Spinel Crystal Structure Research Articles

CeO2-conjugated CoFe layered double oxides as efficient non-noble metal catalysts for NH3-decomposition enabling carbon-free hydrogen production

CeO2-conjugated Co1.5Fe1.5 LDOs were synthesized through a one-pot co-precipitation method of Ce-introduced Co1.5Fe1.5 LDHs and their thermal treatment. By manipulating the stoichiometric molar ratio of Ce/(Co + Fe), a series of Cex-Co1.5Fe1.5 LDOs (x = 0.05, 0.1. 0.2, 0.5, and 1, corresponding to the molar ratio for the sum of Co and Fe) was comprehensively characterized to investigate the intricate interplay among factors such as spinel mixed metal oxides, LDH-derived LDOs, and the introduced Ce to achieve high catalytic performance in NH3 decomposition. Notably, Ce0.2-Co1.5Fe1.5 LDOs exhibited remarkable activity, achieving an NH3 conversion of 81.9 % at 450 °C and a WHSV of 6,000 mLNH3 gcat-1h−1, and maintained excellent NH3-conversion with a negligible decrease over 80 h of continuous operation at 550 °C and high WHSV of 30,000 mLNH3 gcat-1h−1. The synergistic interaction between the incorporated CeO2 and Co1.5Fe1.5 LDOs induced modifications of structural properties including the distribution of Co and Fe within the spinel crystal structure, as well as affecting the lattice parameters and electronic properties. These modifications play a pivotal role in ultimately altering metal-N binding energy, which facilitates the efficient activation of absorbed NH3 at the lowest temperature and minimizes the delay in recombinative N2-desorption. Hence, this study aims to highlight a new concept and demonstrate its feasibility for fabricating cost-effective and high-performing catalysts at mild temperatures to meet the growing demand for NH3 as a hydrogen carrier.

Influence of Y Substitutions on the Structural and Magnetic Properties of Mn-Zn Ferrites

The ordinary solid-state reaction method has been used to produce polycrystalline Mn0.5Zn0.5Fe2–xYxO4. X-ray diffraction (XRD) and scanning electron microscopy (SEM) have been used to study the structural and surface morphology of the samples, respectively. The formation of cubic spinel crystal structure is observed in XRD patterns. The Nelson-Riley function is used to determine the lattice parameters. Vegard's rule is followed by the lattice parameter change with Y content in different Mn0.5Zn0.5Fe2–xYxO4. The x-ray density, and the bulk density both increase with Y content due to the higher atomic weight of Y compared to atomic weight of Fe, as well as porosity decreases. SEM micrographs demonstrate that the average grain size decreases with the increase of Y contents. When x = 0.05, the initial permeability shows maximum then starts to decrease for further increase of Y content. For the composition Mn0.5Zn0.5Fe1.95Y0.05O4, the relative quality factor (RQF) is found maximum (3477). With the increase of Y content, the peak value of the relative quality factor shifts to higher frequencies region which is the consequence of Snoek relation. Jagannath University Journal of Science, Volume 11, Number 1, June 2024, pp. 53−63

Marine-derived magnetic nanocatalyst in sustainable ultrasound-assisted synthesis of 2,3-diphenyl-2,3-Dihydroquinazolin-4(1H)-One derivatives

This research presents a sustainable approach to fabricate iron oxide nanoparticles by employing phytochemicals derived from marine grass extract as both reducing and stabilizing agents. Formation of magnetic nanoparticles (MNPs) initially confirmed by ultraviolet–visible spectroscopy (UV–vis) showing absorption peak at 370 nm. X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques unveiled magnetic iron oxide NPs with a rod shape, an average size of 21 nm, and an inverse spinel crystal structure. The participation of organic compounds in the production and stabilization of MNPs was evidenced through Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). A vibrating sample magnetometer (VSM) demonstrated the magnetic properties of iron oxide NPs showing a saturation magnetization value of 21.46 emu/g. The catalytic efficiency of these marine-assisted MNPs was evaluated in a one-pot three-component reaction involving isatoic anhydride, aromatic aldehydes, and amines under ultrasonic conditions. Under optimal conditions, a low dose of 1.5 mg of biobased magnetite nanoparticles yielded dihydroquinazolin-4(1H)-One products with up to 95 % efficiency in a brief duration of 15 min at an ultrasonic power intensity of 130 W. Different directing groups were investigated, and control experiments were carried out to enhance the understanding of the reaction mechanism. The obtained results highlight the synergistic effect of marine grass-mediated magnetic nanocatalysts combined with ultrasonic-assisted synthesis in developing sustainable green methodologies in organic synthesis.

