Imaginary Part Of Impedance Research Articles

Room temperature ac conductivity, dielectric properties and impedance analysis of polypyrrole-zinc cobalt oxide (PPy/ZCO) composites

Zinc-cobalt oxide nanoparticles were fabricated by hydrothermal method. The polypyrrole and zinc cobalt oxide (PPy/ZCO) composites were synthesized by using in-situ chemical polymerization method. These composites were characterized by x-ray diffraction (XRD) which confirmed the crystalline nature of the PPy/ZCO composites. The scanning electron microscopy and energy dispersive x-ray diffraction (EDX) confirmed the spherical structured particles of composites and the chemical composition, respectively. Electrical characterizations of PPy/ZCO composites were analyzed as a function of ZCO concentration in the frequency range of 102–106 Hz. The alternating current (ac) conductivity versus frequency graph for PPy/ZCO composites showed a direct current (dc) plateau in the frequency range of 102–104 Hz, indicating an isolated network within the composites. At the higher frequencies, there was an increase in ac conductivity obeying the universal dynamic response (UDR). The UDR suggested that the conduction in the PPy/ZCO composites was due to hopping along the polymer chains due to filler nanoparticles. The nature of response of real and imaginary part of impedance (Nyquist plot) revealed that the conduction has attribution from the effects of grains and grain boundaries.

Co effect on the structural, chemical and frequency depended electrical properties of YbFeO3 perovskite oxide compound

We have synthesized YbFe1−xCoxO3 (x = 0, 0.01, 0.05, 0.10) compounds by the conventional solid-state method. Structural and chemical analysis of the synthesized compounds have been carried out by XPS, SEM and EDX techniques. Frequency dependent (1–107 Hz) electrical properties including the loss tangent, real and imaginary part of impedance and resistivity have been examined in wide range temperature (from − 100 to 100 °C with 20 °C step) using Dielectric/Impedance Spectrometer (Novocontrol). The frequency dependent loss tangent plots have showed different dielectric relaxations peaks and the activation energies of the compounds have been calculated from those peaks using Arrhenius relation. The resistivity measurement results revealed that the increasing Co doping ratio decreases the resistivity of the compounds.

Admittance of Organic LED Structures with an Emission YAK-203 Layer

The current-voltage characteristics and admittance of multilayer structures for organic LEDs based on the PEDOT:PSS/NPD/YAK-203/BCP system have been experimentally investigated in a wide range of the measurement conditions. It is shown that at voltages corresponding to the effective radiative recombination of charge carriers, a significant decrease in the differential capacitance of the structures is observed. The frequency dependences of the normalized conductance of LED structures are in good agreement with the results of numerical simulation in the framework of the equivalent circuit method. Changes in the frequency dependences of the admittance with a change in temperature are most pronounced in the temperature range of 200–300 K and less noticeable in the temperature range of 8–200 K. From the frequency dependences of the imaginary part of impedance, the charge carrier mobilities are found at various voltages and temperatures. The mobility values obtained by this method are somewhat lower than those determined by the transient electroluminescence method. The dependence of the mobility on the electric field is well approximated by a linear function. As the temperature decreases from 300 to 220 K, the mobility decreases several times.

Influence of different solvents on the structural, optical, impedance and dielectric properties of ZnO nanoflakes

