Complex Impedance Plane Research Articles

Impedance spectroscopy analysis of complex perovskite Ho(Ni1/2Zr1/2)O3

The complex perovskite oxide Holmium nickel zirconate, Ho(Ni1/2Zr1/2)O3(HNZ) is synthesized by solid-state reaction technique. The X-ray diffraction pattern of the sample at room temperature shows a monoclinic phase. The microstructure analysis is done by scanning electron microscope. Alternating current impedance spectroscopy is applied to investigate the electrical properties of HNZ in a temperature range from 313 K to 723 K and in a frequency range from 100 Hz to 1 MHz. The complex impedance plane plots show that the relaxation mechanism in HNZ is due to grain boundary effect. Scaling behavior of imaginary part of impedance indicates that relaxation in HNZ describes the same mechanism at various temperatures. The frequency dependent conductivity data are fitted to the universal power law. The frequency dependent electrical data are also analyzed in the framework of electric modulus formalism.

Dielectric Relaxation and Hopping Conduction in La2NiO4+δ

An ac conductivity as well as dielectric relaxation property of La2NiO4.1is reported in the temperature range of 77 K–130 K and in the frequency range of 20 Hz–1 MHz. Complex impedance plane plots show that the relaxation (conduction) mechanism in this material is purely a bulk effect arising from the semiconductive grain. The relaxation mechanism has been discussed in the frame of electric modulus spectra. The scaling behavior of the modulus suggests that the relaxation mechanism describes the same mechanism at various temperatures. The logarithmic angular frequency dependence of the loss peak is found to obey the Arrhenius law with the activation energy of~0.09 eV. The frequency-dependent electrical data are also analyzed in the frame of ac conductivity formalism. The ac conductivity has been found to follow a power-law behavior at a limited temperature and frequency region where Anderson localization plays a significant role in the transport mechanism for La2NiO4.1.

Enhancement of electrical and magnetic properties of Cd2+ doped Mn–Zn soft nanoferrites prepared by the sol–gel autocombustion method

Nanocrystalline Mn–Zn soft ferrites with chemical formula Mn0.5Zn0.5−xCdxFe2O4 (x=0.0–0.35) were synthesized using the sol–gel autocombustion method. The formation of single phase cubic spinel structure was confirmed from X-ray diffraction (XRD) pattern for all samples. The average crystallite size was calculated using Scherrer's formula and it remains within the range 24–50±2nm. The structural parameters, lattice constant, XRD density, polaron length, polaron radius, lattice strain and porosity, have been calculated using XRD data. The variation in dielectric constant, dielectric loss tangent, AC conductivity and complex impedance analysis were studied in the frequency range from 20Hz to 5MHz at room temperature. The values of dielectric constant and loss tangent were found to be lowest for the concentration x=0.25. The high values of DC electrical resistivity (2.2×1011Ωcm at 373K) and activation energies suggests the conduction in Cd2+ doped Mn–Zn ferrite system is due to hopping of polarons. Complex impedance plane plots were used to separate the grain and grain boundary effects in Mn0.5Zn0.5−xCdxFe2O4. Vibrating sample magnetometer measurements carried out at room temperature shows that saturation magnetization and magnetic moment increased with increase in cadmium content up to x=0.25. The addition of Cd improves the magnetic and electrical properties of Mn–Zn ferrites.

Investigation of Grain Size Effect on the Impedance of CaCu<sub>3</sub>Ti<sub>4</sub>O<sub>12</sub> from 100 Hz to 1 GHz of Frequency

CaCu3Ti4O12 (CCTO) is a cubical perovskite phase and sintered ceramics exhibit very high dielectric constant at room temperature. The speculated origins of the high dielectric constant are the existence of insulative barrier layer at grain boundaries and domain boundaries which created an internal barrier layer capacitance (IBLC) at the microstructure of CCTO. The relation of grains and domains electrical resistance were studied in this work by using impedance spectroscopy (IS). A series of samples with different heat treatment temperature were tested to investigate their microstructure by using field emission scanning electron microscopy (FESEM). The grains and domains resistance was calculated from a wide frequency range of impedance complex plane measurement (100 Hz to 1 GHz). The FESEM and IS analyses showed the dependency of grains and domains resistance to average grains size of CCTO microstructure.

