Synthesis,transport and dielectric properties of polyaniline/Co<Subscript>3</Subscript>O<Subscript>4</Subscript> composites

Conducting polyaniline/cobaltous oxide composites have been synthesized using in situ deposition technique by placing fine graded/cobaltous oxide in polymerization mixture of aniline. The a.c. conductivity and dielectric properties are studied by sandwiching the pellets of these composites between the silver electrodes. It is observed that the values of conductivities increase up to 30 wt% of cobaltous oxide in polyaniline and decrease thereafter. Initial increment in conductivity is due to extended chain length of polyaniline where polarons possess sufficient energy to hop between favourable sites. Beyond 30 wt% of cobaltous oxide in polyaniline, blocking of charge carriers takes place reducing the conductivity values. It can be noted that the value of dielectric constant increases up to 10 wt% of cobaltous oxide. Thereafter, it decreases up to 30 wt% of cobaltous oxide and again increases up to 40 wt% of cobaltous oxide and decreases thereafter. The observed behaviour is attributed to the variation of a.c. conductivity. And it is observed that the dielectric loss increases up to 10 wt% of cobaltous oxide in polyaniline, decreases to a lower value of 20 wt% of cobaltous oxide and increases to 35 wt% and thereafter decreases. These values go in accordance with the values of dielectric constant. The results obtained for these composites are of greater scientific and technological importance.     

Dielectric,humidity behavior and conductivity mechanism of Mn<Subscript>0.2</Subscript>Ni<Subscript>0.3</Subscript>Zn<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> ferrite prepared by co-precipitation method

Mn–Ni–Zn ferrite with the chemical formula of Mn_0.2Ni_0.3Zn_0.5Fe₂O₄ was prepared by co-precipitation method. The X-ray diffraction (XRD) results show that the prepared sample crystallizes in the cubic spinel structure with the space group of Fm3m. The morphological analysis of the sample was investigated by scanning electron microscopy (SEM). The dielectric properties of Mn_0.2Ni_0.3Zn_0.5Fe₂O₄ ferrite were studied in a frequency range from 20 Hz to 10 MHz and at a temperature range from 293 to 733 K. The dielectric constant decreases with the increasing frequency for all the temperature values chosen. The AC conductivity mechanism was found the small polaron type of conductivity, and in addition to that, the DC conductivity can be explained by Arrhenius type conductivity. According to the dielectric results, relaxation process fits Cole–Cole model. Finally, the effect of the relative humidity upon the impedance of the sample was discussed for a frequency range between 20 Hz and 10 MHz. It is found that the impedance values decrease almost linearly with the increasing % RH (relative humidity) values at low frequencies, while the impedance of the sample is independent of % RH at high frequencies.     

Synthesis,structure, and magnetic properties of rare-earth-doped Ni<Subscript>0.75</Subscript>Zn<Subscript>0.25</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nickel zinc ferrite

We have developed processes for the synthesis of Ni_0.75Zn_0.25Fe_2–xLn_xO₄ ferrite solid solutions with the spinel structure and investigated the effect of the rare-earth elements Nd, Gd, Yb, and Lu on the chemical composition, extent, lattice parameters, and magnetic properties of the solid solutions. The results demonstrate that rare-earth solubility in the parent spinel reaches ≈2.5 at %, which leads to changes in the magnetic characteristics of the material, in particular in its saturation magnetization M_s, T_C, and coercive force H_c.     

Piezoelectric and magnetic properties of PZT-(Ni<Subscript>0.284</Subscript>Zn<Subscript>0.549</Subscript>Cu<Subscript>0.183</Subscript>)Fe<Subscript>1.984</Subscript>O<Subscript>4</Subscript> composites

The piezoelectric/piezomagnetic composite, PZT/Ni_0.284Zn_0.549Cu_0.183Fe_1.984O₄, was fabricated by the mixed oxide method. The phase assemblage, piezoelectric strain constant and saturation magnetization were investigated. The results indicate that the PZT phase is compatible with Ni_0.284Zn_0.549Cu_0.183Fe_1.984O₄ phase, and dense diphasic ceramic composites were obtained. It is found that piezoelectric strain constant decreases exponentially as the amount of doped piezomagnetic materials in the composite increases. Correspondingly, saturation magnetization of the composite also decreases with the increasing weight fraction of piezoelectric materials. Three reasons cause the results. First, the grain growth of piezomagnetic phase at the co-sintering temperature reduces grain size and continuity of the piezoelectric phase. Second, the pore size and porosity in composite increase dramatically with increasing amount of piezomagnetic phase. Third, the low resistivity of the composite prevents the poling process and reduces the piezoelectric strain constant. The tailoring of microstructure to achieve a high performance piezoelectric/piezomagnetic composite is proposed based on the analysis.     

