Dielectric properties of ZnNb2 O 6 -TiO 2 mixture thin films

ZnNb₂O₆-TiO₂ mixture thin films with multilayer structures were fabricated via a sol-gel spin coating process. TiO₂ layers were deposited on the pre-crystallized ZnNb₂O₆ layers in order to suppress the formation of the ixiolite phase which always forms in the bulk system. The phase constitution of the thin films, confirmed by X-ray diffraction (XRD), could be controlled by the annealing temperatures, which, in turn, influenced the dielectric properties of the thin films. TiO₂ layers crystallized as the anatase phase and then transformed to the rutile phase at temperatures higher than 725^∘C. Dielectric constants of the mixture thin films, measured at 1 MHz with an MIM (metal-insulator-metal) structure, increased from 27 to 41 with dielectric losses below 0.005 as the annealing temperature increased from 700^∘C to 900^∘C. The increase in the dielectric constants was understood to originate from the increasing amounts of the rutile phase. Temperature coefficients of capacitance (TCC) were also measured between 25^∘C and 125^∘C, which showed a decreasing manner from positive values to negative values with increasing annealing temperatures. When annealed at 850^∘C, the TCC of the thin films could be tuned to be approximately 0 ppm/^oC with dielectric constant and dielectric loss of 36 and 0.002, respectively.     

高频下纳米二氧化硅 /环氧树脂复合材料的介电特性研究

采用溶剂一超声波法较好的实现了纳米SiO2的分散,用透射电子显微镜(TEM)观测了纳米SiO2在丙酮中的分散状态。制备了纳米SiO2／环氧树脂复合材料,研究了电场频率与复合材料介电常数和介质损耗的关系。结果表明：纳米SiO2/环氧复合材料的介电常数随电场频率的升高而逐渐降低,随纳米SiO2含量的增加而增大;复合材料的介质损耗随着频率的增高而增加,在高频区变化缓慢。     

Dielectric properties of epoxy nanocomposites

The dielectric properties of epoxy nanocomposites with insulating nano-fillers, viz., TiO₂, ZnO and AI₂O₃ were investigated at low filler concentrations by weight. Epoxy nanocomposite samples with a good dispersion of nanoparticles in the epoxy matrix were prepared and experiments were performed to measure the dielectric permittivity and tan delta (400 Hz-1 MHz), dc volume resistivity and ac dielectric strength. At very low nanoparticle loadings, results demonstrate some interesting dielectric behaviors for nanocomposites and some of the electrical properties are found to be unique and advantageous for use in several existing and potential electrical systems. The nanocomposite dielectric properties are analyzed in detail with respect to different experimental parameters like frequency (for permittivity/tan delta), filler size, filler concentration and filler permittivity. In addition, epoxy microcomposites for the same systems were synthesized and their dielectric properties were compared to the results already obtained for nanocomposites. The interesting dielectric characteristics for epoxy based nanodielectric systems are attributed to the large volume fraction of interfaces in the bulk of the material and the ensuing interactions between the charged nanoparticle surface and the epoxy chains.     

Oxygen permeation properties and surface modification of acceptor-doped CeO2/MnFe2O4 composites

The preparation and oxygen permeation properties of the (Ce_0.8Pr_0.2)O_2−δ − x vol% MnFe₂O₄ composites, where x = 0 to 35, have been investigated. The samples were prepared by the Pechini method. In the case of Ce_0.8Pr_0.2O_2−δ, an oxygen flux density of 6 μmol⋅cm⁻²⋅s⁻¹ (L = 0.0247 cm) and the maximum methane conversion of 50% were attained at 1000^∘C. Unlike composites consisting of Gd-doped CeO₂ and MnFe₂O₄, the oxygen permeability of the (Ce_0.8Pr_0.2)O_2−δ – x vol% MnFe₂O₄ composites was almost constant regardless of the volume fraction of MnFe₂O₄; however, the optimum volume fraction of MnFe₂O₄ was determined to be 5 to 25 in the context of the chemical and mechanical stabilities under methane conversion atmosphere. In addition, the surface modification of the (Ce_0.8Gd_0.2)O_2−δ – 15 vol% MnFe₂O₄ composite was performed by using the FePt nanoparticles. The catalyst loading of 2.8 mg/cm² on the both side of the 0.3 mm-thick (Ce_0.8Gd_0.2)O_2−δ – 15vol% MnFe₂O₄ composite increased the oxygen flux density from 0.30 to 0.76 μmol⋅cm⁻²⋅s⁻¹ in the case of He/air gradients; however, the effect seems to be reduced in the case of high oxygen flux density caused by a large pO₂ gradient. Moreover, the Langmuir-Blodgett film of the FePt nanoparticles were successfully prepared on the tape-cast (Ce_0.8Gd_0.2)O_2−δ – 15vol% MnFe₂O₄ composite. Hydrophobic treatments for the surface of the composite were crucial to achieve high transfer ratio for the deposition of the LB film.     

