Electric Modulus Representation Research Articles

Chitosan/Microcrystalline Cellulose Overlaid rGO/Fe3O4 Films: Broadband Dielectric Spectroscopy Investigations

Hybrid and straightforward inorganic/organic composites that can be used simultaneously for energy storage are reported. Films from chitosan (Cs) with microcrystalline cellulose (MCC) implanted with reduced graphene oxide (rGO) and/or magnetic Fe3O4 nanoparticles were fabricated. The reinforcement of the Cs/MCC films with rGO and /or Fe3O4 was studied through Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy with energy dispersive electron spectroscopy. In addition, their magnetic, conductivity, dielectric constant, and dielectric loss behaviors were studied. The magnetic investigations of the two films loaded with Fe3O4 have supper paramagnetic behavior. The saturation magnetization was decreased with the presence of rGO. At lower frequencies, the contribution of charge transport and interfacial polarization causes a sudden and nearly linear increase in permittivity with decreasing frequency. Unfortunately, no indication of electrode polarization was found, which reduces the ability of the prepared composition to store electrical energy. The electric modulus representation was employed to determine the relaxation time of the interfacial polarization quantitatively and numerically. No indication of electrode polarization was found.

Exploring the AC conductivity and dielectric properties of PVA films doped with Erythrosin B

Erythrosin B (EB) doped in PVA film was processed utilizing the casting procedure, and the structure was investigated via the Fourier Transformation infrared technique (FTIR). FTIR analysis presented a strong formation of intermolecular hydrogen bonds among PVA and EB hydroxyl groups (OH). Characteristic temperature and frequency variation of dielectric behavior and AC electrical conductivity for films of PVA doped with Erythrosin B were analyzed at (293–383 K) temperature and (102–106 Hz) frequency. The AC conductivity dependency indicates that the predominant conduction mechanism in PVA doped with Erythrosin B films follows the correlated barrier hopping (CBH) model. The charge carriers’ hopping involving localized states causes a relaxation process. Estimates were made for the AC conductivity activation energy and the conductivity relaxation energy. Frequency and temperature affect the dielectric constant (ε′) and the dielectric loss (ε″). The complex impedance spectrum (Z′ versus Z″) showed single semicircular arcs with a decreased radius with increasing temperature. The relaxation peaks in the electric modulus representation are clearly defined, and the relaxation period has been calculated.

Antibacterial activity and dielectric properties of the PVA/cellulose nanocrystal composite using the synergistic effect of rGO@CuNPs

This work aims to enhance the performance of the polyvinyl alcohol (PVA) composite by using cellulose nanocrystal (CNC) as reinforcement and copper nanoparticles (CuNPs)/reduced graphene oxide (rGO) as conducting and antimicrobial reagents. Firstly, rGO was loaded onto CuNPs using an eco-friendly microwave method. Different techniques characterized the components and prepared composites, which indicated the incorporation of cellulose nanocrystals and rGO@CuNPs within the polyvinyl alcohol matrix. Utilizing the clear zone of inhibition, the antibacterial test was quantified. Compared to the neat composite, the rGO@CuNPs loaded polyvinyl alcohol/ cellulose nanocrystal composites exhibited no bacterial growth against S. aureus, E. coli, and C. albicans. However, all composites did not have antifungal activity against A. niger. The combination of conductivity and interfacial polarization is the reason for the abrupt increase of permittivity with decreasing frequency. Besides, adding rGO@CuNPs improved the electrical conductivity. DC-Conductivity increased about a decade after adding cellulose nanocrystal to polyvinyl alcohol, then another decade after adding CuONPs. The electric loss modulus representation shows a systematic shift in the peak position towards higher frequencies, decreasing the so-called conductivity relaxation time. This is the main reason for the enhancement of conductivity. The systematic attenuation of peaks' height with increasing conductivity is still unclear.

Dielectric Study of Tetraalkylammonium and Tetraalkylphosphonium Levulinate Ionic Liquids.

