Dielectric Properties Research Articles

Improvement of ferroelectric and dielectric properties in BaTiO3/LaNiO3 superlattices by regulating the ferroelectric layer thickness

Ferroelectric superlattices exhibit rich functional characteristics. Yet, the ferroelectric properties are always unsatisfactory due to the presence of depolarization field resulting from the polarization discontinuities between the component materials, which has become a bottleneck problem hindering the improvement of ferroelectric properties and further industrial applications. Here, the BTO/LNO superlattices composed of ferroelectric (BaTiO3, BTO) and metallic (LaNiO3, LNO) materials were prepared by pulsed laser deposition (PLD). The periodic thickness of the LNO layers was fixed to 2 unit cells, while the periodic thickness of the BTO layers was changed. We demonstrate experimentally that by regulating the BTO periodic thickness, BTO/LNO superlattices exhibit excellent and adjustable ferroelectric and dielectric properties. The enhancement of electrical properties is closely related to the increase of tetragonality (c/a) combined with the effect of the ultra-thin LNO layers and the accumulation of oxygen vacancies at superlattice interfaces on reducing the depolarization field. We hope this work will provide an effective strategy for optimizing the ferroelectric properties of ferroelectric superlattices based on the component material and periodic structure regulation.

Synergistic enhancement of dielectric strength and thermal conductivity in meta-aramid-based composite films via honeycomb cavities filling strategy

Owning superior dielectric and mechanical properties, poly (m-phenylene isophthalamide) (PMIA) fiber is an ideal insulation material for next-generation electric and electronic devices. However, its low thermal conductivity poses a risk of thermal breakdown. Moreover, PMIA films prepared using the unique protonation method exhibit a honeycomb-like structure with numerous air pockets, further reducing heat transfer efficiency. Herein, we propose a strategy of honeycomb cavities filling to synergistically improving the dielectric strength and thermal conductivity of PMIA-based composite films. To achieve a denser configuration, the nanodiamond (ND) fillers modified by polydopamine (PDA) are uniformly filled in the cavities within the PMIA skeleton, serving as thermally conductive reinforcements. In the 15 wt% composite film, the breakdown strength and thermal conductivity measure 334 kV/mm and 1.12 W/(m·K), respectively, which are 42.3% and 833% higher than that of the pure one. Furthermore, the underlying mechanisms are studied based on density functional theory and multi-physics simulations.

An investigation for optical, photocatalytic, photoluminescence and dielectric properties of Cd0.40Ni0.60ZnO2 annealed nanocomposites

We report here the optical, photoluminescence (PL), and dielectric properties of Cd0.40Ni0.60ZnO2 nanocomposites annealed between 200 and 600oC. An increase in annealing temperature (Tann) up to 600oC correlates with a gradual increase in the crystallite and particle sizes. The surface area, pore radius, and pore volume are increased as Tann increases from 200oC to 300oC, and then decreased, but still higher than of 200oC. Similar behaviors were obtained for the absorbance carrier density, photocatlytic efficiency, degradation rate, PL intensity, dielectric constant, dielectric loss, ac conductivity, F-factor, series resistance, and electronic polarizability. While the energy gap, binding energy, impedance of grains and their boundaries, and effective capacitance show an opposite behavior. The relaxation times at the peak of dielectric parameters are between 11.54 and 159.24ns and between 35.23 and 24273.73ns, respectively. The Cole-Cole plot shows a single semicircle at Tann < 400oC and two successive semicircles at Tann> 500oC. The energy of PL of visible emissions is independent on the chosen Tann. These findings indicated that the nanocomposite annealed at 300oC can be used for water purification, telecommunications, solar cells, supercapacitor, and white light-emitting diodes (LEDs).

