Ac Conductivity Spectra Research Articles

Transport phenomena and conductivity mechanism in Sm doped Bi4V2−xSmxO11 ceramics

Abstract The polycrystalline samples of Sm doped Bi4V2−xSmxO11 with x = 0.05, 0.10, 0.15 and 0.20 ceramics were prepared by using solid-state reaction technique. The structural characterization of the prepared samples were confirmed by X-ray powder diffraction (XRD) and showed an orthorhombic and monoclinic phase. The nature of Nyquist plot confirms the presence of both grain and grain boundary effects for all Sm doped compounds. The grain resistance decreases with rise in temperature for all the samples and exhibits a typical negative temperature co-efficient of resistance (NTCR) behavior. The ac conductivity spectrum obeys Jonscher's universal power law. The modulus analysis suggests a possible hopping mechanism for electrical transport processes of the materials. The nature of variation of dc conductivity suggests the Arrhenius type of electrical conductivity for all the samples.

Structural, optical and electrical properties of YbInSe thin films

In this work, the compositional, the structural, the vibrational, the optical and the electrical characterizations of the YbInSe compound are investigated by means of energy dispersion X-ray analysis, scanning electron microscopy and X-ray diffraction, Raman spectroscopy, ultraviolet -visible light spectrophotometry, impedance spectroscopy and temperature dependent electrical conductivity, respectively. The 300nm thick YbInSe films which were prepared by the co-evaporation of the source materials under a vacuum pressure of 10−5mbar, are observed to exhibit nanocrystalline clusters of size of 27nm regularly distributed among an amorphous structure. The most intensive Raman active lines are observed at 150 and 254cm−1. In addition, the optical analysis has shown that the films exhibit a direct forbidden electronic transitions type energy band gap of 1.07eV. The optical transitions are associated with interband tail states of width of 0.28eV. Moreover, the real and imaginary parts of dielectric spectra which were analyzed in the frequency range of 270–1000THz, were analyzed in accordance with the single oscillator and the Lorentz models, respectively. The modeling allowed determining the oscillator and dispersion energies, the terahertz free carrier scattering time, the free holes effective mass, the carrier density, the drift mobility and the reduced resonant frequency for the YbInSe films. In the electronic part of study, the temperature dependent dc electrical conductivity analysis, indicated the domination of the variable range hopping transport mechanism below 335K, the thermal excitation of charge carriers in the range of 337–390K and the extrinsic-intrinsic transition property at 390K. The ac conductivity spectra which were recorded in the frequency range of 10–1500MHz, revealed the domination of the correlated barrier hopping of free carriers between pairs of localized states at the Fermi level.

Renormalization approach to the electronic localization and transport in macroscopic generalized Fibonacci lattices

Electronic transport and wavefunction localization are two closely related phenomena, but their behavior in truly macroscopic aperiodic lattices is a non-widely addressed issue. We study in this article the electrical conductivity of generalized Fibonacci (GF) lattices through the Kubo-Greenwood formula, while the localization of electronic wavefunction is analyzed by means of the Lyapunov exponent and participation ratio (PR). For periodic chains, an analytical expression of the Lyapunov exponent is obtained. We have also developed for the first time a real-space renormalization method to calculate the PR of macroscopic GF lattices described by tight-binding Hamiltonians. Moreover, we report a novel unified renormalization method for the Kubo-Greenwood formula applied to GF chains. For quasiperiodic lattices, the results reveal a power-law decay of the spectral averages for both PR and DC conductivity when the system length increases. In addition, we present a systematic analysis of the AC conductivity spectra observing truly large resonant peaks in comparison to the ballistic one. The electrical conductance of GF nanowires is also investigated. Finally, the results suggest that PR could not be proper for the analysis of critically localized states.

