Tetrahedral Sites Research Articles

Sol-gel synthesis of Cobalt-Bismuth substituted strontium hexaferrites and insight into structural refinement, Microstructural, dielectric and spectroscopic properties

Bi and Co-substituted strontium (SrFe12O19) hexaferrites were synthesized using the auto-combustion sol–gel method. The structural, Rietveld refinement, microstructural, spectroscopic, and dielectric characterizations were analyzed with X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and Dielectric analysis, respectively. The XRD investigation of Sr1-xBixFe12-yCoyO19 with (x = 0–0.5, y = 0–1.0) confirmed the single phase of M−type hexagonal ferrites. The change in the value of lattice constant ‘a’ in between 5.87 and 5.95 and ‘c’ 22.07 to 23.81 to be noted. The crystallite size of prepared specimens was determined in (20–29) nm range. The specific stretching vibrations in the FTIR results approves (Fe/Co-O and Bi-O) at three different positions 437.59, 549.94, and 587.53 cm−1. The existence of these band from 437 to 588 cm−1 confirmed the hexagonal structure of these ferrites. The force constants at octahedral sites increased from 1.75 to 2.02 (Dyne cm−1) x 105 and shows insignificant behavior at tetrahedral sites in between (3.33–3.54) Dyne cm−1 x 105 with Bi-Co substitution. The first band 582 cm−1 (ʋ1), is due to the maximum restoring force and vibrations at the tetrahedral site. The second band at a lower wavenumber of ∼ 402 cm−1 (ʋ 2) is due to the vibrations at the octahedral site. The microstructure of all synthesized samples of M−type hexagonal ferrites confirmed using the SEM analysis. The dielectric measurements in 0 to 3 GHZ frequency was done and effect of Bi-Co has been observed. The dielectric constant of all specimens shows the increasing trend from 1.5 GHz to 2.5 GHz with the frequency of the applied AC field. A slight increase was observed in the AC conductivity of these ferrites with the increasing concentration of Bi and Co ions.

Refinement of the crystal structure of christofschäferite-(Ce) and the modular aspect of the chevkinite polysomatic series with the general formula of {A<sub>4</sub>B(T<sub>2</sub>O<sub>7</sub>)<sub>2</sub>}{C<sub>2</sub>D<sub>2</sub>O<sub>8</sub>}<sub>m</sub> (m = 1, 2)

Research subject. The crystal structure of christofschäferite-(Ce) was previously refined in terms of the P21/m low-symmetrical space group, which allowed the local features of cationic arrangements to be determined. In this work, we set out to refine the crystal structure of christofschäferite-(Ce) in terms of the P21/a high-symmetrical space group based on the previously collected diffraction data. A topology-symmetrical analysis of the members of the chevkinite group with the general formula of A4BC2D2(Si2O7)2O8 was conducted. Materials and methods. A magmatic rock sample with christofschäferite-(Ce) inclusions was found in the vicinity of the Laacher See volcano, near Mendig, Eifel Mountains, Rhineland-Palatinate (Rheinland-Pfalz), Germany. The crystal structure was studied using single-crystal X-ray analysis. Results. Despite an increase in the symmetry to the P21/a space group (in comparison with the previous data with the P21/m space group), the main patterns of cation distribution between the octahedral and tetrahedral sites are preserved. However, due to the lover number of cationic sites, this distribution becomes more disordered. Based on a crystal chemical analysis of the crystal structures of natural and synthetic members of the chevkinite group in the framework of the OD theory, it is possible to combine them into a united OD family with the same OD groupoid. Conclusions. According to the OD theory, there are two structural OD-subgroups of the chevkinite group (chevkinite and perrierite). The crystal structure and symmetry of possible MDO-polytypes are predicted.