Novel CdFe2O4 nanoparticles facile synthesis and their applications towards practical ammonia detection: an effect of annealing

Cadmium ferrite (CdFe2O4) nanoparticles were synthesized via a simple co-precipitation method, and the effect of annealing temperature over the prepared samples’ structural, morphological, and optical properties was analyzed by varying the temperatures 700, 800, and 900 °C. The x-ray diffraction (XRD) studies revealed that the prepared samples are highly crystalline in nature and belong to a cubic spinel crystal structure, and the crystallite size increases from 32 to 59 nm with respect to the increasing temperature. The surface morphology of the ferrite samples showed the uniformly distributed highly agglomerated particles with larger voids for the ferrite nanoparticles annealed at 900 °C. Optical properties of the prepared CdFe2O4 samples were carried out by diffused reflectance spectroscopy (DRS) and the optical band gap of the samples were found to be 2.57, 2.55 and 2.53 eV. The Vibrating sample magnetometer (VSM) studies at room temperature showcased that the nanoparticle samples possess ferromagnetic behavior, and the magnetization (Ms), Coercivity (Hc), and Retentivity (Mr) values were found to be 27.5 × 10−3 emu g−1, 237.60 Oe, and 1976 × 10−6 emu/g for the CdFe2O4 sample annealed at 900 °C. The gas sensing studies were carried out with the presence of target gas ammonia, and its significant sensing parameters such as gas responsivity (S%), rise time, and recovery times were determined, and these values of CdFe2O4 samples annealed at 900 °C were observed to be 1610%, 7.1 s, and 2.2 s. Our findings strongly suggest that the CdFe2O4 samples annealed at 900 °C hold significant promise as a multifunctional material, particularly in gas-sensing applications. This potential opens an exciting avenue for further research and development.

Expanding the Phase Space for Halide-Based Solid Electrolytes: Li-Mg-Zr-Cl Spinels.

Chloride-based solid electrolytes are intriguing materials owing to their high Li+ ionic conductivity and electrochemical compatibility with high-voltage oxide cathodes for all-solid-state lithium batteries. However, the leading examples of these materials are limited to trivalent metals (e.g., Sc, Y, and In), which are expensive and scarce. Here, we expand this materials family by replacing the trivalent metals with a mix of di- and tetra-valent metals (e.g., Mg2+ and Zr4+). We synthesize Li2Mg1/3Zr1/3Cl4 in the spinel crystal structure and compare its properties with the high-performing Li2Sc2/3Cl4 that has been reported previously. We find that Li2Mg1/3Zr1/3Cl4 has lower ionic conductivity (0.028 mS/cm at 30 °C) than the isostructural Li2Sc2/3Cl4 (1.6 mS/cm at 30 °C). We attribute this difference to a disordered arrangement of Mg2+ and Zr4+ in Li2Mg1/3Zr1/3Cl4, which may block Li+ migration pathways. However, we show that aliovalent substitution across the Li2-z Mg1-3z/2Zr z Cl4 series between Li2MgCl4 and Li2ZrCl6 can boost ionic conductivity with increasing Zr4+ content, presumably due to the introduction of Li+ vacancies. This work opens a new dimension for halide-based solid electrolytes, accelerating the development of low-cost solid-state batteries.

