Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ)混合导体导电性能的研究

用直流四电极法测量了空气和氮气气氛下Ba0.5Sr0.5Co0.8Fe0.2O3-δ(BSCF)的总电导率,用电子阻塞电极法测量了空气气氛下BSCF的氧离子电导率。结果表明575℃之前,BSCF呈现p型半导体的导电特征,总电导率温度升高而增大,随氧分压降低而减小;但在575～650℃总电导率显著下降,这与BSCF材料中晶格氧的逸出有关。通过电子阻塞电极法测得的BSCF氧离子电导率σi和温度T的关系符合Arrhe-nius公式,氧离子电导活化能Ea=140.7kJ/mol。通过透氧实验,由Wagner方程计算出来的氧离子电导率与电子阻塞电极法测量得到的值在700℃以下吻合;但700℃后,由于高氧端的气体与膜表面晶格氧的交换以及低氧端表面晶格氧与气相氧交换成为控速环节,使计算出来的氧离子电导率明显低于测量得到的值,并且二者差别随温度升高越来越大。     

BaCo_(0.7)Fe_(0.2)Nb_(0.1)O_(3-δ)离子-电子混合导体电导性能研究

用四电极法研究了BaCo0.7Fe0.2Nb0.1O3-δ(BCFN)离子-电子混合导体的总电导率随温度的变化规律;通过阻塞电极法测量了BaCo0.7Fe0.2Nb0.1O3-δ氧离子电导率随温度的变化规律;通过计算得到了电子电导率随温度的变化规律。研究结果表明,在温度低于550℃以下时,电子电导起了决定作用,随着温度的升高总电导率和电子电导率均呈现出显著增加的趋势,表现为P型半导体特征;当温度在550~650℃时,由于晶格氧的脱附,消耗了自由电子,导致电子电导率略有下降,使得总电导率表现出类似的变化规律,通过计算得到在550℃以下BCFN混合导体的电子电导的表观活化能为0.30eV;当温度高于650℃以上时,由于氧空位增加导致氧离子电导率随温度升高迅速增大,使得总电导率又呈现增加的趋势,计算得到氧离子迁移活化能为1.18eV;O2-TPD研究结果证明了在550~650℃时存在明显的晶格氧的脱附峰,晶格氧的脱附显著影响了BCFN混合导体电子电导率和总电导率。当温度低于650℃以下时,电子的迁移数接近100%,当温度高于650℃以上时,氧离子的迁移数迅速增大,900℃氧离子迁移数可达到8.97%。     

纸页水分测量中数学模型的研究

本文给出了含水纸页的电导率测试实验的方法和结果，拟合出了电导率随水份变化的两段数学模型。尤为重要的是，归一化的电导率－水份关系数学模型对于不同种类、不同规格的纸页，在不同的温度、湿度等环境条件下，具有相同的电导率转折点。这一实验结果，对于诸如纸页、布匹、粮食、烟草、茶叶、棉花、土壤、煤炭、泥料和陶瓷等物品水份含量的电导法测定［１］有着积极的指导意义。     

热处理对聚苯胺导电性及其介电性能的影响

采用苯胺化学氧化聚合制得盐酸掺杂态聚苯胺(PANI-HCl),考察了导电率以及介电常数随热处理温度的变化,并通过FT-IR、TGA、DSC和XRD等测试手段研究了空气气氛中不同热处理温度对PANI-HCl的掺杂程度以及微观结构的影响.结果表明:PANI-HCl在低于100℃的热处理保持优异的电导率和介电常数,电导率的数量级在100,介电损耗角正切tgδε≈0.35～0.49,当温度上升至160℃,电导率数量级下降到10-7,tgδε在0.1以下,其原因是由于热处理对掺杂态聚苯胺进行了脱掺杂,而且改变了聚苯胺的微观结构.     

聚甲基丙烯酸多缩乙二醇二酯－锂盐－增塑剂聚合物电解质的离子电导

合成了一系列甲基丙烯酸多缩乙二醇二酯（ＰＥＤ），并且考察了溶剂含量、盐浓度、增塑剂种类对由ＰＥＤ、锂盐、溶剂组成的聚合物电解质的电导率的影响。当溶剂含量局于８０ｍｏｌ％，盐含量相同时，不同分子量的ＰＥＤ形成的电解质的电导率非常接近，表明增塑剂在盐的解离和离子迁移过程中起主导作用。研究了四种增塑剂：碳酸乙烯酯（ＥＣ）、碳酸丙烯酯（ＰＣ）、四乙二醇（ＴＥＧ）和ＰＥＧ＿（４００），发现其增塑效果同它们的介电常数大小的顺序相吻合。对于室温电导率，在ＬｉＣＬＯ＿４盐浓度为０．９ｍｏｌ／１时，存在最大值。但当温度上升时，电导率对盐浓度的依赖性发生了改变，通过离子－离子对－三离子之间的平衡随温度的变化可以很好地解释该种现象。本文还研究了电导率的温度依赖性，发现在盐浓度低于０．５ｍｏｌ／ｌ时，符合阿仑尼乌斯关系。     

