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Atomic doping is widely employed to fine-tune crystal structures, energy band structures, and the corresponding electrical properties. However, due to the difficulty in precisely regulating doping sites and concentrations, establishing a relationship between electricity properties and doping becomes a huge challenge. In this work, a modulation strategy on A-site cation dopant into spinel-phase metal sulfide Co 9 S 8 lattice via Fe and Ni elements is developed to improve the microwave absorption (MA) properties. At the atomic scale, accurately controlling doped sites can introduce local lattice distortions and strain concentration. Tunned electron energy redistribution of the doped Co 9 S 8 strengthens electron interactions, ultimately enhancing the high-frequency dielectric polarization (ɛ' from 10.5 to 12.5 at 12 GHz). For the Fe-doped Co 9 S 8 , the effective absorption bandwidth (EAB) at 1.7 mm increases by 5%, and the minimum reflection loss (RL min ) improves by 26% (EAB = 5.8 GHz, RL min = -46 dB). The methodology of atomic-scale fixed-point doping presents a promising avenue for customizing the dielectric properties of nanomaterials, imparting invaluable insights for the design of cutting-edge high-performance microwave absorption materials., (© 2024 Wiley‐VCH GmbH.)

This work illustrates broadband dielectric response, design, fabrication and testing of a microstrip patch antenna based on flexible silicone rubber–BaBiLiTeO6 composites. The composites were fabricated by hot pressing silicone rubber and low-loss BaBiLiTeO6 ceramics. Phase purity, thermal stability and morphology of the composites were studied using X-ray diffraction, thermogravimetric analysis and scanning electron microscopy (SEM). The dielectric response of the composites were investigated from 1 MHz to 26 GHz to test their applicability in 5G communication systems. The relative permittivity and dielectric loss of the composite vary between 6–8 and 0.02–0.05, respectively, for 0.25 Vf of the ceramics from 1 MHz to 26 GHz. The observed relative permittivity is compared with various theoretical models, and the Jayasundere-Smith relation provides a better match for ε r . A stable dielectric response is observed even after several bending cycles of the composite. As the volume fraction of BaBiLiTeO6 ceramics increases from 0 to 0.25, thermal conductivity and diffusivity of the composites increases, whereas the coefficient of thermal expansion and specific heat capacity decreases. A microstrip patch antenna that can radiate at 2.48 GHz with a return loss of −13.2 dB was designed and optimized using high-frequency structure simulator (HFSS) software. The physical and chemical properties of silicone rubber–BaBiLiTeO6 composites indicate that this material is a candidate for flexible components in microwave communication devices. [ABSTRACT FROM AUTHOR]

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Dielectric materials with thermally responsive property are being pursued in fields such as next‐generation sensors, smart switches, and novel actuators. These applications require that the dielectric materials have mechanical durability and stable serviceability besides thermally responsive dielectric behavior. Herein, we report a novel thermally responsive, mechanically durable, and low‐cost dielectric composite simply fabricated by vacuum impregnating polyethylene glycol (PEG) into kapok fiber and compounding them with polyvinylidene fluoride. A remarkable dielectric susceptibility, controlled dielectric transition temperature, and obvious thermal hysteresis of the composite films induced by the solid–liquid phase transition of PEG are demonstrated. The effect of molecular weights of PEG on the dielectric response behaviors is evaluated. Such thermally responsive dielectric materials with satisfactory mechanical durability will offer a chance toward constructing thermally responsive systems for reliable and stable operation. [ABSTRACT FROM AUTHOR]

In this study, we used Monte Carlo simulations to explore the dielectric properties of a graphene-type nanolattice, revealing significant effects on blocking temperature. The ferroelectric interaction and external electric field parameters greatly influence the nanolattice's dielectric and thermal properties. We observed a polarization plateau and multiple hysteresis loops, indicating stability and various polarization states. Unexpected ferroelectric behavior in graphene-based systems was confirmed experimentally in moiré heterostructures, validating theoretical predictions. This aligns with models like the Ising model and enhances material stability and response, offering insights for precise control over dielectric properties in nanotechnology. [ABSTRACT FROM AUTHOR]

The influence of thermal and thermobaric (TBT) effects on the structure, microstructure, and dielectric properties of ceramics based on solid solutions of the La1.8Ca0.2Ni0.8M0.2O4+δ (M = Co, Cu) composition was studied. TBT treatment of the samples leads to a change in the grain morphology of ceramics and an increase in the dielectric constant compared to its value only after heat treatment. The change in the anisotropy of the coordination (La,Ca)O9 and (Ni,M)O6 polyhedra after TBT contributed to interlayer polarization in the crystal structure of La1.8Ca0.2Ni0.8M0.2O4+δ.

