Crystal Structures and Chemical Bonding of Magnesium Carbide at High Pressure
2015
Liu, Hanyu | Gao, Guoying | Li, Yinwei | Hao, Jian | Tse, John S.
Recent studies of the magnesium carbide (Mg–C) system under pressure were motivated by the successful high-pressure and high-temperature synthesis of Mg₂C and Mg₂C₃. Here, we systematically investigate the high-pressure structures and chemical bonding of the Mg₂C, Mg₂C₃, and MgC₂ system using the swarm optimization technique in combination with first-principles electronic structure methodology. The structural evolution with pressure of the Mg–C systems clearly shows a systematic trend with a progressive increase of electron donation from the Mg to C. To accommodate the electrons, the C valence sp orbitals rebybridized continually and adopted different modes of chemical bonding. We demonstrated that the evolution of the electronic and crystal structures can be explained from a Zintl–Klemen charge-transfer concept. Therefore, at sufficiently high pressure metallic MgC₂ and Mg₂C transformed to semiconductors, while Mg₂C₃ undergoes an insulator–metal transition. The present results established the richness of carbon bonding of different stoichiometries under high pressure.
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