Stable Dielectric Properties Research Articles

Wide temperature range of stable dielectric properties in relaxor BaTiO3-based ceramics by co-doping synergistic engineering

Capacitor with good temperature stability is widely used in electronic devices. However, temperature stability suffers from limited improvement through traditional doping. In this study, the wide-temperature stability of BaTiO3-based ceramics is achieved by B site co-doping synergistic engineering. Element Ca is added to the ceramic to reduce the Curie temperature by optimizing the crystal structure, and subsequently, Nb is introduced to further suppress and broaden the dielectric peak by forming the core-shell structure. As excepted, 3%Nb doped 0.8BTC-0.2BMT ceramics possessed a temperature coefficient of capacitance at 25 °C (TCC25°C) being less than ±15% in the wide temperature range of −55 °C–180 °C, and an excellent energy storage density of 1.13 J cm−3. High dielectric constant (εr = 1076) and low dielectric loss (tanδ ∼ 0.06) meet the higher standards of the current capacitor industry, such as X8R requirements. This study provides a theoretical foundation for the design and preparation of high-performance dielectric materials.

Polymer-derived SiOC reinforced with core–shell nanophase structure of ZrB2/ZrO2 for excellent and stable high-temperature microwave absorption (up to 900 °C)

Microwave absorbing materials for high-temperature harsh environments are highly desirable for aerodynamically heated parts and engine combustion induced hot spots of aircrafts. This study reports ceramic composites with excellent and stable high-temperature microwave absorption in air, which are made of polymer-derived SiOC reinforced with core–shell nanophase structure of ZrB2/ZrO2. The fabricated ceramic composites have a crystallized t-ZrO2 interface between ZrB2 and SiOC domains. The ceramic composites exhibit stable dielectric properties, which are relatively insensitive to temperature change from room temperature to 900 °C. The return loss exceeds − 10 dB, especially between 28 and 40 GHz, at the elevated temperatures. The stable high-temperature electromagnetic (EM) absorption properties are attributed to the stable dielectric and electrical properties induced by the core–shell nanophase structure of ZrB2/ZrO2. Crystallized t-ZrO2 serve as nanoscale dielectric interfaces between ZrB2 and SiOC, which are favorable for EM wave introduction for enhancing polarization loss and absorption. Existence of t-ZrO2 interface also changes the temperature-dependent DC conductivity of ZrB2/SiOC ceramic composites when compared to that of ZrB2 and SiOC alone. Experimental results from thermomechanical, jet flow, thermal shock, and water vapor tests demonstrate that the developed ceramic composites have high stability in harsh environments, and can be used as high-temperature wide-band microwave absorbing structural materials.

Fractal analysis and ferroelectric properties of Nd(Zn1 2Ti1 2)O3(NZT)

The challenges in productivity of satellite mobile devices are growing rapidly to overcome the question of miniaturization. The intention is to supply the electrical and microwave properties of materials by discovering their outstanding electronic properties. Neodymium Zinc Titanate (NZT) can be a promising ferroelectric material due to its stable dielectric and microwave properties. The grain size and shape of NZT have a strong influence on overall material performances. Therefore, shape, reconstruction and property of the coming compound take an important part and can be predicted before being utilized in the devices. The significant of this research is to define ferroelectric properties of NZT and to characterize it by using Fractal Nature Analysis (FNA). FNA is a powerful mathematical technique that could be applied to improve the grain shape and interface reconstruction. The fractal structure is identified by its self-similarity. The self-similarity of an object means a repetition of shapes in smaller scales. A measure of this structure is computed using the Hausdorff dimension. It is for the first time in this investigation the Fractal analysis method is applied for the microwave materials microstructure reconstruction which makes this research an innovative work and will open the door for Curie–Weiss law fractal correction. In connection to our previous research for dielectric properties fractalization, we had some characterization and reconstruction data which include the Hausdorff dimension (HD).

