基于热膨胀性质的ZrO2 固体电解质性能与相关系模型

ZrO₂固体电解质室温下各相的相对含量、高温可相变量是决定材料抗热震性和导电性能的关键因素.固体电解质抗热震性与导电性能的匹配,对低氧含量下的钢水定氧起着重要作用.以此为前提,建立了电解质材料体系的抗热震性与室温相比例之间的线性模型,提出了其高温电导率与相变之间的演化模型.为制备用于测低氧活度的高精度冶金氧传感器提供参考依据.     

交流阻抗谱方法对钇稳定氧化锆晶界电性能的研究

采用交流阻抗谱技术测量了多晶钇稳定的氧化锆固体电解质的晶界离子电导率,并根据砖层模型估算了多晶陶瓷样品的晶界体积分数,分析了晶界体积分数与电性能的关系.     

KNb1-xMgxO3-δ的高温高压合成及输运性质研究

采用高温高压法制备了KNb1-xMgxO3-δ (x=0.0～0.3)氧离子导电材料,使用XRD、TG-DTA及交流复阻抗谱对样品的结构和离子导电性进行了表征.实验结果表明,高压降低了合成温度,合成的KNb1-xMgxO3-δ系列固溶体与其母体 KNbO3一样都为正交钙钛矿结构,晶胞参数随掺杂量的增加而略微增大.固溶体KNb1-xMgxO3- δ具有离子导电特征,通过拟合阻抗谱数据获得了该材料晶粒电导、晶界电导和体电导率与温度的关系.样品的晶界电阻较高,晶界效应十分明显,离子跳跃传导可能在其输运机制中占据主导地位.在x=0.1附近,电导率达到最大值,700℃时为1.2×10-3S* cm-1.     

KNb_(1-x)Mg_xO_(3-δ)的高温高压合成及输运性质研究

采用高温高压法制备了KNb1-xMgxO3 -δ(x =0 .0～ 0 .3)氧离子导电材料 ,使用XRD、TG-DTA及交流复阻抗谱对样品的结构和离子导电性进行了表征。实验结果表明 ,高压降低了合成温度 ,合成的KNb1-xMgxO3 -δ系列固溶体与其母体KNbO3 一样都为正交钙钛矿结构 ,晶胞参数随掺杂量的增加而略微增大。固溶体KNb1-xMgxO3 -δ具有离子导电特征 ,通过拟合阻抗谱数据获得了该材料晶粒电导、晶界电导和体电导率与温度的关系。样品的晶界电阻较高 ,晶界效应十分明显 ,离子跳跃传导可能在其输运机制中占据主导地位。在x =0 .1附近 ,电导率达到最大值 ,70 0℃时为 1.2× 10 - 3 S·cm- 1。     

基于Zview和Origin软件的交流阻抗谱的实验数据处理

以固体氧化物燃料电池(SOFC)电解质的研究为例,具体介绍了基于Zview软件和Origin8.5软件对交流阻抗实验数据进行处理和分析的方法。通过等效电路处理可区分电解质的晶粒电阻、晶界电阻以及界面电阻,获得电导率与温度的变化关系等重要的实验结果,为本科生关于氧化物电解质交流阻抗以及导电性能方面的研究项目进行数据处理和分析提供借鉴和参考。     

Ba0.98Ce0.8Tm0.2O3-α的离子导电性及其燃料电池性能

用高温固相反应法制备了Ba_0.98Ce_0.8Tm_0.2O_3-α钙钛矿型氧化物固溶体,粉末X射线衍射表明该固溶体为单相. 用交流阻抗谱技术和气体浓差电池方法研究了样品在500～900 oC、不同气体气氛中的导电性,以及该样品为固体电解质的氢-空气燃料电池性能. 该电池能稳定地工作,在900 oC时,电池的最大功率密度为110.2 mW/cm²,高于以Ba_xCe_0.8RE_0.2O₃^- (x≤1, RE=Y, Eu, Ho)为固体电解质的氢-空气燃料电池的功率密度     

Pr0.7Ca0.3MnO3陶瓷晶界势垒的交流特性

采用固相烧结方法制备了Pr1-xCaxMnO3(x=0.3)钙态矿结构锰氧化物陶瓷样品,对其在磁场和电场下的直、交流输运性质做了系统研究.通过测量加磁场和零场下的Ⅰ-Ⅴ曲线,得到其居里温度为150K,与VSM测试结果一致.通过测量加磁场与零场下交流的阻抗频谱,发现加磁场后样品的晶界电阻明显减小,而晶粒电阻几乎保持不变,表明Pr1-xCaxMnO3陶瓷多晶样品的CMR效应源于样品的晶界.为确定晶界处的势垒高度,测量了样品在不同频率下的阻抗温谱,根据Arrhenius定律拟合得出势垒高度为117 meV,与用直流R-T数据拟合得出的激活能一致.     

