Conductivity Isotherms Research Articles

Percolation phase transition, self-organization processes and thermal conductivity in PbSe1-xTex semiconductor solid solutions at small Te concentration

ABSTRACT The isotherms of the lattice thermal conductivity λ L for the PbSe1-xTex semiconductor solid solutions (х = 0–0.045) were obtained in the temperature range T = (200–600) K. The λ L(x) dependences exhibit a general trend to a decrease in λ L with increasing x, but the peaks are observed near x = 0.007, 0.015 and 0.0025 indicating the presence of phase transformations. We associated the first peak with a percolation-type phase transition to the impurity continuum and estimated the critical index for λ L within the framework of dynamic scaling theory. The second and third peaks were attributed to the self-organization processes in the PbSe1-xTex after the percolation threshold reaching. The effective cross-sections σ s for phonon scattering by impurity (Te) atoms were determined experimentally and calculated theoretically using the Klemens theory. The data obtained are another confirmation of our assumption about the presence of such percolation-type phase transition in any solid solution.

Ionic conductivity and relaxation dynamics in amorphous Li2.94Mn0.06/nPS4 (M = Mg, Ca, Al) and Li2.94CaPS3.94Xy0.06/y (X = I, N) solid electrolytes

Amorphous Li3PS4, Li2.94Mn0.06/nPS4 (M = Mg, Ca, Al) and Li2.94Ca0.03PS3.94Xy0.06/y (X = N, I) solid electrolytes were successfully prepared by planetary ball-milling method. Their structure was investigated using XRD and Raman spectroscopy. The data obtained from complex impedance spectroscopy was analyzed to study the ionic conductivity and relaxation dynamics in the prepared samples. The data was interpreted using conductivity isotherms, electrical modulus and dielectric loss tangent. Among the samples, Li2.94Al0.02PS4 exhibited highest ionic conductivity at 25 °C, which was about 6.6 x 10−4 Scm−1. Electrical modulus and dielectric loss tangent analysis suggested that grain boundary polarization and ionic conductivity increased with multivalence cation doping.

Investigating the phase diagram-ionic conductivity isotherm relationship in aqueous solutions of common acids: hydrochloric, nitric, sulfuric and phosphoric acid

The relationship between phase diagram features around the solid–liquid equilibrium region and ionic conductivity in aqueous solutions is not well understood over the whole concentration range as is the case for acidic aqueous solutions. In this work, we have studied the ionic conductivity (κ) as a function of molar fraction (x) and temperature (T) for four acid/water solutions namely, monoprotic hydrochloric acid (HCl) and nitric acid (HNO3), diprotic sulfuric acid (H2SO4) and triprotic phosphoric acid (H3PO4) along with their binary phase diagrams. The connection between the main features of the phase diagrams and the trends in the ionic conductivity isotherms is established with a new insight on the two pertinent dominant conductivity mechanisms (hopping and vehicular). Ionic conductivity at different temperatures were collected from literature and fitted to reported isothermal (κ vs. x) and iso-compositional (κ vs. T) equations along with a novel semi-empirical equation (κ = f (x, T)) for diprotic and triprotic acids. This equation not only has the best fit for acids with different valency; but also contains four parameters, less than any other similar equation in literature. This work is one of few that advances the understanding of the intricate relationship between structure and ionic transport in various acidic aqueous solutions.

Structural, optical, and impedance spectroscopy of the pseudobrookite Pb0·5Ba0·5Fe2O5 synthesized by sol–gel route

Pseudobrookite of general formula Pb0·5Ba0·5Fe2O5 was synthesized by the sol–gel route. X-ray diffraction confirms the orthorhombic Pnma space group of our sample. UV–Vis absorption spectroscopy was used to characterize this material's optical properties. We used the Tauc model and absorption measurements to estimate the direct optical band gap at 3.53 eV. We also calculate the Urbach energy, the optical extinction coefficient, and the refractive index. In addition, the skin depth, optical conductivity, and Cauchy parameters were investigated in relation to the incident photon's wavelength. Electrical conductivity data flow the Jonscher's power law and show that PBFO has two different conducts; Semiconductor behavior in the temperatures region [400 K–520 K]. Then, a metallic trend was detected beyond TS-M = 520 K. The correlated barrier hopping (CBH) model is the appropriate model to describe the conduction process in low temperature range. On the other hand, the conduction is ensured by the non-overlapping small polaron tunneling (NSPT) at high temperature zone. The scaling study shows that the conductivity spectra deviate from Summerfield and Ghosh scaling. The random barrier model (RBM) is employed to correct the Summerfield approach and we note that the conductivity isotherms are combined into a single master curve. The estimated activation energies values from dc-conductivity, hopping frequency and relaxation time are very close. The behavior of dielectric parameters was examined using the Maxwell-Wagner theory of interfacial polarization. The dielectric-relaxation phenomenon is shown by the behaviors of imaginary parts of impedance (Z″) and modulus (M″). The ideal electrical equivalent circuit for simulating the Nyquist curves (i.e. Z′′(Z′)) for our pseudobrookite is (Rg + Rgb//CPEgb). Finally, the entropy (ΔS), and enthalpy (ΔH) were established as thermodynamic parameters.

