Crystal Structures and Phase Transitions of Fullerenes

Abstract

Fullerenes, a new allotrope of carbon, are hollow spherical all carbon molecules composed of six-membered and five-membered rings. Structural studies on C₆₀ and C₇₀ in the solid state at ambient and high pressure are reviewed Phase transitions under high pressures are associated with molecular rotation, orientational ordering, polymerization, and/or crushing of molecules. Tentative p-T phase diagrams for solid C₆₀ and C₇₀ are given. Under appropriate pressure and temperatures, fullerenes in the solid state transform to polymers and diamond. Bulk moduli at low pressures (≤1GPa) are also summarized.