Dielectric and mechanical properties of hot-pressed SiCN/Si3N4composites

A series of high temperature radar wave-absorbing materials, SiCN/Si₃N₄ceramics, were prepared by hot-pressing. The nanometer SiCN powder, used as an absorber in the SiCN/Si₃N₄ceramic, was synthesized through laser pyrolysis of ((CH₃)₃Si)₂NH) and NH₃. The dielectric and mechanical properties of the prepared ceramics were investigated. XRD and SAED were conducted to study the growth of crystals in the ceramics. The results showed that the transformation of Si₃N₄from α to β was inhibited. The growth of the rod-like β -Si₃N₄grains in SiCN/Si₃N₄ceramics was retarded during hot-pressing process due to the existence of the nanometer SiCN particles. The relative density and the strength of the composites both decreased with the increase of the SiCN content in the composites. The dielectric properties of the ceramics prepared at different temperatures were very different. For the samples sintered at 1600^∘C and 1700^∘C, both the real and imaginary parts of the complex permittivity of them increased as the content of SCN powder in the sample obviously. For the sample with same concentration of SCN, the real and imaginary parts of them varied with the sintering temperature. SAED pattern revealed that structure of the SiCN in SiCN/Si₃N₄sintered at 1800^∘C tended to crystallize fully. Its real, imaginary parts and dissipation factor were much lower than those sintered at 1600^∘C and 1700^∘C greatly. Supported by national natural science foundation of China (No. 50572090)     

Dielectric properties of epoxy/clay nanocomposites - effects of curing agent and clay dispersion method

Effects of the differences in the curing agent and filler dispersion method on the dielectric properties were examined for epoxy/clay nanocomposites. Irrespective of the clay dispersion method, relative permittivity and electrical conductivity are higher in the samples cured with the amine. Moreover, negative heterocharge accumulates in the vicinity of the anode in the amine-cured samples, whereas positive homocharge accumulates in the acid anhydride-cured samples. From the results of UV photon absorption and PL measurement, the bandgap or the energy at which the photon absorption increases drastically is smaller in the amine-cured samples than in the acid anhydride-cured samples. Ion migration can occur easily in the amine-cured samples whose electrical conductivity and relative permittivity are higher than the acid anhydride-cured samples. The curing agent gives the strongest effect, while the existence of clay affects secondly and the filler dispersion method has the weakest effect.     

自动压力凝胶用环氧复合绝缘材料的组成对性能的影响

为了解自动压力凝胶用环氧复合绝缘材料的组成对性能的影响,研究了环氧树脂、固化剂、硅微粉的含量对环氧复合绝缘材料的凝胶时间、流动性和机电性能的影响。结果表明,在一定原料配比范围内,固化剂含量的增加,将使环氧复合绝缘材料的流动性增加,固化速度增大,弯曲强度增加,对材料的击穿强度影响较小,但使贮存(罐藏)寿命缩短;硅微粉的含量增加．将使环氧复合材料的贮存寿命、弯曲强度和电气强度增加,而流动性下降,固化速度减小。     

Enhanced dielectric properties of Bi1.5ZnNb1.5O7 thick films via cold isostatic pressing

Dense Bi_1.5ZnNb_1.5O₇ thick films were prepared on Ag/Al₂O₃ substrates using screen-printing technology at a lower temperature of 825?°C. A novel pretreatment of cold isostatic pressing was introduced to enhance the quality of thick films. After cold isostatic pressing prior to sintering, the microstructure of thick films was improved with a more compact morphology and better dielectric properties, and the permittivity and dielectric loss of thick films sintered at 900?°C were about 160 and 0.006. The obvious tunability of thick films was also observed, and the tunability value reached about 3?% for thick films sintered at 900?°C under 400?kV/cm. The enhanced properties and low-temperature sintering made this compound a potential candidate for Low Temperature Co-fired Ceramic (LTCC).     