Unraveling the phase diagram-ion transport relationship in aqueous electrolyte solutions and correlating conductivity with concentration and temperature by semi-empirical modeling

The relationship between structure and ion transport in liquid electrolyte solutions is not well understood over the whole concentration and temperature ranges. In this work, we have studied the ionic conductivity (κ) as a function of molar fraction (x) and Temperature (T) for aqueous solutions of salts with nitrate anion and different cations (proton, lithium, calcium, and ammonium) along with their liquid-solid phase diagrams. The connection between the known features in the phase diagrams and the ionic conductivity isotherms is established with an insight on the conductivity mechanism. Also, known isothermal (κ vs.. x) and iso-compositional (κ vs.. T) equations along with a proposed two variables semi-empirical model (κ = f (x, T)) were fitted to the collected data to validate their accuracy. The role of activation energy and free volume in controlling ionic conductivity is discussed. This work brings us closer to the development of a phenomenological model to describe the structure and transport in liquid electrolyte solutions.

Studies of structural, dielectric, and optical properties of CuCoFeO4 spinel for high frequency, microwave, and optoelectronic applications

In this study, we synthesized by the sol-gel method the CuCoFeO4 spinel and studied its structural, dielectric, and optical properties. The sample exhibits a regular cubic spinel structure (Fd3¯m space group). Semiconductor behavior with the CBH model was observed from the variation in electrical conductivity as a function of frequency and temperature. Summerfield scaling merges conductivity isotherms into a single master curve. Non-Debye relaxation is shown in the electric modulus of the prepared composition. The impedance spectra indicate the effects of both grain and grain boundary contributions on electrical properties. The impedance analysis is presented with electrical processes modeling in the sample. This is done using an equivalent circuit model comprising a parallel RC circuit for grains and grain boundaries. The obtained simulated results agree with the measured results. Maxwell-interfacial Wagner's polarization theory was used to explain dielectric constant change. The synthesized material exhibits low dielectric constants and dielectric losses at higher frequencies, as well as high electrical resistivity. These properties make CuCoFeO4 spinel a suitable candidate for high-frequency applications and microwave absorption devices. Moreover, CuCoFeO4 spinel presents low band gap energy, making it a suitable material for visible-light absorption.

THE DENSITY AND ELECTRICAL CONDUCTIVITY OF MOLTEN SALT MIXTURES OF BERYLLIUM FLUORIDE WITH ALKALINE METALS CHLORIDE

Information about the density and electrical conductivity of salt melts is of interest both for assessing the possibility of their use for electrolytic obtaining and refining of beryllium and other technological processes, and analyzing the possible interaction of components. Data on the density of molten saline systems containing fluoride and alkaline metals chloride are obtained by hydrostatic weighing. The balloon and the thread of the suspension were made of platinum. Berylia oxide used the material and cover of thermocouple. In system BeF2–MeCl (Me = Li, Na, K, Cs) и BeF2–(Li–K)eut–Cl investigated from 9 to 14 molten saline mixtures containing from 0 to 100% beryllium fluoride with an increase in temperature by 100–200 K from the melting point of the mixture with an average step of 10 K. Due to the behavior of the individual fluoride of beryllium when heated above the melting temperature (high viscosity and intense evaporation), the density of molten salt was measured by maximum pressure in the gas bubble. Simultaneously with the density of the capillary method, the electrical conductivity of these melts was measured. Material of the measuring cell—beryllium oxide, measuring electrodes—platinum rods with a diameter of 1 mm. The permanent cells were determined and regularly controlled by melting of high-purple potassium chloride. All operations for the preparation of saline mixtures, the selection of samples for chemical analysis and the measurement of properties were carried out in an isolated atmosphere of a dry and additionally cleaned argon. The measurement results are presented on the graphs and in the form of the first and second-order polynomas, reflecting the dependence of density and electrical conductivity on temperature for various compounds of saline mixtures. The values of the simultaneously measured density and electrical conductivity values were used to calculate the molar volume and molar electrical conductivity of electrolytes. The isotherms of the molar volume are almost linear in nature, which indicates the weak interaction of the components of the melt. The isotherms of molar electrical conductivity have a characteristic outrage in the area of compositions containing about 30 mol % beryllium fluoride, which may be associated with the formation of complex compounds in the liquid phase.

