Superconductivity and phase diagram in iron-based arsenic-oxides ReFeAsO 1−δ (Re = rare-earth metal) without fluorine doping

Here we report a new class of superconductors prepared by high-pressure synthesis in the quaternary family ReFeAsO 1−δ (Re=Sm, Nd, Pr, Ce, La) without fluorine doping. The onset superconducting critical temperature ( T c ) in these compounds increases with the reduction of the Re atom size, and the highest T c obtained so far is 55 K in SmFeAsO 1−δ . For the NdFeAsO 1−δ compound with different oxygen concentration a dome-shaped phase diagram was found.