Dielectric Polarization Research Articles

Engineering Phase to Reinforce Dielectric Polarization in Nickel Sulfide Heterostructure for Electromagnetic Wave Absorption.

Engineering phase transition in micro-nanomaterials to optimize the dielectric properties and further enhance the electromagnetic microwave absorption (EMA) performance is highly desirable. However, the severe synthesis conditions restrict the design of EMA materials featuring controllable phases, which hinders the tunability of effective absorption bandwidth (EAB) and leads to an unclear loss mechanism. Herein, a seed phase decomposition-controlled strategy is proposed to induct nickel sulfide (NiSx) absorbers with controllable phases and hollow sphere nature. Transmission electron microscopy holography and theoretical calculations evidence that the reconstruction of atoms in phase transition induces numerous heterogeneous interfaces and lattice defects/sulfur vacancies to cause varied work functions and local electronic redistribution, which contributes to reinforced dielectric polarization. As a result, the optimized NiS2/NiS heterostructure enables enhanced EM attenuation capability with a wide EAB of 5.04GHz at only 1.6mm, compared to that of NiS2 and NiS. Moreover, the correlation between EAB and NiS phase content is demonstrated as the "volcano" feature. This study on the concept of phase transition of micro-nanomaterials can offer a novel approach to constructing highly efficient absorbers for EMA and other functionalities.

Substantial physicochemical pretreatment and rapid delignification of lignocellulosic banana, pineapple and papaya fruit peels: A study on physical-chemical characterization

Lignocellulosic biomass is a promising precursor for producing various value-added products. The present study examines the potentiality of yellow banana peel (YBP), pineapple peel (PAP), and papaya peel (PP) as substrates for producing reducing sugar. The primary characterization studies were performed using XRD, FTIR, proximate, ultimate and fibre analysis. Results indicate that banana peels are more fibrous and have greater hemicellulose susceptibility (19.55 ± 0.488 wt%) than other peels (15.4 ± 0.38 and 15.9 ± 0.39 wt%). Pretreatment investigations were conducted utilizing various parameters of physical (hot water and microwave hot water) and chemical (acid and alkali) techniques. The findings suggest that higher delignification was found for alkali at 0.03 M ammonia (81.1%) and microwave at 545 W (34.4%). Based on the individual higher performance, the study hypothesizes to combine microwave and ammonia as microwave-ammonia pretreatment (MAP) to enhance the reducing sugar. As a result, 0.03 M ammonia and 545W for 2 min of MAP delignified the banana (94.5%), pineapple (90%), and papaya (80.4%), respectively. The main mechanism involved in the processes is the electromagnetic waves disrupts heterogeneous structures through dielectric polarization which stimulates the enzymatic hydrolysis with short duration to produce more reducing sugars.. The MAP with cellulase (MAPC) was enzymatically hydrolyzed using Cellic ® CTec2 at 25FPU/g for 48hrs to improve the higher reducing sugar content of bananas (168 mg/g substrate), pineapples (160 mg/g substrate), and papayas (145 mg/g substrate). The study found that the combined pretreatment interrupts the cellulose microfibril glycosidic linkages which increaseses hexose releasethat could potentially be used for producing viable products.

Morphology engineering of heterogeneous carbon particles toward boosted dielectric polarization for ultrathin and strong loss absorber

Micron-carbon particles with polymorphous concave polyhedron have been easily prepared via high-efficiency spray drying-carbonization process, which is aimed at boosting dielectric polarization toward the feature of high the real part of the complex permittivity accompanied with low level dielectric loss for achieving ultrathin absorber. In addition, the effect of geometry on the microstructure and microwave absorption (MA) performances was systematically studied for the first time. A minimum reflection loss (RLmin) of −55.07 dB under ultrathin thickness of 1.23 mm and a broad effective absorption bandwidth (<-10 dB) of 4.0 GHz at 1.3 mm were obtained for composites filled with polymorphous concave polyhedral carbon particles, meanwhile the loading contents have been reduced from 30 wt% spherical filler to 22.5 wt% polymorphous concave polyhedral filler. Optimized MA performance with strong loss and ultrathin thickness has been identified as attenuation mechanism dominated by interference cancellation and assisted by dielectric loss for the first time. This work not only provides an insight to realize engineering applications of carbonaceous absorbents but also reveals the intrinsic attenuation mechanism of microwave absorbing materials.

