AC Conductivity Behavior Research Articles

Polyaniline: tin oxide polymeric nanocomposite films. An electrical and dielectric study

Abstract A conducting nanocomposite film of 60 nm nano-SnO2-polyaniline (PANI) and polyvinyl alcohol (PVA) has been synthesized and analyzed in terms of AC conductivity and dielectric behavior. The conducting polymer nanocomposite of PANI/60 nm (SnO2) and polyvinyl alcohol (PVA) has been prepared via in situ polymerization technique. The morphology of the nanocomposite film has been studied by SEM. The film has been characterized in terms of DC conductivity. The dielectric behavior and AC conductivity of the nanocomposite film have been investigated in the frequency range of 2 Hz to 90 KHz. The film has high dielectric constant which may be correlated with polarization. It has been observed that both dielectric loss and dielectric constant decrease with an increase in frequency.

Dielectric relaxation, AC conductivity behavior and its relation to microstructure in mechanochemically synthesized Mn-doped CeO2 nanocrystals

A simple mechanical alloying process has been implemented to obtain cerium oxide nanocrystallites monodoped with transition metal element (Mn). The microstructural, compositional and crystallographic information are investigated by employing Rietveld refinement using X-ray diffraction (XRD) data, energy dispersive X-ray (EDX) pattern and analyzing high resolution transmission electron microscopy (HRTEM) images. The results reveal that the sample exhibits a single phase cubic fluorite-type Ce0.95Mn0.05O2-δ structure. Rietveld analysis shows the coexistence of Ce3+ and Ce4+ ions in the sample. HRTEM image reveals the sheer plastic deformation on lattice planes. The frequency and temperature dependent electrical behavior of the undoped, Mn-doped and sintered samples are analyzed by impedance spectroscopy, dielectric relaxation and ac conductivity studies. The correlated barrier hopping (CBH) model has well explained the ac conduction mechanism. The release of electrons during the reduction of Ce4+ and/or Mn4+ ions to Ce3+ and/or Mn3+/Mn2+ ions by the exclusion of excess oxygen in the lattice are responsible for the electronic conductivity of the samples. The activation energy of the sintered sample is estimated both from relaxation and hopping processes and the estimated values ascertain that the charge carrier hopping process in the samples is accompanied by the dielectric relaxation.

Reassess study of high temperature electric transport properties of PbTiO3

In the present study we obtained the detailed dielectric properties of PbTiO3. The formation of the materials was confirmed through basic structural analysis using x-rays diffraction collected at room temperature. Differential scanning calorimetry confirms a first order phase transition at 763 K. Furthermore, DC conductivity as well as pyroelectricity measurements were conducted in the temperature range (400–823 K), from which the polarizability as a function of temperature was evaluated. On the other hand, AC conductivity behavior as a function of both temperature and frequency (0.12–102 kHz), shows a semiconducting like behavior indicating an adiabatic conduction mechanism. While the ferroelectric phase transition was established at 763 K from the permittivity data as a function of temperature. The behavior of the frequency and temperature exponents of the AC electrical conductivity confirm the correlated barrier hopping “CBH” mechanism of conduction. Thermal activation energy is obtained from DC and AC conductivity as well. Dielectric modulus was also studied as a function of both temperature and frequency.

Electrical and mechanical studies on ferroelectric lithium rubidium sulphate crystals

Slow evaporation method was used to grow single crystals of lithium rubidium sulphate with high transparency. Single crystal X-ray diffraction analysis shows that at room temperature, the crystal belongs to a monoclinic system with the space group [Formula: see text]/[Formula: see text]. Some physical parameters like plasma energy, Penn gap, Fermi energy and electronic polarizability have been evaluated for the grown crystal. The relation between electronic polarizability and diamagnetic susceptibility for the crystal has been established on the basis of Kirkwood’s semiempirical equation. The ac conductivity and dielectric behavior of the grown crystal were systemically investigated as a function of frequency and temperature. The title compound obeys Jonscher’s power law relations: [Formula: see text], with exponent [Formula: see text]. From the conduction study, it is observed that both small and large polarons take part in conduction process, and at low temperature, both the band and hopping mechanisms are responsible for conduction. From impedance and modulus studies, it is observed that only one conduction relaxation is observed in the crystal at low frequency. The activation energy of the dielectric relaxation (0.41[Formula: see text]eV) and that of the conduction ([Formula: see text][Formula: see text]eV) are in agreement, as a result, there is no difference among the conduction and relaxation species at high temperature. Differential scanning calorimetric analysis of the crystal shows three endothermic peaks at 166[Formula: see text]C, 185[Formula: see text]C, and 202[Formula: see text]C, from which various thermodynamic parameters such as [Formula: see text], [Formula: see text] and [Formula: see text] have been calculated. From Vickers hardness test, we have determined the mechanical strength, and other parameters which include fracture toughness, brittleness index, yield strength, and stiffness constant for the crystal.

