Maxwell Wagner Type Interfacial Polarization Research Articles

Dielectric and electrocaloric properties of BCTZ composite with cobalt zinc ferrite nanoparticles

Dielectric and electrocaloric properties of a multiferroic composite constituted from Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCTZ) and Co0.4Zn0.6Fe2O4 (CZF), chosen for their closely related transition temperatures, are reported. Dielectric characteristics of the composites in the 1 kHz−10 MHz angular frequency range are described by two Cole-Cole relaxation models (domain wall and charge carrier) whereas for frequency <1 kHz, it is explained by Maxwell-Wagner type interfacial polarization using Jonscher power law. The effect of CZF phase on the dipolar mechanisms as a function of CZF mole fraction and the temperature are discussed. The electrocaloric property of the composites is estimated indirectly by Maxwell thermodynamic relation.

Study of CoCe0.05Fe1.95O4-polypyrrole composite for efficient electromagnetic interference shielding

The synthesis of nanocomposites with magnetic and microwave absorbing properties was achieved via sol-gel process merge with the self-combustion methodology. The X-ray diffraction results showed that nanocomposites consisted of a single spinel phase and no impurities were detected. The hysteresis loop showed the nanocomposites' ferromagnetic character. Measurements of saturation magnetization, alternating current susceptibility, cation distribution, and Curie temperature were taken to evaluate the magnetic properties. The permittivity (ε′, ε″) varied as a function of frequency in accordance with Maxwell-Wagner type interfacial polarization. The actual and fictitious components of microwave permeability showed a maximum at lower frequencies and decreased as frequency increased. Due to its superparamagnetic behavior, the composite has potential applications in shielding technologies.

Influence of the A-site cation on structural, morphological, magnetic, optical and transport properties of R2CoMnO6(R = Nd, Y, Ho and Er) double perovskite oxides

The A-site substituted double perovskite oxides (DPOs) have in the recent decades gained much attention due to their various interesting properties and possible applications. For this reason, R2CoMnO6 (R = Nd, Y, Ho, and Er) DPOs have been synthesized using the auto-combustion sol-gel method. X-ray diffraction analysis suggests the crystal structure, i.e., monoclinic for all under-investigated DPOs at room temperature (RT), consisting of space group P2 1 /n which is confirmed by Rietveld refinement. Crystallite size is calculated using Scherrer and Williamson-Hall methods, and it was found that the crystallite size decreased with decreasing ionic radii from 55–29 nm on average. The micrographs were obtained by using a field-emission scanning electron microscope (FE-SEM), which reveals an almost homogeneous distribution of grains throughout the surface of all DPOs. All observed infrared and Raman active phonon modes have been assigned to vibrations of atoms and groups of atoms consistent with the prediction of group theory. The intermediate band gap values (1.34–1.63 eV) determined by the Tauc relations suggest the semiconducting nature of these DPOs which makes them promising materials for photovoltaic applications. Dc electrical resistivity and dielectric measurements also suggest semiconducting behaviour above ambient temperature, which is attributed to a small polaron hopping conduction mechanism. The Maxwell-Wagner type interfacial polarization has described the nature of the frequency-dependent dielectric constants in these DPOs. The dielectric (ac) study also suggests the small polaron hopping conduction mechanism in all samples, which supports our findings in resistivity measurements.

Structural, Magnetic, and Electrical Properties of CoFe2O4 Nanostructures Synthesized Using Microwave-Assisted Hydrothermal Method.

