Pressure and temperature effects on the anisotropic and thermodynamic properties of NiAl and FeAl

We present the elastic constants of NiAl and FeAl compounds under high pressure and high temperature by using a first-principles approach. The temperature dependent elastic constants are predicted from the combinations of static volume-dependent elastic constants derived from the first-principles total-energy method within the density-functional theory (DFT). The calculated lattice and elastic constants at ground state are in agreement with the existing experimental and other theoretical values. Using the density-functional perturbation theory (DFPT) under the quasi-harmonic approximation (QHA), the temperature and pressure dependencies of the bulk modulus, the volume expansion, the thermal expansion, as well as the heat capacity at constant pressure are systematically investigated in the ranges of 0-1200 K and 0-50 GPa.