Optimizing the synthesis of ZnFe2O4 through chemical and physical methods: effects of the synthesis route on the phase purity, inversion, and magnetic properties of spinel zinc ferrite

Abstract In this work, ZnFe2O4 ferrites were prepared by chemical (coprecipitation) and ceramic (ball-milling) methods. The effects of the synthesis route on the phase purity, crystallinity, particle size distribution, and magnetic properties were investigated to identify the most appropriate conditions for the syhnthesis of high quality ferrites. The samples were exmined by X-ray diffraction, scanning electron microscopy, thermal gravimetric analysis, Fourier transform infrared spectroscopy, vibrating sample magnetometry, and Mössbauer spectroscopy. The XRD patterns revealed that a high-purity spinel phase was obtained by coprecipitation at pH ≥ 7 by calcining the pristine powder at T ≥ 900 °C, whereas a single spinel phase was obtained at T ≥ 700 °C in the ball-milling method. The crystallite size of the spinel phase exhibited general increasing trends with the increase of the pH value under the same heat-treatment conditions, and with the increase of the calcination temperature. Additionally, the mean physical particle size exhibited an increasing trend with the increase of the calcination temperature. The VSM measurements revealed a noticeable degree of inversion in the spinel ferrites prepared by coprecipitation (exhibiting the highest degree at pH = 10), and an insignificant degree of inversion in the spinel ferrites prepared by the ceramic method. However, calcining the powder exhibiting the highest degree of inversion (prepared by coprecipitation at pH = 10) at 1100 °C resulted in ordering the zinc ions at tetrahedral sites of the spinel structure. Mössbauer spectra for representative zinc ferrite samples prepared by the two methods revealed a major central doublet (with a small magnetic sextet corresponding to the α-Fe2O3 phase in the sample at pH = 7). The hyperfine parameters of the doublet observed in the Mössbauer spectra of the samples, and the corresponding magnetization behavior revealed a higher degree of ionic disorder in the spinel ferrite prepared by coprecipitation.

Probing Bond Length and Compositional Disorder in β‐(AlxGa1−x)2O3 Alloys Using Extended X‐Ray Absorption Fine Structure Spectroscopy

Local structure of β‐(AlxGa1−x)2O3 alloys with Al contents is determined from extended X‐ray absorption fine structure spectroscopy (EXAFS). A model to fit the EXAFS data for monoclinic β‐(AlxGa1−x)2O3 is suggested to independently determine local structure parameters. An increase in compositional disorder corresponding to the near neighbors (NNs) for lower Al contents establishes that the Al atom does occupy tetrahedron sites in addition octahedron sites even for smaller Al contents. NNs and next‐nearest neighbor (NNN) bond lengths corresponding to tetrahedron and octahedron coordinated gallium (Ga) atoms with surrounding oxygen (O) atoms as well as tetrahedron–tetrahedron/octahedron–octahedron coordinated GaGa atoms on average decrease with Al content up to x = 33.3% and then they saturates with further increase in Al content. However, tetrahedron–octahedron coordinated GaGa atoms move far apart with Al content up to x = 33.3% and then it saturates. The physical picture indicates the creation of tetrahedra and octahedra sublattices locally for β‐(AlxGa1−x)2O3, and their sizes decrease, but they move far apart up to a certain Al content. Thereafter, both saturate. Thus, EXAFS provide a clear insight into the evolution of local structure of β‐(AlxGa1−x)2O3 with Al content, which is useful for better understanding of their physical properties.

Determine elastic parameters and nanocrystalline size of spinel ferrites MFe2O4 (M = Co, Fe, Mn, Zn) through X-ray diffraction and infrared spectrum: Comparative approach

MFe2O4 (M = Co, Fe, Mn, Zn) nanoparticles were successfully synthesized by coprecipitation. Analyzing the X-ray diffraction by the Rietveld method confirmed the spinel ferrite structure of the samples. Rietveld refinement results show that Co, Mn and Zn occupy both the tetrahedral and octahedral sites. Variation in elastic parameters was determined by Fourier transform infrared spectroscopy, and cation distribution was deduced from X-ray diffraction. X-ray diffraction peak expansion was analyzed by employing a variety of calculating methods such as modified Scherrer, Williamson–Hall, size–strain, and Halder–Wagner to determine the crystallite size and elastic parameters of the cubic-structured MFe2O4 nanoparticles, including intrinsic strain, stress, and energy density. Comparison of the results obtained from these different methods revealed that they are ideally suited to each other. Moreover, the transmission electron microscopy image confirmed that the average size of MFe2O4 (M = Co, Fe, Mn, Zn) nanoparticles ranges from 10 to 14nm, consistent with the dimensions obtained from the preceding methods.

