Impedance Plots Research Articles

3D-printed flexible flow-field plates for bendable polymer electrolyte membrane fuel cells

3D-printed flexible flow-field plates are employed in this study to realize a bendable polymer electrolyte membrane fuel cell (PEMFC). The prepared bendable PEMFC consists of a membrane electrode assembly (MEA), current collectors, and flow-field plates. The performance of the fuel cell is measured in the flat and bent positions. Polarization curves and impedance plots are analyzed to assess the fuel cell performance. A peak power density of 87.1 mW cm−2 is obtained for the fuel cell with the maximum bending, while a power density of 30.2 mW cm−2 is obtained in the flat position. The enhanced performance is attributed to the compressive stress applied to the reaction sites of the MEA during bending of the fuel cell. The compressive stress is calculated using finite element analysis (FEA). According to the FEA results, the compressive stress occurring at the MEA intensifies as the curvature of the fuel cell increases, resulting in significantly decreased ohmic and charge transfer resistances. The successfully realized bendable fuel cell with 3D-printed flexible flow-field plates exhibits flexibility, decent performance, and a simple structure. It is also competitive in terms of the cost of manufacturing owing to the use of 3D printing.

Wideband, polarization independent electromagnetic wave absorber using cross arrow resonator and lumped SMD resistors for C and X band applications

In this work, a polarization independent and wideband electromagnetic (EM) waves absorbing frequency selective surface (FSS) structure is presented. The unit cell of the proposed FSS consists of an assembly of cross arrow resonators with four SMD resistors mounted on it, to enhance the absorbance bandwidth. This unit cell also possesses a four-fold symmetry which makes it polarization insensitive. The designed unit cell is compact with the length and width dimensions as 0.19λL × 0.19λL, and thickness of 0.13λL, where λL is the guided wavelength corresponding to the lowest operating frequency. The proposed absorber is theoretically and experimentally tested for its absorbance, cross-polarization level, and radar cross section (RCS) characteristics. The computer-aided simulation and practical measurements indicate that the proposed absorber offers more than 90% (with a fractional bandwidth of 93%) absorbance for normal incidence at 4.5–12.4 GHz frequency band. The cross-polarization reflection coefficient analysis indicates that the proposed FSS configuration behaves as an absorber and not a polarization convertor. The input impedance plot, surface current distribution, and E-field distribution of the unit cell were also analyzed and presented to understand the absorbance mechanism. The RCS of the proposed FSS is compared with the RCS of a reflective (metallic) sheet to analyze its suitability for practical applications (RCS reduction) within the working band. The 3D simulated and 2D calculated RCS results indicate that the proposed FSS is suitable for wideband EM wave absorber applications.

A comparative study of corrosion resistance of epoxy-based coating incorporated chitosan, silica and hybrid compound of chitosan/silica on mild steel

Purpose This study aims to propose that the corrosion resistance of the neat epoxy coating can be further enhanced by incorporating reinforcing agents. Design/methodology/approach Chitosan, silica and their hybrid compound were used to study the subject of corrosion resistance of epoxy coating systems. This work used 3.5 Wt.% NaCl solution as the electrolyte, and electrochemical impedance spectroscopy (EIS) was used to investigate the electrochemical behaviour of the studied coating systems. Standard and accelerated states were used without and with scratch on the coating layer. Findings It was found that the impedance value of composite coating incorporated with the hybrid compound was significantly higher at 1010 Ω after 14 days of exposure in both testing states. The breakpoint frequency (fb) determination also proves with large capacitive region at low-to-high frequency of impedance plots corresponding to the high corrosion resistance. Originality/value The hybrid compound consisting of chitosan as organic biopolymer and silica as inorganic material, respectively, served as a promising reinforcing agent for composite coating as a promising corrosion inhibitor. Different states of EIS measurement were used which are standard (without scratch) and accelerated (with scratch) states associated with the fb values.

