Fe-doped Samples Research Articles

Optimization of thermoelectric properties for microwave sintered Fe-doped ZnO

ZnO is a promising thermoelectric ceramic material, but the low electrical conductivity and high thermal conductivity restrict its satisfactory thermoelectric performance. Chemical doping is an effective way to improve the thermoelectric properties of ZnO. Due to the valence states and similar ionic radii of Fe3+ and Zn2+, Fe was selected as the effective dopant for ZnO. In this work, Fe-doped ZnO samples were prepared using hydrothermal synthesis and microwave sintering technology under oxygen-depleted conditions. The electrical conductivity of sintered Fe-doped ZnO was greatly improved owing to the energy band adjustment. The maximum power factor of 3108 μW/mK2 at 800 K was obtained from Zn0.997Fe0.003O, which is about 4.4 times greater than that of pure ZnO. Meanwhile, the small grain size (300–500 nm) and residual pores resulted from microwave rapid sintering in an oxygen-depleted environment, as well as the point defects caused by Fe3+ substituting for Zn2+, significantly reduced the thermal conductivity. Finally, the highest ZT value of 0.91 has been achieved in Zn0.997Fe0.003O at 800 K.

Construction dual active sites on SnO2 via Fe doping for effective ciprofloxacin photodegradation

Adjusting the electronic structure via doping and enhancing the active sites of photocatalysts are proven strategies for improving the photodegradation of pollutants. However, the photodegradation mechanism involving doping elements and their impact on pollutant adsorption and activation at active sites remain unclear. In this study, Fe-doped SnO2 photocatalysts were synthesized using the hydrothermal method, featuring small particle sizes and highly active sites. It was found that doping SnO2 with 3 mol% Fe3+ significantly enhances its photocatalytic efficiency in degrading Ciprofloxacin, outperforming pure SnO2 by approximately 18.6 times. Spectroscopy methods, combined with density functional theory calculations, revealed that the presence of Lewis acid sites and oxygen vacancies serve as active sites in the Fe-doped SnO2 samples. Furthermore, a detailed photodegradation mechanism for Fe-doped SnO2 was proposed based on the band energy structure and analysis of free radical results. This research provides new insights into the mechanism of photocatalytic degradation of Ciprofloxacin by elucidating the interactions between the active sites of the photocatalyst and Ciprofloxacin molecules.

Green-assisted synthesis of highly defective nanostructured Fe-doped SnO2: Magnetic and photocatalytic properties evaluation

Here we present a comprehensive characterization of the properties of undoped and Fe-doped SnO2 nanoparticles prepared with Syzygium cumini leaves extract. The phytochemicals present in the leaves extract act as cation chelating and capping of the nanoparticles. It is observed a relative high concentration of tin (up to 10 %) and oxygen (up to 5%) vacancies promoted by surface adsorbed OH− and by Fe-doping, respectively. The magnetic characterization reveals a ferromagnetic with a saturation monetization up to 20×10−3 emu/g for the higher defective and Fe-doped sample. This behavior associated mainly to tin vacancies for the undoped samples, and to the formation of bound magnetic polarons between the incorporated Fe and the oxygen vacancies for the doped samples. Oxygen vacancies and incorporated Fe improve the SnO2 photocatalytic efficiency in the visible range of the electromagnetic spectrum by decreasing the SnO2 effective bandgap from 3.6 eV for the undoped SnO2 sample to only 1.9 eV for the Fe-doped SnO2 sample, and by acting as electron-trapping centers increasing the system quantum efficiency. Due to the ferromagnetic behavior of the studied samples, it was also considered the effect of spin-dependent processes in the observed photocatalytic improvement. Our results highlight the key role of defect engineering strategies to optimize the physical and chemical properties of semiconductor oxides for application in the development of spintronic and quantum information devices, and in systems devoted to wastewater purification through advanced oxidation processes.