Ionic transport in K2Ti6O13

Abstract The increasing demand for batteries forced the development of energy storage systems that rely on materials consisting of abundant elements in the Earth’s crust. Switching from Li+ to K+ as the main ionic charge carrier needs highly conducting potassium-bearing electrolytes to realize K+ ion batteries (PIBs). The knowledge gained from the design of Li-ion batteries (LIBs) and Na-ion batteries (NIBs) may conceptually inspire also the establishment of PIBs. Considering, for instance, the hexatitanates Na2Ti6O13, Li2Ti6O13, and H2Ti6O13, which were previously investigated as components for LIBs and NIBs, here we investigated ion dynamics in the K-analog K2Ti6O13. Ionic transport in polycrystalline samples of K2Ti6O13 was studied in a moisture-free atmosphere by broadband impedance spectroscopy in a temperature range from 20 °C to 450 °C. The current study aims at establishing a correlation between structural features of K2Ti6O13 and long-range ionic transport. As expected for K+ transport in K2Ti6O13 with its geometrically obstructed structure, the overall activation energy of ion transport in the ternary oxide takes a rather high value of 0.97(2) eV. Almost the same result (0.95(3) eV) is obtained for the migration activation energy, which we extracted from the analysis of crossover frequencies of the corresponding conductivity isotherms. By comparing our results with those of Na2Ti6O13 (0.82 eV), Li2Ti6O13 (0.65 eV), and H2Ti6O13, we clearly see how the size of the mobile cation correlates with both specific conductivities and activation energies. This comparison points to K+ being the main charge carrier in K2Ti6O13. It also helps in laying the foundations to derive the relevant structure-property relationships in this class of materials.

Thermophysical and Transport Properties of the BaCl2-CsCl High Temperature Ionic Liquid Mixtures

High temperature ionic liquids (HTILs) densities and transport properties for mixtures BaCl2‑CsCl, x(BaCl2) = 0-1, have been studied as a function of composition and temperature. In terms of Arrhenius theory, the temperature correlation of all measured properties was made and discussed. Thermodynamic properties (isothermal compressibility, molecular volume, lattice energy, heat capacity, molar Gibbs energy, enthalpy and entropy) were derived for all the studied HTILs from experimental data. The viscosity isotherms show negative deviations from linearity, while conductivity isotherms have positive deviations which may be related to the formation of highly negative changed ion associated species. The evolution of the excess quantities: viscosity deviation (Δη), excess molar viscosity (ΔEη), excess molar conductivity (ΔEκ), show a very good parallelism. The linear behavior between conductivity and viscosity was determined using the fractional Walden rule and the average slope was found far from unity.

Thermal, moisture and mechanical properties of Seacrete: A sustainable sea-grown building material

The ever-increasing global demand for concrete engenders concerning sustainability issues. In addition to the large CO2 emissions induced by the production of cement, the fabrication of concrete requires important mining and excavation for the extraction of specific minerals, sand, and aggregates, which can endanger local ecosystems. Seacrete (also known as “Seament” or “Biorock”) has previously been suggested as a potential alternative to traditional cementitious materials. Seacrete is artificial electrolytically precipitated calcium carbonate around a steel-frame cathode in which electrical current flows and that is submerged in seawater. Previous studies showed that it is ideal for the restoration of coral reefs and marine ecosystems. Furthermore, Seacrete is a very interesting sustainable concrete-like construction material for buildings and other human infrastructures. Indeed, it can be produced nearby all coastlines without any need for mining, extraction or transportation of additional material. In addition, the fabrication of Seacrete can easily be powered by low-intensity or local intermittent renewable energy sources. Previous publications pointed out that the mechanical properties and strength of Seacrete are similar to that of concrete, but no investigation has been conducted on other properties. For the first time, the current experimental study assesses the thermal and moisture properties of Seacrete. This article reports the density, compression strength, puncture resistance, specific heat capacity, thermal diffusivity, thermal conductivity, and water vapour sorption isotherms of two types of Seacrete, namely low-voltage and high-voltage Seacrete. Finally, this study emphasizes that all the aforementioned material properties of Seacrete are similar to that of concrete, confirming that the former can be considered for the construction of certain building elements and infrastructures.

