High-Pressure and High-Temperature Stability of Antifluorite Mg2C by in Situ X-ray Diffraction and ab Initio Calculations

International audience; The high-pressure and high-temperature formation and stability of recently discovered magnesium carbide Mg2C were studied by in situ X-ray diffraction up to 20 GPa and 1550 K. The insights into the thermodynamics of Mg2C under extreme conditions, and its metastability at 0.1 MPa and 300 K, were provided by ab initio calculations of total energies and phonon density of states as a function of pressure. We illustrate how the compound found occasionally in high-pressure experiments could be systematically predicted and discovered in a time-saving way. Similar theoretical approaches can be useful for prediction of synthesis conditions and recovery of new solids.