Abstract
The discovery of high-temperature superconductivity in a layered iron arsenide1 has led to an intensive search to optimize the superconducting properties of iron-based superconductors by changing the chemical composition of the spacer layer between adjacent anionic iron arsenide layers2,3,4,5,6,7. Superconductivity has been found in iron arsenides with cationic spacer layers consisting of metal ions (for example, Li+, Na+, K+, Ba2+) or PbO- or perovskite-type oxide layers, and also in Fe1.01Se (ref. 8) with neutral layers similar in structure to those found in the iron arsenides and no spacer layer. Here we demonstrate the synthesis of Lix(NH2)y(NH3)1−yFe2Se2 (x~0.6; y~0.2), with lithium ions, lithium amide and ammonia acting as the spacer layer between FeSe layers, which exhibits superconductivity at 43(1) K, higher than in any FeSe-derived compound reported so far. We have determined the crystal structure using neutron powder diffraction and used magnetometry and muon-spin rotation data to determine the superconducting properties. This new synthetic route opens up the possibility of further exploitation of related molecular intercalations in this and other systems to greatly optimize the superconducting properties in this family.
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Acknowledgements
We are grateful to the ISIS facility including the GEM Xpress service for access to neutron and muon instruments and we thank A. Daoud-Aladine and R. I. Smith for technical assistance at ISIS. We acknowledge financial support from the UK EPSRC (grant EP/I017844/1) and STFC (grant EP/G067481/1).
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M.B-L., D.G.F., Y.H. and S.J.S. prepared the samples, D.G.F., A.J.C., S.J.S. and S.J. Clarke performed the diffraction data collection and structural analysis. J.D.W., T.L., P.J.B. and S.J.B. performed the μSR measurements, M.B-L., S.J. Cassidy, A.J.C. and S.J. Clarke performed the magnetometry and other characterization measurements. S.J. Clarke conceived the project and, with S.J.B., wrote the manuscript.
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Burrard-Lucas, M., Free, D., Sedlmaier, S. et al. Enhancement of the superconducting transition temperature of FeSe by intercalation of a molecular spacer layer. Nature Mater 12, 15–19 (2013). https://doi.org/10.1038/nmat3464
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DOI: https://doi.org/10.1038/nmat3464
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