Electrical characterization of CaBi4Ti3ZrO15 ceramic

Layered structured ceramic compounds have significant characteristics in the field of materials research. A new Aurivillius structured compound, CaBi4Ti3ZrO15, is processed by using solid-state reaction technique process. It is calcined at 830 °C followed by a sintering process at 880 °C. Orthorhombic structure of the material is confirmed from X-ray diffraction analysis. Grain size analysis is done through the scanning electron microscopy. Relative permittivity of the sample rises with rise in frequency and temperature and no phase transition is noticed in the experimental temperature regime. The complex impedance spectroscopy method is employed to study the immittance properties of the material within the range of frequency from 100 Hz to 10 MHz and temperature range from 30 to 500 °C. The complex impedance plot confirms the electrical behaviour of the compound which is because of the bulk and bulk interface effect. Absence of third semicircle in the complex impedance plane indicates the complete absence of electrode–materials effect on overall electrical response for this compound. The presence of non-Debye-like relaxation formalism is seen in the Nyquist plots. The temperature-dependent conductivity shows negative temperature coefficient of resistance character obeying Arrhenius equation. The temperature-dependent conductivity shows semiconducting properties of the sample. The response of hysteresis plot for the sample (P-E loop) confirms the ferroelectric property within the material.

Theoretical and experimental study of the phase coexistence and impedance response in multiferroic Gd doped La0.665Bi0.33Ba0.005GdxMn1-xO3 ceramics

Polycrystalline samples of La0.665Bi0.33Ba0.005GdxMn1-xO3 (LBBGMO) (x = 0.25, 0.45, and 0.65) were prepared via using conventional solid–state reaction method. The preliminary structural studies were carried out by X-ray diffraction at room temperature (RT). Rietveld refinement analysis of diffraction data confirmed that for x = 0.25 and 0.45, the structure was orthorhombic but co-existence of orthorhombic and rhombohedral were observed for x = 0.65. The average crystallite size calculated from the W–H plot of all the samples and reported 20.4753 nm, 16.6014 nm, 16.0821 nm for x = 0.25, 0.45 and 0.65 respectively. The dielectric constant for all samples had a negative value at low frequency and positive for higher frequency range. The presence of one semicircle in Nyquist plot were observed, which shows the grain effect in all ceramic materials. At all observed temperatures, the frequency dependence of impedance plots has been utilized to characterize the electrical conduction of the sample which demonstrated the NTCR character (Negative Temperature Coefficient of Resistance). The ac conductivity variation with frequency dependence was well fitted according to Jonscher's power law and ac conductivity increases with increasing temperature.

Dielectric Properties of Colossal-Dielectric-Constant Na1/2La1/2Cu3Ti4O12 Ceramics Prepared by Spark Plasma Sintering.

In the current study, we report on the dielectric behavior of colossal-dielectric-constant Na1/2La1/2Cu3Ti4O12 (NLCTO) ceramics prepared by mechanochemical synthesis and spark plasma sintering (SPS) at 850 °C, 900 °C, and 925 °C for 10 min. X-ray powder diffraction analysis showed that all the ceramics have a cubic phase. Scanning electron microscope observations revealed an increase in the average grain size from 175 to 300 nm with an increase in the sintering temperature. SPS NLCTO ceramics showed a room-temperature colossal dielectric constant (>103) and a comparatively high dielectric loss (>0.1) over most of the studied frequency range (1 Hz–40 MHz). Two relaxation peaks were observed in the spectra of the electrical modulus and attributed to the response of grain and grain boundary. According to the Nyquist plots of complex impedance, the SPS NLCTO ceramics have semiconductor grains surrounded by electrically resistive grain boundaries. The colossal dielectric constant of SPS NLCTO ceramics was attributed to the internal barrier layer capacitance (IBLC) effect. The high dielectric loss is thought to be due to the low resistivity of the grain boundary of SPS NLCTO.

Impedance spectroscopy of the calcium copper zirconate quadruple perovskite

In this communication, the study of Raman and impedance spectroscopy of a calcium copper zirconate (Ca3CuZr4O12) quadruple perovskite prepared by solid-state reaction method is reported. Appearance of Raman peaks suggests presence of the vibrational modes of all constituent elements present in the prepared material. The frequency and temperature dependence of electrical plots are very much helpful to evaluate the effect of microstructure in the conduction mechanism. The study of the impedance plots shows the NTCR (negative temperature coefficient of resistance) nature, the effect of grains and grain boundaries, and the conduction mechanism of the sample. The difference between the Z″ and M″ peaks increase with temperature confirming a non-Debye relaxation mechanism. The perfect semicircular arcs in Nyquist plots confirm semiconductor nature; which is also well supported from results of the impedance and modulus plots. Based on the experimental results it can be assumed that the prepared sample may be used for electronic and storage device applications.