对苯酚和己内酰胺制备的新型离子液体的研究

对弱酸苯酚与弱碱己内酰胺以不同配比制备的离子液体进行了研究,考察了其物理化学性质(熔点、密度、电导率、溶解性等).结果表明,合成的离子液体的熔点随二者物质的量比的不同而变化,当物质的量比为3.5 : 1时熔点最低,为-22℃.离子液体的密度比水的密度大,且随温度的升高,密度增大.离子液体的电导率为10-4S/m数量级,且随温度的升高,电导率增大,电导率与温度符合Arrhenius方程.溶解性试验表明,离子液体具有较强的溶解能力,能与水、醇类、酯类等一般溶剂互溶.IR测试结果显示,所合成的离子液体具有苯酚和己内酰胺的特征峰.     

基于环境参数融合的智能气体传感器设计

由于温度、湿度等环境参数对半导体气体传感器的测量精度有着较大的影响,对此提出了基于神经网络方法的智能气体传感器设计方法,利用神经网络对气体传感器的各种环境参数进行数据融合,以获取准确的被测气体浓度值。实验证明,该方法可以有效地提高气体传感器的测量精度,使气体传感器输出的满量程误差在±0 8%以内。通过该神经网络融合逆模型,还可以方便地根据环境参数的变化实现对气体传感器输出的补偿,从而实现传感器的智能化。     

电容式微含水量检测系统设计

针对在线检测火药含水量的实际要求,设计平板电容水分检测传感器,利用水的相对介电常数远大于被检物料的相对介电常数的原理,构建和电容传感器相关的交流电桥和测量电路,并设计自补偿电路,使得桥路输入为零时输出也为零。由于所测含水量范围为0.5%~3.5%,测量准确度为0.1%,为提高系统的测量准确度,分别对影响含水量的温度、湿度和重量容积比加以考虑,建立多参数校正的水分在线检测系统。经过大量实验验证:该系统性能稳定,测量精度高,具有很好的实用价值。     

石英纤维/KH308复合材料的介电性能

为研究石英纤维/聚酰亚胺（KH308）复合材料介电性能与纤维体积分数、频率、温度和吸水率之间的关系,通过热压成型法,制备了4种不同纤维体积含量的石英纤维/KH308复合材料,采用高Q谐腔法分别测试这4种复合材料在不同状态下的介电常数和介电损耗。结果表明：石英纤维/KH308复合材料的介电常数随着纤维体积分数增加而变大,介电损耗随纤维体积分数变化不大;7~18 GHz频率下,复合材料的介电常数和介电损耗基本不随频率变化;25~300℃下,复合材料的介电常数随温度增加变化比较平缓,而介电损耗随温度的增加而降低;复合材料吸水后,介电常数和介电损耗都会增加;复合材料介电常数ε<4,介电损耗tanδ<0.1,能满足导弹天线罩透波材料介电性能的要求。     

差分表面等离激元共振传感仿真研究

从薄膜光学理论出发,对不同金属膜厚度、不同实折射率和不同复介电常数的环境介质的表面等离激元共振(SPR,Surface Plasmon Resonance)信号进行了分析,给出了最佳金属膜厚度,并且,折射率与共振角呈线性关系(R=0.999 4).分析了采用差分处理时,随环境介质的复介电常数变化的光反射率曲线.结果表明,同组两个探测器信号的和随环境介电常数的虚部变化,与实部无关,其信号差则相反,因此,能够同时测量环境介质的介电常数的实部和虚部.     

