AC Conductivity Behavior Research Articles

AC conductivity behaviour and charge carrier concentrations of some vanadate glassy system

The investigation of wide range of temperature and frequency dependent conductivity of some semiconducting glassy system reveals DC conductivity, crossover frequency and frequency exponent. The composition dependence of AC conduction activation energy and the permissible energy of polaron migration have also been computed. The Nernst-Einstein relation proves that the concentration of mobile charge carriers does not undertake a substantial part in electrical conduction.

Ion Transport Mechanism in Flexible PMMAIL/LiTf Films

Acrylates such as poly (methyl methacrylate) (PMMA) has been widely studied as polymer electrolyte film due to its good mechanical stability towards lithium electrode. However, commercial PMMAs even at high molecular weight are not able to produce flexible films due to their polar nature that prone to form interchain crosslinking via hydrogen bonding. Therefore, the formation of hydrogen bonding was hindered by incarcerating ionic liquid (IL) of 1-methyl-3-pentamethyldisiloxymethylimidazolium bis(trifluoromethylsulfonyl)imide, [(SiOSi)C1C1im] [NTf2] during free radical polymerization of MMA. Interestingly, the synthesized PMMA containing IL (PMMAIL) produced flexible and free standing films with ionic conductivity of ~10-7 S cm-1. Though the ionic conductivity obtained is comparable with other doped PMMA film electrolytes that had been studied, it is still considered as low for application in energy storage devices. As an alternative, in this study, lithium triflate (LiTf) salt was added into the PMMAIL system and the highest ionic conductivity obtained was 2.65 ×10-4 S cm-1 with addition of 30 wt.% LiTf at ambient temperature. The temperature dependence conductivity and AC conductivity behaviour of PMMAIL/LiTf were further investigated in order to fully understand the ion transport mechanism that occurred in the system. It was found that the PMMAIL/LiTf system fits the Arrhenius behaviour and Correlated Barrier Hopping (CBH) model. Â

Temperature dependent dielectric properties and AC conductivity studies on titanium niobium oxide (TiNb2O7) thin films

The dielectric properties of TiNb2O7 (TNO) thin films are studied in Metal-Insulator-Metal configuration (Au/TiNb2O7/Pt) devices. The temperature dependence of the dielectric dispersion and the AC conductivity behavior is strongly dependent on TNO thin film thickness. Low thickness (∼236 nm) films shows considerably less variation with temperatures than their thicker counterparts (∼480 nm). These behaviors are explained on physical basis – nearly constant loss (NCL) and Jonscher's Universal Dielectric Response (UDR). The TNO thin films show large dielectric constant (∼59–73) and moderate dielectric loss (∼0.07–0.11). The AC conductivity values of the thin films lie in the range of about (10−8 to 10−9) at 10 kHz. The thicker films show DC conductivity values which are thermally activated with an activation energy of about 0.44 eV. This is slightly higher (about 0.1 eV) than ωp in Jonscher's UDR response and this discrepancy is explained on the basis of mixed ionic electronic conduction in TNO thin films. The possible role of growth morphology in the dielectric response is also briefly mentioned.

Dielectric Modulus and Conductivity Scaling Approach to the Analysis of Ion Transport in Solid Polymer Electrolytes

Solid polymer electrolyte films (SPEs) based on poly(methyl methacrylate) are prepared using a solution cast technique. The temperature‐dependent behavior of dielectric, modulus spectra and ac conductivity has been investigated. The long tail of the real part of modulus (M′) in the low frequency indicates the capacitive nature of the samples. The frequency dependence of imaginary part of modulus (M″) shows a non‐Debye relaxation that has been explained using the Kohlrausch–Williams–Watts stretched exponential function. The activation energy for the relaxation is almost same as the activation energy for the conduction. The relaxation time obtained from the tangent loss graph (τδ) is about two orders of magnitude larger than that obtained from the imaginary part of modulus graph (τm). The ac conductivity has been found to obey Jonscher's universal power law. Transport parameters show that addition of filler creates additional hopping sites for the charge carriers and also increases the charge carrier density. It is also 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 Summerfield scaling. POLYM. ENG. SCI., 60: 297–305, 2019. © 2019 Society of Plastics Engineers

