Function Of Fe Concentration Research Articles

Structure and Magnetic-field Induced Effects in Mn-Ni(Fe)-Sn Metamagnetic Shape Memory Alloys

Martensitic structures, transformation behavior and some magnetic properties of a new series of Mn49Ni42-xFexSn9 (x = 0 – 4 at.%) metamagnetic shape memory alloys have been studied as a function of Fe content and magnetic field. Fe doping decreased sharply the martensitic transformation temperatures. The XRD patterns showed different phases including orthorhombic structure, the L21 cubic phase and the fcc γ-phase at room temperature depending on Fe content. The magnetization curves, M-H, exhibited obvious metamagnetic transitions.

Electronic structure and phase separation of superconducting and nonsuperconductingKxFe2−ySe2revealed by x-ray photoemission spectroscopy

We have investigated the electronic structure of superconducting (SC) and nonsuperconducting (non-SC) K${}_{x}$Fe${}_{2\ensuremath{-}y}$Se${}_{2}$ using x-ray photoemission spectroscopy (XPS). The spectral shape of the Fe 2$p$ XPS is found to depend on the amount of Fe vacancies. The Fe 2${p}_{3/2}$ peak of the SC and non-SC Fe-rich samples is accompanied by a shoulder structure on the lower binding energy side, which can be attributed to the metallic phase embedded in the Fe${}^{2+}$ insulating phase. The absence of the shoulder structure in the non-SC Fe-poor sample allows us to analyze the Fe 2$p$ spectra using a FeSe${}_{4}$ cluster model. The Fe 3$d$-Se 4$p$ charge-transfer energy of the Fe${}^{2+}$ insulating phase is found to be $\ensuremath{\sim}$2.3 eV which is smaller than the Fe 3$d$-Fe 3$d$ Coulomb interaction of $\ensuremath{\sim}$3.5 eV. This indicates that the Fe${}^{2+}$ insulating state is the charge-transfer type in the Zaanen-Sawatzky-Allen scheme. We also find a substantial change in the valence-band XPS as a function of Fe content and temperature. The metallic state at the Fermi level is seen in the SC and non-SC Fe-rich samples and tends to be enhanced with cooling in the SC sample.

Local structure of Fe in Fe-doped misfit-layered calcium cobaltite: An X-ray absorption spectroscopy study

Polycrystalline Ca3Co4−xFexO9+δ ceramics (x=0, 0.01, 0.03, 0.05) were fabricated using a simple thermal hydro-decomposition method and a spark plasma sintering technique. Thermoelectric property measurements showed that increasing Fe concentration resulted in a decrease in electrical resistivity, thermopower and thermal conductivity, leading to an improvement in the dimensionless figure-of-merit, >35% for x=0.05 at 1073 K. An X-ray absorption spectroscopy technique was used to investigate the local structure of Fe ions in the Ca3Co4−xFexO9+δ structure for the first time. By fitting data from the extended X-ray absorption fine structure (EXAFS) spectra and analyzing the X-ray absorption near-edge structure (XANES) spectra incorporated with first principle simulation, it was shown that Fe was substituted for Co in the the Ca2CoO3 (rocksalt, RS) layer rather than in the CoO2 layer. Variation in the thermoelectric properties as a function of Fe concentration was attributed to charge transfer between the CoO2 and the RS layers. The origin of the preferential Fe substitution site was investigated considering the ionic radii of Co and Fe and the total energy of the system.

Synthesis and electrical properties of Fe-doped Y0.08Sr0.92TiO3 mixed ionic–electronic conductor

A single phase perovskite Y0.08Sr0.92Ti1−xFexO3−δ (x=0.20, 0.40 and 0.50) was fabricated at 1350°C in air by the sol–gel method and its mixed ionic–electronic conductivity was investigated as a function of Fe content. Fe was selected as a B-site dopant with the primary aim to improve the ionic conductivity of SrTiO3-based materials. With increasing Fe-doping amount, the electrical and ionic conductivities of Y0.08Sr0.92Ti1−xFexO3−δ increased in 400–900°C and 600–950°C, respectively. The possible charge compensation mechanism of Y0.08Sr0.92Ti1−xFexO3−δ can be described as Y0.08Sr0.92FexTi4+0.92-xTi3+0.08O3-(δ+x/2) or Y0.08Sr0.92FexTi4+0.92−x1Ti3+0.08−x2 O3−(δ+x1/2) (x=x1+x2).

