Superconductivity in Ba5Ir7Ge4 derived from MgCu2-type Laves phase BaIr2

We successfully synthesized the new compound Ba₅Ir₇Ge₄ at ambient pressure by adding Ge to BaIr₂, which is a high-pressure stable MgCu₂-type Laves phase. Rietveld analysis revealed that Ba₅Ir₇Ge₄ crystallizes by replacing part of the Ir₄ tetrahedra in BaIr₂ with Ge₄Ir tetrahedra, forming in a network of corner-sharing Ge₄Ir and Ir₃Ge tetrahedra. While BaIr₂ has a cubic structure, Ba₅Ir₇Ge₄ adopts a new prototype structure with a tetragonal space group I4₁/a (no.88) (a = 12.9726(2) Å, c = 8.2703(2) Å). Our experiments demonstrated that Ba₅Ir₇Ge₄ is a type-II superconductor with a transition temperature (T_c) of 3.2 K, which is slightly higher than that of BaIr₂. Electronic structure calculations show that the density of states (DOS) at the Fermi energy is primarily contributed by the d states in the Ir atoms forming the Ir₃Ge tetrahedra. Despite having smaller DOS at the Fermi level, Ba₅Ir₇Ge₄ exhibits a slightly higher T_c than that of BaIr₂, which can be attributed to its higher Debye temperature.