Probing electronic structure of biomineralized hydroxyapatite inside nanoclay galleries

Hydroxyapatite, the most abundant mineral in the human body, is also an important component in design of biomaterials for bone tissue regeneration. Synthetic hydroxyapatite mineralized in the laboratory often does not exhibit the same biological and morphological properties of biogenic hydroxyapatite in human bone. A biomimetic hydroxyapatite structure is synthesized using biomineralization routes inside the clay galleries of montmorillonite clay. Amino acids are used to modify the clay galleries. These amino acids are used to mineralize hydroxyapatite. The molecular interactions between nanoclay, modifiers inside nanoclay (amino acids) and biomineralized hydroxyapatite result in unique morphology, structure and stoichiometry of the biomineralized hydroxyapatite. Prior studies have indicated that this biomineralized hydroxyapatite inside nanoclay galleries is an effective component of tissue engineering bone scaffolds that elicits an optimal biological response from human mesenchymal stem cells. Here, a detailed electron energy-loss spectroscopy (EELS) study is reported that elucidates the differences in hydroxyapatite, biomineralized hydroxyapatite and β-tricalcium phosphate (β-TCP). Comparison of EELS low-loss transitions and energy loss near-edge structure (ELNES) of P-L2,3 edges for these three compounds is done to determine if there are differences in their electronic structures. These changes observed experimentally are compared with prior predictions and simulations using molecular dynamics studies. The simulations predict attractive and repulsive interactions between phosphate, modified MMT clay and aminovaleric acid (amino acid) molecules. Kramers-Kronig analysis is performed on the loss spectra obtained to yield the real and imaginary parts of the dielectric function of the apatites (ε1 and ε 2). We have also used the ε2 spectra obtained to calculate the AC conductivity spectra for the apatites. This study represents a unique experimental probe into molecular interactions in complex biomineralized hydroxyapatite structures. The small changes observed in the energy loss spectra appear to play important biological roles in biomineralized hydroxyapatite such as the ability to differentiate human mesenchymal stem cells into osteoblasts without growth media.

Correlation between structure and oxygen ion dynamics in Y substituted La2Mo2O9 ionic conductors

We have measured the ac conductivity and dielectric spectra for La2-xYxMo2O9 (0.05 ≤ x ≤ 0.20) in wide temperature and frequency ranges. We have obtained the mean square displacement and the spatial extent of nonrandom sub-diffusive regions for oxygen ions by analyzing the ac conductivity and dielectric spectra respectively. The structure of the samples has been studied using X-ray photoelectron spectra, X-ray and electron diffraction. It is observed that the composition dependence of these characteristic lengths is correlated with the distance between oxygen ions obtained from structural studies.

Occurrence of electrical percolation threshold and observation of phase transition in chitosan(1−x):AgI x (0.05 ≤ x ≤ 0.2)-based ion-conducting solid polymer composites

This paper reports on the investigation of electrical percolation threshold and ion transport mechanism for ion-conducting solid polymer composites based on chitosan. The composite samples were prepared by solution cast technique. The result of DC conductivity versus percolation threshold (\(\varPhi^{ - 1/3}\) ) confirmed that at low AgI concentration, the tunneling effect governs ionic conduction mechanism. Nevertheless, at high filler concentration, the DC conductivity showed a plateau behavior. The DC conductivity as a function of reciprocal temperature revealed that the ion conduction mechanism is slightly temperature dependent and the ion–ion correlational effect is dominant. A steep increase in DC conductivity above 323 K is observed, which indicated the existence of some phase transition near the beta (β)-phase. The drop of DC conductivity at high temperatures is anticipated from the impedance plots. The AC conductivity spectrum exhibited three distinct regions at low temperatures. The high-frequency regions of AC conductivity spectra were almost temperature independent at low temperatures (303–323 K) and obeyed the Jonscher’s power law. The variation in frequency exponent versus temperature reveals that ion conduction mechanism follows QMT and CBH models at low and high temperatures, respectively. The valuable achievement of this work is that the temperature dependence of DC conductivity and the frequency exponent (s) is correlated to interpret the Ag+ ion dynamic and ion–ion correlational effect. The Argand plots were used to explain the relaxation processes.