Molecular dynamics simulations and FTIR Spectroscopy investigations on the hydration, transport, and dielectric properties of the NaF(aq) system at various concentrations

Sodium fluoride has many applications in various fields, such as dentistry, geochemistry, and rechargeable battery technology. Indeed, the determination of the hydration structures, dynamics, and dielectric properties of the NaF electrolyte in aqueous solutions is a crucial element in order to optimize its performance and predict its intervention mechanisms in industrial processes. In this study, we used the molecular dynamics approach to study the NaF(aq) binary system at different concentrations ranging from 0.1 to 1.0 mol.kg−1 using the OPLS-AA force field combined with the extended simple point load water model (SPC/E). Thus, the ions were represented as charged Lennard-Jones particles. The radial distribution functions (RDF) have been calculated to analyze the hydration shell structures of different ion pairs. The microstructures, self-diffusion coefficient, and dielectric constant were determined by molecular dynamics at various concentrations. Moreover, our FTIR spectroscopy data confirm the results obtained from molecular simulations.

Barium titanate–silicon elastomer based body coupled antenna for wearable microwave head imaging applications

This paper presents a flexible monopole antenna fed by a coplanar waveguide (CPW) feeding line with a barium titanate (BaTiO3) silicon-elastomer impedance matching layer for microwave head imaging applications. The operating frequency bandwidth of the proposed antenna is 614 MHz which is from 0.475 GHz to 1.089 GHz. In biomedical microwave sensing and imaging applications, the major challenge is the high power loss due to reflection between the BaTiO3 and the antenna due to impedance mismatch. Therefore, the proposed BaTiO3 silicon-elastomer composite is designed to have dielectric property of 20 which acts as an impedance matching layer for the monopole antenna. The proposed antenna has dimensions of 70×30×6 mm. The flexibility of the antenna is provided by the use of the silicon elastomer. It has been shown that the power radiated into an artificial head phantom improved by almost 160% as compared to antenna without impedance matching layer. Moreover, the SAR level is 0.0286 W/kg when 1 mW of power is transmitted, which is well below the limit set by the regulation. This makes the antenna suitable for wearable biomedical applications due to its wideband characteristic and improved power penetration into human head.

Role of oxygen vacancy on rapid densification and giant dielectric properties of flash sintered Ca2+ and Ta5+ co-doped TiO2 ceramics

(Ca, Ta) co-doped TiO2 ceramics were successfully prepared using flash sintering technology, and the effects of oxygen vacancies on the rapid densification and giant dielectric properties were studied. The results suggest that the maximum volume fraction of oxygen vacancies in flash-sintered samples is approximately 10%. Oxygen vacancies decrease the barrier energy level of atomic diffusion and provide convenient diffusion channels, resulting in rapid densification of the sample within 24 min at 1100 °C. All flash-sintered samples exhibit high relative density, exceeding 95%. Oxygen vacancies promote the electron-pinning defect dipole effect at low temperatures. As the temperature increases, carriers such as oxygen vacancies move to the grain boundary, forming an internal barrier layer capacitance effect. The optical dielectric constant reaches 7.25 × 104, and the dielectric loss drops to 0.09. Oxygen vacancy play an important role in both flash sintering technology and the giant dielectric properties of co-doped TiO2 ceramics.

Learning Electronic Polarizations in Aqueous Systems.

The polarization of periodically repeating systems is a discontinuous function of the atomic positions, a fact which seems at first to stymie attempts at their statistical learning. Two approaches to build models for bulk polarizations are compared: one in which a simple point charge model is used to preprocess the raw polarization to give a learning target that is a smooth function of atomic positions and the total polarization is learned as a sum of atom-centered dipoles and one in which instead the average position of Wannier centers around atoms is predicted. For a range of bulk aqueous systems, both of these methods perform perform comparatively well, with the former being slightly better but often requiring an extra effort to find a suitable point charge model. As a challenging test, we also analyze the performance of the models at the air-water interface. In this case, while the Wannier center approach delivers accurate predictions without further modifications, the preprocessing method requires augmentation with information from isolated water molecules to reach similar accuracy. Finally, we present a simple protocol to preprocess the polarizations in a data-driven way using a small number of derivatives calculated at a much lower level of theory, thus overcoming the need to find point charge models without appreciably increasing the computation cost. We believe that the training strategies presented here help the construction of accurate polarization models required for the study of the dielectric properties of realistic complex bulk systems and interfaces with ab initio accuracy.

