Hyper-expanded interlayer separations in superconducting barium intercalates of FeSe.
TL;DR: The values of Tc are primarily dependent on Ba content, and are further modulated by the interlayer spacing through facile intercalation and deintercalation of ammonia.
About: This article is published in Chemical Communications.The article was published on 2015-04-09 and is currently open access. It has received 26 citations till now. The article focuses on the topics: Intercalation (chemistry) & Barium.
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TL;DR: In this paper , a time-resolved synchrotron X-ray total scattering study sheds light on the evolution of different structural length scales involved during the intercalation of the layered iron-selenide host by organic molecular donors, aiming at the formation of the expanded-lattice Lix(C5H5N)yFe2-zSe2 hybrid superconductor.
Abstract: A time-resolved synchrotron X-ray total scattering study sheds light on the evolution of the different structural length scales involved during the intercalation of the layered iron-selenide host by organic molecular donors, aiming at the formation of the expanded-lattice Lix(C5H5N)yFe2-zSe2 hybrid superconductor. The intercalates are found to crystallize in the tetragonal ThCr2Si2-type structure at the average level, however, with an enhanced interlayer iron-selenide spacing (d = 16.2 Å) that accommodates the heterocyclic molecular spacers. Quantitative atomic pair distribution function (PDF) analysis at variable times suggests distorted FeSe4 tetrahedral local environments that appear swollen with respect to those in the parent β-FeSe. Simultaneously acquired in situ synchrotron X-ray powder diffraction data disclose that secondary phases (α-Fe and Li2Se) grow significantly when a higher lithium concentration is used in the solvothermal reaction or when the solution is aged. These observations are in line with the strongly reducing character of the intercalation medium's solvated electrons that mediate the defect chemistry of the expanded-lattice superconductor. In the latter, intralayer correlated local distortions indicate electron-donating aspects that reflect in somewhat enlarged Fe-Se bonds. They also reveal a degree of relief of chemical pressure associated with a large distance between Fe and Se sheets ("taller" anion height) and a stretched Fe-Fe square planar topology. The elongation of the latter, derived from the in situ PDF study, speaks for a plausible increase in the Fe-site vacancy concentration. The evolution of the local structural parameters suggests an optimum reaction window where kinetically stabilized phases resemble the distortions of the edge-sharing Fe-Se tetrahedra, required for a high-Tc in expanded-lattice iron-chalcogenides.
2 citations
TL;DR: In this paper, a unique cation ND4(1−δ)+ exists between FeSe layers and induces a large distortion of the FeSe4 tetrahedron in N 0.81(1)D3.24(2)Fe2Se2 by neutron and X-ray powder diffraction.
TL;DR: In this article, the local structure of layered Nax(NH3)yMoSe2 system was studied by Mo K-edge extended X-ray absorption fine structure (EXAFS) measurements performed as a function of temperature.
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TL;DR: In this paper , the crystal structures and superconducting properties of typical FeSe-based superconductors containing ammonia/organic molecules intercalation discovered in recent years are briefly summarized.
Abstract: As an important part of Fe-based superconductors, FeSe-based superconductors have become a hot field in condensed matter physics. The exploration and preparation of such superconducting materials form the basis of studying their physical properties. With the help of various alkali/alkaline-earth/rare-earth metals, different kinds of ammonia/organic molecules have been intercalated into the FeSe layer to form a large number of FeSe-based superconductors with diverse structures and different layer spacing. Metal cations can effectively provide carriers to the superconducting FeSe layer, thus significantly increasing the superconducting transition temperature. The orientation of organic molecules often plays an important role in structural modification and can be used to fine-tune superconductivity. This review introduces the crystal structures and superconducting properties of several typical FeSe-based superconductors containing ammonia/organic molecules intercalation discovered in recent years, and the effects of FeSe layer spacing and superconducting transition temperature are briefly summarized.
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TL;DR: In this article, the superconductivity of iron-based oxyarsenide Sm[O1-xFx]FeAs was reported, with the onset resistivity transition temperature at 55.0K and Meissner transition at 54.6 K. This compound has the same crystal structure as LaOFeAs with shrunk crystal lattices.
Abstract: We report the superconductivity in iron-based oxyarsenide Sm[O1-xFx]FeAs, with the onset resistivity transition temperature at 55.0K and Meissner transition at 54.6 K. This compound has the same crystal structure as LaOFeAs with shrunk crystal lattices, and becomes the superconductor with the highest critical temperature among all materials besides copper oxides up to now.
1,456 citations
TL;DR: Chen et al. as discussed by the authors reported the discovery of bulk superconductivity in the related compound SmFeAsO1-xF x, which has a ZrCuSiAs-type structure.