固体电解质Rb4Cu16I7Cl13制备及离子导电性研究

液态固体电解质材料的离子电导率低,安全性问题在一定程度上限制了其发展与应用,而固体电解质材料在室温下具有很好的稳定性和高的离子电导率值,具有较好的应用前景.本文采用机械化学球磨法制备固体电解质Rb₄Cu₁₆I₇Cl₁₃粉末,探索制备工艺和球磨参数,对其晶体结构进行解析、观察粉体微观结构、通过交流阻抗谱及等效电路分析得到了离子电导率与活化能、并详细探讨其离子传导性能与晶体结构的关系以及化学成分稳定性进行研究.实验结果表明,在480 rpm转速下球磨6 h时可得到纯的固体电解质Rb₄Cu₁₆I₇Cl₁₃物相.粉体晶粒尺寸分布均匀,均在20 nm-400 nm之间,室温下固体电解质Rb₄Cu₁₆I₇Cl₁₃离子电导率可达到0.213 S/cm且活化能为0.087(9)eV.在真空干燥条件下存放5天和12天后观察了微观形貌和化学稳定性...     

蓝宝石衬底上Gd2O3掺杂CeO2氧离子导体电解质薄膜的生长及电学性能

采用反应磁控溅射方法,在(0001)蓝宝石单晶衬底上,制备了纳米多晶Gd2O3掺杂CeO2(GDC)氧离子导体电解质薄膜,采用X射线衍射仪(XRD)、原子力显微镜(AFM)对薄膜物相、结构、粗糙度、表面形貌等生长特性进行了表征,利用交流阻抗谱仪测试了GDC薄膜不同温度下的电学性能;实验结果表明,GDC薄膜为面心立方结构,在所研究的衬底温度范围内,均呈强(111)织构生长;薄膜表面形貌随衬底温度发生阶段性变化:衬底温度由室温升高到300℃时,对应球形生长岛到棱形生长岛的转变,当完全为棱形岛生长时(300℃),生长岛尺寸显著增大;从400℃开始,则发生棱形生长岛到密集球形生长岛的转变,球形生长岛尺寸明显减小.生长形貌的转变反映着薄膜生长初期不同的成核机理,很可能与蓝宝石(13001)面的表面结构随温度变化有关;GDC多晶电解质薄膜的复平面交流阻抗谱主要源于晶界的贡献,根据Arrhenius图求得电导活化能Ea在1.2-1.5 ev范围内,接近于晶界电导的活化能值,并且随衬底温度升高Ea减小(Ea300 > Ea400> Ea600 );电导活化能以及晶粒尺寸不同,导致GDC薄膜电导率随测试温度的变化规律不同.     

碳纳米管光混频器产生太赫兹功率的理论分析

以光混频器电路模型为基础,理论分析了碳纳米管(CNT)材料光混频器产生太赫兹功率的大小.通过对光混频器电导、天线的阻抗和外加偏置电压的模拟结果表明:提高光混频器电导、天线阻抗和外加偏置电压都能够提高输出太赫兹波功率,在小信号输入条件下,输出功率理论上能够达到数十微瓦.     

Impedance spectroscopy studies on chemically deposited CdS and PbS polycrystalline films

Room temperature impedance spectroscopy measurements on chemically deposited CdS and PbS films were performed using the ‘sandwich’ geometry. The experimental data for both materials represented by the complex plane diagrams showed two well-defined semicircles. The results were analyzed in terms of the ‘brick-layer’ model, appropriate for polycrystalline materials in which the crystallites and its boundary are well developed. According to this model, the equivalent circuit which best represent the polycrystalline films, consists of two RC circuits connected in series, one representing the grain and the other the grain boundaries. By fitting the spectral response of the equivalent circuit to the impedance measurements, electrical and structural parameters were obtained.     

