States Of Transition Metal Ions Research Articles

Fabrication of zirconium borosilicate glasses using municipal waste ash for radiation shielding applications; optical and structural investigations

In this study, three borosilicate glass systems were successfully prepared by using the melting–annealing technique from municipal waste ash and doped with ZrO2 at 0, 0.1, and 0.3 wt.%. The glasses were analyzed by electron dispersive X-ray spectroscopy (EDX), which indicated their rich compositions with various metal ions, and X-ray diffraction analysis (XRD) confirmed their amorphous glassy nature. The effects of gamma radiation at 80 kGy on the optical, physical, structural, and chemical properties of the glasses were evaluated. The optical spectra contained ultraviolet peaks at 260–340 nm and visible peaks at 440–470 nm due to the different valence states of transition metal ions, e.g., Ti4+/Ti3+, Cu2+/Cu+, Zn2+, Fe3+/Fe2+, and/or Zr4+. The optical band gap energy (Egap) decreased from 2.0 to 1.0 eV and from 2.8 to 1.90 eV for indirect and direct transitions after irradiation, respectively, whereas the linear refractive index (n) increased. Fourier transform-infrared spectroscopy (FTIR) indicated high structural stability against irradiation due to the connected borosilicate network comprising trigonal BO3 and tetrahedral BO4 and SiO4 units. The band at 960 cm−1 in the undoped and 0.1% Zr4+ glasses shifted to 980 cm−1 in 0.3% Zr4+ glass because of the different compositions and silica contents of the glasses. Analysis of the chemical durability of the glasses in H2O at 100 °C indicated their high chemical stability before and after irradiation with a weight loss not exceeding 0.05%. BO3, BO4, SiO4, transition metal ions, and ZrO2 all contributed to the compact structure of the glasses, and their high stability against irradiation indicates the potential applications of the glasses in radiation shielding.

Modulating the doping state of transition metal ions in ZnS for enhanced photocatalytic activity.

Transition metal ions (M = Ag+, Cu2+, Co2+, and Cr3+) are surface or homogeneously doped into ZnS via facile cation-exchange reaction, and while Ag+ and Cu2+ doping does not induce sulphur vacancies (Vs) or zinc vacancies (VZn), Co2+ and Cr3+ doping induces Vs. The surface doped catalysts exhibit greatly higher activity than the ZnS and homogenous doped catalysts for H2 evolution and CO2 reduction. The important role of the doping state on affecting the photo-absorption, carrier separation efficiency, and photoreaction kinetics has been systemically investigated and proposed. This work sheds light on the future design and fabrication of high-performance photocatalysts by element doping.

Density-Based Descriptors of Redox Reactions Involving Transition Metal Compounds as a Reality-Anchored Framework: A Perspective

Description of redox reactions is critically important for understanding and rational design of materials for electrochemical technologies, including metal-ion batteries, catalytic surfaces, or redox-flow cells. Most of these technologies utilize redox-active transition metal compounds due to their rich chemistry and their beneficial physical and chemical properties for these types of applications. A century since its introduction, the concept of formal oxidation states (FOS) is still widely used for rationalization of the mechanisms of redox reactions, but there exists a well-documented discrepancy between FOS and the electron density-derived charge states of transition metal ions in their bulk and molecular compounds. We summarize our findings and those of others which suggest that density-driven descriptors are, in certain cases, better suited to characterize the mechanism of redox reactions, especially when anion redox is involved, which is the blind spot of the FOS ansatz.

Improving Na+ Diffusion and Performance of P2-Type Layered Na0.6Li0.07Mn0.66Co0.17Ni0.17O2 by Expanding the Interplanar Spacing.