Magnetic nanostructures of CoFe2O4 were synthesized via a microwave-assisted hydrothermal route. The prepared nanostructures were investigated using X-ray diffraction (XRD), field emission electron microscopy (FE-SEM), energy dispersive X-ray (EDX) spectroscopy, high-resolution transmission electron microscopy (HR-TEM), selective area electron diffraction (SAED) pattern, DC magnetization, and dielectric spectroscopy measurements. The crystal structure studied using HR-TEM, SAED, and XRD patterns revealed that the synthesized nanostructures had a single-phase nature and ruled out the possibility of any secondary phase. The lattice parameters and unit cell volume determined from the XRD data were found to be 8.4821 Å and 583.88 Å3. The average crystallite size (~7.0 nm) was determined using Scherrer's equation. The FE-SEM and TEM micrographs revealed that the prepared nanostructures had a spherical shape morphology. The EDX results showed that the major elements present in the samples were Co, Fe, and O. The magnetization (M) versus temperature (T) measurements specified that the CoFe2O4 nanostructures showed ferromagnetic ordering at room temperature. The blocking temperature (TB) determined using the M-T curve was found to be 315 K. The magnetic hysteresis (M-H) loop of the CoFe2O4 nanostructures recorded at different temperatures showed the ferromagnetic behavior of the CoFe2O4 nanostructures at temperatures of 200 K and 300 K, and a superparamagnetic behavior at 350 K. The dielectric spectroscopy studies revealed a dielectric constant (ε') and loss tangent (tanδ) decrease with the increase in the frequency, as well as demonstrating a normal dispersion behavior, which is due to the Maxwell-Wagner type of interfacial polarization. The values of ε' and tanδ were observed to increase with the increase in the temperature.

Comparison of Structural, dielectric and magnetic investigation of Cr3+ substituted Mg-Cu, Mg-Zn, and Mg-Ni ferrites system

• Studied the effect of Cr 3+ substitution on the structural, dielectric, and magnetic properties of Mg 0.5 M 0.5 Fe 1.5 Cr 0.5 O 4 (M = Cu, Zn, and Ni) ferrite system prepared by sol–gel method. • The XRD patterns showed a single spinel phase. • The magnetic saturation (M s ), magnetic moment (M r ), and Coercivity (H c ) is found to be the highest for the Cr substituted Mg-Ni ferrite system. • All the synthesized samples showed ferrimagnetic behavior. • Thus, the magnetic and structural properties of (Mg 0.5 M 0.5 Fe 1.5 Cr 0.5 O 4 (M = Cu, Zn, and Ni) NPs can be favorable for their potential use in high-density recording media applications. Effect of Cr 3+ substitution on the structural, dielectric, and magnetic properties of Mg 0.5 M 0.5 Fe 1.5 Cr 0.5 O 4 (M = Cu, Zn, and Ni) ferrite system prepared by sol–gel method. All ferrites prepared samples’ powder; X-ray diffraction patterns confirmed the formation of single-phase cubic spinel structures with Fd -3 m space group. It possesses a monophasic cubic-spinel lattice structure with an average crystallite size ranging from 25 to 44 nm. The lattice constant determined by XRD analysis falls between 8.497 Å and 8.392 Å. Furthermore, the crystallite size determined by XRD data is well matched with the particle size determined by scanning electron microscopy images. Using an LCR Meter, the dielectric parameters of the samples, such as dielectric constant ( ε ’) and dielectric loss tangent (tan δ ), were studied as a function of frequency in the range of 100 Hz to 5 MHz at room temperature. The dielectric constant and loss tangent among the samples show a normal dielectric behavior with a frequency which reveals that the dispersion is a result of the Maxwell-Wagner type interfacial polarization and hopping of electrons between the Fe 2+ and Fe 3+ ions. The hysteresis curve exhibits the particles are soft ferrimagnetic with maximum saturation magnetization, Ms = 38.55 emu/g due to Cr substituted Mg-Ni ferrite. The squareness ratios were discovered to be less than 0.5, indicating that our particles have a single-domain ferrimagnetic isotropic nature. Thus, the magnetic and structural properties of (Mg 0.5 M 0.5 Fe 1.5 Cr 0.5 O 4 (M = Cu, Zn, and Ni) NPs can be favorable for their potential use in high-density recording media applications.

Electrical impedance behaviour of carbon fibre reinforced cement-based sensors at different moisture contents

Carbon fibre reinforced cement-based sensors offer a potential low-cost and high-performance alternative to externally applied sensors for health monitoring of concrete structures. This paper focuses on the moisture dependence of bulk conductivity for carbon fibre reinforced cement-based sensors with fibre contents 0.1–1.5 vol%. Under two-point AC impedance spectroscopy at frequencies 1 Hz–10 MHz, the electrode polarization (EP) process, an electrical double layer polarization process (EDLP), and the bulk Maxwell-Wagner type interfacial polarization process (MWP) were identified. While reducing the saturation degree from 100 % to 0 %, the fractional change of bulk conductivity (FCS) underwent three different stages, which consists of a non-linear stage at 100–80 % saturation, a linear stage at 80–20 % saturation, and a final stage at 20–0 % saturation. The results gave insights into the stability of cement-based sensors under field conditions, and the underlying mechanisms of behaviour. From this, a route towards appropriate use of cement-based sensors in mechanical sensing and potentially moisture sensing without further external measures can be realised.

