title: Disorder and defects are not intrinsic to boron carbide.
abstract: A unique combination of useful properties in boron-carbide, such as extreme hardness, excellent fracture toughness, a low density, a high melting point, thermoelectricity, semi-conducting behavior, catalytic activity and a remarkably good chemical stability, makes it an ideal material for a wide range of technological applications. Explaining these properties in terms of chemical bonding has remained a major challenge in boron chemistry. Here we report the synthesis of fully ordered, stoichiometric boron-carbide B13C2 by high-pressure-high-temperature techniques. Our experimental electron-density study using high-resolution single-crystal synchrotron X-ray diffraction data conclusively demonstrates that disorder and defects are not intrinsic to boron carbide, contrary to what was hitherto supposed. A detailed analysis of the electron density distribution reveals charge transfer between structural units in B13C2 and a new type of electron-deficient bond with formally unpaired electrons on the C-B-C group in B13C2. Unprecedented bonding features contribute to the fundamental chemistry and materials science of boron compounds that is of great interest for understanding structure-property relationships and development of novel functional materials.
authors.affiliation: Max-Planck-Institut fuer Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Muelheim an der Ruhr, Germany.|Laboratory of Crystallography, University of Bayreuth, D-95440 Bayreuth, Germany.
authors.forename: Swastik
authors.initials: S
authors.lastname: Mondal
authors.affiliation: Laboratory of Crystallography, University of Bayreuth, D-95440 Bayreuth, Germany.|Bayerisches Geoinstitut, University of Bayreuth, D-95440 Bayreuth, Germany.
authors.forename: Elena
authors.initials: E
authors.lastname: Bykova
authors.affiliation: Laboratory of Crystallography, University of Bayreuth, D-95440 Bayreuth, Germany.
authors.forename: Somnath
authors.initials: S
authors.lastname: Dey
authors.affiliation: Laboratory of Crystallography, University of Bayreuth, D-95440 Bayreuth, Germany.
authors.forename: Sk Imran
authors.initials: SI
authors.lastname: Ali
authors.affiliation: Laboratory of Crystallography, University of Bayreuth, D-95440 Bayreuth, Germany.
authors.forename: Natalia
authors.initials: N
authors.lastname: Dubrovinskaia
authors.affiliation: Bayerisches Geoinstitut, University of Bayreuth, D-95440 Bayreuth, Germany.
authors.forename: Leonid
authors.initials: L
authors.lastname: Dubrovinsky
authors.affiliation: Laboratory of Crystallography, University of Bayreuth, D-95440 Bayreuth, Germany.|Bayerisches Geoinstitut, University of Bayreuth, D-95440 Bayreuth, Germany.
authors.forename: Gleb
authors.initials: G
authors.lastname: Parakhonskiy
authors.affiliation: Laboratory of Crystallography, University of Bayreuth, D-95440 Bayreuth, Germany.
authors.forename: Sander
authors.initials: S
authors.lastname: van Smaalen