Single Phase Spinel Structure Research Articles

Temperature dependent magnetic and electrical transport properties of lanthanum and samarium substituted nanocrystalline nickel ferrite and their hyperthermia applications

Structural, optical, temperature dependent magnetic and electrical properties have been investigated for the nanocrystalline NiFe1.97RE0.03O4 (RE = La3+ and Sm3+) compound. Without any signs of a secondary REFeO3 phase, the Rietveld refinement reveals a single-phase spinel structure possessing cubic symmetry for current samples. The decrease in lattice constant has been observed as a result of RE ions substitution. The TEM micrographs reveal nanosized particles with an average size of 35 ± 3 nm and 32 ± 3 nm for La3+ and Sm3+ substituted samples. EDX spectra of both samples show good compositional homogeneity. HRTEM micrographs of both samples show well resolved lattice fringes and their inter-planar spacing matches with that obtained from the Rietveld analysis of the XRD patterns. The concentration of Fe2+ and Fe3+ ions has been estimated from the XPS spectra analysis and it is found to be ∼ 22% and 78% for NiFe1.97La0.03O4 and, 20% and 80% for NiFe1.97Sm0.03O4 compound. The optical energy band gap for rare earth substituted samples is found to be more than that of pure nickel ferrite. The value of saturation magnetization (Ms) and magneto-crystalline anisotropy constant (K1) estimated from the “Law of Approach to Saturation” equation for rare earth substituted samples are found to be less than that of pure nickel ferrite. However, an enhanced value of coercivity has been observed with RE substitution. ZFC (zero field cooling) and FC (field cooling) DC magnetization curves measured at 100 Oe in the temperature range of 60–400 K reveal a combination of weak and intermediate forms of magnetic interaction between the particles for both samples. Temperature dependent analysis of saturation magnetization and coercivity employing modified Bloch’s law and Kneller’s relation supports the nanomagnetic behavior of both samples. Under an AC magnetic field of 14.92 kA/m and frequency 337 kHz, the SAR and ILP values have been found to be ∼ 331 W/g and 4.22 nHm2/kg for NiFe1.97La0.03O4 and, ∼ 241 W/g and 3.21 nHm2/kg for NiFe1.97Sm0.03O4. The dielectric relaxation data have been analyzed at various temperatures ranging from 40 to 300 0C over the frequency range 100 Hz-1 MHz using electrical impedance spectroscopy. The dielectric constant for rare earth substituted samples is found to be more and their AC conductivity is observed to be less than that of pure nickel ferrite. The analysis of temperature dependent AC conductivity employing Jonscher’s power law suggests that the charge carrier’s conduction mechanism of both samples follows the small polaron hopping mechanism below 200 0C, thereafter; it follows the correlated barrier hopping mechanism. The activation energy estimated by imaginary impedance spectra is found to be 0.411 eV and 0.398 eV for NiFe1.97La0.03O4 and NiFe1.97Sm0.03O4 which is more than that of pure nickel ferrite. The Cole-Cole plots at different temperatures suggest the presence of non-Debye-type relaxation. The modeling of Cole-Cole plots with equivalent circuits for both samples confirms the contribution of both grain and grain boundary in electrical conduction. The estimated stretching exponential factor by fitting the modified KWW (Kohlrausch-Williams-Watts) equation to the imaginary modulus curve reveals relatively more dipole-dipole interaction in NiFe1.97Sm0.03O4 than that of the La3+ substituted sample.

