First-principles investigation of the structural, mechanical and thermodynamic properties of Al2Cu phase under various pressure and temperature conditions

The crystal structure, phase stability, mechanical and thermodynamic properties of the Al2Cu (theta), Al2Cu (theta') and Al2Cu (Omega) phases are studied by the first-principles method. The predicted lattice constants are consistent with the available literature data. theta, theta' and O phases are thermodynamically stable, and do not undergo any phase transition under pressure. The values of B for Omega are larger than that for theta and theta' phases, while the values of G for theta are smaller than that for Omega and theta' phases. The studies also reveal that pressure can improve the elastic anisotropy of the theta, theta' and O phases. The Debye temperature, heat capacity and thermal expansion coefficient for the phases are determined by the quasi-harmonic Debye model. Under identical conditions, the values of TD from high to low is in the following order: theta' > Omega > theta. The heat capacity and thermal expansion coefficient for theta, theta' and Omega phases decrease with pressure when the temperature is kept constant. In contrast, thermal expansion coefficient a is more sensitive to any changes in pressure than any temperature change in the temperature range, 300-800 K.