Enhanced performance of magnetoelectric voltage coefficient in giant magnetostrictive (Ni0.7Mg0.3Fe2O4)/piezoelectric (BaZr0.2Ti0.8O3) composites

The non-toxic lead-free multiferroic composite samples Ni0.7Mg0.3Fe2O4/BaZr0.2Ti0.8O3 were synthesized by using standard double sintering ceramic method. The composite samples are found to exhibit dielectric response, which might be associated with Maxwell-Wagner type interfacial polarization and Koop's phenomenological theory. The variation of DC conductivity with respect to temperature revealed the conduction of electrons i.e. due to the small polarons hopping mechanism. The synthesized ME composite samples show a representative magnetic hysteresis (M − H) loop type behaviour at room temperature. In a previous report, the response of ME voltage coefficient 4.262 mVcm-1.Oe was determined for (30%) Ni0.8Mg0.2Fe2O4 + (70%) BaZr0.2Ti0.8O3 composites at 5.0 kOe applied DC magnetic field. But in this report, we improved the ME voltage coefficient for the composition 50% (Ni0.7Mg0.3Fe2O4) + 50% (BaZr0.2Ti0.8O3) which is a lead-free ME composite with the massive ME voltage coefficient of 8.562 mV/cm.Oe was achieved. Hence, the estimated results can provide experimental guidance for the optimal design of high-performance magnetoelectric devices and render better support for the technological development in the field of magnetoelectricity.

Temperature-dependent electrical and magneto-dielectric properties of 0.7Bi0.99Nd0.01Fe0.99(Co, Ti)0.01O3-0.3CaTiO3 composite

0.7Bi0.99Nd0.01Fe0.99(Co, Ti)0.01O3-0.3CaTiO3 (BNFCTO-CaTO) composite was prepared by using sol-gel method. The structural formation was investigated using the XRD pattern, which confirms the presence of distorted rhombohedral structure with space group R3c and the superlattice orthorhombic crystal structure with space group Pbmn. The dielectric behavior of BNFCTO-CaTO has been studied within the frequency range of 100 Hz to 1 MHz from 300 K to 773 K. The sample shows dielectric dispersion in low frequency region that can be explained by Maxwell-Wagner type interfacial polarization. The temperature-dependent dielectric plot shows an anomaly near to magnetic transition temperature (TN) of BiFeO3 and shows relaxor behavior. Furthermore, BNFCTO-CaTO shows a strong magneto-dielectric coupling effect at room temperature.

Structural, dielectric, impedance and electric modulus analysis of Ni substituted copper spinel ferrites nanoparticles for microwave device applications

A series containing five samples of nickel substituted copper spinel ferrite (NixCu1-xFe2O4) nanoparticles with five different nickel concentrations varying as x = 0.00, 0.03, 0.06, 0.09, 0.12, fabricated with the aid of sol-gel auto-combustion technique. Through X-ray diffraction analysis, the structural properties of the compound were determined, which revealed that the prepared nanomaterials possess a spinel nature which was confirmed due to the existence of a secondary phase. The crystallite size was ascertained by applying the Scherrer formula, which was brought up in the range of 8–11 nm. The experimental parameters such as magnetic stirring speed, the molarity of reactants, synthesis temperature, the quantity of citric acid, and annealing were kept controlled. The substitution of nickel in copper spinel ferrite made a significant effect on the structural variables such as crystallite size stacking fault, lattice strain, micro-strain, dislocation density, bulk density, Impedance Analyzer (LCR meter) was used to get the dielectric properties in the frequency extended from 1 Hz to 20 MHz. From the obtained results it was depicted that the synthesized nanomaterials might be able to give response to the electromagnetic radiations, hence these can be usefully applied in microwave devices. Tangent loss and dielectric constant are varied due to Ni2+ content. Impedance loss shows the grain boundaries are dominant as a function of Ni2+ content. Inverse relation of AC frequency with the dielectric constant exposed the existence of Maxwell–Wagner type interfacial polarization. The various dielectric plots give awareness about the conducting grains and resistive grain boundaries that play a vital role in understanding the dielectric relaxation in the material. The ac conductivity is also determined due to Ni2+ content. From the observed electrical parameters, it can be propounded that the prepared nanocrystalline particles hold semiconducting nature and can be employed as a dielectric in low-frequency devices, and might be utilized as a conductor in high-frequency devices.

