Ac Conductivity Spectra Research Articles

Ion transport mechanism and dielectric relaxation behavior of PVA-imidazolium ionic liquid-based polymer electrolytes

Solid polymer electrolytes based on poly(vinyl alcohol) (PVA) with different wt% ionic liquid (IL), 1-Butyl-2, 3-dimethylimidazolium tetraflouroborate [BDMITFB] were prepared using the solution cast technique. Prepared samples were characterized using the AC impedance spectroscopic technique. AC conductivity spectra of a PVA-IL-based system at different concentrations/temperatures have been discussed. The fitted AC conductivity spectra using Jonscher’s power law (JPL) exhibits the correlated barrier hopping (CBH) type conduction mechanism. The scaled AC conductivity spectra of PVA-IL-based films with temperature/concentrations collapsed into a single master curve indicating the ion conduction mechanism have the same origin. For higher IL loaded samples (20 and 25 wt%) mobility, μ dc conductivity, σdc as well as total number density of charge carriers, N increases with increasing IL content in PVA. Dielectric permittivity (ε′ and ε″) and electric modulus (M′ and M″) study of prepared samples has been done. Temperature-dependent dc conductivity for prepared polymeric films follows the Arrhenius type thermally activated process.

Multifarious polarizations in high-performance colossal permittivity titanium dioxide ceramics

The (La1/2Ta1/2)xTi1-xO2 and (Er1/2Ta1/2)xTi1-xO2 ceramics with x = 0.01 and 0.03 were synthesized by a conventional solid-state reaction. The analysis of EDS mapping, ac conductivity spectra, impedance analysis, XPS, and DC bias indicate that electrons-pinned defect-dipole (EPPD) polarization plays the main role in both the (La1/2Ta1/2)0.01Ti0.99O2 and (Er1/2Ta1/2)0.01Ti0.99O2 ceramics, while the interfacial polarization and hopping polarization are respectively highlighted by the (La1/2Ta1/2)0.03Ti0.97O2 and (Er1/2Ta1/2)0.03Ti0.97O2 ceramics. Besides, the dielectric responses reveals that the interfacial polarization and hopping polarization are much slower than EPDD polarization and lead to poor frequency-, temperature-stability and higher dielectric loss (tanδ). Then the conclusion can be drawn that the outstanding dielectric properties can be achieved only the EPDD polarization takes the absolute dominant position, and excellent properties are obtained in (Er1/2Ta1/2) 0.01Ti0.99O2 ceramic with ultra-low loss of tanδ≈0.0095 (@1 kHz) and excellent frequency, temperature and DC bias stability.

Increase of metallic silver nanoparticles in Chitosan:AgNt based polymer electrolytes incorporated with alumina filler

Abstract In the present work, the possibility of increasing the amount of metallic silver particles in chitosan (CS)-based polymer nano-composites was discussed. To prepare the electrolyte, a fixed amount of silver nitrate (AgNO3) inorganic salt was added to the natural CS biopolymer. Various techniques, such as UV–vis, SEM, EDX and impedance spectroscopy, were used to characterise the samples. Remarkable enhanced surface plasmonic resonance (SPR) peaks were observed at 420 nm in the UV–vis spectra of the samples incorporated with various amounts of alumina (Al2O3) nano-particles. The intensity of SPR peaks increased with increasing alumina concentration. The SEM image of pure CS showed a smooth surface and little white specks were observed in the SEM image of CS: AgNO3 system. The number of white specks were increased on the surface of the samples incorporated with 1 and 3 wt% of alumina. The sharp intense peaks due to metallic silver particles appeared in the EDX spectra at 3–3.6 keV. The second loop did not manifest for the CS: AgNO3 system because the amount of Ago nanoparticles were low. The distinguishable second loops were observed in impedance plots of CS: AgNO3 systems containing 1 and 3 wt% of alumina filler. The second loop in impedance plots was ascribed to metallic silver particles and its diameter increased with increasing alumina concentrations. The experimental data was fitted with electrical equivalent circuits (EEC). The EEC model reveals that the samples filled with Al2O3 filler needs two circuits for exhibiting best fitting. The dielectric constant increased at 1 wt% of alumina and then it decreased as alumina was increased to 3 wt%. The AC conductivity spectra were presented for all of the samples. The maximum DC conductivity of about 2.3 × 10−6 S/cm was obtained for the CS: AgNO3 system doped with 1 wt% alumina. The DC conductivity decreased at 3 wt% alumina due to the reduction of more silver ions to metallic silver particles.

