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.

Crystallization and dielectric properties of lead-free glass-ceramic composites with Gd_2O_3 addition

Lead-free glass-ceramic composites in barium sodium niobate silica system with Gd2O3 addition were synthesized through melt-casting fol-lowed by controlled crystallization technique. Crystallization and dielectric properties of the Gd2O3 adding glass-ceramic composites were investigated. With the increase in the concentration of Gd2O3, the glass transition temperature and the crystallization temperature of the pre-cursor glass shift towards the higher temperature. The crystallization behavior that occurred during the heat treatment procedure leads to the enhancement of dielectric constant. All the three compositions of glass-ceramic composites exhibit ferroelectricity when tested at room tem-perature. Both the values of the remanent polarization and coercive field are enhanced regularly with the gradual increase in the concentration of Gd2O3 additive under the same testing field.

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.

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.

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。

PYROELECTRIC PROPERTY OF TGS-PVDF COMPOSITE MATERIAL

Ⅰ. INTRODUCTIONToday, the composite material becomes an important aspect in the development of material science. The low-cost pyroelectric material, a new type of functional composite material made from the mixture of single crystal powders and polymer and used in IR detection, is also developing, because it possesses not only good pyroelectric and piezoelectric properties,

高介电复合材料及其介电性能的研究

研究了金属/铁电体/聚合物三元复合材料的介电常数和介电损耗。发现金属粒子的加入除了可以提高铁电体/聚合物复合材料的介电常数外,还可以非常明显地降低其介质损耗。金属/铁电体/聚合物三元复合材料是一种很有应用前景的高介电材料。

(1-x)Na_(0.5)Bi_(0.5)TiO_3-xNaNbO_3系无铅压电陶瓷的机电性能

采用传统陶瓷的制备方法,制备了(1-x)Na0.5Bi0.5TiO3-xNaNbO3(x=0～0.08)压电陶瓷。X射线衍射分析表明:所研究的组成 均能够形成纯钙钛矿(ABO3)型固溶体。不同频率下陶瓷材料的介电常数温度曲线显示该体系材料具有典型的弛豫铁电体特征,且随着x 的增加,其弛豫性特征愈明显。室温下陶瓷材料的饱和电滞回线表明:所研究组成均为铁电体,材料的剩余极化强度Pr在x=0.02时具有最 大值。检测了不同组成陶瓷的压电性能,发现材料的压电常数d33和平面机电耦合系数Kp随着x值的增加先增加后降低,在x=0.02时,陶瓷 的d33=88pC/N,Kp=0.1792,为所研究组成中的最大值,材料的介电常数εT33/ε0和介电损耗tanδ则随x值的增加而增加。

铅基钙钛矿型结构铁电薄膜的介电及热释电性能研究

用改进的溶胶 -凝胶旋转涂覆技术 ,在Pt/Ti/SiO2 /Si基片上研制出 1～ 2 μm厚 ,具有钙钛矿型结构的PbTiO3、PLT和PZT铅基铁电薄膜。该类铁电薄膜具有良好的结晶特性、优异的介电和热释电性能。

天线罩材料的研究进展

天线罩要在复杂的外部环境下保证飞行器中天线和雷达的正常工作,不仅要满足气动外形和透波性能的要求,还要承受气动载荷的作用。为此,综述了国内外天线罩的发展,对天线罩在设计与制备中的部分问题进行了评述与分析。介绍了天线罩的设计和材料选择原则,分析了当今常用材料体系的优劣并对天线罩材料体系的研究进展进行了归纳。重点介绍了树脂基纤维增强天线罩和高温陶瓷导弹天线罩的主要材料体系,并对各种体系天线罩材料的特点及国内外研究现状进行了评述。研究表明开展低成本高性能的复合材料,尤其是三维空间纤维增强复合材料天线罩的研究是天线罩材料今后的发展方向。