Correlation between microstructure and degradation in conductivity for cubic Y2O3-doped ZrO2

The application of Yttria-stabilized Zirconia (YSZ) as solid electrolyte in high-temperature solid oxide fuel cells (SOFC) is well established. However, the strong decrease of the ionic conductivity in 8.5 mol% Y₂O₃-doped ZrO₂ at high temperature has not yet been clarified completely. To contribute to the understanding of the degradation process, transmission electron microscopy (TEM) was applied to analyze the microstructure in YSZ electrolyte substrates in as-sintered and aged material. Selected area electron diffraction and conventional TEM imaging were performed to investigate the evolution of different phases and phase transitions in YSZ. Grain boundary charging and the possible formation of a glassy phase at grain boundaries after aging were investigated using transmission electron holography and high-resolution TEM. The ionic conductivity was characterized by dc-conductivity measurements and impedance spectroscopy.     

Mixed ionic and electronic conductivity study of charge transfer complexes of some substituted pyridines with iodine monochloride (ICl) by AC impedance spectroscopy

Mixed ionic and electronic conductivity of three solid charge transfer (CT) complexes of pyridine, 4-methylpyridine (γ-picoline) and 3,5-dimethylpyridine (3,5-lutidine) with ICl (iodine monochloride) are reported. Electrical parameters of the prepared complexes in the pellet form are evaluated at various temperatures and at wide frequency range by employing AC complex impedance spectroscopic technique. Suitable equivalent circuits for the Nyquist plots, which provide the most realistic model of the electrical properties of the CT complexes, have been suggested. Both transport number measurements and impedance spectra reveal that the conduction in γ-picoline-ICl complex is mainly due to ions, in 3,5-dimethylpyridine-ICl complex, it is due to both ions and electrons and in pyridine-ICl complex, it is predominantly due to electrons. The a.c. conductivity measurements of the CT complexes have been carried out in the frequency range of 10–10⁵ Hz within the temperature range of 303–353 K. The variation of a.c. conductivity with frequency follows the Jonscher’s universal power law. The temperature dependence of electrical conductivity suggests the semiconducting behaviour of the materials.     

Electrical conductivity of yttria-stabilized zirconia with cobalt addition

Yttria-stabilized zirconia is the most developed solid electrolyte for use in high-temperature solid oxide fuel cells. Commercial yttria-stabilized zirconia powders reach high densification at temperatures higher than that of the usual anode materials. Reduction of the sintering temperature of the solid electrolyte could allow for co-firing of both ceramic components, thereby reducing production costs. The main purpose of this work was to study the effect of small cobalt additions on densification and on electrical conductivity of 8 mol% yttria-stabilized zirconia. Linear shrinkage results show that the onset temperature for shrinkage decreases with increasing cobalt content. Impedance spectroscopy measurements reveal that the electrical conductivity depends on the sintering profile. For specimens sintered at 1400 °C for 0.1 h the electrical conductivity of grains and grain boundaries are almost unchanged with that of 8YSZ. In contrast, for specimens sintered at the same temperature but for 0.5 h of soaking time, the electrical conductivity is higher in 0.025 mol% samples and is lower for 1 mol% Co doped 8YSZ. Degradation of the microstructure by increased porosity was obtained for high additive contents.     

AC impedance analysis of LaLiMo2O8 electroceramics

Complex impedance analysis of a new rare earth-based ceramic oxide, LaLiMo₂O₈, prepared by a standard solid-state reaction technique has been carried out. Material formation under the reported conditions has been confirmed by X- ray diffraction studies. A preliminary structural analysis indicates the crystal structure to be orthorhombic. Electrical properties of the material sample have been studied using AC impedance spectroscopy technique. Impedance spectrum results indicate that the electrical properties of the material are strongly dependent on temperature and it bears a good correlation with the sample microstructure (i.e. the presence of bulk, grain boundary, etc.) in different temperature ranges. Evidences of temperature-dependent electrical relaxation phenomena in the material have also been observed. The bulk resistance, evaluated from complex impedance spectrum has been observed to decrease with rise in temperature showing a typical negative temperature coefficient of resistance (NTCR)-type behavior like that of semiconductors. The DC conductivity shows typical Arrhenius behavior when observed as a function of temperature. The AC conductivity spectrum has provided typical signature of an ionically conducting system and is found to obey Jonscher's universal power law. Modulus analysis has indicated the possibility of hopping mechanism for electrical transport processes in the system with non-exponential-type conductivity relaxation.     

