Incorporation Of Fe Ions Research Articles

Structural characterization, electrical and magnetic properties of (In0.97-xFexMg0.03)2O3 films

Structural, electrical, and magnetic properties of (In0.97-xFexMg0.03)2O3 films with different Fe concentration are investigated. The doped Fe ions replace the In1 sites of In2O3 lattice with the mixed-valence of +2 and +3 states and form FeIn1+2VO complex based on the real-space multiple-scattering simulation. The room temperature ferromagnetic hysteresis loop of Fe/Mg co-doped In2O3 films shows ferromagnetic ordering with coercivity Hc of about 150-300 Oe. Obvious increase of ferromagnetic hysteresis loop and saturation magnetic moment with a maximum value of 8.45 emu/cm3 (x = 0.08) are observed due to the more incorporation of Fe ions. All the films exhibit n-type conductive behavior, which are mainly dominated by Mott variable range hopping with strong localization of carriers. Interestingly, the contribution of positive and negative magnetoresistance (MR) strongly correlates with Fe dopant and temperature. It can conclude that the FeIn1+2VO complex based on bound magnetic polaron model plays a key role for achieving the intrinsic ferromagnetism.

A Novel Approach for Designing a Sub-Bandgap in CuGa(S,Te)2 Thin Films Assisted with Numerical Simulation of Solar Cell Devices for Photovoltaic Application.

As a well-explored chalcopyrite material, copper gallium sulfide CGS has been considered a potential material for solar cell absorber layers. However, its photovoltaic attributes still require to be improved. In this research, a novel chalcopyrite material, copper gallium sulfide telluride CGST, has been deposited and verified as a thin film absorber layer to fabricate high-efficiency solar cells by experimental testing and numerical simulations. The results display the intermediate band formation in CGST with incorporation of Fe ions. Electrical studies showed enhancement in mobility from 1.181 to 1.473 cm2 V-1 s-1 and conductivity from 2.182 to 5.952 S cm-1 for pure and 0.08 Fe-substituted thin films. The I-V curves display the photoresponse and ohmic nature of the deposited thin films, and the maximum photoresponsivity (0.109 A W-1) was observed for 0.08 Fe-substituted films. Theoretical simulation of the prepared solar cells was carried out using SCAPS-1D software, and the obtained efficiency displayed an increasing trend from 6.14 to 11.07% as the Fe concentration increased from 0.0 to 0.08. This variation in efficiency is attributed to the decrease in bandgap (2.51-1.94 eV) and the formation of an intermediate band in CGST with Fe substitution, which is evidenced in UV-vis spectroscopy. The above revealed results open the way to 0.08 Fe-substituted CGST as a promising candidate as a thin film absorber layer in solar photovoltaic technology.

Engineering the physical properties of CdS thin films through incorporation of Fe dopant for photodetector applications

Pure CdS and 1, 2, 3, 4, and 5 wt% Fe-doped CdS thin films have been fabricated on glass substrates at a coating temperature of 450 °C by a simple and economical spray-pyrolysis technique. The prepared samples have been characterized by various analytical techniques to assess their crystalline, morphological, optical, and photo-sensing properties. X-ray diffraction (XRD) analysis has revealed the presence of the hexagonal wurtzite phase of CdS, with (002) as the predominant plane. With the incorporation of the Fe dopant into CdS, the peak of the predominant plane (002) increases, suggesting an increase in the crystallinity of the samples. The CdS:Fe4% sample showed the largest crystallite size of 49 nm. The morphologies of the prepared thin films reveal uniform clusters of very fine nanoparticles, with the incorporation of Fe ions in CdS improving the particle size and porosity, which is beneficial for light harvesting. UV/Vis studies have indicated an improvement in the optical absorption of the CdS:Fe4% sample, with a reduction in the band gap to 2.29 eV. Photoluminescence (PL) spectra feature broad emission peaks at around 460, 535, and 640 nm, the intensities of which increase with the incorporation of the Fe dopant, suggesting improved radiative recombination of excitons and defect sites, such as S vacancies and Cd vacancies. Photo-sensing studies of the fabricated devices showed the highest photocurrent (28 μA), responsivity (5.59 × 10−1 AW−1), detectivity (9.05 × 1010 Jones), and external quantum efficiency (180%), as well as the shortest response time (0.1 s) and recovery time (0.2 s), for the CdS:Fe4% photodetector, suggesting that this sample is best suited for commercial application in photodetectors.

