3d Ions Research Articles

Valence band spectroscopic study of Co-doped TiO2 nanoparticles using synchrotron based advanced spectroscopic techniques

In this work, we investigate the effects of Co-doping and high-temperature annealing from 400° C to 800 °C on the structural, optical, and electronic characteristics of titanium dioxide (TiO2) nanoparticles (NPs). Sol-gel route was adopted to prepare Ti0.95Co0.05O2 (TCO) NPs. The microstructural characterization using transmission electron microscopy suggests that the grain sizes of TCO NPs enhance with annealing temperatures. The selected area electron diffraction patterns of TCO annealed at 400° C, 600° C, and 800° C show the rings which correspond to anatase, mixed, and rutile phases respectively. Energy dispersive X-ray mapping in scanning transmission electron microscopy mode exhibits the distribution of NPs and their elemental compositions. UV–Visible absorption spectra show a prominent shift to the visible region with slight variation in bandgaps. The electron energy loss spectroscopy confirms the divalent and tetravalent nature of Co and Ti ions respectively. The photo-electron spectroscopic measurements mainly valence band and resonant photoelectron spectroscopies were used to investigate the electronic environment of Co ions in the TiO2 matrix. Valence band spectroscopic results of TiO2 NPs demonstrate the role of O-2p-derived states, but for TCO samples, Co-derived states are also seen. The resonant photo-electron spectra indicate that Co 3d ions are strongly hybridized with Ti3+ defective states.

Terahertz EPR spectroscopy using a 36-tesla high-homogeneity series-connected hybrid magnet

Electron Paramagnetic Resonance (EPR) is a powerful technique to study materials and biological samples on an atomic scale. High-field EPR in particular enables extracting very small g-anisotropies in organic radicals and half-filled 3d and 4f metal ions such as MnII (3d5) or GdIII (4f7), and resolving EPR signals from unpaired spins with very close g-values, both of which provide high-resolution details of the local atomic environment. Before the recent commissioning of the high-homogeneity Series Connected Hybrid magnet (SCH, superconducting + resistive) at the National High Magnetic Field Laboratory (NHMFL), the highest-field, high-resolution EPR spectrometer available was limited to 25 T using a purely resistive “Keck” magnet at the NHMFL. Herein, we report the first EPR experiments performed using the SCH magnet capable of reaching the field of 36 T, corresponding to an EPR frequency of 1 THz for g = 2. The magnet’s intrinsic homogeneity (25 ppm, that is 0.9 mT at 36 T over 1 cm diameter, 1 cm length cylinder) was previously established by NMR. We characterized the magnet’s temporal stability (5 ppm, which is 0.2 mT at 36 T over one-minute, the typical acquisition time) using 2,2-diphenyl-1-picrylhydrazyl (DPPH). This high resolution enables resolving the weak g-anisotropy of 1,3-bis(diphenylene)-2-phenylallyl (BDPA), Δg = 2.5 × 10–4 obtained from measurements at 932 GHz and 33 T. Subsequently, we recorded EPR spectra at multiple frequencies for two GdIII complexes with potential applications as spin labels. We demonstrated a significant reduction in line broadening in Gd[DTPA], attributed to second order zero field splitting, and a resolution enhancement of g-tensor anisotropy for Gd[sTPATCN]-SL.

A comparative study on the local structures of the V4+ and Cu2+ centers in WO3

Abstract The local structures and electron paramagnetic resonance (EPR) parameters (the g factors g i and the hyperfine structure constants A i , with i = x, y, z) of the V4+ and Cu2+ centers in WO3 were theoretically investigated based on the perturbation formulas of the EPR parameters for 3d1 and 3d9 ions under rhombically compressed and elongated octahedra, respectively. In these formulas, the adopted crystal-field parameters (CFPs) are obtained from the superposition model which enables connection of the CFPs and hence the EPR parameters to the rhombic distortion. Based on the calculations, the impurity-ligand distances of the studied [VO6]8− (or [CuO6]10−) cluster are found to suffer the axial compression (or elongation) δz of about 0.098 Å (or 0.132 Å) along the z-axis, and the additional planar bond length variation δr (≈0.052 or 0.047 Å) along x- and y-axis, respectively, due to the Jahn–Teller (JT) effect.

