Structure of Polymeric Carbon DioxideCO2−V

Abstract

The structure of polymeric carbon dioxide (${\mathrm{CO}}_2\mathrm{\text{-}}\mathrm{V}$) has been solved using synchrotron x-ray powder diffraction, and its evolution followed from 8 to 65 GPa. We compare the experimental results obtained for a 100% ${\mathrm{CO}}_2$ sample and a 1 mol % ${\mathrm{CO}}_2/\mathrm{He}$ sample. The latter allows us to produce the polymer in a pure form and study its compressibility under hydrostatic conditions. The high quality of the x-ray data enables us to solve the structure directly from experiments. The latter is isomorphic to the $\beta$-cristobalite phase of ${\mathrm{SiO}}_2$ with the space group $I\overline{4}2d$. Carbon and oxygen atoms are arranged in ${\mathrm{CO}}_4$ tetrahedral units linked by oxygen atoms at the corners. The bulk modulus determined under hydrostatic conditions, $B_0=136(10)\mathrm{GPa}$, is much smaller than previously reported. The comparison of our experimental findings with theoretical calculations performed in the present and previous studies shows that density functional theory very well describes polymeric ${\mathrm{CO}}_2$. DOI: http://dx.doi.org/10.1103/PhysRevLett.108.125701 © 2012 American Physical Society