Spinel Structure Research Articles

The role of phase transformation (tetragonal – spinel) on the structural and mechanical properties of Ni doped CuFe2O4

Nano-ferrites of Cu1–xNixFe2O4 (x = 0 to 1 with step 0.2) system was synthesized utilizing the flash auto combustion process annealed at 600oC for 3 h. The structural characterization for synthesized samples was carried out using x-ray Diffraction (XRD), Fourier transition infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The hardness of the prepared material was measured using micro-indentation creep technology. XRD pattern verified the creation of a single-phase cubic spinel structure. The undesired CuO phase forms around \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:2\ heta\\:={50}^{^\\circ\\:}\\:$$\\end{document}for pure Copper ferrite and decreases with increasing Ni content. The average crystalline size decreases from 27.92 nm to 13.28 nm by doping process from x = 0.2 to x = 1 which retards the growth of crystalline size. FTIR spectra are distinguished by the presence of two prominent absorption bands, ν2 for the octahedral site and ν1 for the tetrahedral site, in the range of approximately 593 and 471 cm− 1, respectively. FTIR analysis verified the formation of the ferrite system’s spinel structure. The TEM images show a nanocrystalline nature with some agglomeration and the crystallites are spherical in shape which their sizes are agrees well with that obtained from XRD measurements. The hardness decreases as the dwell time increases. The hardness and yield strength (Y) values were significantly improved due to the decrease in the crystallite size after Ni doping. The stress exponent (n) value increases by increasing Ni content which means that the mechanical properties improved due to increment of resistance.

The potential of Gd doping as a promising approach for enhancing the adsorption properties of nickel-cobalt ferrites.

The study shows that the addition of gadolinium ions has a significant impact on the structure, morphology, and adsorption properties of Ni-Co spinel ferrite that was synthesized by the sol-gel auto-combustion method. The research also indicates that the higher the Gd content, the greater the increase in the lattice parameter, which suggests that Gd3+ ions uniformly replaced the octahedral Fe3+ ions. The morphology and chemical composition of Gd-doped Ni-Co ferrites have been studied using SEM and EDS. Gd adding to the NiCoFe matrix increases the BET surface area by 50% (from 48 to 72 m2/g) and promotes the formation of mesopores with an average radius from 3.9 to 4.9nm. The pHPZC values of Gd-doped ferrites are in the range of 7.22-7.39, which means that the ferrite surface will acquire a positive charge at natural pH, so this will promote the adsorption of Congo red anionic dye through electrostatic interaction forces. Langmuir, Freundlich, and Dubinin-Radushkevich models were used to explain the mechanism of CR adsorption on the Ni0.5Co0.5GdxFe2-xO4 adsorbent surface. The ionic-covalent parameter has been estimated to describe the surface acid-base properties. Overall, this study highlights the potential of Gd3+ doping as a promising approach for enhancing the adsorption properties of nickel-cobalt ferrites.

Polyvinylpyrrolidone mediated electrospun ZnO-ZnFe2O4 composite nanofibers for removing malachite green from water

This study explores the application of ZnO-ZnFe2O4 composite nanofibers for the adsorption of Malachite Green (MG) dye from water. The composite nanofibers were fabricated using simple polyvinylpyrrolidone (PVP) mediated electrospinning method by changing zinc and iron precursor weight ratio named as Zn–Fe (1-1), Zn–Fe (2–1) and Zn–Fe (1–2). The diameter of 1D nanofibers was found to be 40–60 nm. The formation of hexagonal wurtzite structure of ZnO and cubic spinel structure of ZnFe2O4 was confirmed by XRD and HRTEM analysis. The effects of various parameters such as pH, contact time and initial concentration on the adsorption process were investigated. The Zn–Fe (1-1) nanofibers showed higher adsorption efficiency than other two. The adsorption results demonstrated excellent adsorption performance, with a maximum adsorption capacity of 146.77 mg/g at pH = 7 for Zn–Fe (1-1). Furthermore, the adsorption kinetics and isotherms were analyzed to understand the adsorption mechanism and equilibrium behaviour. It was found that the nanofibers material can be recycled and reused up to five cycles.

