Nanotwinned Boron Suboxide (B6O): New Ground State of B6O

• Published in: Nano letters 2016-07, Vol.16 (7), p.4236-4242
• Main Authors: An, Qi, Reddy, K. Madhav, Dong, Huafeng, Chen, Ming-Wei, Oganov, Artem R, Goddard, William A
• Format: Article
• Language: English
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.6b01204

Nanotwinned structures in superhard ceramics rhombohedral boron suboxide (R-B6O) have been examined using a combination of transmission electron microscopy (TEM) and quantum mechanics (QM). QM predicts negative relative energies to R-B6O for various twinned R-B6O (denoted as τ-B6O, 2τ-B6O, and 4τ-B6O), consistent with the recently predicted B6O structure with Cmcm space group (τ-B6O) which has an energy 1.1 meV/B6O lower than R-B6O. We report here TEM observations of this τ-B6O structure, confirming the QM predictions. QM studies under pure shear deformation and indentation conditions are used to determine the deformation mechanisms of the new τ-B6O phase which are compared to R-B6O and 2τ-B6O. The lowest stress slip system of τ-B6O is (010)/⟨001⟩ which transforms τ-B6O to R-B6O under pure shear deformation. However, under indentation conditions, the lowest stress slip system changes to (001)/⟨110⟩, leading to icosahedra disintegration and hence amorphous band formation.