IR-Active Phonons and Structure Elements of Isotope-Enriched Boron Carbide,

The IR phonon spectra of 10B, 11B, and 13C isotope-enriched boron carbide with the compositions B4.3C, B6.5C, and B10C are presented. Specific phonons are attributed to the stretching and the bending mode of a small concentration of CCC chains, whose occurrence seems to depend on the specific preparation conditions. Based on the assumption that the electron deficiency is compensated by structural defects, the concentrations of CBC, CBB, CCC, and BsquareB arrangements are determined for the whole homogeneity range. Then the concentrations of B12 and B11C icosahedra result from the compound stoichiometry. The concentration of BsquareB arrangements, calculated this way, excellently agrees with the concentration of B(3) vacancies obtained by neutron scattering.