Atomic-Scale Valence State Distribution inside Ultrafine CeO2 Nanocubes and Its Size Dependence

Xiaodong Hao, Akira Yoko, Chunlin Chen, Kazutoshi Inoue, Mitsuhiro Saito, Gimyeong Seong, Seiichi Takami, Tadafumi Adschiri, Yuichi Ikuhara

Research output: Contribution to journalArticlepeer-review

28 Citations (Scopus)

Abstract

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.

Original languageEnglish
Article number1802915
JournalSmall
Volume14
Issue number42
DOIs
Publication statusPublished - 2018 Oct 18

Keywords

  • Ce valence states distribution
  • STEM-EELS
  • cerium oxide
  • lattice expansion
  • nanosize effect

ASJC Scopus subject areas

  • Biotechnology
  • Biomaterials
  • Chemistry(all)
  • Materials Science(all)

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