Dependent Impedance Research Articles

Substitutional effect of copper replacement by cadmium on structural, microstructural and electrical properties of Cu1–xCdxO oxides

In this communication, sol–gel method was employed to synthesize Cd substituted CuO oxides. The substitutional effect of Cd at Cu site in Cu1–xCdxO oxides on the structural, microstructural and electrical properties has been understood. Structural studies reveal single phase nature without any detectable impurity. Scherrer’s formula and Williamson–Hall (W–H) plot analysis suggest that size of the particles increases with increase in Cd content. Microstructural studies show the enhancement in an average grain size as well as improvement in the granular compactness in the CCO samples having higher Cd content. To realize substitutional effect of Cd at Cu site in CCO system on the electrical properties, frequency dependent dielectric, impedance and ac conductivity were recorded. Variations in these electrical properties with frequency and Cd content have been understood in detail. Different theoretical aspects like relaxation mechanism, universal dielectric behavior (UDR) and power law fits have been employed.

Exponential Convergence Rates of Nonlinear Mechanical Systems: The 1-DoF Case With Configuration-Dependent Inertia

This letter provides a proof of global exponential stability for a large class of uni-dimensional mechanical systems with configuration dependent inertia and impedance. It also contextually contributes with a strict bound on the exponential decay, connecting the Lyapunov exponent of the nonlinear system with the convergence rate of the corresponding worst-case linear system.

Studies on effect of Ca-doping on structure and electrochemical properties of garnet-type Y3-xCaxFe5O12-δ

In this study, effect of Ca-doping on electrical and electrochemical properties of garnet structure Y3-xCaxFe5O12-δ (x ​= ​0, 0.05, 0.1, 0.3, 0.5 and 0.7) was investigated. Cubic-phase (Ia-3d) garnet was prepared through sol-gel method and sintered at 1100 ​°C for 2 ​h in air. Highest oxygen non-stoichiometry (δ ​= ​0.19) was found in x ​= ​0.3 member. X-ray absorption spectroscopy (XAS) confirmed the formation of hole carriers (Fe.Fe) due to Ca-substitution for Y in Y3Fe5O12. 4-Probe DC measurements showed that electrical conductivity increased with an increase in Ca amount until x ​= ​0.1 (1.58 ​S/cm at 750 ​°C) and then decreased due to decrease in the concentration of the charge carriers. Lowest area specific resistance (ASR) of 1 Ωcm2 was seen at 750 ​°C in air for the symmetrical cell with x ​= ​0.3 garnet-LSGM composite electrode. Studies on pO2 dependent ASR and impedance spectroscopy genetic programming (ISGP) analysis revealed that oxygen dissociation and partial reduction of adsorbed oxygen molecule co-limit the electrochemical performance for oxygen reduction reaction (ORR).

Charge transport mechanism in BaFe12O19 and BaFe11CoO19

The conduction and charge transport mechanism of cobalt substituted barium hexaferrite (BaCoM) were studied by impendence spectroscopy at different temperatures and compared with BaM. Frequency dependent impedance spectra showed two distinct relaxations in BaM whereas a single relaxation peak was present in BaCoM. The relaxation frequencies were found to be temperature dependent. Scaling behaviour confirmed the dynamic conduction process is temperature independent and deviates from Debye type relaxation. Brick layer model has been employed to investigate the charge conduction through grain and grain boundaries. Arrhenius plot of conductivity showed two sharp transitions in three different temperature regime which indicates parallel conduction mechanism in the system. The frequency dependent conductivity was fitted with Jonscher’s power law at different temperatures. The variation in frequency exponent with temperature confirmed the evidence of three types of conduction process. Higher conductivity and different transition temperature was observed for BaCoM as compared to BaM. The conduction process was in accordance with overlapping-large polaron tunnelling model.

Laser-scribed graphene (LSG) as new electrode material for impedance-based cellular assays

Impedance-based monitoring of cell-based assays has evolved to a multi-functional tool in fundamental and applied biomedical research. The majority of studies rely on gold-films as the electrode material which serves as growth surface and electrode at a time. Besides all its favorable properties like inertness, biocompatibility and superior electrochemical characteristics, gold-film electrodes in contact to cell culture medium show a capacitance of the electrode/electrolyte interface that may become limiting for the sensitivity of the readout. This study describes the use of laser-scribed graphene (LSG) as an alternative electrode material in impedance-based cell monitoring. LSG electrodes are prepared from commercial polyimide foils by simple CO2-laser-induced carbonization. The resulting electrodes show a 25times larger interface capacitance than standard gold-film electrodes due to their foam-like surface topography. Furthermore, LSG-electrodes are (i) highly compatible with cell attachment, (ii) easy to prepare in customized geometries from μm to cm with tunable surface topography and (iii) accessible by roll-to-roll production lines. We conclude from time- and frequency dependent impedance measurements of cell-covered LSG electrodes in direct comparison to the reference material gold that LSG provides an enormous potential to improve the sensitivity of impedance-based monitoring and electric-field mediated manipulation of adherent cells.