Impedance spectroscopy study on the ionic conductivity processes of the novel LiFeVO<Subscript>4</Subscript> phase

The recently discovered compound LiFeVO₄ was prepared by solid-state reaction at 570 °C during a 7-h period. The X-ray diffraction pattern revealed an orthorhombic crystal structure. Thermogravimetric measurements revealed a reversible mechanism which was attributed to absorption–desorption of humidity. Impedance spectroscopy measurements were carried out at 25 °C steps in the temperature range from 25 to 500 °C and equivalent circuits were drawn to fit the impedance measurement results at each temperature level. The elements of the equivalent circuits were assigned to bulk, grain boundary, and along grain boundary conductivity. All three conduction mechanisms were found to be humidity sensitive. Arrhenius plots were plotted for the bulk and grain boundary conductivity processes. The activation energy for the bulk conductivity process was calculated to be 0.25 eV over the temperature range from 175 to 500 °C and the activation energy for the grain boundary conductivity process was calculated to be 0.41 eV from 300 to 500 °C and 0.20 eV from 175 to 275 °C. An explanation for the existence of these two grain boundary activation energies is attempted. The dependence of the material conductivity mechanisms on humidity suggests that LiFeVO4 could be used as a humidity sensor.     

Enhanced ionic conductivity in LAGP/LATP composite electrolyte

Nasicon materials(sodium superionic conductors) such as Li_(1.5)Al_(0.5)Ge_(1.5)(PO_4)_3(LAGP) and Li_(1.4)Al_(0.4)Ti_(1.6)(PO_4)_3(LATP) have been considered as important solid electrolytes due to their high ionic conductivity and chemical stability.Compared to LAGP, LATP has higher bulk conductivity around 10~(-3) S/cm at room temperature; however, the apparent grain boundary conductivity is almost two orders of magnitude lower than the bulk, while LAGP has similar bulk and grain boundary conductivity around the order of 10~(-4) S/cm. To make full use of the advantages of the two electrolytes, pure phase Li_(1.5)Al_(0.5)Ge_(1.5)(PO_4)_3 and Li_(1.4)Al_(0.4)Ti_(1.6)(PO_4)_3 were synthesized through solid state reaction, a series of composite electrolytes consisting of LAGP and LATP with different weight ratios were designed. XRD and variable temperature AC impedance spectra were carried out to clarify the crystal structure and the ion transport properties of the composite electrolytes. The results indicate that the composite electrolyte with the LATP/LAGP weight ratio of 80:20 achieved the highest bulk conductivity which shall be due to the formation of solid solution phase Li1.42 Al0.42 Ge0.3 Ti1.28(PO4)3, while the highest grain boundary conductivity appeared at the LATP/LAGP weight ratio of 20:80 which may be due to the excellent interfacial phase between Li_(1+x)Al_xGe_yTi_(2-x-y)(PO_4)_3/LATP. All the composite electrolytes demonstrated higher total conductivity than the pure LAGP and LATP, which highlights the importance of heterogeneous interface on regulating the ion transport properties.     

Nonlinear least-squares analyses of complex impedance and admittance data for solid electrolytes

A nonlinear least-squares curve fitting technique, suitable for use with a laboratory minicomputer, is described for the analysis of a complex impedance (admittance) spectrum in which distortions of the various shapes constituting the complex plane plot occur because of overlapping time constants. With this technique, estimates of the parameter values occurring in an equivalent circuit are first obtained by a geometrical-fitting procedure and these are then used as the initial parametric values in a complex least-squares method which simultaneously fits the real and imaginary parts of the impedance (admittance) to a model (equivalent circuit), thereby yielding best-fit values of the circuit parameters as well as their confidence intervals. The method is illustrated by analyzing: (1) artificial, computer-generated impedance (admittance) data constructed for some simple RC circuits commonly used to model solid electrolyte behavior; and (2) measured admittance response of the fast sodium ion conductor NASICON at 486 K.     

Dielectric and electrical properties of a tungsten bronze tantalate ceramic

Using high temperature solid state reaction the polycrystalline sample of K₂Pb₂Dy₂W₂Ti₄Ta₄O₃₀ was prepared. Single-phase compound formation was confirmed by preliminary X-ray structural analysis. The surface morphology recorded by scanning electron microscope at room temperature exhibits a dense uniform grain distribution on the surface of the sample. Ferroelectricity in the material is confirmed by the variation of polarization with temperature. The temperature and frequency dependence of electrical parameters (impedance, modulus, conductivity, etc.) of the material exhibits a strong correlation with its microstructure (i.e., bulk, grain boundary, etc.) and electrical properties. A typical Arrhenius behavior was observed in the temperature dependence of dc conductivity. The nature of frequency dependence of ac conductivity obeys Jonscher's universal power law. The variation of current with temperature shows that the material has high pyroelectric coefficient and figure of merit, thus making it useful for pyroelectric sensors with working temperature upto 500 °C.