An investigation of CO2 conversion capacity for PCN series doped with different 3d ions (Fe2+, Co2+ and Cu2+)

Three porphyrinic Zr-MOFs (PCN-222, PCN-224 and PCN-226) doped with transition metals (Fe2+, Co2+ and Cu2+) are investigated for the potential application in carbon neutral, including the CO2 capture and conversion capacity as well as the stable cyclicity in the changeable environment. Based on the obtained structure properties, the adsorption quantities of CO2 and adsorption energies of the active sites (Fe2+, Co2+ and Cu2+) are calculated for the three PCN systems. As for the conversion capacity of these PCNs, the entire reduction pathway from CO2 to CH4 via an eight-electron transfer process is depicted by calculating the free energy (ΔG) and the energy barrier (ΔE), which can be modified by the different 3d ions doping. From the high separation efficiency of the products (CH4/CO2) and stability (thermostability in high temperature), the recyclability of these PCN is ultimately evaluated and found favorable for the industrial utilization. Therefore, the present work significantly supports that transition metals doping in different MOFs could yield the promising carbon capture and utilization (CCU) properties.

Robust ferromagnetic insulator and modulated Curie temperature in Ho[formula omitted]CoMnO[formula omitted]: Strain effects

Ferromagnetic insulators (FMI) have gained much attention because of their potential utilization in magnetic tunnel junctions and spin filters as they possess a spin current, which transport magnetic excitations instead of electrical current. Herein, strain (biaxial [110] and hydrostatic [111] impact on the physical properties of monoclinic Ho2CoMnO6 (HCMO) double perovskite oxide is investigated with the inclusion of strong electron correlation and spin–orbit coupling. The structural stability of the unstrained and strained systems is analyzed by computing the formation of enthalpy, which revealed that all the motifs are thermodynamically stable and can be grown at ambient conditions. The unstrained system exhibits an FM order due to a strong correlation between Ho (4f) and Co/Mn (3d) ions and has partial spin magnetic moments of 3.96 and 2.64/2.94 μB, respectively. The Co and Mn ions contain ＋ 2 and ＋ 4 oxidation states having the electronic configuration of t2g5eg2 and t2g3eg0 with 32 spin state, respectively. A definite large indirect band gap Eg of 1.8 eV exists in the valence and conduction band, which confirms the insulating nature of the unstrained HCMO. Furthermore, the estimated Curie temperature (TC) by applying classical Heisenberg Hamiltonian is 84 K, which nearly meets the experimental value of 77 K. Interestingly, it is found that the FM interactions between Ho 4f and Co/Mn 3d ions are energetically stable in all strained motifs as found in unstrained one. Similarly, the insulating nature is also preserved in all strained motifs for the whole considered range. A gradual enhancement in TC value is also observed under the applied strain and a maximum value of 114 K is attributed to the hydrostatic compressive strain of −5%.

Magnetic phase diagram of SmMn[formula omitted]Fe[formula omitted]O[formula omitted] substitutional system

We present the magnetic phase diagram of SmMn1−xFexO3 substitutional solid solution in the whole concentration range 0≤x≤1 as determined from magnetization measurements and as supported by already known data published on this substitutional system. We have found that the evolution of the Néel temperature is very similar to other REMn1−xFexO3 (RE= Pr, Gd, Tb). We have confirmed that very simple magnetic phase diagram for low x concentrations and the complicated one for high x concentrations is typical for all, REMn1−xFexO3 (RE= Pr, Sm, Gd and Tb) compounds. This means that the magnetism in this orthorhombically distorted perovskite series is driven by the 3d ions and the RE ions are responsible only for the minor corrections to the magnetic phases.