Quantification of the strong, phonon-induced Urbach tails in β-Ga2O3 and their implications on electrical breakdown

In ultrawide bandgap (UWBG) nitride and oxide semiconductors, increased bandgap (Eg) correlates with greater ionicity and strong electron–phonon coupling. This limits mobility through phonon scattering, localizes carriers via polarons and self-trapping, broadens optical transitions via dynamic disorder, and modifies the breakdown field. Herein, we use polarized optical transmission spectroscopy from 77 to 633 K to investigate the Urbach energy (Eu) for many orientations of Fe- and Sn-doped β-Ga2O3 bulk crystals. We find Eu values ranging from 60 to 140 meV at 293 K and that static (structural defects plus zero-point phonons) disorder contributes more to Eu than dynamic (finite temperature phonon-induced) disorder. This is evidenced by lack of systematic Eu anisotropy, and Eu correlating more with x-ray diffraction rocking-curve broadening than with Sn-doping. The lowest measured Eu are ∼10× larger than for traditional semiconductors, pointing out that band tail effects need to be carefully considered in these materials for high field electronics. We demonstrate that, because optical transmission through thick samples is sensitive to sub-gap absorption, the commonly used Tauc extraction of a bandgap from transmission through Ga2O3 >1–3 μm thick is subject to errors. Combining our Eu(T) from Fe-doped samples with Eg(T) from ellipsometry, we extract a measure of an effective electron–phonon coupling that increases in weighted second order deformation potential with temperature and a larger value for E||b than E||c. The large electron–phonon coupling in β-Ga2O3 suggests that theories of electrical breakdown for traditional semiconductors need expansion to account not just for lower scattering time but also for impact ionization thresholds fluctuating in both time and space.

Exploring structural and optical properties of Cu-doped and Fe-doped sodium borate glasses

This study investigated the structural and optical properties of Cu-doped and Fe-doped sodium borate glasses. X-ray diffraction (XRD) patterns confirmed that both samples were amorphous, with no sharp peaks. However, differences in the width and center of the high-intensity humps suggested variations in atomic packing and field strength between the two samples. Fourier transform infrared (FTIR) spectra showed wider vibrational modes and stronger absorption in the Fe-doped sample, confirming its higher atomic packing and field strength. Luminescence spectra indicated that the Cu-doped sample had a higher ratio of Cu2+:Cu3+ than the Fe-doped sample of Fe2+:Fe3+, resulting in greater UV–visible region absorption. Optical parameters such as absorbance, transmittance, and reflectance supported these findings, with the Fe-doped sample exhibiting higher absorbance band edges. Quality factor (Q.F.) analysis revealed that the Fe-doped sample had a larger Q.F. than the Cu-doped sample, indicating lower energy losses. Furthermore, the optical conductivity of both samples increased with photon energy, with the Cu-doped sample dominating in all energy regions. Finally, both samples exhibited high effective atomic numbers, suggesting potential applications in radiation shielding, with the Cu-doped sample having a wider radiation shielding window. Finally, the findings unique structural and optical properties suggests the Cu-doped and Fe-doped sodium borate glasses to a lot of potential applications in various fields including radiation shielding, optics, electronics, and energy storage.

Mössbauer and magnetic studies of Fe-doped ZnO nanoparticles prepared by solution co-precipitation method

A series of Zn[Formula: see text]FexO ([Formula: see text], 0.015, 0.045, 0.075) nanoparticles were synthesized using the solution co-precipitation method, and their structural and property characteristics were investigated. X-ray diffraction (XRD) analysis revealed that all Zn[Formula: see text]FexO samples exhibited a hexagonal wurtzite crystal structure with the P63mc space group. The introduction of Fe doping led to a slight lattice distortion in the samples. The morphology of the nanoparticles, including polydispersion and agglomeration, as well as the presence of the second phase ZnFe2O4, was examined by scanning electron microscope (SEM) and transmission electron microscope (TEM). UV–Vis diffuse reflectance spectroscopy demonstrated that the band gap of Zn[Formula: see text]FexO lies between 3.152 and 3.163[Formula: see text]eV. With the increase in Fe ion doping, the band gap shows a slight decreasing trend. Mössbauer spectroscopy revealed that iron ions in the nanoparticles existed in a trivalent state and exhibited two different configurations: One involved iron replacing zinc without creating a vacancy, while the other involved iron substituting zinc with a vacancy. The ferromagnetic nature of the Fe-doped samples can be attributed to the exchange interaction between two Fe[Formula: see text] ions mediated by the F-center mechanism.

