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Made available in DSpace on 2020-12-12T02:48:18Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-10-20 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Mechanical and microstructural characteristics of Ti-6Al-4V/stainless steel (SS) dissimilar friction stir welds have been well described in the literature; however, little is known about the electrochemical properties of such welds in terms of the passive film stability of TiO2 grown in oxidizing media. To clarify this issue, potentiodynamic polarization, cyclic voltammetry, and electrochemical impedance measurements were carried out in the Ti-6Al-4V alloy to analyze the effects of Fe and Cr contamination from the underlying SS on the passive film stability of TiO2 in concentrated (6.0 and 11.5 mol L–1) HNO3 solutions. Lower transpassive potentials were observed for samples in the stirred zone (SZ) than those of the base metal (BM) due to Fe and Cr contamination. Anodic charges obtained during cyclic voltammetry using 6.0 mol L–1 HNO3 showed that the grown passive film was completely dissolved and regrown after consecutive scans, except for the BM sample. According to the results of X-ray photoelectron spectroscopy (XPS) analyses an Al depleted layer was obtained for the latter condition, which confirms the stability of TiO2 film. The increasing values of charge transfer resistance obtained through electrochemical impedance measurements at distinct potentials in the passive region also supported the stability of the TiO2 film grown in 6.0 mol L–1 HNO3 solution. The formation of a medium frequency inductive loop and low frequency constant phase element are related to the dissolution of the oxide film and adsorption of NO3 species into the formed passive film, respectively, as evidenced by XPS analyses. Departament of Chemistry Federal University of São Carlos Institute of Science and Technology (ICT) Federal University of São Paulo (UNIFESP), São José dos Campos Departament of Materials Engineering Federal University of São Carlos Helmholtz-Zentrum Geesthacht (HZG) Institute of Materials Research Materials Mechanics Solid State Joining Processes (WMP), Max-Planck-Str. 1 São Paulo State University (UNESP) Institute of Chemistry Department of Phyical Chemistry São Paulo State University (UNESP) Institute of Chemistry Department of Phyical Chemistry CNPq: # 150782/2019–5 CAPES: 1639995 CNPq: 311163/2017–3

Electrical impedance myography (EIM) is a noninvasive approach to muscle assessment based on the measurement of the electrical impedance in frequency range of interest. In this paper, fatigue-induced electrical impedance models of biceps tissues are investigated. After the dataset used is briefly described, complete set of parameters of the modified Fricke model, utilizing Foster I RC network-based fractional-order capacitor (FOC), are computed. The goodness of fitting of proposed FOCs and bioimpedance models were evaluated visually and statistically. The fit accuracy of designed electrical impedance models is ${\mathbf{R}}_{{\text{R}},{\text{X}}}^2 \geq 0.9978$. Proposed models provide more intuitive representation of the electrical behavior of biceps tissues. EIA standard compliant E96 series lumped parameter-based practical models give an appropriate explanation of fatigue effect on biceps tissues from resistance and capacitance point of view.

Background:Electrical impedance spectroscopy (EIS) is a fast, non-invasive, and safe approach for electrical impedance measurement of biomedical tissues. Applied to dental research, EIS has been used to detect tooth cracks and caries with higher accuracy than visual or radiographic methods. Recent studies have reported age-related differences in human dental tissue impedance and utilized fractional-order equivalent circuit model parameters to represent these measurements. Objective: We aimed to highlight that fractional-order equivalent circuit models with different topologies (but same number of components) can equally well model the electrical impedance of dental tissues. Additionally, this work presents an equivalent circuit network that can be realized using Electronic Industries Alliance (EIA) standard compliant RC component values to emulate the electrical impedance characteristics of dental tissues. Results: To validate the results, the goodness of fits of electrical impedance models were evaluated visually and statistically in terms of relative error, mean absolute error (MAE), root mean squared error (RMSE), coefficient of determination (R2), Nash&ndash, Sutcliffe&rsquo, s efficiency (NSE), Willmott&rsquo, s index of agreement (WIA), or Legates&rsquo, s coefficient of efficiency (LCE). The fit accuracy of proposed recurrent electrical impedance models for data representative of different age groups teeth dentin supports that both models can represent the same impedance data near perfectly. Significance: With the continued exploration of fractional-order equivalent circuit models to represent biological tissue data, it is important to investigate which models and model parameters are most closely associated with clinically relevant markers and physiological structures of the tissues/materials being measured and not just &ldquo, fit&rdquo, with experimental data. This exploration highlights that two different fractional-order models can fit experimental dental tissue data equally well, which should be considered during studies aimed at investigating different topologies to represent biological tissue impedance and their interpretation.

This paper briefly contributes to synthesis of non-integer order frequency filters. Well known method of construction of desired frequency responses based on locations of zeroes and poles is generalized to fractional-order (FO) domain. Several prototypes of FO transfer functions are geometrically interpreted using a complex plane. Each transfer function has a single real degree of freedom and corresponding unique frequency responses. Proposed approach is verified by example of very simple two-band FO audio equalizer.

