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Title: Thermodynamic ground state of MgB{sub 6} predicted from first principles structure search methods

Crystalline structures of magnesium hexaboride, MgB{sub 6}, were investigated using unbiased structure searching methods combined with first principles density functional calculations. An orthorhombic Cmcm structure was predicted as the thermodynamic ground state of MgB{sub 6}. The energy of the Cmcm structure is significantly lower than the theoretical MgB{sub 6} models previously considered based on a primitive cubic arrangement of boron octahedra. The Cmcm structure is stable against the decomposition to elemental magnesium and boron solids at atmospheric pressure and high pressures up to 18.3 GPa. A unique feature of the predicted Cmcm structure is that the boron atoms are clustered into two forms: localized B{sub 6} octahedra and extended B{sub ∞} ribbons. Within the boron ribbons, the electrons are delocalized and this leads to a metallic ground state with vanished electric dipoles. The present prediction is in contrast to the previous proposal that the crystalline MgB{sub 6} maintains a semiconducting state with permanent dipole moments. MgB{sub 6} is estimated to have much weaker electron-phonon coupling compared with that of MgB{sub 2}, and therefore it is not expected to be able to sustain superconductivity at high temperatures.
Authors:
 [1] ;  [2] ;  [3] ;  [1] ;  [3] ;  [2]
  1. State Key Lab of Superhard Materials, Jilin University, Changchun 130012 (China)
  2. (Canada)
  3. Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2 (Canada)
Publication Date:
OSTI Identifier:
22255210
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 140; Journal Issue: 4; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; BORON; DECOMPOSITION; DENSITY FUNCTIONAL METHOD; DIPOLE MOMENTS; ELECTRIC DIPOLES; ELECTRON-PHONON COUPLING; ELECTRONS; GROUND STATES; MAGNESIUM; MAGNESIUM BORIDES; ORTHORHOMBIC LATTICES; SOLIDS; SUPERCONDUCTIVITY