Polymeric Fullerene Phases Formed Under Pressure

Abstract

Fullerenes, in particular C₆₀, can form covalent intermolecular bonds (“polymerize”) when treated at high temperature under high pressure. This contribution briefly reviews some recent advances in this field. Short overviews are given of the pressure-temperature phase diagrams of pristine C₆₀ and C₇₀ and of their physical properties under high pressure. The paper has its main emphasis on the structures and properties of the one- and two-dimensional (chains and planes) polymeric phases of C₆₀ created in the range 1–9 GPa (10–90 kbar) and up to 1100 K. Their structures, as obtained from studies on polymerized single crystals, the treatment conditions used to obtain well-defined structures, and some selected physical properties, including the surprising discovery of ferromagnetism, are discussed. The paper presents the results of both ex situ and in situ structural studies. Three-dimensional polymers, and the possibility to create well-defined three-dimensional structures by high-pressure treatment of low-dimensional polymers, are also discussed. Finally, a short section devoted to higher fullerenes discusses the polymeric forms of C₇₀, including the ordered zigzag chain phase recently created under hydrostatic pressure conditions.