Discovery of superconductivity in NbSiSb with a VSiSb-type structure and implications of interstitial doping on its physical properties.

We report on the discovery, structural analysis, and the physical properties of NbSiSb - a unknown compound crystallizing in the VSiSb-type structure with the tetragonal space group 4/ and unit cell parameters = 10.3638(2) Å and = 4.9151(2) Å. We find NbSiSb to be a metal undergoing a transition to a superconducting state at a critical temperature of ≈ 1.6 K. The bulk nature of the superconductivity in this material is confirmed by the observation of a well defined discontinuity in specific heat with a normalized specific heat jump of Δ( )/ = 1.33 mJ mol K. We find that for NbSiSb, the unoccupied sites on the 4b Wyckoff position can be partially occupied with Cu, Pd, or Pt. Low-temperature resistivity measurements show transitions to superconductivity for all three compounds at ≈ 1.2 K for NbCuSiSb, and ≈ 0.8 K for NbPdSiSb as well as for NbPtSiSb. The addition of electron-donor atoms into these void positions, henceforth, lowers the superconducting transition temperature in comparison to the parent compound.