<i>Ab initio </i>predictions of electronic, structural, mechanical, phonon, and optical properties of the Zr2GaC and Hf2GaC MAX phases under high pressure

The structural stability, electronic, mechanical, phonon, and optical properties of M2GaC (M = Zr, Hf) MAX phases have been investigated using first-principles calculations under high pressure. It is found that the compressibility of Zr₂GaC is better than that of Hf₂GaC along the c-axis, and pressure enhanced the resistance to deformation. The electronic structure calculations indicated that M₂GaC is metallic, and the metallicity of Zr₂GaC increased more than that of Hf₂GaC at higher pressure. Moreover, mechanical properties, including elastic constants, elastic moduli, Vickers hardness, Poisson’s ratio anisotropy index, and Debye temperature, are reported under high pressure. It is observed that C₁₁ and C₃₃ increases rapidly compared with other elastic constants with an increase in pressure, and elastic anisotropy of Hf₂GaC is higher than that of the Zr₂GaC. Formation energy, elastic constants, and phonon calculations revealed that both compounds are thermodynamically, mechanically, and dynamically stable. Finally, 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 GP.