Structural design and properties of crystalline polyarylene ether nitrile copolymer

In this paper, the bisphenol A segment is introduced into the molecular chain by molecular design to avoid high molecular weight crystalline PEN, while having good crystallization ability due to the internal plasticization of the bisphenol A segment. Three PEN copolymers with different structures were synthesized by adjusting the structures of the crystalline segments. Firstly, the crystallization ability, thermal and mechanical properties of PEN with different structures were studied. Then, for the hydroquinone/bisphenol A copolymerized PEN with a tensile strength of 121.7 MPa, an elongation at break of 9.94%, stable dielectric properties and good crystallization ability, the effects of hot-pressing conditions on the properties were investigated. The results show that temperature and pressure have a synergistic effect while the temperature factor dominates. Finally, the best processing conditions were confirmed. This is a guideline for the study of semi-crystalline PEN and provides a theoretical basis for application.

Ultra-low dielectric loss and high thermal stability achieved by hierarchical microcapacitor structure in nanocomposites via surface topological modulation

The urgent need for miniaturized high-reliable electronic devices requires polymer film capacitors with stable dielectric properties under extreme environments. The traditional surface coating structure can barely boost the performance of energy storage dielectric materials, which are confronted with a high dielectric loss and low breakdown strength. Herein, reduced polyaniline (R-PANI) grows in the form of vertically oriented nanorods on the surface of porous carbon embedded with ultrafine BaTiO3, resulting in a hierarchical microcapacitor structure. The surface topology modulation of R-PANI dramatically increases the aspect ratio of the nanoparticles perpendicular to the external electric field, thus suppressing the leakage current and restraining the subsequent dielectric loss of the nanocomposite. The nanocomposite filled with 8 wt% C@BT@R-PANI exhibits a breakdown strength of 316.50 MV/m, a high dielectric constant of 66.8, and an ultra-low dielectric loss of 0.00663 at 1 kHz. Under a moderate electric field of 150 MV/m, the energy density increases to 2.75 J/cm3 and the charge-discharge efficiency (η) reaches 80.09%. In addition, the nanocomposite exhibits an excellent dielectric-thermal stability in the range of 30–150 °C, making it a potential candidate for high-temperature dielectric materials.

Tuning of dielectric and magnetic performance of graphene oxide via defect regulation by metal oxide nanoparticle for high temperature device

Graphene oxide (GO) is used as a dielectric material in device applications. However, relatively low dielectric constant, high loss, and low working temperature significantly constrain their widespread application. The electrical and magnetic properties of GO can be regulated by using different fillers. Here, we try to regulate the defects of Zinc Oxide ( ZnO) by doping Fe ions and then make composites with GO (GO@ZnO-Fe) towards the increment of the dielectric constant and reduce the loss of GO. The morphology and microstructure characterization of GO composites ensured the enhancement of interlayer cross-links and lateral bridging between the edges of adjacent GO sheets in the presence of ZnO and ZnO-Fe nanofillers. The layered structure of GO produced charge accumulation based on the Maxwell- Wagner (MW) polarization, and after compositing, with ZnO nanofillers, the dielectric constant of GO increases from 350 to 470. But the use of Fe doped ZnO nanofiller increased the maximum dielectric constant to∼ 2240 due to the synergic effect of ZnO and Fe ions. At the same time, the loss is also decreased simultaneously with increasing Fe doping (tanδ =96 for GO and 30 for composite). The dielectric surge occurs at different high temperatures for different composites of GO, and before the surge, the dielectric constants are thermally stable. The conductivity and magnetic properties of the composites increases compared to GO due to the presence of Fe2+/Fe3+ ions. The increase of Fe doping composites displayed thermally stable dielectric properties with a high dielectric constant (7100) and low loss over a broad temperature. Our work demonstrates an efficient method of tuning the dielectric, conductive and magnetic properties of GO-based materials that hold great potential in high-temperature electronic applications.

Tuning high-temperature dielectric properties of poly ether ether ketone by using self-crosslinkable polyetherimide and nanoparticles

Polymer dielectric materials operating at high temperatures are widely needed for advanced electrical and electronic systems. However, currently commercial polymer dielectrics are limited to relatively low operating temperatures. Here, a series of polyether ether ketone (PEEK)-based blends with self-crosslinkable polyetherimide (c-PEI) has been prepared as high temperature dielectrics by melt blending. The obtained polymer blends maintain stable dielectric properties over a wide frequency and temperature range. At 160 °C，the dissipation factor of the blend film is only 0.0019 which is only 14% of the pristine PEEK. Crosslinked networks in polymer blends could efficiently restrict the movement of polymer segments which suppress the dielectric loss and enhance high temperature performance. Furthermore, the introducing of Al2O3 improve the dielectric constant of the polymer blend, which compensated for the decreased dielectric constant due to crosslinking. In addition, the c-PEI/PEEK blends could be produced by industrial-grade continuous production process. This work presents a feasible strategy to large-scale fabrication of high-temperature dielectric materials by melt blending with self-crosslinkable polymers.