Structural,optical spectroscopy,optical conductivity and dielectric properties of BaTi<Subscript>0.5</Subscript>(Fe<Subscript>0.33</Subscript>W<Subscript>0.17</Subscript>)O<Subscript>3</Subscript> perovskite ceramic

Fe and W co-substituted BaTiO₃ perovskite ceramics, compositional formula BaTi_0.5(Fe_0.33W_0.17)O₃, were synthesized by the standard solid-state reaction method and studied by X-ray diffraction, scanning electron microscopy and spectroscopy ellipsometry. The prepared sample remains as double phases with the perovskite structure. The structure refinement of BaTi_0.5(Fe_0.33W_0.17)O ₃ sample was performed in the cubic double and hexagonal setting of the \(\text {Fm}\boldsymbol {\bar {{3}}\mathrm {m}}\) and P6 ₃ /mmc space groups. Spectral dependence of optical parameters; real and imaginary parts of the dielectric function, refractive index, extinction coefficient and absorption coefficient were carried out in the range between 1.4 and 4.96 eV by using the ellipsometry experiments. Direct bandgap energy of 4.36 eV was found from the analysis of absorption coefficient vs. photon energy. In addition, the oscillator energy, dispersion energy and zero-frequency refractive index values were found from the analysis of the experimental data using Wemple–DiDomenico single-effective-oscillator model.     

Complex permittivity and electromagnetic interference shielding properties of Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript>/polyaniline composites

Ti₃SiC₂/insulating polyaniline (Ti₃SiC₂/PANI) composites were prepared by solution blending and subsequently by hot-pressing process. The dielectric permittivity and electromagnetic interference (EMI) shielding effectiveness (SE) of the composites were determined in the frequency range of 8.2–12.4 GHz (X-band). Both real and imaginary permittivities increase with the increasing Ti₃SiC₂ content, and which are attributed to the enhanced displacement current and conduction current. The EMI SE of the composites can be greatly improved by addition of Ti₃SiC₂ filler, which may be ascribed to the increase of electrical conductivity of the composites. It is also found that the reflection of electromagnetic radiation is a dominant mechanism for EMI shielding of the composite. An average EMI SE of 23 dB can be achieved in the X-band range for the composite with 25 wt% Ti₃SiC₂ content, which shows the potential of the Ti₃SiC₂/PANI composites as EMI shielding materials for commercial applications.     

Synthesis and characterization of magnetic and microwave absorbing properties in polycrystalline cobalt zinc ferrite (Co<Subscript>0.5</Subscript>Zn<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>) composite

In this research work, magnetic and microwave absorption loss and other response characteristics in cobalt zinc ferrite composite has been studied. Cobalt zinc ferrite with the composition of Co_0.5Zn_0.5Fe₂O₄ was prepared via high energy ball milling followed by sintering. Phase characteristics of the as-prepared sample by using XRD analysis shows evidently that a high crystalline ferrite has been formed with the assists of thermal energy by sintering at 1250 °C which subsequently changes the magnetic properties of the ferrite. A high magnetic permeability and losses was obtained from ferrite with zinc content. Zn substitution into cobalt ferrite has altered the cation distribution between A and B sites in spinel ferrite which contributed to higher magnetic properties. Specifically, Co_0.5Zn_0.5Fe₂O₄ provides electromagnetic wave absorption characteristics. It was found that cobalt zinc ferrite sample is highly potential for microwave absorber which showed the highest reflection loss (RL) value of ??24.5 dB at 8.6 GHz. This material can potentially minimize EMI interferences in the measured frequency range, and was therefore used as fillers in the prepared composite that is applied for microwave absorbing material.     

Electrical properties of Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Mn<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> + BaTiO<Subscript>3</Subscript> ME composites

Polycrystalline samples of mixed composites of Ni_0.93Co_0.02Mn_0.05Fe₂O₄ + BaTiO₃ were prepared by conventional double sintering ceramic method. The phase analysis was carried out by using X-ray diffraction technique. Variation of dc resistivity and thermo emf was studied as a function of temperature. AC conductivity (σ_ac) was investigated in the frequency range 100 Hz–1 MHz. The loss tangent (tan δ) measurements conclude that the conduction mechanism in these samples is due to small polaron hopping. The magnetoelectric conversion factor, i.e. dc(ME) _H was studied as a function of intensity of magnetic field and the maximum value 407 μV/cm/Oe was observed at a field of 0.8 kOe in a composite with 85% BaTiO₃ and 15% Ni_0.93Co_0.02Mn_0.05Fe₂O₄ phase.     

