Superconductive CaC6 prepared from flexible graphite sheets

The host graphite material of choice for most CaC6 studies is highly oriented pyrolytic graphite (HOPG), which can affect the resulting properties of prepared graphite intercalation compounds (GICs). In order to gain a better understanding of the superconductivity of CaC6, we examined CaC6 prepared from Grafoil and PGS. To confirm their superconductivity, the dependences of the magnetic moment on temperature under a constant magnetic field were measured over 2–20 K. The resulting CaC6 transitioned to a superconducting state at around 11 K, independent of purity and homogeneity, while slight differences that depended on the host materials were observed. The transition to a superconducting state at 11.5 K occurred provided that a small amount of CaC6 was present. The co-existence of LiC6 and other GICs, and the residual Li atoms in the CaC6 had little effect on the transition temperature. The transition temperature of the CaC6 prepared from PGS was slightly lower than that of the CaC6 prepared from HOPG and Grafoil.