Effect Of Fe Substitution Research Articles

Effects of Fe substitution for Mn on structural, magnetic and magnetocaloric properties of TbMn2-xFexSi2

The structural and magnetic properties of TbMn2-xFexSi2 compounds (x = 0.0–0.4) have been investigated in details by high-resolution synchrotron x-ray and neutron powder diffraction, specific heat, and dc magnetization measurements. The replacement of Fe for Mn in TbMn2-xFexSi2 does not change the crystal structure but leads to a significant contraction of the unit cell (dV/dx ∼ - 6 Å3) and modification of three magnetic phase transition temperatures – the Curie temperatures Tc1, Tc2 and the Néel temperature TN. For example, the Tc1, Tc2 and TN values of TbMn2Si2 decrease from Tc1 = 50 K, Tc2 = 64 K and TN = 500 K to Tc1 = 27 K, Tc2 = 37 K and TN = 440 K for TbMn1.6Fe0.4Si2. Detailed neutron diffraction investigations have allowed us to determine the magnetic structures and construct the magnetic phase diagram as well as confirm the presence of magnetoelastic coupling effects. The significantly different responses of Tc1 and Tc2 to applied magnetic fields (e.g. dTc1/dB = 0.52 K/T and dTc2/dB = 4.7 K/T for TbMn1.6Fe0.4Si2), leads to expansion of the temperature region (ΔT = Tc2- Tc1) for the canted ferromagnetic state Fmc-ii between Tc1 and Tc2. In the case of TbMn1.6Fe0.4Si2, ΔT increases from ΔT = 9 K for applied magnetic field B = 0.2 T to ΔT = 36 K for B = 6 T, resulting in plateau-like behaviour of magnetic entropy change and enhances the relative cooling power (RCP) in this system. Under a change of magnetic field of 0 T – 5 T, the maximum value of the magnetic entropy changes -ΔSmax and adiabatic temperature change, ΔTad are derived to be -ΔSmax = 13.1 J/kg K and ΔTad = 8.4 K with the RCP = 411 J/kg for x=0.4 sample. The plateau-like magnetocaloric effect and relatively large RCP make these materials potentially suitable for application in cryogenic magnetic refrigeration.

Fe-induced modifications in the magnetic and dielectric response of EuTiO3: Unraveling the linkage to oxygen vacancies

EuTi1−xFexO3 (x = 0.0–0.5) is studied to analyze the effect of Fe substitution on structural, dielectric and magnetic properties. We found that Fe substitution in place of Ti increases the barrier for charge carrier hopping therefore, suppresses the electrical conduction in the material. It has also been observed that characteristic G-type antiferromagnetic ordering of pure EuTiO3 can be significantly modified with Fe doping. Interestingly, formation of oxygen vacancies due to Fe substitution allows next nearest neighbor Eu ion interaction and generates ferromagnetic response in the magnetic hysteresis loops. Magnetic phase transition temperature also shifts to the higher temperature side with the increase in Fe concentration till x = 0.3 which implies strengthening of magnetic interaction. Schematic models based on the crystal and electronic structure are presented to explain the observed dielectric and magnetic response and it is concluded that both features can be tuned by the Fe substitution.

Weyl points and anomalous transport effects tuned by the Fe doping in Mn3Ge Weyl semimetal

The discovery of a significantly large anomalous Hall effect in the chiral antiferromagnetic system—Mn3Ge—indicates that the Weyl points are widely separated in phase space and positioned near the Fermi surface. In order to examine the effects of Fe substitution in Mn3Ge on the presence and location of the Weyl points, we synthesized (Mn 1−α Fe α)3 Ge ( α=0−0.30 ) compounds. The AHE was observed in compounds up to α = 0.22, but only within the temperature range where the magnetic structure remains the same as the Mn3Ge. Additionally, positive longitudinal magnetoconductance and planar Hall effect (PHE) were detected within the same temperature and doping range. These findings strongly suggest the existence of Weyl points in (Mn 1−α Fe α)3 Ge ( α=0−0.22 ) compounds. Further, we observed that with an increase in Fe doping fraction, there is a significant reduction in the magnitude of anomalous Hall conductivity, PHE, and positive longitudinal magnetoconductance, indicating that the Weyl points move further away from the Fermi surface. Consequently, it can be concluded that suitable dopants in the parent Weyl semimetals have the potential to tune the properties of Weyl points and the resulting anomalous electrical transport effects.

