Superconductivity in ternary chalcogenides Bi2Ni3X2 (X = S, Se)

The physical properties of parkerite and its related compound, Bi2Ni3X2 (X = S, Se), were studied. The electrical resistivity of both compounds shows typical metallic behaviour up to 400 K. The resistivity and specific heat measurements at low temperatures reveal that these compounds are superconducting with a transition temperature of ∼0.7 K. The upper critical fields at 0 K, μ0Hc2(0), are 95 mT (Bi2Ni3S2) and 75 mT (Bi2Ni3Se2). In the normal state, the electronic specific heat coefficient, γ, and the Debye temperature, ΘD, are found to be 11.4 mJ mol-1 K-2 and 189 K, respectively, for Bi2Ni3S2, and 12.2 mJ mol-1 K-2 and 173 K, respectively, for Bi2Ni3Se2. From the electronic specific heat in the superconducting temperature range, it was found these compounds belong to the weak-coupling BCS superconductors