Conductivity Relaxation Time Research Articles

Ion transport in surface functionalized SnO2 nanoparticles dispersed imidazolium ionanofluids: Decoupling from structural relaxation

The focus of the present work is the study of conductivity and structural relaxation dynamics of a series of ionanofluids, prepared by dispersing different extents of ionic liquid tethered SnO2 nanoparticles, i.e., nanoscale hybrid ionic fluid, (NHIF) in imidazolium ionic liquid host. Measurements have been made using temperature dependent dielectric spectroscopy and differential scanning calorimetry (DSC). Our study reveals that with increasing NHIF content in the host, the ion conductivity relaxation becomes increasingly faster than the structural relaxation at any measured temperature. For 20.0 wt% NHIF the structural relaxation time is longer than the conductivity relaxation times by more than six decades in the vicinity of the glass transition temperature (Tg), i.e. the decoupling index Rt(Tg) is >6. In contrast to the host ionic liquid, the observed unusual behaviour with increasing NHIF content is appropriately correlated to the corresponding depression of crystallinity and a sharp rise in fragility index in ionanofluids. The study suggests that the conjunction of ionic liquid tethered nanoparticles and ionic liquid provides a promising way to design highly conductive ionanofluids solvents with numerous application perspectives.

Conduction and dielectric relaxations in PVA/PVP hydrogel synthesized cerium oxide

Dielectric relaxation at higher frequencies with dc conductivity contribution is observed in PVA/PVP hydrogel synthesized Nano-crystalline Cerium oxide (CeO2), which is a typical oxygen ion conductor. The material is characterized using XRD, FTIR, Raman spectroscopy, SEM, TEM, UV-Vis and Impedance spectroscopy. Impedance spectroscopic data of the material are studied with combined Cole-Cole type conduction and dielectric relaxations and the results revealed that the material possesses two types of dipoles, pinned dipole and free dipole. The electrical parameters extracted from the analysis are found to be independent of ac data representations. The dc conductivity σc, conduction relaxation time τc and dielectric relaxation time τd show Arrhenius behavior. Conduction process follows Barton–Nakajima–Namikawa (BNN) relation and dielectric process follows fractional Debye–Stokes–Einstein (DSE) equation. Time-temperature scaling of complex impedance data suggests that the conduction mechanism is slightly temperature dependent. Intrinsic defects created in the material and hopping of charge carriers generate a combined relaxation in the material.

Исследование пьезоэлектрического резонанса в стехиометрических кристаллах LiNbO-=SUB=-3-=/SUB=- в области высоких температур и проводимости

In order to establish conditions of lithium niobate based piezoelectric resonators application at high temperatures and high conductivity in a wide range of temperatures (~ 300 – 850К) we have researched piezoelectric, ferroelectric, dielectric properties and ion conductivity of near-stoichiometric LiNbO3stoich crystals. We have revealed that piezo-resonance is observed in LiNbO3stoich in a certain temperature range ΔТ (correspondingly, in certain static conductivity relaxation time Δtau_V range) and frequencies range Δomega_R provided that tau_V-1<<omegaR. Such patterns are probably applicable not only to LiNbO3stoich crystals, but also to other piezoelectric materials.

Improvement of charge transport for hydrothermally synthesized Cd0.8Fe0.2S over co-precipitation method: A comparative study of structural, optical and magnetic properties

Here, we have elucidated the structural, optical, magnetic and electrical properties of Cd0.8Fe0.2S which is considered as diluted magnetic semiconductor (DMS). Cd0.8Fe0.2S materials were synthesized using co-precipitation (compound 1) and hydrothermal (compound 2) method. The particle size and the polycrystalline phase of the synthesized materials are significantly influenced by the synthesis procedures. Presence of antiferromagnetic coupling confirms the magnetic behavior of materials. The current-voltage (I-V) characteristics exhibit lower barrier height for the device based on compound 2 (0.59 eV) than the other device (0.64 eV). Furthermore, the 19 times enhanced mobility and lesser density of states near the Fermi level for the Al/compound 2/ITO configured device is enlightened by the space charge conduction mechanism. But, the interface resistances of the devices cannot be distinguished by the I-V characteristics. Therefore, we have tackled the problem by simulating the Nyquist plots obtained from impedance spectroscopy. We have fitted the Nyquist plots with the appropriate equivalent circuit and explained the mechanism of charge transport through the Schottky interface. The higher dc conductivity and lower relaxation time of diode fabricated by compound 2 confirm the outcomes obtained from I-V characteristics. The effect of particle size on charge transport was also analyzed.