Dominance of the cubic Laves phase in the GdТAl substitutional compounds

The GdFeAl compound contains 42.8 wt% of the cubic phase of the MgCu2 (Fd3m)-type and 57.2 wt% of the hexagonal phase of the MgZn2 (P63/mmc)-type, the GdFeSi compound is a tetragonal of the CeFeSi (P4/nmm)-type phase, the GdCrAl and GdVAl compounds do not exist. In the GdFeAl1-xSix, GdFe1-xCrxAl and GdFe1-xVxAl substitutional compounds, the content of the cubic phase sharply increases and amounts to 62.3%, 99% and 99%, respectively, for the composition x = 0.2. The Curie temperature ТС(х) increases for the hexagonal and cubic phases in GdFeAl1-xSix, while for the tetragonal phase it decreases with increasing x. These various changes of ТС(х) are uniformly explained by the corresponding various changes of the density of states at the Fermi level N(EF) in the model of exchange interaction between the R and 3d ions in R-3d intermetallics, in which Tc ∼ N(EF). Ab initio calculations of N(EF) for the cubic, hexagonal and tetragonal phases in the GdFeAl1-xSix compounds have been carried out. The ТС(х) decreases in the GdFe1-xCrxAl and GdFe1-xVxAl systems for the hexagonal and cubic phases with increasing x. The saturation magnetization increases in the GdFeAl1-xSix, GdFe1-xCrxAl and GdFe1-xVxAl systems as x increases.

Gamma-Ray Irradiation Induced Ultrahigh Room-Temperature Ferromagnetism in MoS2 Sputtered Few-Layered Thin Films

Defect engineering is of great interest to the two-dimensional (2D) materials community. If nonmagnetic transition-metal dichalcogenides can possess room-temperature ferromagnetism (RTFM) induced by defects, then they will be ideal for application as spintronic materials and also for studying the relation between electronic and magnetic properties of quantum-confined structures. Thus, in this work, we aimed to study gamma-ray irradiation effects on MoS2, which is diamagnetic in nature. We found that gamma-ray exposure up to 9 kGy on few-layered (3.5 nm) MoS2 films induces an ultrahigh saturation magnetization of around 610 emu/cm3 at RT, whereas no significant changes were observed in the structure and magnetism of bulk MoS2 (40 nm) films even after gamma-ray irradiation. The RTFM in a few-layered gamma-ray irradiated sample is most likely due to the bound magnetic polaron created by the spin interaction of Mo 4d ions with trapped electrons present at sulfur vacancies. In addition, density functional theory (DFT) calculations suggest that the defect containing one Mo and two S vacancies is the dominant defect inducing the RTFM in MoS2. These DFT results are consistent with Raman, X-ray photoelectron spectroscopy, and ESR spectroscopy results, and they confirm the breakage of Mo and S bonds and the existence of vacancies after gamma-ray irradiation. Overall, this study suggests that the occurrence of magnetism in gamma-ray irradiated MoS2 few-layered films could be attributed to the synergistic effects of magnetic moments arising from the existence of both Mo and S vacancies as well as lattice distortion of the MoS2 structure.

The Nature of d0 Ion Effect on the Electrochemical Activity of the O2–/O–-Redox-Couple in Oxyfluorides with the Disordered Rock-Salt Structure

The effect of the nature of the transition metal ion (electron configuration 3d0 and 4d0) on the local structure and electrochemical properties of lithium-rich oxyfluorides with disordered rock-salt structure Li1 + x(MеMn3+)1 – xO2 – yFy, where Mе = Ti4+, Nb5+, 0.2 ≤ x ≤ 0.288 and 0.05 ≤ y ≤ 0.15 is studied. The compounds are thoroughly investigated by the methods of X-ray diffraction analysis, scanning electron microscopy, granulometry, electron spin resonance spectroscopy, and galvanostatic cycling. The galvanostatic-cycling curves of the compounds have two plateaus in the voltage regions of 3.3–3.4 and 4.1–4.3 V. They can be attributed to redox-processes involving two couples: Mn3+/Mn4+ and O2–/O–. In the case of Ti-containing oxyfluorides with disordered rock-salt structure, with the increasing of fluorine content the contribution from O2–/O–-couple during the electrochemical process decreases. In both systems of the oxyfluorides with disordered rock-salt structure we observed formation of paramagnetic clusters Mn3+–O–Mn4+ whose number increased with the increasing of Mn content. The largest clusterization is observed for the sample Li1.266Nb0.217Mn0.55O1.85F0.15. At the same time, the diffusion coefficient for Nb-containing oxyfluorides with disordered rock-salt structure is lower by order of magnitude than for the Ti-containing ones. This may be connected with the strongest clustering of Mn3+ ions, which hinders the Li+ ion macrodiffusion and, as a consequence, deteriorates the kinetics of the process.

