Structural stability and physical properties of MAX phases M₂SX (M=Sc, Y, X=B, C, N) via first-principles calculations

The structural, mechanical, lattice-dynamic, anisotropic, electronic and thermal properties of M2SX (M=Sc, Y; X=B, C, N) are investigated based on density functional theory. The calculated results indicate that all the phases satisfy the thermodynamic, mechanical and dynamic stability criteria. The mechanical properties are in good agreement with the reported values, and the results show that Sc2SN exhibits the highest bulk modulus B (145.7 GPa), shear modulus (103.0 GPa) and Young's modulus E (250.0 GPa) with brittle behavior. The elastic anisotropy of M2SX indicates that Sc2SC is the most isotropic among the 6 phases. The electronic structure reveals that Sc2SC and Y2SC are indirect-bandgap semiconductors with 0.927 eV and 1.260 eV bandgap, and the other phases exhibit metallic characteristics. The Debye temperature, lattice thermal conductivity, minimum thermal conductivity, heat capacity and entropy have also been calculated for M2SX phases. The tendency for lattice thermal conductivity in high temperature: K ( lat ) (M2SN) > K ( lat ) (M2SC) > K ( lat ) (M2SB). All the present calculated data will provide useful guidance for development and research on the novel S-based MAX phases in the future.