Dielectric Polarization Processes Research Articles

Effect of Hot Pressing on the Optical, Thermal, and Dielectric Properties of Solution Cast Prepared Nanocomposite Films Based on a Poly(Vinylidene Fluoride-co-Hexafluoropropylene) and Poly(Ethylene Oxide) Blend Matrix with Dispersed Zinc Oxide Nanoparticles

In our research described herein, the hot pressing treatment at 90 °C under 2 tons of pressure on solution cast polymer nanocomposite (PNC) films based on a host matrix of poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) and poly(ethylene oxide) (PEO) with varying polymer blend compositions (20, 50, and 80 wt% P(VDF-HFP) or PEO) and 2 wt% zinc oxide (ZnO) nanofiller, was performed; the effects of this treatment and the composition variations on the optical, thermal, and dielectric properties was explored. The ultraviolet-visible wavelength range study revealed slightly reduced absorbance and a little increased energy band gap after the hot pressing of the nanocomposite films. Differential scanning calorimetry of the solution cast-hot pressed (SC-HP) PNC films explained the reduced thermal stability of the poly(ethylene oxide) crystallites and also the degree of crystallinity. The broadband dielectric measurements of these materials, at 27 °C, confirmed significant changes in various dielectric polarization processes, demonstrating a large redistribution of constituent interfaces by the hot press treatment. Additionally, the 90 °C hot pressed PNC film of equal polymer compositional ratio was further hot pressed at 130 °C and 160 °C, step by step, and characterized to examine the variations in dielectric properties. The properties of these thermally treated composite films are discussed concerning their use for flexible device applications.

Electric Field Calculation During Voltage Transients in HVDC Cables: Contribution of Polarization Processes

The simulation of electric field transients in HVDC cables can be a fundamental tool to support insulation system design when operation dynamics, which includes voltage polarity inversions and load variation, becomes significant during the expected cable life. The field behavior during voltage and temperature transients is associated with intrinsic and extrinsic ageing processes that can affect the cable design life. Traditional models employed for electric field simulations consider only the non–linear, steady–state dependence of conductivity on temperature and field magnitude, but they neglect the transient behavior of permittivity and conductivity, that is, polarization and charge trapping phenomena. These processes impact on the duration of the field transient and thus ageing. This paper discusses the numerical implementation of an electro–quasistatic model that can be used to perform transient simulations of electric fields in HVDC cables insulation. With respect to the model traditionally employed, the presented one is extended with Debye's equations for dielectric polarization processes. The model is implemented numerically using finite differences, or the Occhini equivalent circuit: this paper demonstrates that the two approaches are equivalent. Numerical simulations show that, during transients, polarization processes slow down the electric field dynamics and reduce its maximum intensity.

High Magnetic Field Affecting Dielectric Polarization and Partial Discharge Behavior of Epoxy Resin

In this article, a joint measurement of dielectric polarization, depolarization, and potential recovery is carried out to investigate the instantaneous and relaxation polarization characteristics of epoxy resin in high magnetic field. The dielectric polarization of epoxy resin is converted to a combination of weakened instantaneous polarization and the relaxation polarization with reduced amplitude and increased speed. Changes in dielectric polarization processes leads to the decrease of relative permittivity. Furthermore, partial discharge (PD) of internal defects is harder to be initiated in high magnetic field. However, the discharge frequency is increased and the phase distribution becomes wider in the case of ac. In the case of dc, discharge lasts for longer time in high magnetic field. The experimental results are caused by the coupling effects of high-speed polarization and abnormal charge accumulation at the gas-solid interface due to the effects of Lorentz force on charges generated by PD.

