Stability mechanic and elastic, anisotropy, and thermophysical properties of RNi 5 H 6 (R = Sc, Y, or La) intermetallic hydrides under stress

The work in hand presents the elastic, elastic anisotropy, and thermoelectric and thermophysical properties and the effect of pressure variation on them for RNi 5 H 6 (R = Sc, Y, or La), in which all calculations have been investigated by using the first-principles method within the full-potential linearized augmented plane wave method implemented in wien2k package. Both the framework of the generalized gradient approximation (GGA96) and the IReLast package implemented in Wien2k have been used to describe the exchange–correlation potential and to determine elastic constants and mechanical properties, respectively. Additionally, the quasi-harmonic Debye model is employed within Gibbs2. The calculated elastic constants and modulus satisfy Born’s mechanical stability criteria, meaning that the three hydrides in this study are mechanically stable. Meanwhile, their mechanical behaviors reveal that these hydrides have a ductile character and are elastically anisotropic, whereas ScNi 5 H 6 is considered highly ductile and relatively low hardness compared to others. In addition, we observed that the changeability of the properties related to the elastic constants increases with pressure, while mechanical stability remains valid. Due to these hydrides’ positive Cauchy pressure, the chemical bonds have metallic characteristics. The substitution led to a decrease in the anisotropy of the mechanical quantities. These hydrides’ bulk modulus and Debye temperatures decrease from ScNi 5 H 6 to LaNi 5 H 6 . As the atomic radius of rare earth atoms decreases, the substitution leads to an increase in both the Debye temperature and bulk modulus. In contrast, this led to a decrease in the volume, specific heat at constant pressure, heat capacity at constant volume, thermal expansion, thermal expansion coefficient, and entropy.