Résumé
Non molecular CO... 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... includes several non molecular phases above 30 GPa. Among these, the first discovered was CO...-V which appeared silica-like. Theoretical studies suggested that the structure of CO...-V is related to that of ...-cristobalite with tetrahedral carbon coordination similar to silicon in SiO..., but reported experimental structural studies have been controversial. We have investigated CO...-V obtained from molecular CO... 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... ...-cristobalite, space group ..., in which the CO... tetrahedra are tilted by 38.4... about the c-axis. The existence of CO4 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... and potential implications for Earth and planetary interiors. (ProQuest: ... denotes formulae/symbols omitted.)