Increasing Fe Substitution Research Articles

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.

Physicochemical studies of iron/vanadate doped hydroxyapatite/polycaprolactone nanofibers scaffolds

Altering nanofibrous structures to be used for wound healing applications is crucially needed to improve quality of life. Co-substituted hydroxyapatite (HAP) with different iron (Fe)/vanadate (VO43−) ions contributions are involved in polycaprolactone (PCL), where the electrospinning method is used to fabricate PCL polymer. XRD explains both powder and nanofibrous scaffold structural features. The surface morphology for powdered Fe/V-HAP@PCL shows changes in grains size from 1.59–6.26 µm to 2.0–3.76 for the minimum and maximum Fe composition. The roughness average increased by increasing Fe substitution from 37.0 to 56.5 nm, while (Rq) rises from 49.8 to 73.7 nm. The surface morphology of nanofibers shows a diameter range from around 0.97–3.19 µm to 0.44–1.91 µm. Further, the roughness parameter of Ra rose from 34.96 to 59.49 nm. TEM micrographs revealed the diameters of nanofibrous scaffolds are around 200–360 nm. Mechanical parameters vary upon increasing dopant ions in HAP; tensile strength rises from 1.61 ± 0.8 to 4.93 ± 0.8 MPa. Moreover, the contact angle decreased by increasing Fe ion, in which values declined from 101.2 ± 2.5 to 85 ± 4.3°. Enhancing cell viability from 90.3 ± 3.1% to 97.5 ± 2.8% for the minimum and maximum Fe ions composition., The porosity of the nanofibrous surface improved, which illustrated increasing cell growth upon increasing dopant ion. Hence, modulating the nanofibrous scaffold by controlling the composition of doped metal ions could be advantageous for biomedical applications.

Effect of Fe Substitution on Dielectric, Electrical and Photocatalytic Behavior of ZnO Nanoparticles

Aims: To develop a simple and cost effective synthetic strategy for the preparation of Fe substituted ZnO nanoparticles. Background: The optoelectronic, electrical, dielectric, optical and magnetic properties of nanocrystalline transition metal substituted ZnO are being explored worldwide for a variety of applications in optoelectronic devices, solar cells, transparent thin film transistors, ultraviolet photodetector, piezoelectric devices, light emitting diodes as well as in the biomedical field. Fe substituted ZnO nanoparticles are being looked upon as promising material in dilute magnetic semiconductor system. Objective: To establish chemical identity and purity in order to ensure the complete substitution of Fe3+ in ZnO lattice and study the effect of Fe substitution on dielectric, electrical and photocatalytic behavior of ZnO nanoparticles. Methods: The nearly spherical ZnO and Fe substituted ZnO nanoparticles were synthesized at a low temperature via solution combustion synthesis employing metal nitrate and sucrose. Results: The powder X-ray diffraction measurement has revealed the monophasic character and complete substitution of Fe in the wurtzitic ZnO lattice. The lattice constants and aspect ratio of Fe substituted ZnO were nearly constant and comparable to that of pristine ZnO. The average crystallite size was found to decrease with increasing Fe substitution. SEM images revealed porous spongy network like morphology. TEM measurements revealed a nearly spherical particle with narrow size distribution between 10 nm - 25 nm. Conclusion: The dielectric constant and dielectric loss decrease upto x = 0.04 and increases with further increase in Fe concentration. The lower value of dielectric loss in the higher frequency region indicates the less lossy nature of Fe substituted samples. AC conductivity behaviour suggests small polaron hopping type of conduction mechanism. The RT DC resistivity was found to decrease with increasing Fe substitution. Pristine ZnO displayed very high degradation efficiency for photodegradation of MB dye. The photodegradation efficiency was found to decrease considerably with increasing Fe substitution.