Effect of double substitution on hydrogen absorption-desorption properties of Ti2CrV alloy

Doubly substituted Ti2CrV alloy with composition Ti1.5Sc0.3CrVNi0.2 was prepared by arc melting method followed by annealing. The annealed alloy exists in body centred cubic (BCC) structure and shows fast kinetics for hydrogen absorption and desorption at room temperature. BCC phase of the alloy undergoes phase transformation to face centred cubic (FCC) hydride phase with H atoms occupying tetrahedral sites in the lattice, reaching an overall H/M ratio >2.2 (storage capacity ∼ 4 wt%). Storage capacity decreases by 40% in the 2nd cycle and then stabilizes at a value of ∼2.5 wt% for the subsequent 10 cycles. A drastic reduction in hydride desorption temperature upon double substitution (Sc and Ni substitution in Ti2CrV alloy) has been confirmed by DSC studies. Furthermore, the change in isotope effect in doubly substituted Ti2CrV alloy is discussed in light of thermal stabilities of the hydrides and deuterides.

Theoretical study on hydrogen permeation and fault slip of γ-Ni/γ'-Ni3Al interface with alloying elements (Zr, Nb, Ru, Re, and Hf)

In order to elucidate the role of hydrogen behavior at γ-Ni/γ'-Ni3Al interface with alloying elements, we performed comprehensive research of the permeation and slip properties by using DFT calculations. The result figures out that the alloying elements (Zr, Nb, Ru, Re, and Hf) tends to occupy corner-point sites in γ-Ni phase, while Re has the lowest substitution formation energy. The octahedron interstitial site is the favorable position for hydrogen adsorption due to its lower solution energy compared to the tetrahedron site. The diffusion energy barrier of hydrogen follows the influence order of Zr < Ru< Hf < Re < Nb. Meanwhile, Nb-doped interface has the highest hydrogen diffusion coefficient and permeability compared to other doped interfaces. By analyzing the partial density of states, the hybridization between Re-d orbital and neighbor Ni-d orbital is conducive to affect the permeability behavior of hydrogen. The generalized stacking fault energy reveals that all the alloying elements can improve the creep strength of γ-Ni/γ'-Ni3Al interface. As a barrier, Hf element is more effective to improve the dislocation slip resistance. These results can help people deepen the understanding of hydrogen behavior with alloying elements at the γ-Ni/γ'-Ni3Al interface and provide fundamental theories data for the further design of Ni-based superalloy.

First-principles investigations and MOCVD growth of Si-doped β-Ga2O3 thin films on sapphire substrates for enhancing Schottky barrier diode characteristics

In the realm of high-power electronics, the potential of gallium oxide (β-Ga2O3) as a front-runner material has garnered significant attention due to its wide bandgap and the capacity to withstand high critical electric fields. To push the boundaries of performance for β-Ga2O3 devices, a meticulous exploration into the effects of silicon (Si) doping on β-Ga2O3 films was carried out using the metalorganic chemical vapor deposition (MOCVD) technique with various tetraethoxysilane (TEOS) flow rates (0–30 sccm). The Si-doped β-Ga2O3 films were systematically studied and characterized using XRD, SEM, and XPS techniques. XRD patterns demonstrated the preservation of the β-Ga2O3 monoclinic structure in the Si-doped β-Ga2O3 films, without any evidence of secondary phases. In addition to this, first-principles calculations were performed to explore the incorporation of Si atoms in Ga2O3 supercells, which revealed the preference of Si atoms to occupy substitutional Ga tetrahedral sites within the Ga2O3 lattice. Through the utilization of Si-doped β-Ga2O3 films, a unique design of donut-shaped Schottky barrier diode (SBD) was successfully engineered. Remarkably, the Si-doped β-Ga2O3 SBD (employed with 20 sccm TEOS flow rate) exhibited the breakdown voltage (Vbr) of 497 V and Baliga's Figure of Merit (BFOM) value of 1.16 kW/cm2, which is five-order higher BFOM compared to undoped β-Ga2O3 SBD. This substantial improvement in BFOM underscores the significant potential of Si-doped β-Ga2O3 films for high-power electronics, opening avenues for enhanced device efficiency and capabilities.