Enhanced electrochemical and thermal properties of Sm2O3 coated Li[Li1/6Mn1/2Ni1/6Co1/6]O2 for Li-ion batteries

For EV vehicles of the future, a lithium ion battery with highly enhanced electrochemical and thermal properties has been widely investigated. Here we introduce Sm₂O₃ as a new surface coating source for the cathode material of Li-ion batteries and explore the effects of the Sm₂O₃ coating using XRD, EIS, and DSC measurements. The cathode material used is Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂. The XRD and TEM results indicate that the Sm₂O₃ is coated on the surface of the cathode material without changing the layered structure of the core Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂. With the Sm₂O₃ coating, the cycling performance during 50 cycles using 6 C rate, as well as 1 C rate, is highly improved, five times better. The EIS results show that film resistance and the charge transfer resistance decrease in comparison with the pristine Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂. Furthermore, the DSC results show a highly enhanced thermal property. We highly recommend the Sm₂O₃ coating for Li-ion batteries for various applications.     

SF_6—CO_2混合气体的绝缘强度

研究表明,虽然SF_6—CO_2混合气体在均匀电场中的击穿强度稍逊于同样混合比的SF_6—N_2混合气体,但在不均匀电场中的击穿强度、特别是在雷电冲击电压下的击穿强度,却优于SF_6—N_2.此外,SF_6—CO_2在气膜复合绝缘中的局部放电特性也优于SF_6—N_2混合气体.     

Ba 3 Co 2 Fe 24 O 41 /polyimide composites with magnetic and dielectric properties

Ba3Co2Fe24O41(Co2Z)/polyimide(PI) composites were synthesized via in-situ polymerization process, using the micron-sized Co2Z particles prepared by the solid-state reaction. X-ray diffractometer...     

Dielectric properties of Pb[(Mg1/3Nb2/3),Ti]O3 with Bi modification

Bi(Mg_2/3Nb_1/3)O₃ was partially substituted into a Pb(Mg_1/3Nb_2/3)O₃⋅PbTiO₃ perovskite system and resultant changes in the phase developments and dielectric properties were investigated. Two major structures of columbite and rutile, along with a small fraction of Mg₄Nb₂O₉ (α-Al₂O₃ structure), were developed in the B-site precursor system, whereas only a perovskite was observable after the addition of PbO and Bi₂O₃. The replacement of Bi for Pb resulted in a great reduction in the maximum dielectric constants as well as a substantial decrease in the dielectric maximum temperatures.     

蒙脱土改性环氧树脂复合材料的制备及性能研究

采用长链烷基季胺盐对蒙脱土进行有机改性,将改性后的蒙脱土与双酚A型环氧树脂以及酸酐固化剂充分混合固化制得复合材料。利用X射线衍射仪(XRD)、扫描电镜(SEM)对材料的微观结构进行表征,并对材料的力学性能、热性能进行了研究。结果表明蒙脱上的加入使得复合材料的力学性能和热性能与纯环氧树脂固化物相比有不同程度的提高。     

电极表面粗糙度对SF_6、SF_6/N_2及SF_6/CO_2绝缘特性的影响

本文采用机加工形成的不同粗糙度的电极,研究SF_6,SF_6/N_2及SF_6/CO_2的绝缘特性,并与计算结果进行比较。     

Dielectric properties of Zn- and/or Nb-substituted Pb[(Mg1/3Ta2/3),Ti]O3 ceramics

Ceramic powders of Pb[(Mg_1/3Ta_2/3),Ti]O₃, with the octahedral components substituted separately as well as simultaneously by Zn and Nb, were synthesized by a two-step B-site precursor method. Prepared powders were examined by X-ray diffraction (XRD) to monitor the phase developments and also to determine the crystallographic aspects. The weak-field low-frequency dielectric constant and loss values of the sintered specimens were determined. Temperature-dependent dielectric constant values were further analyzed in terms of diffuseness/sharpness in the phase transition modes. The internal microstructures of the ceramics were examined by scanning electron microscopy (SEM).     

