Congratulations to Prof. Kevin Hemker and Dr. Kelvin Xie as well as their teammates from Caltech and The University of Sydney on the publication of their paper, “Breaking the Icosahedra in Boron Carbide.”
The manuscript elaborates on how the team employed a state-of-art characterization technique – Laser-assisted Atom Probe Tomography, to unravel the atomic structure and bonding of boron carbide ceramics. Surprisingly, they discovered that the 12-atom icosahedra disintegrated during their experiments. Statistical analyses of event multiplicity and stoichiometry in the atom probe dataset substantiated that the icosahedra in boron carbide are less stable than their interconnecting chains. Comparisons with quantum mechanics (QM) simulations further indicate that this instability plays a role in the amorphization of boron carbide.
“About ten years ago, we discovered that boron carbide undergoes amorphization and suffers a dramatic loss of strength during ballistic impact, but a fundamental understanding of the underlying mechanism for this amorphization has not been fully established.” says Hemker. Dr. Xie added, “We were surprised to discover that the icosahedra were less stable than the chains, and we began to wonder if this might be related to amorphization and the sudden loss of ballistic performance. To obtain atomistic understanding of such events, we sought the help of Professor Goddard’s group at Caltech.”
Professor William A. Goddard III (referenced above) adds, “The use of quantum mechanics (QM) simulations to model field evaporation in atom probe experiments in a new approach.” Professor Julie Cairney (The University of Sydney) also pointed out “Atom probe has been generally used to identify the chemical and spatial information of individual atoms and clusters. In this work, the temporal, spatial and compositional information provided by atom probe tomography makes it a unique platform for elucidating the relative stability and interactions of primary building blocks in hierarchically crystalline materials”.
To our knowledge these are the first atom probe experiments on boron carbide, and the finding that boron carbide icosahedra are destroyed during the evaporation process was unexpected given the inherent structural stability of Bucky balls. Th research also illustrates that the interpretation of the temporal, spatial and compositional information shows APT to be a unique platform for elucidating atomic-scale stability and interactions.
The research was supported by grants from the Army Research Laboratory, Defense Advanced Research Projects Agency, and National Science Foundation. Click here to view the full article.