Non-overlapping Small Polaron Tunneling Research Articles

Summerfield scaling model and electrical conductivity study for understanding transport mechanisms of a Cr3+ substituted ZnAl2O4 ceramic.

Solid-state and sol-gel procedures were used to prepare ZnAl1.95Cr0.05O4 nanocrystal spinels. From the results obtained by X-ray diffraction (XRD) and transmission electron microscopy (TEM), it can be concluded that the samples prepared by sol-gel synthesis are better crystallized than the ones resulting from the solid-state method. Studies by spectroscopy of impedance were done in function of frequency (40-107 Hz) and temperature (540-680 K) in the sample prepared by sol-gel synthesis. The electrical conductivity spectra obey Jonscher's law and two models were observed studying the variation of the exponent 's' as a function of temperature, Correlated Barrier Hopping (CBH) and Non-overlapping Small Polaron Tunnelling (NSPT). The predominant conduction mechanism is bipolaron hopping. The scaling behavior of conductivity spectra was checked by Summerfield scaling laws. The time-temperature superposition principle (TTSP) points to a common transport mechanism working for the low and middle frequency ranges. The scaling mechanism fails in the high-frequency ranges suggesting that conduction dynamics, and the usual hopping distance of mobile species, have changed. The values obtained for the activation energy from the hopping frequency, conductivity σ dc, bulk resistance R gb, and relaxation (f max), in the temperature range of 540-680 K, are very close. A higher and negative temperature coefficient of resistivity (TCR coefficient) equal to -2.7% K-1 is found at 560 K. This result shows that our compound is suitable for uncooled infrared bolometric applications and infrared detectors.

Synthesis, morphological, electrical, and conduction mechanism studies of a sodium cerium diphosphate compound.

A NaCeP2O7 compound was successfully synthesized by a high-temperature reaction with the solid-state method. Analyzing the XRD pattern, of the studied compound, confirms the orthorhombic phase with the Pnma space group. The examination of SEM images reveals that the majority of grains are around 500 to 900 nm with a uniform distribution. As for the EDXS analysis, all chemical elements were detected and found in the appropriate ratio. The curves of temperature-dependent imaginary modulus M'' versus angular frequency reveal the presence of one peak at each temperature, proving that the dominant contribution is associated with the grains. The frequency dependence of the conductivity of alternating current is explained using Jonscher's law. The close values of the activation energies obtained from the jump frequency and extracted from the dielectric relaxation of the modulus spectra, as well as from the continuous conductivity imply that the transport takes place by the Na+ ions hopping mechanism. The charge carrier concentration in the title compound has been evaluated and shown to be independent of temperature. The exponent s increases with the increase in temperature; this behavior proves that the non-overlapping small polaron tunneling (NSPT) is the appropriate conduction mechanism model.

Lead-free double perovskite Cs2MBiCl6 (M = Ag, Cu): insights into the optical, dielectric, and charge transfer properties.

Recently, double perovskites have shown excellent potential considering the instability and toxicity problems of lead halide perovskites in optoelectronic devices. Here, the double perovskites Cs2MBiCl6 (M = Ag, Cu) were successfully synthesized via the slow evaporation solution growth technique. The cubic phase of these double perovskite materials was verified through the X-ray diffraction pattern. The investigation of Cs2CuBiCl6 and Cs2AgBiCl6 utilizing optical analysis showed that their respective indirect band-gap values were 1.31 and 2.92 eV, respectively. These materials, which are double perovskites, were examined using the impedance spectroscopy technique within the 10-1 to 106 Hz frequency and 300-400 K temperature ranges. Jonncher's power law was utilized to describe AC conductivity. The outcomes of the study on charge transportation in Cs2MBiCl6 (where M = Ag, Cu) suggest that the non-overlapping small polaron tunneling mechanism was present in Cs2CuBiCl6, whereas the overlapping large polaron tunneling mechanism was present in Cs2AgBiCl6.