Formation of quaternary [formula omitted] epilayers driven by thermally induced interdiffusion between spinel [formula omitted] epilayer and [formula omitted] substrate

Zinc aluminogallate, Zn(AlxGa1−x)2O4 (ZAGO), a single-phase spinel structure, offers considerable potential for high-performance electronic devices due to its expansive compositional miscibility range between aluminum (Al) and gallium (Ga). Direct growth of high-quality ZAGO epilayers however remains problematic due to the high volatility of zinc (Zn). This work highlights a novel synthesis process for high-quality epitaxial quaternary ZAGO thin films on sapphire substrates, achieved through thermal annealing of a ZnGa2O4 (ZGO) epilayer on sapphire in an ambient air setting. In-situ annealing x-ray diffraction measurements show that the incorporation of Al in the ZGO epilayer commenced at 850 °C. The Al content (x) in ZAGO epilayer gradually increased up to around 0.45 as the annealing temperature was raised to 1100 °C, which was confirmed by transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy. X-ray rocking curve measurement revealed a small full width at half maximum value of 0.72 °, indicating the crystal quality preservation of the ZAGO epilayer with a high Al content. However, an epitaxial intermediate β–(AlxGa1−x)2O3 layer (β - AGO) was formed between the ZAGO and sapphire substrate. This is believed to be a consequence of the interdiffusion of Al and Ga between the ZGO thin film and sapphire substrate. Using density functional theory, the substitution cost of Ga in sapphire was determined to be about 0.5 eV lower than substitution cost of Al in ZGO. Motivated by this energetically favorable substitution, a formation mechanism of the ZAGO and AGO layers was proposed. Spectroscopic ellipsometry studies revealed an increase in total thickness of the film from 105.07 nm (ZGO) to 147.97 nm (ZAGO/AGO) after annealing to 1100 °C, which were corroborated using TEM. Furthermore, an observed increase in the direct (indirect) optical bandgap from 5.06 eV (4.7 eV) to 5.72 eV (5.45 eV) with an increasing Al content in the ZAGO layer further underpins the formation of a quaternary ZAGO alloy with a tunable composition.

Structural, magnetic, dielectric and spectroscopic impedance analysis of magnesium iron oxide thin films synthesized by electrodeposition: Effect of preferred orientation

Magnesium iron oxide is the most valuable and versatile spinel system with reduced eddy current and dielectric losses. Spinel ferrites are electrically non-conductive. The electrodeposition is used to synthesize thin films on Cu substrate. A set of five thin films is prepared by varying the in-situ oxidation time (10 min, 15 min, 20 min, 25 min and 30 min) and a fixed deposition time of 25 min. The x-ray diffractometer XRD (phase confirmation), Scanning Electron Microscope SEM (morphological analysis), Fourier transforms infra-red spectroscope FT-IR (bond-formation), impedance analyzer (dielectric-measurements) and vibratory sample magnetometer VSM (magnetic properties) has been utilized to examine the prepared samples. All the studied samples have been found, single-phase spinel structures. XRD shows the pure phase formation of spinel MgFe2O4 at 20 min, 25 min, and 30 min. The exchange of the preferred orientation (PO) from (731) mixed phase to (533) spinel is observed. This change in preferred orientation has been caused the changes in the properties of prepared thin films. The average lattice constant, cell volume, x-ray density and crystallite size of magnesium-iron oxide were found at 8.3814 Å, 588.58 (Å)3, 3.2098 g/cm3 and 24.0392 nm respectively. In FTIR analysis of magnesium-iron oxide, two characteristic spinel bands are observed below 700 cm−1. The SEM result showed a smooth granular structure at 30 min. The normal behavior of the dielectric constant and single semicircle is observed in cole-cole plot. All the prepared thin films are ferromagnetic in nature. At 30 min, a higher dielectric constant, 20.2 (log f = 5) and 162.3 emu/cm3 saturation magnetization. The remarkable dielectric and magnetic findings are promising for using electrodeposited thin films in electronic and spintronic devices.

