Acta Phys. -Chim. Sin. ›› 2017, Vol. 33 ›› Issue (10): 2106-2112.doi: 10.3866/PKU.WHXB201705186

• ARTICLE • Previous Articles    

Investigation of the Growth Mechanism and Compositional Segregations of Monodispersed Ferrite Nanoparticles by Transmission Electron Microscopy

Wei-Yan LIU1,Ya-Dong LI1,2,Tian LIU1,Lin GAN1,2,*()   

  1. 1 Division of Energy and Environment, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, Guangdong Province, P. R. China
    2 Electron Microscopy Laboratory, Materials and Devices Testing Center, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, Guangdong Province, P. R. China
  • Received:2017-03-30 Published:2017-07-17
  • Contact: Lin GAN E-mail:lgan@sz.tsinghua.edu.cn
  • Supported by:
    the Guangdong Natural Science Foundation for Distinguished Young Scholars, China(2016A030306035);Shenzhen Basic Research Program, China(JCYJ20160531194754308)

Abstract:

Understanding the growth mechanism of nanocrystals is crucial for the synthesis of high-quality monodispersed nanoparticles. In contrast to the widely studied growth mechanism of metal nanocrystals, the growth mechanism of metal oxide nanoparticles is still poorly understood. Exemplified by cobalt/manganese ferrite nanoparticles prepared by thermal decomposition, we reveal the growth mechanism and associated compositional segregations of bimetallic metal oxide nanoparticles by using transmission electron microscopy combined with electron energy loss spectroscopy (EELS). We found that a two-stage heating protocol, involving a first-stage heating at a relatively lower temperature followed by a second-stage heating at a relatively higher temperature, is crucial to synthesize monodispersed ferrite nanoparticles. Controlling the reaction time of the first-stage heating can effectively decouple the nucleation stage and growth stage of ferrite nanoparticles, leading to monodispersed nanoparticles with a narrow size distribution. EELS spectrum imaging further reveals previously unreported compositional segregations in the as-prepared ferrite nanoparticles, suggesting that an Fe-rich core formed at the nucleation stage and a Co-/Mn-rich shell formed at the growth stage. Our results provide useful insight into the synthesis of high-quality monodispersed metal oxide nanoparticles as well as a correct understanding of the surface chemistry and related physiochemical properties of spinel oxide nanocrystals prepared by thermal decomposition.

Key words: Nanocrystal growth mechanism, Ferrite nanocrystals, Surface segregation, Transmission electron microscopy, Electron energy loss spectroscopy

MSC2000: 

  • O642