Crosslinking Methodology for Imidazole-Grafted Silicone Elastomers Allowing for Dielectric Elastomers Operated at Low Electrical Fields with High Strains.

For improved actuation at low voltages of dielectric elastomers, a high dielectric permittivity has been targeted for several years but most successful methods then either increase the stiffness of the elastomer and/or introduce notable losses of both mechanical and dielectric nature. For polydimethylsiloxane (PDMS)-based elastomers, most high-permittivity moieties inhibit the sensitive platinum catalyst used in the addition curing scheme. In contrast to the classical addition curing pathway to prepare PDMS elastomers, here, an alternative strategy is reported to prepare PDMS elastomers via the crosslinking reaction between multifunctional imidazole-grafted PDMS with difunctional bis(1-ethylene-imidazole-3-ium) bromide ionic liquid (bis-IL). The prepared IL-elastomer entails uniformly dispersed IL and presents stable mechanical and dielectric properties due to the covalent nature of the crosslinking as opposed to previously reported physical mixing in of ILs. The relative permittivity was improved up to 200% by including the bis-IL in the elastomer, and Young's modulus was around 0.04 MPa. As a result of the excellent combination of properties, the dielectric actuator developed exhibits an area strain of 20% at 15 V/μm. The novel strategy to prepare PDMS elastomers provides a new paradigm for achieving high-performance dielectric elastomer actuators by a simple methodology.

Temperature stable dielectric properties of Mg2TiO4–MgTiO3–CaTiO3 Ceramics Over a Wide Temperature range

The zero resonant frequency temperature coefficient (τf) of microwave dielectric ceramics (MWDCs) at high and low temperature have attracted great attention in the development of microwave communication equipment. In this work, the Mg2TiO4–MgTiO3–CaTiO3 (MMC) ceramics with meeting the application requirements of 5G communication were prepared by traditional solid-phase sintering after investigating the relationship among phase compositions of xMg2TiO4-(0.931-x)MgTiO3-0.069CaTiO3 and 0.34Mg2TiO4-0.591MgTiO3-yCaTiO3, sintering process, and dielectric properties in detail. The results show that the dielectric properties of MMC ceramics are strongly affected by the phase relative contents of MgTiO3, Mg2TiO4 and CaTiO3. For instance, MMC ceramics with approximate τf = 0 is contributed by mutual compensation of Mg2TiO4 and MgTiO3, in which the Mg2TiO4 phase plays an important role in decreasing the τf value; and the increase of CaTiO3 will greatly increase the εr value for MMC ceramics, while has a negative effect in the Q × f value. After three-phase regulation, the 0.32Mg2TiO4-0.611MgTiO3-0.069CaTiO3 microwave dielectric ceramic has a better dielectric temperature stability, associated with dielectric properties of εr = 19.7, Q × f = 55,400 GHz (at 8.43 GHz), τf- = 4.5 ppm/°C (−40 °C–25 °C), and τf+ = −5.1 ppm/°C (25 °C–90 °C).

Dielectric and energy storage properties of all-organic sandwich-structured films used for high-temperature film capacitors

Dielectric polymers with ultrahigh power density are widely utilized in the fields of modern electronics and power systems. This article proposes the all-organic sandwich-structured films with ferroelectric polymer poly (vinylidene fluoride-hexafluoropropylene) and linear polymer poly (ethylene terephthalate) (PET) as the energy storage dielectrics for film capacitors. The morphological characterizations, thermal, dielectric, and energy storage performances have been investigated to evaluate the comprehensive properties of the sandwich-structured films. Excellent interlaminar interfaces are observed between poly(vinylidene fluoride-hexafluoropropylene) and PET layers. Compared with pure PET films, the sandwich-structured films exhibit improved thermal stability and dielectric constant, but some degradation in loss factor and breakdown strength. With the increase of ambient temperature, the sandwich-structured films still show improved and stable dielectric properties and insulating strength up to 125 °C. The sandwiched all-organic film shows an improved energy density (Ud) as high as 8.2 J/cm3 and concurrently an immense charge-discharge efficiency of 86.4%. This strategy offers a feasible idea to enhance the thermal, dielectric, and energy storage capability of dielectric films with a layered architecture, which facilitates the evolution of flexible film capacitors.

