Ab initio predictions of structure and physical properties of the Zr2GaC and Hf2GaC MAX phases under pressure

Abstract

The electronic structure, structural stability, mechanical, phonon, and optical properties of Zr₂GaC and Hf₂GaC 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 Zr₂GaC is higher than that of Hf₂GaC along the c-axis, and pressure enhanced the resistance to deformation. The electronic structure calculations reveal that M₂GaC is metallic in nature, and the metallicity of Zr₂GaC increased more than that of Hf₂GaC 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 C₁₁ and C₃₃ increase rapidly compared with other elastic constants with an increase in pressure, and the elastic anisotropy of Hf₂GaC is higher than that of the Zr₂GaC. The optical properties revealed that Zr₂GaC and Hf₂GaC 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.