Natural fuel assisted synthesis of Mg–Cu ferrite nanoparticles: Evaluation of structural,dielectric, magnetic and humidity sensing properties

The effects of lemon juice and annealing treatment on phase composition, vibrational modes, microstructural and dielectric behavior of Mg doped copper ferrite nanoparticles have been synthesized and analyzed in detail in this present work. The various characterization techniques are used to examine the phase, microstructural, vibrational and dielectric nature of the samples at different annealing temperatures (600 °C and 900 °C). The phase and microstructure of Mg substituted CuFe₂O₄ nanoparticles have been analyzed by XRD, SEM and TEM. The secondary phase peaks free XRD spectra revealed that the as burst and the annealed Mg–CuFe₂O₄ nanoparticles have single phase cubic spinel structure. The average crystallite size of the as burnt, annealed 600 °C and annealed 900 °C of as prepared nanoparticles are calculated as 8.9 nm, 12.8 nm and 31.6 nm respectively. Another verification of the spherical shaped particle's size was confirmed by TEM analysis and it found as average size of 28.7 nm, this result is well matched with XRD analysis. The effect of size with impact of annealing treatment on magnetic and dielectric properties also analyzed. The size-dependent Mg–CuFe₂O₄ nanostructures exhibit promising sensing properties which ensure them as a potential candidate for humidity sensor applications. The as-burnt and annealed samples both show a humidity response over the humid range of 10–95 %RH. The sample annealed at 900 °C has the highest average sensor response (6.02 MΩ/%RH) among the as-burnt sample (6.38 MΩ/%RH) and annealed sample at 600 °C (7.11 MΩ/%RH).     

A study of the structural and morphological properties of Ni–ferrite,Zn–ferrite and Ni–Zn–ferrites functionalized with starch

Zinc–ferrite, nickel–ferrite and mixed nickel–zinc ferrites were successfully synthesized via the thermal decomposition method from acetylacetonate complexes. To control the particle size and enhance dispersibility in an aqueous medium, starch, a natural and biocompatible compound, was used for the first time for coating such magnetic powders. X-ray powder diffraction (XRPD) was performed to study the structural properties of all samples. The presence of a single-phase spinel structure as well as the cation distribution in both sites of all investigated magnetic powders was confirmed. The values of unit cell parameters obtained from the results of the Rietveld analysis decreased, while the average crystallite size increased with increasing Ni²⁺ content. The average microstrain parameters unambiguously showed a change in the spinel structure with cation distribution. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) analyses were also utilized to characterize the synthesized materials, corroborating the XRPD data. The obtained results indicated that functionalization by starch was successfully achieved.     

Chemical synthesis,compositional, morphological,structural, optical and magnetic properties of Zn1−xDyxS nanoparticles

Zn_1−xDy_xS (x=0, 0.02 and 0.04) nanoparticles (NPs) were synthesized by chemical refluxing technique at 100 °C. The prepared samples were analyzed by studying their compositional, morphological, structural, optical and magnetic properties. EDS analysis confirmed the presence of zinc, dysprosium and sulfur in the samples in near stoichiometric ratio. The X-ray diffraction patterns do not show any Dy related peaks for the as-synthesized ZnS nanoparticles. The average diameter of the particles confirmed by TEM studies, was in the range 2–4 nm. Raman studies revealed that all the samples are single phase and exhibit cubic structure. From DRS studies, the band-gap was found to be in the range of 3.85–3.70 eV. All the doped ZnS nanoparticles exhibit ferromagnetic behavior with the Curie temperature higher than room temperature and the magnetic properties of doped ZnS nanoparticles depend on the concentration of Dy ions.     

Co-precipitation of a Ni–Zn ferrite precursor powder: Effects of heat treatment conditions and deagglomeration on the structure and magnetic properties

A Ni–Zn ferrite precursor powder was synthesized by co-precipitation upon adding ammonia to an aqueous solution of the precursor iron, nickel, and zinc nitrate salts. The powder was calcined at a range of temperatures (200–1200 °C) and the crystalline phase evolution was assessed by X-ray diffraction coupled with Rietveld refinement. Intermediate phases (NiFe₂O₄ and Fe₂O₃) with increasing crystallinity coexisted in the system up to 1000 °C. The required Ni_0.8Zn_0.2Fe₂O₄ phase could only be attained at 1200 °C. The magnetic properties measured using a vibrating sample magnetometer revealed high magnetization saturation level (～59 emu/gm) above 400 °C. The coercivity showed a steady decrease with increasing heat treatment temperature, leading to a change from a hard to soft magnetic state. The BET specific surface area and the SEM morphology were found to be dependent on calcination temperature, atmosphere (air or N₂) and on the milling procedure.     

