Complex Impedance Behavior Research Articles

Temperature dependent transition effects on the dielectric properties of PVA/Y2O3 polymer nanocomposites

This study investigates the dielectric properties, including dielectric constant (ɛ′), dielectric loss (ɛ″), tangent delta (tan δ), and AC conductivity (σac), of PVA/Y2O3 polymer nanocomposites (PNCs). The dielectric behavior of the PNCs was examined as a function of frequency and temperature. The results revealed that the addition of Y2O3 nanoparticles to the PVA matrix influenced the dielectric properties of the composites. In contrast to pure PVA, the PVA/Y2O3 PNCs with a 15 wt% Y2O3 loading exhibited high values of ɛ′, ɛ″, tan δ and σac are 647.49, 1607.48, 9.70 and 1.024 × 10−5, respectively, at low frequency and at particular temperature. Furthermore, the electrical properties of PVA/Y2O3 PNCs were also investigated using the Cole-Cole plots. These plots provide valuable insights into the complex impedance behavior and allow for comprehensive understanding of the electrical response of the nanocomposites.

Negative temperature co-efficient of resistance behaviour of Cr doped ZnO nanoceramics

Here, High Energy Ball Milling (HEBM) is used to prepare Cr doped ZnO (Zn1-xCrxO, x = 0–0.04) nanoceramics and their electrical behaviour is studied in detail. The X-ray diffraction suggests a hexagonal wurtzite structure. The Rietveld refinement XRD pattern of the sample calcined at 900 °C suggests that up to 4 at% of Cr can be doped into the ZnO structure. After sintering, the growth in the particle size was observed for Cr doped ZnO samples. The complex impedance behaviour of samples suggests a decrease in resistance with temperature. This shows the Negative Temperature Coefficient of Resistance (NTCR) characteristic of the Cr doped ZnO sample in the studied temperature range (300–500 °C). At higher temperature, the electrical relaxation behaviour is of the non-Debye type as observed from the relaxation time distribution. The equivalent electrical circuit of ZnO and Cr doped ZnO ceramic samples are a parallel arrangement of bulk capacitance (Cb) and bulk resistance (Rb).

Towards an Impedance-Based Analysis of SOFC-Stacks

To understand the performance and durability limitations in SOFC stacks and systems, impedance spectroscopy is becoming increasingly important. However, in the analysis of entire stacks, gradients over the active cell area are averaged out, preventing access to local phenomena.To get better insight into the spatial distribution of performance losses in a stack layer, incremental cells and repeat units with an active electrode area of 1 cm² are investigated in this study.Impedance spectroscopy and the subsequent impedance data analysis by the distribution of relaxation times (DRT) is applied to deconvolute the polarization processes in the Ni/CGO fuel electrode and the LSM air electrode of the investigated electrolyte supported cell. To ensure an appropriate deconvolution of air and fuel electrode processes, next to full cells symmetrical anode and cathode cells are applied. In case of Ni/CGO fuel electrodes charge transfer and gas diffusion overlap in the spectrum and the assignment has to be done indirectly using inert gas mixtures [1].In Figure 1 impedance spectra and DRTs of fuel and air electrode obtained from symmetrical cells are compared with the full cell spectrum. This analysis enables a clear allocation of the processes in the single cell to Ni/CGO fuel electrode and LSM air electrode.Next to the cell testing in an inert, ideal environment namely an Al2O3 flow field with gold and nickel contact grids respectively, the study is expanded to stack like conditions. The additional losses due to contact resistances and gas supply limitations are studied similar to Kornely et al. [2] for single repeat units (single cell + contact layer + metallic interconnects). In this contribution a physio-chemical equivalent circuit model based on these measurements will be presented and the complex impedance behavior of single cells and repeat units will be discussed.

Towards an Impedance-Based Analysis of SOFC-Stacks

This proceeding aims to understand the performance of SOFC stacks using impedance spectroscopy. For the stack analysis, gradients over the active cell area are averaged out, preventing access to local phenomena. Hence, to get better insight into the spatial distribution of losses, single cells with an active electrode area of 1 cm² are characterized at 850 °C based on EIS and DRT-analysis. To ensure an appropriate deconvolution of processes, symmetrical anode and cathode cells are also tested. Next to the ideally contacted cells, metallic interconnecting repeat units are analyzed to study the impact of contacting and gas supply in the stack. The effect of fuel utilization was also investigated by mimicking different locations in the stack. In this contribution, the complex impedance behavior of the stack based on polarization losses will be discussed. The paper also provides disentangled information often lost or averaged out in stacks.

