A theoretical investigation of ThCr2Si2-type Pd-based superconductors XPd2Ge2 (X = Ca, Sr, La, Nd)

Abstract

ThCr2Si2-type Pd-based superconductors CaPd2Ge2, SrPd2Ge2, LaPd2Ge2, and NdPd2Ge2 have the critical temperature of 1.69 K, 3.12 K, 1.12 K, and 1.30 K respectively. Using the first-principles investigation based on the density function theory, we have investigated the physical properties including structural, mechanical, electronic, chemical bonding, optical and thermodynamic properties of these compounds. Our optimized lattice parameters are good accord with the experimental lattice parameters. The analysis of the mechanical properties ensures that these compounds exhibit ductile in nature and show anisotropic behavior. The study of the band structure and density of states (TDOS and PDOS) reveals the metallic nature of XPd2Ge2 (X = Ca, Sr, La, Nd). At the Fermi level the major contribution comes from Ge-4p states for CaPd2Ge2, SrPd2Ge2, LaPd2Ge2, and from Nd-4f states for NdPd2Ge2. The investigated chemical bonding and total charge density reveal the ionic, covalent and metallic bonding exist in four compounds. The observed optical functions of these compounds reveal the high reflectivity in the low energy region which indicates that these compounds might be used as coating materials to reduce solar heating. The large negative value of the real dielectric function also ensures the metallic behavior of these phases. We have also calculated the Debye temperature, melting temperature and minimum thermal conductivity. Finally, we have calculated the superconducting properties of all compounds.