Random-Site Cation Ordering and Dielectric Properties of PbMg1/3Nb2/3O3-PbSc1/2Nb1/2O3

(1 ? x)PbMg_1/3Nb_2/3O₃-(x)PbSc_1/2Nb_1/2O₃ (PMN-PSN) solid solution crystals have been grown by the flux method in the whole concentration range. X-ray supercell reflections due to B-cation ordering were observed for as-grown crystals from the 0.1 ≤ x ≤ 0.65 compositional range. Though the ordered domains are rather large (～50 nm) the relaxor-like dielectric behavior is observed for compositions with x < 0.6. The diffusion of the dielectric permittivity maximum in as-grown crystals is the lowest at x = 0.6 and increases towards the end members of solid solution. Such behavior is explained within a Bragg-Williams approach by employing the random layer model. At x ～ 0.6 the excitation energy determined from the Vogel-Fulcher relation exhibits a jump which we regard to changing the kind of the polar regions from PbMg_1/3Nb_2/3O₃ to PbSc_1/2Nb_1/2O₃ related type.     

热老化条件下LDPE/TiO2纳米复合材料介电特性研究

电力电缆在运行过程中普遍存在的热老化现象容易加速绝缘失效,限制设备使用寿命,甚至引发电力系统故障。纳米粒子掺杂改性可以提高聚乙烯基体材料的热稳定性,开展相关研究可以为提高电缆绝缘寿命提供解决方案。以低密度聚乙烯(LDPE)/二氧化钛(Ti O_2)纳米复合材料为研究对象,分别研究了热老化条件下纳米粒子质量分数、老化时间、老化温度对材料介电特性的影响。实验结果表明,掺杂Ti O_2纳米粒子能够改善LDPE基体材料的介电特性,当Ti O_2纳米粒子填充质量分数为0.5%时,纳米复合材料介电特性最佳。老化时间和老化温度是影响材料介电特性劣化的两个重要因素,随着老化时间推移和老化温度提高,纳米复合材料的介电性能劣化现象越明显。对聚乙烯材料进行纳米改性的同时降低电缆运行环境温度,对提高电缆绝缘寿命具有重要意义。     

Sintering and dielectric properties of Bi1.5ZnNb1.5O7 cubic pyrochlore ceramics via high-energy milling technology

The dense Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramics is synthesized by high-energy milling technology from the coarse Bi_1.5ZnNb_1.5O₇ cubic pyrochlore powders prepared by solid state route. The sintering and dielectric properties of the Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramics are investigated, which show that the sintering temperature of the prepared ceramics could be effectively lowered to 800°C and the bulk density reach 6.889 g/cm³ approximately 97% of the theoretical density of Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramics. The excellent dielectric properties of the ceramics sintered at 850°C has been obtained with the relative permittivity of 160 and the dielectric loss of 10^?4. This route would be a low-cost and mass production for lowering the sintering temperature of the Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramics without sintering aids.     

中频变压器用环氧树脂/纳米BN复合介质的导热和电气性能研究

为了研究中频变压器用环氧树脂复合材料的导热和电气特性,本文选取高导热纳米氮化硼(BN)颗粒作为填料,利用盐酸多巴胺对其进行表面修饰,采用溶液法制备了环氧树脂/纳米BN复合材料试样(BN质量分数分别为1％、2％和5％),通过扫描电子显微镜对试样的微观形貌进行分析,测试了试样的热导率、体积电导率、中频击穿场强和表面电位衰减特性.结果表明:纳米BN的添加提高了环氧树脂的热导率;1 wt％和2 wt％纳米BN的添加降低了环氧树脂的电导率和载流子迁移率;随着电压频率的升高,试样的击穿场强降低;随着纳米BN浓度的增加,击穿场强呈现出先升高后降低的趋势;纳米BN能够缓解环氧树脂击穿场强随频率升高的影响,降低环氧树脂的表面电位衰减速度.上述结果表明,适量添加1 wt％和2 wt％的纳米BN能够提高中频变压器用环氧树脂复合材料的导热和电气性能.     

局部电场畸变对SF_6/N_2和SF_6/CO_2混合气体耐电强度的影响

本文用半椭球凸出物模型计算了在SF_6/N_2和SF_6/CO_2中电极表面粗糙度对耐电强度的影响。计算表明:在电场畸变严重时,两种混合气体的击穿强度均高于纯SF_6,且SF_6/CO_2优于SF_6/N_2。这一结论并为实验结果所证实。