Boosting energy storage performance in Na0.5Bi0.5TiO3-based lead-free ceramics modified by a synergistic design

Na0.5Bi0.5TiO3-based relaxor ferroelectric ceramics have attracted widespread attention due to their potential applications in energy storage capacitors for pulse power system. We herein propose a synergistic strategy of introduction of 6s2 lone pair electrons, breaking the long-range ferroelectric order, and band structure engineering for high performance energy storage by introducing Bi(Mg0.5Sn0.5)O3 (BMS) with weak ferroelectric active cations into 0.7Na0.5Bi0.5TiO3-0.3SrTiO3 (BNT-ST) to form BNT-ST-BMS ceramics. The doped ceramics display the excellent dielectric stability versus temperature and frequency. The suitable BMS doping can increase the band gap of the BNT-ST ceramic and effectively avoids early dielectric breakdown and polarization saturation. The BNT-ST-BMS ceramic in the composition of x = 0.08 exhibits an outstanding recoverable energy storage density (Wrec) of 5.99 J/cm3, together with a good efficiency (ƞ) of 76% as well as an excellent dielectric stability versus temperature (Δεr/εr(150°C) ≤ ±15%) and frequency. The findings in this work demonstrate that the BNT-ST-BMS ceramics have exceptional potential as candidate materials for pulse power and high voltage capacitors applications, and provide a path for the development of the other lead-free energy storage materials.

Phase Engineering on Amorphous/Crystalline γ‐Fe2O3 Nanosheets for Boosting Dielectric Loss and High‐Performance Microwave Absorption

AbstractTo design and develop efficient microwave absorbents via phase engineering is still less studied. The unique properties caused by constructing heterophase structure hold the potential to strengthen absorbing capability toward microwave radiation. Herein, amorphous/crystalline γ‐Fe2O3 nanosheets (Fe‐H) are carefully fabricated through a controlled annealing process. The matched Fermi levels formed on both sides of the heterophase interface not only provides efficient interfacial polarizations but also facilitates the transport of electrons with less scattering over the whole Fe‐H nanosheets. Thereby, both of the conduction loss and dielectric polarization relaxation are promoted, leading to a strengthened attenuation toward electromagnetic wave radiation. The as‐synthesized Fe‐H sample exhibited a minimum reflection loss of ‐89.5 dB centered at a thickness of 2.00 mm, associated with an effective absorption bandwidth (reflection loss ≤ ‐10 dB) reaching 6.45 GHz. All of these behaviors are superior to its pure amorphous absorbent and bare crystalline counterpart. Furthermore, this heterophase engineering strategy is valid when extended to Co and Ni based oxides, suggesting its universality and generality for promoting microwave absorption. Henceforth, this study indicates a favorable potential of the synthesis and application of amorphous/crystalline materials as heterophase microwave absorbents.

Low-dimensional lead chromate-based hybrid system for capacitance and polarization performances: a flexible device for pressure-induced voltage generator

AbstractOrganic molecule–functionalized lead chromate nanoparticle was synthesized using a complexation strategy route. The structural characterization revealed the single-phase lead chromate system belongs to monazite-type monoclinic structure with the space group of P21/n. The unit cell consists of an alternating chain of polyhedra (PbO9) and tetrahedra (CrO4) units, connected via edge and corner-sharing arrangement. A flexible device of lead chromate was fabricated and investigated dielectric capacitance, electrical impedance, conductivity, and field dependent polarization performances under different frequency and temperature environments. The device displayed a maximum dielectric constant (εʹ) value ~ 2400 at 120°C under 100 Hz frequency condition. High dielectric constant value is originated from the orientation polarization of CrO4 unit and space charge contribution in the system. AC conductivity of the device suggested the polaronic charge carriers control the overall conduction process via localized hopping mechanism. A fatigue-free polarization behavior was observed in the device under the applied field of 4.0 kV/mm, for 103 cycles and retained the polarization value ~ 0.26 μC/cm2 over the switching cycles. Lead chromate–based device also showed pressure-induced voltage generation under different pressure conditions and could have the potential application as a voltage generator.