In this work, we have synthesized the ZnO nanoflakes using three different solvents, i.e., isopropyl alcohol (IPA), DI (de-ionized) water and ethanol via co-precipitation technique. XRD analysis revealed the hexagonal wurtzite crystal structure for all synthesized samples. The crystallite size is least for ZnO nanoflakes synthesized using ethanol and highest for IPA by applying Scherrer's formula as well as W–H plot. The optical properties were analyzed using UV–Visible spectroscopy and revealed that the maximum optical band gap has been obtained using ethanol as a solvent while the least band gap is observed for IPA. The expansion of light absorption region from UV to visible region can lead to its application in various fields such as optical LEDs, photocatalysis, laser diodes, etc. FTIR spectrum verifies the presence of vibrational modes of the ZnO bond, stretching and bending bonds of OH bonds and O=C=O stretching bond in the prepared samples. The plot for frequency-dependent dielectric loss exhibits the change in dielectric properties. The Nyquist diagrams reveal the semi-circular arc depicting the variation between real and imaginary parts of impedance. The results show that the electrical conductivity increases with frequency and temperature. The activation energy is found using Arrhenius equation with the plot of conductivity versus temperature and the values of activation energy for ZnO nanoflakes synthesized using IPA, DI water, and ethanol is found to be 0.23 eV, 0.29 eV and 0.41 eV, respectively.

Quantitative Detection of Living Yeast Fraction From Mixed Living and Dead Cell Solution by Micro Electrical Impedance Spectroscopy

An empirical model is proposed to detect the living cell fraction $\varPhi $ in a multi-mixed cell solution by micro electrical impedance spectroscopy (EIS) as $\varPhi = -1.46/\psi _{0} + 1.97$ . The living cell indicator $\psi _{0}$ is defined by a quotient of the extrema in the impedance imaginary parts of the detected cell solution’s medium, $Z_{{extmed}}$ , and referenced $Z_{{extmedref}}$ . The theoretical effectiveness of the model is examined by an electrochemical simulation. In addition, the sensor size versatility is discussed by a comparison experiment that reveals that the sensor size has little effect on the detection result. To support real-time detection, $Z_{{extmed}}$ and $Z_{{extmedref}}$ are replaced by the impedance of the cell solution, $Z_{{extm}}$ , and $Z_{{extmref}}$ . The versatility of real-time detection is discussed by a medium similarity coefficient $\eta (f)$ that is defined to explain the effect of replacement. The results reveal the feasibility of the replacement as $\eta > 95$ % in the injected current frequency range of $\psi _{0}$ by micro EIS.

Relationship between the carbon nanotube dispersion state, electrochemical impedance and capacitance and mechanical properties of percolative nanoreinforced OPC mortars

The homogeneous dispersion of carbon nanotubes, (CNTs), in a cementitious matrix is a crucial procedure that affects both mechanical properties and electrical conductivity of the nanocomposite. Electrochemical Impedance Spectroscopy, (EIS), can be very useful in studying and characterizing the impact of the CNT content in nanoreinforced cementitious materials in a quantitative way. In this study, measurements of the resistance, reactance and capacitance reveal the nature of circuit elements formed by the nanotube network in cement mortars reinforced with various amounts of carbon nanotubes and provide insight of the nanotubes’ dispersion state. Resistivity results show that percolation threshold was reached between CNT weight fractions of 0.1% and 0.15 wt%. Below percolation, a consistency between resistive and capacitive phases exists, i.e., resistivity, reactance and capacitance were found to decrease as the nanotube content increases. After the continuous conductive network was formed, and percolative behavior was achieved, resistivity values show a little dependence on the CNT content. However, the presence of CNT entanglements was found to contribute to an amplified energy storage ability, as both the imaginary part of impedance (reactance) and capacitance were increased. A correlation between capacitance, flexural strength and modulus of elasticity was observed for the first time. Capacitance values provide valuable information on the energy storage ability of the material and how the actual CNT dispersion state affects the mechanical properties of percolative nanoreinforced cementitious materials. Finally, a general micromechanics model, modified by taking into account the conductive mechanisms below and above percolation threshold, was successfully implemented. The theoretically determined values of the overall electrical conductivity are in good agreement with the experimental results.

