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

Abstract

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 (EF), phonon dispersion curves (PDC), performing AIMD simulations, and deriving mechanical stiffness coefficients (Cij). 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 (Tm), minimum thermal conductivity (Kmin), Grüneisen parameter (γ), thermal expansion coefficient (TEC), Debye temperature (ΘD), and lattice thermal conductivity (kph). Given the elevated values of ΘD, Tm, a favorable TEC, and low values of kph and Kmin, 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 Kph 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.