A comprehensive investigation of dielectric properties of epoxy composites containing conducting fillers: Fluffy carbon black and various types of reduced graphene oxide

AbstractThe dielectric properties of epoxy nanocomposites with conducting nanofillers, such as graphene based and fluffy carbon black (FCB) were investigated in the frequency range of 40 to 30 MHz using an impedance analyzer to measure the dielectric permittivity, tan δ and AC conductivity. At very low filler loadings, epoxy nanocomposites showed remarkable dielectric characteristics. Dielectric constant of the composites decreased with increasing frequency and increased with filler loading. This is related to a decrease in interfacial polarization with increasing frequency and greater interfacial polarization with increase in filler loading. Dielectric loss peaks of epoxy nanocomposites with frequency suggested that both DC conductivity and dielectric polarization processes due to inhomogeneity within the nanocomposites contribute towards dielectric loss. Rising of AC conductivity of the composites with frequency was mainly due to hopping of charge carriers. An AC conductivity of 8.33 × 10−4 S/m and 2.455 × 10−5 S/m at 30 MHz was recorded for FCB/epoxy at 5 phr composite and neat epoxy. This composite also exhibited the maximum dielectric permittivity, 3.16 at 40 Hz and 0.82 at 30 MHz. The distinctive dielectric properties of epoxy‐based nano dielectric systems are due to the significant volume fraction of interfaces in the bulk of the material and the consequent interactions between charged nanoparticle surface and epoxy chains.

Nonlinear Conductivity and Space Charge Characteristics of SiC/Silicone Rubber Nanocomposites.

To achieve a preferable compatibility between liquid silicone rubber (LSR) and cable main insulation in a cable accessory, we developed SiC/LSR nanocomposites with a significantly higher conductivity nonlinearity than pure LSR, whilst representing a notable improvement in space charge characteristics. Space charge distributions in polarization/depolarization processes and surface potentials of SiC/LSR composites are analyzed to elucidate the percolation conductance and charge trapping mechanisms accounting for nonlinear conductivity and space charge suppression. It is verified that SiC/LSR composites with SiC content higher than 10 wt% represent an evident nonlinearity of electric conductivity as a function of the electric field strength. Space charge accumulations can be inhibited by filling SiC nanoparticles into LSR, as illustrated in both dielectric polarization and depolarization processes. Energy level and density of shallow traps increase significantly with SiC content, which accounts for expediting carrier hopping transport and surface charge decay. Finite-element multiphysics simulations demonstrate that nonlinear conductivity acquired by 20 wt% SiC/LSR nanocomposite could efficiently homogenize an electric field distributed in high-voltage direct current (HVDC) cable joints. Nonlinear conductivities and space charge characteristics of SiC/LSR composites discussed in this paper suggest a feasible modification strategy to improve insulation performances of direct current (DC) cable accessories.

Study of the Accelerated Degradation of the Insulation of Power Cables under the Action of the Acid Environment

Over operation time, there are a number of internal and external factors that change the characteristics of dielectric materials that are part of the electrical equipment. In areas with high pollution, an important requirement is the acidic chemical compounds in the soil in which the power cables are laid, which penetrate the insulation by infiltration, resulting in changes in the parameters of electrical insulation and causing a decrease in operating time. The paper is focused on the analysis, through a series of experimental determinations, of the effects of stresses to which the power cables laid in acidic environments are subjected, by simulating the operating conditions in the laboratory, obtaining concrete results. It also describes the direct current test installation used in the laboratory and presents the two stages of testing the cable sample inserted in the electrolyte, the first being a stage of accelerating the degradation of the insulation by supplying higher voltages to require insulation, and the second stage being the testing in the absence of the electric field, under the direct action of the chemical compounds from the installation tank. Given that in alternating current, the electric field causes an additional heating of the dielectric due to energy losses by electric polarization, the test is performed in direct current, precisely to be able to monitor the variation of insulation resistance in relation to temperature and losses through conduction currents, as a result of the Joule–Lenz effect and not as a result of the dielectric polarization process. At the same time, the power of the direct current source used is lower compared to that of an alternative current test source and does not contribute to the generation of electrical discharges during testing.