Effect of Silver Doped Zinc Oxide as Nanofiller for the Development of Biopolymer Nanocomposites from Chitin and Cashew Gum

Nanocomposites based on chitin (CT) and cashew gum (CG) with different concentrations of silver doped zinc oxide nanoparticles (Ag–ZnO) were prepared and characterized by FTIR, UV, XRD, TEM, SEM, DSC, TGA, electrical conductivity measurements. FTIR spectra showed that the characteristic absorption band of the blend was shifted to a higher frequency in nanocomposites, indicating the intermolecular interaction between the blend and nanoparticles. The change in the UV absorption of nanocomposites relative to that of pure blend indicated the successful encapsulation of crystalline metal oxide nanoparticles in the blend matrix. XRD patterns showed that the diffraction peak of the composites were shifted near to the metal oxide peak which indicated that the surface of Ag–ZnO was perpendicular to CT/CG and changed from a semi-crystalline nature to a crystalline structure. The morphological analysis using SEM and TEM showed a uniform attachment of nanoparticles within the CT/CG blend. DSC analysis showed the increased glass transition temperature by the addition of nanoparticles. Thermal stability of nanocomposites was higher than the blend and thermal stability increased with an increase in the content of nanoparticles. The different electrical properties such as AC conductivity and dielectric behaviour of the composites were increased with an increased loading of nanoparticles.

AC conductivity and dielectric properties of B2O3-WO3-TeO2- Li2O glasses

Glass with composition (20-x)B2O3-10WO3-70TeO2- xLi2O with 0 ≤ x ≤ 20 have been prepared by conventional melt quench technique. The impedance spectroscopy technique is employed on these samples and the data are analyzed using Cole-Cole type impedance response function. The AC conductivity behavior of the present glasses has been investigated in the frequency range from 100Hz to 1MHz and as a function of temperature the measured. Ac data are analyzed using the power law to explain the observed depressive behavior of the electrical conductivity. The temperature and composition dependence scaling behavior in the AC conductivity are satisfactorily explained by scaling the AC conductivity σ′(ω) by hopping frequency ωp. The frequency response of dielectric constant and dielectric loss tanδ as a function of temperature were studied.

Alternating current conduction mechanisms of RbMgPO4 compound

Rubidium magnesium monophosphate (RbMgPO4) compound was prepared from highly pure constituents by solid state reaction. It was characterized by X-ray powder diffraction, IR, Raman, differential scanning calorimetry (DSC) and impedance spectroscopy. The infrared and Raman spectra were interpreted on the basis of PO43− vibrations. DSC revealed two displacive and reversible phase transitions at T1 = 442/432 K and T2 = 460/445 K (heating/cooling). The electrical conductivity was measured in the frequency and temperature range 200 Hz-5 MHz and 423 K–523 K, respectively. The obtained results were analysed by fitting the experimental data to an equivalent circuit model. The temperature dependence of alternating and direct current conductivities (σac, σdc) confirms the observed transitions in the calorimetric study; they were described in terms of Arrhenius relation. The activation energy’s values were determined in each phase. The AC conductivity behavior is ensured by a single process defined as a hopping transport mechanism. The conductivity frequency dependence was interpreted using the correlated barrier-hopping model (CBH) in all phases.