Effects of Co-substitution on the structural and magnetic properties of NiCoxFe2−xO4 ferrite nanoparticles

The sol–gel auto-combustion method was used to prepare nanocrystalline powders of Co-substituted nickel ferrite with the general formula NiCo_xFe_2−xO₄ (x=0.0, 0.1, 0.25, and 0.5). The effects of Co-doping on the structural, morphological, and magnetic properties of the samples were subsequently evaluated by X-ray diffraction (XRD), Fourier transform infrared (FTIR), field emission scanning electron microscopy (FE-SEM), and vibrating sample magnetometer (VSM). Using the MAUD program, the full pattern fitting of Rietveld method was employed to determine the exact coordinate of the atoms, unit cell dimensions, and ion occupancy. X-ray diffraction measurements by Rietveld refinement confirmed the crystalline structure and phase purity of all the ferrites prepared. FTIR results also confirmed the formation of a spinel phase and FE-SEM images showed that the particles were in the nanosize range. Moreover, Rietveld analysis and saturation magnetization (M_s) revealed that Co³⁺ replaced Fe³⁺ in the tetrahedral A-sites up to x=0.1. then, it replaced Fe³⁺ in both A- and B-sites for x≥0.25. Finally, VSM results demonstrated that while M_s remained nearly constant with increasing Co³⁺ substitution, coercivity (H_c) increased significantly. It may be suggested that the larger magneto-crystalline anisotropy of Co³⁺ ions is responsible for the increased H_c observed in the Co-doped Ni ferrite samples.     

Synthesis of dysprosium/Mn–Cu ferrite binary nanocomposite: Analysis of structural,morphological, dielectric,and optomagnetic properties

Manganese–copper ferrite (MCFO) and dysprosium (Dy)-doped manganese–copper ferrite nanocomposites (Mn_0.5Cu_0.5Dy_xFe_2−xO₄) (x = 0, 0.05, 0.10, and 0.15) were synthesized by sonochemical method. Crystal structure and the structural parameters of the MCFO were analyzed based on the doping concentration of Dy ion. It was observed that the average crystalline size of the synthesized nanocomposite decreases when the concentration of Dy increases. The existing spherical surface morphology of the MCFO and Dy-doped MCFO nanocomposites were obtained through scanning electron microscopy. In the UV spectrum, the pristine MCFO sample showed an absorbance peak at 743 nm whereas the absorbance values of Dy-doped ferrite nanocomposite considerably shifted (blue) toward a lower wavelength (231–222 nm). The dielectric parameters of all ferrite nanocomposites were studied in the frequency range of 100 Hz to 5 MHz. The dielectric spectrum revealed that dielectric constant and loss tangent decreased with increased doping concentration of Dy ion. The saturation magnetization also changed with Dy doping in MCFO. The impact of Dy on manganese–copper ferrite changed the optical, dielectric and magnetic properties of the prepared binary ferrite nanocomposite, which can be used for microwave-absorbing material applications.     

Effect of heat treatment on the optical properties of sol–gel-derived,fully dielectric solar control coatings on glass

TiO₂ and zeolite were used as high index and low index dielectric materials respectively to generate fully dielectric solar control coatings on glass. TiO₂|Zeolite|TiO₂ trilayer stacks as well as single layer TiO₂ and zeolite coatings were generated on soda lime glass substrates using dip-coating technique. The coatings were densified at 450°C in air using a conventional muffle furnace and a conveyorized belt furnace with a total cycle time of 330 and 30 min, respectively, per layer. The effect of heat-treatment time on the optical properties of multilayered and single-layered coatings was studied. Spectroscopic ellipsometric analysis was carried out on individual layers of the stack to elucidate thickness, roughness, and refractive index data. The ellipsometry data were subsequently used as inputs to simulate the UV–Vis–NIR transmittance spectra of the trilayer stacks generated by TFCalc^® software, for comparison with experimentally obtained data. The morphology and phase compositions of the coatings were studied using scanning electron microscopy and grazing angle incidence X-ray diffraction analysis. Different heat treatment schedules were found to result in different optical properties. The results from the present study could be used to recommend suitable heat treatment schedules for generating solar control coatings that could be used for either architectural or automotive applications.     

