非晶氧化铝超薄膜中的电荷输运特性

研究了反应射频磁控溅射制备的非晶氧化铝薄膜中电荷输运过程,发现交流和直流电导导电机制是明显不同的。对直流输运,以Poole-Frenkel发射发射模式为主,而新样品的直流电导则常常是带陷阱的空间电荷限制电流模式。交流电导则是由所谓的声子辅助的定域载流子的跳跃引起的。电导的温度特性表明,交流电导有两种不同的导电机制,即低温区的浅陷阱发和 高温区的因氧缺陷导致的深陷阱的发射过程,直流电导与交流电导在高温区趋于一致。     

Y2O3稳定ZrO2材料的电导活化能

在313－473K温度范围内测定了一种Y2O3稳定ZrO2材料（YSZ）的交流电导率谱，进而导出了材料的直流电导率并分析了其随温度的变化关系。研究发现：在低温下材料的电导尖化能随温度的升高而增大。这一实验现象与在高温下所观察到的活化能随温度升高而降低规律截然相反。通过分析材料中氧空位的解缔及迁移机制，对YSZ材料中电导活化能随温度的变化关系作出了一个合理的解释。     

半固态锂电池电极浆料导电性能的评价方法研究

半固态锂电池是一种新型电化学储能技术,以电极浆料作为电化学反应的主体材料。电极浆料是将电极活性材料和导电剂分散于电解液中形成的固液混合体系,导电性能的优劣决定其是否能够实现良好的电化学性能。本论文以不同导电添加剂配比的磷酸铁锂电极浆料为研究对象,分别采用直流电导率仪、电化学阻抗谱测试以及固定频率交流电测试的方法进行电导率的测定,并与半电池在不同电流密度下的充放电性能进行了比较。研究认为对电极浆料进行电化学阻抗谱测试是有效的导电性能评价方法,但模型建立和数值模拟的过程较为复杂;通过电化学工作站对样品施加固定频率的交流电亦可得到相应的阻抗,测试结果稳定,操作简单高效,可用于对电极浆料导电性能的初步评价和比较。     

La0.5Sr0.5CoO3-δ薄膜的制备及其电学性能

采用离子束溅射法在氧化钇稳定的氧化锆（YSZ）和SiO2衬底上溅射＜薄膜，测试了不同工艺制备的La0.5Sr0.5CoO3-δ薄膜样品的XRD谱和电导率。分析了薄膜表面微结构以及电学性能。结果表明：在YSZ衬底上生长的La0.5Sr0.5CoO3-δ薄膜随着热处理温度的升高取向增强，当薄膜经过750℃热处理后结晶度最好；各样品直流电导率在低温段的Arrhenius曲线近似为直线，表明材料的导电行为符合小极化子导电机制；交流电导率在低频段（＜100kHz）电导率主要是靠晶界导电贡献的，而在高频区（＞100kHz），样品对交流电响应更加明显，电导率主要是靠晶粒导电贡献的。     

Y2O3稳定ZrO2材料的电导活化能

在313～473K温度范围内测定了一种Y2O3稳定ZrO2材料(YSZ)的交流电导率谱,进而导出了材料的直流电导率并分析了其随温度的变化关系.研究发现:在低温下材料的电导活化能随温度的升高而增大.这一实验现象与在高温下所观察到的活化能随温度升高而降低的规律截然相反.通过分析材料中氧空位的解缔及迁移机制,对YSZ材料中电导活化能随温度的变化关系作出了一个合理的解释.     

Dy掺杂La2／3Ca1/3MnO3锰氧化物制备及低磁场下电输运性质

用溶胶-凝胶法制备了系列掺杂（La1-xDyx）2/3Ca1／3MnO3多晶纳米晶体,粒度在100nm左右。对系列样品电输运性质的研究表明,（La1-xDyx）2/3Ca1／3MnO3体系的电输运行为对Dy掺杂量极为敏感。随着Dy含量的增加,样品的转变温度向低温方向移动,峰值电阻显著变大;随着磁场的增加,其转变温度向高温方向略有移动;磁场增加引起的材料磁有序状态提高,使材料的磁电阻进一步变大。     