AC conductivity studies of polyethylene oxide-garnet-type Li7La3Zr2O12 hybrid composite solid polymer electrolyte films

We have investigated both AC dielectric permittivity and ionic conductivity of hybrid composite solid polymer electrolyte (CSPE) films (~100 μm) comprised of sub-micron sized aluminum substituted cubic Li7La3Zr2O12 (LLZO) particles dispersed in polyethylene oxide-LiClO4 (PEO-LiClO4) matrix with [EO]:[Li] = 15:1. Homogeneous CSPE films with 50 wt% LLZO (PEO-LLZO-LiClO4) exhibit good flexibility and mechanical robustness up to 120 °C. The electrochemical potential stability window measured for these films was ~5.2 V vs. Li+/Li. The complex AC permittivity and conductivity were determined using the measured electrical impedance spectra in the range of 1 Hz to 300 kHz and found to be heavily affected by the electrode polarization in low frequency region. We have analyzed the data using an expression for complex AC conductivity that generalizes the power-law dependence taking into account the effect of electrode polarization and involving ionic and polymer segmental relaxation times in its description. This expression describes very well the observed behavior of AC dielectric permittivity and conductivity in the entire measured frequency region. The ionic and segmental relaxation times obtained from fitting the experimental data indicate a strong coupling between the ionic motion and segmental dynamics. Further, the observed temperature dependent conductivity follows the Vogel-Tammann-Fulcher (VTF) behavior implying a close correlation between ionic conductivity and segmental relaxation in these polymer electrolytes. The VTF model yields an activation energy of 0.32 eV for PEO-LiClO4 film, and 0.07 eV for PEO-LLZO-LiClO4 composite film, consistent with the observed enhancement in conductivity by two orders of magnitude at 30 °C upon the addition of LLZO particles.

AC conductivity and dielectric behavior of Cu-S-Te chalcogenide glassy system

Abstract Here, the development of new chalcogenide glassy system has been reported. The AC conductivity and dielectric behaviour of them have been studied. X-ray diffraction (XRD) has been used as probe to reveal microstructure of them. Almond-West Formulism and Electric modulus formalism have been employed to interpret AC conductivity data and to explore their dielectric behavior respectively. Structural parameter (β) and dislocation density of them have been estimated to interpret electrical measurements data.

Dielectric relaxation and AC conductivity behaviour of Se80Te15Bi5/PVA nanocomposite film

Abstract An analytical approach has been applied to investigate the dielectric properties and ac conductivity behaviour of a new polymer nanocomposite (PNC) of polyvinyl alcohol (PVA) doped with nanocolloids of Se80Te15Bi5 glass over a frequency range of 100 Hz–5 MHz for temperatures ranging from 298 K to 448 K. An increase in dielectric constant and relaxation time for PNC has been seen as compared to pure PVA. The Cole-Cole model of relaxation shows good agreement with experimental data. The ac conductivity (σac) behaviour has been found to follow the Jonscher's power law Aωs. Prevailing mechanism of conduction has been confirmed to be correlated barrier hopping (CBH) type. The synthesized PNC has been used as an active layer in the fabrication of a memory device. Electrical characterization of the device has been done by current-voltage (I–V) and capacitance-voltage (C–V) measurements. The switching between high conductive (ON) and low conductive (OFF) states of the device may be attributed to charge trapping and de-trapping in Se80Te15Bi5 nanocolloids. The retention characteristic of the device, determined by capacitance-time (C-t) measurements indicates its good reliability and stability.

Synthesis, characterization, DFT calculations, electric and dielectric properties of (C6H10(NH3)2) CdCl4 H2O organic-inorganic hybrid compound

