title: Synthesis of Bulk BC8 Silicon Allotrope by Direct Transformation and Reduced-Pressure Chemical Pathways.
abstract: Phase-pure samples of a metastable allotrope of silicon, Si-III or BC8, were synthesized by direct elemental transformation at 14 GPa and ∼900 K and also at significantly reduced pressure in the Na-Si system at 9.5 GPa by quenching from high temperatures ∼1000 K. Pure sintered polycrystalline ingots with dimensions ranging from 0.5 to 2 mm can be easily recovered at ambient conditions. The chemical route also allowed us to decrease the synthetic pressures to as low as 7 GPa, while pressures required for direct phase transition in elemental silicon are significantly higher. In situ control of the synthetic protocol, using synchrotron radiation, allowed us to observe the underlying mechanism of chemical interactions and phase transformations in the Na-Si system. Detailed characterization of Si-III using X-ray diffraction, Raman spectroscopy, (29)Si NMR spectroscopy, and transmission electron microscopy are discussed. These large-volume syntheses at significantly reduced pressures extend the range of possible future bulk characterization methods and applications.
authors.affiliation: IMPMC, UPMC Sorbonne Universités, UMR CNRS 7590, Muséum National d'Histoire Naturelle, IRD UMR 206 , F-75005 Paris, France.
authors.forename: Oleksandr O
authors.initials: OO
authors.lastname: Kurakevych
authors.affiliation: IMPMC, UPMC Sorbonne Universités, UMR CNRS 7590, Muséum National d'Histoire Naturelle, IRD UMR 206 , F-75005 Paris, France.
authors.forename: Yann
authors.initials: Y
authors.lastname: Le Godec
authors.affiliation: The European Synchrotron Radiation Facility , 71 av. des Martyrs, F-38000 Grenoble, France.
authors.forename: Wilson A
authors.initials: WA
authors.lastname: Crichton
authors.affiliation: The European Synchrotron Radiation Facility , 71 av. des Martyrs, F-38000 Grenoble, France.
authors.forename: Jérémy
authors.initials: J
authors.lastname: Guignard
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington , Washington, D.C. 20015, United States.
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Strobel
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington , Washington, D.C. 20015, United States.
authors.forename: Haidong
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington , Washington, D.C. 20015, United States.
authors.forename: Hanyu
authors.initials: H
authors.lastname: Liu
authors.affiliation: Institut des Matériaux de Paris Centre FR 2482 , F-75252 cedex 05 Paris, France.|LCMCP, UPMC Sorbonne Universités, UMR CNRS 7574 , F-75005 Paris, France.
authors.forename: Cristina
authors.initials: C
authors.lastname: Coelho Diogo
authors.affiliation: IMPMC, UPMC Sorbonne Universités, UMR CNRS 7590, Muséum National d'Histoire Naturelle, IRD UMR 206 , F-75005 Paris, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Polian
authors.affiliation: IMPMC, UPMC Sorbonne Universités, UMR CNRS 7590, Muséum National d'Histoire Naturelle, IRD UMR 206 , F-75005 Paris, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Menguy
authors.affiliation: Department of Chemistry, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Juhl
authors.affiliation: LCMCP, UPMC Sorbonne Universités, UMR CNRS 7574 , F-75005 Paris, France.
authors.forename: Christel
authors.initials: C
authors.lastname: Gervais
authors.forename: Nasim
authors.initials: N
authors.lastname: Alem