Defect design and vacancy engineering of NiCo2Se4 spinel composite for excellent electromagnetic wave absorption

Vacancy engineering presents an appealing method for modifying the electronic structure of spinel architectures. However, based on well-defined vacancy concentrations, how to design anionic vacancies to modulate electromagnetic parameters as well as electromagnetic wave absorption (EMA) properties is less studied. Here, NiCo2Se4 spinel structures were prepared using different selenization methods, and the Se vacancy defect concentration was controlled by changing the annealing temperature, thus regulating the EMA properties. Among them, the design of the hollow structure effectively enhanced the EMA performance. Moreover, the increase of Se vacancy concentration increases the conductivity loss while regulating the electronic structure, and also acts as an unsaturated site to induce the formation of dipoles to optimize the polarization loss. The effective absorption bandwidth (EAB) of NiCo2Se4-130 reaches 8.48 GHz at 2.4 mm at the highest Se vacancy concentration. This work establishes a direct relationship between vacancy concentration and the electromagnetic wave dissipation capability, offering valuable insights for the development of advanced EMA materials.

Crystal structure, chemical bonds and microwave dielectric properties of ultra-low loss Li2Mg2GaTi2O8F ceramics

Ceramics of Li2Mg2GaTi2O8F (LMGTOF) were prepared by the traditional solid-state method. XRD and TEM results confirmed that a single phase of Li2Mg2GaTi2O8F, with an Fd-3m space group and a cubic spinel structure, was formed by the ceramics. It was shown by the results that the lattice parameters of the ceramics at 1050 °C were measured as a = b = c = 8.36576 Å, with a volume of V = 585.485549 Å3. Furthermore, it was observed through the analysis of the Raman peak at 718 cm−1 that an inverse relationship was exhibited between the Raman shift and εr. Similarly, an opposing trend was also demonstrated between the Q × f value and FWHM. By bond valence analysis, it was shown that Mg2+, Ga3+, and Ti4+ ions were in a “rattling” state, and the large positive deviation between εcorr and εtheo was attributed to the strong “rattling” effect induced by the cations. At 1050 °C, the best microwave dielectric properties (εr = 14.58, Q × f = 76,689 GHz, and τf = −52 ppm/°C) were exhibited by LMGTOF ceramics.

Interface enhanced magnetoelectric coupling effect of multiferroic liquids based on CoFe2O4@BaTiO3 core shell particles

A new type CoFe2O4@BaTiO3 (CFO@BTO) multiferroic liquid with different CoFe2O4 (CFO) particle sizes was constructed, and its magnetic properties, electrical properties, and magnetoelectric coupling effects were systematically studied. XRD results show that the CFO phase has a spinel structure, whereas the BaTiO3 (BTO) phase has a perovskite structure, with no obvious heterophase formation. It can be seen from the SEM diagram that the CFO powder has a cuboid shape, and the CFO particle size (1.56 × 0.58 × 0.48 µm, 3.16 × 1.04 × 0.66 µm, 6.47 × 1.53 × 1.40 µm, and 11.19 × 2.64 × 2.28 µm) gradually increased with increasing calcination temperature(T = 450 ℃, 550 ℃, 650 ℃, 750 ℃). TEM results show that the composite particles have obvious core-shell structure. From the hysteresis loop, it can be seen that the saturation magnetization (Ms) of the CFO@BTO powder gradually increases with increasing CFO size. The sedimentation stability of the multiferroic liquid gradually decreases, the dielectric constant and residual polarization (Pr) decrease first and then increase, and the magnetoelectric coefficient and magnetoelectric coupling coefficient increase first and then decrease. When the particle size of the CFO is 6.47 × 1.53 × 1.40 µm, the maximum magnetoelectric coupling coefficient is 210.76 V/(cm·Oe) under an applied magnetic field of 50 Oe, which realizes a strong magnetoelectric coupling effect at room temperature.

