Ab initio study of defective chains in icosahedral boron carbide B ₄C

Two kinds of chain defects have been studied in icosahedral boron carbide, with the density functional theory: (i) The boron chain vacancy at the center of the chain, modeled by (B₁₁C^p)C-V-C, is found to be metastable at low pressure, and to transform to (B₁₁C^p) C-C with a discontinuous variation of volume at high pressure. (ii) The formation of a carbon-carbon bond in the defective chain, modeled by (B ₁₁C^p)C-C, is found to be metastable both at low and high pressure. The energy barrier for the formation of a carbon-carbon bond in presence of an interstitial boron atom is shown to be very high.