High-pressure phase transitions of Mg_2Ge and Mg_2Sn: First-principles calculations

摘要

Phase transitions of the anti-fluorite compounds Mg_2Ge and Mg_2Sn under high pressure were investigated using the first-principles plane-wave method within the pseudopotential and generalized gradient approximations. The calculated results show that Mg_2Ge and Mg_2Sn undergo two first-order phase transitions at high pressure and the sequence of the pressure-induced phase transitions is from the anti-fluorite to the anti-cotunnite, and then to the Ni_2In-type structure. The high pressure behaviors of Mg_2Ge and Mg_2Sn are similar to Mg_2Si and the isostructural alkali-metal oxide Li_2O. Moreover, the electronic and optical properties of both the anti-fluorite and the high-pressure phases are presented.