Abstract:Here we report a new quaternary iron-arsenide superconductor Nd[O 1-x F x ]FeAs, with the onset resistivity transition at 51.9 K and Meissner transition at 51 K. This compound has the same crystal structure as LaOFeAs, and becomes the second superconductor after Pr[O 1-x F x ]FeAs that superconducts above 50 K.

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