Exploration of New 212 MAX Phases: M2AB2 (M = Mo, Ta; A = Ga, Ge) via DFT Calculations

In this paper, four new MAX phases M₂AB₂ (M = Mo, Ta; A = Ga, Ge) are explored, and the elastic, electronic, thermal, and optical properties are studied to anticipate their potential applications. The stability is confirmed by calculating formation energy (E_F), formation enthalpy (ΔH), phonon dispersion curve (PDC), and elastic constant (C_ij). The study reveals that M₂AB₂ (M = Mo, Ta; and A = Ga, Ge) exhibits significantly higher elastic constants, elastic moduli, and Vickers hardness values than their counterpart 211 borides. Higher Vickers hardness values of Ta₂AB₂ (A = Ga, Ge) than Mo₂AB₂ (A = Ga, Ge) are explained in terms of bond overlap population (BOP). The density of states (DOS) and electronic band structure (EBS) reveal the metallic nature of the titled borides. The melting temperature (T_m), Grüneisen parameter (γ), minimum thermal conductivity (K_min), Debye temperature (Θ_D), and other parameters of M₂AB₂ (M = Mo, Ta; A = Ga, Ge) are computed. These findings suggest that the studied compounds exhibit superior thermal properties compared to 211 MAX phases and are suitable for thermal barrier coating (TBC) applications. The optical characteristics are examined, and the reflectance spectrum indicates that the materials have the potential to mitigate solar heating.