Structural, Optical, Magnetic, and Dielectric Properties of Cr3+ Substituted Cobalt Aluminate Nanoparticles

The present study investigates the influence of Cr3+ substitution on structural, optical, dielectric, and magnetic properties of cobalt aluminates in the aluminates series CoAl2-xCrxO4, 0.00 ≤ x ≤ 0.20. These series of nanoparticles are effectively synthesized using the co-precipitation method. The cubic spinel aluminate structure is confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopic measurements. Transmission electron microscopy (TEM) analysis shows the formation of spherical nanoparticles, which are homogeneous in shape and size. The optical properties of the prepared samples have been investigated by means of optical absorbance spectra. The optical band gap $$ \kern0.5em {E}_{\mathrm{opt}}^i $$ and Urbach energy Eu are estimated. At room temperature, the magnetization of undoped CoAl2O4 reveals a weak ferromagnetic behavior. This ferromagnetism is increased for the sample with x = 0.05, and the samples with higher Cr3+ content have a tendency to be superparamagnetic on account of the formation of single-domain particles as a consequence of small particle size. Real part of dielectric constant (e′), dielectric loss (tanδ), ac conductivity (σac), real part of impedance (Z′), and imaginary part of impedance (Z″) are analyzed as a function of frequency and Cr3+ content. The results show that the dielectric loss (tanδ), dielectric permittivity (e′), and ac conductivity (σac) decrease with the increase in Cr3+ content, x = 0.05, and then increase with a further increase in Cr3+ content. The increase in these parameters has been explained on the basis of the hopping mechanism. From the Cole–Cole diagram, the value of the relaxation time τ can be calculated and it has been found to increase with increasing the Cr3+ content. Actually, a high dielectric constant makes these materials good for energy storage at high frequencies.

Assessment of Ripening Degree of Avocado by Electrical Impedance Spectroscopy and Support Vector Machine

Avocado, a climacteric fruit, exerts high rate of respiration and ethylene production and thereby subject to ripening during storage. Therefore, its ripening is a significant factor to impart optimum quality in postharvest storage. To understand the dynamics of ripening and to assess the degree of ripening in the avocado, electrical sensing technique is utilized in this study. In particular, electrical impedance spectroscopy (EIS) is found to uncover the physiological and structural characteristics in plants and vegetables and to follow physiological progressions due to environmental impacts. In this work, we present an approach that will integrate EIS and machine learning technique that allows us to monitor the ripening degree of the avocado. It is evident from our study that the impedance absolute magnitude of the avocado gradually decreases as the ripening stages (firm, breaking, ripe, and overripe) proceed at a particular frequency. In addition, principal component analysis shows that impedance magnitude (two principal components combined explain 99.95% variation) has better discrimination capabilities for ripening degrees compared to impedance phase angle, impedance real part, and impedance imaginary part. Our classifier utilizes two principal component features over 100 EIS responses and demonstrates classification over firm, breaking, ripe, and overripe stages with an accuracy of 90%, precision of 93%, recall of 90%, f1-score of 90%, and auc of 88%. The study offers plant scientists a low cost and nondestructive approach to monitor postharvest ripening process for quality control during storage.

Room-temperature magnetoelectric coupling, dielectric and impedance studies of 0.5Zn0.3Ni0.7Fe2O4–0.5HoMnO3 nanocomposite

We have investigated strain mediated magnetoelectric (ME) coupling and impedance properties in 0.5Zn[Formula: see text]Ni[Formula: see text]Fe2O4–0.5HoMnO3 nanocomposites at room-temperature. The ME voltage is measured in both longitudinal and transverse direction at a frequency of 173 Hz. The impedance, real and imaginary parts of impedance and dielectric constant have been carried out in presence of DC magnetic field. With the application of magnetic field, slight decrease in dielectric constant has been observed. The impedance, real and imaginary parts of impedance are found to increase with the increase in the applied magnetic field. Nyquist plots have been fitted using three parallel combinations of resistances–capacitance circuits. Fitted parameters show the dominant role of grain boundaries, grains and interface of two types of grains of the sample.