Microstructure, charge carrier conduction mechanism model, dielectric properties and leakage current analysis of Dy2FeMnO6 nanomaterial

The structure, microstructure, charge transport properties, dielectric properties, and leakage current density of Dy2FeMnO6 synthesized by the auto combustion method are investigated in this study. The monoclinic crystal structure of the sample with space group P21/n was observed. The CoO6 and MnO6 octahedra were found distorted and tilted. The calculation of the bond valence sum confirmed the +3 and + 3/+4 oxidation states of Fe and Mn, respectively. The average crystallite, particle, and grain sizes were 43.01, 94, and 187.68 nm, respectively. The anticipated stoichiometry of the constituent elements was confirmed by energy–dispersive X–ray spectra. The frequency–dependent conductivity obeyed Jonscher’s power law, and the frequency exponent associated with this law increased with temperature, indicating the non–overlapping small polaron tunnelling (NSPT) mechanism for charge conduction. The enhancement of the dielectric loss tangent with temperature was consistent with the dc conductivity. The frequency dependence of dielectric properties was explained using Havriliak–Negami formalism. The sample followed Vogel–Fulcher law, which is similar to the relaxor ferroelectrics, and the ferroelectricity increased with frequency. Conduction, migration, and dielectric relaxation all have similar activation energies. The sample exhibited low leakage current density, which followed Schottky emission with a barrier height of 0.02(4) eV. The obtained results were compared with other rare–earth–based double perovskites.

Implementing a sol-gel route to adjust the structural and dielectric characteristics of Bi and Fe co-doped BaTiO3 ceramics

The present work explores the impact of Fe insertion on the physical properties of Ba0.95Bi0.05Ti1-xFexO3 (x = 0.025, 0.050, and 0.075) prepared via sol gel method. The resulting samples crystallize in the tetragonal structure with space group P4mm and their morphological features point out the variation of the microstructure with Fe content. In turn, the dielectric constant versus temperature plot reveals the existence of two transition phases: the first one is ferroelectric-paraelectric transition phase (TF-P) and the second one is ferroelectric orthorhombic - ferroelectric tetragonal phase (TO-T). Analysis of conductivity curves using Jonscher’s augmented equation (for x = 0.025) and Jonscher’s power law (for x = 0.075) suggests the Non-Overlapping Small Polaron Tunneling (NSPT) model as a conduction mechanism.

Physical insights into the grain size effect on the electrical properties of nanocrystalline La2Zr2O7 pyrochlores

The role of grain size on the electrical properties of nanocrystalline La2Zr2O7 (LZO) ceramics prepared by chemical co-precipitation is reported. Grain size from 10 to 70 nm was obtained. The XRD and Raman scattering showed a pyrochlore structure of La2Zr2O7. Morphology and chemical analysis were done by SEM and XPS, respectively. Electrical conductivity studies using impedance spectroscopy resolved the conductivity borne to grain and grain boundary with a non-Debye nature of conduction. The activation energy (Ea) for electrical conduction through grain was almost the same for all the grain sizes and equal to 1.20 ± 0.03 eV. However, the Ea of the grain boundary had decreased from 1.17 eV to 0.78 eV with an increase in grain size, and the conduction is due to oxygen ion migration. The conduction mechanism was governed by the non-overlapping small polaron tunneling model. Additionally, ion-ion correlation in conduction is increased with increasing grain size.

Dielectric Behaviour and Electrical Conductivity of α-BiNbO4 and β-BiNbO4 Ceramics

In this work, orthorhombic (α-BiNbO4) and triclinic bismuth niobate (β-BiNbO4) ceramics were prepared by a wet chemical route. The structure of the obtained powders was characterised by X-ray diffraction and the morphology by scanning electron microscopy. The dielectric measurements were performed in the radiofrequency region, at different temperatures, using the impedance spectroscopy technique. The α-BiNbO4 sample presented a temperature-dependent relaxation process, with the corresponding activation energy being calculated through the Arrhenius equation. The AC conductivity dependence on the frequency was in agreement with Jonscher’s universal power. The conduction mechanism in the α-BiNbO4 compound is governed by two processes, which can be ascribed to a hopping transport mechanism. The correlated barrier hopping model until 280 K and the non-overlapping small polaron tunnelling model above 280 K are the most suitable models to describe the conductivity of this sample. In the β-BiNbO4 compound, the motion of mobile charge carriers involves localised hopping between neighbouring sites.

