Lattice stabilities, mechanical and thermodynamic properties of Al₃Tm and Al₃Lu intermetallics under high pressure from first-principles calculations

The effects of high pressure on lattice stability, mechanical and thermodynamic properties of L1₂ structure Al₃Tm and Al₃Lu are studied by first-principles calculations within the VASP code. The phonon dispersion curves and density of phonon states are calculated by using the PHONONPY code. Our results agree well with the available experimental and theoretical values. The vibrational properties indicate that Al₃Tm and Al₃Lu keep their dynamical stabilities in L1₂ structure up to 100 GPa. The elastic properties and Debye temperatures for Al₃Tm and Al₃Lu increase with the increase of pressure. The mechanical anisotropic properties are discussed by using anisotropic indices A^{m G}, A^U, A^Z, and the three-dimensional (3D) curved surface of Young's modulus. The calculated results show that Al₃Tm and Al₃Lu are both isotropic at 0 GPa and anisotropic under high pressure. In the present work, the sound velocities in different directions for Al₃Tm and Al₃Lu are also predicted under high pressure. We also calculate the thermodynamic properties and provide the relationships between thermal parameters and temperature/pressure. These results can provide theoretical support for further experimental work and industrial applications.