It is desirable to calibrate electrochemical impedance spectroscopy (EIS) instrumentation using a Randles circuit. This presents a challenge as realistic loads, simulated by this circuit, contain theoretical components (Warburg elements) that are difficult to model. This paper proposes a state-space solution to this problem that facilitates digital realizations of high accuracy Randles circuit approximations for the purposes of verifying and calibrating instrumentation. Using Valsa, Dvořak, and Friedl's network approximation of a Warburg element, a collection of state-space relations describing the impedance of a Randles circuit are derived.

Electric double layer capacitor (EDLC) has seen widespread applications in energy storage for smooth operation of power systems. However, successful integration of EDLC into energy internet requires comprehensive understanding of its electrical response under various operation conditions. This work employs molecular dynamic simulations to study the physical mechanism behind the short-term memory effect reported in discharging process of EDLC. The physical meaning of constant phase element for EDLC is also revealed with equivalent circuit of transmission line model of resistors and capacitors.

The aim of this paper is to present an application of the generalized Warburg element and Constant Phase Element (CPE) for non-Fickian diffusion modeling. These distributed elements are intended to provide a better fit of low-frequency impedance data than the standard finite-length Warburg element in the case of most batteries. In addition, the current study demonstrates the ambiguity of the finite-length Warburg element if impedance data is insufficient within the very-low-frequency impedance spectrum. In order to select the appropriate Randles circuit for non-Fickian diffusion modeling, several configurations have been investigated. Based on the best fit of impedance data, the State-of-Charge (SoC) dependency of the Randles circuit parameters has also been analyzed. This study concerns a Samsung ICR18650-26F 2600 mAh battery cell which was subjected to Electrochemical Impedance Spectroscopy (EIS) measurements between 10 mHz and 100 kHz as a function of SoC. The results were plotted and compared in the form of Nyquist plots. The Randles circuit parameters such as the resistances Rs and Rct, double-layer Cdl, leaky capacitance CPE andWarburg coefficients were estimated using ZView software. The present paper shows that CPE – and its QPE form – is a recommended choice to yield the best fit in terms of non-Fickian diffusion impedance. In addition, using CPE is a better alternative to avoid problems with initial values and multiple local solutions, which may exist in the case of the Warburg element. The resultant Randles circuit parameters and their SoC characteristics can be effectively used in further electrochemical modeling.

This paper introduces new promising applications of VCA822 active device in the fractional-order design of two-ports including very simple and compact solutions of integrator, differentiator, low-pass and high-pass filter. Key feature of the designed circuits is their tunability controlled by current gain of VCA822 not available in case of solution with standard op-amps. Block (principal) structure of the device is explained in detail. PSpice simulation results of the designed circuits indicate usability of these ideas and also simple tunability of the application verified with a fractional-order constant phase element with the order alpha = 1/4.

We introduce a spectral response of impedance of CZTSe nanoscale Ge bi-layers solar cells with an improved equivalent circuit model. Improved AC circuit models are applied, considering a realistic device structure with lumped bulk resistance, resistance, and capacitance of one heterojunction interface, and two effective back-contact interfaces. The impedance model is characterized by series/parallel resistance, and constant phase element to accurately analyze the device structure, which shows a good agreement of the fitting to data $(\chi^{2}=4.19\ \times\ 10^{-4})$ . Two indicative parameters of back-contact interfaces are close to 1, implying the improved back-contact interface by adding nanolayer Ge (2.5 nm) between CZTSe and MoSe 2 . Resistances of both back-contact interfaces are less than 0.3% of the CdS/CZTSe heterojunction interfaces.

In this study, calcined ZrTe3O8 powder mixed with 7%wt of CuO was sintered at 750 °C. The new doped ceramic ZrTe3O8:7%CuO was synthesized using solid state reaction method and was studied with X-ray diffraction (XRD). At room temperature, the title compound crystallizes in cubic space group Ia 3 ‾ , with lattice parameter a = 11.328(3) A, and exhibits a complex network of interconnected closed chains built up of TeO4E (E = electronic lone pair of Te (IV) atoms). The Zr/CuO6 octahedra are inserted into these chains ensuring the stability of the structure by Zr/Cu –O–Te bonding contacts. IR and Raman spectroscopic study are employed as means to obtain preliminary structural information and confirms the presence of the ZrO6 and TeO4E groups. Optical properties of the ceramic were explored by using UV–Vis absorption. The magnetic results reveal the appearance of a weak ferromagnetic behavior at low temperature (TC = 46.172 K). In addition, dielectric data were analyzed using real and imaginary permittivity e ’ and e ’’ respectively, the tan (δ) and the electrical modulus ( M ’ and M″) for the sample ZrTe3O8:7%CuO at various frequencies. The Z ’ and Z ’’ versus frequency plots are well fitted to an equivalent circuit model composed of a series combination of two parallel combinations of resistance Ri and constant phase element CPEi.

International audience; The electric properties of an electrode can be evaluated by the determination of the capacitance. However, the literature reports a large panel of experimental protocols for capacitance determination, which involve either cyclic voltammetry (CV) or electrochemical impedance spectroscopy (EIS). In fact, substantial discrepancies in the assumptions are made between both techniques as in CV, the system is usually considered as ideal (and the current-scan rate relationship is assumed to remain linear at all frequencies), whereas in EIS, the system is usually considered as non-ideal and a CPE element is introduced. In this work, the electric properties of two electrode configurations, namely an Au blocking electrode and an Al electrode with a thin oxide film were investigated using EIS and CV. The capacitive domain was determined for both systems assuming the presence of an ideal and non-ideal system. The results collected from CV revealed a limited linearity between the current and scan rate for both electrode configurations. Finally, a CPE element was introduced to determine the capacitance from CV data and compared to EIS results.