Here, we report the composite effect of aluminum doping on the dielectric response of Diamond-Like Carbon (DLC) thin films. In addition, the contribution from preparation parameters like acetylene flow rate is also considered to understand sample behavior. AC conductivity study shows the existence of a nonlinear increase of conductivity with frequency leading toward the Jump Relaxation Model (JRM). The transition frequency (f t) is observed, which increases with conductivity. The study reveals that dielectric response is influenced by space charge conductivity, prompting us to adopt the modified Debye law. Deviation from ideal Debye behavior is also confirmed in dielectric modulus analysis. The deviation is frequency-dependent, and a higher deviation is observed in the high-frequency region. Plotting of the Master curve shows the presence of different relaxation dynamics in different samples. A current-voltage (I-V) study of different samples is also undertaken, showing higher values (greater than unity) of the ideality factor. [Display omitted] • AC conductivity increases with acetylene flow as well as with higher Al doping. • A very high value of dielectric permittivity is observed in present samples. • A single dielectric relaxation peak exists for samples with lower Al content. • The highest Al concentration shows double relaxation peaks. • The ideality factor is found to be greater than unity for all the samples. [ABSTRACT FROM AUTHOR]

• CeMn 1-x A x O 3 (A = Co, Ni and x = 0, 0.05, 0.10, 0.15) perovskite nanomaterials were synthesized using a modified polyacrylamide gel method. • The XPS analysis discloses that Mn has mixed oxidation states of Mn4+, Mn3+ and Mn2+, while Ni have oxidation states of Ni3+ and Ni2+, and Co has a Co3+ oxidation state. • The Co and Ni doped CeMnO 3 nanomaterial produced enhanced dielectric characteristics. • The Cole–Cole plot of doped CMO nanomaterial shows two semi-circle arcs, indicating the concurrent influence of both grains and grain boundaries. Nanostructured perovskite materials doped with transition metal ions have attracted significant attention due to their unique electronic and dielectric properties. In this study, we present the synthesis and thorough characterization of cobalt (Co) and nickel (Ni) ion-doped CeMnO 3 (CMO) perovskite nanoparticles using a modified polyacrylamide gel method. Our structural analysis suggests that the perovskite phase stabilizes with an orthorhombic phase (Pbnm space group). Morphological analysis conducted via field emission scanning electron microscopy (FESEM) unveils the formation of clustered nanospherical particles. X-ray photoelectron spectroscopy (XPS) reveals mixed oxidation states of Ce, Mn, and Ni ions. Furthermore, UV–Vis and photoluminescence spectra analyses demonstrate a distinctive reduction in band gap and suppressed charge carrier recombination upon doping. The substitution of Ni and Co ions also enhances the screening effect, reducing Coulombic interaction between photoexcited electrons and holes and subsequently increasing the dielectric constant. Analysis of the Cole-Cole plot demonstrates the augmentation of capacitance with Ni substitution. These findings collectively suggest that the decreased dielectric loss and enhanced dielectric constant support the feasibility of these materials for application in storage devices. [ABSTRACT FROM AUTHOR]

This paper proposes a rational approximation-based approach to find positive real parameters for the extended Debye model (EDM), aimed at condition assessment of insulation systems of power transformers. The EDM can model the slow and fast polarization phenomenon, including relaxation mechanisms with different relaxation times within a composite dielectric material. In the proposed approach, the complex permittivity of the transformer's composite insulation is approximated via rational functions, as given by the vector fitting (VF) software tool, and the EDM parameters are identified from the obtained poles/residues. To guarantee positive real parameters, i.e., a physically realizable circuit, VF is internally modified to calculate the final residues of the rational approximation via a constrained linear least-squares problem without resorting to further post-processing algorithms, as in existing methods, hence without affecting fitting accuracy. The effectiveness of the parametrized EDM is demonstrated in two ways: (a) by reconstructing frequency domain spectroscopy (FDS) curves provided via measurements in new oil-immersed power transformers and (b) by the comparison of the calculated polarization current given by EDM versus real measurements in time domain. The achieved fitting accuracy in most of the cases is above 99 percent for the reconstructed FDS curves, while the polarization current waveform is reproduced with good agreement. [ABSTRACT FROM AUTHOR]

Lead-free La0.02Ba0.97TiO3 (2LBT) ceramic was elaborated via the molten-salt method characterized by XRD and Raman spectroscopy. Further their electric, dielectric, and ferroelectric properties were investigated. XRD results demonstrate that the sample possessed a pure-tetragonal structure with a space group of P4/mmm. The notable effect of incorporating the La3+ cation into an A-site sublattice was clarified using Raman spectroscopy. Significant improvements have been demonstrated in dielectric properties. The observed relaxation is attributed to Maxwell–Wagner polarization. 2LBT sample demonstrated a 3 phase transition with negligible frequency dispersion indicating diffuse phase transition at the specific temperature range (292–700 K). Upper than 700 K, 2LBT sample provided a pointy transition. The electrical properties obtained from the complex electric modulus reveal a conduction process owing to the short-range mobility of charge carrier. Both ac and dc electrical conductivities are considered vs. frequency and temperature. [ABSTRACT FROM AUTHOR]