Facilitating the strength-ductility balance in Ni3Al via Fe co-substitution at two sites

In this work, the effect of Fe substitution on the stability and deformation mechanism of Ni3Al was studied using first principles calculations. The results show that Fe is more likely to occupy the Ni site in terms of energy at low substitution concentrations, but occupying the Al site is more favorable for the stability of the system. The results also show that FeNi substitution brings ductility to the intermetallics while FeAl substitution ensures strength. In addition, the results for the generalized stacking fault energies at high substitution concentrations are different from those at low concentrations because of the change in the matrix. Therefore, dual-site substitution of Fe in appropriate proportions can help Ni3Al overcome the strength-ductility trade-off. This work provides useful knowledge for better design and utilization of Ni3Al-based multicomponent intermetallics.

Selective occupancy of Fe substitution enhance the room-temperature ferromagnetism of (FexNi1-x)2P nanocrystals: Experimental and theoretical studies

Understanding the heteroatoms occupancy in metal phosphides is significant to regulate their properties. (FexNi1-x)2P (0 ≤ x ≤ 0.5) nanocrystals were prepared by thermal decomposition. Effects of Fe substitution on structure, morphology and magnetic properties were studied. As the Fe content increases, (FexNi1-x)2P maintain hexagonal structure with morphologies changing from sphere to irregular sheet. Atomic HAADF-STEM image reveals that the atom configuration matches well with [001] crystallographic orientation. (FexNi1-x)2P nanocrystals show room-temperature ferromagnetism. The Ms values and magnetocrystalline anisotropy are enhanced by increasing Fe substitution. The Ms value of (Fe0·5Ni0.5)2P reaches 2.092 emu/g, 19.5 times larger than Ni2P. XPS and Mössbauer spectra show that Fe2+/Fe3+ selectively occupy tetrahedral and pyramidal positions due to the difference of ionic radius, resulting in enhanced room-temperature ferromagnetism. First-principles calculations show that Fe substitution can induce ferromagnetic ordering in Ni2P, and Fe substitution in pyramidal positions induces larger magnetic moment, further confirming the experimental results.

Multifunctional Effect of Fe Substitution in Na Layered Cathode Materials for Enhanced Storage Stability.

Developing stable cathode materials that are resistant to storage degradation is essential for practical development and industrial processing of Na-ion batteries as many sodium layered oxide materials are susceptible to hygroscopicity and instability upon exposure to ambient air. Among the various layered compounds, Fe-substituted O3-type Na(Ni1/2Mn1/2)1-xFexO2 materials have emerged as a promising option for high-performance and low-cost cathodes. While previous reports have noted the decent air-storage stability of these materials, the role and origin of Fe substitution in improving storage stability remain unclear. In this study, we investigate the air-resistant effect of Fe substitution in O3-Na(Ni1/2Mn1/2)1-xFexO2 cathode materials by performing systematic surface and structural characterizations. We find that the improved storage stability can be attributed to the multifunctional effect of Fe substitution, which forms a surface protective layer containing an Fe-incorporated spinel phase and decreases the thermodynamical driving force for bulk chemical sodium extraction. With these mechanisms, Fe-containing cathodes can suppress the cascades of cathode degradation processes and better retain the electrochemical performance after air storage.

Effect of Fe substitution over ZSM-48 on performance of n-dodecane hydroisomerization and distribution of isomers