Impact of substituting Cu2+/Ce3+ cations on the structural, magnetic and electrical properties of cobalt nano ferrites

The nano ferrite compounds Co1-xCuxFe2-yCeyO4 (with x values of 0.0, 0.25, 0.5, and 0.75, and y values of 0.0, 0.03, 0.06, and 0.09) were synthesized through the sol-gel auto-combustion method. The characteristics of spinel ferrites were tailored by creating nano ferrites with desirable properties, which were then sintered at 1150 °C for 2 h in the presence of rare earth (Ce3+) and transition metals (Cu2+). They were investigated using dielectric, FTIR, FESEM, XRD, VSM, and DC electrical resistivity experiments. XRD examination verified the samples' cubic spinel structure by measuring the average crystallite size, x-ray density, and lattice constant. FESEM images revealed grain sizes ranging from 41.07 to 156 nm. FTIR spectra in the range of 415 cm−1 to 430 cm−1 further supported the substitution of Cu2+/Ce3+ ions in the tetrahedral sites, indicated by an increase in the lattice parameter. Measurements of the remanence ratio, saturation magnetization, anisotropy constant, coercivity, and magnetic moment, among other magnetic characteristics, were made. Higher concentrations of Cu2+/Ce3+ ions were found to considerably reduce magnetic saturation (Ms), coercivity (Hc), and remanence (Mr). These materials were semiconducting because their activation energy varied between 0.52 and 0.62 eV, and their DC resistivity increased with increasing Cu2+/Ce3+ concentration. Above 1 MHz, the dielectric properties became frequency-independent and decreased with increasing frequency. These ferrites seem highly potential for devices working at high frequency.

On the synthesis and formability of high-entropy oxides

This paper reports on a straightforward and general solution-based synthesis method for high-entropy oxides (HEOs) of different types and compositions. The flexibility and simplicity of this method are hoped to drive development of new HEOs and study of their properties and applications. Thirteen HEOs with rock salt, fluorite, spinel, and perovskite structures were synthesized using a Pechini-type synthesis at temperatures significantly lower than those necessary in solid-state synthesis (400–900 °C). Metal nitrates, nitrites, chlorides, and even water-sensitive alkoxides were used as the metal precursors with the present method. The HEOs were characterized using powder X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Relaxation of cation size and charge rules and formability of HEOs are also discussed. The present results indicate that the classical criteria for material stability do not readily translate to high-entropy systems. For example, the well-known criteria for Goldschmidt and octahedral tolerance factors established for ordinary perovskites do not seem to describe formability of perovskite HEOs well. The discussed relaxation of cation size and charge rules will contribute to the understanding of HEO systems and development of new HEO phases.

Multiferroic properties of electrospun CoFe2O4–(Ba0.95Ca0.05)(Ti0.89Sn0.11)O3 nanocomposites for magnetoelectric and magnetic field sensing applications

Multiferroic CoFe2O4–Ba0.95Ca0.05Ti0.89Sn0.11O3 composite nanofibers (CFO–BCTSn NFs) were synthesized using a sol–gel electrospinning method. Scanning electron microscopy revealed the morphology of the composites, with fiber diameters ranging from 120 to 150 nm. Transmission electron microscopy confirmed the structure of the nanofibers, while X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy verified the formation of the spinel structure of CFO and the perovskite structure of BCTSn, with no additional phases detected. The magnetic properties of the CFO–BCTSn NFs were demonstrated by magnetic hysteresis loops (M-H), and piezoresponse force microscopy confirmed their piezoelectricity. Magnetoelectric coupling was evidenced by comparing the M-H hysteresis loops of electrically poled and unpoled CFO–BCTSn NFs samples. These composite nanofibers have the potential to be utilized in innovative, lead-free magnetoelectric and magnetic field sensing technologies at the nanoscale.