Dielectric response measurement is widely used to characterize oil/oil-impregnated pressboards in order to evaluate the condition of transformer insulation. Insulation systems with oil can exhibit voltage dependence at low frequencies. This is due to the limited number of mobile charges in the liquid, rather than to the dielectric relaxation processes that may, in some cases, be of more interest to study. This work investigates the voltage-dependent properties of oil/oil-impregnated pressboards under ac voltages with regard to the complex permittivities. Frequency-domain spectroscopy (FDS) measurements are made with a dc voltage added to the ac voltage stimulus. Considered influences are the voltage amplitudes and polarity as well as the dependence on temperature. Properties of the space-charge polarization in the oil and oil-impregnated pressboard are calculated and discussed based on the dc-biased measurements. It is seen that using the dc bias in the FDS measurements of oil/oil-impregnated pressboard can significantly decrease the voltage dependence of the results that are caused by ion drift and consequent depletion of ions from the bulk liquid. Based on the dc-biased measurements, the complex permittivity due to the linear and nonlinear polarization can be separated. [ABSTRACT FROM AUTHOR]

In this work, we studied the nature of repolarization processes in KNN-0.05Ta ceramics in the temperature range of structural phase transition. We have found the anomalous behavior of reverse dependences ε'(Ε=), while measuring the response in weak ac-fields in the sample exposed to the constant bias field. Behavior of ε'(Ε=) was compared with the polarization loops measured in sinusoidal fields of various amplitudes. [ABSTRACT FROM AUTHOR]

In this work, novel double perovskites RBaFeTiO 6 (R = Pr, Nd) have been prepared through the sol-gel process. The structural, morphological, spectral, and dielectric behaviors were investigated by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, dielectric measurements, and impedance spectroscopy. The objective of this work is to study these properties and investigate the effect of rare earth cations. XRD analysis confirmed the disordered cubic double perovskite structure of all prepared samples. The lattice parameters, bond lengths, and bond angles determined from the Rietveld refinement analysis are found to be dependent on the R3+ cation size. SEM and TEM micrographs indicated an irregular size distribution of the grains forming these double perovskites. The elemental composition and the stoichiometry of the prepared samples were verified by energy-dispersive X-ray spectrometer (EDX) elemental mapping. Raman and infrared spectroscopies have affirmed the influence of the rare earth element on vibrational properties and bond lengths. The dielectric properties were studied as a function of frequency. Electrical conduction follows Jonscher's universal power law and the conduction is attributed to the localized relaxation (reorientational) hopping mechanism. The presence of both negative (NTCR) and positive (PTCR) temperature coefficients of resistance in these materials is also affirmed by impedance spectroscopy. [ABSTRACT FROM AUTHOR]

The interest in developing and testing dielectric nanofluids for electrotechnical purposes has increased significantly in the last ten years. A number of works have been published reporting dielectric and thermal properties for these liquids that enhance those of conventional insulating fluids. Some authors propose that the application of dielectric nanofluids to transformer insulation could improve the reliability of transformers and open new possibilities for transformer design. However, this will not be feasible until thorough studies on the interaction of these materials with other elements of the transformer, specially the solid insulation, are carried out. In this work, the effect of the presence of nanoparticles on the dielectric response of oil and oil-paper insulation is analysed in laboratory conditions. Specimens have been prepared to emulate the insulation system of transformers and the dielectric response in the frequency domain of these specimens has been characterized. The dependence of nanoparticle concentration on the dielectric response has been analysed. Proposing physical mechanisms that explain the experimental results observed over the oil and the paper samples. Some conclusions are extracted in this work that may be of interest if nanofluids are considered as liquid insulation for transformers.

The mechanisms of increasing the dielectric response of the BaTiO3/BaZrO3 ferroelectric superlattices in comparison with the characteristics of the bulk materials of the lattice are discussed. It is assumed that changes in the dielectric response in superlattices are caused by mechanical stresses arising in layers of the superlattice due to the mismatch of the sizes of the unit cells that make up the lattice of single-crystal layers. These stresses lead to the formation of longitudinal polarization in the layers of barium titanate and to the related contribution of the transverse component of the dielectric tensor to the effective permeability of the superlattice in the direction normal to the plane of the layers. The misfit stresses cause the appearance of a ferroelectric phase transition in the barium zirconate the lattice layers with an increase in the dielectric constant of these layers in the direction normal to the plane of the lattice layers. Highlights: Mismatch stresses in ferroelectric superlattices