Exploring Study of Magnetic and Electrical Properties of Tl3+ Doped Co0.5Ni0.5Fe2O4 Spinel Ferrites

Co0.5Ni0.5Fe2-xTlxO4 (x=0, 0.05, 0.1, 0.15, and 0.2) spinel ferrites were prepared via the sol-gel technique. The XRD analysis revealed a single-phase spinel structure. The lattice constant ‘a’ increased from 8.223-8.269Å with doping of Tl+3 due to larger ionic radii of Tl+3 than Fe+3 ions. The mass susceptibility at 300K decreased from 7.46 x 10-3-4.15 x 10-3 cm3/g due tothe weakening of AB interactions followed by a decrease in Curie temperature from 453K to 408K. The electrical permittivity follows the Maxwell-Wagner model and Koop’s theory. The dc resistivity of ferrites at 300K increased from 1.82x109-9.23x109 ?-cm with increasing Tl+3 contents due to increased hopping lengths. The activation energy obtained from Arrhenius plots increased from 0.126 to 0.131eV, increasing Tl+3contents

Hydrothermal synthesis of nickel substituted magnesium ferrites (NixMg1-xFe2O4) and insight into the detailed structural, magnetic and electrochemical properties

A series of single-phase nickel (Ni+2) substituted magnesium Mg-spinel ferrites (NixMg1-xFe2O4) were synthesized by hydrothermal technique and investigated for morphological, structural, magnetic, and electrochemical properties. Experimental characterization techniques revealed that single-phase spinel structure was confirmed by X-ray diffraction, lattice parameter dropped with increasing Ni concentrations, nanoparticles clustered together, the nanoparticles in the SEM micrographs of different sizes are clustered together. Raman spectra showed lower wave numbers, FTIR spectrum showed that peaks move towards lower wave numbers because of nickel's substitution, and this shortens the Fe-O bond hence reduces the lattice parameter, saturation magnetization increased, coercivity decreased, specific capacitance decreased, and loop size increased. These ferrites are suitable for energy storage applications.

Phase-Pure High-Entropy Spinel Oxide (Ni,Fe,Mn,Cu,Zn)3O4 via Thermal Plasma: A Promising Electrocatalyst for Oxygen Evolution Reaction

High-entropy oxide (HEO) has recently emerged as a potential candidate material for electrochemical water splitting, with excellent activity and catalytic stability, as an alternative to the state-of-the-art oxygen evolution reaction (OER) catalyst. The main characteristics of HEO are its unique structure and the ability to tune physical, chemical, and mechanical properties. On tuning these properties, it exhibits high thermal stability, electrical conductivity, and catalytic activity. In this work, by utilizing a carbonaceous thermal plasma with Ar and CO2 as the major plasma-forming gases, a single-phase (NiFeMnCuZn)3O4 high-entropy oxide material has been produced at a discharge power of 12 kW for the first time. The as-synthesized powder was annealed at various temperatures (300, 350, and 400 °C) and characterized using various microscopic and spectroscopic tools. The dynamic light scattering study showed that the as-synthesized powder had a single-phase spinel structure with an average particle size of ∼140 nm. The synthesized materials were subjected to electrocatalytic water oxidation reaction studies. The results show that HEO annealed at 350 °C has an excellent OER catalytic activity in 1 M KOH electrolyte, with an overpotential of 308 mV at a current density of 50 mA cm–2 and a Tafel slope of 54 mV dec–1. Further, Operando-EIS analysis at different potentials evidences that HEO annealed at 350 °C shows less resistance toward the charge-transfer kinetics at the interface. This work provides insight into the rapid synthesis of phase-pure HEO electrocatalysts with excellent performance in energy-related applications.

A Comparative Study on the Effect of Different Sintering Temperatures on Structural and Magnetic Properties of Mg–Zn Ferrite Nanoparticles

The current study involved the synthesis of magnesium zinc ferrite (Mg0.8Zn0.2Fe1.4Al0.6O4) using the sol–gel method. Various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Infrared (FTIR), vibrating sample magnetometer (VSM), and radiofrequency (RF) induction were utilized to analyze the properties of the synthesized ferrite nanoparticles. The objective was to examine how different sintering temperatures affected the structural and magnetic characteristics of Mg0.8Zn0.2Fe1.4Al0.6O4. The XRD analysis confirmed the presence of a well-defined single phase crystalline structure with a spinel arrangement. Increasing the annealing temperature resulted in larger nanoparticles, ranging from 28.38 nm to 30.14 nm. SEM provided information about the morphology, agglomeration, and grain size of the ferrite, revealing a grain size ranging from 326 nm to 485 nm. The FTIR spectroscopy indicated a single-phase spinel structure for the prepared sample. The magnetic properties of the sample were evaluated using VSM, showing a maximum magnetization of 45.6 emu/gm and the least coercivity of 90 Oe at an annealing temperature of 900 °C. RF induction at a frequency of 108 kHz exhibited superior results for the sample annealed at 900 °C compared to those annealed at 700 °C and 800 °C. At this frequency, the specific absorption rate (SAR) value was high, making it suitable for magnetic hyperthermia applications. The prepared magnesium zinc ferrite demonstrated suitability for both low and high frequency devices, and it could be employed in various technological applications, including microwave devices, inductor cores, transformers, and other electronic devices.