Inverting destructive electrochemical reconstruction of niobium nitride catalyst to construct highly efficient HER/OER catalyst

Electrochemical reconstruction (ECR) is an inevitable phenomenon and also a post-synthetic method in generating real-time active catalysts from pristine materials for various industrial electrochemical processes. Constructive ECRs have commonly been reported in literature, but destructive ECR, especially in the case of non-oxide (S, Se, P, N, etc.) materials, has often gone unnoticed due to insufficient understanding of the process. Herein, we demonstrated an “active site optimization” concept for transforming a destructive ECR into a constructive ECR while using oxygen evolution reaction (OER) as a model electrochemical process. Under alkaline H2 evolution conditions, pristine Nb4N5 does not undergo electrochemical reconstruction and exhibits an outstanding performance that reached a current density of −10 mA cm−2 at 7 mV of overpotential (without iR-correction). However, under alkaline OER conditions, pristine niobium nitride is subjected to destructive ECR and formed inactive KNbO3 species. The incorporation of Fe ion has re-directed the destructive ECR toward a constructive path by developing new active sites. The Fe-incorporated real-time catalyst resulted in an enhanced catalytic OER reaction that reached a current density of 1 A/cm2 with an overpotential of 438 mV. This work provided a comprehensive explanation on the detrimental impact of ECR on electrochemical reactivity of pristine catalysts, and simultaneously presented a conceptual demonstration of a potential strategy to re-direct an ECR path toward a desired direction that improves catalytic activity.

Structure, dynamics and mechanical properties evolution of calcium-silicate-hydrate induced by Fe ions: A molecular dynamics study

The adsorption of Fe ions in the calcium-silicate-hydrate (C-S-H) is of great importance as it involves the corrosion process of reinforced concrete structures. In this paper, molecular dynamics simulation was carried out to study the structure, dynamics and mechanical properties evolution of C-S-H induced by Fe ions. Through the analyses of local structure, atomic dynamics and bond stability, the results show that Fe ions are in tetrahedral coordination in the C-S-H and form 3 shells with neighbor atoms which are consistent with the extended X-ray absorption fine structure (EXAFS) results. In addition, the incorporation of Fe ions could reduce the polymerization of silicate chains by disordering the distribution of Os and Si atoms and weakening the strength of Si-O bonds. On the contrary, the connection between Caw (interlayer Ca atoms) and O atoms was slightly enhanced by Fe ions. The mechanical properties of C-S-H in three directions all decrease with the increasing Fe/Ca ratios (i.e., corrosion degree) as the silicate chains and interlayer connection were weakened by Fe ions. Hopefully, the properties of Fe ions adsorbed in the C-S-H could provide new insights on understanding and predicting performance of concrete structure under corrosion environment.

Synergistic effects of Fe and Mn dual-doping in Co3S4 ultrathin nanosheets for high-performance hybrid supercapacitors

Dopant engineering in nanostructured materials is an effective strategy to enhance electrochemical performances via regulating the electronic structures and achieving more active sites. In this work, a robust electrode based on Fe and Mn co-doped Co3S4 (FM-Co3S4) ultrathin nanosheet arrays (NSAs) on the Ni foam substrate is prepared through a facile hydrothermal method followed by a subsequent sulfurization reaction. It has been found that the incorporation of Fe ions is beneficial to higher specific capacity of the final electrode and Mn ions contribute to the excellent rate capability in the reversible redox processes. Density functional theory (DFT) calculations further verify that the Mn doping in the Co3S4 obviously shorten the energy gap of Co3S4, which favors the electrochemical performances. Due to the synergetic effects of different transition metal ions, the as-prepared FM-Co3S4 ultrathin NSAs exhibit a high specific capacity of 390 mAh g−1 at 5 A g−1, as well as superior rate capability and excellent cycling stability. Moreover, the corresponding quasi-solid-state hybrid supercapacitors constructed with the FM-Co3S4 ultrathin NSAs and active carbon exhibit a high energy density of 55 Wh kg−1 at the power density of 752 W kg−1. These findings demonstrate a new platform for developing high-performance electrodes for energy storage applications.