Employing a modified sol-gel combustion technique, BiFeO 3 and Bi 0.85 Ba 0.15 Fe 1-x Al x O 3 (x = 0, 0.025 and 0.050) nanoparticles were synthesized, and the effects of these dopants were investigated analyzing the experimental findings and adopting the DFT + U approach. Rietveld analysis of XRD revealed a deformed perovskite rhombohedral structure for all the Ba–Al co-doped nanoparticles, which was also validated by theoretical study. Suppression of the low-frequency dispersion promoting outstanding dielectric stability was observed due to Al3+ doping, and the least dielectric constant along with the highest resistivity was reported for BBFAO-2.5. The band gap of co-doped nanoparticles (x = 2.5 & 5) decreased to 1.95 eV and 1.98 eV, respectively, compared to 2.06 eV, and 2.09 eV for BBFAO-0 and pure BFO. The average particle size of all the co-doped nanoparticles was below the repeat length of the cycloid structure, which is favorable for improved magnetic properties. Remanent magnetization, coercivity, and squareness increased as the motion of domain walls is inhibited by the smaller-sized nanoparticles. DFT + U study further endorses the findings of the experimental study. Analysis of DOS revealed the emergence of shallow impurity states around VBM due to doping, which can operate as active trap centers and impede carrier recombination. Thus, it can be inferred that, Ba–Al co-doped nanoceramics with intriguing dielectric, optical, and magnetic properties are a promising candidate for high-frequency microwave devices, magnetic memory and storage devices, near UV-detector, and solar photocatalysis applications. [ABSTRACT FROM AUTHOR]

The frequency-dependent dielectric responses of non-uniformly dispersed porous carbon fiber/mullite composites fabricated by gel-casting are intensively investigated in the X-band range. Experimental data have shown the frequency dependence of dielectric permittivity and electrical conductivity of the overall composite. The dielectric responses of non-uniformly dispersed porous carbon fiber/mullite composites in X-band are quantitatively modeled through a multi-scale homogenization method based on the effective-medium approximation. The non-uniform dispersion of carbon fibers and micro-pores in the mullite ceramic has been included via a corresponding multi-scale geometric setting. The effective dielectric permittivity and electrical conductivity of the composite both enhance with the fiber volume concentration. It is demonstrated that the decreasing dielectric permittivity and increasing electrical conductivity with respect to the AC frequency can be attributed to frequency-dependent dielectric relaxation and electron hopping effects at the interface. Furthermore, improving the uniform dispersion of carbon fibers in the mullite is essential to achieve the enhanced dielectric response of porous carbon fiber/mullite composites. The present paper can provide the directions to design the porous carbon fiber/mullite composites for micro-electronic devices in the high-temperature environment. [ABSTRACT FROM AUTHOR]

The dielectric response of magnetic alkali borosilicate glasses containing single-domain magnetite nanoparticles was studied upon heating and cooling in magnetic fields from 0 to 10 Т in the temperature range from 5 to 100 K in the frequency range from 1 Hz to 160 kHz. An anomaly of the dielectric response was observed for the single-domain nanoparticles of magnetite in the temperature range of 15–50 K, position of which corresponds to the transition into the relaxor state observed in bulk material. A temperature hysteresis of this anomaly was found upon heating and cooling, which decreased as the observation frequency decreased. [ABSTRACT FROM AUTHOR]

The mechanisms of increasing the dielectric response of the BaTiO3/BaZrO3 ferroelectric superlattices in comparison with the characteristics of the bulk materials of the lattice are discussed. It is assumed that changes in the dielectric response in superlattices are caused by mechanical stresses arising in layers of the superlattice due to the mismatch of the sizes of the unit cells that make up the lattice of single-crystal layers. These stresses lead to the formation of longitudinal polarization in the layers of barium titanate and to the related contribution of the transverse component of the dielectric tensor to the effective permeability of the superlattice in the direction normal to the plane of the layers. The misfit stresses cause the appearance of a ferroelectric phase transition in the barium zirconate the lattice layers with an increase in the dielectric constant of these layers in the direction normal to the plane of the lattice layers. Highlights: Mismatch stresses in ferroelectric superlattices [ABSTRACT FROM AUTHOR]

Investigation on current conduction mechanism through Tb and Mn codoped Bismuth Ferrite grafted polyvinyl alcohol (BTFMO-PVA) nanocomposite film above room temperature (300 K – 415 K) is reported here in detail. A detailed study on dielectric properties of the sample is done over a wide temperature range in a frequency range of 20 Hz - 2MHz. The conduction is attributed to correlated barrier hopping model. Bipolaron hopping dominates over single-polaron hopping in this system. Complex electric modulus spectra and complex modulus spectra are well explained by suitable models to understand the effective dielectric response. The sample responds to the externally applied magnetic field exhibiting negative magnetocapacitance at room temperature.

