Transmission Electron Microscopy and Electron Energy‐Loss Spectroscopy Study of Nonstoichiometric Silicon‐Carbon‐Oxygen Glasses

Crystallization behavior of Si‐C‐O glasses in the temperature range of 1000°–1400°C was investigated using transmission electron microscopy (TEM) in conjunction with electron energy‐loss spectroscopy (EELS). Si‐C‐O glasses were prepared by pyrolysis of polysiloxane networks obtained from homogeneous mixtures of triethoxysilane, T H , and methyldiethoxysilane, D H . Si‐C‐O glass composition depended on the molar ratio of the precursors utilized. At a ratio of T H /D H = 1, the formation of a carbon‐rich glass was observed, whereas a ratio of T H /D H = 9 yielded a Si‐C‐O glass with excess free silicon. Both materials were amorphous at 1000°C, but showed a distinct difference in crystallization behavior on annealing at high temperature. Although T H /D H = 1 revealed a small volume fraction of SiC precipitates in addition to a very small amount of residual free carbon at 1400°C, T H /D H = 9 showed, in addition to SiC crystallites, numerous larger silicon precipitates (20–50 nm), even at 1200°C. Both materials underwent a phase separation process, SiC x O 2(1‐x) → x SiC + (1 ‐ x )SiO 2 , when annealed at temperatures exceeding 1200°C.