Effect of tin doping on the structural, optical, and dielectric properties of unintentionally β-Ga2O3 single crystal

Abstract This paper studied the structural, optical, electrical, and dielectric properties of the undoped and 0.05 mol% Sn-doped β-Ga2O3 single crystals through comprehensive characterizations by X-ray diffraction (XRD), Raman scattering, Optical transmittance spectroscopy, X-ray photoelectron spectroscopy (XPS), Ultraviolet photoelectron (UPS) spectroscopy, and dielectric measurements. The optical bandgap decreases as Sn content increases. The results of XPS showed that Sn atoms were successfully added to the host β-Ga2O3 crystal. The position of the Fermi level of 0.05 mol% Sn-doped β-Ga2O3 is calculated to be 2.56 eV above the valence band and 1.85 eV beneath the conduction band. Also, the computed value of the work function of 0.05% mole Sn-doped β-Ga2O3 is 4.53 eV. AC conductivity increases, while dielectric loss and dielectric constant decrease with increasing frequency.

Essential oil-derived robust and heat-resistant polybenzoxazine-POSS composites as low dielectric matrixes

Polybenzoxazines (PBozs) are regarded as prime candidates as low dielectric matrixes. However, the fabrication of high-performance PBozs that combines low dielectric property with high thermal stability using sustainable resources as the starting raw materials remains a significant challenge. In this work, we constructed a novel main-chain benzoxazine (Boz) oligomer from natural essential oil-derived compounds (eugenol and p-menthane diamine) to fulfill the principles of green chemistry. To enhance their low dielectric properties, polar C-Si unit on the main-chain and cellular structure of polyoctahedral silsesquioxanes (POSS) as the cross-linkers were introduced in PBoz-POSS composites. The obtained composites demonstrated excellent thermal stability, mechanical property, and with remarkable low dielectric constants. Coupled with their exceptional hydrophobicity and heat resistance, these materials are promising matrixes for low dielectric application in contemporary electronic industries.

Novel in situ synthesis of copper oxide nanoparticles in epoxy network: kinetics, composite mechanical and dielectric properties

Novel in situ synthesis of copper oxide nanoparticles in epoxy network: kinetics, composite mechanical and dielectric properties

Influence of proteins on the dielectric characteristics of 5CB and 8CB liquid crystals

ABSTRACT In this paper, we study the influence of the protein Bovine Serum Albumin (BSA) on the dielectric properties of liquid crystals (LCs) such as 4-cyano-4-pentyl biphenyl (5CB) and Octyl-4-biphenylcarbonitrile (8CB). Studying the effect of proteins on the dielectric properties of LC is essential for both fundamental research and practical applications in material science, biomedical engineering, biotechnology, and optoelectronic devices. It helps understand the protein behaviour on the surface of LCs, which offers an opportunity to develop novel sensing platforms. A polarising optical microscope (POM) was used to examine the correlation between textures formed by LCs interacting with different concentrations of BSA. In the dielectric studies, dielectric parameters such as impedance (Z), real (Z’) and imaginary (Z’’) parts of the impedance, and the tangential loss (tan δ) were measured. The investigation involved analysing relaxation times using the collected data, revealing distinct behaviours between 5CB and 8CB liquid crystals. Bode and Nyquist’s plots were constructed and analysed to investigate the changes LCs undergo while interacting with BSA. An equivalent electrical circuit (EEC) was constructed using Bode and Nyquist data, from which circuit element values were successfully extracted. The results obtained from the POM studies and the interferences drawn from the EIS can help enhance the performance of protein-based liquid crystal devices.