In the present work, the crystal structure, ferroelectric and dielectric properties of the dense single-phase Li2CaTa2O7 ceramics with A-site ordered double-layer Ruddlesden-Popper structures have been investigated by the experiments and first-principles calculations. A polar Pna21 phase was determined by the Rietveld refinement against the X-ray diffraction pattern at room temperature, and it was confirmed by its lowest calculated energy and rigid phonon modes. The ferroelectricity was found by observing the ferroelectric hysteresis loop at room temperature, and its remanent polarization was similar to the value calculated from the Berry phase and Born effective charge approaches. The ferroelectricity is a non-conventional proper one since its polarization is induced from the displacement of oxygen anions instead of tantalum cations based on the individual atomic polarization. A first-order transition from an antiferroelectric to paraelectric phase around 900 K was found by the DSC and variable-temperature dielectric measurements. From the present work, the room-temperature ferroelectricity is experimental confirmed in the present ceramics, inspiring the search for new ferroelectricity in the ceramics with A-site ordered Ruddlesden-Popper structures.

This paper reviews a procedure that allows for extracting primary photoelectron or Auger electron emissions from homogeneous isotropic samples. It is based on a quantitative dielectric description of the energy losses of swift electrons travelling nearby surfaces in presence of stationary positive charges. The theory behind the modeling of the electron energy losses, implemented in a freely available QUEELS-XPS software package, takes into account intrinsic and extrinsic effects affecting the electron transport. The procedure allows for interpretation of shake-up and multiplet structures on a quantitative basis. We outline the basic theory behind it and illustrate its capabilities with several case examples. Thus, we report on the angular dependence of the intrinsic and extrinsic Al 2s photoelectron emission from aluminum, the shake-up structure of the Ag 3d, Cu 2p, and Ce 3d photoelectron emission from silver, CuO and CeO2, respectively, and the quantification of the two-hole final states contributing to the L3M45M45 Auger electron emission of copper. These examples illustrate the procedure, that can be applied to any homogeneous isotropic material.

Chair 3D Co(II) phosphite frameworks have been prepared by the ionothermal method. It belongs to chiral space group P3221, and the whole framework can be topologically represented as a chiral 4-connected qtz net. It shows a multistep dielectric response arising from the reorientation of Me2-DABCO in the chiral cavities. It can also serve as a pron conductor with high conductivity, 1.71 × 10−3 S cm−1, at room temperature, which is attributed to the formation of denser hydrogen-bonding networks providing efficient proton-transfer pathways.

Dielectric polarization and electric polarization of electrodes are the common features of polar materials. We described methods to analyze their contributions and showed that both dependencies on temperature of dielectric conductivity and electrode polarization and the exponents characterizing these dependencies are excellent markers of phase transitions. Proposed methods were applied to several compounds, such as liquid crystals, pharmacological compounds, monoalcohols, polyalcohols, and various thermodynamic phases. Common behavior was noted for materials under study. In similar phases, various substances have the same values of the exponents characterizing electric conductivity and contribution from the electrode polarization. These exponents show discontinuities at phase transition temperatures between crystal-like and liquid-like phases.

The demand for self-powered, flexible, and wearable electronic devices has been increasing in recent years for physiological and biomedical applications in real-time detection due to their higher flexibility and stretchability. This work fabricated a highly sensitive, self-powered wearable microdevice with Poly-Vinylidene Fluoride-Tetra Fluoroethylene (PVDF-TrFE) nano-fibers using an electrospinning technique. The dielectric response of the polymer was improved by incorporating the reduced-graphene-oxide (rGO) multi-walled carbon nano-tubes (MWCNTs) through doping. The dielectric behavior and piezoelectric effect were improved through the stretching and orientation of polymeric chains. The outermost layer was attained by chemical vapor deposition (CVD) of conductive polymer poly (3,4-ethylenedioxythiophene) to enhance the electrical conductivity and sensitivity. The hetero-structured nano-composite comprises PVDF-TrFE doped with rGO-MWCNTs over poly (3,4-ethylenedioxythiophene) (PEDOT), forming continuous self-assembly. The piezoelectric pressure sensor is capable of detecting human physiological vital signs. The pressure sensor exhibits a high-pressure sensitivity of 19.09 kPa -1 , over a sensing range of 1.0 Pa to 25 kPa, and excellent cycling stability of 10,000 cycles. The study reveals that the piezoelectric pressure sensor has superior sensing performance and is capable of monitoring human vital signs, including heartbeat and wrist pulse, masticatory movement, voice recognition, and eye blinking signals. The research work demonstrates that the device could potentially eliminate metallic sensors and be used for early disease diagnosis in biomedical and personal healthcare applications.

