High pressure Raman study of Na₄Ca(CO₃)₃ from the ambient pressure to 11 GPa

ABSTRACT

Na-Ca double carbonates were found as the inclusions in ‘superdeep’ Juina diamonds and as the products of high pressure experiments and thus are regarded as the potential host of CO₂ in the deep mantle. Recently, Na-rich carbonate (21.0% wt. of Na₂O vs. 13.6% wt. of CaO) was reported as the product of experiment with carbonated eclogite treated at 21 GPa and 1200°C. Na/Ca ratio of this carbonate corresponds to Na₄Ca(CO₃)₃ phase with cubic symmetry synthesized at 6 GPa. The stability of Na₄Ca(CO₃)₃ at higher pressures has not been investigated yet. Herein, we report an in situ Raman study of Na₄Ca(CO₃)₃ carbonate up to 11 GPa in order to reveal stability of its structure at mantle pressures. Obtained results strongly imply for reversible phase transition near 8 GPa associated with decrease of symmetry. The observed phase transition questions the stability of cubic Na₄Ca(CO₃)₃ under conditions of mantle transition zone.

KEYWORDS:

• Na-carbonates
• Raman spectroscopy
• deep carbon cycle
• high pressure
• diamond anvil cell

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The research was supported by a Russian Science Foundation (grant number 21-77-00016). Authors acknowledge Anastasia Brazhnikova for participation in data collection. Diffraction experiments were carried at the European Synchrotron Radiation Facility and supported by approval of ESRF Proposal ES-810.