Assessing the stability fields of molecular and polymeric CO2

We investigated the stability of polymeric $\mathrm{C}{\mathrm{O}}_{2}$ over a wide range of pressures, temperatures, and chemical environments. We find that the $I\overline{4}2d$ polymeric structure, consisting of a three-dimensional network of corner sharing $\mathrm{C}{\mathrm{O}}_{4}$ tetrahedra, forms at 40--140 GPa and from a $\text{CO-}{\mathrm{N}}_{2}$ mixture at 39 GPa. An exceptional stability field of 0--286 GPa and 100--2500 K is documented for this structure, making it a viable candidate for planetary interiors. The stability of the tetrahedral polymeric motif of $\mathrm{C}{\mathrm{O}}_{2}\text{\ensuremath{-}}\mathrm{V}$ is a consequence of the rigidity of $s{p}^{3}$ hybridized orbitals of carbon in a closed-packed oxygen sublattice.