Pressure-induced effects on the mechanical and thermophysical properties of LiAl₂X (X = Rh, Pd, Ir and Pt) ternary intermetallic compounds

Abstract

Using the projected augmented wave pseudo-potentials (PAW) approach and the generalized gradient approximation (GGA) of Perdew–Burke–Ernzerhof (PBEsol) in the framework of the density functional theory as implemented in the Quantum Espresso code, the mechanical behaviour as well as the thermo-physical properties of LiAl₂X (X = Rh, Pd, Ir and Pt) ternary intermetallic compounds under high hydrostatic pressure up to 10 GPa have been predicted. Our finding on the elastic stiffness constants, aggregate elastic modulus, Debye temperature, limiting angular vibrational frequency, vibrational energy as well as the vibrational free energy of LiAl₂X (X = Rh, Pd, Ir and Pt) compounds shows that all these quantities increase monotonically with increasing pressure up to 10 GPa; while the elastic compliance constants (except S₁₂), the vibrational entropy and the constant volume heat capacity of LiAl₂X (X = Rh, Pd, Ir and Pt) decrease monotonically with increasing pressure. At room-temperature and zero-pressure, the obtained values of the Debye temperature θ_D are 486.10 K for LiAl₂Rh, 462.51 K for LiAl₂Pd, 401.36 K for LiAl₂Ir and 406.62 K for LiAl₂Pt, respectively; while at room-temperature and pressure of 10 GPa, the values obtained of θ_D are around: 528.29 K for LiAl₂Rh, 507.80 K for LiAl₂Pd, 428.81 K for LiAl₂Ir and 442.88 K for LiAl₂Pt, respectively. In addition, the analysing of the generalized mechanical stability criteria under isotropic pressure shows that all our materials of interest are mechanically stable up to 10 GPa.