Dielectric and optical properties of Ni- and Fe-doped CeO2 Nanoparticles

Ni- and Fe-doped CeO2 nanoparticles were prepared by a chemical co-precipitation method and then heat treated at 300 °C. The structural, morphological, and compositional properties of the prepared nanoparticles were studied by powder X-ray diffraction (XRD), Energy Dispersive Spectroscopy (EDS), Scanning Electron Microscopy (SEM) and Fourier-Transform Infrared (FT-IR) Spectroscopy. The powder XRD results revealed that all the samples exhibit the typical cubic fluorite structure of CeO2. The EDS and FTIR analyses confirmed the formation of CeO2 nanoparticles and the incorporation of Fe and Ni ions in the crystal lattice of CeO2. The photoluminescence (PL) properties were investigated to assess the effect of Fe- and Ni-doping on the emission properties of CeO2 nanoparticles. The impacts of the type of dopant on the dielectric properties and ac conductivity of the prepared nanoparticles were investigated. It was observed that the dielectric constant of Ni-doped CeO2 nanoparticles measured at low-frequency region is much greater than that of Fe-doped CeO2 nanoparticles. The difference was explained on the basis of interfacial/space charge polarization, with Ni-doped CeO2 nanoparticles having a more heterogeneous dielectric structure. The universal Jonscher power law was well adjusted to the ac conductivity spectra. It was shown that the Fe-CeO2 composite nanoparticles are less conductive than the Ni-doped CeO2 ones.

Investigation of Ac conductivity mechanism and dielectric relaxation of semiconducting neodymium-vanadate nanocomposites: temperature and frequency dependency

A few binary nanocomposite systems of the overall composition formula xV2O5–(1-x) Nd2O3 for x = 0.2, 0.4, 0.6 and 0.8 has been synthesized via the rapid cooling process. The identification of crystal morphology, lattice fringes of the nanocrystallites, and the selected area electron diffraction patterns have been carried out using the transmission electron microscopy (TEM). TEM micrographs confirm the nanocrystallite development and amorphous character of the nanocomposites. The ac conductivity has been explored in the frequency window from 42 Hz to 5 MHz and in a wide temperature range. The dependency of ac conductivity spectra on frequency and temperature obey Almond-West formalism and Jonscher’s universal power-law. With an increment in temperature, ac conductivity increases, indicating semiconducting behavior. The power-law exponent (s) values are less than unity and increase in relation to the temperature, suggesting non-overlapping small polaron tunneling (NSPT) is the relevant ac conductivity mechanism. The reducing nature of the ac conductivity activation energy, the activation energy for polaron migration and tunneling distance are responsible for the rising of ac conductivity. The increment in the density of defect states within the mobility gap makes ac conductivity to rise as well. The scaled spectra of ac conductivity prove that conductivity relaxation process is temperature independent but composition dependent. In the electrical conduction process, only 66%–71% of the total charge carriers are involved. The values of dielectric constant (ε/) and dielectric loss (ε//) increase with temperature rise and drop with a rise in frequency. The coinciding scaled complex electric modulus spectra (M/ and M//) point out that the dynamical relaxation mechanism is a non-Debye type and is independent of temperature but depend on composition.

