Fe Co-doping Research Articles

Electrochemical performance of LiMnPO4 by Fe and Zn co-doping for lithium-ion batteries

To study the effect of Fe and/or Zn doping on the performance of LiMnPO4, LiMn0.9Fe0.1−x Zn x PO4/C (x = 0, 0.05, and 0.1) composites were synthesized by a solid-state process. They are all single phase with olivine structure but LiMn0.9(FeZn)0.05PO4/C reveals a different morphology. The Fe-Zn co-doping remarkably enhances the performance of LiMnPO4 due to the presence of Fe and Zn in olivine framework resulting in the decrease of charge transfer resistance and Mn ion dissolution. Compared with LiMn0.9Fe0.1PO4/C and LiMn0.9Zn0.1PO4/C, LiMn0.9(FeZn)0.05PO4/C exhibits much higher discharge capacity and better rate capability. It delivers the capacities of 151.3 mAh g−1 at 0.1 C and 128.4 mAh g−1 at 1 C and retains 96.7 % of the initial capacity after 100 cycles.

Ferromagnetic properties of Cu- and Fe-codoped nanocrystalline CdO powders: Annealing in hydrogen promote long-range ferromagnetic order

A mixture of cadmium acetate dihydrate, bis(acetylacetonato)copper, and tris(acetylacetonato)iron complexes is thermally co-decomposition to synthesizes Cu and Fe-codoped CdO (CdO:Cu:Fe) powders. The aim of this study is to examine the effect Fe doping on the appearance and development of room temperature ferromagnetism (RT-FM) in the presence of Cu ions as catalyst. X-ray diffraction (XRD) and X-ray fluorescence (XRF) measurements were carried out to study powders purity and crystalline structure. The XRD results show that Cu and Fe ions are incorporated in the ZnO crystal lattice by occupying Zn sites thereby forming ZnO:Cu:Fe solid solution (SS), whereas XRF confirms the purity of the obtained SS. The magnetic properties of the as-prepared and H-annealed (CdO:Cu:Fe–H) SS powders was investigated as a function of %Fe doping level. It was observed that the magnetic behaviour of pure as-synthesised CdO is mainly diamagnetic with slight FM phase. However, its behaviour with Cu and Fe codoping transforms to the mostly paramagnetic overlapped with small FM behaviour. More importantly, it was found that that annealing under H2 atmosphere induces the reduction of CdO to form pure Cd metal, resulting in total transformation to FM behaviour with strength increases consistently with doping. Furthermore, with hydrogenation a tremendous enhancement of FM parameters takes place so that the Ms increases by about 1230% reaching a very high value of 1.43emu/g for 1.8%Fe doping level of CdO.

Structural and Magnetic Properties of Mn/Fe co-Doped ZnO Thin Films Prepared by Sol–Gel Technique

Mn/Fe co-doped ZnO thin films are prepared by simple sol-gel and spin coating method. Five different sols with the change in concentration (1-5 wt%) of both Mn and Fe are synthesized. Molar ratio of Mn and Fe is kept constant, i.e., 1:1. Sols are spun onto glass and copper substrates by spin coating method followed by the post magnetic field annealing at 300 °C for 1 h. Effect of Mn and Fe codoping on ferromagnetic properties of ZnO is reported in this paper. Structural and magnetic properties of as prepared and annealed samples are investigated by X-ray diffractometer (XRD) and vibrating sample magnetometer (VSM). Scanning electron microscope is used to study the surface morphology of co-doped films. XRD results show incorporation of Mn and Fe in the host lattice upto a dopant concentration of 4 wt%. However, small crystallites of Mn and Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> are observed by increasing the dopant concentration to 5 wt%. VSM results indicate room temperature ferromagnetism in all samples without the presence of any secondary phases. Low value of shape anisotropy is observed in the case of Mn doped ZnO. However, no shape anisotropy is observed in the case of co-doped thin films. Moreover, Mn/Fe co-doped thin films show magnetic hysteresis equivalent to that of multilayered structure, indicating that such complex structures used in spintronic devices can be replaced by a single ZnO layer with codoping of Mn and Fe.