Interfacial effects on ferroelectric and dielectric properties of GO reinforced free-standing and flexible PVDF/ZnO composite membranes: Bias dependent impedance spectroscopy

Flexible membranes with attractive ferroelectric and dielectric properties are promising for numerous technological devices, such as, energy storage and harvesting devices, sensors etc. Here we report the development of conducting nanofiller containing inorganic semiconductor and organic polymer based tri-phase composite membranes and demonstrate their ferroelectric and frequency dependent dielectric characteristics. The graphene oxide (GO) nanosheet reinforced free-standing, flexible and β-phase abundant PVDF/ZnO composite membranes are fabricated by simple, low-cost and scalable chemical method. The ferroelectric properties of the PVDF polymer based composite membranes are modified through incorporation of small amount of GO and ZnO without sacrificing the mechanical flexibility as evidenced by electrical polarization characteristics. The ferroelectric polarization for PVDF/ZnO and PVDF/ZnO/GO membranes are respectively 15.98 and 14.14 μC/cm2 at only 15 kV/cm electric field which are distinctly superior than PVDF-copolymer and PVDF-perovskite based composites as reported recently. Furthermore, as per our knowledge for the first time we have studied the effects of external electric field on dielectric relaxation times originating from the electrical responses from core grains and grain-boundary or interfaces by using dc bias dependent impedance spectroscopy. The modulation in dielectric permittivity of the composite membranes is attributed to the formation of complete β-crystalline phase in PVDF/ZnO/GO membranes and introduction of active interfaces facilitating induced electrical polarization. These studies provide significant insight into the interfacial effects on the electrical transport, ferroelectric and dielectric properties of tri-phase PVDF/ZnO/GO polymer membrane, an emerging energy material.

A state-space formulation of a discontinuous Galerkin method for thermoacoustic stability analysis

A hybrid approach for thermoacoustic stability analysis is formulated in a state-space framework. The approach distinguishes between regions of the computational domain with and without important interactions between acoustics and mean flow or unsteady heat release, respectively. The former regions are modeled by a discontinuous Galerkin finite element method (DG-FEM) for the linearized Navier-Stokes equations in conservative form. The latter are represented by reduced-order models of acoustic wave propagation or dissipation, and provide complex-valued, frequency dependent impedance boundary conditions for the DG-FEM domain. The flow-flame coupling is modeled by a flame transfer function that governs a volumetric source term for the fluctuating heat release rate.The respective (sub-)models are formulated and interconnected in a state-space framework, which facilitates the monolithic formulation of hybrid thermoacoustic models. Moreover, the state-space interconnect framework makes it possible to formulate thermoacoustic stability analysis as a linear eigenvalue problem – even if flame transfer function or acoustic boundary conditions depend in a non-trivial manner on frequency.The approach is first verified against analytical solutions for a duct with mean flow across a thin heat source, similar to a Rijke tube. Then the thermoacoustic eigenmodes of a premixed, swirl-stabilized combustor are computed in order to validate the method against experimental data for a configuration of applied interest. For this second validation case, a detailed comparison against predictions of a low-order network-model is also presented.

A strategy for in situ determination of self-healing state for strain hardening cementitious composites

In strain-hardening cementitious composites, the bridging effect of fibers can control crack openings to very small values so the cracks can be self-healed in the presence of water. To rely on autogeneous self-healing to enhance the durability of structures, a method to assess the state of self-healing is required. A new strategy is presented in this paper for in-situ measurement of the healing effect without pre-knowledge of the environmental condition (such as moisture). Exploiting the fact that the electrical conductivity in the crack is lower than that of the undamaged section, the effective macroscopic cracking effect is first distinguished by frequency dependent impedance measurements both along (parallel to) and across the cracks. Dielectric spectroscopy along the cracks is found to correlate well with gravimetric measurements and can therefore, be used for inverse approximation of moisture content. The effect of moisture change on the equivalent resistance in the direction across the cracks can then be derived approximately from measurements under various moisture contents. The approximated resistance vs moisture curve is found to reflect the evolution of autogenous self-healing, and a curve indicating almost complete healing agrees well with the recovery in member stiffness measured from loading test.