A series of Fe substituted ZSM-48 nanocrystal aggregates were synthesized by the dynamic hydrothermal method. Through incorporation of Fe into ZSM-48 framework, the acidity of ZSM-48 zeolites has been modified. The hydroisomerization performances of n-dodecane were investigated on Pt supported ZSM-48 and Fe incorporated ZSM-48 zeolites. Fe incorporated ZSM-48 catalysts show higher n-C12 hydroisomerization selectivity compared with parent sample due to weaker acid strength of Si–OH–Fe than Si–OH–Al. High temperature favor the generation of the multi-branched isomers (mainly dimethyl isomers) following the “Key-Lock” mode. Meanwhile, 5-methylundecane is the main product in the monomethyl isomers (MOB) and 2,6-dimethyldecane is the main product in the multi-branched isomers (MUB), which suggests the excellent shape selectivity of ZSM-48 and the “Key-Lock” mode is preferred on ZSM-48 catalysts regardless Fe substituted or not. The relationship between the mono-methyl isomers and the butene-TPD results has been correlated and investigated. Four desorption peaks corresponding to butene weakly adsorbed over Si–OH, Fe–OH or Lewis acid sites, the “Key-Lock” mode adsorbed butene, the “Pore-Mouth” mode adsorbed butene and the strongly adsorbed butene respectively, can be distinguished. ZLC results indicate that Fe modified ZSM-48 can effectively increase n-hexane diffusion rate and reduce the activation energy of diffusion of n-hexane, which is benefit for the hydroisomerization performance. SMOB/SMUB can be altered by Fe modification, however, the distribution of the mono-methyl isomers can hardly be affected.

Tailoring hydrogenation and anti-oxidation properties of titanium - iron - chromium alloys by regulating zirconium content at room temperature

The effects of Fe substitution by Zr on the microstructure, hydrogen storage properties and oxidation resistance of the TiFe0.85-xCr0.15Zrx (x = 0, 0.05, 0.10, 0.15) alloys are studied in this work. It is shown that all the alloys are consisted of TiFe phase, MgZn2-type phase and minor Ti phase. The introduction of Zr causes no change for the TiFe main phase. All the alloys absorb hydrogen directly under mild conditions without any activation process. As Zr content increases, the maximum hydrogen storage capacity of the first hydrogenation increases while the reversible hydrogen storage capacity decreases. The marked change of the first hydrogenation properties may be due to the formation of the bright phase (MgZn2-type phase). The decrease of the reversible hydrogen storage capacity is due to the formation of the stable hydrides Cr2ZrH3 and TiH2, which start to decompose at around 700 °C. During the air exposure test, the alloys with higher Zr content show good oxidation resistance. For the PCT measurement, the alloys with higher Zr show lower hydrogen absorption and desorption platform pressure, which means more stable hydrides are formed during the first hydrogenation. Moreover, the rate limiting step model of the first and fifth hydrogenation processes of all the alloys has also been investigated in detail.

A structural study and some magnetic properties of YCo12-xFexB6 (x = 0–4.5) solid solution

We report on the effects of Fe substitution on the structural and magnetic properties of the YCo12-xFexB6 series of compounds by combining scanning electron microscopy, energy dispersive X-ray microanalysis, X-ray powder diffraction and magnetic measurements. The rhombohedral R3̅m structure of the YCo12-xFexB6 is retained up to about x = 4.5 Fe atom per formula unit, a value that we assign to the estimated solubility limit for polycrystalline samples. The unit cell is found to expand regularly upon increasing the iron content with a rate of 1.55 Å3 per Fe atom, the expansion being larger along the basal plane. Clues for the preferential substitution scheme of Fe for Co are discussed. It is also shown that Fe for Co substitution induces dramatic changes on the magnetic properties such as a strong decrease of the ordering temperature and a significant reduction of the spontaneous magnetization.

Effect of iron substitution in cryptomelane on the heterogeneous reaction with isoprene

Biogenic isoprene is an important pollutant for regional air quality. Being ubiquitously distributed on the earth surface, manganese (hydr)oxides should play a vital role in the transformation of isoprene. Cryptomelane is a typical manganese oxide with isomorphous substitution of Fe for Mn, but less attention has been paid to its heterogeneous reaction with isoprene. When Fe3+ replaces Mn3+, K+ is depleted and Mn3+ is oxidized to Mn4+. In contrast, oxygen vacancies are formed when Fe3+ substitutes Mn4+. Fe substitution creates weak crystallites and abundant mesopores, resulting in the increase of isoprene adsorption. As found by theoretical calculations, the Mn4+–O2- bonds at the cross sections of the tunnels is more active than that on the outer wall of the tunnels. After the adsorption of isoprene, bridging carboxylate species and hydrogen-bonding water are produced and the surface octahedra are distorted, i.e., Mn4+O6 → Mn3+O6-δ. As the heat facilitates the breakage of Mn4+–O2-, the increase of environmental temperature enhances the oxidation of isoprene. The above findings shed light on the effect of Fe substitution in cryptomelane to enhance the oxidation of isoprene, and illustrates that heterogeneous reaction with isoprene impairs the transformation of other environmental substances on cryptomelane.

