Superconductivity and Characterization of the High-Pressure Reaction Products of Carbon Diselenide, CSe2

Abstract The physical properties and the structure of black solids obtained by the high-pressure reaction of CSe2 were examined by IR, X-ray diffraction, scanning electron microscope, electron diffraction, thermal analyses and magnetic experiments. The crystalline solid, which was metallic (σ(RT)≈50 S cm−1) at ambient pressure became superconductor above 20 GPa(Tc(onset)=6 K), while the amorphous solid was insulating. Contrary to the previously proposed one- or two-dimensional polymerization structure of (CSe2)x, it has been revealed that the metallic CSe2 sample have a rather complex structure that is composed of the crystalline hexagonal Se, graphite and some amorphous parts. Thus, the high conductivity and the diamagnetism of the crystalline solid at ambient pressure seems to come from graphite part and the superconductivity seems to come from hexagonal Se part. The superconducting transition behavior depended on the path of the pressure-cooling steps. The superconducting state was observed only when the pressure was increased at the low temperature.