Ab initio predictions of structure and physical properties of the Zr(2)GaC and Hf(2)GaC MAX phases under pressure

The electronic structure, structural stability, mechanical, phonon, and optical properties of Zr(2)GaC and Hf(2)GaC MAX phases have been investigated under high pressure using first-principles calculations. Formation enthalpy of competing phases, elastic constants, and phonon calculations revealed that both compounds are thermodynamically, mechanically, and dynamically stable under pressure. The compressibility of Zr(2)GaC is higher than that of Hf(2)GaC along the c-axis, and pressure enhanced the resistance to deformation. The electronic structure calculations reveal that M(2)GaC is metallic in nature, and the metallicity of Zr(2)GaC increased more than that of Hf(2)GaC at higher pressure. The mechanical properties, including elastic constants, elastic moduli, Vickers hardness, Poisson’s ratio anisotropy index, and Debye temperature, are reported with fundamental insights. The elastic constants C(11) and C(33) increase rapidly compared with other elastic constants with an increase in pressure, and the elastic anisotropy of Hf(2)GaC is higher than that of the Zr(2)GaC. The optical properties revealed that Zr(2)GaC and Hf(2)GaC MAX phases are suitable for optoelectronic devices in the visible and UV regions and can also be used as a coating material for reducing solar heating at higher pressure up to 50 GPa.