Pressure-induced reversible phase transition on Mo2Ga2C

Abstract

The newly carbide α-Mo2Ga2C with P63/mmc space group presents a unique top-packed Ga double layer structure. Pressure-induced phase transition of Mo2Ga2C has been investigated by in-situ high-pressure synchrotron radiation X-ray diffraction, Raman spectroscopy combined with diamond anvil cell technique, and first-principle calculations. Both experimental and theoretical results show that a first-order phase transition from P63/mmc to P3¯m1 occurs at ∼22 GPa, where the high-pressure phase named β-Mo2Ga2C has a close-packed Ga double layer zig-zag structure. The isothermal pressure-volume relationship of Mo2Ga2C is described by the second-order Birch-Murnaghan equation of state, yielding K0 = 139(2) GPa, K0′ = 4(fixed), and V0 = 144.5(1) Å3 for α-Mo2Ga2C; K0 = 187(3) GPa, K0′ = 4(fixed), and V0 = 137.9(2) Å3 for β-Mo2Ga2C. The instability caused by the repulsive force between the Ga atoms in the top-packed double-layer under pressure mainly accounts for the phase transition. The newly discovered β-Mo2Ga2C reveals that the MAX-like M2A2X type ternary compounds with different compositions may form various structures with different space groups.