A位阳离子无序对La_(2/3)Ca_(1/3)MnO_3结构和输运性能的影响

利用固相反应法合成了(La1-xDyx)2/3Ca1/3MnO3(x=0、0.1、0.2)材料,研究阳离子无序对微结构和电输运性能的影响。Rietveld方法拟合XRD结果表明,随着Dy掺杂浓度的增加,晶胞参数和Mn-O键长键角发生了明显的变化,造成MnO6八面体畸变。电输运性能显示:样品电导率随Dy掺杂量的增加而减小,其导电机制符合半导体小极化子模型。Dy掺杂浓度的增加使得钙钛矿ABO3的A位阳离子无序度增加,影响了样品的微结构;A位无序效应增强了载流子的晶格散射,抑制了电导率。     

含碳复合体系的流变学性质和导电性质

利用高级流变扩展系统研究了含碳复合体系的流变学性质随温度的变化关系。研究发现,在逾渗阈值前后复合体系的流变学行为表现出很大的差异,高温时复合体系的储能模量随填充浓度的增加而急剧增大,损耗因子在100℃附近出现峰,峰位随碳含量的增加向高温方向移动,当体系浓度在逾渗阈值以上时趋于平坦;直流电导率和交流电导率测量表明电导逾渗阈值和流变学逾渗阈值非常相近;最后尝试对不同温度下的电导率-频率曲线进行了叠加。     

摩擦发电微流体传感器特性的有限元仿真研究

近年来,摩擦发电技术被广泛应用于信号传感领域,尤其是对封闭管道中液体输运的信号监测。为阐释基于摩擦发电效应的微流体传感器的工作原理,通过有限元仿真模拟,研究这种微流体传感器的信号产生过程及其传感特性,并通过实验测得该传感器在检测微流体运动时输出的交流电信号,验证仿真模型的正确性。另外在仿真模拟中,通过控制变量法,探讨基于摩擦发电效应的微流体传感器的传感性能随介电层厚度、电极间距及液体长度与电极宽度之比的变化规律。结果表明这种微流体传感器的输出信号强度随介电层厚度的增大而减小,而随电极间距的增大表现出先增大后减小的趋势,随液体长度与电极宽度的比值变化呈先增大后保持恒定的变化规律,该项研究工作将为研制更高传感性能的微流体传感器提供一定理论指导。     

磁场对Ni/硅橡胶复合材料交流电导率及介电性质的影响

采用硅橡胶（110型）与金属（镍粉）按质量比为1∶2.7进行配料, 应用室温二次固化合成Ni/硅橡胶压敏复合材料样品。室温下测量了样品的压阻效应, 比较了外加0.024 T磁场前后样品的介电性质。结果表明, 当压强从3.75kPa到312.5kPa时, 样品直流电阻率下降了8个数量级。与加磁场前相比, 0.024T的磁场使得低频(40~104Hz)交流电导率提高了2.46倍, 介电常数提高了20%, 介电损耗提高了2倍, 这主要是由复合材料中铁磁绝缘体铁磁颗粒膜的隧道磁电阻效应以及磁电耦合引起的。撤去磁场后交流电导率、介电常数和介电损耗均不能回到加磁场前的初始值, 这与Ni粉的铁磁性有关。Ni/硅橡胶压敏复合材料的压阻、 磁电阻效应及磁电耦合等物理性质在磁传感器件、 信息储存等领域有潜在的应用价值。      

Impedance spectroscopy and conductivity studies on B site modified (Na0.5Bi0.5)(Nd x Ti1 − 2x Nb x )O3 ceramics

Nd and Nb doped sodium bismuth titanate ceramics have been synthesized and characterized. Structural properties were obtained based on the XRD pattern analysis, indicating rhombohedral symmetry at room temperature. Impedance and conductivity (DC and AC) studies were done on polycrystalline samples. The results indicate that DC and AC conduction occurs by different mechanism in each case. The possible mechanism in the present case is discussed.     

