Oxidation States Of Iron Ions Research Articles

Crystal field anisotropy correlated charge disproportionation in Ruddlesden-Popper Sr3-xCaxFe2O7-δ perovskites

A series of Ca2+-doped Ruddlesden-Popper phase perovskites Sr3-xCaxFe2O7-δ (x = 0∼0.4) were synthesized. Strong asymmetric FeO6 octahedral distortion was confirmed at x = 0.2 owing to the anisotropic chemical pressure applied from preferable occupation of Ca2+ ion at Sr2 site. Unusual high-charged oxidation state of iron ion with enhanced p→d charge transfer was collectively evidenced by X-ray photoelectron spectroscopy and Mössbauer spectroscopy. Combined electron emission spectroscopy further revealed a narrowing of the surface band gap accompanied by an apparent lowering of the conduction band edge at x = 0.2. These observations can be explained by a nontrivial partial charge disproportionated (CD) regime: d5L + d5L → d5L1−n + d5L1+n, which reflects a significant correlation between anisotropic chemical pressure and CD ground state. The d5L1−n ground state, which dominates the conduction band, is largely stabilized by enhancing the d(Fe)-p(O) hybridization along the c-axis. In addition, abrupt changes in both magnetism and dc electrical properties were also observed at x = 0.2. It is believed that the anisotropic crystal field correlated electronic state fluctuation of iron may facilitate magnetic phase competition and carrier transport. This work provides a comprehensive understanding of the crystallographic anisotropy and correlated valence electron behavior in Fe-base Ruddlesden-Popper perovskites, as well as quasi two-dimensional perovskite materials.

Impact annealing temperature process on oxidation state of iron ions and structural phase transition in magnetite nanoparticles

Impact annealing temperature process on oxidation state of iron ions and structural phase transition in magnetite nanoparticles

Influence of alkaline earths on EPR spectra of lithium borate glasses doped with Fe (III) ions

Lithium borate glasses containing Fe (III) transition metal ion having composition 15RO-25Li2O-59B2O3-1Fe2O3 (where R= CaO, SrO and BaO) are synthesized via melt quench route. These glasses were characterized using X-ray diffraction (XRD). Electron paramagnetic resonance spectra of prepared glasses have been studied. The recorded spectra mainly consists of an intense resonance signals at g ∼ 4.282 and also at g ∼ 2.0032 along with a shoulder in the region of g ∼ 8.033 which is a characteristic of iron ions in the (3+) valence state in all the studied glasses. The number of spins participating in resonance (N) and its paramagnetic susceptibilities (χ) have also been evaluated. The spin concentration and the paramagnetic susceptibility at g = 2.0032 and at g = 4.282 increase by the substitution of alkaline earths from CaO to BaO respectively. The peak-to-peak line width ΔB for the resonance lines at g ≈ 4.282 and at g ≈ 2.0032 and the line intensity of the resonance centered at g ≈ 4.282 and at g ≈ 2.0032 have been evaluated. This EPR spectra has been analyzed in the light of different oxidation states of iron ions in order to understand the influence of alkaline earths as modifier oxide on the structure of glass matrix.

Structure and chemical durability of ZnO–B2O3–P2O5–R n O m glass system with Fe2O3 additive

ZnO–B2O3–P2O5–RnOm glasses containing different concentrations of Fe2O3 (ranging from 0 to 5 mol %) were prepared. A number of studies viz., glass transition temperature (Tg), density (α), thermal expansion coefficient (a), chemical durability, infrared spectroscopic and X-ray diffraction (XRD) patterns of these glasses had been carried out. The results of these studies have been analyzed in the light of different oxidation states of iron ions. The physical properties coupled with infrared spectroscopic and XRD indicates that the iron ions (when present in the concentration range, 0–2 mol %) exist mostly in trivalent state and occupy both tetrahedral and octahedral substitutional positions and are found to increase the rigidity of the glass network. However, in the concentration range of 2–5 mol %, the iron ions in the glass network seem to be existing by and large in Fe2+ state, occupying predominantly octahedral positions and are acting as modifiers.