Effect of Ni Substituted MgZrTa2O8 Ceramics on Sintering Characteristics and Microwave Dielectric Properties

Herein, Mg1−x Ni x ZrTa2O8 (x = 0, 0.1, 0.3, 0.5, 0.8, 1) ceramics are synthesized using a solid‐phase reaction method. Ni2+ replacing Mg2+ improves the drawback of high sintering temperature and poor temperature stability. The samples have the relative density above 95% at the optimal sintering temperature. The sintering temperature of Mg1−x Ni x ZrTa2O8 reduces from 1475 °C to 1400 °C. And single‐phase Mg1−x Ni x ZrTa2O8 ceramics with monoclinic wolframite structure are analyzed. According to the Rietveld refinement results, with the doping of Ni2+, the transformation of unit cell volume leads to the shift of the main peak in the XRD pattern to a higher angle in 0 ≤ x ≤ 0.3 and a lower angle in 0.5 ≤ x ≤ 1. The εr of Mg1−x Ni x ZrTa2O8 is comparable to MgZrTa2O8. At 1400 °C, the Q×f is increased from 10,598 GHz in the undoped sample to 43,041 GHz in Mg0.9Ni0.1ZrTa2O8 ceramic. The absolute values of τf of ceramic samples decrease with the excessive Ni2+. The desirable dielectric properties (εr = 20.79, Q×f = 43,041 GHz, τf = −33.04 ppm/°C) are obtained at 1400 °C. Ni substitution is effective for MgZrTa2O8 ceramic to optimize densification temperature and retain the high Q×f value.This article is protected by copyright. All rights reserved.

Controlling the physical properties of Ni1-xMnxFe2O4 multiferroic by the enhancement of ferroelectric phase through the increase of Mn content

The nanoparticles of the spinel ferrite system Ni1-xMnxFe2O4 with x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 were prepared using the auto combustion flash method technique, by using the nitrates as cations source and urea as a fuel agent for combustion. The XRD pattern validates the formation of cubic spinel structure of Ni1-xMnxFe2O4 nanoparticles and traces of hematite phase. By increasing the annealing temperature, the lattice parameter and crystallite size were increased. At various frequencies, the dielectric properties and initial permeability were measured as a function of temperature. The DC resistivity was found to have a linear relationship with temperature, with two regions and one break point at Curie temperature (TC). SEM and TEM analyses are used to investigate the morphology of the samples, as well as the size and shape of the crystallites. The samples' morphology revealed the formation of a uniform and spherical structural distribution. The material transfer to multiferroic at high Mn content accordingly the ferroelectric and ferrimagnetic properties appear, which give the ability of the material to become magnetoelectric material.

Efficient gradient heating-up approach for rapid growth of high-quality amorphous ZrO2 dielectric films

Abstract High-k oxide dielectric films are indispensable for low-power-consumption oxide thin-film transistors (TFTs) applied in advanced and portable electronics. However, high-quality oxide dielectric films prepared by solution process typically require sophisticated processes and long thermal annealing time, severely limiting both the throughput manufacturing and cost-effectiveness. In this study, the influence of different heating-up methods on the surface morphology and dielectric properties was systematically investigated. Gradient heating-up method could not only substantially improve the surface morphology and quality of high-k ZrO2 films but also efficiently shorten the annealing time. The gradient heating-up process was further designed on the basis of thermal behavior of the xerogel-like precursor, which successfully realize the preparation of high-quality ZrO2 films with an annealing time of 5 min (i.e. the efficiency of thermal treatment increased by about 89%). The ZrO 2 film presented excellent dielectric properties, including a low leakage current density of ~10−8 A/cm2 (at 2 MV/cm), a large areal capacitance of 169 nF/cm2 and a high dielectric constant of 20.41 (1 MHz). Furthermore, InSnZnO TFT based on the ZrO2 gate dielectrics shows an acceptable device performances, such as a high carrier mobility of 2.82 cm2/V s, a high on/off current ratio of ~105 and a low subthreshold swing of 0.19 V/decade at a low operation voltage of 5 V. This work provide a highly promising approach to fabricate high-quality solution-processed high-k oxide dielectric films employed for large-scale and low-power-consumption electronics.&amp;#xD;

