Physical properties of ThCr2Si2-type Ni-based compounds SrNi2M2 (M= As and Ge): DFT based Ab-inito calculations

Highlights: • In this research work, we have performed the detailed physical properties including structural, elastic, electronic and optical properties of SrNi₂As₂ and SrNi₂Ge₂ by using CASTEP code based on the density functional theory. • The optimize lattice parameters are very close to the experimental data for both compounds. • The materials possess metallic behavior. • SrNi₂As₂ and SrNi₂Ge₂ compounds are ductile in nature and shows anisotropic characteristics. • The compound possesses good absorption coefficient and conductivity in the high energy region. -- Abstract: ThCr₂Si₂-type Ni-based superconductors SrNi₂As₂ and SrNi₂Ge₂ have the critical temperature of 0.62 K and 1.1 K respectively have been reported recently. Employing the first-principles method based on the density function theory, we have studied the physical properties including structural, elastic, electronic and optical properties of these compounds. For both phases our optimized lattice parameter are good accord with the experimental lattice parameters. The elastic constant for both compounds are positive which reveal that these superconductors possess the mechanical stability in nature. The analysis of the mechanical properties assures that these compounds exhibit ductile in nature and show anisotropic behavior. Bulk modulus indicates that these compounds are soft. The study of the band structure and density of states (TDOS and PDOS) reveals the metallic nature of SrNi₂As₂ and SrNi₂Ge₂. At the Fermi level the major contribution comes from Ni-3d, As-4p for SrNi₂As₂ and Ni-3d, Ge-4p for SrNi₂Ge₂. The analysis of DOS, and Mulliken atomic populations revel a complex bonding in SrNi₂As₂ and SrNi₂Ge₂ with ionic, covalent and metallic characteristics. The analysis of the dielectric function also ensures the metallic behavior of these compounds. The investigated optical functions of these compounds reveal the high reflectivity which indicates that SrNi₂M₂ (M= As and Ge) having the same characteristics could be good candidate materials to reduce solar heating up to ∼14 eV.