Superconducting iron-selenide layered systems by hydrothermal syntheses
Physical Chemistry of Solids and Surfaces, Material Characterisation
Final Report Abstract
In our project on iron-based superconducting materials, we made a series of discoveries that provide new insights into superconducting substances and the interactions between superconductivity, magnetism, and crystal structure. At the beginning of the funding period, we discovered the compound [(Li0.8Fe0.2)OH]FeSe, which is both superconducting (up to 42 K) and ferromagnetic (up to 10 K) - a unique phenomenon. We successfully grew millimeter-sized crystals and also synthesized the sulfur counterpart [(Li0.8Fe0.2)OH]FeS, as well as the series [(Li0.8Fe0.2)OH]FeSe1-xSx. Even small amounts of sulfur suppress superconductivity while preserving the magnetic properties. Further investigations of [(Li0.8Fe0.2)OH]FeSe revealed two superconducting states (at 40 K and 35 K) and confirmed the coexistence of superconductivity and magnetism. Surprisingly, hydrothermally synthesized β-FeSe is not superconducting. X-ray structural analysis at low temperatures showed the formation of a different crystal structure, in which the distances between the iron atoms differ, potentially explaining the absence of superconductivity. The hydrothermal synthesis method was also used for iron sulfide (FeS), which is superconducting at 4 K. Unlike FeSe, FeS shows no structural changes upon cooling, and its superconductivity disappears under pressure. Experiments on the hydrothermal synthesis of FeSe intercalation compounds led to the discovery of the compound [Na6(H2O)18][Fe4Se8], with iron atoms fluctuating between the Fe3+ and Fe2+ states. The crystal structure contains [(Fe4Se4)Se4]6- clusters surrounded exclusively by H2O molecules. In collaboration with our partners, we studied the magnetism of the mixedvalence clusters using µSR measurements. The results show that the fluctuation frequency decreases with decreasing temperature; however, the expected ground state with S = 0 was surprisingly not achieved. Further hydrothermal syntheses during the second funding period yielded mixed results, while solvothermal methods using ethylenediamine were more successful. We succeeded in intercalating neutral molecules into FeSe, but these compounds were not superconducting. Presumably, charge transfer is necessary to achieve high transition temperatures. Later in the project, we achieved the electrochemical intercalation of tetramethylammonium (TMA) into FeSe. (TMA)0.5Fe2Se2 is a new superconducting material with a transition temperature of 42 K. In the series (TMA)0.5Fe2Se2-xSx, the transition temperature decreases with increasing sulfur content. In collaboration with partners, we investigated the interplay of superconductivity, magnetism, and nematicity in FeSe1-xSx. Under pressure, all three phenomena could coexist, raising new questions about their significance for superconductivity.
Publications
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Coexistence of 3d-ferromagnetism and superconductivity in [(Li0.8Fe0.2)OH]FeSe Dirk Johrendt, Electronic Materials and Applications (EMA) 2015, Orlando, USA
Dirk Johrendt
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Coexistence of low-moment magnetism and superconductivity in tetragonal FeS and suppression of Tc under pressure. Physical Review B, 93(14).
Holenstein, S.; Pachmayr, U.; Guguchia, Z.; Kamusella, S.; Khasanov, R.; Amato, A.; Baines, C.; Klauss, H.-H.; Morenzoni, E.; Johrendt, D. & Luetkens, H.
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Effect of cobalt substitution in the ferromagnetic superconductor [(Li0.8Fe0.2)OH]FeSe,
Z. anorg. allg. Chem. 2016, 642, 989
U. Pachmayr; S. Kamusella; H.-H. Klauss & D. Johrendt
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Structural transition and superconductivity in hydrothermally synthesized FeX (X = S, Se). Chemical Communications, 52(1), 194-197.
Pachmayr, U.; Fehn, N. & Johrendt, D.
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Superconductivity and Crystal Structures in Solvothermally synthesized FeX, MRS Spring Meeting 2016, Phoenix, USA
U. Pachmayr; J. Stahl & D. Johrendt
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Coexistence of multiphase superconductivity and ferromagnetism in lithiated iron selenide hydroxide [(Li1−xFex)OH]FeSe. Physical Review B, 97(2).
Urban, Christian; Valmianski, Ilya; Pachmayr, Ursula; Basaran, Ali C.; Johrendt, Dirk & Schuller, Ivan K.
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Progress and perspectives in materials chemistry of iron-based superconductors, APS March Meeting 2018, Los Angeles, USA
Dirk Johrendt
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Systematic dimensional reduction of the layered β-FeSe structure by solvothermal synthesis. Dalton Transactions, 47(10), 3264-3271.
Stahl, J.; Shlaen, E.; Singer, H. & Johrendt, D.
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Extended Magnetic Dome Induced by Low Pressures in Superconducting FeSe1−xSx. Physical Review Letters, 123(14).
Holenstein, S.; Stahl, J.; Shermadini, Z.; Simutis, G.; Grinenko, V.; Chareev, D. A.; Khasanov, R.; Orain, J.-C.; Amato, A.; Klauss, H.-H.; Morenzoni, E.; Johrendt, D. & Luetkens, H.
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FeSe(en)0.3 – Separated FeSe layers with stripe-type crystal structure by intercalation of neutral spacer molecules
Juliane Stahl & Dirk Johrendt
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Electrochemical Synthesis and Crystal Structure of the Organic Ion Intercalated Superconductor (TMA)0.5Fe2Se2 with Tc = 43 K. Journal of the American Chemical Society, 143(8), 3043-3048.
Rendenbach, Bettina; Hohl, Timotheus; Harm, Sascha; Hoch, Constantin & Johrendt, Dirk
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Iron Selenide Intercalated by Uncharged Molecules: Superconductivity in FeSe(C2H7NO)0.3. Zeitschrift für anorganische und allgemeine Chemie, 650(24).
Schöneich, Marlo & Johrendt, Dirk
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Water Encapsulated [(Fe4Se4)Se4]6– Clusters in [Na6(H2O)18][Fe4Se8]. Inorganic Chemistry, 63(50), 23907-23913.
Pachmayr, Ursula; Rendenbach, Bettina; Lammer, Nadine; Kamusella, Sirko; Klauss, Hans-Henning; Holenstein, Stefan; Luetkens, Hubertus & Johrendt, Dirk
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Effects of Chemical Pressure on Superconductivity in Electrochemically Intercalated (TMA)yFe2(Se1−xSx)2 (TMA = Tetramethylammonium). Advanced Functional Materials.
Lammer, Nadine; Werhahn, Dominik; Moritz, Leonard & Johrendt, Dirk
