Structure of single-phase superconducting K3C60

Stephens, Peter W.; Mihály, L.; Lee, Peter L.; Whetten, Robert L.; Huang, Sampson C.; Kaner, Richard B.; Deiderich, François; Holczer, K.

doi:10.1038/351632a0

Cited by 743 publications

(290 citation statements)

References 8 publications

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“…6 In these materials, cations occupy the interstitial voids that already exist in the host e.g., in the fcc lattice of C60 (Figure 1). 7 Reaction of potassium with picene (C22H14), a phenacene composed of five fused benzene rings, has been reported to afford superconductivity at 18 K. 8 Superconductivity in other alkali-metal polyaromatic hydrocarbons (PAHs) was subsequently reported in phenanthrene-, dibenzopentacene-and coronene-based materials, with the highest reported Tc of 33 K claimed 2 in potassium-doped 1,2:8,9-dibenzopentacene. [9][10][11] Despite the significant interest in these materials, to date no crystal structure has been determined for any of the alkali-metal PAH systems.…”

Section: Introductionmentioning

confidence: 99%

Redox-controlled potassium intercalation into two polyaromatic hydrocarbon solids

et al. 2017

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Alkali metal intercalation into polyaromatic hydrocarbons (PAHs) has been studied intensely following reports of superconductivity in a number of potassium-and rubidium-intercalated materials. There are however no reported crystal structures to inform understanding of the chemistry and physics because of the complex reactivity of PAHs with strong reducing agents at high temperature. Here we present the synthesis of crystalline K2Pentacene and K2Picene by a solid-solid insertion protocol that uses potassium hydride as a redox-controlled reducing agent to access the PAH dianions, enabling determination of their crystal structures. In both cases, the inserted cations expand the parent herringbone packings by reorienting the molecular anions to create multiple potassium sites within initially dense molecular layers, and thus interact with the PAH anion π-systems. The synthetic and crystal chemistry of alkali metal intercalation into PAHs differs from that into fullerenes and graphite, where the cation sites are pre-defined by the host structure.Reaction of alkali and alkaline earth metals with carbon-based molecular solids has been extensively studied in the search for novel magnetic and electronic properties, with a particular focus on superconductivity. [1][2][3][4][5][6] For example, alkali metal intercalation into solid C60 produces A3C60 superconductors, with Tc as high as 38 K for Cs3C60 at 7 kbar. 6 In these materials, cations occupy the interstitial voids that already exist in the host e.g., in the fcc lattice of C60 (Figure 1). 7 Reaction of potassium with picene (C22H14), a phenacene composed of five fused benzene rings, has been reported to afford superconductivity at 18 K. 8 Superconductivity in other alkali-metal polyaromatic hydrocarbons (PAHs) was subsequently reported in phenanthrene-, dibenzopentacene-and coronene-based materials, with the highest reported Tc of 33 K claimed 2 in potassium-doped 1,2:8,9-dibenzopentacene. [9][10][11] Despite the significant interest in these materials, to date no crystal structure has been determined for any of the alkali-metal PAH systems. This structural information is a prerequisite for materials design and for understanding of both physical properties and reaction chemistry.Picene, like many other PAHs (including molecules such as phenanthrene 12 which is reported to afford superconductivity on cation insertion), crystallises in the herringbone structure, 13 with layers consisting of two parallel one-dimensional chains of molecules with opposing inclinations defined by an intermolecular angle, ω, of 57.89(7)° (Supplementary Figure 1). 14 The largest voids in the structure are located between the picene layers, adjacent to the saturated C-H bonds and far from the electron density of the PAH π-systems ( Figure 1a). This contrasts with C60, where the octahedral and tetrahedral voids in the fcc lattice are adjacent to the conjugated π-electron system (Figure 1b Pentacene is the linear isomer of picene, and also adopts the herringbone structure, 16 with ω = 52...

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Section: Introductionmentioning

confidence: 99%

Redox-controlled potassium intercalation into two polyaromatic hydrocarbon solids

et al. 2017

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“…These show peculiarities in both their crystal structure and vibrational spectra. At room temperature, K 4 C 60 and Rb 4 C 60 form a bct crystal, 15 with merohedral disorder similar to that in A 3 C 60 : 16 in the bct cell of K 4 C 60 there is only a C 2 molecular axis in the c direction, and the overall tetragonal structure is realized by the anions occupying two standard orientations with equal probability. In Cs 4 C 60 an orthorhombic distortion was found at room temperature, 17 resulting in a lattice compatible with D 2h , one of the subgroups of the icosahedral group yielding complete ordering of the C 60 balls.…”

