Spinel Crystal Structure Research Articles

Studies on characterization, magnetic and electrochemical properties of nano-size pure and mixed ternary transition metal ferrites prepared by the auto-combustion method

Abstract

Processing, thermal and dielectric investigations of polyester nanocomposites based on nano-CoFe2O4

The present study aims at developing polyester/CoFe2O4 polymer nanocomposites, with enhanced thermal and electrical properties. The X-ray diffraction data of the samples revealed the semi-crystalline polyester nature and spinel crystal structure of CoFe2O4 nanoparticles. The average crystal size obtained from Scherer equation is 44 nm, which is smaller than that estimated from W–H method (59 nm). FTIR spectroscopy proved the complexation and interaction between polyester segments (–COOH and –OH) and CoFe2O4 nanoparticles via hydrogen ponding. DSC analysis showed changes in Tg values up to 116 °C and polyester/CoFe2O4 have revealed more thermal stability at temperatures Tonset, Tmax and T50 as seen from the TGA-DTG investigations. Dielectric real permittivity (ε′) expressively increased by adding the CoFe2O4 nanoparticles, that is related to Maxwell-Wagner-Sillars (MWS) effect in hetero-phase composites. It has been found that CoFe2O4 nanoparticles enhanced the dissipation factor (tan(δ)) for all nanocomposites. The relative energy density (URelative) values are 4.39, 8.02, 10.7 and 11.3 for the polymer nanocomposites doped with 5.0, 10.0, 15.0 and 20.0 wt% of CoFe2O4 nanoparticles. Finally, the DC conductivity of nanocomposites increased with increasing the CoFe2O4 concentration.

Effect of Silver Nanoparticles on Properties of Cobalt Ferrites

Ferrite nanomaterials in the form of CoAgxFe2−xO4 (x = 0.0, 0.03, 0.07, 0.1, and 0.2) have been prepared by the citrate autocombustion method. Structural analysis was carried out by x-ray diffraction. Fourier-transform infrared spectroscopy confirmed the formation of a spinel crystal structure. High-resolution transmission electron microscopy revealed the formation of particles with mixed morphologies. The average particle size ranged from 22 nm to 31 nm. Vibrating-sample magnetometry revealed that the saturation magnetization Ms and coercivity Hc were affected by the grain size variation. The electrical properties of the samples were investigated over the frequency range from 102 Hz to 105 Hz. Electric modulus analysis showed that the conduction was due to short-range mobility of charge carriers. The variation of the dielectric loss with frequency at different temperatures indicated two types of conduction mechanism. All these results suggest that the synthesized materials can be recommended for fabrication of exchange spring magnets and electrode materials.

Impacts of Egg White Assisted Combustion and Ceramic Methods on Structural, Morphological and Magnetic Properties of Nickel Manganite System

This study focuses on two different techniques for preparation of nickel manganite (NiMn2O4) system. One approach is conventional ceramic method, and the second is based on replacing the ceramic route with green synthesis mediated by egg white. The goal of this strategy is produce a single nanomagnetic phase of NiMn2O4 using a mostly simple one-step method with specific characteristics as seen in the second route compared to the ceramic method. The as synthesized system was characterized by using various techniques such as X-ray diffraction (XRD), scanning electron micrographs (SEM), and Energy dispersive X-ray spectrometry (EDS). XRD, EDS and SEM analyses confirm a successful synthesis of NiMn2O4 single phase with cubic spinel and sponge crystal structures. The particles are polycrystalline in their nature and average crystallite size ranged between 76 and 90 nm. Egg white assisted combustion method imparted amelioration in the system crystallization, size of grain, distribution of cation and magnetic properties of the as prepared materials. The magnetic mensuration suggested that the obtained nickel manganite shows ferromagnetism at room temperature with an optimum value (3.56 emu/g) of saturation magnetization.

