Structural and physical properties of the MAX phases RE2SX (RE = La ∼ Lu; X=B, C, N) via first-principles calculations

Abstract

MAX phase layered compounds have high temperature stability, excellent mechanical properties, good thermal conductivity and electronic properties. In order to provide a certain theoretical basis for further experimental exploration of the MAX phase with rare-earth (RE) element, a detailed study of the RE₂SX (RE = La∼Lu, X = B, C, N) MAX phase has been performed by using first-principles calculations. The study comprehensively examines the mechanical properties, elastic anisotropy, dynamical stability and thermal properties of the RE₂SX phase, and the results demonstrate that 37 RE₂SX phases satisfied the thermodynamical, mechanical and dynamical stabilities among the 45 compounds. The mechanical properties of the 37 stable phases were systematically analyzed, including bulk modulus, shear modulus, Young's modulus and hardness. Among these phases, La₂SN, Ce₂SB/N, Pr₂SB/N, Nd₂SB/N, Pm₂SB, Sm₂SB, Eu₂SB, and Gd₂SB were identified as exhibiting promising ductility potential. In the RE₂SX carbides, the occupied states on the Fermi level of the RE₂SC phase are very small, with the conduction band is mainly occupied by the valence electrons of the RE and S atoms, suggesting that these carbides exhibit notable electronic characteristics. These results can enhance our understanding of RE₂SX phases and provide valuable guidance for future experimental research.