at moderate P-T condition*

We report the formation of extended network polymers of singly bonded CO4 by catalytic oxidation reactions of CO₂ at relatively low pressures, using Raman spectroscopy, X-ray diffraction, and visual observations. The results indicate that there are three different solid phases; a needle-like phase (NP), a rock-like phase (RP), and a transparent phase (TP), formed as temperature increases at 8 GPa. The spectral evidence indicates these transformations accompany the sp² hybridized C=O in molecular CO₂ to sp³ hybridized C-O single bonds. The diffraction data of the quenched RP at ambient temperature at 8 GPa indicates a layered tetragonal structure of CO4 tetrahedra with ρ=2.85g/cm³ – a similar density to that of extended CO₂-V at the same pressure.