Silicon in intericosahedra chains of boron carbide
Oleksandr Vasiliev, Valerii Muratov, Petro Mazur, Vladyslav Bilyi, M. V. Karpets, V.L. Bekenev, В. В. Гарбуз, Tetiana Khomko, Valerii Kartuzov
Abstract
Interaction between boron carbide and silicon was studied at 1400–1700 ℃ in a vacuum. The results at 1400 ℃ suggest that silicon substitutes a single atom of carbon per formula unit B12C3, producing a phase with increased lattice parameters. Temperature increase improves the degree of transformation, but at 1700 ℃, the product starts to lose silicon. Analysis of DFT formation energies of configurations with B12C3 and B12C2Si stoichiometries shows that B12C2Si may have two ground states with practically equal stability. The first is B11Si(C-B-C) with silicon in icosahedral polar position, and the second is B12(C^Si^C), where the silicon is in the middle of an angular chain. The latter is suggested to be more favorable during the synthesis, while the former is very close to equilibrium with its precursor B11C(C-B-C), and its formation may be inhibited. Comparison of XRD patterns for the synthesis products and modeled structures seems to confirm this suggestion.