Structural evolution, dielectric relaxation, and charge transport characteristics of formamidinium lead iodide (FAPbI3) perovskite

Recently, hybrid halide perovskite solar cells have drawn the researchers’ attention, owing to their high-power conversion efficiency. Among the different compounds, MAPbI3 (MA = Methylammonium CH3NH3) and FAPbI3 (FA = Formamidinium CH(NH2)2) are especially potential candidates since their bandgap suited the energy range of visible light. Here, the hybrid perovskite FAPbI3 is successfully synthesized via the inverse temperature crystallization method. Different characterization techniques such as variable-temperature structural analyses, differential scanning calorimetry (DSC), and impedance spectroscopic analysis show that FAPbI3 presents a phase transition at T = 300 K from the hexagonal to the cubic symmetry. Optical analysis of FAPbI3 shows the direct band-gap value of ∼1.4 eV. FAPbI3 is characterized by impedance spectroscopy technique performed in the 10−1–106 Hz frequency and 210–390 K temperature ranges. The alternating current (AC) conductivity is illustrated in terms of Jonncher's power law. The study on charge transportation within FAPbI3 suggests the presence of the NSPT (non-overlapping small polaron tunneling) and OLPT (overlapping large polaron tunneling) models in the hexagonal and cubic phases, respectively.

Dielectric properties and impedance spectroscopy of NASICON type Na3Zr2Si2PO12

We report the temperature dependent dielectric properties and impedance spectroscopy investigation of Na3Zr2Si2PO12 in the frequency range of 20 Hz–2 MHz. The Rietveld refinement of x-ray diffraction pattern confirms the monoclinic phase with C2/c space group. The d.c. resistivity behavior shows its strong insulating nature at low temperatures, and follows Arrhenius law of thermal conduction with an activation energy of 0.68 eV. Moreover, detailed analysis of temperature dependent I–V data shows a transition from ohmic to space charge limited conduction (SCLC) mechanism at around 5 V applied electric field. The decrease in electric permittivity (εr) with frequency is explained based on the space polarization mechanism and its increment with temperature by thermal activation of charge carriers. The dielectric loss (D = tanδ) peak follows the Arrhenius law of thermal activation with an energy of 0.25 eV. We observe an enhancement in a.c. conductivity with frequency and temperature due to the decrease in the activation energy, which results in enhancing the conduction between defect states. Further, we observe an abrupt increase in the a.c. conductivity at high frequencies, which is explained using the universal Jonschers power law. The analysis of a.c. conductivity shows two types of conduction mechanisms namely correlated barrier hopping and non-overlapping small polaron tunnelling in the measured temperature range. The imaginary part of the electric modulus confirms the non-Debye type relaxation in the sample. The shifting of the relaxation peak towards higher frequency side with an increase in temperature ensures its thermally activated nature. The scaling behavior of the electric modulus shows similar type of relaxation over the measured temperature range. The combined analysis of electric modulus and impedance with frequency shows the short-range mobility of charge carriers.

Dielectric Properties of Polyaryletherketone/CaCu3Ti4O12 Nanocomposite Films Fabricated via Cast Film Extrusion Process

Polymer composites prove to be the best choice for improving the dielectric properties of polymers. This work mainly focuses on studying the dielectric behavior of polyaryletherketone (PAEK), a high-temperature polymer, and its nanocomposite films with CaCu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> (CCTO) ceramics. The dielectric constant of PAEK improves significantly after the addition of CCTO nanoceramics and shows nearly frequency-independent behavior. The dielectric loss of these nanocomposites is low and is in the range of 0.004–0.006 at room temperature and 1 kHz. Dielectric properties exhibit very good temperature stability up to 150 °C. Activation energies calculated from both electric modulus and conductivity analyses show that the movement of charge carriers is responsible for both relaxation and conduction processes. The conductivity mechanism follows the correlated barrier hopping (CBH) model at low temperatures and the nonoverlapping small polaron tunneling (NSPT) model at high temperatures. Breakdown characteristics are analyzed using Weibull probability distribution. These PAEK/CCTO nanocomposites are proposed as potential materials for high-temperature dielectric applications.

Dielectric, AC Conductivity, and DC Conductivity Behaviours of Sr2CaTeO6 Double Perovskite.

Relatively new double perovskite material, Sr2CaTeO6, has been prepared through conventional solid-state procedures. Structural, dielectric, and optical characteristics of this exquisite solid-state material were analysed in this study. The single-phase monoclinic P21/n structure of this prepared compound was well correlated with the literature review. Good distribution of grain sizes and shapes was observed in the morphological study of this compound. The discussions on its optical and dielectric properties are included in this manuscript. High dielectric real permittivity, low dielectric loss, and good capacitance over a range of temperatures possessed by this compound, as shown in dielectric and electrical modulus studies, indicated good potential values for capacitor applications. The Ro(RgQg)(RgbQgb) circuit fitted well with the impedance and electrical modulus plot of the compound. Its relatively high electrical DC conductivity in grain at high frequencies and its increasing value with the temperature are typical of a semiconductor behaviour. This behaviour might be attributed to the presence of minor oxygen vacancies within its lattice structure and provides a long-range conduction mechanism. A small difference between activation energy and Ea of DC conductivity indicates that the same charge carriers were involved in both grains and the grain boundaries’ long-range conduction. The electrical AC conductivity of this compound was found to contribute to the dielectric loss in grain structure and can be related to Jonscher’s power law. The presence of polarons in this compound was exhibited by non-overlapping small polaron tunnelling (NSPT) and overlapping large polaron tunnelling (OLPT) conduction mechanisms over a range of temperatures. Wide optical band gap and Eopt in the range of 2.6 eV to 3.6 eV were determined by using an indirect and direct allowed mechanism of electrons transitions. These values supported the efficient semiconducting behaviour of the grain in this material and are suitable for applications in the semiconductor industry.