Structural, optical, and electrical properties of Mn0.9La0.1Fe2O4 nanocrystalline ferrites and its synthesis through sol-gel method

This work reports the formation of La-doped nano-crystalline manganese ferrite Mn0.9La0.1Fe2O4 through sol–gel route and examined using XRD and dielectric spectroscopy techniques. The single-phased cubic spinel structure of the ferrite is supported by X-ray diffraction (XRD). The mean crystallite dimension appraised from XRD data has been found to be 21 nm and 11 nm for un-doped and La3+ doped MnFe2O4, respectively, along with a significant rebate in the optical band gap. At room temperature, the frequency-dependent dielectric properties were studied in the frequency range (42 Hz − 5 MHz). The dielectric constant of both the samples narrowly lowers with enhancing frequency and, consequently, shows exemplary dielectric dispersion. The AC-conductivity of the un-doped samples enhances with increasing frequency while it decreases with doping. The dispersion in ac-conductivity (σac) and dielectric properties imply the ordinary dispersion of Maxwell-Wagner type due to the process of hopping of electrons between the Fe2+ and Fe3+ ions and interfacial polarization. The band gap of energy is evaluated with the help of the UV–visible spectra and found to be decreased when La3+ doped with MnFe2O4 ferrite.

Hydrothermal synthesis of cobalt substitute zinc-ferrite (Co1-xZnxFe2O4) nanodot, functionalised by polyaniline with enhanced photocatalytic activity under visible light irradiation

Fabrication and development of effective visible-light-responsive photocatalysts are required to tackle critical environmental issues. The aim of this study was to develop a nanocomposite material with improved photocatalytic activity for the degradation of industrial dyes such as Reactive Orange-16 (RO-16), Reactive Blue (RB-222), Reactive Yellow-145 (RY-145), and Disperse Red-1 (DR-1) without the need for a post-separation process after use. Here we report the hydrothermal synthesis of nanodots of Co1-xZnxFe2O4 (x = 0.3, 0.5 and 0.7), coated with polyaniline, by in situ polymerization. The Co1-xZnxFe2O4 nanodots, coated with polyaniline (PANI) nanograins, facilitated optical properties by easily capturing visible light. X-ray Diffraction (XRD) patterns and Scanning Electron Microscopy (SEM) images have confirmed the single-phase spinel structure of Co1-xZnxFe2O4 nanodot and nano-pore size of the Co1-xZnxFe2O4/PANI nanophotocatalyst. The specific surface area of the Brunauer–Emmett–Teller (BET) of the Co1-xZnxFe2O4/PANI photocatalyst was determined to be 24.50 m2/g by multipoint analysis. The final Co1-xZnxFe2O4/PANI (x = 0.5) nanophotocatalyst showed high efficiency in the catalytic degradation of toxic dyes (∼98% within 5 min), with good mechanical stability and recyclability under visible light irradiation. The nanophotocatalyst was re-used and its efficiency was largely maintained, even after seven cycles (∼82%) of degradation. The effects of various parameters, such as initial dye concentration, nanophotocatalyst concentration, initial pH of dye solution, and reaction kinetics were studied. According to the Pseudo-first-order kinetic model, photodegradation data followed the first-order reaction rate (R2 > 0.95) of degradation of dyes. In conclusion, a simple and low-cost synthesis process, speedy degradation and excellent stability of polyaniline-coated Co1-xZnxFe2O4 nanophotocatalyst could be used as a promising photocatalyst for dye-wastewater treatment.