Because of their high reversible capacity and wide operation voltage window, P2-type layered transition metal oxides are considered as one type of potential cathode candidate for sodium-ion batteries. However, they still suffer from low kinetics, phase degeneration, and ambiguous mechanism of Na+ diffusion. Here, we synthesized a P2-type Na0.6Li0.07Mn0.66Co0.17Ni0.17O2 with a high Na+ diffusion performance by sintering a nanoplate-structural precursor with alkali metal salt and proposed a possible mechanism for improving Na+ diffusion. The as-prepared P2-type layered oxide presents a quasi-hexagon shape and demonstrates a discharge capacity of 87 mAh g-1 at a current density of 875 mA g-1 (5 C rate), twice that of the sample synthesized from a non-nanoplate particle precursor. Rietveld refinement and results of X-ray photoelectron spectroscopy reveal the probable mechanism that the expanded interplanar spacing along the c-axis orientation would facilitate Na+ diffusion during Na+ intercalation/deintercalation processes, and the expanded interplanar spacing may arise from a high oxidation state of transition metal ions.

Extraordinary magnetic properties of double perovskite Eu2CoMnO6 wide band gap semiconductor

Some novel magnetic behaviours in double perovskite Eu2CoMnO6 (ECMO) have been reported. The x-ray photoemission spectroscopy study shows the presence of mixed valence states of transition metal ions. The UV–visible absorption spectroscopic study suggests that the ECMO has a direct wide band gap. A second-order magnetic phase transition as a sudden jump in the magnetization curve has been observed around 124.5 K. The large bifurcation between the zero field cooling and field cooling, suggests existence of strong spin frustration in the system. The inverse DC susceptibility confirms the presence of the Griffiths like phase. Sharp steps in magnetization have been observed in the M–H curve at 2 K, which vanishes on increasing temperature. The AC susceptibility study demonstrates the Hopkinson like effect as well as the presence of volume spin-glass-like behaviour. The temperature dependent Raman spectrum shows the presence of spin–phonon coupling.

Structural properties and electrical conductivity mechanisms of semiconducting quaternary nanocomposites: Effect of two transition metal oxides

Several quaternary nanocomposites, doped with two transition metal oxides, of the generalised composition formula 0.4ZnO–0.1P2O5–0.5[xV2O5–(1-x) MoO3] were prepared via the melt quenching process. We investigated the microstructural and conductivity properties of two ternary systems and four quaternary systems to determine the better semiconductor nanocomposite system for wider application purposes. The X-ray diffraction results showed the presence of superposed nanocrystallites within amorphous networks or matrices. Analysis of ultraviolet–visible absorption spectra showed that optical bandgap energy (Eopt) values varied with V2O5 concentration, and there was an inverse relationship between Eopt and average nanocrystallite size. The responsible mechanisms of ac conductivity were examined using the model of Jonscher's universal power-law and Almond–West formalism, and it was found that ac conductivity increased as temperature rose, exhibiting semiconducting features. All the ternary (two examples) and quaternary (four examples) nanocomposite systems established non-linearity in dc conductivity, caused by the small polaron hopping process with dissimilar activation energies at different temperature regions. The power-law exponent (s) of Jonscher's universal power-law revealed that the ac conductivity mechanism could be described by correlated barrier-hopping (CBH) or non-overlapping small polaron tunnelling (NSPT) models for different samples due to major structural alterations. We applied modified CBH and NSPT models (as s > 0.8) to get realistic values of different fitting parameters, and in this process, we also obtained the values of ideal or hypothetical glass transition temperature from the theoretical models. The different activation energies associated with ac conductivity and for the small polaron migration process diminished with an increment in conductivity. Scaled ac conductivity spectra demonstrated that the conductivity relaxation process relied upon the composite structural features and did not depend on temperature. These materials can be used for such applications as gas sensors, even at higher temperatures due to their semiconducting nature and the different valence states of transition metal ions.