Ion Conduction Phenomenon and Electrochemical Performance of Gel Polymer Electrolyte in EDLC Containing Blend Polymer Host, Ionic Liquid, and Mixed Carbonate Plasticizers

A series of gel polymer electrolytes (GPEs) are prepared using a blend polymer host, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (BDMIMBF4) ionic liquid (IL) and mixed organic carbonate-based plasticizers. Conductivity isotherms are analyzed using the modified Almond-West formalism. Ionic transport mechanism and relaxation dynamics are systematically studied using broadband dielectric spectroscopy over a wide frequency and temperature range. Electrical modulus and dielectric spectra are studied to get insight of the conductivity and segmental relaxation phenomena. DC conductivity, along with conductivity and segmental relaxation time followed Vogel-Tammann-Fulcher (VTF) relationship, instead of Arrhenius relationship, suggesting an existence of coupling between the ionic transport and segmental relaxation processes. The dc conductivity values are found to increase gradually with increasing content of IL. At 30 °C IL-200 composition shows a conductivity value of 1.8 × 10–3 S cm–1. Using IL-200 GPE an...

Effect of S-doping toward the optical properties of WO3 nanoparticles

Abstract This study discusses the S-doping effects on WO3 structure and optical constants. The SxWO3 system (x = 0, 0.05, 0.1 and 0.2) was prepared by easy sol-gel method and heat-treated at 500 °C for 8 h. The X-ray diffraction pattern revealed the formation of a single orthorhombic cell for x = 0, 0.1 and 0.2 compositions, while for x = 0.05 a monoclinic unit cell was identified. The variation of the cell parameter and the FTIR analysis (441 cm−1, W=S terminal) confirmed the doping process. The refractive index (n), the extinction coefficient (k), electrical (σe) and optical conductivity (σopt), dissipation factor (tan δ) and dielectric relaxation time (τ) were investigated. The study demonstrated that the S-doping improved some optical constants, particularly light transport properties. Moreover, high S-doping generated defects, which led to decreased electrical conductivity and charge carriers lifetime.

The Influence of Changes in the Structure of Hydrogen Bonds of Water on the Electrophysical Properties of Matrix–Water Systems in Stepwise Heating

Bound and free water are present in a wide variety of solids, that is single crystals, polymers, and biopolymers, as well as in media with a hydrogen bond network, as in water (2.7 ± 0.1 A in length). Some objects behave in the same way as two-component systems (open systems) under external influences and demonstrate an abnormal change in properties at the same temperature as water. This paper presents the results of studies of the temperature behavior of the permittivity, conductivity, and conductivity relaxation time of some hydrophilic polymers, crystallohydrates, and ferroelectrics. The analysis of the results showed that temperature anomalies of the selected properties are observed in the vicinity of 20, 35, 65–75, and near 100°C, which are “special” temperatures for water: in the vicinity of 20, 35, 50°C the destruction of clusters of H2O molecules occurs, while at higher temperatures there is a transition of structural water into free water. It is possible that the discrete nature of the diffuse temperature peaks of the properties is due to the presence of discrete energy levels of protons in the matrix–water system, which during stepwise heating (slow kinetics) leads to a rearrangement or destruction of the OH–O hydrogen bond network, as well as the overfilling of the proton levels in the two-minimum potential, the release of deep traps, and changes in the set of current carriers, their mobility, and the trajectories of transport in bulk.

Dielectric spectroscopic study of the binary mixtures of amino silicone oil and methyl ethyl ketone in the frequency range of 100 Hz to 2 MHz at 298.15 K temperature

Complex dielectric function ε⁎(ω) = ε′(ω) − ε″(ω) of the binary mixtures of amino silicone oil and methyl ethyl ketone were measured using precision LCR meter in the frequency range 100 Hz to 2 MHz at 298.15 K temperature. Complex dielectric function data are represented in different formalisms like complex a.c. conductivity σ⁎(ω), complex modulus M⁎(ω) and complex impedance Z⁎(ω). The refractive index of the same system was determined at 298.15 K temperature using Abbe's refractometer. These presentations are used to find out different parameters such as electrode polarization relaxation time (τEP), relaxation time (τEP′), ionic conduction relaxation time (τσ), dc conductivity (σdc) and static permittivity (ε0) of the liquid samples. Determined parameters are used to gain information about the effect of concentration variation on dielectric and electrical properties of the mixtures. Complex impedance Z⁎(ω) data were fitted to an equivalent circuit, having four elements including capacitance (C2) representing electrode double layer capacitance. The geometric relaxation time was calculated using product of resistor (R2) and capacitor (C1) of the equivalent circuit. Lower frequency dielectric data is dominated by the EP effect. The systematic change is observed in all the parameters with change in concentration of amino silicone oil in methyl ethyl ketone. Viscosity dependence of dc conductivity of the system is also investigated.