Impact of rare earth (RE3+ = La3+, Sm3+) substitution in the A site perovskite on the structural, and electrical properties of Ba(Zr0.9Ti0.1)O3 ceramics.

Undoped Ba(Zr0.9Ti0.1)O3 and rare-earth-doped (Ba1−xRE2x/3)(Zr0.9Ti0.1)O3 (RE3+ = La3+, Sm3+) perovskite compounds were synthesized by the conventional solid-state reaction route. Both solubility of rare earth in Ba(Zr0.9Ti0.1)O3 and formation of perovskite structure with the Pm3̄m space group were verified by the Rietveld method using X-ray diffraction data. SEM micrographs of all ceramics revealed high densification, low porosity, and even homogeneous grain distribution of various dimensions over the total surface. The frequency-dependent electrical properties were analyzed by complex impedance spectroscopy. Different types of studies such as the Nyquist plot, real and imaginary part of impedance, conductivity, modulus formalism, and charge carriers activation energy were used to explain the microstructure–electrical property relationships.

Structural, dielectric, and electrical study of bismuth ferrite-lithium vanadate

The composite, BiFeO3-LiVO3 was synthesized through a solid-state reaction technique. The X-ray diffraction (XRD) confirmed the formation of the tetragonal structure at room temperature. The dielectric constant and dielectric loss increased with the rise in temperature. The Nyquist plot projected the contribution of bulk effect and a slight indication of grain boundary effect. The presence of a temperature-dependent relaxation process occurred in the material. Electrical modulus confirmed the non-Debye type relaxation and indicated the asymmetric peak broadening for the spread of relaxation time. The activation energies were calculated from the ac conductivity by linear fitting. The fitted Jonscher power law was very close which implied a similar type of charge carrier which exists in the conduction mechanism for the system. Thermistor parameters were evaluated using the grain resistance for different temperatures.

Dynamics and power limit analysis of a galloping piezoelectric energy harvester under forced excitation

This paper presents a rigorous analytical solution to the dynamics of a single-degree-of-freedom (SDOF) piezoelectric energy harvester (PEH) under the combined wind and base excitations using the harmonic balance method. The boundaries of the quenching region are predicted using the multi-scale method. An equivalent circuit model (ECM) is established to verify the analytical solution, and the simulation results based on the ECM are in good agreement with the analytical ones. Subsequently, the power limit of the SDOF PEH under the combined excitations is analysed for the first time using the impedance theory based on a simplified model. The maximum power amplitudes at different excitation frequencies are also sought by numerically sweeping the load resistance. It is found that the impedance theory that has been successfully adopted in the literature is inapplicable in analysing the power limit of the SDOF PEH under the combined excitations. The impedance plots obtained based on resistance sweeping clearly indicate that, in contrast to the conclusions given in the literature, impedance matching is not the condition to attain the power limit of the SDOF PEH under the combined excitations. A mathematical proof is provided for a reasonable explanation. Finally, it is demonstrated that numerical simulations based on the original model can verify the power limit calculated based on the simplified model.

Structural and Dielectric Properties of Polyvinyl Alcohol‐TiO2 Doped Thin Films

AbstractPolyvinyl alcohol(PVA)‐titanium dioxide(TiO2) polymer composite films are synthesized by well‐recognized and low cost method of solvent casting. The prepared composite films are characterized by FTIR, XRD, and FESEM. The real electric modulus (M’) spectra show large increment with frequency for 5wt% of TiO2 as compared to other compositions. The appearance of peaks for each concentration of TiO2 in M” spectra specifies that strong coupling in the movement of polymer motion and ions. The impedance plots of real impedance (Z’) versus imaginary impedance (Z”) shows semicircles, which diameter and thereby bulk resistance (Rb) is decreased with the loading of TiO2. AC conductivity (σAC) obeys the universal power law. The prepared PVA/TiO2 films can be used in a direct methanol fuel cell, and in optoelectronic devices.

