Exploration of the structure, properties, and anisotropy of (r, h)-TiAl2 under high pressure

Abstract

In this study, we use the first principles calculation based on the density functional theory (DFT) to investigate the effects of high pressure on the structural, anisotropic, mechanical, and thermal properties and the phase stability of r-TiAl2 (HfGa2 type) and h-TiAl2 (ZrGa2 type). The calculation results of the formation enthalpy indicate that r-TiAl2 and h-TiAl2 remain stable under the 0–40 GPa. There is no phase transition, and the two phase structures are mechanically stable under the applied pressure. The Bulk modulus (B), Shear modulus (G), and Young's modulus (E) increase with increasing pressure from 0 to 40 GPa. The 3D surface structure of the elastic modulus and the universal elastic anisotropy index (AU) indicate that the elastic anisotropy of h-TiAl2 is higher than that of r-TiAl2. In addition, Sound velocity and Debye temperature are investigated from analysis of the elastic constants and moduli. Finally, the density of states and charge density difference are also discussed.