Crystal structure of a new lithium iron vanadate

Iron vanadates and phosphates have been widely explored [1-2] as possible electrode material for Li-ion batteries. In the goal of finding new materials, our approach was to consider existing materials and to investigate the flexibility of their network for possible substitutions. Among the different materials containing iron and vanadium, Cu3Fe4(XO4)6 (X = P, V) are isostructural to Fe7(PO4)6. Lafontaine et al. [3] discussed the structural relationships between β-Cu3Fe4(VO4)6 and several other vanadates, phosphates and molybdates of general formula AxBy(VO4)6. The interesting network flexibility was then demonstrated with the existence of four different crystallographic sites, which can be partially occupied depending on the x+y value : x+y = 7 for β-Cu3Fe4(VO4)6) and x+y = 8 for NaCuFe2(VO4)3. The LixFey(VO4)6 phase was then prepared considering the substitution of Li+ and Fe3+ for Cu2+ ions in β-Cu3Fe4(VO4)6 and the existence of an extra site to accommodate the charge compensation (7 ≤ x+y ≤ 8). As expected, a new lithium iron vanadate, isotructural to mineral Howardevansite was then obtained. Single crystal diffraction data were collected at room temperature on Enraf-Nonius CAD-4 diffractometer. Structure was refined with JANA-2006 program package. Mössbauer and magnetic measurements were also used to check the oxidation state of iron ions, to support the obtained crystal structure and to consider any possible structural/magnetic transitions. All the results will be presented and discussed in this presentation.

Synthesis and Properties Investigation of Non-equivalent Substituted W-Type Hexaferrite

A novel composed W-type hexaferrite Ba1−x La x Co2Fe16O27 was rapidly synthesized via a sol–gel self-combustion reaction. The effects of lanthanum ions on the oxidation state of iron ions and cobalt ions in hexaferrite were explored by X-ray photoelectron spectroscopy. The changes of the Fe 2p X-ray absorption spectra indicated that the nonequivalent substitution can lead to the transition Fe3+→ Fe2+ in Ba1−x La x Co2Fe16O27. However, the oxidation state of cobalt ions was maintained as Co2+. Moreover, the effects of La content on the phase composition, structural parameters, morphology, and static magnetic properties were also investigated in detail by using the X-ray diffractometer, scanning electron microscope, and vibrating sample magnetometer. The results indicated that the structural parameters decreased regularly with increasing the La content, and the magnetic properties were enhanced after substitution, which is beneficial for their application in various electrical devices employed for industrial and military applications.

Influence of alkaline earth oxides (R = Ca, Sr and Ba) on spectroscopic and dielectric studies of iron doped RO–Na2O–B2O3 glasses

Transparent glasses with the composition 20RO–10Na2O–69B2O3–1Fe2O3 (where R=Ca, Sr and Ba) were prepared by melt quenching technique. The amorphous nature of the glass was confirmed by X-ray diffraction pattern of the sample. Physical parameters and spectroscopic studies such as EPR, optical absorption and FTIR were carried out for the glass samples. Besides dielectric properties i.e. dielectric constant (ε′), and loss (tan δ), a.c. conductivity (σac) in the frequency range 103–106Hz and the temperature range 30–300°C in air of the present glasses were also investigated. The dielectric and spectroscopic properties have been analyzed in the light of different oxidation states of iron ions in order to understand the influence of alkaline earth oxides as modifier oxide on the structure and insulating strength/conductivity of glass matrix.

ZASTOSOWANIE PROTEAZ POCHODZENIA MIKROBIOLOGICZNEGO DO OTRZYMYWANIA HYDROLIZATÓW O AKTYWNOŚCI PRZECIWUTLENIAJĄCEJ I PRZECIWDROBNOUSTROJOWEJ Z BIAŁEK ŻÓŁTKA JAJA

