Complex Impedance Diagrams Research Articles

Dielectric properties of Bismuth Titanate (Bi4Ti3O12) synthesized using solution combustion route

Ferroelectric Bismuth Titanate (Bi 4 Ti 3 O 12 ) was prepared by solution combustion route with glycine as fuel. The single phase Bismuth Titanate was obtained after calcination at 800 °C, which was confirmed with the help of X-ray diffraction studies and EDS analysis. SEM micrographs of the calcined powders show agglomerated particles, which is typical of combustion synthesis. Behavior of dielectric constant and dielectric loss as a function of temperature of as prepared sample are reported here. Ferroelectric to paraelectric phase transition occurs at the temperature T c ∼650 °C. Impedance studies were made in the frequency range from 1 KHz to 1 MHz. The semicircles observed in the complex impedance diagrams indicate deviation from the Debye behavior. Activation energy of the sample around T c is found to be ∼0.35 eV and below T c is ∼0.13 eV, which was calculated using the Arrhenius plots.

Fabrication, Structural and AC Impedance Studies of Layer-Structured Bi4Ti3O12 Ceramics

Fabrication, Structural and AC Impedance Studies of Layer-Structured Bi4Ti3O12 Ceramics In the present research bismuth titanate Bi4Ti3O12 (BiT) ceramics was synthesized by the standard solid-state reaction method from the mixture of oxides, followed by free sintering at temperature T=1000°C. BiT ceramics was studied in terms of its chemical composition (EDS), crystalline structure (X-ray), microstructure (SEM) and dielectric properties (ac technique of complex impedance spectroscopy) over a range of frequency (ƒ=100Hz to ƒ=1MHz) and temperature (T=200-500°C). Experimental results confirmed the phase formation. It was found that BiT ceramics crystallized in orthorhombic symmetry, best described with Fmmm space group and the following elementary cell parameters: a=5.409(6)°A, b=5.449(2)°A and c=32.816(2)°A. It was also found that BiT ceramics exhibited the plate-like microstructure and stoichiometric chemical composition. Impedance spectroscopy measurements showed contribution of three overlapping relaxation processes (three semicircles in the complex impedance diagrams were observed) ascribed to bulk, grain boundary and electrode/interface polarization phenomena. Impedance data were fitted to the corresponding equivalent circuit using the complex nonlinear least squares (CNLS) method. The ac conductivity for grains, grain boundaries and electrode processes was calculated from CNLS fit of the impedance data and thus the activation energy of ac conductivity (σAC) and relaxation (τ) was calculated for the three revealed components of the impedance spectra from the slopes of σAC and τ versus 1000/T plots (semi log scale) in the range of ΔT=200-500°C.

Structural and electrical properties of co-doped zirconia electrolyte for intermediate temperature solid oxide fuel cell application

SUMMARY Structural and electrical properties of 8 yttria stabilized zirconia (YSZ) ceramics doped with varying concentrations (0.5–2.0 wt%) of Mg2+ ions were investigated. The result from X-ray diffraction indicates the formation of fully stabilized cubic phase. Scanning electron microscopy observation confirms the marginal decrease in grain size with addition and increase of MgO content. However, a concentration beyond x = 0.5 wt% results in segregation along the grain boundaries. Complex impedance diagrams showed an enhancement in the grain and grain boundary conductivities with doping of magnesium and are strongly dependent on its concentration. It is observed that among the compositions investigated, 8YSZMg0.5 exhibited higher conductivity at all temperatures (600–800 °C) with a maximum conductivity of 0.0345 S/cm at 800 °C. This is further confirmed by the lowest activation energy of Ea = 0.92 eV, estimated for 8YSZMg0.5 in comparison to 1–1.01 eV observed for other compositions. Comparative evaluation of these results with standard 8YSZ electrolytes reveals the possibility of the effective use of 8YSZMg0.5 as a new electrolyte material for intermediate temperature solid oxide fuel cell applications. Copyright © 2011 John Wiley & Sons, Ltd.

Impedance Behavior of SOFC at High Fuel Utilization and a Way of Evaluating Diffusion Contribution

A quantitative evaluation method of gas diffusion resistance is proposed in which measurement of V-I characteristics under constant fuel utilization (Uf) and ac impedance were combined to separate diffusion and electromotive force change contributions from the low frequency semi-circle observed in complex impedance diagrams. Diffusion resistance was evaluated using various hydrogen content mixture diluted with nitrogen, Uf , hydrogen flow rate and current as parameters. From the measurement under various Uf, it was found that the diffusion resistance at low Uf originates mainly from the diffusion of H2O. Also, from the measurement under various hydrogen concentration in inlet fuel, the diffusion resistance was found to become significantly large with decreasing hydrogen content.

