First-principles study of M<sub>4</sub>AlC<sub>3</sub> (M = Ti, Zr) MAX phases under hydrostatic pressure: material design for industrial applications.

Abstract

MAX phase compounds, combining metallic and ceramic properties, are ideal for high-pressure environments due to their excellent electrical and thermal conductivity, corrosion and oxidation resistance, and damage tolerance. This study investigates the structural, mechanical, electronic, thermal, and optical properties of M₄AlC₃ (M = Ti, Zr) under hydrostatic pressure. Negative formation energies and positive phonon dispersion confirm thermodynamic and dynamic stability, while mechanical stability aligns with Born's criteria. Increasing stiffness constants and moduli (bulk, shear, Young's), along with Poisson's and Pugh's ratios, suggest enhanced mechanical performance. Ti₄AlC₃ and Zr₄AlC₃ are brittle below 60 GPa and 40 GPa, respectively, but become ductile above these pressures. A rising machinability index with pressure supports industrial applicability. Anisotropy is confirmed <i>via</i> 3D plots, and DOS analysis reveals metallic nature. Strong UV absorption and conductivity highlight their potential in UV-optical devices. Reflectivity above 60% and high IR reflectance suggest use in thermal coatings and solar heat management. Increasing Debye and melting temperatures under pressure further indicate their suitability for high-temperature applications. These findings support their use in extreme conditions such as aerospace, deep-sea exploration, and ultra-hard ceramic development.