Aurivillius phase Bi5CrxFe1−xTi3O15 (0≤ x ≤1) thin films are prepared by the chemical solution deposition method, and the effect of Cr content on the microstructure, ferroelectric property, and electric transport behavior of Bi5CrxFe1−xTi3O15 films is investigated. X‐ray diffraction analysis shows that all of Bi5CrxFe1−xTi3O15 films are complete solid solution and maintain the Aurivillius structure. The replacement of Fe3+ with smaller Cr3+ decreases anisotropy and lattice aspect ratio in a‐b plane, which is minimized at the composition of Bi5Cr0.5Fe0.5Ti3O15. This changes the grain shape from sphere to plate, and Bi5Cr0.5Fe0.5Ti3O15 film consists of only plate‐like grains. Cr doping increases saturated polarization (Pm) and decreases coercive field (Ec). Cr doping increases Pm of Bi5CrxFe1−xTi3O15 film to 35 μC/cm2, but decreases Ec down to 125 kV/cm. A decrease in the lattice aspect ratio of a‐b plane promotes the alignment of ferroelectric dipoles under electric field. The frequency‐dependent dielectric property and the leakage current show that the plate‐like grains of Cr‐rich Bi5CrxFe1−xTi3O15 films suppress the transport of carriers from grains to grains and prevents a dramatic leakage current increase. The results of this study provide a design rule to control the ferroelectricity of Aurivillius phase Bi5CrxFe1−xTi3O15 thin films by modifying the composition and lattice aspect ratio. [ABSTRACT FROM AUTHOR]

Dielectric response and charge decay test are widely used for evaluating the electric properties of the insulation pressboards in the converter transformer. In this paper, Frequency Domain Spectroscopy (FDS) test, breakdown test, and charge decay characteristics experiments are carried out on the cellulose pressboards modified by TiO 2 with different mass fractions and diameters. The FDS of the modified cellulose pressboards at ambient temperature is measured from 0.0001 to 1000 Hz by IDAX 300. The process is conducted at the laboratory to study the characteristics parameters of the dielectric response behaviors, such as complex relative permittivity. The results show that the values of the relative permittivity for the insulation pressboards modified by TiO 2 (5 wt%, 10 nm) are reduced. To verify the accurate results, the microstructures of the pressboards modified by 5 wt% with 10 nm diameter are observed by a Scanning Electron Microscope (SEM). The breakdown strength tests are carried on the samples modified by 1 wt%, 3 wt%, 5 wt%, 7 wt% with 10 nm TiO 2 under the intensity electric and high-temperature field, respectively. The values of the breakdown strength are increased by 38% and 11.5% for single layer samples and oil/pressboard composite insulation models modified by 5 wt% nano-TiO 2 filler. In addition, the charge decay characteristics are tested on the samples. The proper proportion additions can reduce the trap density. [ABSTRACT FROM AUTHOR]

Poly(3,4-ethylenedioxythio-phene):poly(styrenesulphonate) (PEDOT:PSS) nanofibres were first prepared via electrospinning method. Microstructural arrangement of the nanofibres was investigated by scanning electron microscopy technique. Then, the effect of beta irradiation with different absorbed doses on their impedance spectra were investigated in the frequency range from 5 to 13 × 106. It was observed that beta irradiation leads to a considerable decrease in both real and imaginary parts of the complex dielectric function, and alternating current conductivity of the nanofibres. The obtained frequency dependent conductivity data were discussed in terms of pair approximation. It was established that, for all beta irradiation doses, the frequency dependence of the conductivity is characterized by the presence of four frequency regions with different slopes. Analysis of the impedance data revealed that chain scission via chain cross-linking and free radical formation are most likely mechanisms for changes in impedance parameters. Two clear semicircles in Nyquist plot have been successfully explained by employing two parallel R-CPE equivalent circuits in series configuration. An overall evaluation of the obtained data indicates that electrospun PEDOT:PSS nanofibres have great potential for the development of highly sensitive impedance-based beta radiation sensor. [ABSTRACT FROM AUTHOR]

A series of double-perovskite La2Co1−zFezMnO6 (z = 0, 0.2–1.0) ceramics were synthesized using a well-established sol–gel method. The series of samples with a monoclinic phase and a P21/n symmetry were characterized by XRD, FTIR, conductivity, and capacitance measurement to extract charge-transport and dielectric characteristics at room temperature. The obtained IR spectra fitted well with the Lorentz oscillator model to calculate the damping factor, optical frequency, and oscillator strength and compared with the theory, which gave better agreement. The calculated activation energies from the Arrhenius plot supported the semiconducting nature of all samples. The temperature and frequency-dependent dielectric parameters, such as the real part (εr′), imaginary part (ε″) of the dielectric constant, dielectric loss (tanδ), and ac-conductivity (σac) were extracted. The dielectric constant (εr′, ε″) and dielectric loss (tanδ) were enhanced at a low frequency, while the ac-conductivity (σac) displayed higher values at higher frequencies. The enhancement in the dielectric parameters with increasing iron concentrations arose due to the higher surface volume fraction of iron (Fe3+) ions than the cobalt (Co3+) ions. The radius of the Fe3+ (0.645 Å) was relatively higher than the Co3+ ions (0.61 Å), significantly influenced by the grains and grain boundaries, and enhanced the barrier for charge mobility at the grain boundaries that play a vital role in space charge polarization.