Dielectric relaxation and conduction mechanism in Ba2GdTaO6

The double perovskite oxide barium gadolinium tantalate, Ba2GdTaO6 (BGT) is synthesized by solid-state reaction technique. The Rietveld refinement of the X-ray diffraction pattern of the sample shows cubic phase at room temperature. Fourier transform infrared (FTIR) spectrum shows two primary phonon modes of the sample at around 587cm−1 and 858cm−1. Raman spectrum of the sample taken at 488nm excitation wavelength, shows three primary strong peaks at 832, 384 and 106cm−1. Group theoretical study is performed to assign the different vibrational modes of BGT. Dielectric spectroscopy is applied to investigate the ac electrical conductivity of BGT in a temperature range from 333K to 673K and in a frequency range of 42Hz–1MHz. The complex impedance plane plots show that the relaxation (conduction) mechanism in this material is purely a bulk effect arising from the semiconductive grains. The relaxation time corresponding to dielectric loss is found to obey Arrhenius law with an activation energy of 0.32eV. The electric modulus formalism is adopted to interpret the relaxation mechanism of BGT.

Re-evaluation of electrical conductivity of anhydrous and hydrous wadsleyite

Recent laboratory electrical conductivity measurements of the main mantle constituent minerals have represented considerable efforts to determine the effects of water content on electrical conductivity. However, there are large discrepancies between the results of Yoshino et al. (2008a) and those of Dai and Karato (2009a) on hopping conduction and the effects of water on the electrical conductivity of wadsleyite. To investigate the cause of these discrepancies, the electrical conductivity of anhydrous and hydrous wadsleyite were newly measured under low and high temperature conditions by impedance spectroscopy. The conductivity values of dry wadsleyite aggregates with less than 2ppm H2O by weight were similar to those for hopping conduction reported by Yoshino et al. (2008a) and distinctly higher than those of Dai and Karato (2009a). For hydrous wadsleyite, at temperatures below 1000K, the electrical conductivity in an Arrhenius plot was repeatable along the heating–cooling paths and was similar to the results of Yoshino et al. (2008a). The impedance spectrum in the complex impedance plane of hydrous wadsleyite showed a semicircular shape, and the infrared spectrum did not show any shape change after the conductivity measurements. In contrast, when the temperature exceeds 1000K, the electrical conductivity in an Arrhenius plot showed higher activation enthalpy. The impedance spectra were greatly distorted and the impedance arc contained at least two relaxation processes. This shape is similar to those reported by Dai and Karato (2009a) who measured the conductivity above 1000K. The infrared spectra showed a large contribution from molecular water after conductivity measurements, suggesting significant dehydration during the conductivity measurements. In summary, the results obtained from conductivity measurements at higher temperatures (>1000K) do not represent the proton conduction in the grain interior.

Electrical properties and microwave dielectric behavior of holmium substituted barium zirconium titanate ceramics

Structural, microwave dielectric and electrical properties of (Ba1−xHox)(Zr0.52Ti0.48)O3 with the mole fraction of x=0.1 and 0.2 have been investigated. The results obtained from these studies indicate the substitution of Ho-ions within the barium zirconium titanate. The microwave dielectric parameters were measured using the time domain reflectometry (TDR) method in the frequency range 10MHz to 30GHz. The dielectric constant as a function of temperature exhibited diffuse phase transition behavior for x=0.1 Ho-substituted ceramics accompanied with lower value of dielectric constant. Complex impedance (Z∗) planes show frequency dependent behavior as the response for the grain resistance mechanisms. This mechanism has been represented by an RC equivalent circuit. Our results along with the observation of negative temperature coefficient of resistance (NTCR) upon Ho3+ ions substitution clearly suggest the design and development of novel microwave dielectric resonators based on barium zirconium titanate materials substituted with rare earth ions.

Preparation and characterization of ceria co-doped with Ca and Mg

The aim of the present investigation was to study the effect of doping of magnesium and calcium on the ionic conductivity of CeO2 in the system Ce1−xCax−yMgyO2−x (x=0.150) for its use as a solid electrolyte in the intermediate temperature solid oxide fuel cells (IT SOFC).Attempts have been made to synthesize a few compositions in this system with x=0.150 and y=0.000, 0.050, 0.060, 0.065 and 0.070. The precursor materials have been synthesized by auto-combustion method. Solid solution forms in compositions with y≤0.060. Microstructures of thermally etched samples have been studied by scanning electron microscopy (SEM). In order to evaluate the total electrical conductivity, σt, use is made of complex plane impedance analysis. Impedance measurements were made in the frequency range 1Hz–1MHz and temperature range 250–500°C. It is found that co-doped samples show higher conductivity than undoped and singly doped samples.

