Computational assessment of structural, mechanical, and thermal properties of ordered MAX phases V2ZrSiC2 and Ti2ZrSiC2 for high-temperature applications

Abstract

Chemically ordered quaternary MAX phases offer a route to tailor stiffness, anisotropy, and transport in layered carbides. Using all-electron FP-LAPW DFT (GGA-PBE), we investigate V2ZrSiC2 and Ti2ZrSiC2 in α- and β-stacking variants. EOS fits show strong stacking sensitivity: α polytypes are stiffer (bulk moduli ∼216 GPa for V2ZrSiC2 and ∼192 GPa for Ti2ZrSiC2) than β polytypes (∼178 and ∼157 GPa). Elastic constants satisfy the Born criteria, and VRH averages indicate higher shear/tensile rigidity and hardness for Ti2ZrSiC2 (G ≈ 136 GPa, E ≈ 328 GPa, HV ≈ 21 GPa) than for V2ZrSiC2 (G ≈ 121 GPa, E ≈ 305 GPa, HV ≈ 14 GPa), while V2ZrSiC2 retains higher incompressibility (B ≈ 214 GPa). Both phases are metallic with transition-metal d states dominating near EF, and phonon dispersions show no imaginary modes along the sampled path. Quasi-harmonic Debye–Gruneisen results yield ΘD ∼669 K (V2ZrSiC2) and ∼726 K (Ti2ZrSiC2); Slack-type estimates give kph ∼10–11 W m−1 K−1 at 300 K with an approximate 1/T decrease. The computed linear CTE at 1300 K (αL ≈ 0.95 and 1.06 × 10−5 K−1) lies between representative α-Al2O3 and YSZ values, supporting screening-level thermo-expansion compatibility for coating-stack layers. Energies above the convex hull are ∆Ehull ∼ 0.10–0.19 eV/atom, indicating metastability at T = 0 K with respect to competing phases and motivating further synthesis-focused thermodynamic analysis alongside oxidation and interface-stability assessment.