Dielectric properties, polarization process, and charge transport in granular (FeCoZr)x(Pb(ZrTi)O3)(100−x) nanocomposites near the percolation threshold

This paper presents the research of dielectric properties of (FeCoZr)x(Pb(ZrTi)O3)(100−x) granular metal–dielectric nanocomposites below the percolation threshold. Tested materials have been prepared by using the ion beam sputtering technique in the atmosphere of argon and oxygen. The impedance spectroscopy method has been used to investigate the polarization processes and dielectric relaxation mechanism in the granular nanocomposites. AC measurements in the frequency region of 50 Hz to 1 MHz and measuring temperature range of 81–293 K have been performed. Interfacial, in the low frequency region, and dipolar, in intermediate and high frequency regions, types of polarization processes were observed. The interfacial relaxation process testifies to charge accumulation at the interfaces (grain boundaries) between conductive nanoparticles surrounding an insulative matrix, as well as the space charge region around the contact area between the measurement probes and tested sample. Dipolar polarization corresponds to electric dipole formation after applying to the material an external electric field. The conduction mechanism in the tested material is considered to be hopping carrier exchange and takes place between metallic phase nanograins. It corresponds to the exponential frequency dependence of conductivity. The relaxation mechanism in the (FeCoZr)x(Pb(ZrTi)O3)(100−x) layer has been estimated as a near-Debye process with relaxation time distribution. The nanocomposite exhibits dielectric type and capacitive characteristics in the whole measuring frequency range.

A comparative study of different metal oxide nanoparticles dispersed PVDF/PEO blend matrix-based advanced multifunctional nanodielectrics for flexible electronic devices

Polymer nanocomposites (PNCs) are technologically smart multifunctional, flexible, and stretchable-type materials of high scientific and industrial interest. In this study, PNC films based on host polymer matrix of poly(vinylidene difluoride) (PVDF) blended with poly(ethylene oxide) (PEO) (compositional ratio PVDF/PEO = 75/25 wt/wt%) and 5 wt% different metal oxide nanoparticles (i.e., Al2O3, SnO2, TiO2, and ZnO) as nanoinclusions have been developed by casting from solution. These films were characterized with advanced techniques namely; SEM, EDX, XRD, FTIR, DRS, and UV–vis spectroscopy for confirmation of their technological applications. The results evidence that these metal oxide nanoparticles produce significant alterations in the polymers spherulitic morphology, creates a large number of micro- to nano-sized pores, lowers the β-phase content of the PVDF and crystalline phase of PEO, and also the degree of crystallinity of the host matrix. Among these metal oxides, the Al2O3 nanoparticles considerably enhance the dielectric permittivity while other nanofillers anomalously alter the dielectric polarization processes and MWS relaxation of the PNC films in the frequency range 20 Hz – 1 MHz at ambient temperature. AC electrical conduction is found relatively high for the Al2O3 and low for ZnO nanoparticles containing PNC films. The optical energy bandgap of these PNC films are sturdily ruled by the characteristic optical properties of the nanofillers. The physical, morphological, structural, dielectric, and optical parameters of these metal oxide nanofillers are considered for the demonstration of relative changes in the investigated properties of the PNC materials. Experimental results evidence multifunctionality of these PNC materials to be used as controllable nanodielectrics for the development of flexible-type macro- and microelectronic devices in the advances of porous membrane technology, UV-shielders, and the optical bandgap tuners.

Dielectric polarization and relaxation processes of the lithium-ion conducting PEO/PVDF blend matrix-based electrolytes: effect of TiO2 nanofiller

