Formation of Nanofoam carbon and re-emergence of Superconductivity in compressed CaC6

Li, Yanling; Luo, Wei; Chen, Xiao‐Jia; Zhang, Zhi; Lin, Hai‐Qing; Ahuja, Rajeev

doi:10.1038/srep03331

Cited by 26 publications

(29 citation statements)

References 41 publications

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“…8). Despite the fact that the metal valences are different in LiC 6 (Pmmn) and a previously predicted metastable phase of CaC 6 [110], these two compounds have identical crystal structures. Although these lithium carbides are not thermodynamically stable, they are metastable with all positive phonon frequencies.…”

Section: B Diverse Carbon Structuresmentioning

confidence: 79%

Structural diversity in lithium carbides

2015

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The lithium-carbon binary system possesses a broad range of chemical compounds, which exhibit fascinating chemical bonding characteristics that give rise diverse and technologically important properties. While lithium carbides with various compositions have been studied or suggested previously, the crystal structures of these compounds are far from well understood. In this work we present the first comprehensive survey of all ground state (GS) structures of lithium carbides over a broad range of thermodynamic conditions, using ab initio density functional theory (DFT) crystal structure searching methods. Thorough searches were performed for 29 stoichiometries ranging from Li12C to LiC12 at 0 GPa as well as 40 GPa. Based on formation enthalpies from optimized van der Waals density functional calculations, three thermodynamically stable phases (Li4C3, Li2C2 and LiC12) were identified at 0 GPa, and seven thermodynamically stable phases (Li8C, Li6C, Li4C, Li8C3, Li2C, Li3C4, and Li2C3) were predicted at 40 GPa. A rich diversity of carbon bonding, including monomers, dimers, trimers, nanoribbons, sheets and frameworks, was found within these structures, and the dimensionality of carbon connectivity existing within each phase was observed to increase with increasing carbon concentration. Of particular interest, we find that the wellknown composition LiC6 is actually a metastable one. We also find a unique coexistence of carbon monomers and dimers within the predicted thermodynamically stable phase Li8C3, and different widths of carbon nanoribbons coexist in a metastable phase of Li2C2 (Imm2). Interesting mixed sp 2 -sp 3 carbon frameworks are predicted in metastable phases with composition LiC6.

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Section: B Diverse Carbon Structuresmentioning

confidence: 79%

Structural diversity in lithium carbides

2015

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“…It should be also noted that the critical temperature of CaC 6 can be further modified with increasing pressure. Many theoretical and experimental investigations proved that T C in CaC 6 exhibits an interesting increasing-decreasingincreasing behavior under pressure [18,[20][21][22][23][24]. In particular, the critical temperature increase linearly to the value of 15.1 K, when the pressure increases to 7.5 GPa.…”

Section: Introductionmentioning

confidence: 99%

“…Recently however, Li et al have reported the reemergence of the superconductivity in the heavily compressed CaC 6 (p 39 GPa), applying pressure via the theoretical calculations [24]. In particular, the authors have stated that the predicted phase III (space group Pmmn) with the formation of the carbon nanofoam is found to be stable at a wide pressure range with the critical temperature up to 14.7 K at 78 GPa.…”

Section: Introductionmentioning

confidence: 99%

Isotropic and anisotropic description of superconducting state in CaC6 compound

2015

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Abstract. The thermodynamic parameters of the superconducting state in CaC6 have been determined in the framework of the isotropic and anisotropic Eliashberg formalism. The obtained results determine the anisotropy effect on the values of the thermodynamic functions. In particular, it has been found that the anisotropy of the electron-phonon coupling constant and the Coulomb pseudopotential significantly affects the order parameter and the wave function renormalization factor, which determines the electron effective mass. These results mean that anisotropy should be also visible in the total normalized density of states. In the case of the thermodynamic critical field, anisotropy lowers its value in the low-temperature area. On the other hand, it does not affect the specific heat jump at the critical temperature.

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“…A large number of BCS superconductors have been theoretically proposed161718 as the development of computational crystal structure prediction tools1920 and methods. In this paper, we perform a systematic search for thermodynamically stable calcium bismuth at ambient and high pressure by using the variable-composition ab initio evolutionary algorithm212223 and density functional theory (DFT).…”

mentioning

confidence: 99%

Rich stoichiometries of stable Ca-Bi system: Structure prediction and superconductivity

Fan

2015

Sci Rep

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Using a variable-composition ab initio evolutionary algorithm implemented in the USPEX code, we have performed a systematic search for stable compounds in the Ca-Bi system at different pressures. In addition to the well-known tI12-Ca2Bi and oS12-CaBi2, a few more structures were found by our calculations, among which phase transitions were also predicted in Ca2Bi (tI12 → oI12 → hP6), Ca3Bi2 (hP5 → mC20 → aP5) and CaBi (tI2 → tI8), as well as a new phase (Ca3Bi) with a cF4 structure. All the newly predicted structures can be both dynamically and thermodynamically stable with increasing pressure. The superconductive properties of cF4-CaBi3, tI2-CaBi and cF4-Ca3Bi were studied and the superconducting critical temperature Tc can be as high as 5.16, 2.27 and 5.25 K, respectively. Different superconductivity behaviors with pressure increasing have been observed by further investigations.

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Formation of Nanofoam carbon and re-emergence of Superconductivity in compressed CaC6

Cited by 26 publications

References 41 publications

Structural diversity in lithium carbides

Structural diversity in lithium carbides

Isotropic and anisotropic description of superconducting state in CaC6 compound

Rich stoichiometries of stable Ca-Bi system: Structure prediction and superconductivity

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