Polarized photoluminescence from Sn, Fe, and unintentionally doped β-Ga2O3

In this work, we demonstrate that β-Ga2O3 shows orientation-dependent polarized photoluminescence (PL) emission and give a comprehensive insight into gallium oxide's PL spectral properties. We characterized the polarization and spectral dependencies of both the incident and emitted light for (−201) unintentionally doped (UID) as well as (−201) and (010) Sn-doped and Fe-doped crystals. We observed for UID and Sn-doped samples that the electron to self-trapped hole and native defect-related emission bands are linearly polarized with polarized emission intensities ordered as E || c (and c*) > E || a (and a*) > E || b. Furthermore, the spectral shape of emission does not change between the UID and Sn-doped samples; instead, the Sn-doping quenches the total PL spectral intensity. For Fe-doped samples, polarized red emission caused by unintentional Cr3+ doping generates emission intensities ordered E || b > E || c (and c*) > E || a (and a*). It is also observed that in some circumstances, for some doped crystals, the PL spectra can show variations not only in intensity but also in spectral shape along different polarization directions. As an example, the PL emission band for emission along c is blueshifted relative to that along a in Sn-doped β-Ga2O3.

Impact of morphology and oxygen vacancy content in Ni, Fe co-doped ceria for efficient electrocatalyst based water splitting.

Designing a highly efficient, low-cost, sustainable electrocatalyst for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) through water splitting is a current challenge for renewable energy technologies. This work presents a modified sol-gel route to prepare metal-ion(s) doped cerium oxide nanostructures as an efficient electrocatalyst for overall water splitting. Nickle (Ni) and iron (Fe) co-doping impacts the morphology in cerium oxide resulting in 5 nm nanoparticles with a mesoporous-like microstructure. The high level 20 mol% (1 : 1 ratio) of Ni + Fe bimetal-ion(s) doped CeO2 shows excellent HER and OER activities compared to the monodoped Fe/Ni and pristine CeO2. The co-doped catalysts required a low overpotential of 104 mV and 380 mV for HER and OER, respectively, in 1 M KOH, at a current density of 10 mA cm-2. The Tafel slopes of 95 mV dec-1 and 65 mV dec-1 were measured for HER and OER with the same representative samples which demonstrated excellent stability even after continuous operation for 20 hours in the alkaline medium. The unique morphology, enhanced oxygen vacancy (Ov) content and the synergistic effects of dopants in CeO2 play essential roles in enhancing the activities of Ni + Fe doped samples.

Impact of electron irradiation on semi-insulating and conductive β-Ga2O3 single crystals.

The damage behavior and defect evolution in Si-doped and Fe-doped β-Ga2O3 crystals were investigated using an electron irradiation of 1 MeV at a dose of 1 × 1016 cm-2 in conjunction with structural and optoelectronic characterizations. Distinct decline in electron spin resonance (ESR) signal with g = 1.96 and a UV luminesce of 375 nm were observed in Si-doped β-Ga2O3 due to the capture of free carriers by irradiation defects. As for the Fe-doped sample, both defect-related blue emission and Cr3+ impurity-related red luminescence underwent prominent suppression after electron irradiation, which can be correlated to the creation of VO and VGa defects and the formation of non-radiative recombination. Noticeably, neither VO- nor VGa-related ESR signals were detected in Fe-doped and Si-doped β-Ga2O3 irrespective of irradiation; g = 2.003 resonance was observed in Mg-doped β-Ga2O3 and it experienced remarkable augmentation after electron irradiation. We assigned the g = 2.003 peak to the VGa acceptor. Besides, although the Raman mode of 258 cm-1 in Si-doped β-Ga2O3 has been suggested to be electron concentration dependent, no obvious change in peak intensity was observed before and after electron irradiation.

