Synthesis and characterization of polyureasilazane derived SiCN ceramics
- CONCAVE Research Centre, Department of Mechanical and Industrial Engineering, Concordia University, 1455 de Maisonneuve Boulevard West, Montreal, Quebec H3G 1M8 (Canada)
Samples of SiCN ceramics were synthesized by thermal treatment of commercially available CERASET{sup TM} polyureasilazane, used as liquid-polymer precursor, at pyrolysis temperatures of 1000, 1050, 1100, 1150, and 1200 deg. C. Electron paramagnetic resonance (EPR) signals due to sp{sup 2}-hybridized carbon-related dangling bonds were recorded over the 4-300 K temperature range at X band (9.6 GHz), and the spectra showed the presence of an intense EPR line with g=2.0027 at room temperature for all samples; at liquid helium temperature an additional line was seen present as a shoulder to main line. These two signals are due to carbon-related dangling bonds present as (i) defects on the free-carbon phase and (ii) within the bulk of SiCN ceramic network. The value of the antiferromagnetic exchange constant between dangling bonds in the various samples, not hitherto available in the literature, was estimated from the temperature variation of the EPR linewidth to be anywhere from J=-12 to J=-15 K in the samples synthesized at 1000, 1100, and 1150 deg. C. The EPR linewidth of the samples decreased with increasing pyrolysis temperature of a sample, being 0.07 mT at X band at room temperature for the samples synthesized at 1150 and 1200 deg. C, which can be used potentially as stable g markers, due to their very narrow linewidth. The W-band (95 GHz) room-temperature spectrum of the sample pyrolyzed at 1100 deg. C exhibited only one line consistent with the X-band spectrum. At higher frequency of G band (170 GHz) the EPR spectra are better resolved, clearly showing the presence of a strong (g=2.0027) and a weak (g=2.0032) EPR line at room temperature, and the latter corresponds to the line present at X band as shoulder at liquid-helium temperature. In addition, nuclear magnetic resonance measurements were carried out to confirm the existence of free-carbon phase and oxygen atoms in the samples.
- OSTI ID:
- 20795836
- Journal Information:
- Journal of Applied Physics, Vol. 99, Issue 11; Other Information: DOI: 10.1063/1.2202291; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ANTIFERROMAGNETIC MATERIALS
ANTIFERROMAGNETISM
CARBON
CERAMICS
ELECTRON SPIN RESONANCE
ELECTRONS
EXCHANGE INTERACTIONS
GHZ RANGE 100-1000
HELIUM
LANDE FACTOR
NUCLEAR MAGNETIC RESONANCE
OXYGEN
PARAMAGNETISM
POLYMERS
PYROLYSIS
SIGNALS
SILICON COMPOUNDS
SPECTRA
SYNTHESIS
TEMPERATURE RANGE 0273-0400 K