Fabrication of Functional Nanocrystalline Bulk Structures through Self-organization of Ceramics Nanocrystals

要制备具有功能的纳米晶体体结构，首先必须合成高度分散、尺寸分布窄的纳米晶体。我们尝试合成了Y_<0.15>Zr_<0.85>O_<1.93>(YSZ)纳米晶，ZrO_2,TiO_2,SnO_2,CeO_2，Nb2O_5在水中高度分散，无明显聚集。由于材料的性能在很大程度上取决于结构特征，我们还挑战了纳米晶体的晶相和形貌的控制。因此，我们开发了一种简单的方法，通过用有机配体四甲基铵（N(CH_3)_4^+）盖上表面能来控制单斜和四方ZrO_2纳米晶体的选择性生长。此外，还采用类似的方法合成了SnO_2纳米立方和TiO_2纳米带等形貌可控的纳米晶体。高度分散的纳米晶体在干燥过程中自发组织形成纤维状块状材料。在500℃下烧结得到透明多晶纤维。探索并发现了纳米晶体的另一种应用。该纳米晶体可用于共沉淀法制备纳米复合材料的核。该方法制备的纳米晶（La_<0.85>Sr_<0.15>）_<0.98>MnO_3(LSM)/YSZ和NiO/YSZ复合材料应用于固体氧化物燃料电池电极，表现出优异的电化学性能和长期稳定性。

Highly dispersed nanocrystals with narrow size distribution must be synthesized as a first step of fabrication of functional nanocrystalline bulk structures. We have attempt to synthesize such ceramics nanocrystals and successfully obtained nanocrystalline Y_<0.15>Zr_<0.85>O_<1.93>(YSZ),ZrO_2,TiO_2,SnO_2,CeO_2,Nb2O_5 highly dispersed in water without significant aggregation. We also challenged the control of crystalline phase and morphology of the nanocrystals, since the performance of the materials strongly depends on the structural characteristics. Consequently, we have developed a facile route for the selective growth of monoclinic and tetragonal ZrO_2 nanocrystals through surface energy control by the capping with an organic ligand, tetra-methyl ammonium (N(CH_3)_4^+). In addition, morphology controlled nanocrystals such as SnO_2 nanocubes and TiO_2 nanoribons were synthesized with similar approach. The highly dispersed nanocrystals spontaneously organized through drying and formed fibrous bulk material. The bulk material can be sintered at 500℃ and transparent polycrystalline fiber was obtained.Another application of the nanocrystals was explored and found. The nanocrystals can be applied for nuclei of nanocomposite fabrication in co-precipitation process. The nanocrystalline (La_<0.85>Sr_<0.15>)_<0.98>MnO_3(LSM)/YSZ and NiO/YSZ composites fabricated by the method was applied for solid oxide fuel cell electrodes and demonstrated superior electrochemical performance and long-term stability.