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.
At a glance
- Iron-based layered superconductor La[O1−xFx]FeAs (x = 0.05–0.12) with Tc = 26 K. J. Am. Chem. Soc. 130, 3296–3297 (2008). , , &
- Superconductivity at 55 K in iron-based F-doped layered quaternary compound Sm[O1−xFx]FeAs. Chin. Phys. Lett. 25, 2215–2216 (2008). et al.
- Superconductivity in the iron selenide KxFe2Se2 (0 < x < 1.0). Phys. Rev. B 82, 180520 (2010). et al.
- Superconductivity at 43 K in SmFeAsO1−xFx. Nature 453, 761–762 (2008). et al.
- Structural and magnetic phase diagram of CeFeAsO1−xFx and its relation to high-temperature superconductivity. Nature Mater. 7, 953–959 (2008). et al.
- Superconductivity at 38 K in the iron arsenide Ba1−xKxFe2As2. Phys. Rev. Lett. 101, 107006 (2008). , &
- Structure and superconductivity of LiFeAs. Chem. Commun. 45, 5918–5920 (2008). et al.
- Superconductivity in the PbO-type structure α-FeSe. Proc. Natl Acad. Sci. USA 105, 14262–14264 (2008). et al.
- Extreme sensitivity of superconductivity to stoichiometry in Fe1+δSe. Phys. Rev. B 79, 014522 (2009). et al.
- Compositional control of the superconducting properties of LiFeAs. J. Am. Chem. Soc. 132, 10467–10476 (2010). et al.
- Control of the competition between a magnetic phase and a superconducting phase in cobalt-doped and nickel-doped NaFeAs using electron count. Phys. Rev. Lett. 104, 057007 (2010). et al.
- Pressure evolution of the low-temperature crystal structure and bonding of the superconductor FeSe (Tc = 37 K). Phys. Rev. B 80, 064506 (2009). et al.
- Electronic and magnetic phase diagram of β-Fe1.01Se with superconductivity at 36.7 K under pressure. Nature Mater. 8, 630–633 (2009). et al.
- Cation vacancy order in the K0.8+xFe1.6−ySe2 system: Five-fold cell expansion accommodates 20% tetrahedral vacancies. Chem. Sci. 2, 1054–1058 (2011). et al.
- A novel large moment antiferromagnetic order in K0.8Fe1.6Se2 superconductor. Chin. Phys. Lett. 28, 086104 (2011). et al.
- Uniform patterns of Fe-vacancy ordering in the Kx(Fe,Co)2−ySe2 superconductors. Chem. Mater. 23, 4311–4316 (2011). et al.
- NMR in the 245 iron-selenides Rb0.74Fe1.6Se2: Determination of the superconducting phase as iron vacancy-free Rb0.3Fe2Se2. Phys. Rev. Lett. 108, 237002 (2012). et al.
- Nanoscale layering of antiferromagnetic and superconducting phases in Rb2Fe4Se5 single crystals. Phys. Rev. Lett. 109, 017003 (2012). et al.
- An experimental study on the preparation of tochilinite-originated intercalation compounds comprised of Fe1−xS host layers and various kinds of guest layers. Geochim. Cosmochim. Acta 73, 4862–4878 (2009). et al.
- Observation of superconductivity at 30 K~46 K in AxFe2Se2 (A = Li, Na, Ba, Sr, Ca, Yb, and Eu). Sci. Rep. 2, 426 (2012). et al.
- A structural investigation of deuterated ammonium titanium sulfide ((ND4)+)0.22(ND3)0.34TiS2 by time-of-flight neutron powder diffraction. Solid State Ion. 26, 47–54 (1988). , , &
- Absence of superconductivity in LiCu2P2. J. Am. Chem. Soc. 133, 1751–1753 (2011). et al.
- TOPAS Academic: General Profile and Structure Analysis Software for Powder Diffraction Data, 5 (Bruker AXS, 2010).
- Crystal structure of the sodium cobaltate deuterate superconductor NaxCoO2·4xD2O (x≈1/3). Phys. Rev. B 68, 214517 (2003). , , , &
- Relationship between crystal structure and superconductivity in iron-based superconductors. Solid State Commun. 152, 644–648 (2012). et al.
- Pnictogen height as a possible switch between high-Tc nodeless and low-Tc nodal pairings in the iron-based superconductors. Phys. Rev. B 79, 224511 (2009). , , , &
- Crystal structure of the new FeSe1−x superconductor. Chem. Commun.5607–5609 (2008). et al.
- Superconductivity at Tc = 44 K in LixFe2Se2(NH3)y. Eur. Phys. J. B 85, 279–283 (2012). et al.
- Evolution of two-gap behavior of the superconductor FeSe1−x. Phys. Rev. Lett. 104, 087004 (2010). et al.
- Universal correlations between Tc and ns/m* (carrier density over effective mass) in high-Tc cuprate superconductors. Phys. Rev. Lett. 62, 2317–2320 (1989). et al.
- Metastable 11 K superconductor Na1−yFe2−xAs2. Inorg. Chem. 51, 8161–8167 (2012). et al.
- Synthesis of a new alkali metal-organic solvent intercalated iron selenide superconductor with Tc~45 K. J. Phys. Condens. Matter 24, 382202 (2012). et al.
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