Mesoporous anion-cation-codoped Co9S8 nanorings for enhanced electrocatalytic oxygen evolution reactions

Recently, the design and synthesis of Co9S8 micro/nanostructures have attracted attention as electrochemical energy storage and conversion devices due to their low cost and environmental friendliness. Herein, Co9S8 nanorings were synthesized via a one-step solvothermal method with the incorporation of Fe ions, subsequently, properly selenized to boost their electrocatalytic performance. The morphology and structure of the series of cation and anion regulated Co9S8 nanorings were characterized, the electrochemical oxygen evolution reaction (OER) properties were assessed. It is worth noting that the as-prepared catalysts, especially the innovative Fe and Se ions double doped Co9S8 nanorings, denoted as Se/Fe-Co9S8-0.14, exhibited good electrocatalytic OER performance with low overpotential (298 mV) and high durability under alkaline conditions. This work provides a new perspective to develop non-noble metal Co9S8-based OER electrocatalysts with a superior electrocatalytic performance.

Synthesis of hydroxyapatite containing iron ions by soft solution method and evaluation of photo-Fenton reaction

ABSTRACT Hydroxyapatite (HAp) is widely studied owing to its high adsorption capacity for various substances. In this study, HAp containing iron ions (FeAp) was synthesised by a simulated body fluid method, and the solid-solution state of iron in FeAp crystals was investigated to evaluate the photo-Fenton reaction. The crystalline phase and lattice parameters of the sample were determined through X-ray diffraction analysis. The lattice parameters revealed lattice contraction along the a-axis direction for FeAp, indicating the incorporation of Fe ions. The results of methylene blue decolourisation experiments and potential measurements with a scanning probe microscope before and after the addition of H2O2 suggested that FeAp undergoes a photo-Fenton reaction. Thus, it was confirmed that iron in the crystals contributed to the photo-Fenton reaction.

Structural evolutions and oxidation behavior of Fe-doped silicon oxycarbide nanocomposites at medium temperatures

A novel Fe ion doped silicon oxycarbide (SiFeOC) ceramic was prepared by solvothermal method using methyltrim ethoxysilane, dimethyl dimethoxy silicane, and ferric nitrate as raw materials. Compared with pure SiOC ceramic, the incorporation of Fe ion into SiOC ceramic significantly enhanced phase separation of the SiOC network. Transmission electron microscopy and X-ray diffraction analysis showed that the SiFeOC ceramics were made up of amorphous SiOC, SiC and Fe3Si phases after pyrolysis at 1573 K. The anti-oxidation capabilities of such nanocomposites were also investigated at medium temperatures. Results showed that SiFeOC ceramics had better oxidation resistance properties than pure SiOC ceramics, and the phase compositions of those samples were also analyzed after the oxidation test process. This work provides a guidance to fabricate metal-modified SiOC ceramics with desired structures.

Narrow Band Gap and Room-temperature Ferromagnetism in KNb1−x FexO31−δ

We have investigated the structure, optical and magnetic properties of ferroelectric KNb1−xFexO3−δ (x=0, 0.01, 0.03, 0.05, 0.10, 0.15, 0.20, 0.25) synthesized by a traditional solid-state reaction method. According to the X-ray diffraction and the results of Rietveld refinement, all the samples maintain orthorhombic distorted perovskite structures with Amm2 space group without any secondary phase, suggesting the well incorporation of Fe ions into the KNbO3 matrix. With the increase of Fe concentration, the band gap of each sample is decreased gradually, which is much smaller than the 3.18 eV band gap of pure KNbO3. Through X-ray photoelectron spectrum analysis, the increased density of oxygen vacancy and Fe ions may be responsible for the observed decrease in band gap. Compared with the pure KNbO3, Fe doped samples exhibit room-temperature weak ferromagnetism. The ferromagnetism in KNb1−xFexO3−δ with low-concentration dopants (x=0.01–0.10) can be attributed to the bound magnetic polaron mediated exchange. The enhancement of magnetism for the high-concentration (x=0.10–0.20) doped samples may arise from the further increase of magnetic Fe ions.