Visible light driven (Fe, Cr)-codoped La2Ti2O7 photocatalyst for efficient photocatalytic hydrogen production

Highly visible-light response (Fe, Cr)-codoped La2Ti2O7 photocatalysts are synthesized by sol–gel process. The crystal phase, morphology and optical absorption activity of the samples are characterized by X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, and UV–vis diffuse reflectance spectra. The results reveal that the calcination temperature and dopant concentration have strong influence on the phase structures, crystallinity and morphology. The UV–vis diffuse reflectance spectra indicate that Fe and Cr ions codoping can extend optical absorption to the visible-light region and narrow the band gap obviously. The photocatalytic hydrogen and oxygen production activities are evaluated in CH3OH and AgNO3 aqueous solution under solar light irradiation. NiOx (0.5 wt%) loaded (Fe, Cr)-0.005-LTO-1150 shows the best photocatalytic H2 production activity with the productivity of 360.203 μmol g−1 h−1 and the apparent quantum efficiency of 2.44%, which suggests that the synergistic effect of Fe and Cr codoping is favorable to enhance the photocatalytic efficiency. The photocurrent of (Fe, Cr)-codoped La2Ti2O7 is more than two times of that for Fe-doped La2Ti2O7 photocatalyst. The efficient photocatalytic hydrogen production and the high photocurrent of (Fe, Cr)-0.005-LTO-1150 are originated from the optimized combination of the physical–chemical properties, the small band gap and the low recombination rate of photoelectron–holes.

High-temperature thermoelectric properties of La and Fe co-doped Ca–Co–O misfit-layered cobaltites consolidated by spark plasma sintering

A series of Ca3Co4−yFeyO9 and Ca3−xLaxCo4−yFeyO9 ceramics was prepared by sol–gel method followed by spark plasma sintering. The X-ray diffraction analysis indicates that Fe is substituted at the Co-site in rock salt Ca2CoO3 layers. The partial substitution of Fe at Co-site shows a simultaneous increase in the electrical conductivity and thermopower, which results in an increased power factor. For (La, Fe) co-doped specimens, although, the electrical conductivity is decreased but the thermopower is increased sufficiently to obtain a higher power factor. The temperature dependent electrical conductivity data represents that hole-hopping is the dominant conduction mechanism for all the pure and doped specimens above 573K. The thermal conductivity is greatly suppressed by (La, Fe) co-doping because of the increased phonon scattering. A larger ZT value of 0.32 at 1000K was achieved with (La, Fe) co-doping which is about 70% higher than that of pure Ca3Co4O9.

Electronic and optical performances of Si and Fe-codoped TiO2 nanoparticles: A photocatalyst for the degradation of methylene blue

The effect of substitutional Si, Fe, and Si and Fe (co)doping on the electronic structure and optical properties of anatase and rutile TiO2 have been investigated by the density functional theory. The calculated results indicate that Si doping TiO2 will induce an obvious band gap narrowing by mixing O 2p with Si 3p states, and a series of impurity energy levels (Fe 3d) appear in edge of the VB and the CB through Fe doping. The synergistic effects of Si and Fe codoping can extend optical absorption edge, which leads to higher visible-light photocatalytic activities than pure and monodoped anatase TiO2. Si and Fe-codoped TiO2 nanoparticles was prepared by a sol–gel-solvothermal method, and the photocatalytic activity of TiO2 nanoparticles was examined by measuring the rate of methylene blue decomposition. The experimental results show that Si and Fe-codoped TiO2 sample exhibits better optical absorption performance and higher photocatalytic activities for the degradation of methylene blue than pure and monodoped TiO2, which verifies the reliability of our calculated results.

The optical absorption and hydrogen production by water splitting of (Si,Fe)-codoped anatase TiO2 photocatalyst

The electronic and optical properties are studied using the density functional theory in (Si,Fe)-codoped anatase TiO2. The calculated results suggest that the synergistic effects of (Si,Fe) codoping can effectively induce the redshift of optical absorption edge, which leads to higher visible-light photocatalytic activity for hydrogen production by water splitting than pure anatase TiO2. To verify the reliability of our calculated results, nanocrystalline (Si,Fe)-codoped TiO2 is synthesized by a sol-gel-solvothermal method, and excellent absorption performance and photocatalytic activity for hydrogen production by water splitting are observed in our experiments.

Tunable magnetic and transport properties of p-type ZnMnO films with n-type Ga, Cr, and Fe codopants

ZnMnO films codoped with Ga, Cr, and Fe were deposited on sapphire substrates via pulsed laser deposition. The structures, magnetization, and transport properties of p-type ZnMnO films can be tuned using n-type Ga, Cr, and Fe codopants. The Coulombic attraction between n- and p-type dopants favorably decreases the energy of system, thereby preventing dopant aggregation and effectively enhancing dopant solubility. The above noncompensated n–p codoping can provide a certain amount of carrier density and local spins and results in the room temperature magnetizations and low temperature positive or negative magnetoresistances in ZnO wide gap semiconductors.