Impact of shape and size of particles on the magnetic properties of chromium doped cobalt ferrite

The hydrothermal method was used to synthesize CoCrxFe2−xO4 (x = 0, 0.2, 0.4, 0.6, 0.8 at %) nanoparticles. X-Ray Diffraction (XRD) analysis indicates that nanoparticles have a single-phase spinel structure. The lattice constant (a) was calculated by the Rietveld method through MAUD program. The crystallite size (D), mean ionic radii of A and B sites, bond lengths, interionic bond angels and distances of samples were also calculated. Variation of structural parameters agrees with the cation distribution determined in the magnetic study section. The FESEM images confirmed the data extracted from XRD analysis. The change of particles' shape from spherical to octahedral by Cr doping was also observed. The particles’ size of all the samples was studied by drawing the size distribution plots. It was indicated that the size of ferrite particles was varying in the range of 21–110 nm. Increment of Cr3+ content caused the saturation magnetization to be declined, while the coercive field illustrated an opposite behaviour. The effect of size and shape of particles as well as the cation distribution were key factors employed to justify the magnetic properties of Co–Cr ferrite structures. The novel outcome of this work is that the coercive field of the ferrite samples can be tailored as a parameter for high coercivity-needed applications by the effect of shape and size of particles.

Optical studies of pure and (Cu, Co) doped nickel zinc ferrite films deposited on quartz substrate

In this work, the optical properties of pure and doped films were investigated as a function of annealing temperature. Films with compositions Ni0.5Zn0.5Fe2O4, Ni0.35Cu0.2Zn0.45Fe2O4, and Ni0.35Co0.2Zn0.45Fe2O4 were deposited on quartz substrate using the sol–gel method. The grown films were annealed at 500 and 800 °C in a rapid thermal annealing furnace. The single-phase spinel structure of these films was confirmed by x-ray diffraction (XRD) results. The average crystallite size calculated from the XRD data was observed to increase with the annealing temperature and decrease for films doped with Cu and Co. The lattice constant was observed to decrease with the annealing temperature and increase for films doped with Cu and Co. The cross-sectional images obtained from field emission scanning electron microscope were used to calculate the thickness of these films. Ultraviolet-visible spectroscopy was used to obtain the absorbance spectra as a function of wavelength in the range of 200–800 nm. The bandgap obtained from the absorbance spectra was seen to decrease for films annealed at higher temperatures for pure and doped films. Furthermore, the bandgap of doped films was seen to decrease in comparison to that of pure films. Optical parameters such as refractive index, extinction coefficient, optical conductivity, and real and imaginary parts of the dielectric constant were observed to increase with the reduction in the bandgap.

Structural, Mossbauer spectra and magnetic properties of Ni(1-x) Cdx Fe2O4 by solid state Reaction method

The preparation of Ni-Cd ferrite having the chemical formula Ni(1-x)CdxFe2O4 where x varies from 0, 0.1, 0.2, 0.3, 0.4, and 0.5 were synthesized by solid state reaction method. The X-ray analysis shows the existence of single phase spinel structure with increase of lattice parameter and density with increasing Cd contents were as the porosity decreases. The particle size was calculated by X-ray broadening studies. The Vickers hardness of Ni-Cd ferrite system variation between 532 to 568.6. The increase in hardness of composites results from increased Cd-content. The Atomic Force Microscopy (AFM) showed that the average grain size was increases with the increase in Cd content. The variation of dielectric constant, loss tangent and AC conductivity as a function of frequency in frequency range 100Hz-5MHz was studied. The dielectric constants decreases with increasing frequency for all the samples and follow the Maxwell-Wagner's interfacial polarization. The Hall coefficient was found to be positive. It demonstrates that the majority of charge carriers of p-type. The magnetic properties of Ni(1-x)CdxFe2O4 ferrites were strongly affected by the Cd content. The Mossbaure spectra show canted spin structure for all the samples.