Natural antioxidants with high safety and long-term effect are subject of many studies because they are an alternative to chemical antioxidants which, in larger quantities, can be toxic. One type of natural antioxidants may be foodderived peptides. The aim of this study was to obtain antioxidant and antimicrobial peptides from egg yolk phosvitin and immunoglobulin Y (IgY) with participation of microbial proteinases from Bacillus amyloliquefaciens (neutrase), B. thermoproteolyticus Rokko (thermolysin), Streptomyces griseus (pronase) and Aspergillus melleus. The progress of hydrolysis was monitored by the degree of hydrolysis (DH) and free amino groups concentration measurement. The resulting hydrolysates were subjected to an assessment of their ability to reduce the oxidation state of metal ions, scavenging of 2,2-di(4-tert-octylphenyl)-1picrylhydrazyl (DPPH) free radicals and chelating iron ions. The highest degree of hydrolysis of both proteins was obtained during the reaction with proteinase from S. griseus. The highest level of reduction in the oxidation state of iron ions was observed in IgY 24hour hydrolysates obtained with the participation of enzyme from B. thermoproteolyticus Rokko (409.7 μg Fe/mg). However, the 24-hour hydrolysates of IgY obtained after degradation with the proteinase from A. melleus, possessed the highest free radical scavenging activity equal to1.46 μM trolox/mg. The highest activity of chelating iron ions, equal to 891.64 μg Fe/mg, was observed for products obtained during the 24-hour hydrolysis of phosvitin with the participation of protease from B. thermoproteolyticus Rokko.

Effect of Oxidation State of Iron Ions on the Viscosity of Alkali Silicate Melts

Effect of Oxidation State of Iron Ions on the Viscosity of Alkali Silicate Melts

Synthesis, structural and magnetic properties of La1 − xCaxFeO3 prepared by the co-precipitation method

Lanthanum calcium ferrite La1 − xCaxFeO3 (where x = 0.05, 0.10 and 0.15) were synthesized by co-precipitation method. The structural refinement confirmed that all samples formed with the orthorhombic (Pbmn) structure with small impurities (LaFeO3 and Fe2O3). Fourier transformed infrared spectroscopy (FT-IR) results indicated that the electronic imbalance caused by the partial substitution for La3 + by Ca2 + is compensated by an oxidation state of iron ions. Mossbauer spectra at room temperature (RT) show five 6-line sub-spectra corresponding to Fe3 + (superposition of 3 spectra), Fe4 + and Fe5 + in all samples. Magnetic hysteresis loops of these samples showed a significant weak ferromagnetic component at RT.

Controlling morphology and phase of pyrite FeS2 hierarchical particles via the combination of structure-direction and chelating agents

Pyrite FeS2 hierarchical microparticles consisting of cubic-like crystals with well defined {100} faceted cubic textures were successfully synthesized using a simple hydrothermal method with the presence of ethylenediamine (en) and polyvinylpyrrolidone (PVP). The roles of PVP and en in the synthesis process were elucidated by the investigation of morphology and crystalline phases of the products under different reaction conditions and by the analysis of atomic structures of the pyrite (100) and (111) surfaces with different termination layers. While en chelates with Fe2+ and reacts with S8 of the reaction agents to help with dispersion and nucleation as well as the role of reducing agent, PVP acts as both a phase regulator due to its reducing ability and a surface capping agent to bind the iron atoms at the FeS2 (111) surface and direct the formation of {100} facets. It was found that the oxidation state of iron ions and the species of anions in the iron reagents also played important roles in the formation of crystalline phase and morphology of the products. The pyrite hierarchical microparticles could be utilized as a new semiconductor ink for solution processing of photovoltaic devices and photodetectors as well as cathode materials for lithium batteries.

One-Pot Synthesis of Highly Monodispersed Ferrite Nanocrystals: Surface Characterization and Magnetic Properties

In the present study, a facile one-pot synthetic route, utilizing a strong polar organic solvent, N-methyl 2-pyrrolidone (NMP), is demonstrated to obtain highly monodispersed ferrite nanocrystals. The equimolar mixture of oleic acid, C(17)H(33)COOH (R-COOH), and oleylamine, C(18)H(35)NH(2) (R'-NH(2)), was used to coat the magnetic nanocrystals. Structural and magnetic properties of the ferrite nanocrystals were studied by a multitechnique approach including X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM), and Mössbauer spectroscopy. FTIR spectral analysis indicates oleylamine helps in deprotonation of oleic acid, resulting in the formation of an acid-base complex, R-COO¯:NH(3)(+)-R', which acts as binary capping agent. Structural and coordination differences of iron were studied by XPS and Mössbauer spectral analysis. XPS analysis was carried out to examine the oxidation state of iron ions in iron oxide nanocrystals. The presence of a magnetically dead layer (∼0.38 and ∼0.67 nm) and a nonmagnetic organic coating (∼2.3 and ∼1.7 nm) may substantially reduce the saturation magnetization values for CoFe(2)O(4) and Fe(3)O(4) nanocrystals, respectively. The energy barrier distribution function of magnetic anisotropy was derived from the temperature dependent decay of magnetization. A very narrow energy barrier distribution elucidates that the ferrite nanocrystals obtained in this study are highly monodispersed.