Study of structural properties and conduction mechanisms of La0.67Ca0.2Ba0.13Fe0.97Ti0.03O3 perovskite

In the present investigation, the La0.67Ca0.2Ba0.13Fe0.97Ti0.03O3 perovskite structure is prepared using the auto combustion method. The Rietveld refinement of the X-ray diffraction results indicates that the prepared compound crystallizes in the orthorhombic structure with the Pnma space group. Morphologic and elastic properties are analyzed using electron microscopy and Raman spectroscopy techniques. The nanoparticles size of the investigated perovskite structure was determined using TEM microscopy and the nanocrystallites values were obtained from XRD patterns. The Raman investigation confirms that the prepared compound reveals similar vibration modes compared to the reported modes of the LaFeO3 structure. The semi-conductor behavior of the prepared compound is explained based on the small polaron hopping conduction mechanism. The conductivity spectra are studied using the universal Jonscher power law. The dynamic region of the spectra confirms the activation of the non-overlapping small polaron tunneling and the correlated barrier hopping conduction processes. Impedance analysis confirms the important role of the grain boundary contribution to the electrical properties of the studied structure. Also, the electrical conduction and the relaxation phenomena are related to the same origin. Different physical parameters of this compound are determined, which can orient their use in specific applications.

Influence of V2O5 concentration on structural and electrical transport properties of semiconducting ternary glass and glass-ceramics nanocomposite system

The effects of V2O5 concentration on semiconducting xV2O5–(1-x) (0.25Nd2O3–0.75ZnO) glass nanocomposites were investigated by structural, optical, and electrical conductivity studies. The composition dependency of physical attributes like density, molar volume, bond dissociation energy, number of bonds per unit volume, etc., was established. Using X-ray diffraction and field-emission scanning electron microscopy, we identified the presence of different nanocrystallites and amorphousness. DC electrical conductivity was caused by the small polaron hopping due to the presence of V4+ and V5+ valence states, enhanced as the small polaron radius was reduced with rising V2O5 concentration. The non-overlapping small polaron tunnelling (NSPT) model was the preferred AC conduction process, and reducing nature of tunnelling distance enhanced AC conductivity with increasing V2O5 concentration. We modified the existing NSPT model to get reasonable values for fitting parameters. The scaled AC conductivity spectra revealed temperature independence and the composition-dependent conductivity relaxation process of small polarons.

Effect of rare earth on structural, morphological, vibrational, magnetic and dielectric properties of RFe0.5Cr0.5O3 (R = Nd, Eu) perovskites

RFe0.5Cr0.5O3 (R = Nd,Eu) perovskites were synthesized through solid-state reaction. The structural analysis evidences the orthorhombic symmetry of these materials in accordance with their tolerance factor. The lattice parameters, bond lengths, and bond angles, as obtained by Rietveld refinement, vary systematically with the size of R3+ cations. The structural stability and thermally activated expansion of the crystal lattice are affirmed by means of a high-temperature X-ray diffraction (HT-XRD) study. The microstructure of the prepared powders is investigated using scanning electron microscopy (SEM), as well as X-ray diffraction (XRD) through the calculation of the crystallite size. Diffuse reflectance spectra indicate that these materials behave as semiconductors, and the gap energies are calculated. Room-temperature Mössbauer spectroscopy highlights the presence of magnetic frustration phenomenon in both materials. The frequency-dependent dielectric study reveals a colossal dielectric constant in agreement with the Maxwell-Wagner relaxation mechanism resulting from intergrain boundaries, as asserted by impedance spectroscopy. The conductivity mechanism is provided by the correlated barrier hopping model for EuFe0.5Cr0.5O3 perovskite, and the non-overlapping small polaron tunneling mechanism for NdFe0.5Cr0.5O3 material. High-temperature dielectric measurements reveal two anomalous features attributed to the magnetodielectric effect and the onset of ferroelectric-paraelectric transition, respectively. Metallic behavior is identified at higher temperatures for both materials.