Strontium-substituted La0.75Ba0.25−xSrxFeO3 (x = 0.05, 0.10 and 0.15) perovskite: dielectric and electrical studies

La0.75Ba0.25−xSrxFeO3 perovskite compounds with different strontium concentrations were synthesized via the sol–gel method. X-ray diffraction (XRD) data indicated that all obtained samples crystallize in the orthorhombic structure with the Pnma space group. The dielectric properties of these samples, using complex impedance spectroscopy technique have been carried out as function of frequency and temperature as well. An adequate electrical equivalent circuit has been used to evaluate the grain and grain boundary contributions in complex impedance results. Furthermore, the AC conductivity spectra obey to Jonscher’s universal power law. The behavior of the exponent “S” suggests that the conduction mechanism follows the overlapping large polaron tunneling (OLPT) process for x = 0.05, while for both compounds x = 0.10 and x = 0.15 the non-overlapping small polaron tunneling (NSPT) is the applicable model. The behavior of e″ as a function of both frequency and temperature has been described by Giuntini model.

An investigation of S–Se–Te semiconducting glassy alloys: Structural characterization and electrical conductivity

A sequence of chalcogenide glassy alloys, xS-(1-x) (0.5Te-0.5Se) for x = 0.1, 0.14, 0.24 and 0.34 have been prepared using well-established melt quenching method. The XRD patterns reveal the existence of crystallinity, superimposing over the amorphous glassy matrix. The effects of increasing values of mean crystallite size and optical band gap energy with composition cause electrical conductivity to reduce. The DC conductivities of the present system have been explored using Mott and Greaves's variable range hopping model. The values of temperature dependent small polaron hopping distance (Rhop) and hopping energy (Whop) are in agreement with the nature of DC conductivity. The anomaly of the sample for x = 0.14 may arise due to the lesser number of localized or defect states within the mobility gap and higher values of small polaron hopping distance and average hopping energy. The well-known Meyer-Neldel rule, Jonscher's Universal power-law and Almond-West formalism have been employed to investigate the AC conductivity spectra. The reducing nature of power-law exponent (s) with increasing temperature of the samples for x = 0.1 and 0.14 indicates that correlated barrier hopping (CBH) model is the best model for AC conduction mechanism. On the other hand, non-overlapping small polaron tunneling (NSPT) process is the suitable AC conduction mechanism of the samples for x = 0.24 and 0.34 due to the increasing nature of s with temperature. The conductivity scaling signifies temperature independency and composition dependency of electrical relaxation process.

Influence of NaNbO3 on the structural, optical and dielectric properties of 0.05(K0.5Bi0.5TiO3)–0.95(NaNbO3) composites ceramics

A new polycrystalline lead-free 0.05(K0.5Bi0.5TiO3)–0.95(NaNbO3) (KBT–NN) composites ceramics have been prepared by solid-state reaction method and their structural, optical, dielectric, ferroelectric and impedance properties are investigated. X-ray diffraction and Rietveld refinement data reveal that this composites ceramics possesses a perovskite-type orthorhombic structure after the diffusion of K0.5Bi0.5TiO3 into the NaNbO3. An appreciable change in its vibrational phonon modes of KBT on addition of NaNbO3 is exhibited in the material as observed from Fourier-transform infrared spectroscopy (FT-IR) spectrum. The optical band gap energy of the sample is determined from the diffused absorbance spectra to be 3.2 eV, which may be useful in photo-catalytic application. In the frequency range of 130–900 cm−1, different vibrational modes are observed from Raman spectrum. Field emission scanning electron microscopy (FE-SEM) images reveal a well-defined and homogeneous morphology. Polarization vs. electric field study confirms the ferroelectricity. Dielectric and complex impedance spectroscopic studies are performed over a wide range of frequency (i.e., 103–106 Hz) and temperature (30°–500 °C) and it is found that Jonscher’s power law is well applicable to the alternating current (ac) conductivity spectrum. The direct current (dc) conductivity of the material, which depends upon temperature, exhibits the decrease resistance with increase of temperature similar to that of semiconductors. The dc conductivity confirms that the conduction mechanism is influenced by oxygen vacancies.