Magnetic and electronic properties of Fe and Ni codoped SnO2

We have investigated Fe and Ni codoping effect into SnO2. Room-temperature diluted ferromagnetic semiconductors with the enhancement of magnetization can be prepared in case of codoping. The saturation magnetization can be controlled by means of the Fe and Ni codoping ratios. The electronic structures were investigated by x-ray absorption spectroscopy (XAS) and Mössbauer spectrometry. Fe3+ states were revealed by the isomer shift values. XAS revealed Ni2+ states, which suggests that the double-exchange-like ferromagnetic interaction between the diluted magnetic ions mediated by oxygen vacancies becomes a possible origin of room-temperature ferromagnetism.

High-temperature thermoelectric properties of Ca0.9Y0.1Mn1−x Fe x O3 (0 ≤ x ≤ 0.25)

Polycrystalline compounds of Ca0.9Y0.1Mn1− x Fe x O3 for 0 ≤ x ≤ 0.25 were prepared by solid-state reaction, followed by spark plasma sintering process, and their thermoelectric properties from 300 to 1200 K were systematically investigated in terms of Y and Fe co-doping at the Ca- and Mn-sites, respectively. Crystal structure refinement revealed that all the investigated samples have the O′-type orthorhombic structure, and the lattice parameters slightly increased with increasing Fe concentration, causing a crystal distortion. It was found that with increasing the content of Fe doping, the Seebeck coefficient of Ca0.9Y0.1Mn1− x Fe x O3 tended to increase, while the tendency toward the electrical conductivity was more complicated. The highest power factor was found to be 2.1 × 10−4 W/mK2 at 1150 K for the sample with x = 0.05 after annealing at 1523 K for 24 h in air. Thermal conductivity of the Fe-doped samples showed a lower value than that of the x = 0 sample, and the highest dimensionless figure of merit, ZT was found to be improved about 20 % for the sample with x = 0.05 as compared to that of the x = 0 sample at 1150 K.

Synthesis and characterization of Ti–Mn and Ti–Fe codoped Li3V2(PO4)3 as cathode material for lithium ion batteries

Ti–Mn and Ti–Fe codoped Li3V2(PO4)3 samples, i.e. Li3V2−2xTixMnx(PO4)3 and Li3V2−2xTixFex(PO4)3 (x = 0, 0.05, 0.1, 0.15, 0.2 and 0.25), are prepared by a sol–gel method. Li3V2−2xTixMnx(PO4)3 and Li3V2−2xTixFex(PO4)3 are phase-pure when x is not higher than 0.05. LiMnPO4 and LiFePO4 begin to form as impurity phases in Li3V2−2xTixMnx(PO4)3 and Li3V2−2xTixFex(PO4)3, respectively, when x is equal to 0.1. And another impurity of Mn2P2O7 appears in Li3V2−2xTixMnx(PO4)3 when x is equal to 0.2. All these impurities increase with increasing x. XPS analyses indicate that the oxidation states of Ti, Mn and Fe are +4, +2 and +2 respectively. The first charge/discharge capacities of both Li3V2−2xTixMnx(PO4)3 and Li3V2−2xTixFex(PO4)3 at 0.2 C decline with an increase of x. Both the high-rate discharge capability and long term cycling performance of Li3V1.9Ti0.05Fe0.05(PO4)3 are much better than those of Li3V2(PO4)3, which can be attributed to the smaller particle size, larger lattice parameters and better structural stability induced by Ti and Fe codoping. However, the electrochemical performance of Li3V1.9Ti0.05Mn0.05(PO4)3 is worse than that of Li3V2(PO4)3, which is due to the structural instability induced by the incorporation of Mn.