Synthesis, structural and microwave absorption properties of Cr-doped zinc lanthanum nanoferrites Zn1-Cr La0.1Fe1.9O4 (x=0.09, 0.18, 0.27 and 0.36)

Cr-doped zinc-lanthanum nanoferrites Zn 1- x Cr x La 0.1 Fe 1.9 O 4 ( x = 0.09, 0.18, 0.27, and 0.36) were successfully synthesized using sonochemical reactors. Effect of powder production parameters were extensively studied and powder characterization was performed. Existence of cubic spinel structures in the prepared nanoferrites with the average crystallite size ranging from 35 to 51 nm was confirmed by X-ray diffraction studies. An electrochemical impedance analyzer was used to measure the dielectric constant ( ε ′), loss tangent (tan δ), and complex dielectric constant ( ε ") with respect to frequency and composition ratio. Maxwell–Wagner polarization and hopping mechanism were calculated to distinguish the variations in ε ′, tan δ, and ε ". The Nyquist impedance plots for nanoferrites revealed the pseudocapacitance as well as resistive behavior. Vibrating sample magnetometer studies reveled the ferromagnetic behavior of nanoferrites. Substantially increased saturation magnetization and decreased coercivity were noted with respect to increased Cr 2+ ions in the prepared nanoferrites. It was found that the addition of chromium in Zn 1- x Cr x La 0.1 Fe 1.9 O 4 nanoferrites enhances the optical, electrical, and magnetic properties of the nanoferrites.

Optical and dielectric investigations on Ag: CdZnTe hybrid polyvinyl alcohol freestanding films

Hybrid freestanding films of polyvinyl alcohol incorporated with silver and CdZnTe quantum dots were synthesized. The effect of varying silver concentration on optical and dielectric properties were studied. Structural and morphological analysis of hybrid films were done using X-ray diffraction and transmission electron microscopy. Optical parameters like absorption coefficient, extinction coefficient, refractive index, optical bandgap, urbach energy and optical conductivity were studied for the polymer nanocomposite for 0 to 0.3 wt percentage of silver content. With increasing silver content, a decrease in bandgap energy and an increase in urbach energy was observed. Dielectric constants, loss tangent and AC conductivity values of hybrid films were found to improve, with silver addition and highest values were obtained for 0.2 wt percentage. Complex impedance plots provided semicircles and Cole-Cole parameters were calculated. The nature of impedance plot revels single relaxation process and this was effectively modelled through an equivalent RC parallel circuit.

Green Approach to Corrosion Inhibition of Carbon Steel by Fucus spiralis extract in 1 M HCl Medium

The extract of Fucus spiralis (FS) was tested as a corrosion inhibitor of carbon steel in a 1M HCl medium. The anti-corrosion properties were analyzed by gravimetric and electrochemical techniques such as potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). The surface characterization of carbon steel submerged in the optimal solution was carried out using UV-Visible, UV-Vis-NIR, and Optical microscopy analyses. Electrochemical and gravimetric results demonstrated that inhibitory efficiencies increase with increasing inhibitor concentration and the efficiency reaches 87% at a concentration of 0.5 g/L. According to Tafel extrapolated polarisation measurements, the FS also worked as a mixed-type corrosion inhibitor and changed the mechanism of anodic reactions. EIS analysis showed that a depressed capacitive loop dominates the Nyquist plot of impedance and enhances the polarization resistance (Rp) to 161.9 Ω cm2 with a reduction of the double layer capacity (Cdl) of carbon steel to 61.8 μF/cm2. This protection is assured by an adsorption mechanism based on the isothermal Langmuir adsorption model, which positively affects the thermodynamic parameters. UV-Visible, UV-Vis-NIR analyses exhibited that inhibitor decreases the iron oxides like hematite, Magnetite, and Goethite, Maghemite, Lepidocrocite, δ-FeOOH of the metal surface and delays the dissolution of the bare metal of iron to the ferrous ions, notably that optical morphology showed that FS extract decreases the aggressivity of HCl.