Structural, dielectric and ferroelectric properties of lead free Gd-modified BiFeO3–BaTiO3 solid solution

Due to the high Curie temperature the rare-earth-modified bismuth ferrite (BiFeO3 or BFO) and/or its derivatives have uncomplicated lead-free chemistries and simple perovskite structures have attracted the materials community. So, in this report, structural, micro-structural, ferroelectric and electrical characteristics of a rare-earth (Gd)-modified perovskite BiFeO3–BaTiO3 solid solution, fabricated by a cost effective solid-state reaction technique, have been presented. The structural analysis using X-ray diffraction pattern and data indicates the evolution of a mono-phase distorted perovskite structure with the existence of rhombohedral structure. The ambient temperature scanning electron micrograph of Gd modified BiFeO3–BaTiO3 solid solution exhibits uniform grain distribution over the surface. The dielectric parameters are found to be frequency and temperature dependent. The well defined polarization–electric field hysteresis loop of the samples at room temperature suggest that Gd substitution at the Bismuth site of the solid solution strongly affects remnant and saturated polarization of the materials. The ac conductivity spectra obeys the Jonscher’s power law. Based on the derived parameters of Gd modified BiFeO3–BaTiO3 solid solution, it is expected to fabricate a functional device.

Improved dielectric and electrical properties of PANI achieved by using low cost mineral additive

In the present study, polyaniline (PANI) conducting polymer was mechanically doped with volcanic basalt rock (VBR), sodium metasilicate (Na 2 SiO 3 ), and sodium tetraborate (borax) minerals at 10 to 50 wt%, to improve the dielectric response. The influence of these mineral additives on the complex dielectric, electrical modulus, and AC impedance spectra of the PANI was investigated. It was revealed that among the mineral additives, the highest s' is achieved for 50 wt % sodium metasilicate doped PANI composite. In addition, the appearance of peaks in the imaginary component of the electric modulus plots, for especially borax and sodium metasilicate doped samples, indicates the existence of a relaxation process. In addition, the Cole-Cole plots in the complex electrical modulus plane suggests a non-Debye type of relaxation. The single semi-circle arcs observed in Nyquist plots for PANI/Na 2 SiO 3 composites indicates a dominant grain (bulk) contribution. Moreover, the bulk resistance and capacitance values for PANI/Na 2 SiO 3 composites were found to be in the order of MΩ-GΩ and pF, respectively. While the AC conductivity spectrum of the PANI/VBR composites obeys the Nearly Constant Loss model, the PANI/Borax and PANI/Na 2 SiO 3 composites were found to obey the Super Linear Power Law model. In conclusion, the low cost Na 2 SiO 3 additive with different weight percentages for PANI shows remarkable effects on the dielectric and electrical properties.

Tunable negative permittivity in Ti3SiC2 MAX phase/Polymethyl methacrylate metacomposites at radio-frequency region

Metacomposites with negative permittivity have triggered tremendous fundamental and practical attention in recent years. In this paper, Ti3SiC2 MAX phase/Polymethyl methacrylate (PMMA) metacomposites with different Ti3SiC2 content were prepared. Weakly negative permittivity value (between [Formula: see text] and 0) was observed near percolation (Ti3SiC2 content of 60[Formula: see text]wt.%), attributing to moderate carrier concentration in Ti3SiC2 networks, and negative permittivity was tuned by tailoring conductive Ti3SiC2 networks. AC conductivity spectra and negative permittivity spectra of composites over percolation were explained by Drude model, indicating metal-like conduction behavior and low-frequency plasmonic oscillation in composites. The impedance response of composites was analyzed by equivalent circuit models, manifesting correspondence between inductor and negative permittivity. This work presented a new type of metacomposite constructed by Ti3SiC2 MAX phase and further revealed the generation mechanism of negative permittivity, which will greatly facilitate the practical applications of MAX phase in metacomposites.

Non suitability of silver ion conducting polymer electrolytes based on chitosan mediated by barium titanate (BaTiO3) for electrochemical device applications

