Discovery of superconductivity in Nb(4)SiSb(2) with a V(4)SiSb(2)-type structure and implications of interstitial doping on its physical properties

We report on the discovery, structural analysis, and the physical properties of Nb(4)SiSb(2) – a hitherto unknown compound crystallizing in the V(4)SiSb(2)-type structure with the tetragonal space group I4/mcm and unit cell parameters a = 10.3638(2) Å and c = 4.9151(2) Å. We find Nb(4)SiSb(2) to be a metal undergoing a transition to a superconducting state at a critical temperature of T(c) ≈ 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 ΔC(T(c))/γT(c) = 1.33 mJ mol(−1) K(−2). We find that for Nb(4)SiSb(2), 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 T(c) ≈ 1.2 K for Nb(4)Cu(0.2)SiSb(2), and T(c) ≈ 0.8 K for Nb(4)Pd(0.2)SiSb(2) as well as for Nb(4)Pt(0.14)SiSb(2). The addition of electron-donor atoms into these void positions, henceforth, lowers the superconducting transition temperature in comparison to the parent compound.