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Updated: Mar 30, 2026

Negative Additive Manufacturing of Complex Shaped Boron Carbides
Published on: September 18, 2018
Atomic-Level Understanding of "Asymmetric Twins" in Boron Carbide
Kelvin Y Xie1, Qi An2, M Fatih Toksoy3
1Department of Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Abstract:
Recent observations of planar defects in boron carbide have been shown to deviate from perfect mirror symmetry and are referred to as "asymmetric twins." Here, we demonstrate that these asymmetric twins are really phase boundaries that form in stoichiometric B(4)C (i.e., B(12)C(3)) but not in B(13)C(2). TEM observations and ab initio simulations have been coupled to show that these planar defects result from an interplay of stoichiometry, atomic positioning, icosahedral twinning, and structural hierarchy. The composition of icosahedra in B(4)C is B(11)C and translation of the carbon atom from a polar to equatorial site leads to a shift in bonding and a slight distortion of the lattice. No such distortion is observed in boron-rich B(13)C(2) because the icosahedra do not contain carbon. Implications for tailoring boron carbide with stoichiometry and extrapolations to other hierarchical crystalline materials are discussed.
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