Green synthesis of NiFe2O4 nanoparticles using Hyphaene thebaica: A facile route towards magnetic and photocatalytic application

Wastewaters from textile industries contribute to significant volumes of colored and hazardous material pollution. Photocatalytic degradation offers a method to reduce organic pollutants, such as dye-containing effluents effectively. Nickel Ferrite (NiFe2O4) receives the most attention in spinel ferrites since it has diverse applications in catalysis, sensor technology, spintronics, magnetocaloric refrigeration, high-density data storage devices, etc. We performed the green synthesis of NiFe2O4 nanoparticles by fruit extract of a gingerbread tree (Hyphaene thebaica). We characterized it with Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), and Raman spectroscopy. The XRD indicates the inverse-spinel structure of the F3dm space group with crystallite size measured as 30 nm. SEM and TEM revealed the spheroidal structure of NiFe2O4 NPs. The green synthesized NiFe2O4 has tetrahedral and octahedral stretching vibrations of Ni–O and Fe–O, as suggested by FTIR. Doublet-like peak behavior in the Raman spectrum indicated the presence of a mixed spinel structure. We studied magnetic behavior in two different modes, and magnetization measurements showed a soft ferromagnetic behavior with a saturation magnetization of 1.527 emu g−1. For photocatalytic potential, the degradation efficiency was 97 % after 90 min at adding 1 g/L of NiFe2O4 nano-catalyst, which shows the high catalytic activity of NiFe2O4 NPs under visible light conditions.

Microwave dielectric properties of novel Mg3Ga2TiO8 ceramic

Mg3Ga2TiO8 ceramics were prepared using a solid-phase method. The ceramics sintered at 1440 °C exhibited excellent microwave dielectric properties (εr = 12.07, Q × f = 89,270 GHz, and τf = −40.7 ppm/°C). The typical spinel structure of the Mg3Ga2TiO8 ceramic was confirmed through Rietveld refinement and Raman spectroscopy. High-resolution transmission electron microscopy indicated local lattice distortion in the Mg3Ga2TiO8 ceramics, with a Vickers hardness of 12.53 GPa. The values of εr and Q × f for the Mg3Ga2TiO8 ceramics were affected by the relative density. The theoretical εr obtained from the C-M equation was lower than the measured εr, plausibly due to underestimation of the polarizability of the Ti ions. According to the P-V-L theory, Ti2-O1 has the highest fi value, contributing 29.92 % to εr. The contribution rate of the Ga2-O1 bond to U was 35.76 %, with the greatest impact on Q × f.

CaAl1.5Fe0.5O4/6%Ni-ZnO nanocomposites: Synthesis, characterization and effective photocatalyst for the photocatalytic degradation of methylene blue dye

This study focuses on synthesizing and analyzing properties of calcium aluminate photocatalytic nanoparticles using the microwave (MW) combustion method by following the rules of green chemistry and investigates their effectiveness in the adsorption of methylene blue (MB) dye which is a crucial contaminant that enters water resources. The synthesized nanoparticles, including CaAl2O4 (CAO), CaAl1.5Fe0.5O4 (CAFO), 6 %Ni-ZnO (NZO), and CaAl1.5Fe0.5O4/6%Ni-ZnO (CAFONZO) composites, were characterized using various techniques. XRD analysis confirmed the formation of spinel structures in all samples. The crystallite size and lattice constants were determined, showing a reduction in Crystallite size of CAO from 45.98 nm to 37.55 nm after Fe3 + doping. Then, with the formation of CAFONZO Crystallite size 13.99 nm was obtained. FT-IR analysis revealed the chemical interactions between atoms in the spinel structures Nitrogen adsorption/desorption isotherms were used to determine the specific surface area of nanoparticles, pore volume, and pore size. Specific surface area of CAO, CAFO, and CAFONZO are 1.637, 1.745, and 9.903 (m2/g), respectively. SEM and TEM images provided insight into the morphology and size of the nanoparticles. According to TEM images, after Fe3 + doping, the size of particles decreased from 85 to 32 nm. UV-DRS was performed to determine the optical band gap energy of the photocatalysts. The calculated band gap values of pure CAO, CAFO, and NZO nanoparticles were 3.2 eV, 2.5 eV, and 2.7 eV, respectively. Mott-Schottky analysis indicated the type of semiconductors and the energy levels of the conduction and valence bands. Valence band (VB) values of CAFO and NZO are 2.86 eV and 2.03 eV, respectively. The photocatalytic activity of the nanoparticles was evaluated by degrading MB under visible light illumination. The adsorption studies were conducted by varying the dosage, pollutant concentration, and pH. The results showed that CAFONZO nanoparticles exhibited the highest photocatalytic efficiency, achieving 96 % degradation of MB within 120 min. The combined photocatalyst demonstrated improved efficiency compared to the individual components.