Nanometer size 3d–4d and 3d–5d substitutional clusters: Promising candidates for magnetic storageapplications

Spin-polarized density-functional calculations including spin–orbit coupling (SOC) have been performed for FemRhn and FemPtn clusters having N=m+n,N≤19 atoms. The spin magnetic moments, orbital magnetic moments, and the magnetic anisotropy energies have been determined. A significant enhancement of magnetic anisotropy energies is found by the substitutional nanoalloying of Fe with Rh and Pt atoms. We obtained a remarkable non-monotonous dependence of the MAE as a function of Fe content, i.e., upon going from pure Fe to pure Rh and Pt. The substitutional nanoalloying boost the magnetic anisotropy energies by creating significant cluster symmetry lowerings.

Structure and activity of iron-doped TiO2-anatase nanomaterials for gas-phase toluene photo-oxidation

The structural (from local to long range order) and electronic evolution of Fe-doped anatase nanomaterials is evaluated using in situ synchrotron based X-ray total scattering/diffraction and absorption techniques and Raman spectroscopy. These methods are combined with UV-visible spectroscopy and infrared diffuse reflectance (DRIFTS) to maximize the level of structural and morphological information regarding these materials. Fe doping of anatase nanomaterials generates solids having Fe at substitutional positions of the structure, and anion vacancies as charge neutrality entities. These structural modifications lead to materials with decreasing band gap energy as a function of Fe content. Concomitantly, mid-gap electronic states are observed to appear. At the same time, the presence of Fe alters the primary particle shape of the anatase without changing significantly the primary particle size. In contrast with previous results, analysis of the combined results strongly indicates that UV and visible photocatalytic activity are here dominated by morphological rather than structural/electronic issues.

Effects of iron concentration and cationic site disorder on the optical properties of magnetoelectric gallium ferrite thin films

Room-temperature dielectric function e = e1 + ie2 spectra of magnetoelectric Ga2−xFexO3 (x = 0.9, 1.0, and 1.4) thin films are determined by spectroscopic ellipsometry (SE) as a function of Fe concentration x. The SE data are analysed by a multilayer model with a series of Tauc-Lorentz oscillators. While the threshold energies slightly decrease as x increases, the oscillator strength shows a strong composition-dependence for the major optical structure at ∼3.5 eV. The experimental data are compared to the e spectra obtained by density functional theory (DFT) calculations. Even though the overall shape of e spectra is consistent, the experimental data and calculated spectra show a clear discrepancy in the oscillator's strength ratio of the two optical structures at ∼3.5 and ∼6.0 eV. The DFT calculations suggest that a significant disordering in the cationic (Ga and Fe) sites in Ga2−xFexO3 is present in thin films, which influences their optical properties. This work demonstrates a successful application of optical characterization for determining the cationic sites occupation in thin films, which in turn improves our understanding of Physics and Chemistry in Ga2−xFexO3 thin films and paves a pathway to the development of new multifunctional devices.

Determination of Fe3+/Fe using the electron microprobe: A calibration for amphiboles

Iron is a common constituent in minerals from the Earth’s crust and upper mantle and often occurs in minerals as mixtures of two valence states, Fe 3+ or Fe 2+ . Quantification of the values of Fe 3+ /FeTotal, where FeTotal = Fe 3+ +Fe 2+ , in minerals may be necessary to accurately apply certain mineral equilibria to determine equilibrium values of important variables such as temperature (T), pressure (P), and oxygen fugacity (ƒO2). Most useful would be an analytical technique that permits determination of values of Fe 3+ /FeTotal within a single mineral grain that is contained within a standard petrographic thin section, and the excellent spatial resolution and relative accessibility of the electron microprobe (EMP) have resulted in various attempts to use this instrument to determine values of Fe 3+ /FeTotal. These efforts have typically involved quantifying characteristics of the FeLα and/or FeLβ peaks. In this paper, we employ the method of Fialin et al. (2001), who have shown that the location of the FeLα peak changes as a function of Fe content and values of Fe 3+ / FeTotal, to determine values of Fe 3+ /FeTotal in amphiboles. We have characterized the FeLα peak in several amphiboles with known values of Fe 3+ /FeTotal using the electron microprobe at Texas A&M University. Initial analyses employed a beam current of 20 nA in an effort to avoid Fe-oxidation due to electron beam generated H-loss (Wagner et al. 2008). Subsequent analyses were conducted at 100 nA, and the results are consistent with the 20 nA data only when relatively short duration analytical times were used. The position of the FeLα peak was determined for three suites of amphiboles that have been experimentally treated such that grains in any one of these mineral suites are chemically identical except for differences in the values of Fe 3+ /FeTotal. A linear relation between the FeLα peak location and value of Fe 3+ /FeTotal was observed for each of these three amphibole suites. These three lines differ from one another in both their slope and intercept and these differences vary as a function of Fe content. Thus, these amphiboles served as the basis for the derivation of a relation between Fe content and FeLα peak location, both measured with the EMP, and the value of Fe 3+ /FeTotal as originally determined with 57 Fe Mossbauer spectroscopy. The relation between the relative peak position (RPP = hematite standard FeLα peak position – amphibole FeLα peak position), Fe content, and Fe 3+ /FeTotal is