High energy storage density and temperature stable dielectric properties of (1-x)Bi0.5(Na0.82K0.18)0.5Ti0.99(Y0.5Nb0.5)0.01O3-xNaNbO3 ceramics

The development of lead-free ceramics with high energy storage density is critical due to the human health and environmental hazards of lead and the demand to miniaturize and integrate electronic devices. Nevertheless, the high applied electric field limits their use in integrated circuits. In this work, (1-x) Bi0.5(Na0.82K0.18)0.5Ti0.99(Y0.5Nb0.5)0.01O3-xNaNbO3 (BNKTYN-100xNN) ceramics were prepared, and excellent energy storage properties were obtained. It has revealed that NaNbO3 dopant reduces remanent polarization and increases relaxor degree. BNKTYN-9NN ceramics has high energy storage density (Wrec =1.6 J/cm3) and responsivity (ξ = Wrec/E = 145.5 J/(kV•m2)) under 110 kV/cm. Meanwhile, good temperature stability (20–120 °C) and fatigue resistance (105 cycles) were also obtained in BNKTYN-9NN ceramics. In addition, doping NaNbO3 suppresses the dielectric anomaly peak, and BNKTYN-9NN ceramics has excellent temperature-stable dielectric permittivity from 53° to 447°C. These results suggest that BNKTYN-100xNN ceramics are promising for energy storage equipment.

Morphology-Controlled Fabrication Strategy of Hollow Mesoporous Carbon Spheres@f-Fe2O3 for Microwave Absorption and Infrared Stealth.

The design and development of radar--infrared compatible stealth materials are challenging in the field of broadband absorption due to the contradiction of stealth requirements and mechanisms in different frequency bands. However, hollow structures show great promise for multispectral stealth because they can lengthen the attenuation path of electromagnetic waves (EMWs) for microwave absorption, interrupt the continuity of heat-transport channels, and lower the thermal conductivity to realize infrared stealth. Here, a new morphological fabrication strategy has been developed to efficiently prepare compatible stealth nanomaterials. In a specific hydrothermal process, the confined growth of flake α-Fe2O3 (f-Fe2O3) outside of hollow mesoporous carbon spheres (HMCS) is achieved using NH3·H2O as a shape-controlled reagent. The introduction of f-Fe2O3 helps to lower infrared emissivity and improve high-frequency impedance matching, which depends on the stable dielectric property of the specific flake shape. Moreover, the size of f-Fe2O3 can be regulated by changing the constituent proportion in the hydrothermal suspension to obtain excellent performance. The minimum reflection loss (RL) of the HMCS@f-Fe2O3-6 composite is -34.16 dB at 2.4 mm, and the effective absorption bandwidth (EAB) reaches 4.8 GHz. Furthermore, the lowest emissivities of the HMCS@f-Fe2O3-6-20 wt %/polyetherimide (PEI) film in the 3-5 and 8-14 μm infrared wavebands are 0.212 and 0.508, respectively. These discoveries may pave the way for the development of radar-infrared compatible stealth materials from the perspective of microstructural design.

Enhancing high-frequency dielectric and mechanical properties of SiO2/PTFE composites from the interface fluorination

To achieve polytetrafluoroethylene (PTFE)-based composites for high-frequency applications with low dielectric constant, low dielectric loss tangent and low coefficient of thermal expansion (CTE), a novel pentafluorostyrene (PFS) interface modifier was used to achieve excellent performance for SiO2/PTFE composite materials. The effects of PFS modification on the microstructure, dielectric properties and thermal properties of SiO2/PTFE composites were investigated. It is found that the use of PFS greatly improves the interfacial compatibility of the composites, on the one hand the dielectric properties are effectively improved, on the other hand the steric resistance of PTFE matrix is enhanced and the CTE is reduced. When the PFS content of 5 wt%, the CTE of SiO2/PTFE is reduced to 86 ppm/°C. The dielectric loss of the composites varies from 0.71 × 10−3 to 1.53 × 10−3 at frequencies from 5 to 40 GHz. The composites also show stable dielectric properties across the applied temperature (0–150 °C). Benefiting from the high density and uniform microstructure of the PFS-modified composite, enabling it to withstand higher frequency and temperature applications.