Enhancing Electrochemical Sensor Performance: Studies of Electrodes Tailored with ZnO/ZnFe2O4 Nanoparticles

Spinel metal oxides possess excellent magnetic, electrical, and optical properties. They take AB2O4 (face centered cubic) form with oxygen anions providing tetrahedral (Td) and octahedral (Oh) sites for A+2 and B+3 cations. Spinel can have a normal, inverse, or mixed form based on the occupancy of different cations in Td and Oh sites. The peculiarity of the spinel crystal structure is that its composition can be easily modified without affecting the crystal structure based on the type of cation. The type of cation in the composition defines if the spinel has a normal or inverse form [1]. Based on these premises, we have already synthesized ZnxNi1-xFe2O4 (x =0, 0.2, 0.4, 0.6, 0.8, 1) nanomaterials achieving a clear gradual transition from inverse (x=0) to normal (x=1) spinel. Synthesized nanomaterials were employed as mediators in electron transfer between the screen-printed carbon working electrode and paracetamol to understand the effect of chemical composition and crystal structure on the electron transfer at the electrochemical interface [1]. Normal spinel ZnFe2O4 was found to be the best nanomaterial in terms of sensitivity and kinetic rate constant. In further works, with the aim to understand the effect of ionic radii on sensitivity and electron transfer rate constant in electrochemical sensing of paracetamol, we have focused on the normal spinel structure and modified the composition by varying the concentration of Fe3+ with Cr3+ and Bi3+ [2,3]. This study also proved that the normal spinel ZnFe2O4 has the highest sensitivity and electron transfer rate constant towards paracetamol sensing.In this work, we will present the synergic effect that can be obtained by interfacing ZnFe2O4 with ZnO nanomaterials by tuning the band gap of the heterogeneous structure. The aim is to understand the effect of band gap on sensitivity and electron transfer rate constant in electrochemical sensing. ZnFe2O4, ZnO, and ZnO/ZnFe2O4 nanomaterials are synthesized by a simple, single step auto combustion technique using the respective metal nitrates as precursors. Nanomaterial morphology and particles size are investigated by scanning electron microscopy. X-ray diffraction technique is employed to analyze the crystal structure and identify different phases in the newly synthesized materials. Then, commercially available screen-printed carbon electrodes with carbon working electrode and carbon counter electrodes are used for the electrochemical measurements in combination with an external double junction Ag/AgCl as a reference electrode. The synthesized nanomaterials are mixed with 1-butanol and a 5 μL solution is used to modify the surface of the carbon working electrode to mediate the redox reactions between the carbon surface and the molecule of interest. Primarily the sensors are characterized using cyclic voltammetry with ferri/ferrocyanide redox couple as a probe molecule. Improvement in sensitivity is observed for ZnFe2O4 (8.85 ± 0.50 μA/mM), ZnO (8.50 ± 0.30 μA/mM), and ZnO/ZnFe2O4 (8.22 ± 0.16 μA/mM) sensors compared to the bare carbon one (6.30 ± 0.40 μA/mM). By performing cyclic voltammetry at different scan rates (ν) from 25 to 125 mV/s, a good linearity of redox currents with respect to v0.5 is observed and redox peak positions are varying linearly with ln(ν). Peak-to-peak separation (ΔEp) is reduced for ZnO/ZnFe2O4 sensors compared to the carbon one. All these results suggest a faster electron transfer at the interface when the modified electrodes are used. Laviron model is employed to calculate the electron transfer rate coefficient and constant. The rate constant for ZnFe2O4 (41.8 ± 2.6 ms-1), ZnO (46.0 ± 4.0 ms-1), and ZnO/ZnFe2O4 (33.1 ± 4.5 ms-1) sensors is 3 to 5 times higher as compared to the bare carbon one (9.97 ± 0.78 ms-1). We are currently studying the potential application of ZnO/ZnFe2O4 nanomaterials in electrochemical sensing of small molecules relevant in biomedical field (dissolved oxygen, pH) and pharmaceutical drugs (paracetamol) to assess the potential for their use in different clinical settings.