The Dielectric Tunability of Fe-Doped Pb<sub>0.3</sub>Sr<sub>0.7</sub>TiO<sub>3</sub> Thin Films Prepared by Sol-Gel Method

Fe-doped Pb0.3Sr0.7TiO3 (PST) thin films have been fabricated on Pt/Ti/SiO2/Si substrates with sol–gel method. The structure and surface morphology of Fe-doped PST thin films were investigated as a function of Fe concentration by x-ray diffraction (XRD) and atomic force microscopy (AFM). The dielectric measurements were conducted on metal-insulator-metal capacitors at the frequency from 100 Hz to 1M Hz at room temperature. It’s found that the dielectric constant, dielectric loss and tunability of Fe-doped PST films decreased with the increase of Fe content. The effects of Fe doping on the microstructure, dielectric and tunable properties of thin films were analyzed. Though the undoped PST thin film exhibited the highest dielectric constant of 2011 and the largest tunability of 76%, the 6 mol% Fe doped PST thin films had the highest figure of merit (FOM) of 17.9 for its lowest dielectric loss.

Investigation of structural, optical and magnetic properties in PbTi 1− xFe xO 3 ceramics

We have been successful in preparation of PbTiO 3 by partly substituting Ti site by Fe ions using solid state reaction method. PbTi 1− x Fe x O 3 perovskite has been studied as a function of Fe concentration using X-ray diffraction, absorption, Raman scattering and magnetization measurements. PbTi 1− x Fe x O 3 system exhibits ferromagnetic ordering at room temperature. There appears an anomalous change in the lattice constants, optical band gap, Raman spectroscopy as well as magnetization of sample with x = 0.30. The result also suggests the limit of dissolubility of Fe ions doped in PbTiO 3.

Prediction of Solidification Paths in Al-Si-Fe Ternary System and Experimental Verification: Part I. Fe-Containing Hypoeutectic Al-Si Alloys

The effects of Fe content and cooling rate on the solidification path and formation behavior of the Al5FeSi (β) phase in Fe-containing hypoeutectic Al-Si alloys were studied based on thermodynamic analysis and pertinent experiments. The thermodynamic calculations were performed using the Thermo-Calc program. For analyses in the high alloy region of the Al-Si-Fe ternary system, a thermodynamic database for Thermo-Calc was correctly updated and revised by the collected up-to-date references. For thermodynamics-based predictions of the solidification path in Fe-containing hypoeutectic Al-Si alloys, liquidus projection (including various invariant, monovariant, and bivariant reactions and isotherms) and equilibrium phase fraction were calculated as functions of composition and temperature in the Al-Si-Fe ternary system. The calculated results were compared to experimental results using various casting runs. In order to analyze the solidification path as a function of Fe content, two representative hypoeutectic Al-Si alloys with different Fe levels were designed. To better understand the influence of cooling rate on the formation behavior of the β phase, the two alloys were solidified under slowly- and rapidly-cooled conditions, respectively. The cooling curves of the solidified alloys were recorded by thermal analysis and various important solidification events were detected using the first derivative of the cooling curves. Microstructures of the casting samples were studied by combined analyses of optical microscopy (OM) and scanning electron microscopy (SEM). For the slowly-cooled condition with the high Fe level, the primary β phase enveloping the Al8Fe2Si (α) phase was mainly formed by the quasi-peritectic reaction of L + α → (Al) + β (612°C). For the rapidly-cooled condition with the high Fe level, the primary β phase with morphology of a curved needle was mainly formed by the reaction of L → (Al) + β (579∼612°C).