The effect of TiO2 nanofiller concentration on the dielectric polarization and relaxation processes of (75PEO/25PVDF)/25 wt% LiClO4–x wt% TiO2 (x = 0, 2, 5, 10, 15, and 20) compositions based nanocomposite solid polymer electrolyte (NSPE) films has been investigated by employing the dielectric relaxation spectroscopy. The SEM micrographs demonstrate that the dispersion of TiO2 nanoparticles enormously alters the spherulitic morphology with the development of some cracks, pores, and wrinkles of these solution-cast prepared NSPE films. The X-ray diffraction study confirms that the heterostructures of these NSPE materials are semicrystalline and their degree of crystallinity increases irregularly with the increase of TiO2 concentration, however the crystallinity of host polymer blend matrix of these electrolytes decreases. The complex dielectric permittivity spectra of these NSPE materials in the frequency range from 20 Hz to 1 MHz at 27 °C reveal that there is a dominant contribution of electrode polarization and interfacial polarization at lower frequencies, whereas the high frequency permittivity values attribute to dipolar and ionic polarizations. Four types of relaxation processes have been probed by the ‘master curve representation’ of the dielectric and electrical spectra of these solid ion–dipole complexes. It is observed that the addition of TiO2 nanoparticles up to 10 wt% in these electrolytes influences the dielectric properties anomalously, but a huge decrease in the dielectric polarization and increase in the relaxation times are noted resulting in a significant decrease in the ionic conductivity of the film at 20 wt% TiO2 concentration. The dependence of dc ionic conductivity of these lithium-ion conducting NSPE materials on the chain segmental relaxation time and also the degree of crystallinity has been explored. The results of these NSPE materials have also been compared with the TiO2 nanoparticles loaded different polymer matrices and salts based electrolytes and discussed appropriately. These lithium-ion based electrolyte films are accredited for the solid-state ion-conducting energy storing devices from their electrochemical parameters characterized by LSV, CV, and CA techniques.

Predominantly chain segmental relaxation dependent ionic conductivity of multiphase semicrystalline PVDF/PEO/LiClO4 solid polymer electrolytes

The solid polymer electrolyte (SPE) films comprise poly(vinylidene fluoride) (PVDF)/poly(ethylene oxide) (PEO) blend (75/25 wt/wt%) as host polymer matrix with lithium perchlorate (LiClO4) as ionic dopant for different salt concentrations (i.e., 5, 10, 15, 20, 25, and 30 wt%), and also varying compositional weight ratio PVDF/PEO blends (i.e., 75/25, 50/50, 25/75, and 10/90 wt/wt%) with 25 wt% concentration of LiClO4 were prepared by solution casting at 70 °C. The results obtained from X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy revealed that there is enormous alteration in the α- and β-phase crystals of the PVDF and the size and content of the PEO crystallites, and also the degree of crystallinity of these SPE materials with the variation of salt concentration and the polymer blend composition. Dielectric relaxation spectroscopy (DRS) was employed over the frequency range from 20 Hz to 1 MHz, at 27 °C for the study of the complex impedance, dielectric permittivity, dielectric loss tangent, ac electrical conductivity, and electric modulus spectra of the SPE films. All these spectra were analyzed separately and simultaneously by a novel ‘master curve representation’ procedure to unveil the contribution of various dielectric polarization processes (i.e., electrode, interfacial, molecular (dipolar), and the ionic) and their relaxations which are exhibited with increasing order of frequency and have substantial overlapping with the adjacent processes in these heterogeneous ion conducting materials. The loss tangent spectra of these materials manifest prominent dielectric relaxation peaks which attribute to the cation coordinated polymer chain segmental dynamics. The high frequencies ac electrical conductivity data of all these materials obey the power law, whereas the Nyquist plots of impedance data exhibit reasonably distinguishable bulk and electrode polarization frequency regions for the electrolytes having salt concentration ≥20 wt%. The inverse correlation observed between the relaxation time and the dc ionic conductivity establishes that the transportation of ions is predominantly coupled to the polymer chain segmental motion which assists the hopping between favourable conduction sites in the ion-dipole complexes. The SPE films are comparatively stiffer and have a slightly higher degree of crystallinity when the salt concentration is ≤ 15 wt% and they exhibit distinct dielectric, dc ionic conductivity, and relaxation behaviour as compared to that of the softer and lower crystallinity films having salt concentration ≥20 wt%. These SPE films possess good electrochemical performance and close-to-unity total ion transference numbers. Among these two sets of the SPE films, the maximum dc ionic conductivity was noted 2.01 × 10−5 S/cm at 27 °C for the 75PVDF/25PEO–30 wt% LiClO4 film from the set of different salt concentrations, and 5.61 × 10−6 S/cm for 25PVDF/75PEO–25 wt% LiClO4 film from the set of varying compositions of the polymer blend matrix. The considerable ionic conductivity values of these SPE films at ambient temperature and also their promising electrochemical performance corroborate them as novel ion conductors suitable for the development of solid-state rechargeable lithium-ion batteries.

