High pressure-High temperature phases of Carbon Dioxide

The phase diagram of CO$_{2}$ has not been understood adequately above 40 GPa and high temperatures, particularly regarding the stabilities and boundaries of various extended phases that include a-carbonia, Phase V, Phase VI, and to an extent Phase III. We have studied the phase diagram of CO$_{2}$ above 40 GPa and at high temperatures, using both ohmically and laser-heated diamond anvil cells. We found the co-existence of several extended phases over a large pressure region, which we attribute to the metastability of the extended phases and the extraordinarily large pressure gradients at these pressures. We determined the relative stability fields of the co-existing phases, which may offer the physico-chemical mechanism for the existence of carbonate minerals in deep Earth's mantle.