Superconductive CaC6 prepared from flexible graphite sheets

► CaC6from Grafoil and PGS transitioned to a superconducting state at around 11 K. ► The transition occurred, provided that a small amount of CaC6 was present. ► The transition temperature was independent of purity and homogeneity in the CaC6. ► The transition temperature of the CaC6 prepared from PGS was slightly lower.