Dielectric response of poly(vinyl alcohol)–zinc selenide nanocomposite film

Poly(vinyl alcohol)–zinc selenide (PVA–ZnSe) nanocomposite films have been prepared, which offer higher effective permittivity than pure PVA. There is an about 2.5-fold increase (at 420 K) in the effective permittivity at 100 kHz for the 4 wt % ZnSe nanostructure impregnated PVA film as calculated from the dielectric reinforcement function. Prevailing relaxation mechanisms in the nanocomposite films, within the frequency range of 100 Hz ≤ f ≤ 1 MHz and in the temperature range of 298 ≤ T ≤ 420 K, have been discussed on the basis of available theoretical approaches in the literature. AC conductivity behavior reveals that correlated barrier hopping is the ac charge transport mechanism for the nanocomposite films, and the maximum barrier heights vary inversely with the weight percent inclusion of ZnSe nanostructures.

Impedance spectroscopy study of (NH4)3H (SeO4)2: Evidence of increase in lattice disorder in the low temperature phases

The ac conductivity behavior of superprotonic (NH4)3H (SeO4)2 in low temperature phases IV and III, at temperatures between 240K and 350K, has been studied to evidence the evolution of molecular dynamics and its relation to proton transport mechanism. The conductivity was analyzed in the frequency range of the Jonscher's regime, within the classical hopping model, where the conductivity is calculated for hopping of carriers between sites over potential barriers whose height distribution is related to the random spatial distribution of these sites. The complex electric modulus formalism was used for analysis of electric relaxation in (NH4)3H(SeO4)2.

Electrical and mechanical behavior of PMN-PT/CNT based polymer composite film for energy harvesting

Abstract The pyrochlore-free 30-PMN-PT/CNT/PVDF based piezoelectric flexible composite film has been synthesized for potential application in piezoelectric energy harvesting. Electrical characterization reveals that the maximum output voltage and current generated by the 30 vol.% PMN-PT/CNT/PVDF composite is ∼4 V and 30 nA respectively, comparable with the available literature. Further, impedance analysis has revealed a significant improvement in permittivity at low frequency and high temperature with a minimal dielectric loss. AC conductivity behavior fits well with Johnscher’s universal power law that predicts the motion of the charge carriers is translational with sudden hopping. The Nyquist plots indicate the contributions of both grain and grain boundaries at lower temperature (25–100 °C) and additional electrode effect of higher temperature (100–150 °C) on the capacitive and resistive properties of the composite. Mechanical characterization of the composite shows an increase in Young’s modulus of 705 MPa compared to 597 MPa in pure PVDF.

Vibrational spectroscopic and dielectric properties investigations of phase transitions in KMgPO4 compound

The potassium orthophosphate KMgPO4 with a β-tridymite structure was synthesized via solid-state reaction. X-ray diffraction study confirms the formation of a single phase material which crystallizes at room temperature in monoclinic system. This compound has been investigated by vibrational spectroscopy in the temperature range573–723 K. Thermal analysis shows that this composition undergoes two phase transitions at T1=633Kand T2=693 K.The evolution of Raman line ν and half –width Δν versus temperature introduces huge changes which are associated with the phase transitions originating from the reorientation of the PO4 tetrahedron. Besides, an analysis of the dielectric constants ε′ and ε″versus temperature at several frequencies shows a distribution of relaxation times. This relaxation is probably due to the change in dynamical state of the K+ cation. The ac conductivity behavior can be understood in terms of the motions of K+ cations along the tunnels which are formed by six-membered rings of MgO4 and PO4 tetrahedron linked by common vertices. The activation energies values obtained from the thermal evolution of the conductivity are: Ea1=0.52 eV (T<633 K), Ea2=1.15 eV (633 K <T<693 K) and Ea3=0.96 eV(T>693 K).

Preparation and characterization of PbO/carboxymethyl cellulose/polyvinylpyrrolidone nanocomposite films