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confidence: 99%

“…We first consider their role in A 3 C 60 , which adopts a remarkably similar molecular arrangement in the ab plane 16 with two standard orientations, connected formally by a 90°r otation around the c axis. In Rb 3 C 60 and K 3 C 60 the rearrangement between the two standard orientations can also occur through a 44.5°jump around a C 3 axis, lying in the crystallographic ͗111͘ direction, and it has been shown by neutronscattering experiments that this motion involves a considerably lower-energy barrier than the jump around C 2 .…”

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Ordered low-temperature structure inK4C60detected by infrared spectroscopy

et al. 2002

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Infrared spectra of a K 4 C 60 single-phase thin film have been measured between room temperature and 20 K. At low temperatures, the two high-frequency T 1u modes appear as triplets, indicating a static D 2h crystal-field stabilized Jahn-Teller distortion of the C 60 4Ϫ anions. The T 1u (4) mode changes into a known doublet above 250 K, a pattern which could have three origins: a dynamic Jahn-Teller effect, static disorder between ''staggered'' anions, or a phase transition from an orientationally ordered phase to one where molecular motion is significant. The electronic structure of fulleride salts has been a topic of intense interest since their discovery. Three recent reviews summarized the situation: Reed and Bolskar 1 focused on isolated ions; Forró and Mihály 2 treated fulleride solids; and Gunnarson 3 concentrated on the theory of superconductivity and on band-structure calculations, including the important concepts of the Jahn-Teller ͑JT͒ effect. 4 Fulleride anions with charges other than 0 or 6 are susceptible to Jahn-Teller coupling between electrons occupying partially filled t 1u orbitals and H g phonons. Because of the high degeneracy of the phonons involved, the coupled electronic Hamiltonian acquires an SO͑3͒, higher than the original icosahedral configuration. 5 Thus the electronic structure of the outer shell can be discussed in complete analogy with p electrons on an atom. 2 In any uniaxial crystal field, one expects a twofold orbital splitting to e 2u and a u , whereas in a biaxial system the degeneracy is completely lifted, resulting in three distinct electronic levels. ͓It follows from the SO͑3͒ symmetry that the principal axes of the distortions can be taken as the axes of the crystallographic unit cell, regardless of the position of the molecule within the crystal.͔ In solids the orbital splitting is small compared to the bandwidth; thus electron correlation has to be taken into account. The most comprehensive theoretical treatment of this interplay was given by Fabrizio and co-workers, who introduced the concept of the ''Mott-Jahn-Teller insulator'' ͑M-JT͒. 6,7 The model of p-like electrons on a spherical or ellipsoidal surface was indeed succesful in the interpretation of NMR, 8,9 photoelectron spectroscopy, 10,11 resonance Raman, 12 and magnetic 13 data. The situation becomes different, however, once we try to measure properties that reflect the internal degrees of freedom within the C 60 ball itself. Typical examples are magnetic resonance measurements and vibrational spectroscopy. When atomic motion has to be taken into account, the symmetry can no longer be regarded as spherical. Instead, the actual shape of the molecule is determined by the combined internal ͑JT͒ and external ͑crystal field͒ distorting forces. If these result in a potential surface with several shallow wells, then the balls will assume different shapes and positions with respect to the lattice. The result will be either static disorder or random fluctuations between the minima, called the dynamic Jahn-Teller effect....

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“…[5] include the discussion of a geometry of systems with topological defects such as fullerenes [52,53,54,55,56,57,58], Schwarzites [59], ionic crystals [60,61], and other hexagonal systems with atomistic defects.…”

Section: Chemical Measures and Geometrymentioning

confidence: 99%

Discrete differential geometry and the properties of conformal two-dimensional materials

Barraza‐Lopez

2015

Synthetic Metals

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Two-dimensional materials were first isolated no longer than ten years ago, and a comprehensive understanding of their properties under non-planar shapes is still being developed. Strictly speaking, the theoretical study of the properties of graphene and other two-dimensional materials is the most complete for planar structures and for structures with small deformations from planarity. The opposite limit of large deformations is yet to be studied comprehensively but that limit is extremely relevant because it determines material properties near the point of failure. We are exploring uses for discrete differential geometry within the context of graphene and other two-dimensional materials, and these concepts appear promising in linking materials properties to shape regardless of how large a given material deformation is. A brief account of additional contributions arising from our group to two-dimensional materials that include graphene, stanene and phosphorene is provided towards the end of this manuscript.

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Structure of single-phase superconducting K3C60

Cited by 743 publications

References 8 publications

Redox-controlled potassium intercalation into two polyaromatic hydrocarbon solids

Redox-controlled potassium intercalation into two polyaromatic hydrocarbon solids

Ordered low-temperature structure inK4C60detected by infrared spectroscopy

Discrete differential geometry and the properties of conformal two-dimensional materials

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