Investigation on structural, optical, and electrical properties for sintered Mg–Zn aluminate systems

In the present work, the insulating MgAl2O4 and a semiconducting ZnAl2O4 were mixed as Zn0.5Mg0.5Al2O4 compound, which is synthesized by chemical co-precipitation method. We have investigated the structural, optical, and electrical properties for Zn0.5Mg0.5Al2O4 at different sintering temperatures. By X-ray diffraction (XRD) data analysis, the phase identification and intermediate phase formation were confirmed through the appearance of the superlattice peak at 2θ = 49.1° for (331) plane. The particle sizes of sintered samples were examined through high-resolution transmission electron microscopy (HRTEM) analyses. The weight percentages of Zn, Mg, Al, and O ions in the samples were obtained from EDX analysis. The cation distribution in the sintered Zn0.5Mg0.5Al2O4 samples was analyzed using solid-state nuclear magnetic resonance (SS-NMR) spectra. In addition, the UV absorbance spectra reveal an inter-bandgap region for the Zn0.5Mg0.5Al2O4 system. The optical bandgap was found to be a blue shift as observed from absorbance spectra on sintering. The frequency dependence impedance spectra and AC conductivity expose the contribution of grain, grain boundaries, and electrode–sample interface effects very clearly. The frequency dispersive nature of the dielectric constant and tan δ was measured and analyzed. The disparity observed due to the sintering of the sample was discussed and reported.

Bicontinuous Cubic and Hexagonal Columnar Liquid Crystalline Ion-Conductors at Room Temperature in Ion-Doped Dendritic Amphiphiles

A bicontinuous cubic (Cubbi) liquid crystalline (LC) phase consisting of three dimensional (3D) conducting networks is a promising structural platform for ion-conductors. For practical applications using this fascinating LC structure, it is necessary to suppress crystallization at room temperature (RT). Herein, we report the Cubbi structure at RT and the morphology–dependent conduction behavior in ionic samples of a non-crystallizable dendritic amphiphile. In the molecular design, branched alkyl chains were used as an ionophobic part instead of crystallizable linear alkyl chains. Two ionic samples with Cubbi and hexagonal columnar (Colhex) LC phases at RT were prepared by adding different amounts of lithium salt to the amphiphile. Impedance analysis demonstrated that the Cubbi phase contributed to the faster ion-conduction to a larger extent than the Colhex phase due to the 3D ionic networks of the Cubbi phase. In addition, the temperature–dependent impedance and electric modulus data provided information regarding the phase transition from microphase-separated phase to molecularly mixed liquid phase.

Intrinsic anisotropy and pinning anisotropy in nanostructured YBa2Cu3O7−δ from microwave measurements

Anisotropy is an intrinsic factor that dictates the magnetic properties of YBa2Cu3O7−δ and therefore has a great impact on many applications. Artificial pinning centres are often introduced in an attempt to mitigate its effect, resulting in less anisotropic electrical and magnetic properties. However, the nanoengineering of superconductors makes the quantification of the anisotropy itself uncertain: the intrinsic anisotropy due to the layered structure, quantified by the anisotropy factor γ, mixes with the additional anisotropy due to pinning. As a consequence, there is no consensus on the experimental anisotropy factor γ that can result in YBa2Cu3O7−δ when directional (twin planes, nanorods) or isotropic defects are present. We present measurements of the magnetic field and angular dependent surface impedance in very different nanostructured YBa2Cu3O7−δ films, grown by a chemical route and by pulsed laser deposition with different kind of defects (nanorods, twin planes, nanoparticles). We show that the surface impedance measurements are able to disentangle the intrinsic anisotropy from the directional pinning anisotropy, thanks to the possibility of extracting the true anisotropic flux–flow resistivity and by correctly exploiting the angular scaling. We find in all films that the intrinsic anisotropy γ = 5.3 ± 0.7. By contrast, the pinning anisotropy determines a much more complex, feature–rich and nonuniversal, sample–dependent angular landscape.

