How and why elemental boron undergoes self charge transfer between 19 and 89 GPa (Abstract/Comunicazione in rivista)

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  • How and why elemental boron undergoes self charge transfer between 19 and 89 GPa (Abstract/Comunicazione in rivista) (literal)
Anno
  • 2008-01-01T00:00:00+01:00 (literal)
Alternative label
  • Gatti, C.; Oganov, A. R.; Chen, J.; Ma, Y. (2008)
    How and why elemental boron undergoes self charge transfer between 19 and 89 GPa
    (literal)
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  • Gatti, C.; Oganov, A. R.; Chen, J.; Ma, Y. (literal)
Pagina inizio
  • C70 (literal)
Pagina fine
  • C70 (literal)
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  • Published on Acta Cryst A64, C70 (2008) (literal)
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  • A64 (literal)
Rivista
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  • 30’ lecture delivered by C. Gatti (literal)
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  • 1 (literal)
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  • Boron has nearly 20 polymorphs with non-trivial chemical bonding, complex structures and similar energies. It is the only light element for which the ground state is not experimentally established at ambient conditions. Using high-pressure experiments and an ab-initio evolutionary methodology, the structural stability of B under pressure was explored. At low pressures (<19 GPa) B adopts covalent structures based on icosahedral B12 clusters, and at high pressures (>89 GPa) it forms a superconducting ?-Ga-type phase. At intermediate pressures a new insulating phase, ?-B, has been found to be stable. Its structure consists of distorted B12 clusters and B2 pairs: (B2)?+(B12)?-, with a significant charge transfer (CT).Using Bader's theory, ? amounts to ?0.34-0.48, based on either PAW or DFT-LCAO densities. Electron charge flows from B2 to B12 units for their corresponding frozen 3D sublattices act as n-doped and p-doped semiconductors, respectively. The CT occurring in this unique phase affects its physical properties and results from the Lewis acid-base interaction of the B12 and B2 groups. It is the ability of B to form clusters with very different electronic properties and the very low packing efficiency of icosahedral structures which leads to ?-B, the first experimentally established autoionized form of an element. An analysis of bonding within and between the B2 and B12 subunits and its relationship with the observed CT in ?-B is also outlined. (literal)
Note
  • Comunicazione (literal)
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  • 1 CNR-ISTM, Physical Chemistry and Electrochemistry, via Golgi 19, Milano, MI, 20133, Italy; 2 Laboratory of Crystallography, Department of Materials, ETH Zurich, Wolfgang-Pauli-Str. 10, CH-8093 Zurich, Switzerland 3 Geology Department, Moscow State University, 119992 Moscow, Russia 4 Center for the Study of Matters at Extreme Conditions, Florida International University , Miami, FL 33199, USA, 5 Mineral Physics Institute and Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100, USA, 6 Department of Mechanica Engineering, Texas University of Technology,7th St. & Boston Ave. Lubblock, Texas 79409, USA (literal)
Titolo
  • How and why elemental boron undergoes self charge transfer between 19 and 89 GPa (literal)
Abstract
  • Boron has nearly 20 polymorphs with non-trivial chemical bonding, complex structures and similar energies. It is the only light element for which the ground state is not experimentally established at ambient conditions. Using high-pressure experiments and an ab-initio evolutionary methodology, the structural stability of boron under pressure was explored.1 At low pressures (<19 GPa) boron adopts covalent structures based on icosahedral B12 clusters, and at high pressures (>89 GPa) it forms a superconducting alpha-Ga-type phase. At intermediate pressures a new insulating phase, gamma-B, has been found to be stable.1 Its structure consists of distorted B12 clusters and B2 pairs : (B2)delta+(B12)delta-, with a significant charge transfer (CT), substantiated by several theoretical measures and physical properties. Using Bader's theory, delta amounts to about 0.34-0.48, based on either PAW or DFT-LCAO densities. Electron charge flows from B2 to B12 units for their corresponding frozen 3D sublattices act as n-doped and p-doped semiconductors, respectively. The CT occurring in this unique phase affects its physical properties (electronic band gap, infrared absorption, dielectric properties, etc.) and results from the Lewis acid-base interaction of the B12 and B2 groups. It is the ability of boron to form clusters with very different electronic properties and the very low packing efficiency of icosahedral structures (34% for gamma-B12) which leads to gamma-B, the first experimentally established autoionized form of an element. An analysis of bonding within and between the B2 and B12 subunits and its relationship with the observed CT in gamma-B is also outlined. (literal)
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