Enhancement of performance and kinetics of layered Li2MnO3 by Fe doping

Layered Li2MnO3 exhibits great potential as a high-capacity cathode used in lithium-ion batteries, but materials synthesized by traditional solid-phase methods exhibit poor activity and poor cycling stability. In this work, Li2MnO3 nanoparticles were synthesized by solid state method combined with high-energy ball milling, in which Fe was doped at transition metal sites to obtain a Li-rich cathode material (Li1.32Fe0.034Mn0.64O2). We systematically studied the effects of Fe doping and calcination temperature on the crystal structure and electrochemical properties and conducted kinetic studies using the galvanostatic intermittent titration technique (GITT), electrical impedance spectroscopy (EIS) and density functional theory (DFT) calculations. Our results demonstrate that the performance was significantly improved, its discharge capacity is about 235 mAh g−1 after 10 cycles compared 138 mAh g−1 of the pristine sample. The GITT and EIS results show that the Fe-doped sample had smaller charge transfer impedance, larger lithium-ion diffusion coefficient and lower internal polarization than the pristine. The activation energy results show the Fe-doped sample has larger activation energy at the late discharging period due to the anion redox reaction activation, indicting its O activation is more active than Li2MnO3. Moreover, the DOS results showed that the Fe-doped sample had a narrow band-gap, indicating good electrical conductivity. The CI-NEB results showed that the Fe-doped sample had a high transition metal ion migration energy barrier, indicating that its structure was stable. In conclusion, Fe doping is helpful to active the anion redox reaction in Li2MnO3 and improve its electrochemical performance as a low cost and high-capacity cathode materials.

Synthesis of High Near-Infrared Reflective Black Pigment Based on YMn2O5

Y(Mn0.95M0.05)2O5 (M = Al, Fe, Ga, Ti, and Zr) samples were synthesized via a sol–gel method using citric acid to find a new near-infrared (NIR) reflective black pigment. Among these samples, the optical reflectance of Y(Mn0.95Fe0.05)2O5 and Y(Mn0.95Ga0.05)2O5 in the near-infrared region was found to be larger than that of YMn2O5. Then, the concentration of the dopant (Fe or Ga) was changed between 0 and 15%, and the resulting UV–Vis–NIR reflectance spectra were measured. As a result, the optical reflectance of the Fe-doped samples decreased in the near-infrared region, while that of the Ga-doped samples increased. Accordingly, Y(Mn1−xGax)2O5 (0 ≤ x ≤ 0.20) samples were synthesized, and the crystal structure, particle size, optical properties, and color of the samples were characterized. The single-phase samples were obtained in the composition range of 0 ≤ x ≤ 0.15, and the lattice volume decreased with increasing Ga3+ concentration. Optical absorption below 850 nm was attributed to the charge transfer transition between O2p and Mn3d orbitals, and the absorption wavelength of Y(Mn1−xGax)2O5 shifted to the shorter wavelength side as the Ga3+ content increased, because of the decrease in the Mn3+ concentration. Although the sample color became slightly reddish black by the Ga3+ doping, the solar reflectance in the near-infrared region reached 47.6% at the composition of Y(Mn0.85Ga0.15)2O5. Furthermore, this NIR reflectance value was higher than those of the commercially available products (R < 45%).

MOF-derived flower-like Fe-doped Co3O4 porous hollow structures with enhanced n-butanol sensing properties at low temperature

Metal oxide-based gas sensors are widely used in the detection of toxic and harmful gases due to their advantages of high precision, convenient use and stable performance, but their application range is limited due to the high working temperature. In this work, MOF-derived flower-like Fe-doped Co3O4 porous hollow structures are obtained using a simple solvothermal method. The obtained samples are characterized in terms of their crystalline structure, morphology, chemical composition, optical properties and specific surface area. This study systematically investigates the sensing performance of pristine and Fe-doped Co3O4 samples. The results show that the 2 at% Fe-Co3O4 sample has the best n-butanol sensing properties. This sample exhibits high response and rapid response/recovery speed at a low working temperature of 110 °C, as well as good repeatability and anti-humidity features. The enhanced sensing properties can be attributed to several factors, including the adjustment of baseline resistance, increase in oxygen vacancies, decrease in bandgap, and the formation of unique hollow and porous structures. Overall, this work provides valuable insights into the potential applications of Fe-doped Co3O4 materials in sensing technologies.

