Density functional theory study of pressure‐induced structural, mechanical, electronic, optical, and thermal properties of Mo ₂ AC (A = Al, Ga, Ge)

Abstract We use first‐principles density‐functional theory (GGA‐PBE) to quantify the pressure response (0–20 GPa) of (A = Al, Ga, Ge) MAX phases across structure, mechanics, electronics, optics, and thermal properties. Normalized lattice parameters (, ) reveal anisotropic compression with preferential shortening along , reflecting rigid Mo–C octahedral layers and more compliant Mo–A bonding. All phases satisfy pressure‐corrected mechanical‐stability criteria and stiffen under compression; for example, the bulk modulus of increases from 200 to 284 GPa. Pugh ratios show lies near the brittle threshold ( G / B 0.660.56), whereas (0.540.43) and (0.35) are ductile. Formation energies are negative and become more negative with pressure, indicating enhanced thermodynamic stability. The Mo 4d–dominated DOS at the Fermi level decreases modestly with pressure. Optical spectra display strong interband absorption at 2–5 eV, high static refractive indices ( n (0) 6–16), mid‐UV reflectivity plateaus ( R 0.54–0.78), and a loss‐function plasmon near 25–30 eV that blueshifts under compression. Thermally, exhibits the highest Debye temperature (598–647 K) and melting point (2020–2484 K), while shows the lowest minimum lattice thermal conductivity (0.67–0.80 ), favoring thermal‐barrier applications. These pressure‐tunable optical and thermal responses support ceramics for aerospace coatings, thermal‐barrier layers, and high‐temperature structural components. To our knowledge, this work reports the first pressure‐dependent optical spectra for , presents full 3D elastic‐anisotropy mapping, and establishes the pressure trend of the Debye temperature for .