Deciphering the influence of support in the performance of NiFe2O4 catalyst for the production of hydrogen fuel and nanocarbon by methane decomposition

Wet chemical synthesis route was used to synthesis nickel ferrite (NiFe2O4) nanoparticle. Later on the synthesized NiFe2O4 were supported on the surface of three traditional supports such as Al2O3, MgO and TiO2 to get NiFe2O4/Al2O3, NiFe2O4/TiO2 and NiFe2O4/MgO catalysts. The activity profile of each catalyst was evaluated in a fixed-bed reactor for direct methane decomposition at 800 °C. For both fresh and spent catalysts, many characterization techniques have been employed mainly XRD, FESEM, HRTEM, Raman spectroscopy, TGA, and nitrogen adsorption-desorption isotherm. X-ray powder diffraction studies revealed that all synthesized catalysts have a cubic spinel crystal structure. The XRD confirm the presence of NiFe2O4 particles in the component of fresh NiFe2O4/MgO, NiFe2O4/TiO2 and NiFe2O4/Al2O3 catalysts. Temperature Program Reduction (TPR) unveiled the presence of Ni oxides and Fe oxides by displaying reduction peaks in their respective temperature regions. The N2 adsorption-desorption isotherms of the fresh all catalysts reveal that these catalysts have a mesoporous structure. Activity data concluded NiFe2O4/MgO to be the most active catalysts among the tested catalysts methane conversion magnitude of 41.13 % and H2 formation rate of 84.40 × 10−5 mol H2 g−1 min−1. On the other hand, the H2 formation rate drastically declined and very poor activity of both NiFe2O4/TiO2 and NiFe2O4/Al2O3 catalysts was observed in the current work. XRD patterns, FESEM images and TGA analysis of spent NiFe2O4/MgO catalyst shown the filamentous carbon formation which secondarily confirm its higher activity, while its absence in catalysts of NiFe2O4/TiO2 and NiFe2O4/Al2O3. TGA analysis of the carbon deposited on the NiFe2O4/MgO catalyst showed that the amount of carbon was approximately 64 wt%. It was suggested that the formation of nickel-iron carbide revealed by XRD studies of spent catalysts may be the factor related to their poor activity while discussing the structure-activity relationship. Likewise, the higher degree of dispersion related to NiFe2O4/MgO as displayed by XRD, FESEM and TPR investigations, played a vital role in accelerating the rate of hydrogen formation.

Structural, Mössbauer and magnetic study of (Mn0.2Co0.2Ni0.2Cu0.2X0.2)Fe2O4 (X=Fe, Mg) spinel high-entropy oxides fabricated via reactive flash sintering

Herein, it is reported the concomitant synthesis and sintering in a single step of (Mn0.2Co0.2Ni0.2Cu0.2X0.2)Fe2O4 (X=Fe, Mg), a spinel-structured high-entropy oxides, by the reactive flash sintering technique. A single phase, identified with a spinel crystal structure Fd3̅m, was obtained in just 30 min at a furnace temperature of 1173 K. The structural and magnetic properties of the prepared compounds were assessed by the combined use of various techniques, aiming to understand the correlations between functional properties and crystal structure. Characteristic features of the Mössbauer spectra prove the existence of different nonequivalent Fe environments . Both compositions display soft magnetic behavior, characterized by low coercive fields and saturation magnetization reached at low fields. Thus, the substitution of nonmagnetic Mg2+ for magnetic Fe2+ results in a decrease in magnetic parameters due to the weakening of the super-exchange interaction among the magnetic moments.

Enhanced photoelectrochemical water splitting and photocatalytic decomposition performance of visible light active MgMnO3 perovskite nanostructure

