Complex Impedance Plane Research Articles

Interdependence between structure and electrical characteristics in Sm-doped barium titanate

Conventional solid-state method was used to prepare powders of pure and barium titanate (BT) doped with different concentration of samarium. Influence of samarium addition on the structure modification, grain growth inhibition and microstructure development was studied. Dielectric properties of doped samples were significantly modified. With doping, a diffuse kind of ferro-para phase transition was induced, phase transitions positions were shifted and dielectric permittivity values were lowered in comparison with pure barium titanate. Detailed impedance and modulus data analysis were presented. The impedance complex plane showed two semicircular arcs for pure BT and one single depressed semicircular arc for all doped ceramics. Different electro-active regions in the modulus plane plots were also distinguish. The comparison between impedance and modulus scaling behavior presented the localized movement of charge carriers in the pure barium titanate and both, short and long range relaxations in the ceramics doped with 0.05 mol% of Sm. P-E hysteresis loops have shown the dilution of ferroelectric properties with Sm doping.

Dielectric relaxation and Ac conductivity of perovskites CH3NH3PbX3 (X = Br, I)

ABSTRACTMAPbX3 (MA = CH3NH3, X = Br, I) are synthesized by the chemical route. The Rietveld refinement of the room temperature X-ray diffraction pattern of the materials shows that MAPbBr3 is crystallized in the cubic Pm3m crystal symmetry whereas MAPbI3 crystallizes in the tetragonal phase with space group I4/mcm. The dielectric relaxation of MAPbX3 has been studied in the frequency range from 42 Hz to 0.2 MHz in the electric modulus formalism. The relaxation time is determined by the reciprocal of the frequency where the maximum of the imaginary part of the electric modulus is centred. The relaxation mechanism of the samples is investigated by the Cole-Cole model. The complex impedance plane plots are analyzed by an electrical equivalent circuit consisting of a resistance and a capacitance. The frequency dependent conductivity spectra follow the power law.

Impedance spectroscopy study of Bi 0.5 (Na 0.74 K 0.16 Li 0.10 ) 0.5 TiO 3 -Ba(Zr 0.05 Ti 0.95 )O 3 ceramics prepared via combustion technique

Abstract Lead free (1- x )Bi 0.5 (Na 0.74 K 0.16 Li 0.10 ) 0.5 TiO 3 - x Ba(Zr 0.05 Ti 0.95 )O 3 or BNKLT-100 x BZT, 0.025 ≤ x ≤ 0.125, ceramics with single-phase perovskite structure were prepared via a combustion technique. Impedance spectroscopy was conducted over a wide temperature and frequency range in order to investigate the influences of BZT on electrical properties and conduction mechanisms. Analysis using impedance complex plane plots combined with spectroscopic plots of the imaginary component of the impedance and electric modulus revealed an electrically homogeneous microstructure with increasing BZT content. With the increase in BZT content, the resistivity increased from ~10 6 Ω-cm at x = 0.025 to ~10 7 Ω-cm at x = 0.125. The activation energy determined from an Arrhenius-type plot of conductivity was also found to increase from 0.97 eV ( x = 0.025) to 1.62 eV ( x = 0.125), which is close to half of the optical bandgap, suggesting a change in conduction mechanism towards an intrinsic electronic conduction mechanism. IS measurement under different oxygen partial pressure was also performed on selected sample. The possible defect chemistry conditions responsible for the observed electrical properties will also be discussed.

Adaptive distance protection scheme with quadrilateral characteristic for extremely high‐voltage/ultra‐high‐voltage transmission line

Traditional distance protection may mal-operate or refuse to operate in the case of non-metallic faults, endangering the safety of power system. Therefore, a new adaptive distance protection scheme based on the impedance complex plane is proposed in this study. First, by utilising the phase relationship between the negative sequence current at the relaying point and the current at the fault point, the fault supplementary impedance angle caused by the fault resistance is calculated. Then, the effective fault impedance from the fault point to the relaying point is obtained by the trigonometric function relationship of the effective fault impedance, measured impedance and fault supplementary impedance on the impedance complex plane. On this basis, the criterion of the adaptive distance protection is constructed. Finally, test results on real-time digital simulator demonstrate that the protection scheme proposed in this study is applicable to various types of faults, and has a good adaptability to different system operating conditions. Compared with traditional distance protection scheme, the proposed scheme is immune to the fault resistance, thus mal-operation or operation-rejection of distance protection caused by the fault resistance could be effectively avoided.