Magnetic properties and environment sites in Fe doped SnO2 nanoparticles

Sn1−xFexO2 nanoparticles (x = 0, 0.05, 0.10 and 0.15) were synthesized by co-precipitation. X-ray diffraction and electron diffraction images showed that only rutile type phase was present in the samples. Electron microscopy was used as a tool for revealing morphology, distribution size and structure characteristics of the nanoparticles; while Energy Dispersive X-Ray Spectroscopy analysis confirmed the selected stoichiometry. 57Fe and 119Sn Mössbauer spectroscopy at Room Temperature showed a lattice disorder induced by the incorporation of Fe ions in the structure. No magnetic hyperfine ordering was detected for 57Fe probes and the asymmetry in their quadrupolar splittings is explained as a texture effect at the nanoparticles shells. Quadrupolar splitting at 119Sn probe reached a maximum for x = 0.1, being this fact attributable to a highest distorted environment. Magnetic hysteresis loops were measured at different temperatures showing, for Fe doped samples, a combination of paramagnetism and weak ferromagnetism.

Tuning the surface anisotropy in Fe-doped NiO nanoparticles

Ni(1-x)FexO nanoparticles have been obtained by the co-precipitation chemical route. X-ray diffraction analyses using Rietveld refinement have shown a slight decrease in the microstrain and mean particle size as a function of the Fe content. The zero-field-cooling (ZFC) and field-cooling (FC) magnetization curves show superparamagnetic behavior at high temperatures and a low temperature peak (at T = 11 K), which is enhanced with increasing Fe concentration. Unusual behavior of the coercive field in the low temperature region and an exchange bias behavior were also observed. A decrease in the Fe concentration induces an increase in the exchange bias field. We argue that these behaviors can be linked with the strengthening of surface anisotropy caused by the incorporation of Fe ions.

Bifunctional Fe-SBA-15-SO3H Mesoporous Catalysts with Different Si/Fe Molar Ratios: Synthesis, Characterization and Catalytic Activity

Bifunctional Fe-SBA-15-SO3H mesoporous materials with different Si/Fe molar ratios (3, 5, and 7) have been synthesized via a simple direct hydrothermal method and characterized by XRD, N2-adsorption/desorption, TG/DTG and FT-IR techniques, and used as solid acid catalysts in the esterification of lactic acid with methanol. XRD and N2 sorption characterizations show successful iron doping within the mesoporous channels of SBA-15-SO3H. The FT-IR and TG/DTG characterizations also reveal the presence of iron. With the incorporation of Fe ions into the SBA-15-SO3H, the acid sites substantially increased because of the selfseparated acidity of the hydrolysis of Fe 3+ solutions. However, in the Si/Fe = 3 molar ratio, the catalytic conversion decreased which is caused by the reduced cooperation effect between the acid pairs due to the weakened hydrogen bonds and collapse of the pore structure. This further suggests that the mesoporous structure decreases with the decrease in Si/Fe ratio.

Mössbauer spectroscopy study of iron complexes in a poly(methacrylic acid) hydrogel matrix

Using Mossbauer spectroscopy, we have studied iron complexes resulting from the interaction of aqueous iron salt solutions with poly(methacrylic acid) (PMAA) gel. In these complexes, the di- and trivalent Fe ions are linked to the PMAA through the COO− functional group. From the observed dynamics of the variation in the intensities of the di- and trivalent iron in the Mossbauer spectra of the gels with incubation time and iron concentration in solution, we have inferred a model for the incorporation of Fe ions into a gel matrix.

Bulk synthesis and high-temperature ferromagnetism of (In1−xFex)2O3−σ with Cu co-doping

The synthesis and magnetic properties of (In1−xFex)2O3−σ bulk ceramics with Cu co-doping are reported. Magnetic Fe ions are found to have high thermodynamic solubility (up to 20%) in the In2O3 host compound. The lattice constant decreases almost linearly as Fe doping concentration increases indicating the incorporation of Fe ions into the host lattice. The samples with high Fe concentration annealed under Ar reduced atmosphere were found to be ferromagnetic, and the Curie temperature is around 750K. The extensive structural and magnetic studies rule out the possibility that the observed magnetism is derived from magnetic impurity phases.