Molecular dynamics potentials in magnetite (Fe3O4) modeling

This paper involves modeling iron oxidation to form magnetite using molecular dynamics. Magnetite has two different oxidation states of iron ions: one type carries the maximum charge of +2e and the other type carries the maximum charge of +3e. The problem is how to decide which type each iron ion belongs to. This is not a trivial problem because, in molecular dynamic simulations, each iron ion normally carries a fractional charge, say +0.25e, not fully +2e or +3e. This paper introduces a novel implementation in modeling magnetite formation with satisfactory results when compared to actual experiment results.

Viscosity Measurement of Calcium Ferrite Based Slags during Structural Relaxation Process

In the present study, we measured the viscosity change with the melting time (melting temperature: 1873 K, 1773 K or 1673 K, atmosphere: air) of calcium ferrite (CaO·Fe2O4(CF)) based slags (CF, CF–5wt%SiO2 and CF–5wt%Al2O3) by the rotating crucible method. Moreover, the viscosity changes were discussed from the viewpoints of the iron oxidation states (Fe2+ and Fe3+) and the coordination number of Fe3+.Viscosity of the CF based slags decreased with the melting time at all the temperature (1673 K, 1773 K or 1873 K). Viscosities of the slags became constant after the melting time of 120 min at 1873 K and at 1773 K. In the case of the melting at 1673 K, the viscosity of the slags became constant after 240 min. The results of the chemical analysis indicated that the oxidation state of iron ions in the quenched CF slag was not changed during the viscosity measurements. We could not directly observe the change in the coordination structure of Fe3+ in CF based slags during the melting time, because the CF based slag could not be vitrified due to the limitation of quenching rate in the present study. However, the data of the viscosity and the structural information for 40CaO–40SiO2–20Fe2O3 (mol%) slag indicated that the coordination structure of Fe3+ strongly affect the viscosity of iron-containing slags. The decreases in the viscosity of the CF based slags would be also controlled by the change in the coordination number of Fe3+.

Formation mechanism of LiFePO4/C composite powders investigated by X-ray absorption spectroscopy

Abstract The local structure and oxidation states for both the precursors and the LiFePO 4 /C composite powders were investigated by X-ray absorption spectroscopy (XAS) to provide a deep insight into their formation mechanism. It was found that the local structure and oxidation states of the precursors and the synthesized LiFePO 4 /C powders as well as the electrochemical properties of the synthesized powders were strongly influenced by the R ratio ( R : molar ratio of citric acid to total metal ions). The oxidation states of iron ions of the precursors for R = 1 and 0.75 consist mainly of Fe(II) and traces of Fe(III). However, the oxidation state of iron ions of the precursor for R = 0.5 comprises mainly of Fe(III). The oxidation state of iron ions of all the synthesized powders is Fe(II). The structure of the precursors and the synthesized powders for R = 1 and 0.75 is more ordering than that for R = 0.5. It is in good agreement with the observation of the cation mixing obtained from the Riteveld analysis of the XRD data. The better the electrochemical performance is, the more ordering the structure or the less the cation mixing. However, the effect of the R values on the carbon content is also essential for the electrochemical properties of the synthesized LiFePO 4 /C composite powders. Increasing the carbon content leads to the increase in the electronic conductivity but impedes the Li + ion diffusion of the composite materials. Consequently, the powders synthesized at the optimal R ratio of 0.75 exhibited the highest initial capacity, about 150 mAh g −1 when cycled at 1/40 C rate at room temperature. The structural scheme of the precursors and the synthesized powders and the formation mechanism of the LiFePO 4 /C composite powders are also addressed in this work.