Influence of temperature and Pr-doping on the dielectric properties of Ca2−xPrxMnO4 compounds and structural transition effects

ABSTRACTComplex perovskite oxides Ca2−xPrxMnO4 (x = 0–0.5) compounds were synthesized by a solid-state reaction technique. A tetra–ortho structural transition was observed. Impedance spectroscopy was used to study the electrical behavior in the frequency range 40 Hz–1 MHz and in the temperature range 80–350 K. Frequency-dependent conductivity spectra were found to obey the Jonscher's power law. Complex impedance plane plots have indicated that the dielectric response is mainly intrinsic. Materials bulk response was found to be dominated by non-localized or localized conduction, depending on temperature and frequency.

Effect of praseodymium ions on manganese based spinel ferrites

The dielectric and electrical properties of praseodymium substituted MnFe2O4 ferrite as a function of frequency (1MHz–3GHz) at room temperature have been studied. The dielectric constant and complex dielectric constant of these samples decreased with an increase of the praseodymium concentration, following the Maxwell–Wagner two-layer model. Complex impedance analysis has been used to separate the role of grains and the grain boundary's resistance of MnPryFe2-yO4 (y= 0.00, 0.025, 0.05, 0.075, 0.10. The values of the activation energy, calculated from the direct current conductivity, increase with the substitution of praseodymium, which suggests that the conduction mechanism in the present ferrite system is due to polaron hopping. The complex impedance plane plots show a single semicircle, which indicates that the capacitive and resistive properties of the materials are due to the contribution of grains and grain boundaries in ferrites. All these properties suggest that our prepared spinel ferrites are suitable for high frequency multilayer chip inductors.

Ceramic-Based Multisite Platinum Microelectrode Arrays: Morphological Characteristics and Electrochemical Performance for Extracellular Oxygen Measurements in Brain Tissue

Ceramic-based multisite Pt microelectrode arrays (MEAs) were characterized for their basic electrochemical characteristics and used for in vivo measurements of oxygen with high resolution in the brain extracellular space. The microelectrode array sites showed a very smooth surface mainly composed of thin-film polycrystalline Pt, with some apparent nanoscale roughness that was not translated into an increased electrochemical active surface area. The electrochemical cyclic voltammetric behavior was characteristic of bulk Pt in both acidic and neutral media. In addition, complex plane impedance spectra showed the required low impedance (0.22 MΩ; 10.8 Ω cm2) at 1 kHz and very smooth electrode surfaces. The oxygen reduction reaction on the Pt surface proceeds as a single 4-electron reduction pathway at -0.6 V vs Ag/AgCl reference electrode. Cyclic voltammetry and amperometry demonstrate excellent electrocatalytic activity toward oxygen reduction in addition to a high sensitivity (-0.16 ± 0.02 nA μM-1) and a low limit of detection (0.33 ± 0.20 μM). Thus, these Pt MEAs provide an excellent microelectrode platform for multisite O2 recording in vivo in the extracellular space of the brain, demonstrated in anaesthetized rats, and hold promise for future in vivo studies in animal models of CNS disease and dysfunction.

Effect of low Cobalt doping on morphology and properties of calcium ferrite and its application as cathode in Solid Oxide Fuel Cell

