Chemical analysis of superconducting phase in K-doped picene

Potassium-doped picene (K_3.0picene) with a superconducting transition temperature (T _C) as high as 14 K at ambient pressure has been prepared using an annealing technique. The shielding fraction of this sample was 5.4% at 0 GPa. The T _C showed a positive pressure-dependence and reached 19 K at 1.13 GPa. The shielding fraction also reached 18.5%. To investigate the chemical composition and the state of the picene skeleton in the superconducting sample, we used energy-dispersive x-ray (EDX) spectroscopy, MALDI-time-of-flight (MALDI-TOF) mass spectroscopy and x-ray diffraction (XRD). Both EDX and MALDI-TOF indicated no contamination with materials other than K-doped picene or K-doped picene fragments, and supported the preservation of the picene skeleton. However, it was also found that a magnetic K-doped picene sample consisted mainly of picene fragments or K-doped picene fragments. Thus, removal of the component contributing the magnetic quality to a superconducting sample should enhance the volume fraction.