Superconductivity in the Niobium-rich compound Nb5Se4

The niobium rich selenide compound Nb5Se4 was synthesized at ambient pressure by high-temperature solid-state reaction in a sealed Ta tube. Resistivity and heat capacity measurements reveal that this compound is superconducting, with a T_c = 1.85K. The electronic contribution to the specific heat γ and the Debye temperature are found to be 18.1 mJ/mol/K^2 and 298 K respectively. The calculated electron-phonon coupling constant λ_ep = 0.5 and the ΔC_p/γTc = 1.42 ratio imply that Nb5Se4 is a weak coupling BCS superconductor. The upper critical field and coherence length are found to be 1.44 T and 15.1 nm, respectively.