Polytype Distribution in Circumstellar Silicon Carbide
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.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Jun 07, 2002
- Source ID
- 10.1126/science.1071136
Entities
People
- F. J. Stadermann
- R. S. Lewis
- S. Amari
- Scott R. Messenger
- T. J. Bernatowicz
- T. L. Daulton
Organizations
- Argonne National Laboratory
- United States Naval Research Laboratory
- University of Chicago
- Washington University in St. Louis