Single crystals of a new organic-inorganic material (C6H10(NH3)2) CdCl4·H2O, were grown through a slow evaporation at room temperature and were characterized using X-ray diffraction, FT–IR, FT–Raman, UV–Vis and impedance spectroscopy analyses. This compound crystallizes in the monoclinic system (P21/c space group). The [CdCl4]2- anions form an infinite sheet of octahedrons and diprotonated (C6H10(NH3)2)2+ cations that are arranged in an opposite way. The crystal pattern is stabilized by 2D network via non-covalent N–H⋯Cl, N–H⋯O and O–H⋯Cl interactions. The density functional theory DFT was applied to investigate molecular structure and vibrational modes. The calculations were performed by using B3LYP functional method combined with LanL2DZ basis set. The optimized structure and the vibrational spectra are in good agreement with the experimental measurements. The topological atom-in-molecules (AIM) and the Hirshfeld Surface (HS) analyses were carried out to investigate quantitatively the intermolecular contacts in crystal packing in a visual manner. The optical properties were investigated by optical absorption explains the eventual charge transfer interactions that take place within the molecules. Finally the electrical and the dielectric properties of this compound were investigated by means of impedance spectroscopy measurements over a wide range of frequencies and temperatures, 209 Hz–5 MHz and 300–393 K, respectively. Nyquist plots reveal a non-Debye type relaxation process and confirmed that the complex impedance curves of the title compound obeyed the Cole–Cole formalism. Furthermore, The AC conductivity behavior of the compound has been analyzed by the Jonscher's universal power law.

Investigation on electrical conductivity and dielectric property of La0.8Pb0.2(Fe,Ti)0.5O3ceramic nanoparticles

The modification of the structure lanthanum orthoferrites (LaFeO[Formula: see text] to obtain ceramic materials with enhanced structural, optical, and electrical properties constitutes an active area of research. The preparation of La[Formula: see text]Pb[Formula: see text](Fe, Ti)[Formula: see text]O3(LPFTO) ceramic nanoparticles by following a cation substitution approach from LaFeO3using sol–gel and sintering methods is described. The electrical and dielectric properties of the obtained material are investigated. The contribution of grain and grain boundary in the conduction mechanism is demonstrated by complex impedance analysis. The LPFTO ceramic nanoparticles exhibit a giant dielectric constant of the order of 108. The conductivity analysis suggests the occurrence of thermally activated semiconductor behavior. Moreover, the ferromagnetic–paramagnetic semiconductor transition temperature is observed at 385[Formula: see text]K. The ac conductivity behavior satisfies the nonoverlapping small-polaron tunneling (NSPT) model.

High electrical conductivity of (1-x)NiO/xFe2O3(x = 0.0, 0.3, 0.5, 0.7 and 1) nanoparticles for solid-state electronics

Abstract The mixed metal oxides have a significant increase in material science engineering applications. Mixed metal oxides of (1-x)NiO/xFe2O3 nanoparticles (NPs) (x = 0.0, 0.3, 0.5, 0.7 and 1) were obtained by the mechanical mixing method, and their films were achieved by the drop coating method. Raman spectroscopy was used for identifying these NPs. Dielectric relaxation and ac conductivity behavior of (1-x)NiO/xFe2O3 NPs (x = 0.0, 0.3, 0.5, 0.7 and 1) were studied. The dielectric constant, e1, and the dielectric loss, e2, for pure Fe2O3 NPs were found higher than that for pure NiO NPs. Moreover, with increasing the concentration of Fe2O3 NPs, the value of e1 and e2 increased in the mixed (1-x)NiO/xFe2O3 NPs. The complex dielectric modulus the real, M1, and imaginary, M2, parts were investigated as well as the dielectric relaxation time. The total conductivity was investigated as a function of frequency for (1-x)NiO/xFe2O3 NPs (x = 0.0, 0.3, 0.5, 0.7 and 1) then the improvement of its values was verified due to the addition of Fe2O3 NPs. The AC activation energy, ΔEac, was calculated, which increases (0.0081–0.0090) at a constant frequency of 1 MHz as Fe2O3 NPs content increased. These values of ΔEac reflected that the hopping conduction is the common current transport mechanism. On the other hand, the activation energy of the relaxation process, ΔEr, decreased (0.875–0.322) as a function of Fe2O3 NPs content increased.

