NANOCRYSTALS
Symmetrical Crystals Created

Researchers Pulickel Ajayan and G. Ramanath have created large symmetrical crystals that rarely occur in nature. These crystals could be harder than conventional engineering materials. The discovery was made during attempts to make superconducting nanostructures with a simple technique used to create carbon nanotubes. The research appeared as the cover story in the June 13 issue of the Journal of Physical Chemistry. Ajayan and Ramanath collaborated with other researchers at the University of Ulm in Germany.

The researchers used boron carbide, a common engineering material, in the high-temperature experiment. In the ashes, they discovered large crystals with five-fold crystallographic symmetry.

Nanosize five-fold symmetrical, or icosahedral, crystals are fairly common, but these larger micron-size crystals with five-fold symmetry are rare in nature because their smaller units cannot repeat their pattern infinitely to form space-filling structures. As the nuclei of these crystals grow, the strain on the crystals increases. This causes them to revert to their common bulk crystal structures.

Ajayan believes that the inherent structure of boron carbide, which has icosahedral units in the unit cell, allows the crystals to grow to micron size without the strain.

“These crystals are unique due to their high symmetry,” Ajayan says. “Because of the hardness inherent to the crystal structure, we could anticipate a better material for engineering, specific-ally coatings. It is exciting and fulfilling to find something that is quite rare in nature, although we need to conduct further measurements to understand its potential.”

CONTACT: Theresa Bourgeois, (518) 276-2840, bourgt@rpi.edu