Broad sintering temperature range and stable microwave dielectric properties of Mg2TiO4–CeO2 composite ceramics

There has been extensive research on microwave dielectric materials considering their application in 5G and 6G communication technologies. In this study, the sintering temperature range of Mg2TiO4–CeO2 (MT-C) ceramics was broadened using a composite of CeO2 and Mg2TiO4 ceramics, and their microwave dielectric performance was stabilized. Low-loss MT-C composite ceramics were prepared using the solid-phase reaction method, and their microwave dielectric properties, microscopic morphologies, and phase structures were investigated. The proposed MT-C ceramics contained Mg2TiO4 and CeO2 phases; their average grain size was maintained at 2–4 μm in the sintering temperature range of 1275–1425 °C, and the samples were uniformly dense without porosity. The cross-distribution of Mg2TiO4 and CeO2 grains in the samples inhibited the growth of ceramic grains, providing uniform and dense surfaces. The dielectric loss of MT-C ceramics remained constant in the temperature range of 1300–1425 °C at 9 × 10−4 (8.45 ≤ f ≤ 8.75 GHz). As opposed to the base material, MT-C ceramics are advantageous owing to their wide sintering temperature range and the stable microwave dielectric properties, and there are suitable substrate materials for further industrial applications.

ЭЛЕКТРОИЗОЛЯЦИОННАЯ ТЕРМОСТОЙКАЯ БЕССВИНЦОВАЯ ЭМАЛЬ ДЛЯ ЗАЩИТЫ ЭЛЕМЕНТОВ РАДИОЭЛЕКТРОННОЙ АППАРАТУРЫ

In present work electrical insulating coatings based on BaO–B2O3–SiO2 glass-forming system for use in electronic circuits on a metal substrate were investigated. The synthesized compositions in terms of chemical resistance belong to the class of stabilized glasses. The tests were showed that the experimental compositions significantly exceed the known coatings in terms of dielectric properties. Positive data on the stability of dielectric properties and on the quality of the defect-free coating layer were obtained.

Interfacial crosslinking enabled super-engineering polymer-based composites with ultra-stable dielectric properties beyond 350 °C

The polymer composites exhibiting reliable dielectric properties at high temperatures (>300 °C) are urgently required for cutting-edge electronic applications. In the present work, an interfacial reactive agent named 4-aminophxylphthalonitrile (4-APN), was covalently modified on the surface of the multiwalled carbon nanotubes (MWCNTs) to prepare the nitrile-functionalized multiwalled carbon nanotubes (MWCNTs-CN), which was further incorporated into the phthalonitrile end-capped polyarylene ether nitrile (PEN-ph) matrix to fabricate the high-temperature resistant PEN-ph/MWCNTs-CN composites. It was found that through facile heat-treatment, the crosslinked PEN-ph/MWCNTs-CN (7 wt%) composites exhibited a high glass transition temperature of 430 °C and stable dielectric properties (dielectric constant of 22.08 at 1 kHz) up to 350 °C. Meanwhile, the energy storage density of the composite membrane increased from 0.59 to 2.18 J/cm3 with the increase of filler content, showing an increase of 269.5%. The nitrile-functionalization of MWCNTs can not only improve the interfacial compatibility between MWCNTs-CN and PEN-ph matrix resin but also make MWCNTs-CN play a role as a crosslinker to further improve the mechanical, thermal, and dielectric properties of the composites. Therefore, the PEN-ph/MWCNTs-CN composites prepared by interfacial crosslinking reaction in this work will serve as the candidate materials for high-temperature-resistant energy storage applications.

Chemically Tunable Organic Dielectric Layer on an Oxide TFT: Poly(p-xylylene) Derivatives.

