Phase transitions of boron carbide: Pair interaction model of high carbon limit

作者：Yao Sanxi; Huhn W P; Widom M^*

来源：Solid State Sciences, 2015, 47: 21-26.

DOI：10.1016/j.solidstatesciences.2014.12.016

• Boron carbide
• Density functional theory
• Multi-histogram method
• 3-state Potts like transition
• Ising like transition

Boron Carbide exhibits a broad composition range, implying a degree of intrinsic substitutional disorder. While the observed phase has rhombohedral symmetry (space group R (3) over barm), the enthalpy minimizing structure has lower, monoclinic, symmetry (space group Cm). The crystallographic primitive cell consists of a 12-atom icosahedron placed at the vertex of a rhombohedral lattice, together with a 3-atom chain along the 3-fold axis. In the limit of high carbon content, approaching 20% carbon, the icosahedra are usually of type B-11 C-p, where the p indicates the carbon resides on a polar site, while the chains are of type C-B-C. We establish an atomic interaction model for this composition limit, fit to density functional theory total energies, that allows us to investigate the substitutional disorder using Monte Carlo simulations augmented by multiple histogram analysis. We find that the low temperature monoclinic Cm structure disorders through a pair of phase transitions, first via a 3-state Potts-like transition to space group R3m, then via an Ising-like transition to the experimentally observed R (3) over barm symmetry. The R3m and Cm phases are electrically polarized, while the high temperature R (3) over barm phase is nonpolar.

• 出版日期2015-9