Ultrathin High-Entropy Fe-Based Spinel Oxide Nanosheets with Metalloid Band Structures for Efficient Nitrate Reduction toward Ammonia.

Spinel oxides with tunable chemical compositions have emerged as versatile electrocatalysts, however their performance is greatly limited by small surface area and low electron conductivity. Here, ultrathin high-entropy Fe-based spinel oxides nanosheets are rationally designed (i.e., (Co0.2Ni0.2Zn0.2Mg0.2Cu0.2)Fe2O4; denotes A5Fe2O4) in thickness of ≈4.3nm with large surface area and highly exposed active sites via a modified sol-gel method. Theoretic and experimental results confirm that the bandgap of A5Fe2O4 nanosheets is significantly smaller than that of ordinary Fe-based spinel oxides, realizing the transformation of binary spinel oxide from semiconductors to metalloids. As a result, such A5Fe2O4 nanosheets manifest excellent performance for the nitrate reduction reaction (NO3 -RR) to ammonia (NH3), with a NH3 yield rate of ≈2.1mmol h-1 cm-2 at -0.5V versus Reversible hydrogen electrode, outperforming other spinel-based electrocatalysts. Systematic mechanism investigations reveal that the NO3 -RR is mainly occurred on Fe sites, and introducing high-entropy compositions in tetrahedral sites regulates the adsorption strength of N and O-related intermediates on Fe for boosting the NO3 -RR. The above findings offer a high-entropy platform to regulate the bandgap and enhance the electrocatalytic performance of spinel oxides.

Tuning benzene activity of cobalt-based spinel catalysts with cation substitution

Cobalt-based spinel oxides are promising low-cost catalysts for volatile organic compounds (VOCs) elimination. Herein, we prepared the cobalt-based spinel oxides (MCo2O4: M = Ni, Cu, Co, Zn) by a one-step solvothermal method to evaluate the influence of cation substitution on benzene combustion. The cation distribution on tetrahedral and octahedral sites could influence the degree of inversion in cobalt-based spinel oxides, thus achieving the regulation of Co-O bond strength. NiCo2O4 catalyst with the inverse spinel structure had the weak Co-O bond strength, which is conducive to the activation of lattice oxygen to improve the activity of benzene degradation. This work provides deep insights into the influence of the cation substitution on the cobalt-based spinel catalysts for the efficient benzene oxidation.

Exploring the impact of annealing temperature on morphological, structural, vibrational and electron paramagnetic resonance properties of starch-mediated spinel CoAl2O4: Experimental and DFT study

In the present work, CoAl2O4 nanoparticles were successfully synthesized using the simple auto-combustion sol-gel method employing starch as an organic fuel source. The effect of the annealing temperature on the structural, vibrational, morphological, and magnetic properties is studied. The obtained spherical nanoparticles have grain sizes ranging from 23.54 nm to 46.50 nm. X-ray diffraction (XRD) patterns reveal the formation of a face centered cubic (fcc) spinel phase with the Fd-3m space group for all prepared samples. The calculated average crystallite sizes exhibit an increase from 24.65 nm to 56.27 nm, consistent with the observed grain sizes. Density Functional Theory (DFT) calculations are applied to reach the optimized cell parameters as well as to confirm the structural properties of the synthetized CoAl2O4 nanoparticles. Geometry optimization of the CoAl2O4 spinel oxide is performed using the CASTEP module of Materials Studio software. The optimized unit cell, lattice parameter and unit cell volume were obtained from this simulation. The combined experimental and density functional theory study of structural properties of CoAl2O4 revealed that an increase in the calcination temperature leads to an increase in the volume of the unit cell and hence to an increase in the particles size. Fourier-transform infrared spectroscopy (FTIR) further corroborated these findings by demonstrating subtle shifts in characteristic CoAl2O4 absorption peaks with varying annealing temperatures. These peak shifts suggest a potential redistribution of Al³⁺ and Co2⁺ ions between tetrahedral and octahedral sites within the spinel structure. Electron paramagnetic resonance (EPR) spectroscopy revealed a magnetic state transition as a function of both the annealing temperature and the resulting crystallite size. Occupancy fluctuations of Al³⁺ and Co2⁺ ions at specific sites have also impacted on the nanoparticles color since the hue of the material depends on the valence state and the cationic coordination environment in the CoAl2O4 crystal lattice. Correlations between structural, vibrational, magnetic and color properties are presented to understanding how synthesis parameters influence CoAl2O4 characteristics which is essential for tailoring materials for specific applications.