Optical and electrical properties of impurity-less multiferroic bismuth ferrite nanoparticles

Synthesis of high-purity multiferroic bismuth ferrite (BFO) nanoparticles is a big challenge for researchers. In this research, we synthesized high-purity BFO nanoparticles by a modified sol-gel method. BFO nanoparticles were characterized for structural, morphological, optical, electrical, and multiferroic properties. The Rietveld refinement revealed the rhombohedral crystal structure with R3c space group and devoid of impurity phases. Measured average particle size from FESEM and TEM images were 152 and 148 nm, respectively. The ferroelectric and ferromagnetic properties of synthesized nanoparticles were investigated in detail. The leakage current density and the space-charge-limited current were analyzed to study the effect of impurities. The dielectric properties were measured and characterized for dielectric constant, dielectric loss, resistance, reactance, impedance, resistivity, conductivity, electric modulus, and Cole-Cole plot. The calculated optical bandgap energy from UV–Vis–NIR spectroscopy and photoluminescence spectroscopy were 2.057 eV and 2.087 eV, respectively.

Impedance Spectroscopy Analysis of PbSe Nanostructures Deposited by Aerosol Assisted Chemical Vapor Deposition Approach.

This research endeavor aimed to synthesize the lead (II) diphenyldiselenophosphinate complex and its use to obtain lead selenide nanostructured depositions and further the impedance spectroscopic analysis of these obtained PbSe nanostructures, to determine their roles in the electronics industry. The aerosol-assisted chemical vapor deposition technique was used to provide lead selenide deposition by decomposition of the complex at different temperatures using the glass substrates. The obtained films were revealed to be a pure cubic phase PbSe, as confirmed by X-ray diffraction analysis. SEM and TEM micrographs demonstrated three-dimensionally grown interlocked or aggregated nanocubes of the obtained PbSe. Characteristic dielectric measurements and the impedance spectroscopy analysis at room temperature were executed to evaluate PbSe properties over the frequency range of 100 Hz–5 MHz. The dielectric constant and dielectric loss gave similar trends, along with altering frequency, which was well explained by the Koops theory and Maxwell–Wagner theory. The effective short-range translational carrier hopping gave rise to an overdue remarkable increase in ac conductivity (σac) on the frequency increase. Fitting of a complex impedance plot was carried out with an equivalent circuit model (Rg Cg) (Rgb Qgb Cgb), which proved that grains, as well as grain boundaries, are responsible for the relaxation processes. The asymmetric depressed semicircle with the center lower to the impedance real axis provided a clear explanation of non-Debye dielectric behavior.

Electrical and Humidity-Sensing Properties of EuCl2, Eu2O3 and EuCl2/Eu2O3 Blend Films

Impedance-type humidity sensors based on EuCl2, Eu2O3 and EuCl2/Eu2O3 blend films were fabricated. The electrical properties of the pure EuCl2 and Eu2O3 films and EuCl2/Eu2O3 blend film that was blended with different amounts of EuCl2 were investigated as functions of relative humidity. The influences of the EuCl2 to the humidity-sensing properties (sensitivity and linearity) of the EuCl2/Eu2O3 blend film were thus elucidated. The impedance-type humidity sensor that was made of a 7 wt% EuCl2/Eu2O3 blend film exhibited the highest sensitivity, best linearity, a small hysteresis, a fast response time, a small temperature coefficient and long-term stability. The complex impedance plots were used to elucidate the role of ions in the humidity-sensing behavior of the EuCl2/Eu2O3 blend film.

Experimental-structural study, Raman spectroscopy, UV‐visible, and impedance characterizations of Ba0.97La0.02Ti0.9Nb0.08O3 polycrystalline sample