RTM工艺中树脂固化温度与介电性能

RTM为闭模成型工艺, 难以观察到模腔内树脂的充模与固化反应过程。利用介电分析仪对RTM工艺进行在线监测, 测得了树脂固化过程中不同模具温度下树脂反应的温度及离子导电率、 不同纤维含量条件下的介电常数以及不同纤维织物方式下的离子导电率。实验结果表明: 固化反应放热使复合材料局部温度升高, 并形成复杂的温度梯度分布; 在较高温度和较低纤维含量条件下, 离子导电率变化较快, 对树脂固化反应的影响较大; 不同织物方式的玻璃纤维对离子导电率也有一定的影响, 玻璃纤维复合毡比方格布影响大。      

Dielectric relaxation related to single-ionized oxygen vacancies in (Pb1−xLax)(Zr0.90Ti0.10)1−x/4O3 ceramics

The dielectric relaxation phenomenon has been studied in lanthanum modified lead zirconate titanate ceramics in the high temperature paraelectric phase. The high temperature dielectric response revealed an anomalous behavior, which is characterized by an increase of the real component of the dielectric permittivity with the increase of the temperature. At the same time, a similar behavior, with very high values, has been observed in the imaginary component of the dielectric permittivity, which can be associated with conduction effects related to the conductivity losses. The frequency and temperature behavior of the complex dielectric permittivity has been analyzed considering the semi-empirical complex Cole-Cole equation. The activation energy value, obtained from the Arrhenius’ dependence for the relaxation time, was found to decreases with the increase of the lanthanum concentration and has been associated with single-ionized oxygen vacancies. The short-range hopping of oxygen vacancies is discussed as the main cause of the dielectric relaxation.     

Electrical Relaxation in Mixed Alkali Bi2O3-K2O-Li2O-Fe2O3 Glasses

A new glass system(Bi2O3)50(Fe2O3)10(Li2O)x(K2O)40-x, where x changes in steps of 5 mole fraction between 0 and 40, was selected to study the electrical relaxation and the mixed alkali effect(MAE)phenomena.Measurements of ac conductivity σac, dielectric permittivity ε' and loss factor tanδ in the frequency range of 0.12～102 kHz and in the temperature range of 300～650 K were carried out. The temperature dependence of the ac conductivity shows a slow increasing rate at low temperature and high frequency and a rapid increase at high temperature and low frequency. At constant temperature, the ac conductivity is found to be proportional to ωs, where s is the frequency exponent, which is less than 1. Analysis of the conductivity data and the frequency exponent shows that the overlapping large polaron tunnelling(OLPT)model of ions is the most favorable mechanism for the ac conduction in the present glass system. The ac response, the dc conductivity and dielectric relaxation have the same activation energy and they originate from the same basic transport mechanism. The results of the dielectric permittivity show no maximum peak in the temperature and frequency range studied. This absence of maximum peak is an indication of non-ferroelectric behavior of all the studied samples. The MAE has been detected in the ac conductivity, which is the same as the classical MAE in the dc conductivity. The electrical parameters such as dielectric permittivity ε' and real dielectric modulus M'show a typical minimum deviation from linearity by about two orders of magnitude. The loss factor tanδ and the imaginary dielectric modulus M" are insignificantly dependent on composition even at the same transition temperature Tg.     

Effect of thermal treatment conditions on the properties of onion-like carbon based polymer composite

Dielectric properties of onion-like carbon (OLC) and polyurethane composite prepared using different procedures were investigated in the frequency range up to 1 MHz. We show that broadband dielectric spectroscopy is powerful tool to determine technological fingerprints in the studied materials. It is demonstrated that cured samples annealed at temperature close to the melting point (450 K) exhibit substantially higher dielectric permittivity and electrical conductivity in comparison with untreated samples. With the increase of temperature of an untreated sample, its dielectric permittivity, electric conductivity and critical frequency increase, while Maxwell–Wagner mean relaxation time and aggregate sizes of OLC decreases. Annealing of the composite at temperature close to the melting temperature produce sample with more homogeneous distribution of OLC. The temperature dependence of conductivity of the homogeneous sample is mainly caused by a weak positive temperature coefficient effect.     

FTIR and dielectric studies of nickel doped potassium hexa-titanate (K2Ti6O13) fine ceramics

The dielectric and electrical properties such as relative permittivity $(\varepsilon^{\prime } )$ , loss tangent (tanδ), and ac conductivity (σ_ac) have been studied in the temperature range 373–773 K at three different frequencies 100, 200, 400 kHz for doped potassium hexa-titanate (K₂Ti₆O₁₃) samples. It was observed that dielectric constant and loss tangent decreases while ac conductivity increases with the increase in frequency. The temperature dependent relative permittivity showed a phase transition for all samples. Dielectric loss mechanism was observed to include space charge polarization and dipole orientation. Moreover, electron-hopping conduction was observed to be dominant in the low temperature region, whereas intratunnel ionic conduction prevailed at higher temperatures. Fourier transform infrared spectroscopy analysis was also carried out to identify the chemical bonds present in the specimens.     

