New Superconductor (Na0.25K0.45) Ba3Bi4O12: A First-principles Study

Abstract: A new superconductor (Na0.25K0.45)Ba3Bi4O12, having an A-site-ordered double perovskite structure, with a maximum Tc ~ 27 K has very recently been discovered through hydrothermal synthesis at 593 K. The structural, elastic, electronic, and thermal properties of the new synthesized compound have been investigated theoretically. Here we have employed the pseudo-potential plane-wave (PP-PW) approach based on the density functional (DFT) theory, within the generalized gradient approximation (GGA). The elastic constants (Cij), Pughs ratio, Cauchys pressure and other elastic parameters are derived and analyzed using energy strain method for the first time. We have discussed the bonding nature in the light of the electronic valence charge density. Both electron and hole-like Fermi surfaces are present in the compound under study which indicate the multiple-band nature of (Na0.25K0.45)Ba3Bi4O12. The compound is indicated to be a strongly coupled superconductor which is based on the estimated e-ph coupling constant. The thermodynamic properties such as bulk modulus, Debye temperature, heat capacities and volume thermal expansion coefficient at elevated temperature and pressure are calculated and analyzed for the first time by using quasi-harmonic model. Key words: double perovskite, superconductor, elastic properties, electronic properties, thermal properties