Structural and dielectric properties of ion beam irradiated polymer/silver composite films

In this work, flexible nanocomposite films that are composed of silver (Ag) nanoparticles, polyaniline (PANI) and methylcellulose (MC) were manufactured using the casting solution fabrication technique. The manufactured films were characterized using X-ray diffraction and Fourier transform infrared spectroscopy, which confirming the preparation of the composite samples. The MC/PANI/silver films were then irradiated with oxygen (O)-ion beams at a range of fluences (8 × 1017, 16 × 1017 and 24 × 1017 ions/cm2). The electrical conductivity, complex impedance behavior, electric modulus and energy density of pure and irradiated films were determined throughout the frequency range 100 Hz–5 MHz. The oxygen-beam irradiation of MC/PANI/silver films caused a significant modification in dielectric parameters. Also, the dielectric constant ε′ improved from 0.68 to 3.17, and the conductivity was modified from 1.47 × 10−6 to 25.9 × 10−6 S/cm. The findings of the present study will pave the way for the use of irradiated MC/PANI/silver nanocomposite films in a variety of applications, including microelectronic devices, batteries and supercapacitors.

Influence of ion beam and silver nanoparticles on dielectric properties of flexible PVA/PANI polymer composite films

ABSTRACT In this work, a solution cast technique was used to prepare flexible nanocomposite films of PVA/PANI/Ag with different concentrations of PANI and AgNPs. The samples were described by X-ray diffraction (XRD), transmission electron microscope (TEM), and infrared spectroscopy, which confirmed the successful synthesis of the nanocomposite films. After that, the PVA/10%PANI/6%Ag nanocomposite film was irradiated by different influences of the oxygen ion beam (8 × 1017, 16 × 1017, and 24 × 1017 ions/cm2). The Ac conductivity, dielectric properties, electric modulus, complex impedance behaviour, and the energy density efficiency of the non-irradiated and irradiated films were measured in the frequency range of 100–106 Hz. The results revealed significant changes in these parameters with an increase in concentrations of PANI and Ag nanoparticles inside the host and also with ion beam irradiation. The reported improvements in this study would open the road for appropriating the unirradiated and irradiated nanocomposite films for electromagnetic shielding and optoelectronic applications.

Influence of B-site cations ordering on magnetization and dielectric relaxations in Li–Ni spinel ferrites

Ho-substituted Li–Ni ferrites with composition L i1.2Ni0.4HoxFe2-xO4; 0≤ x ≤ 0.15 were synthesized by a self-ignited sol-gel process. An annealing temperature of 950 °C is estimated via thermal-gravimetric (TGA) analysis. X-ray diffraction (XRD) scans have confirmed the formation of the ferrite phase with a spinel structure in all samples. Substitution of Ho ions on the B-site significantly reduced the porosity from 38 -to 23% and the crystallite size from 23.4 -to 21.7 nm. Microstructural analysis revealed a denser structure with an increase in Ho content. Dielectric results showed that both the dielectric loss and dielectric constant depict a nonlinear variation with the addition of Ho. Complex impedance behavior with a single semicircle for all samples suggests the predominant effect of the grain boundary mechanism. The substitution of Ho ions in place of Fe ions significantly decreased the electrical conductivity. The anisotropic Ho3+ ions reinforce the L-S coupling which consequently enhanced the coercive force from 145 -to 389 Oe, and thus the anisotropy constant.

Origin of colossal permittivity and low dielectric loss in Na1/3Cd1/3Y1/3Cu3Ti4O12 ceramics

We designed a new type of perovskite-related dielectric material Na1/3Cd1/3Y1/3Cu3Ti4O12 (NCYCTO) with colossal permittivity via a solid-state method. A decent dielectric performance of colossal permittivity ~4.0 × 104 and low dielectric loss ~0.065 was achieved in NCYCTO ceramics sintered at 1060 °C for 15 h. Electronic heterogeneity structure in NCYCTO ceramics was confirmed combined with the analysis of the dielectric properties, conductivity characteristics and complex impedance behavior, which consist of semiconductor grains and large resistance insulating grain boundary. Notably, internal barrier layer capacitor effect was adopted to explain the decent dielectric performance based on the analysis of dielectric response behavior and complex impedance. Our finding in this work not only explored the dielectric response of the new type of giant dielectric ceramics Na1/3Cd1/3Y1/3Cu3Ti4O12 but also provides useful insight to simultaneously realize the low dielectric loss and colossal permittivity in ACu3Ti4O12 dielectric ceramics.