Can large lattice volume always facilitate ion diffusion in solids?

Large lattice volume is usually expected to expand the bottleneck size and enlarge free volume for fast Li ion transport in solids. But the universality of lattice expansion decreasing activation energy barrier for Li ion migration is still debatable. Herein, our molecular dynamics simulations and density functional theory calculations detect the unconventional phenomenon of lattice expansion increasing activation energy barrier for Li ion migration in β-Li3PS4, Li4SnS4 and Li4GeS4 sulfides with the hcp-type anion sublattice, and discover the underlying mechanism. On one hand, lattice expansion enlarges the relative energies between the octahedral and tetrahedral Li sites, and correspondingly increase activation energy barrier for tetrahedral Li ions migration along the Tet-Oct-Tet migration paths in β-Li3PS4, Li4SnS4 and Li4GeS4. On the other hand, the lattice dynamics calculations show Li energy landscapes of β-Li3PS4, Li4SnS4 and Li4GeS4 are anharmonic and enlarging lattice volume make the local minimum of Li potential energy surface flatter, simultaneously reduce the relative energy of Li occupation site, eventually resulting in the higher activation energy barrier for Li ion migration. Thus, understanding the effect of lattice volume on ion migration in solids should not only consider the factor of bottleneck size and free volume, but also combine the aspects of Li ion occupation type, Li ion migration path and anion sublattice type. These new understandings of the lattice expansion increasing activation energy barrier for ion migration would further promote the further optimization and rational design of superionic conductors by element doping or strain engineering.

Advancements in multiferroic, dielectric, and impedance properties of copper–yttrium co-doped cobalt ferrite for hydroelectric cell applications

This paper explores yttrium and copper co-doped cobalt ferrite [Co1−x Cu x Fe1.85Y0.15O4] synthesized via the sol–gel auto-combustion route (0.0 ⩽ x ⩽ 0.08). Investigating the impact of co-dopants on CoFe2O4, the study reveals altered cation distribution affecting the structure, multiferroic, and electrical properties. X-ray diffraction studies show nanocrystalline co-doped cobalt ferrites with lattice expansion and smaller grains due to Cu–Y co-doping. Fourier transform infrared spectroscopy confirms inverse spinel family classification with tetrahedral lattice shrinkage. Field emission scanning electron microscopy indicates a grain size of approximately 0.12 μm. Ferroelectric analysis reveals a peak saturation polarization of 23.42 μC cm−2 for 8% copper doping, attributed to increased Fe3+ ions at tetrahedral sites. Saturation magnetization peaks at 54.4706 emu g−1 for 2% Cu2+ ion substitution [Co0.98Cu0.02Fe1.85Y0.15O4] and decreases to 37.09 emu g−1 for 4% Cu substitution due to irregular iron atom distribution at tetrahedral sites. Dielectric studies uncover Maxwell–Wagner polarization and high resistance in grain and grain boundaries using impedance spectroscopy. Fabricated hydroelectric cells exhibit improved ionic diffusion, suggesting their use in potential hydroelectric cell applications.

