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Atomic‐Scale Valence State Distribution inside Ultrafine CeO2 Nanocubes and Its Size Dependence
Small ( IF 13.0 ) Pub Date : 2018-09-09 , DOI: 10.1002/smll.201802915
Xiaodong Hao 1, 2 , Akira Yoko 1 , Chunlin Chen 1 , Kazutoshi Inoue 1 , Mitsuhiro Saito 3 , Gimyeong Seong 4 , Seiichi Takami 5 , Tadafumi Adschiri 1, 4, 6 , Yuichi Ikuhara 1, 3, 7
Affiliation  

Atomic‐scale analysis of the cation valence state distribution will help to understand intrinsic features of oxygen vacancies (VO) inside metal oxide nanocrystals, which, however, remains a great challenge. In this work, the distribution of cerium valence states across the ultrafine CeO2 nanocubes (NCs) perpendicular to the {100} exposed facet is investigated layer‐by‐layer using state‐of‐the‐art scanning transmission electron microscopy‐electron energy loss spectroscopy. The effect of size on the distribution of Ce valence states inside CeO2 NCs is demonstrated as the size changed from 11.8 to 5.4 nm, showing that a large number of Ce3+ cations exist not only in the surface layers, but also in the center layers of smaller CeO2 NCs, which is in contrast to those in larger NCs. Combining with the atomic‐scale analysis of the local structure inside the CeO2 NCs and theoretical calculation on the VO forming energy, the mechanism of size effect on the Ce valence states distribution and lattice expansion are elaborated: nano‐size effect induces the overall lattice expansion as the size decreased to ≈5 nm; the expanded lattice facilitates the formation of VO due to the lower formation energy required for the smaller size, which, in principle, provides a fundamental understanding of the formation and distribution of Ce3+ inside ultrafine CeO2 NCs.

中文翻译:

超细CeO2纳米立方体内部的原子尺度价态分布及其尺寸依赖性

阳离子价态分布的原子尺度分析将有助于了解金属氧化物纳米晶体内部氧空位(V O)的内在特征,然而,这仍然是一个巨大的挑战。在这项工作中,使用最新的扫描透射电子显微镜-电子能量损失逐层研究了垂直于{100}暴露面的超细CeO 2纳米立方体(NC)上铈价态的分布。光谱学。当尺寸从11.8 nm变为5.4 nm时,证明了尺寸对CeO 2 NC内部Ce价态分布的影响,表明大量Ce 3+阳离子不仅存在于较小的CeO 2 NC的表面层中,而且还存在于中心层中,这与较大的NC中的阳离子相反。结合对CeO 2 NCs内部局部结构的原子尺度分析和对V O形成能的理论计算,阐述了尺寸效应对Ce价态分布和晶格扩展的机理:纳米尺度效应诱导了整体随着尺寸减小到≈5nm,晶格膨胀;由于较小的尺寸所需的较低形成能,因此扩展的晶格有助于V O的形成,原则上,这提供了对Ce 3+的形成和分布的基本了解内部超细CeO 2 NC。
更新日期:2018-09-09
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