Confined In-Situ Encapsulation of Co/C Composites with Increased Heterogeneous Interface Polarization for Enhanced Electromagnetic Performance.

It is an urgent problem to realize reliable microwave absorption materials (MAMs) with low density. To address this issue, a series of controlled experiments w ere carried out, which indicated that the tubular structure enables excellent microwave absorption properties with a lower powder filling rate. This performance is attributable to the combined dielectric and magnetic loss mechanisms provided by Co/C and the interface polarization facilitated by multiple heterogeneous interfaces. Particularly, Co@C nanotubes, benefiting from the enhanced heterointerface polarization due to their abundant specific surface area and the reduced electron migration barrier induced by their 1D stacked structure, effectively achieved a dual enhancement of dielectric loss and polarization loss at lower powder filling ratios. Furthermore, the magnetic coupling effect of magnetic nanoparticle arrays in tubular structures is demonstrated by micromagnetic simulation, which have been few reported elsewhere. These propertied enable Co@C nanotubes to achieve minimum reflection lossand maximum effective absorption broadband values of 61.0dB and 5.5GHz, respectively, with a powder filling ratio of 20wt% and a thickness of 1.94mm. This study reveals the significance of designing 1D structures in reducing powder filling ratio and matching thickness, providing valuable insights for developing MAMs with different microstructures.

Electrorheological effect of self-crosslinked polymerized ionic liquids containing different types of ion spacers

In this paper, we synthesized five self-crosslinked polymerized ionic liquids (S-PILs) containing distinct ion spacers but identical mobile counterions. The structural characterization of these S-PILs was carried out using Fourier transform infrared spectroscopy and wide-angle X-ray scattering. The electrorheological (ER) effect was investigated using rheological measurement and broadband dielectric spectroscopy. The results showed that the ER effect of S-PIL with phosphorus-containing ion spacers was the weakest, that of S-PIL with imidazole-containing ion spacers and S-PIL with pyridine-containing ion spacers was increased, and that of S-PIL with amino-containing ion spacers was the strongest. Dielectric spectra analysis showed that the interfacial polarization time of S-PIL with phosphorus-containing ion spacers was the longest, resulting in its weakest ER effect. The interfacial polarization times of S-PIL with imidazole-containing ion spacers and S-PIL with pyridine-containing ion spacers were increased but their conductivities were relatively large, which led to strong electrode polarization and weakened their ER effect. S-PILs with amino-containing ion spacers had moderate conductivity and suitable polarization time, so they had the strongest ER effect. Finally, we discussed the reasons for these different conductivity and dielectric polarization by combining the dissociation degree of counterions calculated by Raman spectroscopy and the activation energy of ion movement calculated by conductivity data. The study provides a molecular-level understanding for the rational design and preparation of S-PILs with high ER performance.

Magnetoelectric coupling response of novel mullite coated Ni–Zn–Cu-ferrite nanocomposite

Novel multiferroic nanocomposite fabricated by Ni–Zn–Cu-ferrite (NZCF)-mullite is reported in this article. The crystallographic phases are confirmed by X-ray diffraction. The static magnetic properties are measured for both bare NZCF and mullite encapsulated NZCF nanocomposite which show the successful retention of the magnetic behaviors of the nanocomposites even at higher annealing temperature of 1200 °C. The dielectric response is estimated and high value of dielectric constant (∼210.7 at 100 Hz) is observed for the mullite encapsulated NZCF nanocomposite due to the formation of interfacial polarization in the nanocomposite. The temperature dependent dielectric response suggests the presence of dielectric polarization in the NZCF-mullite nanocomposite. Magnetocapacitance (MC) study of the NZCF-mullite nanocomposite sample is observed at room temperature (RT). The observed MC and its variation with magnetic field confirm the presence of strong interactions between the magnetic and ferroelectric order parameters in the nanocomposite sample.

Enhancement of microwave absorption performance of FeSiCr magnetic powder by dielectric polarization modulation

The Fe3O4@C@FeSiCr composite was successfully prepared by compounding flaky FeSiCr magnetic powder with an organo-metallic frameworks (MIL-88(Fe)), and then subjecting to carbonization heat treatment. The dielectric polarization characteristics is regulated by adjusting the heat treatment temperature. The absorbing performance is optimum when the carbonization heat treatment temperature is 700 °C, the minimum value of reflection loss (RLmin) is −35.71 dB at 5.68 GHz. The effective absorption bandwidth (RL ≤ −10 dB) of the composite material covers 4–16 GHz when the coating thickness is from 1.0 to 3.0 mm. This work provides an important value for the application of FeSi-based soft magnetic materials in the field of microwave absorption.