Effects of Ca–Gd co-substitution on the structural,magnetic, and dielectric properties of M-type strontium hexaferrite

Sr_1−xCa_xFe_12−xGd_xO₁₉ (x = 0, 0.04, 0.08, 0.12, 0.16, 0.20) hexaferrites were characterized by several techniques, such as X-ray diffraction, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, and vibrating sample magnetometer. Structural results indicate the formation of a pure-phase Sr_1−xCa_xFe_12−xGd_xO₁₉ hexaferrite with space group P6₃/mmc. SEM photography confirms that there are a smaller number of defects due to the reduced porosity and surface area (increased particle size). Magnetic investigations showed a rise of the coercive force from 5069.8 to 5757.4 Oe and saturation magnetization from 79.25 to 80.68 emu/g. The maximum values appear to be for sample x = 0.16, which may be useful in such as permanent magnets, and high-density media for magnetic storage devices. Dielectric parameters, such as conductivity, the real part of permittivity, dielectric loss, dielectric tangent loss, and complex modulus, were studied. Impedance analysis shows that the conduction process is mainly governed by the long-range movement of the charge carriers based on the Debye model for x = 0.12.     

Sol-gel synthesis,structural, morphological and magnetic properties of BaTiO3–BiMnO3 solid solutions

In this study, solid solutions of (1-x)BaTiO₃-xBiMnO₃ have been synthesized by an aqueous sol-gel method. It was determined that single-phase compounds can be obtained up to x = 0.6 and with further increase in percentage of BiMnO₃ component additional crystal phases were detected. Perovskite crystal structure was determined for all synthesized compounds regardless of chemical composition. Raman spectra of synthesized solid solutions showed gradual change of the shape with an increase of BiMnO₃ fraction. It was demonstrated that partial substitution of BaTiO₃ by BiMnO₃ led to the drastic growth of grains of the end products. Magnetization measurements showed that all BiMnO₃-containing samples are characterized by paramagnetic behavior. Clear correlation between magnetization values and composition of the materials was observed, magnetization values increased with increasing of BiMnO₃ content in solid solutions.     

Electrical properties of low-temperature-fired ferrite–dielectric composites

The effects of the BaO·(Nd_0.8Bi_0.2)₂O₃·4TiO₂ (BNBT) to NiCuZn ferrite ratio and addition of Bi₂O₃–B₂O₃–SiO₂–ZnO (BBSZ) glass on the sintering behavior, microstructure evolution, dielectric and magnetic properties of BNBT–NiCuZn ferrite composites were investigated in developing low-temperature-fired composites for high frequency electromagnetic interference (EMI) devices. The results indicate that these composites can be densified at 900 °C and exhibit superior dielectric and magnetic properties with the addition of BBSZ glass. The dielectric system used in the ferrite–dielectric composites reported in the previous studies mostly belong to the ferroelectricity group, which are not suitable for use in the high frequency range (>800 MHz) due to the selfresonance frequency limit. In this study, the dielectric constant remains nearly a constant over a wide range of frequencies (100 MHz to 1 GHz) and the magnetic resonance frequencies are larger than 100 MHz for the BNBT + BBSZ glass–NiCuZn ferrite composites. Therefore, the BNBT + BBSZ glass–NiCuZn ferrite composites can be a good candidate material for high frequency EMI device applications.     

