Several superconducting transition temperatures in the range of 30–46 K were reported in the recently discovered intercalated FeSe system (A1-xFe2-ySe2, A = K, Rb, Cs, Tl). Although the superconducting phases were not yet conclusively decided, more than one magnetic phase with particular orders of iron vacancy and/or potassium vacancy were identified, and some were argued to be the parent phase. Here we show the discovery of the presence and ordering of iron vacancy in nonintercalated FeSe (PbO-type tetragonal β-Fe1-xSe). Three types of iron-vacancy order were found through analytical electron microscopy, and one was identified to be nonsuperconducting and magnetic at low temperature. This discovery suggests that the rich-phases found in A1-xFe2-ySe2 are not exclusive in Fe-Se and related superconductors. In addition, the magnetic β-Fe1-xSe phases with particular iron-vacancy orders are more likely to be the parent phase of the FeSe superconducting system instead of the previously assigned β-Fe1+δTe.
We have grown highly crystalline β-FeSe type iron chalcogenide nanowires (NWs) by annealing thin film that is prepared by a pulsed laser deposition method. Three kinds of NWs with compositions of Fe 0.8 Se, Fe 0.88 Se 0.32 Te 0.68 and Fe 0.88 Te 0.91 S 0.09 have been prepared and carefully characterized by a high-resolution transmission electron microscope (HRTEM). The NWs reveal ideal tetragonal structure with crystal growth along the [100] direction. Energy dispersive spectroscopy (EDS) studies and HRTEM images show the NWs to have good compositional uniformity, except for the existence of a thin layer of oxide on the surface. No superconducting transition was observed in the FeSe x NWs, which is possibly caused by Fe deficiency. The other two types of NWs show relatively higher and sharper superconducting transitions than their bulk counterparts. Interestingly, a resistive transition tail is observed in the NWs with diameter smaller than 100 nm, which might originate from a phase slip process in the quasi-one-dimensional system. The success in producing these high quality NWs provides a new avenue for better understanding the origin of superconductivity in β-FeSe type iron chalcogenides.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.