Dielectric and piezoelectric properties of(Li,Ce) modified NaBi_5Ti_5O_(18) composite ceramics

Nominal （Li0.5Ce0.5）x（Na0.5Bi0.5）（1-x）Na0.5Bi4.5Ti5O18 composite ceramics were fabricated using conventional solid-state reaction method. The coexistence of bismuth layer-structured phase and perovskite phase was determined in these ceramics using XRD technique. At room temperature, the x=0.11 sample showed the largest piezoelectric constant, d33, of about 26.5 pC/N and the largest electromechanical coupling factor, kt, of about 30%. Even after annealing at 500 ℃, the value of d33 was still about 19 pC/N, in x=0.08-0.11 samples. Moreover these composite ceramics showed low temperature coefficients of dielectric constant and high electrical resistivity in the temperature region of 450-550 ℃. These results indicated that （Li, Ce） modified NaBi5Ti5O18 composite ceramics were promising piezoelectric materials for high-temperature applications.

Composite Materials Damage Modeling Based on Dielectric Properties

Composite materials, by nature, are universally dielectric. The distribution of the phases, including voids and cracks, has a major influence on the dielectric properties of the composite materials. The dielectric relaxation behavior measured by Broadband Dielectric Spectroscopy (BbDS) is often caused by interfacial polarization, which is known as Maxwell-Wagner-Sillars polarization that develops because of the heterogeneity of the composite materials. A prominent mechanism in the low frequency range is driven by charge accumulation at the interphases between different constituent phases. In our previous work, we observed in-situ changes in dielectric behavior during static tensile testing, and also studied the effects of applied mechanical and ambient environments on composite material damage states based on the evaluation of dielectric spectral analysis parameters. In the present work, a two dimensional conformal computational model was developed using a COMSOL™multi-physics module to interpret the effective dielectric behavior of the resulting composite as a function of applied frequency spectra, especially the effects of volume fraction, the distribution of the defects inside of the material volume, and the influence of the permittivity and Ohmic conductivity of the host materials and defects.

The Effect of γ-Radiations on Dielectric Properties of Composite Materials PE + x vol% TlGaSe₂

The purpose of the paper is to study the effect of gamma irradiation on the temperature dependence of the dielectric constant and dielectric loss (tanδ) of composite materials PE + x vol% (0≤ x ≤ 10). Measurements are carried out with an alternating current at a frequency of 1 kHz using the measuring bridge E-20. Measurements are carried out at temperature range 300 - 450 K, irradiated at doses of 50, 100 and 150 kGy. It is revealed that in all irradiated samples with increasing volumetric filler content increase the dielectric characteristics of composites PE + x vol%. TlGaSe2. Temperature variation of the dielectric parameters, after gamma irradiation are the result of occurring in the electron-ion and polarization at the interface of the matrix polymer with filler of TlGaSe2.

Preparation and Characterization of Multi Shape ZnO/PVDF Composite Materials

Two different morphologies of ZnO（lotus-shaped, rod-shaped） and ZnO/PVDF composite materials were prepared. The morphologies of ZnO and composite materials were characterized by scanning electron microscopy（SEM） and transmission electron microscopy（TEM）. Fourier transform infrared spectroscopy（FT-IR）, thermal gravimetry（TG）, and X-ray diffraction（XRD） were also used to characterize the chemical structures and phase composites of ZnO and ZnO/PVDF composite materials. Breakdown voltage, dielectric constant and dielectric loss of ZnO/PVDF composite materials were also tested. Microstructure analysis showed that ZnO nanoparticles dispersed uniformly in the matrix. And the dielectric constant expresses a significantly improvement while the dielectric loss and breakdown voltage expresses no significant change. Moreover, dielectric constant keeps an improvement tendency with increasing content of ZnO.

Some Factors Influencing the Dielectric Properties of Natural Rubber Composites Containing Different Carbon Nanostructures

Natural rubber based composites containing different carbon nanofillers (fullerenes, carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs)) at different concentrations have been prepared. Their dielectric properties (dielectric permittivity, dielectric loss) have been studied in the 1 - 12 GHz frequency range. Some factors (electromagnetic field frequency, fillers concentration, fillers intrinsic structure) influencing the dielectric behavior of the composites have been investigated. The dielectric properties of the developed natural rubber composites containing conductive fillers (fullerenes, CNTs, GNPs) indicate that these composites can be used as broadband microwave absorbing materials.

