Coherent interfaces between crystals in nanocrystal composites.
Coherent interfaces between crystals in nanocrystal composites.
复制标题
DOI：
10.1021/nn101708q
复制
发表时间：
2010-09
期刊：
影响因子：
17.1
通讯作者：
Hongwei Liu;Zhanfeng Zheng;Dongjiang Yang;Xuebin Ke;E. Jaatinen;Jin-cai Zhao;Huaiyong Zhu
中科院分区：
文献类型：
--
作者：
Hongwei Liu;Zhanfeng Zheng;Dongjiang Yang;Xuebin Ke;E. Jaatinen;Jin-cai Zhao;Huaiyong Zhu
许多材料是多晶的或由不同相的晶体组成。然而，由纳米尺度的晶体组成的材料（纳米晶体）并不像通常认为的那样是简单的随机取向晶体的聚集体。我们发现，在四种由两种不同相的纳米晶体组成的不同材料中，不同相的纳米晶体通过不同的方法结合在一起形成界面，相邻晶体之间具有紧密的晶体注册（相干界面）。制备方法为：在钛酸盐纳米纤维上沉积Ag(2)O纳米粒子；由tio2 (2)(B)纳米纤维相变为tio2 (2)(B)与锐钛矿混合相的纳米纤维；将包覆锐钛矿纳米晶体的单晶钛酸纤维芯脱水；在钛酸盐纳米纤维表面附着沸石Y纳米晶体。这一发现表明，纳米晶体系统中普遍存在择优取向和相干界面，并且根据我们的结果，它们在很大程度上不受所使用的制造工艺的影响。这是因为首选取向要求两个连接晶体的接合晶体面具有相同的基底间距，并且晶体可以在原子水平上紧密互锁以形成热力学稳定的界面。因此，优选取向和相干界面在不同纳米晶体之间形成的纳米结构中占主导地位，并在复合纳米结构的组装中起关键作用是合理的。在混合相材料中，不同相晶体之间的取向和界面极难确定。尽管如此，相干界面的热力学稳定性使我们能够应用相变不变线应变理论来预测首选取向（从而预测相干界面的结构）。理论预测与透射电镜（TEM）分析结果一致。这意味着我们可以在没有TEM测量的情况下获得混合相材料的取向和界面结构的知识，并且这些知识对于全面理解依赖于界面的许多材料和过程的性质是必不可少的。
Numerous materials are polycrystalline or consist with crystals of different phases. However, materials consisting of crystals on the nanometer scale (nanocrystals) are not simply aggregates of randomly oriented crystals as is generally regarded. We found, that in four different materials that consist of nanocrystals of two different phases and were obtained by different approaches, the nanocrystals of different phases are combined coherently forming interfaces with a close crystallographic registry between adjacent crystals (coherent interfaces). The four materials were fabricated by (i) depositing Ag(2)O nanoparticles on titanate nanofibers, (ii) phase transition from TiO(2)(B) nanofibers to the nanofibers of mixed TiO(2)(B) and anatase phases, (iii) dehydration of the single crystal fibril titanate core coated with anatase nanocrystals, and (iv) attaching zeolite Y nanocrystals on the surface of titanate nanofibers. The finding suggests that preferred orientations and coherent interfaces generally exist in nanocrystal systems, and according to our results, they are largely unaffected by the fabrication process that was used. This is because the preferred orientations require that the engaged crystal planes from two connected crystals have the same basal spacing and that the crystals can interlock tightly at the atomic level to form thermodynamically stable interfaces. Hence it is rational that the preferred orientations and coherent interfaces dominant the nanostructures formed between the different nanocrystals and play a key role in assembling the composite nanostructures. The orientation and interfaces between crystals of different phases in mixed-phase materials are extremely difficult to determine. Nonetheless, the thermodynamic stability of the coherent interfaces allows us to apply phase-transformation invariant line strain theory to predict the preferred orientation (and thus the structure of the coherent interfaces). The theoretical predications agree remarkably with the transmission electron microscopy (TEM) analysis. This implies that we may acquire knowledge of the orientation and the interface structures in the mixed-phase materials without TEM measurement, and the knowledge is essential for comprehensively understanding properties of the many materials and processes that depend on the interfaces.