Fe doping effect on the structural, ferroelectric and magnetic properties of polycrystalline BaTi1−xFexO3 ceramics

BaTi1−xFexO3 (x = 0–0.08) ceramics were prepared by conventional solid-state reaction. The Fe doping effect on the structure, electrical and magnetic properties was analyzed. The Fe substitution would reduce the degree of tetragonality and ferroelectricity. The hexagonal phase began to emerge and increased after x = 0.04 by the X-ray diffraction. Meanwhile, ferroelectricity is diminished due to an increase of the non-ferroelectric hexagonal and pinning of domain wall motioned by oxygen vacancies with the increasing Fe substitution. It is found that the nonlinear change of magnetic properties with the increasing Fe concentration. The critical role of the valence state of Fe ions and the accompanied oxygen vacancies on the magnitude of magnetic properties is discussed. Our investigations suggest that the competition of Fe4+–O2−–Fe4+, Fe3+–O2−–Fe4+ and Fe3+–O2−–Fe3+ interaction are coexisted, and the Fe4+–O2−–Fe4+ super-exchange interaction is responsible for the larger magnetism at x = 0.04. From the analyze of XPS spectra, the higher content of Fe4+ and lower oxygen vacancies at x = 0.04 verify that Fe4+–O2−–Fe4+ super-exchange interaction is the origin of larger magnetism.

Magnetization and ac susceptibility study of the cubic chiral magnet Mn1−xFexSi

We present a comprehensive and systematic magnetization and ac susceptibility study of Mn$_{1-x}$Fe$_{x}$Si over an extensive range of ten Fe concentrations between $x$ = 0 - 0.32. With increasing Fe substitution, the critical temperature decreases but the magnetic phase diagrams remain qualitatively unaltered for $x$ $\leq$ $x^*$ $\approx$ 0.11 with clear boundaries between the helical, conical, and skyrmion lattice phase as well as an enhanced precursor phase. A notably different behavior sets in for $x$ $=$ 0.11, 0.13 and 0.14, where certain characteristics of helimagnetic correlations persist, but without clear phase boundaries. Although a qualitative change already sets in at $x^*$, the transition temperature and spontaneous magnetization vanish only at $x_C$ = 0.17 where also the average magnetic interactions change sign. Although the Curie-Weiss temperature reaches -12~K for $x$ = 0.32, no signature of long-range magnetic order is found down to the lowest temperature, indicating a possible significant role for quantum fluctuations in these systems.

Effect of Fe doping on the performance of suspension plasma-sprayed PrBa0.5Sr0.5Co2−xFexO5+δ cathodes for intermediate-temperature solid oxide fuel cells

Abstract PrBa 0.5 Sr 0.5 Co 2–x Fe x O 5+δ (PBSCF) (X = 0, 0.3, 0.4, and 0.5) is investigated as cathode material for intermediate-temperature solid oxide fuel cells. Suspension plasma spraying is used as a low cost and large-scale manufacturing process to prepare PBSCF cathodes. Fe substitution effects on the crystal structure and electrochemical performance are characterized. All plasma-sprayed PBSCF cathodes exhibit a pure and stable cubic structure. The suspension plasma-sprayed PBSCF deposits show a porous and fine structure, and the microstructures are insensitive to Fe substitution. Subsequent to Fe doping, the polarization resistance of PBSCF cathodes rapidly decreases for increasing Fe substitution concentration from 0 to 0.4. Further increase of the Fe doping concentration increases the cathode polarization instead. At 600 and 700 °C, a 20% Fe-doped (x = 0.4) PBSCF cathode exhibits remarkably low area-specific polarization resistances (R p ) of 0.074 Ω cm 2 and 0.012 Ω cm 2 , respectively. Moreover, the R p of all cathodes remains almost identical after isothermal annealing at 600 °C for 300 h. Furthermore, the thermally-sprayed porous metal-supported cell assembled with the optimal PBSCF cathode shows excellent performance with peak power densities of 0.37, 0.8, and 1.35 W cm −2 at 500, 600, and 700 °C, respectively.

