Long-Range Ordered Carbon Clusters: A Crystalline Material with Amorphous Building Blocks

Abstract

Amorphous Crystals One usually thinks of a crystal as containing atoms, molecules, or other ordered units arranged in a periodic fashion to make a larger structure. L. Wang et al. (p. 825 ; see the Perspective by D. Wang and Fernandez-Martinez ) compressed a solvate of xylene in C 60 (fullerene) to very high pressures at room temperature, which caused the fullerene molecules to collapse and form amorphous clusters but with each cluster retaining its position in the original crystal lattice because of the interaction with the intercalated xylene molecules. Thus, a crystal was formed from amorphous constituents. On heating at atmospheric pressure, the xylene disappeared and the sample became completely amorphous.

High-pressure studies with x-rays using diamond anvil cells

“…Wang et al [422] showed that C60 molecules from a crystalline solvated fullerene phase undergo an order-to-disorder transition under HP but keep their translational symmetry (Fig. 22).…”

“…The HP form has a distorted Mcarbon structure [661] and is super hard, capable of indenting cubic-diamond single crystals. Similarly, compressing fullerenes causes crushed C60 cages, forming superhard forms of carbon that are quenchable to ambient pressure [422,662]. Individual C60 molecules are estimated to have an extremely high elastic modulus of 800-900 GPa [663].…”

Pressure-induced transformation and superhard phase in fullerenes: The effect of solvent intercalation

“…Above 20 GPa, the pressure dependence of the H g (7) mode exhibits a transition and its frequency becomes almost pressure independent, which is consistent with the low compressibility of the phase formed as determined by X-ray diffraction (XRD) measurements. [15] It is worth noting that when a 514 nm laser was used for excitation the H g (8) mode became dominant above 20 GPa, instead of the H g (7) mode which dominated when the 830 nm laser was used.…”

“…[12][13][14] Recently, Wang et al reported that compression of solvated fullerenes (C 60 /m-xylene) produces a carbon phase composed of ordered amorphous carbon clusters (OACC). [15] Such formed OACC with a long range periodic structure is challenging the categorization of solid-state materials (including crystalline, amorphous, and quasicrystalline phases). Moreover, this phase exhibits very high hardness and can indent diamond anvils at high pressure.…”

“…Solvated C 60 single crystals were prepared on a glass substrate by evaporating a saturated C 60 /m-xylene solution at room temperature. [15,16] The as-prepared samples contain solvent and have a hexagonal structure (P63, a = b = 2.37 nm and c = 1.012 nm). The solvent was removed by heating samples at 150 o C under vacuum, transforming it into a FCC structure (here called desolvated sample).…”