Structural, magnetic and dielectric properties of Cr substituted yttrium iron garnets

AbstractChromium substituted polycrystalline Yttrium Iron Garnets (Y3Fe5–xCrxO12 with x = 0 to 0.5) were prepared in single‐phase form with lattice constant in the range of 12.3775 Å to 12.3560 Å. All samples exhibit ferrimagnetic transition with transition temperature (Tc) in the range of 547 K for x = 0 to 494 K for x = 0.5. The saturation magnetization value at room temperature is found to increase with Cr concentration that is, from 24.8 to 26.6 emu/g and this is attributed to the preferential occupation of Cr3+ ions at octahedral site of Fe3+ ions. The frequency dependence of impedance data shows the relaxation and thermal activation of charge carriers across grains and grain boundaries. The complex impedance spectra were modeled by considering equivalent circuits having contributions from the resistance and constant phase element due to grains and grain boundaries and capacitance across grain boundaries. The dielectric constant is found to increase from 20 to 52 as the Cr concentration is increased and it is attributed to hopping of charge carriers across Fe2+–Fe3+ centers. The Arrhenius plots of relaxation time of charge carriers and conductivity show an anomaly in the vicinity of ferrimagnetic transition temperature and it highlights the presence of magneto‐electric coupling.

Breakdown of the Simple Arrhenius Law in the Normal Liquid State.

It is common practice to discuss the temperature effect on molecular dynamics of glass formers above the melting temperature in terms of the Arrhenius law. Using dielectric spectroscopy measurements of dc conductivity and structural relaxation time on the example of the typical glass former propylene carbonate, we provide experimental evidence that this practice is not justified. Our conclusions are supported by employing thermodynamic density scaling and the occurrence of inflection points in isothermal dynamic data measured at elevated pressure. Additionally, we propose a more suitable approach to describe the dynamics both above and below the inflection point based on a modified MYEGA model.

Investigation of ionic conductivity and relaxation in plasticized PMMA-LiClO4 solid polymer electrolytes

We have studied ion conduction and relaxation in plasticized PMMA-LiClO4 solid polymer electrolyte for different salt concentrations over a wide range of temperature. We have measured the complex conductivity spectra in a wide frequency range of 0.01 Hz–3 GHz and analyzed the experimental results using the random barrier model coupled with the contribution of electrode polarization in low frequency region. The temperature dependence of ionic conductivity and charge carrier relaxation time obtained from the analysis follows Vogel-Tammann-Fulcher behavior. The nearly constant loss response has been observed at low temperatures and/or at high frequency region. The temperature and frequency range of nearly constant loss response depends on the salt concentration in polymer matrix. The electric modulus spectra have been used to study charge carrier relaxation further. The stretched exponent, obtained from Kohlrausch-Williams-Watts (KWW) function, indicates highly non-exponential relaxation in the polymer electrolytes.

Effect of annealing treatment on crystalline and dielectric properties of PVDF/PEG-containing ionic liquid composites

To investigate the effect of poly(ethylene glycol)-containing ionic liquid (IL) and thermal annealing treatment on crystallization and dielectric relaxation behavior of poly(vinylidene fluoride) (PVDF), a series of PVDF/IL composites have been prepared using a solution-cast method. The interaction between imidazolium cation of ILs and >CF2 groups of PVDF can transfer nonpolar α phase to polar β and γ phase as a template at the primary crystallization, and then the interaction between PEG of ILs and >CF2 groups of PVDF can facilitate the PVDF chains in amorphous region to bring more polar phase and decrease the degree of crystallization for PVDF composites according to the template under thermal annealing treatment. The experimental dielectric data were analyzed within the formalisms of complex permittivity and electric modulus. In the frequency spectra of PVDF composites, dc conductivity, electrode and Maxwell-Wagner-Sillars (MWS) interfacial polarization resulted in high values of dielectric permittivity. The incorporation of ILs into the matrix and thermal annealing treatment can accelerate dc conductivity. The temperature dependence of relaxation time of dc conductivity follows the Arrhenius equation. The effect of annealing treatment on charge carrier movement mechanism was resulted from the increase of ion mobility induced by polymer chain segmental motion and polar phase crystals.