Sensitivity and complex impedance of nanometer zirconia thick film humidity sensors

Nanometer zirconia (ZrO 2) with grain size 20 nm was used to make thick film humidity sensor on silicon substrate. The impedance of the sensor changed from 10 6 Ω to 10 2 Ω when the relative humidity (RH) varied from 11% to 98%. The curve of impedance vs frequency showed good linearity when the measured frequency was in between 100 Hz and 1 kHz. The temperature influenced the impedance of the sensor. Complex impedance (Nyquist) diagrams of the sensor at different relative humidities and temperatures were drawn. An equivalent circuit with resistors and capacitors was built to explain the conduction process of the sensor. In low RH range, the conduction process was dominated mainly by conduction and polarization of the grains of nanometer zirconia, while in high RH range, by decomposition and polarization of the absorbed water.

Electrochemical studies on the stability and corrosion resistance of new zirconium‐based alloys for biomedical applications

AbstractThe biocompatibility of commercially pure zirconium and its alloys is closely related to their surface properties with both the composition of the protecting oxide film and the surface topography playing an important role. This article is a study of corrosion behavior of new zirconium alloys for orthopedic implants, which are supposed to be used instead of some implant materials that have a higher citotoxicity. For this reason, zirconium and its alloys will be employed widely in biomedical applications. The higher stability and corrosion resistance exhibited by zirconium are due to the spontaneous formation of a passive zirconium oxide film, which protects the metal from further oxidation. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) are used as electrochemical techniques. Measurements were carried out to investigate the corrosion behavior of zirconium and Zr2.5Nb, Zr3Ta, and Zr2.5Nb3Ta alloys in aerated Hank solution at 37 ± 0.2 °C. The results of EIS were compared with those obtained by potentiodynamic polarization techniques. Impedance spectra were represented both in complex impedance diagram (Nyquist plot) and Bode plots. The EIS measurements have confirmed this stability range and pointed out the formation of oxide layers on the electrode surfaces. Copyright © 2008 John Wiley & Sons, Ltd.

Influence of substitution on dielectric and impedance spectroscopy of Sr 1 − xBi 2 + yNb 2O 9 ferroelectric ceramics synthesized by chemical route

Nanocrystalline powders of Sr 1 − x Bi 2 + y Nb 2O 9 (SBN, x = 0.0, 0.1, 0.2, 0.3, and 0.4; y = 0, 0.066, 0.133, 0.200, and 0.266) were prepared by aqueous solution method using water-soluble Sr–EDTA, Bi–EDTA and Nb–tartarate as the starting materials. XRD showed that the samples were free from fluorite or pyrochlore phase within heat-treatment temperature from 550 to 600 °C. Average crystallite size and particle diameter were observed to be between 10 and 25 nm, which were analyzed through XRD and TEM, respectively. Bi-substitution has substantially improved the sinterability of SBN and enabled to achieve high density (96%), which was otherwise difficult in the case of pure SBN. The dielectric properties of SBN ceramics were significantly enhanced by the partial replacement of Sr 2+ ions by the trivalent bismuth ions. The complex impedance diagrams of Bi-substituted SBN, x = 0.4 ceramics exhibited only one semicircle indicating a significant contribution from the grains. In contrast, the impedance plots for pure and other substituted SBN ceramics show an additional low-frequency semicircle, which was attributed to the blocker size effects. The dielectric behavior of pure and Bi-substituted SBN ceramics was rationalized using the impedance and modulus data.

Impedance spectroscopy of YSZ electrolyte containing CuO for various applications

The electrical properties of yttria stabilized zirconia (YSZ) electrolyte containing different amounts of CuO (0–1 mol%) have been studied. The complex impedance diagrams showed an increase in the grain boundary resistivity with CuO addition. The bulk resistivities were comparable to those of the CuO free YSZ except for the sample containing 1 mol% CuO which showed a small increase in resistivity. The results showed the possibility to sinter YSZ at low temperature 1250 °C to a very high sintered density by adding a small amount of CuO (0.3 mol%). The conductivity of the latter is nearly equal to that of YSZ sintered at 1500 °C. This might be a step forward in the development of oxygen pumps by reducing the electrolyte sintering temperature which leads to better quality and low cost.