Features of the production and study of electrophysical characteristics (BeO + TiO2)-ceramics by impedance spectroscopy

The resulting electrically conductive two-component BeO ceramics with the addition of micro and nanocrystalline TiO 2 powder, which can be used as a material absorber of scattered microwave radiation in high-power electronic devices. The nature of the appearance of electrical conductivity and absorption of the microwave field in (BeO + TiO 2 )-ceramics has not been completely established. The impedance spectroscopy method was the first to investigate the electrical and dielectric characteristics of this ceramics in the frequency range from 100 Hz to 100 MHz, depending on the presence of a micro- and nanosized TiO 2 phase in the composition of BeO ceramics. It has been established that the static resistance of ceramics with the addition of a TiO 2 nanopowder is significantly reduced compared with the resistance of the original ceramics with TiO 2 micropowder. It is shown that the real and imaginary components of the dielectric constant of the studied ceramics increase to abnormally large values as the frequency of the effective electric field decreases, and in the high frequency range f ≥ 10 8 Hz, the process of dielectric relaxation begins, leading to an increase in the dielectric loss angle. The dielectric characteristics of ceramic samples are determined under blocking conditions for through conduction. The effect of TiO 2 micropowder additives on dielectric polarization processes with increasing frequency up to 12·10 9 Hz is considered. Ill. 8. Ref. 26.

Features of the Preparation and Study of Electrophysical Characteristics (BeO+TiO2)-Ceramics by Impedance Spectroscopy

An electrically conducting two-component BeO-ceramic with the addition of micro- and nano-crystalline TiO2 powder is prepared that can be used as a material for scattered microwave radiation absorption in high-power electronic devices. The nature of the occurrence of electrical conductivity and absorption of the microwave field in (BeO + TiO2)-ceramics is not completely established. Impedance spectroscopy is used for the first time to investigate the electrical and dielectric characteristics of this ceramic in the frequency range from 100 Hz to 100 MHz in relation to presence of micro- and nano-sized TiO2 phase within the BeO ceramic composition. It is established that the static resistance of ceramics with addition of a TiO2 nanopowder is significantly reduced compared with the resistance of original ceramic with TiO2 micropowder. It is shown that real and imaginary components of the dielectric constant of the ceramic studied increase to abnormally large values with a reduction in frequency of the effective electric field, and in the high frequency range f ≥ 108 Hz the process of dielectric relaxation commences leading to an increase in dielectric loss angle. Dielectric properties of ceramic samples are determined under blocking conditions for through conduction. The effect of TiO2 micropowder additions on dielectric polarization processes with frequency increasing up to 12 × 109 Hz is considered.

English

The present work is focused on investigating the effect of rare earth ion on structural, magnetic and transport properties of (Cu0.5Zn0.5Fe2-x)SmxO4[x = 0.00, 0.05 and 0.10] ferrites which were prepared by solid state reaction technique at 1100°C for 3 h. The X-ray diffraction analysis revealed that rare earth free sample shows formulation of single phase cubic spinel structure with no extra peak whereas Sm substituted Cu-Zn ferrite samples show additional peaks that correspond to a secondary orthoferrite phase. Lattice parameter, bulk density, X-ray density and porosity of the studied samples are increased with Sm substituted ions. Lattice parameter of both series are slightly decrease with increase Sm content. The initial permeability decreases with increasing Sm ions in ferrite. Quality factor signifies the merit of the material from the application point of view. The dielectric constant was found to decrease continuously with increasing frequency and remain almost constant at higher frequency range. The dielectric behavior of the experimental ferrite samples can be explained on the basis of the mechanism of the dielectric polarization and conduction process. The saturation magnetization decreases with increasing rare earth Sm contents. Key words: Solid state reaction technique, sintering temperature, quality factor, dielectric polarization.

