Nickel-based phosphide superconductor with infinite-layer structure, BaNi2P2

Analogous to cuprate high- T c superconductors, a NiP-based compound system has several crystals in which the Ni–P layers have different stacking structures. Herein, the properties of BaNi2P2 are reported. BaNi2P2 has an infinite-layer structure, and shows a superconducting transition at ∼3 K. Moreover, it exhibits metallic conduction and Pauli paramagnetism in the temperature range of 4–300 K. Below 3 K, the resistivity sharply drops to zero, and the magnetic susceptibility becomes negative, while the volume fraction of the superconducting phase estimated from the diamagnetic susceptibility reaches ∼100 vol.% at 1.9 K. These observations substantiate that BaNi2P2 is a bulk superconductor.