Suppression of inactive sites in NiMo@amorphous alumina catalysts for hydrodesulfurization reaction: Effect of Ga doping

Hydrodesulfurization (HDS) reaction activity depends on the formation of active NiMoS (completely sulfided multilayer type 2 sites) and inactive NiAl2O4/NixSy phases on the catalyst surface. These inactive phases not only itself inactive for the reaction but also hinder the formation of active NiMoS phases. In addition, the formation of strong Mo-O-Al bonds also lowers the reducibility of the catalyst, suggesting lesser catalytic activity (type 1 sites, partially sulfided single-layer sites). To this end, we report the formation of NiMo/Ga doped amorphous alumina (A-Al2O3) catalysts prepared by the colloidal synthesis method. A-Al2O3 was chosen as a support because it has lower surface energy, better physicochemical properties, and enhanced acidic sites than the crystalline alumina phase, which favours the formation of type 2 sites or weak metal-support interaction (completely sulfided multilayer NiMoS sites). Further, the Ga doping in A-Al2O3 support substitute the tetrahedral Al sites and form GaAl2O4 phases by reducing NiAl2O4 inactive sites, and the free Ni decorate the edges of MoS2 to form HDS active NiMoS sites. Therefore, NiMo/Ga doped A-Al2O3 catalyst (at 1 wt% Ga loading) reported enhanced HDS catalytic activity (25%), HDS reaction rate constant (kHDS-2.15 times) and turn over frequency (TOF-1.3 times) than the conventional NiMo/γ-Al2O3 catalysts.

A Functional Air-Stable Li9.8GeP1.7Sb0.3S11.8I0.2 Superionic Conductor for High-Performance All-Solid-State Lithium Batteries.

Solid-state electrolytes (SSEs) based on sulfides have become a subject of great interest due to their superior Li-ion conductivity, low grain boundary resistance, and adequate mechanical strength. However, they grapple with chemical instability toward moisture hypersensitivity, which decreases their ionic conductivity, leading to more processing requirements. Herein, a Li9.8GeP1.7Sb0.3S11.8I0.2 (LGPSSI) superionic conductor is designed with a Li+ conductivity of 6.6 mS cm-1 and superior air stability based on hard and soft acids and bases (HSAB) theory. The introduction of optimal antimony (Sb) and iodine (I) into the Li10GeP2S12 (LGPS) structure facilitates fast Li-ion migration with low activation energy (Ea) of 20.33 kJ mol-1. The higher air stability of LGPSSI is credited to the strategic substitution of soft acid Sb into (Ge/P)S4 tetrahedral sites, examined by Raman and X-ray photoelectron spectroscopy techniques. Relatively lower acidity of Sb compared to phosphorus (P) realizes a stronger Sb-S bond, minimizing the evolution of toxic H2S (0.1728 cm3 g-1), which is ∼3 times lower than pristine LGPS when LGPSSI is exposed to moist air for 120 min. The NCA//Li-In full cell with a LGPSSI superionic conductor delivered the first discharge capacity of 209.1 mAh g-1 with 86.94% Coulombic efficiency at 0.1 mA cm-2. Furthermore, operating at a current density of 0.3 mA cm-2, LiNbO3@NCA/LGPSSI/Li-In cell demonstrated an exceptional reversible capacity of 117.70 mAh g-1, retaining 92.64% of its original capacity over 100 cycles.

Investigation of structural, electrical, and magnetic variations of Ni-Zn-Co ferrites by substituting rare earth Ho3+ for high-frequency applications

The investigation of structural, magnetic, and electrical properties of Ni0.6Zn0.3Co0.1HoxFe2−xO4 (NZCHF, 0 ≤ x ≤ 0.2) ferrites, synthesized through the sol–gel autocombustion method, has been undertaken. The refined x-ray diffraction (XRD) analysis was performed for XRD data analysis using Fullprof Suite software and it confirmed a single-phase cubic spinel structure, with the determination of crystallite size, refinement parameters and lattice constants. The bulk density of the samples consistently remained lower than the x-ray density, with densities increasing proportionally to the enhancement of Ho concentration. FTIR analysis corroborated the presence of metal-oxygen bonds within the ferrite possessing a spinel cubic structure. 57Fe Mossbauer spectroscopy showed that the hyperfine magnetic field of tetrahedral (A) and octahedral (B) sites decreased with the substitution of Ho3+ ions that preferentially occupy the B site. The impedance analyzer and vibrating sample magnetometer (VSM) were utilized to measure the real and imaginary parts of the complex permeability and magnetic properties of the samples, respectively. Complex impedance plots were scrutinized to discern the contributions of grain and grain boundary resistances, providing insights into the electrical behavior of the ferrite samples. Furthermore, the introduction of Ho concentration led to alterations in other key properties of the ferrites, including coercivity (H c ), retentivity (M r ), anisotropy constant (K), and magnetic moment (μ B ).The impact of the rare-earth content on the magnetic features of the prepared NiZnCo ferrite microspheres was investigated by analyzing magnetic-hysteresis (M-H) loops, which showed soft ferrimagnetism. Concurrently, the dielectric constant and dielectric loss tangent of the studied samples exhibited a decrease with the rise in Ho3+ concentration. The expected reduction in tan loss in the prepared samples is attributed to the increase in ac resistivity associated with the higher Ho3+ content.

