Superconductivity and Chemistry

Simon, Arndt

doi:10.1002/anie.199717881

Cited by 243 publications

(167 citation statements)

References 142 publications

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“…Given the difficulty in making extrapolations between the physics of superconductivity and the chemical stability of compounds that will be superconducting, there are as many strategies for finding new superconductors as there are researchers looking for them (3)(4)(5). Most such search strategies fail, because the interactions that give rise to superconductivity can also lead to competing electronic states or can be strong enough to tear potential compounds apart (6,7).…”

Section: T He Prediction Of New Superconductors Remains An Elusive Goalmentioning

confidence: 99%

Endohedral gallide cluster superconductors and superconductivity in ReGa ₅

Xie

Luo

Phelan

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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We present transition metal-embedded (T@Ga n ) endohedral Gaclusters as a favorable structural motif for superconductivity and develop empirical, molecule-based, electron counting rules that govern the hierarchical architectures that the clusters assume in binary phases. Among the binary T@Ga n endohedral cluster systems, Mo 8 Ga 41 , Mo 6 Ga 31 , Rh 2 Ga 9 , and Ir 2 Ga 9 are all previously known superconductors. The well-known exotic superconductor PuCoGa 5 and related phases are also members of this endohedral gallide cluster family. We show that electron-deficient compounds like Mo 8 Ga 41 prefer architectures with vertex-sharing gallium clusters, whereas electron-rich compounds, like PdGa 5 , prefer edge-sharing cluster architectures. The superconducting transition temperatures are highest for the electron-poor, corner-sharing architectures. Based on this analysis, the previously unknown endohedral cluster compound ReGa 5 is postulated to exist at an intermediate electron count and a mix of corner sharing and edge sharing cluster architectures. The empirical prediction is shown to be correct and leads to the discovery of superconductivity in ReGa 5 . The Fermi levels for endohedral gallide cluster compounds are located in deep pseudogaps in the electronic densities of states, an important factor in determining their chemical stability, while at the same time limiting their superconducting transition temperatures. Although one can analyze the superconductivity, once discovered, through materials physics-based "k-space" pictures based on Fermi surfaces, energy band dispersions, and effective interactions, often it is chemists, whose viewpoint is instead from "real space" rather than k-space, who find such superconductors in the first place (1, 2). Given the difficulty in making extrapolations between the physics of superconductivity and the chemical stability of compounds that will be superconducting, there are as many strategies for finding new superconductors as there are researchers looking for them (3-5). Most such search strategies fail, because the interactions that give rise to superconductivity can also lead to competing electronic states or can be strong enough to tear potential compounds apart (6, 7).One chemical perspective for increasing the odds of finding superconductivity is to postulate that it runs in structural families. The perovskites are a well-known example of this in metal oxides, and in intermetallic compounds, the "122" ThCr 2 Si 2 structure type is a good example (8-10). It is the discovery of these new structural families of superconductors that often leads, sometimes slowly or sometimes quickly, to advances in new superconducting materials. Here we show that a previously unappreciated chemical family, the endohedral gallium cluster phases, is a favored chemical family for superconductivity. Further, we analyze the occurrence and hierarchical structures of such phases from a molecular perspective and then use that perspective to predict the existence and structure of a previously un...

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Section: T He Prediction Of New Superconductors Remains An Elusive Goalmentioning

confidence: 99%

Endohedral gallide cluster superconductors and superconductivity in ReGa ₅

Xie

Luo

Phelan

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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“…Superconductivity up to 17 K occurred with increasing carbon content and the possibility to form the diatomic C n− 2 species. By rewriting the general formula as (RE 1−x M x ) 2/y C 2 a valence electron rule is derived from the plot of T c versus charge n per C 2 unit [22]. In spite of quite different compound and structure types, REC 2 and RE 2 C 3 , respectively, compiled in the plot the T c values exhibit a systematic distribution.…”

Section: Compound Superconductorsmentioning

confidence: 99%

Superconductivity and the periodic table: from elements to materials

Simon

2015

Phil. Trans. R. Soc. A.

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Based on the normal-state electronic band structure, the necessary condition for a metal to become a superconductor is the simultaneous occurrence of flat and steep bands at the Fermi level. The sufficient condition at least for conventional superconductors is a strong enough coupling of the flat band states to the lattice, e.g. via phonons. Selected elements (Te) and compounds of the rare earth metals ( RE 2 C 3 , REC 2 , RE 2 X 2 C 2 with X =halogen) and MgB 2 serve as examples to illustrate the idea.

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“…However, only very few attempts have been made on inorganic compounds, and these have been on data sets collected as texture patterns, a technique which unfortunately is only mastered in very few laboratories, notably those related to the pioneers of electron crystallography in Moscow (Vainshtein et al, 1992). Recently, the structures of several unknown compounds including zeolites (Nicolopoulos et al, 1995), ceramic oxides (Sinkler et al, 1998) and a precipitate Al m Fe in aluminium alloys (Gjùnnes et al, 1998) have been solved by exploiting electron diffraction data.…”

Section: Introductionmentioning

confidence: 99%

“…These regions frequently contain octahedral M 6 clusters which are linked (condensed) via common corners, edges and/or faces. Structures containing condensed metal clusters often exhibit interesting physical properties including superconductivity (Simon, 1997). In a recent study on systems with the metals Ti, Zr or Ta and non-metals S, Se and P, many compounds had been synthesized and their structures solved, either by X-ray single-crystal diffraction and/or by HREM combined with crystallographic image processing .…”

Section: Introductionmentioning

confidence: 99%

Structures of nanometre-size crystals determined from selected-area electron diffraction data

et al. 2000

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The structure of a new modi®cation of Ti 2 Se, the -phase, and several related inorganic crystal structures containing elements with atomic numbers between 16 and 40 have been solved by quasi-automatic direct methods from singlecrystal electron diffraction patterns of nanometre-size crystals, using the kinematical aproximation. The crystals were several thousand times smaller than the minimum size required for single-crystal X-ray diffraction. Atomic coordinates were found with an average accuracy of 0.2 A Ê or better. Experimental data were obtained by standardized techniques for recording and quantifying electron diffraction patterns. The SIR97 program for solving crystal structures from three-dimensional X-ray diffraction data by direct methods was modi®ed to work also with two-dimensional electron diffraction data.

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Superconductivity and Chemistry

Cited by 243 publications

References 142 publications

Endohedral gallide cluster superconductors and superconductivity in ReGa ₅

Endohedral gallide cluster superconductors and superconductivity in ReGa ₅

Superconductivity and the periodic table: from elements to materials

Structures of nanometre-size crystals determined from selected-area electron diffraction data

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Superconductivity and Chemistry

Cited by 243 publications

References 142 publications

Endohedral gallide cluster superconductors and superconductivity in ReGa 5

Endohedral gallide cluster superconductors and superconductivity in ReGa 5

Superconductivity and the periodic table: from elements to materials

Structures of nanometre-size crystals determined from selected-area electron diffraction data

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Endohedral gallide cluster superconductors and superconductivity in ReGa ₅

Endohedral gallide cluster superconductors and superconductivity in ReGa ₅