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

The high-pressure and high-temperature formation and stability of recently discovered magnesium carbide Mg 2 C were studied by in situ X-ray diffraction up to 20 GPa and 1550 K. The insights into the thermodynamics of Mg 2 C 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.