ABS/石墨复合材料的交直流导电特性及流变性能

研究了石墨填充丙烯腈-丁二烯-苯乙烯共聚物(ABS)复合材料的直流(DC)和交流(AC)导电特性和线性粘弹行为。电性能测试结果表明,石墨体积分数为13.21%~16.36%时,ABS/石墨复合材料的DC电阻率突降6个数量级,说明发生电学逾渗;同时,AC电阻率在低频区不随频率而变化,且AC阻抗复平面图中阻抗实部与阻抗虚部呈现半圆弧,进一步证明导电网络的形成。流变性能测试结果表明石墨体积分数为10.24%~13.21%时复合体系的储能模量和复数黏度出现跳跃,损耗因子(tanδ)的峰值减小且逐渐向高频移动,说明复合体系从"类液态"转变为"类固态",发生流变逾渗现象。流变逾渗阈值小于导电逾渗阈值是因为传递电子时石墨之间的距离比阻碍聚合物分子链运动时石墨之间的距离小。     

DC conductivity and interfacial polarization in PMMA/nanotube and PMMA/soot composites

This work focuses on the DC conductivity and interfacial polarization of poly(methyl methacrylate) (PMMA) composites made with single wall nanotubes (SWNTs) and nanotube precursor soot. We aim to compare and contrast the behavior of the two nanofillers in an effort to determine if the precursor material imparts tunable electrical properties to PMMA. The DC activity of the polymers and composites was determined by extrapolating AC conductivity versus frequency plots to zero. Activation energies and DC conductivities were obtained through Arrhenius plots. The conductivity increased with temperature for all the samples in conjunction with viscous flow. Both nanotubes and nanosoot increased the DC conductivities. Activation energies for the SWNT decreased slightly upon the addition of nanotubes to the matrix. However, the activation energies increased with soot content in the matrix, indicating obstruction of motion or possible bridging caused by the soot. Cole-Cole plots were effectively used to determine the extent of interfacial polarization in the composite samples. Plots shifted toward the origin with the addition of carbon nanotubes or with soot concentration indicating a Maxwell-Wagner-Sillars process.     

Microtubule alignment and manipulation using AC electrokinetics

The kinesin-microtubule system plays an important role in intracellular transport and is a model system for integrating biomotor-driven transport into microengineered devices. AC electrokinetics provides a novel tool for manipulating and organizing microtubules in solution, enabling new experimental geometries for investigating and controlling the interactions of microtubules and microtubule motors in vitro. By fabricating microelectrodes on glass substrates and generating AC electric fields across solutions of microtubules in low-ionic-strength buffers, bundles of microtubules are collected and aligned and the electrical properties of microtubules in solution are measured. The AC electric fields result in electro-osmotic flow, electrothermal flow, and dielectrophoresis of microtubules, which can be controlled by varying the solution conductivity, AC frequency, and electrode geometry. By mapping the solution conductivity and AC frequency over which positive dielectrophoresis occurs, the apparent conductivity of taxol-stabilized bovine-brain microtubules in PIPES buffer is measured to be 250 mS m(-1). By maximizing dielectrophoretic forces and minimizing electro-osmotic and electrothermal flow, microtubules are assembled into opposed asters. These experiments demonstrate that AC electrokinetics provides a powerful new tool for kinesin-driven transport applications and for investigating the role of microtubule motors in development and maintenance of the mitotic spindle.     

Transport properties of microwave sintered pure and glass added MgCuZn ferrites

A series of pure stoichiometric and 1 wt% lead borosilicate (PBS) glass added MgCuZn ferrite with the general formula Mg_0.5Cu_xZn_0.5−xFe₂O₄ with x = 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 were synthesized by microwave sintering technique. Single phase spinel structure is exhibited by the XRD patterns of these ferrites. DC and AC conductivity were investigated as a function of composition, temperature and frequency. DC conductivities were also estimated using the impedance spectroscopy analysis of Cole–Cole plots. The DC conductivities thus obtained are in good agreement with the experimental results. All the investigated samples exhibited two regions of conductivity one in the low temperature and the second in the high temperature region. It is observed that PBS glass added samples have lower conductivities than pure samples. Due to their lower conductivities and sintering temperatures the 1 wt% PBS glass added samples are suitable for multilayer chip inductor (MLCI) and high definition TV deflection yoke material application.     