Effect of Fe substitution with Co on the magnetic properties of Fe80P13C7 amorphous alloys: An abinitio molecular dynamics study

In this study, we analyze the effect of Fe substitution with Co on the magnetic properties of Fe80P13C7 amorphous alloy using experimental measurements and first-principle molecular dynamic calculations of the distribution functions, Voronoi polyhedra, and density of states of Fe80-xCoxP13C7 (x = 0, 5, 10, 15 at.%) alloys. The experimental results demonstrate that the saturation magnetization (Ms) of Fe80-xCoxP13C7 (x = 0, 5, 10, 15 at.%) increases and then decreases with increasing Co content, and that maximum Ms is achieved when the composition of Co is 5 at.%. This trend is consistent with the one determined using simulations. Compared to the other amorphous alloys investigated herein, Fe75Co5P13C7 exhibits the highest local symmetry, which explains why it has the largest exchange splitting energy and largest Ms. In addition, increasing substitution of Fe atoms with Co does not appreciably affect the magnetic moment of Co atoms, but it increases the magnetic moment of Fe atoms, particularly those adjacent to Co. This indicates that Co atoms can induce an increase in the magnetic moment of the Fe atoms surrounding them.

Experimental investigation of the phase equilibria in Co–Fe-Sm system with special attention to the effect of Fe substitution in structure and magnetic properties of intermetallic phases

Phase equilibria in the Sm–Co, Sm–Fe and Co–Fe-Sm systems were investigated in detail using DTA, X-ray diffraction, SEM and EPMA. Based on the experimental data from the present work, the liquidus and solidus projections, the isothermal section at 1000 °C and the Scheil reaction scheme for the Co–Fe-Sm system over the whole concentration range were constructed. The phase diagram of the Sm–Co system was revised. The Sm-rich region of the Sm–Fe system was studied for the first time. The stability domains of the intermetallic phases (binary phases and their extension inside ternary) were defined. Three continuous solid solutions Sm2(Co,Fe)17, Sm(Co,Fe)3 and Sm(Co,Fe)2 were found in the Co–Fe-Sm system at the solidus temperatures. In contrast to a previous analysis of the phase diagram for the system, wide homogeneity regions were revealed for the SmCo5 and Sm2Co7 phases and alternative invariant four-phase equilibria. The magnetic properties of samples containing Sm2(Co,Fe)17 phase were measured. The values of the Curie temperature and the magnetic moment of these samples were quite close to those earlier presented in the literature.

Effect of Fe substitution on the structural, microstructural and dielectric properties of sodium bismuth titanate

Lead free sodium bismuth titanate (NBT) is widely being studied as an emerging room temperature multiferroic and as a ferroelectric material with potential to replace toxic lead based ceramics. Various elements can be substituted in the A-site or B-site to improve its electrical and magnetic properties. In this work, pure and Fe substituted NBT having the chemical formula Na0.5Bi0.5Ti(1-x)FexO3 (x = 0.00, 0.02) were synthesized using sol gel auto ignition method to study the effect of Fe substitution on the properties of NBT. XRD analysis confirmed the rhombohedral symmetry of the synthesized samples and the crystallite size of the samples were calculated using Scherrer’s formula. The morphological property of the samples was studied from the SEM images. UV–Visible Spectroscopy method was employed to study the optical properties of the samples. The dielectric properties of the samples were measured as a function of frequency in the range 100 Hz to 1 MHz at room temperature and also as a function of temperature in the range of 298 K- 473 K using an Agilent HP4284 LCR meter. Usual dispersive behavior of dielectric constant was observed for both the samples at the studied temperature range. Study of frequency and temperature dependence of the AC conductivity suggested that the conduction process in the materials is thermally activated. Jonchers’ universal power law was used to fit the AC conductivity curves to describe the dynamics of charge carrier with suitable conduction mechanism.