Structural, optical, electrical and gas sensor properties of Fe-doped CdO thin films synthesized by spray pyrolsis

In this study, the structural, optical, electrical and gas sensor properties of Fe-doped CdO thin films synthesized using the spray pyrolysis method were investigated as a function of Fe doping. The characterizations of the thin films were made by using X-ray diffraction (XRD), X-ray photoelectron (XPS), ultraviolet–visible (UV-VIS), field emission-scanning electron microscope (FE-SEM), atomic force microscope (AFM) and Hall measurements. In addition, the response values of the films for H2 gas were determined by a current-sensitive gas sensor measurement system. XRD analyzes revealed that the produced films were in polycrystalline cubic structure and their unit cell volumes were reduced by Fe doping. The mean particle size and mean dislocation density of Fe doped samples were obtained as 11.99 nm and 6.98 × 1015 (line/m2), respectively. XPS results showed that the experimentally obtained doping ratios of the produced films were very close to the planned doping ratios and the formation of CdxFe(1-x)-O2 and CdxFe(1-x)-O3 on the surfaces of the samples decreased with the increment of Fe doping. UV-VIS measurements demostrated that the band gap is generally reduced due to doping, in line with the Moss-Burstein effect. According to Hall results, the mobility of the samples increases with increasing doping. SEM and AFM analyzes revealed that Fe doping to CdO causes nanoroads formation on thin film surfaces, and nanoroads disappear in 4 % and 5 % doped films. In addition to the specified characterizations, how these changes in the surface morphology of the films with Fe doping affect the H2 gas responses of the samples is also explained in the study.

Magneto-optical properties of Fe-doped bismuth oxide nanorods for photocatalytic and antimicrobial applications

Pure and Fe-doped Bi2O3 nanorods were synthesized using a hydrothermal method and characterized by XRD, FTIR, Raman, FE-SEM, BET, UV–VIS, VSM, and PL. The impact of Fe doping on Bi2O3 causes variation in properties. The 0.5% Fe-doped sample exhibited high surface area (21.732 m2/g) and defects, resulting in exceptional photocatalytic efficiency (93.37%) for Methylene Blue dye degradation under visible light. In addition, their magnetic properties were also investigated, along with observing improved antimicrobial activity. The 0.5% Fe-doped Bi2O3 exhibited a notable 20 mm diameter zone of inhibition against bacteria and 23 mm against fungi, highlighting. This study highlights the versatile potential of Fe-doped Bi2O3 nanorods in photocatalysis and antimicrobial applications.

Synthesis of Fe and La doped SnO2 system in ambient and non-ambient conditions: Effect on lattice structure, chemical state, optical and dielectric properties

The effect of Fe and La doping in SnO2 structure have been investigated by synthesizing the material using mechanical alloying and post-heat treatment under ambient and non-ambient atmospheres. The material has been characterized by employing Powder X-ray Diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), UV–Visible spectroscopy, and Broadband dielectric spectroscopy. The material has formed bi-phased lattice structure, consisting of tetragonal phased SnO2 structure (space group P 42/m n m) and a secondary phase, for the samples that were mechanically alloyed in air and heat treated in different atmospheres. The α-Fe2O3 (space group R- 3 c) has been identified as the secondary phase for Fe doped SnO2 system and small amount (5%.) of La2O3 (cubic structure with space group I a-3) has been identified as the secondary phase for mechanically alloyed (in air) La doped SnO2 system. The N2 atmosphere played a crucial role in forming the single-phased SnO2 structure in mechanically as-alloyed samples and also for determination of the phase fraction in bi-phased lattice structure during the incorporation of Fe and La in SnO2 system. XPS confirmed the multiple charge states for Fe (Fe3+, Fe2+, Fe0) and Sn (Sn4+, Sn2+) ions. The bandgap energy in the Fe and La-doped SnO2 system has reduced in the range of 2.18 eV–2.37 eV and 2.81 eV–2.90 eV, respectively in comparison to band gap ∼ 3.6-3.8 eV for SnO2 system. The band gap reduction has been controlled mainly by the SnO fraction in SnO2 structure. The electrical conductivity of Fe and La-doped samples has been found in the order of ∼ 10−7 S/cm to 10−9 S/cm. The Fe-doped samples have shown higher electrical conductivity than the La-doped samples. The nitrogen environment during mechanical alloying or heat-treatment played a significant role in determining high electrical conductivity and dielectric constant, and low dielectric loss constant of the samples.