Hierarchical assembly of carbon nanotubes-liquid crystal nanocomposite

Fabrication of liquid crystalline (LC) nanomaterials in an aligned pattern along the multiwalled carbon nanotubes (CNT) has been reported here. The nanocomposite was prepared by sonicating esterified CNTs and the ferroelectric liquid crystal (FLC) in chloroform. The nanohybrid shish kebab (NHSK) like pattern was observed in SEM analysis. The nanocomposite materials were characterized by Fourier transform infrared spectroscopy (FTIR), polarizing optical microscopy and electron microscopy. The DC and AC electrical properties of the composite materials were investigated. The DC conductivity of the nanocomposite increased by 2 order from the FLC materials and AC relaxation has been observed, in the nanocomposite, which was totally absent in the FLC materials.     

Electrical transport studies in AsSe glasses

The DC and AC conductivity studies of AsSe glasses over a wide range of compositions have been reported and discussed. The contribution to conductivity from transport among extended states has been delineated and the possible existence of a characteristic temperature is indicated. Two conductivity maxima have been observed as a function of composition in AC conductivities at lower temperatures.     

Electrical transport properties of polyvinyl alcohol–selenium nanocomposite films at and above room temperature

Here, we report the DC and AC electrical properties of polyvinyl alcohol (PVA)–selenium (Se) nanocomposite films in the temperature (T) range 298 K ≤ T ≤ 420 K and in the frequency (f) range 120 Hz ≤ f ≤ 1 MHz. The introduction of selenium nanoparticles into the PVA matrix slightly increases the values of DC conductivity whose temperature dependency obeys Vogel–Fulcher–Tammann law. The AC conductivity follows a power law with frequency in which the temperature dependence of the frequency exponent suggests that the correlated barrier hopping is the dominant charge transport mechanism for the nanocomposite films. Comparative discussions with Dyre’s random free-energy barrier model have also been made in this regard. The increase in AC conductivity with increase in nanoparticles concentration was also observed and attributed to the corresponding increase in conducting channels in the PVA matrix. The real part of the dielectric constant increases either with increase in temperature or with increase in selenium nanoparticles loading into the polymer matrix, which may be attributed to the enhancement of interfacial polarization. The frequency dispersion of the dielectric spectra has been modeled according to the modified Cole–Cole equation. Well-defined peaks were appeared in the plotting of imaginary part of electric modulus with frequency above room temperature, which was fitted with suitable equations to account for the deviations from ideal Debye-type behavior. Though the current–voltage characteristics are linear at smaller voltages, it appreciably becomes nonlinear at higher voltages. This nonlinearity has been accounted in light of Werner’s model and back to back Schottky diode model.     

AC and DC Conductivity Studies on Lead-Free Ceramics: Sr1–xCaxBi4Ti4O15(x = 0, 0.2, 0.4, 0.6, 0.8)

Sr_1–xCa_xBi₄Ti₄O₁₅ [x = 0, 0.2, 0.4, 0.6, 0.8] ceramics are synthesized by solid-state reactive technique. Structural analyses are done by x-ray diffraction data. Morphological studies were carried out by scanning electron microscope, and the data showed plate-like structures. To understand the conductivity mechanism, frequency and temperature dependency of AC and DC conductivity studies are carried out. The conductivity measurements are done using an impedance analyzer (Wayn–Kerr) in the temperature range 100–600°C. The frequency-dependent AC conductivity at different temperatures indicates that the conduction process follows the universal power law, and the hopping frequency shifts toward higher frequency side with increase in temperature, below which the conductivity is frequency independent. The variation of DC conductivity confirms that the ceramics exhibit negative temperature coefficient of resistance behavior at high temperature. DC conductivity values do not show any linearity with doping concentration; for a particular composition SCBT06, the DC conductivity was low.     

Studies on electrical conduction in Bi4SrTi4O15

The ferroelectric Bi₄SrTi₄O₁₅ has been synthesized and a study of the electrical (AC) conductivity was made on both poled and unpoled samples in the frequency range from 100 Hz to 1 MHz and from room temperature to 550°C. In the case of unpoled samples the activation energy was found to be 0·54 eV and subsequent to poling it was lowered to 0·39 eV indicating an increased conductivity after poling. Further the conductivity increased with increasing frequency and temperature. DC conductivity measurements were also carried out. Dielectric measurements indicate a peak in the dielectric constant at 530°C.