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

Abstract

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) Å and c = 4.9151(2) Å. We find Nb₄SiSb₂ 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 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 ≈ 1.2 K for Nb₄Cu_0.2SiSb₂, and T_c ≈ 0.8 K for Nb₄Pd_0.2SiSb₂ as well as for Nb₄Pt_0.14SiSb₂. The addition of electron-donor atoms into these void positions, henceforth, lowers the superconducting transition temperature in comparison to the parent compound.