Hierarchical structures based on Li<Subscript>0.35</Subscript>Zn<Subscript>0.3</Subscript>Fe<Subscript>2.35</Subscript>O<Subscript>4</Subscript>/polyaniline nanocomposites: synthesis and excellent microwave absorption properties

For the first time, the hierarchical structures of Li_0.35Zn_0.3Fe_2.35O₄(LZFO)/polyaniline nanocomposites were successfully synthesized by interfacial polymerization. Firstly, the LZFO particles were prepared by the sol–gel method, and subsequently the PANI nanorods, composed of nanoneedle-like PANI, were grafted on the surface of the LZFO. A novel microtopography, urchin-like, of LZFO/PANI was prepared by a simple, efficient and controllable two-step method. The crystal structure, chemical bonding states and morphology of samples were characterized by means of Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Scanning and Transmission electron microscopy (SEM/TEM). The bandwidth of reflection loss exceeds 10 dB in the frequency was 5.56 GHz (3.36–8.48, 10.32–10.76 GHz), and the maximum reflection loss can reach ??49.4 dB at 4.96 GHz with the thickness of 5.1 mm. The enhanced microwave absorption properties of LZFO/PANI nanocomposites are mainly ascribed to the multi-level structure and the improved impedance matching, and make it a potential candidate for microwave absorption materials.     

Synthesis and microwave absorption property of ternary composites: polyaniline/CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/Ba<Subscript>3</Subscript>Co<Subscript>2</Subscript>Fe<Subscript>24</Subscript>O<Subscript>41</Subscript>

Polyaniline (PANI)/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite was prepared by an in-situ polymerization method. The phase structure, morphology and magnetic properties of the as-prepared PANI/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite were characterized by XRD, FT-IR, SEM, TEM, and VSM, respectively. The microwave absorption properties of the composite were investigated by using a vector network analyzer in the 2–18 GHz frequency range. The results show that the maximum reflection loss value of the PANI/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite reaches ?30.5 dB at 10.5 GHz with a thickness of 3 mm and the bandwidth of reflection loss below ?10 dB reaches up to 1.2 GHz. The excellent microwave absorption properties of the as-prepared PANI/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite due to the enhanced impedance match between dielectric loss and magnetic loss.     

Dielectric and ferromagnetic properties of BaTiO<Subscript>3</Subscript>/Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Cu<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> composites

xBaTiO₃ + (1 − x)Ni_0.93Co_0.02Cu_0.05Fe₂O₄ (x = 0.5, 0.6, 0.7, 0.8) composites with ferroelectric–ferromagnetic characteristics were synthesized by the ceramic sintering technique. The presence of constituent phases in the composites was confirmed by X-ray diffraction studies. The average grain size was calculated by using a scanning electron micrograph. The dielectric characteristics were studied in the 100 kHz to 15 MHz. The dielectric constant changed higher with ferroelectric content increasing; and it was constant in this frequency range. The relation of dielectric constant with temperature was researched at 1, 10, 100 kHz. The Curie temperature would be higher with frequency increasing. The hysteresis behavior was studied to understand the magnetic properties such as saturation magnetization (M _s). The composites were a typical soft magnetic character with low coercive force. Both the ferroelectric and ferromagnetic phases preserve their basic properties in the bulk composite, thus these composites are good candidates as magnetoelectric materials.     

Synthesis and excellent microwave absorption property of polyaniline nanorods coated Li<Subscript>0.435</Subscript>Zn<Subscript>0.195</Subscript>Fe<Subscript>2.37</Subscript>O<Subscript>4</Subscript> nanocomposites

In this work, Li_0.435Zn_0.195Fe_2.37O₄ (LZFO) was firstly prepared by the sol–gel process, and then core–shell polyaniline (PANI) nanorods/LZFO composites were successfully synthesized by interfacial polymerization. The structures and morphologies of samples were characterized by means of X-ray diffraction, Fourier transform infrared spectra, and scanning electron microscopy. The average size of the pure ferrites was about 0.75 μm and the size distribution was 0.3–1.0 μm. The results indicated that the composites with different morphologies and structures resulted in different electromagnetic properties. The electromagnetic absorption test demonstrated that the PANI nanorods/LZFO possessed the best absorption property. The value of the minimum reflection loss was ?51.1 dB at 9.86 GHz, and the absorption bandwidth exceeding ?10 dB was 2.3 GHz (from 3.7 to 6 GHz) and 2 GHz (from 15.7 to 17.7 GHz). The excellent electromagnetic wave absorption properties of the nanocomposites were attributed to the improved impedance matching and the enhanced interfacial effects.     