In situ monitoring of the electrochemical degradation of polymer films on metals using the bending beam method and impedance spectroscopy

Electrochemical and mechanical properties of thin poly(3,4-ethylenedioxythiophene) (PEDOT) films deposited on gold and platinum have been investigated in aqueous sulfuric acid solutions. At sufficiently positive electrode potentials overoxidation of the polymer takes place on both metals. Structural changes of the polymer layer caused by overoxidation (degradation) could be detected by using the electrochemical bending beam method. The impedance spectra recorded after overoxidation differed considerably from the impedance spectra of freshly made electrodes. The most interesting feature was the appearance of an arc (or a “depressed semicircle”) at high frequencies in the complex plane impedance plot, which indicates that the charge transfer process at the metal/film interface is hindered by the degradation process. Changes of the effective mass of the film were studied by electrochemical quartz crystal microbalance (EQCM). The morphological changes of the PEDOT film during overoxidation were analyzed by scanning electron microscopy (SEM).

Dielectric Relaxation in Complex Perovskite Oxide Sr(Gd<sub>0.5</sub>Nb<sub>0.5</sub>)O<sub>3</sub>

The complex perovskite oxide a strontium gadolinium niobate (SGN) synthesized by solid-state reaction technique has single phase with tetragonal structure. X-ray diffraction (XRD) technique and scanning electron microscopy (SEM) were used to study the structural and microstructural properties of the ceramics, respectively. The XRD patterns of SGN at room temperature show a tetragonal structure. Studies of the dielectric constant and dielectric loss of compound as a function of frequency (50 Hz to 1 MHz) at room temperature, and as a function of temperature (60°C to 420°C) indicate polydispersive nature of the material. The logarithmic angular frequency dependence of the loss peak is found to obey the Arrhenius law with activation energy ~0.18 eV. The small value of activation energy of the compound (~0.18 eV) can be explained by mixed ionic-polaronic conductivity mechanism. The grain size of the pellet sample was found to be 1.92 μm. The frequency-dependant electrical data are analyzed in the framework of conductivity and electric modulus formalisms. The complex plane impedance plot shows the grain boundary contribution for higher value of dielectric constant in the law frequency region.

Effect of cation disorder on structural, magnetic and dielectric properties of La2MnCoO6 double perovskite

The origin of dielectric anomalies and magnetodielectric response of La2MnCoO6 has been investigated by means of ultra-high resolution synchrotron x-ray powder diffraction, neutron powder diffraction, resistivity, magnetization and dielectric measurements. The study has been performed on two different bulk samples presenting different degrees of Mn/Co order: 95 and 74%. Beside the well-known influence on magnetic properties, our results show that the main effect of disorder lies on the electrical resistivity. Bond distances clearly show Mn4+/Co2+ valence states in the well-ordered sample, while for the disordered one this picture still holds. AC resistivity data show dielectric anomalies and a small magnetodielectric effect, but impedance complex plane analyses prove that these phenomena appear at the frequency–temperature region where extrinsic effects dominate the dielectric response.

Effect of strontium (Sr) doping on the conductivity of ceria

A few compositions in the system Ce 1− x Sr x O 2− x with 0.05 ≤ x ≤ 0.20 have been prepared by auto-combustion method. More than 93% of theoretical density has been achieved by sintering at 1350 °C for 4 h. Solid solution has formed in the composition with x = 0.05. All other compositions have been found to contain XRD lines of SrCeO 3 beside the major fluorite phase. Complex plane impedance analysis has clearly revealed the contribution of grains, grain boundaries, and electrode specimen interface to the total observed resistance of the sample. Conduction occurs mainly due to diffusion of O 2− ions through oxygen vacancies as indicated by values of activation energy of conduction. Composition, Ce 0.95 Sr 0.05 O 1.95 exhibits the highest ionic conductivity 3.26 × 10 −3 S cm −1 at 500 °C among the series. Ionic conductivity decreases gradually with increasing x. This is due to the formation of a second phase SrCeO 3 and increasing probability of formation of neutral associated defect pairs, S r ′ ′ Ce − V O .