Synthesis and characterization of CoFe2O4 and Ni-doped CoFe2O4 nanoparticles by chemical Co-precipitation technique for photo-degradation of organic dyestuffs under direct sunlight

Cobalt ferrite and nickel doped cobalt ferrite nanoparticles (NPs) was victoriously developed through chemical co-precipitation technique. The spinel crystal structure of prepared samples was confirmed by powder X-ray diffraction studies (PXRD) and also the crystalline size was calculated. Optical properties of the samples were analyzed using UV–Visible spectrophotometer and Photoluminescence (PL) studies. The bandgap was calculated using Tauc's plot and is found to be 1.83 eV, 1.92 eV, 2.12 eV, and 2.21eV for pure cobalt ferrite and (3, 7, 11) wt% Ni-doped CoFe2O4 samples respectively. Further, the morphological and the compositional weight percentage (wt %) was examined using a Scanning Electron Microscope (SEM) and Energy Dispersive X-ray spectrum (EDAX) respectively. Towards application, the photocatalytic activity of the synthesized NPs was studied under direct sunlight and the maximum efficiency was obtained as 83.41%, 63.62% and 82.76% for Methylene Blue (MB), Rhodamine B (RhB) and Crystal Violet (CV) respectively.

Electrical and Electrochemical Behavior of Binary Li4Ti5O12–Polyaniline Composite

Polyaniline (PANI), and nanocrystallites of pure Li4Ti5O12 (LTO) and V-doped Li4Ti5O12 (V-LTO) spinel structure have been synthesized. The pure and doped Li4Ti5O12 was synthesized by solid-state reaction, whereas the samples containing PANI were prepared by the in-situ oxidation polymerization method. As-prepared materials were characterized by XRD, FT-IR and SEM techniques. The electrical and electrochemical properties were studied using impedance spectroscopy (EIS), cyclic voltammetry (CV), galvanostatic charge–discharge methods (GCD) techniques. The doping of LTO with vanadium caused marked changes in each of particle size, electrical conductivity, and electrical capacitance without any transforming in the spinel crystal structure of the LTO material. Electrochemical studies showed that the specific capacitance of a hybrid electrode built of the binary materials LTO and PANI is higher than that of its individual single material. It shows a specific capacitance of 108 F/g, an energy density of 30 Wh/kg, and a power density of 2160 W/kg at 4 A/g as well as high cycling performance, with 88.3% capacitance retained over 1000 cycles. The high electrochemical performance of the V-LTO/PANI composite electrode can be attributed to the synergistic effects of the singular constituents and the enhancement of electronic conduction in the hybrid electrode materials.

Heterogeneous integration of single-crystalline complex-oxide membranes.

Complex-oxide materials exhibit a vast range of functional properties desirable for next-generation electronic, spintronic, magnetoelectric, neuromorphic, and energy conversion storage devices1-4. Their physical functionalities can be coupled by stacking layers of such materials to create heterostructures and can be further boosted by applying strain5-7. The predominant method for heterogeneous integration and application of strain has been through heteroepitaxy, which drastically limits the possible material combinations and the ability to integrate complex oxides with mature semiconductor technologies. Moreover, key physical properties of complex-oxide thin films, such as piezoelectricity and magnetostriction, are severely reduced by the substrate clamping effect. Here we demonstrate a universal mechanical exfoliation method of producing freestanding single-crystalline membranes made from a wide range of complex-oxide materials including perovskite, spinel and garnet crystal structures with varying crystallographic orientations. In addition, we create artificial heterostructures and hybridize their physical properties by directly stacking such freestanding membranes with different crystal structures and orientations, which is not possible using conventional methods. Our results establish a platform for stacking and coupling three-dimensional structures, akin to two-dimensional material-based heterostructures, for enhancing device functionalities8,9.

Mn-Co-Ni-O thin films prepared by sputtering with alloy target

The thin film of heat-sensitive materials has been widely concerned with the current trend of miniaturization and integration of sensors. In this work, Mn1.56Co0.96Ni0.48O4 (MCNO) thin films were prepared on SiO2/Si substrates by sputtering with Mn–Co–Ni alloy target and then annealing in air at different temperatures (650–900 °C). The X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) analysis indicated that the main crystalline phase of MCNO thin films was spinel crystal structure; the surface of the thin films was very dense and uniform. The electrical properties of the thin films were studied in the temperature range of–5–50 °C. The MCNO thin film with a low room temperature resistance R25 of 71.1 kΩ and a high thermosensitive constant B value of 3305 K was obtained at 750 °C. X-ray photoelectron spectroscopy (XPS) analysis showed that the concentration of Mn3+ and Mn4+ cations in MCNO thin films is the highest when annealing temperature is 750 °C. The complex impedance analysis revealed internal conduction mechanism of the MCNO thin film and the resistance of the thin film was dominated by grain boundary resistance.