Effect of mechanical milling on structural,dielectric and magnetic properties of BaTiO3–Ni0.5Co0.5Fe2O4 multiferroic nanocomposites

The coexistence of ferroelectricity and ferromagnetism has triggered great interest in multiferroic materials. Multiferroic with strong room temperature magnetoelectric (ME) coupling can provide a platform for future technologies. In this paper, we have investigated the effect of mechanical milling on the properties of multiferroic nanocomposites synthesized by mixing barium titanate (BaTiO₃) (BT) and nickel cobalt ferrite (Ni_0.5Co_0.5Fe₂O₄) (NCF). This process has resulted into reliable disposal of a given quantity of NCF nanoparticles in BT grid and composite samples of different particle sizes (<500 nm) have been obtained by varying the duration of ball-milling for 12, 24, and 48 h. The presence of NCF within BT powder has been confirmed by X-ray Diffraction (XRD) and magnetization measurements (MH). Structural analysis was performed by using Reitveld refinement method that shows that the tetragonality of BaTiO₃ structure get reduced in submicron range. Variations in ferroelectric and dielectric properties with reduction in particle size/milling duration have been studied by P-E loop tracer and Impedance analyzer. The dielectric constant value of 400 has been observed for BT-NCF0 that increases to 9.7 K for composite sample ball mill at 48 h whereas remnant polarization increases to 4.2 μC/cm². These composites with high dielectric constant that changes with temperature and particles size find application in energy storage devices, sensor and memory devices.     

Effects of excess NaClO4 on phases,size and magnetic properties of Ni–Zn ferrite powders prepared by combustion synthesis

Ni_0.4Zn_0.6Fe₂O₄ powders were prepared by combustion synthesis with different amount of NaClO₄. Phases, particle size and magnetic properties of the powders and annealed powders were systematically investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and vibrating sample magnetism (VSM). The excess content of NaClO₄ offered significant advantages with respect to the size, morphology and magnetic properties of the powders. After annealing, sub-micro ferrite spherical powders with spinel phase in a range of 500–800 nm can be obtained. With the increase of the NaClO₄ content, the saturation magnetization of the powders shows a maximum value at 68.8 emu/g when w=0.4, whereas the coercivity stayed nearly constant. The maximum saturation of annealed powders by combustion synthesis is much higher than the range reported in the literature.     

Electrodeposition of Zn–Mn alloys in acidic and alkaline baths. Influence of additives on the morphological and structural properties

Electrodeposition of Zn–Mn alloys on steel was achieved using alkaline pyrophosphate-based baths or acidic chloride-based baths. Cyclic voltammetry was used to determine the potential ranges where the various redox processes were taking place. It appeared that the reduction of Mn(II) was generally hidden by the other reduction reactions, especially by the hydrogen evolution reaction. Zn–Mn alloys containing up to 25 at.% Mn in the alkaline bath and 12 at.% in the acidic bath could be obtained at the cost of very low current efficiencies. The characterisation of the deposits obtained either by galvanostatic polarisation or potentiostatic polarisation was performed by Scanning Electron Microscopy and X-Ray Diffraction. Various Zn–Mn phases were obtained, depending on the current densities, the composition of the deposit and that of the electrolytic bath. Two commercial additives usually used for zinc electrodeposition, one in alkaline baths, the other in acidic baths, were tested. Their effects upon the composition, the morphology and the microstructure of the deposit were investigated.     

Rietveld refined crystal structure,magnetic, dielectric,and electric properties of Li- substituted Ni–Cu–Zn ferrite and Sm,Dy co-doped BaTiO3 multiferroic composites

The conventional solid-state reaction technique is used to fabricate the multiferroic xLi_0.1Ni_0.3Cu_0.1Zn_0.4Fe_2.1O₄(LNCZFO)+(1-x)Ba_0.95Sm_0.05Ti_0.95Dy_0.05O₃(BSTDO) composites. To determine the ferrite and ferroelectric phases, the Rietveld refinement analysis is used. The excellent fit of experimental diffraction data is confirmed by the low values of reliability factors and the goodness of fit index, and so the crystal structure is perfect. Increasing the LNCZFO phase in the composites causes the formation of more ferrite grains and enhancement of magnetization values. The anisotropy field varies due to compressive stress created by a lattice mismatch between the BSTDO and LNCZFO phases. The dielectric peak shifts to higher temperatures as the ferrite phase increases, indicating that magnetoelectric interaction between the constituent phases exists in composites. At 100 kHz, the diffuseness exponent ranged from 1.01 to 1.79, indicating that a diffuse phase transition (DPT) occurred for some composites. As the ferrite content increases, the DPT effect decreases, resulting a narrower dielectric peak. The small polaron hopping mechanism is responsible for electrical conduction, which followed Jonscher's power law. The magnitude of the angular frequency exponent factor increases with frequency, indicating an increase in charge carrier mobility from long to short range.     