Influence of Erbium doping on the electrical behaviour of CaCu3Ti4O12 ceramics probed by impedance spectroscopy analysis

Herein, the preparation and impedance spectroscopic investigation of pure and Er doped CaCu3Ti4O12 ceramics is reported. FTIR spectroscopy and powder XRD analysis elucidate the surface functionality and crystalline nature of the products respectively. Scanning Electron Microscopy images substantiate the homogenous formation of nanoparticles and the EDS analysis confirms the elemental composition of the products. A relatively high dielectric constant (εr = 26,749) is found for Er doped CaCu3Ti4O12 ceramics than that of pure CaCu3Ti4O12 ceramics (εr = 5885) at 10 Hz (at 800 K). Nyquist plot of pure and Er doped CaCu3Ti4O12 ceramics indicates the presence of a non-Debye type of relaxation phenomenon, which is further validated from the electrical modulus analysis. The variation of temperature dependent relaxation time of pure and Er doped CaCu3Ti4O12 ceramics is estimated from both the imaginary part of impedance and electrical modulus analysis.

Effect of Cu-doping on structural and electrical properties of Ni0.4−xCu0.3+xMg0.3Fe2O4 ferrites prepared using sol–gel method

ABSTRACTNi0.4−xCu0.3+xMg0.3Fe2O4 spinel ferrites were prepared by sol–gel technique. X-ray diffraction results indicate that ferrite samples have a cubic spinel-type structure with space group. The electrical properties of the studied samples using complex impedance spectroscopy technique have been investigated as a function of frequency at different temperatures. We found that the addition of copper in Ni0.4−xCu0.3+xMg0.3Fe2O4 ferrite system can improve its conductivity. Dielectric properties have been discussed in terms of hopping of charge carriers between Fe2+ and Fe3+ ions. For all samples, frequency dependence of the imaginary part of impedance (Z") shows the existence of relaxation phenomenon. The appropriate equivalent circuit configuration for modeling the Nyquist plots of impedance is of the type of (Rg + Rgb//Cgb).

Temperature dependent impedance spectroscopy of (Co3O4)x/CuTl-1223 nanoparticles-superconductor composites

Cobalt oxide (Co3O4) nanoparticles and Cu0.5Tl0.5Ba2Ca2Cu3O10-δ (CuTl-1223) superconducting phase were prepared by sol-gel and solid-state reaction methods, respectively. Co3O4 nanoparticles were added in CuTl-1223 superconducting matrix to get (Co3O4)x/CuTl-1223; x = 0–2.0wt% composites. Different experimental techniques like X-ray diffraction, dc-resistivity measurements and complex impedance spectroscopy were used for characterization of these composites. Crystal structure of CuTl-1223 superconducting phase remained unchanged after addition of Co3O4 nanoparticles, which suggested that these nanoparticles were settled at grain-boundaries. Superconducting transport properties were decreased after inclusion of Co3O4 nanoparticles. Role of Co3O4 nanoparticles addition at the grain-boundaries of the host CuTl-1223 phase was investigated and overall decreasing trend was observed in both real and imaginary part of impedance. The decrease in blocking factor by varying the content of Co3O4 nanoparticles is the evidence of increase in conductivity of grain-boundaries. The impedance master curves indicated the temperature independent dynamic process with non-Debye type relaxation phenomenon. The temperature dependent ac-conductivity with increasing contents of these Co3O4 nanoparticles was also investigated and increasing trend was observed.

Effect of iron doping at Mn-site on complex impedance spectroscopy properties of Nd0.67Ba0.33MnO3 perovskite

ABSTRACTThe effect of Fe-doping at Mn-site on the structural and electrical properties of Nd0.67Ba0.33Mn1−xFexO3 (0 ≤ x ≤ 0.05) perovskites has been investigated. X-ray diffraction patterns show that the structural parameters change slightly due to the fact that the Fe3+ ions replacing the Mn3+ have similar ionic radius. The electrical properties of these samples have been investigated using complex impedance spectroscopy technique. a function of the frequency at different temperatures. When increasing the Fe-content, a decrease of dc conductivity was observed throughout the whole explored temperature range and the deduced activation energy values are found to increase from 128 meV for x = 0 to 166 meV for x = 0.05. The curves of the imaginary part of impedance (Z″) show the presence of relaxation phenomenon in our samples. The complex impedance spectra show semicircle arcs at different temperatures and an equivalent circuit of the type of Rg + (Rgb//Cgb) has been proposed to explain the impedance results.