This paper provides readers with three partial results that are mutually connected. Firstly, the gallery of the so-called constant phase elements (CPE) dedicated for the wideband applications is presented. CPEs are calculated for 9&deg, (decimal orders) and 10&deg, phase steps including &frac14, &frac12, and &frac34, orders, which are the most used mathematical orders between zero and one in practice. For each phase shift, all necessary numerical values to design fully passive RC ladder two-terminal circuits are provided. Individual CPEs are easily distinguishable because of a very high accuracy, maximal phase error is less than 1.5&deg, in wide frequency range beginning with 3 Hz and ending with 1 MHz. Secondly, dynamics of ternary memory composed by a series connection of two resonant tunneling diodes is investigated and, consequently, a robust chaotic behavior is discovered and reported. Finally, CPEs are directly used for realization of fractional-order (FO) ternary memory as lumped chaotic oscillator. Existence of structurally stable strange attractors for different orders is proved, both by numerical analyzed and experimental measurement.

This paper reports the effect of interlayer species on the electrical and dielectric behaviours of a lamellar structure. The successful intercalation of three oxyanions ( $$\text {CO}_{3}^{2-}$$ , $$\text {NO}_{3}^{-}$$ and $$\text {H}_{2}\text {PO}_{4}^{-})$$ in the interlayer space of NiAl-layered double hydroxide (LDH) was confirmed by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis and inductively coupled plasma. Using complex impedance spectroscopy measurements, equivalent circuit consisting of three serially connected R-CPE units was established for each sample. Each unit contains a resistance and a constant phase element representing contributions of grain, grain boundary and electrode interface, which allowed the determination of their electrical parameters. The adjustment of experimental data of conductivity by the double power law allowed the determination of $$\sigma _{\mathrm {dc}}$$ and other conductivity parameters, and therefore, the investigation of the effect of intercalated anions on NiAl LDH electrical behaviour. Indeed, dihydrogenophosphates intercalated sample was found to decrease $$\sigma _{\mathrm {ac}}$$ over the frequency range of measure, comparing to the other anions. The intercalation of this anion has also an effect on dielectric properties, it reduces the value of dielectric constant of NiAl LDH, and shifts the maximum of tan $$\delta $$ towards medium frequencies with a decrease in the value of loss tangent above $$10^{5}$$ Hz. Carbonate and nitrate intercalated LDH showed a similarity in their effect on electrical and dielectric properties of NiAl LDH.

This paper targets on the design and analysis of specific types of transfer functions obtained by the summing operation of integer-order and fractional-order two-port responses. Various operations provided by fractional-order, two-terminal devices have been studied recently. However, this topic needs to be further studied, and the topologies need to be analyzed in order to extend the state of the art. The studied topology utilizes the passive solution of a constant-phase element (with order equal to 0.5) implemented by parallel resistor&ndash, capacitor circuit (RC) sections operating as a fractional-order two-port. The integer-order part is implemented by operational amplifier-based lossless integrators and differentiators in branches with electronically adjustable gain, useful for time constant tuning. Four possible cases of the fractional-order and integer-order two-port interconnections are analyzed analytically, by PSpice simulations and also experimentally in the frequency range between 10 Hz and 1 MHz. Standard discrete active components are used in this design for laboratory verification. Practical recommendations for construction and also particular solutions overcoming possible issues with instability and DC offsets are also given. Experimental and simulated results are in good agreement with theory.

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.

The potential opportunities of perovskite-based technology to further advance in the photovoltaic field and implement an extensive industrial application, will mainly depend on whether some of its weaknesses, such as current density-voltage (J−V) hysteresis, can be overcome. In this sense, a critical aspect is the understanding and the subsequent accurate description of hysteresis in perovskite cells. Here, we present the theoretical underpinnings to interpret non-ideal transient dynamics in stepwise-JV measurements, using electrical analysis strategies and fractional calculus tools. Our model was validated with experimental measurements of CsFAPbIBr-based photovoltaic perovskites of different active layer thicknesses with persistent long-range time photocurrents. It is reported that hysteresis phenomena increase with more pronounced non-ideal capacitive effects suggesting that more trapping events limit ion motion and carrier transport. Our main interest is to provide valuable information about the memory-based slow timescale dynamics, which exhibits a significant impact on the appearance of hysteresis and, to a large extent, on the operation of the solar cell.

A selection of electrodes was analysed using cyclic-voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and a large apparent resistance was observed with CV that was absent with EIS. The explanation for this resistance anomaly was traced to the constant phase element (CPE) behaviour which is exhibited by the electrode double-layer capacitance. Computer simulations of the transient-response of an RQ network (where Q represents a CPE) to a voltage ramp revealed bi-exponential behaviour, with two separate time-constants. One is equal to the product of R and Q, but the other is fixed at about 0.3 s. This finding is supported by observation, by mathematical derivation, and by a novel mixed-domain five-component equivalent circuit model. In addition, example code is provided as a basis for transient simulations of constant phase elements with arbitrary voltage waveforms. This explanation assists in the correct interpretation of potentially misleading cyclic voltammetry results.

