Pressure-induced phase transformations in Mg3P2 from first-principles calculations

The phase behavior of Mg3P2 was investigated at increasing pressure from ambient to 100 GPa using first-principles calculations. It transformed first from anti-C (Ia-3) to anti-A (P-3m1) at 2.5 GPa, and then to antipost-perovskite (P63/mmc) at 35 GPa. Remarkably, we found a new low-enthalpy structure with space group C2/c to be favored above 65 GPa. The electronic calculations predict Mg3P2 to be initially a semiconductor, but to become a metal at 35 GPa in the P63/mmc structure, and remain so in the new C2/c structure at 65 GPa. Phonon dispersions demonstrate that the four phases are dynamically stable in their respective low-enthalpy pressure ranges. Charge transfers in the phases are also calculated and discussed.