Erbium substituted nickel–cobalt spinel ferrite nanoparticles: Tailoring the structural,magnetic and electrical parameters

In this article, we have reported an effective, rapid as well as economical Er³⁺ substituted Ni_0.4Co_0.6Fe₂O₄ ferrite nanoparticles synthesized via surfactant-assisted co-precipitation route. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), dielectric properties, current-voltage (I–V) measurements, and vibrating sample magnetometry (VSM). XRD and FTIR confirmed the face-centered (FCC) spinel structure of all compositions of the synthesized spinel ferrite nanoparticles. The deviations in the lattice constant granted with the variation in size of the guest (Er³⁺) and host (Fe³⁺) cations. These ferrites were also subjected for electrical, magnetic and dielectric investigations. I–V measurements showed that resistivity values decreased from 6.20 × 10⁷ Ω cm to 0.03 × 10⁷ Ω cm with the increased Er³⁺ contents. Saturation magnetization increased from 35.99 to 39.95 emu/g. This high value of saturation magnetization suggested the possible utilization of such ferrites for practical applications such as microwave and recording devices fabrication. Interestingly, the magnetic and dielectric properties of nickel-cobalt ferrite nanoparticles showed ample improvement upon Er³⁺ substitution. The results clearly indicate the potential of Er⁺³ substituted spinel ferrite particles in various advanced technological devices fabrication.     

Structural,morphological, magnetic hysteresis and dielectric properties of cobalt substituted barium–lead hexagonal ferrites for technological applications

M-type, Ba_0.4Pb_0.6Fe_12-xCo_xO₁₉ (x = 0.00, 0.10, 0.20, 0.30, 0.40) hexaferrites, synthesized using citrate gel auto combustion method, and heated at 950 °C, 4 h for lossless applications. XRD analysis shows the development of the M-phase, along with PbM and hematite. The microstructural analysis reveals the stacking clusters of hexagonally shaped platelets. TEM image and SAED pattern of x = 0.3 composition shows polycrystalline nature and formed particles observed to fused with neighbouring particles. M − H loops of all samples reveal hard magnetic behaviour and possess multi-domain structure. The maximum saturation magnetization of 55.427 A m²/kg is observed in x = 0.10 composition and coercivity of prepared hexaferrites was found to vary from 0.058 T to 0.390 T. The cobalt substitution has a strong influence on the dielectric properties of prepared hexaferrites. The value of ac conductivity increases with cobalt substitution from x = 0.00 to x = 0.10, and followed by a reduction from x = 0.10 to x = 0.40. The same trend is observed for the dielectric constant. The low value of loss tangent for all compositions shows apt scope for lossless application.     

Morphological,structural, dielectric and electrical properties of PEO–ZnO nanodielectric films

The morphological, structural, dielectric and electrical properties of aqueous solution-cast prepared poly(ethylene oxide)–zinc oxide (PEO–ZnO) nanocomposite films have been investigated as a function of ZnO nanoparticle concentrations up to 5 wt%. Scanning electron microscopy (SEM) images of these films show that the morphology of pristine PEO aggregated spherulites changes into fluffy, voluminous and highly porous with dispersion of ZnO nanoparticles into the PEO matrix. X-ray diffraction (XRD) study confirms that the crystalline phase of PEO greatly reduces at 1 wt% ZnO, and it again increases gradually with further increase of ZnO concentration. The dielectric relaxation spectroscopy (DRS) over the frequency range 20 Hz–1 MHz reveals that the real part of complex dielectric permittivity at audio frequencies decreases non-linearly whereas it remains almost constant at radio frequencies for these polymeric nanocomposites. Dispersion of nanosize ZnO particles into the PEO matrix reduces the values of dielectric permittivity which also exhibits a correlation with the dispersivity of ZnO nanoparticles. The relaxation peaks observed in the dielectric loss tangent and electric modulus spectra reveal that the electrostatic interactions of nanoscale ZnO particles with the ethylene oxide functional dipolar group of PEO monomer units decrease the local chain segmental dynamics of the polymer. Real part of ac conductivity spectra of these films have been analyzed by power law fit over the audio and radio frequency regions, respectively, and the obtained dc conductivity values for these regions differ by more than two orders of magnitude. The temperature dependent relaxation time and dc conductivity values of the nanodielectric material obey the Arrhenius relation of activation energies and confirm a correlation between dc conductivity and PEO chain segmental motion which is exactly identical to the characteristics of solid polymer electrolytes. Results imply that these nanocomposite materials can serve as low permittivity flexible nanodielectric for radio frequency microelectronic devices and also as electrical insulator for audio frequency operating conventional devices in addition to their suitability in preparation of solid polymer electrolytes.     

