First principles study of structural, elastic, and thermodynamic properties of LiAl2X (X = Rh, Pd, Ir and Pt) intermetallic compounds

The equilibrium structural parameters, thermodynamic properties, elastic constants, and several other related properties of LiMAl2 (M = Rh, Pd, Ir and Pt) ternary intermetallic compounds have been investigated, employing the projected augmented wave pseudopotentials (PAW) approach in the framework of the density functional theory (DFT) as implemented in the Quantum Espresso code. Our findings on the lattice parameters of LiMAl2 (M = Rh, Pd, Ir and Pt) compounds agree well with the experimental ones, while our obtained results of the elastic constants are in general slightly higher than the theoretical ones reported previously in literature. Our results concerning the mechanical stability criteria indicate that all LiMAl2 (M = Rh, Pd, Ir and Pt) are mechanically stable at equilibrium, while the analyses of both Zener anisotropy factor and elastic anisotropy index show that all these compounds are highly anisotropic in their elastic properties. According to Mukhanov et al.’s (Philos. Mag. 89:2117, 2009) model, the Vickers hardness HV of LiMAl2 (M = Rh, Pd, Ir and Pt) increases gradually and almost linearly with increasing pressure. The Debye temperature θD as well as the melting point Tm of the aggregate materials are calculated using two different empirical expressions. The obtained values of θD are around 499.5 (546.4) K for LiRhAl2, 478.7 (520.6) K for LiPdAl2, 411 (451) K for LiIrAl2, and 417.3 (455.2) K for LiPtAl2 compound, respectively; while those of Tm are found to be around 1566 (1448) K for LiRhAl2, 1436 (1316) K for LiPdAl2, 1650 (1502) K for LiIrAl2, and 1615 (1489) K for LiPtAl2, respectively. Our calculated data show that the behavior of the thermodynamic properties with increasing temperatures is monotonic for all our materials of interest. Graphical abstract