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

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.