Journal of Statistical Physics

, Volume 150, Issue 3, pp 432–441 | Cite as

A Free Energy Model of Boron Carbide

Article

Abstract

The assessed phase diagram of the boron-carbon system contains a single nonstoichiometric boron-carbide phase of rhombohedral symmetry with a broad, thermodynamically improbable, low temperature composition range. We combine first principles total energy calculations with phenomenological thermodynamic modeling to propose a revised low temperature phase diagram that contains two boron-carbide phases of differing symmetries and compositions. One structure has composition B4C and consists of B11C icosahedra and C-B-C chains, with the placement of carbon on the icosahedron breaking rhombohedral symmetry. This phase is destabilized above 600 K by the configurational entropy of alternate carbon substitutions. The other structure, of ideal composition B13C2, has a broad composition range at high temperature, with rhombohedral symmetry throughout, as observed experimentally.

Keywords

Boron carbide Third law First principles Thermodynamics 

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Copyright information

© Springer Science+Business Media New York 2012

Authors and Affiliations

  1. 1.Department of PhysicsCarnegie Mellon UniversityPittsburghUSA

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