Light-controlled switching of the spin state of iron(III)

Controlled switching of the spin state of transition metal ions, particularly of FeII and FeIII, is a prerequisite to achieve selectivity, efficiency, and catalysis in a number of metalloenzymes. Here we report on an iron(III) porphyrin with a photochromic axial ligand which, upon irradiation with two different wavelengths reversibly switches its spin state between low-spin (S = 1/2) and high-spin (S = 5/2) in solution (DMSO-acetone, 2:598). The switching efficiency is 76% at room temperature. The system is neither oxygen nor water sensitive, and no fatigue was observed after more than 1000 switching cycles. Concomitant with the spin-flip is a change in redox potential by ~60 mV. Besides serving as a simple model for the first step of the cytochrome P450 catalytic cycle, the spin switch can be used to switch the spin-lattice relaxation time T1 of the water protons by a factor of 15.

Floating Orbitals Reconsidered: The Difference an Imaginary Part Can Make

Floating orbitals for valence electrons have made cameo appearances at several stages in the history of quantum chemistry. Most often, they were considered as potentially useful basis functions and, more recently, also as muses for the development of subatomistic force fields. To facilitate computation, these orbitals are generally taken to be real spherical Gaussians. However, the computational advantages carry over to complex Gaussians. Here, we explore the potential utility of an imaginary part. Analytical equations for two mobile electrons show that an imaginary part shifts the balance between contributions to the exchange energy that favor parallel versus antiparallel electron spins. However, an imaginary part also carries a large kinetic energy penalty. The imaginary part is therefore negligible for two valence electrons, except in the case of strong core–valence exchange interactions. This consideration allows a self-consistent model for the nd2 triplet ground states of transition metal ions versus the ns2 singlet ground states of main group ions.

Impact of High Valence State Cation Ti/Ta Surface Doping on the Stabilization of Spinel LiNi0.5Mn1.5O4 Cathode Materials: A Systematic Density Functional Theory Investigation

AbstractSurface modification of a high‐voltage spinel LiNi0.5Mn1.5O4 cathode is a common method to improve its cycling performance for next generation lithium‐ion batteries, but the exact surface structural stabilization mechanism is not well‐understood. Here, detailed density function theory investigations based on the first‐principles calculations of high valence state Ti‐/Ta‐surface‐doped LiNi0.5Mn1.5O4 are reported. The migration of Ni/Mn ions is simulated into the surface structure of bare and Ti‐/Ta‐coated LiNi0.5Mn1.5O4. The calculation results suggest that Ti/Ta doping promotes Ni/Mn migration toward the formation of the rocksalt phase. Integrated net spin suggests that the valence state of transition metal ions, especially Ni, around Ti/Ta are slightly reduced in the fully charged state, resulting in a weakened surface oxidative property toward electrolyte. Both Ti/Ta doping and the consequent formation of the rocksalt phase not only stabilizes the oxygen frame of LiNi0.5Mn1.5O4 by forming stronger metal‐O bonds but also suppresses the oxygen evolution during cycling. The stabilized anion frame of oxygen further mitigates the dissolution of Mn ions from the lattice into the electrolyte. These computer simulations are in good accordance with experimental observations. The surface structural stabilization mechanism of the high valence state cation Ti‐/Ta‐coated LiNi0.5Mn1.5O4 can certainly be expanded to improve other cathode electrode materials.

Strain induced ferromagnetism and large magnetoresistance of epitaxial La1.5Sr0.5CoMnO6 thin films

In this study, the structural, magnetic, and magneto-transport properties of La1.5Sr0.5CoMnO6 (LSCMO) thin films deposited on a SrTiO3 (001) substrate were investigated. A normal θ/2θ x-ray diffraction, rocking curve, ϕ-scan, and reciprocal space mapping data showed that prepared LSCMO thin films are single phase and highly strained with epitaxial nature. Temperature vs. magnetization of LSCMO films exhibits strain-induced ferromagnetic ordering with TC ∼ 165 K. In contrast to the bulk samples, there was no exchange bias and canted type antiferromagnetic and spin glass behavior in films having thickness (t) ≤ 26 nm. Temperature dependent resistivity data were explained using Schnakenberg's model and the polaron hopping conduction process. The slope change in resistivity and magnetoresistance maximum (∼65%) around TC indicates the existence of a weak double exchange mechanism between the mixed valence states of transition metal ions. Suppression of spin dependent scattering with the magnetic field is attributed for the large negative magnetoresistance in LSCMO films.