The effect of Cadmium Substitution on the structural and magnetic properties of Nickel Ferrite

Nickel – Cadmium ferrites having the chemical formula (Ni1-xCdxFe2O4), (0 ≤ X ≤ 0.5) were prepared by using powders technology method. The particle size of the ferrite samples were estimated from X-ray diffraction studies after the confirmation of the formation of single phase spinel structure of the ferrites. We found that the Lattice constant and density (ρx-ray) increased with Cd content while the porosity was noticed to decrease. Also the magnetic testing showed decreases in values the Coercive Force from (0.408 KA/m) to (0.384 KA/m) and the Remnant Magnetization from (0.056 Tesla) to ( 0.048 Tesla) and the Magnetic Relative permeability is the within range (0.137 ~ 0.125) with increasing of the Cadmium concentration while the Magnetic Susceptibility was noticed to increase from (0.862) to (0.875).

Synthesis and Characterization of Rare Earth Doped Ferrite / Polyethylene Oxide Nanocomposites

Nano-sized Li0.5Ni0.48Tb0.02Dy0.1Fe1.9O4 spinel ferrite nanoparticles were synthesized employing the micro-emulsion synthesis method. Polyethylene oxide was prepared through in-situ polymerization route. The ferrite-polymer nanocomposites have been synthesized by combining Li0.5Ni0.48Tb0.02Dy0.1Fe1.9O4 ferrite with polyethylene oxide polymer. Spectral, structural, morphological, and dielectric properties of the prepared nano-ferrite powders as well as nanocomposites were investigated by “X-ray diffraction analysis” (XRD), “scanning electron microscopy” (SEM), “Fourier transform infrared spectroscopy” (FTIR) and dielectric measurements. XRD analysis confirmed the synthesis of single-phase spinel structure only. The dielectric parameter was augmented with an increase of ferrite amount. FTIR spectra confirmed the existence of interactions between polyethylene oxide and ferrite particles. SEM study revealed that the nanocomposites comprised core/shell structure and inhomogeneous distribution of grain size. The dielectric parameters such as “real part of dielectric constant” (?), “imaginary part of dielectric constant” (?"), “tan loss”, “AC conductivity” and “quality factor” were investigated in the required range of frequency; that is, 1 MHz – 3 GHz. The peaking behavior has been observed for real (??) and “imaginary (???) parts of dielectric constant” and “dielectric loss” (tan?). “The peaking behavior” was detected beyond 1.5 GHz. A decrease in “the dielectric constants” and “dielectric loss” was found to with the increasing frequency. Dielectric parameters have been well elucidated by explaining “Debye-type relaxation model” in agreement with two layer “Koop's phenomenological theory”. The present investigated samples might have potential applications in high frequency.

Effect of Mn and Zn binary Co-substitution on structure and magnetic properties of cobalt ferrites

Mn-Zn binary co-substituted cobalt ferrite (Co1-x(MnZn)xFe2O4 (0 ≤ x ≤ 0.4)) was synthesized by conventionally compacting and magnetic field assisted injection molding. XRD and SEM analysis characterized the single-phase spinel structure, preferred 〈001〉 orientation, and uniform grain size. XPS analysis reveals the cation redistribution in the mixed spinel structure of co-substituted samples, which has a direct consequence on magnetic properties. The addition of Mn-Zn increases the saturation magnetization (Ms), while decreases magnetocrystalline anisotropy constant (K1), leading to a decrease of magnetostrictive saturation field (HS). For pressure samples, the maximum (dλ/dH)max is −0.15 ppm/Oe under 300 Oe applied field at x = 0.2. The samples with 〈001〉 fiber texture were prepared by magnetic field alignment of the semi-solid slurry to achieve higher magnetostrictive properties. The highest magnetostriction λS reaches −432 ppm, which is 200 % higher than pressed samples, and the corresponding maximum strain derivative (dλ/dH)max reaches −0.88 ppm/Oe at a lower magnetic field.