Study Of Electrical Relaxation Mechanism Of TiO2 Doped Bi-polymer Systems

Polyvinyl alcohol (PVA) /Poly (tetrafluoroethylene) (PTFE)/Titanium oxide (TiO2) was prepared by ( 5, 10 and 15 wt %) TiO2 loading. The miscibility, thermal property and microstructure of the composites were characterized by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The electrical relaxation dynamics including dielectric and electrical conductivity was examined as a function broadband of frequency and temperature. The dielectric data was analyzed via the electric modulus. The Maxwell-Wagner-Siller (MWS) effect corresponds to interfacial polarization at low frequency follows Arrhenius behavior. The α-mode relaxation is attributed to glass-rubbery transition in composites, obeys the Vogel- Taman-Fulcher (VTF) model. A slight bump was noted at relatively high temperature and high frequencies termed as Intermediate dipolar effect (IDE) obeys the Arrhenius behavior. Conductive mechanism was analyzed via AC conductivity spectra. However, DC conductivity follows Arrhenius equation. The overall studies confirm that the self relaxation mechanism of PVA/PTFE composites were modified by TiO2, offers the tuning conductivity as a function of the temperature which can be used in various electronic applications.

Impedance, scaling behavior and conduction mechanism in double perovskite Pr2CuZrO6 ceramic

Double perovskite oxide Pr2CuZrO6 (PCZO) has been synthesized by solid-state reaction technique in the temperature range from 30 to 310 °C and in the temperature range from 100 Hz to 1 MHz. The X-ray diffraction pattern of the sample at room temperature shows monoclinic structure. An analysis of the real and imaginary parts of impedance as well as electric modulus shows a distribution of relaxation times. The Cole–Cole model is used to investigate the relaxation mechanism of PCZO. The frequency-dependent maxima in the imaginary impedance and imaginary electric modulus are found to obey an Arrhenius law with activation energy ~0.35 eV. The frequency-dependent electrical data is also analyzed in the framework of conductivity. The combined Z″/Z″m and M″/M″m plots indicates that the charge carriers are localized in PCZO in the higher temperature range. The ac conductivity spectra follow the universal power law and Summerfield scaling.

Structural studies and impedance spectroscopy of sol–gel derived Bi0.9Pr0.1FeO3 nanoceramics

Nano-crystalline Bi0.9Pr0.1FeO3 (BPFO) ceramics have been synthesized by a sol–gel technique. The Rietveld refinement of the room temperature powder X-ray diffraction pattern confirms that the BPFO crystallizes in the rhombohedral R3c space group symmetry. SEM image of the sintered BPFO ceramic shows particles with same shape and fine grain morphology with the average grain size of 53±12nm. The electrical properties of the ceramic are analysed by impedance spectroscopy. Grain and grain-boundary effect is observed in the material at lower temperature range which has been confirmed by electric modulus formalism. The ac conductivity spectrum obeys the Johnscher's power law. The activation energy calculated from dc conductivity is found to be 0.373eV, which represents the conduction of small polaron over barrier between two sites of the lattice.

Dynamics and relaxation of charge carriers in poly(methylmethacrylate)-based polymer electrolytes embedded with ionic liquid.

In the present paper, we have studied dynamics and relaxation of the charge carriers in polymethylmethacrylate-lithium bis(trifluoromethane sulfonyl)imide polymer electrolytes embedded with 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid. We have analyzed the frequency dependent conductivity spectra using the random free-energy barrier model coupled with the contribution of electrode polarization in the low frequency region. The temperature dependence of ionic conductivity, and relaxation time obtained from the analysis of the spectra exhibits Vogel-Tammann-Fulcher type behavior. The Barton-Nakajima-Namikawa relation is consistent with the results obtained from the random free-energy barrier model. The scaling of ac conductivity spectra has been performed to understand the effect of temperature as well as the composition on the relaxation mechanism. The analysis of the ac conductivity also clearly indicates the existence of a nearly constant loss phenomenon at low temperatures or at high frequencies.