Effects of Content of Chopped Glass Fibers on the Properties of Silica Filled PTFE Composites

In this work, the polytetrafluoroethylene (PTFE)-based composite substrates were manufactured by mixing, calendering, hot-pressing sintering. The composition of all the samples was PTFE, SiO2 and chopped E-glass fibers. The effects of content of E-glass fibers on the properties of the SiO2 filled PTFE composites were investigated, including density, water absorption, dielectric properties (εr, tanδ), coefficient of thermal expansion (CTE) and temperature coefficient of dielectric constant (τε). The compositions of inorganic materials mixture are (62 ? x) % SiO2 + x % E-glass fiber (x: mass ratio to composites, x = 0, 1, 1.5, 2, 2.5, 3). The results show that as the content of E-glass fibers is 2.5 wt.%, this composite obtains optimal properties, including excellent dielectric properties (εr^2.9123, tanδ~0.0011), acceptable water absorption of 0.075%, temperature coefficient of dielectric constant of 10 ppm/?C and coefficient of thermal expansion of 15.87 ppm/?C.

Enhancement in the Electrical and Thermal Properties of Ethylene Vinyl Acetate (EVA) Co-Polymer by Zinc Oxide Nanoparticles

EVA/ZnO nanocomposites of 1%, 2% and 4% ZnO were fabricated by direct probe sonicator method. The ZnO nanopowders were prepared by solvothermal method. As the particle size of the filler incorporated to the polymer matrix decreases, the properties of the polymer-filler interface show dominance over its bulk properties. The dielectric constant and dielectric loss of the composites at ambient temperatures are found to decrease with increasing frequency. The thermal analysis using TGA-DTA is also performed and it is found that the thermal stability of the nanocomposites increases with increasing the filler concentrations. The thermal parameters such as thermal diffusivity (α) and thermal effusivity (e), the thermal conductivity (k) and heat capacity (Cp) were studied using photopyroelectric technique. The band gap of the samples was also determined and found to decrease with increasing filler concentrations. The tensile strength and peel strength of the samples were also investigated and it is found to increase with small inclusion of filler material.

Investigation on structural, dielectric and ferroelectric properties of samarium-substituted BiFeO_(3)–PbTiO_(3) composites

The polycrystalline samples of 0.8BiSm_(x)Fe_(1-x)O_(3)–0.2PbTiO_(3)(x=0.05;0.10;0.15 and 0.20)were prepared by using the conventional solid-state reaction technique and sintered at high temperature(850℃).X-ray diffraction(XRD)confirms the distorted rhombohedral crystal structure for all the composites at room temperature.The surface morphology was checked by field-emission scanning electron microscope(FESEM)technique and homogeneous mixing of the components was confirmed by energydispersive analysis of X-ray(EDAX).The detailed study of dielectric properties of the composites reveals an increasing nature of dielectric constant(ε_(r))and loss tangent(tanδ)with the increase of temperature due to thermal activation.The Arrhenius plots of temperature dependence of AC conductivity yield the activation energy within the material at high-temperature range.The ferroelectric study shows that the remnant polarization decreases with the increase of Samarium(Sm)concentration.

涂层层数对镍粉/石墨基复合材料介电性能和吸波性能的影响

为了解制备工艺对涂覆型吸波材料性能的影响,实验研究涂层层数对镍粉/石墨基复合材料的介电性能及吸波性能的影响机制。选用PU2540型聚氨酯为黏结剂,镍粉、石墨为功能粒子,涤/棉平纹织物为基布,采用纺织涂层(刮涂法)工艺制备了涂层层数不同的镍粉/石墨基涂层复合材料。测试该复合材料的介电常数(实部、虚部、损耗角正切值)和反射损耗,分析涂层层数对复合材料介电性能和吸波性能的影响。结果表明:在测试频率1^(1)000 MHz范围内,3层的镍粉/石墨基复合材料对电磁波的极化能力、损耗能力及耦合能力最强;在测试频率10~3000 MHz范围内,涂层层数2层的复合材料的吸波性能最好,反射损耗最小峰值为-26.460 dB;3种涂层层数不同的复合材料在不同频段表现出不同的吸波特性。所得结果可为开发经济实用的吸波材料提供理论参考。