AC conductivity and electrical relaxation of a promising Ag2S-Ge-Te-Se chalcogenide glassy system

In this study, we developed a chalcogenide glassy system comprising (Ag2S)x-(0.4Ge-0.3Te-0.3Se)1-x, where x = 0.05, 0.10, and 0.20. The formation of Ag2S and GeSe2 nanocrystallites with small sizes and the development of GeTe, Ag2GeS3, TeS, and Se5.95Te1.05 phases with high Ag2S contents were confirmed by X-ray diffraction. The Fourier transform-infrared spectra demonstrated the characteristic vibration of Ag–S at 500–600 cm−1. Kinetic analysis of conductivity suggested that the Meyer–Neldel energy was due to polarons hopping from trap to trap induced by multiple phonon excitation. Tunneling of polarons through the grain boundary when x = 0.1 could be interpreted based on the modified non-overlapping small polaron tunneling model. By contrast, the correlated barrier hopping model was more appropriate for explaining the dominant conduction mechanism when x = 0.05 and 0.2. The lower relaxation times when x = 0.05 and 0.2 indicated a higher rate of polaron hopping. The temperature independence of the relaxation process was confirmed based on the scaling process.

Structural, electro-chemical and conduction mechanism in spinel NiFe2O4/NFO supercapacitor electrode material

In the present work we have synthesized spinel nickel ferrite (NiFe2O4/NFO) nanoparticles by hydrothermal route using urea as basic medium. The prepared material was structurally characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy and Transmission electron microscopy (TEM). The structural analysis result clears that formation of single-phase nano structure of NFO system with particle size ∼23 nm. The electrical properties were examined in terms of impedance, relaxation mechanism and activation energy. Simultaneously the conductivity spectrum was analyzed in terms of hopping mechanism. Due to the increase of frequency exponent (n) with respect to temperature, the results are discussed using non overlapping small polaron tunneling (NSPT) model. In addition, NFO nanoparticle exhibits noble electrochemical behavior through a specific capacitance value of 560 Fg-1 in 3 M solution. The estimated optical band gap energy from the UV–visible spectrum for direct transition (n = 2) is found to be 2.5eV. In brief the present work gives useful guidance for preparing the NFO sample for energy storage and multifunctional device applications.

Impedance spectroscopic study of charge transport and relaxation mechanism in the lead-free hybrid perovskite CH3NH3CuCl3

In the field of commercialization, organic–inorganic hybrid perovskite materials are becoming more popular these days in view of their prospective use in solar cells and also in other optoelectronic applications. In this paper, a non-toxic CH3NH3CuCl3 (MACuCl3) hybrid perovskite is successfully synthesized via the slow evaporation solution growth technique. The monoclinic phase of the material is checked using the X-ray diffraction measurement. The chemical composition of the prepared compound is discussed by a scanning transmission electron microscope coupled with the energy dispersive X-ray spectroscopy (STEM-EDS). Such systematic characterizations as differential scanning calorimetry (DSC) measurements and dielectric measurements indicate that MACuCl3 goes through a reversible phase transition at T1 ≈ 350/352 K MACuCl3 demonstrates a semiconducting property with a direct band gap value of approximately 2.54 eV. Over the 10−1-106 Hz frequency range, the dielectric constant, the loss factor, the electric modulus and also the electrical conductivity of MACuCl3 show strong temperature dependence. The Nyquist plot confirms the various contributions of grains and grain boundaries to the total impedance. In the high-frequency region, the dielectric constant tends to increase with temperature. The modified Cole–Cole plot asserts that while the relaxation time decreases with the rise in temperature, the space charge and free charge conductivity increase the moment the temperature climbs. In accordance with the modified Kohlrausch-Williams-Watts (KWW) equation, an asymmetrical nature corresponding to the non-Debye type of the perovskite is noticed in the electric modulus spectra at different temperatures. Moreover, the imaginary part of the electric modulus spectra is found to shift from the non-Debye toward the Debye type with the increase in temperature despite not getting the exact Debye response and emerging as a semi-conductor material. The study of the charge transfer mechanism of MACuCl3 is carried out based on Elliott's theory. The conduction mechanism in MACuCl3 is interpreted through the following two approaches: the overlapping large polaron tunneling (OLPT) model (phase 1) and the non-overlapping small polaron tunneling (NSPT) model (phase 2). Moreover, the high dielectric constant of MACuCl3 which is associated with a low dielectric loss makes it a possible candidate for energy harvesting devices.