Iron oxide (Fe2O3) synthesized via solution-combustion technique with varying fuel-to-oxidizer ratio: FT-IR, XRD, optical and dielectric characterization

This study addresses the effect of fuel-to-oxidizer ratio (∅ =1.47, 1.57, 1.67, 1.77 and 1.87) on the structural, optical and dielectric properties of iron oxide nanoparticles synthesized through solution-combustion technique with glycine as the fuel. The synthesized samples were characterized using scanning electron microscopy, energy dispersive X-ray (EDX) spectroscopy, Fourier transform-infrared spectroscopy (FT-IR), ultraviolet–visible (UV-VIS) diffuse reflectance spectroscopy (DRS), X-ray powder diffraction (XRPD) with Rietveld refinement, thermogravimetric analysis (TGA) and frequency-dependent dielectric analysis. Electron micrographs show no change in morphology with respect to ∅. The EDX results revealed the existence of Fe and O. FT-IR confirmed the metal-oxygen (M − O) functional groups of iron oxides typically present near ∼ 570 and ∼ 520 cm−1. The synthesized samples showed typical reflectance spectrum of iron oxides during UV–Vis DRS analysis, where the maximum optical band gap of 1.80 eV was displayed by Fe2O3 with ∅ = 1.67. The diffraction peaks were indexed with two phases: α-Fe2O3 and γ-Fe2O3. It was observed that the γ-phase decreased as ∅ increased. Rietveld refinement showed that ∅ = 1.47 had γ-phase as the majority (96.46 wt%), while ∅ = 1.87 had α-phase as the majority (79.90 wt%). The average crystallite size of α-phase was found to be 44.72 nm, while that of the γ-phase was 27.53 nm. The real and imaginary parts of dielectric constant, dielectric tangent loss, electric modulus, impedance and ac conductivity with respect to varying frequency were studied. All the parameters display typical trends shown by Fe-based ceramics agreeing to the Maxwell-Wagner type of interfacial polarization. The modulus studies revealed that the samples show non-Debye type relaxations and it can be concluded that these materials are well suited for high-frequency applications.

Study of XRD, dielectric properties and DC electrical conductivity of Li-Zn-Al ferrite synthesized by sol–gel combustion method

A series of nanocrystalline aluminum (Al3+) doped Lithium-Zinc ferrites (LZA) having general chemical formula Li0.5(1- x )Zn x Fe2.5- y Al y -0.5 x O4 with x = 0.1 and y = 0.2 (S1C1), 0.4 (S1C2), 0.6 (S1C3) and 0.8 (S1C4) were synthesized by citrate sol-gel combustion method. The structural characterizations of the samples were carried out by X-Ray Diffraction (XRD) studies. Morphological investigations were performed using Scanning Electron and Transmission Electron Microscopies. XRD analysis confirmed the formation of single phase of the reported samples. All the samples crystallized in spinel cubic crystal structure with Fd-3m (227) space group. Crystallite size was estimated in the range of 19 nm to 21 nm using Scherrer formula. The variation of D.C. electrical conductivity as a function of temperature of as-prepared samples revealed the semiconducting nature. The dielectric constant (ε'), dielectric loss factor (ε") and the dielectric loss tangent (tan δ) were studied in the frequency range of 1 KHz to 1 MHz at room temperature by using LCR Meter. The values of dielectric constant, dielectric loss factor and dielectric loss tangent were found to decrease with addition of Al3+ content as well as with the increase in the frequency. The observed dielectric dispersion at lower frequency is attributed to Maxwell-Wagner type of interfacial polarization due to hopping of charge between Fe+2 and Fe+3. High value of resistivity (≈106 Ω-cm) and low value of dielectric constant and dielectric loss are the prime achievements of the present research work which make these investigated nanoferrites useful for the microwave devices.