High-throughput powder diffraction on beamline I11 at Diamond

A new capability designed for high-throughput (HT) structural analysis using the synchrotron powder diffraction beamline (I11) at Diamond Light Source is reported. With a high-brightness X-ray beam, multi-analyser detectors and fast data-acquisition procedures, high-quality diffraction data can be collected at a speed of ∼15–30 min per powder pattern for good crystalline materials. Fast sample changing at a rate of a few seconds per specimen is achieved with a robotic arm and pre-loaded capillary specimens on a multi-tray carousel (200-sample capacity). Additional equipment, such as an automatic powder-loading machine and a pre-alignment jig for the sample capillaries, is available to reduce preparation time. For demonstration purposes, the first results presented here are those from standard reference powders of Si, TiO2and TiO2/Si mixtures, obtained by analysing the data using Le Bail (instrumental calibration) and Rietveld refinements (quantitative agreement within 1%). The HT hardware was then used to study the structural phase evolution of a library of 31 La4Ni3−xFexO10heterometallic ceramic powders in less than 1 d. The powders were generated from a single heat treatment (at 1348 K in air for 12 h) of nanoceramic oxide co-precipitate precursors, made using a newly developed HT synthesis robot. Crystallographic details (symmetry and lattice parameters) were obtained as a function of Fe concentration. The results revealed that this approach was able to produce a pure Ruddlesden–Popper-type phase with an iron content of up tox= 0.5, significantly higher than has been achieved previously using more conventional synthesis routes and thus demonstrating the power of using the HT approach.

Multiscale modeling of the influence of Fe content in a Al–Si–Cu alloy on the size distribution of intermetallic phases and micropores

A multiscale model was developed to simulate the formation of Fe-rich intermetallics and pores in quaternary Al–Si–Cu–Fe alloys. At the microscale, the multicomponent diffusion equations were solved for multiphase (liquid-solid-gas) materials via a finite difference framework to predict microstructure formation. A fast and robust decentered plate algorithm was developed to simulate the strong anisotropy of the solid/liquid interfacial energy for the Fe-rich intermetallic phase. The growth of porosity was controlled by local pressure drop due to solidification and interactions with surrounding solid phases, in addition to hydrogen diffusion. The microscale model was implemented as a subroutine in a commercial finite element package, producing a coupled multiscale model. This allows the influence of varying casting conditions on the Fe-rich intermetallics, the pores, and their interactions to be predicted. Synchrotron x-ray tomography experiments were performed to validate the model by comparing the three-dimensional morphology and size distribution of Fe-rich intermetallics as a function of Fe content. Large platelike Fe-rich β intermetallics were successfully simulated by the multiscale model and their influence on pore size distribution in shape castings was predicted as a function of casting conditions.

Generation of Hydroxyl Radicals from Ambient Fine Particles in a Surrogate Lung Fluid Solution

While it has been hypothesized that the adverse health effects associated with ambient particulate matter (PM) are due to production of hydroxyl radical (*OH), few studies have quantified *OH production from PM. Here we report the amounts of *OH produced from ambient fine particles (PM2.5) collected in northern California and extracted in a cell-free surrogate lung fluid (SLF). On average, the extracted particles produced 470 nmol *OH mg(-1)-PM2.5 during our 15-month collection period. There was a clear seasonal pattern in the efficiency with which particles generated *OH, with highest production during spring and summer and lowest during winter. In addition, nighttime PM was typically more efficient than daytime PM at generating *OH. Transition metals played the dominant role in *OH production: on average (+/-sigma), the addition of desferoxamine (a chelator that prevents metals from forming *OH) to the SLF removed (90 +/- 5) % of *OH generation. Furthermore, based on the concentrations of Fe in the PM2.5 SLF extracts, and the measured yield of *OH as a function of Fe concentration, dissolved iron can account for the majority of *OH produced in most of our PM2.5 extracts.

High temperature ferromagnetism of the vacuum-annealed (In1−xFex)2O3 powders

(In1−xFex)2O3 (x=0.02, 0.05, 0.2) powders were prepared by a solid state reaction method and a vacuum annealing process. A systematic study was done on the structural and magnetic properties of (In1−xFex)2O3 powders as a function of Fe concentration and annealing temperature. The X-ray diffraction and high-resolution transmission electron microscopy results confirmed that there were not any Fe or Fe oxide secondary phases in vacuum-annealed (In1−xFex)2O3 samples and the Fe element was incorporated into the indium oxide lattice by substituting the position of indium atoms. The X-ray photoelectron spectroscopy revealed that both Fe2+ and Fe3+ ions existed in the samples. Magnetic measurements indicated that all samples were ferromagnetic with the magnetic moment of 0.49–1.73μB/Fe and the Curie temperature around 783K. The appearance of ferromagnetism was attributed to the ferromagnetic coupling of Fe2+ and Fe3+ ions via an electron trapped in a bridging oxygen vacancy.

