Abstract
The high-pressure phase diagram of has been calculated using density-functional perturbation theory. We find that phase transitions of silica do not correspond to any observed seismic discontinuities within the Earth. We analyze the breakdown of close packing occurring in above and conclude that it is due to asphericity and deformability of ions, which can generally lead to the formation on non-close-packed structures at high pressure. Our calculations indicate that pyrite-structured , stable above , has no soft modes down to ambient pressure and could, therefore, be quenchable. Above a cotunnite-type phase is stable.
1 More- Received 11 October 2004
DOI:https://doi.org/10.1103/PhysRevB.71.064104
©2005 American Physical Society