The Nature of d0 Ion Effect on the Electrochemical Activity of the O2–/O–-Redox-Couple in Oxyfluorides with the Disordered Rock-Salt Structure

The Nature of d0 Ion Effect on the Electrochemical Activity of the O2–/O–-Redox-Couple in Oxyfluorides with the Disordered Rock-Salt Structure

Electronic Structure and Magneto-Structural Correlations Study of Cu2UL Trinuclear Schiff Base Complexes: A 3d-5f-3d Case.

The magnetic properties of trinuclear Schiff base complexes M2AnLi (MII = Zn, Cu; AnIV = Th, U; Li = Schiff base; i = 1-4, 6, 7, 9), exhibiting the [M(μ-O)2]2U core structure with adjacent M1···U and M2···U and next-adjacent M1···M2 interactions, featuring 3d-5f-3d subsystems, have been investigated theoretically using relativistic ZORA/B3LYP computations combined with the broken symmetry (BS) approach. Bond order and natural population analyses reveal that the covalent contribution to the bonding within the Cu-O-U coordination is important thus favoring superexchange coupling between the transition metal and the uranium magnetic centers. The calculated coupling constants JCuU between the Cu and U atoms, agree with the observed shift from the antiferromagnetic (AF) character of the L1,2,3,4 complexes to the ferromagnetic (ferro) of the L6,7,9 ones. The structural parameters, i.e., the Cu···U distances and the Cu-O-U angles, as well as the electronic factors driving the magnetic couplings are discussed. The analyses are supported by the study of the mixed ZnCuULi and Cu2ThLi systems, where in the first complex the CuII (3d9) ion is replaced by the diamagnetic ZnII (3d10) one, whereas in the second complex the UIV (5f2) paramagnetic center is replaced by the diamagnetic ThIV (5f0) one.

3d Ion-Driven Hexanuclear Heterometallic Clusters with Amazing Structures and Magnetic Properties

By using a heptadentate Schiff base ligand with three NO2 pockets to react with 3d and 4f acetate precursors, three series of M4Ln2 complexes (M, Ln = Ni, Gd for 1NiGd; Ni, Dy for 2NiDy; Co, Gd for 3CoGd; Co, Dy for 4CoDy; Cu, Gd for 5CuGd; Cu, Dy for 6CuDy) have been obtained and characterized. X-ray single-crystal diffraction analyses indicated that Ni4Ln2 series exhibit butterfly structures with extended wings, the Co4Ln2 series are made up of four fused linear defective open cubes, and the Cu4Ln2 series display H-typed topology structures. The dc magnetic susceptibility data revealed that all of the Gd derivatives possess significant magnetic entropy change, whereas the alternating current (ac) magnetic susceptibility measurements identified that only the NiDy derivative displays single-molecule magnet behavior with energy barrier of 15.69 K under zero dc field. These results reveal that 3d ions are important in adjusting the structure and magnetic properties for 3d–4f complexes.

A theoretical study of structure properties and stability in different ligands coordinated Cu-MOFs

A comprehensively theoretical study of structural properties and thermostability is performed to investigate the role of ligands in Metal Organic Frameworks (MOFs). By fitting the experimental EPR spectra, the high order perturbation formulae of a 3 d9 ion in four Cu-MOFs with ligands btm, bte, btp and btb are adopted for orthorhombically and tetragonally elongated octahedral [CuO2N4]12− groups so as to reveal the local environment around central Cu2+, including the detail structure information and local electromagnetic properties. Since the application of MOFs are normally limited by the unsatisfied thermostability, the molecule dynamic (MD) calculation based on density functional theory (DFT) is performed to clarify the influence on the stability of MOFs from the different ligands. Based on the above investigations, the mechanism of ligands substitution in MOFs can be comprehensively understood, which would be useful for designing and synthesizing novel MOFs.

Manganese Luminescent Centers of Different Valence in Yttrium Aluminum Borate Crystals.