Broadband dielectric spectroscopy in a broad temperature range was employed to study ionic conductivity and dynamics in tetraalkylammonium- and tetraalkylphosphonium-based ionic liquids (ILs) having levulinate as a common anion. Combining data for ionic conductivity with data obtained for viscosity in a Walden plot, we show that ionic conductivity is controlled by viscosity while a strong association of ions takes place. Higher values for ionic conductivities in a broad temperature range were found for the tetraalkylphosphonium-based IL compared to its ammonium homolog in accordance with its lower viscosity. Levulinate used in the present study as anion was found to interact and associate stronger with the cations forming ion-pairs or other complexes compared to the NTf2 anion studied in literature. In order to analyze dielectric data, different fitting approaches were employed. The original random barrier model cannot well describe the conductivity especially at the higher frequencies region. In electric modulus representation, two overlapping mechanisms contribute to the broad low frequencies peak. The slower process is related to the conduction mechanism and the faster to the main polarization process of the complex dielectric permittivity representation. The correlation of the characteristic time scales of the previous relaxation processes was discussed in terms of ionic interactions.

Dielectric study and AC conduction mechanism of gamma irradiated nano‑composite of polyvinyl alcohol matrix with Cd0.9Mn0.1S

Nanocomposite of PVA and Cd0.9Mn0.1S was prepared by solution casting technique. The formed nanocomposite was irradiated by γ-ray with dosage ranging from 10 to 120 kGy. The dielectric properties of PVA/Cd0.9Mn0.1S nanocomposites were studied as a function of frequency (100 Hz–5 MHz) in a temperature range of (303–413 K). The data were analyzed in the dielectric loss (e″), electric modulus (M″) and conductivity representation (σ′). Contributions from the polymer matrix and reinforcing phase are discerned in the relaxation response. The α-relaxation and a strong frequency dispersion are identified in the e″ spectra at high temperatures, which are attributed to the segmental motion of the polymer main chain and to conductivity contribution and /or interfacial polarization, respectively. However, two peaks are detected in the M″ spectra: a main α-relaxation at high frequency and ρ-relaxation relating to the conduction process at low frequency. The temperature dependence of both the ρ-relaxation time obtained from the modulus and dc conductivity (σdc) obeys the Arrhenius law with almost similar activation energies, ≈ 0.67 eV. The change of the frequency exponent, s, with temperature reveals that the ac conductivity is governed by the correlated barrier hopping (CBH) mechanism. The dielectric constant (e′) and dielectric loss (e″) are dose dependent showing highest value for 30 kGy irradiated sample in the α-dipolar relaxation region. With increasing γ dose, the ac conductivity increases whereas the binding energy of the charge carriers Wm decreases supporting the dominance of the chain scission in polymer.

Relaxor state and electric relaxations induced by the addition of Bi and Mn ions to Pb(Zr0.70Ti0.30)O3 ceramics

Abstract The (1 − x)Pb(Zr0.70Ti0.30)O3–xBiMn2O5 ceramics (PZT-BM), where x = 0, 0.02, 0.055, 0.11, 0.15, 0.22 and 1, were studied. We determined how addition of nonpolar BM influenced electrical properties of the ferroelectric PZT ceramics. Impedance spectroscopy measurements in broad frequency and temperature ranges were performed and several contributions to impedance response were identified. A crossover to the relaxor state was observed in the PZT-BM ceramics by doping with Bi and Mn ions. The relaxation times for the electric conductivity relaxation and dipole relaxation were estimated from electric modulus representation of the data. Activation energy values of the conductivity process, estimated for T > 510 K, decreased from 0.82 to 0.37 eV when BM content increased. The occurrence of the high-frequency dipole relaxation was assigned to the charge transfer of Ti3+/Ti4+, Zr3+/Zr4+ and Mn3+/Mn4+ ions. Occurrence of the ferroelectric relaxor features were deduced from the non-Arrhenius dependence of the relaxation times. Superposition of the relaxor features and electric relaxations provides high value permittivity (e′ > 1000) in wide temperature range (~ 250–573 K). This effect corresponds to the disorder and precipitation of ions that were shown using x-ray photoelectron spectroscopy and the time of flight–secondary ion mass spectrometry.