EPR of transition metal ions in microplasma coatings on the surface of Ti − 0 , 3al and Ti − 6Al − 4V titanium alloys

The study focuses on the EPR examination of titanium oxidation states and doped transition metal ions in microplasma coatings on the surface of details made of Ti−0,3al and Ti−6Al−4V titanium alloys, depending on the duration and modes of the microplasma oxidation process. No Ti3+ states are observed in the anodic mode of microplasma oxidation. When the microplasma process is conducted in the anodic-cathodic mode, paramagnetic Fe3+ and Ti3+ states are observed in the Ti−0,3al alloy, and V4+ and Ti3+ states are found in the Ti−6Al−4V alloy. The removal of the technological layer mostly containing low-temperature titanium oxides eliminates the EPR spectra of the mentioned paramagnetic states of transition metal ions. The anodic mode of microplasma oxidation followed by the anodic-cathodic mode at the final stage does not yield paramagnetic states of transition metal ions, which is very important for many applications of microplasma oxidation of coatings because the Ti3+ state is chemically active and may affect many chemical processes occurring on the oxide layer surface. Meanwhile, the inverse sequence of the microplasma oxidation modes gives rise to paramagnetic states of transition metal ions in the technological layer.

Key factors in Sr-doped LaBO3 (B = Co or Mn) perovskites for NO oxidation in efficient diesel exhaust purification

Perovskites have attracted attention in recent years as an economic alternative to noble metals in oxidation processes. Synthesis conditions of LaCoO3 and LaMnO3 perovskites have been studied varying citrate to nitrate molar ratio in the starting solution, pH and calcination protocol, with the aim of obtaining high purity perovskites, absence of impurities, and with enhanced textural properties. Once synthesis conditions were established, strontium was incorporated in the perovskite lattice as a textural and structural promoter, by substituting lanthanum with different doping levels, i.e. La0.9Sr0.1BO3, La0.8Sr0.2BO3, La0.7Sr0.3BO3, La0.6Sr0.4BO3 and La0.5Sr0.5BO3 with B = Co or Mn. The prepared solids were characterized in terms of crystalline phase identification (XRD), specific surface area (N2 adsorption–desorption at −196 °C), reducibility and oxidation state of transition metal ions (H2-TPR), quantification of adsorbed oxygen species (O2-TPD) and surface elemental composition (XPS). Charge imbalance associated to strontium (Sr2+) incorporation in the perovskite lattice in substitution of lanthanum (La3+) was preferentially balanced by Mn4+ promotion in La1−xSrxMnO3 perovskites, whereas formation of oxygen vacancies seems to be the mechanism for charge compensation in La1−xSrxCoO3 perovskites, where Co ions remained as Co3+ ions. Strontium doped perovskites further improved NO conversion compared to the non-substituted formulations. The best NO oxidation performance was obtained with La0.7Sr0.3CoO3 and La0.9Sr0.1MnO3 samples, achieving maximum NO conversion of 83 and 65% at 300 and 325 °C, respectively. Higher oxidation capacity of La0.7Sr0.3CoO3 sample was associated to the higher oxygen mobility and exchange capacity between oxygen in the lattice and gas phase oxygen. It is worth noting that prepared perovskites presented far higher NO oxidation capacity than platinum-based NSR model catalysts, confirming perovskites as an economic alternative to catalyze NO oxidation reactions in automotive catalysis.

