Boron carbide: Consistency of components, lattice parameters, fine structure and chemical composition makes the complex structure reasonable

• Additive contributions of structural elements establish the transformation from a-rhombohedral to boron carbide.
• The approximate model describes consistently structure-relevant properties of the complex structure.
• Using this model, several uncommon properties of boron carbide become easily explainable.
• The compounds of single crystals claimed by the authors to deviate from B4.3C are critically analysed and corrected.

The complex, highly distorted structure of boron carbide is composed of B12 and B11C icosahedra and CBC, CBB and B□B linear elements, whose concentration depends on the chemical composition each. These concentrations are shown to be consistent with lattice parameters, fine structure data and chemical composition. The respective impacts on lattice parameters are estimated and discussed. Considering the contributions of the different structural components to the energy of the overall structure makes the structure and its variation within the homogeneity range reasonable; in particular that of B4.3C representing the carbon-rich limit of the homogeneity range. Replacing in B4.3C virtually the B□B components by CBC yields the hypothetical moderately distorted B4.0C (structure formula (B11C)CBC). The reduction of lattice parameters related is compatible with recently reported uncommonly prepared single crystals, whose compositions deviate from B4.3C.

Structural change from α-rhombohedral boron to boron carbide. Impact of the different structure elements on the c axis.Figure optionsDownload as PowerPoint slide