Dielectric dispersion and antiferromagnetism in BiTbxFe1−xO3 (x=1.0, 0.75)

Bismuth terbium oxide, BiTbO3 (BT) and bismuth terbium iron oxide, BiTb0.75Fe0.25O3 (BTF) are synthesized by the solid-state reaction technique. Rietveld refinement of the room temperature powder X-ray diffraction pattern of both BT and BTF confirms cubic phase with lattice parameter a=5.4451 (2) and 5.4896 (3) Å respectively. Raman spectroscopy studies have been made to investigate vibrational properties for both the samples. The dielectric relaxation behavior of the samples is investigated by alternating current impedance spectroscopy (ACIS) in the frequency range from 42Hz to 1.10MHz and in the temperature range from 303to 673K. The complex impedance plane plots and ac conductivity spectra reveal the presence of grain, grain-boundary and electrode effect in BT. Both BT and BTF are antiferromagnetic in nature with Néel temperature of 33.8and 51.9K respectively.

Charge-carrier relaxation dynamics and ac conductivity scaling of poly(3,4-ethylenedioxythiophene) nanoparticles

An investigation of the dielectric characteristics of poly(3,4-ethylenedioxythiophene) nanoparticles has been conducted in the frequency range 20 Hz–2 MHz and the temperature range of 80–300 K through the studies of dielectric permittivity, modulus formalism and ac conductivity. High-resolution transmission electron micrographs confirm the formation of well-ordered spherical nanoparticles. Micro-Raman spectra confirm the conformational transition from benzenoid to quinoid structure with increasing dopant concentration. Linear variation of imaginary permittivity with frequency suggests that the dc conduction process is more significant than interfacial polarisation. The presence of single relaxation peak in the imaginary modulus formalism indicates the Debye-type relaxation. The decrease of frequency exponent with temperature confirms that the charge transport takes place through correlated barrier hopping mechanism. The scaling of ac conductivity spectra confirms that the relaxation dynamics of charge carriers in the poly(3,4-ethylenedioxythiophene) nanoparticles system is temperature independent.

Chromium Effects on the Structural and Electrical Properties in La0.7Ba0.2Ca0.1Mn1−x Cr x O3

In this paper, we study the structural and electrical properties of the perovskite manganite La0.7Ba0.2 Ca0.1Mn1−xCrxO3, synthesized by the solid-state reaction method. The Rietveld refinement of X-ray diffraction data indicates that there is no structural change owing to Cr substitution in La0.7Ba0.2Ca0.1Mn1−xCrxO3 (0 ≤ x ≤ 0.15). The conductivity of all samples was measured as a function of frequency in the range between 40 and 106 Hz and a temperature ranging from 160 to 300 K. The ac conductance spectrum is found to obey the Jonscher universal power law: Gac = Gdc + Aωn. The variation of the conductivity exponent (n) with temperature confirms the presence of hopping in the conduction process. According to dc conductance study, electronic conduction is found to be dominated by thermally activated hopping. The Cr content affects the activation energy (Ea). Its values decrease from Ea = 72 meV for x = 0 to Ea = 34 meV for x = 0.15.