Structural,electrical and magneto-electric characteristics of complex multiferroic perovskite Bi<Subscript>0.5</Subscript>Pb<Subscript>0.5</Subscript>Fe<Subscript>0.5</Subscript>Ce<Subscript>0.5</Subscript>O<Subscript>3</Subscript>

The polycrystalline sample of bismuth based-complex multiferroic of a composition Bi_0.5Pb_0.5Fe_0.5Ce_0.5O₃ was prepared by a high-temperature solid-state reaction technique (calcinations temperature = 900 °C, sintering temperature = 960 °C, time = 4 h). Preliminary structural analysis using XRD data exhibits the formation of a single-phase compound. Studies of surface morphology of the ceramic sample of the compound, recorded at room temperature using a scanning electron microscope, show uniform distribution of grains of different size with few voids. Detailed studies of dielectric properties (ε_r, tan δ) supported the existence of multiferroic properties in the above complex system. The analysis of impedance parameters, recorded in a wide frequency (1 kHz–1 MHz) and temperature (room temperature to 450 °C) range of the material provide better understanding of (a) role of grains and grain boundaries in resistive and capacitative characteristics, (c) structure-properties relationship and (b) type of relaxation process occurred in the material. Study of temperature dependence of dc conductivity of the compound shows the existence of negative temperature coefficient of resistance in it. The nature of variation of ac conductivity with temperature of the material follows the Josher’s universal power law. Study of magneto-electric characteristics of the sample at room temperature has provided many useful and new data on magneto-electric coupling coefficient of different orders.     

An efficientfficient,controllable and facile two-step synthesis strategy: Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@RGO composites with various Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles and their supercapacitance properties

An efficient,controllable,and facile two-step synthetic strategy to prepare graphene-based nanocomposites is proposed.A series of Fe3O4-decorated reduced graphene oxide (Fe3O4@RGO) nanocomposites incorporating Fe3O4 nanocrystals of various sizes were prepared by an ethanothermal method using graphene oxide (GO) and monodisperse Fe3O4 nanocrystals with diameters ranging from 4 to 10 nm.The morphologies and microstructures of the as-prepared composites were characterized by X-ray diffraction,Raman spectroscopy,nitrogen adsorption measurements,and transmission electron microscopy.The results show that GO can be reduced to graphene during the ethanothermal process,and that the Fe3O4 nanocrystals are well dispersed on the graphene sheets generated in the process.The analysis of the electrochemical properties of the Fe3O4@RGO materials shows that nanocomposites prepared with Fe3O4 nanocrystals of different sizes exhibit different electrochemical performances.Among all samples,Fe3O4@RGO prepared with Fe3O4 nanocrystals of 6 nm diameter possessed the highest specific capacitance of 481 F/g at 1 A/g,highlighting the excellent capability of this material.This work illustrates a promising route to develop graphene-based nanocomposite materials with a wide range of potential applications.     

Synthesis and microwave absorption properties of sandwich-type CNTs/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/RGO composite with Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> as a bridge

A novel sandwich-type CNTs/Fe₃O₄/RGO composite with Fe₃O₄ as a bridge was successfully prepared through a simple solvent-thermal and ultrasonic method. The structure and morphology of the composite have been characterized by Fourier-transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. This new structure can effectively prevent the agglomeration of GO and the combination of CNTs/Fe₃O₄ and RGO shows a strong reflection loss (R_L) (?50 dB) at 8.7 GHz with absorber thickness of 2.5 mm. Moreover, compared with CNTs/Fe₃O₄/GO composite, it is found that the thermal treating process is beneficial to enhance the microwave absorption properties, which may be attributed to high conductivity of RGO. On this basis, the microwave absorbing mechanism is systematically discussed. All the data show that the CNTs/Fe₃O₄/RGO composite exhibits excellent microwave absorption properties with light density and is expected to have potential applications in microwave absorption.     