Effect of Fe substitution on temperature coefficient of resistance and magnetoresistance of La0.67Ca0.33MnO3 polycrystalline ceramics

La0.67Ca0.33MnO3 perovskite manganate exhibits high temperature coefficient of resistance (TCR) and large magnetoresistance (MR) effect, these enable novel multifunctionalities. Mn site substitution can change magnetic order of the manganates, thereby tailoring both electrical and magnetic transport. Herein, La0.67Ca0.33Mn1-xFexO3(0 ≤ x ≤ 0.06) polycrystalline ceramics were prepared by sol-gel route. The effect of Fe substitution on TCR and MR of La0.67Ca0.33MnO3 was studied. Fe replacing Mn ions, would weaken double exchange, and significantly reduced Curie temperature and ferromagnetism. Additionally, Fe doping promoted the development of grain. TCR increased first with Fe content x and then decreased, and reached 45.2%·K-1 at x = 0.01, which is the highest value reported. Notably, with Fe doping, MR gradually increased and reached 81.1% (1 T) at x = 0.06. Fe doping can significantly enhance TCR and MR, which generates promising potential in (uncooled) thermistor/infrared detecting and magnetic sensors.

Improved mechanical properties and corrosion resistance of Zr-Cu-Al-Ni-Ti bulk metallic glass by Fe substitution for Ni

Herein, the effects of Fe substitution for Ni on glass-forming ability (GFA), mechanical properties and corrosion resistance of Zr56Cu24Al9Ni7-xTi4Fex (x = 0, 1, 3, 5, and 7 at.%) bulk metallic glass (BMGs) were investigated. Trace addition of Fe to 3 at.% slightly affects the GFA of alloys, but Fe over-dosage results in an intense susceptibility to crystallization and failure to form metallic glasses. Furthermore, the compressive strength and plasticity of Zr56Cu24Al9Ni4Ti4Fe3 alloy are significantly enhanced to 1709 MPa and 5.55%, respectively, compared to 1677 MPa and 1.22% for pristine alloy. Meanwhile, the corrosion resistance is greatly improved by Fe addition to 3 at.% then deteriorated with its excess addition. The Zr56Cu24Al9Ni4Ti4Fe3 alloy exhibits the widest passivization zone and the largest Rct, indicating an enhanced corrosion performance. Overall, the synergistic effect of Fe substitution on mechanical and corrosion performance opens a new horizon for design of toxic-free Zr-based BMGs for potential application.

Magnetic Impurity Effects on Ferromagnetic Fluctuations in Heavily Overdoped (Bi,Pb)2Sr2Cu1−yFeyO6+δ Cuprates

We investigated the effects of Fe substitution on ferromagnetic fluctuations in the superconducting overdoped and non-superconducting heavily overdoped regimes of Bi-2201 cuprates by magnetization and electrical resistivity measurements. It was found that the spin-glass state was induced at low temperatures by the Fe substitution. The Curie constant and the effective Bohr magneton, estimated from magnetic susceptibility, as well as the dimensionality of the ferromagnetic fluctuations from the resistivity, suggest the enhancement of the ferromagnetic fluctuations caused by the Fe substitution. A ferromagnetic spin-cluster model is proposed for the heavily overdoped regime of Bi-2201, whereas an antiferromagnetic spin-cluster model has been proposed for the overdoped regime of Bi-2201 [Hiraka et al., Phys. Rev. B 81, 144501 (2010)].

Effect of Fe substitution by Mn and Cr on first hydrogenation kinetics of air-exposed TiFe-based hydrogen storage alloy

This study investigated how Fe substituted with Mn and Cr affected the microstructure and the first hydrogenation kinetics of a TiFe-based hydrogen storage alloy. Vacuum arc melting was used to prepare TiFe1-xMx ingots (M = Mn, Cr, x = 0.1, 0.2, 0.3). Thermodynamic calculations were performed to predict the phase formation behavior. The TiFe0.9Mn0.1 alloy was expected to form a single TiFe phase, and all other alloys were calculated to have dual-phase microstructures with TiFe and Laves phases. Based on the microstructure analysis results, the phase formation behaviors of the alloys showed a trend similar to the thermodynamic calculation results. The first hydrogenation kinetics was examined at room temperature (20 °C) with a hydrogen pressure of 40 bar. The samples for the kinetic analysis were prepared by crushing the ingots in air. The TiFe0.9Mn0.1 alloy with a single TiFe phase did not absorb hydrogen, while the alloys containing Laves phase absorbed hydrogen without any thermal activation process. As for the microstructure and kinetics analysis results, both the percentage and composition of the Laves phases affected the first hydrogenation kinetics.

