Discovery of superconductivity in Nb4SiSb2 with a V4SiSb2-type structure and implications of interstitial doping on its physical properties

We report on the discovery, structural analysis, and the physical properties of Nb4SiSb2 - a hitherto unknown compound crystallizing in the V4SiSb2-type structure with the tetragonal space group I4/mcm and unit cell parameters a = 10.3638(2) angstrom and c = 4.9151(2) angstrom. We find Nb4SiSb2 to be a metal undergoing a transition to a superconducting state at a critical temperature of T-c approximate to 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 Delta C(T-c)/gamma T-c = 1.33 mJ mol(-1) K-2. We find that for Nb4SiSb2, 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 approximate to 1.2 K for Nb4Cu0.2SiSb2, and T-c approximate to 0.8 K for Nb4Pd0.2SiSb2 as well as for Nb4Pt0.14SiSb2. The addition of electron-donor atoms into these void positions, henceforth, lowers the superconducting transition temperature in comparison to the parent compound.

Automated summary

We report on the discovery, structural analysis, and physical properties of a previously unknown compound Nb4SiSb2, which undergoes a transition to a superconducting state at a critical temperature of approximately 1.6 K. We find that the addition of Cu, Pd, or Pt atoms into unoccupied sites in Nb4SiSb2 lowers the superconducting transition temperature.