Investigation of alumina nanofiller impact on the structural and dielectric properties of PEO/PMMA blend matrix-based polymer nanocomposites

Polymer nanocomposite (PNC) films have been prepared by the solution-cast method using a polymer blend of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) (PEO/PMMA = 50/50 wt%) as organic host matrix and x wt% Al2O3 nanoparticles (x = 0, 1, 3, and 5) as inorganic nanofiller. The morphological and structural behavior of these PNC films has been examined by employing the scanning electron microscope (SEM), X-ray diffractometer (XRD), and Fourier transform infrared (FTIR) spectrometer, whereas their dielectric polarization and relaxation processes are characterized by carrying out the dielectric relaxation spectroscopy (DRS) over the frequency range 2 × 101 to 1 × 106 Hz. Impact of Al2O3 nanofiller on the spherulite and porous morphology, degree of crystallinity, polymer-polymer and polymer-nanoparticle interactions, complex dielectric permittivity, ac electrical conductivity, and the polymers structural dynamics has been explored. It is revealed that initially 1 wt% dispersion of Al2O3 in the PEO/PMMA blend matrix significantly reduces the crystallinity and dielectric permittivity, and hinders the cooperative chain segmental dynamics of the polymers which unevenly changes with the further increase of Al2O3 concentration up to 5 wt%. The dielectric and electrical parameters of these materials have also been compared with the PNC materials based on other polar polymer host matrices containing different oxide inorganic nanoparticles. The results of this work provide a guideline to design and fabricate the alumina nanoparticles loaded flexible-type polymer nanodielectric materials for advanced technologies.

Poly(vinylidene fluoride)-Based composites modulated via multiscale two-dimensional fillers for high dielectric performances

Ultrathin two-dimensional (2D) semiconductor molybdenum disulfide (MoS2) nanosheets have wide applications in electronic devices. Incorporation of MoS2 nanosheets into poly(vinylidene fluoride) (PVDF) renders a type of dielectric composite regulated with 2D architecture. However, due to the semiconducting behavior of MoS2, the accompanying high dielectric loss prevents the composite being good dielectrics. Aluminum flakes (AFs), another 2D structure in micron scale, were thus introduced into the MoS2/PVDF composite to block leakage path as well as providing another source for electric polarization. The effects of multiscale 2D fillers on adjusting the dielectric and electrical properties of the ternary MoS2/AFs/PVDF composites were investigated systematically. The largely suppressed dielectric loss and electrical conductivity of ternary composite compared with those of MoS2/PVDF composite is ascribed to the parallel arranged self-passivated AFs, which effectively inhibit the direct connection and overlapping of MoS2 nanosheets along the electric field direction. Meanwhile, formation of numerous micro-capacitors with AFs as electrodes and MoS2/PVDF composite as dielectric medium makes an additional contribution to the high dielectric constant of the ternary composite. Furthermore, the dielectric polarization and relaxation process of composites were investigated in terms of electric modulus to explain the variation tendency of dielectric and electric property of the composites.

Performances and impedance spectroscopy of Small-molecule bulk heterojunction solar cells based on PtOEP: PCBM

Small-molecule bulk heterojunction (SBHJ) solar cells based on platinum octaethylporphyrin (PtOEP) as donor material and phenyl-C61-butyric acid methyl ester (PCBM) as the acceptor were fabricated using spin coating techniques with weight ratios from 1:0.1 to 1:9. The formation of charge transfer complex CTC in the PtOEP: PCBM blend was specified from the redshift of the PtOEP absorption peak after blending with PCBM. The photovoltaic performance for PtOEP: PCBM blends were investigated using the external quantum efficiency (EQE) besides the current density–voltage (J–V) characteristics under illumination100 mW/cm2 (AM1.5G). The BHJ solar cell with PtOEP: PCBM ratio of 1:9 exhibited the best performance. The impedance spectroscopy (IS) was examined in the frequency range from 25 Hz to 1 MHz. The equivalent circuit model was evaluated in details to evaluate the impedance spectroscopy parameters. Dielectric constant \({\varepsilon ^\prime }\), dielectric loss \({\varepsilon ^{\prime \prime }}\) and dielectric modulus were included and discussed in terms of dielectric polarization processes. Dielectric modulus displays the non-Debye relaxation in PtOEP: PCBM BHJ solar cells.

