Zr 5 Sb 3−x Ru x , a new superconductor in the W 5 Si 3 structure type

We report that at low Ru contents, up to x = 0.2, the Zr 5 Sb 3−x Ru x solid solution forms in the hexagonal Mn 5 Si 3 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 W 5 Si 3 structure type. We find that tetragonal Zr 5 Sb 2.4 Ru 0.6 is superconducting at 5 K, significantly higher than the transition temperature of hexagonal Zr 5 Sb 3 ( 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 W 5 Si 3 and Tl 5 Te 3 structure types, both of which support superconductivity, are derived from the parent Al 2 Cu type structure, in which superconductors are also found. Electronic structure calculations show that in Zr 10 Sb 5 Ru, a model for the new superconducting compound, the Fermi level is located on a peak in the electronic density of states.