Silver doped indium sulfide (In2S3:Ag) thin layers were prepared by spray pyrolysis. The Ag concentration varies in the range of 0–6 at%. The X-ray diffraction (XRD) indicates the presence of cubic phase of β-In2S3 and the crystallite size values exhibit a maximum at an Ag concentration of 4%. In addition, morphological analysis by atomic force microscopy (AFM) shows that the film surface is continuous, compact, free of cracks and depends on the Ag concentration. This observation is remarkable by evolution of surface roughness values. The films reveal a semiconductor behavior. This is observed because the electrical conductance increases with the increase of measurement temperature and the analysis of the Nyquist diagram shows the appearance of half circles, whose radius decreases by increasing the temperature from 300 K to 600 K. The electrical equivalent circuit of undoped In2S3 and In2S3:Ag4% at 460 K and 470 K contains two components connected in serial. The first is composed of a resistance R1, an inductance L and a constant phase element CPE1 in parallel and the other covers R2 and a constant phase element CPE2 that are connected in parallel. Inductive and capacitive effects exist in these materials and they depend on frequency. For Ag concentration equal or greater than 4%, the equivalent circuit is a parallel association of a resistor with a constant phase element. The activation energy is minimum for an Ag concentration of 4%., This work was supported by Spanish Ministry of Science and Innovation, Spain - Grant ID: CTQ2016-79561-R (MODENA), Fundacion Ramon Areces, Spain -Grant ID: CIVP18A3940 and Xunta de Galicia, Spain - Grant IDs: Galician Competitive Research Group ED431C-2017/22, AEMAT Strategic Partnership ED431E-2018/08. Authors would like to thank the use of RIAIDT - USC analytical facilities.

The potential opportunities of perovskite-based technology to further advance in the photovoltaic field and implement an extensive industrial application, will mainly depend on whether some of its weaknesses, such as current density-voltage (J−V) hysteresis, can be overcome. In this sense, a critical aspect is the understanding and the subsequent accurate description of hysteresis in perovskite cells. Here, we present the theoretical underpinnings to interpret non-ideal transient dynamics in stepwise-JV measurements, using electrical analysis strategies and fractional calculus tools. Our model was validated with experimental measurements of CsFAPbIBr-based photovoltaic perovskites of different active layer thicknesses with persistent long-range time photocurrents. It is reported that hysteresis phenomena increase with more pronounced non-ideal capacitive effects suggesting that more trapping events limit ion motion and carrier transport. Our main interest is to provide valuable information about the memory-based slow timescale dynamics, which exhibits a significant impact on the appearance of hysteresis and, to a large extent, on the operation of the solar cell.

In this study, BaFe2O4 nanoparticles with a crystallite size of 86 nm were produced using the sol–gel method and applied in the photoreduction of chromate. The spinel phase was identified by X-ray diffraction and scanning electron microscopy-energy-dispersive X-ray analysis. The structure was refined in orthorhombic symmetry by Rietveld analysis. A forbidden band (Eg) of 2.03 eV was extracted from the diffuse reflectance data and the optical transition was directly permitted. The thermal dependence of the electrical conductivity (σ) followed an exponential law with an activation energy of 0.23 eV. In addition, photo-electrochemical characterization of the spinel was conducted to establish the energy diagram for the hetero-system BaFe2O4/SnO2/HCrO4− solution in order to assess the interfacial reaction mechanism. Similar to most spinels, BaFe2O4 exhibits p-type behavior with a flat band potential (Efb) of 0.52 VSCE. Therefore, the potential of the conduction band (ECB) is sufficiently negative to be involved in an electronic injection with SnO2. The photoluminescence spectrum obtained for the rutile contained an intense peak at 590 nm and its intensity was substantially reduced in the hetero-system. Electrochemical impedance spectroscopy detected a depressed arc assigned to a constant phase element and its resistance (1.64 kΩ cm2) decreased to 1.05 kΩ cm2 under visible light, thereby confirming the semiconductor behavior. The reduction of Cr(VI) was successfully achieved with the BaFe2O4/SnO2 hetero-system under visible light as an application. Photocorrosion was prevented by using oxalate (C2O42−) as a scavenger to captures the holes and improve the photo-activity. The quasi-total chromate reduction had a reduction efficiency of 99% with a concentration of 30 mg L−1 under a light flux of 16 mW cm−2. The kinetics followed a first-order model with a photocatalytic half-life of 38 min and the results were fitted in an appropriate manner to the Langmuir–Hinshelwood model. Moreover, BaFe2O4/SnO2 exhibited photocatalytic efficacy for five successive runs and the final reduction efficiency was still 92%.

