Structural, electronic and thermodynamic properties of carbonates at high pressures and temperatures by in situ spectroscopy and electronic structure calculations

Project 2 investigates the high pressure (HP) and high temperature (HT) stability of different carbonate minerals by means of Raman and optical absorption spectroscopy in the infrared and visible spectral range. To support the experimental results, additional theoretical density functional theory calculations are performed. The experiments are done in diamond anvil cells, which are internally heated. Samples include synthetic and natural samples of Mg(X-1)FeXCO3, CaCO3, SrCO3 and CaMg(CO3)2. Beside these solid state experiments a smaller portion of the project deals with phase relations and melting behavior in the anhydrous and hydrous CaCO3–MgCO3 system performed in a multi-anvil press.

One focus of the project lies on the pressure induced electronic high spin to low spin transition of Mg(X-1)FeXCO3. In previous work the pressure or depth range where the spin transition occurs was controversially debated and project 2 was able to put tight constraints on the pressure range at ambient and at high temperature. Other focii were related to the stability of the high-pressure CaCOcalcite(cc)-related polymorphs and to the stability of the high-pressure polymorphs of dolomite CaMg(CO3)2 up to 30 GPa and 800 K. For both compounds P/T diagrams were experimentally constrained. In situ high-pressure and high-temperature experiments on strontianite SrCOare on the way and will be finished in summer 2017.