Electrical conductivity of albite at high temperatures and high pressures

The electrical conductivity of low albite has been measured using a complex impedance spectroscopic technique at 1.0–3.0 GPa and 773–1073 K in the frequency range of 10 −1 to 10 6 Hz in a YJ-3000t multi-anvil press. Within this frequency range, the complex impedance plane displays a semi-circular arc that represents a grain interior conduction mechanism. The electrical conductivity of albite increases with increasing temperature, and the relationship between electrical conductivity and temperature fits the Arrhenius formula. Pressure has a weak effect on the electrical conductivity of albite in the experimental pressure-temperature ( P - T ) range in the present work. The pre-exponential factors decrease, and the activation enthalpy increases slightly with increasing pressure. The activation energy and activation volume of albite are 0.82 ± 0.04 eV and 1.45 ± 0.28 cm 3 /mol, respectively. Comparison with previous results with respect to albite indicates that our data are similar to previous data within the same temperature range. The dominant conduction mechanism in albite is suggested to be ionic conduction, where loosely bonded sodium cations, the dominant charge carriers, migrate into interstitial sites within the feldspar aluminosilicate framework. The Na diffusivity inferred from electrical conductivity of albite in this study using the Nernst-Einstein relation is consistent with that of previous studies on natural albite.

CaCu<SUB>3</SUB>Ti<SUB>4</SUB>O<SUB>12</SUB> Nanoparticles Using Polyvinyl Pyrrolidone: Synthesis and Dielectric Properties

Nanocrystalline CaCu3Ti4O12 powders with particle sizes of 39.28 8.12 nm were synthesized by a simple modify sol-gel using PVP (Poly-vinyl-pyrrolidone). The synthesized precursor was characterized by TG-DTA to determine the thermal decomposition and crystallization temperature which was found to be at above 500 degrees C. The precursor was calcined at 800 degrees C in air for 8 h to obtain nanocrystalline powders of CaCu3Ti4O12. The calcined CaCu3Ti4O12 powders were characterized by XRD, FTIR, SEM and TEM. Sintering of the powders was conducted in air at 1100 degrees C for 16 h. The XRD results indicated that all sintered samples have a typical perovskite CaCu3Ti4O12 structure and a small amount of CaTiO3. SEM micrographs showed the average grain sizes of 1.86 +/- 0.69 /m for the sintered CaCu3Ti4O12 ceramic prepared using the CaCu3Ti4O12 powders calcined at 800 degrees C. The sintered samples exhibit a giant dielectric constant, epsilon' of approximately 10(3)-10(4). The large low-frequency dielectric permittivity at low temperature is closely related to sub-grain boundary distribution, including conductivity effect. Furthermore, the ceramic shows three semicircles in the complex impedance plane. However, at low frequency, semicircles of sub-grain boundary and grain boundary are considered to represent collapse different electrical mechanisms. The another is ascribed to the contribution of grain. The dielectric behavior at several frequencies and temperatures of these samples can be attributed to electronic inhomogeneities present in material and can be explained based on a microstructural model.

Dielectric and impedance properties of Sr(Sm 0.5Nb 0.5)O 3 ceramics

Perovskite types Sr(Sm 0.5Nb 0.5)O 3, (SSN) ceramics have been prepared through solid state reaction route. The scanning electron microscopy provides information on the quality of the samples and uniform grain distribution over the surface of the samples. The field dependence of the dielectric response was measured in a frequency range from 50 Hz to 1 MHz and in a temperature range from 60 °C to 420 °C indicates polydispersive nature of the materials. An analysis of the dielectric constant ( ɛ′) and tangent loss (tanδ) with frequency is performed assuming a distribution of relaxation times as confirmed by the scaling behavior of electric modulus spectra. The frequency dependence of the electric modulus peak is found to obey Arrhenius law with activation energy of ∼0.026 eV. The complex plane impedance plot shows the grain boundary contribution for higher value of dielectric constant in the law frequency region. The frequency dependence of electrical data is also analyzed in the framework of conductivity and electric modulus formalisms. Both these formalisms show qualitative similarities in relaxation times. The scaling behavior of imaginary part of electric modulus M″ suggests that the relaxation describes the same mechanism at various temperatures in SSN.

