Changes in structure and electronic state from ${\mathrm{C}}_{60}$ fullerene to amorphous diamond

Changes in electronic state and structure from ${\mathrm{C}}_{60}$ fullerene to amorphous diamond under shock compression were examined by electron energy-loss spectroscopy and electron diffractometry for the recovered samples from the 50 to 55 GPa compressions. Three transient states were distinguished. In the first transient state, the fcc structure was almost unchanged, and the π plasmon was prohibited owing to decreasing intercluster distance. In the second state, the basic stacking structure of clusters was barely retained, and intercluster bondings were generated. In the third state, the fullerene structure collapsed to be amorphous, while ${\mathit{sp}}^3$ bonding was partly produced. Finally, complete ${\mathit{sp}}^3$ bonds were entirely reproduced, whereas the diamond structure in the long-range order was not reconstructed.