Influence of modifier on dielectric and ferroelectric properties of aluminosilicate glasses

Glasses with compositions SiO2-CaO-Al2O3-TiO2-Na2O were prepared by conventional melt quench technique. The dielectric properties of these glasses with a variation in alkali content over a frequency range from 20Hz to 1MHz and temperature variation of 30–280°C have been investigated. The electric modulus representation has been used to provide comparative analysis of the ion transport properties in these glasses. The conductivity isotherms show a transition from frequency independent dc region to dispersive region where the conductivity continuously increases with increasing frequency. The present glasses exhibit conductivity in the range of 10−5 to 10−3S/m which is higher than the alkali containing silicate glasses. Hysteresis loop observed at room temperature confirms the ferroelectric nature of glasses.

Polyvinyl pyrrolidone/Mg(ClO4)2 solid polymer electrolyte: structural and electrical studies

Polymer electrolytes comprising polyvinyl pyrrolidone (PVP) as host polymer and Mg(ClO4)2 as dopant salt have been prepared by solution casting technique using double-distilled water as solvent. The changes in the structural properties on the incorporation of dopant were investigated by XRD and FTIR analysis. The ionic conductivity and dielectric behavior were explored using AC impedance spectroscopy. The ionic conductivity increases with increasing dopant concentration. The conductivity enhancement with the increasing salt concentration is correlated with the increase in amorphous nature of the electrolytes. The frequency dependence of electrical conductivity obeys the universal Jonscher power law. The electrical modulus representation shows a loss feature in the imaginary component. The distribution of relaxation times was indicated by a deformed arc form of the Argand plot. The relative dielectric constant (er) decreases with increase in frequency in the low frequency region whereas a frequency-independent behavior is observed in the high frequency region. The total ionic transference number studies have confirmed that the mobile charge carriers are ions. Results obtained by cyclic voltammetry on SS/60 mol% PVP/40 mol% Mg(ClO4)2 SPE/SS symmetrical cell show evidence for reversibility.

Influence of precursor molar concentration on the electrical and magnetic properties of synthesized MnS nanocrystals

MnS Nanocrystals have been synthesized with 1:1, 1:2 and 2:1 molar ratio of precursors using wet chemical method. The electrical and magnetic properties of as-synthesized MnS nanocrystals have been investigated using the impedance spectroscopy and vibrating sample magnetometer respectively. An increase in dielectric constant from 68.5 to 87.9 with increasing Mn content and decrease to 54.1 with increase in the sulfur content was observed. Both the dielectric constant and the loss factor increased with temperature due to the Maxwell–Wagner type interfacial space-charge polarization. The Cole–Cole plot confirmed that the conduction in as-synthesized samples are through the grain and grain boundaries. The resistance and capacitance of grain and grain boundaries have been calculated. The grain resistance varies from 248 to 199 Ω whereas the grain boundary resistance varies from 16 to 6.7 KΩ over the temperature ranges of 323–473 K for 1:1 sample. It endorsed the NTCR type behavior in all the samples. The electric modulus representation revealed the well-defined relaxation peaks. The relaxation time versus temperature behavior revealed that the relaxation time decreases with increase in temperature. AC-conductivity (σac) increases with increasing frequency and temperature. σac increases from 1.58 × 10−5 to 1.51 × 10−3 S cm−1 with the increase of Mn content and then decreases to 1.22 × 10−8 S cm−1 with increase of sulfur content. The activation energy is found to be 0.35 eV (1:1), 0.64 eV (1:2) and 0.28 eV (2:1) at 3 kHz. The chemically modified MnS nanocrystals exhibit paramagnetic behavior. A typical saturation magnetization of 0.56, 0.38, and 0.57 emu/g and coercivity of 2.31, 8.42, and 5.57 Oe at room temperature for 1:1, 1:2 and 2:1 sample respectively.