高介电复合材料的微观界面设计及研究进展

高介电复合材料是一类具有高介电常数、低介电损耗及高储能密度等特点的复合材料,在现代电子和介电储能等方面具有重要的研究价值和广泛的应用前景。高介电复合材料的结构设计对其介电性能有显著影响,通过不同类型的结构设计,可以合成具有特殊界面结构的复合材料,并将高介电常数、低介电损耗及高击穿强度等优势结合在一起,使复合材料的性能明显改善和增强。本文从材料结构设计角度出发,综述了有效提升复合材料的介电性质的微观结构构筑方法,包括构筑核壳结构、层状结构等微观结构并展望了未来可能的研究方向。

THE PROPERTIES OF FERROELECTRIC-ELECTRET COMPOSITE FILMS AND THEIR MEASUREMENTS

In recent years, great interest has been shown in the study of composite films. In pyroelectric materials, much more attention has been drawn to the composite films of triglycine sulphate (TGS) single crystal powders and polyvinylidene fluoride (PVDF). However, traditional methods are most likely to lead to wrong results if simply used to

Preparation and Properties of Ferroelectric Composite ATGS-PVDF

In recent years, more studies have been carried out on the composite of triglycine sulfate (TGS)and poly vingledene fluoride (PVDF) as pyroelectric materials.Experimental results show that the grain size, composition ratio and preparation methods have great influence on the properties of the composites. A new-type and useful pyroelectric composite film may be obtained by

Characterization of PZT/PVC Composites Added with Carbon Black

A new three-phase PZT C/PVC composite comprising PZT（50 vol%）,nanocrystalline PVC （50 vol%） and a small volume fraction f of black（C0was prepared by the hot-pressing technique.The dielectric property of the composite as α function of the frequency and the dielectric and piezoelectric properties as α function of the volume fraction f of C were studied.The measured dielectric property demonstrates that α percolation transition occurs in the three-phase composites as in normal two-phase metal-insulator continuum media.The dielectric constant varies slightly with f at f〈0.1 and increases rapidly when f is close to the percolation threshold at 1kHz.The optimum properties were obtained for f=0.5 before the percolation threshold in the PZT/C/PVC（50/f/（50-f）vol%）composite with its d33（20pC/N） being 50% higher than that of the PZT/PVC（50/50vol%）,and its g33（47.23×10^-3Vm/N）and Kp（0.25） much higher than the earlier reported values,XRD patterns and P-E hysteresis loops were used to interpret the experimental results.

Engineering of dielectric composites on electromagnetic and microwave absorbing properties for operation in the X-band

In this study,carbon black(CB)powder-loaded polyurethane(PU)composites(CB-PU composites)were prepared by melt mixing method with different volume percentages(45,50,55,58 and 61 vol.%)of CB in the PU matrix.The prepared CB-PU composites had been further studied for surface morphology using the field-emission scanning electron microscopy(FESEM)technique.Dielectric properties in terms of real permittivity(ε′)and imaginary permittivity(ε′′)of the fabricated composites were computed using an Agilent E8364B vector network analyzer in the frequency range of 8-12 GHz(X-band).Dielectric loss factor of the prepared CB-PU composites was computed in terms of the dielectric loss tangent(tanδ_(e)=ε′′/ε′).Microwave absorbing properties were appraised in terms of the reflection loss(RL)which in turn was calculated for varying thicknesses of the prepared composites from the measured real and imaginary permittivity data.The minimum RL was observed as−20.10 dB for the absorber with a thickness of 2.2 mm and the bandwidth achieved was 1.92 GHz for RL≤−10 dB.Based on the above results these CB-PU composites have potential use as effective microwave absorbers in 8-12-GHz(X-band)frequency range.

柔性PDMS基介电复合材料的电场及击穿损伤形貌演变规律研究

与其它储能设备相比,由介电复合材料制得的介质电容器在快速充放电能力与高功率密度方面极具优势,如何提高介电复合材料能量密度与优化其击穿性能已成为当前研究热点之一。为进一步调控并兼顾介电常数与击穿性能,本工作基于DBM(Dielectric Breakdown Model,介电击穿模型),采用有限元数值模拟,研究了无机填料的分布对柔性聚二甲硅氧烷(PDMS)基介电复合材料体系的电场与发生介电击穿时击穿损伤形貌演变的具体影响。研究结果表明:填料与基体边界处存在较大的介电差异,可以使用较大介电常数的聚合物基体或较小介电常数的无机填料来减小其界面处的高电场区域,继而提高复合材料的耐击穿能力;同时发现当无机填料分散更均匀时,其树状损伤通道更容易产生分支,此种情况将使介电击穿的树状损伤通道的损伤位点增多,延缓其损伤速度,继而提高复合材料的耐击穿性能。该研究结果将为开发高储能密度且具有优异击穿性能的有机-无机复合电介质材料提供坚实的理论依据。

