Abstract: The novel In-based MAX phase Zr₃InC₂ has recently attracted considerable attention for its excellent physical properties, yet investigations into its behaviour under high pressure remain limited. This study systematically investigates the effects of pressure on the crystal structure, mechanical properties, electronic structure, and thermodynamic behavior of the novel MAX phase Zr₃InC₂ using first-principles calculations based on density functional theory (DFT). Comparative analysis with Zr₃AlC₂ reveals how substituting Al with In at the A-site influences structural and physical properties, as well as responses under high-pressure conditions. Calculated lattice parameters for both Zr₃InC₂ and Zr₃AlC₂ show good agreement with previous experimental reports. Results indicate pronounced anisotropic compression, with significantly higher compressibility along the c-axis than the a-axis. Elastic constants and phonon dispersion curves confirm mechanical and dynamic stability of Zr₃InC₂ up to 50 GPa. Poisson’s ratio analysis suggests brittle behavior at ambient pressure, ductility first appears at 40 GPa. The discrepancy between the Poisson's ratio and the Cauchy pressure at 50 GPa suggests that Zr₃InC₂ may be near the critical region of a brittle-to-ductile transition under high pressure. Compared with Zr₃AlC₂, Zr₃InC₂ exhibits greater sensitivity in mechanical properties under high pressure. Electronic structure calculations reveal its metallic nature. Thermodynamic analysis shows a relatively low thermal expansion coefficient at ambient pressure, while increased pressure leads to a significant rise in Debye temperature and minimum thermal conductivity. These findings highlight the tunability of Zr₃InC₂’s thermodynamic properties under pressure, offering theoretical support for potential high-temperature applications.

Key words: high pressure, first principles, MAX phase, crystal structure, electronic structure