Calcination Effect on the Photoluminescence, Optical, Structural, and Magnetic Properties of Polyvinyl Alcohol Doped ZnFe2O4 Nanoparticles

Spinel ferrite based nanoparticle material has been at the forefront of contemporary nanotechnology for use in various industrial and biomedical applications. The preparation and characterization of zinc ferrite nanoparticles (ZFNPs) doped with polyvinyl alcohol (PVA) are reported in this work. The formulated ZFNP/PVAs were characterized using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible spectroscopy, photoluminescence (PL) and a vibrating sample magnetometer (VSM). The XRD established the cubic spinel crystal structure of the as-prepared and calcined sample with an increase in the crystallite size after the calcination. The SEM analysis showed a spherical morphology within the range of 10-40 nm after calcination. The bandgap energy was enhanced after calcination. The PL analysis revealed a prominent peak in the UV band, which showed the characteristics of the formulated nanostructure. Transformation to a superparamagnetic nature was observed after calcination. It is noteworthy that after calcination of the formulated ZFNP/PVAs, the structural, optical, bandgap energy, morphology, photoluminescence and the magnetic properties were influenced and enhanced for various applications, chiefly for hyperthermia, magnetic resonance imaging, drug delivery and allied disciplines.

Magnetised photocatalyst TiO2/Fe3O4 nanocomposite capable to photodegrade organic dye

In this study, methylene blue (MB) is used as a measure of the photocatalytic capabilities of the prepared TiO2/Fe3O4 photocatalyst nanocomposite. The nanocomposite was suspended in the dye aqueous solutions placed in a UV chamber under UV-C (254 nm) light irradiation. The TiO2/Fe3O4 nanocomposite was characterised by XRD, FESEM, TEM and EDX analysis. The TiO2/Fe3O4 nanocomposite crystal structure retained TiO2 pure anatase of tetragonal crystal structure (SG: I4/amd) and Fe3O4 cubic spinel crystal structure with average crystalline size of (62.1 ± 5.7) nm. The optimum performance of the magnetic nanocomposite was monitored through few categories, such as concentration of photocatalyst, doping amount of Fe3O4 nanoparticle into the nanocomposite and sintering temperature. The TiO2/Fe3O4 nanocomposite optimum loading was detected at 3.0 wt%. The nanocomposite performed well at 1 wt% of Fe3O4 doping and 350 °C of sintering temperature. The reliability of the TiO2/Fe3O4 nanocomposite was also conducted where it was successfully repeated for at least 3 times with no obvious changes observed in the degradation efficiency.

Structural and electrochemical investigation on pure and nickel doped cobalt ferrite nanoparticles for supercapacitor application

Hydrothermal method was employed for the synthesis of pure Cobalt ferrite and Nickel doped Cobalt ferrite nanoparticles. The crystallinity, morphological and the electrochemical investigation of the prepared samples were studied using X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM), FT-IR and Cyclic voltammetry (CV) study analysis. The cubic spinel crystal structure was revealed by the XRD pattern. The average crystallite size for the pure cobalt ferrite and the nickel doped cobalt ferrite doped samples were 20 nm and 25 nm respectively. The lattice constant of the pure and the doped samples were 8.29 Å and 8.36 Å respectively. SEM analysis revealed the presence of nanoclusters. The EDS patterns confirmed the presence of the elements Ni, Co, Fe and O without any impurity. The infra-red spectra showed the features of higher and lower energy bands corresponding to tetrahedral (T-band) and the presence of octahedral (O-band) complexes confirmed the creation of spinel ferrites. The electrochemical behavior of the prepared nanoparticles was investigated through Cyclic Voltammetry (CV) study analysis using 2 M of KOH electrolyte solution. The potential window was limited as 0 V to 0.6 V at various scan rates 10, 30, 50, 80 and 100 mV/s. Cyclic Voltammetry study revealed that the Nickel dopant increased the specific capacitance than the pure Cobalt ferrite. The specific capacitance of the pure cobalt ferrite and the nickel doped cobalt ferrite samples were obtained as 517 F/g and 561 F/g respectively.

