Dielectric properties and electrical conduction in yttrium iron garnet (YIG)

The dielectric properties (dielectric constant and loss) of a single crystal of yttrium iron garnet (Y₃Fe₅O₁₂) were measured in the temperature range 77–725 K and in the frequency range 100 Hz-1 MHz. AC conductivity was derived from dielectric constant and loss. DC conductivity was measured in the temperature range 30–725 K. Thermoelectric power (TEP) was measured from 77–800 K. On the basis of the results, conduction in this garnet is interpreted as due to small polarons. The nature of conduction at different temperature ranges is discussed in the light of existing reports on defect formation.     

Characterization of RF-sputtered garnet films

Noncrystalline garnet films of nominal composition Y₃Fe₅O₁₂ and Y₂GdFe₅O₁₂ were synthesized by RF sputtering. The AC and DC resistivity data have been discussed in line with the model of Mott and Davis where conduction occurs through excitation of carriers into localized states at the band edges and hopping at energies close to the band tails.     

Thermal conductivity and dielectric properties at low temperatures of an epoxy-resin after electron-irradiation

Measurements of the thermal conductivity and of the dielectric properties of an electronirradiated epoxy-resin are presented. The experimental results for varying radiation doses of structural investigations of electron-irradiated epoxy-resin¹ are discussed.     

Thermal conductivity and dielectric properties at low temperatures of an epoxy-resin after fast and thermal neutron-irradiation

Measurements of the thermal conductivity and of the dielectric properties of an epoxy-resin irradiated by fast and thermal neutrons are presented. The discussion of the experimental results accounts for the radiation dose and energy of neutrons.     

Study of dielectric properties of nanophase silver iodide

Dielectric properties of nanophase AgI are studied over the frequency range from 100 kHz to 3 MHz at different temperatures. The values ofε, tanδ andσ _ac are considerably larger than those reported for crystalline pellets of AgI, but they show a similar trend in variation with frequency and temperature. The increase in these values are attributed to the defect structure of the nano-particles.     

Ce:YIG纳米粉体结构与磁性的研究

用共沉淀法制备纳米级的Ce:YIG石榴石粉体颗粒.颗粒尺寸的计算结果表明平均粒径为70nm,这与通过TEM观察到的几乎一致.与氧化物工艺相比,所制备的粉体化学活性高,烧结温度显著降低,由1300℃降低到约900℃.最后对粉体的磁性能与烧结温度的关系进行了讨论.     

纳米晶钛酸铅的合成及其介电性能的研究

采用硬脂酸凝胶法(SAG)制各了纳米晶PbTiO3，用差热—热重分析、红外光谱分析、X光衍射分析及透射电镜等手段对产物的形成过程、晶型、粒径进行了表征。通过对材料介电性能的研究发现，纳米晶钛酸铅在接近静态条件下的低频介电常数远大于常规材料的介电常数，随着粒径的减小，纳米晶钛酸铅的低频介电常数逐渐增大。     

石墨烯纳米片/环氧树脂复合材料的制备与介电性能研究

以天然鳞片石墨为原料,通过Hummers法制备氧化石墨,微波热解剥离制备出少层数的石墨烯纳米片。以硅烷偶联剂KH-560为改性剂,超声共混制备石墨烯纳米片/环氧树脂复合材料。采用FT-IR和SEM分析样品的微观结构和形貌,测试其介电性能。结果表明,随着石墨烯纳米片添加量的增加,复合材料介电常数呈现先增大后减小的趋势,当石墨烯纳米片含量为0.3%(质量分数)时,介电常数达到最大;石墨烯纳米片对复合材料介电损耗的影响与之相反;偶联改性使复合材料的介电常数增大,介电损耗减小。     