Impedance spectra of polymer electrolytes

The authors present a phenomenological view on dielectric relaxation in polymer electrolytes. Polymer electrolytes are seen as molecular mixtures of an organic polymer and an inorganic salt. The following is based on systems with high molar mass poly(ethylene oxide) (PEO) and epoxidized natural rubber with 25 mol% of epoxide content (ENR-25) filled with lithium perchlorate (LiClO4). Dielectric properties of these systems have been studied as a function of salt content at room temperature. Additionally, properties of neat low molar mass PEO were studied as function of temperature. Relaxation-coined dielectric behavior rules the system with PEO in the frequency that ranged up to 106 Hz. Imaginary parts of impedance, tangent loss, and electric modulus spectra show distribution of relaxation times. Comparison of tangent loss (tan δ) spectra and imaginary part of electric modulus (M″) spectra reveals that localized motion dominates long-range motion of dipoles in the low-frequency range. However, discrepancy between them decreases with growing salt content. Scaling of tan δ spectra demonstrates that distribution of relaxation times does not depend on salt content in the range of low frequencies. The ENR-25 system exhibits solely relaxation like a macroscopic dipole. In conclusion, the system with PEO is characterized by individual relaxation of well-interacting dipoles, whereas the system based on ENR-25 is coined by immobilized dipoles that lead in the state of high-salt content to the relaxation behavior of a macroscopic dipole.

Structural, electrical and optical properties of sol-gel synthesized cobalt substituted MnFe2O4 nanoparticles

We report the structural, electrical and optical properties of Co substituted manganese ferrite of the composition Mn1−xCoxFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) synthesized by sol-gel technique. X-ray diffraction (XRD) patterns confirm the formation of single-phase cubic spinel structure. The average crystallite size of these materials is found to be in the range of 20–35nm and lattice constant is found to decrease as Co2+ concentration is increased. The permittivity (ɛ), dielectric loss (tanδ) and ac conductivity (σac) have been determined at room temperature as a function of frequency (42Hz to 5MHz). The results of dielectric properties indicate the normal Maxwell-Wagner type dielectric dispersion due to interfacial polarization. DC electrical resistivity has been performed using two probe technique. The decrease of resistivity with temperature confirms the semiconducting nature of the samples. Real and imaginary part of impedance ( Zʹ and Zʺ) suggest existence of one relaxation mechanism which is attributed to the co-effect of grains and grain boundaries. The energy band gap as determined from the UV–visible spectra decreases gradually with the Co increasing content.

Dielectric and complex impedance properties of γ-rays irradiated Neodymium substituted Co-Zn nanoferrites

Nanosized Co1−xZnxFe2−yNdyO4 ferrites with x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0; y=0.0 and 0.1 were synthesized by solution combustion method. All the compositions have been characterized by XRD, SEM technique and irradiated by γ–rays of 60Co source. Dielectric constant, dielectric loss tangent, ac conductivity and complex impedance are studied in the frequency range 100kHz–10MHz for pristine and irradiated composition. The X-ray diffraction patterns revealed the spinel cubic structure. The lattice parameter has increased with increasing Zn2+ ion concentration. The values of dielectric constant, loss tangent, real and imaginary parts of impedance have been decreased while ac conductivity increased with increasing frequency. The dielectric parameters and ac conductivity were found to increase and attain maximum at x=0.4; y=0.0, x=0.6; y=0.10 and beyond that decreased for further substitution of Zn2+ ion concentration. The lattice parameter and dielectric parameters were significantly reduced with Nd3+ ion substitution and increased after γ-irradiation attributed to the conversion of ferric ions to ferrous due to ionizing effect of γ-radiation. Nyquist plots revealed existence of multiple electrical responses.

