  Analogous to cuprate high-Tc 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.