Structural,Conductivity, and Dielectric Properties of Co<Subscript>0.5</Subscript>Mg<Subscript>0.5</Subscript>La<Subscript>0.1</Subscript>Fe<Subscript>1.9</Subscript>O<Subscript>4</Subscript> Ferrite Nanoparticles

The ferrite-based Co_0.5Mg_0.5La_0.1Fe_1.9O₄ nanoparticle system has been synthesized by using the chemical co-precipitation technique. XRD and SEM were used for the structural and morphological characterization of the nanoparticles. The XRD analysis of the synthesized samples confirmed the formation of the single-phase cubic spinel phase without any impurity or secondary phases, and the average crystallite size and lattice parameters were found as 11.89 nm and 8.376 nm, respectively. The cation distribution obtained is found as (Mg_0.19Fe_0.81)_A(Mg_0.31Fe_1.09Co_0.5La_0.1)_BO₄ from Rietveld refinement. The dielectric properties of the sample have been investigated in the frequency range of 20 Hz to 1 MHz. The DC and AC conductivity results obtained from the experiments are explained by the Verwey and correlated barrier hopping (CBH) models, respectively. The optical band gap energy of the sample is found as 0.24 eV. The results denoted the semiconductor nature of the sample, and the sample is a good candidate for applications in high-frequency transformers used for different purposes in the electronics industry.     

Removal and reuse of Ag nanoparticles by magnetic polyaniline/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanofibers

For the treatment of wastewater containing Ag nanoparticles (NPs), PANI/Fe₃O₄ nanofibers were firstly prepared by a novel self-assemble. And then, the efficiency for the removal of Ag NPs from wastewater was investigated. The magnetic performance of PANI/Fe₃O₄ nanofibers could be optimized by adjusting the pH of the self-assemblied system. Under pH of 3, the as-prepared nanofibers exhibited the highest magnetism and also displayed good efficiency (>?12 mg g^?1) for the removal of Ag NPs. Importantly, the resulted product (PANI/Fe₃O₄/Ag composite) could act as a catalysis for cleaning durable pollutant, 4-nitrophenol. After 10 cycles, only slight decrease in rate constant was found, indicating excellent reusability. Those approaches provide a new way to merge the recovery of Ag NPs as pollutants and reuse of recovered Ag NPs as recyclable material for environmental remediation.     

Study of structural,morphological and magnetic properties of Ba<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>Fe<Subscript>12</Subscript>O<Subscript>19</Subscript>

Single-phase barium Strontium hexaferrite (Ba_0.5Sr_0.5Fe₁₂O₁₉—BSF) was synthesized by sol–gel method using metal nitrates as source and d-Fructose as a fuel. The phase formation, surface morphology and magnetic properties of the samples were analyzed by X-ray Diffraction, High-resolution Scanning Electron Microscope (HR-SEM) and Vibrating Sample Magnetometer (VSM). X-ray analysis indicates that the sintered samples were remained in hexagonal structure. The densities of the sintered samples at 1,150 °C were found to be 93% of theoretical density. HR-SEM and VSM studies reveal that the sintered samples were resulted in hexagonal structure with good magnetic properties. The average diagonal of the grains varies from 0.95 to 1.7 μm. The thermal treatment effects the growth of the hexagonal grains of ferrites.     

Fast microwave synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Ag magnetic nanoparticles using Fe<Superscript>2+</Superscript> as precursor

A simple and quick microwave method to prepare high performance magnetite nanoparticles (Fe₃O₄ NPs) directly from Fe has been developed. The as-prepared Fe₃O₄ NPs product was fully characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The results show that the as-prepared Fe₃O₄ NPs are quite monodisperse with an average core size of 80 × 5 nm. The microwave synthesis technique can be easily modified to prepare Fe₃O₄/Ag NPs and these NPs possess good magnetic properties. The formation mechanisms of the NPs are also discussed. Our proposed synthesis procedure is quick and simple, and shows potential for large-scale production and applications for catalysis and biomedical/biological uses.     

Local amorphization of atomic structure in Mg<Subscript>0.54</Subscript>Zn<Subscript>0.46</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> ferrites

The structure of Mg_0.54Zn_0.46Fe₂O₄ ferrites has been studied using x-ray diffraction techniques. It is established that high-temperature annealing (T = 1280°C, τ = 0.5–8.0 h) leads to a change in the crystal structure of samples, which is accompanied by their local amorphization.