Electrochemical mechanism and effects of Fe doping and grinding process on the microstructural and electrochemical properties of Na2Co1-xFexSiO4 cathode material for sodium-ion batteries

Sodium-based orthosilicates are considered promising candidates as positive electrode materials for rechargeable sodium-ion batteries (SIBs). Na2Co1-xFexSiO4 (NCFS), with x = 0.1 and 0.2 cathode materials have been synthesized by low cost method (improved solid-state). The effects of Fe substitution and grinding process on the structural, morphological, and electrochemical properties of Na2Co0.9Fe0.1SiO4 (NCFS1) and Na2Co0.8Fe0.2SiO4 (NCFS2) are deeply investigated. The prepared Na2Co1-xFexSiO4 cathodes are indexed based on the orthorhombic system with Pca21 space group with a slight difference in lattice parameters. The morphological properties are strongly determined by the suspension formalism, which has an impact on the electrochemical performances. The ball-milling process leads to enhanced electrochemical performance and higher reversible capacity although with capacity fading after 100 cycles. Na2Co0.8Fe0.2SiO4 demonstrated an initial discharge capacity at C/50 of 131.4 mAh.g−1 (1C= 272.7 mA.g−1) that is two times higher than that of the Na2Co0.9Fe0.1SiO4 (54.6 mAh.g−1 (1C= 272.27 mA.g−1)). All the above features and insights make the new materials highly promising for use as potential cathode material for SIBs.

Effect of Fe substitution on first hydrogenation kinetics of TiFe-based hydrogen storage alloys after air exposure

This study investigated how Fe substitution with Ni, Co, Cu, Mn, and Cr affected the first hydrogenation behavior of air-exposed TiFe-based hydrogen storage alloys. The alloy ingots were crushed into powders and exposed to air for 1 h to analyze the first hydrogenation kinetics. Although Fe was substituted with up to 30% of Ni, Co, and Cu, the alloys had a single TiFe phase. In addition, the TiFe0·7Ni0·2Co0.1 and TiFe0·7Co0·2Ni0.1 alloys also had a single TiFe phase in spite of the simultaneous substitution. The composition of the oxide layer changed by the addition of Ni, Co, and Cu, but the alloys did not absorb hydrogen. In the TiFe0·8Mn0.2 and TiFe0·8Cr0.2 alloys, a dual-phase microstructure consisting of TiFe and Mn/Cr-rich C14 Laves phase was formed, with a larger amount in TiFe0·8Cr0.2. Both samples absorbed hydrogen after air exposure without any thermal activation process. Comparing the first hydrogenation kinetics, TiFe0·8Cr0.2 had a shorter incubation time and faster hydrogen absorption rate than TiFe0·8Mn0.2.

Role of Fe (x = 0–0.15) Substitution on Structural, Magnetic, and Transport Properties of the La0.7Sr0.3FexMn1−xO3 System

This paper investigates the effect of Fe substitution on the structural, magnetic and transport properties of the La0.7Sr0.3MnxFe1−xO3 (LSMO) system where x ranged between 0 and 0.15. Samples were prepared using a non-aqueous sol-gel synthesis method. Structural and chemical analysis confirmed the Fe3+ substitution at Mn3+ sites without any impurity phase resulted in a small change in structural parameters of the LSMO. The change in magnetic behavior and Curie temperature of the Fe-doped LSMO is explained through competitive exchange interactions developed in the system. The temperature-dependent resistivity demonstrated that the resistivity of the samples increased with Fe concentration due to different conduction mechanisms related to the ferromagnetic-metallic and paramagnetic-insulating regions. The magneto-transport measurement showed significant improvement in the magnetoresistance due to Fe doping at Mn site, which was attributed to enhancement of the spin-glass phase in Fe doped LSMO system. The reduction in magnetoresistance for higher Fe concentration is explained with the help of percolation threshold mechanism.