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Massive Icosahedral Boron Carbide Crystals Bingqing Wei, Robert Vajtai, Yung Joon Jung, Florian Banhart,
 

Summary: LETTERS
Massive Icosahedral Boron Carbide Crystals
Bingqing Wei, Robert Vajtai, Yung Joon Jung, Florian Banhart,
Ganapathiraman Ramanath, and Pulickel M. Ajayan*,
Department of Materials Science and Engineering, Rensselaer Polytechnic Institute,
Troy, New York 12180-3590, and Zentrale Einrichtung Elektronenmikroskopie,
UniVersitašt Ulm, 89069 Ulm, Germany
ReceiVed: December 20, 2001; In Final Form: March 21, 2002
We have discovered massive icosahedral multiply twinned particles of boron carbide among soot produced
during the arc evaporation of carbon and boron in the presence of magnesium. The observation is striking
because 5-fold symmetry in large micron size crystals is extremely rare. It is suggested that the icosahedral
structural unit that builds up the rhombohedral crystal structure of bulk B4C provides a template for the
formation of these large icosahedral crystals. The physical properties of boron carbide, known for its hardness,
could be further improved in these crystals because of their unusually high symmetry.
Large crystals having 5-fold symmetry are rare in nature
because these systems have no long-range translational sym-
metry. However, smaller icosahedral quasicrystal morphologies
and local structures showing 5-fold symmetry have been found
in several materials systems. Examples of these range from
biological materials to minerals, such as viruses,1 proteins,2

  

Source: Ajayan, Pulickel M. - Department of Mechanical Engineering and Materials Science, Rice University

 

Collections: Materials Science