AC conductivity and dielectric relaxation in V2O5–P2O5–B2O3 glasses

We investigated the AC conductivity in 60V2O5–(40 − x)P2O5–xB2O3 (x = 5, 10, 20, 30 and 35 mol%) glasses as a function of temperature. The measurements were carried out in the frequency range from 20 Hz to 1 MHz with varying temperatures (303–473 K). The samples were characterized by using X-ray diffraction (XRD) and thermogravimetric-differential thermal analysis (TG-DTA) techniques. The molar volume increases monotonically with the decrease in density. The AC conductivity increases with B2O3 content and temperature. The AC conductivity exhibited a Jonscher's universal power law and it is observed that as the temperature increases, frequency exponent (s) decreases. The dielectric constant of the sample decreases with increasing frequency and increases with temperature and concentration of B2O3. The electric modulus representation has been used to provide comparative analysis of the ion transport properties in these glasses. Scaling by using electric modulus shows overlap on single master curve signifying that the conduction mechanism is independent of temperature.

Dielectric studies of Poly (Ethylene glycol)-Polyurethane/Poly (Methylmethacrylate)/Montmorillonite Composite

Semi Inter penetrating Polymer Network (IPN) of [poly (ethylene glycol)-polyurethane-polymethylmethacrylate] [60:40]-montmorillonite (MMT) nanocomposites with different weight percentages of MMT are synthesized. The formation of the composite and its structural properties are characterized by Fourier transform infrared, X-ray diffraction pattern (XRD) and scanning electron microscopy (SEM) images. Differential scanning calorimetry (DSC) and XRD patterns show the amorphous nature of the composites. The Thermo Gravimetric Analysis (TGA) shows the enhanced thermal stability of the composite compared with the semi IPN without fillers. The conductivity behavior, frequency dependent modulus properties and dielectric properties of these prepared composites are studied by using ac impedance spectroscopy (EIS) in the frequency range 1Hz-1MHz. It is found from the impedance results that conductivity increases from 2.17×10−7 S/cm to 2.32×10−6 S/cm with increase of MMT concentration up to 5wt % and it decreases with further increase of MMT content. The dielectric analysis shows that dielectric permittivity (ɛ′) and dielectric loss (ɛ″) values decreases with increase in frequency at lower frequency region whereas frequency independent behavior is observed in the high frequency region. The electrical modulus representation shows a peak in the imaginary component. The ionic conduction relaxation times of the composites obtained from this peak maximum are in good correlation with the electrode polarization relaxation time and conductivity values.

Application of AC Impedance Spectroscopy for Characterization of BiNbO<sub>4</sub> Ceramics

Impedance spectroscopy is known as an important technique used for describing the electrical processes occurring in a system on applying an ac signal as input perturbation. In the present paper results of a study of BiNbO4 ceramics fabricated by mixed oxide method and sintered by free sintering are reported. Results on the ac response of the electroceramic samples by impedance spectroscopy at temperature T= 100 – 400 °C are given. The usual representation (i.e. Z” vs. Z’ where Z’ and Z” are the real and imaginary parts of the complex impedance, respectively) as well as the alternative representations of the impedance measurement (electrical modulus representation) was used to interpret the impedance spectra of BiNbO4 ceramics in order to obtain separate contributions of the bulk, grain boundary and electrode processes. The Kramers-Kronig data validation test was employed in the impedance data analysis. Experimental data of impedance spectroscopy were fitted to the corresponding equivalent circuit using the complex non-linear least squares method. Agreement between experimental and simulated data was established.