Electrode reaction of Sr 1− xLa xCo 0.8Fe 0.2O 3− δ with x = 0.1 and 0.6 on Ce 0.9Gd 0.1O 1.95 at 600 ≤ T ≤ 800 °C

The electrode reaction of the perovskite phases Sr 1− x La x Co 0.8Fe 0.2O 3− δ ( x = 0.1 and 0.6) on Ce 0.9Gd 0.1O 1.95 has been investigated by impedance spectroscopy in the temperature range 600 ≤ T ≤ 800 °C. Thick porous electrodes ( t ∼ 20 μm) were sprayed on Ce 0.9Gd 0.1O 1.95 and ac impedance spectra were recorded on symmetrical cells at the equilibrium. The analysis of the complex impedance diagrams clearly indicates the presence of two contributions. The low frequency one was assigned to the gas phase oxygen diffusion through the porous electrode and a finite length diffusion (Warburg) impedance was used to describe the high frequency (HF) data. The polarization resistance of the HF impedance contribution ( R w) is higher for x = 0.1 while the activation energy of R w is higher for x = 0.6. The variations of R w versus the La content, temperature and thickness indicate that the Warburg-type impedance contains information of both bulk oxygen diffusion and surface processes.

Microstructural, dielectric, impedance and electric modulus studies on vanadium—doped and pure strontium bismuth niobate (SrBi2Nb2O9) ceramics

SrBi2Nb2O9 (SBN) and SrBi2(Nb0.9V0.1)2O9 (SBVN) ceramics were fabricated from the powders consisting of μm sized grains, obtained via the solid state reaction route. V2O5 was found to be an effective microstructure modifier and grain growth truncator for SBN ceramics. X-ray structural studies carried out on SBVN ceramics confirmed the existence of preferential orientation (c-planes) of the grains. V2O5 addition has substantially improved the sinterability of SBN and enabled to achieve high density (95%) which was otherwise difficult in the case of pure SBN. The dielectric properties of SBN ceramics were significantly enhanced by the partial replacement of Nb ions by pentavalent vanadium ions. The complex impedance diagrams of dense SBVN ceramics exhibited only one semicircle indicating a significant contribution from the grains. In contrast, the impedance plots for the porous (density 88%) SBN ceramics show an additional low-frequency semicircle which was attributed to the blocker (pore) size effects. The dielectric behavior of SBN and SBVN ceramics was rationalized using the impedance and modulus data.

AC impedance behavior of a practical-size single-cell SOFC under DC current

AC impedance measurements were carried out using practical-size planar disc-type SOFC which employs lanthanum gallate as a solid electrolyte. The data were obtained under practical conditions of gas flow rate and DC current. Under these conditions, the gas conversion impedance (GCI), which originates from the change of the electromotive force (EMF) caused by the change in anodic gaseous concentrations along the flow direction, was observed in the low-frequency range of the data obtained. The overlapping impedance together with GCI on the low-frequency arc was also estimated. Experimentally obtained GCI was in good agreement with that calculated. It was concluded that GCI was predominant in the impedance data obtained under practical conditions. The shift of the high-frequency intercept in the complex impedance diagrams was shown to appear as a result of the change in the distribution of gaseous composition in the anode. The dependency of the low-frequency arc on temperature was also shown, and it was assumed that the overlapped impedance varies as the temperature changes. The validity of the impedance measurement, as a diagnostic means to evaluate the gas flow in SOFC stack, was suggested.

Impedance analysis of a disk-type SOFC using doped lanthanum gallate under power generation

Impedance measurements were carried out under practical power generation conditions in a disk-type SOFC, which may be utilized as a small-scale power generator. The tested cell was composed of doped lanthanum gallate (La 0.8 Sr 0.2 Ga 0.8 Mg 0.15 Co 0.05 O 3− δ ) as the electrolyte, Sm 0.5 Sr 0.5 CoO 3 as the cathode electrode and Ni/Ce 0.8 Sm 0.2 O 2 cermet as the anode electrode. The cell impedance was measured between 10 mHz and 10 kHz by varying the fuel utilization and gas flow rate and plotted in complex impedance diagrams. The observed impedance shows a large semi-circular pattern on the low frequency side. The semi-circular impedance, having a noticeably low characteristic frequency between 0.13 and 0.4 Hz, comes from the change in gas composition, originally caused by the cell reaction. The change in impedance with the fuel utilization (load current) and the gas flow rate agreed qualitatively well with the theoretical predictions from a simulation. This impedance was dominant under high fuel-utilization power-generation conditions. The impedance, which described the activation polarizations in the electrode reactions, was comparatively small and scarcely changed with the change in fuel utilization (load current) and gas flow rate.

