Elastic Constants and Related Properties of Ti₄AC₃ (A = Si, Au, Ir) MAX Phases: A Comparative First-Principles Study

MAX-phase materials exhibit metallic-ceramic properties. The Ti₄AC₃ (A = Si, Au, Ir) 413-type MAX phases are investigated here using systematic density functional theory to examine structural stability, elastic behavior, mechanical performance, thermal properties, and electronic characteristics. Optimized lattice parameters agree with existing theoretical and experimental data. Single-crystal elastic constants satisfy the Born criteria, confirming mechanical stability. Using the Voigt-Reuss-Hill method, polycrystalline moduli are derived: Ti₄IrC₃ has the highest bulk modulus (B = 227.7 GPa), and Ti₄SiC₃ has the largest shear modulus (G = 148.1 GPa) and Young's modulus (E = 354.5 GPa). Ti₄AuC₃ shows lower moduli, indicating greater ductility (ν = 0.293; G/B = 0.481). Elastic anisotropy is significant in all three phases, with Ti₄AuC₃ being the most anisotropic. Electronic density of states analysis reveals strong Ti-C covalent bonding that underpins stiffness, while A-site bonding (Si, Au, Ir) influences ductility and anisotropy. This comprehensive comparison elucidates the structure-property relationships of Ti₄AC₃ (A = Si, Au, Ir) MAX phases and supports their design for targeted applications in aerospace, energy, and mechanical engineering.