Cobaltite perovskites, such as polycrystalline complex brownmillerite oxide Ca2Fe2−xCoxO5, possess high catalytic activity with potential application as cathode materials for Solid oxide fuel cells. However, high Co concentration can lead to high thermal expansion coefficient, which makes them incompatible with widely used Zirconia electrolytes. In the present work we employ low Co concentration and elucidate the effect of morphology on the physical properties of wet chemical synthesized Ca2Fe2−xCoxO5 (x = 0, 0.01, 0.03). Oxygen stoichiometry was determined from iodometry titration at room temperature. Co incorporation in the lattice, as low as 1 mol%, reveals a change in morphology and grain size. We also evaluate the role of Ca2Fe2−xCoxO5 samples as cathode material in a bilayer (Cathode/Electrolyte) based on Ce0.9Sm0.1O2 (Samarium doped Ceria) solid electrolyte. Alternating Current (A.C) impedance spectroscopy showed variation in ionic conductivity with respect to temperature for Ca2Fe2−xCoxO5 (x = 0, 0.01, 0.03) in a temperature range from 400 °C to 800 °C. Activation energy with respect to Co-doping and temperature is reported. The complex impedance plane plots show a relaxed mechanism due to grain size effect. Scaling behavior of imaginary part of impedance indicates that relaxation follows similar mechanism at various temperatures.

Dielectric properties of single crystalline Ba(Ti0.99Zr0.01)2O5 prepared by the floating zone method

Zr4+-substituted single crystalline BaTi2O5 (Ba(Ti0.99Zr0.01)2O5) was prepared by the floating zone method, and its dielectric properties were investigated. The growth direction of Ba(Ti0.99Zr0.01)2O5 was parallel to the b axis. The Curie temperature of Ba(Ti0.99Zr0.01)2O5 was 710 K, which was 42 K lower than that of BaTi2O5. The complex impedance plane plot of BaTi2O5 in the b direction showed a semicircle associated with ferroelectric response and a spike associated with ionic conduction at 623 K. On the other hand, the complex impedance plot of Ba(Ti0.99Zr0.01)2O5 showed a single semicircle, suggesting almost no ionic conduction. The electrical conductivity of Ba(Ti0.99Zr0.01)2O5 was approximately half of that of BaTi2O5.

Effect of oxygen partial pressure during preparation of rutile-type FeNbTiO6 on electrical and dielectric properties, thermopower and Mössbauer spectra

Electrical and dielectric properties were measured on rutile-type FeNbTiO6, sintered in air, CO2 or 5%H2/CO2 atmosphere between temperatures of 1423 and 1573K. The individual samples show characteristic differences in DC and AC conductivity, dielectric constant ε(ω) (ω is angular frequency), dielectric loss and dissipation factor. Attempts were made to distinguish between bulk, grain boundary (GB) and sample–electrode (SE) processes. Samples show very high relaxor-like ε(ω) peaks at 500−600K using Ag-paint contacts as expected from previous studies during preparation in air that is of interest for industrial application; utilizing Pt-paint and using slightly reducing sintering conditions, a clear variation was observed. These findings point to a notable influence of GB and/or SE effects on the experimental ε(ω), in addition to the intrinsic origin by polar nanoregions, as suggested earlier. Complex plane impedance plots are characterized by semicircular arcs due to bulk, GB and/or SE charge transport. The derived DC conductivity σDC shows Arrhenius behavior with activation energy of EA≈0.27–0.37eV and σDC(300K) ≈1×10−6–3×10−4Ω−1cm−1 for the bulk, EA≈0.7–0.9eV and σDC(300K)≈5×10−10–1×10−4Ω−1cm−1 for GB and/or SE processes, depending on the preparation conditions. The thermopower is small and negative, hence n-type conduction occurs and the charge carriers are electrons or electron polarons. 57Fe Mössbauer spectroscopy enabled to gain knowledge of local nonstoichiometry in the environment of Fe cations, presumably affecting electrical conduction in the bulk and GBs; after sample preparation in reducing conditions, apart from Fe3+ also the presence of Fe2+ ions was established.

High temperature electrical characterization of nano-crystalline BaTiO3 synthesized using Ba(NO3)2 and TiO2

