Unveiling New Polymorphs and Phase Stability in the CaSiO3 System at Upper Mantle and Transition Zone Conditions

We propose conducting in-situ XRPD experiment to investigate the P-T stability and structure of CaSiO3 polymorphs and their destabilization phases in the P/T range of 0-15 GPa and 300-1500 K, corresponding to Earth's upper mantle and transition zone. Existing research point to the intricate nature of the phase diagram of CaSiO3. It reveals the presence of apx. five distinct polymorphs characterized by tetrahedral silicon units, with stability observed up to approximately 8 GPa. Beyond, there is a transition to a mixture of Ca2SiO4 and CaSi2O5 phases, the crystal structures of which may still be undetermined. These phases hold significant importance as accessory components within the Earth's mantle and are frequently encountered as inclusions in diamonds. Reconstructing the precise phase diagram, including the crystal structures and the pressure-temperature stability ranges of each phase, will contribute to a more accurate understanding of the depths at which diamonds originate.