Synthesized Fe-doped Co3O4 nanoparticles-based anode for high-performance lithium-ion batteries application

ABSTRACT Co3O4 has been considered a promising anode material because of its high theoretical capacity (890 mAh/g) and remarkable energy density. Unfortunately, it suffers from low initial coulombic efficiency, rapid capacity fading, poor electronic conductivity, large volume changes, and aggregation during the lithium ion intercalation/deintercalation process. In this work, a series of Fe2+-doped Co3O4 nanostructured materials Co3(1-x)Fe3xO4 (x = 0, 0.01, 0.02 and 0.03) were produced by a simple chemical co-precipitation method. The Fe doping led to a slight increase of the lattice parameter, which is beneficial to the rapid diffusion of Li+ ion during the lithiation/delithiation process. Meanwhile, the Fe-doped Co3O4 sample exhibited an excellent rate capability of 886.47 mAh/g at 500 mA/g, and outstanding cyclic stability (1156.91 mAh/g for 50 cycles, with the capacity retention rate of 83.53% at the current density of 100 mA/g), demonstrating improved electrochemical performance, compared with that of pure Co3O4. The good electrochemical performance profited from the formation of oxygen vacancies by Fe doping, which provided more space for Li+ diffusion and improved the electronic conductivity of the anode material. This work provides a simple way to improve the comprehensive electrochemical performance of the transitional metal oxide Co3O4 anode electrodes for lithium-ion batteries.

Structural, and magnetic studies of a novel homemade spray pyrolysis synthesized Fe-doped CeO2 thin films

Thin film samples of pure CeO2 and Fe-doped CeO2 were prepared via a homemade spray pyrolysis set-up with an aim to explore its suitability for use as functional materials in spintronics applications. Compressed air was used as a carrier gas to spray deposit the films on preheated glass substrate at an optimum temperature of 400 °C. Structural analysis using X-ray diffraction confirm the single-phase formation of CeO2 for pure and Fe-doped samples. Field emission electron microscope images illustrate the fairly uniform deposition of thin films with nanocrystalline nature. Energy dispersive X-ray analysis confirm the near stoichiometry of doped Ce1-xFexO2 (x = 0, 0.05, 0.1) samples. Magnetic behavior of the samples were studied using Vibrating Sample Magnetometer which show a dominant diamagnetic behavior for both Fe-doped and pure CeO2 thin films. Insufficient number of oxygen vacancies produced during the deposition of thin films is expected to the cause for the absence of ferromagnetic ordering at room temperature.

Reduction of Typical Diesel NOx Emissions by SCR-NH3 Using Metal-Exchanged Natural Zeolite and SBA-15 Catalysts

In this work, the catalytic performance of clinoptilolite (CLIN) and SBA-15 catalysts, doped with Fe and Cu, was evaluated in the selective catalytic reduction of NO using NH3 as a reducing agent (SCR-NH3). Both Cu-CLIN and Fe-CLIN were obtained by ion-exchange using natural clinoptilolite zeolite originating from the Hrabovec deposit (northeast Slovakia region). Cu-SBA-15 and Fe-SBA-15 were prepared by impregnation into SBA-15 mesoporous synthesized silica. Standard catalytic activity tests were carried out on a bench-scale laboratory apparatus using a reaction mixture of a standard test. GHSV of 48,000 h−1 was adopted based on the space velocity of a real NH3-SCR catalyst for diesel vehicles (100–550 °C). All Cu-doped samples showed better NO conversion values than Fe-doped samples. Clinoptilolite catalysts were more active than those based on SBA-15. Maximum NO conversions of about 96% were observed for Cu-CLIN and Fe-CLIN at 350–400 °C, respectively. Moreover, Fe-CLIN also showed higher stability in the presence of SO2 and water steam at 350 °C. These results demonstrate the potential of metal-doped natural clinoptilolite to be used as cost-effective catalysts applied to the abatement of NOx emissions generated in automotive combustion processes.