ABSTRACTThe reaction of Ba(NO3)2 with TiO2 was studied by thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques up to 1000°C and in nitrogen atmosphere. It was found that the formation of BaTiO3 takes place above 600°C. BaTiO3 powder was prepared by calcination of Ba(NO3)2 and TiO2 precursor mixture at 800°C for 8 h. X-ray diffraction analysis of the synthesized BaTiO3 confirmed the formation of tetragonal phase. Average crystallite size was found to be 44 nm, For the electrical and morphological characterization pellets of the obtained powder were sintered at 1000 °C for 12 h. Scanning electron micrograph (SEM) exhibits spherical and rod shaped grains. The dielectric constant, dissipation factor, complex plane impedance and ac conductivity of the sintered pellet has been measured in the temperature range of 40–600°C and frequency range of 100 Hz–2 MHz. DC conductivity of the sample was obtained from the impedance data. The conductivities (both ac and dc) and relaxation time (τ) exhibit two regions of temperature dependence, namely region I, which represents (280–450°C) and region II, which governs (450-600°C). Conduction and relaxation in both the temperature regions are explained in terms of hopping of electrons and doubly ionized oxygen vacancies (VO••).

Effects of substitution of Ti4+ by Nb5+ on the electrical properties of BaTi2O5 prepared by a floating zone method

Nb5+-substituted single-crystalline BaTi2O5 (Ba(Ti1−xNbx)2O5+z) was synthesised by a floating zone method, and the effect of Nb5+ substitution on the dielectric properties of Ba(Ti1−xNbx)2O5+z was investigated. The growth direction of Ba(Ti1−xNbx)2O5+z was parallel to the b axis. The a lattice constant and β angle increased from 1.6906 to 1.6918nm and from 103.09° to 103.13° at x=0–0.7at%, respectively. With increasing x, the Curie temperature of Ba(Ti1−xNbx)2O5+z decreased from 750 to 652K. A complex impedance plane plot of BaTi2O5 at 598K in the b direction showed a semicircle at high frequencies and a spike inclined at 45° to the real axis at low frequencies, indicating ionic conduction of bulk BaTi2O5. At x>0.002 (0.2at%), the complex impedance plots of Ba(Ti1−xNbx)2O5+z showed no inclined spike, suggesting dominantly electronic conduction. The electrical conductivity of Ba(Ti1−xNbx)2O5+z increased with temperature with an activation energy of 1.4 to 1.7eV and was minimum at x=0.001 (0.1at%). The spontaneous polarisation of Ba(Ti0.998Nb0.002)2O5+z was 2.7×10−2Cm−2, which was 2.5 times higher than that of BaTi2O5.

Synthesis & characterization of Dy and Ca Co-doped ceria based solid electrolytes for IT-SOFCs

Numerous compositions in the system, Ce1−x−yDyxCayO2−δ have been synthesized using citrate-nitrate auto-combustion route. Samples sintered at 1350 °C for 4 h have density more than 93% of the theoretical value. Single phase formation has been confirmed by X-ray diffraction in all the samples. Reitveld refinement has been carried out to confirm the cubic fluorite structure with space group Fm3¯m. Surface morphology of the sintered samples show the distinct grains and grain boundaries. Complex plane impedance analysis has been employed to separate the contribution of the grains, grain boundaries and electrode/specimen interface polarizations. A significant improvement in the electrical conductivity has been observed by partial replacement of Dy3+ with Ca2+ in Ce0.80Dy0.20O1.90 (keeping total number of oxygen vacancies fixed). Composition, Ce0.83Dy0.14Ca0.03O1.90 shows the highest conductivity, 1.45 × 10−2 S/cm at 600 °C. This value is about two orders of magnitude higher than that of singly Dy3+ doped ceria (6.01 × 10−4 S/cm) at the same temperature.

Rietveld refinement, impedance spectroscopy and magnetic properties of Bi0.8Sr0.2FeO3 substituted Na0.5Bi0.5TiO3 ceramics