Polyaniline–calcium titanate perovskite hybrid composites: Structural, morphological, dielectric and electric modulus analysis

This paper reports hybrid composites based on polyaniline (PANI) and calcium titanate (CaTiO3) perovskite as a nanofiller synthesized by in-situ polymerization technique. Their structure and morphology were investigated by X-ray diffraction analysis and scanning electron microscopy. The XRD analysis shows that the addition of CaTiO3 in polyaniline reduced the amorphous structure of polyaniline transforming it into semi-crystalline nature, which agrees well with the higher conductivity. Scanning electron microscopy of composites showed a more compact and homogenous structure with uniform distribution of CaTiO3 in the polymer matrix. Dielectric parameters such as dielectric constant, loss factor, and dielectric loss, real and imaginary parts of electric modulus were measured and evaluated as a function of frequency and temperature as well. The variation of dielectric properties and ac conductivity reveals that the dispersion is due to the Maxwell-Wagner type of interfacial polarization. The observed ac conductivity behavior of polyaniline in the presence of calcium titanate was discussed in the framework of Jonscher’s power law. The result showed that ac conductivity increases with the rise of the frequency of applied field and temperature analogous to the semiconducting behavior of composites. Temperature-dependent behavior of frequency exponent seems to obey correlated barrier hopping conduction mechanism. The relaxation behavior of the synthesized samples was analyzed by the electric field modulus and was found to decrease with temperature and CaTiO3 content and increase with frequency.

Transport properties in spinel ferrite/graphene oxide nanocomposites for electromagnetic shielding

Herein, (Co0.5Ni0.5)Cr0.3Fe1.7O4/graphene oxide nanocomposites were fabricated by ultrasonication technique, using pure spinel ferrite and graphene oxide synthesized by sol-gel method and modified Hummers' method, respectively. The effect of graphene incorporation with ferrite nanoparticles was studied by X-ray diffraction (XRD), electrical and dielectric measurements. XRD analysis revealed the spinel phase for the ferrite sample and confirmed the formation of graphene oxide. The crystallite size was found in the range of 37−43 nm and the porosity increased with the increase in the concentration of graphene oxide in the composites. The DC electrical resistivity of spinel ferrite was found equal to 3.83×109 Ω.cm and it substantially decreased with the increase in the percentage of graphene oxide at room temperature. The real and imaginary part of relative permittivity followed the Maxwell-Wagner type of interfacial polarization. AC conductivity confirmed the conduction by hopping mechanism and increased on increasing the GO content. The coupling of magnetic ferrite with graphene oxide tunes the magneto-electrical properties for potential applications at high frequencies.

Low-frequency carrier kinetics in triple cation perovskite solar cells probed by impedance and modulus spectroscopy

Organometallic halide perovskites-based solar cells have emerged as next-generation photovoltaic technology. However, many of its intriguing optoelectronic properties at low frequency are highly debated. Here, we investigate the low-frequency carrier kinetics of the state-of-the-art triple cation perovskite Cs0.06FA0.79MA0.15Pb(I0.85Br0.15)3 solar cells using bias-dependent impedance and modulus spectroscopy under dark and illumination conditions. We observe a strong dependence of dielectric permittivity on frequency in 1 Hz to 1 MHz region with a dielectric relaxation, which is observed to follow the Maxwell-Wagner type interfacial polarization possibly originating from the grain boundary/ionic defects. Furthermore, correlating the impedance and modulus spectra reveals the localized charge carrier relaxation in this triple cation device from which we obtain a phenomenological picture of the hopping process and developing an understanding of the charge carrier kinetics in these high-efficiency perovskite photovoltaics.

Optical studies and dielectric response of [DMA]2MCl4 (M = Zn and Co) and [DMA]2ZnBr4.