Characterization of Bi4Ge3O12 single crystal by impedance spectroscopy

Bi4Ge3O12 (bismuth germanate - BGO) single crystals were produced by the Czochralski technique and their electrical and dielectric properties were investigated by impedance spectroscopy. The isothermal ac measurements were performed for temperatures from room temperature up to 750 °C, but only the data taken above 500 °C presented a complete semicircle in the complex impedance diagrams. Experimental data were fitted to a parallel RC equivalent circuit, and the electrical conductivity was obtained from the resistivity values. Conductivity values from 5.4 × 10(9) to 4.3 × 10-7 S/cm were found in the temperature range of 500 to 750 °C. This electrical conductivity is thermally activated, following the Arrhenius law with an apparent activation energy of (1.41 ± 0.04) eV. The dielectric properties of BGO single crystal were also studied for the same temperature interval. Permittivity values of 20 ± 2 for frequencies higher than 10³ Hz and a low-frequency dispersion were observed. Both electric and dielectric behavior of BGO are typical of systems in which the conduction mechanism dominates the dielectric response.

Impedance spectroscopy of Bi 4Ti 3O 12 ceramic produced by self-propagating high-temperature synthesis technique

Bi 4Ti 3O 12 (bismuth titanate—BIT) ferroelectric ceramic was synthesized by self-propagating high-temperature synthesis (SHS) technique. The microstructure, electric and dielectric properties were determined and the results were compared to a reference sample produced by solid state reaction. The powders from SHS had agglomerated particles with average size of 200 nm. Bi 4Ti 3O 12 100% crystalline phase was reached after SHS reaction followed by sintering at 1050°C/2 h. The sintered bodies presented high relative density (98%) and small grain size (around 5 microns). The electrical and dielectric properties of the samples were studied using the impedance spectroscopy technique, and the three observed semicircles in the complex impedance diagrams were associated to the bulk, plate boundaries and grain boundaries of the sintered ceramics. The samples produced through SHS presented the same bulk conductivity as the reference one, and lower conductivity of the grain and plate boundaries. The same dielectric constant ε′=200, at 300 °C and f=1 MHz, was found for SHS sample and for the reference. For higher temperatures, at this same frequency, SHS samples presented higher relative permittivity than the reference, and for temperatures above T c both samples presented the same Curie–Weiss parameters. The differences observed in the electrical conductivity and relative permittivity, were attributed to the differences in the grain size and defect concentration. The anomaly in the permittivity curves near 550 °C is also discussed.

Temperature effect on graphite KS44

Graphite Lonza KS44 in a solution 1 M LiClO4 in a propoylene carbonate ethylene carbonate (1 M:1 M) mixture was lithiated and delithiated galvanostatically at room temperature and at the elevated temperature of 55 ?C. Voltage?time profiles and complex impedance diagrams were recorded and are discussed for this particular system. It was confirmed that this type of graphite shows a relatively small current loss consumed by exfoliation, if lithiated at room temperature. However, the voltage?time curve of the first charging at 55 ?C shows a long voltage plateau at 0.7 Vvs. Li/Li+, which corresponds to 540 mAh g-1 of irreversible capacity attributed to exfoliation. The solid electrolyte layer formed at elevated temperature although less protecting in the sense of electrolyte reduction, shows a remarkably higher electrical resistance than that formed at room temperature. A comparison of the impedance diagrams of lithiated and delithiated samples allows the conclusion that mass transfer through the graphite, not that through the solid electrolyte layer, plays a dominant role in the mass transfer limitations.

Dielectric response and complex impedance spectroscopy studies in pulsed laser ablated (Ba, Sr)TiO3 thin films

The dielectric response of pulsed laser ablated barium strontium titanate (Ba, Sr)TiO3 thin films was studied as a function of frequency, time and ambient temperature. Both time and frequency responses followed the ”universal power law’ pertaining to the universal dielectric response model theorized by Jonscher. Theoretical fits were used to compare the experimental results and determine the temperature dependence of the theoretical parameters such as n(T) and a(T) used in the universal model. Complex impedance spectroscopy was used to investigate the grain, grain boundary, and electrode/film interface responses. The complex spectroscopic plots revealed the major response originated from the bulk grains while in the case of polycrystalline samples the grain boundary contributed significantly. Arrhenius plot of the bulk resistance calculated from complex impedance diagrams showed a significant difference in the activation energy ranging from 1.17 to 1.23 eV for samples grown at different substrate temperatures.