Influence of ultrathin gahnite anti-reflection coating on the power conversion efficiency of polycrystalline silicon solar cell

Current research has concentrated on the development of ZnAl2O4 (gahnite) spinel nanostructure through anti-reflection coating (ARC) material for improved power conversion efficiency (PCE) of polycrystalline silicon solar cells. Radio frequency magnetron sputtering technique was adopted to deposit transparent polycrystalline gahnite nano-microfilms at room temperature. Material deposition was performed in a pure argon atmosphere on polycrystalline silicon solar cell substrates with a coating duration of 5–45 min. The influence of gahnite spinel nanostructure-integrated coating on the efficiency of silicon solar cell was explored by investigating physical, electrical, optical characteristics and temperature distribution profiles. The synthesized ARC material has gahnite spinel crystal structure composed of two-dimensional (2D) nanosheets. Atomic force microscopy study revealed that the thickness of synthesized gahnite 2D nanosheets was about 50 nm. The resistivity of gahnite coated with the time duration of 35 (T-IV) minutes on silicon solar cell was measured to be 1.93 × 10−3 Ω cm. The nano-microfilms showed a great optical transmittance (97%) in the wavelength range of 300–800 nm. The maximum PCE of 21.27% at open atmospheric condition and 23.83% at controlled atmospheric condition had been achieved for 35 (T-IV) minutes of gahnite nano-microfilm coating and it has been proved that gahnite nano-microfilms assists the absorption of more photons on a polycrystalline silicon solar cell substrate. The results acquired indicate that the gahnite nano-microfilm is an appropriate ARC material for polycrystalline silicon solar cells to enhance the PCE.

Effect of Mn Substitution on Structure and Magnetic Properties of Cobalt Ferrite Nanoparticles

The Mn substituted Co-ferrite nanoparticles (MnxCo1–xFe2O4, x = 0 and 0.5) were prepared by co-precipitation method. Samples show single-phase cubic spinel crystal structure. Average crystallite size decreases with Mn substitution. Elemental composition of the samples is confirmed by energy dispersive X-ray analysis. A well-defined hysteresis loop indicates the existence of ferromagnetic ordering in the samples. An increase in saturation and remnant magnetization is observed with Mn substitution. The decrease in resonance field in ferromagnetic resonance spectra is related to the increase in internal magnetic field which indicate the increase in the ferromagnetic interaction in Mn substituted sample.

Fast response and highly selective nitrogen dioxide gas sensor based on Zinc Stannate thin films

NO2 sensors based on Zn2SnO4 (Zinc Stannate) films were synthesized using spray pyrolysis method. The effect of substrate temperature (phase formation) on NO2 response is studied. XRD, SEM and AFM techniques were used to study structural, morphological and topographical analysis of the films, respectively. Zn2SnO4 films exhibits polycrystalline nature having cubic inverse spinel crystal structure. SEM and AFM studies show that the film deposited at 400 °C possess flakes like morphology and the voids present in the surface increases the roughness. Zn2SnO4 sensor shows highest sensor response of 29.3 at moderately low (200 °C) operating temperature towards 40 ppm NO2 concentration. As low response time as 8 s and recovery time of 58 s are recorded for the sensor at its highest response. The pristine Zn2SnO4 films show outstanding gas sensing properties and demonstrated excellent response and recovery kinetics without any surface modification by noble metal or surfactant.

Magnetization reversal in NiFe2O4/SrTiO3 nanoheterostructures grown by laser molecular beam epitaxy

NiFe2O4/SrTiO3(001) nanoheterostructures have been fabricated by laser molecular beam epitaxy method. Surface morphology and crystal structure of Ni-ferrite films were analysed by atomic force microscopy (AFM), reflection of high energy electron diffraction (RHEED), X-ray diffraction (XRD). X-ray methods prove the presence of inverse spinel crystal structure of films that was confirmed by measurements of spectral dependence of optical polar Kerr (PMOKE) effect. Study of magnetization reversal for different orientations of magnetic field carried out by vibration sample magnetometry (VSM) and longitudinal magneto-optical Kerr effect (LMOKE) are presented. In-plane magnetization loops exhibit 90° period indicating presence of biaxial magnetic anisotropy. Asymmetry of LMOKE hysteresis loops is related to manifestation of quadratic in magnetization effects in reflection of light.

Fabrication of a flexible binder-free lithium manganese oxide cathode for secondary Li - Ion batteries

The binder-free technology is used to produce flexible self-standing cathodes for secondary Li-ion batteries containing commercial materials: lithium manganese oxide (LMO) and multiwall carbon nanotubes (CNT). The fragmentation of commercial LMO by short time ball-milling with low energy intensities, allows one to reduce the particle size from tens of microns to the micron and submicron level, while maintaining its spinel crystal structure. The electrode exhibits high electrical conductivity (46 S m−1) due to homogeneous distribution of LMO particles in the matrix of CNT. Electrochemical assessment of the electrode revealed good cyclic stability and a high reversibility of 93% after 120 galvanostatic charge/discharge cycles at 0.6C, with an initial specific discharge capacity of about 110 mA h⋅g−1 and 80 mA h⋅g−1 at high current rate of 2C.