Photocatalytic Activity of Fe and Ce Co‐doped Mesoporous TiO2 Catalyst under UV and Visible Light

AbstractThe catalysts of un‐doped, single‐doped and co‐doped mesoporous titanium dioxide (MTiO2) were prepared by a template method with tetrabutyltitanate (Ti(OC4H9)4) as a Ti source material and Pluronic P123 as a template. The photo‐absorbance of the obtained catalysts was measured by UV‐vis absorption spectroscopy, and the photocatalytic activities of the prepared samples under UV and visible light were estimated by measuring the degradation rate of methyl orange (MO) (50 mg/L) in an aqueous solution. It was shown that the co‐doped MTiO2 could be activated by visible light and could thus be used as an effective catalyst in photo‐oxidation reactions. The effect of Fe and Ce co‐dopants on the material properties was investigated by X‐ray diffraction (XRD), scanning electron microscopy (SEM) and N2 adsorption‐desorption isotherm measurement. The characterizations indicated that the photocatalysts possessed a homogeneous pore diameter of ca. 10 nm with high surface area of ca. 150 m2/g. The photocatalytic activity of MTiO2 co‐doped with Fe and Ce was markedly improved due to the synergistic actions of the two dopants.

Fabrication and magnetic properties of Fe and Co co-doped ZrO2

We investigate the effects of Fe and Co co-doping on the magnetic and electronic properties of ZrO2 ceramics prepared by a sol-gel method, and study their dependence on the annealing temperature. Dilute Fe and Co co-doping into ZrO2 exhibits ferromagnetic behavior at room temperature for annealing temperatures above 900 °C, accompanying the phase transition from tetragonal to monoclinic structure in ZrO2. The electronic structures are studied by x-ray absorption spectroscopy and Mössbauer spectroscopy, which suggest that the Fe3+ and Co2+/Co3+ mixing states are dominant in Fe and Co co-doped ZrO2.

Enhanced photocatalytic activity and stability of nano-scaled TiO 2 co-doped with N and Fe

Titanium dioxide (TiO 2) nanoparticles co-doped with N and Fe were prepared via modified sol–gel process. The products were characterized by transmission electron microscopy (TEM), N 2 adsorption, X-ray diffraction (XRD), Raman spectroscopy, UV–vis spectroscopy, photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS). It is shown that the prepared TiO 2 particles were less than 10 nm with narrow particle size distribution. The addition of MCM-41 caused the formation of Ti–O–Si bond which fixed the TiO 2 on MCM-41 surface, thus restricted the agglomeration and growth of TiO 2 particles. The photocatalytic performance in the degradation of methylene blue showed that N, Fe co-doped TiO 2 exhibited much higher photocatalytic activity than doped sample with nitrogen or Fe 3+ alone under both UV and visible light. N, Fe co-doping decreased the loss of doping N during the degradation reaction, thus increased the photocatalytic stability. It was also found that the nitridation time had significant influence on the photocatalytic activity of prepared TiO 2 catalysts.

Preparation and photocatalytic activity of TiO 2 nanoparticles co-doped with Fe and La

The catalysts of un-doped, single-doped and co-doped titanium dioxide (TiO 2) nanoparticles were prepared by a sol–gel method with Ti(OC 4H 9) 4 as a Ti source material. The photo-absorbance of the obtained nanoparticles was measured by UV–vis diffusive reflectance spectroscopy (UV–vis DRS), and the photocatalytic activity of the prepared samples under UV and visible light was estimated by measuring the degradation rate of phenol (50 mg/L) in an aqueous solution. The effect of Fe and La co-dopants on the material properties was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and N 2 adsorption–desorption isotherm measurement. It was shown that the co-doped TiO 2 could be activated by visible light and could thus be used as an effective catalyst in photo-oxidation reactions. The photocatalytic activity of TiO 2 co-doped with Fe and La is markedly improved due to the synergistic actions of the two dopants.

Thermoelectric Properties of ZnO Ceramics Co-Doped with Al and Transition Metals

The effect of co-doping with transition metals (Fe, Ni, and Sm) on the thermoelectric properties of Al-doped ZnO (AZO) ceramics was studied. The electrical conductivity σ of AZO was significantly (12%) increased by Ni co-doping, while an unfavorable deterioration in σ was observed for Fe- or Sm-co-doped AZO. Hall-effect measurements indicated that the electron mobility of AZO decreased due to co-doping in all samples. Only the Ni-co-doped AZO sample showed significant enhancement in electron density, resulting in its black color. The thermal conductivity κ decreased drastically due to Ni or Sm co-doping of AZO, while only a small change was observed for Fe co-doping of AZO. The κ value at 1073 K for Ni-co-doped AZO was 77% of that for AZO. A dimensionless figure of merit ZT = 0.126 was attained at 1073 K for Ni-co-doped AZO, representing an improvement over that of conventional AZO by a factor of 1.50.

