LaGaO3基氧离子导体的研究进展

综述了8年来LaGaO3基氧离子导体的发展，分析了掺杂对LaGaO3结构及导电性能的影响，总结了合成方法、应用，指出了存在的问题及解决问题的途径。     

过渡和碱土金属掺杂对LaGaO3固体电解质电性能影响

采用固相反应法合成碱土金属Sr、Mg与过渡金属Fe或Co复合掺杂的LaGaO3基氧化物LSGMC和LSGMF;通过TG/DTA研究LSGMC和LSGMF的形成过程;采用直流四端子法测量样品在400℃-850℃温度区间的电导率;利用EDS和XRD等技术分析样品的微区成分和晶体结构等.结果表明,约在1000℃开始形成钙钛矿相,经1400℃烧结,获得单一正交钙钛矿结构;在测试温度范围,电导率与温度的关系符合Arrhenius方程,合成的LSGMC和LSGMF为氧离子导体;在相同温度下,Sr、Mg和Fe或Co复合掺杂氧化物LSGMC和LSGMF与仅Sr、Mg双掺杂氧化物LSGM相比具有较高的离子电导率,说明少量过渡金属Fe或Co的掺杂,有利于提高离子电导率.     

中温固体电解质LaGaO3的制备

分别采用固相反应法、凝胶燃烧法分别制备了镓酸镧基固体电解质粉体(La0．9Sr0.1Ga0．8Mg0．2O3-δ)．讨论了煅烧温度对粉体物相的影响,比较了两种方法所制备粉体的特点．X射线衍射分析表明．固相反应法制备需经1250℃下预烧15h,1500℃下煅烧24h．得到La0．9Sr0.1Ga0．8Mg0．2O3-δ粉体颗粒尺寸在1μm,而凝胶燃烧法仅需在1400℃煅烧10h可以合成La0．9Sr0.1Ga0．8Mg0．2O3-δ粉体,粉体颗粒尺寸150nm。     

Gd0.8Sr0.2 CoO3-Sm0.2Ce0.80 O1.9复合阴极制备及性能研究

为探索适于中温条件下使用的固体氧化物燃料电池的阴极材料,用固相反应法制备了Gd0.8Sr0.2CoO3(GSC)阴极粉体,用X射线衍射考察了GSC的成相温度.采用丝网印刷法将GSC-(Sm2O3)0.1(CeO2)0.8(SDC)沉积在SDC电解质圆片上,制成对称阴极,在不同温度下烧结.用交流阻抗谱从500～750℃测量了GSC-SDC复合阴极和SDC电解质之间的界面电阻.结果表明,GSC-SDC复合阴极的界面电阻比GSC阴极降低了3～5倍;750℃时,GSC-SDC阴极的界面电阻仅为0.15Ω·cm2.     

La、Nb掺杂固相反应法合成SrTiO3热电性能的优化

SrTiO₃作为钛矿型金属氧化物半导体,具有环境友好、原料来源丰富等优点。本研究发现了一种制备高新热电性能SrTiO₃材料的新工艺,对比固相反应法直接烧制的SrTiO₃陶瓷,采用本工艺的PAS+埋烧热处理方法可以降低制备反应温度,并且所得材料的功率因子得到显著提高。该项发现主要研究了在此工艺下制备的不同La、Nb掺杂比(5%-15%)的样品性能变化情况。结果表明,该工艺下制备的SrTiO₃样品中La15Nb15样品在873K时的最大功率因子可达1.279mW·m^-1·K^-1。但是部分样品热导率也会出现一定程度的增加。综合效果是材料热电优值ZT得以提升,在873K时La10Nb5样品的ZT值达到了0.28。     

固相反应法、柠檬酸盐法制备(NaBi)0.5TiO3陶瓷及性能表征

分别用固相反应法和柠檬酸盐法合成了(NaBi)0.5TiO3陶瓷前驱体,并烧制成相应的陶瓷。用激光粒度分析仪、XRD、SEM分别对前驱体和陶瓷的粒度、相组成、显微结构等进行表征,并检测不同烧结温度下的压电常数d33。研究表明,用柠檬酸盐法合成的NBT前驱体所需合成温度低于固相反应法;所制陶瓷具有更高的压电常数d33,在1150℃下烧结,d33可达61.6pc/n。     

双掺杂铈基电解质材料的研究

主要针对掺杂Zr4+的CeO2基电解质材料进行研究,并引入了第二种掺杂离子Sc3+,以期望能进一步改善其电性能。分析了该两种元素不同掺杂比例对电解质的电导率、微观性质及热过程的影响,并对产生这些差异的原因进行了初步探讨。采用固相法制取双掺杂的CeO2基电解质粉体,并对其最佳条件做了详细的分析。实验结果表明:在微观性质方面,经XRD分析可知,Sc3+改善了ZrO2在CeO2的固溶情况;在电性能方面,应用交流阻抗谱法分析了双掺杂的CeO2基电解质,可知其电导率有一定程度的提高,并得出Sc3+∶Zr4+∶Ce4+在摩尔比为5∶25∶7时活化能最小,电导率最佳。     

