Possible new metastable Mo2Ga2C and its phase transition under pressure: a density functional prediction

The newly synthesized novel double-Ga layer nanolaminated carbide Mo 2 Ga 2 C is stimulating tremendous research interests. In the present exploration of Mo 2 Ga 2 C structure, another plausible metastable structure with close-packed Ga layers is predicted from density functional calculations. This new structure (denoted as m -structure) is slightly less stable by only 52 meV/atom than the experimentally determined structure ( e -structure) with on-top stacked Ga layers. Importantly, this m -structure is dynamically stable from the calculated phonon dispersion. Moreover, the stability behavior of this m -structure under compression shows that possible phase transition from e -phase to m -phase could occur under a pressure above 24.3 GPa, which requires further experimental confirmation. Phase transition model is proposed, and the energy barrier for phase transition is further derived. The electronic structures show that Mo–C bonds and Ga–Ga bonds are weaker in metastable m -phase than in e -phase. During compression, more strengthening of Ga–Ga and Mo–Ga bonds and less weakening of Mo–Mo bonds in m -phase explain the stabilization of m -phase under pressure.