Influence of Ni substitution on Structural, Optical, magnetic and transport properties of Mn0.5-xNixZn0.4Cu0.1Fe1.95Al0.05O4

A series of spinel ferrites Mn0.5-xNixZn0.4Cu0.1Fe1.95Al0.05O4 have been prepared by auto-combustion technique. X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) have been used for structural and morphological investigations. The XRD patterns confirm the formation of cubic spinel structure of ferrites. The lattice constants decrease with the increase of Ni contents due to the smaller ionic radii of Ni2+ compared to Mn2+ as well as particle size decreases. Density is increased and porosity is decreased with the increase of Ni contents in the samples due to the higher atomic weight of Ni2+ compared to Mn2+. The FESEM analysis reveal that the average size of the irregularly shaped grains increased with Ni contents. The mixed spinel structure is further confirmed by the FTIR spectra, which show a doublet band at about 600 cm−1. The observed optical band gap and the particle size variations are comparable, and the quantum size effect supports this conclusion. The real part of initial permeability and relative quality factor increase with the increase of Ni contents due to increase of density and grain size as well as decrease of porosity. Also, it is found that magnetic loss decreased with the increase of Ni contents. All the samples exhibit ferrimagnetic behavior and the number of Bohr magneton has been calculated for all compositions. The dielectric constant shows large value in the lower frequencies and decreases with frequency shows dispersion due to Maxwell-Wagner space charge polarization. The investigation of electric modulus has demonstrated the existence of the hopping conduction mechanism. The AC conductivity is very low at lower frequency region and very large at higher frequency region which can be explain according to the polaron hopping model of Austin and Mott. The AC conductivity enhances nearly linearly with frequency, suggesting that the mechanism of conduction is due to small polaron hopping, which can be described according to Jonscher’s power law. Also, the effect of grain and grain boundary resistance on transport properties has been investigated using complex impedance analysis and it has been observed that both exhibit an increase trend as the Ni content increases.

One-step synthesis of Pt@(CrMnFeCoNi)3O4 high entropy oxide catalysts through flame spray pyrolysis

High entropy oxides (HEOs) show great prospects in catalysis owing to their widely tunable component structures and ease of combination with active metals. However, the development of HEO catalysts is limited by the lack of efficient synthesis methods due to the difficulty of homogeneously mixing at least five elements. In this work, flame spray pyrolysis (FSP) is successfully employed to synthesize (CrMnFeCoNi)3O4 HEO with a single phase spinel structure in one step, which is verified by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and energy-dispersive X-ray spectroscopy (EDS). Taking CO catalytic oxidation as a probe reaction, the Pt@(CrMnFeCoNi)3O4 HEO catalyst synthesized by FSP in one step is compared with the catalyst whose Pt is impregnated on (CrMnFeCoNi)3O4 HEO support. The FSP-made catalysts have a higher catalytic reaction rate and better redox ability, which lowers the temperature of complete CO conversion by nearly 100 °C. Furthermore, it can be observed that the flame parameters can be optimized to modify the particle size and oxygen vacancies of the HEO nanoparticles, thus enhancing the catalytic performances. This work demonstrates that FSP is an effective method for the one-step synthesis of HEO catalysts with excellent catalytic performance, providing a new perspective for the synthesis of HEO-based materials.