Triethylene Glycol Stabilized CoFe2O4 Nanoparticles

We report on the synthesis and detailed composition, thermal, micro-structural, ac?Cdc conductivity performance and dielectric permittivity characterization of triethylene glycol (TREG) stabilized CoFe₂O₄ nanoparticles synthesized by polyol method. XRD analysis confirmed the inorganic phase as CoFe₂O₄ with high phase purity. Microstructure analysis with TEM revealed well separated, spherical nanoparticles in the order of 6?nm, which is also confirmed by X-ray line profile fitting. FT-IR analysis confirms that TREG is successfully coated on the surface of nanoparticles. Overall conductivity of nanocomposite is approximately two magnitudes lower than that of TREG with increase in temperature. The ac conductivity showed a temperature dependent behavior at low frequencies and temperature independent behavior at high frequencies which is an indication of ionic conductivity. The dc conductivity of the nanocomposites and pure TREG are found to obey the Arrhenius plot with dc activation energies of 0.258?eV and 0.132?eV, respectively. Analysis of dielectric permittivity functions suggests that ionic and polymer segmental motions are strongly coupled in the nanocomposite. TREG stabilized CoFe₂O₄ nanoparticles has lower ???? and ???? than that of pure TREG due to the doping of cobalt. As the temperature increases, the frequency at which (????) reaches a maximum shifted towards higher frequencies. On the other hand, the activation energy of TREG for relaxation process was found to be 0.952?eV which indicates the predominance of electronic conduction due to the chemical nature of TREG. Contrarily, no maximum peak of tan ?? was observed for the nanocomposite due to the being out of temperature and frequency range applied in the study.     

Effect of Zn Substitution on Electrical Properties of Nanocrystalline Cobalt Ferrite

Nanocrystalline cobalt ferrites substituted with Zn with formula, Co_1?x Zn _x Fe₂O₄ (x=0.0–1.0) were prepared by the hydrothermal method. In this process, triethylene glycol was used both as a solvent and surfactant. The ac conductivity measurements of the samples showed a temperature-dependency at lower frequencies and independency at higher frequencies, which indicates the ionic conductivity. The ac conductivity depends on the temperature. This conductivity can be fitted with the well-known power law model in higher frequency. The dc conductivity is assumed to obey the Arrhenius equation. The dielectric behavior in various temperatures ranges revealed frequency dependency in a reciprocal power law. The dissipation of energy stored within the nanoparticle was found to act upon the reciprocal power law of the frequency dependency. Both the analysis of electrical conductivity and the dielectric permittivity functions suggest that the ionic and polymer segmental mobility could strongly be coupled in the nanoparticles.     

铁电复合物PZT/P[VDF(77)-TrFE(23)]退极化场系数的电场与温度效应

用自建的适合厚片材料测量的介电测试系统研究了不同组分含量的ＰＺＴ／Ｐ（ＶＤＦ（７７）－ＴｒＦＥ（２３））０－３型铁电复合物厚片介电系数的电场和温度依赖性,在低电场和室温附近的温度范围,由Ｂｒｕｇｇｅｍａｎ方程预测的介电系数和实验值较为接近。Ｙａｍａｄａ模型通过退极化场系数Ｌｚ的变化,可拟合复合物介电系数的电场和温度依赖关系。结果显示Ｌｚ随电场的升高而降低,随温度的改变（升温、降温过程）而与复合物介     

异质材料电磁特性及局域场增强效应研究

采用准静电模型仿真了两相异质材料的等效介电常数和局域场分布,结果表明,对于介质一介质型异质材料,三维模型等效介电常数仿真值与Bruggeman公式相符,并位于Hashin-Shtrikman上下界之间;异质材料内两相介电常数差异越大,其内局域场越强.对于由导电相和介质相构成的异质材料,仿真结果表明,异质材料内的电场分布受导电相填充比、形状和电导率等因素的影响;导电相导电性越好,其局域场增强现象越明显.     

Irreversible anomalies in the electrical properties of oxides with the tetragonal tungsten bronze structure

The anomalies in the electrical properties of (Pb,Sr,Ba)₄Li₂Nb₁₀O₃₀ solid solutions were studied by measuring dielectric permittivity and electrical conductivity as functions of temperature and time (during isothermal holding). The anomalies were shown to occur in defect-rich ferroelectrics. Both the dielectric permittivity and conductivity vary exponentially with time during isothermal holding. The effects of heating rate and UV irradiation time are analyzed. The results can be accounted for in the framework of a fluctuation-cluster model.