Structural, electronic and thermodynamic properties of carbonates at high pressures andtemperatures by in situ spectroscopy and atomic-scale simulations

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The scientific goal of this project is to determine the phase behavior of selected carbonate solid solutions by vibrational spectroscopy at pressures (P) up to 80 GPa and temperatures (T) up to 1000 K. While room temperature measurements will be performed in Mao type piston cylinder diamond anvil cells (DAC), DACs with internal gasket heaters (DAC-HT) will be employed for experiments at combined high P and high T conditions. We will additionally document the electronic state of Fe2+ in several carbonates at different pressures by collecting and interpreting optical spectra in the visible to nearinfrared (VIS to NIR) spectral range, and investigate the P und T conditions of Fe2+ highspin to lowspin state transitions. Complementary electronic structure calculations in the framework of density functional theory (DFT) and molecular dynamics simulations will be performed to link the electronic and atomic structure and dynamics of the respective carbonates to their vibrational and thermodynamic properties. This study will contribute to the goals of the Research Unit as described in the main proposal, i.e. to the understanding of phase relations, crystal chemistry, physical properties, and reactions of carbonates at conditions of the transition zone and the lower mantle.