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

具有窄尺寸分布的高度分散的纳米晶体必须合成作为功能纳米晶体块体结构制造的第一步。我们尝试合成了这种陶瓷纳米晶，并成功地得到了Y_<0.15>Zr_<0.85>O_<1.93>（YSZ），ZrO_2，TiO_2，SnO_2，CeO_2，Nb_2O_5纳米晶在水中高度分散，无明显团聚。我们还对纳米晶体的晶相和形态的控制提出了挑战，因为材料的性能在很大程度上取决于结构特征。因此，我们开发了一种通过有机配体四甲基铵（N（CH_3）_4^+）的表面能控制来选择性生长单斜和四斜ZrO_2纳米晶的简单途径。此外，我们还用类似的方法合成了形貌可控的纳米晶，如SnO_2纳米立方体和TiO_2纳米带。高度分散的纳米晶体通过干燥自发组织并形成纤维状块状材料。该材料在500℃下烧结，得到了透明的多晶纤维，探索并发现了纳米晶的另一个应用领域，即在共沉淀法中，纳米晶可作为纳米复合材料制备的晶核。将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，显示出上级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.