Synthesis and superconducting properties of CaC₆

Abstract

Among the superconducting graphite intercalation compounds, CaC 6 exhibits the highest critical temperature T c = 11.5 K. Bulk samples of CaC 6 are obtained by immersing highly oriented pyrographite pieces in a well-chosen liquid Li-Ca alloy for 10 days at 350• C. The crystal structure of CaC 6 belongs to the R3m space group. In order to study the superconducting properties of CaC 6 , magnetisation was measured as a function of temperature and direction of magnetic field applied parallel or perpendicular to the c-axis. Meissner effect was evidenced, as well as a type II superconducting behaviour and a small anisotropy. In agreement with calculations, experimental results obtained from various techniques suggest that a classical electron-phonon mechanism is responsible for the superconductivity of CaC 6 . Application of high pressure increases the T c up to 15.1 K at 8 GPa.

Recent advances in superconductivity of covalent superconductors

“…1). An excellent review has been published recently [51], which would make redundant an overview of the growth, structure and superconductivity in this section. We shall, however, fill a gap in that review and compare superconducting transition temperatures in metal-intercalated fullerite and graphite (see Fig.…”

Superconductivity in covalent semiconductors

“…The highest T = 11.5 K was obtained for relatively large calcium [83] and therefore, we may hope to see a further increase for lighter elements.…”

“…An excellent review has been published a few months ago [83], virtually obliterating this section. We [73,81,84] and graphites [83] plotted vs. the radius of the metal ion A + (bottom panel).…”

Electronic structures and three-dimensional effects of boron-doped carbon nanotubes

“…Therefore their doping has been attempted in order to achieve high-transition-temperature superconductivity. In fact, several studies have revealed superconductivity in carrier-doped carbon materials, such as intercalated graphite compounds [1][2][3] and fullerene compounds [4][5][6], where carrier doping is realized via alkali-metal or alkaline-earth-metal doping. In the case of diamond, superconductivity has been realized by boron doping [7].…”