We apply a combination of experimental measurements and molecular dynamic (MD) simulations to describe imidazolium ionic liquids with porous carbon electrode. On the experiment's side, electrochemical measurements are conducted on two types of porous carbon electrodes prepared from different pore size distributions. The general trend of variations for impedance are identified at various temperatures and electrode geometries in Nyquist plots. On the simulation's side, fundamental geometries including slit and cylindrical pores are modeled to determine the ions' behaviours during charging and discharging process. By examining the local charges variations, the electrode charging or polarization are correlated with ion dynamics or relaxation, particularly in the vicinity of electrode. In one-to-one correspondence to experiments, linear segment of impedance for individual pores gives rise to the constant phase element in fitting of porous electrode's equivalent circuit. Our MD simulations explored the path of implementing the techniques of cyclic voltammetry and electrochemical impedance spectroscopy.

Water uptake in commercially available epoxy coating on mild steel using impedance spectroscopy and gravimetry was studied. The water content in the coating was determined using the Brasher-Kingsbury equation and various methods of coating capacitance calculation used in the literature. The obtained results were compared with reference gravimetric data. An overestimation of values obtained from impedance data in relation to gravimetric data was observed. It was found that the calculation of the effective coating capacitance needs to use both constant phase element (CPE) parameters. Using principal component analysis (PCA) a strong correlation between them and gravimetric data was found. The use of formula of effective capacitance in the Brasher-Kingsbury equation has allowed to obtain significant compliance with gravimetric data.

Single phase samples of Mg doped Y-type hexaferrites with a composition of Ba2(Co1−xMgx)2Fe12O22 for x = 0–0.5 were prepared using the solid state route. The values of lattice constant and the unit cell volume are found to decrease systematically with increase in Mg concentration. The analysis of impedance spectra and the thermal activation of relaxation process show the contributions from both grains and grain boundaries with decrease in activation energies as Mg concentration is increased. The complex impedance spectra show a deviation from an ideal Debye type and they are modelled using an equivalent circuit consisting of resistances of grains and grain boundaries, grain capacitance and a constant phase element. However at higher temperature (T ≥ 573 K), the contribution of electrode resistance is also taken into account. The analysis of electrical conductivity data show that it is controlled by small polaron tunneling model. The magnetization measurements show that the saturation magnetization marginally decreases from 26.6 emu/g for x = 0–22.7 emu/g for x = 0.5 along with decrease in ferrimagnetic transition temperature from 613 to 581 K.

The dielectric spectroscopy (DS) measurement is an attractive noninvasive method to reveal the intrinsic information of biological materials and cell cultures. However, the presence of a double layer due to electrode polarization within the lower RF and microwave range significantly affects the accurate analysis of dielectric properties of ionic liquids. In this paper, we measure the broadband DS of five saline solutions with a microfluidic coplanar waveguide (CPW) transmission line sensor across the frequency range from 40 kHz to 110 GHz. Derived from a parallel-plate structure that is transformed from the quasi-TEM CPW sensor through a conformal mapping technique, a broadband spectroscopy modeling method is proposed, where a Cole-Cole function or a constant phase element formula is used depending on the ionic concentrations and the measurement window. Validation analysis on the five saline solutions demonstrates the capability of the modeling method in separating relaxation properties of the bulk sample from the double-layer effects. ispartof: IEEE TRANSACTIONS ON NANOBIOSCIENCE vol:17 issue:4 pages:387-393 ispartof: location:United States status: published

The influences of temperature and chloride content on the corrosion resistance of stainless steels (SS) in acid solution were investigated employing polarisation curves (PC) and electrochemical imp...

CuYO2.25, prepared by soft chemistry, crystallizes in a pseudo delafossite structure and exhibits p-type conductivity. The oxygen inserts reversibly in the layered lattice and the conduction occurs by small polaron hopping with an activation energy of 0.22 eV and a hole mobility of 8.6 × 10−5 cm2 V−1 s−1. The thermal analysis under reducing atmosphere (H2/N2, 1/9) shows a two-step process. The effective Bohr magneton per Cu2+ ion, calculated from the magnetic data, is smaller than that of Cu2+ (S = ½ S(S + 1)0.5 μB), due to antiferromagnetic coupling between half-filled Cu2+ dz2 orbitals. The photo-electrochemical characterization and electrochemical impedance spectroscopy (EIS) have been reported for the first time. The capacitance vs. potential plot (C−2–V) shows a linear behavior from which a flat band potential of 0.62 VSCE and a hole density NA of 7.45 × 1017 cm3 have been determined. The valence band, located at 3.84 eV/0.91 VSCE below vacuum, is made up of Cu-3d orbital. The Nyquist representation exhibits a straight line due to Warburg impedance with an angle of ~ 45° ascribed to a constant phase element (CPE), and an equivalent circuit for the junction is proposed.