We present an extensive study of the luminescence characteristics of Mn impurity ions in a YAl3(BO3)4:Mn crystal, in combination with X-ray fluorescence analysis and determination of the valence state of Mn by XANES (X-ray absorption near-edge structure) spectroscopy. The valences of manganese Mn2+(d5) and Mn3+(d4) were determined by the XANES and high-resolution optical spectroscopy methods shown to be complementary. We observe the R1 and R2 luminescence and absorption lines characteristic of the 2E ↔ 4A2 transitions in d3 ions (such as Mn4+ and Cr3+) and show that they arise due to uncontrolled admixture of Cr3+ ions. A broad luminescent band in the green part of the spectrum is attributed to transitions in Mn2+. Narrow zero-phonon infrared luminescence lines near 1060 nm (9400 cm-1) and 760 nm (13,160 cm-1) are associated with spin-forbidden transitions in Mn3+: 1T2 → 3T1 (between excited triplets) and 1T2 → 5E (to the ground state). Spin-allowed 5T2 → 5E Mn3+ transitions show up as a broad band in the orange region of the spectrum. Using the data of optical spectroscopy and Tanabe-Sugano diagrams we estimated the crystal-field parameter Dq and Racah parameter B for Mn3+ in YAB:Mn as Dq = 1785 cm-1 and B = 800 cm-1. Our work can serve as a basis for further study of YAB:Mn for the purposes of luminescent thermometry, as well as other applications.

Simulating Spin–Orbit Coupling with Quasidegenerate N-Electron Valence Perturbation Theory

We present the first implementation of spin-orbit coupling effects in fully internally contracted second-order quasidegenerate N-electron valence perturbation theory (SO-QDNEVPT2). The SO-QDNEVPT2 approach enables the computations of ground- and excited-state energies and oscillator strengths combining the description of static electron correlation with an efficient treatment of dynamic correlation and spin-orbit coupling. In addition to SO-QDNEVPT2 with the full description of one- and two-body spin-orbit interactions at the level of two-component Breit-Pauli Hamiltonian, our implementation also features a simplified approach that takes advantage of spin-orbit mean-field approximation (SOMF-QDNEVPT2). The accuracy of these methods is tested for the group 14 and 16 hydrides, 3d and 4d transition metal ions, and two actinide dioxides (neptunyl and plutonyl dications). The zero-field splittings of group 14 and 16 molecules computed using SO-QDNEVPT2 and SOMF-QDNEVPT2 are in good agreement with the available experimental data. For the 3d transition metal ions, the SO-QDNEVPT2 method is significantly more accurate than SOMF-QDNEVPT2, while no substantial difference in the performance of two methods is observed for the 4d ions. Finally, we demonstrate that for the actinide dioxides the results of SO-QDNEVPT2 and SOMF-QDNEVPT2 are in good agreement with the data from previous theoretical studies of these systems. Overall, our results demonstrate that SO-QDNEVPT2 and SOMF-QDNEVPT2 are promising multireference methods for treating spin-orbit coupling with a relatively low computational cost.

Syntheses and magnetic properties of a bis-bidentate nitronyl nitroxide radical based on triazolopyrimidine and its metal complexes.

A novel bis-bidentate nitronyl nitroxide radical based on triazolopyrimidine, NIT-2-TrzPm (NIT-2-TrzPm = (2-(2'-triazolopyrimidine)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxy-3-oxide)) and six new transition metal complexes of this ligand, namely [M(hfac)2(NIT-2-TrzPm)]·CH2Cl2 (M = Mn (1Mn) and Co (2Co)), [M(hfac)2]2(NIT-2-TrzPm) (M = Mn (3Mn) and Co (4Co)), [Mn(NIT-2-TrzPm)2(MeOH)2](ClO4)2·MeOH (5Mn), and [Co(NIT-2-TrzPm)2(MeOH)2]2(ClO4)4·4MeOH (6Co) were prepared and characterized structurally and magnetically. These complexes can be selectively synthesized by controlling the reaction ratio of M(hfac)2·2H2O to the radical ligand (for 1Mn to 4Co) or using metal perchlorates as the starting materials (for 5Mn and 6Co). Single crystal X-ray crystallographic analyses confirmed that 1Mn and 2Co are isostructural 3d-2p MII-radical complexes, in which the NIT-2-TrzPm radical acts as a terminal bidentate ligand chelating to one 3d ion, while 3Mn and 4Co are isostructural 3d-2p-3d MII-radical-MII complexes with the NIT-2-TrzPm radical acting as a bridging ligand between two 3d ions. For complexes 5Mn and 6Co, two NIT-2-TrzPm ligands from the equatorial positions coordinate with the metal center to form the 2p-3d-2p structures with the axial positions occupied by two methanol molecules. Magnetic analysis on the MnII complexes revealed the existence of a strong antiferromagnetic interaction between the MnII and the NIT radical spin, while weak ferromagnetic coupling for Mn⋯Mn and Rad⋯Rad in the Mn-NIT-Mn and Rad-Mn-Rad spins was confirmed. Interestingly, although the NIT-bridged complexes 3Mn and 4Co possess significantly different magnetic anisotropy, field-induced slow magnetic relaxation can be observed in both complexes, which was assigned to the phonon bottleneck effect for 3Mn and field-induced SMM behavior for 4Co. To the best of our knowledge, 3Mn is the first example of the NIT-bridged binuclear MnII complex undergoing slow magnetic relaxation.

