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 o f the different structure groups o f boron and icosahedral boron-rich borides are made. In detail, the lattice vibrations o f the alpha-rhombohedral boron structure group are systematically investigated by group theory. Reflectivity spectra o f boroncarbide o f different chemical com position and preparation and o f 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 o f the phonon spectra o f this structure group is derived. The plasma resonance spectra o f boron carbide and B60 yield qualitative information on the dependence o f electronic transport on material properties.