Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy Study of Nonstoichiometric Silicon-Carbon-Oxygen Glasses |
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Authors: | Christian Turquat,Hans-Joachim Kleebe,G. Gregori,Steffen Walter,Gian D. Sorarù |
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Affiliation: | Institute for Materials Research (IMA-I), University of Bayreuth, D-95440 Bayreuth, Germany;Metallurgical and Materials Engineering Department, Colorado School of Mines, Golden, Colorado 80401;Materials Engineering Department, University of Trento, I-38050 Trento, Italy |
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Abstract: | 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, TH, and methyldiethoxysilane, DH. Si-C-O glass composition depended on the molar ratio of the precursors utilized. At a ratio of TH/DH= 1, the formation of a carbon-rich glass was observed, whereas a ratio of TH/DH= 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 TH/DH= 1 revealed a small volume fraction of SiC precipitates in addition to a very small amount of residual free carbon at 1400°C, TH/DH= 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 O2(1-x)→ x SiC + (1 - x )SiO2, when annealed at temperatures exceeding 1200°C. |
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Keywords: | high temperature glass silicon oxycarbide |
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