On the Calculation of the Electrical Conductivity of Hot Dense Nonideal Plasmas

Factors affecting the calculation of the electrical conductivity of hot dense nonideal plasma systems are revisited and scrutinized. Essential features relevant to truncation of the internal partition function, Coulomb strong coupling, electronic excited states, in addition to high ionization boundary and Coulomb logarithm, are thoroughly investigated and assessed. Particular interest has been given to the study of the frequently occurring problem of producing intersecting conductivity isotherms at high densities. An improved model for the prediction of the electrical conductivity of hot dense matter is developed and used to calculate the electrical conductivity of partially ionized and partially degenerate matter at high energy density. Compared to results from competitive models in the literature, predictions from the present model have shown better physical behavior in avoiding the problem of producing intersecting isotherms at high densities.

Ion transport studies in PVA:NH4CH3COO gel polymer electrolytes

Ion conducting gel polymer electrolytes (GPEs) are being intensively studied for their potential applications in various electrochemical devices. The poly(vinyl alcohol)-based GPE films containing ammonium acetate (NH4CH3COO) salt have been studied for various concentrations of salt. The gel electrolyte films (GPEs) have been prepared using solution casting technique. Structural characterization carried out using X-ray diffraction reveals an increase in the amorphous nature of the samples on increasing salt concentration up to 70 wt%. The complexation of polymer and salt has been studied by Fourier-transform infrared analysis. Ionic conductivity of the GPEs has been found to increase with salt concentration and reaches an optimum for an intermediate concentration. The room temperature conductivity isotherm exhibits a maximum in conductivity of 2.64 × 10−4 Scm−1 for 65 wt% salt concentration. The temperature dependence of ionic conductivity exhibits a combination of Arrhenius and Vogel–Tamman–Fulcher behavior. Ion transport in the electrolyte system has been explored using dielectric response of the material and the observed variation in conductivity is suitably correlated to the change in charge carrier concentration and mobility of charge carriers.

Investigation on the Deterioration Mechanism of Tuff Stones Used for the Exteriors at the Former Koshien Hotel

The former Koshien Hotel is an historic Japanese architectural structure, where two different tuffs called Nikkaseki and Tatsuyamaishi were used to build the exterior. Despite its cultural significance, the building’s exterior is deteriorating in many ways, with water permeation being the main factor. In this study, the hygrothermal properties of both Nikkaseki and Tatsuyamaishi were measured in order to examine the correlation between deterioration mechanisms and the tuff characteristics in detail. The basic physical properties, pore size distribution, vapor permeability, hydraulic conductivity, and sorption isotherm were measured. The results of a comparison of two tuffs led us to hypothesize that the main reason behind Nikkaseki’s deterioration is expansive freezing, while that of Tatsuyamaishi is caused by repeating dehydration or dry-wet cycles.

Ion conduction and relaxation mechanism in ionogels embedded with imidazolium based ionic liquids

The impact of physicochemical properties of imidazolium based different ionic liquids such as BDMIMBF4, BMIMBF, and EMIMBF4 on the ion conduction and relaxation mechanisms in ionogels is investigated using broadband dielectric spectroscopy. The complex conductivity isotherms of these ionogels are analyzed using a universal power law coupled with a modified Poisson-Nernst-Planck model for the contribution of electrode polarization dominated in the low frequency region. The effect of electrode polarization is analyzed by using the Macdonald-Coelho model to determine free-ion diffusivity and number density in these ionogels. The relaxation process of ions is also systematically studied using electric modulus spectroscopy over wide frequency and temperature ranges. The temperature dependence of the ionic conductivity, free-ion diffusivity, and relaxation times follows the Vogel-Tammann-Fulcher relationship, indicating existence of coupling between the ion transport and segmental dynamics in these ionogels. The EMIMBF4 ionic liquid doped ionogel shows the highest ionic conductivity, lowest relaxation time, highest free-ion diffusivity and highest number density due to the smallest size of cations, highest static dielectric constant, and lowest viscosity of the EMIMBF4 ionic liquid. It is observed that the stretched exponents for different ionogels obtained from Havriliak-Negami and Kohlrausch-Williams-Watts fits of electric modulus are lower than unity, indicating highly nonexponential relaxation in the investigated ionogels.

