Atomic structure and vibrational properties of icosahedral B4C boron carbide

The atomic structure of icosahedral B4C boron carbide is determined by comp aring existing infrared absorption and Raman diffusion measurements with th e predictions of accurate ab initio lattice dynamical calculations performe d for different structural models, a task presently beyond x-ray and neutro n diffraction ability. By examining the inter- and intraicosahedral contrib utions to the stiffness we show that. contrary to recent conjectures, intra icosahedral bonds are harder.