Partially collapsed cristobalite structure in the non molecular phase V in CO2 Journal Article uri icon

DCO ID 11121/3899-5437-1463-7133-CC

in language

  • eng

is Contribution to the DCO

  • YES

year of publication

  • 2012

abstract

  • Non molecular CO2 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 CO2 includes several non molecular phases above 30 GPa. Among these, the first discovered was CO2-V which appeared silica-like. Theoretical studies suggested that the structure of CO2-V is related to that of beta-cristobalite with tetrahedral carbon coordination similar to silicon in SiO2, but reported experimental structural studies have been controversial. We have investigated CO2-V obtained from molecular CO2 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 SiO2 beta-cristobalite, space group I (4) over bar 2d, in which the CO4 tetrahedra are tilted by 38.4 degrees about the c-axis. The existence of CO4 tetrahedra (average O-C-O angle of 109.5 degrees) is thus confirmed. The results add to the knowledge of carbon chemistry with mineral phases similar to SiO2 and potential implications for Earth and planetary interiors.

volume

  • 109

issue

  • 14