Clean energy production and environmental remediation are imperative for sustainable future. Specially, exploration of multifunctional catalyst, for production of low-cost and eco-friendly hydrogen (H2) fuel as well as efficient decomposition of emerging pollutants are certainly needed. This study investigates magnesium manganese oxide (MgMnO3), a perovskite oxide, synthesized by simple citrate sol–gel technique, and its structural, morphological, optical, and photoelectrochemical properties were analyzed for the photodegradation of ciprofloxacin (CIP) antibiotic, methylene blue (MB) dye, and photoelectrochemical (PEC) water splitting. The cubic spinel crystal structure of MgMnO3 was confirmed through powder X-ray diffraction (XRD) analysis. FE-SEM images of the MgMnO3 material revealed a cauliflower-like morphology, consisting of an assembly of microspherical grains of varying sizes. UV–Vis spectroscopy exhibited broad absorption in the UV–Visible region, and the Tauc plot estimated a band gap of 1.54 eV. The MgMnO3 catalyst showed 88% and 96% for photodecomposition of CIP (10 mg/L) and MB (10 mg/L), respectively, using 35 mg and 30 mg of catalyst quantity over 90 min. In addition, MgMnO3 photoelectrode showcases superior photoelectrochemical behavior, exhibiting maximal photocurrent density of 13.21 mA cm−2 measured at 1.2 V vs. RHE and achieving a solar-to-hydrogen conversion efficiency of 2.45% compared to MgO and MnO2 photoelectrode. EIS measurements of MgMnO3 show enhanced charge transfer and recombination kinetics. Notably, the MgMnO3 electrode reveals outstanding photoelectrochemical durability, maintaining its stability even after continuous illumination for 9 h. Improved PEC properties could be attributed to wider light absorption, enhanced photo-induced charge-separations, and electron mobility. Thus, present study established an efficient and enduring multifunctional catalyst, catering photocatalytic degradation and PEC H2 generation.

Solution Processing of Spinel Nickel Cobaltite: Exfoliation Mechanism, Dispersion Stability, and Applications.

The exfoliation of nonlayered materials to mono- or few-layers is of growing interest to realize their full potential for various applications. Nickel cobaltite (NiCo2O4), which has a spinel crystal structure, is one such nonlayered material with unique properties and has been utilized in a wide range of applications. Herein, NiCo2O4 is synthesized from NiCo2- Layered double hydroxides using a topochemical conversion technique. Subsequently, bulk NiCo2O4 is exfoliated into mono- or few-layer nickel cobaltene nanosheets using liquid-phase exfoliation in various low-boiling point solvents. An analytical centrifuge technique is also utilized to understand the solute-solvent interactions by determining their dispersion stability using parameters such as the instability index and sedimentation velocity. Among the studied solvents, water/isopropyl alcohol cosolvent is found to have better dispersion stability. In addition, density functional theory calculations are carried out to understand the exfoliation mechanism. It is found that the surface termination arising from the Co-O bond needs the least energy for exfoliation. Furthermore, the obtained nickel cobaltene nanosheets are utilized as an active material for supercapacitors without any conductive additives or binders. A solid-state symmetric supercapacitor delivers a specific capacitance of 10.2 mF cm-2 with robust stability, retaining ∼98% capacitance after 4000 cycles.

Structural and cation distribution analysis of Nickel-Copper/Nickel-Magnesium Substituted Lithium Ferrites

Lithium ferrite (Li0.5Fe2.5O4) shows significant promise in electrical and electronic engineering. It possesses a crystal spinel crystal structure denoted as AB2O4, with "A" and "B" representing specific tetrahedral and octahedral lattice sites respectively. Analysis of X-ray diffraction (XRD) patterns aligns well with the JCPDS card (no. 38-0259), confirming the spinel structure with the Fd3m space group. However, an additional peak at 211 in the basic lithium ferrite suggests a subtle Fd3m to the P4132 phase change with a minor secondary hematite phase. Investigating the cation distribution in these ferrites is crucial for further exploration of their magnetic and dielectric properties. These ferrites find widespread applications in microwave technology and magnetic and electric energy storage devices.