Inorganic materials such as SiOx and SiNx are commonly used as dielectric layers in thin-film transistors (TFTs), but recent advancements in TFT devices, such as inclusion in flexible electronics, require the development of novel types of dielectric layers. In this study, CVD-deposited poly(p-xylylene) (PPx)-based polymers were evaluated as alternative dielectric layers. CVD-deposited PPx can produce thin, conformal, and pinhole-free polymer layers on various surfaces, including oxides and metals, without interfacial defects. Three types of commercial polymers were successfully deposited on various substrates and exhibited stable dielectric properties under frequency and voltage sweeps. Additionally, TFTs with PPx as a dielectric material and an oxide semiconductor exhibited excellent device performance; a mobility as high as 22.72 cm2/(V s), which is the highest value among organic gate dielectric TFTs, to the best of our knowledge. Because of the low-temperature deposition process and its unprecedented mechanical flexibility, TFTs with CVD-deposited PPx were successfully fabricated on a flexible plastic substrate, exhibiting excellent durability over 10000 bending cycles. Finally, a custom-synthesized functionalized PPx was introduced into top-gated TFTs, demonstrating the possibility for expanding this concept to a wide range of chemistries with tunable gate dielectric layers.

Compositional modulation and annealing treatment in BaTiO3 to simultaneously achieve colossal permittivity, low dielectric loss, and high thermal stability

Holmium doped BaTiO3 ceramics were prepared by a solid-state reaction. Colossal dielectric permittivity (≥105) and a very low loss tangent (<1.5%) at 10 kHz were achieved. Furthermore, the ceramics exhibit excellent temperature stability with a broad operating temperature range (25–400 °C). The evolution of the concentrations of oxygen vacancies and reduced Ti3+ was estimated by the XPS. Defect dipole complexes, coupled between the negatively and positively charged defects, are responsible for the observed huge dielectric permittivity. Temperature dependence of dc conductivity demonstrates that the stability of the defect dipole complexes matches the temperature range of stable dielectric properties. The result bridges a relationship between defect dipoles and dielectric behavior to understand the huge permittivity response and low loss mechanism.

High temperature insensitive ultra-thin electromagnetic metasurface based on ytterbium monosilicate ceramic coating

In this article, homogeneous multi-functional materials and artificially design method are proposed to design ultra-thin metasurfaces, which broaden the application over a wide range of temperatures due to their excellent mechanically-thermally stable structure and electromagnetic functional performance. Ideal environmental barrier coating material of ytterbium monosilicate (Yb2SiO5) possesses stable dielectric property over a wide temperature and frequency range. As a thermal corrosion resistant coating, NiCrAlY possesses excellent conductivity at high temperatures. These two materials are selected as substrate and conductive units to composite temperature insensitive ultra-thin refractory metasurface coating (RMC) for wideband radar cross section (RCS) reduction. Three types of RMC patterns are discussed, namely chessboard, staggered, and random. The prototype of staggered pattern was prepared using atmospheric plasma spraying (APS) technique. Both the simulated and experimental results indicated that RCS is reduced remarkably in a wideband frequency, as well as demonstrated stable reduction performance over a broad range of temperatures. Along with a protective layer of Yb2SiO5, only a thickness of 1.4 mm is required. The protective layer is employed to isolate the contact between the structural layer and the outside environment, which can significantly increase the service life of the metasurface. This work brings bright prospects for various kind of metasurfaces in practical high temperature applications and significantly enriches the research of metasurfaces.

Phase equilibria and microwave dielectric properties in the ternary La2O3–TiO2–Nb2O5 system

High-temperature phase relations in the La2O3–TiO2–Nb2O5 ternary system were investigated at 1290 °C using SEM, EDS and XRD, and a subsolidus phase equilibrium diagram was constructed. It was demonstrated that the addition of the La1/3NbO3 to the La2O3:3TiO2 mixture completely stabilizes a perovskite-La2/3TiO3 compound, which is otherwise not stable at stoichiometric composition. On the other hand, a mixture La2O3:TiO2 =1:3 dissolves in La1/3NbO3 up to 15 mol% TiO2. Moreover, a newly defined composition of compound La30Ti16Nb4O87 formed in the La2O3-rich part of the system and a solid solution La3Ti5Nb10O39.5–La2Ti2Nb8O27 were proposed. In the binary subsystem LaTiNbO6-La0.462Ti0.386Nb0.614O3, the components exhibit opposite temperature dependence of resonant frequency in the microwave frequency range. Thus, the dielectric properties of the prepared ceramics can be tailored by varying the component concentration and thermally stable dielectric properties can be achieved for a composition with a LaTiNbO6/La0.462Ti0.386Nb0.614O3 molar ratio of 0.27.