Lattice Vibrations, MIR and FIR Optical Properties of Boron and Icosahedral Boron-Rich Borides I. Alpha-Rhombohedral Structure Group

General remarks on the structure and the lattice vibrations of the different structure groups o f boron and icosahedral boron-rich borides are made. In detail, the lattice vibrations of the alpha-rhombohedral boron structure group are systematically investigated by group theory. Reflectivity spectra of boron-carbide of different chemical com position and preparation and of B60 were measured in the MIR and FIR spectral range. These phonon spectra are analyzed in connection with previous experimental and theoretical results obtained by other authors. A proposal for the intercorrelation of the phonon spectra of this structure group is derived. The plasma resonance spectra of boron carbide and B6O yield qualitative information on the dependence of electronic transport on material properties.