Zr₅Sb_3-xRu_x, a new superconductor in the W₅Si₃ structure type

We report that at low Ru contents, up to x = 0.2, the Zr₅Sb_3-xRu_x solid solution forms in the hexagonal Mn₅Si₃ structure type of the host (x = 0), but that at higher Ru contents (x = 0.4-0.6) the solid solution transforms into the tetragonal W₅Si₃ structure type. We find that tetragonal Zr₅Sb_2.4Ru_0.6 is superconducting at 5 K, significantly higher than the transition temperature of hexagonal Zr₅Sb₃ (x = 0), which has a T_c of 2.3 K. In support of a hypothesis that certain structure types are favorable for superconductivity, we describe how the W₅Si₃ and Tl₅Te₃ structure types, both of which support superconductivity, are derived from the parent Al₂Cu type structure, in which superconductors are also found. Electronic structure calculations show that in Zr₁₀Sb₅Ru, a model for the new superconducting compound, the Fermi level is located on a peak in the electronic density of states.