title: High-Energy Density and Superhard Nitrogen-Rich B-N Compounds.
abstract: The pressure-induced transformation of diatomic nitrogen into nonmolecular polymeric phases may produce potentially useful high-energy-density materials. We combine first-principles calculations with structure searching to predict a new class of nitrogen-rich boron nitrides with a stoichiometry of B(3)N(5) that are stable or metastable relative to solid N(2) and h-BN at ambient pressure. The most stable phase at ambient pressure has a layered structure (h-B(3)N(5)) containing hexagonal B(3)N(3) layers sandwiched with intercalated freely rotating N(2) molecules. At 15 GPa, a three-dimensional C222(1) structure with single N-N bonds becomes the most stable. This pressure is much lower than that required for triple-to-single bond transformation in pure solid nitrogen (110 GPa). More importantly, C222(1)-B(3)N(5) is metastable, and can be recovered under ambient conditions. Its energy density of ∼3.44  kJ/g makes it a potential high-energy-density material. In addition, stress-strain calculations estimate a Vicker's hardness of ∼44  GPa. Structure searching reveals a new clathrate sodalitelike BN structure that is metastable under ambient conditions.
authors.affiliation: Laboratory for Quantum Design of Functional Materials, School of Physics and Electronic Engineering, Jiangsu Normal University, Xuzhou 221116, China.|Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Canada, S7N 5E2.
authors.forename: Yinwei
authors.initials: Y
authors.lastname: Li
authors.affiliation: Laboratory for Quantum Design of Functional Materials, School of Physics and Electronic Engineering, Jiangsu Normal University, Xuzhou 221116, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Hao
authors.affiliation: Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Canada, S7N 5E2.|Geophysical Laboratory, Carnegie Institution of Washington, Washington D.C. 20015, USA.
authors.forename: Hanyu
authors.initials: H
authors.lastname: Liu
authors.affiliation: Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Canada, S7N 5E2.
authors.forename: Siyu
authors.initials: S
authors.lastname: Lu
authors.affiliation: Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Canada, S7N 5E2.|State Laboratory for Superhard Materials, Jilin University, Changchun 130012, China.
authors.forename: John S
authors.initials: JS
authors.lastname: Tse