Presented work focuses on methods for the extended electronic control in the designs of inductance simulators based on single-loop feedback topology. Implementation is based on diamond transistors as voltage-to-current converters and two voltage-mode multipliers connected to different positions in topology (providing amplification or control of equivalent resistance). Presented solutions achieve significantly extended adjustability of equivalent inductance value in comparison to standard approaches based on CMOS differential pair-based operational transconductances amplifiers. Proposed designs of synthetic inductors are based on utilization of integer-order as well as fractional-order (constant phase element) capacitor. Their features are verified both via PSpice simulations and experimental measurements. Results confirmed intended purposes of designs implementing discussed methods. DOI: http://dx.doi.org/10.5755/j01.eie.24.3.20976

Nano-sized tin oxide (SnO2) particles were synthesized using eggshell membrane (ESM), a natural bio-waste from the chicken eggshell. The crystallization of SnO2 into the tetragonal structure was confirmed from powder X-ray diffraction and the crystallite size ranged from 13 to 40 nm. Various shapes including rod, hexagonal and spherical SnO2 nanoparticles were observed from the morphological studies. The electrochemical impedance study revealed a lower charge transfer resistance (Rct) of 8.565 Ω and the presence of a constant phase element which arised due to surface roughness and porosity. Capacitive behavior seen in the cyclic voltammetry curve of the prepared SnO2 nanoparticles, find future applications in supercapacitors.

Constant phase elements (CPE) are widely used in fitting of electrochemical impedance spectra instead of ideal capacitances. The present work begins with a discussion of two commonly used models for conversion of the CPE parameters to an effective capacitance, i.e. Hsu and Mansfeld’s and Brug et al.’s; and then continues with presenting alternative geometric assumptions to derive some other formulae. Afterward, it provides a comparison between the results of the formulae together with comments on their applications. Through discussing the relation between the models, this work offers a better understanding of the mathematics of impedance exhibiting frequency dispersion.

In the present work the electrical properties of polycrystalline 0.9(Na0.5Bi0.5TiO3)–0.1(BiFeO3) and Bi0.8M0.2FeO3-modified Na0.5Bi0.5TiO3, (where M = Ca, Sr, and Ba) lead-free ceramics were investigated through impedance spectroscopy. X-ray diffraction analyses indicate the incorporation of alkaline earth metal ions at A-site of perovskite type ceramics revealing the conservation of crystal structure (rhombohedral structure with R3c space group) in the synthesized compositions. The substitution of alkaline earth metal ions at the A-site in perovskite-structured ceramics led to an enlargement of unit cell. The appearance of depressed semicircle arcs in Nyquist plots suggests non-Debye nature of relaxation occurring in studied samples. An equivalent circuit model comprising of parallel combination of resistance and constant phase element was used for the simulation of Nyquist plots. The mismatching of peaks in the combined spectroscopic plots of Z″ and M″ versus frequency also confirms the occurrence of non-Debye relaxation in BBFO sample. The ac conductivity studies show that the conduction mechanism changes from correlated barrier hopping model (CBH) to overlapping large polaron tunneling, when alkaline metal ions are substituted in place of Bi3+ ions. Activation energy values calculated from conductivity data suggest the presence of oxygen vacancies. The dielectric, impedance and conductivity behaviors are significantly influenced by the distortion of Ti/Fe O6 octahedron.

Knowledge of the dielectric properties of biological cells plays an important role in numerical models aimed at understanding how high intensity ultrashort nanosecond electric pulses affect the plasma membrane and the membranes of intracellular organelles. To this end, using electrical impedance spectroscopy, the dielectric properties of isolated, neuroendocrine adrenal chromaffin cells were obtained. Measured impedance data of the cell suspension, acquired between 1 kHz and 20 MHz, were fit into a combination of constant phase element and Cole-Cole models from which the effect of electrode polarization was extracted. The dielectric spectrum of each cell suspension was fit into a Maxwell-Wagner mixture model and the Clausius-Mossotti factor was obtained. Lastly, to extract the cellular dielectric parameters, the cell dielectric data were fit into a granular cell model representative of a chromaffin cell, which was based on the inclusion of secretory granules in the cytoplasm. Chromaffin cell parameters determined from this study were the cell and secretory granule membrane specific capacitance (1.22 and 7.10 μF/cm2, respectively), the cytoplasmic conductivity, which excludes and includes the effect of intracellular membranous structures (1.14 and 0.49 S/m, respectively), and the secretory granule milieu conductivity (0.35 S/m). These measurements will be crucial for incorporating into numerical models aimed at understanding the differential poration effect of nanosecond electric pulses on chromaffin cell membranes.

Interdigitated, screen-printed platinum microelectrodes are used for non-Faradaic impedance spectroscopy detection of viable Saccharomyces cerevisiae . The time dependence of the complex impedance of both living and heat-inactivated yeast cells immersed in plain medium or immobilized in agar is measured between 0.01 Hz and 1 MHz for 300 min. To understand the processes probed by the impedance measurement, an equivalent electrical circuit, containing a constant phase element, a charge transfer resistance and a suspension resistance, is established and analyzed. For both heat-inactivated and living yeast cells in plain medium, the suspension resistance increases over time caused by sedimentation of the yeast cells into the stray field of the electrodes. The measured increase is found to be larger for living cells than for heat-inactivated ones. The time dependence of the double-layer capacitance is rather dominated by the metabolic activity of living cells, but a possible impact of cell sedimentation cannot be completely neglected. In experiments carried out with cells immobilized in agar, cell sedimentation is suppressed, and thus, the time evolution of the double-layer capacitance is solely caused by metabolic active cells. Therefore, the time-dependent change of the double-layer capacitance can be used to directly monitor the viability of Saccharomyces cerevisiae in situ , since inactivated cells do not contribute to the signal generation in this case.