Combustion synthesis of nano-crystalline Bi2/3Cu3Ti2.90Fe0.10O12 using inexpensive TiO2 raw material and its dielectric characterization

Nano-crystalline Bi2/3Cu3Ti2.90Fe0.10O12 powder was synthesized using a glycine–nitrate solution-combustion process, and applying inexpensive and stable solid TiO2 powder as the titanium source at relatively lower temperature than conventional ceramic methods. X-ray diffraction pattern confirmed the formation of a single phase of the ceramic sintered at 900°C for 12h. Bright-field transmission electron microscopy of the ceramic revealed that particle size is 16±07nm. Scanning electron microscopy image showed the presences of bimodal distribution of grains and the grain sizes were found to be in the range of, 500nm–1.5μm. Energy dispersive X-ray analyses confirmed the purity and stoichiometry of the ceramic. The frequency-dependent AC conductivity spectra obeyed the Jonscher's power law. The impedance spectroscopy study revealed the presence of grain boundary and electrode effects, which were also proved from modulus spectroscopy. The activation energies for grain boundaries and electrode effects were found to be 0.51 and 0.47eV, respectively.

Ion transport study in polymer-nanocomposite films by dielectric spectroscopy and conductivity scaling

The dielectric and conductivity response of polymer nanocomposite electrolytes (films of PMMA4LiClO4 dispersed with nano-CeO2 powder) have been investigated. The dielectric behavior was analyzed via the dielectric permittivity (ε′) and dissipation factor (tanδ) of the samples. The analysis has shown the presence of space charge polarization at lower frequencies. The real part of ac conductivity spectra of materials obeys the Jonscher power law. Parameters such as dc conductivity, hopping rate, activation energies and the concentration of charge carriers were determined from conductivity data using the Almond West formalism. It is observed that the higher ionic conductivity at higher temperature is due to increased thermally-activated hopping rates accompanied by a significant increase in carrier concentration. The contribution of carrier concentration to the total conductivity is also confirmed from activation energy of migration conduction and from Summerfield scaling. The ac conductivity results are also well correlated with TEM results.

Size effect on electrical and magnetic properties of mechanically alloyed CoFe2O4 nanoferrite

Highly crystalline cobalt ferrite (CoFe2O4) nanoparticles with diameter ranging from 5 to 19 nm were prepared by a mechanical alloying method followed by thermal treatment. The formation of a single-phase compound was confirmed by basic X-ray structural analysis, and the nano-structure of the sample was confirmed by high-resolution transmission microscope. The crystallite size of the material was found to be milling time dependent. Relative permittivity and tangent loss of the material are strongly dependent on the crystallite size. The temperature-frequency dependence of dielectric parameters and temperature dependent electrical conductivity has successfully been explained using Maxwell–Wagner and Koop’s phenomenological models. Impedance spectroscopy clearly explains dependence of resistive characteristics and dielectric relaxation of the material. The nature of impedance spectra exhibits a typical negative-temperature-co-efficient of resistance. The magnetic measurement shows that saturation magnetization is particle size dependent. The ac conductivity spectrum of the material shows a typical-signature of an ionic conduction, and is found to obey Jonscher’s universal power law. The change in activation energy with particle size is observed suggesting a typical conduction mechanism in the material.

Study of dielectric, AC-impedance, modulus properties of 0.5Bi0.5Na0.5TiO3·0.5CaCu3Ti4O12 nano-composite synthesized by a modified solid state method

In the present research paper 0.5Bi0.5Na0.5TiO3·0.5CaCu3Ti4O12 nano-composite has been successfully synthesized by a simple, fast, and modified solid state method and shows improvement in both the dielectric constant (εr ~7007) and dielectric loss (tanδ~0.2) at 1kHz, at room temperature. X-ray diffraction analysis showed the existence of Bi0.5Na0.5TiO3 as a minor phase alongside the major phase of CaCu3Ti4O12. Average crystallite size calculated by XRD and particle size observed by transmission electron microscopy analysis were in good agreement. Energy dispersive X-ray analyses showed the presence of Ca, Cu, Bi, Na, Ti, O and demonstrated the purity and stoichiometry of the composite. The low frequency performance of the composite was estimated by measuring the frequency dispersion of the dielectric constant, dielectric loss, and AC electrical conductivity. The AC conductivity spectrum obeyed the Jonscher power law. Complex impedance spectroscopic studies reveal that the electrical relaxation process was temperature dependent and non-Debye type. The temperature dependence of the relaxation time was found to obey the Arrhenius law. The activation energy value (Ea~0.84eV) and relaxation nature of the modulus spectroscopic curve has been governed by the thermal motion and hopping mechanism of oxygen ion vacancies for electrical transport processes.