高功率射频微波用聚四氟乙烯及其复合材料关键技术

随着电子领域朝着高速传输、高连接密度的方向发展,对5G设备中广泛使用的覆铜板提出了低介电常数、低介电损耗、高导热率、高可靠性等技术要求。聚四氟乙烯(PTFE)覆铜板以其优异的介电性能和化学稳定性被广泛应用于高频微波电路领域,但现有PTFE覆铜板的制备在单体纯化、树脂聚合、填料改性、复合材料以及制品加工全链条中存在的问题限制了其实际应用。本文总结了近年来PTFE覆铜板的发展历程以及高频PTFE覆铜板面临的理论及技术难点,分别从高黏结性PTFE的分子设计及序列分布控制、高纯PTFE的全流程杂质含量可控及绿色产业化技术、新型填料制备及表面处理新技术、多相多组分PTFE复合材料的组成与界面设计、覆铜板的加工流变性与结构均匀性控制等方面提出了提升PTFE覆铜板性能的方法,以期能发展从树脂结构、填料改性、复合材料到成型加工的系统基础理论,从而制备高性能PTFE覆铜板。

高强高模聚乙烯纤维纸基复合材料的制备及性能

以高强高模聚乙烯(UHMWPE)短纤维和针叶木浆为原料,通过湿法成型技术结合树脂浸渍热压方法制备了UHMWPE纤维纸基复合材料,研究了原纸制备工艺和浸渍热压工艺对UHMWPE纤维纸基复合材料性能的影响。结果表明,当UHMWPE纤维与针叶木浆质量比为7∶3、针叶木浆打浆度为58°SR、酚醛树脂水溶液质量分数为10%、上胶量为44%、热压工艺为15 min、10 MPa、130℃时,制得的UHMWPE纤维纸基复合材料性能较好。当原纸经过浸渍热压后,所制备的UHMWPE纤维纸基复合材料抗张指数为59.11 N·m/g,与原纸相比抗张指数提高了6.9倍,表面变得更光滑,同时具有较低的介电常数(约1.97)、介质损耗因数(0.45×10^(–2))和较好的热稳定性。

氰基化钛酸钡对聚芳醚腈介电薄膜结构与性能的影响

首先通过化学接枝法在钛酸钡纳米粒子(BT)表面依次接枝了异佛尔酮二异氰酸酯(IPDI)和3-氨基苯氧基邻苯二甲腈(3-APN),得到氰基功能化的钛酸钡纳米粒子(BT-CN);接下来,将其与聚芳醚腈(PEN)复合,制备了聚芳醚腈/氰基化钛酸钡复合介电薄膜。通过傅里叶红外光谱(FTIR)、X射线光电子能谱(XPS)、热重分析仪(TG)证实了BT成功进行了表面功能化。此外,BT-CN的加入可以有效增强PEN复合薄膜的热学、力学和介电性能;相较于纯PEN,复合薄膜的玻璃化转变温度增加了12℃,拉伸强度提高了9.6%,1 kHz时介电常数提高了227.8%。综上所述,氰基功能化有利于改善有机-无机界面相容性,从而进一步提高复合薄膜的综合性能。

温度对石英纤维增强中温固化环氧树脂复合材料性能的影响

研究了温度对石英纤维增强中温固化环氧树脂复合材料性能的影响,对材料导热、热膨胀系数、力学性能以及介电性能等进行了表征。研究结果表明:组成复合材料的树脂和纤维在导热、热膨胀性能上具有明显差异,这是引起材料在受热过程中产生内应力的关键因素;干态条件下,在-50~80℃范围内,复合材料的强度随温度升高而降低,模量无显著变化,复合材料的力学性能稳定性良好;吸湿后材料的力学强度、模量均显著降低,长期湿热环境对复合材料树脂、纤维及二者界面均会产生显著破坏;不同温度下恒温后,AC319树脂和QW280/AC319复合材料的介电常数和损耗均随温度升高而增大,且介电损耗的变化幅度高于介电常数,材料极性基团的可动性(偶极取向能力)是决定树脂及复合材料介电常数和损耗的关键因素;树脂和复合材料的介电常数在升温跟踪过程中表现出相反的变化规律,树脂的介电常数先增后减最后趋于稳定,而复合材料的介电常数则先减后增再趋于稳定,主要由复合材料的界面层所致。