DFT Insights into o‑MAX Phases, Mo₂AAlC₂ (A = Zr, Nb, Ta): Potential Candidates for Thermal Barrier Coating...

In this study, a detailed first-principles investigation based on density functional theory (DFT) was carried out to evaluate the structural stability and the electronic, mechanical, thermodynamic, and optical properties of the newly proposed o-MAX phases Mo₂AAlC₂ (A = Zr, Nb, Ta). The stability assessment involved computing their formation energies (E _F), phonon dispersion curves (PDC), performing AIMD simulations, and deriving mechanical stiffness coefficients (C _ij ). Evaluation of the electronic band dispersion and density of states (DOS) validates the metallic nature of Mo₂AAlC₂ (A = Zr, Nb, Ta). This study offers crucial perspectives on elastic parameters, fracture resistance, hardness parameters, and directional elasticity. The brittle nature of the examined compounds is reflected by the Pugh ratio, Poisson's ratio, and Cauchy pressure. Thermal behavior was further assessed through calculations of multiple governing parameters, such as melting point (T _m), minimum thermal conductivity (K _min), Grüneisen parameter (γ), thermal expansion coefficient (TEC), Debye temperature (Θ_D), and lattice thermal conductivity (k _ph). Given the elevated values of Θ_D, T _m, a favorable TEC, and low values of k _ph and K _min, the investigated phases are promising candidates for thermal barrier coating applications. Furthermore, analysis of phonon-mediated transport reveals pronounced phonon scattering and a suppression of K _ph at elevated temperatures, underscoring the promising role of phonons in next-generation protective barrier implementations. Based on the evaluated optical behavior, the reflectivity of these materials exceeds 44%, suggesting their suitability as coatings to mitigate solar heating of spacecraft bodies.