Frequency dispersion analysis of thin dielectric MOS capacitor in a five-element model

An Al/ZrO2/IL/n-Si (IL: interface layer) MOS capacitor has been fabricated by metal organic decomposition of ZrO2 and thermal deposition Al. We have measured parallel capacitance (Cm) and parallel resistance (Rm) versus bias voltage curves (Cm, Rm–V) at different AC signal frequency (f), and Cm, Rm–f curves at different bias voltage. The curves of Cm, Rm–f measurements show obvious frequency dispersion in the range of 100 kHz–2 MHz. The energy band profile shows that a large voltage is applied on the ZrO2 layer and IL at accumulation, which suggests possible dielectric polarization processes by some traps in ZrO2 and IL. Cm, Rm–f data are used for frequency dispersion analysis. To exclude external frequency dispersion, we have extracted the parameters of C (real MOS capacitance), Rp (parallel resistance), CIL (IL capacitance), RIL (IL resistance) and Rs (Si resistance) in a five-element model by using a three-frequency method. We have analyzed intrinsic frequency dispersion of C, Rp, CIL, RIL and Rs by studying the dielectric characteristics and Si surface layer characteristics. At accumulation, the dispersion of C and Rp is attributed to dielectric polarization such as dipolar orientation and oxide traps. The serious dispersion of CIL and RIL are relative to other dielectric polarization, such as border traps and fixed oxide traps. The dispersion of Rs is mainly attributed to contact capacitance (Cc) and contact resistance (Rc). At depletion and inversion, the frequency dispersion of C, Rp, CIL, RIL, and Rs are mainly attributed to the depletion layer capacitance (CD). The interface trap capacitance (Cit) and interface trap resistance (Rit) are not dominant for the dispersion of C, Rp, CIL, RIL, and Rs.

Linear Irreversible Phenomenological Thermodynamics of Polarization Processes in Rigid Unmagnetic Insulators

AbstractWe show how classical irreversible thermodynamics is used to derive relaxation equations for dielectric polarization processes in insulators. We calculate susceptibilities for multiple polarization processes and show how coupling arises thermodynamically. Furthermore, we derive evolution equations for electromagnetic fields by combining the dielectric relaxation equations with Maxwell’s equations. Analytical solutions for various frequency regimes will be briefly discussed. A complete analogy exists between the dielectric problem, the Kelvin–Voigt viscoelasticity of solid media, and the non-equilibrium (reactive, vibrational) gasdynamic flow. Also, numerical solutions, using the method of characteristics, are given for a generic signal problem in half-space.

Alternating current characterization of nano-Pt(II) octaethylporphyrin (PtOEP) thin film as a new organic semiconductor

Alternating current (AC) conductivity and dielectric properties of thermally evaporated Au/PtOEP/Au thin films are investigated each as a function of temperature (303 K–473 K) and frequency (50 Hz–5 MHz). The frequency dependence of AC conductivity follows the Jonscher universal dynamic law. The AC-activation energies are determined at different frequencies. It is found that the correlated barrier hopping (CBH) model is the dominant conduction mechanism. The variation of the frequency exponent s with temperature is analyzed in terms of the CBH model. Coulombic barrier height Wm, hopping distance Rω, and the density of localized states N(EF) are valued at different frequencies. Dielectric constant ε1(ω,T) and dielectric loss ε2(ω,T) are discussed in terms of the dielectric polarization process. The dielectric modulus shows the non-Debye relaxation in the material. The extracted relaxation time by using the imaginary part of modulus (M″) is found to follow the Arrhenius law.

Theoretical Study of Cellular Piezoelectret Generators

The cellular piezoelectret generator (CPG) has drawn considerable attention as an emerging flexible energy harvester because of its advantages of a simple structure, easy assembly, a low cost, and eco‐friendliness. To facilitate practical applications, an initial theoretical study of CPGs is presented in this work, in which the output characteristics of CPGs can be optimized through an appropriate choice of parameters, including the electret dielectric permittivity, device structure, polarization process, and external load. A good agreement with experimental results is achieved, verifying the validity of the theoretical study. The reported theory offers a complete interpretation of the dynamic working mechanism of CPGs and provides significant guidance for the design of a CPG with enhanced yield.