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Published August 19, 2016 | Published + Supplemental Material
Journal Article Open

New Ground-State Crystal Structure of Elemental Boron


Elemental boron exhibits many polymorphs in nature based mostly on an icosahedral shell motif, involving stabilization of 13 strong multicenter intraicosahedral bonds. It is commonly accepted that the most thermodynamic stable structure of elemental boron at atmospheric pressure is the β rhombohedral boron (β−B). Surprisingly, using high-resolution transmission electron microscopy, we found that pure boron powder contains grains of two different types, the previously identified β−B containing a number of randomly spaced twins and what appears to be a fully transformed twinlike structure. This fully transformed structure, denoted here as τ−B, is based on the Cmcm orthorhombic space group. Quantum mechanics predicts that the newly identified τ−B structure is 13.8  meV/B more stable than β−B. The τ−B structure allows 6% more charge transfer from B_(57) units to nearby B_(12) units, making the net charge 6% closer to the ideal expected from Wade's rules. Thus, we predict the τ−B structure to be the ground state structure for elemental boron at atmospheric pressure.

Additional Information

© 2016 American Physical Society. Received 8 March 2016; revised manuscript received 27 May 2016; published 15 August 2016. QA and WAG were supported by the Defense Advanced Research Projects Agency (Grant No. W31P4Q-13-1-0010, program managers, John Paschkewitz), by the Army Research Laboratory under Cooperative Agreement No. W911NF-12-2-0022, and by the National Science Foundation (Grant No. DMR-1436985, program manager, John Schlueter). KMR, KYX and KH were supported by the Defense Advanced Research Projects Agency (Grant No. W31P4Q-13-1-0001). We gratefully acknowledge Professor Richard Haber and Dr. Chawon Hwang at Rutgers University, for coordinating our access to the commercial boron powders. We thank ARL for permission to use their HRTEM simulation facility. Q. A. and K. M. R. contributed equally to this work. Q. A., K. M. R., K. H., and W. A. G. wrote the Letter. K. M. R. performed the experimental measurements and image simulations including TEM and XRD, K. Y. X. contributed to the TEM, and Q. A. performed the quantum mechanics simulations. Q. A., K. M. R., K. Y. X., K. H., and W. A. G. analyzed the data and discussed the results. K. M. R. first observed the new structure before Q. A. performed the quantum mechanics simulations.

Attached Files

Supplemental Material - PRL-SI-final.pdf

Published - PhysRevLett.117.085501.pdf

Published - PhysRevLett.118.089602.pdf

Supplemental Material - alpha-B-symmetry.cif

Supplemental Material - beta-B105-symmetry.cif

Supplemental Material - beta-B106.cif

Supplemental Material - gamma-B-symmetry.cif

Supplemental Material - tau-B105-symmetry.cif

Supplemental Material - tau-B106.cif


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August 20, 2023
September 8, 2023