[DMA]2ZnCl4, [DMA]2CoCl4 and [DMA]2ZnBr4 crystallized in the monoclinic system, in the P21/n, P21/n and P21/c space groups, respectively. The optical properties of [DMA]2MCl4 (M = Zn and Co) and [DMA]2ZnBr4 were studied using ultraviolet-visible (UV-Vis) spectroscopy in the range of 200–800 nm. The Tauc model was used to determine the band gap energy of each hybrid compound. The calculated values of the direct and indirect band gaps (Egd, Egi) for all samples were found to be in the range of 1.91 eV to 4.29 eV for [DMA]2ZnCl4, 4.76 eV to 5.34 eV for [DMA]2ZnBr4 and 1.77 eV to 3.84 eV for [DMA]2CoCl4. The Urbach energy (Eu), extinction coefficient (k) and refractive index (n) of each compound was calculated. On the other hand, the dispersion of (n) is discussed in terms of the single oscillator Wemple–DiDomenico model. The single oscillator energy (E0), the dispersion energy (Ed), and both the real εr and imaginary parts εi of the dielectric permittivity were estimated. The variation of optical conductivity with the incident photon energy has also been studied. We employed impedance spectroscopy to thoroughly investigate the dipolar dynamics in the prepared materials. The evolution of the dielectric loss, as a function of frequency, showed a distribution of relaxation times, which probably could be of a Maxwell–Wagner type interfacial polarization relaxation, possibly attributed to grain boundary effects or blocking at the contacts. In fact, the current work opens an efficient path to high quality organic–inorganic halide perovskites with good optical properties, which makes them suitable for application in nonlinear optoelectronic devices.

Dielectric and multiferroic properties of 0.8BaTiO3-0.2BiAlO3/Co0.8Cu0.2Fe2O4 composite ceramics

0.8BaTiO3-0.2BiAlO3/Co0.8Cu0.2Fe2O4 composite ceramics with a molar ratio of 6:1 were prepared by hydrothermal method combined with solid-state method, and effects of the sintered temperature and time on the microstructure, dielectric, ferroelectric, and magnetic properties were investigated. XRD result indicates that the composite ceramics show bi-phase structure, and the secondary phase is indexed as Ba3Fe32O51, and proves that we can change the sintered temperature and sintered time to adjust the crystallinity of the composite ceramics and the concentration of impurities. The surface is relatively uniform except for few pores, and the grain size of ferromagnetic phase increases as the function of temperature and time. The dielectric dispersion of composite ceramics is obtained, and the character comes from inhomogeneous structure and Maxwell–Wagner type interfacial polarization. The two peaks of dielectric constant are obtained, and the composite ceramics (1200 °C/4 h) show high dielectric constant and loss due to the interface effect, and this result is confirmed by the AC conductively. The relaxation result is different from the ferroelectric phase, and this may be caused by the thermally activated, the grain size of ferroelectric phase, impurity phase, pore, and defect of composite ceramics. The ferromagnetic result refers that the sintered temperature has obvious influence on the coercive force by the grain size and magnetic anisotropy.

Interplay between the ferrimagnetic and ferroelectric phases on the large magnetoelectric coupling of xLi0.1Ni0.2Mn0.6Fe2.1O4–(1 − x)Bi0.8Dy0.2FeO3 composites

The multiferroic composites of ferromagnetic Li0.1Ni0.2Mn0.6Fe2.1O4 (LNMFO) and ferroelectric Bi0.8Dy0.2FeO3 (BDFO) with the general formula xLi0.1Ni0.2Mn0.6Fe2.1O4–(1 − x) Bi0.8Dy0.2FeO3 have been prepared by the solid-state reaction route. The XRD analysis has ensured that the composites are composed of a mixture of cubic spinel LNMFO and orthorhombic perovskite BDFO phases. Field Emission Scanning Electron Microscope is used to investigate the surface morphology of the studied compositions. The average grain size of the composites has reduced slightly with the enhancement of ferrite part up to 20% and after that it has increased again. The real part of the initial permeability $$(\mu^{\prime}_{i} )$$ was found to be increasing with ferrite content. The real part of dielectric constant $$(\varepsilon^{\prime})$$ exhibits dispersion at low-frequency region because of Maxwell–Wagner type interfacial polarization. The complex impedance spectroscopy has been used to separate the grain and grain boundary contribution to the total resistance. Existence of the hopping conduction mechanism has been confirmed through the study of electric modulus. The hysteresis loops of the compositions are studied to confirm the response of ferrite part to the applied magnetic field. The magnetoelectric voltage coefficients of the composites have reduced with the ferrite part. The maximum magnetoelectric voltage coefficient is nearly 158 × 103 Vm−1 T−1 for the 0.1LNMFO–0.9BDFO composite, which is about three times of the reported value compared to other composites.