Structural studies of NASICON material of different compositions by sol–gel method

The NASICON (Na 1 + x Zr 2Si x P 3 − x O 12) is a well known solid electrolyte material with high ionic conductivity. The ion conductivity can be improved by modifying the structure. The NASICON powders with different compositions (by varying x) have been prepared by sol–gel method. The structural and conductivity measurements have been done by XRD, complex plane impedance analysis and electrochemical cell method. The results indicate that the ac conductivity and Na + ion selectivity are higher for x = 2.05 as compared to other compositions. The enhancement of Na + ion conductivity for x = 2.05 has been attributed to modifications in the orientations of tetrahedral structures which lead to change in the bottleneck size. The results have been confirmed by X-ray diffraction (XRD).

Electrochemical performance of a mechanochemically prepared submicron-sized crystalline Nd 1.8Ce 0.2CuO 4± δ cathode for intermediate temperature solid oxide fuel cells

To produce a Nd 1.8Ce 0.2CuO 4± δ solid solution, the oxide form of the reagents were milled for 36 h and sintered at 1173 K for 8 h in a microwave furnace. The transition from a negative temperature coefficient (NTC) of conductivity to a positive temperature coefficient (PTC) was suppressed due to the submicron size of the crystallites. The low-frequency response in the complex impedance plane fit the Gerischer element. At 973 K, the area specific resistance (ASR) of Nd 1.8Ce 0.2CuO 4± δ /GDC/Nd 1.8Ce 0.2CuO 4± δ sintered at 1073 K for 2 h was 1.92 ohm cm 2.

Electrical conductivity of undoped, singly doped, and co-doped ceria

In order to investigate the effect of single doping and co-doping on the enhancement of ionic conductivity in ceria (CeO2), CeO2 and a few compositions in the system Ce0.85Sm0.15 − xGdxO1.925 (x = 0.00, 0.06, 0.09, and 0.15) were prepared using citrate–nitrate auto-combustion method. Gels were characterized by simultaneous differential thermal analysis and thermogravimetric analysis to confirm the formation of end product from the precursor. All the compositions were found to be single-phase solid solution from their X-ray diffraction pattern. Complex plane impedance analysis clearly revealed the contribution of grains, grain boundaries, and electrode specimen interface to the total value of the resistance. The value of activation energy, Ea, of conduction shows that the conduction process is mainly due to diffusion of O2− ions through oxygen vacancies. Effect of doping has been analyzed using the concept of radius mismatch and effective index reported earlier in the literature.

Dielectric properties of iron doped calcium copper titanate, CaCu 2.9Fe 0.1Ti 4O 12

CaCu 2.9Fe 0.1Ti 4O 12 (CCFTO) has been prepared by a novel semi-wet route and its dielectric properties have been studied in the temperature range 300–500 K. It is found that dielectric constant ( ɛ) decreases drastically in the frequency range 100 Hz to 1 MHz. Complex plane impedance and modulus analysis was done to understand this drastic decrease in ɛ. Oxidation state of various ions was studied using X-ray photoelectron spectroscopy (XPS). The decrease in the permittivity of CCFTO can be attributed to two factors: the suppression of the Ca/Cu disorder in CCFTO which is observed in CaCu 3Ti 4O 12 (CCTO) and the absence of the grain boundary internal barrier layer capacitance mechanism.

Dielectric spectroscopy and confirmation of ion conduction mechanism in direct melt compounded hot-press polymer nanocomposite electrolytes

Solid-type polymer nanocomposite electrolyte (PNCE) comprising poly(ethylene oxide) (PEO), lithium perchlorate (LiClO4) and montmorillonite (MMT) nano-platelets were synthesized by direct melt compounded hot-press technique at 70 °C under 3 tons of pressure. The spectra of complex dielectric function, electric modulus and alternating current (ac) electrical conductivity, and complex impedance plane plots of these materials were investigated in the frequency range 20 Hz to 1 MHz at ambient temperature. The variation of electrode polarization and ionic conduction relaxation times with MMT concentration up to 20 wt.% confirms their strong correlation with direct current ionic conductivity. The predominance of exfoliated MMT structures in PEO matrix and their effect on cation conduction mechanism and ion pairing were discussed by considering a supramolecular transient cross-linked structure. The normalized ac conductivity as a function of scaled frequency of these PNCE materials obey the universal time–concentration superposition behaviour alike the disordered solid ionic conductors.