The pressure dependence of physical properties of (W_2/3Ti_1/3)₃AlC₂ and its counterpart W₃AlC₂ by first-principles calculations

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_2/3Ti_1/3)₃AlC₂ and its counterpart W₃AlC₂ under hydrostatic pressure. The results indicate that the volumetric shrinkage of (W_2/3Ti_1/3)₃AlC₂ 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_2/3Ti_1/3)₃AlC₂ and W₃AlC₂ 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_2/3Ti_1/3)₃AlC₂ and W₃AlC₂ have also been discussed. The results of De- bye temperature reveal that the covalent bonds among atoms in (W_2/3Ti_1/3)₃AlC₂ may be stronger than that of W₃AlC₂. The heat capacity, Cp-Cv, and thermal expansion coeficient of (W_2/3Ti_1/3)₃AlC₂ and W₃AlC₂ were discussed in the ranges of 0{30 GPa and 0{2000 K using quasi-harmonic Debye model considering the phonon effects.