Troy, N.Y. — Researchers at Rensselaer have created large symmetrical crystals that rarely occur in nature. These crystals could be harder than conventional engineering materials. The accidental discovery was made during attempts to make superconducting nanostructures with a simple technique used to create carbon nanotubes.

Pulickel Ajayan and Ganapathiraman Ramanath, faculty members in materials science and engineering at Rensselaer, 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. Because of the hardness inherent to the crystal structure, we could anticipate a better material for engineering, specifically 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,” Ajayan said.

The researchers, their post-doctoral research associates (Bingqing Wei and Robert Vajtai), and a graduate student (Yung Joon Jung) collaborated with colleagues at the University of Ulm in Germany.

Their research appeared as the cover story in the June 13, 2002 issue of the Journal of Physical Chemistry.

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