Ba0.97La0.02Ti0.9Nb0.08O3 (BLT0.9Nb0.08) was elaborated by a simple chemical molten-salt (M-S) reaction. This reaction technique was followed by a process of filtration and evaporation. The compound is subjected to annealing at an elevated temperature (800 °C). The XRD results demonstrate that the BLT0.9Nb0.08 possessed a pure-tetragonal system structure with a space group of P4/mmm. In order to contribute, our solid solution has been scrutinized utilizing Raman Spectroscopy, UV–visible, and the techniques electrochemical impedance spectroscopy (EIS). Raman spectroscopy was carried out at room temperature (RT) on doped ceramic. The incorporation of La3+ in A- site and Nb5+ in B- site into BT lattice was as well discussed. Also, we controlled the frequency of the principle optic modes. No considerable modify was remarked in the frequency. But the only frequency of A1 [TO3] mode was slightly affected by the La and Nb doping. This could reflect the effect of these particles on the B- site, since this mode associates with a distortion of O octahedron around the central Ti ion. Impedance properties of our sample have been tried against to frequency at room-temperature. The imaginary part of the impedance (Z″) versus frequency demonstrates the existence of relaxation phenomena. At RT, Nyquist plots of impedance show a semicircle arcs and an electrical equivalent circuit of association of bulk resistance R1, three resistances-constant phase elements (R//CPE) related in series related in sequential and Warburg element “Ws” has been intended to depict the impedance results. The real (ε′), imaginary (ε′′) parts of the complex permittivity and the dielectric factor Tan(δ) define a drastic reduced with the frequency. The reduced can be deciphered by the Maxwell–Wagner polarization Kind.

Nickel Manganite-Sodium Alginate Nano-Biocomposite for Temperature Sensing

Nanocrystalline nickel manganite (NiMn2O4) powder with a pure cubic spinel phase structure was synthesized via sol-gel combustion and characterized with XRD, FT-IR, XPS and SEM. The powder was mixed with sodium alginate gel to form a nano-biocomposite gel, dried at room temperature to form a thick film and characterized with FT-IR and SEM. DC resistance and AC impedance of sensor test structures obtained by drop casting the nano-biocomposite gel onto test interdigitated PdAg electrodes on an alumina substrate were measured in the temperature range of 20–50 °C at a constant relative humidity (RH) of 50% and at room temperature (25 °C) in the RH range of 40–90%. The material constant obtained from the measured decrease in resistance with temperature was determined to be 4523 K, while the temperature sensitivity at room temperature (25 °C) was −5.09%/K. Analysis of the complex impedance plots showed a dominant influence of grains. The decrease in complex impedance with increase in temperature confirmed the negative temperature coefficient effect. The grain resistance and grain relaxation frequency were determined using an equivalent circuit. The activation energy for conduction was determined as 0.45 eV from the temperature dependence of the grain resistance according to the small polaron hopping model, while the activation energy for relaxation was 0.43 eV determined from the Arrhenius dependence of the grain relaxation frequency on temperature.

A unified equivalent circuit and impedance analysis method for galloping piezoelectric energy harvesters

In the past decade, galloping-based energy harvesters (GPEH) connected with various interface circuits have been developed and analytical models have been built. However, the power performances of these advanced structures and circuits are always treated separately, and a general model is missing to gain insights at a system level. To tackle this issue, this paper proposes a unified analysis framework for GPEHs. Its results are consistent with validated (but disconnected) results in the literature. The method provides an integrated view of the physics of linear GPEHs in multiple domains at the system level, and elucidates the similarities and differences among power behaviors of GPEHs connected with various interface circuits. The framework is based on two major elements: an equivalent circuit that represents the entire system, and an equivalent impedance that represents the interface circuit. Firstly, the electromechanical system is linearized and modeled in the electrical domain by an equivalent self-excited circuit with a negative resistive element representing the external aerodynamic excitation, and a general load impedance representing the interface circuit. Then, a closed-form, analytical expression of the harvested power is obtained based on the Kirchhoff’s Voltage Law, from which the optimal load, maximum power, power limit, and critical electromechanical coupling (minimum coupling to reach the power limit) are determined. In this unified analysis, the exact type of energy harvesting interface circuit is not assumed. After that, the power characteristics of a GPEH connected with five representative interface circuits are analytically derived and discussed, by using the particular equivalent impedance of the interface circuit of interest. It is shown that they are subjected to the same power limit. However, the critical electromechanical coupling depends on the type of circuit. Throughout the discussions, impedance plots are used to illustrate the relationship between the internal system characteristics and external load impedance, facilitating the understanding of system power behavior.