Partially collapsed cristobalite structure in the non molecular phase V in CO2.


Non molecular CO(2) has been an important subject of study in high pressure physics and chemistry for the past decade opening up a unique area of carbon chemistry. The phase diagram of CO(2) includes several non molecular phases above 30 GPa. Among these, the first discovered was CO(2)-V which appeared silica-like. Theoretical studies suggested that the structure of CO(2)-V is related to that of β-cristobalite with tetrahedral carbon coordination similar to silicon in SiO(2), but reported experimental structural studies have been controversial. We have investigated CO(2)-V obtained from molecular CO(2) at 40-50 GPa and T > 1500 K using synchrotron X-ray diffraction, optical spectroscopy, and computer simulations. The structure refined by the Rietveld method is a partially collapsed variant of SiO(2) β-cristobalite, space group I42d, in which the CO(4) tetrahedra are tilted by 38.4° about the c-axis. The existence of CO(4) tetrahedra (average O-C-O angle of 109.5°) is thus confirmed. The results add to the knowledge of carbon chemistry with mineral phases similar to SiO(2) and potential implications for Earth and planetary interiors.

DOI: 10.1073/pnas.1118791109

Cite this paper

@article{Santoro2012PartiallyCC, title={Partially collapsed cristobalite structure in the non molecular phase V in CO2.}, author={Mario A. Santoro and Federico A. Gorelli and Roberto Bini and Julien Haines and Olivier Cambon and Claire Levelut and Javier Antonio Montoya and Sandro Scandolo}, journal={Proceedings of the National Academy of Sciences of the United States of America}, year={2012}, volume={109 14}, pages={5176-9} }