Investigation of structural, morphological, and transport properties of a multifunctional Li-ferrite compound.

The development of multifunctional materials is an exceptional research area, which is aimed at enhancing the versatility of materials in various applications. In this context, the exceptional properties of ferrite materials have attracted the attention of researchers. For this reason, we synthesized LiMn0.5Fe2O4 sintered at a temperature of 1100 °C. The X-ray powder diffraction analysis reveals the presence of one cubic phase with the Fd3̄m space group and confirms the spinel structure formation. Moreover, the elemental analysis by EDX reveals the homogeneous distribution of iron and manganese cations. Scanning electron microscopy shows that the grain size is of the order of 2.48 μm. Impedance spectroscopy was performed in the temperature and frequency ranges from 200 K to 380 K and 40 Hz to 106 Hz, respectively. The Nyquist plots revealed the presence of grains and grain boundary contributions. The semiconductor nature, obtained by the conductivity study, indicates that LiMn0.5Fe2O4 is promising in optoelectronic applications. Dc conductivity is found to be thermally activated with an activation energy of 370 meV, 255 meV, and 199 meV for 200–270 K, 280–330 K, and 340–380 K regions, respectively. From the Jonscher power law, the correlated barrier hopping model (CBH) and non-overlapping small polaron tunneling (NSPT) prevailed in the conduction process. Besides, the temperature coefficient of resistivity (TCR) affirmed that LiMn0.5Fe2O4 is a good candidate for detecting infrared radiations and infrared bolometric applications.

Low-energy ball milling effect on the dielectric response and electrical transport mechanisms of natural clinoptilolite zeolites in a wide temperature range

Zeolites are spectacular natural minerals that can replace other expensive or hazardous materials in wide-range applications by virtue of their unique physico-chemical properties. In this study, a comprehensive investigation of the possible effects of low-energy mechanical ball milling on the dielectric response and electrical conduction mechanisms of natural clinoptilolite zeolites was carried out in 300–800 K temperature range through current-voltage (I-V) and capacitance-conductance (C-G) experimental measurements. Two samples were prepared; one with 1-hour hand grinding and another with 8-hours ball milling. Both samples exhibited a typical semiconductor behavior beyond 400 K and the conductivity obeyed Jonscher power law where transport mechanisms were governed by non-overlapping small polaron tunneling and correlated barrier hopping models at separate temperature ranges. It was mainly deduced that the presence of trapped water molecules within naturally grown zeolites contributes to the increase of both dielectric constant and conductivity. In addition, milling effect on the structural, morphological, mechanical and thermal properties was investigated respectively through X-ray diffraction (XRD), scanning electron microscopy (SEM), particle size analysis (PSA) as well as a combination of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). XRD confirmed the clinoptilolite phase and monoclinic crystal structure of the prepared samples and suggested a decrease in crystallite size with milling. SEM images manifested a corn flake-like structure of clinoptilolite grains and suggested a decrease in porosity, roughness and particle size under stirring effect. The decrease in overall particle size as a result of the milling process was also confirmed by PSA. Through TGA and DTA, the overall mass and water losses were estimated as a function of temperature, and this along with the morphological observation were correlated with the observed electrical and dielectric properties of the prepared samples. All in all, it was deduced that such naturally grown electroceramics have the potential to be used as natural dielectric capacitors as well as semi-insulator (SI) substrates in integrated circuits of electronic devices.

Influence of Electrochemically Exfoliated Graphite Addition on the Dielectric Properties of Epoxy/Montmorillonite Nanocomposites

The influence of hydrophilic electrochemically exfoliated graphite (EEG) and hydrophobic reduced EEG (rEEG) on the electrical conductivity, dielectric properties, and high-frequency dielectric losses of epoxy-based composites with montmorillonite was described. It was confirmed, that the addition of EEG changes the low-temperature conduction mechanism. The electrical conductivity in composite with EEG and montmorillonite was described by correlated barrier hopping model, whereas for composites with montmorillonite and rEEG two models were used: non-overlapping small polaron tunneling and correlated barrier hopping. The addition of EEG drastically changes the activation energy of charge carriers motions from 2.68 to 0.83 eV, whereas the addition of rEEG only to 2.43 eV. Also composite with EEG was characterized by highest high-frequency dielectric losses.