In this study, we report the non-suitability of silver ion conducting polymer electrolytes mediated by barium titanate (BaTiO3) for electrochemical device applications. Various amounts of BaTiO3 fillers have been added to chitosan: silver triflate (CS:AgTf) solution to prepare polymer composites. Electrical impedance spectroscopy (EIS) has been used to characterize electrical properties of the samples. Charge transfer resistance has been correctly estimated for the samples using electrical equivalent circuit (EEC) model. At 3 and 5 wt % of BaTiO3 filler, the charge transfer resistance was found to increase and diameter of the impedance plots are shown to be widened due to the increase of grain boundaries. The dielectric constant is also observed to decrease with the increase of BaTiO3 concentration. DC conductivities for the composite samples are estimated from AC conductivity spectra. The DC conductivity was found to decrease from 4.7 × 10−7 S/cm to 5.4 × 10−9 S/cm for CS:AgTf system incorporated with BaTiO3 filler. Such decrease has revealed that the electrolytes are not suitable for electrochemical device applications. Shifting of relaxation peaks of imaginary part of electric modulus towards low frequency side has indicated the increase of relaxation time and hence the decrease in DC conductivity. The relaxation processes are also studied using Argand plots. The existence of metallic silver nanoparticles has been examined via ultraviolet–visible (UV–Vis) spectroscopy. The UV–Vis spectra showed that surface plasmon resonance (SPR) peaks are broadened and increased in their intensity as the BaTiO3 concentration increased from 1 to 3 wt %. This implied that the reduction rate of silver ions to silver nanoparticles is increased. Moreover, disappearance of SPR peak was found for the BaTiO3 concentration of 5 wt %, revealing the bulk formation of silver metals. Transmission electron microscopy (TEM) images were obtained for the samples, in which the formation of bulk metallic sizes of silvers was found to be obvious. This growth of bulk silver metals at high BaTiO3 concentration was further supported by optical and scanning electron microscopy (SEM) techniques. The distribution of white specs due to silver nanoparticles on the surface of chitosan-silver triflate solid film was investigated. Large white sheets were appeared on the surface of CS:AgTf incorporated with 5 wt% BaTiO3 and related to the huge amount of aggregated metallic silver particles. Sharp intense peaks due to metallic silver particles and weak peaks due to BaTiO3 fillers have been observed in the analyses of energy dispersive X-ray (EDX) spectra.

Structural, electrical and dielectric studies of nano-composite polymer blend electrolyte films based on (70–x) PVA–x PVP–NaI–SiO2

Nano-composite polymer electrolytes (NCPEs) films based on PVA-PVP-NaI-SiO2 have been prepared using solution casting technique. Investigation of prepared films have been made using various experimental techniques like x-ray diffraction (XRD), attenuated total reflection–fourier transform infrared (ATR-FTIR), differential scanning calorimetric (DSC) and ac impedance spectroscopy. XRD determines the structural properties and shows the significant variation in the characteristic peaks related to semi-crystalline/amorphous phase of different PVA-PVP polymer blend ratio for fixed loading of NaI and SiO2. Complexation of PVA-PVP polymer blend with NaI and SiO2 has been confirmed by ATR–FTIR analysis. Variation in glass transition temperature (Tg) and melting temperature (Tm) of PVA-PVP-NaI-SiO2 NCPE system having various concentration of PVP were observed by DSC analysis. It has been observed that ac conductivity spectra strongly obeys the Jonscher's universal power law [σ=σdc+Afn] with power exponent, n < 1. The dielectric permittivity (ε′&ε″) and electric modulus (M′&M″) measurements were performed in a wide frequency range (10 mHz-10 MHz). Variation of conductivity with temperature shows that the ion conduction and polymer segmental motions are closely related and are governed by Arrhenius mechanism. A couple of peaks observed in loss tangent (tan δ) shows two types of relaxation processes interpreted in terms of dipole segmental motion (α-relaxation) and side chain dipole group motion (β-relaxation).

The compatibility of chitosan with divalent salts over monovalent salts for the preparation of solid polymer electrolytes

