Observation of superconductivity at 30∼46K in A(x)Fe(2)Se(2 )(A = Li, Na, Ba, Sr, Ca, Yb, and Eu)

New iron selenide superconductors by intercalating smaller-sized alkali metals (Li, Na) and alkaline earths using high-temperature routes have been pursued ever since the discovery of superconductivity at about 30 K in KFe(2)Se(2), but all have failed so far. Here we demonstrate that a series of superconductors with enhanced T(c) = 30∼46 K can be obtained by intercalating metals, Li, Na, Ba, Sr, Ca, Yb, and Eu in between FeSe layers by the ammonothermal method at room temperature. Analysis on their powder X-ray diffraction patterns reveals that all the main phases can be indexed based on body-centered tetragonal lattices with a∼3.755–3.831 Å while c∼15.99–20.54 Å. Resistivities show the corresponding sharp transitions at 45 K and 39 K for NaFe(2)Se(2) and Ba(0.8)Fe(2)Se(2), respectively, confirming their bulk superconductivity. These findings provide a new starting point for studying the properties of these superconductors and an effective synthetic route for the exploration of new superconductors as well.