Sr、Mg掺杂LaGaO3固体电解质材料的离子导电性研究

采用固态反应法制备了Sr、Mg掺杂的LaGaO3固体电解质材料，研究了不同Sr、Mg掺杂量对LSGM材料的导电性的影响．结果表明，随Sr、Mg掺杂量的增加，LSGM材料的电导率开始增加，达到最大值后，逐步降低，LSGM1520和LSGM2015具有最高电导率，此时材料由单一的立方相组成；LSGM材料的离子电导率随测试温度的升高而增加，ln（σT）与1／T关系曲线呈现两段不同斜率的直线，交点温度为T^＊，当测试温度低于T^＊时，氧离子迁移激活能大于温度高于T^＊的激活能．     

SrTiO3基可逆固体氧化物电池电极材料的研究进展

可逆固体氧化物电池(RSOC)因具备高效可逆的发电和电解产氢性能,被认为是一种具有良好发展前景的能源转化设备。然而,缺乏高活性和稳定性的电极材料是限制RSOC广泛应用的主要因素之一。传统的燃料电极一般采用浸镍的氧化钇稳定氧化锆(Ni-YSZ)材料,而氧电极则以钙钛矿型的氧化物居多。目前使用的燃料电极和氧电极的电化学性能都存在一定的不足。近期,诸多研究报道SrTiO₃基钙钛矿材料具有良好的稳定性和电化学性能,有望成为RSOC电极的热门候选材料。近年来,虽然对RSOC电极的研究较多,但是缺乏对该类材料系统的归纳和总结。因此,本文综述了SrTiO₃基钙钛矿材料在RSOC电极方面的应用进展。首先,系统分析了SrTiO₃基钙钛矿材料在RSOC燃料电极和氧电极的研究现状,介绍了目前常用的SrTiO₃改性的手段和策略,如掺杂其他元素、构建非ABO₃化学计量比氧化物、构建复合材料以及利用原位纳米颗粒出溶技术等;其次,探讨了SrTiO₃基钙钛矿材料应用于对称结构RSOC电极...     

W、Mo添加对Fe-21Cr合金连接板高温性能的影响

Fe-Cr合金是固体氧化物燃料电池(SOF-Cs)连接板材料的最佳候选之一,但仍存在氧化速率较快以及热膨胀系数(TEC)较大等问题。采用热胀系数小的W和Mo元素,研究了W或Mo对Fe-21Cr合金热膨胀系数、面电阻及抗氧化特性的影响。研究结果表明,适量W或Mo的添加可以降低Fe-21Cr合金的热膨胀系数,并提高其750℃高温抗氧化性能。     

Synthesis of pure and Sr-doped LaGaO3, LaFeO3 and LaCoO3 and Sr,Mg-doped LaGaO3 for ITSOFC application using different wet chemical routes

Pure and Sr-doped LaGaO₃, LaFeO₃ and LaCoO₃ and Sr,Mg-doped LaGaO₃ were synthesized by various wet chemical routes, namely combustion, co-precipitation and citrate-gel methods. The effect of the various process parameters on the phase purity, particle size and surface area and morphology of the synthesized powders were determined by XRD, simultaneous TG-DTA, laser light scattering, BET and scanning electron microscopy. The stability of the synthesized pure phases in oxidizing and reducing atmosphere was also studied by thermogravimetry. It was observed that pure and Sr-doped single perovskite phases of lanthanum ferrite, cobaltite and gallate and Sr,Mg-doped lanthanum gallate could be synthesized by combustion and citrate-gel methods under suitable process conditions. Synthesis using the co-precipitation method yielded incomplete reaction irrespective of the calcination temperature adopted. The citrate-gel method yielded better powder properties in terms of particle size and morphology and surface area compared to combustion synthesis. It was found that pure and Sr-doped lanthanum ferrite, lanthanum cobaltite, lanthanum gallate and Sr,Mg-doped lanthanum gallate were stable in the oxidizing atmosphere. In the reducing atmosphere, pure and Sr-doped lanthanum ferrite and Sr,Mg-doped lanthanum gallate was found to be stable at least during the timeframe of the thermogravimetric experiment whereas pure and Sr-doped lanthanum cobaltite was partially reduced in hydrogen atmosphere.     

