Low Thermal Conductivity of Carbon Dioxide at High Pressure: Implications for Icy Planetary Interiors

Carbon dioxide is commonly found in terrestrial planets and its thermal property is relevant to the dynamics and evolution of those terrestrial planets. In this work, we combine time-domain thermoreflectance measurements and first-principles calculations to determine the thermal conductivity of CO₂ up to 70 GPa at room temperature. Our results show that the thermal conductivity of liquid CO₂ is ∼0.22 W m⁻¹ K⁻¹ at 0.3–0.5 GPa and increases to ∼0.28 W m⁻¹ K⁻¹ when the liquid CO₂ transforms into molecular solid phase I (dry ice). Upon further compression, the mean value of thermal conductivity of phase I increases to 1.4–2.1 W m⁻¹ K⁻¹ at ∼10 GPa and then slightly drops across the phase I-III boundary. Phase III exhibits a gentle increase of thermal conductivity with pressure and reaches to a maximum value of ∼4 W m⁻¹ K⁻¹ at ∼45 GPa, but shows an abrupt drop when transforming into a non-molecular amorphous solid. The pressure evolution of CO₂ thermal conductivity across different phases may have significant implications for the heat flow and temperature distribution in the interiors of planets and moons containing CO₂.