Study on the Physical Properties of Ca3CO5 Polymorphs under Lower Mantle Pressure

The physical properties of newly discovered orthocarbonate Ca3CO5 are of significant importance in understanding the carbon cycle and storage in the Earth's interior. Here, the structural, elastic, seismic, and thermal properties of Ca3CO5 polymorphs under the Earth's lower mantle pressure are investigated using first-principles calculations, and the results are compared with those of orthocarbonate Ca2CO4-Pnma. Our findings demonstrate that the pressure of the Cmcm phase of Ca3CO5 to the I4/mcm phase is 53.8 GPa, and the transition pressure and equation of state align with prior research. Additionally, the elastic moduli, densities, and wave velocities of Ca3CO5 polymorphs are similar to those of Ca2CO4-Pnma. However, the azimuthal anisotropies of Ca3CO5 polymorphs are greater than those of Ca2CO4-Pnma. Furthermore, the minimum thermal conductivity and diffusion thermal conductivity of Ca3CO5 polymorphs are smaller than those of Ca2CO4-Pnma. Ultimately, the thermodynamic properties of Ca3CO5 polymorphs are obtained utilizing the quasi-harmonic approximation method. These results provide valuable insight into the physical properties of Ca3CO5, which can aid in further understanding the carbon cycle and storage within the Earth's underground.