Structural engineering of porous biochar loaded with ferromagnetic/anti-ferromagnetic NiCo2O4/CoO for excellent electromagnetic dissipation with flexible and self-cleaning properties

Design of multi-functional microwave absorption materials with strong dissipation ability is a practical approach to address the current issue of electromagnetic radiation pollution. Herein, based on the exchange bias interaction between ferromagnetic and anti-ferromagnetic interfaces, a series of absorbers composed of the porous biochar loaded with ferromagnetic/anti-ferromagnetic NiCo2O4/CoO were successfully prepared via a fairly simple process of one-step calcination. By regulating the calcination temperature, the pore size and porosity of porous carbon, morphology of loaded NPs as well as the electromagnetic response property and impedance matching characteristic in such composites can be modulated. The porous biochar/NiCo2O4/CoO composite prepared under 350 °C possesses a remarkable electromagnetic absorption reflection loss (RL) of –48.41 dB at 9.12 GHz with 2.5 mm thickness, and the effective absorption bandwidth (EAB) of 4.32 GHz with 2.2 mm thickness is located at X band, this is owing to the strong coupling effect of multiple dielectric polarizations, magnetic resonances, and eddy current consumption under matched impedance. In addition, the microwave absorbing patch prepared with this composite exhibits a well-hydrophobic property for self-cleaning function, and the large extensibility with substantial breaking strength endows its practical usage as a flexible absorber.

Evaluation and Failure Mechanism of High‐Temperature Microwave Absorption for Heterogeneous Phase Enhanced High‐Entropy Transition Metal Oxides

AbstractHerein, magnetic and conductive heterogeneous nickel‐matrix alloy is in situ constructed in the high‐entropy transition metal oxide matrix using a reductive circumstance, to form the high‐temperature resistant microwave absorbers. The ohmic, dielectric polarization and magnetic loss are enhanced synergistically, prompting the improvement of loss capacity and optimization of the impedance matching feature. The composites achieve over 90% absorption in the whole Ku band with a thickness of just 1.55 mm at room temperature. Moreover, the in situ high temperature measured microwave absorption keeps stable till 500 °C. In situ characterizations are employed to investigate the evolution processes and failure mechanisms. As the temperature elevates, there are three distinct stages. The absorber goes through minor chemical reactions, consequent elimination of magnetic loss, and a rapid increase in electroconductivity. These behaviors culminate in impedance mismatch, finally worsening its absorption performance at elevated temperatures. The proposed evaluation process reveals how the above irreversible and reversible behaviors affect high‐temperature microwave absorption, providing an effective theoretical basis for the design of high‐temperature microwave absorbers.

Maxwell–Wagner Polarization and Mixed Ferromagnetic and Antiferromagnetic State in Eu2CoMnO6

Herein, the electrical and magnetic properties of polycrystalline Eu2CoMnO6 are explored. More specifically, based on transport, dielectric, and impedance measurements, a thermally activated dielectric polarization near room temperature is reported. The valence states of transition metals in the Eu2CoMnO6 sample are studied by measuring the X‐ray absorption spectra at both Co‐L2,3 and Mn‐L2,3 edges. Moreover, based on magnetization, X‐ray absorption spectroscopy, and X‐ray magnetic circular dichroism measurements, the coexistence of competing ferromagnetic and antiferromagnetic phases is probed. Dielectric measurement shows a large dielectric constant near room temperature along with a large frequency dispersion. The temperature‐dependent resistivity, Cole–Cole plot, and imaginary part of impedance confirm the semiconducting nature of Eu2CoMnO6. Temperature‐dependent magnetization shows a second‐order magnetic transition below 125 K. Isothermal magnetization versus magnetic field loop shows first‐order metamagnetic transition, driven by mixed magnetic state owing to the presence of antisite disorder and antiphase boundary.

