title: Prediction of a new ground state of superhard compound B6O at ambient conditions.
abstract: Boron suboxide B6O, the hardest known oxide, has an Rm crystal structure (α-B6O) that can be described as an oxygen-stuffed structure of α-boron, or, equivalently, as a cubic close packing of B12 icosahedra with two oxygen atoms occupying all octahedral voids in it. Here we show a new ground state of this compound at ambient conditions, Cmcm-B6O (β-B6O), which in all quantum-mechanical treatments that we tested comes out to be slightly but consistently more stable. Increasing pressure and temperature further stabilizes it with respect to the known α-B6O structure. β-B6O also has a slightly higher hardness and may be synthesized using different experimental protocols. We suggest that β-B6O is present in mixture with α-B6O, and its presence accounts for previously unexplained bands in the experimental Raman spectrum.
authors: School of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou 510006, China.|Department of Geosciences and Center for Materials by Design, Institute for Advanced Computational Science, State University of New York, Stony Brook, NY 11794, USA.
authors: Huafeng
authors: H
authors: Dong
authors: Department of Geosciences and Center for Materials by Design, Institute for Advanced Computational Science, State University of New York, Stony Brook, NY 11794, USA.|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.|Northwestern Polytechnical University, Xi'an 710072, China.
authors: Artem R
authors: AR
authors: Oganov
authors: Moscow Institute of Physics and Technology, 9 Institutskiy Lane, Dolgoprudny city, Moscow Region 141700, Russian Federation.|Department of Physics and Electrical Engineering, Anyang Normal University, Anyang, Henan Province 455000, China.
authors: Qinggao
authors: Q
authors: Wang
authors: Department of Geosciences and Center for Materials by Design, Institute for Advanced Computational Science, State University of New York, Stony Brook, NY 11794, USA.
authors: Sheng-Nan
authors: SN
authors: Wang
authors: Department of Geosciences and Center for Materials by Design, Institute for Advanced Computational Science, State University of New York, Stony Brook, NY 11794, USA.|Peter Grünberg Research Center, Nanjing University of Posts and Telecommunications, Nanjing 210003, China.
authors: Zhenhai
authors: Z
authors: Wang
authors: Department of Geosciences and Center for Materials by Design, Institute for Advanced Computational Science, State University of New York, Stony Brook, NY 11794, USA.
authors: Jin
authors: J
authors: Zhang
authors: Department of Geosciences and Center for Materials by Design, Institute for Advanced Computational Science, State University of New York, Stony Brook, NY 11794, USA.
authors: M Mahdi Davari
authors: MM
authors: Esfahani
authors: Department of Geosciences and Center for Materials by Design, Institute for Advanced Computational Science, State University of New York, Stony Brook, NY 11794, USA.|School of Physics and Key Laboratory of Weak-Light Nonlinear Photonics, Nankai University, Tianjin 300071, China.
authors: Xiang-Feng
authors: XF
authors: Zhou
authors: School of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou 510006, China.
authors: Fugen
authors: F
authors: Wu
authors: Department of Geosciences and Center for Materials by Design, Institute for Advanced Computational Science, State University of New York, Stony Brook, NY 11794, USA.
authors: Qiang
authors: Q
authors: Zhu