Microwave dielectric properties of Li2Mg2Ga2Ti3O12 ceramics with spinel-type

Novel spinel-type Li2Mg2Ga2Ti3O12 ceramics were prepared by the solid-state method. Rietveld refinement revealed that the Li2Mg2Ga2Ti3O12 ceramics possess a cubic spinel structure with the Fd3‾m(227) space group. Raman spectrum analysis indicated that the Q × f and FWHM of ceramics exhibit an inverse relationship. According to the P-V-L theory, the Ti-O bond has the highest percentage of contribution to both of bond ionicity and lattice energy, indicating a significant impact on εr and Q × f, respectively. The Li2Mg2Ga2Ti3O12 ceramics showed the best microwave dielectric properties (εr = 15.72, Q × f = 69,633 GHz, and τf = −20 ppm/°C), sintering at an optimum temperature of 1200 °C. Additionally, a dielectric resonance antenna, on the basis of Li2Mg2Ga2Ti3O12 ceramics was designed and simulated.

Preparation of magnetite nanoparticles and their application in the removal of methylene blue dye from wastewater

Wastewater is discharged in large amounts from different industries; thus, wastewater treatment is currently one of the main concerns, advanced oxidation is a promising technique for wastewater treatment. This research aims to synthesize magnetite nanoparticles and study their application in wastewater treatment via adsorption and advanced oxidation processes. Magnetite nanoparticles were synthesized via coprecipitation technique between ferric and ferrous sulfate at a molar ratio of 2:1. The prepared sample was characterized using FTIR, XRD, TEM, BET surface area, zeta potential, VSM, and UV‒visible spectroscopy. XRD confirmed the formation of a single face-centered cubic (FCC) spinel structure of Fe3O4. TEM revealed an average particle size of 29.2 nm and a BET surface area of 70.1 m2 g−1. UV‒visible spectroscopy revealed that the UV–visible peak of the sample was obtained at 410 nm. VSM confirmed the attraction of the sample to a magnet with a magnetization of 60 (emu/g). The removal efficiency of methylene blue was studied using adsorption and advanced oxidation methods. For adsorption, the studied parameters were dye concentration 2–10 ppm, 3–10 pH, and 50:300 mg Fe3O4/L. For advanced oxidation, peroxide was used with nanomagnetite as a catalyst, and the studied parameters were pH 2–11, magnetite dose 20–200 PPM, and peroxide dose 500–2000 PPM. The removal efficiency by adsorption reached 95.11% by adding 50 mg of Fe3O4/L and 10 ppm dye conc at 6.5 pH; on the other hand, in advanced oxidation, it reached 98.5% by adding 110 PPM magnetite and 2000 ppm H2O2 at pH 11. The magnetite nanoparticles were reused for ten cycles of advanced oxidation, for a 10% reduction in removal efficiency at the tenth cycle.

Revealing the Effect of Anion Regulation in NiCo2X4 (X = O, S, Se, Te) on Photoassisted Methanol Electrocatalytic Oxidation.

Designing nonprecious metal anode catalysts for photoassisted direct methanol fuel cells (PDMFCs) remains a challenge. As a semiconductor catalyst with a spinel structure, NiCo2O4 has good methanol catalytic oxidation activity and photocatalytic activity, making it a highly promising anode non-noble metal catalyst for PDMFCs. However, compared with the noble metal catalyst, the photoelectrocatalytic activity remained to be improved. In this report, an anion regulation strategy was adopted to improve the photoassisted methanol electrocatalytic activity. Using a CoNi-Aspartic (CoNi-Asp) nanorod as the precursor, the anion-regulated NiCo2X4 (X = O, S, Se, Te) was prepared by oxidation, sulfuration, selenization, and telluridation reactions. The regulation of anions and their effects on the electronic structure, intermediate product, and photoelectric catalytic performance of NiCo2X4 (X= O, S, Se, Te) was systematically discussed. Photoelectrochemical characterization and adsorption energy of •OH revealing the volcano-like correlation between the anion in NiCo2X4 (X = O, S, Se, Te) and their photoelectrocatalytic performance. The narrowest band gap (2.239 eV), the highest •OH adsorption energy (-3.32 eV), and the highest ratio of Co3+/Co2+ (2.19) ensure the best photoelectric catalytic performance of NiCo2S4, under the visible light irradiation, the photoresponse current density was 1.9 A g-1, the current density at 0.6 V was up to 21.9 A g-1. After 9 h of stability testing, the current retention rate was 80%. This report sheds an idea for the rational design of non-noble anode catalysts for PDMFCs.