磷酸铝-聚醚砜层状复合材料的隔热及介电性能

采用高温煅烧成型工艺在聚醚砜(PES)基体表面复合了AlPO4耐热层,制备得到了AlPO4-PES层状复合材料。利用SEM、激光共聚焦显微镜三维形貌分析(CLSM-3D)、FTIR和TGA等分析技术对AlPO4-PES微观结构、化学成分以及热稳定性进行了表征。研究了AlPO4含量对AlPO4-PES层状复合材料的热导率和介电性能的影响。结果表明:AlPO4层显著地改变了PES基体的微观结构,二者之间通过物理方式紧密结合;随着AlPO4含量的增加,AlPO4-PES层状复合材料的热稳定性明显增强,而热导率却不断降低;AlPO4-PES层状复合材料的介电常数和介电损耗均随着AlPO4含量的增加而减小,并且在0.1~5MHz测试范围内表现出良好的频率稳定性。     

制备工艺对 CaO - MgO - Nb2 O5-TiO2微波介质陶瓷结构与介电性能的影响

采用普通固相合成法和铌铁矿前驱体法合成了CaO-MgO-Nb2O5-TiO2微波陶瓷粉体,讨论了这两种粉体制备方法对CaO-MgO-Nb2O5-TiO2微波陶瓷微观结构和介电性能的影响.两种方法相比:前驱体法合成制得的CaO-MgO-Nb2O5-TiO2陶瓷粉体具有物相纯,粉体煅烧温度较低的特点;在1300℃下烧结保温5 h获得的陶瓷材料晶粒均匀、致密,并且其微波陶瓷的介电性能得到了改善.     

PST陶瓷的微结构和电性能研究

研究了Pb含量对PbxSr1-xTiO3（x=0．2～0．8）陶瓷微结构和介电性能的影响，当x＜0.45时，c/a≈1，晶体为立方顺电相；x≥0．45时，c/a＞1，晶体为四方铁电相；随着Pb/Sr比增大，PST陶瓷气孔率下降，致密度增加，晶粒尺寸逐渐增大，居里峰近似线性地向高温方向移动，并具有一致的居里外斯常数，剩余极化强度（Pt）、矫顽场强（Ec）都增大。     

双马来酰亚胺/钛酸钡复合材料介电性能的研究

以双马来酰亚胺（BMI）为树脂基体，压电陶瓷BaTiO，为功能填料，采用浇铸的方法制备了BMI/BaTiO3复合材料。考察了复合材料的介电性能，并用多种混合法则对复合材料的介电常数进行拟合分析。研究结果表明，BaTiO3含量的增加提高了材料的介电常数，同时增加了材料的介电损耗；BMUBaTiO3复合材料的介电性能具有良好的频率稳定性：使用Lichterecker混合规则的拟合结果与实验测试结果具有很好的一致性。     

聚苯胺@粉煤灰漂珠复合材料的导电及介电性能

为获得具有良好电流变性能的分散相粒子,利用γ-氨基丙基三乙氧基硅烷(APTES)修饰粉煤灰漂珠(FAFB),将聚苯胺(PAn)以化学键的方式偶联在修饰后的FAFB(mod-FAFB)表面,形成以mod-FAFB为核、PAn为壳的核-壳结构复合材料。采用FTIR、SEM、数字式四探针以及LCR介电谱仪对PAn@mod-FAFB复合材料的结构与性能进行分析,讨论了不同mod-FAFB含量对PAn@mod-FAFB复合材料导电性能及介电性能的影响。结果表明:以化学键接枝聚合的PAn@mod-FAFB核-壳结构复合材料电导率相对较高,且随mod-FAFB含量的增加而减小;在较低交变电场频率(100~2 000kHz)下其相对介电常数较大,且随mod-FAFB含量的增多,PAn@mod-FAFB复合材料的介电常数明显减小;PAn@mod-FAFB复合材料的介电损耗相对较小,随mod-FAFB含量的增多而急剧减小。     

