title: Nanotwinned Boron Suboxide (B6O): New Ground State of B6O.
abstract: 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.
authors.affiliation: Materials and Process Simulation Center, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Qi
authors.initials: Q
authors.lastname: An
authors.affiliation: WPI Advanced Institute for Materials Research, Tohoku University , Sendai 980-8577, Japan.
authors.forename: K Madhav
authors.initials: KM
authors.lastname: Reddy
authors.affiliation: Department of Geosciences and Center for Materials by Design, Institute for Advanced Computational Science, State University of New York , Stony Brook, New York 11794-2100, United States.
authors.forename: Huafeng
authors.initials: H
authors.lastname: Dong
authors.affiliation: WPI Advanced Institute for Materials Research, Tohoku University , Sendai 980-8577, Japan.
authors.forename: Ming-Wei
authors.initials: MW
authors.lastname: Chen
authors.affiliation: Department of Geosciences and Center for Materials by Design, Institute for Advanced Computational Science, State University of New York , Stony Brook, New York 11794-2100, United States.|Skolkovo Institute of Science and Technology , Skolkovo Innovation Center, 3 Nobel St., Moscow 143026, Russia.|Moscow Institute of Physics and Technology , 9 Institutskiy Lane, Dolgoprudny City, Moscow Region 141700, Russian Federation.|International Center for Materials Discovery, Northwestern Polytechnical University , Xi'an, 710072, China.
authors.forename: Artem R
authors.initials: AR
authors.lastname: Oganov
authors.affiliation: Materials and Process Simulation Center, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: William A
authors.initials: WA
authors.lastname: Goddard
keywords: DFT; Superhard ceramics; deformation mechanism; stacking faults energy