Defect structures and (ferro)magnetism in Zn1-xFexO nanoparticles with the iron concentration level in the dilute regime (x = 0.001 – 0.01) prepared from acetate precursors

Zn1-xFexO nanoparticles with the iron concentrations level in the dilute regime (x = 0.001–––0.01) were produced by a sol–gel route from acetate precursors along with an un-doped and 3 at.% Fe-doped reference. The X-ray diffraction of the un-doped and 0.1–1 at.% Fe-doped samples reveal the reflections for only the ZnO wurtzite structure. Fe doping enhances the a-axis lattice constant, the unit cell volume and the microstrain. Iron doping reduces the average crystallite/particle size (confirmed by Scanning Electron Microscopy), improving the surface-to-volume ratio or the concentration of defective surface sites. XPS identifies the iron in both Fe3+ and Fe2+ states. XPS and 57Fe Mossbauer spectroscopy indicate a broad distribution (distortion) of Fe3+ sites on the surface of ZnO nanoparticles. The blue shift and broadening of the UV emission, and quenching of defect-related photoluminescence in the Fe-doped samples verify the presence of iron in the ZnO lattice and surface intrinsic defects. 0.1–1 at.% Fe-doped ZnO show room temperature ferromagnetism, RTFM, characteristic of dilute magnetic semiconductors, DMS. The magnetization measurements with temperature evidence an antiferromagnetic alignment and an increase of ferromagnetic contribution with Fe doping up to 1 at.%. Zn0.97Fe0.3O reference is a superparamagnetic ZnO/ZnFe2O4 nanocomposite with a blocking temperature of 20 K; HRTEM shows (ultra)fine ZnFe2O4 particles at the surface of ZnO nanoparticles. The analysis of experimental data of 0.1–1 at.% Fe-doped ZnO was done in terms of iron coupling with intrinsic defects, which can generate surface Fe3+ states with geometries similar to the Fe3+ in inverse spinel ZnFe2O4. The superexchange interaction (resembling that in the inverse spinel ZnFe2O4) between the Fe3+ sites with distorted configuration resulting in ferrimagnetism was hypothesised as a possible mechanism of RTFM. Experimental (structural, local chemical, magnetic, optical) and interpretation results can be used to optimize the processing conditions for Fe-doped ZnO to serve as an effective DMS, e.g. for spintronic applications.

Defects altered n/p-type Fe/Ga modified ZnO for photo-sensing applications

Sol-gel prepared Fe/Ga co-doped ZnO, i.e., Zn0.9844(Fe1−xGax)0.0156 nanoparticles, with varying proportions of Fe/Ga, have been investigated. Individual Fe or Ga modified ZnO is well studied in reports. Structural properties, especially lattice defects and disorder, have not been correlated well enough to the electronic properties and related applicability. Fe-doping is reported to reduce conduction, while Ga-doping enhances the same. To understand the structural changes and how it is related to the modifications in the electronic properties, an attempt is being made to co-doped Fe/Ga in the ZnO lattice so that an understanding of the complex competition of these opposite natures can be studied. Sol-gel prepared Fe/Ga modified ZnO with P63mc space group is investigated for this purpose. The structural, defects and electronic behavior of modified and pristine ZnO have been detailed using: X-ray diffraction, Raman spectroscopy, UV–vis/PL spectroscopy and Hall-effect measurements. Changes in the electronic behavior i.e., conductivity in light ON and OFF conditions is also well studied and correlated with defects. A theoretical analysis of the same was performed using the electron localization function of the system which reveals a weaker electron cloud around Fe but a stronger around Ga as compared to Zn, thereby resisting and aiding the conduction process in Fe-doped and Ga-doped samples. The mobility, carrier concentration, and Hall coefficient parameters are modified along with the modified native defects of ZnO.