Synthesis of iron-containing nitrogen-doped titania by hydrothermal method and its photocatalytic activity

By a hydrothermal method, iron and nitrogen co-doped TiO2 and iron oxide impregnated nitrogen-doped TiO2 were prepared. The obtained Fe and N co-doped TiO2 showed mixed anatase, rutile, and brookite phases, and high specific surface areas above 160 m2/g. The Fe co-doping was proved to be effective to enhance the visible light absorption ability; however, the photocatalytic activity in deNOx experiment decreased due to the increase in the amount of lattice vacancy. On the other hand, the photocatalytic activity of N-doped TiO2 was improved by the impregnation of iron oxide.

Effects of Fe-doping of ceria-based materials on their microstructural and dynamic oxygen storage and release properties

The structural/textual characteristics and dynamic oxygen storage capacity (DOSC) of Fe0.1Ce0.9Ox and Fe0.1Ce0.6Zr0.3Ox samples prepared by sol–gel method are investigated by X-ray powder diffraction (XRD), Raman, Hydrogen temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and mass spectrometry with CO/O2 transient pulses. The dynamic oxygen storage capacity and rate are largely promoted by Fe doping, and their thermal stability is enhanced by Fe and Zr co-doping. The DOSC (at 673 K) are ordered as: Fresh: Fe0.1Ce0.6Zr0.3Ox (566.6 μmol/g) > Fe0.1Ce0.9Ox (551.8 μmol/g) > Ce0.67Zr0.33O2 (287.5 μmol/g) > CeO2 (140.3 μmol/g); Annealed1,173K: Fe0.1Ce0.6Zr0.3Ox (101.6 μmol/g) > Ce0.67Zr0.33O2 (45.3 μmol/g) > Fe0.1Ce0.9Ox (44.9 μmol/g) > CeO2 (43.3 μmol/g). The H2-TPR results showed that Fe-incorporation improve the total oxygen storage capacity (TOSC) of mixed oxide and low temperature activity. The TOSC are ordered as: Fe0.1Ce0.9Ox (1.53 mmol/g) > Fe0.1Ce0.6Zr0.3Ox (1.42 mmol/g) > Ce0.67Zr0.33O2 (1.16 mmol/g) > CeO2 (0.88 mmol/g). XRD and Raman results indicate that Fe0.1Ce0.9Ox and Fe0.1Ce0.6Zr0.3Ox are characterized with the fluorite-type cubic structure similar to CeO2. TPR and XPS analyses reveal that the introduction of Fe into ceria and ceria-zirconia mixed oxides strongly modified the structural and textural properties, which influenced the kinetics of bulk oxygen diffusion.

Chemical and magnetic profile of magnetic semiconductors as probed by polarized neutron reflectivity

We investigate the depth dependence of magnetic species in co-doped dilute magnetic semiconductor (DMS) specimens. We also compare the reliability of the nuclear and magnetization depth profile of these specimens on different polarized neutron reflectivity instruments. These reflectometers were not only angle dispersive instruments but also wavelength dispersive instruments. Measurements indicate a segregation of DMS species onto the top into the cap layer for lower Fe doping. However, for higher Fe doping, as we alter the doping concentrations of magnetic species, no segregation and lower clustering tendencies are indicated. Thus sensitive depth profiling, for specimens with such low magnetic-ion concentrations, may not be a challenge for brighter sources and careful measurements. Our results show that homogeneity can be achieved with Fe co-doping within a Ge matrix which can make it a potential candidate for spintronic applications.

Characterization and ferroelectricity of Bi and Fe co-doped PZT films

Co-doping of thin Pb(Zr,Ti)O 3 (PZT) films with Bi and Fe to optimize the ferroelectric properties has recently gained attention particularly, for ferroelectric random access memory applications (FeRAM). This study was undertaken to understand how co-doping PZT with one atomic% Bi and Fe impacts the characteristics of capacitor ferroelectric and material properties. XRD patterns of PZT-BiFeO 3 (BF) and PZT 150 nm thick showed strong (1 1 1) orientation and changing the sample stage angle Chi to 50° revealed multiple PZT and PZT-BF diffractions peaks. Bi and Fe co-doping of PZT results in a 0.01 Å decrease in lattice dimensions which indicates that Bi and Fe are substituting into the PZT lattice. Polarization hysteresis loops show similar characteristics but pulse measured polarization values were higher for PZT-BF than PZT which indicates PZT-BF has potential for thin film ferroelectric devices.