Ba substituted SrFe2O4 (SrBa0.3Fe1.7O4) for the removal of fluoride ions (F−1) from the drinking water

Current study investigates hydrothermally prepared SrBa0.3Fe1.7O4 for the adsorption of fluoride ions (F−1) from drinking water. X-ray diffraction patterns show given sample has a single-phase spinel structure. Scanning electron microcopy confirmed nano-sized particles in the range 12–15 nm. Fourier transform infrared spectroscopy results indicate presence of small absorption peaks due to low temperature sintering and useful elastic parameters have been analyzed as well. The Magnetic Hysteresis was measured by using Vibrating sample magnetometer between -9KOe to 9 KOe. The results revealed the soft magnetic behavior. Prepared ferrites have been investigated for time dependent and isothermal adsorption models. Pseudo second order and Temkin isotherm model best fitted the experimental results. Finally, these ferrites have been used to remove the fluoride ions from different drinking water sources in Lahore and have shown promising results.

Structure and magnetic properties of (Mg1/6Zn1/6Mn1/6Co1/6Ni1/6Fe1/6)3O4 nanocrystalline high-entropy oxide synthesized using a sol-gel auto combustion approach

A sol–gel auto-combustion method is used in this study to synthesize a new class of single-phase high-entropy oxide (HEO) (Mg1/6Zn1/6Mn1/6Co1/6Ni1/6Fe1/6)3O4. The as-synthesized compound exhibits a single-phase spinel structure with an 8.3224 Å lattice parameter and an average crystallite size of 10 nm as determined by X-ray diffraction (XRD) data analysis. Raman and Fourier transform infrared results are in agreement with the XRD results. A scanning electron microscopy-based energy dispersed spectroscopy study suggests the formation of a porous structured morphology with a uniform elemental distribution. In addition, high-resolution transmission electron microscopy and surface analyses further confirm the formation of a pure spinel structure with a particle size of 12–20 nm and a mesoporous character with a pore size of 4.55 nm. X-ray photoelectron spectroscopy indicates mixed-valence states of elements (Mn, Fe, Co, and Ni) and their occupations over tetrahedral and octahedral sites. The temperature-dependent magnetization exhibited a bifurcation between zero-field-cooled and field-cooled magnetizations. From the M−H curves, the magnetization decreased monotonically with the increase in temperature (M is 22 emu/g at 2 K and 7.2 emu/g at 300 K). The coercivity decreased by approximately-one order of magnitude (HC = 1700 Oe at 2 K and HC = 200 Oe at 370 K). Finally, a comprehensive magnetic characterization of the as-synthesized HEO indicates their ferrimagnetic nature. The novel physical properties of the as-synthesized HEO could be useful in various potential applications.

Influence of La3+ substitutions on structural, dielectric and electrical properties of spinel cobalt ferrite

La3+ doped cobalt ferrites with composition CoLaxFe2−xO4 (0.00 ≤ x ≤ 0.20) were synthesized by a co-precipitation method. X-ray diffraction (XRD) analysis confirm the formation of single-phased spinel structure for all synthesized samples. The result of La3+ doping on dielectric and electrical properties of cobalt ferrites was investigated. Dielectric constant and dielectric loss decrease with increasing frequency whereas alternating current (AC) electrical conductivity increases with increasing frequency. The AC electrical conductivities were effectively modeled by employing the Jonscher’s power law. Role of grain and grain boundary on impedance has been explored from nyquist plots and equivalent electrical circuits were proposed to clarify the impedance spectroscopy results. The Direct Current (DC) electrical resistivities were estimated by two probe method within the temperature range of 303K–700K. DC electrical resistivity decreases with increasing temperature and explained by hopping mechanism. DC electrical resistivity and drift mobility decreases with La3+ doping. Activation energies were calculated by employing the Arrhenius plot. Activation energy found to increases with La3+ substitutions. Maximum value of DC electrical resistivity achieved was 9.26 x 10+8 (Ω-cm) with crystallite size 17 nm. Current-Voltage (I–V) measurements were carried out within 0→6V→0V→ –6V→0V voltage range. It is worth mentioning that all doped sample exhibited remarkable and improved nonlinear hysteresis loop-type behavior than pour sample. Variation in resistance, in current-voltage loops, is clarified by considering space charge limited conduction (SCLC) model and oxygen vacancies migration across the metal-semiconductor interface. Out study suggest that La3+ doped cobalt ferrites may be tested as an active material for possible applications in non-volatile memory devices and neuromorphic applications.