Proton and oxide-ionic conduction in Sr- and Zn-doped LaGaO3

The ionic conduction behaviors in La_0.9Sr_0.1Ga_0.9Zn_0.1O_3−α under different atmospheres at 600–1,000 °C were studied by various electrochemical methods including ac impedance, hydrogen and oxygen concentration cells, electrochemical hydrogen and oxygen pumping, etc. The proton conduction in this oxide was investigated for the first time. The hydrogen concentration cell and oxygen concentration cell showed stable electromotive forces close to the theoretical ones calculated from Nernst’s equation, indicating that the conduction was almost pure ionic under hydrogen atmosphere or dry oxygen atmosphere. The electrochemical hydrogen pumping rates coincided with the theoretical ones calculated from Faraday’s law, confirming that La_0.9Sr_0.1Ga_0.9Zn_0.1O_3−α is a proton conductor under hydrogen atmosphere. A similar result for electrochemical oxygen pumping was obtained, indicating that it is an oxide-ionic conductor under dry oxygen atmosphere. The ionic conductivity was about 0.06 S cm⁻¹ at 1,000 °C.     

Microstructure and ionic conductivity of Sr- and Mg-doped LaGaO3

Samples of Sr- and Mg-doped LaGaO₃ (LSGM) with various concentrations of Sr and Mg were prepared by using solid-state reaction method. Results show that ionic conductivities increase with the increase of relative densities. It can also be known that the optimized concentration in with high conductivity is LSGM1520 or LSGM2015. The results also show that, in various concentrations of LSGM, equiaxed, rode-like, polygonal secondary phases such as LaSrGaO₄ or LaSrGa₃O₇ were detected besides (La,Sr)(Ga,Mg)O₃ by means of SEM and EDX. With the increase of doped elements, i.e. x + y, the grain size increases.     

Preparation and microstructure of ZrO2-and LaGaO3-based high-porosity ceramics

We have studied the effects of the morphology and concentration of pore formers on the microstructure and gas permeability of porous zirconia-and lanthanum-gallate-based oxygen-ion-conducting ceramics. The results have been used to optimize the preparation conditions and composition of the ceramics. The resultant dense, fine-grained materials have porosities of up to }~56%.     

Synthesis of Sr- and Fe-doped LaGaO3 perovskites by the modified citrate method

Fine particle strontium and iron substituted lanthanum gallates La_1–x Sr _x Ga_1–y Fe _y O_3–, where x = 0.2, 0.4, and 0.6; y = 0.2, 0.4, 0.6, and 0.8, have been synthesized by a modified citrate method. The formation of these powders was confirmed by the X-ray powder diffraction (XRD) and the fine particle of La_0.6Sr_0.4Ga_0.2Fe_0.8O_3– was investigated by scanning electron microscopy (SEM), and particle size analysis. The single phase of La_0.8Sr_0.2Ga_0.4Fe_0.6O_3–, La_0.6Sr_0.4Ga_0.2Fe_0.8O_3–, and La_0.4Sr_0.6Ga_0.2Fe_0.8O_3– powders could be obtained both with and without calcination. The amount of the secondary phase increased when the amount of Sr in La_1–x Sr _x Fe_0.6Ga_0.4O_3– was more than 0.2 (x > 0.2) and the amount of Fe in La_0.6Sr_0.4Ga_1–y Fe _y O_3– and La_0.4Sr_0.6Ga_0.2Fe_0.8O_3– was less than 0.8 (y < 0.8). The results indicated that in the pH range of 1.36–9.27, the single phase of La_0.6Sr_0.4Ga_0.2Fe_0.8O_3– was formed without calcination and the pH had negligible effects on the structure and lattice parameter. The fine particle of these calcined powders (<4 m) was obtained with the average particle size 1.70 m at pH = 1.36 and with the average particle size between 0.56–0.60 m at pH range between 3.39–9.27, and with a lattice parameter about 3.9 Å.     

A Valence Electron Structure of Sr- and Mg-doped LaGaO3 Criterion of Ionic Conductivity Ceramics

The valence electron structures of Sr- and Mg-doped LaGaO3 ceramics with different compositions were calculated by Empirical Electron Theory of Solids and Molecules （EET）. A criterion for the ionic conductivity was proposed, i.e. the 1/（nAnB） increases with increasing the ionic conductivity when x or y〈20% （in molar fraction）.     

Phase Composition, Microstructure, and Thermal Expansion of B2O3-Modified LaGaO3-Based Ceramics

Data are presented on the phase relations in the La₂O₃–SrO–Ga₂O₃system and the effect of B₂O₃additions on the structure and morphology of (La,Sr)(Ga,Mg)O_{3 –} ceramics. The formation of the perovskite phase (La,Sr)GaO₃is shown to proceed through La₄SrO₇and La₂SrO_{4 +} . The unit-cell of (La,Sr)(Ga,Mg)O_{3 –} is found to vary linearly with Sr + Mg content. The introduction of boron-containing additions reduces the sintering temperature of the ceramics by up to 200°C.     

A Valence Electron Structure Criterion of Ionic Conductivity of Sr- and Mg-doped LaGaO_3 Ceramics

The valence electron structures of Sr- and Mg-doped LaGaO3 ceramics with different compositions were calculated by Empirical Electron Theory of Solids and Molecules (EET). A criterion for the ionic conductivity was proposed, i.e. the 1/(nAnB) increases with increasing the ionic conductivity when x or y≤20% (in molar fraction).