High-pressure compressibility and vibrational properties of (Ca,Mn)CO3

Abstract

Knowledge of potential carbon carriers such as carbonates is critical for our understanding of the deep-carbon cycle and related geological processes within the planet. Here we investigated the high-pressure behavior of (Ca,Mn)CO 3 up to 75 GPa by synchrotron single-crystal X-ray diffraction, laser Raman spectroscopy, and theoretical calculations. MnCO 3 -rich carbonate underwent a structural phase transition from the CaCO 3 -I structure into the CaCO 3 -VI structure at 45–48 GPa, while CaCO 3 -rich carbonate transformed into CaCO 3 -III and CaCO 3 -VI at approximately 2 and 15 GPa, respectively. The equation of state and vibrational properties of MnCO 3 -rich and CaCO 3 -rich carbonates changed dramatically across the phase transition. The CaCO 3 -VI-structured CaCO 3 -rich and MnCO 3 -rich carbonates were stable at room temperature up to at least 53 and 75 GPa, respectively. The addition of smaller cations (e.g., Mn 2+ , Mg 2+ , and Fe 2+ ) can enlarge the stability field of the CaCO 3 -I phase as well as increase the pressure of the structural transition into the CaCO 3 -VI phase.