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Large Symmetrical Crystals Created
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, 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.
Researchers at Rensselaer have created large
symmetrical crystals that rarely occur in nature. These crystals
could be harder than conventional engineering materials.
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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, and 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 in the June 13 issue of
the Journal of Physical Chemistry as the cover story.
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