The effect of bulk iron concentration and heterogeneities on the copper activation of sphalerite

Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to study the Cu activation of the (1 1 0) surface of sphalerites with Fe content varying from 0 to 14.79 wt%. Time resolved AFM images show the development of surface oxidation products at high-energy step edges. These small protrusions evolve into larger conglomerates and finally full surface coverage with time. Surface morphology changes show an increase in the number of cleavage steps and the size of precipitates as a function of Fe concentration. Both of these factors contribute to the increased rate of Cu activation of high Fe sphalerite as compared to low Fe sphalerite. XPS analysis of the sphalerites Cu activated for 1 h at pH 5, indicates an increased Cu concentration and the formation of disulphide and polysulphide that correlates with an increase in bulk Fe content.

Ab initio calculations of the elastic properties of ferropericlase Mg 1− xFe xO ( [formula omitted

Ferropericlase Mg 1− x Fe x O is believed to be the second most abundant mineral in the Earth’s mantle. Therefore, the electronic and elastic properties of ferropericlase are important for the understanding of the Earth’s interior. Ab initio total energy calculations have been performed for Fe concentrations x ≤ 0.25 . The equation of state (EOS) clearly shows a volume expansion as a function of Fe concentration, consistent with experimental data. Magnetic moment calculations as a function of pressure show a high-spin to low-spin transition of Fe 2+, and the theoretical transition pressure increases with iron composition. At ambient pressure, we have found that the shear constant C 44 reproduces well the experimental data as a function of Fe concentration. The MgO and Mg 0.9Fe 0.1O minerals show an increasing C 44 with pressure, whereas the Δ C 44 / Δ P is slightly negative after 26 GPa for Mg 0.8Fe 0.2O. The C 44 softening could be related to the transition from the cubic to a rhombohedrally distorted phase, recently found by experiment.

Superconducting properties of Tl-2223 phase substituted by iron

Bulk superconducting samples of type Tl2Ba2Ca2Cu3-xFexO10-δ; with 0 ⩽ x ⩽ 0.4, have been prepared using a single step of solid-state reaction. The prepared samples have been characterized using X-ray powder diffraction (XRD), scanning electron microscope (SEM) and microprobe analysis (MPA). The tetragonal structure of Tl-2223 did not change with the partial replacement of Cu2+ by Fe3+ ions, whereas the lattice parameters were found to vary as function of Fe-content. The superconducting transition temperature Tc determined from electrical resistivity and ac magnetic susceptibility measurements shows suppression in its value as Fecontent increases. The suppression in Tc was attributed to the magnetic disorder and Cooperpairs breaking. The critical current density Jc and field irreversibility Bir were calculated as function of Fe-content.

Local structures of nanostructured [formula omitted] alloys

The structural and magnetic properties of mechanically alloyed ( Fe x Co 1 - x ) 75 C 25 ( x = 0 , 0.2, 0.5, 0.8, 1) alloys were studied as a function of Fe content. The local structural change of FeCo–C has been investigated by means of XRD, EXAFS and Mössbauer spectrometry. XRD pattern from 25 h alloyed FeCo–C powders indicated cohenite like phases. EXAFS analysis showed ( FeCo ) 3 C phase formation in x = 0.2 , 0.5 and 0.8, respectively. Mössbauer analysis reveals that Fe(Co) 3 C phase as dominant phase decreased with the Fe content decrease, in a good agreement with EXAFS analysis.

Structure and electrochemical properties of Sm 0.5Sr 0.5Co 1 − xFe xO 3 − δ cathodes for solid oxide fuel cells

Crystal structure, thermal expansion coefficient, electrical conductivity and cathodic polarization of compositions in the system Sm 0.5Sr 0.5Co 1 − x Fe x O 3 − δ with 0 ≤ x ≤ 0.9 were studied as function of Co / Fe ratio and temperature, in air. Two phases, including an Orthorhombic symmetry for 0 ≤ x ≤ 0.4 and a cubic symmetry for 0.5 ≤ x ≤ 0.9, were observed in samples of Sm 0.5Sr 0.5Co 1 − x Fe x O 3 − δ at room temperature. The adjustment of thermal expansion coefficient (TEC) to electrolyte, which is one of the main problems of SSC, could be achieved to lower TEC values with more Fe substitution. High electrical conductivity above 100 S/cm at 800 °C was obtained for all specimens, so they could be good conductors as cathodes of IT-SOFC. The polarization behavior of SSCF as a function of Fe content was evaluated by means of AC impedance using LSGM electrolyte. It was discovered that the Area Specific Resistance (ASR) of SSCF increased as the amount of substitution of Fe for Co increased. When the amount of Fe reached to 0.4, the highest ASR was obtained and then the resistance started decreasing above that. The electrode with a composition of Sm 0.5Sr 0.5Co 0.2Fe 0.8O 3 − δ showed high catalytic activity for oxygen reduction operating at temperature ranging from 700 to 800 °C.