Employing the Microemulsion Synthesis Technique to Investigate the Structural and Magnetic Properties of Multicomponent Ferrite Nanoparticles

AbstractCoFe2O4, ZnFe2O4, NiFe2O4, Co0.5Ni0.5Fe2O4, Ni0.5Zn0.5Fe2O4, and Co0.5Zn0.5Fe2O4 are among the multicomponent ferrite nanoparticles that are created using the reverse microemulsion technique and a mixed surfactant. These nanoparticles are thoroughly characterized using techniques such as vibrating sample magnetometer (VSM), energy dispersive X‐ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FT‐IR), and X‐ray diffraction (XRD). All the nanoparticles display a cubic spinel crystal structure, according to the X‐ray investigation. As the concentration of zinc increases, there is a noticeable rise in the lattice constant because the size of Zn+2 is more than Co+2. This study also investigates the relationship between the magnetic characteristics of nanocrystals and their matching size, composition, and features.

Crystal Structure, Morphology, and Magnetic Properties of Magnetic Nanocomposites with Iron Oxide Core and Zinc Oxide/Titanium Oxide Shell

In this work, we successfully synthesized a magnetic nanocomposite material (Fe3O4@ZnO/TiO2) with an iron oxide core and a zinc oxide/TiO2 shell (Fe3O4@ZnO/TiO2). The purpose of this study was to characterize the Crystal Structure, Morphology, and Magnetic Properties of Magnetic Nanocomposites with Iron Oxide Core and Zinc Oxide/Titanium Oxide Shell. The crystal structure of the sample was analyzed using X-ray diffraction, which identified three distinct phases: Fe3O4, ZnO, and TiO2. These phases respectively exhibited cubic spinel, hexagonal wurtzite, and tetragonal crystal structures. Transmission Electron Microscopy (TEM) characterization confirmed that the sample had a magnetic core–shell structure, with superparamagnetic properties and excellent stability owing to its spinel cubic structure, which is the primary magnetic material structure of the sample. The successful formation of the Fe3O4@ZnO/TiO2 nanocomposite represents a significant advancement in the synthesis of materials. This could serve as a basis for further investigations into magnetic materials, opening up possibilities for their application across diverse fields.

Optimization radiation shielding properties of aluminum-based spinel minerals through the crystal tetrahedral and octahedral voids and their ions composition

In this research paper, we delve into the influence of crystal structure, void volumes and their ionic composition along with the atomic packing factor on the radiation attenuation properties of Al-based spinel compounds. The study investigates various Al-spinel chemical compositions explores their applications in radiation shielding. Analyzing mass attenuation coefficient (MAC) of six spinel minerals across different energy regions, we observe specific trends in scattering processes with the following sequential order: MACPleonaste > MACGahnite > MACHercynite > MACGalaxite > MACCeylonite > MACSpinel. The results demonstrated that the MAC values were influenced by the spinel chemical composition, crystal structure, and atomic arrangement in the lattice. Furthermore, the correlation between MAC values and the tetrahedral volume (Vtet), octahedral volume (Vocta), and the ratio of void volumes to the unit cell volume (R) was examined. Optimal void volumes and divalent and trivalent ion compositions were determined for different spinel minerals, leading to enhanced radiation shielding efficiency. The findings offer valuable perspectives for refining and optimization of spinel materials for use in radiation applications.

Investigation of NiCoOx catalysts for anion exchange membrane water electrolysis: Performance, durability, and efficiency analysis

