First-principles study of superconducting ScRhP and ScIrP pnictides

Abstract: For the first time, we have reported in this study an ab initio investigation on elastic properties, Debye temperature, Mulliken population, Vickers hardness, and charge density of superconducting ScRhP and ScIrP phosphides. The optimized cell parameters show fair agreement with experimental results. The elastic constants and moduli, Poisson's as well as Pugh's ratio and elastic anisotropy factors have also been calculated to understand the mechanical behavior of these ternary compounds. Their mechanical stability is confirmed via the calculated elastic constants. The calculated values for Poisson's and Pugh's ratio indicate the ductile nature of these compounds. ScIrP is expected to be elastically more anisotropic than ScRhP. The estimated value of Debye temperature predicts that ScRhP is thermally more conductive than ScIrP and the phonon frequency in ScRhP is higher than that in ScIrP. The hardness of ScRhP is lower due to the presence of anti-bonding Rh-Rh in ScRhP. The investigated electronic structure predict that the metallic conductivity of ScRhP reduces significantly when Rh is replaced with Ir. The main contribution to the total density of states (TDOS) at Fermi-level (EF) comes from the d-electrons of Sc and Rh/Ir in both compounds. These two ternary compounds are characterized mainly by metallic and covalent bonding with little ionic contribution. As far as superconductivity is concerned, the matrix elements of electron-phonon interaction are noticeably enhanced in ScIrP compared to that in ScRhP.