J. Mater. Sci. Technol. ›› 2019, Vol. 35 ›› Issue (12): 2851-2858.DOI: 10.1016/j.jmst.2019.07.004

• Orginal Article • Previous Articles     Next Articles

Initial nucleation of amorphous Si-B-C-N ceramics derived from polymer-precursors

Ling-yan Lia1, Hui Gua*(), Vesna Šrotb, Peter van Akenb, Joachim Billc*()   

  1. a.Materials Genome Institute, School of Materials Science and Engineering, Shanghai University, 99 Shangda Road, Shanghai, 200444, China
    b. Stuttgart Center for Electron Microscopy, Max-Planck-Institute for Solid-State Research, Heisenbergstrasse 3, 70569, Stuttgart, Germany
    c. Institute of Materials Science, University of Stuttgart, Heisenbergstrasse 5, 70569, Stuttgart, Germanya
  • Received:2019-09-26 Online:2019-12-05 Published:2019-12-18
  • Contact: Gu Hui,Bill Joachim

Abstract:

Nucleation behavior of amorphous Si–B–C–N ceramics derived from boron-modified polyvinylsilazane procusors was systematically investigated by transmission electron microscopy (TEM) combined with spatially-resolved electron energy-loss spectroscopy (EELS) analysis. The ceramics were pyrolyzed at 1000°C followed by further annealing in N2, and SiC nano-crystallites start to emerge at 1200°C and dominate at 1500°C. Observed by high-angle annular dark-field imaging, bright and dark clusters were revealed as universal nano-structured features in ceramic matrices before and after nucleation, and the growth of cluster size saturated before reaching 5nm at 1400°C. EELS analysis demonstrated the gradual development of bonding structures successively into SiC, graphetic BNCx and Si3N4 phases, as well as a constant presence of unexpected oxygen in the matrices. Furthermore, EELS profiling revealed the bright SiC clusters and less bright Si3N4-like clusters at 1200–1400°C. Since the amorphous matrix has already phase separated into SiCN and carbon clusters, another phase separation of SiCN into SiC and Si3N4-like clusters might occur by annealing to accompany their nucleation and growth, albeit one crystallized and another remained in amorphous structure. Hinderance of the cluster growth and further crystallization was owing to the formation of BNCx layers that developed between SiC and Si3N4-like clusters as well as from the excessive oxygen to form the stable SiO2.

Key words: Precursor derived ceramics, Si-B-C-N, Nucleation, High-angle annular dark-field imaging, Electron energy-loss spectroscopy