Investigating the dielectric properties and low-frequency relaxation process of TlGaSe2 crystals

The dielectric and impedance spectra of TlGaSe2 crystals have been studied at temperatures in the 100–500 K range in the alternating current (AC [Formula: see text]1 V). It has been shown that the conductivity of TlGaSe2 crystals is mainly an ionic characteristic at temperatures above 400 K. The well-defined peak at the frequency dependence of the imaginary part of impedance [Formula: see text] is observed in the 215–500 K temperature range. In a constant field, there occurs a significant decrease in electrical conductivity [Formula: see text] in due course. The ionic contribution to conductivity (76% at [Formula: see text]) has been estimated from a kinetic change in electrical conductivity [Formula: see text] under the influence of a constant electric field. The diagram analysis in a complex plane [Formula: see text] has been conducted by applying the method of an equivalent circuit of the substation. It has been determined that the average relaxation time of the electric module of the sample is [Formula: see text].

Characteristics of the electromagnetic wave field far away from the radiation source

A solution to the Sommerfeld problem of the far (in terms of wavelengths) field of a vertical electrical dipole placed at the interface between two media has been found. The characteristics of a surface electromagnetic wave that propagates over a medium with highly inductive surface impedance δ have been determined. The spatial characteristics of the wave are expressed through the real and imaginary parts of impedance δ. It has been proved that the surface electromagnetic wave is the major contributor to the electromagnetic field of the ground wave in the case of highly inductive radio paths.

Study on ionic conductivity and dielectric properties of PEO-based solid nanocomposite polymer electrolytes

The ionic conductivity and dielectric properties of the solid nanocomposite polymer electrolytes formed by dispersing a low particle-sized TiO2 ceramic filler in a poly (ethylene oxide) (PEO)-AgNO3 matrix are presented and discussed. The solid nanocomposite polymer electrolytes are prepared by hot press method. The optimum conducting solid polymer electrolyte of polymer PEO and salt AgNO3 is used as host matrix and TiO2 as filler. From the filler concentration-dependent conductivity study, the maximum ionic conductivity at room temperature is obtained for 10 wt% of TiO2. The real part of impedance (Z′) and imaginary part of impedance (Z″) are analyzed using an LCR meter. The dielectric properties of the highest conducting solid polymer electrolyte are analyzed using dielectric permittivity (e′), dielectric loss (e″), loss tangent (tan δ), real part of the electric modulus (M′), and imaginary part of the electric modulus (M″). It is observed that the dielectric constant (e′) increases sharply towards the lower frequencies due to the electrode polarization effect. The maxima of the loss tangent (tan δ) shift towards higher frequencies with increasing temperature. The peaks observed in the imaginary part of the electric modulus (M″) due to conductivity relaxation shows that the material is ionic conductor. The enhancement in ionic conductivity is observed when nanosized TiO2 is added into the solid polymer electrolyte.

Structural and electrical properties of La0.9Dy0.1MnO3 prepared by sol–gel technique

Nanosized particles of La0.9Dy0.1MnO3 were prepared by sol–gel technique using citric acid as a chelating agent. The compound was analysed by powder X-ray diffraction technique and found to be single-phased orthorhombic in structure with space group Pnma which was confirmed with standard JCPDS data. The structural and morphological characterisations of synthesised material were carried out using XRD, Fourier transform infrared spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectrometer. The magnetic study at room temperature shows the paramagnetic behaviour of the material. The existence of space charge polarisation and relaxation is due to the presence of oxygen vacancy illustrated from the real and imaginary part of impedance, respectively. The activation energy of synthesised material is calculated using Arrhenius equation from the impedance spectroscopy which corresponds to the existence of oxygen vacancy.