Enhanced thermo-mechanical stability of Sc 2 TlC and Sc 2 PbC MAX-phase carbides under hydrostatic pressure

This work presents a first-principles investigation of the pressure-dependent structural, elastic, thermal, and optical properties of the layered MAX-phase carbides Sc 2 XC ([Formula: see text], Pb) using density functional theory under hydrostatic pressures ranging from 0 GPa to 12[Formula: see text]GPa. The evolution of elastic wave velocities, Debye temperature, melting temperature, and lattice thermal conductivity is systematically analyzed to assess the thermo-mechanical stability of these compounds under compression. At ambient pressure, Sc 2 TlC exhibits longitudinal, transverse, and average sound velocities of 4725.66, 2653.43, and 2952.76[Formula: see text]m[Formula: see text]s[Formula: see text], respectively, which increase markedly to 5619.72, 3219.24, and 3576.39[Formula: see text]m[Formula: see text]s[Formula: see text] at 12[Formula: see text]GPa, accompanied by an enhancement of the Debye temperature from 317.99[Formula: see text]K to 400.93[Formula: see text]K. Similarly, Sc 2 PbC shows a substantial rise in Debye temperature from 275.52[Formula: see text]K to 372.13[Formula: see text]K over the same pressure range, indicating improved lattice stiffness and phonon stability. The lattice thermal conductivity at 300[Formula: see text]K increases significantly with pressure, reaching 73.56[Formula: see text]W/m[Formula: see text][Formula: see text][Formula: see text]K for Sc 2 TlC and 60.24[Formula: see text]W/m[Formula: see text][Formula: see text][Formula: see text]K for Sc 2 PbC at 12[Formula: see text]GPa, reflecting enhanced phonon transport under compression. Optical properties reveal pronounced anisotropy, characterized by exceptionally high extinction coefficients along the xx-direction ([Formula: see text]–60 at 0[Formula: see text]eV) and negative refractive indices along the zz-direction ([Formula: see text] at 0[Formula: see text]eV), indicative of metallic and plasmonic behavior. Overall, the results demonstrate that Sc 2 TlC and Sc 2 PbC combine excellent mechanical robustness with pressure-tunable thermal transport and strongly anisotropic optical responses, highlighting their potential for high-temperature structural applications, advanced thermal management, plasmonic devices, and anisotropic optoelectronic technologies.