Dielectric studies of epoxy/polyester powder coatings containing titanium dioxide, silica, and zinc oxide pigments

Dielectric measurements are reported covering a frequency range from 10−3 to 105 Hz and a temperature range from ~355 to 410 K for a pigmented epoxy/polyester resin powder coating system. A large low frequency ohmic conduction was observed in all these systems and the electrical modulus representation was used to aid analysis. A space charge relaxation indicative of heterogeneity in the matrix was observed in the pure resin and the pigmented coatings. In the pure resin, the heterogeneity is associated with nanoscale phase separation. A study with the resin modified with Modaflow, an ester copolymer dispersion agent, shows that the dipole relaxation is more ideal and the activation energy for dipole relaxation is reduced compared with that observed in the pure resin. The introduction of titanium dioxide pigment reduces the activation energy but also increases the magnitude of the ohmic conductivity and space charge contributions to the dielectric permittivity. All the systems exhibit heterogeneity and in the case of a pigmented system charge carriers can be introduced into the system by the pigment. Clear differences are observed between TiO2 produced via the chloride and sulfate routes, reflecting different levels of charge carriers and ion mobile in the resin system. High levels of mobile ions were also observed when zinc oxide and silica were used as pigments.

Kinetics of free radical polymerization probed by dielectric relaxation spectroscopy under high conductivity conditions

Polymerization kinetics of tri-ethylene glycol dimethacrylate (TrEGDMA)/2,2-azobis-isobutyronitrile (AIBN) mixtures (0.1% w.t.) at different temperatures was investigated by using dielectric relaxation spectroscopy. The dielectric spectra at the polymerization temperatures studied are dominated by high conductivity leading us to employ the electric modulus representation in order to extract information about the evolution of the system during isothermal reaction. An intense peak appears in the imaginary component of the complex dielectric modulus which is related to conductivity. The variation of the strength of this peak and of its relaxation time with the polymerization time allows us to determine the polymerization degree evolution and the moment in which vitrification is attained, which can be compared with results obtained by temperature modulated DSC in a previous work (Viciosa MT, Hoyo JQ, Dionísio M, Gómez Ribelles JL. Journal of Thermal Analysis and Calorimetry 2007; 90:407–414). The study was completed with a detailed analysis of conductivity carried out in the unreacted system using both dielectric modulus and conductivity representations.

Complex Impedance Study of Fine and Coarse Grain TiO2 Ceramics

Titanium dioxide (TiO2) ceramics with various grain sizes were investigated by impedance spectroscopy techniques. Dielectric loss peak identified in coarse grain TiO2 was attributed to space charge polarization occurring at the grain boundaries. Electric modulus representation of the impedance data showed two types of relaxation processes in coarse grain TiO2, whereas only one type was observed in fine grain TiO2. Long‐range migration of oxygen vacancies was found to be the dominant conduction mechanism for fine grain TiO2, while electron hopping between localized states was attributed to dielectric relaxation in coarse grain TiO2.

Determining the structural relaxation times deep in the glassy state of the pharmaceuticalTelmisartan

By using the dielectric relaxation method proposed recently by Casalini and Roland(2009 Phys. Rev. Lett. 102 035701), we were able to determine the structuralα-relaxationtimes deep in the glassy state of the pharmaceutical, Telmisartan. Normally, deep in the glassy stateτα is so long that it cannotbe measured but τβ, which is usually much shorter, can be directly determined. Themethod basically takes advantage of the connection between theα-relaxation andthe secondary β-relaxation of the Johari–Goldstein kind, including a relation between their relaxation timesτα andτβ, respectively.Thus, τα of Telmisartan were determined by monitoring the change of the dielectricβ-loss,ε′′,with physical aging time at temperatures well below the vitrification temperature. The values ofτα were compared with those expected by the coupling model (CM). Unequivocalcomparison cannot be made in the case of Telmisartan because itsβ-loss peak is extremely broad, and the CM predicts only an order ofmagnitude agreement between the primitive relaxation frequency and theβ-peak frequency. We also made an attempt to analyze all isothermal and agingsusceptibility data after transformation into the electric modulus representation. Theτα found in the glass state by using the method of Casalini and Roland in themodulus representation are similar to those obtained in the susceptibilityrepresentation. However, it is remarkable that the stretching parameterβKWW − M = 0.51 in the electric modulus representation gives more precise fitsto the aging data than in the susceptibility representation withβKWW = 0.61. Our results suggest that the electric modulus representation may be useful as analternative to analyze aging data, especially in the case of highly polar glassformers havinga large ratio of low frequency and high frequency dielectric constants, such as theTelmisartan studied.