Investigating the effect of multiple grain–grain interfaces on electric transport behavior of [50 wt% BaFe12O19–50 wt% Na0.5Bi0.5TiO3] magnetoelectric nanocomposite system

Polycrystalline [50wt% BaFe12O19 (BaM)–50wt% Na0.5Bi0.5TiO3 (NBT)] particulate novel magnetoelectric nanocomposite system was successfully fabricated by solid state reaction technique. The Rietveld refinement of X-ray diffraction pattern was provided the evidence about the pure phase formation of desired nanocomposite system as well as the presence of both ferrimagnetic (FM) BaM & ferroelectric (FE) NBT phases separately. The Field Scanning Electron Micrograph (FESEM) and Scanning Tunneling Electron Micrograph (STEM) explored the information about grain size and connectivity of the composite system. The XPS study was helped to examine the presence of oxygen vacancy (Ov) as well as multi oxidation states of transition metal ions for nanocomposite system.In this report we have systematically examined the conduction mechanism of different interfaces (BaM-BaM, BaM-NBT and NBT-NBT) by the help of complex impedance spectroscopy technique. From our investigation it was observed that, different interfaces activates at different temperature ranges. Due to absence of OV, BaM-NBT interfaces conduction dominants over BaM-BaM interfaces conduction even at room temperature (RT). The mechanism behind the appeared high dielectric loss (tanδ) at RT which was reduced when NBT-NBT interfaces were activates at higher temperature was explained by Maxwell-Wagner type interfacial polarization concept.

Opportunities of research in multiferroic materials using Angle Dispersive X-ray Diffraction (ADXRD) beamline on Indus-2 synchrotron source

Synchrotron beamlines have advantages of higher flux and wide tunability of photon beam compared to laboratory based equipment for performing x-ray diffraction and x- ray absorption spectroscopy (XAS). In this paper we report capabilities of angle dispersive x- ray diffraction beamline (BL-12) on Indus-2 synchrotron source for structural and spectroscopic characterisation of multiferroic materials. Brief description of the beamline along with the photon beam specifications at the experimental station is given. Results on low temperature XRD measurements on mixed spinel system (Fe1.5Co1.5O4) between 30K and 300K and subsequent Reitveld refinement reveal that there are no phase changes but the lattice parameter show anomalous changes between 100 and 150K. It has been explained how XANES spectra on a type II multiferroic, Co3TeO6, and Fe1.5Co1.5O4 can be used for the determination of charge and spin states of transition metal ions.

Magnetic order and electronic properties of Li2Mn2(MoO4)3 material for lithium-ion batteries: ESR and magnetic susceptibility studies

We describe the application of electron spin resonance (ESR) and magnetic susceptibility methods to study the magnetic properties and valence state of transition metal ions in Li2Mn2(MoO4)3 polyanion compound previously studied for its cathode-active properties in lithium containing batteries. ESR measurements of Li2Mn2(MoO4)3 have shown the presence of Mn2+ ions in the octahedral environment of oxygen ions. It is found that the part of manganese ions occupy the anti-site positions in lithium sublattice. The absence of the ESR signal from molybdenum ions indicates that they are non-magnetic and adopt the 6+ valence state. Considerable overlapping between 3d orbitals of transition metal and 2p oxygen orbitals has been experimentally established. This leads to the indirect exchange interaction and antiferromagnetic ordering of manganese ions at 1.4 K.

Understanding of Capacity Loss/Fading of Li-Rich Layer-Structured Cathode Materials Based on Structural/Electrochemical Analyses

Li-rich layer-structured cathode materials formulated as xLi2MnO3 -(1-x)LiMO2(M = Mn, Ni, Co, etc.) have received much attention due to their surprisingly high reversible capacity for Li-ion battery applications. For the understanding of these materials, a systematic study on complicated crystal structures and reaction mechanisms during electrochemical charge/discharge cycles is employed. Although Li-rich layer-structured cathode material show a reversible capacity as high as 250 mAh/g at low rate, its electrochemical properties such as capacity loss at first cycle, rate capability and capacity fading still need to be examined and characterized. In this study, several compositions of xLi2MnO3 -(1-x)LiMO2 (M = Mn, Ni, Co, etc.) were investigated. The TEM structural analysis shows that the evidence of spinel phase after cycling. It is believed that the transition from layered structure to spinel structure may induce a large lattice distortion resulting in lattice breakdown and capacity. In additions, the phase transition is caused by the redox reaction of transition metal ions through charging/discharging tests. Thus, the cycling behavior of Li-rich layer-structured oxides is studied by changing the oxidation state of transition metal ions in the layered structures. XRD, SEM, TEM will be used for characterization of cycled cathode materials.