We herein presented the investigation on the structural, electrical and magnetic properties of (1−x)(Na0.5Bi0.5TiO3)–x(Bi0.8Sr0.2FeO3) polycrystalline ceramic samples, with x=0.1, 0.3, 0.5 and 0.7. These samples were prepared by conventional solid state reaction method and the crystalline phase of prepared ceramics was identified with the help of X-ray diffraction pattern. Rietveld analysis of the obtained XRD data confirmed that all the synthesized samples adopt the rhombohedral crystal structure with R3c space group. Impedance spectroscopic measurements were performed on all the compositions in the frequency range 10Hz–5MHz to probe the electrical microstructure of polycrystalline (1−x)(Na0.5Bi0.5TiO3)–x(Bi0.8Sr0.2FeO3) ceramics, which changes significantly as a function of x (content of BSFO). A significant increase in dielectric constant has been observed with increase in BSFO concentration, which was attributed to enhancement of oxygen vacancies. Detailed study of impedance complex plane plots revealed the presence of non-Debye type relaxation for all the prepared systems and enabled us to separate the contribution from grains and grain boundaries. Equivalent circuit model (RgCPEg)(RgbCPEgb)(ReCPEe) was employed to explain the impedance data for all the prepared samples. The activation energies obtained from electric modulus as well as dc conductivity increase with increase in BSFO content, which approaches the value 1eV and indicates an Arrehenius type thermally activated process. Remnant magnetization (Mr) and coercive field (Hc) are found to be increase with BSFO concentration.

Electrical transport properties of CoMn0.2−xGaxFe1.8O4 ferrites using complex impedance spectroscopy

In this study, we report the influence of Ga content on the microstructural, magnetic, and AC impedance properties of Co-based ferrites with compositions of CoMn0.2−xGaxFe1.8O4 (x=0, 0.1, and 0.2) prepared by the solid-state reaction method. Experimental results showed that the as-prepared Co-based ferrites had a single-phase spinel structure; the Curie temperature of Co-based ferrites decreased with increasing Ga content. All ferrite samples exhibited a typical hysteresis behavior with good values of saturation magnetization at room temperature. The electrical properties of Co-based ferrites were investigated using complex impedance spectroscopy analysis in the frequency range of 100 kHz-50 MHz at temperatures of 150 to 250 oC. The impedance analysis revealed that the magnitudes of the real part (Z’) and the imaginary part (Z”) of complex impedance decreased with increasing temperature. Only one semicircle was observed in each complex impedance plane plot, which revealed that the contribution to conductivity was from the grain boundaries. It was found that the relaxation time for the grain boundary (τgb) also decreased with increasing temperature. The values of resistance for the grain boundary (Rgb) significantly increased with increasing Ga content, which indicated that the incorporation of Ga into Co-based ferrites enhanced the electrical resistivity.

Effect of Sintering Atmosphere on Microstructure and Dielectric Properties of Sr(Fe0.5Nb0.5)O3 Ceramics

The Sr(Fe0.5Nb0.5)O3 (SFN) dense ceramics were sintered at 1450°C in N2, air and O2 atmosphere for 3 h, respectively. All ceramics sintered at various atmospheres exhibited a single phase with perovskite structure in the space group Pmm(221). The microstructure and dielectric properties of SFN ceramics were related to the sintering atmospheres. The dielectric constant of the sample sintered in N2 atmosphere reached the highest value (about 23,000) at room temperature. With the increasing of the oxygen partial pressure, the dielectric constant decreased significantly. Moreover, the complex plane impedance plots even demonstrated that the samples were electrically heterogeneous and consisted of low resistive grains and high resistive grain boundaries. The giant dielectric phenomenon of SFN ceramics was therefore attributed to the IBLC model. The resistivity of grain boundary increased drastically with increasing the oxygen concentration while the resistivity of grain increased inconspicuously. With XPS analysis, it was illustrated that the oxygen vacancy concentrations of SFN ceramics decreased with increasing oxygen concentration, which indicated that a higher value of dielectric constant of SFN ceramics was obtained at lower oxygen concentration. The results strongly indicated that further improvement of the dielectric characteristics in the present ceramics is expected by optimizing sintering atmospheres.

Electronic and Ionic Conductivity of La0.95Sr0.05Ga0.95Mg0.05O3-δ (LSGM) Single Crystals

The defect chemistry and charge transport properties of La0.95Sr0.05Ga0.95Mg0.05O3-δ (LSGM) single crystals, grown by the Czochralski technique, were studied by impedance spectroscopy performed over a wide temperature range (180–800°C) and oxygen partial pressures from 0.21 to 1013 mbar. Owing to ion blocking Pt thin film electrodes impedance data showed a Warburg type 45° slope in the complex impedance plane. The spectra were analyzed by means of a generalized transmission line model which yielded the electronic and ionic conductivity, chemical and dielectric capacitance and the oxygen chemical diffusion coefficient. Activation energies for electronic (0.89 eV) and ionic charge transport (0.95 eV at low and 0.56 eV at high temperatures) were determined. Oxygen partial pressure dependent measurements revealed that the p-type conductivity is exactly proportional to pO21/4 and that the ionic transference number approaches 1 for low oxygen partial pressures and low temperatures. Additional Hebb-Wagner type DC polarization experiments were carried out to determine the n- and p-type conductivities in a broad chemical potential range and to verify the results obtained by the AC impedance measurements.

