The pressure dependence of physical properties of (W2/3Ti1/3)3AlC2 and its counterpart W3AlC2 by first-principles calculations

Abstract

First-principles calculations based on density functional theory (DFT) were used to investigate the mechanical properties, elastic anisotropy, electronic structure, optical properties and thermodynamic properties of a new quaternary MAX phase (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] and its counterpart W[Formula: see text]AlC[Formula: see text] under hydrostatic pressure. The results indicate that the volumetric shrinkage of (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] is faster than that of axial shrinkage under hydrostatic pressure. The stress–strain method and Voigt–Reuss–Hill approximation were used to calculate elastic constants and moduli, respectively. These compounds are mechanically stable under hydrostatic pressure. Moreover, the moduli of (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] and W[Formula: see text]AlC[Formula: see text] increase with an increase in pressure. The anisotropic indexes and surface constructions of bulk and Young’s moduli were used to illustrate the mechanical anisotropy under hydrostatic pressure. Electronic structure and optical property of (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] and W[Formula: see text]AlC[Formula: see text] have also been discussed. The results of Debye temperature reveal that the covalent bonds among atoms in (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] may be stronger than that of W3AlC[Formula: see text]. The heat capacity, [Formula: see text]–[Formula: see text], and thermal expansion coefficient of (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] and W[Formula: see text]AlC[Formula: see text] were discussed in the ranges of 0–30 GPa and 0–2000 K using quasi-harmonic Debye model considering the phonon effects.