A New Layered Iron Arsenide Superconductor: (Ca,Pr)FeAs₂

A new iron-based superconductor, (Ca,Pr)­FeAs2, was discovered. Plate-like crystals of the new phase were obtained, and its crystal structure was investigated by single-crystal X-ray diffraction analysis. The structure was identified as the monoclinic system with space group P21/m, composed of two Ca­(Pr) planes, Fe2As2 layers, and As2 zigzag chain layers. Plate-like crystals of the new phase showed superconductivity, with a Tc of ∼20 K in both magnetization and resistivity measurements.