Lead oxide nanoparticles (PbO NPs) and carboxymethyl cellulose (CMC)/polyvinylpyrrolidone (PVP) nanocomposite films were prepared by sol‐gel and solution casting methods respectively. The structural properties of the samples were investigated by X‐ray diffraction (XRD), high‐resolution transmission electron microscopy (HR‐TEM) and Fourier transformation infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) revealed the good dispersion of PbO NPs on the surface of the blend films. CMC film exhibits a transmittance (T) of 72%, increased after mixing with PVP and then decreased to &lt;38% after adding 4.0 wt% PbO NPs. Both the direct and indirect optical band gaps (Eg) of CMC equal to 3.97 and 3.7 eV, respectively. These values were increased after PVP addition and then decreased after loading PbO NPs. The conduction mechanism in CMC/PVP blend has changed from Schottky emission to Poole–Frenkel due to the effects of temperature and PbO NPs content. The effect of adding PVP &amp; PbO NPs on the DC conductivity and the activation energy Ea values of the CMC are discussed. The dielectric constant (ε′) was investigated in the frequency and temperature ranges of 1 kHz–1.0 MHz and 293–393 K respectively. Its values depend on both the PbO content and temperature. The AC conductivity σac was increased with increasing PbO content. The correlated barrier hopping (CBH) was found to be the most appropriate mechanism for explaining the AC conduction behavior. POLYM. COMPOS., 39:3712–3725, 2018. © 2017 Society of Plastics Engineers

Impedance spectroscopy and ferromagnetic properties of Bi0.8Gd0.2FeO3 multiferroics

Multiferroic Bi0.8Gd0.2FeO3 (BGFO) ceramics were prepared by a rapid-liquid phase sintering process. BGFO ceramics can be sintered at a sintering temperature range of 875°C–940°C and shown a pure orthorhombic (space group, Pnma) structure. The crystal symmetry and lattice parameters were determined from the Rietveld analysis for the experimental data. BGFO ceramics sintered at 900°C exhibited high theoretical relative density (∼98%), strong ferroelectricity and good magnetism. BGFO ceramics exhibited the similar dielectric relaxation properties to the typical relaxor ferroelectrics. The role of oxygen vacancies at high temperature in dielectric and ac conductivity behavior was also discussed. The diffusing of structure defects between the grain and grain boundary was established using Impedance Spectroscopy (IS).

Ac conductivity and dielectric behavior of hydrated homoionic alkali-cations-exchanged montmorillonite

ABSTRACTThe dielectric properties of a series of homoionic alkali-exchanged montmorillonites were studied at different treatment temperatures and various water loadings by means of complex impedance spectroscopy. To date, however, this method has been underutilized in clay minerals studies. The main objective of the present work is to understand the relaxation mechanisms of water molecules interacting with different hydration centers in clay minerals, with a view to eventually control their interactions with the alkali extra-framework cations. The other part of our study is to study the dielectric properties such as real and imaginary parts of dielectric permittivity, loss tangent, and ac conductivity in the frequency range 10−2–106 Hz and temperature range 173–333 K of these clay minerals. The obtained results have been discussed in terms of the Jonscher model.

AC Conductivity and Dielectric Behavior of Silicophosphate Glass Doped by Nd2O3

Silicophosphate glasses of nominal composition (P2 O 5 50%-SiO2 30%-Na2O 20%) and Nd2 O 3 additive (0.5 and 2 wt%) were prepared and dielectric behavior has been studied over a temperature range (302–483 K) in the frequency range (0.5 - 3243 kHz). Frequency dependence of AC conductivity (σ ac), has been explored using the universal power law. Disparity of the frequency exponent (s) with temperature was examined in terms of diverse conduction mechanisms. The principal conduction mechanisms were found correlated to both barrier hopping (CBH) and quantum mechanical tunneling (QMT) models. Temperature dependence of σ ac (ω) showed a linear increase with different frequencies. In addition, the capacitance, loss tangent, dielectric loss and dielectric constant were calculated over variable temperature ranges and frequencies.

Ac conductivity and dielectric behavior of a−Si:H/c−Si1−yGey/p−Si thin films synthesized by molecular beam epitaxial method

Abstract In this work, a thin film SiGe was synthesized by the solid source Molecular Beam Epitaxy and identified by X-ray diffractometry and Raman spectroscopy. The effect of the Ge fraction on the structural, electrical conduction and relaxation was studied in detail using impedance analysis. The results of the modulus study reveal the presence of two distinct relaxation processes suggesting the presence of grains and grain boundaries in the sample. The value of exponent ‘ s ’ calculated from the plot of log (σ) versus log (w) ranges 0.32–0.8 suggested that the conduction phenomena in the studied samples pursue hopping conduction. The impedance data were well fitted by two equivalent electrical circuits and confirms the presence of two distinct relaxation processes. The results indicate that the SiGe thin films fabricated by this method are applicable for SiGe-based electronic and optical devices. Moreover, fabrication of high quality SiGe thin films on Si thin film enables the application in solar cell.