Unveiling complex magnetic behaviour and effective photo-Fenton catalytic activity in the mixed phases of spinel and wurtzite structures of Fe-incorporated ZnO nanocrystals

A comprehensive exploration was conducted on the structural features, optical bandgap, magnetic characteristics and photo-Fenton catalytic activity of chemically synthesized Fe-substituted ZnO nanocrystals. Previous studies have demonstrated that undoped ZnO adopts a hexagonal wurtzite structure. X-ray powder diffraction analysis disclosed the persistence of the wurtzite hexagonal structure in 1 % Fe-incorporated ZnO, while the presence of a secondary cubic phase of spinel type structures (ZnFe2O4) emerged in the ZnO lattice with Fe content ≥ 3 %. Remarkably, the proportion of the secondary phase is systematically increased from 2.75 % to 17.90 % as the Fe content was raised from 3 % to 10 %. Microscopy analysis unveiled hexagonal, spherical, and rod-like structures across all nanocrystals. Selected area electron diffraction patterns further confirmed the coexistence of cubic and hexagonal phases. Raman spectroscopy indicated a decline in crystalline quality and the introduction of defects and disorder in the host lattice due to Fe integration. The absorption spectra were taken to assess the impact of Fe substitution on the optical properties and revealed a decreasing trend in the optical bandgap from 3.23 to 3.21 eV and 2.21–2.05 eV with rising Fe content. The first band gap is related to the ZnO and the latter is the optical band gap of ZnFe2O4. The photoluminescence plots displayed near band edge emissions as well as visible emissions, which intensified with increased Fe-doped nanocrystal concentrations. X-ray photoelectron spectroscopy analysis affirmed the integration of Fe2+ and Fe3+ cations into the ZnO matrix. Thorough magnetic investigation uncovered complex magnetic behaviour attributed to the emergence of a secondary spin glass-like phase within the weak ferromagnetic ZnO host. The co-existence of two phases containing Fe2+ and Fe3+ ions enhanced the photo-Fenton catalytic activity, leading to the complete decomposition of various organic pollutants such as methylene blue and crystal violet. The photocatalytic test also showed the ZnO co-hosting ZnFe2O4 had a decolouration efficiency of 80.62 % and 77.88 % for methyl orange and thymol blue dyes. The coexistence of two phases in Fe-incorporated ZnO nanocrystals reveals complex magnetic behaviour and enhanced photo-Fenton catalytic activity. This finding holds potential for designing innovative materials applicable in futuristic spintronics devices and waste water treatment methodologies.

Raman spectroscopic study of liebenbergite and Ni2SiO4 spinel at high pressure and high temperature: nickel effects on the vibration properties of olivine and spinel structures

Raman spectroscopic study of liebenbergite and Ni2SiO4 spinel at high pressure and high temperature: nickel effects on the vibration properties of olivine and spinel structures

Construction of Surface Ruoct─O─Cooct Units With Optimized Cooct Spin States for Enhanced Oxygen Reduction and Evolution.

The introduction of noble metal into spinel structure is an effective strategy to develop efficient oxygen evolution/reduction reaction (OER/ORR) catalysts. Herein, surface Cooct is substituted by Ruoct in Rux-Mn0.5Co2.5-xO4/NCNTs by ion-exchange, where presence of Ruoct─O─Cooct unit facilitates electron transfer. This strong electron coupling effect leads downward shift in d-band center and a narrowing of d-p bandgap. The increased charge density of Cooct bridged with Ruoct dioxygen optimizes adsorption of oxygen intermediates (*OH) and occupation of electrons in eg-orbital octahedral. The measured ORR/OER voltage difference is only 0.71V. The peak power density of assembled zinc-air battery reaches 148.8mW h cm-2, and energy density at 100mA cm-2 reaches 813.6mA h gZn -1, approaching a theoretical value of 820mA h gZn -1. The catalyst demonstrates stable operation for over 500h at 10mA cm-2 and over 200h at 50mA cm-2. This work provides new insights to guide fabrication of advanced oxygen electrocatalysts.