Impact of zinc oxide on dielectric properties of forsterite coated titanium based medical implants

Zinc oxide-doped forsterite solutions are synthesized through the sol-gel approach by varying the weight percentage of zinc oxide. These solutions are then applied to titanium (Ti) substrates to form zinc oxide-doped forsterite coated Ti substrate samples using the dip-coating method. The structural and surface morphology analyses of the samples are conducted using x-ray Diffraction (XRD) and Scanning Electron Microscope (SEM). Dielectric properties, encompassing dielectric constant, dielectric loss, alternating current conductivity, loss tangent, and relaxation time are explored at room temperature over a frequency range of 200 MHz to 20 GHz utilizing a Vector Network Analyzer (VNA) setup. The impact of zinc oxide on the structure, morphology, and dielectric properties of the samples, particularly in medical implant applications, is extensively discussed. The results indicate that samples with a higher weight percentage of zinc oxide demonstrate superior dielectric characteristics.

Nanocomposite marvels: Miniaturized high bandwidth microstrip patch antenna for X-band applications

Zinc aluminate (ZnAl2O4) is widely recognized as a ceramic in high demand across various microwave applications. Furthermore, blending dielectric materials with ZnAl2O4 has demonstrated improvements in its dielectric properties, offering promising potential for advancing microstrip patch antenna technology. This paper presents the fabrication and characterization of a sol-gel composite nanoparticle consisting of titanium dioxide (TiO2) and zinc aluminate (ZnAl2O4) for use in a microstrip patch antenna designed for X-band applications. The composite nanoparticle, with a molecular composition of xTiO2(1-x)ZnAl2O4 where x = 8 %, was investigated using X-ray diffraction (XRD), revealing dominant peaks corresponding to ZnAl2O4 and TiO2 with a calculated crystallite size of 16.9 nm. Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FESEM), and energy dispersive spectroscopy (EDS) were employed to assess functional groups, morphology, and elemental composition of the nanoparticles. The dielectric properties of the nanoparticles, characterized by a dielectric permittivity of 20.2 and a dielectric loss of 0.19, were measured using an LCR meter. These nanoparticles were utilized to fabricate a prototype patch antenna, exhibiting promising performance in both simulated and measured results. The fabricated patch antenna operated at 8.51/8.49 GHz with a return loss (RL) of − 25.94/−19.97 dB, featuring an enhanced bandwidth of 2.62/2.87 GHz and a voltage standing wave ratio (VSWR) below 2. Additionally, the antenna demonstrated a gain of 2.14, directivity of 3.58, and radiation efficiency of 59.7 %, making it suitable for X-band applications.

Impact of ultraviolet aging on the composition and characteristics of multifunctional composite coatings

AbstractMultifunctional composite coatings exposed to environmental conditions are prone to aging and potential functional failure due to ultraviolet (UV) radiation. This study investigates the impact of UV radiation on the structure and properties of low infrared emissivity composite coatings, comprising ethylene propylene diene monomer (EPDM) as the matrix and antistatic carbon fiber (CF) and flaky floating aluminum powder as fillers. In addition to analyzing the photochemical degradation reactions of the composite coating under UV irradiation, the role of fillers in resisting UV aging is elucidated. The performance parameters examined include infrared (IR) emissivity, surface resistivity, mechanical properties, and dielectric properties. The results indicate that after UV aging, EPDM undergoes the most significant changes, leading to the formation of carbonyl groups. CFs experience mild UV aging and an increase in resistivity. Aluminum powder, on the other hand, remains largely unchanged after UV aging and its addition significantly reduces the UV aging rate of the composite coating, resulting in a low IR emissivity of as low as 0.2 after UV aging. Among them, Coating 4 exhibits the best overall performance after UV aging.Highlights The UV aging mechanism of EPDM and the role of fillers were revealed. The UV aging of the coating significantly reduced the infrared emissivity (Reduced from 0.5 to 0.2). Al powder effectively reduced the UV degradation rate of the coating by reflecting UV light. The properties of the double‐formulated coating perform best after UV aging.