AC conductivity and broadband dielectric spectroscopy of a poly(vinyl chloride)/poly(ethyl methacrylate) polymer blend

Alternating-current (ac) conductivity and dielectric relaxation behaviour of a poly(vinyl chloride)/poly(ethyl methacrylate) polymer blend have been investigated intensively in a frequency range from \(1 \times 10^{-1}\) to \(2 \times 10^{7}\) Hz through a temperature range from 300 to 393 K. The variation of \(\sigma _{\mathrm{ac}}\) of pure and polyblend samples showed a plateau region at high temperature and low frequency and this plateau region is decreased with decreasing temperature. Values of the exponent n are less than unity indicative of the correlated barrier hopping for conduction. The values of the exponent n are used to calculate the binding energy (\(W_{\mathrm{m}})\) of the charge carriers. The investigation of the frequency dependence of \(\varepsilon ^{\prime }\) for pure and polyblend samples showed a dielectric dispersion. The high values of dielectric constant at a low frequency and high temperature are attributed to the effects of space charge due to the electrode polarization. The complex electric modulus (M*) of pure and polyblend samples has been investigated. It is found that the real part of the complex electric modulus, \(M^{\prime }\) is increased non-linearly as the frequency increased and reached the steady state at higher frequencies for all samples. On the other hand, the imaginary part of the complex electric modulus, \(M^{\prime \prime }\) is characterized by a relaxation peak. The different modes of relaxation, such as interfacial polarization and dipolar relaxation, are detected in low and high frequency regions in the variation plot of \(M^{\prime \prime }\) against frequency. The activation energy values of both interfacial polarization and \(\upalpha \)-relaxation are calculated.

Structural distortion, piezoelectric properties, and electric resistivity of A-site substituted Bi3TiNbO9-based high-temperature piezoceramics

High-temperature piezoceramics Bi3-xCexTiNbO9+δ (BCTN-100x, x=0, 0.02, 0.04, 0.06, 0.07, 0.08, 0.10) were prepared by a solid-state reaction method. The crystal structure, microstructure, dielectric behaviour, piezoelectricity, temperature stability and electrical conduction mechanisms of BCTN-100x ceramics were studied. All Ce-doped Bi3TiNbO9 ceramics had a single Aurivillius phase structure. Ce substitution influenced the crystal structure, leading to a high piezoelectric constant (d33=17 pC/N) but decreasing the Curie temperature slightly (TC=883 °C). The resistivity of Ce-doped BTN ceramics increased by two orders of magnitude compared with that of the pure BTN. Furthermore, the dc and ac conduction mechanisms were studied, indicating that the conduction mechanism is closely related to temperature for dc and ac conduction behaviour. In addition, we analysed the dielectric relaxation processes and attributed them to the motion of oxygen vacancies, which deviates from the ideal Debye-model.

In Situ Measurement of Dielectric Permittivity and Electrical Conductivity of CoCl2/BaCl2 Doped PVDF Composite at Elevated Temperature

This work describes the synthesis and in situ characterization of polyvinylidene fluoride (PVDF) composite films doped with different weight percentage of CoCl2/BaCl2. The solution casting method was used for fabrication of composite films. XRD and SEM were used to analyse the surface morphology of PVDF composite films which confirms the formation of β and α phase predominately. The XRD spectra confirm the reduction in intensities of some peaks associated with α and β phase’s pre dominantly with the insertion of dopants. Dielectric permittivity and ac conductivity of the PVDF composites were measured at elevated temperature. The frequency dependence of dielectric permittivity and ac conductivity behaviour of PVDF composites with different weight percentage of Co/Ba fillers were investigated. The results reveal that the addition of Co/Ba to the host Polymer PVDF affects the dielectric permittivity and conductivity of PVDF composite. The results further reveals that the annealing influences the overall crystallization process and various phases of doped PVDF composite which in turn may affect the piezoelectric behaviour, which is prerequisite for sensing and actuator application of these PVDF composites. Thus the behaviour of sensors and devices based on doped PVDF composite can be predicted at elevated temperature. This study focused to understand the interaction between PVDF and Co/Ba dopants at elevated temperature.

