【作者】 黄端平；

【导师】 徐庆；

【作者基本信息】 武汉理工大学 ， 材料物理与化学， 2006， 博士

【摘要】 A₂BO₄型La₂NiO_4+δ体系化合物具有优良的氧离子传输性能和合适的热膨胀系数(～13.0×10^-6K^-1)，很有希望成为中温固体氧化物燃料电池（SOFC）的新型阴极材料。本论文采用氨基多羧酸配合物法合成La₂NiO_4+δ体系材料，研究La₂NiO_4+δ体系材料的结构和导电性能随组成与制备工艺条件的变化规律，探讨La₂NiO_4+δ体系材料的导电性能与晶体结构、显微结构和电子结构的内在联系，其目的在于探索La₂NiO_4+δ体系的新型化学合成方法和弄清影响La₂NiO_4+δ体系材料导电性能的各种因素及其作用机理。 采用氨基多羧酸配合物法合成了La₂NiO_4+δ体系粉料，探讨了氨基多羧酸配合物前驱体的热分解行为及合成产物的形成过程，研究了合成条件对合成粉料的晶体结构和显微形态的影响。结果表明，以二乙三氨五乙酸（H₅DTPA）为络合剂，金属阳离子与H₅DTPA的摩尔比为3：1.7时可获得单一K₂NiF₄相的La₂NiO_4+δ超细粉料；非晶态氨基多羧酸配合物前驱体中H₅DTPA与金属阳离子形成双齿配位结构；在氨基多羧酸配合物前驱体的热处理过程中，700℃时开始形成K₂NiF₄结构的物相，但同时还存在少量的杂相，在900～950℃下热处理后形成单一K₂NiF₄结构的合成产物。在合成温度较低（900～950℃）和合成时间较短（～2h）的条件下，合成出具有单一K₂NiF₄结构的La₂NiO_4+δ体系超细粉料，解决了La₂NiO_4+δ体系合成困难的问题。 采用常规固相烧结法制备了La₂NiO_4+δ体系陶瓷，研究了烧结温度对材料的结构和导电性能的影响。结果表明，烧结温度对La₂NiO_4+δ体系陶瓷的显微结构和实际化学计量产生明显的影响，合理控制La₂NiO_4+δ体系陶瓷的烧结温度对于获得优良的导电性能具有重要作用。根据导电性能的研究结果，确定La₂NiO_4+δ陶瓷的最佳烧结温度为1300℃。La₂NiO_4+δ陶瓷总电导率的最大值达到102.9S·cm^-1，在中温范围内（600～800℃）的总电导率为75.5～95.3S·cm^-1，明显优于传统固相法制备La₂NiO_4+δ陶瓷的导电性能，体现出氨基多羧酸配合物法在制备La₂NiO_4+δ材料方面的优越性。 研究了Sr²⁺的A位取代对La₂NiO_4+δ结构与导电性能的影响。La_2-xSr_xNiO_4+δ（x=0.1～0.3）体系材料具有四方结构（空间群为I4／mmm）。对于[NiO₆]八面体结构，Sr²⁺的引入引起Ni-O₁键（对应于ab轴平面）和Ni-O₂键（沿c轴方向）的键长降低，Ni-O₂键与Ni-O₁键的键长比降低，表明[NiO₆]八面体结构的对称性增强。在岩盐层中，Sr²⁺取代部分La³⁺使得沿c轴方向的La／Sr-O₂×（1）键的键长增大，表明岩盐层的层间距增大。Sr²⁺的A位取代引起La₂NiO_4+δ的非化学计量氧含量（δ）降低，Ni³⁺的相对含量增加。在La_2-xSr_xNiO_4+δ（x=0～0.3）体系陶瓷中，Sr²⁺含量的增加显著提高了材料的总电导率水平，在x=0.2时材料总电导率水平达到最佳。与Sr²⁺含量较低的组成相比，在1550℃下烧结的La_1.7Sr_0.3NiO_4+δ陶瓷在高温段总电导率随温度的变化比较平缓，在高温段仍然保持较高的总电导率。在600～800℃温度范围内，在1500℃下烧结的La_1.8Sr_0.2NiO_4+δ陶瓷和在1550℃下烧结的La_1.7Sr_0.3NiO_4+δ陶瓷的总电导率分别为95.9～114.2S·cm^-1和101.7～107.0S·cm^-1，基本达到对中温SOFC阴极材料导电性能的基本要更多还原

【Abstract】 Recently, oxygen hyperstoichiometric La₂NiO_4+δ based compounds with a K₂NiF₄ structure have attracted growing attention as a novel mixed electronic-ionic conductor. These materials exhibit high oxygen diffusion and surface exchange coefficients at intermediate temperatures （600-800 ℃） together with moderate thermal expansion coefficients around 13.0×10^-6 K^-1, making them a promising candidate material for cathode of intermediate temperature Solid Oxide Fuel Cells （SOFCs）. In this dissertation, a polyaminocarboxylate complex method has been developed to synthesis La₂NiO_4+δ based compounds. The influence of composition and sintering condition on the structure and mixed conducting properties of the resulting La₂NiO_4+δ based ceramics have been investigated. The contribution of change in crystal structure, microstructure and electronic structure to the mixed conducting properties of La₂NiO_4+δ based ceramics has been examined. La₂NiO_4+δ based compounds with a pure K₂NiF₄ phase have been derived from a polyaminocarboxylate complex precursor with diethylenetriaminepentaacetic acid （H₅DTPA） as ligand. The thermal decomposition behavior of the polyaminocarboxylate complex precursor and the formation process of the desired product were investigated. It has been found that the mole ratio of total metal cation to H₅DTPA and calcining temperature play a determinant role on the phase development and morphology of the resulting powders. A mole ratio of total metal cation to H₅DTPA of 3:1.7 was determined to be moderate in synthesizing La₂NiO_4+δ based compounds. A bidentate coordination of the carboxylate groups to metallic cations was certified for the amorphous polyaminocarboxylate complex precursor. The K₂NiF₄ phase appeared in addition to small amounts of intermediate phases after calcining the precursor at 700 ℃. Fine and uniform powders （100-200 nm） with a pure K₂NiF₄ phase can be obtained by calcining the polyaminocarboxylate complex precursor at 900-950 ℃ for 2h in air, providing an advantageous alternative to the conventional solid state reaction route in synthesizing La₂NiO_4+δ based compounds.The influence of sintering temperature on the structure and mixed conducting properties of the resulting La₂NiO_4+δ based ceramics was investigated. It has been proved that the microstructural evolution and stoichiometrical change of the specimens during sintering are responsible for the variation in the mixed conducting properties with sintering temperature. Therefore, adequately controling sintering temperature was considered to be crucial in order to achieve desired mixed conducting properties. With respect to the mixed conducting properties, the preferred sintering temperature was ascertained to be 1300 ℃ for La₂NiO_4+δ. La₂NiO_4+δ ceramic sintered at 1300 ℃ gives a maximum electrical conductivity of 102.9 S·cm^-1 at 450 ℃ and electrical conductivities of 75.5-95.3 S·cm^-1 at 600-800 ℃, which are obviously higher than those of the specimen made by the更多还原