Electrical and Mechanical Properties of $C_{70}$ Fullerene and Graphite under High Pressures Studied Using Designer Diamond Anvils

We compare electrical and mechanical properties of ${\mathrm{C}}_{70}$ fullerene with high purity graphite to $48\mathrm{GPa}$ at room temperature using designer diamond anvils with embedded electrical microprobes. The electrical resistance of ${\mathrm{C}}_{70}$ shows a minimum at $20\mathrm{GPa}$ with transformation to an amorphous insulating phase complete above $35\mathrm{GPa}$, while graphite remains conducting. Nanoindentation shows hardness values 220 times larger for the pressure quenched amorphous phase than for similarly treated graphite. Our studies establish that the amorphous carbon phase produced from ${\mathrm{C}}_{70}$ has unique properties not attainable from graphite.