Study of structural and electrical properties along with magnetic properties of Ni0.5−xMgxCu0.2Cd0.3Fe2O4 nanoferrites synthesized by employing sol–gel auto-combustion method

The mixed ferrite sample Ni0.5−xMgxCu0.2Cd0.3Fe2O4 (0.0 ≤ x ≤ 0.5, in the steps 0.1) has been synthesized employing sol–gel auto-combustion process. From XRD diffractograms, it has been observed the simple cubic spinel structure of the ferrite samples. With the substitution of Mg ion, both the experimental and theoretical lattice constant increased. For x = 0.0, the value of experimental lattice constant has been found 8.459 A, which increases to a value 8.490 A for x = 0.5. The surface morphology has been studied by FESEM images. Besides, the chemical composition and the elemental distribution of the sample have been revealed by EDS study. From the vibration band, the formation of spinel ferrite has been confirmed from the FT-IR spectra. It is seen that the samples exhibit ferrimagnetic behavior at room temperature, which has been shown by the magnetic measurement done by VSM. Dielectric constant, dielectric loss tangent, ac conductivity, and impedance Spectroscopy have been analyzed within the range 20 Hz–15 MHz. In the lower frequency region, a typical dielectric dispersion based on Maxwell–Wagner type interfacial polarization has been observed. Dielectric loss tangent exhibits an analogous sort of behavior as that of dielectric constant. The grain and grain boundary effect on electric properties have been studied from the complex impedance analysis. It has been seen that both the grain resistance and grain boundary resistance increase with the substitution of Mg2+ content. A rise in ac conductivity has been observed with the increase in frequency.

The mechanical and dielectric properties of polypropylene reinforced with BiSr2CaCu2O6.5 ceramic

In this work, novel polypropylene/BiSr2CaCu2O6.5 (PP/Bi-1212) thick film composites having ceramic content varying between 0.5% and 6% were prepared to enhance both the dielectric and mechanical properties of PP. The surface morphologies of the samples were determined by scanning electron microscope. The crystallinity change in PP due to Bi-1212 filler was also described by differential scanning calorimetry analysis. The highest crystallinity degree was observed for the PP/0.5% Bi-1212 composite. The tensile parameters such as Young’s modulus, tensile strength, percentage strain at break and energy at the break of the samples were also determined by analyzing the stress–strain curves. The highest tensile strength, stiffness, percentage strain at break and energy to break values were observed for the PP/(0.5%Bi-1212 composite. The complex electrical properties of the samples were also investigated by impedance spectroscopy measurements performed at room temperature between 10 Hz and 40 MHz frequency. The complex impedance, permittivity, ac conductivity and electrical modulus analyses revealed that 1% Bi-1212 additive changed the frequency dependence of the real and imaginary parts of the complex permittivity considerably and increased the dc conductivity of PP by approximately 0.2 million times. In this context, the percolation concentration for the conductivity of PP can be determined as approximately 1.0 wt% Bi-1212 filler. The electrical modulus analysis also indicated that the higher filler additive led the Maxwell–Wagner-type interfacial polarization in PP. Ultimately, it has been suggested that 3.0% of Bi-1212 added PP composite can be used as a dielectric material for decoupling capacitor applications.

Dielectric and ferroelectric properties of CoCr2O4 nanoceramics

CoCr2O4 nanoceramics are prepared by sol–gel auto combustion method. Synchrotron X-ray diffraction analysis affirms the single-phase pristine cubic structure with space group [Formula: see text]. Debye–Scherrer method estimates the crystallite size of main intense peak to be [Formula: see text][Formula: see text]nm. Prominent bands obtained in infrared spectra at 448 and 599[Formula: see text]cm[Formula: see text] are due to metal–oxygen stretching bond present at tetrahedral and octahedral sites. Dielectric parameters decrease as frequency increases from [Formula: see text] to [Formula: see text][Formula: see text]Hz that can be interpreted by Maxwell–Wagner-type interfacial polarization. Complex impedance spectra (Nyquist plot) reveal arc like behavior, which is mainly due to intergrain (grain boundary) resistance that also exhibits conducting nature of the nanoceramics. Weak ferroelectricity is mainly associated with the partial reversal of the polarization. Leakage current behavior follows the Ohmic and Child square law. Electron conduction process was interpreted by space-charge limited current (SCLC) mechanism. Leakage current behavior observed in cobalt chromite nanoceramics is mainly attributed to the oxygen vacancies.