Figure 4

Superconductivity in electrochemically K- and Na-intercalated FeSe.

(a) Temperature dependence of magnetic susceptibility for parent FeSe and electrochemically intercalated FeSe (EC(K)-FeSe and EC(Na)- FeSe). (b) XRD spectra for parent FeSe and EC(K)-FeSe at room temperature. For the EC(K)-FeSe, the black cross indicates the experiments and the red line indicates the fitting result based on the Le Bail analysis. Below the XRD spectrum, the blue and pink vertical bars indicate expected diffraction positions for the parent FeSe and the ThCr₂Si₂-type structure. The (002) peak for the ThCr₂Si₂-type structure was indicated by the arrow. (c) EDX spectra for EC(K)-FeSe and EC(Na)-FeSe. In the case of EC(Na)-FeSe, the peaks of C, O and F are observed because of the use of PVDF as the binder.