Dielectric relaxation and electrochemical studies on trihexyl tetradecyl phosphonium chloride [P14,6,6,6][Cl] ionic liquid

The conductivity relaxation, charge transport and electrochemical performance of trihexyl tetradecyl phosphonium chloride ([P14,6,6,6][Cl]) ionic liquid were studied by broadband dielectric spectroscopy and electrochemical workstation. Dielectric spectroscopy reviews polarity fluctuations due to the collective rotational dynamics of dipolar species and in electrically conductive systems an additional translational contribution due to charge transport was reported. The conductivity relaxation was fitted with Random barrier model by Dyre and secondary relaxation was fitted with Havriliak –Nigami function. The temperature dependence of the conductivity relaxation time can be described by Vogel – Fulcher – Tamman (VFT) equation. From the VFT fits the glass transition temperature was estimated as Tg=195.03K·The secondary relaxation was detected below the glass transition temperature and activation energy, Ea=15kJ/mol was estimated from the Arrhenius law. The electrochemical behaviour of [P14,6,6,6][Cl] was studied by fabricating an electrochemical supercapacitor and cyclic voltammetry, impedance spectroscopy and charge-discharge investigations were conducted to assess the performance of the supercapacitor. A very high specific capacitance of 370F/g with high rate scalability (up to 1000 cycles) and increased operation voltage of 3.5V were achieved to propose this electrolyte is a promising electrolyte for practical supercapacitor applications.

Effects of anhydrous AlCl3 dopant on the structural, optical and electrical properties of PVA–PVP polymer composite films

Polymer composite films based on PVA–PVP with AlCl3 as the dopant at different concentrations were prepared using solution casting technique. XRD patterns reveal the increase in amorphousity of the films with AlCl3 doping. Optical absorption studies exhibit that the values of optical absorption coefficient, direct and indirect optical band gaps are found to decrease with increase in AlCl3 concentration. It confirms the charge transfer in complexes between the polymer and the dopant. The dielectric studies show the increase in dielectric constant at low frequency with increasing AlCl3 concentration and temperature. The ac conductivity and ionic conductivity increase with the AlCl3 content and the maximum value at room temperature is found to be 6.89 × 10−4 and 8.05 × 10−5 S/cm for higher AlCl3 doped PVA–PVP film. The estimated ionic conductivity value is three or four orders of magnitude greater than those obtained in the certain representative polymer-salt complexes as reported earlier. Electrical modulus plots confirm the removal of electrode polarization and the low conductivity relaxation time with Al doping. The activation energy estimated from the temperature dependent dc conductivity plot is agreed well with the migration energy calculated from the temperature dependent electric modulus plot.

Influence of SnO2 nanoparticles on the relaxation dynamics of the conductive processes in polyaniline

The effect of stannic oxide (SnO2) nanoparticles on the electrical conductivity relaxation and distribution of relaxation times within the 4-Dodecylbenzenesulfonic acid (DBSA) doped polyaniline (Pani) was investigated using electrical impedance spectroscopy. A temperature dependent Kohlrausch–Williams–Watts (KWW) type temporal relaxation function in the time domain was generated from the analysis of the frequency dependence of the dielectric modulus (imaginary component). The thermal evolution of the characteristics parameters of the KWW function was evaluated and using these parameters the temperature dependent average conductivity relaxation time and associated macroscopic conductivity of different samples were estimated. The study revealed that SnO2 nanoparticles within the polyaniline matrix induced faster relaxation of charge carriers that essentially enhanced the conductivity of the nanocomposite. The observed phenomena were well supported by the observed improvement of the localization length of the charge carriers within the nanocomposite.

Anomalous electrical conductivity in selenite glassy nanocomposites

CuI doped selenite glass-nanocomposite system has been prepared using melt-quenching route. Their microstructure and electrical transport properties have been studied. It is observed from X-ray diffraction (XRD) study that the size of CuSeO3 nanocrystallite is found to be almost same, but the variation of selenium oxide nanoparticles does not follow any trend. Fourier transform infrared spectra (FT-IR) reveal that major bands are attributed to the SeO stretching vibration. We have investigated the electrical conductivity of these glass-nanocomposites in a wide frequency and temperature range. Dc conductivity show thermally activated anomalous nature, which may be explained from their structural point of view. Ac conductivity data have been analyzed using a power law model. It has been observed that mobile ion concentration is independent of temperature. Conductivity relaxation time has been calculated from the modulus formalism and shows thermally activated nature. The nature of variation of corresponding activation energy indicates that ionic relaxation starts for higher CuI content. A schematic model has been proposed to explain the transformation of chains into clusters in the compositions and formation of more bridging SeOSe bonds, which results an enhancement of ionic conductivity of the present glass-nanocomposite system.

