system of itinerant electrons it is shown that the stabilization of the AF phase with decreasing arsenic concentration, while maintaining the number of d-electrons, is a consequence of changes in the shape of the density of electronic states that occur with a decrease in unit-cell volume.

Magnetization reversal process at atomic scale in systems with itinerant electrons

The magnetic response of itinerant electrons systems to an external magnetic field is investigated on the basis of a microscopic Hamiltonian from which the spin-polarized electronic structure is determined. The magnetic moment and grand thermodynamic potential of the d-electronic subsystem on a particular atomic site in the presence of the external field are calculated as a function of the moment’s orientation for fixed electron configuration of its local environment. Self-consistent magnetic solutions strongly depend on the d-electron number, determined by the position of the d level relative to the Fermi energy. For parameters corresponding to α-Fe, two branches of self-consistent solutions with high and low magnetic moments are found. For parameters corresponding to bulk Cr, a Fe impurity in the Cr matrix and a Cr impurity in the Fe matrix, there are only low-spin solutions. The theory is also applied for describing magnetization reversal processes in exchange spring magnets. A slab of Fe was considered as a soft magnetic layer. The influence of the hard magnet is modeled by the inclusion of an external magnetic field applied to the interface Fe layers. The dependence of the hysteresis loop on the thickness of the Fe slab and on the value of the interface field is investigated.

Magnetic properties of single crystals of the Cr x Mn1 − x S solid solutions (0 ≤ x < 0.3)

The CrxMn1 − xS single crystals have been synthesized based on manganese monosulfide as a result of cation substitution, and their magnetic properties have been studied. It has been established that the CrxMn1 − xS solid solutions with a face-centered cubic NaCl structure are formed in the concentration region 0 ≤ x < 0.3. The unit cell parameter of the solid solution decreases as the degree of substitution increases due to the variation in the ionic radius of cations. These substances are antiferromagnets. An increase in the degree of cation substitution in the CrxMn1 − xS solid solutions is accompanied by a decrease in the number of 3d electrons in the d shell of manganese monosulfide and causes a decrease in the magnetic transition temperature from 149 K (x = 0) to 96 K (x = 0.29), which differs from previously known results.

AES and XPS investigations of the surface layers of porous silicon with Fe, Co, and Ni embedded pores

A Composite material of porous silicon with pore embedded d-metals por-Si(Me) can be used for fabricating memory cells. Por-Si layers have been produced by electrochemical etching of n-type silicon (100) according to the conventional process. Fe, Co, and Ni galvanic deposition in por-Si has been performed using aqueous solutions of corresponding sulfate salts. The Auger profiles of the obtained por-Si(Fe), por-Si(Co), por-Si(Ni) nanocomposites have shown that its surface layers (up to 40 nm thick) contained about 10% Fe and no more than 1% Co and Ni. These facts confirm data that Co and Ni, unlike Fe, penetrate deep into the silicon pores. The value of the magnetic moment for the nanocrystalline Ni atom incorporated into the por-Si(Ni) has been estimated based on the dependence of the relative intensity of the maxima for the 3s multiplet splitting of the X-ray phase spectra on the number of uncoupled d-electrons in systems with 3d metals. The obtained value ∼2.4 μB exceeds the atomic magnetic moment in bulk metallic Ni.

Mott transition in multiorbital models for iron pnictides

The bad-metal behavior of the iron pnictides has motivated a theoretical description in terms of a proximity to Mott localization. Since the parent compounds of the iron pnictides contain an even number of 3d-electrons per Fe, it is important to determine whether a Mott transition robustly exists and the nature of the possible Mott insulating phases. We address these issues in a minimal two-orbital model and a more realistic four-orbital model for the parent iron pnictides using a slave-spin approach. In the two-orbital model with two electrons per Fe, we identify a transition from metal to Mott insulator. The critical coupling, $U_c$, is greatly reduced by the Hund's coupling. Depending on the ratio between the inter- and intra-orbital Coulomb repulsions, the insulating state can be either a spin-Mott insulator or an orbital-Mott insulator. In the four-orbital model with four electrons per Fe, we find an orbitally selective metal-to-insulator transition in the case of zero Hund's coupling; the transition to a Mott insulator in the $xz$ and $yz$ orbitals takes place at the same critical coupling as the transition to a band insulator in the $xy$ and $x^2-y^2$ orbitals. In the presence of a finite Hund's coupling, however, the localization transition is into a spin-Mott state.

Surface Electronic/Atomic Structure and Activation Energy on Pt(111), Pt3Cu(111), and PtCu(111) for PEFC Cathode

Theoretical analysis of oxygen reduction reaction (ORR) on cathode Pt(111), Pt3Cu(111), and PtCu(111) surfaces in a polymer electrolyte fuel cell (PEFC) is performed to investigate the ORR mechanisms on Pt(111) and the effect of alloying. From density functional theory (DFT) calculations, we found that the difference in adsorption energy of O2 molecules on the surface has a strong relation with the number of d-electrons and the position of the d-band center of the surface Pt atoms. From the results of the activation energy calculations using the unity bond index–quadratic exponential potential (UBI-QEP) method, we show that the oxygen atom coverage on Pt(111) surface has a strong influence on the ORR activity. In addition, it was found that Pt3Cu(111) and PtCu(111) surfaces have lower coverage compared with that of Pt(111) surface, which results in the enhancement of ORR activity.

Ab initio calculations of MgH 2, MgH 2:Ti and MgH 2:Co compounds

The understanding of hydrogen bonding in magnesium and magnesium based alloys is an important step toward its prospective use. In the present study, a density functional theory (DFT) based, full-potential augmented plane waves method of calculation, extended with local orbitals (FP-APW+lo), was used to investigate the stability of MgH 2 and MgH 2:TM (TM = Ti and Co) 10 wt % alloys and the influence of this alloying on hydrogen storage properties of MgH 2 compound. Effects of a possible spin polarisation induced in the system by transition metal (TM) ions were considered too. It has been found that TM-H bonding is stronger than the Mg–H bond, but at the same time it weakens other bonds in the second and third coordination around a TM atom, which leads to overall destabilization of the MgH 2 compound. Due to a higher number of d-electrons, this effect is more pronounced for Co alloying, where in addition, the spin polarisation has a noticeable and stabilising influence on the compound structure.