Electrochemical and Chemical Characterization of NdBa1-XCo2-YFeYO5+ δ Cathodes for IT-SOFCs

Neodymium- and cobalt-based layered perovskite oxides with increasing Fe substitution (NdBaCo2-yFeyO5+δ, y = 0.0 ÷ 0.4) were prepared via the molten citrate technique and fully characterized. The physic-chemical properties were investigated via XRD, TG-DTA, ICP-MS and cerimetric titrations. The electrical conductivity was measured and EIS was performed on symmetrical cells with GDC electrolyte. Iron substitution triggers a structural change from orthorhombic to tetragonal, and cell size increases with iron content. Co and Fe increase their average oxidation state, and the oxygen content increases at increasing Fe. The electrical conductivity is lowered by doping, with a relative maximum at y = 0.2. The y = 0.4 composition shows the lowest polarization resistance (0.17 Ω*cm2 at 700°C). The ORR mechanism investigated by ECM and physical 1D modeling shows that the first electronation of the oxygen atom on the MIEC surface and the bulk diffusion of the oxygen vacancies in the MIEC lattice are the rate determining steps.

Martensitic phase transition, inverse magnetocaloric effect, and magnetostrain in Ni50Mn37-xFexIn13 Heusler alloys

In this paper, we have performed the martensitic phase transition, inverse magnetocaloric effect, and magnetostrain in Ni50Mn37-xFexIn13 (x = 1–4) Heusler alloys. Experimental results indicate that the martensitic phase transition temperature in these materials decreases dramatically with increasing Fe substitution for Mn, which can be explained by the hybridization between Ni and Mn atoms. Large magnetic entropy for Ni50Mn35Fe2In13 could be achieved above room temperature under the applied magnetic field up to 80 kOe. In addition, an enhanced magnetostrain (0.28%) at 110 K associated with the phase transition in Ni50Mn33Fe4In13 was observed after the martensitic phase transformation induced by demagnetization at 100 K. The reason for the enhanced strain has been discussed in detail.

Effect of Fe substitution for Co on structure, electrical resistivity, and magnetic properties of Heusler type Co2−xFe1+xSi alloys

The effect of substitution of Fe for Co on structure, electrical resistivity, and magnetic properties of full Heusler type Co2−xFe1+xSi (0 ≤ x ≤ 1) alloys was investigated. The order-disorder transitions were studied by X-ray diffraction measurements followed by Rietveld refinement analysis as well as by 57Fe Mössbauer spectroscopy. The results revealed that these alloys consist of mostly L21 ordered phase and some B2 disordered phase up to x < 0.25. However, for x ≥ 0.25, the alloys consisted of L21 ordered phase and DO3 disordered phase. The electrical resistivity behaviour with temperature showed two distinct regions. In region I, the resistivity exhibited two-magnon scattering mechanism (T9/2 dependence) showing a signature of half-metallic ferromagnetism. However, in region II, the resistivity behaviour was governed by Tn power law and n value was found to vary from 2.98 to 1.38 with increasing Fe content. The room temperature magnetization studies confirmed the enhancement of the magnetic moment with increasing Fe substitution up to x = 0.5 in Co2−xFe1+xSi alloys. However, upon further increasing Fe content, the magnetic moment was found to decrease and this was explained in terms of localization effects originating mainly in the Co anti-site disorder.

Thermal and electrochemical properties of PrBa0.5Sr0.5Co2−xFexO5+δ (x = 0.5, 1.0, 1.5) cathode materials for solid-oxide fuel cells

Layered perovskite PrBa0.5Sr0.5Co2−xFexO5+δ (PBSCF, x = 0.5, 1.0, 1.5) oxides are designed and evaluated as cathode materials for solid-oxide fuel cells. Effect of Fe/Co molar ratio on structural, thermal and electrochemical properties for PBSCF is systematically investigated. With increasing x from 0.5 to 1.5, the structure does not change but the lattice parameters increase. At the same time, thermal expansion coefficient decreases, which is helpful to thermally match with the electrolyte. From X-ray photoelectron spectra, it can be seen that both Fe and Co exist in a mixed oxidation state. Fe ions are prone to high oxidation state (Fe3+ and Fe4+), while Co ions basically exhibit low oxidation state (Co2+ and Co3+). The PBSCF samples exhibit a semiconductor–metal transition in the temperature range of 250–300 °C. With increasing Fe substitution content for Co, the electrode polarization resistance increases. The PBSCF (x = 0.5) cathode exhibits the highest power density of 697 mW cm−2 at 850 °C. The cell power output strongly depends on microstructure, electronic conductivity and electrochemical resistance.