Electromagnetic Characteristics of Shape Memory Spring

Electric impedance is widely used in imaging and detection techniques. The applications range from non-destructive testing, structural health monitoring, and geophysical imaging to medical imaging. The frequency of the signal used for the measurement ranges from less than 1 Hz to about 1 GHz. This paper addresses the measurement and evaluation of the phase dependent electrical resistance, inductance, capacitance, and impedance of a shape memory alloy (SMA) spring (BMX 150, Toki Corporation). The material characteristics can be obtained by means of their electromechanical impedance. Experimental procedures are implemented and the electrical characteristics are obtained for a wide range of frequency. The electrical resistance, inductance, impedances of the austenite and martensite phase are determined, also the quality factor of the Bio Metal coil to be (9.465 – 9.95) Ω and (10.358 – 10.8) Ω, (0.458 – 0.38) μH and (0.458 – 0.36) μH and, (9.47 – 10.24) Ω and (10.36 – 11.11) Ω respectively for the frequency range of 100 kHz - 1MHz. The quality factor of the Bio Metal ranges between 0.03 and 0.2 during heating and, 0.028 and 0.022 during the cooling phase. The experimental results herein show that an equivalent circuit of the SMA spring is a series resistor-inductor circuit with a parasitic capacitance effect. The electromagnetic behaviour of SMA is determined using a finite element tool.

Electronic classification of barcoded particles for multiplexed detection using supervised machine learning analysis

Wearable biosensors are of great interest in recent years due to their potential in health related applications. Multiplex biomarker analysis is needed in wearable devices to improve the sensitivity and reliability. Electronic barcoding of micro-particles has the possibility to enable multiplexed biomarker analysis. Compared with traditional optical and plasmonic methods for barcoding, electronically barcoded particles can be classified using ultra-compact electronic readout platforms. Nano-electronic barcoding works by depositing a thin layer of oxide on the top half of a micro-particle. The thickness and dielectric property of the oxide layer can be tuned to modulate the frequency dependent impedance signature of the particles. A one to one correspondence between a target biomarker and each barcoded particle can potentially be established using this technique. The barcoded particles could be tested with wearable devices to enable multiplex analysis for portable point-of-care diagnostics and real-time monitoring. In this work, we fabricated nine barcoded particles by forming oxide layers of different thicknesses and different dielectric materials using atomic layer deposition and assessed the ability to accurately classify particle barcodes using multi-frequency impedance cytometry in conjunction with supervised machine learning.

Structural, Optical, Magnetic, and Electrical Properties of Ni0.5Co0.5Al2O4 System

In this present work, we have focused on the effect of cobalt substitution in the nickel aluminate system. The aluminate samples were synthesized by the chemical precipitation method. The structural and optical properties of the NiAl2O4, CoAl2O4, and Ni0.5Co0.5Al2O4 samples were studied through X-ray diffraction and UV-DRS absorbance spectral analysis. The XRD pattern confirms the cubic phase with the space group of Fd-3 m through its analysis of the diffraction peaks. The UV absorption peaks around at 360, 480, 551, 580, and 621 nm extend the formation of NiAl2O4, CoAl2O4, and Ni0.5Co0.5Al2O4 system. The surface morphological images of the samples were scanned by using the scanning electron microscope. The room temperature magnetic nature of the aluminate samples was carried out using VSM, and the observed result reveals a weak ferromagnetic and super-paramagnetic nature for NiAl2O4 and Ni0.5Co0.5Al2O4, respectively. The temperature dependence impedance spectra and AC conductivity were measured using an impedance analyzer at selected temperatures, and that reveals the bulk resistance of the grain and the grain boundary region of the sample. The observed results were analyzed and discussed.

Reduced impedance in dual substituted strontium cobaltite nanoparticles for renewable energy applications

Sr1−xBaxCo1−xFexO3−δ (BSCF) nanoparticles were successfully synthesized with three modified wet chemical techniques; composite mediated hydrothermal method (CMHM), without water and surfactants (WOWS) sol-gel and co-precipitation methods. The probable electrical conduction mechanism of synthesized BSCF was explored via complex impedance analysis. Various physicochemical characterization techniques were employed to study the dependence of structure, homogeneity, physical parameters and electrical properties of BSCF on synthesis procedures. X-ray Diffraction (XRD) confirmed the formation of cubic BSCF perovskite structure. Fourier Transform Infrared Spectroscopy (FTIR) spectra indicated the presence of the fingerprint region of perovskite (ABO3−δ) structure. Scanning Electron Microscopy (SEM) images revealed uniformly diffused, micro porous and agglomerated morphology. Differential Thermal Analysis (DTA) and Thermogravimetry (TGA) verified the formation of intermediate metal carbonates that were decomposed to the final product. Nyquist plots against frequency (20 Hz–3 MHz) revealed single semi-circular arcs. The arc showed significant grain boundary contribution to total electrical conduction behaviour of BSCF material synthesized by CMHM and co-precipitation methods. Modulus analysis showed the Debye type conductivity relaxation in CMHM synthesized material. The AC conductivity graphs followed Jonscher’s power law. Temperature dependent (RT to 600 °C; 10 kHz) impedances showed decreasing trend that was an indication of thermally activated conduction process. A Correlation was established among structural and electrical conduction properties. Hydrothermally synthesized BSCF samples exhibited minimum impedances and maximum AC conductivity, which makes them a potential candidate for cathode material in (IT-SOFCs) applications.

