High-pressure, high-temperature syntheses of super-hard α-rhombohedral boron-rich solids in the B-C-N-O

Herve Hubert, Laurence Garvie, Bertrand Devouard, Paul F. McMillan

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14 Scopus citations


We prepared α-rhombohedral (α-rh.) B-rich materials in the B-C-N-O system at high-pressures and temperatures. Samples were synthesized using a multianvil device and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and parallel electron energy-loss spectroscopy (PEELS). The B-C-O compounds were obtained by reducing B2O3 with B, or mixtures of B and C between 1 to 10 GPa and 1200° and 1800 °C . In the B-O system we synthesized boron suboxide (nominally B6O) of high purity, crystallinity, and close to stoichiometric. Quantitative analyses give B6O0.95 and B6O0.77 for high-pressure and room-pressure samples, respectively. Between 4 to 5.5 GPa, B6O formed as macroscopic near-perfect regular icosahedra (to 30 μm in diameter). In the B-C-O system, intermediate phases were prepared showing evidence of solid solution between B4C and B6O. Boron carbide crystals, to 20 μm, containing a significant amount of O, typically B6C1.1O0.33 and B6C1.28O0.31, were grown for mixtures in which B and C were reacted with excess B2O3 at 7.5 GPa and 1700 °C. We also report the first conclusive bulk synthesis of a new boron nitride, B6N1-x. This subnitride was synthesized from B and hexagonal BN at 7.5 GPa and 1700 °C. XRD and PEELS shows that the boron subnitride has the α-rh. B structure and average composition B6N0.92.

Original languageEnglish (US)
Pages (from-to)315-320
Number of pages6
JournalMaterials Research Society Symposium - Proceedings
StatePublished - Dec 1 1998
EventProceedings of the 1997 MRS Fall Symposium - Boston, MA, USA
Duration: Dec 2 1997Dec 4 1997

ASJC Scopus subject areas

  • General Materials Science
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering


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