Ultrafast growth of large-area monolayer MoS2 film via gold foil assistant CVD for a highly sensitive photodetector

Two-dimensional molybdenum disulfide (MoS2) is a promising material for ultrasensitive photodetectors owing to its tunable band gap and high absorption coefficient. However, controlled synthesis of high-quality, large-area monolayer molybdenum disulfide (MoS2) is still a challenge in practical application. In this work, we report a gold foil assistant chemical vapor deposition method for the synthesis of large-size (>400 μm) single-crystal MoS2 film on a silicon dioxide (SiO2) substrate. The influence of Au foil in enlarging the size of single-crystal MoS2 is investigated systemically using thermal simulation in Ansys workbench 16.0, including thermal conductivity, temperature difference and thermal relaxation time of the interface of SiO2 substrate and Au foil, which indicate that Au foil can increase the temperature of the SiO2 substrate rapidly and decrease the temperature difference between the oven and substrate. Finally, the properties of the monolayer MoS2 film are further confirmed using back-gated field-effect transistors: a high photoresponse of 15.6 A W−1 and a fast photoresponse time of 100 ms. The growth techniques described in this study could be beneficial for the development of other atomically thin two-dimensional transition metal dichalcogenide materials.

Hyperbranched poly(amidoamine)/kaolinite nanocomposites: Structure and charge carrier dynamics

An ex-situ approach was applied to prepare nanocomposites from hyperbranched poly(amidoamine) and modified kaolinite (Ka-DCA). The structure of the polymer and the corresponding nanocomposites was investigated by FTIR, DSC, SAXS and TEM. SAXS might suggest a partly exfoliated structure of the nanocomposites, which was supported by TEM. The molecular dynamics was studied by means of broadband dielectric spectroscopy (BDS). The dielectric spectra are dominated by a conductivity contribution at higher temperatures for all samples investigated. The obtained results further indicated that DC conductivity is increased by 4 orders of magnitude with increasing concentration of Ka-DCA nanofiller. Further, a significant separation between the conductivity relaxation time and that of segmental dynamics was observed. The decoupling phenomenon and the conductivity mechanism were discussed in detail. This study provides insights about the influence of the nanofiller on the structure and the conductivity contribution of nanocomposites of hyperbranched polymers including the decoupling phenomenon and fragility.

Study of dielectric anisotropy and other related parametersof a liquid crystal compound 7OAOB

ABSTRACTTemperature-dependent dielectric anisotropy has been measured for the compound 4,4′-di-n-heptyloxy-azoxy benzene (7OAOB) by using a digital LCR bridge (HIOKI 3532-50 LCR HiTESTER). The compound 7OAOB is found to exhibit negative dielectric anisotropy in the nematic and smectic-C phase. Frequency-dependent electrical conductivity has been measured for this compound. The dc conductivity has also been obtained from frequency-dependent total conductivity studies by using universal power law equation. The activation energy of the dc conduction process and relaxation time has been determined in different mesophases. The behavior of splay elastic constant (K11) with temperature has been examined for this compound. From the studies of UV-visible spectra, the values of energy band gap have been evaluated.

Theoretical estimation of quench occurrence and propagation based on generalized thermoelasticity for LTS/HTS tapes triggered by a spot heater

The present study deals with the thermal characteristics and mechanical behaviors of low/high temperature superconducting (LTS/HTS) composite tapes during quench processes triggered by a spot heater. Based on the generalized thermoelastic theory, a dynamic thermoelastic model with a relaxation time is developed which takes into account the temperature dependence and finite speed of heat propagation for the superconducting tapes under cryogenic condition. The analyses were performed using the finite element method to solve the coupled differential equations of dynamic heat conduction and elastic equilibrium. The results show that the thermoelastic behaviors exhibit a strong relevance to quench characteristics of the superconductors. As a quench occurs, the thermoelastic strain-rate has an obvious jumping variation with the instant of time of its peak being fortunately coincident with the time at which the critical temperature is reached. Such a jumping change of strain-rate could be a way of estimation and detection of quench occurrence, and the theoretical predictions coincide with the existing experimental observations on thermoelastic strain-rate in LTS magnets. For a HTS tape, the thermoelastic strain-rate or temperature-rate variation and a small jump also are illustrated as the quench occurrence is determined. Additionally, the normal zone propagation velocities for the LTS/HTS tapes are predicted by the critical temperature and thermoelastic strain-rate to show quite good agreements with the results evaluated by Wilson’s formula for a LTS tape or the experimental measurements for a HTS tape. The influences of the relaxation time of heat conduction and thermoelastic coupling on the thermal distribution and strain profile are also discussed in details.