Nickel-Based Oxyphosphide Superconductor with a Layered Crystal Structure, LaNiOP

A layered oxyphosphide, LaNiOP, was synthesized by solid-state
reactions. This crystal was confirmed to have a layered structure
composed of an alternating stack of (La3+O2-)+ and (Ni2+P3-)-.
We found that the resulting LaNiOP shows a superconducting
transition at ∼3 K. This material exhibited metallic conduction and
Pauli paramagnetism in the temperature range of 4−300 K. The
resistivity sharply dropped to zero and the magnetic susceptibility
became negative at <4 K, indicating that a superconducting
transition occurs. The volume fraction of the superconducting phase
estimated from the diamagnetic susceptibility reached ∼40 vol %
at 1.8 K, substantiating that LaNiOP is a bulk superconductor.