Exceptional magnetic properties of Fe substituted nickel chromite

The NiCr2−xFexO4, (x=0.1,0.3,0.5) samples have a cubic structure at room temperature. For the sample with x=0.1, the lattice constant is determined to be a0=8.319Å with a cubic spinel (Fd-3m) structure. The ferrimagnetic Néel temperature (TN) of NiCr2O4 is determined to be 80K by zero field cooled magnetization curves under the external field of 100Oe. With increasing Fe substitution, TN increases, and for x=0.1, TN is determined to be 135K. For the sample with x=0.1, the Mössbauer spectrum at 4.2K was fitted to two magnetic components of the magnetic hyperfine fields Hhf=488 and 472kOe and isomer shifts δ=0.29 and 0.28mm∕s. The electric quadrupole splittings (ΔEQ) were found to be nearly zero below the TN=135K. For the spectrum at 295K, the ΔEQ are observed with large values of 0.54 and 0.37mm∕s, respectively. The values of the isomer shifts show that for all temperature ranges, the states are ferric (Fe3+). The Mössbauer spectra below the TN show the line broadening with the Jahn-Teller distortion and accompanying relaxation effects, respectively.

Spray pyrolysis synthesis of nanostructured LiFe xMn 2− xO 4 cathode materials for lithium-ion batteries

A series of partially Fe-substituted lithium manganese oxides LiFe x Mn 2− x O 4 (0 ≦ x ≦ 0.3) was successfully synthesized by an ultrasonic spray pyrolysis technique. The resulting powders were spherical nanostructured particles which comprised the primary particles with a few tens of nanometer in size, while the morphology changed from spherical and porous to spherical and dense with increasing Fe substitution. The densification of particles progressed with the amount of Fe substitution. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. The as-prepared powders were then sintered at 750 °C for 4 h in air. However, the particles morphology and pure spinel phase of LiFe x Mn 2− x O 4 powders did not change after sintering. The as-sintered powders were used as cathode active materials for lithium-ion batteries, and cycle performance of the materials was investigated using half-cells Li/LiFe x Mn 2− x O 4. The first discharge capacity of Li/LiFe x Mn 2− x O 4 cell in a voltage 3.5–4.4 V decreased as the value x increased, however these cells exhibited stable cycling performance at wide ranges of charge–discharge rates.

Magnetic and transport properties ofBi0.5Ca0.5FexMn1−xO3 (0≤x≤0.6)

A series of Fe-substituted manganitesBi0.5Ca0.5FexMn1−xO3 (0≤x≤0.6) was synthesized by ceramic technology. The crystal lattice parameters change monotonicallywith increasing Fe substitution for Mn as found from x-ray powder diffraction and neutrondiffraction investigations at room temperature. Magnetic properties were studied between 5and 1300 K in fields up to 16 kOe. All the compounds are antiferromagnetic below acertain temperature, which decreases with increasing Fe substitution, and forx≥0.1 the antiferromagnetism is accompanied by a weak ferromagnetism. The charge/orbitalorder exists in the pure form for the compounds without or with very low Fe substitution(x = 0 and0.05). A new magnetic cluster state exists in the paramagnetic region of manganites with Fe substitutionx≥0.3, but only in the presence of magnetic field.The conductivity of compounds measured between 100 and 600 K is of semiconducting type,and there is no magnetoresistivity effect in fields up to 7 kOe.