X-ray photoelectron and mössbauer spectroscopy studies of the valence state of transition metal ions in Co1–x Fe x Cr2O4 (x = 0.1, 0.2, 0.5) ceramics

The valence state of transition metal ions in the Co1–x Fe x Cr2O4 (x = 0.1, 0.2, 0.5) system has been investigated using X-ray photoelectron and Mossbauer spectroscopy. It has been shown that, in this system, there are Fe2+ and Fe3+ ions. The relative Fe3+/Fe2+ contents have been determined by fitting the experimental Fe 2p photoelectron spectra by a superposition of theoretical spectra of the Fe2+ and Fe3+ ions, as well as using Mossbauer spectroscopy.

Effect of nonmagnetic impurity doped on the structural and magnetic properties of quasi-one-dimensional antiferromagnet LiCuVO4

Zn2+ ions doped quasi-one-dimensional spin-chain materials LiCu1-xZnxVO4(x=0, 0.1, 0.2) were prepared by solid-state reaction and the effect of nonmagnetic Zn2+ ions on the crystal structure, valence state and magnetic properties of them were studied by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and dc magnetization. The elongation of a and b axes and the shrinkage of c axis indicate a reduced effect of the Jahn-Teller distortion after Zn2+ ions doping, while the valence state of transition metal ions in LiCu1–xZnxVO4 remains unchanged since the equivalence doping of Zn2+ ions on the Cu2+ sites. The corrected Bonner-Fisher equation fitting to the susceptibility indicates that isolated dimers and spins are created along with the departure from infinite spin chains to finite ones.

Determination of methemoglobin in human blood after ionising radiation by EPR

In the present work presents results of investigations of radiation influence on blood of patients examined by radio-isotopes diagnosis (Tc99m), blood of Chernobyl clean-up workers and human blood irradiated by LINAC using Electron Paramagnetic Resonance (EPR). The EPR spectroscopy reveals information on electronic states of transition metal ions, particularly Fe3+ in different spin states. It is shown that EPR spectra of blood of patients before examination has signal from metal-protein transferrin (g=4.3) and after administration of radioisotope proves signal of Fe3+ (methemaglobin) in the high spin state (g=6.0). The EPR spectra of Chernobyl liquidator display number of signals including low and high state of ion Fe3+ (g = 2.0 and g=6.0), and transferrin (g=4.3). The EPR spectra of irradiated human blood by LINAC (linear accelerator) have only signal Fe3+ (methemaglobin) in low-spin state with g = 2.0.

Mechanical and Dielectric Behaviour of CaCu3Ti4O12 and Nb Doped CaCu3Ti4O12 Poly(vinylidene fluoride) Composites

PVDF has been reinforced with different amount of CaCu3Ti4-5x/4NbxO12 with x=0.05 powder prepared by solid state ceramic method. Composites were prepared by melt extrusion method. Phase composition was studied using powder X-ray diffraction (XRD). Microstructural, dielectric, and mechanical properties have also been studied. These composites have Young’s modulus more than that of pure PVDF. Two dielectric relaxations, one at low frequency and the other at high frequency, have been observed in these composites. Dielectric relaxation at low frequencies is of Maxwell-Wagner type while the one observed at high frequency is due to hopping of electrons among different valent states of transition metal ions. Nature of dielectric relaxation has been analysed using H-N function.