Ferroelectrics, Piezoelectric, and Impedance Spectroscopy Characterizations of CuO Doped (Na0.52 K0.44)(Nb0.9 Sb0.06)O3 –0.04LiTaO3 Lead Free Ceramics

CuO was used to reduce the sintering temperature of (Na0.52 K0.44)(Nb0.9 Sb0.06)O3 –0.04LiTaO3 (NKNSLT) piezoelectric ceramics. XRD analysis reveals the formation of single phase perovskite structure. SEM has been used to investigate the grain morphology of the material. Impedance plots have been used as a tool to analyze the electrical properties of the sample as a function of frequency and temperature. Detailed studies of dielectric properties of the compound as a function of temperature at different frequencies suggest that the compound has a dielectric anomaly of ferroelectric to paraelectric type at 360°C, and exhibits diffuse phase transition. The Nyquist plot (Z′′ vs Z′′) revealed the presence only of the grain boundary effect in the materials. Bulk resistance is observed to decrease with an increase in temperature showing a typical negative temperature coefficient of resistance (NTCR). The plot of normalized complex dielectric modulus a function of frequency exhibits both short and long-range conduction in the ceramics. The ac conductivity spectrum was found to obey Jonscher's universal power law.

Dielectric, ac-impedance and modulus spectroscopic studies of nano-crystalline Bi0.5Na0.5TiO3 synthesized by using one pot glycine assisted solution combustion from inexpensive TiO2

Nano-crystalline Bi0.5Na0.5TiO3 (BNT) ceramic has been successfully synthesized for the first time by solution combustion synthesis using glycine as the fuel, inexpensive solid TiO2 powder as the raw material, and metal (Bi and Na) as nitrates. Phase formation, the crystalline nature, morphology, and chemical purity of the fabricated BNT were investigated with TGA, XRD, SAED patterns, SEM, TEM, and EDX analyses. TG/DTA analysis of the dry powder gives pre information about the formation of final product around 900 °C, which is a relatively lower temperature than other conventional ceramic methods. XRD patterns confirmed the formation of a single phase of all the sintered ceramics. The bright-field TEM image revealed that the particle size was in the range of 20–35 nm, which was in near agreement with the average crystallite size obtained from XRD. SEM images of the sintered BNT ceramics showed the average grain sizes were in the range of 150 nm–0.5 µm. EDX studies showed the presence of bismuth, sodium, titanium, and oxygen, which confirmed the stoichiometry and purity of the ceramics. The AC conductivity spectrum obeyed the Jonscher power law. The natures of relaxation behavior of the ceramics were rationalized by using impedance and modulus spectroscopy. The dielectric behavior of the ceramics exhibited Debye-like relaxation, and could be explained based on a Maxwell–Wagner model. The activation energies calculated from the grain-boundary relaxation time constant were found to be in the range of 1.5–1.7 eV.

Dynamics of lithium ions in borotellurite mixed former glasses: correlation between the characteristic length scales of mobile ions and glass network structural units.

We have studied the mixed network former effect on the dynamics of lithium ions in borotellurite glasses in wide composition and temperature ranges. The length scales of ion dynamics, such as characteristic mean square displacement and spatial extent of sub-diffusive motion of lithium ions have been determined from the ac conductivity and dielectric spectra, respectively, in the framework of linear response theory. The relative concentrations of different network structural units have been determined from the deconvolution of the FTIR spectra. A direct correlation between the ion dynamics and the characteristic length scales and the relative concentration of BO4 units has been established for different compositions of the borotellurite glasses.