Anion exchange membrane (AEM) water electrolysis is a promising method for hydrogen production using inexpensive metal oxide catalysts. This study investigates the catalytic activity and performance of nickel cobalt oxide (NiCoOx) catalysts in AEM water electrolysis for hydrogen production. The catalysts were synthesized with varying ratios of Ni to Co. The NiCoOx catalysts were coated on nickel foam gas diffusion layer (GDL) at the anode. Scanning electron microscopy (SEM) analysis revealed a distinct flaky structure of the NiCoOx catalyst. X-ray diffraction (XRD) studies confirmed the presence of NiCo2O4 spinel crystal structure in the catalysts. Linear sweep voltammetry (LSV) measurements for Oxygen evolution reaction (OER) in three electrode systems showed that NiCoOx (1:3) exhibited the highest catalytic activity, with a current density of 238 mA cm−2 at 1.8 V. Tafel analysis indicated that NiCoOx (1:3) had the lowest Tafel slope, suggesting faster reaction kinetics and lower overpotential for higher current density. Chronoamperometry tests demonstrated the stability of the catalysts at various current densities, and long-term stability testing of NiCoOx (1:3) for 500 h revealed minimal voltage increase during OER, demonstrating its stability in prolonged operation. NiCoOx (1:3) displayed the highest activity among the catalysts at different temperatures, with current densities reaching 1700 mA cm−2 at 2.2 V and 70 °C for single-cell electrolysis. The Nyquist plots and equivalent circuit analysis reveal that the NiCoOx (1:3) catalyst exhibits lower activation resistance and higher efficiency in oxygen evolution reaction compared to other catalyst compositions. Temperature-dependent measurements demonstrate decreased resistances (ohmic, activation, and membrane) with increasing temperature, indicating improved reaction kinetics and ion conductivity. Long-term durability tests reveal the stable operation of the catalyst, while short-term tests confirm its effectiveness at higher current densities for single-cell electrolyzer operation. These findings highlight the importance of electrochemical Impedance Spectroscopy (EIS) and equivalent circuit fitting in optimizing AEM water electrolysis performance, aiding the development of efficient and durable electrolyzers for hydrogen production.

Investigations of the structure and tunable magnetic properties of Cu doped cobalt chromite nanoparticles

This article reports the synthesis, microstructural, magnetic and optical properties of copper ions substituted cobalt chromite nanoparticles. We have prepared four nanosized chromite samples with a general composition of CuxCo1-xCr2O4 (x = 0.0, 0.1, 0.2 and 0.3) using conventional wet chemical co-precipitation method. The x-ray diffraction profiles verified the presence of pure spinel crystal structure of the samples. Using the Williamson-Hall (W-H) method, the average crystallite size of all the samples were calculated to be between 11 nm and 16 nm. A tensile microstrain in all the samples was noticed. Surface morphology and average particle size of doped cobalt chromite nanocrystals was examined using HRTEM images. A moderate increment in the optical band gap was detected with increasing Cu ions in cobalt chromite nanoparticles which is attributed to the nanosize effect of the samples. The presence of all five distinctive Raman active modes in the chromite samples ensured phase purity and a decrease in crystal symmetry was also observed as the amount of Cu dopants was increased. Due to low magnetic moment of Cu2+ ions when compared with Co2+ ions, incorporation of copper ions reduces the coercive field of the host chromite system. With increasing Cu percentage in chromite especially for 30 % Cu doped sample, the spin-spiral transition TS vanishes which indicates TS is affected by the dopant concentrations.

Impact of Cd+2 substitutions on structural and mechanical properties of Co0.6Ni0.4-xCdxFe2O4 (0.00≤ x≤0.40) system

This article presents the structural and mechanical properties of Co0,6Ni0,4-xCdxFe2O4spinel ferrite nanoparticles. The as prepared samples were characterized by thermo-gravimetric differential thermal analysis to examine their phase transition. TGA/DTA analysis confirmed the reaction is endothermic in nature and the process completion temperature around 714.24oC is good for annealing the prepared ferrite powder. X-ray diffraction pattern revealed, Co0,6Ni0,4-xCdxFe2O4 have been well crystallized to spinel crystal structure. The average crystallite size ranging from 14.52nm to 16.92nm. FTIR spectra showed, two significant absorption bands (ν1 and ν2) in between 400 cm−1and 600 cm−1confirmed the spinel structured ferrites. Morphological observations revealed, the grain size of prepared ferrites lies in the range 0.85 to 0.21 μm. Raman spectra peak positions of both tetrahedral and octahedral sublattice shifted towards higher energy position.