Dielectric properties of diamond/SiC composite fabricated by Si vapor infiltration process

The dielectric properties and polarization mechanism are important for the application of high thermal conductivity electronic packaging materials. In this work, diamond/SiC composites were prepared by the silicon vapor infiltration process, and the effect of diamond content on permittivity of composites was investigated in detail in the range of 100 MHz to 1 GHz, and the mechanism of dielectric polarization was also discussed. The results show that the real part of permittivity of composite is greater than that of either component, due to the presence of interfaces and defects. As the diamond content increases, both the real and imaginary parts of permittivity show a trend of rapid decrease and then slow increase. Particularly, the minimum values of the real and imaginary parts of permittivity of diamond/SiC composite are 27 and 0.3, respectively. In the low frequency stage (<400 MHz), the dielectric loss of the composite is mainly caused by the conductivity loss, while in the high frequency stage (400 MHz∼1 GHz), the polarization loss plays a dominant role. The polarization loss of diamond/SiC composite mainly originates from several Debye relaxation processes, which are the interfacial polarization formed at the diamond/graphite and graphite/SiC interfaces.

Impedance analysis of electrolyte processes in a solid oxide cell

AbstractElectrochemical impedance spectroscopy and the distribution of relaxation times are powerful tools to study polarization processes in solid oxide cells (SOC). Commonly the measured polarization resistance is solely attributed to polarization phenomena in the electrodes whereas the electrolyte is assumed to act as purely ohmic series resistance.In this study an electrolyte supported SOC is investigated by impedance spectroscopy from the nominal operating temperature range of 700–900°C down to temperatures as low as 350°C. At such low temperatures the dielectric polarization of the electrolyte is shifted into the accessible frequency range, providing access to additional processes which are deconvoluted and quantified. It is discussed to which extent the additional layers like gadolinia doped ceria diffusion barrier and electrode layers influence the electrolyte processes as grain and grain boundary.

The strange case of enhancing the resistivity by extended sintering time in (Bi0.5Na0.5)TiO3–BaTiO3 solid solution

With the presence of volatile elements in the composition of a ceramic material, longer sintering time presumably creates more vacancies. In the case of (Bi0.5Na0.5)TiO3–BaTiO3 lead-free piezoelectric ceramics and when batched and calcined with a Bi2O3 deficient stoichiometry, there can be a surprising increase in resistivity with increasing sintering time. It is deduced that the extended sintering time reduces the concentration of bismuth vacancies (and the ionically compensating oxygen vacancies). This is also associated with a decrease of depolarization temperature, Td, and possibly a change in dielectric polarization phenomena from normal to relaxor ferroelectric. These observations do not occur in pure (Bi0.5Na0.5)TiO3, suggesting that they are actually facilitated by the Ba2+ content in the solid solution BNT−BT. Microstructural observations indicate the formation of BaTi2O5 secondary phase which considerably grows as sintering goes on. With more Ti4+ being incorporated to the secondary phase, the stoichiometry of the solid solution can be restored, so is the resistivity and the observed trends in decreased Td.

Enhancement of the Dielectric and Energy Storage Properties of Lead-Free BNSLT Ceramics by Zr4+ Substitution into B-Sites

(Bi0.38Na0.30Sr0.28)0.98La0.02Ti1-xZrxO3 (abbreviated as BNSLT1-xZrx, with x = 0 − 0.05) lead free ceramics were fabricated using the solid-state combustion method. The phase structure, microstructure and electrical properties of the ceramics were investigated. The coexistence of the rhombohedral (R) and tetragonal (T) phases was found in all samples. Rietveld refinement confirmed that as x increased from 0 to 0.05, the rhombohedral phase increased from 41 to 60%. A nearly equal R:T phase ratio of 49:51 was obtained for x = 0.01. All ceramics displayed polygonal grain shapes with anisotropic grain growth. The average grain size of the ceramics was in the range of 0.46–0.79 µm. The optimal Zr4+ content resulted in increased grain growth and reduced pores, leading to improved electrical properties. The highest density (5.52 g/cm3), maximum dielectric constant (ε m =2156), maximum polarization (Pmax=15.36 µC/cm2) and high energy storage properties (Wtotal=0.49 J/cm3, Wrec=0.45 J/cm3, Wloss=0.05 J/cm3 and η = 90.54% at 60 kV/cm) were obtained from x = 0.01 caused by a morphotropic phase boundary (MPB) and good morphology.