Frequency switchable correlated transports in perovskite rare-earth nickelates

Delta-temperature thermistor functionality in correlated rare-earth nickelates sheds light on regulations for the working state of electronic devices using AC-frequency dependent impedance without altering the materials.

Time Domain Characterization of the Cole-Cole Dielectric Model.

The Cole-Cole model for a dielectric is a generalization of the Debye relaxation model. The most familiar form is in the frequency domain and this manifests itself in a frequency dependent impedance. Dielectrics may also be characterized in the time domain by means of the current and charge responses to a voltage step, called response and relaxation functions respectively. For the Debye model they are both exponentials while in the Cole-Cole model they are expressed by a generalization of the exponential, the Mittag-Leffler function. Its asymptotes are just as interesting and correspond to the Curie-von Schweidler current response which is known from real-life capacitors and the Kohlrausch stretched exponential charge response.

Resonance frequency analysis of lead-acid cells: An EIS approach to predict the state-of-health

Abstract We present in this work a new electrochemical impedance spectroscopy approach for lifetime prediction of lead-acid cells under imposed aging conditions. Frequency dependent impedance fluctuations are being monitored during charging and discharging sequences of battery for two distinct states of charges. We monitored the battery impedance behavior in two distinct states: at 100% state of charge, and secondly, at 75% state-of-charge. During the aging process, we encompassed the impedance plots vs frequency shifting diagrams, in the framework of a single parameter, we refer here to resonant frequency of the circuit. The validation of our model was demonstrated by comparing the resonance frequency values in three fabricated cells, thus emphasizing the changes that appear in the various physical details, depending on battery fabrication methodology. For State-of-Charge = 100% the degradation of the battery is leading to an important variation of its resonance frequency, while for State-of-Charge = 75%, the fluctuations of resonance frequency are significantly smaller. Monitoring just one parameter, we developed an accurate fitting model function capable to predict the lead-acid cells aging process. We can say that for the cell produced under controlled conditions, we get a larger lifetime and an inferior degradation speed to the cells manufactured in laboratory.

Room temperature colossal magnetodielectric effect in La0.4Gd0.1Ca0.5MnO3

We have studied the contribution induced by a low magnetic field (0.6T and 1.2T) on the frequency dependent permittivity, impedance and conductivity recorded at room temperature for La0.4Gd0.1Ca0.5MnO3 polycrystalline compound. Strong magnetodielectric (MD) coupling has been detected at room temperature. Colossal value of negative MD (more than 50%) has been observed under 1.2T field. The MD response is found to be stable in the studied frequency range (up to 2 MHz) suggesting the possibility of using this compound for technological applications at room temperature. The significant MD coupling has been correlated with the presence of charge ordering transition near room temperature.

Sub-rf period electrical characterization of a pulsed capacitively coupled argon plasma

Transient plasmas (such as pulsed power plasmas) can be of interest to both industry, where they allow for new processing windows, and basic science, where their dynamics are of interest. However, their study requires time resolved diagnostic techniques. One powerful diagnostic is current and voltage (IV) measurements, which along with the power and impedance calculated from them, can be used to characterize a plasma. This is especially true as it is an outside the chamber, noninvasive technique and can be used in systems where a probe or fiber optic bundle/window will affect processing results or fail due to deposition. To obtain accurate IV values, frequency dependent probe calibrations must be performed and frequency dependent parasitic impedances in the system and propagation delay between the forward traveling fundamental frequency and backward traveling harmonic frequencies must be taken into account. To separate the fundamental and harmonic frequencies, a fast Fourier transform (FFT) is traditionally performed in continuous wave plasmas. In transient plasmas, a time resolved FFT is necessary. This article presents a method to perform each of these steps while demonstrating their importance and giving some measurements of a pulsed power, 75 mTorr, capacitively coupled argon plasma.