Abstract In this study the compatibility of chitosan (CS) with divalent inorganic salt is discussed. Solid polymer electrolytes (SPEs) consist of CS as a host polymer and magnesium triflate (MgTf) as a dopant divalent salt have been prepared by solution cast technique. The room temperature DC ionic conductivity of CS-based SPE containing 50 wt% of MgTf is determined to be around ≈10−4 S/cm. The surface morphology of the films are then examined using a field emission scanning electron microscopy (FE-SEM). The crystalline phase of pure CS is found to reduce upon the addition of MgTf salt. The compatibility of CS with divalent salts are discussed at high salt concentration on the bases of the surface morphology and X-ray diffraction (XRD) results. The smooth surface micrographs and broad peaks of XRD spectra are interpreted in reference to lattice energy and cationic size of salt. The smooth surface and low resistance (Rb = 47.8 Ohm) at high salt content (50 wt%) are clear signs that CS is more compatible with divalent salts than with other monovalent salts. At low temperature range, the DC conductivity versus 1000/T is shown to follow the Arrhenius equation. The dispersion region of AC conductivity spectra has been used to calculate the frequency exponent, s. Based on the value of s as a function of temperature, different ion transport models have been discussed to interpret the pattern of DC ionic conductivity versus 1000/T. The appearance of peaks in M″ spectra and their absence in ɛ″ spectra reveals that the relaxation process is a non-Debye type.

Weakly Radio-Frequency Negative Permittivity of Poly(vinylidene fluoride)/Ti3SiC2 MAX Phase Metacomposites

While metal or carbon materials served as conductive phase in fabricating metamaterials or metacomposites have been widely investigated, MAX phases could provide alternative route. In this paper, Poly(vinylidene fluoride)/Ti3SiC2 MAX phase metacomposites with different Ti3SiC2 content were fabricated. Electrical and dielectric properties of metacomposites were analyzed. Percolating phenomenon was observed over the percolation threshold (fc). Below fc, ac conductivity spectra were explained by Jonscher’s power law, indicating hopping conduction behavior. Above fc, ac conductivity of composites follows Drude model, suggesting the metal-like conductive behavior. Weakly negative permittivity behavior was observed and explained by Lorentz and Drude model, suggesting the combinative contribution of induced electric dipole resonance and low-frequency plasmonic oscillation. The impedance performance of composites were also clarified by Nyquist plots and equivalent circuit analysis, manifesting the capacitive-inductive shift of composites. This work presented a novel route to metacomposites with weakly negative permittivity which greatly benefitted the practical applications of MAX phase in metacomposites.

Dielectric and electrical characterization of lead-free complex electronic ceramic: (Bi1/2Li1/2)(Zn1/2W1/2)O3

A Lead-free complex perovskite compound of (Bi1/2Li1/2)(Zn1/2W1/2)O3 has been synthesized by using high-temperature solid-state reaction technique. The structural, micro-structural, dielectric constant, tangent loss, electrical impedance, modulus, conductivity and polarization characteristics of the prepared compound have been studied over a wide range of temperature (150–500 °C) and frequency (1 kHz–1 MHz). The X-ray diffraction structural analysis reveals tetragonal structure of the compound with cell parameters; a = 10.6055 (36) A, c = 13.8275 (36) A, c/a = 1.3038 and volume V = 1555.27 A3. The acquired room temperature scanning electron micrograph exhibits the homogeneous distribution of fibre-type of grains throughout the surface of specimen. The dielectric constant and tangent loss of the material at a frequency of 1 kHz are found to be 4000 and 11 respectively. The ac conductivity spectrum provides the information about the conduction mechanism and semiconducting nature of the compound. The impedance spectrum provides an insight into the contributions of grain and grain boundary effects in the resistive and capacitive characteristics of the materials. The frequency dependence of complex modulus analysis shows the presence of non-Debye type of relaxation behaviour in the material.

Low-temperature sintering Graphene/CaCu3Ti4O12 nanocomposites with tunable negative permittivity

Since negative permittivity demonstrated in metamaterials, how to effectively tune negative permittivity still the challenge to satisfy practical applications. Meta-composites could provide alternative routes to tunable negative permittivity. In this paper, Graphene/CaCu3Ti4O12 (GR/CCTO) meta-composites with different GR content were fabricated by low-temperature pressureless sintering. Microstructures and compositions of GR/CCTO were investigated in detail. The electrical and dielectric properties of GR/CCTO nanocomposites were investigated at 10 kHz −1 MHz and 20 MHz - 1 GHz region respectively. AC conductivity spectra showed different variation trends which were explained by Jonscher's power law or Drude model, indicating conductive mechanism transformation from hopping conduction to metal-like conduction. Lorentz-type and/or Drude-type negative permittivity behaviors were observed at radio-frequency region. Tunable negative permittivity were realized by changing GR content in GR/CCTO nanocomposites. Correspondence between inductive characteristic and negative permittivity was manifested by equivalent circuit analysis of impedance response of GR/CCTO composites. This work not only presents novel routes to tune negative permittivity, but also further clarifies negative permittivity generation mechanism, which will greatly facilitate applications in impedance matching, electromagnetic shielding and multi-layer high-k capacitors etc.

