New transformations of CO2 at high pressures and temperatures -: art. no. 075701

CO2 laser heating of solid CO2 at pressures between 30 and 80 GPa shows that this compound breaks down to oxygen and diamond along a boundary having a negative P-T slope. This decomposition occurs at temperatures much lower than predicted in theory or inferred from previous experiment. Raman spectroscopy and x-ray diffraction were used as structural probes. At pressures higher than 40 GPa the decomposition is preceded by the formation of a new CO2 phase (CO2-VI). These findings limit the stability of nonmolecular CO2 phases to moderate temperatures and provide a new topology of the CO2 phase diagram.