B位Cr替代对BiFeO3介电特性的影响

采用传统的固相反应法制备了BiFe1-xCrO3（x=0，0．01，0．1,0．3，0．5）系列陶瓷样品，运用X射线衍射仪对样品进行结构分析发现，随着Cr含量的增加BiFeO3的微观结构发生了改变；利用HP3458A型万用表在室温下测量样品的电阻率随Cr含量的变化关系发现适当的Cr替代可以在一定程度上提高样品的电阻率；室温下利用HP4294A型阻抗分析仪在100Hz～100kHz的频率范围内测试样品的介电性能随频率的变化关系，结果表明介电常数岛随着Cr替代量的增加先增大然后又减小，而tanδ则随着Cr替代量的增加出现了较为复杂的变化．     

The threshold voltage,dielectric and conductivity properties of C60-doped smectic A liquid crystal

Abstract

Influence of fullerenes C₆₀ on the threshold voltage, dielectric and conductivity properties of smectic A liquid crystal 4-hexyloxyphenyl ether 4′-hexyloxy 3′-nitrobenzoic acid is investigated. It is shown that the transverse component of the real part of dielectric permittivity increases at the additive of fullerenes while the longitudinal component decreases. In this case, a maximum of dielectric absorption shifts to the high-frequency region. Conductivity increases at low frequencies and decreases at the high ones. Experimental results are explained by location of fullerenes between liquid crystal molecules reducing their interaction. As a result, the order parameter and viscosity of the matrix decrease.     

稀土改性二氧化钛的电流变行为与介电性能关系

采用sol-gel法制备了掺杂稀土改性TiO2颗粒,与甲基硅油配制成电流变液,对电流变液的介电性能进行了测试,结果表明改性后TiO2电流变液的介电常数和介电损耗比纯TiO2电流变液均显著提高,其中介电常数提高2－3倍,△ε′＝ε′100Hz－ε′10kHz明显增大,1kHz的介电损耗角正切大于0．1左右电流变液的介电常数与介电损耗达到最大值。稀土掺杂引起TiO2电流变液的介电性能改变是导致改性TiO2电流变液流变学行为变化的起因。另外,电流变液介电性能温度特性的变化可用来解释电流变液的流变学性能随温度变化关系。     

锰掺杂对PMN-PZT陶瓷介电性能的影响

研究了锰掺杂对富锆PMN-PZT（铌镁酸铅一锆钛酸铅）陶瓷材料的相组成、微观结构、介电性能等方面的影响，并对实验结果作出物理机理的解释。实验结果表明：适量的锰掺杂有助于陶瓷晶粒的生长，并能有效地降低PMN-PZT陶瓷材料的介电常数和介电损耗，在锰掺杂量为3．0％（原子分数）时，εr：197、tanδ=0．15％，作为用于红外热释电探测器的陶瓷材料具有良好的介电性能。     

Structural and dielectric properties of Pb(Li1/4Sm1/4Mo1/2)O3 ceramics

The ceramic samples of lithium-samarium modified lead molybdate, Pb(Li_1/4 Sm_1/4 Mo_1/2)O₃ (PLSM)—a member of ABO₃ family were prepared by solid state reaction technique at ≈ 600–700°C. Preliminary X-ray analysis suggests the formation of single phase orthorhombic compound of PLSM. Studies of surface morphology, uniform particle/grain distribution, and presence of elements in the compound were completed using scanning electron microscope (SEM). Measurements of dielectric constant (ɛ), loss (tanδ) and conductivity (σ) at different frequencies and temperatures provided that the compound has a strong dielectric anomaly at 107°C.     

BaTiO3/SrTiO3多层膜的制备及其介电性质

采用脉冲激光沉积法在Pt／Ti／SiO2／Si衬底上制备了BaTiO3／SrTiO3(BTO／STO)多层膜。XRD结果表明：多层膜呈现出明显的(110)择优取向,与Ba0.5Sr0．5TiO3单层膜相比,多层膜的相对介电常数得到了明显的增强,而介电损耗仍然保持在较低的水平。室温下频率为10kHz时,BTO／STO(n=6)多层膜的相对介电常数为506,而介电损耗仅为0．033。薄膜的C-V特性研究表明：多层膜呈现出较好的电容调谐度。