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Polytype distribution in circumstellar silicon
carbide
Daulton T. L., Bernatowicz T. J., Lewis R. S., Messenger
S., Stadermann F. J., and Amari S. (2002). Science, 296 (07
June 2002), 1852-1855.
doi:10.1126/science.1071136
ABSTRACT
The inferred crystallographic class of circumstellar
silicon carbide based on astronomical infrared spectra is
controversial. We have directly determined the polytype
distribution of circumstellar SiC from transmission electron
microscopy of presolar silicon carbide from the Murchison
carbonaceous meteorite. Only two polytypes (of a possible
several hundred) were observed: cubic 3C and hexagonal 2H
silicon carbide and their intergrowths. We conclude that
this structural simplicity is a direct consequence of the
low pressures in circumstellar outflows and the
corresponding low silicon carbide condensation
temperatures.
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