title: The formation of sp3 bonding in compressed BN.
abstract: Attributed to their specific atomic bonding, the soft, graphite-like, hexagonal boron nitride (h-BN) and its superhard, diamond-like, cubic polymorph (c-BN) are important technological materials with a wide range of applications. At high pressure and temperature, h-BN can directly transform to a hexagonal close-packed polymorph (w-BN) that can be partially quenched after releasing pressure. Previous theoretical calculations and experimental measurements (primarily on quenched samples) provided substantial information on the transition, but left unsettled questions due to the lack of in situ characterization at high pressures. Using inelastic X-ray scattering to probe the boron and nitrogen near K-edge spectroscopy, here we report the first observation of the conversion process of boron and nitrogen sp(2)- and p-bonding to sp(3) and the directional nature of the sp(3) bonding. In combination with in situ X-ray diffraction probe, we have further clarified the structure transformation mechanism. The present archetypal example opens two enormous, element-specific, research areas on high-pressure bonding evolutions of boron and nitrogen; each of the two elements and their respective compounds have displayed a wealth of intriguing pressure-induced phenomena that result from bonding changes, including metallization, superconductivity, semiconductivity, polymerization and superhardness.
authors.affiliation: HPCAT, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA. ymeng@hpcat.aps.anl.gov
authors.forename: Yue
authors.initials: Y
authors.lastname: Meng
authors.forename: Ho-Kwang
authors.initials: HK
authors.lastname: Mao
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Eng
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Trainor
authors.forename: Matthew
authors.initials: M
authors.lastname: Newville
authors.forename: Michael Y
authors.initials: MY
authors.lastname: Hu
authors.forename: Chichang
authors.initials: C
authors.lastname: Kao
authors.forename: Jinfu
authors.initials: J
authors.lastname: Shu
authors.forename: Daniel
authors.initials: D
authors.lastname: Hausermann
authors.forename: Russell J
authors.initials: RJ
authors.lastname: Hemley
mesh_terms: D001896:Boron Compounds / Q000737:chemistry*; D002623:Chemistry Techniques, Analytical / Q000379:methods*; D008420:Manufactured Materials; D013057:Spectrum Analysis
chemical_list: D001896:Boron Compounds; C017282:boron nitride