Exploration of temperature dependent dielectric relaxation and correlated barrier hopping (CBH) conduction mechanism of hydrothermally synthesized CuO nanoflakes

In this study, we have reported the temperature-dependent relaxation and hopping conduction mechanism of the hydrothermally synthesized nanoflake like cupric oxide (CuO) by employing complex impedance spectroscopy technique. The non-Debye type relaxation mechanism has been explored from the impedance and modulus formalism. Frequency dependent ac conductivity analysis suggests that the material follows correlated barrier hopping (CBH) model and also satisfies the Jonscher’s universal power law at various temperatures. Moreover, the density of localized states of the synthesized material near Fermi level was estimated at different frequency. We have also elucidated the activation energy, the hopping distance and the maximum barrier height of the materials. It has been observed that the scaling behavior of the conductivity isotherms can be explained by the time temperature superposition (TTS) principle. Two important parameters of the synthesized sample such as the number density of the charge carrier and the charge carrier mobility are also calculated. This study has tried to enlighten the behaviour of relaxation and conduction mechanism of CuO nanoflake at various temperatures and explained it from the theoretical point of view.

Conductivity, Thermal and Electrochemical Stability of Solutions of Lithium Bis(Oxalato) Borate in Sulfolane

Lithium bis(oxalato) borate (LiBoB) is promising lithium salt for electrolyte solutions of lithium-ion and lithium batteries because of high thermal and hydrolytic stability as well as high electrochemical stability of BoB- anion in wide potential range [1,2]. Sulfones are promising solvents and co-solvents for high-voltage batteries [3-7]. Sulfolane (tetramethylene sulfone) is the most known representative of sulfones. It has high dielectric permittivity (43.3 at 30 °C), high oxidizing stability (≥5 V vs. Li/Li+), high flash point (> 166 °C [8]) and low toxicity [3-5]. This work summarizes the results of studies on the conductivity, viscosity, electrochemical and thermal stability of LiBoB solutions in sulfolane with concentration range of 6·10-4 – 1.1 mol L-1. The maximum of specific conductivity is 1,7·10-3 S·cm-1 at 30 ºС and corresponds to ~0.8 mol L-1 (Fig. a). Activation energy of conductivity of 1M LiBoB in sulfolane is 23.3±0.5 kJ mol-1. Solutions of LiBoB in sulfolane are viscous (Fig. b). Activation energy of viscous flow for 1M LiBoB in sulfolane is 29.4±0.5 kJ mol-1. Association constant and limiting molar conductivity (λ0) of LiBoB in sulfolane are 6 mol-1·L and 8·10-4 S·m2·mol-1, correspondingly. The decomposition temperature (temperature at the initial decomposition) of 1M LiBoB in sulfolane is 286 °C, estimated by DSC method (Fig. c), and 260 °C, estimated by DTA method (Fig. d). Anodic stability of 1M LiBoB in sulfolane is ~5.8 V vs. Li/Li+, estimated at Pt working electrode. Therefore, lithium bis(oxalato) borate dissociates well in sulfolane, its solution has moderate conductivity, high thermal and electrochemical stability. Figure. Isotherms of specific conductivity (a) and dynamic viscosity (b) of LiBoB solutions in sulfolane; DSC (c) and DTA (d) of 1M LiBoB in sulfolane. This work was performed as part of a Government Order to Ufa Institute of Chemistry of the Russian Academy of Sciences by the Ministry of Science and Higher Education of the Russian Federation (Theme No. AAAA-A17-117011910031-7). References R. Younesi, G. M. Veith, P. Johansson, K. Edstrӧm, T. Vegge // Energy Environ. Sci., 2015, 8, pp. 1905-1922.Z. Liu, J. Chai, G. Xu, Q. Wang, G. Cui //Coordination Chemistry Reviews, 2015, 292, pp. 56-73.K. Xu // Chemical Reviews, 2004, 104 (10), pp. 4303-4417.A. Abouimrane, I. Belharouak, K. Amine // Electrochemistry Communications, 2009, 11, pp. 1073-1076.N. Shao, X.-G. Sun, S. Dai, D. Jiang // J. Phys. Chem. B., 2011, 115, pp. 12120-12125.S. Li, W. Zhao, C. Xiaoling, Y. Zhao, B. Li, H. Zhang, Y. Li, G. Li, X. Ye, Y. Luo // Electrochimica Acta, 2013, 91, pp. 282-292.F. Wu, H. Zhou, Y. Bai, H. Wang, C. Wu // ACS Appl. Mater. Interfaces, 2015, 7 (27), pp. 15098-15107.Electrolytes for Lithium and Lithium-Ion Batteries / Editors T. R. Jow, K. Xu, O. Borodin, M. Ue. // Modern Aspects of Electrochemistry, Springer, 2014, V. 58, 476 p. DOI: 10.1007/978-1-4939-0302-3. Figure 1