Synthesis and electrochemical performance of α-Al2O3 and M-Al2O4 spinel nanocomposites in hybrid quantum dot-sensitized solar cells

The aim of this study is to describe the performance of the aluminum oxide nanoparticle and metal aluminate spinel nanoparticle as photo-anodes in quantum dot photovoltaic. By using a sol–gel auto combustion method, Al2O3 NPs, CoAl2O4, CuAl2O4, NiAl2O4, and ZnAl2O4 were successfully synthesized. The formation of Al2O3 NPs and MAl2O4 (M=Co, Cu, Ni, Zn) nanocomposite was confirmed by using several characteristics such as XRD, UV–Vis, FTIR, FE-SEM, and EDX spectra. The XRD shows that the CoAl2O4 has a smaller crystallite size (12.37 nm) than CuAl2O4, NiAl2O4, and ZnAl2O4. The formation of a single-phase spinel structure of the calcined samples at 1100 °C was confirmed by FTIR. Our studies showed that the pure Al2O3 NPs have a lower energy gap (1.37 eV) than synthesized MAl2O4 under UV–Vis irradiation. Due to the well separation between the light-generated electrons and the formed holes, the cell containing ZnAl2O4 nanocomposite with CdS QDs has the highest efficiency of 8.22% and the current density of 22.86 mA cm−2, while the cell based on NiAl2O4 as a photoelectrode, six cycles of CdS/ZnS QDs, and P-rGO as a counter electrode achieved the best (PCE) power conversion efficiency of 15.14% and the current density of 28.22 mA cm−2. Electrochemical impedance spectroscopy shows that ZnAl2O4 and NiAl2O4 nanocomposites have the highest life times of the photogenerated electrons (τn) of 11*10−2 and 96*10−3 ms, respectively, and the lowest diffusion rates (Keff) of 9.09 and 10.42 ms−1, respectively.

The influence of aluminum’s crystalline structure on the elastic, dielectric, and electrical properties of Ni ferrite

The authors investigate the effect of Al on the structural, elastic, and electrical properties of a Ni nano ferrite. Six samples of NiAl x Fe 2−x O 4 (where x = 0.00, 0.20, 0.40, 0.60, 0.80, and 1.00) were synthesized using flash auto combustion. As shown in XRD patterns, the lattice appears as a Fd-3m space group, a single-phase spinel structure with average crystallite size ranging from 22.4–24.7 nm for all samples. SEM and TEM images showed a uniform and spherical structural with a narrow size distribution. The results manifest significant changes in the elastic and electrical properties due to the presence of Al. As Al content increased, the bulk B, shear G, and Young E moduli decreased and remained in the same order of hundreds in the GPa range: however, the values of the Debye temperature θ D increased. The dielectric parameters ε′, ε″, and tan δ decreased as the frequency of the applied field and Al content increased: they also decreased as temperature increased. The relaxation times were for all samples. The electric moduli M′ and M″ increased as the frequency of the applied field and Al content increased, but they decreased as temperature increased. The relaxation times are dispersed depending on Al content, frequency, and temperature. The Cole-Cole curve showed two semicircles corresponding to the grain and grain boundary with the electrical relaxation of the non-Debye form. The electric impedance Z′ and Z″ increased as the frequency of the applied field and temperature increased, although they decreased as Al content increased. These results indicate that Ni-Al ferrite has respectable dielectric properties, which opens the door for many applications in control and safety monitoring tools, where dynamic process temperature sensors are of great importance and the temperature dependency of the material is significant.