Widely-used complex plane analysis of impedance data is insufficiently sensitive to characterize fully the bulk properties of YSZ single crystal. Instead, more extensive data analysis is needed which uses a combination of parallel, admittance-based formalisms and series, impedance-based formalisms. Bulk electrical properties are measured at higher frequencies and contain contributions from both long range conduction and local dielectric relaxation. At lower frequencies, electrode–sample contact impedances are measured and are included in full equivalent circuit analysis. The impedance of YSZ crystal of composition 8 mol% Y2O3 in the (110) orientation, with Pt electrodes, was measured over the temperature range 150–750◦C and frequency range 0.01 Hz-3 MHz. Full data analysis required (i) a parallel constant phase element (CPE)–resistance (R) combination to model the electrode response, (ii) a series R-C element to represent local reorientation of defect dipoles and (iii) a R-C-CPE element to represent long range oxide-ion conduction; (ii) and (iii) together model the bulk response. The dielectric element underpins all discussions about defect structure and properties of YSZ but has not been included previously in analysis of impedance data. The new equivalent circuit that is proposed should allow better separation of bulk and grain boundary impedances of YSZ ceramics.

We investigated the effect of repetitive switching of polarization on the ferroelectric Pt/Pb(Zr0.52Ti0.48)O3/Pt thin film capacitor by using impedance spectroscopy. From the Cole-Cole plot, the equivalent circuit is described as a combination of the bulk part (a capacitor), the interface part (the constant phase element (CPE), and a parallelly-connected resistor). The circuit parameters were analyzed at various stages of switching. An early increase and a subsequent decrease of the bulk capacitance may represent the wake-up and fatigue phenomena, respectively. The change in the interface part was characterized by an increase in resistance and the growth of n, the exponent of CPE, which may have come from a reduction of defects and the diminished inhomogeneity in the interfacial layer, respectively. The change in the resistance and the coefficient of the CPE in the interface part collectively resulted in an increase in the interfacial impedance. The coercive voltage, which may have intrinsically increased due to the repetitive switching, was even larger as a result of the increased interfacial impedance.

In this paper, the authors propose a theory to describe the behavior of the new type of fractal element which exihibit complex-conjugated power-law exponents. To explain the impedance behaviour of these elements, log-periodic corrections are employed. So far, the impedance of fractal elements are studied which shows power law behaviour in a limited frequency band; and they are modeled as band limited constant phase element. However, the proposed theory is able to describe the impedance behaviour of the fractal element in the entire frequency zone of measurement. To validate the theory, NanoTubes (MWCNTs) based 10 fractal elements are fabricated which exihibit sinusoidal type phase response in the frequency zone from 1 Hz to 4 MHz (it is to be noted that the measurement range of the instrument is 10 mHz to 4 MHz). The derived fitting formula is expressed in the squared log-normal term and contain log-periodic corrections. The proposed fitting formula, incorporated in the paper, will facilitate to explore the deterministic nature of the log-periodic oscillations in complex systems. Earlier these oscillations were considered random or counterintuitive and is misinterpreted as the results of measurement artifacts. Besides, it will find application in modelling the spatially extended systems and also to the analysis of nonlinear dynamics in a complex system. Moreover, one can combine the conventional resistance, capacitance and inductance in one “hybrid” combination using the theory.

The capacitances of electrochemical systems determined from cyclic voltammetry (CV) are difficult to compare due to the unavoidable constant-phase element (CPE) behavior of such systems. These difficulties can be illustrated by simulated voltammograms of simplified circuits composed of a resistor in series with a CPE (R-CPE circuits). The capacitance extracted from CV of R-CPE circuits follows a power law relationship with sweep rate. By comparing the CV-obtained capacitance with that obtained from electrochemical impedance spectroscopy (EIS) data, a critical sweep rate can be defined as the rate where these capacitances intersect. This critical rate can be used to formulate an effective time constant for R-CPE circuits. Sweep rates at least two orders of magnitude below the critical rate should be used in CV to mitigate the influence of the system's time constant on the measured capacitance. To allow for more accurate comparisons of supercapacitors, the CPE parameters R, Q, and α should be reported, rather than the capacitance vs. sweep rate data from CV measurements.

Electrochemical impedance spectroscopy was used to study electrochemical lithium insertion into the electrodes based on germanium nanowires in a temperature range of +20 to −40 °C. Since such electrodes have a regular structure and do not contain binders and conductive additives, they are described by a relatively simple equivalent circuit including the electrolyte resistance (Rs), the resistance of the solid electrolyte film (RSEI) on the surface of germanium nanowires, the capacitance of the solid electrolyte film (CSEI), the charge transfer resistance (Rct), a constant phase element (CPE), reflecting the capacitance of the double layer, and the Warburg impedance (W), reflecting the diffusion of lithium in germanium. It is characteristic of the RSEI and Rct values to grow with an increase in the lithiation degree from 0.3 to 0.9, respectively, by 28% and 16%. A decrease in temperature leads to an increase in the values of Rs, RSEI, and Rct in accordance with the Arrhenius law with activation energies of 21.8, 24.1, and 36.5 kJ/mol, respectively. At the same time, the SEI capacity is independent of temperature.