Conduction and dielectric relaxation studies on substituted iron(II) phthalocyanine thin film

The dc conductivity and complex impedance behavior of spin-coated 2,9,16,23-Tetra(chloro)-3,10,17,24-tetra(4-(4-methoxyphenyl)- 8 methylcoumarin-7-yloxy)phthalocyaninatoiron-(II) (7) thin film was investigated over a temperature range of 298–550 K. The results obtained on dc conductivity reveals that the conduction is dominated by the variable range hopping in three dimension. Analysis of the frequency dependent conductivity data shows that the variation of the frequency exponent (n) is consistent with the predictions of the correlated barrier hopping (CBH) model below 425 K. On the other hand, the temperature dependence of n becomes stronger than model predictions above 425 K. Complex dielectric formalism was used in order to investigate the dielectric relaxation mechanism in the film. Non-Debye type relaxation process was observed. It was found that the imaginary part of the dielectric function varies as Bωs with s in the range of 0.35–0.68.

Structural, dielectric and AC conductivity studies of Zn substituted nickel ferrites prepared by combustion technique

A series of zinc doped nickel ferrites having the chemical formula Ni1−xZnxFe2O4 [x = 0.0, 0.25, 0.50, 0.75, 1.0] were synthesized by combustion method. The powder X-ray diffraction results confirm the formation of single phase cubic spinel structure. The lattice parameter was found to increase from 8.348 to 8.443 A with increase in the Zn content. Average crystallite size calculated using Debye–Scherrer equation and Williamson–Hall plots confirms the nano crystalline nature of the samples. The EDAX analysis indicates the correct elemental composition of the synthesized powders. Fourier transform infrared spectra show the characteristic peaks of Ni–Zn spinel ferrites. The morphological features of the powder were examined by SEM and reveal the fine crystalline nature of the powder. A systematic study on the dielectric properties such as dielectric constant (ɛ′), dielectric loss tangent (tan δ) and AC conductivity (σac) were investigated as a function of Zn content and frequency in the range from 100 Hz to 1 MHz at room temperature. Complex impedance behavior was explained by means of the cole–cole plot.

Gas sensor properties of surface modification on nebuliser spray coated ZnO nanostructure thin films

Zinc oxide (ZnO) thin films deposited on glass substrates at various temperatures 300, 400 and 500°C by the nebuliser spray pyrolysis technique. X-ray diffraction results indicate that the films are polycrystalline in nature having hexagonal crystal structure with preferred grain growth orientation along (002) plane. The crystallite size increases along (002) plane with temperature increase from 350 to 500°C and attains a maximum 109 nm at 500°C. High resolution scanning electron microscopy study shows the formation of good quality film on total substrate surface with uniformly distributed tiny spherical shaped grains at 350°C. The ultraviolet–visible–near infrared spectroscopy confirms the possibility of good transparent ZnO thin films deposited with an average transmission of ∼85% in the visible region. Optical band gap energy increases from 3.19 to 3.27 eV with the substrate temperature of 350–500°C. The depression of near band edge (NBE) emission and deep level emission of the films were estimated through photoluminescence measurements. As the substrate temperature increases, the peak of NBE emission is found to have a blue shift towards lower wavelength side, and the same result is also found from the band gap energy determination of optical transmittance measurement. The complex impedance behaviour of the pure and ZnO sensors at 175°C with 250 ppm of ammonia has been studied.