Effect of Fe substitution on optical, electrical, electrochemical and dielectric properties of (Zn, Fe)S chalcogenide pellets

In the present work ternary chalcogenide p-type semiconductor Zn 1− x Fe x S has been prepared by co-precipitation method for x=0.18 and 0.4 concentrations of Fe. The precipitate was repeatedly sintered at 800 °C in sealed quartz ampoules for a total of 165 h The material was then characterized by X-ray diffraction, X-ray fluorescence (XRF), EDAX, EPMA, diffuse reflectance spectroscopy, thermoelectric, electrochemical and capacitance measurement techniques. Compositional analysis techniques, viz. XRF, EDAX and EPMA reflected the composition of the solutions from which precipitation was carried out while X-ray reveals a sphalerite crystal structure. Capacitance measurements indicate that the relaxation effects are enhanced with increasing Fe substitution. Thermoelectric measurements indicate p-type conductivity in agreement with the results obtained by electrochemical analysis. The flat band potential V fb has values 2.94 V ( x=0.18) and 2.66 V ( x=0.4) as obtained by Mott–Schottky plot. Similarly the optical band gap was found to decrease with increase in Fe concentration.

CRYSTAL-CHEMICAL STUDY BY XANES OF TRIOCTAHEDRAL MICAS: THE MOST CHARACTERISTIC LAYER SILICATES

A crystal-chemical study of trioctahedral micas previously characterized by single-crystal XRD has been performed by XANES spectroscopy at the Si and Al K edges. XANES, being a local structural probe, can investigate distortion and modification of the tetrahedral sheet with increasing Fe for Mg substitution in the octahedral sheet. Comparison of XANES spectra allows determining the size of the tetrahedral site occupied by either Si or Al. The Si-O distance remains essentially unchanged whereas the Al-O distance appears to increase. The behavior may be interpreted as a tilt of the tetrahedra, initially rotated to match the ideal mica geometry, with increasing Fe substitution in the octahedral sheet.

Effect of Fe on the crystal growth morphology of Bi-Sr-Ca-Cu-O

The effect of Fe on the crystal growth of was studied by a floating zone method. The result shows that the planar solid-liquid growth interface breaks down into a cellular growth interface with increasing Fe substitution in the feed rods of . The size of the single crystals decreases with the increase in Fe substitution in the feed rods. When Fe substitution content y is 0.06 in a feed rod, the Bi-2212 single crystals in an as-grown bar are too small to be visible. The maximum thickness along the c-axis of the pure Bi-2212 single crystals is as large as 2 mm. The solubility limit of Fe in Bi-2212 crystals is 0.025. The Fe substitution in Bi-2212 crystals depress sharply not only the superconductivity transition temperature but also the homogeneity of the superconducting phase in the crystals.

Thermal decomposition of some siderite-magnesite minerals using DSC

Members of the siderite-magnesite series of carbonates have been investigated in nitrogen using differential scanning calorimetry. The mineral specimens contained between 0.3–0.95 mole fraction iron. Decomposition temperatures decreased markedly with increasing Fe substitution. Enthalpies of decomposition showed a linear dependence upon the degree of Fe and Fe + Mn substitution. The fit (R2=0.995) in the case of Fe + Mn suggested that DSC can be used to distinguish members of the series. Decomposition products consisted of substituted iron oxides in most cases.

Stabilization of the tetragonal phase and superconducting behavior in RBa2(Cu1-xFex)3Oy (R=Y,Gd; 0

The structure and superconductivity for $\mathrm{Y}{\mathrm{Ba}}_{2}{({\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x})}_{3}{\mathrm{O}}_{y}$ and $\mathrm{Gd}{\mathrm{Ba}}_{2}{({\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x})}_{3}{\mathrm{O}}_{y}$ ceramics ($0\ensuremath{\le}x\ensuremath{\le}0.15$) have been studied by x-ray diffraction and resistivity measurements. In each family of materials (but more rapidly in the Gd ceramics), increasing Fe substitution leads to the stabilization of the tetragonal perovskite structure and suppression of superconductivity, apparently owing to pair breaking by the Fe moments. Anomalous behavior at higher Fe substitution is attributed to the combined influence of Gd and Fe moments.