Influence of synthesis route on structural, optical, and electrical properties of TiO2

TiO2 samples with two different morphology were synthesized via sol–gel and hydrothermal techniques. The effect of synthesis procedure on structural, morphological, optical, and electrical properties was studied. Rietveld analysis revealed that anatase phase having tetragonal structure dominates at room temperature. The presence of anatse phase of TiO2 was further confirmed by the analysis of various peaks obtained from the Raman spectra. The field-emission scanning electron microscopy (FESEM) and transmission electron microscopy micrographs depicted the formation of two different kinds of morphologies with average particle size ranging from 9.87 to 11.35 nm. The FESEM micrographs showed homogeneous particle distribution for sol–gel synthesized sample, whereas it depicted rod-like structure in the sample synthesized via hydrothermal technique. The X-ray photoelectron spectroscopy analysis clearly indicated the presence of appropriate chemical composition and valency states of Ti and O element in TiO2 samples. The optical bandgap was estimated from the UV–visible spectra and found to be in corroboration with the reported values. The conductivity spectra were analyzed using Jonscher power law. The values of activation energy suggested that the conduction mechanism is thermally activated. The conductivity isotherms were scaled through Ghosh scaling model. In the sol–gel synthesized sample, the conduction mechanism was found to be independent of temperature in the entire measured temperature range; however, the hydrothermally synthesized sample depicted that the conduction mechanism is temperature-dependent in the measured temperature range. This discrepancy was understood in terms of structural changes and charge trapping within the structure.

Uncompensated-spins induced weak ferromagnetism in Ca3Mn2O7: Magneto-conductive and dual magneto-capacitive effects

Temperature dependent magnetization study on single phase orthorhombic Ruddlesden-Popper manganite Ca3Mn2O7 evidences antiferromagnetic (AFM) ordering below 123 K. Field-dependent magnetization M(H) depicts off-centered hysteretic loops below ~110 K—confirming the existence of both weak ferromagnetism (WFM) and exchange bias, whose development upon cooling is examined in detail. WFM is attributed to the formation of uncompensated-spin-clusters within the AFM-matrix, stabilized by the high-anisotropy in the manganite, favoring Dzyaloshinskii-Moriya (D-M) interaction. Temperature dependence of an evaluated average canting angle from the M(H) loops provides a quantitative measure of the WFM-evolution. Dielectric measurements exhibit magneto-conductive effects concurrent to the WFM-onset. Temperature dependence of the low-frequency/dc-limit of Jonscher-fits to the conductivity isotherms confirms the presence of relatively more-conductive clusters, embedded in the insulating-bulk. Nyquist impedance-analysis of complex impedance reveals two relaxations, yielding dual magnetic-field effects; the lumped circuit parameters feature anomalies across the magnetic phase changes.

Conductivity relaxation and photocurrent generation in reduced graphene oxide-poly(9,9′-dioctyl-fluorene-co-bithiophene) composite with application in temperature sensing

The electrical transport properties and photocurrent generation in a reduced graphene oxide-poly(9,9′-dioctyl-fluorene-co-bithiophene) (RGO-F8T2) composite were investigated. The semiconducting nature of the RGO-F8T2 composite was jointly demonstrated by dc and ac conductivity measurements. The dc conductivity obtained from both dc and ac measurements follows the Arrhenius relationship with the activation energy of the order of 80 meV. The RGO-F8T2 composite also showed excellent temperature sensing properties. The temperature coefficient of resistance was compared to commercially available Platinum, Polysilicon, and Germanium temperature sensor. The conductivity relaxation mechanism in the RGO-F8T2 composite depicted the mechanism behind ac conduction. This was due to phonon assisted tunneling between the defect states. The density of states at the Fermi level increases by one order of magnitude for the temperature change of 301 to 433 K. The scaling of conductivity isotherms established the occurrence of intramolecular energy transfer from disordered to ordered chain segments or both in the composite. The photocurrent generation in the RGO-F8T2 composite thin film under simulated solar light illumination was also studied. Here, a linear variation of the photosensitivity with the variation of the incident light intensity was observed.

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...