The effects of temperature and frequency on the conductivity and dielectric properties of cotton fabric impregnated with doped PEDOT:PSS

The ac electrical conductivity and dielectric properties of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), abbreviated to PEDOT:PSS, and PEDOT:PSS cotton fabric were investigated over the frequency range of 10 Hz–13 MHz and temperatures ranging from 30 to 100 °C using impedance spectroscopy. Before experimentation raw cotton fabric was impregnated with PEDOT:PSS using the drop-casting and drying method to make the material conductive. Impedance plots of the conductive fabric with 21.7 wt% of PEDOT:PSS showed the presence of significant concavity of a parabola with peak reactance increased with increasing temperature indicating metallic behavior. The associated ac conductivity spectra indicate that the conduction process is thermally activated at various temperatures. Furthermore, the variation of the dc conductivity confirms that the PEDOT:PSS fabric exhibits the usual metallic behavior for all temperatures investigated. The magnitude of the dielectric constant is observed to be insensitive to variations in temperature. At low frequencies, the value of dielectric constant decreases with increasing the frequency. At high frequencies, the magnitude of dielectric constant have relatively constant values for all temperatures as frequency increases.

Conductivity spectra of lithium ion conducting glassy ceramics

Study of ac conductivity spectra of Li2O doped different glassy ceramics in wide frequency and temperature regime using Jonscher's power law model and Almond-West formalism reveals that Li+ migration depends upon nature of doping reagent. It also points that the ratio of power law pre-factor to the exponent (–log10 A/S) indicates temperature and composition dependency of present conductors. Motion of Li+ may predict that the process of conduction is percolation or pseudo three dimensional types. These glassy ceramics should be suitable candidates for lithium ion battery application. Improvements in the capacity of modern lithium (Li) batteries can be made by enhancing conductivities and ionic diffusivities in various anode and cathode materials. Fundamentally, such improvements can be achieved in the present electrolyte compositions. It is also interestingly noted that constantly changing nature of electrical conduction in present systems are strongly microstructure dependent.

Electrical and optical properties of lead-free 0.15(K0.5Bi0.5TiO3)–0.85(NaNbO3) solid solution

Polycrystalline lead free 0.15(K0.5Bi0.5TiO3)–0.85(NaNbO3) ceramic is synthesized using conventional solid state reaction technique. Structural, dielectric, optical and impedance properties of the sample are investigated. X-ray diffraction (XRD) study reveals K0.5B0.5TiO3 (KBT) diffusing into the NaNbO3 (NN) lattices to form a new perovskite-type solid solution with orthorhombic structure (space group Pmc2 1 ) at room temperature. Addition of small amount of KBT transforms NN ceramic from anti-ferroelectric to ferroelectric material. The XRD data has been refined using Rietveld refinement technique. FTIR spectra reflect an appreciable change in its vibrational phonon modes of the sample. The optical band gap is estimated to be 3.02 eV from the diffused absorbance spectra, which is useful in photo catalytic applications. Different vibrational modes in the frequency range of 130–900 cm−1 is observed from the Raman spectrum. FESEM micrograph reveals the homogeneous grains and well-defined grain boundaries with some few pores. Dielectric and complex impedance spectroscopic studies are carried out in a wide range of frequency (i.e., 103–106 Hz) and temperature (30–475 °C). The presence of ferroelectric properties is confirmed from P–E loop. A strong correlation between its microstructure and electrical parameters is established from the study of the electrical properties of the material. The ac conductivity spectrum obeys Jonscher’s power law. Negative temperature coefficient of resistance behavior of the material is inferred from temperature dependence of dc conductivity.