Bipolarons in boron icosahedra
- 15 February 1987
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review B
- Vol. 35 (6) , 2929-2933
- https://doi.org/10.1103/physrevb.35.2929
Abstract
Small-bipolaron hopping has been proposed as the mechanism of electrical transport in the boron carbides, compounds composed of boron-rich icosahedra linked by carbon-containing chains. We present a simple model of small-bipolaron formation and of the small-bipolaron hopping activation energy. We then consider, by means of a molecular-orbital calculational technique, a cluster model of bipolaron formation in a boron icosahedron set in charge-neutral surroundings. A lower limit of 3.7 eV is calculated for the bipolaron formation energy, of which 1.0 eV is related to site distortion and 2.7 eV to filling of icosahedral bonding orbitals. We have therefore established within our model that small-bipolaron formation will be energetically favored in the boron carbides.Keywords
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