APPLICATION OF ESR TO HIGH-Tc SUPERCONDUCTORS AND RELATED MATERIALS IV: ALKALI K DOPING EFFECTS ON THE SUPERCONDUCTING CHARACTERISTICS OF K3C60

Several samples of K3C60 have been made by the calcination of C60 powder plus K flakes in evacuated quartz tubes at temperatures between 100°C and 700°C for 24 hours. The non-resonant microwave absorption (NRMA) measurements have been done below Tc for these samples. From the linewidths and intensities of the NRMA signals, the superconducting properties (Tc superconducting volume fraction and vortex size) have been studied as a function of the calcination temperature.