Origin of Temperature Coefficient of Resonance Frequency in Rutile Ti1−xZrxO2 Microwave Ceramics

In this study, we report the effect of Zr4+ doping on the optical energy gap and microwave dielectric properties of rutile TiO2. Rietveld analysis explicitly confirmed that Zr4+ occupies the octahedral site, forming a single-phase tetragonal structure below the solubility limit (x &lt; 0.10). Notably, at x = 0.025, a significant enhancement in Q × fo was observed. This enhancement was attributed to the reduction in dielectric loss, associated with a decrease in oxygen vacancies and a lower concentration of Ti3+ paramagnetic centers. This conclusion was supported by Raman and electron paramagnetic resonance spectroscopy, respectively. The origin of high τf in rutile Ti1−xZrxO2 is explained on the basis of the octahedral distortion/tetragonality ratio, covalency, and bond strength.

Dielectric Characterization of Solutions of Galactomannan Extracted from Adenanthera pavonina L.: Effects of Purification and Ethanol Concentration

Galactomannans are polysaccharides obtained from legume seed extraction. They present a chemical structure consisting of D-mannose chains linked by glycosidic bonds and galactose branches. The main focus lies in their use as thickeners in the food industry, aimed at improving the dielectric properties of food during heating processes within the radiofrequency and microwave ranges. In this work, the prepared galactomannan samples were electrically analyzed through impedance spectroscopy, which is a powerful physical technique. From the experimental measurements, the dielectric permittivity and loss tangent of the galactomannan solutions were analyzed and the electrical modulus formalism was used to study the dielectric relaxations. Crude galactomannans exhibited higher values of permittivity, conductivity, and losses compared to purified galactomannans. Increasing ethanol concentration in galactomannan purification causes an increase in the permittivity and conductivity of galactomannan solutions. In a 1% solution, at 1 kHz, the permittivity increased from 378.56 to 538.09, while in the 2% solution, this increase was from 656.22 to 1103.24. Regarding the conductivity, at the same frequency, the increase was from 1.6 × 10−3 to 3.3 × 10−3 Ω−1m−1 and from 2.9 × 10−3 to 5.5 × 10−3 Ω−1m−1, respectively. The rise of the ethanol concentration in galactomannan purification led to a decrease in the relaxation time, from 448.56 to 159.15 μs and from 224.81 to 89.50 μs in the solution with 1 and 2%, respectively. The results suggest that galactomannan from Adenanthera pavonina L. has potential for use in the food industry.

Environmental benefits of microwave-assisted self-healing technology for pavements - A Life Cycle Assessment comparative study

The maintenance and rehabilitation of roads is becoming a key challenge in the pavement industry to decrease the consumption of natural resources. Microwave-assisted self-healing technology extends the life-service of asphalt pavements for roads reducing the need for fossil fuels over its lifespan and saving the use of natural resources. This technique takes advantage of the thermoplastic and dielectric properties of asphalt mixtures that allows cracks to be closed, hence, heal and restore the asphalt mixtures mechanical behaviour without implementing more invasive traditional maintenance operations like milling and replacing the pavement. A Life-Cycle Assessment was carried out to determine the potential environmental benefits of using this technology quantifying its potential environmental impacts. Different scenarios in which the heating energy and the addition of slag varies has been evaluated and compared with a conventional road. Results shows that this technology could decrease a significant number of environmental impacts over the lifecycle.