Structural, optical, and dielectric properties of M/SnO2 (M= Al2O3, NiO, Mn3O4) nanocomposites

The structural parameters, optical properties, and dielectric constants at a frequency (f) range of 0.1–20 MHz, and temperature (T) range of 300–400 K of hydrothermally synthesized M/SnO2 nanocomposites (for simplicity M denotes oxides of Al, Ni, or Mn) were compared. Rietveld refined X-ray powder diffraction (XRD) analysis demonstrated the formation of hexagonal, cubic, or spinel crystal structures of Al2O3, NiO, or Mn3O4 phases, respectively, besides the tetragonal rutile crystal structure of SnO2. The impact of Al addition on the optical band gap of SnO2 is negligible while it decreased or increased by incorporation of Ni or Mn, respectively. The residual lattice dielectric constant of SnO2 was increased, while the real part of the dielectric constant and the ac conductivity of SnO2 were decreased by M incorporation. The dielectric parameters are remarkably affected by selected M, T, and f values and their changes agree with the Maxwell-Wagner model. The Q-factor of SnO2 was increased by M addition while decreased with increasing T. The Ni/SnO2 obeys the hole conduction at T ≤ 330 K, while Mn/SnO2 and Ni/SnO2 obey the electronic conduction at T > 330 K. The binding energy is independent of the chosen T for SnO2, whereas it sharply increases for Ni/SnO2 and slightly decreases for Al/SnO2 and Mn/SnO2. The F-factor of SnO2 was slightly decreased by M addition, but it was increased with T for SnO2, Al/SnO2, and Mn/SnO2 while was decreased for Ni/SnO2. The Cole-Cole plots for M/SnO2 composites were analyzed, and the components of the equivalent circuit were determined. The electrical impedance, resistance of grains, resistance of grain boundaries, and equivalent resistance of SnO2 were increased by M incorporation, whereas equivalent capacitance was decreased. The findings recommend the SnO2-based nanocomposites for applications in optoelectronics, lithium batteries, supercapacitors, and solar cell devices.

Machine learning‐based crystal structure prediction for high‐entropy oxide ceramics

AbstractPredicting the crystal structure is essential to address the reliance on serendipity for facilitating the discovery and design of high‐performance high‐entropy oxides (HEOs). Here, three classic algorithms‐based machine learning models to predict the crystal structure of HEOs are successfully established and analyzed by combining five metrics, and the XGBoost classifier shows excellent accuracy and robustness with ACC and F1 scores up to 0.977 and 0.975, respectively. SHAP summary plot indicates that the anion‐to‐cation radius ratio (rA/rC) has the greatest impact on crystal structure, followed by difference in Pauling and Mulliken electronegativities (ΔχPauling and ΔχMulliken). It is noteworthy that the rA/rC, ΔχPauling, and ΔχMulliken lower than 0.35, 0.1, and 0.2, respectively, tend to lead to a fluorite crystal structure, whereas rock‐salt and spinel crystal structures are always formed. This work is expected to facilitate the discovery and design of HEOs with tailorable crystal structures and properties.

Investigation on bio-synthesized Ni- and Al-doped cobalt ferrite using lemon juice as eco-fuel

Pure and doped cobalt ferrite (CoFe2O4) nanoparticles were prepared using sol-gel auto-combustion route with the aid of lemon juice as eco-fuel. In this study, Ni2+ and Al3+ ions were chosen as the dopants. The cubic spinel crystal structure of the synthesized ferrite samples was elucidated from the powder X-ray diffraction analysis. The crystallographic parameters associated with the samples were obtained from the Rietveld profile refinement of the diffraction patterns. The precise lattice parameter obtained from the Nelson-Riley extrapolation method is found nearly matches with the lattice parameter obtained from the Rietveld refinement of respective samples. The average crystallite size and microstrain accompanying with the samples were estimated from various methods such as via the Debye-Scherrer method, Williamson-Hall analysis and size-strain plot. By employing Tauc’s plot method, the optical parameters such as the direct bandgap, sub-bandgap and the Urbach energy of all the samples were calculated by analyzing the UV-Visible reflectance spectra. The room temperature magnetic properties of all the samples were estimated from the vibrating sample magnetometry. The nature of magnetic hysteresis revealed the semi-hard ferrimagnetism of the prepared cobalt ferrite samples. Also, the variation of magnetic properties with doping was analyzed. The weakening of interaction among the ions in tetrahedral and octahedral sites causes a decrease in the values of remanent magnetization, saturation magnetization and coercivity of doped samples.