Dielectric behavior and AC electrical conductivity analysis of PMMA films

PMMA films of different thickness (0.006, 0.0105, 0.0206, 0.0385 and 0.056cm) were synthesized by casting process. The temperature and frequency dependence of dielectric constant and AC electrical conductivity measurements at various frequencies (10kHz-10MHz) and temperatures (293-373K) were carried out. Few anomalies in dielectric studies were observed near 313 and 373 K respectively. These points were related to glass transitions temperature. The variation of activation energy and conduction behavior was studied .From the AC conduction studies, it is confirmed that the mechanism responsible for the conduction process is hopping of carriers. The variations of the dielectric constant and loss as function of frequency at different temperature was observed and the results were discussed. The calculated activation energy varied with the thickness, temperature, and applied frequency. Conductivity plots against frequency suggested that the response obeying the universal power law concerning the AC conductivity and dielectric behavior of polymer. The polarizability a increases with temperature but decreases with thickness indicating weekends and rising of intermolecular forces respectively.

The dielectric and electrical properties of bismuth oxide nanoparticles within organic network: the effect of temperature and the role of polarons

In this communication, we report the dielectric property of organic molecule functionalized bismuth oxide nanoparticles under different temperature and frequency condition. A large value of dielectric constant and a non-Debye type of relaxation phenomena has been witnessed due to the polaron induced polarization of the system. The frequency dependent electrical modulus of the material is discussed in the light of localized and non-localized relaxation process of the polaron. The AC-conductivity behaviour is modeled based on two different mechanisms, (a) polaron tunneling (at lower frequency) and (b) polaron hopping (at higher frequency). The organic-inorganic hybrid system also exhibited a unipolar resistive switching performance with a stable ON/OFF current ratio (∼102) when used as an active material for a suitable device under a DC-bias.

The role of the calcium concentration effect on the structural and dielectric properties of mixed Ni–Zn ferrites

The calcium substituted nickel-zinc ferrites with the formula of CaxNi0.75−xZn0.25Fe2O4 (x = 0, 0.25, 0.5 and 0.75) have been prepared by using the chemical co-precipitation method. The X-ray diffraction (XRD) analyses reveal the results that all the samples crystallize in cubic spinel structure and the lattice constants of the samples for x = 0, 0.25, 0.50 and 0.75 are found to be 8.334, 8.348, 8.380 and 8.538 A, respectively. The crystallite size of the samples, obtained from Debye Scherrer’s equation, varies between 12 nm and 27 nm. The scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analyses have been conducted to reveal and determine the morphology and stoichiometry of all the prepared CaxNi0.75−xZn0.25Fe2O4 ferrite samples. The SEM images show that the partical sizes for all the samples are at nano size in accordance with the XRD results and EDX results confirm the contents of the produced samples. The dielectric and impedance properties of the prepared ferrite samples have been investigated in the frequency range from 20 Hz to 10 MHz and in the temperature range from 350 to 700 K. The real and imaginary parts of dielectric constant, tan θ, AC and DC conductivity values decrease with increasing calcium content (except x = 0). Contrary to this behavior, real and imaginary parts of impedance increase with increasing calcium content. The general AC conductivity behavior of all samples is like semiconductor behavior. The conductivity mechanism of the sample with x = 0 is explained by the mechanism of correlated barrier hopping (CBH), while it has turned into overlapping large polaron tunneling (OLPT) mechanism for all other samples. From the relaxation time graphs obtained from the impedance data, activation energies of the grain and grain boundaries are obtained. The Nyquist plots are also presented in the temperature range of 350–700 K to determine the conductivity mechanism of the prepared samples and all the plots show only one semi-circle, which means that the dominant transmission comes from the grain boundaries.

STRUCTURAL, OPTICAL, ELECTRICAL AND DIELECTRIC PROPERTIES OF PVA-YCl3 FILMS

Polyvinyl alcohol (PVA) films doped with 10[Formula: see text]wt.% of yttrium chloride (YCl[Formula: see text] have been made by casting from their aqueous solutions. The structure of un-annealed and annealed PVA-YCl3 films was studied using X-ray diffraction (XRD) patterns and Fourier-transform infrared spectroscopy (FTIR). Both FTIR and XRD revealed that the crystalline ratio of the studied samples increased due to the effect of annealing. The effect of annealing on the optical properties has been studied. Dispersion of the refractive index was described using the single oscillator model. The single oscillator energy and the dispersion energy were estimated. The calculated optical band gap of all PVA-YCl3 films was 5.0[Formula: see text]eV. The behavior of ac conductivity showed that the conduction mechanism of PVA-YCl3 films was correlated barrier hopping model. The dielectric constant and dielectric loss index were decreased with the increase of the field frequency. The electric modulus granted a straightforward technique for assessing the dielectric relaxation time. The calculated activation energy obtained from the electric modulus mechanism was 0.172[Formula: see text]eV.