Анти-ян-теллеровское диспропорционирование и перспективы спин-триплетной сверхпроводимости в соединениях d-элементов

We argue that the unusual properties of a wide class of materials based on Jahn-Teller 3d and 4d ions with different crystal and electronic structures, from quasi-two-dimensional unconventional superconductors (cuprates, nickelates, ferropnictides/chalcogenides, ruthenate SrRuO4), manganites with local superconductivity to 3D ferrates (CaSr)FeO3, nickelates RNiO3 and silver oxide AgO with unusual charge and magnetic order can be explained within a single scenario. The properties of these materials are related to the instability of their highly symmetric Jahn-Teller "progenitors" with the ground orbital E-state to charge transfer with anti-Jahn-Teller disproportionation and the formation of a system of effective local composite spin-singlet or spin-triplet, electronic or hole bosons moving in a non-magnetic or magnetic lattice. These unusual systems are characterized by an extremely rich variety of phase states from non-magnetic and magnetic insulators to unusual metallic and superconducting states.

Oxygen-deficient dopant-free Ti3O5 and Ti2O3 ferromagnetic two-dimensional nanostructures for spin-based electronic devices

In reduced two-dimensional titanium suboxide (TinO2n−1, n = 2, 3, 4…) nanostructures, exchange interactions between the reduced d1 ions and singly charged oxygen vacancy defects induce a remarkably strong dilute ferromagnetic property.

Ag(III)···Ag(III) Argentophilic Interaction in a Cofacial Corrole Dyad.

Metallophilic interactions between closed-shell metal centers are exemplified by d10 ions, with Au(I) aurophilic interactions as the archetype. Such an interaction extends to d8 species, and examples involving Au(III) are prevalent. Conversely, Ag(III) argentophilic interactions are uncommon. Here, we identify argentophilic interactions in silver corroles, which are authentic Ag(III) species. The crystal structure of a monomeric silver corrole is a dimer in the solid state, and the macrocycle exhibits an atypical domed conformation. In order to evaluate whether this represents an authentic metallophilic interaction or a crystal-packing artifact, the analogous cofacial or "pacman" corrole was prepared. The conformation of the monomer was recapitulated in the silver pacman corrole, exhibiting a short 3.67 Å distance between metal centers and a significant compression of the xanthene backbone. Theoretical calculations support the presence of a rare Ag(III)···Ag(III) argentophilic interaction in the pacman complex.

Spin–orbit coupling, orbitally entangled antiferromagnetic order, and collective spin–orbital excitations in

With electron filling n = 1 in the compound, the octahedrally coordinated orbitals are strongly active when the tetragonal distortion induced crystal field is tuned by external agent such as pressure. Considering the full range of crystal field induced tetragonal splitting in a realistic three-orbital model, collective spin–orbital excitations are investigated using the generalized self-consistent plus fluctuation approach. At ambient pressure, an entangled orbital + antiferromagnetic order is found to be stabilized beyond a critical value (∼30 meV) of spin–orbit coupling which is in the realistic range for 3d ions. The behavior of the calculated energy scales of collective excitations with crystal field is consistent with that of the transition temperatures with pressure as obtained from susceptibility and resistivity anomalies in high-pressure studies.