The phenomenological theory for the anomalous electric double layer (EDL) impedance response (see J. Phys. Chem. C 118, 2014, 5122-5133) for rough heterogeneous electrodes is simplified for roughness features larger than the electrolyte screening length. The electrochemical impedance responses (EIS) of moderately rough polycrystalline Pt electrodes in NaNO 3 electrolyte dissolved in aqueous and viscous media are analyzed and interpreted with the phenomenological theory. Experiments support predictions of theory for the EDL relaxation on rough and heterogeneous electrode, and also emphasize that the dynamics can be decomposed into compact layer and diffuse layer processes. Influence of viscosity is used to unravel the characteristic high frequency diffuse EDL dynamics through NaNO 3 solution in 90% glycerol (by volume). These experiments also contrast the influence of concentration on EDL dynamics in aqueous and viscous media. EIS identifies four phenomenological regimes along with their characteristics frequencies. Finally, this phenomenological theory brings in significant physical insight and provides a useful method for interpreting experimental results.

The focus in supercapacitor research typically falls into one of two categories: (i) the rational design and engineering of electrode materials and electrolyte formulation to achieve high performance devices at competitive costs, and (ii) the modeling of their resulting behavior in response to constant-current charging/discharging, cyclic voltammetry or impedance spectroscopy. However, less work has been dedicated to new ways for charging these devices. In this work we show that charging a supercapacitor, modeled as a constant phase element with a series resistor, using a linear voltage ramp results in higher stored charge and higher effective capacitance value than when using a linear current ramp. This is despite the reciprocity of the device, as we proved analytically. The theoretical analysis and numerical simulations are in excellent agreement with the experimental results carried out on a commercial supercapacitor. The findings can be viewed as a step towards finding the optimum charging waveforms for these devices that would maximize their effective capacitance.

In the present investigation, three 5-amino-8-hydroxyquinolines derivatives namely, 5-aminomethyl-8-hydroxyquinoline (AMHQ), 5-N-acethylaminomethyl-8-hydroxyquinoline (ACAMHQ), 5-N,N′-dimethylaminomethyl-8-hydroxyquinoline (DMHQ) were prepared and characterized by IR, 1H NMR, 13C NMR, Elemental analysis and Mass spectrometry. These three 5-amino-8-hydroxyquinolines derivatives were tested in the inhibition of corrosion of carbon steel (CS) in 1 M HCl using electrochemical impedance spectroscopy (EIS), Tafel polarization, weight loss, scanning electronic microscopy (SEM) and UV–visible spectroscopy. It was found that the inhibition efficiency of AMHQ, ACAMHQ and DMHQ increased with increasing concentration. For the three organic compounds, the DMHQ shows better efficiency than the other two products reaches 97% at 10− 3 M concentration. Polarization studies showed that AMHQ, ACAMHQ and DMHQ inhibitors were of mixed type in nature. The experimental data maked from EIS method show a frequency distribution and therefore a modeling element with frequency dispersion behavior, a constant phase element (CPE) has been utilized. To determine certain thermodynamic parameters of activation, the effect of temperature on corrosion rate was studied. The adsorption of 5-substituted-8-hydroxyquinolines derivatives on the carbon steel (CS) surface followed Langmuir adsorption isotherm. Scanning electron microscopy (SEM) and UV–visible spectroscopy were carried out on inhibited and uninhibited carbon steel samples to characterize the surface. Theoretical calculations were performed to gain further insight into the interaction of the inhibitors with carbon steel.

The semiconducting properties of the Scheelite CaWO4, synthesized by nitrate route, were investigated by the photocurrent technique and capacitance measurements in acidic solution (pH ∼ 5). CaWO4 crystallizes in the tetragonal symmetry with a large optical gap (4.88 eV) and a low electrical conductivity (σ300K = 2.63 × 10−5 Ω−1 cm−1). The photo-electrochemical characterization shows n type semi conductivity with a wide depletion length (∼110 nm). The Nyquist representation, measured in the range (10−3–105 Hz), indicates a predominant bulk contribution with a constant phase element which takes its origin from the electrode roughness. The results of CaWO4 are relevant for its applications to electro-photocatalysis. The conversion percentages of Phenobarbital reached respectively 54% and 66% with electro-catalysis and electro-photocatalysis under UV/C irradiation. The oxidation obeys to a first order kinetic with a rate constant of 1.98 × 10−3 min−1 and 2.7 × 10−3 min−1, respectively.

Cyclic voltammetry is a very useful tool for estimating several parameters such as electron transfer kinetics, diffusivity of active species, and effective surface area in a redox system. In cyclic voltammetry modeling, a simulated cyclic voltammogram is usually treated by neglecting the nonlinear effects of an electrical double layer and ohmic resistance. However, this approach leads to inaccurate prediction of such parameters. In this study, numerical modeling, including the combined effects of ohmic resistance, constant phase element, mass transfer, and faradaic processes, of cyclic voltammetry was carried out to show that, using this approach, nonlinear behaviors of the time-domain response of cyclic voltammetry can be encompassed. The model showed a good agreement with the experimental measurements. Furthermore, the numerical investigation of ohmic resistance and constant phase element effects on a cyclic voltammogram were performed.