Mg2+ Doped ZCFAO Spinel Ferrite: Structural, Optical, Dielectric and Magnetic Explorations

AbstractA series of Mg doped ZCFAO (Zn0.3−xMgxCu0.7Al0.3Fe1.7O4 (0.05 ≤ x ≤ 0.25) spinel samples were synthesized by solid state reaction method. XRD, was utilized to investigate the structure phase, microstructural characteristics, The optical properties were analyzed; Biological instruments Sp-150 potentiostate is employed to investigate the dielectric measurements in the frequency range of 10 Hz to 1 MHz at various temperatures from 300 to 650 K. Vibrating sample magnetometer VSM was employed to examine the magnetic characteristics in the applied magnetic field ranging from − 20 to 20 kG. The creation of a single-phase cubic spinel was validated by X-ray analysis. The leverage of replacing Zn by Mg leads to enhancement in the lattice parameters, reducing both of the degree of inversion, crystal distortion and compelled these samples to be normal spinel. It turned out that as the degree of inversion sank, the crystallite size declined. The values of dislocations density was found in the order of 10−5 which reveal improving and completing the crystallization of the ferrite samples. The samples have an optical energy gap in the range 3.1–3.38 eV, according to the inferred optical characteristics. The dielectric constant revealed the normal behavior of spinel ferrite it decreases with increasing frequency and enhanced with increasing temperature. It seems that the microstructure of the compound consists of both high-conductive grains and low-conductive grain boundaries, which has been confirmed by the complex impedance. Additionally, the presence of the Maxwell–Wagner relaxation process is also detected. This information can provide valuable insights into the properties and behavior of the compound. Using Nyquist plot, the sample impedance characteristics were interpreted while taking grain and grain boundary contributions into account. The magnetic properties proved that doping ZCFAO with diamagnetic cations (Mg) increases both of saturation magnetization from 16.416 up to 29.983 emu/g and the magnetocrystalline anisotropic constant from 1319.24 to 1612.804 because the two main factors that influence the magnetic properties are the distribution of cations between the octahedral and tetrahedral sites and the magnetic moment of each of its cations. Novelty of our work replacing Zn by Mg (both of them diamagnetic materials) enhance the magnetic properties. Synthesized materials may reexamine the mechanisms underlying Mg2+ induced cationic exchange in ZCFAO and have prospective uses as soft-magnetic materials.

Constructing Bipolar Dual-Active Sites through High-Entropy-Induced Electric Dipole Transition for Decoupling Oxygen Redox.

It remains a significant challenge to construct active sites to break the trade-off between oxidation and reduction processes occurring in battery cathodes with conversion mechanism, especially for the oxygen reduction and evolution reactions (ORR/OER) involved in the Zinc-air batteries (ZABs). Here, we propose using a high-entropy-driven electric dipole transition strategy to activate and stabilize the tetrahedral sites, while enhancing the activity of octahedral sites through orbital hybridization in a FeCoNiMnCrO spinel oxide, thus constructing bipolar dual-active sites with high-low valence states, which can effectively decouple ORR/OER. The FeCoNiMnCrO high-entropy spinel oxide (HESO) with severe lattice distortion, exhibits a strong 1s→4s electric dipole transition and intense t2g(Co)/eg(Ni)-2p(OL) orbital hybridization that regulates the electronic descriptors, eg and t2g, which leads to the formation of low-valence Co tetrahedral sites (Coth) and high-valence Ni octahedral sites (Nioh), resulting in a higher half-wave potential of 0.87 V on Coth sites and a lower overpotential of 0.26 V at 10 mA cm-2 on Nioh sites as well as a superior performance of ZABs compared to low/mild entropy spinel oxides (L/MESO). Therefore, entropy engineering presents a distinctive approach for designing catalytic sites by inducing novel electromagnetic properties in materials across various electrocatalytic reactions, particularly for decoupling systems. This article is protected by copyright. All rights reserved.