Electromechanical and dielectric properties of PMN–PT ferroelectric ceramics are investigated. In particular, dielectric response studies focus on the investigation of the influence of the DC applied electric field on the dielectric permittivity as a function of temperature and frequency. Results reveal an electric field driven dielectric anomaly in the dielectric permittivity curves, 𝜀(E), which in turn prevails in the whole ferroelectric phase region and continuously vanishes for temperatures near the paraelectric-ferroelectric phase transition temperature. A schematic model for the domains dynamics of the studied material is proposed taking into account the simultaneous contribution of both 90∘ and 180∘ domains walls.

(1–x)Bi0.5Na0.5TiO3–xBaTiO3lead-free ceramics have been obtained from the conventional solid-state reaction sintering method. The structural properties were investigated from X-ray diffraction and Raman spectroscopy techniques. Results revealed well-crystallized ceramic samples with perovskite structure. Microstructural properties, obtained from scanning electron microscopy measurements, have shown high density with very low porosity level. The dielectric response, analyzed as a function of the temperature and several frequencies, showed very broad peaks with a strong frequency dependence of the temperature for the maximum dielectric permittivity for the modified system. Results were analyzed considering the influence of the BaTiO3 content on the studied physical properties.

Capacitors in electrical and electronic systems composed of thin film dielectrics operate under extremely high electric fields. Dynamics of charge transport and relaxation are closely correlated to the energy storage properties and electrical degradation of thin film dielectrics for capacitive applications. In this paper, the dielectric relaxation properties of poly (vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) copolymer films are investigated over a broad frequency range from 10 mHz to 10 MHz and temperature range from −130 °C to 130 °C. The dielectric responses correlated to bulk and interfacial processes are clarified by varying the thickness and interfacial contact status of P(VDF-HFP) films. A low frequency process originating from the quasi-DC (QDC) process and a dielectric dispersion process correlated to the interfacial polarization are identified based on the Dissado-Hill dielectric response model and the equivalent circuit analysis. The high permittivity and high operation electric field of P(VDF-HFP) for capacitive energy storage give rise to improved blocking capacitance associated with the interface, suggesting the enhanced interfacial polarization. This work provides insights into the bulk and interface charge dynamics of polymer thin film dielectrics. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Electromechanical and dielectric properties of PMN–PT ferroelectric ceramics are investigated. In particular, dielectric response studies focus on the investigation of the influence of the DC applied electric field on the dielectric permittivity as a function of temperature and frequency. Results reveal an electric field driven dielectric anomaly in the dielectric permittivity curves, 𝜀 (E) , which in turn prevails in the whole ferroelectric phase region and continuously vanishes for temperatures near the paraelectric-ferroelectric phase transition temperature. A schematic model for the domains dynamics of the studied material is proposed taking into account the simultaneous contribution of both 90 ∘ and 180 ∘ domains walls. [ABSTRACT FROM AUTHOR]

(1– x) Bi 0. 5 Na 0. 5 TiO3– x BaTiO3lead-free ceramics have been obtained from the conventional solid-state reaction sintering method. The structural properties were investigated from X-ray diffraction and Raman spectroscopy techniques. Results revealed well-crystallized ceramic samples with perovskite structure. Microstructural properties, obtained from scanning electron microscopy measurements, have shown high density with very low porosity level. The dielectric response, analyzed as a function of the temperature and several frequencies, showed very broad peaks with a strong frequency dependence of the temperature for the maximum dielectric permittivity for the modified system. Results were analyzed considering the influence of the BaTiO3 content on the studied physical properties. [ABSTRACT FROM AUTHOR]

Abstract Processing of materials in the form of ceramics normally involves several steps including calcination at a relatively low temperature for synthesis of the end-product powder and sintering at a high temperature for densification. The work we have been developing introduces a novel approach enabling synthesis plus sintering of materials in a single running experiment by using electric fields, ending with dense ceramics that display grains noticeably finer than in conventional processing. This new paradigm is fully illustrated with experiments conducted on amorphous CaCu3Ti4O12 precursor powder, shown to experience, on heating, crystallization through intermediate phases, followed by chemical reaction leading to synthesis of the end-product powder, plus densification depending on field adjustment. The processing time and furnace temperature are considerably reduced, demonstrating that enhanced synthesis and sintering rates applied under field input. Similar results found in Bi2/3Cu3Ti4O12 are also shown. The different factors that may contribute to this unique scenario, including Joule heating, defect generation, and reduction of free energy for nuclei formation promoted by the applied field, are briefly discussed. Overall, the findings we bring here are exclusive as they show an exploitable way that allows rapid processing of materials with good control over particle and grain coarsening.