Dielectric properties of PEO–PVP–MMT nanocomposite hydrocolloids

The relative complex dielectric function, electric modulus, alternating current electrical conductivity and complex impedance behaviour of aqueous poly(ethylene oxide) (PEO) and poly(vinyl pyrrolidone) (PVP) blend with montmorillonite (MMT) clay nano-platelets as colloidal suspensions have been investigated over the frequency range 20 Hz to 1 MHz at 15, 30 and 45 °C. The direct current ionic conductivity and real part of permittivity of the hydrocolloids have increased whereas electrode polarization relaxation time has decreased with the increase of MMT concentration, and these dielectric parameters have significantly varied with change of the temperature. The hydrogen bond complex formation between PEO, PVP and dispersed MMT nano-platelets in aqueous solutions has been discussed. The correlation between complex structures and the dielectric parameters of these materials have been confirmed.

On the intrinsic electrochemical nature of the inductance in EIS—A Monte Carlo simulation of the two-consecutive steps mechanism: The rough 3D case and the surface relaxation effect

In this paper, a two-consecutive steps anodic dissolution mechanism is simulated at the atomic level by a Monte Carlo algorithm on a 3D lattice. In contrast with a previous work restricted to the 2D flat case, it is shown that the steady state and transient behaviors are controlled not only by the adsorbed intermediate coverage degree but also by the area of the rough interface build up by the dissolution of interfacial atoms. It is established that the complex impedance behavior results from a combination of the individual frequency responses of these two quantities. The emphasis is put on the specific properties of the impedance induced by the surface roughness relaxation for which a kinetic description is proposed and compared to the Monte Carlo data. It is clearly concluded that, by taking into consideration the surface re-arrangement, the number of frequency domains in the impedance may be larger than predicted by the derivation of a kinetic model on a flat interface.

Hydrogen interaction on metal/hydrogenated amorphous silicon Schottky structures: adsorption/desorption effects

In this work we study metal/hydrogenated amorphous silicon structures (metal/a-Si:H). The a-Si:H is deposited at a high rate by DC magnetron sputtering on N-type doped silicon substrate. The metal is deposited by DC sputtering on the a-Si:H. Nickel, magnesium and platinum are used. The current–voltage (I–V) curves show a rectifying contact. The hydrogen is injected in the vacuum chamber at low pressure (1 mbar) to interact with the metal/a-Si:H structure. The interaction effect is observed on the I–V characteristics and on the complex impedance behavior. These effects may be explained by a thermal activation of hydrogen adsorption/desorption phenomena which is localized in the interfacial zone. The hydrogen is chemisorbed in the interfacial zone and modifies its electrical charge.

Effects of water salinity, saturation and clay content on the complex resistivity of sandstone samples

Abstract Complex resistivity measurements were made on sandstone samples in the frequency range from 10 Hz to 2 MHz. The main objective was to investigate the frequency response of complex resistivity and phase angle as a function of salinity, water saturation and clay content. The results showed the classical frequency dependence behaviour where the complex resistivity decreases with increasing frequency. The complex impedance behaviour in the intermediate frequency range (10–100 kHz) was used to relate the effect of frequency dispersion with interface polarization and, hence, pore geometry, specific surface area and permeability. Both water saturation and salinity were found to influence the gradient and the relaxation frequency of the complex resistivity versus frequency relationship. A variation in water saturation from full to partial saturation resulted in a dramatic increase in the gradient and a clear shift of the relaxation frequency. Both the saturation and salinity dependence can be attributed to the polarization of both the rock-fluid and fluid-fluid interfaces within the pore space, which depend on the geometry and physical characteristics of the interfacial layers. The results presented in this paper can have important applications in identifying low resistivity and low contrast pay zones.

Impedance spectroscopy of teeth with and without approximal caries lesions--an in vitro study.