Vibrational spectra, dielectric properties, conductivity mechanisms and third order nonlinear optical properties of guanidinium 4-aminobenzoate

The frequency response of dielectric permittivity measurements at temperatures 35 °C and 100 °C suggests enhanced inherent optical quality and few defects in the crystal. The Cole-Cole plot shows the presence of grain and grain boundary, it is found that single relaxation is observed in the crystal. The ac and dc conductivity and dielectric behavior of the grown crystal were systemically investigated as a function of frequency and temperature. The third order nonlinear optical property extensively studied by z-scan technique revealed high third order nonlinearity in the form of self-defocusing and two-photon absorption with saturable absorption. The strong intermolecular charge transfer interaction evident from NBO and AIM studies confirms the NLO property of the material. The detailed vibrational assignments were carried out on the basis of potential energy distribution (PED) analysis and scaled quantum mechanical force field calculation using MOLVIB program. The red shifted NH stretching wavenumbers and the broadening of corresponding bands in the solid state as well as the gas phase spectra, optimized molecular geometry and NBO analysis have confirmed the presence of N-H⋯O hydrogen bonding in G4AB.

Low Temperature Range Dielectric Properties and AC Conductivity Behavior of Ta2O5 Thin Film Capacitor Formed with Sol-Gel Spin Coating Method

Kalınlığı 75 nm olan tantal penta oksit (Ta2O5) ince film kondansatör Sol-Gel döner kaplama işlemi ile Corning cam taşıyıcılar üzerinde elde edildi ve film kondansatörün dielektrik sabiti ε¢, dielektrik kayıp faktörü ε² ve AC iletkenlik davranışı 293–193 K sıcaklık aralığında, 10 Hz–100 kHz frekans değerlerine bağlı olarak incelendi. Ta2O5 ince film kondansatörün dielektrik sabiti ε¢, azalan sıcaklıkla 1 kHz değeri için, 293–193 K aralığında 15 ila 7 değerlerinde bulundu. Dielektrik sabiti ε¢ ve dielektrik kayıp ε² nün azalan sıcaklık ve frekans değerleri ile azalmakta olduğu belirlendi. Maksimum engel yüksekliği Wm, farklı sıcaklıklarda dielektrik kayıp faktörü ε" nün frekansa bağlılığından hesaplandı ve değeri sırasıyla 10 Hz–2 kHz ve 2 kHz–12 kHz frekans aralığı için 0,14 eV ve 0,093 eV olarak bulundu. Bu tip dielektrik özellikler taşıyıcı zıplama, yüzeylerarası ve dipolar polarizasyon mekanizmaları ile ilişkilendirildi. Ta2O5 ince film kondansatörün AC iletkenliğinin sıcaklığa bağlılığının yüksek frekans bölgesinden çok düşük, frekans bölgesine bağlı olduğu bulundu. AC iletkenliğin sıcaklığa bağlılığının engel üzerinden zıplamayla ilişkilendirilmiş (CBH) modeli ile uyumlu olduğu belirlendi.

The role of B-site substitution on the structural and dielectric properties of samarium orthoferrite polycrystals

Polycrystalline samples of SmFeO3, SmFe0.5Co0.5O3, and SmFe0.5Cr0.5O3 were prepared by the conventional solid state reaction method. Powder x-ray diffraction pattern confirmed the formation of orthorhombic structure without any impurity phase. Dielectric and impedance properties of the sintered samples were studied as a function of temperature and frequency ranging from 300 K to 550 K and 100 Hz to 50 MHz respectively. The dielectric studies showed interesting properties like dielectric anomaly around spin reorientation temperature suggesting that the magnetic and electric order parameter may be coupled. The behavior of AC conductivity with temperature was explained by hopping mechanisms and the activation energy was found decreased for the doped samples. Nyquist and electric modulus spectra revealed the grain and grain boundary contributions of the sintered samples. The experimental results suggest that the spin reorientation can be tuned in the samarium orthoferrites by changing the B-site ion.