Phase composition, microstructure and electric response of Li0.05SnxNi0.95 – xO (x = 0, 0.025, 0.05, 0.1) ceramics were systematically investigated. Colossal dielectric permittivity (>5000) is observed in the frequency range of 102–105 Hz at room temperature which becomes highly frequency-independent with increasing temperature. Secondary Sn-rich phase is detected in the grain boundary regions and it has a remarkable influence on the dielectric properties. Impedance spectroscopy analysis demonstrates that the microstructure is electrically heterogeneous, consisting of semiconducting grain and insulating grain boundary. Defect dipoles or polyvalent cations induced at high temperature may activate an electron hopping process under electric field, resulting in the enhancements of grain conductivity and polarization effect. This behaviour should be considered as the origin of the observed dielectric response.

Dielectric fluids or commonly oils serve as the protection of any power utility components, which make it selection crucial for utility. Due to its significance, consistent research has been performed and new insulants have been introduced for power utilities to attain better, reliable, and a longer lifespan than the former one. Nanotechnology-based insulating liquids are still under research but show the potential to achieve the objective of smart and futuristic insulation. This paper provides the critical review for the development of insulating liquid and promising results shown by the nanoparticles dispersed fluid termed nanofluids. The state-of-the-art research illustration includes synthesis, experimental investigation, and dielectric and physio-mechanical characterization of nanofluids. The enhancements in the characteristics of nanofluids are elucidated along with its possible mechanisms and shortcomings.

In this paper we critically discuss several examples of two-dimensional electronic systems displaying interaction-driven metal-insulator transitions of the Mott (or Wigner–Mott) type, including dilute two-dimension electron gases (2DEG) in semiconductors, Mott organic materials, as well as the recently discovered transition-metal dichalcogenide (TMD) moiré bilayers. Remarkably similar behavior is found in all these systems, which is starting to paint a robust picture of Mott criticality. Most notable, on the metallic side a resistivity maximum is observed whose temperature scale vanishes at the transition. We compare the available experimental data on these systems to three existing theoretical scenarios: spinon theory, Dynamical Mean Field Theory (DMFT) and percolation theory. We show that the DMFT and percolation pictures for Mott criticality can be distinguished by studying the origins of the resistivity maxima using an analysis of the dielectric response.

The results of studying the processes of dielectric relaxation in thin nanocrystalline films of vanadium dioxide are presented. The existence of a non-Debye relaxation process was revealed, which is due to the presence of a distribution of relaxators over relaxation times according to the Cole-Davidson model. The activation energy of the dielectric relaxation process was found to be Ep = (0.9 ± 0.1) eV. The observed regularities are explained by a model which views the system as a set of relaxators whose physical parameters have different numerical values due to the Gaussian size distribution of nanocrystallites of the VO2 film. The temperature change in the parameters of the dielectric relaxation process, detected at T = 340 K, indicates that a complex Mott-Peierls semiconductor-metal phase transition occurs at a given temperature in the VO2 nanocrystalline film.

Results of studies of dielectric response and polarization in PbCo1/3Ta2/3O3 (PCT) single crystals grown by spontaneous crystallization are presented. Anomalies in the temperature dependence of the complex dielectric permittivity at 350, 270, 183, and 105 K have been observed. Using the thermally stimulated depolarization method, the temperature region of remnant polarization existence has been revealed below 270 K. It is assumed that in PCT, as well as in PbCo1/3Nb2/3O3 (PCN), in low-temperature region the phase separation caused by continuous switching of charge (valence) of Co2+/Co3+ and Ta4+/Ta5+ ions is realized. [ABSTRACT FROM AUTHOR]

This paper proposes a rational approximation-based approach to find positive real parameters for the extended Debye model (EDM), aimed at condition assessment of insulation systems of power transformers. The EDM can model the slow and fast polarization phenomenon, including relaxation mechanisms with different relaxation times within a composite dielectric material. In the proposed approach, the complex permittivity of the transformer’s composite insulation is approximated via rational functions, as given by the vector fitting (VF) software tool, and the EDM parameters are identified from the obtained poles/residues. To guarantee positive real parameters, i.e., a physically realizable circuit, VF is internally modified to calculate the final residues of the rational approximation via a constrained linear least-squares problem without resorting to further post-processing algorithms, as in existing methods, hence without affecting fitting accuracy. The effectiveness of the parametrized EDM is demonstrated in two ways: (a) by reconstructing frequency domain spectroscopy (FDS) curves provided via measurements in new oil-immersed power transformers and (b) by the comparison of the calculated polarization current given by EDM versus real measurements in time domain. The achieved fitting accuracy in most of the cases is above 99 percent for the reconstructed FDS curves, while the polarization current waveform is reproduced with good agreement.