Caries diagnosis by the measurement of electrical resistance is hampered by polarization effects when dc or single-low-frequency ac currents are used. Electrical impedance spectroscopy, measuring impedance over a large range of frequencies, will provide more detailed information about the electrical characteristics of teeth. It was the aim of this study (a) to characterize the complex impedance behavior of whole extracted teeth, measured at the approximal surface, and (b) to identify parameters of the complex impedance behavior of the teeth which would be useful in distinguishing between degrees of carious involvement. Thirty-nine extracted premolar teeth with 59 unrestored and undamaged (excepting caries) approximal surfaces were selected. The tooth surfaces were divided into three groups according to their macroscopic appearance: sound (group S, n = 16), white- or brown-spot lesion present (group L, n = 33), or cavitated (group C, n = 10). The teeth were inserted into a jig which allowed for counter-electrode contact via a conducting gel. The working electrode consisted of a carbonated fiber material. Electrical impedance measurements were performed over a maximum range of about 1 MHz to 0.1 Hz. We analyzed electrical impedance data by fitting equivalent circuits. Fit was evaluated numerically and visually. The complex impedance spectra divided naturally into three groups which corresponded almost perfectly with the classifications of S,L, and C. The groups differed most in the dc resistance (Rdc), as calculated from the impedance parameters. Mean Rdc for groups S, L, and C were 68 M omega, 5.9 M omega, and 321 k omega, respectively. These means were significantly different from each other (log-transformed data, ANOVA, p < 0.001; Tukey multiple comparisons, p < 0.001). It is concluded that the in vitro performance of electrical impedance spectroscopy in differentiating among sound, non-cavitated carious, and cavitated approximal tooth surfaces is excellent.

Ionic conductivity of a novel smectic polymer electrolyte

Polymers having the following general formula have been synthesised ▪ where R is a long chain alkyl substituent such as -C 16H 33. The number of skeletal oxygen atoms n = 5 or 6 (coded C16O5 or C16O6) so that the helix formed by association of neighbouring side groups R, has 18 or 21 skeletal bonds per rotation and so imitates the PEOLi + or PEONa + 2 1 helix. Complexes with LiBF 4 in stoichiometries of 1 mol salt per structural (helical) repeat unit and 0.5 mol per repeat have been prepared. Small-angle- and wide-angle X-ray diffraction, thermal analysis and hot stage polarised light microscopy have been used to show that the complexes form smectic systems in the uncomplexed and complexed forms. In the complexes, cations are enclosed within the helices and the anions lie between planes of helices and the alkyl side chains so that the overall d spacing is 42.9 Å. The -C 16H 33 side chains melt at ca. 40 °C in the complexed material, to give a liquid crystal phase. The liquid crystal-isotropic transition varies slightly according to polymer and stoichiometry and is 89 °C for C16O5:LiBF 4 (1:1). The ionic conductivity-temperature relationship shows well-defined transitions at the phase changes and the complex impedance behaviour also reflects the several states of the system. The conductivity of the (1:1) complex is higher than the (1:0.5) complex and is comparable to P(EO) 6:LiBF 4 in the crystal and istropic phases, but is somewhat lower over the temperature range of the liquid crystal phase.

Electrical behaviour of CaO-doped ThO2

The total a.c. conductivity of a CaxTh1−xO2−x solid solution with fluorite-type structure was measured at 1360 Hz with 0⩽x⩽0.25 and at temperatures of 100 to 600° C. The complex impedance behaviour was investigated at frequencies of 10 to 105 Hz and temperatures of 300 to 500° C. The complex dielectric permittivity was calculated at this frequency and in that temperature range. The activation energy for the bulk conductivity was calculated. Its value is about 1.48 eV forx<0.03 and about 1.25 forx⩾0.03.

The electrode resistance of ZrO 2Y 2O 3(-Bi 2O 3) solid electrolytes with Pt electrodes

The electrode resistance ( R e1) at low over-voltages has been determined for Bi 2O 3 free and Bi 2O 3 doped yttria-stabilized zirconia with sputtered platinum electrodes. The anode and cathode resistances are measured separately and are equal. Bi 2O 3 causes a decrease of the electrode resistance at small overvoltage and with 5 × 10 −4 < P O 2 ⩽ 1 atm. The rate determining step for the electrode reaction under the measuring conditions probably is a charge-transfer process in which oxygen adsorbs dissociatively on the bismuth free and associatively on the bismuth doped samples. The complex impedance behaviour of the electrode reaction can be interpreted in terms of R-C circuits in the P O 2 range of 10 −2−1 atm.

Glassy Carbon/KCl-Solution Interface Impedance. Mechanical Surface Treatment Effect

Abstract The dependence of complex impedance behaviour on mechanical surface treatment of glassy carbon electrodes in standard water KCl solutions at room temperature was investigated. A considerable frequency dependence of both the real and the imaginary term of the impedance was observed in the entire 1-50 kHz range of frequencies used for electrodes of different surface roughness. The results are discussed in the light of the Levie theory.