A note on overpotential dependence of AC impedance data

Charge-transfer resistance [R-ct = (d eta/di)(eta=0)] and Tafel plots of current density (i) versus overpotential (eta) data are generally known to yield values of the energy-transfer coeffficient (alpha) and exchange current density (i(o)) of an electrochemical reaction. In the present investigation, the resistance (d eta/di)(eta not equal 0) that could be calculated by differentiating a wide range of i - eta curves was also shown to provide the values of alpha and i(o), by plotting ln(d eta/di)(eta not equal 0) against eta. Since alpha and i(o) could also be evaluated directly from the experimental DC polarization data, the procedure was not of significant importance.. Nevertheless, it was considered important in evaluating alpha and i(o) from AC impedance data, because the procedure was based on data analysis, which was much simpler than that reported in the literature. A cobalt electrode prepared from fine metal powder was used in 1 M KOH electrolyte and the hydrogen evolution reaction was studied by AC impedance at several potentials. The resistance values measured from the complex plane impedance diagram were plotted against the potential, and the values of alpha and i(o) were evaluated.

An ac impedance study of the anodic dissolution of iron in sulfuric acid solutions containing hydrogen sulfide

Abstract The anodic dissolution of iron in sulfuric acid solutions with H 2 S was investigated by means of ac impedance and steady-state polarization curves. The results show that H 2 S can accelerate markedly both the anodic dissolution and cathodic hydrogen evolution in most cases, but it can also exhibit a strong inhibiting effect upon iron dissolution under certain special conditions. Usually, the Nyquist diagrams measured at lower positive potentials consist of two overlapping capacitive loops, one of which is a characteristic capacitive loop caused by the adsorption of H 2 S on the electrode surface. At higher positive potentials, the original characteristic low frequency capacitive loop disappears, and the complex plane impedance diagrams for the iron electrode consist of an inductive loop and a capacitive loop. Based on the impedance behaviour of iron in the presence of H 2 S, two reaction models were proposed to interpret its dissolution mechanism in acidic solutions with H 2 S.

The electrochemical behavior and impedance characteristics of the passive film on carbon steel in nitric acid solutions

Abstract The impedances of passivated carbon steel in 1.0 M HNO 3 were measured at various polarization potentials. Complex impedance diagrams having two capacitive loops in the high frequency range and a Warburg response at low frequencies were obtained. The charge transfer at the metal|oxide interface was a reversible reaction, and the resistance was independent of the potential. The impedance of the charge transport in passive films can be described by a nonlinear transport equation. The diffusion coefficient in the passive film formed on carbon steel in 1.0 M HNO 3 was about 9.8×10 −17 cm 2 s −1 , and the charge transport in the film followed a diffusion mechanism. The surface layer of the film was a stable n-type semiconductor phase in the low potential range (0.4 to 1.3 V), but it can be converted to a metal-like layer due to degeneration of the surface layer at high potentials (>1.3 V).

Structure determination of the new layered compound Cs 2TiP 2O 8 and ionic conductivity of Cs 2MP 2O 8 (M=Ti, V)

A new titanium pyrophosphate Cs 2TiP 2O 8 with a layer structure and isotypic with Cs 2VP 2O 8 has been synthesised using solid state reactions. The structure determination of this material, from X-ray powder diffraction, shows that it crystallises in the orthorhombic space group Pnma with the parameters a=13.521(0) Å, b=7.253(2) Å and c=9.439(9) Å. The basic structure of this new compound consist in [Ti 2P 4O 16] ∞ layers parallel to the (100) plane sandwiching Cs atoms. These layers built up from TiO 5 square pyramids and P 2O 7 groups forming [TiP 2O 8] ∞ and [TiPO7] ∞ chains running along [010] and [001] directions respectively. The ionic conductivity was measured and compared for the compounds Cs 2MP 2O 8 (M=Ti, V) over the frequency range 1 Hz–10 MHz, and temperatures between 523 K and 873 K for Cs 2TiP 2O 8, and between 423 and 703 K for Cs 2VP 2O 8, using complex impedance diagrams. The conductivities were analysed by an Arrhenius equation of the form σ= σ 0 exp(− E a/ k T). The activation energy calculated were E a(Ti)=0.80 eV and E a(V)=0.88 eV.