Effects of mechanical grinding on C-60 and Ca5C60 superconductor

The effects of mechanical grinding on polycrystalline C-60 and Ca5C60 superconductor are examined. It has been found that mechanical grinding may severely degrade phases of C-60 (fcc) and Ca5C60 (sc). The grinding destroys the long-range ordering of crystals and produces a partial amorphous state. The damage of crystal leads to the disappearance of superconductivity for Ca5C60. The samples with an amorphous phase can be recrystallized by annealing at 600 degrees C for pure C-60 and Ca5C60. Magnetic susceptibility measurements indicated that the superconductivity of the degraded sample did not recover easily to the initial state.