Preparation and characterization of a new graphite superconductor: CaSrC.

We have produced a superconducting binary-elements intercalated graphite, CaSrC, with the intercalation of Sr and Ca in highly-oriented pyrolytic graphite; the superconducting transition temperature, T , was ~3 K. The superconducting CaSrC sample was fabricated with the nominal x value of 0.8, i.e., CaSrC. Energy dispersive X-ray (EDX) spectroscopy provided the stoichiometry of CaSrC for this sample, and the X-ray powder diffraction (XRD) pattern showed that CaSrC took the SrC-type hexagonal-structure rather than CaC-type rhombohedral-structure. Consequently, the chemical formula of CaSrC sample could be expressed as 'CaSrC'. The XRD pattern of CaSrC was measured at 0-31 GPa, showing that the lattice shrank monotonically with increasing pressure up to 8.6 GPa, with the structural phase transition occurring above 8.6 GPa. The pressure dependence of T was determined from the DC magnetic susceptibility and resistance up to 15 GPa, which exhibited a positive pressure dependence of T up to 8.3 GPa, as in YbC, SrC, KC, CaC and CaKC. The further application of pressure caused the rapid decrease of T . In this study, the fabrication and superconducting properties of new binary-elements intercalated graphite, CaSrC, are fully investigated, and suitable combinations of elements are suggested for binary-elements intercalated graphite.