Dielectric properties of non-swelling bentonite: The effect of temperature and water saturation

In the present work, dielectric and conductivity measurements in the frequency range of 10 mHz–1 MHz were carried out by means of a high-resolution broadband spectrometer on non-swelling bentonite samples, at various low levels of hydration. The evolution of dielectric response was also examined after annealing of the samples up to 260 °C. Conductivity results in conjunction with the electric modulus representation ( M ∗) is proved to be the most suitable for the analysis of the dielectric data. Dielectric response is dominated by ionic (surface and bulk) conductivity as well as by grain polarization due to migration of ions along the clay layers. Both mechanisms are strongly affected by the concentration of bound water and the thermodielectric effect. Havrilliak–Negami dielectric relaxation functions were used to model the observed relaxations mechanisms in modulus formalism and the fitting parameters were evaluated at various water contents of the measured samples.

Ac conductivity and dielectric relaxation in ionically conducting soda–lime–silicate glasses

The frequency dependent conductivity and dielectric relaxation of alkali ions in some soda–lime–silicate (Na 2O–CaO–SiO 2) glasses are investigated over a frequency range from 50 Hz to 1 MHz and in a temperature range from room temperature to 603 K by using alternating current impedance spectroscopy. The conductivity isotherms show a transition from frequency independent dc region to dispersive region where the conductivity continuously increases with increasing frequency. The electric modulus representation has been used to provide comparative analysis of the ion transport properties in these glasses. The scaling behavior of imaginary part of electric modulus indicates that all dynamical processes occurring at different frequencies give the same activation energy.

Studies of structural, thermal and electrical behavior of polymer nanocomposite electrolytes

Structural, thermal and electrical behavior of polymer-clay nanocomposite electrolytes consisting of polymer (polyethylene oxide (PEO)) and NaI as salt with different concentrations of organically modified Na + montmorillonite (DMMT) filler have been investigated. The formation of nanocomposites and changes in the structural properties of the materials were investigated by X-ray diffraction (XRD) analysis. Complex impedance analysis shows the existence of bulk and material-electrode interface properties of the composites. The relative dielectric constant (er) decreases with increase in frequency in the low frequency region whereas frequency independent behavior is observed in the high frequency region. The electrical modulus representation shows a loss feature in the imaginary component. The relaxation associated with this feature shows a stretched exponential decay. Studies of frequency dependence of dielectric and modulus formalism suggest that the ionic and polymer segmental motion are strongly coupled manifeasting as peak in the modulus (M) spectra with no corresponding feature in dielectric spectra. The frequency dependence of ac (alternating current) conductivity obeys Jon- scher power law feature in the high frequency region, where as the low frequency dispersion indicating the presence of electrode polarization effect in the materials.

Evidence of secondary relaxations in the dielectric spectra of ionic liquids

We investigated the dynamics of a series of room temperature ionic liquids based on the same 1-butyl-3-methyl imidazolium cation and different anions by means of broadband dielectric spectroscopy covering 15 decades in frequency (10^(-6)-10^9 Hz), and in the temperature range from 400 K down to 35 K. An ionic conductivity is observed above the glass transition temperature T_{g} with a relaxation in the electric modulus representation. Below T_{g}, two relaxation processes appear, with the same features as the secondary relaxations typically observed in molecular glasses. The activation energy of the secondary processes and their dependence on the anion are different. The slower process shows the characteristics of an intrinsic Johari-Goldstein relaxation, in particular an activation energy E_{beta}=24k_{B}T_{g} is found, as observed in molecular glasses.