Nanostructure and Optical Properties of Fe3O4: Effect of Calcination Temperature and Dwelling Time

In this work, we reported the nanostructure and optical properties of the Fe3O4 nanoparticles. The Fe3O4 have been synthesized from local iron sand Halmahera Utara by using the coprecipitation method at a temperature of 80°C and NaOH concentration of 3M. The nanoparticles were calcined at 150°C and 250°C for 4 hours consecutively, while the calcination dwelling time was 2 hours and 4 hours at a temperature of 250°C. The results show that a formation of Fe3O4 nanoparticles with a spinel crystal structure. The lattice parameter of nanoparticles decreases with an increase of calcination temperature and dwelling time due to higher thermal energy driving the atom to move closer to each other. Hence, the crystallite size of the nanoparticles increases due to the expansion process to the grain of the nanoparticles. The optical gap energy of the nanoparticles decreases due to the formation of a larger particle. It also confirms that the existence of Fe3+-O and Fe2+-O bonds in the nanoparticles which are characteristic functional group bond of Fe3O4 in the tetrahedral and octahedral sublattice. This result can prove that a higher calcination temperature and longer dwelling time can improve the nanostructure and optical properties of Fe3O4.

A new class of spinel high-entropy oxides with controllable magnetic properties

A new class of high-entropy spinel oxides, (Cr0.2Fe0.2Mn0.2Ni0.2Zn0.2)3O4 and (Cr0.2Fe0.2Mn0.2Co0.2Zn0.2)3O4 nanocrystalline powders, has been synthesized by solution combustion synthesis. Their microstructures and magnetic properties were compared with those of (Cr0.2Fe0.2Mn0.2Co0.2Ni0.2)3O4. All the oxides were identified to have the spinel crystal structure (Fd-3m) with average crystallite size of about 24 nm, and their lattice parameters found to decrease with reduction in the electronegativity of Ni2+, Co2+ and Zn2+. Furthermore, nonmagnetic Zn2+ substitution for either magnetic Co2+ or Ni2+ weakened the ferromagnetic ordering and magnetic moments, showing the controllable magnetic property of this new class of high-entropy oxides.

Development of sol-gel derived gahnite anti-reflection coating for augmenting the power conversion efficiency of polycrystalline silicon solar cells

Abstract The present research is focused on developing ZnAl2O4 (gahnite) spinel as an antireflection coating material for enhanced energy conversion of polycrystalline silicon solar cells (PSSC). ZnAl2O4 has been synthesized using dual precursors, namely aluminum nitrate nonahydrate and zinc nitrate hexahydrate in ethanol media. Diethanolamine has been used as a sol stabilizer in sol-gel process for ZnAl2O4 nanosheet fabrication. ZnAl2O4 nanosheet was deposited layer-by-layer (LBL) on PSSC by spin coating method. The effect of ZnAl2O4 coating on the physical, electrical, optical properties and temperature distribution in PSSC was investigated. The synthesized antireflection coating (ARC) material bears gahnite (ZnAl2O4) spinel crystal structure composed of two dimensional (2D) nanosheets. An increase in layer thickness proves the LBL deposition of ARC on the PSSC substrate. The ZnAl2O4 2D nanosheet comprising ARC on the PSSC was tested and it exhibited a maximum of 93 % transmittance, short-circuit photocurrent of 42.364 mA/cm2 and maximum power conversion efficiency (PCE) 23.42 % at a low cell temperature (50.2 °C) for three-layer ARC, while the reference cell exhibited 33.518 mA/cm2, 15.74 % and 59.1 °C, respectively. Based on the results, ZnAl2O4 2D nanosheets have been proven as an appropriate ARC material for increasing the PCE of PSSC.

Structural and Magnetic Properties of Spinel Ferrite Nanoparticles.

In this paper we review the magnetic properties of spinel ferrite nanoparticles pointing out the primary role of the crystalline structure besides finite size and surface/interface effects. The details of the spinel crystal structure of bulk spinel ferrite materials and their influence on both the magnetization and magnetocrystalline anisotropy are recalled. Moreover, we review some results published in the literature over the last years about how the structure of magnetic nanoparticles influences their magnetic features. Perspectives about the challenges to improve the applications in several fields are finally reported.