Structural and AC conductivity study of CdTe nanomaterials

Cadmium telluride (CdTe) nanomaterials have been synthesized by soft chemical route using mercapto ethanol as a capping agent. Crystallization temperature of the sample is investigated using differential scanning calorimeter. X-ray diffraction and transmission electron microscope measurements show that the prepared sample belongs to cubic structure with the average particle size of 20nm. Impedance spectroscopy is applied to investigate the dielectric relaxation of the sample in a temperature range from 313 to 593K and in a frequency range from 42Hz to 1.1MHz. The complex impedance plane plot has been analyzed by an equivalent circuit consisting of two serially connected R-CPE units, each containing a resistance (R) and a constant phase element (CPE). Dielectric relaxation peaks are observed in the imaginary parts of the spectra. The frequency dependence of real and imaginary parts of dielectric permittivity is analyzed using modified Cole–Cole equation. The temperature dependence relaxation time is found to obey the Arrhenius law having activation energy ~0.704eV. The frequency dependent conductivity spectra are found to follow the power law. The frequency dependence ac conductivity is analyzed by power law.

Dielectric Relaxation of Rare Earth Ordered Double Perovskite Oxide Ba2ErTaO6

The electrical properties of rare-earth based ordered double perovskite oxide barium erbium tantalate, Ba2ErTaO6 synthesized by solid-state reaction method are investigated. The x-ray diffraction pattern of the sample shows cubic Fm3m phase at room temperature with ordering of the B cations. Fourier transform infrared spectrum shows two primary phonon modes of the sample at around 350 cm−1 and 600 cm−1. The dielectric relaxation of the sample is investigated in the frequency range from 50 Hz to 1.1 MHz and in the temperature range from 303 K to 673 K. Electric modulus and electrical impedance data are fitted to the Cole–Cole equation. The frequency dependent conductivity spectra follow the power law. Summerfield scaling is used to explain the conduction mechanism. The scaling behavior of the imaginary part of the impedance spectra suggests that the relaxation shows the same mechanism at various temperatures. The complex impedance plane plots show that the relaxation (conduction) mechanism in this material is mainly due to grain boundary effect for all temperatures and grain effect for low temperature. The relaxation frequency corresponding to dielectric loss is found to obey Arrhenius law with activation energy of 0.50 eV. The values of activation energy indicate that the dielectric relaxation and the conduction mechanism are due to adiabatic small polaronic hole hopping mechanism.

Impedance spectroscopy of chitosan/poly(vinyl alcohol) films

Polymer films were cast from aqueous solutions of chitosan (CS) and poly(vinyl alcohol) (PVA) in employing tetraethoxysilane (TEOS) as a crosslinking agent. Different amounts of TEOS were used and the presence of siloxane bond was confirmed by Fourier transform infrared (FTIR) spectroscopy. The swelling behavior of the films was determined by exploring the time-dependent swelling in distilled water. The swelling kinetics showed a linear increase and achieved maximum value within half an hour. The emergence of one arc in complex impedance plane plot exhibited the presence of one type of relaxation process. The ac conductivity was also calculated which was increased from 2.55 × 10−12 to 9.05 × 10−12 Ω−1cm−1 as the amount of crosslinker was increased from 2 to 6 %. Further increase in the amount of crosslinker (up to 10 %) reduced the conductivity to minimum value of 0.24 × 10−12 Ω−1cm−1. The novel properties of the biocompatible films can be utilized in biomedical applications concerning the biological systems which require smaller charge in medicinal apparatus, bioelectrodes coatings, etc.