Structural,dielectric and magnetic properties of Bi–Mn doped SmFeO3

We have studied the structural, magnetic, dielectric and impedance properties of the Sm_1-xBi_xFe_1-yMn_yO₃ [SmFeO₃ (SFO), Sm_0.9Bi_0.1FeO₃ (SBFO), Sm_0.9Bi_0.1Fe_0.9Mn_0.1O₃ (SBFMO)] polycrystalline samples synthesized by solid-state reaction method. Rietveld refinement of room temperature (RT) powder x-ray diffraction pattern confirms the orthorhombic crystal structure with Pnma/Pbnm space group. The average particle size of Bi doped and co-doped (Bi–Mn) samples determined from SEM analysis are 5.6 μm and 5.2 μm, respectively. Room temperature field-dependent magnetization increases, suggesting the presence of magnetic contribution due to the Rare earth-Fe ion interaction which persists even at RT. However, with co-doping of Bi and Mn, a decrease in magnetization is observed, which corresponds to the dilution of Fe³⁺-Fe³⁺ interactions due to the presence of Mn³⁺ ions. The observed values of magnetization at 90 kOe for Bi doped sample is (2.87 emu/g) approximately two times and for codoped (0.7 emu/g) sample is nearly half of that of pristine sample (1.51 emu/g). Dielectric measurements as a function of frequency/temperature and impedance analysis using equivalent circuit model reveal grain and grain boundary contributions of SBFO (at high temperature) and SBFMO (for all temperature) samples towards the electrical properties indicating the electrically heterogeneous nature of these samples. However, for SFO sample grain contribution is dominant. Observed value of dielectric constant varies from ~10³-10⁴ with Bi–Mn doping. The conduction mechanism of the studied samples has been explained by considering Jonscher power law. Arrhenius law fitting of AC conductivity data manifests two types of conduction mechanisms in these samples. The depressing nature of the semicircular arc observed in the Nyquist plot of all the samples indicates the presence of a non-Debye type of relaxation.     

Effects of amorphous silica nanoparticles and polymer blend compositions on the structural,thermal and dielectric properties of PEO–PMMA blend based polymer nanocomposites

The polymer nanocomposite (PNC) films consisted of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blend matrices dispersed with nanoparticles of amorphous silica (SiO₂) have been prepared by solution-cast method followed by melt-press technique. Effects of SiO₂ concentration (x?=?0, 1, 3 and 5 wt%) and PEO–PMMA blend compositional ratios (PEO:PMMA?=?75:25, 50:50, and 25:75 wt%) on the surface morphology, crystalline phase, polymer-polymer and polymer-nanoparticle interactions, melting phase transition temperature, dielectric permittivity, electrical conductivity, electric modulus and the impedance properties of the PNC films have been investigated. The crystalline phase of the PNC films decreases with the increase of PMMA contents which also vary anomalously with the increase of SiO₂ concentration in the films. The melting phase transition temperature and polymer-nanoparticle interactions significantly change with the variation in the compositional ratio of the blend polymers in the PNC films. It is observed that the effect of SiO₂ on the dielectric and electrical properties of these PNCs vary greatly with change in the compositional ratio of PEO and PMMA in the blends. The dielectric relaxation process of these films confirm that the polymers cooperative chain segmental dynamics becomes significantly slow when merely 1 wt% SiO₂ nanoparticles are dispersed in the polymer blend matrix.