Pressure-induced phase transitions and mechanical properties of ternary nanolaminated carbide Mo2Ga2C from first-principles calculations

Abstract

The newly synthesized ternary carbide Mo2Ga2C (P63/mmc, Z = 2) with novel double-Ga layers, the firstly reported member of the well-known MAX-like phases, is stimulating extensive research interests. Here, motivated by the recent experimental and theoretical works, the high-pressure structure evolution behavior of Mo2Ga2C up to 150 GPa has been extensively investigated using an efficient crystal structure search approach combined with first-principles calculations. Besides the experimental high-pressure trigonal P-3m1 phase, a new orthorhombic Amm2 phase was firstly identified and was confirmed to be dynamically stable above 90 GPa. The occurrence of this Amm2 phase follows the strong twist of CMo6 octahedrons in P-3m1 phase and the coordination number of Mo increases from six to seven under compression. Pressure-induced phase transition from P63/mmc to P-3m1 at 22 GPa and P-3m1 to Amm2 at 90 GPa was characterized as first order with a volume reduction of 2.3% and 2.5%, respectively. Inspections of electronic and crystal structures suggested an enhanced Ga–Ga covalent hybridization in the predicted Amm2 phase, which becomes much less compressible under compression. The mechanical parameters and elastic anisotropy behaviors of both P63/mmc and P-3m1 phases were then systematically studied, and the (101¯0)[1¯21¯0] directions were found to be their possible dislocations slip system.