Influence of ionic size on the optical and thermodynamical properties of chitosan based polymer composites with different ammonium halides

The biopolymer chitosan has been dissolved with 1% of acetic acid and the same has been embedded with different salts of ammonium halides like NH4F, NH4Cl, NH4Br, and NH4I with different concentrations to make the composites. The density, refractive index, and ultrasonic velocity of the said composite materials were measured and the space-filling factor along with polarizability and dielectric constant is obtained from refractive index data. From the refractive index data, the parameters like dielectric constant(ε), polarizability(α), and space-filling factor are calculated and from the ultrasonic velocity, the thermodynamical properties like relaxation strength (r s), acoustic impedance (Z), adiabatic compressibility (βs), intermolecular free length (Lf) and surface tension (σ) were calculated. The ultrasonic velocity of chitosan solution is 1515 ms− 1. The addition of ammonium halides leads to increase in ultrasonic velocity. The intermolecular free length (Lf), adiabatic compressibility (βs), and relaxation strength (r s) are decreasing and all other parameters are increasing with respect to ionic size and concentration of ammonium halides. All the results are analyzed and discussed with respect to the ionic size of the ammonium salts and concentrations.

Soda-lime-silica glass structure with MoO3 doping: An optical approach

MoO3 incorporated sodium-lime-silicate glasses of composition 55SiO2 - 25Na2O - 5CaO - 10ZnO - 5MgO(1-x): MoO3 (x) (x = 0, 0.1, 0.3, 0.5, and 1) were prepared using the melt-quench technique. The transmittance and absorbance spectrum of the glasses were detected by UV–VIS spectroscopy between the wavelength range of 250–900 nm. The optical transmittance of the doped glasses was significantly enhanced by adding MoO3 to the base glass structure. The indirect band gap (Eg) and Urbach energy (EU) values have been evaluated with the help of absorption spectra. Band gaps range from 3.478 to 3.752 eV, and Urbach energies range from 0.223 to 0.709 eV. Advanced optical characterization of glasses was obtained using standard equations by analyzing important optical parameters such as molar volume, refractive index, optical dielectric constant, molar refraction, electronic polarizability, and metallization criterion. All the data has been discussed in accordance with the MoO3 contributions. The glass structure with 0.1 % MoO3 doped, coded as M-01, showed a different change in the measurements and calculations than the other glasses. The glass structure under consideration exhibits superior characteristics in terms of light transmittance, band gap value, and metallization criterion, while displaying comparatively lower values for Urbach energy, refractive index, optical dielectric constant, and electronic polarizability.

Enhanced Electrorheological Performance of Core-Shell-Structured Polymerized Ionic Liquid@Doubly Polymerized Ionic Liquid Microspheres Prepared via Evaporation-Assisted Dispersion Polymerization.

A polymerized ionic liquid (PIL) provides a platform for the development of a high-performance water-free polyelectrolyte-based electrorheological fluid (ERF) because of the presence of large-size hydrophobic ion pairs. However, the large-size hydrophobic ion pairs also easily result in a low glass-transition temperature of an ordinary linear PIL, and consequently, the PIL-based ERF has to be subject to a high leaking current density and a narrow working temperature range. In this paper, we prepared a kind of core-shell-structured polymerized ionic liquid@doubly polymerized ionic liquid (PIL@D-PIL) microsphere with a linear PIL as the core and a physically cross-linked D-PIL as the shell via an evaporation-assisted dispersion polymerization method. The core-shell structure of the sample was observed by scanning electron microscopy and transmission electron microscopy. The thermal properties of the sample were tested by differential scanning calorimetery and thermogravimetric analysis. The ER effect and dielectric polarization of PIL@D-PIL microspheres when dispersed in an insulating nonpolar liquid were studied by a rheometer and dielectric spectroscopy. It shows that the glass-transition temperature and thermal stability of a PIL increased after coating with the D-PIL shell. Under electric fields, the ERF of the PIL@D-PIL microspheres exhibits a significantly reduced leaking current density and an enhanced operating temperature range compared to the ERF of single-PIL microspheres. The PIL@D-PIL microspheres can still maintain good ER effect even if the temperature is higher than the glass-transition point of the PIL core due to the protection of the D-PIL shell.