Observable Two-Step Nucleation Mechanism in Solid-State Formation of Tungsten Carbide

Linfeng Fei, Xianglai Gan, Sheung Mei Ng, Hui Wang, Ming Xu, Wei Lu, Yanchun Zhou, Chi Wah Leung, Chee Leung Mak, Yu Wang

Research output: Journal article publicationJournal articleAcademic researchpeer-review

28 Citations (Scopus)


The nucleation of crystals from ubiquitous solid-state reactions impacts a wide range of natural and synthetic processes and is fundamental to physical and chemical synthesis. However, the microscopic organization mechanism of amorphous precursors to nanoscale clusters of ordered atoms (nucleus) in an all-solid environment is inaccessible by common experimental probes. Here, by using in situ transmission electron microscopy in combination with theoretical simulations, we show in the reactive formation of a metal carbide that nucleation actually occurs via a two-step mechanism, in which a spinodal-structured amorphous intermediate reorganizes from an amorphous precursor and precedes the emergence of a crystalline nucleus, rather than direct one-step nucleation from classical consideration. We further isolated a series of sophisticated dynamics during formation and development of the nucleus in real-space and interpreted them by thermodynamic favorability. We anticipate that such an indirect organization mechanism which contains a metastable intermedium among the free energy gap between precursors and nanocrystals has its chance in underlying most solid-state crystallizations, whereas the as-established experimental method represents a step forward in exploring fundamentals in chemical reaction, material engineering, etc.

Original languageEnglish
Pages (from-to)681-688
Number of pages8
JournalACS Nano
Issue number1
Publication statusPublished - 22 Jan 2019


  • crystal nucleation
  • in situ heating
  • in situ transmission electron microscopy
  • nanoparticles
  • transition metal carbides
  • tungsten carbide
  • two-step nucleation

ASJC Scopus subject areas

  • General Materials Science
  • General Engineering
  • General Physics and Astronomy


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