Abstract: The recently discovered layered rare-earth metal oxypnictides have reinvigorated research into high-temperature superconductivity. The first of these, found only a few months ago, had a transition temperature of 26 K. A recent paper in Nature reported an iron–arsenic-based material superconducting at 43 K with the application of pressure. Previously only copper oxides superconductors had beaten the 40 K barrier. Now Chen et al. report bulk superconductivity in the samarium–arsenide oxide SmFeAsO1−xFx with a transition temperature of 43 K without this pressure. A report on the discovery of bulk superconductivity in samarium-arsenide oxides SmFeAsO1−xFx with a transition temperature as high as 43 K. Since the discovery of high-transition-temperature (high-Tc) superconductivity in layered copper oxides, extensive effort has been devoted to exploring the origins of this phenomenon. A Tc higher than 40 K (about the theoretical maximum predicted from Bardeen–Cooper–Schrieffer theory1), however, has been obtained only in the copper oxide superconductors. The highest reported value for non-copper-oxide bulk superconductivity is Tc = 39 K in MgB2 (ref. 2). The layered rare-earth metal oxypnictides LnOFeAs (where Ln is La–Nd, Sm and Gd) are now attracting attention following the discovery of superconductivity at 26 K in the iron-based LaO1-xF x FeAs (ref. 3). Here we report the discovery of bulk superconductivity in the related compound SmFeAsO1-xF x , which has a ZrCuSiAs-type structure. Resistivity and magnetization measurements reveal a transition temperature as high as 43 K. This provides a new material base for studying the origin of high-temperature superconductivity.
1,325 citations
TL;DR: It is reported that increasing the pressure causes a steep increase in the onset Tc of F-doped LaOFeAs, to a maximum of ∼43 K at ∼4 GPa, which is the highest Tc reported to date.
Abstract: The hunt for new materials exhibiting high-temperature superconductivity is on again. A complex iron-based oxide, containing lanthanum and arsenic, was recently found to exhibit a transition temperature (Tc) of about 26 K when doped with fluoride ions. That's respectable, but far from the heights achieved in copper oxide superconductors. Now Takahashi et al. show that the application of around 40,000 atmospheres of pressure can raise the Tc of this material substantially, to about 43 K. This is the highest tc yet reported for a non-copper-based material. What is more, this record is unlikely to last for long: the complexity of 'iron oxypnictides' of this type offers considerable flexibility for chemical modification, and we can expect to hear of yet higher transition temperatures. This paper — and the prospect of a new wave of superconductor fever — is the subject of an Editorial in the 24 April issue of Nature (452, 914; 2008). The application of pressure can raise the superconducting transition temperature of oxypnictide (a pnicogen being a group V element) substantially, to a maximum value of about 43 K. This is the highest transition temperature yet reported for a non-copper-based material, but this record is unlikely to last for long: the material system offers considerable flexibility for chemical modification, and we can reasonably anticipate that this record will soon be superseded. The iron- and nickel-based layered compounds LaOFeP (refs 1, 2) and LaONiP (ref. 3) have recently been reported to exhibit low-temperature superconducting phases with transition temperatures Tc of 3 and 5 K, respectively. Furthermore, a large increase in the midpoint Tc of up to ∼26 K has been realized4 in the isocrystalline compound LaOFeAs on doping of fluoride ions at the O2- sites (LaO1-xFxFeAs). Experimental observations5,6 and theoretical studies7,8,9 suggest that these transitions are related to a magnetic instability, as is the case for most superconductors based on transition metals. In the copper-based high-temperature superconductors, as well as in LaOFeAs, an increase in Tc is often observed as a result of carrier doping in the two-dimensional electronic structure through ion substitution in the surrounding insulating layers, suggesting that the application of external pressure should further increase Tc by enhancing charge transfer between the insulating and conducting layers. The effects of pressure on these iron oxypnictide superconductors may be more prominent than those in the copper-based systems, because the As ion has a greater electronic polarizability, owing to the covalency of the Fe–As chemical bond, and, thus, is more compressible than the divalent O2- ion. Here we report that increasing the pressure causes a steep increase in the onset Tc of F-doped LaOFeAs, to a maximum of ∼43 K at ∼4 GPa. With the exception of the copper-based high-Tc superconductors, this is the highest Tc reported to date. The present result, together with the great freedom available in selecting the constituents of isocrystalline materials with the general formula LnOTMPn (Ln, Y or rare-earth metal; TM, transition metal; Pn, group-V, ‘pnicogen’, element), indicates that the layered iron oxypnictides are promising as a new material platform for further exploration of high-temperature superconductivity.
1,084 citations
TL;DR: In this paper, the composition of the spacer layers present in iron-based superconductors is altered to increase the temperature below which they superconduct, and intercalating FeSe with molecular spacer layer is also shown to enhance the superconducting transition temperature.
Abstract: Altering the composition of the spacer layers present in iron-based superconductors is one strategy for increasing the temperature below which they superconduct. Now, intercalating FeSe with molecular spacer layers is also shown to enhance the superconducting transition temperature.
365 citations
TL;DR: It is reported that in the superconducting iron chalcogenides, a secondsuperconducting phase suddenly re-emerges above 11.5 GPa, after the Tc drops from the first maximum of 32 K at 1 GPa.
Abstract: Pressure has an essential role in the production(1) and control(2,3) of superconductivity in iron-based superconductors. Substitution of a large cation by a smaller rare-earth ion to simulate the pressure effect has raised the superconducting transition temperature T-c to a record high of 55 K in these materials(4,5). In the same way as T-c exhibits a bell-shaped curve of dependence on chemical doping, pressure-tuned T-c typically drops monotonically after passing the optimal pressure(1-3). Here we report that in the superconducting iron chalcogenides, a second superconducting phase suddenly re-emerges above 11.5 GPa, after the T-c drops from the first maximum of 32 K at 1 GPa. The T-c of the re-emerging superconducting phase is considerably higher than the first maximum, reaching 48.0-48.7 K for Tl0.6Rb0.4Fe1.67Se2, K0.8Fe1.7Se2 and K0.8Fe1.78Se2.
305 citations