AC conductivity and dielectric behavior in mixed electronic-ionic 30Li2O–4MoO3–(66–x)TeO2–xV2O5 glass system

AC conductivity, dielectric property, and electric modulus formalism of lithium molybdenum tellurite glasses containing vanadium with compositions 30Li2O–4MoO3–(66–x)TeO2–xV2O5 (x = 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2) have been studied in the frequency range 10−2 Hz to 1 MHz and temperature range 323–413 K to investigate the effects of mixed ionic–electronic carriers in the glasses. The variation of AC conductivity with V2O5 showed a nonlinear increase for x ≤ 0.6 mol% before decreasing to a minimum at 0.8 mol% V2O5. The decrease in σ AC attributed to some forms of blocking effect on Li+ ions caused by the mixed ionic–electronic (MIE) effect. Meanwhile, dielectric constant showed a general increase for x ≤ 0.6 before an anomalous decrease at x = 0.8 mol% V2O5, which was followed by a large increase at x > 0.8 mol%. The decrease at x = 0.8 mol% coincided with the σ AC drop at the same location. This decrease was also suggested related to the MIE that induced a blocking effect, which caused the restricted dipole movement.

Effect of Vanadium Doping on Microstructure and Dielectric Behavior of CaCu&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;Ti&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;12&amp;lt;/sub&amp;gt; Ceramics

In this work, effect of vanadium doping of CaCu₃Ti₄O₁₂ (CCTO) on microstructure and complex dielectric constant over wide frequency (100 Hz-1 MHz) and temperature (0°C – 160°C) ranges has been studied. The vanadium doping of CCTO system results in an increase of grain size, the grains being surrounded by melted-like grain boundaries. Real parts of dielectric constant of all samples are similar at low frequency (<1 kHz). In doped samples, above 1 kHz, a relaxation appears which is evidenced by a drop of real part of permittivity and a peak of its imaginary part. This relaxation phenomenon is very significant at relatively low doping rates and then decreases again as vanadium content increases. AC conductivity behavior of vanadium-doped CCTO can be divided in three regions depending on conduction processes. The calculated activation energies were close to 0.46 eV.

Synthesis, refinement of the structure, and AC conductivity behavior of sodium lithium orthonavadates

The Na x Li1-x CdVO4 (x = 0.5, 1) orthovanadates were prepared using a solid-state reaction method. The x-ray diffraction patterns (XRDP) of both materials reveal the formation of the Na2CrO4 structure. Vibrational study confirms the existence of [VO4]3− group. Electrical measurements of our compounds have been investigated using complex impedance spectroscopy (CIS) in the frequency and temperature range 209 Hz–1 MHz and 589–703 K, respectively. Nyquist plots reveal the presence of tow contributions, an equivalent circuit was proposed. DC conductivity shows electrical conduction in the material as a thermally activated process. The AC conductivity is explained using the non-overlapping small polaron tunneling (NSPT) conduction mechanism. A relationship between crystal structure and ionic conductivity was established and discussed.

Dielectric relaxation and ac conductivity behavior of carboxyl functionalized multiwalled carbon nanotubes/poly (vinyl alcohol) composites

We study the dielectric relaxation and ac conductivity behavior of MWCNT-COOH/Polyvinyl alcohol nanocomposite films in the temperature (T) range 303–423K and in the frequency (f) range 0.1Hz–1MHz. The dielectric constant increases with an increase in temperature and also with an increase in MWCNT-COOH loading into the polymer matrix, as a result of interfacial polarization. The permittivity data were found to fit well with the modified Cole-Cole equation. Temperature dependent values of the relaxation times, free charge carrier conductivity and space charge carrier conductivity were extracted from the equation. An observed increment in the ac conductivity for the nanocomposites was analysed by a Jonscher power law which suggests that the correlated barrier hopping is the dominant charge transport mechanism for the nanocomposite films. The electric modulus study revealed deviations from ideal Debye-type behavior which are explained by considering a generalized susceptibility function. XRD and DSC results show an increase in the degree of crystallinity.