Oxidation state and effective pair potential of Fe4+ ions in perovskite-type SrFeO3 annealed under high oxygen pressure

The cubic perovskite-type SrFeO3 have been obtained by annealing under high oxygen pressure of 100 MPa at 600K. X-ray absorption fine structure (XAFS) observations on Fe K-edge have been performed from 25 K to 900 K to investigate the temperature variation of the local structure and oxidation state of iron ion in the perovskite-type SrFeO3. The edge features of Fe K-edge XANES spectra and the first differential curves of XANES spectra change gradually and greatly with increasing temperature from 600k to 900K. There is no clear change near the Neel temperature. In the higher temperature region than 600 K, the threshold energy shifted to the low energy side (∼2 eV) indicating that Fe4+ ion more reduced to Fe3+ in air. The temperature dependence of EXAFS Debye-Waller factors was investigated and harmonic effective pair potentials, V(u)= αu2/2, have been evaluated. The potential coefficients α for Fe-O, Fe-Sr and Fe-Fe distances are 6.0, 5.48 and 4.0 eV/A2, respectively.

The effect of the oxidation state of iron ions on the competitive complexation of malvidin by caffeic or ellagic acid

The complexation behavior of malvidin with ellagic and caffeic acid and ferrous and ferric ions was studied in model wine solutions by means of experimental photoluminescence studies and model calculations. Our results show the significant role of caffeic acid in the anthocyanin-polyphenol interaction (also known as copigmentation). According to our results in the presence of caffeic acid the impact of ferrous and ferric ions is negligible. These results also highlight the less important role of ellagic acid compared to caffeic acid in the formation of copigmentation complexes.

Local order changes induced in calcium–sodium–phosphate glasses by transition metals

The structural effects caused by transition metal oxides (TMO) added to calcium–sodium–phosphate glasses are investigated with respect to the local order up to atomic environment using differential thermal analysis (DTA) and X-ray photoeffect spectroscopy (XPS). Reference data are collected from 50P 2O 5·30CaO·20Na 2O host glass. Different influences of TMO on the crystallisation temperature and glass stability are observed if Ag 2O or Fe 2O 3 is added to the host glass. The melting temperature is diminished by Ag 2O and is enhanced by Fe 2O 3. The data point out higher values for glass stability of iron containing glasses. XPS data support that in this glass system the oxidation state of iron ions is 3+ and Fe 2O 3 acts as a glass network former. By TMO addition the valence band of the host glass is shifted from 2.6 eV to negative values of the binding energy.

Environment of Fe 3+ ion and its influence on dielectric and spectroscopic properties of Pbo–Nb 2O 5–P 2O 5 glasses

PbO–Nb 2O 5–P 2O 5 glasses containing different concentrations of Fe 2O 3 (ranging from 0 to 3 mol%) were prepared. A number of studies viz., chemical durability, differential thermal analysis, spectroscopic (infrared, optical absorption ESR spectra) and dielectric studies (constant ε′, loss tan δ, AC conductivity σ AC over a range of frequency and temperature) of these glasses have been carried out. The results of these studies have been analyzed in the light of different oxidation states of iron ions. The analysis indicates that the iron ions (when present in the concentration range, 0.2–1.0 mol%) exist mostly in trivalent state and occupy both tetrahedral and octahedral substitutional positions and are found to increase the rigidity of the glass network. However, in the concentration range of 1.0–2.5 mol%, the iron ions in the glass network seem to be existing by and large in Fe 2+ state, occupying predominantly octahedral positions and are acting as modifiers.

Thermoluminescence studies on PbO–Sb 2O 3–As 2O 3 glasses doped with iron ions

Thermoluminescence (TL) studies on PbO–Sb 2O 3–As 2O 3 glasses doped with different concentrations (0–1.0 mol%) of Fe 2O 3 have been carried out. The TL light output has been observed to decrease with increase in the concentration of Fe 2O 3 up to 0.6 mol%. For further increase in the content of Fe 2O 3, the TL light output has been observed to increase. Results of these studies (coupled with data on optical absorption, ESR and magnetic susceptibility measurements) have been analyzed in the light of different oxidation states of iron ions.