Insights Into the Structural and Thermodynamic Behavior of Gold-Based MAX Phases M2AuC (M = Cr, V)

Abstract

A comprehensive first-principles investigation of the structural, mechanical, electronic, and thermodynamic properties of M₂AuC (M = Cr, V) MAX phases using the FP-LAPW method within the WIEN2k framework is performed. Both compounds that crystallize in a hexagonal Cr₂AlC-type structure (space group P6₃/mmc) exhibit negative formation energies with respect to their constituent elemental reference states, indicating favorable formation from the elements; however, stability against decomposition into competing binary or ternary phases requires further phase-stability analysis. Phonon dispersion analyses show the absence of imaginary frequencies, validating their dynamical stability. The computed elastic constants satisfy the Born–Huang criteria, indicating mechanical stability up to 30 GPa. Both compounds exhibit elastic anisotropy and show a tendency toward ductile mechanical behavior, while their elastic indicators suggest predominantly nondirectional bonding with an appreciable ionic contribution. Electronic band structures and density of states reveal metallic behavior primarily governed by M-d and Au-d orbitals. Thermodynamic analyses based on the quasi-harmonic Debye model show that heat capacity approaches the Dulong–Petit limit at high temperatures, while Debye temperature and thermal expansion exhibit typical temperature- and pressure-dependent trends. These findings establish M₂AuC (M = Cr, V) as mechanically robust, dynamically stable metallic materials with promising high-temperature applications.