Magnetic, Electric, and Antimicrobial Properties of Chromium‐ Doped Cobalt Zinc Ferrite Nanoplates

AbstractIn the present work, Co0.5Zn0.5CrxFe2‐xO4 (CZFCO) (x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) has been successfully driven from self‐ignited sol‐gel method, using citric acid as a chelating agent. The powder XRD patterns are confirming the formation of single‐phase cubic crystallographic structure with satisfying the Fd‐3m space group. The Rietveld refinement process is carried out to obtain the structural information, including lattice parameters, cell volume, and bond length. Crystallite size and micro‐strain values are found by the Debye Scherrer formula as well as by HR‐TEM the particle size is shown at about 7.86 nm and the presence of two distinct lattice fringes. The SEM digital images display soft wart grains nature, where the majority of grains are forming a dense agglomerate nature with nano plate texture. EDS spectra reflect the presence of all the elements without impurities. The formations of spinel ferrite and metal‐oxygen bond were approbated by FT‐IR Spectra. Further, RT UV‐Vis spectra (DRS) show a decrease in the optical band gap from 1.56 eV to 1.46 eV. The magnetic properties indicate soft ferromagnetic behaviour and as increasing Cr dopant saturation magnetization and coercivity significantly decrease while in the case of X=0.5 suddenly enhanced the Ms, this well corroborates with cation distribution. X‐ray photoelectron spectroscopy (XPS) technique has confirmed the presence of all elements and shows the valance of the Cr is +3 and +2 states at respected octahedral and tetrahedral sites. RT dielectric studies firmly agreed with the Maxwell‐Wagner type of polarization following Koop's theory. RT Impedance spectra suggest consent of the Debye type of relaxation and the Cole‐Cole map shows semi arc‐shaped curve fitted with Gaussian distribution. The imaginary and real parts of the relative permeability of frequency‐dependent curves decayed and firmly showed the favourable character of electric properties. Finally, all the antimicrobial activity results suggested the potential utility of derived compounds as antibacterial agents.

Magnetic, Optical, Electrical and Antimicrobial Properties of MnCuZnFe2O4 Nanoparticles

AbstractThe Mn0.92Cu0.08‐yZnyFe2O4 (y=0.02, 0.04, 0.06 and 0.08) nanoparticles (MCZF NPs) were synthesized via the hydrothermal process at low operating temperature. The MCZF system generated a cubic spinel structure as seen by the X‐ray diffraction patterns. The average crystallite size was observed to be increasing from 25 to 30 nm. The broad (γ1) and narrow (γ2) absorption bands were seen in FTIR spectra and the cation distributions at tetrahedral (A) and octahedral (B) sites, respectively, was indicated. The surface morphology was analyzed using electron microscopy. Clarification was provided for the dependence of the optical bandgap shift (Eg~1.96–2.15 eV) on the concentration of substituent. The superparamagnetic nature of MCZF can be advantageous for biomedical applications and it was demonstrated by the magnetization versus applied magnetic field (M−H) loops. Small values of remanence magnetization (Mr) and coercivity (Hc) were found using magnetization versus magnetic field (M−H) curves at y=0.02, 0.04, 0.06, and 0.08. This proved that MCZF NPs exhibited the superparamagnetic behavior. The cation distribution at two sublattices was also estimated using a two‐sublattice model. The greatest zone of inhibition in an antibacterial study of MCZF (produced by the green method) was 10.8 mm for Pseudomonosa aeruginosa and 9.4 mm for Staphylococcus aureus.